JPH02113039A - Porous film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a film of small pore size, having high mechanical strength and carrying a thin layer of ultra-high-molecular weight polyethylene thereon by impregnating a (non)woven fabric base with said ultra-high-molecular weight polyethylene. CONSTITUTION:The objective porous film with a thin layer of ultra-high- molecular weight polyethylene on its surface can be obtained by impregnating (A) a (non)woven fabric as base with (B) said ultra-high-molecular weight polyethylene >=500000 in viscosity-average molecular weight. Specifically, the process is as follows: ultra-high-molecular weight polyethylene >=500000 in viscosity- average molecular weight is dissolved in a good solvent and the resultant solution is made to contact with a (non)woven fabric as the base for the objective film to effect impregnation of the solution into the base and, at the same time, form a thin layer from said solution on the base surface followed by immersing the resulting product in a poor solvent and then removing the good solvent.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a porous membrane comprising a woven fabric as a base material, a non-woven fabric and an ultra-high molecular weight polyethylene (hereinafter referred to as σHPE), and a novel method thereof. It concerns the manufacturing method.

(Prior technology) Separator for tM, capacitor spacing a, each +x min mg
It is known to use porous membranes made of polyethylene, polypropylene, polytetrafluoroethylene, etc. (for example, Japanese Patent Publication No. 40119/1983), and it is also known that woven or nonwoven fabrics can be used.

(Problem to be solved by the invention) By the way, these porous membranes, woven fabrics, or nonwoven fabrics have
Custom-made products are superior depending on each application (for example, 'i!
When used as a pond separator, it is naturally required that the ionic conductivity be excellent, the mechanical strength be sufficient, and the pore diameter be small.

However, although the pore size of the porous membrane described in J: is small, its mechanical strength is directional. In particular, there was a problem with tear strength, and care had to be taken when handling the weir.

On the other hand, although woven fabrics and nonwoven fabrics do not have any disadvantages in terms of mechanical strength, they have the problem of being difficult to obtain pore diameter uniformity f and small pore diameters.

(A Companion Means for Solving the Problem) The present inventor has conducted extensive studies to solve the above-mentioned problem that the prior art has.

First, the porous membrane and woven or non-woven fabric are dotted.

We considered a composite porous body that is partially bonded in the form of stripes, the uniformity of the pore diameter is ensured by a porous membrane, and a mechanical strength of 7 is given by a woven fabric or a non-woven fabric.

However, when this is used in a battery separator, there are concerns about deterioration and deterioration due to the electrolyte in the culture agent, and when used in a 111 membrane, the area contributing to 1 separation becomes smaller, resulting in a decrease in separation efficiency. The problem arose that this was unavoidable.

Therefore, in addition to further consideration, by using a woven fabric or non-woven fabric as a base material, combining this material with a specific polymer to form a specific structure, and making the polymer porous, 1) the mechanical strength is increased, and the pore diameter is Porous fRI with small porous parts! The present invention was completed by discovering that Il can be obtained.

Specifically, the porous membrane according to the present invention comprises a woven fabric or non-woven fabric as a base material, and a viscosity average molecular weight (hereinafter abbreviated as 1 molecular weight).
The Uf(PE) is characterized by being impregnated inside the base material, existing in a thin layer on the surface of the base material, and having a porous structure. .

The present invention will be described in detail below with reference to six drawings. In the drawing, l is the base material of the porous membrane.

glass, polyester, polyamide, polypropylene,
It is a woven or non-woven fabric made of acrylic or the like. The thickness of the base material 1 is determined depending on the purpose of the porous membrane. For example, in the case of a porous membrane used as a battery separator, the thickness is usually about 10 to 1.
A porous membrane of 300 μm or less is used as a separation membrane (in the case of a porous membrane, a membrane of approximately 30 to 500 μm is usually used).

2 is Ui (PE) which is impregnated into the inside of the base material 1 and fills the countless pores of the base material 1 (the form of this filling is omitted from the figure).
The table dii7ic is also thin (thickness riik regular l~30
0μ groove).

Then, the countless pores of the base material 1 are filled and the surface Vc
It has a porous structure (not shown) with numerous pores. U) The pore size and porosity of IPE 2 can be set depending on the use of the porous membrane, but usually the former is about 0.1 to 10 μvm, and the former is about 30 to
It is 90%.

