Title of Invention	"An Improved Process for Dyeing Leather Using Low Intensity Power Ultrasound for Application in Leather Industry"
Abstract	The present invention relates to an improved process for dyeing leather using low intensity power ultrasound for application in leather industry. This has potential use in the dye yard of leather tanning industry for dyeing any leather with even shade as well as full penetration even at room-temperature at the cost of very low energy consumption even without the aid of conventional drumming or mechanical action. The process steps are: washing the leather by conventional method, adjusting the pH of the leather in the range of 4-6.5, dyeing the leather, as formed in step (ii), at a maximum ultrasonic intensity of 0.5 W/cm2, either continuously or with pulsing, at maximum temperature of 60°C, fixing the dye by conventional method over a period of 20-60 min.

Title of Invention

"An Improved Process for Dyeing Leather Using Low Intensity Power Ultrasound for Application in Leather Industry"

Abstract

Full Text	The present invention relates to an improved process for dyeing leather using low intensity power ultrasound for application in leather industry. This has potential use in the dye yard of leather tanning industry for dyeing any leather with even shade as well as full penetration even at room-temperature at the cost of very low energy consumption even without the aid of conventional drumming or mechanical action. As reported by Kirk ( Chemistry and Technology of Leather, edited by O'Flaherty, W.T.Roddy and R.M.Lollar, Robert E.Krieger publishing company, New York, volume 3, chapter 3, p-1, 1978), leather is colored not only to improve its appearance, but also to make it adaptable for fashion styling with an ultimate objective to increase its value as a commodity. It is conventionally done either during post tanning wet operation by drum dyeing method or during finishing operation by brush or spray dyeing. Conventional methods however also include carrying out of dyeing operation even in paddles. The most prevalent method of dyeing leather in the post tanning bath, as mentioned by Sharphouse ( Leather Technicians' Handbook, published by Leather producers' Association, Northampton, U.K, p-304, 1983), is the drum dyeing, wherein the leather is dyed at 60 - 80°C in drums made of wood or steel fitted with hollow axle through which dye solutions and auxiliary agents are added v- lile rotating the drum at 12 to 1b rpm. Float of the bath a ,d pH of leather are however adjusted depending on the nature of dye used, extent of dyeing requirements in terms of penetration, shade etc. before adding dye to the bath. Crust leathers are also conventionally dyed by drum dyeing method in similar way after wetting back the same using ammonia and wetting agents. Paddle is a curve shaped tank made up of wood or concrete in which mechanical agitation is caused by the rotation of circular wooden blades fitted at the axle of the tank. The paddle dyeing is usually used for fragile leathers like book-binding leathers, skivers and shearlings which are likely to be damaged by the vigorous action of drum. The float used for paddle dyeing is usually considerably higher compared to that used in conventional drum dyeing. As reported by Ludvik ( Study on scope for decrease of pollution load in Leather industry, A report on assistance in pollution control in the tanning industry in South-East Asia, prepared by United Nations Industrial Development Organisation, p-15, 1997), the main limitation of the conventional processes is that external heating arrangement is to be made to ensure that the dyeing operation is carried out at around 60°C for better result. Moreover, full penetration required for certain categories of leather requires the duration of dyeing to be extended even upto 5 hours, whereby the leather quality is likely to be affected due to more mechanical action. Another major drawback of the hitherto known conventional methods is that tfre';exhaustionipf:dye in the bath is only in the range of 50-75%, resulting in the presence of substantial amount of unused dye in the spent liquor, thereby causing not only an enormous wastage from the economical point of view, but also the creation of environmental problems. The ill-effects of mechanical action and the problem of external heating may be overcome by spray dyeing method, whereby a dye solution of required shade is sprayed on the leather. This method is, however, suitable only for surface dyeing and is usually employed in the finishing stage. The above limitations have prompted the researchers to try the option of power ultrasound for dyeing leather. Ultrasound, which is a sound wave with frequency above 16kHz, the human audible range, is produced by ultrasonic transducers, which convert electrical signals of ultrasonic frequency to mechanical vibrations of the same frequency. As reported by Contamine et al (Chemical Engineering Science, 49(248), 5865, 1994) the ultrasound at a frequency range of 20-1000 kHz is known as power ultrasound, which is now well known to have significant effects on the rate of various processes in the chemical industry such as cleaning, homogenisation, emulsification, extraction, partiele:size reduction etc. The power applied to the transducer is available as ultrasonic energy over a working area, while the energy available per unit of working area of the ultrasonic equipment is known as the ultrasonic intensity. Although it is non-conventional, yet the power ultrasound can be employed durfago leather dyeing to accelerate the penetration of dye through the cross-section of leather?and facilitate dyeing, unlike conventional methods, even at stationary condition and at room-ternperature. As reported by Crawford (Ultrasonic Engineering, Butterworths scientific publication, London, Chapter. 8, P-184,1960), dyeing in presence of power ultrasound is carried out in a ultrasound cleaning tank or by immersing ultrasonic horn inside the dye bath, kept in a dyeing vessel. Cujan et al (Leder Waren, 19(4), 180, 1984) used power ultrasound of intensity in the range of 4 -25 W/cm2 at a frequency in the range of 19-23kHz for dyeing cow leather with cross sectional area of 2 xlO"4 cm2 with an inference that it is possible to reduce the duration of dyeing by adopting ultrasonic technique. Xie et al (Proceedings of the International Union of Leather Technologists' and Chemists Societies Congress, London, p-584-599,1997) used a comparatively lower ultrasonic intensity of 1.36 W/cm2 at 38Khz frequency for dyeing cow leather with 4%w/w, dye based on leather weight to achieve an uptake of maximum 3mgs of dye per grn of leather, resulting in an exhaustion of dye to the extent of 7.5%, after a period of 3 hrs of dyeing. It is pertinent to mention here that only acid dyes have been used in the hitherto known processes of ultrasonic dyeing. Although such dyes of much bigger particle size as direct dye, metal complex dye are presently preferred for dyeing of leather to get better result in terms of shade, fastness etc, no prior art is available on the use of these dyes for dyeing leather-using pewer ultrasound. Another major limitation of the hitherto known ultrasonic dyeing of leather is that the high ultrasonic intensity, used in the process results not only in high energy consumption, but also in the enormous rise of temperature of the dye bath resulting in possible damage to certain kind of leather having low shrinkage temperature. Moreover, higher intensity of power ultrasound may also result in the rupture of the leather, damaging its quality. Yet another major drawback of the hitherto known ultrasonic dyeing is that the exhaustion level of the bath is much less compared to that achieved by conventional drum dyeing methods and this is perhaps the major factor which is responsible for discouraging the leather dyers to switch over to the non-conventional option of ultrasonic method of dyeing. The main objective of the present invention is to provide an improved process for dyeing leather using low intensity power ultrasound for application in leather industry, which obviates the drawbacks stated above. Another objective of the present invention is to use power ultrasound of intensity below 0.5 W/ cm2 for dyeing leather. Yet another objective of the present invention is to provide a process of dyeing leather using dyes of bigger particle size like direct dye and rnetal complex dye. Still1 another objective of the present invention is to provide a process to achieve more exhaustion of dye compared to that achieved in the hitherto known methods, to reduce wastage as well as pollution problem. Accordingly the present invention provides an improved process for dyeing leather using low intensity power ultrasound for application in leather industry, which comprises i) washing the leather by conventional method, ii) adjusting the pH of the leather in the range of 4 -6.5, iii) dyeing the leather, as formed in step (ii), at a maximum ultrasonic intensity of 0.5 W/cm2, either continuously or with pulsing, at maximum temperature of 60°C, iv) fixing the dye by conventional method over a period of 20-60 min. In an embodiment of the present invention, the leather used may be such as chrome tanned leather, stripped and bleached vegetable tanned leather, semi chrome leather, crust leather. In another embodiment of the present invention, the chemicals used for adjusting the pH may be such as sodium formate, sodium bicarbonate, neutralising syntans, borax, sodium thiosulphate, either individually or in combination. In yet another embodiment of the present invention, the dye used may be such as acid dye, direct dye, metal complex dye, either individually or in combination. In still another embodiment of the present invention, the float used for dyeing may be in?the range of 100-3000% by volume offwater on leather weight. In yet another embodiment of the present invention, pH for dye fixation may be in the range of 3.5-4. In still another embodiment of the present invention, the dye fixing agent used may be such as formic acid, acetic acid either individually or in combination. In yet another embodiment of the present invention, the amount of dye fixing agent may be in the range of 40-80%w/w, on the amount of dye used. In still another embodiment of the present invention, the ultrasonic dyeing