JPH0929077A - Porous membrane and method for producing the same - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a porous membrane which can be composed of various polymer substrates, in which the flux of the membrane such as water permeation rate is high, and the fine particles do not fall off from the membrane. SOLUTION: Polymer A 50 to 90 wt% and polymer A
Polymer B which is incompatible with and has a high Tg of 20 ° C or more
%, A fibril made of polymer A and slit-shaped micropores are laminated in the thickness direction, the micropores penetrate in the thickness direction, and the polymer B is present in a dispersed state in the film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous membrane used for ultrafiltration, microfiltration, air purification, etc., particularly a porous membrane using polylactic acid and a method for producing the same.

[0002]

2. Description of the Related Art Porous membranes are used in industrial fields such as industrial wastewater / process water treatment, medical fields such as artificial kidney / plasma separation, food-related fields, household water filters, air filters / bag filters, etc. It is used in a wide range of fields such as purification fields.

As a porous membrane material used for such an application, various polymer materials such as polyolefin, polyimide, polysulfone, and fluoropolymer have been studied, and various membranes have been disclosed.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 57-66114, slit-shaped fine holes formed by microfibrils oriented in the long axis direction of fibers and knots made of stacked lamellae are laminated in the thickness direction. There is disclosed a polyethylene porous hollow fiber membrane which penetrates and has a uniform structure in the thickness direction.

This film is manufactured by the melt-shaped drawing method. That is, after performing shaping under a specific spinning condition, an annealing treatment is performed to form a lamella laminated crystal on the shaped article,
Then, the lamella laminated crystal parts are stretched to be separated from each other, and fibrils are grown to form the specific structure. This membrane is characterized by being excellent in mechanical strength because it has the above-mentioned specific structure, and by being excellent in safety because no solvent is used in the manufacturing process.

A method of dispersing fine particles in a crystalline polymer such as polyolefin and stretching it to make it porous is generally known in the field of breathable films and disposable diapers. Japanese Patent Application Laid-Open No. 1-293102 discloses a method for producing a polyolefin hollow fiber membrane such as polypropylene or polyethylene by applying this method to a method for producing a membrane. In this method, the polyolefin fine particles are added and stretched to separate the interface between the polyolefin serving as a matrix and the fine particles to produce a polyolefin porous membrane having a structure in which fine through holes penetrate in the thickness direction. . However, in this method, when a polymer such as a polyolefin whose molecular chains are easily oriented is used as the matrix polymer, it can be produced relatively easily, but in the case of other polymers, it is difficult to make it porous, or it becomes porous. However, in many cases, practically sufficient film performance could not be obtained.

A technique for adding fine particles to an amorphous polymer to make it stretched and porous is disclosed in Japanese Patent Application No. 6-23430. With this method, a porous film of an amorphous polymer can be obtained, but there are problems such as dispersibility of fine particles in a polymer matrix and dropping of fine particles during use of the porous film.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a porous membrane which has a high membrane flux such as air permeation rate and water permeation rate, and which does not have any problems such as dropping of fine particles during use. It is in.

Another object of the present invention is to provide a method for producing the above-mentioned porous membrane composed of various polymer substrates.

[0010]

That is, the present invention provides a glass transition of 50 to 90% by weight of the polymer (A), which is incompatible with the polymer (A) and is higher than the polymer (A) by 20 ° C. or more. A porous film composed of 50 to 10% by weight of a polymer (B) having a temperature, wherein a fibril composed of the polymer (A) oriented in a direction perpendicular to the thickness direction of the porous film and slit-like micropores are provided. The porous membrane is characterized by being laminated in the thickness direction, the slit-shaped micropores penetrating in the thickness direction, and the polymer (B) being dispersed and present in the porous membrane.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The porous film of the present invention has a glass transition temperature (Tg) which is incompatible with the polymer (A) and is higher than the polymer (A) by 20 ° C. or more.
And a polymer (B) having

