|Title of Invention
A PROCESS FOR DYEING TEXTILE SUBSTRATES AND AN APPARATUS FOR CARRYING OUT THE SAME
|The packages of the textile substrates are in the form of yam bobbins of fabric wound on a beam, the supercritical fluid basically impinging on or penetrating the materia! perpendicularly to the axes of the bobbins or beams. During the treatmnt period the values of the treatment temperature change. The invention provides for the values of the treatment temperature during the treatment period being determined by at least two functions of the treatment time and for the supercritical fluid being conditioned differently upon the subsequent function coming into effect. PRICE: THIRTY RUPEES
|The present invention relates to a process for dyeing textile substrates and an apparatus for carrying out the same,
Nonnally, the finishing process for textile substrates, such as fibres, yams, nested fibres, woven goods and hosiery involves repeated treatment in systems using an aqueous solution in which the substrates are boiled, bleached, dyed, washed, etc.
Laboratory-scale textile finishing processes have been developed for the treatment of textile substrates by means of supercritical fluids, in particular supercritical carbon dioxide. These processes are described in DE-OS 39 04 515, 40 04 111, 39 04 513, 39 06 724, 39 06 737, 39 06 735, 42 00 352 and 43 44 021. Pressures between 30 bar and 600 bar are required for such laboratory-scale treatment processes using supercritical fluids.
In these laboratory-scale processes, the textile substrates, which usually consist of small fabric samples measuring a few square centimetres, are treated in appropriate laboratory autoclaves and wetted by the supercritical fluid. However, these processes are not always suitable for industrial-scale application.
In industrial-scale treatment processes, the textile substrates are packaged in a manner which is suitable to maintain an efficient material flow in the textile finishing plant. Yam is bobbined and fabric lots are wound on a beam prior to being treated.
If material on a bobbin or beam is treated by means of a supercritical fluid, the entire package, i.e. the yam bobbin or beam with fabric is placed in an empty autoclave. The autoclave is then hermetically sealed by means of a suitable closure, filled with the supercritical fluid and the treatment pressure is set to a suitable value between 30 bar and 400 bar. At this pressure, the supercritical fluid penetrates the material wound on a bobbin or beam. In view of the diffusion-controlled mass-transfer processes, comparatively long treatment periods are required in order to ensure that the result is as uniform as possible, i.e. that, for instance, the entire lot of material wound on a bobbin or beam has the same colour Intensity. Such long treatment periods constitute a disadvantage in a commercial textile finishing plant.
Various proposals to remedy this disadvantage have been published.
Thus, DE-OS 42 06 952 provides for a piston to be moved to and fro in the autoclave in order to allow the supercritical fluid to impinge on and/or penetrate the material wound on bobbins or beams as a result of this movement. The autoclave must therefore have a larger pressure vessel volume than would
be necessary solely for accommodating the textile materials, as additional volume must be provided for the movement of the piston. This is a disadvantage.
DE-OS 42 06 954 suggests that the autoclave be provided with a circulating pump, in order to circulate the supercritical fluid, thus making it impinge on/or penetrate the material wound on bobbins or beams. To achieve a uniform treatment result, the autoclave is divided into a number of sections, to each of which supercritical fluid can be admitted and which can be operated in parallel or individually. A portion of the material wound on bobbins or beams is admitted to each section. In order to achieve a uniform treatment result for all portions, each individual portion is initially exposed on its own to the circulating supercritical fluid and, subsequently, all sections are operated in parallel, each material portion receiving only part of the circulating fluid.
The complex configuration of the autoclave and the additional treatment time required to achieve a uniform result when the sections are operated in parallel represent a disadvantage.
DE-OS 42 06 955 describes a device for treatment with supercritical fluids, at least two pumps being assigned to the autoclave to which the textile substrate is admitted. The supercritical fluid is circulated through the autoclave by one pump, while the other pump serves for delivering the treatment gas which is also present in sub-critical state. One pump is designed for high delivery rates in order to achieve a uniform result in the treatment of textile substrates. The operation of two different pumps for almost the same task, especially when both pumps are only operated simultaneously for a short period, is not an optimum design from the economic point of view.
DE-OS 42 06 956 describes a device for the treatment of textile substrates which comprises at least two autoclaves. The autoclaves can be interconnected in order to allow the treatment fluid to be withdrawn from one autoclave - for the purpose of removing the substrate - and to be pumped into the other autoclave for Ae treatment of a new lot of substrate. Provision is also made for circulation of the supercritical fluids through one autoclave or through a number of autoclaves connected in series. The fact that a number of autoclaves and a corresponding complex piping system are required to adapt the system to meet the requirements of commercial finishing processes constitutes a disadvantage.