bath may be used in a condition such as static or dynamic or a combination thereof. In yet another embodiment of the present invention, the ultrasonic frequency used may be maximum 100 kHz. Leather is washed by conventional method and pH of the leather is adjusted in the range of 4-6.5 by known method. Dyeing is then done in a fresh float of •100r300©% by: volume of water on the weight of leather using dye in presence of ultrasound at a maximum intensity of 0.5 W/em2 with ultrasonic frequency of maximum 100kHz over a period depending upon the dyeing parameters like shade, type and thickness of leather, penetration requirement, type of dye, etc, either continuously or with pulsing, at a temperature of maximum 60°C in an ultrasonic tank, in a condition, either i static-sondynamic or a combination thereof. The resulting leather is checked fort;penetration of dye by cutting a cross section and then treated with 40- 8Q%w/w, of dye fixing agent on the amount of dye used over a period of 20-60minutes. Finally the leather is taken out of the ultrasonic bath for the subsequent operations by conventional method. The novelty of the present invention lies in selecting an ultrasonic intensity range below 0.5 W/cm2 for dyeirag of leather resulting not only in the dye uptake to a level as high as 85% or more in three hours even maintaining the dye bath in stationary condition, registering a substantial increase in dye-uptake over the hitherto known processes, both conventional and non-conventional, but also enabling the leather to be dyed even with such dyes of bigger particle size as direct dye and metal complex dye, which have not been reported in the prior art, thereby providing am improved eeofriendly method; to Use dye of any particle size for dyeing, that results in maximum dye exhaustion adding little to the load of effluent at the cost of lesser energy consumption. The following examples are given fcy way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example -1 A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to? a thickness of 1.2 mm, was weighed and the weight was noted to be 6.074g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 60.7ml water. 60.74mg of sodium formate was separately dissolved in 0.6 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 60.74mg of sodium bi carbonate, dissolved in 0.6 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 36.4ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 243mg of Acid Red dye was dissolved in 24.3ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom waJI of the ultrasonic tank of area 317.25cm2, thereby producing ultrasound with 0.473 W/cm-2- intensity. After 15 minutes, the instrument was switched off for Srninutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.12g of 80% formic acid was dissolved in 1.2ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle in three feeds with 7minutes interval for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasouiad was switched of!. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 88% on the amount of dye added to the bath. The leather was also subjected to physical testing. Tensile strength was found to be 215 kg/cm2, tear strength was found to be 46 kg/cm, while the elongation at break was determined to be 45%. The grain of the leather was found to crack at a load of 62 k§ while the distension at grain crack was found to be 12 mm. Exam pie-H A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was fioted'to-be 5.9725g.The leather cut piece was washed with three ©hanges of plait^water in a b§aker and then taker in a 1000ml beaker containing 59.7ml water 59,73mg of sodium formate was separately dissolved in 0.60 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of 30minutes, an aqueous solution of 59.73rng of sodium bi carbonate, dissolved in 0.60 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 35.84rnl of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 238.9mg of Acid Red, was dissolved in 24ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.126g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added at the end of eighth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 60 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 99.5% on the amount of dye added to the bath. Example - III A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 6.2765g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 62.8ml water. 62.76mg of sodium formate was separately dissolved in 0.63 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 62.76rng of sodium bi carbonate, dissolved in 0.63 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued •for another -tW after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 37.7ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 em. from the base of the tank. 251.06mg of C.I (Colour Index) Acid Black 194, a metal complex dye, was dissolved in 25.1ml of water at 3G°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.126g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added at the end of eighth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 60 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Piriallythe^teatherpieee-was washed well-in plain water and then taken for subsequent fatliquoring operation • Exhaustion of dye in the bath was calculated to be 85% on the amount of dye added to the bath. Example - IV A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 6.5032g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 65ml water. 65mg of sodium formate was separately dissolved in 0.65 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 65mg of sodium bi carbonate, dissolved in 0.65 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water, This washed leather was then taken in a glass process beaker containing 39ml off>lain water at 30QG and the beaker was.positioned at the centre of an ulfrasonie tank by clamping it at a height of 2 cm. from the base of the tank., '26®&rft&bft®jliAe\d Black 155, asdirect dye, was dissolved in 26ml of water at 30°G and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.13g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added to the dye bath for dye fixation at the end of eighth cycle, in three feeds with 7minutes interval, while continuing the process of ultrasonication in the similar way for a period of 60 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 91.6% on the amount of dye added to the bath. Example - V \ circular piece of 9 cm diameter, which was cut from a full chrome cow crust eathemof.thickness 1.2mm, was^weighed and the weight was noted tebe 5.7643g. The leather cut piece-was put in a beaker containing 57.6mlof )lain water and 0.57ml of 2.5% solution of liquor ammonia under static condition for 16 hours. Then the leather piece was taken in a 1000ml beaker containing 57.6 ml of water. 57.64mg of sodium formate was separately dissolved in 0.58 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 57.64mg of sodium bi carbonate, dissolved in 0.58 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 34.6ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 230.6mg of Acid Red dye was dissolved in 23.1ml of water at 30°C and the resulting dye solution was added to the process, beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. The temperature of the dye bath was maintained at 60°C throughout the dyeing process by circulating hot water through the coil immersed in the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 150W wittf frequency of 33 kHz, generated by the'transducers fixed at the bottom wail of ihe ultrasonic tank of area 317.25 cm2 .thereby producing ultrasound with 0.473 W/cm intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.115g of 80% formic acid was dissolved in 1.2ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 91.1% on the amount of dye added to the bath. Example - VI A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 6.116g. The leather cut piece was washed with three changes of plain,water in a beaker and then taken in a 1000ml beaker containing 61.16ml water. 61.16mg of sodium formate was separately dissolved in 0.61 ml of : water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 61.16mg of sodium bi carbonate, dissolved in 0.61 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 48.92ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 122.32mg of Acid Red dye was dissolved in 12.2ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2, thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. 0.049g of 80% formic acid was dissolved in 0.49ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of tittrasonieation in the similar way for a period of 40 minutes. Then.,the pH of the dye bath was found to.be 3.7 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 99.92% on the amount of dye added to the bath. Example - VII A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 6.9g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 69ml water. 69mg of sodium formate was separately dissolved in 0.69 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 69mg of sodium bi carbonate, dissolved in 0.69 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 2Q.7mrof plain'water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank, 483mg of Acid Red dye was dissolved in 48.3ml of water at 30°C and the resulting dye solution was added to the process teeaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water at 30°C. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 miniates. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.242g of 80% formic acid was dissolved in 2.4ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. v Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 64.96% on the amount of dye added to the bath. Example-VIII A' circular piece of 9 cm 'diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1,25mm, was weighed and the weight was noted to be 6.5726g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 65.7ml ml water. 