JPH0138505B2 - - Google Patents

Description

Detailed Description of the Invention The present invention consists essentially of an ethylene-vinyl alcohol copolymer, has excellent hydrophilicity, good mechanical properties, excellent flexibility, and has a network-like structure consisting of fine pores. The present invention relates to a porous membrane having a structure and a method for manufacturing the same.

In particular, the present invention is effective as a porous membrane suitable for microfilters and battery separators with excellent chemical resistance and excellent permeation performance, and as a plasma separation membrane with excellent anti-hemolytic properties, anti-thrombotic properties, and hygiene. The present invention relates to porous membranes.

Conventionally, as porous membranes made of ethylene-vinyl alcohol copolymers, separation membranes for hemodialysis for artificial kidneys are disclosed in JP-A-49-113859 and JP-A-52-152877. However, since these membranes are used for hemodialysis to allow substances with a molecular weight of 300 to 6,000 to permeate and to block the permeation of high-molecular weight substances such as proteins, the surface pore diameter of these membranes is extremely large, approximately 100 Å. It is judged to be microscopic, with a pore diameter of 0.05.
This is essentially different from the porous membrane of the present invention which has a thickness of ~1μ. At the same time, since the surface pore diameter is extremely small, the permeability such as water permeability is about 1/1000 of that of the porous membrane of the present invention, making it unsuitable for applications in which the porous membrane of the present invention is used. Furthermore, this membrane is made using a wet film formation method, and when it is dried normally, it shrinks and loses its permeability, so it requires special treatment. ing.

In addition, no other prior art related to an ethylene-vinyl alcohol copolymer porous membrane that is effective as a microfilter or a battery separator and has good permeability has been found.

The present inventors have conducted extensive research in order to obtain a porous membrane with excellent permeability that is made of an ethylene-vinyl alcohol copolymer that is hydrophilic and has excellent chemical resistance, biocompatibility, and chemical stability. As a result of repeated efforts, the present invention was completed.

That is, the present invention substantially reduces the ethylene content to 20
Ethylene with a saponification degree of ~60 mol% and a saponification degree of 80 mol% or more
Made of vinyl alcohol copolymer, porosity 30~
85%, forming a network structure consisting of communicating pores with an average pore diameter of 0.05 to 1μ on the surface, and water permeability of 500 to 50,000ml/
This is an ethylene-vinyl alcohol copolymer porous membrane characterized by Hr·m ² ·mmHg.

In addition, the present invention has an ethylene content of 20 to 60 mol%,
Ethylene-vinyl alcohol copolymer with saponification degree of 80 mol% or more, 10-60% by volume, specific surface area 50-500
After mixing 7 to 42 volume % of inorganic fine powder with m ² /g and average primary particle size of 0.005 to 0.5 μ and 30 to 75 volume % of a heat-resistant organic liquid, the mixture is melt-molded, and then the molded product is made of ethylene. - An ethylene-vinyl alcohol copolymer characterized in that an organic liquid and an inorganic fine powder are extracted sequentially or simultaneously using an organic liquid solvent and an inorganic fine powder solvent that do not substantially dissolve the vinyl alcohol copolymer. This is a method for producing a porous polymer membrane.

The ethylene-vinyl alcohol copolymer used in the present invention may be any type of random, block, or graft copolymer, but the ethylene content of the copolymer may be in the range of 20 to 60 mol%. It is necessary that there be. Ethylene content is 20 mol%
If it is less than this, the mechanical properties of the resulting porous membrane when wetted are deteriorated, which is not preferable. Moreover, if it exceeds 60 mol%, the resulting porous membrane loses its hydrophilicity, which is not preferable. In particular, 30 to 45 mol% is preferable since it provides a good balance between hydrophilicity and mechanical properties when wet.

Furthermore, the degree of saponification of the ethylene-vinyl alcohol copolymer needs to be 80 mol% or more. If it is less than 80 mol%, the mechanical properties of the resulting porous membrane will deteriorate, which is not preferable. Preferably it is 95 mol% or more, more preferably 99 mol% or more of substantially complete saponification.

This ethylene-vinyl alcohol copolymer is
Methacrylic acid, as long as it does not impair the physical properties of the porous membrane.
Copolymerizable materials such as methyl methacrylate and acrylonitrile may be copolymerized. Furthermore, a porous membrane obtained by acetalizing the ethylene-vinyl alcohol copolymer with an aldehyde such as formaldehyde or acetaldehyde can also be used in the present invention. The ethylene-vinyl alcohol copolymer preferably has a standard load melting index (SLMI) of 0.01 to 20 at 190°C. If it is less than 0.01, moldability is poor, and if it exceeds 20, mechanical properties deteriorate, which is not preferable.

