JPH01266806A - Porous film having micropore - Google Patents

Abstract

PURPOSE:To increase a number of pore per unit area of a film and to obtain a porous film having minute pores having high separating efficiency per unit area by using a netlike structure comprising polyester or polyolefin having uniform size and shape of pores which are uniformly distributed in a longitudinal and lateral directions of the film. CONSTITUTION:A netlike structure having uniform size and shape of mesh comprising those constituted of drawn polyester monofilament, etc. having uniformly distributed meshes, is inserted between 'Teflon(R)' sheets, and subjected to thermal shrinkage between hot plates of a press at a temp. between a m.p. and a softening point of the thermoplastic resin constituting said network body. The product is pressed further between pressing plates. Thus, a porous film having minute pores contg. 800,000-5,000 pores per 1cm<2> film area is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microporous membrane comprising a polyester or polyolefin network structure having uniformly arranged pores and having uniform pore size and shape.

Various types of microporous membranes have been known so far. However, most of the technologies for manufacturing these microporous materials involve chemical methods, such as solidifying the membrane under special conditions, or adding additives to create micropores in the membrane, which are then extracted later. This is due to methods etc. However, with such chemical methods, it is impossible to uniformly arrange the pores in the membrane and to make the pores uniform in size and shape. In addition, neutrons are applied to a polycarbonate film to make holes, and the holes are enlarged with an alkaline solution to create a membrane filter (Nucleop) with a desired pore size.
ore ), but like this □
The resulting membrane filter has the disadvantage that the holes are randomly perforated by neutrons, so the arrangement of the holes is non-uniform, and that a plurality of holes are connected to form connected holes. Furthermore, as shown in Japanese Patent Application Laid-Open No. 55-41807, by hot pressing a laminated web of many long fibers or short fibers, the low melting point fibers in the web are melted and fused. A method for making filters, especially filters for vacuum cleaners, is also known, but since such a laminate of fiber webs does not have a uniform mesh, it is difficult to obtain a filter with uniform mesh size and shape even by heat pressing. It's not possible. Therefore, although the filter obtained in this way can be used as a filter for vacuum cleaners, etc., it cannot be used as a separation membrane that requires precise fractionation, such as a membrane that separates plasma from blood. It cannot be used.

The present invention solves these drawbacks, and the membrane 1-
A polyester or polyolefin having 800,000 to 5,000 pores per membrane, the pores being substantially uniformly arranged in the vertical and/or horizontal directions of the membrane, and the pores having substantially uniform size and shape. It is a microporous membrane consisting of a network structure.

Since the microporous membrane of the present invention has pores arranged extremely uniformly, the pores per unit area (pore size 0.1 to 5
0 μm) can be set to 800,000 to 5,000 pieces/-, so the separation efficiency per unit area is high and uniform. Also, since the pores are substantially uniform in size and shape, the fractionation is extremely high.

In the present invention, "pores arranged substantially uniformly in the vertical and/or horizontal directions of the membrane" refers to "pores substantially uniformly arranged vertically and/or horizontally" on the membrane surface in the vertical and/or horizontal directions (preferably vertically The holes, which are arranged in an orderly manner in both the horizontal and horizontal directions and at substantially equal intervals in both or each of the horizontal and vertical directions, penetrate the front and back surfaces of the membrane at approximately right angles.

"Substantially uniform pore size and shape" means that the size and shape of all pores arranged in the membrane are the same or substantially the same when viewed from the front and back sides of the membrane. do. Here, the shape of the hole is a circular shape, an oval shape, a quadrangular shape, or other polygonal shape, and among these, a circular shape, a square shape, and a regular polygon shape of square or more are preferable from the viewpoint of separability. In addition, "the size of the hole" means the diameter when the hole is circular, and the maximum diameter when the hole is other shapes.

The number of pores per unit area of the membrane is 800,000 to 5,000 pores/ct.
A, the separation efficiency per unit area of the membrane increases when the number of pores is as large as possible. When the number of particles exceeds 800,000 cells/cd, the strength of the membrane itself decreases, although it depends on the material of the membrane and the size of the pores, and when the number of cells exceeds 5,000 cells/cd, the separation efficiency per unit area of the membrane deteriorates.

The size of the pores can be determined as appropriate depending on the size of the substance to be fractionated, but it is generally in the range of 0.1 to 50 μm. The pore size is 4 to 6 μm, and the size is 0.1 to 0.0 μm when used in a membrane that separates plasma from blood or a membrane that filters ascites to remove bacterial cells.
3 μm, preferably 0.2-0.25. c+m.