65.73g of sodium formate was separately dissolved in 0.66ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of 30minut.es, an aqueous solution of 65.73mg of sodium bi carbonate, dissolved in 0.66 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water. This washed leather was then taken in a glass process beaker containing 39.4ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 262.9mg of Acid Red dye was dissolved in 26.3ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. The temperature of the dye bath was maintained at 30°C throughout the dyeing process by circulating cold water through the coil immersed in the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 150W With; frequency of'33 kHz, generated by the transducers fixed at the bottom wall'of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0,473 W/em?'intensity. After 15 minutes, the instrument was switched off for Srninutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.131 g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with /minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 58.1% on the amount of dye added to the bath. Example - IX A rectangular piece of size 13em x 23 cm , which was cut from a stripped and bleached vegetable tanned buffalo leather shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 40g. The leather was taken in a conventional sample drum for washing with 400ml of plain water and the drum was run for a period of 1 hour. After 1 hour, the drum was "stopped and the float was drained. Then a fresh float of 50ml-of plain water was'taken in the drum .and the leather; was drummed for a period of 2hours with 400mg of borax, which was added in 3 feeds at 10 minutes interval through the axle hole of the drum, after dissolving the same separately in 4 ml of water taken in a beaker. After 2 hours, the pH of the cross section of the leather was found to be 4.0. Then the leather was washed in running water. This washed leather was then taken in the ultrasonic tank containing 600ml of plain water at 30°C. 2.4g of Acid Brown dye was dissolved in 600ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 100W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.315 W/cm2 intensity. After a period of SOminutes, a cross section of the leather was cut while continuing the ultrasonication and the penetration of dye was noted to be thorough. 1.92g of 80% formic acid was dissolved in 19.2ml of water taken in a beaker and was added, in two feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication for a period of another 20 minutes. Then the pM of the dye bath was found to be 4.0 and the ultrasound was switched off, The resulting dyed leather was taken out of the process beaker. Finally the-leather-piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of-dye in the bath was calculated to be 81.3.% on the amount of dye added to the bath.« Example - X A rectangular piece of size 13cm x 23 cm , which was cut from a bleached semi-chrome goat leather shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 30g. The leather was taken in a conventional sample drum for washing with 300ml of plain water and the drum was run for a period of 1hour. After 1 hour, the drum was stopped and the bath was drained. Then a fresh float of 30ml of plain water was taken in the drum and the leather was drummed for a period of 30 minutes with SOOmg of sodium formate which was added through the axle hole of the drum, after dissolving the same separately in 4 ml of water taken in a beaker. After 30 minutes, SOOmg of neutralisation syntan which was dissolved in 3ml of water was added in 3 feeds at 10 minutes interval of time to the drum and the drum was run for a period of 1 hour. The pH of the cross section of the leather was found to be 6.5. Then the leather was washed in running water. This washed leather was then taken in the ultrasonic tank containing 300ml of plain water at 30°C. 1.2g of Acid blue dye was dissolved in 300ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for two times. After second cycle, then 0.3g of metal complex blue dye was dissolved in 10ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank while continuing the ultrasonic process cycle for two more times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.75g of 80% formic acid was dissolved in 7.5ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.7 and the ultrasound was switched off. The resulting dyed leather was taken out of the process feeaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 82.2% on the amount of dye added to the bath. Example-XI A rectangular piece of size 13ern x 23 cm , which was cut from a full-chrome sheep leather, :shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 25g. The leather was taken in a conventional sample drum for washing with 250ml of plain water and the drum was run for a period of thoins-After'!'hour, the drum was.stopped and the &athwas drained. Then a afres'hv'1l0at'.QfJ25rnl=of plain water was taken in the dwm and the leather was forpa^period of 30 minutes with 250rng of sodium thio sulphate which was added through the axle hole of the drum, after dissolving the same separately in 3 ml of water taken in a beaker. After 30 minutes, 150mg of neutralisation syntan which was dissolved in 3ml of water was added in 3 feeds at 10 minutes interval of time to the drum and the drum was run for a period of 1hour. The pH of the cross section of the leather was found to be 5.5. Then the leather was washed in running water. This washed leather was then taken in the ultrasonic tank containing 500ml of plain water at 30°C. 1.25g of Acid yellow dye was dissolved in 250ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. An overhead stirrer was positioned in such a way that its blade could agitate the dye bath as well as the leather to cause continuous dynamic condition throughout the dyeing process. Ultrasound was switched on to generate ultrasonic output power of 75W with frequency of 100 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.236 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.4g of 80% formic acid was dissolved in 4ml of water and 0.25 ml of acetic acid was dissolved in 2.5ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.£ and the ultrasound was switched off. The resulting dyed leather was taker out of-the process beaker. Finally the leather piece was washed well in plain water and then taken foi subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 71.6% on the amount of dye added to the bath. Example - XII A rectangular piece of size 13crn x 23 cm , which was cut from a full-chrome sheep leather shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 25g. The leather was taken in a conventional sample drum for washing with 250ml of plain water and the drum was run for a period of 1 hour. After 1 hour, the drum was stopped and the bath was drained. Then a fresh float of 25ml of plain water was taken in the drum and the leather was drummed for a period of 30 minutes with 250mg of sodium thio sulphate which was added through the axle hole of the drum, after dissolving the same separately in 3 ml of water taken in a beaker. After 30 minutes, 125mg of neutralisation syntan which was dissolved in 3ml of water was added in 3 feeds at TO minutes interval of time to the drum and the drum was run for a period of 1 hour. The pH of the c^oss section of the leather was found, to be 5.5. Thervthe leather was washed in running water. This washed leather was then taken in the ultrasonic tank containing 500ml of plain water at 30°C. 1.25g of Metal complex yellow dye was dissolved in 250ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. An overhead stirrer was positioned in such a way that its blade could agitate the dye bath and the leather to cause dynamic condition for a period of 15 minutes for every 30 minutes throughout the dyeing process. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough. 0.65g of 80% acetic acid was dissolved in 6.5ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 45 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation. Exhaustion of dye in the bath was calculated to be 85.2% on the amount of dye added to the bath. The main advantages of the present invention are the following. 1. Dyeing of any leather is possible with any kind of dye by using the process of the present invention. 2. Energy consumption is very low. 3. Dyeing may be carried out even by keeping the dye-bath in stationary condition. 4. No external heating is necessary. 5. Dye may be exhausted to the extent of 85% or even more resulting in economy on the investment on dyes. 6. The spent dye liquor does not add extra load to the pollution problem. We Claim 1. An improved process for dyeing leather using low intensity power ultrasound for application in leather industry, which comprises (i) washing the leather by conventional method, (ii) adjusting the pH of the leather in the range of 4 -6.5, (iii) dyeing the leather, as formed in step (ii), at a maximum ultrasonic intensity of 0.5 W/cm2, either continuously or with pulsing, at maximum temperature of 60°C, (IV)fixing the dye by conventional method over a period of 20-60 min. 2. An improved process, as claimed in claim 1, wherein the leather used is such as chrome tanned leather, stripped and bleached vegetable tanned leather, semi chrome leather, crust leather. 3. An improved process, as claimed in claims 1 and 2, wherein the chemicals used for adjusting the pH are such as sodium formate, sodium bicarbonate, neutralising syntans, borax, sodium thiosulphate, either individually or in combination. 4. An improved process, as claimed in claims 1 to 3, wherein the dye used is such as acid dye, direct dye, metal complex dye, either individually or in combination. 5. An improved process, as claimed in claims 1 to 4, wherein the float used for dyeing MS in the range of 100-3000% by volume of water on leather weight. 6. An improved process, as claimed in claims 1 to 5, wherein pH for dye fixation is in the range of 3.5-4. 7. An improved process, as claimed in claims 1 to 6, wherein the dye fixing agent used is such as formic acid, acetic acid either individually or in combination. 8, An improved process, as claimed in claims 1 to 7, wherein, the amount of dye fixing agent is in the range of 40-80% w/w, on the amount of dye used. 9. An improved process, as claimed in claims 1 to 8, wherein the ultrasonic dyeing bath is used in a condition such as static or dynamic or a combination thereof. .10. An improved process, as claimed in claims 1 to 9, wherein the ultrasonic frequency used is maximum 100 kHz. 11. An improved process for dyeing leather using low intensity power ultrasound for application in feather industry, as substantially herein described with reference to the examples.

