JPH0790153B2 - Polyolefin permeable membrane and method for producing the same - Google Patents

Description

The present invention relates to a polyolefin permeable membrane and a method for producing the same. More specifically, the present invention relates to a permeable membrane made of polyolefin, which has a fine opening and is excellent in gas permeability, which is effective as a filter for removing particles of a micron unit, and a method for producing the permeable membrane. .

[Conventional technology and its problems]

A porous permeable membrane made of polyolefin is used as a battery separator or various microfilters because of its good mechanical strength and good chemical resistance. The conventional porous film of this type is (1) a method of sintering a polyolefin resin powder.

(2) A method in which the polyolefin resin is melt-stretched and then heat-treated and cold-stretched to form holes.

(3) A method in which a liquid or solid is mixed with a resin, and after molding and processing, the liquid or solid is extracted.

Etc.

However, in (1), for example, the formed pore size is as large as several 10 μm, and it is difficult to control the pore size. In the method (2), anisotropy is generated in the porous film due to the limitation of the manufacturing method, and it is easy to avoid the specific direction. Further, the method (3) has a problem that the film becomes brittle as the porosity of the film is increased.

Further, recently, there has been a demand for a filter having a good removal rate of particles smaller than conventional ones, for example, particles of 0.1 μ or less by chemicals and water used in the electronics industry. However, in order to improve the removal rate of smaller particles in the extension of the above-mentioned conventional technique, if the pore size of the permeable membrane is made small, the amount of permeation is greatly reduced, which causes a problem in terms of economical efficiency in industrial use. Become.

It is possible to improve the amount of permeation by reducing the thickness of the film, but when the film thickness is reduced, its handling, for example, mechanical strength such as pressure resistance at the time of passing, becomes low and it cannot be put to practical use.

Therefore, in the case of cellulose, polyamide, or polysulfone-based resin, an asymmetric membrane in which a thin dense layer is supported by a porous layer having good permeability is produced by a solvent cast method or the like, and is used as an ultrafiltration membrane. However, at present, there is no method suitable for industrialization for obtaining such a structure with polyolefin resin.

[Object of the Invention]

An object of the present invention is to provide a porous permeable membrane made of polyolefin having a high removal rate particularly for particles of 0.1 μm or less and having a high permeation amount, and a method for producing the same.

[Structure of Invention]

The gist of the present invention is a single porous membrane made of polyolefin, one surface of which has a dense porous structure, the other surface has a large pore structure, and a water permeability of 500 / Hr · m. ²
A permeable membrane made of polyolefin, characterized by having atm or more, and 1 to 60% by weight of ultra-high molecular weight polyolefin (A)
And a hydrocarbon plasticizer (B) having a boiling point not lower than the melting point of (A) (B) in an amount of 99 to 40% by weight to obtain a sheet-shaped molded product, which is below the melting point of (A). At a temperature of uniaxially or biaxially to form a stretched sheet, and one side of the stretched sheet is heated to a melting point of (A) or higher and the other side is kept at a melting point of (A) or lower. A method for producing a permeable membrane made of polyolefin, characterized by heat-treating and then extracting (B) with a solvent.

The permeable membrane of the present invention is composed of a single membrane, one surface of which has a porous structure (dense layer) having dense openings, and the other surface has a porous structure having large openings ( Porous layer).

The water permeability of the permeable membrane of the present invention is 500 / Hr · m ² · atm or more, preferably 1000 / Hr · m ² · atm or more.

The dense layer of the permeable membrane of the present invention has a removal rate of 0.1μ spherical particles of 99% or more, preferably a removal rate of 0.04μ spherical particles of 99.
% Or more and the water permeability when the thickness of the membrane is 50μ
It is desirable that the porous structure is 50 / Hr · m ² · atm or more.

Further, the porous layer has a water permeability of 50 μm when the film thickness is 50 μm.
It is desirable that it is 1000 / Hr · m ² · atm or more.

If the water permeability of the dense layer is 50 / Hr · m ² · atm or less, or the water permeability of the porous layer is 1000 / Hr · m ² · atm or less, it is inconvenient to achieve a high permeability as a permeable membrane.

The water permeability and particle removal rate are measured by the following methods.

Permeability (/ m ² Hr, atm) Using a Amicon UF Stirring Cell Model 12 with a differential pressure of 1 kg / cm ² ,
Measure at a temperature of 23 ℃. Before the measurement, the permeable membrane is immersed in an ethanol / water = 1/1 solution for 2 minutes to make it hydrophilic, and then the measurement is performed.

Particle removal rate The used particles are UNIFORM-LATEX-PARTIC of Dow Chemical Company, USA
Using LES particle diameters of 0.091μ and 0.038μ, dilute the above particles with water and conduct a water permeation test in the same manner as in the case of the above water permeability measurement. Measure the concentration before and after passing through the membrane with a UV meter. Find the rate.