The microporous membrane has a thickness of 5 to 200 μm, preferably a thin film of 0 to 30 μm. Fractionability is further improved by reducing the film thickness.

Among thermoplastic resins, polyesters such as polyethylene terephthalate, and polyolefins such as polyethylene and polypropylene are used as materials for the microporous membrane.Among them, polyester has sufficient strength even when the film thickness is reduced. Therefore, separation efficiency is improved, making it optimal.

Next, the method for producing the microporous membrane of the present invention will be described. The structure is heat-treated to shrink at a temperature between the melting point and the softening point of the thermoplastic resin forming the network structure so that the network is not crushed and closed, and then further pressure-treated. This is a method for producing a microporous membrane characterized by the following. According to this method, a microporous membrane having the above-mentioned configuration can be obtained very easily, and therefore, it has great commercial value.

In the present invention, the term "network structure" refers to woven fabrics, knitted fabrics, net-like articles, mesh bodies, etc. obtained from polyester or polyolefin as described above. Among these, woven fabrics are preferred because they tend to have fine meshes, and they also tend to have uniform mesh sizes and shapes.

In addition, the material for the woven fabric is drawn polyester filament (melting point 255-260°C, softening point 238-240°C),
Partially drawn polyester filament (melting point 225-23
5°C1 softening point 195-205°C) and undrawn polyester filament (melting point 150°C, softening point 120°C)
Stretched polypropylene filament (melting point 165-173
℃1 softening point 140-160℃), especially drawn filaments (polyester, polypropylene)
It is preferable to use a woven fabric consisting of the following, since it is stretched both vertically and horizontally, resulting in a microporous membrane with excellent physical strength. Among these, stretched polyester filaments are most suitable. The filament thickness is 0.5
~50 denier, preferably 1-30 denier.

The filament may be a woven fabric made of single yarns or a woven fabric made of plied and twisted yarns.

Furthermore, "mesh substantially uniformly arranged vertically and/or horizontally" means:
It means meshes that are arranged in an orderly manner in the vertical direction and/or in the horizontal direction (preferably in both the vertical and horizontal directions) on the surface, and that are arranged at K in both the horizontal and vertical directions, or at substantially equal intervals in each direction. do. Here, the vertical and horizontal lines may intersect at a right angle or may intersect at a certain angle. The mesh penetrates the front and back surfaces of the mesh structure at approximately right angles.

"The size and shape of the meshes are substantially uniform" means that the size and shape of all the meshes arranged in the network structure are the same or substantially the same when viewed from the front and back surfaces of the network structure. This means that it is almost the same as . Here, the shape of the mesh may be circular, columnar, or other polygonal shape.

Among these, a circular shape, a square shape, and a regular polygon shape of square or more are preferable.

Further, the size of the mesh means the diameter when the mesh is circular, and the maximum diameter when the mesh has other shapes.

The number of meshes per unit area of the network structure varies depending on the number of pores of the intended microporous membrane, the thickness of the filament used, etc., but is approximately 700,000 to 1,500 meshes/crA.

The size of the mesh also varies depending on the size of the pores in the target microporous membrane, but is about 8 to 1000 μm. The mesh size preferably used is 5 to 200 μm.

A network structure such as a woven fabric made of such polyester filaments is heat-shrinked by heating at a temperature between the melting point and the softening point of the structure.

Heat treatment is performed by placing between hot plates adjusted to within this temperature range or using hot rolls (in some cases, multiple rolls).
This is done by passing it in between. The temperature of this heat treatment may be within the range of the melting point and softening point, but it is 5°C higher than the melting point.
It is preferable to carry out the treatment at a temperature lower than 10° C. and higher than the softening point by 10° C. or more, since it is possible to uniformly heat-shrink only the size of the mesh without soaking and closing the shape of the mesh of the network structure. The time for the heat treatment depends on the temperature of the heat treatment, but is approximately 5 seconds to 20 minutes, preferably 1 to 20 minutes.
It's 5 minutes. During heat treatment, it is necessary to heat-shrink the network structure and increase the number of meshes per unit area of the network structure, so excessive pressure that may interfere with heat shrinkage should be avoided. .

Next, by applying pressure to the heat-shrinked network structure, the network structure is compressed and fused to become a thin film, thereby obtaining the desired microporous membrane.