Full Text

The present invention relates to an improved process for dyeing leather using low intensity power ultrasound for application in leather industry. This has potential use in the dye yard of leather tanning industry for dyeing any leather with even shade as well as full penetration even at room-temperature at the cost of very low energy consumption even without the aid of conventional drumming or mechanical action.
As reported by Kirk ( Chemistry and Technology of Leather, edited by O'Flaherty, W.T.Roddy and R.M.Lollar, Robert E.Krieger publishing company, New York, volume 3, chapter 3, p-1, 1978), leather is colored not only to improve its appearance, but also to make it adaptable for fashion styling with an ultimate objective to increase its value as a commodity. It is conventionally done either during post tanning wet operation by drum dyeing method or during finishing operation by brush or spray dyeing. Conventional methods however also include carrying out of dyeing operation even in paddles.
The most prevalent method of dyeing leather in the post tanning bath, as mentioned by Sharphouse ( Leather Technicians' Handbook, published by Leather producers' Association, Northampton, U.K, p-304, 1983), is the drum dyeing, wherein the leather is dyed at 60 - 80°C in drums made of wood or steel fitted with hollow axle through which dye solutions and auxiliary agents are added v- lile rotating the drum at 12 to 1b rpm. Float of the bath a ,d pH of leather are however adjusted depending on the nature of dye used, extent
of dyeing requirements in terms of penetration, shade etc. before adding dye to the bath. Crust leathers are also conventionally dyed by drum dyeing method in similar way after wetting back the same using ammonia and wetting agents.
Paddle is a curve shaped tank made up of wood or concrete in which mechanical agitation is caused by the rotation of circular wooden blades fitted at the axle of the tank. The paddle dyeing is usually used for fragile leathers like book-binding leathers, skivers and shearlings which are likely to be damaged by the vigorous action of drum. The float used for paddle dyeing is usually considerably higher compared to that used in conventional drum dyeing.
As reported by Ludvik ( Study on scope for decrease of pollution load in Leather industry, A report on assistance in pollution control in the tanning industry in South-East Asia, prepared by United Nations Industrial Development Organisation, p-15, 1997), the main limitation of the conventional processes is that external heating arrangement is to be made to ensure that the dyeing operation is carried out at around 60°C for better result. Moreover, full penetration required for certain categories of leather requires the duration of dyeing to be extended even upto 5 hours, whereby the leather quality is likely to be affected due to more mechanical action. Another major drawback of the hitherto known conventional methods is that tfre';exhaustionipf:dye in the bath is only in the range of 50-75%, resulting in the presence of substantial amount of unused dye in the spent liquor, thereby
causing not only an enormous wastage from the economical point of view, but also the creation of environmental problems.
The ill-effects of mechanical action and the problem of external heating may be overcome by spray dyeing method, whereby a dye solution of required shade is sprayed on the leather. This method is, however, suitable only for surface dyeing and is usually employed in the finishing stage. The above limitations have prompted the researchers to try the option of power ultrasound for dyeing leather. Ultrasound, which is a sound wave with frequency above 16kHz, the human audible range, is produced by ultrasonic transducers, which convert electrical signals of ultrasonic frequency to mechanical vibrations of the same frequency. As reported by Contamine et al (Chemical Engineering Science, 49(248), 5865, 1994) the ultrasound at a frequency range of 20-1000 kHz is known as power ultrasound, which is now well known to have significant effects on the rate of various processes in the chemical industry such as cleaning, homogenisation, emulsification, extraction, partiele:size reduction etc. The power applied to the transducer is available as ultrasonic energy over a working area, while the energy available per unit of working area of the ultrasonic equipment is known as the ultrasonic intensity.
Although it is non-conventional, yet the power ultrasound can be employed durfago leather dyeing to accelerate the penetration of dye through the cross-section of leather?and facilitate dyeing, unlike conventional methods, even at
stationary condition and at room-ternperature. As reported by Crawford (Ultrasonic Engineering, Butterworths scientific publication, London, Chapter. 8, P-184,1960), dyeing in presence of power ultrasound is carried out in a ultrasound cleaning tank or by immersing ultrasonic horn inside the dye bath, kept in a dyeing vessel.
Cujan et al (Leder Waren, 19(4), 180, 1984) used power ultrasound of intensity in the range of 4 -25 W/cm2 at a frequency in the range of 19-23kHz for dyeing cow leather with cross sectional area of 2 xlO"4 cm2 with an inference that it is possible to reduce the duration of dyeing by adopting ultrasonic technique. Xie et al (Proceedings of the International Union of Leather Technologists' and Chemists Societies Congress, London, p-584-599,1997) used a comparatively lower ultrasonic intensity of 1.36 W/cm2 at 38Khz frequency for dyeing cow leather with 4%w/w, dye based on leather weight to achieve an uptake of maximum 3mgs of dye per grn of leather, resulting in an exhaustion of dye to the extent of 7.5%, after a period of 3 hrs of dyeing.
It is pertinent to mention here that only acid dyes have been used in the hitherto known processes of ultrasonic dyeing. Although such dyes of much bigger particle size as direct dye, metal complex dye are presently preferred for dyeing of leather to get better result in terms of shade, fastness etc, no prior art is available on the use of these dyes for dyeing leather-using pewer ultrasound.
Another major limitation of the hitherto known ultrasonic dyeing of leather is that the high ultrasonic intensity, used in the process results not only in high energy consumption, but also in the enormous rise of temperature of the dye bath resulting in possible damage to certain kind of leather having low shrinkage temperature. Moreover, higher intensity of power ultrasound may also result in the rupture of the leather, damaging its quality. Yet another major drawback of the hitherto known ultrasonic dyeing is that the exhaustion level of the bath is much less compared to that achieved by conventional drum dyeing methods and this is perhaps the major factor which is responsible for discouraging the leather dyers to switch over to the non-conventional option of ultrasonic method of dyeing.
The main objective of the present invention is to provide an improved
process for dyeing leather using low intensity power ultrasound for application
in leather industry, which obviates the drawbacks stated above.
Another objective of the present invention is to use power ultrasound of
intensity below 0.5 W/ cm2 for dyeing leather.
Yet another objective of the present invention is to provide a process of
dyeing leather using dyes of bigger particle size like direct dye and rnetal
complex dye.
Still1 another objective of the present invention is to provide a process to
achieve more exhaustion of dye compared to that achieved in the hitherto
known methods, to reduce wastage as well as pollution problem.
Accordingly the present invention provides an improved process for
dyeing leather using low intensity power ultrasound for application in leather
industry, which comprises
i) washing the leather by conventional method,
ii) adjusting the pH of the leather in the range of 4 -6.5,
iii) dyeing the leather, as formed in step (ii), at a maximum ultrasonic intensity
of 0.5 W/cm2, either continuously or with pulsing, at maximum temperature of
60°C,
iv) fixing the dye by conventional method over a period of 20-60 min.
In an embodiment of the present invention, the leather used may be such
as chrome tanned leather, stripped and bleached vegetable tanned leather,
semi chrome leather, crust leather.
In another embodiment of the present invention, the chemicals used for
adjusting the pH may be such as sodium formate, sodium bicarbonate,
neutralising syntans, borax, sodium thiosulphate, either individually or in
combination.
In yet another embodiment of the present invention, the dye used may be
such as acid dye, direct dye, metal complex dye, either individually or in
combination.
In still another embodiment of the present invention, the float used for
dyeing may be in?the range of 100-3000% by volume offwater on leather
weight.
In yet another embodiment of the present invention, pH for dye fixation
may be in the range of 3.5-4.
In still another embodiment of the present invention, the dye fixing agent
used may be such as formic acid, acetic acid either individually or in
combination.
In yet another embodiment of the present invention, the amount of dye
fixing agent may be in the range of 40-80%w/w, on the amount of dye used.
In still another embodiment of the present invention, the ultrasonic dyeing
bath may be used in a condition such as static or dynamic or a combination
thereof.
In yet another embodiment of the present invention, the ultrasonic
frequency used may be maximum 100 kHz.
Leather is washed by conventional method and pH of the leather is adjusted in the range of 4-6.5 by known method. Dyeing is then done in a fresh float of •100r300©% by: volume of water on the weight of leather using dye in presence of ultrasound at a maximum intensity of 0.5 W/em2 with ultrasonic frequency of maximum 100kHz over a period depending upon the dyeing parameters like shade, type and thickness of leather, penetration requirement, type of dye, etc, either continuously or with pulsing, at a temperature of maximum 60°C in an ultrasonic tank, in a condition, either i static-sondynamic or a combination thereof. The resulting leather is checked fort;penetration of dye by cutting a cross section and then treated with 40-
8Q%w/w, of dye fixing agent on the amount of dye used over a period of 20-60minutes. Finally the leather is taken out of the ultrasonic bath for the subsequent operations by conventional method.
The novelty of the present invention lies in selecting an ultrasonic intensity range below 0.5 W/cm2 for dyeirag of leather resulting not only in the dye uptake to a level as high as 85% or more in three hours even maintaining the dye bath in stationary condition, registering a substantial increase in dye-uptake over the hitherto known processes, both conventional and non-conventional, but also enabling the leather to be dyed even with such dyes of bigger particle size as direct dye and metal complex dye, which have not been reported in the prior art, thereby providing am improved eeo*friendly method; to Use dye of any particle size for dyeing, that results in maximum dye exhaustion adding little to the load of effluent at the cost of lesser energy consumption.
