Title of Invention

A PROCESS TO INCREASE THE STORAGE LIFE OF ENVIRONMENT FRIENDLY ZINC CARBON DRY CELL

Abstract

We claim; 1. A process rage .life of enviroafnent friendly paste type dry cell wherein hazardous mercury Ks be, efecji^ly replaced by bismuth salt as an inhibitor in the paste enhapdng the stora:^ life of the dry cell without changing other constructional featjrfes. - J A process to increase the storage life of environment friendly paste type dry cell ,as-claimeJ iu ulaiin 1, wherein bismuth salt may be more particularly bismuth trichloride added to starch paste substituting mercury salts wherein bismuth trichloride forming a superficial protective coating through jellified starch paste.

Full Text

FORM - 2 THE PATENT ACT, 1970 COMPLETE SPECIFICATION SECTION 10 A PROCESS TO INCREASE THE STORAGE LIFE OF ENVIRONMENT FRIENDLY ZINC CARBON DRY CELL Old nai-ne MATSUSHITA LAKHANPAL BATTERY INDIA LIMITED, Has been changed to New name An Indian Company incorporated in India Under the Companies Act, 1956 of India having its registered office at Makarpura, GIDC, Vadodara 390 010 State of Gujarat, India The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed : - This invention relates to a process to increase the storage (shelf) Ufe of environment friendly zinc carbon dry cell and more particularly to the development of no mercury added zinc carbon paste type dry cell. It is the primary object of the invention to replace mercury (an environmentally hazardous compound) by a suitable non-hazardous compound as an inhibitor in the process of manufacturing no mercury added paste type zinc carbon dry cell. As illustrated in the Fig No. 1, zinc-carbon dry cell especially paste type consist of cylindrical can shaped zinc anode 1, having upper edge inclined inward as shown. Inside the can, at the bottom an insulating waxed duplex board 2 is placed. Against the interior cylindrical surface of the can contains jellified starch 3 containing ammonium chloride and zinc chloride in water as electrolyte. An inhibitor coating forming a protective layer 4 on the inner surface of the zinc can. Compressed in the form of bobbin 5, in contact with layer 3 and centrally placed on the board 2 is the cathode depolarizer material containing a mixture of natural or/ and synthetic artificial manganese dioxide and conductive carboneous material such as acetylene black moistened with liquid electrolyte. The bobbin 5 is covered nearly one third from the bottom with a layer of paper 6 before placing into the can to avoid breaking and probable contact with zinc. Centrally placed within the depolarizer material is the rod shaped carbon electrode 7 acting as current collector with a metal cap 8 at the upper end. The upper edge of the can covered with a closure 9 containing material such as plastic or pitch as shown for sealing and avoids moisture loss during the storage. The gap/ space 10 between the top of the depolarizing body and the closure serve as an expansion space for the collection of liquid and gases resulting due to the operation of the cell. An outer jacket 11 of either printed paper/ metal sheet covered around the zinc can as a protection for batteries. This invention particularly provides an inhibitor coating process forming a protective layer on the inner surface of the zinc can by a non-hazardous material. BACKGROUND In developing countries like India, paste type zinc-carbon dry cells are used in huge quantum due to its considerably cheaper cost. The cost of such type of dry cell is less due to the quality of raw material used and its construction. Zinc, when used in simple form, as metal can, cannot sustain the localized corrosion due to, traces of heavy metal impurities present in raw materials and poor sealing construction. The localized corrosion of zinc is traditionally overcome by improving the nature of zinc by amalgamation of the inner wall of zinc can in zinc-carbon dry cell. The amalgamation can effectively increase the hydrogen overvoltage of the zinc electrode, suppressing the evolution of hydrogen gas thus improving the corrosion resistance during storage. Although the addition of mercury in the form of mercury salts has considerably improved the service life, shelf life and prevented localized corrosion of dry cell, but the disposal of large quantity of used dry cells inevitably results in a scattering and accumulation of significant amount of mercury that is harmful to living being. It is estimated that a large part of the mercury contamination is due to the abandoned dry cells. Hence, the development of non-hazardous alternate inhibitor becomes the need of the hour. Recent development shows that the localized corrosion or self dissolution of no mercury added zinc can be suppressed either through improving the nature of zinc by alloying with elements such as Indium (In), Bismuth (Bi) or else superficially coating the inner wall of zinc can by salts of metals such as Indium, Lead etc as inhibitor. Attempts have been made through the above process, however the success of increasing the storage life of no mercury added zinc carbon dry cell has been presently limited to only zinc carbon dry cells manufactured wherein the superficial coating is done on inner surface of zinc can through separator paper. This is mainly due to the usage of purer raw material and improved sealed construction technology used in the manufacturing the said dry cells. For zinc