Any polymer may be used as the polymer (A), and it is not particularly limited. For example, polyolefins such as polyethylene and polypropylene; polyester-based polymers such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate. Coalescing;
Wholly aromatic polyesters; aliphatic polyesters such as polycaprolactone, polylactic acid (L-form, D-form, racemic form), polyhydroxybutyric acid, polybutylene succinate, etc.
Examples thereof include cellulose, cellulose derivatives, polyamides, polyacrylonitrile-based polymers, polysulfone-based polymers, polyimide-based polymers, polyarylate-based polymers, polycarbonates, polyphenylene oxides, polystyrene, and poly (meth) acrylate-based polymers. In addition, a copolymer of the above polymer or a compatible blend of two or more kinds of the above polymer or the copolymer thereof can be preferably used.

The polyester polymer used as the polymer (A) in the present invention is a polymer having an ester bond in its structure. Preferred polyester-based polymers include, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, wholly aromatic polyesters, polyarylates, polycaprolactone, polylactic acid (L-form, D-form).
Body, racemic body), polyhydroxybutyric acid, polybutylene succinate, polyethylene adipate, and other aliphatic polyester-based polymers, copolymers of these polyesters, and compatible blends.

The polylactic acid polymer used as the polymer (A) in the present invention is a polymer containing a unit derived from a lactic acid monomer in its structure. Lactic acid contained as a monomer unit is L-form, D-form, DL-form (racemic form)
It may be offset. As a preferred polylactic acid-based polymer,
For example, poly-L-lactic acid, poly-D-lactic acid, poly-DL-
Lactic acid, copolymers of lactic acid and other hydroxy acids, copolymers of lactic acid and lactones, copolymers of lactic acid, dicarboxylic acids and diols, and copolymers of these and compatible blends. .

As the polymer (B), the polymer (A)
Is incompatible with Tg of polymer (A) is 20 ° C
Any polymer may be used as long as it is higher than the above, and is not particularly limited. Polymer (A) and polymer (B)
Is incompatible means that polymer (A) and polymer (B)
When the two are melted or mixed in a solution state, it means that they are phase-separated into at least two phases or more, and may be partially compatible. The Tg can be usually determined by means such as DSC, and the Tg of the polymer (B) determined by this measurement needs to be higher than the Tg of the polymer (A) by 20 ° C. or more.

The Tg value of the polymer (B) is lower than that of the polymer (A), or the polymer (A) is
If the difference is less than 20 ° C.
Stretching of the melt-formed product of the mixture is not suitable because the degree of phase separation is low and it becomes difficult to open pores.

The poly (meth) acrylate polymer used as the polymer (B) in the present invention is a polymer composed of a (meth) acrylate derivative. Examples of preferable poly (meth) acrylate-based polymers include polyalkyl (meth) acrylates such as polymethyl (meth) acrylate, polyethyl (meth) acrylate, polyropyl (meth) acrylate, and polybutyl (meth) acrylate; poly (meth) acrylic. Examples thereof include acids, poly (meth) acrylamide-based polymers; and copolymers and compatible blends thereof.

The cellulose-based derivative used as the polymer (B) in the present invention is a polymer having a cellulose skeleton, and the one in which the hydroxyl group of cellulose is substituted with various functional groups is used. As a preferable cellulose derivative,
For example, cellulose acetates such as cellulose, cellulose acetate, cellulose diacetate, and cellulose triacetate; alkyl celluloses such as methyl cellulose and ethyl cellulose; hydroxyalkyl celluloses such as hydroxycellulose and hydroxypropyl cellulose; chitin, chitosan and derivatives thereof; and Examples thereof include copolymers and compatible blends.

The polyester polymer used as the polymer (B) in the present invention is a polymer having an ester bond in its structure. Preferred polyester-based polymers include, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, wholly aromatic polyesters, polyarylates, polycaprolactone, polylactic acid (L-form, D-form).
Body, racemic body), polyhydroxybutyric acid, polybutylene succinate, polyethylene adipate, and other aliphatic polyester-based polymers, and copolymers and compatible blends of these polyesters.

