Chemistry: electrical current producing apparatus – product – and – Plural concentric or single coiled electrode
Patent
1987-11-19
1990-02-20
Lieberman, Allan M.
Chemistry: electrical current producing apparatus, product, and
Plural concentric or single coiled electrode
429145, 524379, 524522, 525221, C08K 505, C08L 3302, H01M 214
Patent
active
049025902
DESCRIPTION:
BRIEF SUMMARY
This invention relates to adhesives, and has particular but not exclusive reference to adhesives to be used for laminating or joining absorbent or porous materials to one another or to other materials.
The adhesive of the invention is particularly applicable to use with absorbent or barrier materials used in electrochemical cells.
Combinations of absorbent papers or non-woven fabrics and barrier materials have been used for some time in electrochemical cells, particularly alkaline-electrolyte cells. For ease of handling and of feeding into the cell during cell assembly, these materials are often laminated together using adhesives or thermal sealing techniques.
In cylindrical cells, particularly alkaline-electrolyte cells, spirally wound tubes of absorbent or barrier material are often used, held in shape by an adhesive applied to lock the overlapping portions of spirals.
The use of adhesive or thermal sealing usually causes blocking of the pores of the absorbent or barrier material. This in turn causes an increase in electrical resistance, and/or a decrease in the electrolyte absorption capacity of the material and a deterioration in the wetting characteristics of the material. As a result the performance of the cell system is impaired.
Attempts have been made to use adhesives which are compatible with alkaline electro-chemical systems and which do not lead to undesirable blocking of the pores of absorbent or barrier materials. Such adhesives have involved the use of gelling agents based on long-chain polyacrylic acids. These have however had serious practical disadvantages. They suffer from extremely high viscosity and poor flow characteristics, so that it is necessary to use specialised coating and lamination machines for applying the adhesives, and specialised equipment to move the adhesive from a holding tank to the adhesive coating head. Because of the high viscosity and poor flow characteristics, the rate of application of these adhesives is low, which reduces the throughput during the lamination operation, thereby increasing overhead costs and significantly increasing the cost of the finished cell.
An object of the present invention is to provide an adhesive system of low viscosity, which can be used on absorbent or porous materials used in alkaline-electrolyte environments without causing pore blockage.
It has been found that an adhesive system of excellent properties can be formed by a blend of a long chain polyacrylic acid with a short chain polyacrylic acid.
The invention can provide an adhesive of relatively low viscosity, capable of being applied by simple equipment and at a high throughput. The adhesive of the invention has electro-chemical properties superior to conventional lamination adhesives and thermal bonding techniques and does not impair the absorption capacity or wetting characteristics of cell absorbent and separator components, but can even improve the wetting properties of laminated alkaline electrolyte cell separators.
The combination of long chain and short chain polyacrylic acids provides an adhesive system with excellent gelling properties combined with low viscosity. Preferably, the long chain polyacrylic acid comprises branched chains whereas the short chain polyacrylic acid comprises substantially linear or only slightly branched chains. Branched long chain polyacrylic acids have excellent gelling and adhesive properties in aqueous or alkaline solutions, but high viscosity. The smaller substantially linear molecules of the short chain polyacrylic acid reside between the long chain molecules and reduce interference between these, acting in effect as a molecular lubricant, with the result that the viscosity of the mixture is sharply reduced, without impairing the gelling and adhesive properties of the long chain polyacrylic acid.
The long chain polyacrylic acid typically has a molecular weight in the range 1,250,000 to 5,000,000, preferably about 3,000,000. Lower molecular weights have inadequate gelling and adhesive properties; higher molecular weights do not readily form s
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Cornell Ronald S.
Duracell Inc.
Lieberman Allan M.
McVeigh James B.
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