In order to achieve better conditions than those that have become known so far for the commercial aplication of the processes mentioned above, in particular of those covered by the publications of unexamined applications DE-OS 39 04 515, 40 04 111, 39 04 513, 39 06 724, 39 06 737, 39 06 735, 42 00 352 and 43 44 021 mentioned in the introductory part of this patent application, the present invention provides for the treatment of the textile substrates by means of supercritical fluid to take place at temperature levels derived from functions of the treatment time.
The process created by the present invention for the treatment of textile substrates, in particular in package form, i.e. in the form of yam bobbins or fabric layers wound on a beam, by means of supercritical fluid, the fluid basically impinging on or flowing through the packages perpendicularly to the axes of the bobbins or beams, provides for changes in the treatment temperatures during the treatment period.
Different aims may be pursued when treating textile substrates with supercritical fluid. DE-OS 39 724, for instance, provides for a dispersed dye to be dissolved in the supercritical fluid and the dye from the liquor thus formed to be transferred to the substrate by bringing the liquor and the substrate into contact. This contact takes place in an autoclave in which the liquor stagnates to a great extent. The treatment period for dying the fabric sample is 10 minutes.
- — When the febric sample is dyed by the process according to the invention, the liquor flows through the fabric. The liquor is circulated for this purpose. It penetrates the fabric sample and is then discharged from the autoclave. Before the liquor is again admitted to the autoclave, it flows through a bed of pulverised dispersed dye in the saturator. This causes the liquor to be completely saturated with dispersed dye when it again penetrates the fabric sample.
In the process according to the invention, the treatment temperature, i.e. tlie temperature of the liquor flowing through the fabric sample, changes during the treatment cycle, i.e. while the liquor is circulating continuously. The temperature of the circulated liquor can either be increased or reduced. For this purpose, heat is either supplied to or withdrawn from the liquor in a heat exchanger. If, for instance, dispersed dye is used for the treatment of the textile substrate, heat is supplied to the liquor and the treatment temperature is thus increased. In the dyeing process according to the invention, the liquor is heated prior to being laden with dispersed dye. For this purpose, the liquor discharged from the autoclave is first conveyed through the heat exchanger and subsequently through the saturator.
With the supercritical fluid used, in the example quoted carbon dioxide (CO2), a rise in temperature may cause more dispersed dye to dissolve. As a result of the liquor circulation according to the invention, where the liquor is first heated and subsequently laden with dispersed dye, a liquor with a constantly increasing dye concentration flows through the febric sample. The ever greater difference in the concentration between the textile substrates which absorb the dye and the liquor which gives off the dye is favourable for the kinetics of the diffusion processes during the dyeing procedure. Compared to isothermal dyeing, the treatment period is shorter.
Surprisingly, an additional effect resulting from the temperature profile of tlie process according to the invention further reduces the treatment period for dyeing. The transfer of the dye is an endothermic process which takes place on the fibre surface. The liquor, the temperature of which is constantly increased when coming in contact with the textile substrate, supplies surplus heat, which in turn causes the endothermic transfer process to proceed more rapidly.
The reduction in the treatment time achieved by the process according to the invention is of significance from an economic point of view. It is essential for commercial textile finishing plants to dye a large number of yam bobbins in the autoclave per shift. The autoclave is operated batch-wise. For each batch, the autoclave undergoes an operating cycle comprising the following sequential operations: charging the textile materials, e.g. yam bobbins, feeding supercritical fluid and raising the pressure up to the value required for the treatment, treating the batch by circulating the liquor, discharging the supercritical fluid, removing the textile materials.
If, as is customary, mechanical feeding systems are used, the treatment proceeds throughout the major part of the cycle. It is obvious that the dyeing period determined in the laboratory tests, i.e. a period of 10 minutes for a fabric sample, does not meet the requirements for commercial textile finishing processes.
However, when using the process according to the invention for the dyeing of yams in commercial facilities, cross-wound bobbins with a net weight of 1,500 g are dyed evenly within a treatment period of only 60 minutes.
In this process, supercritical COj flows through the bobbin fi-om the centre outwards, the substrate layer through which the CO2 flows being about a thousand times thicker than that of the fabric sample. The comparatively large reduction in the treatment period compared to treatment with a stagnating fluid and a constant treatment temperature is spectacular.
In conventional dyeing processes using aqueous solutions, the dyed yam bobbins have to be dried in several stages, in which they are pre-dried by centrifuging and then finally dried in a high-frequency dryer. These procedures are not required in the process according to the invention since the residual CO2 is completely removed from the yam bobbins and volatalizes without any adverse effect on the environment.