The porous film of the present invention comprises fibrils oriented in a direction perpendicular to the thickness direction, and the gaps between the fibrils form slit-like micropores. The slit-shaped micropores are oriented in a direction perpendicular to the thickness direction, are stacked in the thickness direction and penetrate, and the entire film has a three-dimensional mesh structure having a uniform structure in the thickness direction. There is. The fibrils are composed of the polymer (A), which constitutes the long sides of the slit-shaped micropores, and the polymer (B) is present at the knots of the fibrils corresponding to the short sides of the slit-shaped micropores.

The average width of the slit-shaped fine holes is 0.01 to
10 μm is preferable, and 0.1 to 5 μm is more preferable.
The average length of the slit-shaped fine holes is preferably 0.05 to 50 μm, more preferably 0.5 to 50 μm. The width of the slit is less than 0.01 μm or the length of the slit is 0.
If it is less than 05 μm, the flux of the film tends to decrease, which is not preferable. Conversely, the slit width is 10 μm
When the length exceeds 50 μm or when the slit length exceeds 50 μm, the mechanical strength tends to be poor, and the film cannot be used as a film.

The ratio of the average length to the average width of slit-like micropores (average length / average width) is not particularly limited, but from the viewpoint of mechanical strength, it is preferably 3 or more, more preferably 5 or more, More preferably, it is 8 or more.

The feature of the present invention is that the porous membrane is composed of fibrils oriented in the direction perpendicular to the thickness direction, and the slit-shaped micropores oriented in the direction perpendicular to the thickness direction are laminated in the thickness direction. To form a through hole and has a uniform structure in the thickness direction. Since the membrane of the present invention has such a structure, the flux of the membrane is higher than that of the asymmetric membrane produced by the wet method and the mechanical strength is excellent.

The porous membrane of the present invention comprises the polymer (A) 50
˜90 wt% and polymer (B) 50 to 10 wt%, but within such a composition range, the polymer (A)
And the polymer (B) form a sea-island type phase-separated structure in which the polymer (A) is a sea component (matrix component) and the polymer (B) is an island component (dispersion component), and the polymer (B ) Exists in a dispersed manner. Outside this composition range, it is difficult to form a stable and uniform phase-separated structure, and a porous membrane having the above structure cannot be obtained.

In the porous membrane of the present invention, the polymer (B) is present in a dispersed state in the porous membrane, but the average particle size of the dispersed islands of the polymer (B) is 0.01. ~ 1
0 μm is preferred.

In the porous membrane of the present invention, the polymer (B) is dispersed in the form of islands in the porous membrane, but the polymer molecular chain is present between the polymer (A) and the polymer (B). Since there is an interaction such as entanglement between the particles, it has a feature that particles are less likely to drop during use, as compared with a porous film in which ordinary inorganic fine particles are mixed and made porous.

The porosity of the porous membrane of the present invention is 10 to 90.
% Is preferable in terms of filtration performance.

The shape of the porous membrane of the present invention is not particularly limited, but it is generally used as a hollow fiber membrane or a flat membrane and can be used in a preferable shape depending on the application.

When the porous membrane is a hollow fiber membrane, the outer diameter is preferably 2 mm or less, more preferably 20 to 1000 μm. The wall thickness is 500μ
It is preferably m or less, and more preferably 5 to 400 μm. If the outer diameter of the porous hollow fiber membrane exceeds 2 mm, it tends to be difficult to maintain the hollow shape,
Especially when external pressure is applied, flattening tends to occur. If the outer diameter is smaller than 20 μm, yarn breakage is likely to occur during spinning.

When the porous film is a flat film, the film thickness is 5
˜500 μm, more preferably 5 to 400 μm.