The pressure treatment is carried out by passing the material between plates or between rolls (in some cases, multiple rolls), and the pressure at this time is preferably in the range of 1 to 3ooKp/d (gauge pressure), preferably 100 to 150Kp/d (gauge pressure). Kp/,-,! (gauge pressure). The time for the pressure treatment is 5 seconds to 20 minutes,
Preferably it is 1 to 5 minutes. It is preferable to heat the plate or roll during the pressure treatment. The heating temperature in this case is preferably approximately the same as the heating temperature conditions in the previous step. When carrying out heating and pressure treatment, care must be taken to ensure that the mesh is not soaked and the desired microporous membrane cannot be obtained.

By heat-treating the network structure in this way and then applying pressure, the network structure is thermally shrunk and then compressed, and the network becomes the pores of the microporous membrane. The number of pores per unit area of the obtained microporous membrane is 1.2 to 3 times the number of meshes in the initial network structure, and the size of the pores in the microporous membrane is the same as the size of the mesh. It becomes 1/2 to 1/20 times.

In the method of the present invention, a microporous membrane having pores of a desired size can be obtained by appropriately selecting the conditions for heat treatment and pressurization (or heating pressure).
The conditions also vary depending on the shape of the material of the network structure used. Typical conditions will be specifically explained in Examples below using a stretched polyester filament woven fabric.

The microporous membrane obtained by the method of the present invention has extremely uniform pore size and shape, and the pore size can be made to a desired size, making it excellent in various fields such as the medical industry field. It can be effectively used as a separation membrane with fractionation properties. Specifically, it can be effectively used as a membrane for measuring red blood cell deformability, a membrane for separating plasma in blood, a membrane for hemofilter, a membrane for filtering ascites, or a membrane for removing bacterial bodies and solid particles (SS) from various liquids. .

Examples 1-2 20 denier drawn polyester filament (melting point 2
60'C1 Softening point 240℃) Single yarn length 180
Line/inch x 170 lines/inch polyester mesh for printing gauze (17 (m x 17α; number of meshes 5,600 pieces/-; mesh size 100 l1m uniform; mesh thickness 88 μm; vertical and horizontal filaments intersect at right angles) between 1rullE Teflon sheets,
This mesh was designed to prevent dirt and dust from adhering to it. Next, this was placed between the hot plates of a press set at 250°CK (hot plate spacing: 50), and the time shown in the table below was approximately 15~
2 minutes) The mesh was heat-shrinked by heat treatment. Next, press this on a press plate at 100 Ky/cd (gauge pressure).
Heat pressure (25 minutes) for the time (1.5-2 minutes) as shown in the table below.
0°C). Thereafter, it was taken out, and 7 pieces of Metsu were sandwiched between Teflon and cooled between chrome-plated molds, and when it became hard, it was taken out from the mold to obtain a microporous membrane.

The heat treatment time, heat pressure treatment time, and results are shown in the table below.

Below are blank spaces Examples 3 to 4 Polyester mesh (15X15α; number of meshes: 90,000 pieces/inch) of 750 lengths/inch x width 750 pieces/inch consisting of a single yarn of 5-denier drawn polyester monofilament (melting point 260°C, softening point 240°C) -; mesh size approximately 10 μm; mesh thickness 40 μm; vertical and horizontal filaments intersect at right angles) is sandwiched between 1% thick Teflon sheets and placed between press hot plates set at 250°C (heat plate interval 5 %) and heat for the time shown in the table below (2 to 3 minutes) to heat shrink the mesh, then 100%
Heat at Kp/ad (gauge pressure) for 1.5 minutes (25
0°C), then taken out from the press and placed in a chrome-plated (30oW 7m x 2sQw/m x 1.5W/m) mold, and when the cooling Teflon sheet became hard, it was taken out from the mold to obtain a microporous membrane. Ta.

The membrane prepared in Example 4 was used to measure red blood cell deformability. 20. through a circular membrane with a diameter of 10u. H2
When 0.2 ffi/of human blood was suction-filtered at a pressure of O, the time required for filtration of human blood containing red blood cells with high deformability was shorter than that of human blood with low deformability. As a result, it was found that the deformability of red blood cells can be measured by measuring the time required to filter 0.2 go of human blood using this membrane.

Patent applicant RiRashi Co., Ltd.

Claims (1)

Scope of Claims: (1) The membrane has 800,000 to 5,000 pores per cm^2, and the pores are substantially uniformly arranged vertically and/or horizontally of the membrane, and the pores have a size of A microporous membrane consisting of a polyester or polyolefin network structure that is substantially uniform in size and shape. (2) The microporous membrane according to claim 1, wherein the pore size is in the range of 0.1 to 50μ. (8) The microporous membrane according to claim 1 or 2, which has a thickness of 5 to 200 μm.