The following examples are given fcy way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
Example -1
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to? a thickness of 1.2 mm, was weighed and the weight was
noted to be 6.074g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 60.7ml water. 60.74mg of sodium formate was separately dissolved in 0.6 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 60.74mg of sodium bi carbonate, dissolved in 0.6 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 36.4ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 243mg of Acid Red dye was dissolved in 24.3ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom waJI of the ultrasonic tank of area 317.25cm2, thereby producing ultrasound with 0.473 W/cm-2- intensity. After 15 minutes, the instrument was switched off for Srninutes and then again switched on for 15 minutes. This process cycle
was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.12g of 80% formic acid was dissolved in 1.2ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle in three feeds with 7minutes interval for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasouiad was switched of!. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 88% on the amount of dye added to the bath. The leather was also subjected to physical testing. Tensile strength was found to be 215 kg/cm2, tear strength was found to be 46 kg/cm, while the elongation at break was determined to be 45%. The grain of the leather was found to crack at a load of 62 k§ while the distension at grain crack was found to be 12 mm.
Exam pie-H
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was fioted'to-be 5.9725g.The leather cut piece was washed with three ©hanges of plait^water in a b§aker and then taker* in a 1000ml beaker containing 59.7ml water 59,73mg of sodium formate was separately dissolved in 0.60 ml of
water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of 30minutes, an aqueous solution of 59.73rng of sodium bi carbonate, dissolved in 0.60 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 35.84rnl of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 238.9mg of Acid Red, was dissolved in 24ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.126g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added at the end of eighth cycle, in three feeds with 7minutes
interval, for dye fixation, while continuing the process of ultrasonication in the
similar way for a period of 60 minutes. Then the pH of the dye bath was
found to be 3.5 and the ultrasound was switched off. The resulting dyed
leather was taken out of the process beaker.
Finally the leather piece was washed well in plain water and then taken for
subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 99.5% on the amount of
dye added to the bath.
Example - III
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 6.2765g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 62.8ml water. 62.76mg of sodium formate was separately dissolved in 0.63 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 62.76rng of sodium bi carbonate, dissolved in 0.63 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued •for another -tW after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 37.7ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 em. from the base of the tank. 251.06mg of C.I (Colour Index) Acid Black 194, a metal complex dye, was dissolved in 25.1ml of water at 3G°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water.
Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.126g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added at the end of eighth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 60 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker.
Piriallythe^teatherpieee-was washed well-in plain water and then taken for
subsequent fatliquoring operation •
Exhaustion of dye in the bath was calculated to be 85% on the amount of dye added to the bath.
Example - IV
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 6.5032g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 65ml water. 65mg of sodium formate was separately dissolved in 0.65 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 65mg of sodium bi carbonate, dissolved in 0.65 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water,
This washed leather was then taken in a glass process beaker containing 39ml off>lain water at 30QG and the beaker was.positioned at the centre of an ulfrasonie tank by clamping it at a height of 2 cm. from the base of the tank., '26®&rft&bft®jliAe\d Black 155, asdirect dye, was dissolved in 26ml of water at 30°G and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water.
Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for eight times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.13g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker and was added to the dye bath for dye fixation at the end of eighth cycle, in three feeds with 7minutes interval, while continuing the process of ultrasonication in the similar way for a period of 60 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 91.6% on the amount of dye added to the bath.
Example - V
\ circular piece of 9 cm diameter, which was cut from a full chrome cow crust eathemof.thickness 1.2mm, was^weighed and the weight was noted te*be 5.7643g. The leather cut piece-was put in a beaker containing 57.6mlof )lain water and 0.57ml of 2.5% solution of liquor ammonia under static
condition for 16 hours. Then the leather piece was taken in a 1000ml beaker containing 57.6 ml of water. 57.64mg of sodium formate was separately dissolved in 0.58 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 57.64mg of sodium bi carbonate, dissolved in 0.58 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.5. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 34.6ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 230.6mg of Acid Red dye was dissolved in 23.1ml of water at 30°C and the resulting dye solution was added to the process, beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. The temperature of the dye bath was maintained at 60°C throughout the dyeing process by circulating hot water through the coil immersed in the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 150W wittf frequency of 33 kHz, generated by the'transducers fixed at the bottom wail of ihe ultrasonic tank of area 317.25 cm2 .thereby producing ultrasound with 0.473 W/cm* intensity. After 15 minutes, the instrument was switched off
for Sminutes and then again switched on for 15 minutes. This process cycle
was continued for four times. A cross section of the leather was cut and
penetration of dye was noted to be thorough.
0.115g of 80% formic acid was dissolved in 1.2ml of water taken in a beaker
and was added to the dye bath at the end of fourth cycle, in three feeds with
7minutes interval, for dye fixation, while continuing the process of
ultrasonication in the similar way for a period of 40 minutes. Then the pH of
the dye bath was found to be 3.5 and the ultrasound was switched off. The
resulting dyed leather was taken out of the process beaker.
Finally the leather piece was washed well in plain water and then taken for
subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 91.1% on the amount of
dye added to the bath.
Example - VI
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 6.116g. The leather cut piece was washed with three changes of plain,water in a beaker and then taken in a 1000ml beaker containing 61.16ml water. 61.16mg of sodium formate was separately dissolved in 0.61 ml of : water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 61.16mg of
sodium bi carbonate, dissolved in 0.61 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 48.92ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 122.32mg of Acid Red dye was dissolved in 12.2ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2, thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times.
0.049g of 80% formic acid was dissolved in 0.49ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of tittrasonieation in the similar way for a period of 40 minutes. Then.,the pH of the dye bath was found to.be 3.7 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker.
Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 99.92% on the amount of dye added to the bath.
Example - VII
A circular piece of 9 cm diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 6.9g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 69ml water. 69mg of sodium formate was separately dissolved in 0.69 ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of SOminutes, an aqueous solution of 69mg of sodium bi carbonate, dissolved in 0.69 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 2Q.7mrof plain'water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank, 483mg of Acid Red dye was dissolved in 48.3ml of water at 30°C and
the resulting dye solution was added to the process teeaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water at 30°C. Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 miniates. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.242g of 80% formic acid was dissolved in 2.4ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 40 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker.
v
Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 64.96% on the amount of dye added to the bath.
Example-VIII
A' circular piece of 9 cm 'diameter, which was cut from a chrome tanned cow leather, shaved to a thickness of 1,25mm, was weighed and the weight was
noted to be 6.5726g. The leather cut piece was washed with three changes of plain water in a beaker and then taken in a 1000ml beaker containing 65.7ml ml water. 65.73g of sodium formate was separately dissolved in 0.66ml of water taken in a beaker and the same was added to the beaker containing the leather cut piece while stirring the contents continuously with a mechanical stirrer. After a period of 30minut.es, an aqueous solution of 65.73mg of sodium bi carbonate, dissolved in 0.66 ml of water was added to the beaker in 3 feeds at 10 minutes interval with continuous stirring, which was continued for another 1 hr after adding the final installment. pH of the cross section of the leather was found to be 6.0. The bath was then drained and the leather was washed with two changes of plain water.