In order to impart hydrophilicity to the porous membrane of the present invention, a thin film made of a saponified ethylene-vinyl acetate copolymer on at least a part of the pore wall surface of the slit-like fine pores of the porous membrane, or A hydrophilic crosslinked polymer obtained by polymerizing monomers including diacetone acrylamide and a crosslinkable monomer may be retained. A thin film made of a saponified product of ethylene-vinyl acetate copolymer or a hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linking monomer is at least one of the wall surfaces of the fine pores of the porous membrane. It only has to be held by the department. In other words, it suffices that the polymer is retained so that the hydrophilicity of the porous membrane is substantially improved, and the polymer does not necessarily have to be retained on all the wall surfaces of the pores.

The saponified product of ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) may be any type of copolymer such as random, block or graft. Ethylene content is 20
It is preferably in the range of ˜70 mol%. When the ethylene content is less than 20 mol%, the adhesiveness of the polymer is low and the wall surface of the fine pores of the porous film and the thin film layer tend to be easily peeled off. If it exceeds 70 mol%, the hydrophilicity of the thin film layer tends to decrease.

A hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linking monomer contains diacetone acrylamide as a monomer component in an amount of 50% by weight or more and contains a cross-linking monomer. In addition to these, the non-crosslinkable monomer may be contained as the monomer component.

As the crosslinkable monomer, a monomer having two or more polymerizable unsaturated groups such as vinyl bond and allyl bond which are copolymerizable with diacetone acrylamide, or containing one polymerizable unsaturated bond, and A monomer having at least one functional group capable of forming a chemical bond by a bonding reaction or the like and having a good solvent in common with diacetone acrylamide can be mentioned. Examples thereof include N, N-methylenebisacrylamide, N-hydroxymethyl (meth) acrylamide, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, 2,2-bis (4-methacryloyloxypolyethoxyphenyl). Examples thereof include propane, ethylene di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and trimethylolethane tri (meth) acrylate.

Further, the greater the degree of hydrophilicity of the polymer, the better the water permeation performance of the hydrophilized porous membrane, and water is uniformly permeated from the entire membrane surface in a short time at the start of use. The crosslinkable monomer that forms the crosslinked polymer is preferably a water-soluble crosslinkable monomer having a sufficient degree of hydrophilicity. Such a water-soluble crosslinkable monomer is a crosslinkable monomer having a solubility in water at 30 ° C. of 1.0 g / dl or more, and examples thereof include N, N-
Examples thereof include methylenebisacrylamide and N-hydroxymethyl (meth) acrylamide.

Next, the method for producing the porous membrane of the present invention will be described.

The porous membrane of the present invention comprises the polymer (A),
A shaped product composed of the polymer (A) and the polymer (B) which is incompatible with the polymer (A) and has a Tg higher by 20 ° C. or more than the polymer (A) can be produced by stretching. A polymer (A) having a sea component (matrix component) and a polymer (B) having an island component (dispersion component) is formed in this shaped object, and a sea-island type phase-separated structure is formed, and the polymer (B) is dispersed in the form of particles. It is preferable that the islands of 1) are uniformly dispersed. If the dispersion of the polymer (B) is extremely biased, the stretching in the subsequent step becomes non-uniform and it tends to be difficult to stretch at a high ratio, which is not preferable. In addition, the variation in the diameter of the fine holes also increases.

The mixing ratio of the polymer (A) and the polymer (B) is 50 to 90% by weight of the polymer (A) and 50 to 10% by weight of the polymer (B). When the mixing ratio of the polymer (B) exceeds 50% by weight, a stable sea-island type phase-separated structure is not formed, and thus it becomes difficult to perform the stretching in the subsequent step. If the polymer (B) is less than 10% by weight, only independent pores are formed even when stretched, and it tends to be difficult to form through-holes.