carbon dry cells manufactured wherein superficial coating done using salts of metals mentioned above on the inner surface of zinc can through gelatinzatined starch paste, to increase in storage life was not successful due to poor inhibition property of the said inhibitor salts in prevailing technology such as usage of inferior raw materials and poor seaUng construction. Hence, the process of increasing storage life of paste type zinc carbon dry cell by developing an alternate, non-hazardous inhibitor became the object of the invention, which can replace mercury salt in the prevailing technology with out changing any constructional features. SUMMARY OF THE INVENTION The object of this invention is achieved by substituting mercury salts by bismuth salt more particularly bismuth trichloride as an inhibitor in the starch paste in a predetermined composition in to relation to the weight of zinc can for the manufacturing of no mercury containing zinc-carbon dry cell. Bismuth trichloride which readily hydrolyze in electrolytic aqueous media of the paste to form bismuth oxychloride and in turn reacts with inner wall of the zinc can surface by a replacement reaction forming a thin protective coating of bismuth layer on the zinc surface. The said thin protective coating of bismuth layer prevents the localized corrosion or self-dissolution of zinc and thus increasing the storage (shelf) life. DETAILED DESCRIPTION OF THE INVENTION In this invention bismuth content in the range of 0.003% to 0.3% corresponding to the weight of the zinc can be achieved by substituting mercury salts in predetermined quantity by bismuth trichloride as an inhibitor in the starch paste, for manufacturing of no mercury containing zinc-carbon dry cell. Following Bismuth compositions (as in examples 1, 2, 3 & 4 respectively given hereafter) in the form of bismuth trichloride as given below in Table No. 1, were used to study its effectiveness as an inhibitor to substitute mercury salt in the paste type zinc carbon dry cell. Table No. 1 Example Bismuth content as bismuth trichloride in paste per unit wt. Of Zinc can Example 1 0.003 % Example 2 0.03 % Example 3 0.15% Example 4 0.3 % Each of the above compositions were prepared by mixing the above mentioned percentage of bismuth trichloride to a slurry paste containing combination of natural starches, surface reagent, ammonia in a electrolytic solution of zinc chloride- ammonium chloride- water. The selection of natural starches, surface reagent and ammonia is based on gelatinization temperature, electrolyte holding capacity at gelatinization of different varieties of starches such as com starch, wheat flour and rice starch, wetting ability of surface reagent for effective coating of inhibitor and jellified starch paste adhesion of inner zinc can surface wall and fiirther the base as ammonia solution to adjust the pH respectively. The said slurry paste was thoroughly and homogeneously mixed and allowed for an aging of minimum 12 hours prior to use as a jellified barrier between the cathode and anode. R-20 size, asphalt sealed flashlight zinc carbon dry cells were manufactured using with above prepared paste containing bismuth trichloride as an inhibitor after thermally gelatinizing the same between the cathode and anode and was evaluated for its effectiveness by studying the following three factors as mentioned below, in comparison with mercury containing zinc-carbon dry cell. 1. Service life 2. Storage life 3. Localized pitting behavior The anode alloy composition used during the study was having 99.5 % - 99.7 % of zinc and 0.5 % - 0.3 % of lead. For best performance of the dry cell of this invention the anode alloy composition shall be 0.1% to 1.0% of lead and 0.03 % to 0.1% of cadmium. The iron content as an impurity be less than 50 parts per million in the said anode alloy composition. The initial open circuit potential of freshly prepared R-20 size flashlight zinc carbon dry cells using the said four examples compositions were found to be approximately 10 mV less compared to mercury added zinc-carbon dry cells. This is mainly due to the difference in electrode potential of zinc- bismuth and zinc -mercury interface. In order to evaluate the paste containing the bismuth trichloride as inhibitor with four example compositions on the basis of service life performance, the freshly made R-20 size, asphalt sealed zinc carbon dry cells using the said compositions alongwith mercury added zinc-carbon dry cells with similar asphalt sealed construction were subjected to discharge at medium drain (5 ohm) and low drain (40 ohm) load resistance in both continuos as well as intermitted mode till the cut off voltage of 0.9 volts were recorded/ noted in all the cases. It was found that in all the four example compositions the cells have delivered a service output almost equivalent compared to mercury added zinc-carbon dry cell in continuous discharge at both initial and until 12 months shelf storage in the above mentioned load resistance, whereas a loss of 4 % to 10% in service life is observed in intermittent discharge at both initial and until 12 months shelf storage as shown in Table No. 2. The drain rate, content of bismuth per unit of zinc can and service output in terms of percentage loss is summarized in Table No. 2. The loss of life and equivalent life are depicted by symbol (-) and ( = ) respectively in Table No. 2. Table No. 2 In order to