The inorganic fine powder used in the present invention holds a heat-resistant organic liquid and functions as a carrier. That is, it is substantially inert to the ethylene-vinyl alcohol copolymer during melt molding, prevents the release of a heat-resistant organic liquid with a boiling point of 190°C or higher, facilitates molding, and is further extracted. It has a movement that forms pores. This inorganic fine powder has a specific surface area of 50 to 500 m ² /g.
And they are microparticles or porous particles with an average primary particle size in the range of 0.005 to 0.5μ. Furthermore, the inorganic fine powder can hold at least 2/3 times the volume of the heat-resistant organic liquid.
It is preferable to absorb at least three times the capacity and maintain the powder or granule state.

Examples of the inorganic fine powder used in the present invention include:
Fine powder silicic acid, calcium silicate, aluminum silicate,
Magnesium oxide, alumina, calcium carbonate,
Examples include magnesium carbonate, kaolin clay, diatomaceous earth, and common salt. Among these, finely divided silicic acid is particularly effective, but it is not limited thereto.

The heat-resistant organic liquid used in the present invention is extracted from the molded product and is used to impart porosity to the molded product. The heat-resistant organic liquid has a boiling point at 1 atm of at least 190°C, preferably 200°C.
As mentioned above, it is necessary to have heat resistance to withstand melt molding, more preferably at 230° C. or higher, to be liquid at the melt molding temperature, and to be substantially inert to the polymer. Further, it is preferable that the solubility parameter of the heat-resistant organic liquid is in the range of 14.5 to 16.5. More preferably, it is 15.0 to 16.5. By using a material within this range, a porous membrane with particularly excellent processability such as moldability and extractability, high porosity, and excellent mechanical properties can be obtained.

Heat-resistant organic liquids used in the present invention include diethylene glycol, tetramethylene glycol, meso-erythritol, 1,3-propanediol, glycerin, D-sorbitol, tris(2-oxyethyl)amine, bis(2-oxyethyl) Examples include amines and triethylphosphine oxide. Among these, glycerin is most preferred from the viewpoint of hygiene.

In manufacturing the porous membrane of the present invention, first,
The ethylene-vinyl alcohol copolymer, inorganic fine powder, and heat-resistant organic liquid are mixed. The mixing ratio is 10 to 60% by volume of ethylene-vinyl alcohol copolymer, preferably 15 to 40% by volume, 7 to 42% by volume of inorganic fine powder, preferably 10 to 20% by volume, and 30 to 20% by volume of heat-resistant organic liquid. 75% by volume, preferably
50-70% by volume.

If the ethylene-vinyl alcohol copolymer content is less than 10% by volume, the resin content is too small, resulting in low strength and poor moldability; if it exceeds 60% by volume, a porous film with high porosity cannot be obtained, which is not preferred. If the inorganic fine powder is less than 7% by volume, it will not be able to adsorb the organic liquid necessary to make an effective porous membrane, and the mixture will not be able to maintain a powder or granule state, making it difficult to mold. If it exceeds % by volume, the fluidity during melting will be poor and the resulting molded product will be brittle and cannot be put to practical use. When the heat-resistant organic liquid is less than 30% by volume, the contribution rate of the heat-resistant organic liquid to pore formation decreases, and the porosity of the resulting porous membrane is less than 40%, making it virtually ineffective as a porous membrane. If the amount exceeds 75% by volume, molding becomes difficult.
A porous membrane with high mechanical strength cannot be obtained.

In addition to the above-mentioned three components, there is no problem in adding lubricants, antioxidants, ultraviolet absorbers, plasticizers, molding aids, etc., as necessary, to the extent that the effects of the present invention are not significantly impaired.

For mixing the three components, a Henschel mixer,
A conventional mixing method using a blender such as a V-blender or a ribbon blender is sufficient. As for the mixing order of the three components, rather than mixing the three components at the same time,
First, an inorganic fine powder and a heat-resistant organic liquid are mixed, and the heat-resistant organic liquid is sufficiently adsorbed on the inorganic fine powder.
Next, it is preferable to blend and mix an ethylene-vinyl alcohol copolymer.

This mixture can be processed using an extruder, a Banbury mixer,
The mixture is kneaded using a melt kneading device such as a twin roll or a kneader. The obtained kneaded product is molded by a melt molding method, and the melt molding methods used in the method of the present invention include extrusion molding such as T-die method and inflation method, calendar molding, compression molding, injection molding, etc. Ru. It is also possible to directly mold the mixture using a device having both kneading and extrusion functions, such as an extruder or a kneader-ruder.

With these forming methods, the ternary mixture is 0.025
It is formed into a membrane with a wall thickness of ~2.5mm, but the shape of the porous membrane can be flat membrane, embossed membrane, ribbed membrane, tube-shaped membrane, hollow fiber membrane, etc., as long as the membrane thickness is within the above-mentioned range. It may also be a membrane. Especially from 0.025
T-die extrusion molding is particularly effective for forming thin films of 0.30 mm.

The organic liquid is extracted from the obtained membrane using an organic liquid solvent. The extraction temperature is preferably 10°C or more lower than the melting point of the ethylene-vinyl alcohol copolymer. The solvent used for extraction must not substantially dissolve the ethylene-vinyl alcohol copolymer. Extraction is easily carried out using common extraction methods for membrane-like materials, such as a batch method or a countercurrent multi-stage method. As the solvent used for extraction, common solvents such as alcohols such as methanol, ethanol and isopropyl alcohol, ketones such as acetone, and water are sufficient. Further, the organic liquid is allowed to remain in the porous membrane after extraction to the extent that it does not impair the performance of the product. However, if the residual amount is large, the porosity of the porous membrane will decrease, which is not preferable. The amount of organic liquid remaining in the porous membrane is 3% by volume or less, preferably 2% by volume or less.

The semi-extracted porous membrane after the extraction of the organic liquid is
The solvent may be removed by drying if necessary. When performing industrial production, it is preferable to perform drying to prevent mixing of the extraction solvent of the organic liquid with the inorganic fine powder extraction solvent of the next step. Dry off the solvent at temperature. Drying is carried out under normal pressure or reduced pressure by a common method such as hot air or heated rolls.

The semi-extracted porous membrane after the extraction of the organic liquid is
Next, the inorganic fine powder is extracted using a solvent for the inorganic fine powder. The extraction temperature is preferably 10°C or more lower than the melting point of the ethylene-vinyl alcohol copolymer. Extraction can be easily completed within a few seconds to several tens of hours by a general extraction method such as a batch method or a countercurrent multistage method.

Solvents used for extraction of inorganic fine powder include:
Acids such as hydrochloric acid, sulfuric acid, and hydrofluoric acid are used for calcium carbonate, magnesium carbonate, magnesium oxide, calcium silicate, and magnesium silicate, and alkaline aqueous solutions such as caustic soda and caustic potash are used for silica.
Water is used for bad magnesium sulfate and salt.
Other materials are not particularly limited as long as they do not substantially dissolve the ethylene-vinyl alcohol copolymer and dissolve the inorganic fine powder. It is also possible to simultaneously extract the organic liquid and the inorganic fine powder using a caustic soda aqueous solution or the like. After extraction, the inorganic fine powder is allowed to remain in the porous membrane to the extent that it does not impair the performance of the membrane. The residual amount of the inorganic fine powder in the porous membrane is preferably 3% by volume or less, more preferably 2% by volume or less.

The porous membrane from which the inorganic fine powder has been extracted is dried in the same manner as the drying method described above. Further, in order to increase the porosity, a porous membrane obtained by extracting one or both of the organic liquid and the inorganic fine powder may be uniaxially or biaxially stretched.

The porous membrane of the present invention obtained as described above is
It consists essentially of ethylene-vinyl alcohol copolymer. The structure of this porous membrane is formed by communicating pores formed by the network structure of ethylene-vinyl alcohol copolymer, and the average pore diameter of the surface of the network structure of ethylene-vinyl alcohol copolymer is The pore size is 0.05 to 1μ, preferably 0.08 to 0.05μ, more preferably 0.1 to 0.3μ, and has a narrow pore size distribution.

The porous membrane of the present invention has a porosity of 30 to 85%, preferably 40 to 80%, and more preferably 50 to 75%.

In order to further clarify the structure of the porous membrane of the present invention, the surface structure and cross-sectional structure were observed using a scanning electron microscope (SEM). The porous membrane used for observation was that obtained in Example 1. In addition, in order to take cross-sectional photographs, the porous membrane was impregnated with methanol, frozen in liquid nitrogen, and cut into samples. FIG. 1 is a photograph showing the surface structure of the porous membrane of the present invention, and FIG. 2 is a photograph taken at a magnification of 10,000 times showing the cross-sectional structure. In addition, Figure 3 is a schematic diagram for explaining the photographed locations, where 1 is the surface of the porous membrane, 2 is the cross section of the porous membrane, A is the direction for photographing the surface structure, and B is the direction for photographing the cross-sectional structure. indicates the direction.

It is observed that on the surface of the porous membrane in FIG. 1, there are many approximately circular pores with diameters on the order of submicrons, forming a network structure of ethylene-vinyl alcohol copolymer. The cross section of the porous membrane in FIG. 2 also forms a network structure similar to that in FIG. 1.

The ethylene-vinyl alcohol copolymer porous membrane according to the present invention can be easily dried by a conventional drying method without damaging the pore structure, as described in the manufacturing method above. Furthermore, the dry membrane has excellent mechanical properties and flexibility equivalent to that of the wet membrane, and is easy to handle. Furthermore, since it is a dry film, it can be heat-sealed, and it has extremely excellent assembling processability into filter modules and the like.

Furthermore, since the porous membrane of the present invention is made of an ethylene-vinyl alcohol copolymer, it has excellent water wettability, and when immersed in water, it becomes wet instantly.
Can be used as an instant microfilter or battery separator. On the other hand, when a membrane treated with a surfactant is re-dried after use, the surfactant is eluted and water wettability is lost, but the porous membrane of the present invention permanently retains water wettability. There is. In addition, the porous membrane of the present invention has a high porosity, a narrow pore size distribution, and has a network structure.
Equipped with high water permeability of 50000ml/Hr・m ²・mmHg,
With micropores of 0.05 to 1μ, it has excellent performance in blocking the permeation of substances such as blood cells, bacteria, and fine particles, making it suitable for various filter applications. In particular, ethylene-vinyl alcohol copolymer porous membranes have good biocompatibility, anti-hemolytic properties, and anti-thrombotic properties, as well as good overperformance. It is particularly effective as a medical microfilter such as a membrane or a bacteria removal membrane.

In addition, the porous membrane of the present invention has a caustic potash aqueous solution (specific gravity
1.30, electrical resistance at 20℃) is 0.00005~
Extremely low at 0.0010Ωdm ² /0.1mm thickness. Furthermore, the fine network structure has the effect of blocking the permeation of harmful substances and inhibiting the growth of dendrites. The porous membrane of the present invention having both of these properties, water wettability, and alkali resistance is particularly effective as a battery separator.

As described above, the porous membrane of the present invention is effective for various uses, but it also has other uses such as breathable packaging materials, aeration tubes, printing rolls, and holding materials for impregnating chemicals such as insecticides.

Next, Examples will be shown to clarify the effects of the present invention, but the present invention is not limited to these Examples.

The physical properties shown in the Examples of the present invention were measured using the following measurement method.

Composition ratio (volume %) Calculated from the value obtained by dividing the added weight of each composition by the true specific gravity.

Porosity (%) Porosity = pore volume / porous membrane volume × 100 pore volume = water content − bone dry weight average pore diameter (μ) 200 open pores observed in a scanning electron micrograph of the porous membrane surface Calculated by weighted average of the major and minor axes.

Maximum pore diameter (μ) (bubble point method) Measured according to ASTM 8316-70 and E128-62 Breaking strength (Kg/m ² ), elongation at break (%) ASTM D- measured by Instron type tensile tester
Measured according to 882. (Strain rate 2.0mm/mm・mm) SLMI: Solubility parameter (sp value) measured according to ASTM-D-1238-65T condition E Polymer Handbook Table of Solubility
Depends on the parameter.

Air permeability (seconds/100ml sheets/seconds/100ml・0.1mm) Measured according to ASTM D-726 Method A Electrical resistance (Ωdm ² /sheet・Ωdm ² /0.1m/m) Measured according to JIS-C-2313 The plate is a pure nickel plate. The electrolyte has a specific gravity of 1.30. Water permeability of aqueous caustic soda solution (ml/Hr・m ²・mmHg). Measurement at 25°C and differential pressure of 700 mmHg. Example 1: Fine powder silicic acid [Nipseal VN-3 (trade name), specific surface area 280 m ² /g, average primary particle diameter 16 mμ〕15.5
Volume%, glycerin 59.0% by volume were mixed in a Henschel mixer, and ethylene-vinyl alcohol copolymer (ethylene content 33 mol%, degree of saponification 99
25.5% by volume (more than mol%) was added and mixed again using a Henschel mixer.

The mixture was kneaded into pellets using a 30 m/mφ twin-screw extruder. The pellets were formed into a film using a film manufacturing apparatus comprising a 30 m/mφ twin-screw extruder equipped with a 420 m/m wide T-die. The molded membrane is heated to 80℃
After immersing it in hot water for 20 minutes to extract glycerin, it was dried with a drying roll at 90°C. Next, it was immersed in a 40% caustic soda aqueous solution at 50°C for 10 minutes to extract the finely divided silicic acid, washed with water, and dried with a drying roll at 90°C. The amounts of glycerin and finely divided silicic acid in the obtained ethylene-vinyl alcohol copolymer porous membrane were each 0.5% by volume or less.

The resulting porous ethylene-vinyl alcohol copolymer membrane had a thickness of 150 μm and a porosity of 80%.
According to electron microscopy, there are 4×10 ⁸ pores with an average pore diameter of 0.15μ.
There were ² pieces/cm2. The maximum pore size determined by the bubble post method was 0.3μ, which was twice the average pore size, indicating an extremely narrow pore size distribution. The tensile strength at break of the membrane when dry is 54Kg/cm ² and the tensile elongation at break is 68%, and when wet with water it is 27Kg/cm ² and 110%, respectively, showing excellent mechanical properties in both dry and wet conditions. Ta.

When this membrane was immersed in water, it became wet instantly, and water permeability and electrical resistance could be measured immediately without any pretreatment. Also, the water permeability of this membrane is
2600ml/ ^m2・Hr・mmHg Air permeability is 120 seconds/100c.c.・
It showed extremely excellent transmission performance. In addition, the electrical resistance in a caustic potassium aqueous solution (specific gravity 1.30) is
The resistance was 0.00016Ωdm ² /sheet, which was extremely low as a separator.

Example 2 The ethylene-vinyl alcohol copolymer porous membrane obtained in Example 1 was biaxially stretched 2.5 times in length and 2.5 times in width at 130°C using a TM Long biaxial stretching test device. Ta.

The resulting ethylene-vinyl alcohol biaxially stretched porous membrane had a thickness of 50 μm and a porosity of 85%. The average pore diameter was 0.5μ, and the maximum pore diameter was 1.3μ.

The tensile strength at break of the membrane when dry is 110Kg/ ^cm2 , and the tensile elongation at break is 32%, and when wet with water, it is 48Kg/ ^cm2 and 63, respectively.
% and showed excellent performance. The water permeability of this membrane is
18000ml/ ^m2・Hr・mmHg, air permeability is 3 seconds/100
It showed an extremely excellent transmission performance of cc. Furthermore, the electrical resistance was extremely low at 0.00005Ωdm ² /sheet.

Example 3 A porous membrane was produced according to Example 1, except that 10.5% by volume of finely divided silicic acid, 40% by volume of glycerin, and 49.5% by volume of ethylene-vinyl alcohol copolymer were used.

The resulting ethylene-vinyl alcohol copolymer porous membrane had a thickness of 80μ, an average pore diameter of 0.08μ, and a maximum pore diameter.
It was 0.2μ. The porosity was 41%.

The tensile breaking strength of this membrane when dry is 140Kg/cm ² ,
Tensile elongation at break is 170% and 78 when wet with water, respectively.
Kg/cm ² , 230%, and had excellent mechanical properties. Further, the electrical resistance of this film was 0.00065Ωdm ² /sheet. The water permeability was excellent at 570ml/Hr・m ²・mmHg.

[Brief explanation of drawings]

Fig. 1 is a scanning electron micrograph showing the surface structure of the porous membrane of the present invention, Fig. 2 is a scanning electron micrograph showing the cross-sectional structure, and Fig. 3 is a scanning electron micrograph of Fig. 1 and Fig. 2. FIG. 3 is a schematic diagram illustrating a shaded area in a photograph.

Claims (1)

[Scope of Claims] 1. Consisting essentially of an ethylene-vinyl alcohol copolymer with an ethylene content of 20 to 60 mol% and a saponification degree of 80 mol% or more, a porosity of 30 to 85%, and an average surface pore diameter of 0.05 to 1 μm. Forms a network structure consisting of communicating pores,
An ethylene-vinyl alcohol copolymer porous membrane characterized by a water permeability of 500 to 50,000 ml/Hr·m ² ·mmHg. 2 Ethylene-vinyl alcohol copolymer 10 with an ethylene content of 20 to 60 mol% and a degree of saponification of 80 mol% or more
~60% by volume, specific surface area 50~500m ² /g and average -
7-42% by volume of inorganic fine powder with a secondary particle size of 0.005-0.5μ,
After mixing 30 to 75% by volume of a heat-resistant organic liquid that is substantially inert and has a boiling point of 190°C or higher with the ethylene-vinyl alcohol copolymer, it is melt-molded, and then the ethylene-vinyl alcohol copolymer is melt-molded. An ethylene-vinyl alcohol copolymer characterized in that an organic liquid and an inorganic fine powder are extracted sequentially or simultaneously using an organic liquid solvent and an inorganic fine powder solvent that do not substantially dissolve the alcohol copolymer. Method for manufacturing porous membrane.