JPH0560214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to sealed galvanic cells, such as primary alkaline cells, and specifically to sealed insulating members (hereinafter referred to as seals) used in such cells. Seals are formed from thermoplastic materials such as polypropylene filled with minerals such as talc, calcium carbonate, or mica.

BACKGROUND OF THE INVENTION The common construction of sealed cylindrical galvanic cells is to load the main components into a can and seal the cell by providing a seal at the open end of the can. The seal prevents electrolyte from leaking from the battery and prevents the battery's electrodes from touching each other, insulating them from each other.

The seal reduces the pressure built up inside the battery, as well as suppresses the loss of moisture and the intrusion of oxygen or carbon dioxide into the battery.
It is desirable to be able to permeate hydrogen gas from the battery. Additionally, the seal has a thin section to serve as a vent for the rupturable membrane, and by having a thickness that is small relative to the thickness of the material surrounding the membrane, it is possible to prevent the battery from increasing when gas pressure within the cell increases. Ventilation is provided to prevent the battery from exploding.

DETAILED DESCRIPTION The seal according to the invention is used in cylindrical sealed batteries and is made of thermoplastic materials inert to the electrolyte, such as polypropylene, polyethylene (especially polysulfone for high temperature applications) and their co-seals. It is made by molding, typically injection molding, from a material that is a polymer. The thermoplastic material contains 5 to 45% by weight of mineral filler;
The minerals are selected from the group consisting of talc (theoretically anhydrous magnesium silicate (Mg ₃ SiO ₁₀ (OH) ₂ )), calcium carbonate and mica. The seal is
When a thermoplastic material is melted, injection molded, and solidified in a mold, local internal stress remains depending on the shape and thickness of the seal. Since this can economically deform or damage the product, after the seal is formed, it is held in a furnace for a predetermined period of time to undergo an ``annealing treatment'' to release internal stress. Depending on the purpose for which the seal is used, it is decided whether or not to perform annealing treatment. When polyprene is annealed, it is carried out at temperatures of 70 DEG C. to 155 DEG C. (other suitable temperatures are provided for other thermoplastic materials such as copolymers of polypropylene and polyethylene). The annealing process is preferably carried out in an air circulating oven or tunnel. It is known that in many cases mineral-filled polypropylene, particularly talc-filled polypropylene, is particularly effective. For information on typical seals and how to place them inside a battery, please refer to the pending patent application No. 57-235131 and Japanese Patent Application No. 1983.
-108518.

Plastic parts made by injection molding of talc-filled polypropylene do not have sink marks such as dents or irregularities on the surface. This is particularly important when forming seals with thin films. Furthermore, since the part can be molded without sink marks, molding tolerances and conditions during part molding become less important.

Mineral fillers such as talc can lower the molding temperature. Also, mineral fillers such as talc add smoothness to the surface of the thermoplastic material and can therefore act as a mold release agent for the inner mold. This property is particularly useful because mold release agents in the outer mold, such as silicone, can contaminate the molded part, and this contamination can generate gas within the cell. Mineral fillers (talc, calcium carbonate or mica) do not generate gas within the battery. The shrinkage after molding is small, because the concentration of the filler is high, for example in the case of talc 20 ~
It is especially small when it is within the range of 40%, and the molding of the seal insulation member can be done more precisely. Finally, the cost per piece of mineral-filled plastic is less than that of non-mineral-filled plastic.

The inventors have discovered that substantial mechanical advantages can be obtained by using filled thermoplastic materials. These include the fact that they improve the sealing and venting properties of the component. The filled thermoplastic material has a small coefficient of linear expansion, which is very close to that of the metal can used in battery devices. The sealing material is therefore improved, especially after being subjected to thermal silage. Filled thermoplastic materials have a higher compressive strength than unfilled materials, resulting in an improved crimp seal. This can be further enhanced by annealing the seal insulation member. The annealing process stabilizes the dimensions of the seal insulation member, ie, the physical dimensions of the part remain constant. The annealing process can also relieve any molding stresses created during the molding process.

Since the filler acts as a stress concentration means, even a slight deflection of the thin film can cause ventilation or breakage of the thin film. Annealing a filled seal relieves the formed forming stresses and the increase in membrane failure pressure is greater than the increase in membrane failure pressure when annealing without filler. The target is small. By annealing the filled material, one can know with more certainty what the breaking strength of the thin film is.

Similarly, by deploying a filled thermoplastic material, the rupture of the membrane will cause less spread than an unfilled thermoplastic material, and excessive pressure will not build up within the cell, thus reducing the headspace. The space required can be reduced.
Furthermore, by forming the thin film thicker, the forming tolerances can be further increased while maintaining the tolerances of the ventilation mechanism within a predetermined range.

In addition, less head space is required to rupture the vent, and the seal can be placed a little higher on the can, allowing a greater amount of activator to be loaded into the cell. I can do it.

Since the filled thermoplastic material of the present invention is permeable to hydrogen, a cell loaded with a seal member is gradually vented. This gradual venting allows a sufficient amount of hydrogen to escape from the battery, thereby reducing the occurrence of venting of the battery due to rupture of the thin film. This is important, especially in the case of alkaline batteries, as it can significantly reduce the amount of mercury corrosion and gas suppressant components that must be loaded into the battery, resulting in a more environmentally acceptable product. Not only that, but the working conditions for battery assembly are improved, and costs can be further reduced.

Filled thermoplastic materials have the advantage of being much more resistant to corrosion than glass-filled nylons used as battery seals when exposed to electrolytes, for example 40% potassium mercury solutions.

That is, polypropylene filled with talc, calcium carbonate, or mica does not decompose like glass-filled nylon when exposed to KOH at 71° C. for as long as four weeks.

The term "thermoplastic material containing filler" as used herein refers to talc, calcium carbonate, or mica filler.
45%, usually 15-40%, and the filler material is ground into a very fine powder or is a finely granular material. Furthermore, because the filler material is internal to the molded thermoplastic seal insulation member, there is little exposed surface of the filler material in the molded part. In this regard, when using talc as a filler, it is desirable to use about 20%, but up to 40%, of talc, especially as a filler in polypropylene.

As mentioned above, the annealing process has the advantage of removing stress generated during molding and stabilizing the physical dimensions of the seal insulating member after molding. However, even if the seal is not annealed, it can still exhibit superior performance compared to a similar structure without filler. This is because the manufacturing tolerance of the thin film portion of the seal insulating member can be widened, so it can be molded to a higher wall pressure, and the breaking pressure can be estimated more accurately. In either case, the rupture pressure is somewhat higher, but the pressure reached is not so high that the cathode container is unclipped, the entire member comes off, and the cell is damaged.

Typical analytical values for talc-filled polypropylene are as follows. The melt index of the unfilled polypropylene resin was 10-15, but the melt index after filling was reduced to about 6-10.

Talc is a white powdery material in the form of plates or small plates, does not contain asbestos, and its chemical composition is within the following ranges:

Ingredient % weight MgO 20-32% SiO ₂ 16-46% CaO 9-30% Al ₂ O ₃ 0.5-4% Fe ₂ O ₃ 0.2-4% LOI (loss on ignition) 8-20% Notes: Loss on ignition represents the percentage of carbon dioxide removed by heating the talc.

A typical distribution state of particle size according to the mesh size of the sieve through which it passes is within the following range. Passing mesh size % weight 44 microns 100% 30 microns 94-97% 20 microns 75-90% 10 microns 40-60% 5 microns 18-32% 4 microns 14-24% 3 microns 9-17% 2 microns 5-10 % 1 micron 2-4% Typical values for dry brightness are 84-94. Tap density is 60-80 pounds per cubic foot (954-1272 Kg/m ³ ). Loose density is 24-55 lb/ft (382-875
kg/m ³ ). Specific gravity is 2.8-2.9. talc
The oil absorption amount per 100g is 20-35g. PH is 9-10.5. Hegman fineness is 1 to 3.5. 100% pass through 200 meshes, and 98-99.9% pass through 325 meshes.

Similarly, calcite (calcium carbonate) is shown as:

Ingredient % weight CaCO ₃ 95-98% MgCO ₃ 1-2% Al ₂ O ₃ 0.05-0.2% Fe ₂ O ₃ 0.01-0.2% SiO ₂ 0.1-1% MnO 0.01% Copper Not detected Moisture 0.25% Organic coating ( Typically silane) 0.5-2% Typical particle size is 15 microns (spherical particles)
100% is smaller, 95-99% is smaller than 10 microns, and 100% is smaller than 5 microns.
75-85%, 40-85% smaller than 2.5 microns
60%, and 20-40% are smaller than 1 micron. The average particle size is on the order of 2.5 microns, with a specific gravity of about 2.7 and a refractive index of about 1.55.

Some examples are shown below.

Example 1 Several AA size seals (lids) made of nylon, filler or polypropylene and talc 20
Molded from polypropylene with % filler.
Half of each polypropylene seal was annealed and the other half was not annealed. All seals were completely contained within the battery and crimp sealed, except that the outer jacket was not attached to the battery. Leakage was observed after various storage and use tests were performed.

The results of the leakage test were as follows. After one week of storage at elevated temperature and another week of stabilization at room temperature, the annealed lids and the nylon lids were similar in that they were virtually leak-free (1 out of 30). However, a significant number of lids that were not annealed leaked. The other lids were stored for two weeks at a slightly lower but still significantly higher temperature. As a result of further stabilization at room temperature for one week, one nylon lid and
One lid without filler leaked and the lid with filler did not leak.

Furthermore, after storing the other lids at a very constant temperature for one week and allowing them to stabilize for an additional week at room temperature, 20 out of 30 nylon lids leaked, whereas the annealed lids leaked. The chemical-filled lids performed much better, with only 1 out of 30 leaking.

Similarly, when another group was subjected to repeated temperature cycles from low to relatively high temperatures and then stabilized at room temperature, 15 of the 30 nylon lids leaked. In contrast, only 2 out of 30 annealed filled lids leaked.

For other samples, store at room temperature for 1 day, then
All cells were vented when a current of 1.5 amps was applied. The other lid was stored at high temperature for several days and then a current of 1.5 amps was applied. Then, the annealed polypropylene with filler is 3
Three of the batteries were the same, but one out of three batteries with a nylon lid broke very severely.

Example 2 Several AA, C, and D battery lids were molded with breakable venting membranes all having a thickness of 0.0035 to 0.005 inches (0.0889 to 0.127 mm). Samples were molded without talc filler, with 20% talc filler, and with 40% talc filler.

Some lids were selected as controls and were not immersed in the potassium hydroxide solution.
For other groups of lids, in potassium mercury solution for 2 weeks at room temperature or 2 weeks at high temperature.
Alternatively, it was soaked for two weeks at a very high temperature. Next, a ventilation test was conducted outside the battery. All of the lids that were immersed and stored in KOH had fairly consistent venting results compared to the control group that was not immersed in KOH. In other words, all samples
It was chemically resistant to KOH solutions.

An important conclusion drawn from these venting test results is that the thin membrane portion of the filled polypropylene lid, the venting pressure relief area, is unaffected by the high temperature alkaline electrolyte; Regardless of whether the battery is stored for a long period of time or not, the thin film will rupture under the same pressure and the battery will be ventilated.

Example 3 A further ventilation test was conducted as follows. A 0.0055 inch (0.1397 mm) thick ventilation membrane was molded into the lid, and tests were conducted with various clearances above the membrane. Clearance is the air space between the sealing vent membrane and the metal support plate in the cell. When pressure builds up in the battery and the gas permeable membrane expands, the maximum height to which it can expand is the clearance.
Normally the vent membrane ruptures before reaching the clearance height. An unfilled polypropylene lid did not vent, but small clearances and very high pressures did. On the other hand, the lid filled with 20% talc was vented at a reasonable pressure. With a clearance of 0.091 inch (2.31 mm), an unfilled, unannealed polypropylene lid will reach 850 psi.
(59.7Kg/cm ² ) without ventilation. However, using the same lid with a clearance of 0.145 inches (3.68 mm) vented at 280 psi (19.68 Kg/cm ² ). 20% talc filled, non-annealed polypropylene lid provides 480 psi at the smallest clearances listed above.
(33.74 Kg/cm ² ) and 280 psi (19.68 Kg/cm ² ) for the highest clearance. On the other hand, a polypropylene lid filled with 20% talc and annealed has a minimum clearance of 420 psi (29.52 kg/kg).
^cm2 ), 400psi for largest clearance
Aeration was performed at (28.12Kg/cm ² ).

Example 4 Lids of glass-filled nylon, unfilled propylene, 20% talc-filled polypropylene and 40% torque-filled polypropylene were molded and then incubated in KOH electrolyte at 71°C for one month. saved. After storage, the solution was acidified and analyzed for trace amounts of metal elements. Polypropylene lids contain nickel, cadmium, strontium,
No significant differences were observed in the amounts of cobalt, titanium, molybdenum, lead, copper, iron, vanadium, chromium, aluminum, silicon, or calcium filtered. On the other hand, in the case of glass-filled nylon,
Significant amounts of titanium, copper, iron, vanadium, aluminum, silicon and calcium were leached out.

The filled thermoplastic seal of the present invention may be of any shape, which is beyond the scope of the present invention. However, designers can use greater molding tolerances and design the rupturable vent membrane to be thicker and still achieve the same performance as batteries currently in use.

The scope of the invention as described herein is defined by the claims.

Claims (1)

[Claims] 1. A cylindrical galvanic cell comprising a can with one end open and a disc-shaped sealing member crimped to the open end of the can, wherein the sealing member contains 5 to 45% by weight. formed from a thermoplastic material containing a filler, the thermoplastic material and filler being chemically inert to the electrolyte materials used in the sealed battery, and forming a breakable vent in the member. , A galvanic cell characterized in that its wall thickness is smaller than the wall thickness surrounding the ventilation portion. 2. A battery according to claim 1, wherein the thermoplastic material is selected from the group consisting of polypropylene, polyethylene and copolymers thereof, and the filler is selected from the group consisting of talc, calcium carbonate and mica. 3. A battery according to claim 2, wherein the thermoplastic material is made of polypropylene with talc filler. 4. Talc is 15-40% Claim 3
Batteries listed in section. 5. The battery according to claim 1, wherein the seal is annealed. 6. The battery according to claim 4, wherein the annealing temperature is within the range of 70 to 155°C. 7. The battery according to claim 4, wherein the annealing treatment is performed at 70 to 155°C for one hour or more. 8 The particle size of talc is smaller than 44 microns in maximum dimension, 2% by weight or more is larger than 1 micron, 18% by weight or more is larger than 5 microns, and 40% by weight or more is larger than 10 microns. A battery according to scope 4.