evaluate the paste containing the bismuth trichloride as inhibitor with four example compositions on the basis of storage life performance freshly made cells with all the four above example compositions containing bismuth trichloride and mercury added zinc carbon dry cell were kept at 27 ± 2 °C (ambient temperature) and 40 ± 2°C (High temperature) respectively to study the voltage drop with respect to time. The voltage drop at periodic interval were recorded at both the temperatures and plotted as shown in the Fig No. 2 and Fig No. 3 respectively. Fig No.2: Show the comparative shelf life static open circuit voltage drop vs time curve of zinc carbon dry cell containing four example compositions (marked as Ex-1, Ex- 2, Ex-3 and Ex-4) and mercury added zinc carbon dry cell (marked as mercury added)at 27±2°C. Fig No. 3; Show the comparative shelf life static open circuit voltage drop vs tkne curve of zinc carbon dry cell containing four example compositions (marked as Ex- 1, Ex- 2, Ex-3 and Ex-4) and mercury added zinc carbon dry cell (marked as mercury added) at 40 ± 2 °C As indicated in Fig. No. 2 and Fig No. 3, time is given in abscissa in months and the voltage drop in ordinates in Volts. From Fig No. 2 and Fig No. 3, it is found that dry cells containing all the four example compositions during storage period at both the temperatures, found to be similar to that of zinc-carbon dry cell containing mercury. This indicates the good shelf storage stability of bismuth compound as an inhibitor when added in the form of bismuth trichloride to zinc- carbon paste type dry cell of this invention. Thus corrosion inhibition characteristic of bismuth trichloride increases the storage life of no mercury added environment friendly zinc carbon dry cell. In order to evaluate the paste containing the bismuth trichloride as inhibitor with four example compositions on the basis of localized corrosion such as pitting corrosion on zinc surface (which is very common in no mercury added zinc carbon cells), freshly made R-20 size asphalt sealed dry cells containing all the four example compositions as inhibitors alongwith dry cell with mercuric chloride as inhibitor and dry cells without any added inhibitor were kept on shelf upto its guarantee period at 27°C. The cells were analysed at regular interval to study the inner zinc surface for pitting. On observation it was found that dry cells without any added inhibitor, gave severe locaHzed pitting corrosion leading to oozing out of electrolyte, within two months of shelf storage while both mercuric chloride and bismuth trichloride showed no sign of localized corrosion till its guarantee period. This indicates the excellent corrosion inhibition characteristic of bismuth when added in the form of bismuth trichloride to the paste as an inhibitor and thus increases the storage life of no mercury added environment friendly zinc carbon dry cell. We claim; 1. A process rage .life of enviroafnent friendly paste type dry cell wherein hazardous mercury Ks be, efecji^ly replaced by bismuth salt as an inhibitor in the paste enhapdng the stora:^ life of the dry cell without changing other constructional featjrfes. - Jf ^ A process to increase the storage life of environment friendly paste type dry cell ,as-claimeJ iu ulaiin 1, wherein bismuth salt may be more particularly bismuth trichloride added to starch paste substituting mercury salts wherein bismuth trichloride forming a superficial protective coating through jellified starch paste. 3. A process to increase the storage life of environment friendly paste type dry cell as claimed in claim , wherein bismuth content as bismuth trichloride in the jellified starch paste be in the range from 0.003 to 0,3 % corresponding to the weight of zinc can as an inhibitor. A process to increase torage life of environment friendly paste type dry cell as claimed in claim 1,2 aniherein to enhance the storage life of the dry cell, the alloy composition of zinc can having 0.1 % -1.0 % of lead and 0.03 % - 0.1 % of cadmium. ' ^ A process to increase the storage life of environment friendly paste type dry cell as claimed in claim 1, 2, 3 aii wherein to enhance the storage life of the dry cell, the alloy composition of zinc can having 99.5 % - 99.7 % of zinc, 0.5% -0.3% of lead, ^. A process to increase the storage Ufe of environment friendly paste type dry cell as claimed in claim 1, 2, 3, 4 wherein to enhance the storage life of the dry cell, the iron content as an impurity in zinc can, be less than 50 parts per million. 7. A process to increase the storage Ufe of environment friendly paste type dry cell substantially as described in the specification here before alongwith the Dated this 17th day of September, 2001

Documents:

1034-mum-2001-cancelled page(20-12-2006).pdf

1034-mum-2001-claim(granted)-(21-10-2005).pdf

1034-mum-2001-claims(granted)-(21-10-2005).doc

1034-mum-2001-correspondence(20-12-2006).pdf

1034-mum-2001-correspondence(ipo)-(3-1-2007).pdf

1034-mum-2001-drawing(21-10-2005).pdf

1034-mum-2001-form 1(23-10-2001).pdf

1034-mum-2001-form 13(21-10-2005).pdf

1034-mum-2001-form 19(19-1-2004).pdf

1034-mum-2001-form 2(granted)-(21-10-2005).doc

1034-mum-2001-form 2(granted)-(21-10-2005).pdf

1034-mum-2001-form 3(16-8-2004).pdf

1034-mum-2001-form 6(2-1-2007).pdf

1034-mum-2001-form 8(23-10-2001).pdf

1034-mum-2001-other(2-1-2007).pdf

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