The mixing method of the polymer (A) and the polymer (B) is not particularly limited, and a known mixing method can be used. For example, there are a method of dissolving in a common solvent of the polymer (A) and the polymer (B) and mixing in a solution state, a method of melt-kneading with a uniaxial or biaxial screw extruder, and the like. The mixture composed of the polymer (A) and the polymer (B) mixed by these methods may be directly shaped into a predetermined shape by using various known molding methods, or once formed into a shape such as a pellet. After that, it may be shaped into a predetermined shape by using various known molding methods. For example, when the porous membrane is a flat membrane, it can be formed into a film by a known method such as a melt extrusion molding method using a T die, a compression molding method, and a cast molding method. Further, when the porous membrane is a hollow fiber membrane, it can be shaped into a hollow fiber by a melt shaping method or the like. As the hollow fiber manufacturing nozzle used in the melt shaping, known nozzles such as a double cylinder type and a bridge type can be used.

The melt shaping temperature is preferably higher than the highest temperature of Tg and melting point (Tm) of the polymer (A) and the polymer (B). As a result, the viscosity is high at low temperatures and shaping is difficult, which is not preferable.

When the porous membrane is a hollow fiber membrane, the mixture discharged from the nozzle is preferably wound in a draft ratio range of 1 to 400, more preferably a draft ratio range of 5 to 200. is there. When the draft ratio is less than 1, it tends to be difficult to stably wind the fiber. On the contrary, when the draft ratio exceeds 400, the orientation of the undrawn yarn advances, and the undrawn yarn is drawn at a high ratio in a later step. Tends to be difficult.

Next, the obtained shaped product is stretched. Stretching is usually performed in a direction perpendicular to the thickness direction. The shaped product becomes a porous structure by stretching.

The feature of the present invention resides in that the shaped product is stretched, and by stretching, the fibrils and the slit-like micropores are oriented in a direction perpendicular to the thickness direction. That is, voids and crazes are generated in the matrix polymer (polymer (A)) around the particulate islands of the polymer (B) by stretching, and these expand with stretching to form slit-shaped fine pores, and at the same time, the polymer ( The molecular chain of A) is stretched and fibrillated.

Therefore, the gap between the fibrils is a slit-shaped fine hole, and the longitudinal directions of both the fibril and the slit-shaped fine hole are oriented in the same direction as the stretching direction, that is, in the direction perpendicular to the thickness direction. To do. Further, when the porous membrane is a hollow fiber membrane, stretching is usually performed in the fiber axis direction, so that the longitudinal directions of the fibrils and the slit-shaped micropores are oriented in the fiber axis direction.

Further, since the particulate islands of the polymer (B) are almost uniformly (averagely) dispersed in the matrix polymer (A), the slit-shaped fine pores formed by stretching are laminated in the thickness direction. In addition, it exists almost uniformly in the thickness direction.

The porous membrane of the present invention has a structure in which the fibrils and the slit-shaped micropores formed thereby are oriented in the direction perpendicular to the thickness direction and are uniformly laminated in the thickness direction. Therefore, the flux of the film is high.

Further, the width and length of the slit-like fine holes depend on the particle size and the amount of stretching of the islands of the polymer (B) in particle form, so the particle size of the islands and the particle size distribution and the amount of stretching are controlled. As a result, the width and length of the slit-shaped fine holes can be suppressed.

The stretching temperature is preferably Tg of the polymer (A) or higher. At a temperature lower than the Tg of the polymer (A), it becomes difficult to stretch at a high ratio, which is not preferable.

The deformation rate during stretching may be appropriately selected according to the polymer (A) and is not particularly limited.

As a stretching method, for example, the stretching can be performed continuously between rollers, but a multi-step method of two or more steps may be used.
When the multistage method is used, the stretching temperature, the stretching ratio, the deformation speed, etc. may be changed in each stage. Further, zone stretching or a combination of zone stretching and multistage stretching can also be preferably used. In addition, the stretching may be performed in a batch method without continuously stretching.