In the process according to the invention for the treatment of textile substrates, in particular packages in the form of yam on bobbins or fabric layers wound on a beam, by means of supercritical fluid, where the fluid basically impinges on or flows through the materials perpendiculariy to the axes of the bobbins
or beams and where the values of the treatment temperature cliange during the treatment period, a.. embodiment provides for the different values of the treatment temperature to be derived from at least one function of the treatment time.
The aforementioned dyeing of yam bobbins has shown that the treatment temperature must be increased linearly during the treatment period in order to achieve a uniform distribution of the dye in all yam layers.
The coefficient of temperature rise may involve values between 0.5 °C/min and 2 °C/min. However, due to tlie limited thermal conductivity of the substrate, it is not possible to reduce the treatment period by means of higher temperature rise coefficients. If tlie temperature gradient in the substrate becomes too steep, the substrate will become discoloured.
In order to counteract this mechanism, a temperature rise coefficient lower than that used during the first third of tlie treatment period is set as soon as the first third of the treatment period has elapsed. The temperature rise during the first third of the treatment period is at least 1 °C/min, while it is only 0.5 °C/min only for the remaining treatment period.
A further embodiment of the process according to the invention for the treatment of textile substrates by means of supercritical fluid, in particular for the treatment of packages in the form of yam on bobbins or fabric wound on a beam, where the fluid basically impinges on or flows through the materials perpendicularly to the axes of the bobbins or beams, and where the values of the treatment temperature change during the treatment period, provides for the values of the treatment temperature during the treatment period being derived firom at least two functions of the treatment time and for the supercritical fluid being conditioned differently at the time the subsequent function becomes active.
This embodiment of the process according to the invention permits a particularly economic adjustment to the given conditions of large-scale textile finishing processes, since pre-treatment of the textile substrates proceeds while the first function of the treatment time is in effect. This pre-treatment may involve the removal of dirt particles and yolk. This pre-treatment may, for instance, be carried out as described in DE-OS 40 04 111; it must, however, be adapted to the fluid circulation according to the invention and CO2 should be used as the purification fluid.
The CO2 laden with the substances removed from the substrate during the pre-treatment is regenerated in a separator where tlie CO2 is present in both sub-critical and gaseous state. The entrained substances are precipitated and mechanically separated from tlie gaseous CO2. The CO2 thus obtained is returned to the pre-treatment section. Due to the recirculation of the CO2, there is practically no loss of scmbbing
fluid during the pre-treatment. At the end of the pre-treatment period, treatment continues while the subsequent function is in effect. The subsequent function, for instance, provides for the textile substrate to be dyed at a linearly rising temperature from 90 °C to 120 °C during the remaining time of tlie cycle.
The CO2, which has previously been used as a cleaning fluid and which is always present in regenerated form, i.e. without being laden with dirt particles etc., is temporarily stored in an intermediate storage tank, and is then re-used in the subsequent function, but differently conditioned. This different form of conditioning according to the invention proceeds as follows: the supercritical CO2 is laden with dye and used in this form for dyeing. The treatment fluid is circulated in order to retain the original level of conditioning for each new treatment stage. During the dyeing process, the dye from the supercritical liquor is transferred to the textile substrate to be dyed. Tlie liquor is thus depleted. Fresh dye is therefore admixed to the fluid from which the dye has been removed.
According to the invention, this is achieved by continuously circulating the fluid, thus bringing it repeatedly in contact with pulverised dye and re-saturating it in the process. In this way, the original level of conditioning is constantly maintained while the subsequent function is in effect.
The process according to the invention is preferably used in such applications where the textile substrate to be treated consists of synthetic fibres and/or mixtures of different synthetic fibres and/or mixtures of synthetic fibres and natural fibres.
Such synthetic fibres are, for instance, made from polyester, polyamide, polyimide, polypropylene, polyethylene or similar products. The natural fibres suitable for treatment are silk, cotton, wool, linen and the like.
The process according to the invention permits the use of different substances as the supercritical fluid. Suitable substances are, for instance, alkanes, particulariy ethane, propane or pentane, ammonia, carbon dioxide, carbon monoxide, nitrous oxide, which can be used on their own or in the form of a mixture.
In order to improve the characteristics of the supercritical fluid, for instance to increase its polarity, additional polar substances can be admixed. Among others, water, alcohol and/or salts may be used as a moderator. Carbon dioxide is preferably used as the supercritical fluid since it is not flammable and can be discharged to the atmosphere without any particular precautionary measures.