This washed leather was then taken in a glass process beaker containing 39.4ml of plain water at 30°C and the beaker was positioned at the centre of an ultrasonic tank by clamping it at a height of 2 cm. from the base of the tank. 262.9mg of Acid Red dye was dissolved in 26.3ml of water at 30°C and the resulting dye solution was added to the process beaker, positioned in the ultrasonic tank, which was filled with 2.5 litres of water. The temperature of the dye bath was maintained at 30°C throughout the dyeing process by circulating cold water through the coil immersed in the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 150W With; frequency of'33 kHz, generated by the transducers fixed at the bottom wall'of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0,473 W/em?'intensity. After 15 minutes, the instrument was switched off
for Srninutes and then again switched on for 15 minutes. This process cycle
was continued for four times. A cross section of the leather was cut and
penetration of dye was noted to be thorough.
0.131 g of 80% formic acid was dissolved in 1.3ml of water taken in a beaker
and was added to the dye bath at the end of fourth cycle, in three feeds with
/minutes interval, for dye fixation, while continuing the process of
ultrasonication in the similar way for a period of 40 minutes. Then the pH of
the dye bath was found to be 3.5 and the ultrasound was switched off. The
resulting dyed leather was taken out of the process beaker.
Finally the leather piece was washed well in plain water and then taken for
subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 58.1% on the amount of
dye added to the bath.
Example - IX
A rectangular piece of size 13em x 23 cm , which was cut from a stripped and bleached vegetable tanned buffalo leather shaved to a thickness of 1.3mm, was weighed and the weight was noted to be 40g. The leather was taken in a conventional sample drum for washing with 400ml of plain water and the drum was run for a period of 1 hour. After 1 hour, the drum was "stopped and the float was drained. Then a fresh float of 50ml-of plain water was'taken in the drum .and the leather; was drummed for a period of 2hours with 400mg of borax, which was added in 3 feeds at 10 minutes interval
through the axle hole of the drum, after dissolving the same separately in 4 ml of water taken in a beaker. After 2 hours, the pH of the cross section of the leather was found to be 4.0. Then the leather was washed in running water. This washed leather was then taken in the ultrasonic tank containing 600ml of plain water at 30°C. 2.4g of Acid Brown dye was dissolved in 600ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. Ultrasound was switched on to generate ultrasonic output power of 100W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.315 W/cm2 intensity. After a period of SOminutes, a cross section of the leather was cut while continuing the ultrasonication and the penetration of dye was noted to be thorough.
1.92g of 80% formic acid was dissolved in 19.2ml of water taken in a beaker and was added, in two feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication for a period of another 20 minutes. Then the pM of the dye bath was found to be 4.0 and the ultrasound was switched off, The resulting dyed leather was taken out of the process beaker. Finally the-leather-piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of-dye in the bath was calculated to be 81.3.% on the amount of dye added to the bath.«
Example - X
A rectangular piece of size 13cm x 23 cm , which was cut from a bleached
semi-chrome goat leather shaved to a thickness of 1.2mm, was weighed and
the weight was noted to be 30g. The leather was taken in a conventional
sample drum for washing with 300ml of plain water and the drum was run for
a period of 1hour. After 1 hour, the drum was stopped and the bath was
drained. Then a fresh float of 30ml of plain water was taken in the drum and
the leather was drummed for a period of 30 minutes with SOOmg of sodium
formate which was added through the axle hole of the drum, after dissolving
the same separately in 4 ml of water taken in a beaker. After 30 minutes,
SOOmg of neutralisation syntan which was dissolved in 3ml of water was
added in 3 feeds at 10 minutes interval of time to the drum and the drum was
run for a period of 1 hour. The pH of the cross section of the leather was found
to be 6.5. Then the leather was washed in running water.
This washed leather was then taken in the ultrasonic tank containing 300ml
of plain water at 30°C. 1.2g of Acid blue dye was dissolved in 300ml of water
at 30°C and the resulting dye solution was added to the ultrasonic tank.
Ultrasound was switched on to generate ultrasonic output power of 150W
with frequency of 33 kHz, generated by the transducers fixed at the bottom
wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound
with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off
for Sminutes and then again switched on for 15 minutes. This process cycle
was continued for two times. After second cycle, then 0.3g of metal complex
blue dye was dissolved in 10ml of water at 30°C and the resulting dye solution
was added to the ultrasonic tank while continuing the ultrasonic process cycle
for two more times. A cross section of the leather was cut and penetration of
dye was noted to be thorough.
0.75g of 80% formic acid was dissolved in 7.5ml of water taken in a beaker
and was added to the dye bath at the end of fourth cycle, in three feeds with
7minutes interval, for dye fixation, while continuing the process of
ultrasonication in the similar way for a period of 40 minutes. Then the pH of
the dye bath was found to be 3.7 and the ultrasound was switched off. The
resulting dyed leather was taken out of the process feeaker.
Finally the leather piece was washed well in plain water and then taken for
subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 82.2% on the amount of
dye added to the bath.
Example-XI
A rectangular piece of size 13ern x 23 cm , which was cut from a full-chrome sheep leather, :shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 25g. The leather was taken in a conventional sample drum for washing with 250ml of plain water and the drum was run for a period of thoins-After'!'hour, the drum was.stopped and the &athwas drained. Then a afres'hv'1l0at'.QfJ25rnl=of plain water was taken in the dwm and the leather was forpa^period of 30 minutes with 250rng of sodium thio sulphate
which was added through the axle hole of the drum, after dissolving the same separately in 3 ml of water taken in a beaker. After 30 minutes, 150mg of neutralisation syntan which was dissolved in 3ml of water was added in 3 feeds at 10 minutes interval of time to the drum and the drum was run for a period of 1hour. The pH of the cross section of the leather was found to be 5.5. Then the leather was washed in running water.
This washed leather was then taken in the ultrasonic tank containing 500ml of plain water at 30°C. 1.25g of Acid yellow dye was dissolved in 250ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. An overhead stirrer was positioned in such a way that its blade could agitate the dye bath as well as the leather to cause continuous dynamic condition throughout the dyeing process.
Ultrasound was switched on to generate ultrasonic output power of 75W with frequency of 100 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.236 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.4g of 80% formic acid was dissolved in 4ml of water and 0.25 ml of acetic acid was dissolved in 2.5ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way
for a period of 40 minutes. Then the pH of the dye bath was found to be 3.£
and the ultrasound was switched off. The resulting dyed leather was taker
out of-the process beaker.
Finally the leather piece was washed well in plain water and then taken foi
subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 71.6% on the amount of
dye added to the bath.
Example - XII
A rectangular piece of size 13crn x 23 cm , which was cut from a full-chrome sheep leather shaved to a thickness of 1.2mm, was weighed and the weight was noted to be 25g. The leather was taken in a conventional sample drum for washing with 250ml of plain water and the drum was run for a period of 1 hour. After 1 hour, the drum was stopped and the bath was drained. Then a fresh float of 25ml of plain water was taken in the drum and the leather was drummed for a period of 30 minutes with 250mg of sodium thio sulphate which was added through the axle hole of the drum, after dissolving the same separately in 3 ml of water taken in a beaker. After 30 minutes, 125mg of neutralisation syntan which was dissolved in 3ml of water was added in 3 feeds at TO minutes interval of time to the drum and the drum was run for a period of 1 hour. The pH of the c^oss section of the leather was found, to be 5.5. Thervthe leather was washed in running water.
This washed leather was then taken in the ultrasonic tank containing 500ml of plain water at 30°C. 1.25g of Metal complex yellow dye was dissolved in 250ml of water at 30°C and the resulting dye solution was added to the ultrasonic tank. An overhead stirrer was positioned in such a way that its blade could agitate the dye bath and the leather to cause dynamic condition for a period of 15 minutes for every 30 minutes throughout the dyeing process.
Ultrasound was switched on to generate ultrasonic output power of 150W with frequency of 33 kHz, generated by the transducers fixed at the bottom wall of the ultrasonic tank of area 317.25 cm2 , thereby producing ultrasound with 0.473 W/cm2 intensity. After 15 minutes, the instrument was switched off for Sminutes and then again switched on for 15 minutes. This process cycle was continued for four times. A cross section of the leather was cut and penetration of dye was noted to be thorough.
0.65g of 80% acetic acid was dissolved in 6.5ml of water taken in a beaker and was added to the dye bath at the end of fourth cycle, in three feeds with 7minutes interval, for dye fixation, while continuing the process of ultrasonication in the similar way for a period of 45 minutes. Then the pH of the dye bath was found to be 3.5 and the ultrasound was switched off. The resulting dyed leather was taken out of the process beaker. Finally the leather piece was washed well in plain water and then taken for subsequent fatliquoring operation.
Exhaustion of dye in the bath was calculated to be 85.2% on the amount of dye added to the bath.
The main advantages of the present invention are the following.
1. Dyeing of any leather is possible with any kind of dye by using the process
of the present invention.
2. Energy consumption is very low.
3. Dyeing may be carried out even by keeping the dye-bath in stationary
condition.
4. No external heating is necessary.
5. Dye may be exhausted to the extent of 85% or even more resulting in
economy on the investment on dyes.
6. The spent dye liquor does not add extra load to the pollution problem.