The stretching ratio is not particularly limited, but it is 2-10.
It is preferably double and more preferably 3 to 9 times. Draw ratio is 2
If it is less than twice, the slit-shaped fine holes are independent from each other, and it is difficult to form the through holes, which is not preferable. If the draw ratio exceeds 10 times, the film tends to break during drawing, which is not preferable.

When the porous membrane is a flat membrane, it may be uniaxially stretched or may be biaxially stretched to the extent that mechanical strength is not lowered.

If necessary, the obtained porous hollow fiber may be heat-set at a drawing temperature or higher.

By the method described above, a porous membrane having a structure in which fibrils oriented in a direction perpendicular to the thickness direction and slit-like micropores are laminated in the thickness direction and the slit-like micropores penetrate in the thickness direction is obtained. Manufactured.

[0055]

EXAMPLES The present invention will be described in detail below with reference to examples.

"Air permeation rate" and "water permeation rate"
Since it depends on the film thickness even if the pore size and the porosity of the fine pores are the same, it is preferable to convert the film thickness as an index of the film performance. In a uniform membrane, the air permeation rate and water permeation rate are inversely proportional to the film thickness, so convert using the following formula:
The air permeation rate AFr and the water permeation rate WFr were calculated, respectively.

AFr = AF × t WFr = WF × t where t is the film thickness (μm), and AF is the pressure of 0.5 kg · cm ⁻² from one side of the porous film at 25 ° C. Air permeation speed (1 / m
² · hr · 0.5 kg · cm ⁻² ), WF is a water permeation rate (1) obtained by actually measuring the water permeation amount at a transmembrane pressure of 50 mmHg by flowing water at 25 ° C. from one side of the porous membrane. / M
² · hr · mmHg).

Since the pore wall surface of the pores is difficult to be wet with water, the porous membrane was previously immersed in ethanol, replaced with water and subjected to a hydrophilic treatment, and then the water permeation rate was measured.

Example 1 Poly-L-lactic acid (weight average molecular weight 28.0 × 10 ⁴ , T
m = 179 ° C., Tg = 59 ° C.) 80 parts by weight, polymethylmethacrylate polymer (Acrypet VH, trade name,
20 parts by weight of Mitsubishi Rayon Co., Ltd., Tg about 100 ° C.) was dissolved in 700 parts by weight of chloroform to prepare a mixed solution, which was cast on a glass substrate to prepare a cast film. After drying, the cast film separated from the substrate was stretched at 90 ° C. at a deformation rate of 100% / min to a stretching ratio of 6 times, and heat set at 95 ° C. for 3 minutes at a constant length to obtain a porous flat film.

The obtained porous film had a film thickness of 20 μm. As a result of observing the surface of the porous film with a scanning electron microscope (hereinafter abbreviated as SEM), an average width of 1.2 μm and an average length of 2
It was confirmed that the slit-like micropores of 2 μm were oriented in the direction perpendicular to the thickness direction, penetrated in the thickness direction, and had a substantially uniform structure in the thickness direction. The air permeation rate of this porous membrane is 6.6 × 10 ⁷ μm · 1 / m ² · hr ·
0.5 kg · cm ⁻² , the maximum pore size determined by the bubble point method is 1.3 μm, the average pore size determined by the air flow method is 1.1 μm, and the water permeation rate is 2.7 × 10 ³ μm.
It was m · 1 / m ² · hr · mmHg.

Example 2 Real poly-D-lactic acid (weight average molecular weight 32.0 × 10 ⁴ ,
Tm = 179 ° C., Tg = 59 ° C.) 75 parts by weight, polymethylmethacrylate polymer (Acrypet VH, trade name, manufactured by Mitsubishi Rayon Co., Ltd., Tg about 100 ° C.) 25 parts by weight are 205 ° C. by a uniaxial extruder. And kneaded to obtain pellets. The obtained pellets were subjected to a spinning temperature of 205 ° C. and a discharge linear velocity of 10 c using a double cylindrical hollow fiber manufacturing nozzle.
Spinning was performed at m / min, a winding speed of 1.0 m / min, and a draft ratio of 10. Then, the obtained undrawn hollow fiber is
Stretched at a draw rate of 5 times at a deformation rate of 100% / min and 85 ° C
Heat setting was performed for 3 minutes at a constant length to obtain a porous hollow fiber membrane.

