JPH04126353A - Multi-layered water repellent film - Google Patents

Abstract

PURPOSE:To achieve the long life of an air cell by arranging polytetrafluoroethylene porous layer on both surfaces of an ultra-high molecular weight polyethylene porous, layer. CONSTITUTION:By arranging polytetrafluoroethylene PTFE porous layer on both surfaces of ultra-high molecular weight polyethylene UHPE porous layer, a multi-layered water repellent film is integrated to such a degree that the film is not peeled unless a force is given thereto. The molecular weight of UHPE is approximately no less than 500,000, which is very high. As the PTFE porous layer, it is preferred that the layer has a thickness of approximately 30-200mum, porosity of approximately 5-60%, and porous diameter of approximately 0.1-10mum. The long-life of a button type air cell is thus achieved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a multilayer water-repellent membrane suitable for use in air batteries.

(Prior technology) Air batteries use oxygen in the air as an active material, and are economical and can be used for long periods of time without maintenance as a power source, and have been put to practical use, for example, for navigational aids, various communications, and telephones. However, in recent years, there has been a lot of research into converting it into a button-shaped button.

Then, as a button-type air battery, a negative electrode case (made of metal) and a positive electrode case (made of metal) having air holes are fitted together via a gasket, and the internal space of this case fitted body is divided by a separator. A structure in which a zinc negative electrode is placed in one space, an air electrode (positive electrode) is placed in the other space, and a water-repellent film made of a porous sheet of polytetrafluoroethylene (hereinafter referred to as PTFE) is adhered to the air electrode. was proposed (P. 99 of the latest manual of high-performance batteries J).
~106, ■General Technology Center, published June 30, 1999). Note that a KOH aqueous solution is usually used as the electrolytic solution, and it is impregnated and retained in the zinc constituting the negative electrode. In addition, a diffusion paper may also be attached to the water-repellent film.

(Problem to be solved by the invention) By the way, when putting products into practical use, there is an unavoidable demand for "longer life," and button-type air batteries are no exception, and each component of the battery must have a longer life. Although studies are continuing, no substitute for the PTFE porous sheet has been found at present as a water-repellent membrane.

(Means for Solving the Problems) As a result of various studies to solve the above-mentioned problems of the prior art, the inventors discovered the following fact.

■There are many factors that affect the lifespan of button-type air batteries, and the main factors are changes in the electrolyte concentration due to water vapor and carbon dioxide gas contained in the air flowing into the battery, and the formation of carbonates.

■The amount of water vapor and carbon dioxide gas entering the battery must correspond to the amount of incoming air.

(2) Therefore, it is preferable to set the amount of air to the amount necessary for the battery reaction and to prevent the inflow of an excessive amount of air.

Based on these facts, we continued our research and discovered that the desired objective could be achieved by a combination of an ultra-high molecular weight polyethylene (hereinafter referred to as UHPE) porous layer and a PTFE porous layer, and completed the present invention. I ended up doing it.

That is, the present invention relates to a multilayer water-repellent membrane comprising a UHPE porous layer and PTFE layers disposed on both sides.

The center layer of the multilayer water-repellent membrane according to the present invention is composed of a UHPE porous layer. The molecular weight of the UHPE that forms this center layer is extremely high, about 500,000 or more, whereas the molecular weight of general polyethylene (according to the viscosity method) is about 300,000 or less. Kayouna UHP
E is commercially available under the trade names of, for example, Hizex Million (manufactured by Mitsui Petrochemical Industries, Ltd.) and Ho5talen G [JR (manufactured by Hoechst Co., Ltd.).

This UHPE porous layer has an air permeability (JIS P81
17 Measured value by Gurley method) 10000sec
/100cc or less is preferable. The UHPE porous layer with such air permeability has a thickness of about 1 to 50 μm.
m, porosity of about 5 to 80%, and pore diameter of about 0.1 to 10 μm.

The UHPE porous layer can be a sheet, and such a porous sheet can be formed by, for example, adding UHPE to a good solvent such as xylene, decalin, nonane, decane, undecane, etc. at a concentration of about 0.
．． Obtain a solution dissolved to a concentration of 1 to 20% by weight, then use this solution to form a film using known plastic film forming techniques such as T-die extrusion and inflation.
After that, the packed film material is immersed in a poor solvent (one that does not dissolve UHPE or is compatible with a good solvent) such as water or alcohol (methanol, etc.) to remove the good solvent, and then the film material is removed. It can be obtained by a method of stretching at a temperature of about 10 to 130°C to a stretching ratio of about 20% or more.