A further embodiment of the invention is a device for carrying out the process according to the invention for tlie treatment of a textile substrate and which is equipped with
- at least one dyeing autoclave into which the textile substrate is placed,
- at least one saturator in which the fluid is laden with the active substance (11)
- at least one separator,
- one heat exchanger with the associated heating and cooling facilities,
- one condenser with the associated cooling system and a collecting tank downstream of the condenser,
- one pump (2),
the aforementioned facilities being interconnected by means of piping and valves in such a manner that, on the one hand, a fluid can be circulated via the dyeing autoclave, the pump, the heat exchanger, the saturator and, on the other hand, via the dyeing autoclave, the relief valve, the condenser, tlie collecting tank and the pump, the invention providing for the circulating fluid to be subjected to different temperatures during the period of treatment of the textile substrates, this being achieved with the aid of a process control system.
As a rule, the process control system is in the form of a microprocessor, which is connected with the sensors or actuators which measure and transmit the process parameters or influence them, respectively,via amplifier modules.
The available process control systems allow a high degree of process automation. In addition, the available process control teclinology permits the process to be incorporated into the process automation system of a textile finishing facility.
The dyeing autoclave itself is equipped with facilities for guiding the fluid through the bobbins. These facilities permit the fluid to penetrate the yam package from the inside througli a perforated bobbin tube. Depending on the requirement, the dying autoclave can be designed to accommodate bobbin rows and/or flat material wound on a beam.
Piles with flexible bobbin tubes can be treated in pre-tensioned state. Gaskets are inserted bet^veen the tube ends of the individual bobbins in the row. These gaskets prevent the fluid from bypassing the yam layer on the outside if the piles were not pre-tensioned.
The dyeing autoclave is provided with a mechanised cover closure. Quick-acting clamp closures for pressures between 300 bar and 700 bar are commercially available for autoclaves with an internal diameter of about one meter. For autoclaves with larger diameters, mechanised segment-type closures are used, which are also suitable for all pressures required for the treatment described here.
Supercritical fluids are conveyed by means of reciprocating and centrifugal pumps which are specially designed for this application. In the process described, a centrifugal pump is used if, for instance, a number of long bobbin rows are to be treated simultaneously.
Accordingly, the present invention provides a process for dyeing textile substrates, in particular in the production of yam packages or wound material webs, with supercritical fluid such as herein described with varying treatment temperature, wherein said products are subjected to an afflux flow and/or a through-flow of said supercritical fluid substantially perpendicularly to their package or winding axis, characterized in that said fluid is circulated and is continuously sat»rated with dyestuff in a saturator and the treatment temperature of said circulating fluid is increased or reduced during the treatment period.
Accordingly, the present invention also provides an apparatus for carrying out the process for dyeing a textile substrate according to claim 1 comprising:
at least one dyeing autoclave for receiving the textile substrate,
at least one saturator for charging the fluid with the active substance,
at least one separator,
a heat exchanger with associated heating-cooling device,
a condenser with associated cooling device and a collector arranged
downstream of the condenser and
a pump and the above-identified items of equipment are connected to pipelines and fittings in such a way that on the one hand a fluid can be circulated by way of the dyeing autoclave, the pump, the heat exchanger and the saturator or on the other hand by way of the dyeing autoclave, a relief valve, the condenser and the collector, wherein process control means is provided for imposing variable, namely falling or rising values in respect of the treatment temperature on the circulating fluid during the textile substrate treatment period.
The process and device according to the invention are described in more detail below on the basis of a typical example. Fig. 1 shows a process flow diagram for the device according to the invention.
The process according to the invention mainly serves for the treatment of textile substrates such as, for instance, fibres, yams, materials made up in flat form, non-wovens, laminates and the like. Tliey are dyed, for instance, in that the dye is evenly distributed on the textile substrates and causes them to be dyed evenly. This process may be conducted in such a manner that a pre-wash with an aqueous solution to remove spinning solutions, spooling oil and other hydrophobic substances, and which would injpair the dyeing with supercritical fluids, can be dispensed with.
The process according to the invention primarily serves to treat synthetic fibres and mixtures of these fibres or mixtures of synthetic and natural fibres. The supercritical fluids used in this process are alkanes, particularly ethane, propane or pentane, ammonia, carbon dioxide, carbon monoxide, nitrous oxide; they are either used on theirown or as a mixture. A polar compound, such as, for instance, water, alcohol and/or salts can be added to the supercritical fluid as a moderator.
A process configuration is explained on the basis of a dyeing process for polyester yam. The yam to be dyed and which is made up in the form of cross-wound bobbins is placed in dyeing autoclave (1). Dye (11), the quantity of which is about 0.5% of the weight of the material involved, is fed to the dye tank (14) of the saturator (4).