UHPE has a molecular weight of 500,000 or more, which is larger than that of general polyethylene, which is about 300,000 or less, and by using polyethylene with such a large molecular weight, the strength of the porous structure can be improved to a practical level. Can be maintained at a certain level.

In addition, Uf (PE is manufactured by Mitsui Petrochemical Industries, Ltd.).

The black market name Hi-Zex Million, manufactured by Hoechst, #i product name Hostalen GUR, etc. are commercially available.

Next, a method for manufacturing a porous membrane, which is another embodiment of the present invention, will be described. This method uses UHPE 1 with a molecular cap of more than 500,000
By dissolving the medium and bringing this solution into contact with a woven or nonwoven fabric as a porous membrane base material, the solution is impregnated inside the base material and a thin layer of the solution is formed on the surface of the base material. , then by immersing it in kgjlflj medium and removing the good solvent, UMP
It is characterized by making E' porous.

In the method of the present invention, UHPE is first dissolved in a good solvent. As mentioned above, UHPE has a high molecular weight.

Since it has typical JIlfII properties, it is preferable to use the heating melting method. For example, in a given container Uk
A method can be applied in which a PE powder is added to a good solvent, and the temperature is gradually raised while stirring to dissolve it, and the final temperature at 770°C is usually about 100-180°C.

The required time is approximately 062-10 hours.

The solvent used in this step is not particularly limited as long as it can dissolve Uf(PEt), such as xylene, decalin,
Nonane, decane, undecane, etc. can be used.

Ninth, it has been found that the UilPB 111 degree in the UHPE solution obtained in the above-mentioned solution step 2 is preferably about 0.1 to 2 billion% by weight. If the concentration is too low.

Not only can the UHPE 14 in the resulting porous membrane crack, but it is also difficult to fill the pores of the substrate with the solution. On the other hand, if the # degree is too high, the impregnating property into the inside of the porous base material will be reduced, and it will be difficult to fill the pores of the base material.

The UHPE solution obtained by the above dissolution step IC is:

Then, it is brought into contact with a woven or nonwoven fabric as a base material (M<L). This contact impregnates the inside of the substrate with the UHPEm liquid,
This is carried out to fill the pores of the substrate with the solution and to form a thin purple layer of the solution on the surface of the substrate.

Therefore, the contact between the Ui(PE solution and the substrate requires (a
) A method in which the substrate is immersed in a UHPEm liquid; (b) A method in which UHPE is applied onto the surface of the substrate by a T-die extrusion method, an inflation method, etc.; (C) A method in which UHPE is applied onto the surface of the substrate by a T-die extrusion method, an inflation method, etc.; Method # of applying a solution to the surface of the base material can be adopted. In the case of methods (b) and (C), it is preferable to apply pressure after coating to ensure that the UHPEm liquid is impregnated into the inside of the base material. Maku, UHPE
In order to increase the fluidity of the M solution and improve its ability to impregnate the inside of the substrate, the solution can be heated. The temperature when heating the knife is approximately 18 L for workability, safety, etc.)
The temperature below is preferably 100 to 180°C.

In the present invention, in contact with UHPEm liquid, IIfJ &Zeshimera'!``L'' substrate is then immersed in a poor bath medium. Through the immersion treatment, the good solvent is extracted and removed by the *g medium from the UHPE solution present inside and on the surface of the substrate, and the As a result, UHPE porous nodules are formed inside and on the surface of the substrate.

The poor solvent used here is UMPE'J? Any material may be used as long as it does not dissolve the processing base material and is compatible with the above-mentioned good solvent.
Water and various organic solvents can be used, but 41-fluorols, particularly methanol, are preferred.

The porosity and pore size of the Uf(PE porous material) formed in step 2 above are determined mainly by the degree of compatibility of both solvents used and the rate of extraction of the good solvent into the *solvent.

Therefore, by changing the concentration of the UHPEm liquid or the combination of both mortar, UHPE porous J! The porosity of l and the pore size of the pores can be adjusted.

U in the porous 'lt film obtained by the method of the present invention
The pores ``4'' and the pore diameters of the HPE porous material 11 are as follows.

The above-mentioned nine mouths (although the number may vary depending on the working conditions).