The obtained porous hollow fiber membrane has an outer diameter of 410 μm.
m, inner diameter 300 μm, and film thickness 55 μm. Hollow fiber
The outer surface, inner surface and cross section of the film were observed by SEM.
The result is a slit with an average width of 2.1 μm and an average length of 18 μm.
The micropores are oriented in the direction perpendicular to the thickness direction and penetrate in the thickness direction.
And has a structure that is almost uniform in the thickness direction.
Was recognized. The air permeation rate of this hollow fiber membrane is 8.
5 × 10⁷ μm / 1 / m ^Two ・ Hr ・ 0.5kg ・ cm^-2
And the maximum pore size obtained by the bubble point method is 1.7.
μm, average pore size obtained by air flow method is 1.4μ
m, water permeation rate is 5.0 × 10^Three μm / 1 / m^Two ・ Hr
-It was mmHg.

Example 3 Poly-L-lactic acid (weight average molecular weight 28.0 × 10 ⁴ , T
m = 179 ° C., Tg = 59 ° C.) 70 parts by weight and cellulose triacetate (Tg about 105 ° C.) 30 parts by weight are dissolved in 500 parts by weight of methylene chloride to prepare a mixed solution, which is cast on a glass substrate and cast. A membrane was prepared. After drying, the cast film peeled from the substrate was deformed at 90 ° C at a deformation rate of 1
The film was drawn at a draw ratio of 4 times at 000% / min, and heat set at 95 ° C. for 3 minutes at a constant length to obtain a porous flat film.

The obtained porous film had a film thickness of 40 μm. As a result of observing the surface of the porous film with an SEM, the slit-shaped micropores having an average width of 3.2 μm and an average length of 22 μm are oriented in the direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 1.1 × 10 ⁸
The maximum pore size determined by the bubble point method is 2.1 μm, the average pore size determined by the air flow method is 1.7 μm, and the water permeation rate is 8 μm · 1 / m ² · hr · 0.5 kg · cm ^−2. 0.0 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 4 Poly-L-lactic acid (weight average molecular weight 28.0 × 10 ⁴ , T
m = 179 ° C., Tg = 59 ° C.) 85 parts by weight, polymethylmethacrylate polymer (Acrypet VH, trade name,
15 parts by weight of Mitsubishi Rayon Co., Ltd., Tg about 100 ° C.) was dissolved in 700 parts by weight of chloroform to prepare a mixed solution, which was cast on a glass substrate to prepare a cast film. After drying, the cast film separated from the substrate was stretched at 90 ° C. at a deformation rate of 50% / min to a stretching ratio of 8 times, and then stretched at 95 ° C. for 3 hours.
Heat setting was performed for a fixed length for a minute to obtain a porous flat membrane.

The obtained porous film had a film thickness of 18 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 0.8 μm and an average length of 15 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 5.1 × 10 ⁷
μm · 1 / m ² · hr · 0.5 kg · cm ⁻² , the maximum pore size determined by the bubble point method is 1.1 μm, the average pore size determined by the air flow method is 0.9 μm, and the water permeation rate is 1 0.7 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 5 An ethylene-vinyl alcohol copolymer (Soarnol DC3203, trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) having an ethylene content of 32 mol% was dissolved by heating in a 75% by volume aqueous ethanol solution to give 1% by weight. A solution was prepared. Next, this solution was kept at 50 ° C., and the porous membrane obtained in Example 1 was immersed in the solution and left for 5 minutes. Then, after removing the excess copolymer solution, it was dried in a hot air dryer at 50 ° C. for 2 hours to obtain a hydrophilic porous film.

