JPH0125604B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a microporous membrane 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. It is also known that a membrane filter (Nucleopore) having a desired pore size can be obtained by exposing a polycarbonate film to neutrons to make holes and enlarging the holes with an alkaline solution. Since the holes are randomly drilled by neutrons, the holes are unevenly arranged, and there are also disadvantages in that multiple 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 long fibers or short fibers, the low melting point fibers in the web are melted and fused to form a filter, especially an electrical one. A method for making a vacuum cleaner filter is also known,
Since such a laminate of fiber webs does not have a uniform mesh, it is impossible to obtain a filter with uniform mesh size and shape even by hot pressing.
Therefore, although the filter obtained in this way can be used as a filter for vacuum cleaners, it cannot be used as a separation membrane that requires precise fractionation, such as a membrane that separates blood from blood. It cannot be used. The present invention successfully solves these drawbacks, and has 800,000 to 5,000 pores per cm ² of the membrane, and the pores are substantially uniformly arranged vertically and/or horizontally of the membrane, and This is a method for producing a microporous membrane in which the pores are substantially uniform in size and shape. The microporous membrane obtained by the production method of the present invention has pores arranged extremely uniformly, so the number of pores (pore size 0.1 to 50μ) per unit area is 800,000 to 800,000.
5000 pieces/cm ² , and therefore 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 located 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 elliptical shape, a quadrangular shape, or another polygonal shape, and among these, a circular shape, a square shape, and a regular polygonal 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/cm ²
The separation efficiency per unit area of the membrane increases when the number of pores is as large as possible. When it exceeds 800,000 pieces/cm ² , the strength of the membrane itself decreases, depending on the material of the membrane and the size of the pores, and when it exceeds 5,000 pieces/cm 2
When it is less than cm ² , the separation efficiency per unit area of the membrane becomes poor. The size of the pores can be determined as appropriate depending on the size of the substance to be fractionated, but generally it is in the range of 0.1 to 50μ.For example, when this microporous membrane is used as a membrane for measuring red blood cell deformability. The pore size is 4~6μ
When used as a membrane to separate blood from blood or ascites to remove bacterial cells, the size is 0.1 to 0.3μ, preferably 0.2μ.
~0.25μ. The microporous membrane has a thickness of 5 to 200 microns, preferably 10 to 30 microns. Fractionability is further improved by reducing the film thickness. Materials for the microporous membrane include thermoplastic resins such as polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, nylon 6, nylon 6,6
Examples include polyamides such as cellulose acetate, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, and their respective copolymers or polymer blends thereof. Among these, polyester and polypropylene are preferred from the viewpoint of membrane strength, and polyester is optimal because it has sufficient strength even if the membrane is thinned and therefore improves separation efficiency. Next, a method for manufacturing the microporous membrane of the present invention will be described. The method of the invention has a uniformly arranged mesh;
And the network structure made of thermoplastic resin in which the size and shape of the network are substantially uniform is adjusted to the melting point of the thermoplastic resin forming the network structure so that the network is not immersed and closed. This is a method for producing a microporous membrane, which is characterized by shrinking by heat treatment at a temperature between the softening point and then further pressure treatment. 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 "mesh structure" refers to a woven fabric made of thermoplastic resin as described above,
These include knitted fabrics, net-like fabrics, mesh fonts, etc. 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 woven fabric is stretched polyester filament (melting point 255~
260℃, softening point 238~240℃), partially stretched polyester filament (melting point 225~235℃, softening point 195~
205℃) and undrawn polyester filament (melting point 150℃, softening point 120℃) and stretched polypropylene filament (melting point 165-173℃, softening point 140-160℃)
℃) is preferred, and in particular, it is preferable to use a woven fabric made of stretched filaments (polyester, polypropylene) because it is stretched both vertically and horizontally, so that a microporous membrane with excellent physical strength can be obtained. Among these, stretched polyester filaments are most suitable. The thickness of the filament is 0.5 to 50 deniers, preferably 1 to 30 deniers. The filament may be made into a woven fabric using single yarns or may be made into a woven fabric using plied and twisted yarns. In addition, "mesh substantially uniformly arranged vertically and/or horizontally" refers to "mesh substantially uniformly arranged vertically and/or horizontally" when viewed from the front and back surfaces of the network structure. It means meshes that are arranged in an orderly manner in both the horizontal and vertical directions, and at substantially equal intervals in both or each direction. 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 mesh structure are the same or substantially the same when viewed from the front and back surfaces of the network structure. It means almost the same. Here, the shape of the mesh is a circular shape, an elliptical shape, or another polygonal shape, and among these, a circular shape, a square shape, and a regular polygonal 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 in the target microporous membrane, the thickness of the filament used, etc., but is approximately 700,000 to 1,500 meshes/cm ²
It is. The mesh size also varies depending on the pore size of the target microporous membrane, but is about 8 to 1000 microns. Preferably used mesh size is 5-200μ
It is. A network structure such as a woven fabric made of polyester filament is heat-treated at a temperature between the melting point and the softening point of the structure to cause heat shrinkage. The heat treatment is carried out by passing the material between hot plates whose temperature is adjusted within this range or between heated rolls (in some cases, a plurality of rolls). The temperature of this heat treatment may be within the range between the melting point and the softening point, but if the temperature is 5°C or more lower than the melting point and 10°C or more higher than the softening point, the shape of the network of the network structure can be soaked. This is preferable because only the size of the mesh can be uniformly heat-shrinked without closing the mesh. The time for the heat treatment depends on the temperature of the heat treatment, but is generally about 5 seconds to 20 minutes, preferably 1 to 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. Pressure treatment is performed by placing the material between plates or passing it between rolls (in some cases, multiple rolls), at a pressure of 1 to 300 kg/cm ² (gauge pressure).
The range is preferably 100 to 150 Kg/cm ² (gauge pressure). The time for the pressure treatment is 5 seconds to 20 minutes, preferably 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. However, when performing heat 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 of the number of meshes in the initial network structure.
The size of the pores in the microporous membrane is 1/2 to 1/20 times the size of the mesh. In the method of the present invention, a microporous membrane having pores of a desired size can be obtained by appropriately selecting the conditions of heat treatment and pressurization (or heating pressure); It also varies depending on the shape of the material of the network structure. 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, so it can be used in various fields such as the medical industry. It can be effectively used as a separation membrane having excellent fractionation properties. Specifically, it can be effectively used as a membrane for measuring red blood cell deformability, a blood plasma separation membrane in blood, a hemofilter membrane, a permeability membrane for ascites, or a membrane for removing bacterial cells and solid particles (SS) from various fluids. . Examples 1-2 20 denier drawn polyester filament (melting point 260°C, softening point 240°C) single yarn length 180
Polyester mesh for gauze printing (17cm x 17cm; number of meshes 5600)
Pieces/cm ² ;Mesh size 100μ, uniform;Mesh thickness
A mesh of 88 μm (vertical and horizontal filaments intersect at right angles) was sandwiched between 1 mm thick Teflon sheets to prevent dirt and dust from adhering to the mesh. Next, this was placed between the hot plates of a press set at 250 DEG C. (heat plate spacing: 5 mm), and heat treated for a period of time (1.5 to 2 minutes) as shown in the table below to heat-shrink the mesh. Next, put this on a press board.
Heat and pressure treatment (250° C.) was performed at 100 Kg/cm ² (gauge pressure) for the time (1.5 to 2 minutes) shown in the table below. After that, the mesh was taken out and sandwiched between the Teflon and chrome-plated molds, and cooled.
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.