Usually, the former is about 30-90%, the latter is lJ, 1-10μ
It's a groove.

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

Ru. In addition, in the examples, all "parts" indicating "it" are "spare time parts".

Example 1 100 parts of medium silane, 100 parts of decalin, and 4 parts of UHPE powder (molecular weight: 2,000,000, particle size: 30μ) were placed in a glass container, and the liquid temperature was raised from 25°C to 140°C while stirring, and then Maintain the temperature and continue stirring for 1 hour.
HPE f? I will make you understand.

This UHPE solution was applied to a glass woven cloth (thickness 100 μm, quality *
98 g/rl was extruded on one side using a T-die (temperature 135°C), and then sandwiched between two glass plates.
A pressure of 1 klil/- is applied and held for 1 minute.

In addition, at this time, the temperature was maintained at -135°C. This nv
From ζ, the pores of the glass woven fabric are filled with the UHPE solution, and a thin layer of the UHPE solution is formed on both surfaces of the woven fabric.

Next, this was immersed in methanol (liquid temperature 25°C) for 30 minutes at 1C, then pulled out and air-dried to form a porous g (thickness 140μ
Stirring) All benefits.

This porous membrane has 2 UHpa porous pores (Izo is 1, for example, a run * type 鞞子Cu'4I1. boundary (the magnification is 5υυυ
It can be observed by magnification.

Example 2 A porous membrane (thickness: 150 μm) was obtained in the same manner as in Example 1, except that UMPE with a molecular weight of 600,001 and a particle size of 1st and 1 μm groove was used.

Comparative example 1 Commercially available polypropylene porous membrane (thickness 25 μm).

Comparative example 2 Glass woven fabric used in Example 1.

Comparative Example 3 The polypropylene porous membrane of Comparative Example 1 was layered on one side of the glass woven fabric used in Example 1 to obtain a porous membrane.

For adhesion, a hot melt adhesive containing polyvinyl acetate as a main component was used, and the adhesive was streaked at a distance of 2 m during application and an application interval of 5 B.

Comparative Example 4 U) When working in the same manner as in Example 1 except that low-density polyethylene with a molecular weight of 250,000 and a density of 0.95 was used instead of IPE, countless cracks were observed in the polyethylene porous layer on the surface of the base material. As a result, a practical porous membrane could not be obtained.

The following tests were conducted on the porous membranes of Examples and Comparative Examples, and the results are shown in Table 1.

(A) Pore diameter measurement Scanning electron microscope (magnification is 50x in Comparative Example 2).

t-
A friend who observes and measures.

(BJ ion conductivity measurements were carried out at 25°C and measured according to J4S-C-2313. The electrolyte was a mixture of propylene carbonate and 1.3-dioxolane 41 in a ratio of 1:1,
Dissolve lithium perchlorate in this as an electrolyte.

(C) Tear strength Measured in the vertical and horizontal directions of the valley porous membrane according to JIS-6238, and its weak +tii? Indicated.

Table 1: After measurement, the glass cloth and polypropylene porous membrane peeled off when removed from the electrolyte.

(Effects of the Invention) The present invention is configured as described above, and the UHPE porous layer is supported and reinforced by a nonwoven fabric or a woven fabric.
Porous g with high strength can be provided.

According to the method of the present invention, such a porous membrane can be easily produced.

[Brief explanation of the drawing]

The drawing is a front view showing an example of the porous membrane according to the present invention. 1... Base material 2... Ul-IPE2 1J)-I
P.F.

Claims (2)

[Claims] (1) It consists of a woven or nonwoven fabric as a base material and ultra-high molecular weight polyethylene with a viscosity average molecular weight of 500,000 or more, the polyethylene is impregnated inside the base material and exists in a thin layer on the surface of the base material, and A porous membrane characterized by having a porous structure. (2) Ultra-high molecular weight polyethylene with a viscosity average molecular weight of 500,000 or more is dissolved in a good solvent, and then this solution is brought into contact with a woven or nonwoven fabric as a porous membrane base material to impregnate the inside of the base material with the solution. At the same time, a thin layer of solution is formed on the surface of the substrate, and then this is immersed in a poor solvent.
A method for producing a porous membrane, comprising making ultra-high molecular weight polyethylene porous by removing the good solvent.