The following method is used to obtain the permeable membrane as described above.

As the polyolefin used as a raw material, an ultrahigh molecular weight polyolefin is used. High molecular weight polyolefin has an intrinsic viscosity [η] of 5 dl measured in decalin at 135 ° C.
Polyethylene having a / g or more or polypropylene having a [η] of 7 dl / g or more is suitable.

A hydrocarbon-based plasticizer is used as the compound. As the hydrocarbon plasticizer, a plasticizer that is solid at room temperature and has a boiling point higher than the melting point of the raw material polyolefin (usually higher than 10 ° C.) is preferably used. Specific examples include paraffin waxes, higher alcohols such as capryl alcohol, lauryl alcohol, palmityl alcohol, and stearyl alcohol.

The blending ratio of the raw material polyolefin and the hydrocarbon plasticizer is
Polyolefin 1-60% by weight, hydrocarbon plasticizer 99-40
It is good to set it as a percentage by weight.

It is desirable that the above-mentioned composition is a homogeneous mixture by heating to a temperature above the melting point of the raw material polyolefin using a Banbury mixer or the like to obtain a uniform mixture. Supply hydrogen-based plasticizer to a normal extruder to plasticize and homogenize
It may be extruded directly from a T-die or the like to form a sheet.

The resulting sheet is then stretched at a temperature below the melting point of the raw polyolefin. The stretching may be uniaxial or biaxial. It is considered that the original form of the fine porous structure is formed by this stretching. The draw ratio cannot be specified because it depends on the physical properties of the film to be obtained, but it is usually several times to several tens of times in terms of area ratio.

The stretched sheet material obtained is then heat treated. The heat treatment is carried out by keeping one surface of the stretched sheet material at a temperature below the melting point of the raw material polyolefin and heating the other surface above the melting point. Specifically, for example, one surface of the stretched sheet material is kept in contact with a roll or a metal plate kept at a temperature not higher than the melting point of the raw material polyolefin, and the other surface is heated to a temperature not lower than the melting point of the raw material polyolefin. A method of pressing a metal plate or blowing a hot air is used, but this method is optional.

Regarding the heat treatment temperature, one surface should be kept at about 30-80 ° C lower than the melting point of the raw material polyolefin, while the other surface should be kept at 30-
The heat treatment may be performed at a high temperature of about 70 ° C. The pressure during heat treatment is preferably 0.1 to 50 kg / cm ² .

The surface heated by this heat treatment becomes a porous structure having a large pore size.

Accordingly, a film is formed in which one surface of one film has a dense porous structure and the other surface has a porous structure having a large pore diameter. By forming the porous structure, the dense layer can be thinned without reducing the strength of the film. It also improves the transmittance without lowering the removal rate.

The membrane whose pore size has been adjusted as described above is then subjected to an extraction treatment using a solvent capable of dissolving a hydrocarbon plasticizer such as ethanol or n-hexane to remove the hydrocarbon plasticizer in the membrane. In this way, a porous membrane in which membranes having different pore sizes are integrated is obtained.

The steps of heat treatment and extraction and removal with a solvent must be performed in this order, and if they are reversed, the holes to be formed in the film are crushed and useless. The film thickness depends on the application,
Is usually about 5 to 500 μ.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example-1 20% by weight of ultrahigh molecular weight polyethylene having an intrinsic viscosity [η] = 13.5 and 80% by weight of stearyl alcohol were uniformly kneaded at a temperature of 160 ° C. using a Banbury mixer, and a press molding machine was used before cooling and solidification. A 0.5 mm sheet was obtained. The sheet was sequentially stretched 4 × 4 times at a temperature of 120 ° C. with a biaxial stretching machine to obtain a stretched film of 30μ. The film was heat-treated for 30 seconds with a press in which the temperature of the upper plate was adjusted to 70 ° C and the temperature of the lower plate was adjusted to 170 ° C. Then, stearyl alcohol was dipped in an ethanol solution at 50 ° C. for 1 minute to extract a porous permeable membrane. The thickness of this film was 28μ.

The water permeation rate was 1500 / Hr · m ² · atm, and the removal rate of 0.038μ styrene latex was 99% or more. Observation results of both surfaces of this film by a scanning electron microscope are shown in FIGS. 1 (a) and 1 (b).

Fig. 1 (a) shows the surface in contact with a 70 ℃ hot plate, and Fig. 1 (b) shows 17
This is the surface that was brought into contact with the 0 ° C hot plate.
FIG. 1B shows a magnification of 10,000 times.

Comparative Example-1 A permeable membrane was obtained in the same manner as in Example-1, except that in Comparative Example-1, after biaxial stretching, heat treatment was not performed by sandwiching. The thickness of this film is 20μ and the water permeability is 130 / hr ・ m ²・
Atm and small.