We Claim
1. An improved process for dyeing leather using low intensity power
ultrasound for application in leather industry, which comprises
(i) washing the leather by conventional method,
(ii) adjusting the pH of the leather in the range of 4 -6.5, (iii) dyeing the leather, as formed in step (ii), at a maximum ultrasonic
intensity of 0.5 W/cm2, either continuously or with pulsing, at maximum
temperature of 60°C,
(IV)fixing the dye by conventional method over a period of 20-60 min. 2. An improved process, as claimed in claim 1, wherein the leather used is
such as chrome tanned leather, stripped and bleached vegetable tanned
leather, semi chrome leather, crust leather. 3. An improved process, as claimed in claims 1 and 2, wherein the chemicals
used for adjusting the pH are such as sodium formate, sodium
bicarbonate, neutralising syntans, borax, sodium thiosulphate, either
individually or in combination.
4. An improved process, as claimed in claims 1 to 3, wherein the dye used is such as acid dye, direct dye, metal complex dye, either individually or in
combination.
5. An improved process, as claimed in claims 1 to 4, wherein the float used for dyeing MS in the range of 100-3000% by volume of water on leather
weight.
6. An improved process, as claimed in claims 1 to 5, wherein pH for dye fixation is in the range of 3.5-4.
7. An improved process, as claimed in claims 1 to 6, wherein the dye fixing agent used is such as formic acid, acetic acid either individually or in combination.
8, An improved process, as claimed in claims 1 to 7, wherein, the amount of
dye fixing agent is in the range of 40-80% w/w, on the amount of dye used.
9. An improved process, as claimed in claims 1 to 8, wherein the ultrasonic
dyeing bath is used in a condition such as static or dynamic or a
combination thereof.