For extractive purification, which takes place at a pressure of 280 bar and a temperature of 120 °C, CO2 from the collecting tank (7) is supplied to the dyeing autoclave (1) by means of the pump (2) above the heat exchanger (3) and flows through the yam bobbins (16) from the centre outwards. During this procedure, the saturator (4) is bypassed via a valve (30). Any impurities on the yam, such as spinning solutions and spooling oil and other hydrophobic substances dissolve in the CO2 and are conveyed to the separator (5) via a relief valve (15) provided for pressure regulation. Upon pressure relief, the impurities precipitate and are thus removed in the separator from the CO2 gas, which is now in sub-critical state, and collected. The regenerated CO2 is then retumed to the collecting tank (7).
For the dyeing process which takes place after the purification step, CO2 is conveyed by means of the pump (2) to the dyeing autoclave (1) via the heat exchanger (3) and the saturator (4), where the dye (11) dissolves in the CO2.
The yam in the dyeing autoclave (1) is dyed while the CO2 from the dyeing autoclave (1) is recirculated into the dyeing autoclave (1) by means of pump (2). The dyeing takes place at a constant pressure of 280 bar and an increasing treatment temperature which rises linearly from 90 °C to 120 °C during the entire treatment period.
During the treatment period, the CO2 continuously flows through the saturator (4), where the CO2 is saturated, likewise at rising temperatures, with the dye (11) from the dye tank (14), which then dissolves in the CO2. Since much more dye (11) is provided by the dye tank (14) than is required for evenly dyeing the yam bobbins (16), the CO2 leaving the saturator (4) is always completely saturated with dye (11). After a treatment period of 1 hour the yam is evenly dyed and removed from the dyeing autoclave (I). The yam bobbins are dry and ready for dispatch.
Fig. 1 only shows the main process control function according to the invention. The temperature measuring device (50) of the process control system (10) measures the actual treatment temperature in the dyeing autoclave (1).
If the temperature deviates from the required value, the process control system (10) exerts an influence on the heating and cooling facilities (8) and compensates the deviations. The required values are set by the process control system (10) in accordance with the pre-set time functions. Further procedures, such as pressure control etc. are likewise automated by means of the process control system (10), but are not shown in Fig. 1 for the sake of clarity. The attached reference list serves for further explanation of the process and the device.
1 Dyeing autoclave
3 Heat exchanger
7 Collecting tank
8 Heating and cooling facilities
9 Cooling system
10 Process control system
11 Active substance/dye
14 Dye tank
15 Relief valve
16 Yam bobbin
19 Carrier tube
20 Circulation valve
30 Bypass valve
50 Temperature measuring device
51 Signal line
1. A process for dyeing textile substrates, in particular in the production of yam packages or wound material webs, with supercritical fluid such as herein described with varying treatment temperature, wherein said products are subjected to an afflux flow and/or a through-flow of said supercritical fluid substantially perpendicularly to their package or winding axis, characterized in that said fluid is circulated and is continuously saturated with dyestuff in a saturator and the treatment temperature of said circulating fluid is increased or reduced during the treatment period.
2. The process according to claim 1, wherein the various values of the treatment temperature are specified by at least one function of the treatment time.
3. The process according to claim 1 or claim 2, wherein during the treatment period the values of the treatment temperature are specified by at least two function of the treatment time and the above-critical fluid is conditioned differently at the time of the consequential function becoming operative.
4. An apparatus for carrying out the process for dyeing a textile substrate according to claim 1 comprising:
at least one dyeing autoclave (1) for receiving the textile substrate,
at least one saturator (4) for charging the fluid with the active substance
at least one separator (5),
a heat exchanger (3) with associated heating-cooling device (8),
a condenser (6) with associated cooling device (9) and a collector (7)
arranged downstream of the condenser (6) and
a pump (2)
and the above-identified items of equipment are connected to pipelines and fittings in such a way that on the one hand a fluid can be circulated by way of the dyeing autoclave (1), the pump (2), the heat exchanger (3) and the saturator (4) or on the other hand by way of the dyeing autoclave (1), a relief valve (15), the condenser (6) and the collector (7), wherein process control means (10) is provided for imposing variable, namely falling or rising values in respect of the treatment temperature on the circulating fluid during the textile substrate treatment period.
5. A process for dyeing textile substrates substantially as herein described with
reference to the accompanying drawings.
6. An apparatus for carrying out the process for dyeing a textile substrate
substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|FRIEDRICH-UHDE-STRASSE 15, 44141 DORTMUND,
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date