Comparative Example-2 Using the same materials as in Example-1, a Banbury mixer was used for uniform kneading, and a 0.1 mm sheet was obtained with a press molding machine before cooling and solidification. This sheet was immersed in an ethanol solution at 50 ° C. for 5 minutes to extract stearyl alcohol to obtain a porous permeable membrane. The thickness is 95μ, and the water permeability is
Although it was 3,500 / hr · m ² · atm, the removal rate of 0.091μ styrene latex was 92%.

Example 2 Ultrahigh molecular weight polypropylene [η] = 8.02 25 wt% and paraffin wax 75 wt% were mixed using a Banbury mixer.
Uniform kneading was performed at a temperature of 0 ° C., and a 0.5 mm sheet was obtained in the same manner as in Example-1. The sheet was 4 × at a temperature of 145 ° C.
Sequential stretching of 4 was carried out to obtain a 32 μ film. The film was heat-treated for 30 seconds with a press adjusted to a temperature of 100 ° C. for the upper plate and 200 ° C. for the lower plate, and then paraffin wax was extracted with normal hexane at 50 ° C. to obtain a porous permeable membrane. The thickness of this film was 26μ, the water permeability was 2300 / hr · m ² · atm, and the removal rate of 0.091μ styrene latex was 99% or more.

〔The invention's effect〕

The permeable membrane of the present invention has one layer having a dense layer on one surface and a porous layer on the other side, and can remove fine particles of about 0.1 μ while maintaining the transmittance. Further, according to the production method of the present invention, the formation of the dense layer and the porous layer and the control of the layer thickness can be performed as necessary, and the permeable membrane having various pore sizes applicable to various applications can be easily obtained.

[Brief description of drawings]

1 is a micrograph of the permeable membrane obtained in Example 1,
(A) shows the surface in contact with the 70 ° C hot plate, and (b) shows the surface in contact with the 170 ° C hot plate.

Claims (12)

[Claims] 1. A single porous membrane made of polyolefin, one surface of which has a dense porous structure, the other surface of which has a large pore size, and a water permeability of 500 / Hr · m ^2.・ Atm
The above is a permeable membrane made of polyolefin. 2. The permeable membrane according to claim 1, wherein the removal rate of spherical particles having a diameter of 0.04 μ is 99% or more. 3. The removal rate of spherical particles having a diameter of 0.1 μ is 99% or more and the water permeation rate is 1000 / Hr · m ² · atm or more, according to claim 1. Permeable membrane. 4. The permeable membrane according to any one of claims 1 to 3, wherein the polyolefin is polyethylene having an intrinsic viscosity [η] of 5 dl / g or more measured in decalin at 135 ° C. 5. The permeable membrane according to any one of claims 1 to 3, wherein the polyolefin is polypropylene having an intrinsic viscosity [η] of 7 dl / g or more measured in decalin at 135 ° C. 6. The dense porous structure in the permeable membrane has a particle size of 0.
The removal rate of spherical particles of 1μ is 99% or more, and the water permeation rate when the thickness is 50μ is 50 / Hr · m ² · atm or more. Permeable membrane. 7. The dense porous structure in the permeable membrane has a particle size of 0.
The removal rate of 04μ spherical particles is 99% or more, and the water permeability when the thickness is 50μ is 50 / Hr · m ² · atm or more. Permeable membrane. 8. A sheet using a mixture of 1 to 60% by weight of ultrahigh molecular weight polyolefin (A) and 99 to 40% by weight of a hydrocarbon-based plasticizer (B) having a boiling point higher than the melting point of (A). A molded product is obtained, and the sheet-shaped molded product is stretched uniaxially or biaxially at a temperature not higher than the melting point of (A) to form a stretched sheet, and one surface of the stretched sheet is at least the melting point of (A). A method for producing a permeable membrane made of polyolefin, characterized in that it is heated to 1, the other surface is heat treated so as to keep it at the melting point of (A) or lower, and then (B) is extracted with a solvent. 9. Ultra high molecular weight polyolefin (A) is 135 ° C.
A polyethylene having an intrinsic viscosity [η] measured in decalin of 5 dl / g or more.
The manufacturing method according to item. 10. Ultrahigh molecular weight polyolefin (A) is 13
The production method according to claim 8, wherein the polypropylene has an intrinsic viscosity [η] of 7 dl / g or more measured in decalin at 5 ° C. 11. The hydrocarbon plasticizer (B) is a solid at room temperature and is characterized by being solid.
The manufacturing method according to item. 12. The heat treatment comprises heating one surface of the stretched sheet-like material to a temperature above the melting point of (A) while contacting one surface with the surface of the support set below the melting point of the ultrahigh molecular weight polyolefin (A). 9. The manufacturing method according to claim 8, wherein the manufacturing method is performed by.