[Table] * Shape is a rounded cross * * Shape is a rounded square
Examples 3 to 4 Vertical fibers made of 5-denier drawn polyester monofilament (melting point 260°C, softening point 240°C) single yarn
750 pieces/inch x 750 pieces/inch horizontally polyester mesh (15 x 15cm; number of meshes 90,000 pieces/ ^cm2 ; mesh size approximately 10μ; mesh thickness 40μ; vertical and horizontal filaments intersect at right angles) 1m/
The mesh was sandwiched between m-thick Teflon sheets and placed between press hot plates set at 250℃ (heating plate interval 5m/m) and heated for the time shown in the table below (2 to 3 minutes) to heat shrink the mesh. It was heated and pressed (250℃) for 1.5 minutes at 100Kg/cm ² (gauge pressure), then removed from the press and chrome plated (300W/m
250W/m x 1.5W/m) placed in the mold, and when the cooling Teflon sheet becomes hard, remove it from the mold.
A microporous membrane was obtained.

[Table] The membrane prepared in Example 4 was used to measure red blood cell deformability. When 0.2 ml of human blood was suctioned through a circular membrane with a diameter of 10 mm at a pressure of 20 mm H ₂ O, human blood with highly deformable red blood cells took less time to pass through than blood with small deformable red blood cells. It was hot. By this, using this membrane, 0.2ml
It has been found that the deformability of red blood cells can be measured by measuring the time it takes to pass through human blood.

Claims (1)

[Scope of Claims] 1. A thermoplastic resin network structure having fine meshes arranged substantially uniformly in the vertical and/or horizontal directions, and in which the size and shape of the meshes are substantially uniform. The body is heat-treated to shrink at a temperature between the melting point and the softening point of the thermoplastic resin forming the network structure, and then further pressure-treated to prevent the network from being immersed and closed. A method for producing a microporous membrane characterized by the following. 2 The temperature of the heat treatment is 5°C below the melting point of the network structure.
The method for producing a microporous membrane according to claim 1, which has a softening point of at least 10°C or more and a softening point of at least 10°C. 3. The method for producing a microporous membrane according to claim 1 or 2, wherein the heat treatment time is 5 seconds to 20 minutes. 4 The pressure of pressure treatment is 1 to 300Kg/cm ² (gauge pressure)
A method for producing a microporous membrane according to any one of claims 1 to 3. 5. The method for producing a microporous membrane according to any one of claims 1 to 4, wherein the pressure treatment time is 5 seconds to 20 minutes. 6 Claim 1 in which the network structure is a woven fabric
5. A method for producing a microporous membrane according to any one of items 5 to 5. 7. The method for producing a microporous membrane according to any one of claims 1 to 6, wherein the network structure is a woven fabric made of polyester filaments. 8. The method for producing a microporous membrane according to any one of claims 1 to 7, wherein the network structure is a woven fabric made of stretched or partially stretched polyester filaments. 9. The method for producing a microporous membrane according to any one of claims 1 to 6, wherein the network structure is a woven fabric made of polypropylene filaments.