In addition, the other layer in the present invention, the PTFE porous layer, has a thickness of about 30 to 200 μm and a porosity of about 5 to 6.
0% and preferably has a pore diameter of about 0.1 to 10 μm. The ventilation rate of a PTFE porous layer having such physical properties is about 100 to 5000 sec/100 cc.

This PTFE porous layer may also be a sheet. And, such a PTFE porous sheet was produced in
As described in Japanese Patent No. 3560, a method in which a mixture of PTFE powder and a liquid lubricant is formed into a sheet shape by a method including at least one of extrusion and/or rolling, and the sheet is stretched to make it porous. etc. can be obtained. The liquid lubricant can be removed by extraction, evaporation, etc. prior to stretching, or stretching can be performed under heated conditions and removed by the heat. In addition, to improve mechanical strength, the sheet is made of PTF after stretching.
Calcination can also be carried out by heating to a temperature higher than the melting point of E.

It should be noted that this firing is preferably performed while preventing shrinkage of the sheet, or in order to suppress a decrease in porosity.

The multilayer water-repellent membrane according to the present invention has P on both sides of the UHPE porous layer.
It consists of a porous TFE layer, and the UHPE layer and PTFE layer are usually temporarily attached in consideration of ease of handling.

For temporary attachment, a PTFE porous sheet is layered on both sides of a UHPE porous sheet, and the temperature is approximately 50 to 150°C and the pressure is approximately 1.
It can be done under the condition of ~100kg/cffl. In addition, at the time of this temporary attachment, it is also possible to stretch the film to a stretching ratio of 1 to 2 times.

Due to this temporary adhesion, the UHPE sheet and the PTFE sheet are integrated to such an extent that they cannot be separated unless force is applied, or the bonding strength thereof is not so great.

Of course, it is not necessary to perform this temporary attachment, and the multilayer water-repellent film of the present invention may have the above-mentioned multilayer structure when incorporated into an article such as an air battery.

(Effects of the Invention) The present invention is configured as described above, and although the reason for this is not clear, it provides a useful multilayer water-repellent membrane that can contribute to extending the life of air batteries, for example.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Thickness: 8 μm, porosity: 5%, average pore diameter: 0°5 μm,
A UHPE porous sheet with an air flow rate of 20000 sec/100 cc and a PTFE porous sheet with a thickness of 50 μm, a porosity of 3596, an average pore diameter of 1 μm, and an air flow rate of 1000 sec/100 cc are prepared.

Then, a PTFE porous sheet was placed on both sides of the UHPE porous sheet, and the temperature was 1256C and the pressure was 2 kg/
UHPE by hot stretching at a stretching ratio of 1.2 times under the conditions of cur.
The porous sheet and the porous PTFE sheet were temporarily bonded and integrated to obtain a multilayer film (sample 1) with a thickness of 108 μm. The ventilation rate of this multilayer membrane was 22,000 sec/100 CC.

Example 2 UHPE porous sheet with a thickness of 3 μm and a porosity of 10%
, average pore diameter 1 μm, air flow rate 9000 sec/10
0cc and the hot stretching ratio is 1.
The process was carried out in the same manner as in Example 1 except for doubling the thickness.
A multilayer membrane (sample 2) with a thickness of 0.3 μm and an air permeability of 11,000 sec/100 cc was obtained.

Example 3 UHPE porous sheet with a thickness of 3 μm and a porosity of 10%
, average pore diameter 2 μm, air flow rate 5000 sec/10
0cc and the hot stretching ratio is 1.
．． Work in the same manner as in Example 1 except for multiplying by 12 times,
A multilayer membrane (sample 3) with a thickness of 103 μm and an air flow rate of 7000 sec/100 cc was obtained.

The multilayer film of the above example was incorporated into a button-type air battery (PR536 type) as a water-repellent film, and the duration of continuous discharge was measured. The results are shown in Table 1. In addition, the first
rAJ, "B" and "C" in the table indicate the load resistance during discharge, rAJ is ro, 62Ω", "B" is rl, 5
KΩ", "C" means "6.2Ω".

For comparison, the thickness was 100 μm, the porosity was 20%, the average pore diameter was 0.5 μm, and the air flow rate was 5000 sec/1.
Data obtained when a 00cc PTFE porous sheet (Sample 4) was used as a water-repellent film are also shown.

Table 1

Claims (1)

[Claims] A multilayer water-repellent membrane consisting of a porous polytetrafluoroethylene layer placed on both sides of a porous ultra-high molecular weight polyethylene layer.