.10. An improved process, as claimed in claims 1 to 9, wherein the ultrasonic frequency used is maximum 100 kHz.
11. An improved process for dyeing leather using low intensity power ultrasound for application in feather industry, as substantially herein described with reference to the examples.

Documents:

138-del-1999-abstract.pdf

138-del-1999-claims.pdf

138-del-1999-complete specification (granted).pdf

138-del-1999-correspondence-others.pdf

138-del-1999-correspondence-po.pdf

138-del-1999-description (complete).pdf

138-del-1999-form-1.pdf

138-del-1999-form-19.pdf

138-del-1999-form-2.pdf

« Previous Patent

Next Patent »

Patent Number

195182

Indian Patent Application Number

138/DEL/1999

PG Journal Number

38/2008

Publication Date

19-Sep-2008

Grant Date

24-Nov-2006

Date of Filing

25-Jan-1999

Name of Patentee

Council of Scientific and Industrial Research

Applicant Address

Rafi Marg,New Delhi-110001,India.

Inventors:

#	Inventor's Name	Inventor's Address
1	Venkatasubramanian Sivakumar	Central Leather Research Institute, Adyar, Chennai-600020,India.
2	Paruchuri Gangadhar Rao	Central Leather Research Institute, Adyar, Chennai-600020,India

PCT International Classification Number

C14C 11/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA