JPS5810370A - Manufacture of battery separator - Google Patents

Abstract

PURPOSE:To increase affinity to synthetic resin film and hasten diffusion of monomer inside the film to accelerate reaction rate by adding a surfactant to a monomer solution. CONSTITUTION:By adding a surfactant to water of solvent, acrylic acid is dissolved and also divinylbenzene is emulsified to make coexist two kinds of monomers, and they are irradiated with radiation and can be copolymerized by one reaction. Althought divinylbenzene is insioluble in water, it is emulsified by adding surfactant, contacts uniformly in the form of microlayer on a film surface, and polymerization reaction occurs. As the surfactant which is added to the monomer solution, each one of polyoxyethylene alkyl ether, sorbitan fatty acid ester, polyoxyethylene alkylphenol ether, and polyoxyethylene amyl ester is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a battery separator by a radiation craft polymerization method, and includes
When a vinyl monomer solution is applied to a synthetic resin film to graft-polymerize a vinyl monomer that gives a dissolution nl J, t, to the synthetic resin, a surface active substance h11 is added to the vinyl monomer solution. , thereby accelerating the polymerization rate and obtaining a predetermined craft ratio in a shorter reaction time.

In recent years, as batteries have become higher performance and have longer lifespans, there has been a demand for separators that are durable and have low electrical resistance. In particular, so-called graft membranes in which a vinyl monomer having ion exchange properties such as acrylic acid or methacrylic acid is polymerized onto a hydrocarbon polyolefin sheet or a fluorine-containing polyolefin sheet having excellent chemical resistance are being considered as a separator. As described in U.S. Pat. No. 6,427,206, a method for preparing these graft films is so-called simultaneous irradiation, in which a polyethylene film is swollen in a solvent containing a monomer and then irradiated in the coexistence of the monomer. After pre-irradiating a polyethylene film with ionizing radiation to generate active sites for polymerization in the film, as described in
There is a pre-irradiation method in which graft polymerization is carried out by bringing the material into contact with 7-mer. In either method, the main polymer fluorocarbon is a hydrocarbon polyolefin that has poor durability and has poor affinity with monomers.For this reason, in the simultaneous irradiation method, it is necessary to It is necessary to swell the synthetic resin film with a 7-mer solvent, and irradiation is performed after the 7-mer solvent is impregnated into the film, and the time required for this swelling is 24-mer solvent is the base polymer)・It is limited to species that swell the rum and maintain compatibility with the monomer. On the other hand, in the pre-irradiation method, a craft reaction occurs when a polyethylene film is exposed to ionizing radiation in advance, and the generated reaction active sites come into contact with thousands of particles, and as time passes, the craft rate increases.
'r'! + <, and after a certain reaction time a certain graph l
- When the crafting rate (the crafting rate at this time will be called the final grafting rate) is reached, it becomes necessary to increase the crafting rate ().

In the pre-irradiation method, the reaction does not start immediately even when immersed in the monomer solution after irradiation, but the reaction starts after the time required for the monomer to wet the synthetic resin 1. It took a long time to reach the final grafting rate, which worsened the productivity of the separator.The reaction start time was delayed due to contamination of the surface of the synthetic resin film used in the furnace with oil, grease, etc. Unlike,
The kraft rate varied locally, and to prevent this, the product was subjected to degreasing and other treatments in advance before being used in the reaction, resulting in poor productivity.

The present invention is to provide a uniform and inexpensive separator for seven ponds by eliminating the conventional drawbacks and adding a surfactant to the monomer solution. It has been found that this material has excellent performance as a battery separator made of a kraft film produced by radiation kraft polymerization.

In the present invention, the detailed mechanism of action of the addition of a surfactant is not clear, or it is thought that the addition of a surfactant increases the affinity of the vinyl monomer solution for the synthetic resin film.

That is, in the conventional method, the synthetic resin film has a low affinity for the acrylic acid solution, and the graft polymerization on the film surface does not start until the monomer wets the film surface, and it takes a long time to complete the reaction. However, by adding a surfactant to the monomer solution as in the method of the present invention, the affinity is significantly improved and the reaction starts immediately. The reaction then proceeds from the surface of the film to the inside, and the surfactant promotes the diffusion of monomer 5-1 into the interior, making it possible to accelerate the reaction rate in IF.

The second effect of adding a surfactant is that when soluble polymers are polymerized together or cross-linked with different monomers, the polymerization must be carried out separately by a multi-stage polymerization method to use a granular solvent for each. . For example, when craft polymerizing acrylic acid and crosslinking with divinylbenzene, the former polymerization is carried out using water, which is commercially inexpensive, as a solvent, while the latter is polymerized using expensive organic solvents such as benzene because it is insoluble in ice. According to the present invention, a surfactant is added to water as a solvent to dissolve acrylic acid and emulsify divinylbenzene to form two monomers. Copolymerization can be carried out in a single reaction by coexisting and irradiating with radiation. Although divinylbenzene is non-bathable in ice, it is emulsified by adding a surfactant and comes into uniform contact with the film surface as a micro phase, causing a polymerization reaction.

As described above, two or more monomers with different solubility and different properties can be copolymerized at the same time in the same soot.

In carrying out the present invention, the monomer solution (surfactants to be added include polyoxyethylene argyl ether, sorbitano fat (11 ester), polyoxyethylene ethylene alkyl phenol ether, polyoxyethylene r-myl ester, l, J Nonionic surfactants or cationic and anionic surfactants such as sugar fatty acid esters, argylyl polyether sulfate salts, Nisder salts of higher alcohol sulfates, and stearyl methylhensol ammonium salts. One type or two or more types selected from these can be used.

Moreover, the addition of surfactant to the monomer solution is 0, 1
~5 wt. %, preferably from 0.5 to ]W1.%.

The monomer solvent does not necessarily have to be compatible with the monomer; water and organic solvents include, for example, benzene, toluene, xylene, carbon tetrachloride, and Z; especially on an industrial scale, water is suitable. be.

Ion-exchangeable monomers include acrylic acid, methacrylic acid, malic acid, itaconic acid, and
Further, as monomers having sulfonic groups, styrene/sulfonic acid and vinyl sulfonic acid are used, and as monomers having amide 7 groups, vinylpyrin and the like are used. The appropriate concentration in the reaction solution is 10-5 Q wt%.

In the simultaneous irradiation method, the dose rate of r-rays is reduced to 5.04-5.
X 'l' Q”rad/hr, irradiation time is 5
~24 hours was considered appropriate. In the foresight method, the anatomical line @ 1 to 5 J] Mrad, preferably 5 to 3
(The range of 'J Mrad is good.The reaction temperature is 60゛C.
It was good, preferably in the range of 20~0''C.

4i for synthetic resin fills 1 and 17? lll'/1
1. Hydrocarbon polyolefin resins that have high durability against dissolution, such as polyethylene, polypropylene, polyfuran, fluorine-containing polyolefin resins, such as polyvinyl fluoride, polyhynyritene fluoride, and ethylene tetrafluoride. Copolymers, tetrafluorinated tyrene, copolymers thereof, and the like are used.

Example 1 Low-density polyethylene with Melt Intex 2.2, density 0.922, and thickness 25μ was heated with an electron beam at an accelerating voltage of 600 KV in a nitrogen atmosphere. 2 wires attached at a current of 10 mA
0 Mrad irradiation. Directly oxygen concentration Q2wtPPm
50 parts of the following acrylic acid, 50 parts of water, 0.2 parts of molded plate
5 parts, nonionic surfactant Tritono (Tr].to
n ) A solution consisting of 1 part of X 100 (temperature 2
5°C). After being immersed for 15 minutes and then pulled up, the kraft rate was measured to be 55%.

This membrane was treated with a 251)6KoH aqueous solution at 95°C for about 5 minutes to obtain a potassium salt, which was then treated with 40% KO at 25°C.
The electrical resistance was measured using the z alternating current method and was 50 mΩ・d in an aqueous H solution.For comparison, the monomer reaction solution had a composition that did not contain a surfactant. When the solution was irradiated with an electron beam under the same conditions as in this example and the film was then subjected to the same treatment, the craft ratio was 596.

The figure is a correlation curve diagram between craft rate and reaction time.
A is for this example, and B is for a comparative example.

As can be seen from this figure, the grafting speed of A is 2 to 5 times that of B, and the time required to reach the final crafting rate is A.
It is shortened to ~%.

Example 2 Melt Intex O]5, density 0.955, thickness 50
μ high-density polyethylene, 15 parts of methacrylic acid, 80 parts of Hensefu, 5 parts of edileno tetrachloride, and an anionic surfactant. -N (Triton)X 4 1J 005
After deoxidizing with nitrogen gas for 5 minutes, immediately with Co at a dose rate of 5X + 04ra.
After irradiating at d/hr for 15 hours, the grafting ratio was measured after pulling it and removing the old Nahomopolymer, and it was found to be 48%.
Met. For comparison, a graft membrane obtained in the same manner as in Example 2 without using an anionic surfactant had a crafting rate of 26%.

The electrical resistance of each bundle was measured by performing the same treatment as in Example 1, and each had a resistance of 60Ω・~17ΩΩ.
It was Hl-d. Furthermore, in such a simultaneous irradiation method, a method using a solution containing a surfactant requires less swelling of the film in advance than a conventional method that does not use a surfactant.

Example: melt index 22, density 0.923, thickness 50μ
A low-density polyethylene film was irradiated with an electron beam at 20 Mrad in the same manner as in the example, and 45 parts of acrylic acid deoxygenated with nitrogen gas, 10 parts of divinylbenzene, 45 parts of water, and 0.25 parts of molded plate were prepared. 1 part and 6 parts of a nonionic surfactant was filtered at a rotational speed of 5 L) Orpm's T.
The mixture was stirred using a K Vomo mixer (manufactured by Tokushu Kika Kogyo), immersed in a divinylhenzene emulsified solution (temperature 25°C) and reacted for 60 minutes, then taken up, washed with water and dried. The kraft rate of this membrane was 57%, and the addition rate of nhinylhensen was 1196 out of 5796 based on the measurement of the kraft rate and ion exchange capacity.

The kraft membranes according to each of the following examples have low electrical resistance,
Suitable as a battery separator.

[Brief explanation of drawings]

The figure is a diagram showing the grafting rate-reaction time correlation curve of an example of the present invention and a comparative example. A: According to one embodiment of the present invention B: Comparative example Applicant: Yuasa Battery Co., Ltd. New Technology Development Corporation Agent: Japan Atomic Energy Research Institute Yuasa Battery Co., Ltd.

Claims (1)

[Claims] 1) A vinyl monomer solution is applied to a synthetic resin film by an ionizing radiation irradiation method to form a vinyl monomer having a dissociable group on the synthetic resin film. A method for producing a battery separator, which comprises adding a surfactant to a monomer solution. 2) When a vinyl monomer solution is applied to a synthetic resin film to graft-polymerize a vinyl monomer having a dissociable group to the synthetic resin film by an ionizing radiation irradiation method, a surfactant is added to the vinyl monomer solution and A method for producing a battery separator, which comprises emulsifying at least one other monomer that is insoluble in the vinyl monomer solution. (b) A method for producing a battery separator according to claim 1 or 2, which is a method of irradiating ionizing radiation in the coexistence of a synthetic resin film and a vinyl monomer. 4) The method for producing a battery separator according to claim 1 or 2, which is a method of irradiating the synthetic resin film l with ionizing radiation before contacting the vinyl monomer solution.