The hydrophilized porous film thus obtained has good wettability with water, easily wets when soaked in water, and 3.0 × 10 ³ μm · 1 / m ² · hr without any special hydrophilizing treatment.・ MmH
The water permeation rate of g was shown. A drying treatment and a wetting treatment with water were alternately repeated 10 times on the hydrophilized porous membrane, but no decrease in water permeation rate was observed.

Example 6 The porous hollow fiber membrane obtained in Example 2 was treated with 100 parts by weight of diacetone acrylamide, 5 parts by weight of N-hydroxymethyl acrylamide, 1 part by weight of benzoyl peroxide and 1000 parts by weight of acetone. 1 in solution
After soaking for 2 seconds, it was taken out in nitrogen and air dried for 5 minutes.
Subsequently, this hollow fiber membrane was heat-treated at 65 ° C. for 60 minutes in a nitrogen atmosphere, then immersed in an aqueous solution of 50% by weight of ethanol for 10 minutes, and further ultrasonically washed in warm water for 2 minutes to remove unnecessary components. did. Next, it was dried with hot air to obtain a hydrophilized porous hollow fiber membrane in which the polymer was retained.

The obtained hollow fiber membrane has good wettability with water,
When soaked in water, it was easily wet and showed a water permeation rate of 5.5 × 10 ³ μm · 1 / m ² · hr · mmHg without any special hydrophilization treatment. The hollow fiber membrane was alternately dried and wetted with water 10 times each.
No decrease in water permeation rate was observed.

Example 7 The cast film produced in Example 1 was subjected to a deformation rate of 1 at 70 ° C.
The film was stretched at a draw ratio of 6 times at 00% / min, and heat-set at a constant length at 75 ° C to obtain a porous flat membrane. The obtained porous film had a film thickness of 19 μm. As a result of observing the surface of the porous film with an SEM, slit-like micropores having an average width of 1.5 μm and an average length of 25 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 7.0 × 10 ⁷ μm · 1 / m ² · hr · 0.5 kg · c
m ⁻² , the maximum pore size determined by the bubble point method is 1.6 μm, the average pore size determined by the air flow method is 1.2 μm, and the water permeation rate is 3.2 × 10 ³ μm · 1 / m.
^{It was 2} · hr · mmHg. Example 8 Poly-L-lactic acid (weight average molecular weight 28.0 × 10 ⁴ , T
m = 179 ° C., Tg = 59 ° C.) 60 parts by weight and cellulose triacetate (Tg = 105 ° C.) 40 parts by weight are dissolved in 500 parts by weight of methylene chloride to prepare a mixed solution, which is cast on a glass substrate and cast film. Was produced. After drying, the cast film peeled from the substrate was deformed at 90 ° C at a deformation rate of 1
The film was drawn at a draw ratio of 5 times at 000% / min, and heat-set at 95 ° C. for 3 minutes at a constant length to obtain a porous flat film.

The resulting porous film had a film thickness of 42 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 5.4 μm and an average length of 32 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 2.4 × 10 ⁸
The maximum pore size determined by the bubble point method is 2.9 μm, the average pore size determined by the air flow method is 2.2 μm, and the water permeation rate is 1 μm · 1 / m ² · hr · 0.5 kg · cm ^−2. .1 × 10 ⁴ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 9 The cast film produced in Example 1 was subjected to a deformation rate of 1 at 60 ° C.
The film was stretched at a draw ratio of 6 times at 00% / min, and heat-set at 65 ° C. for 3 minutes at a constant length to obtain a porous flat membrane.

The obtained porous film had a film thickness of 18 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 1.4 μm and an average length of 22 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 6.4 × 10 ⁷
The maximum pore size determined by the bubble point method is 1.4 μm, the average pore size determined by the air flow method is 1.2 μm, and the water permeation rate is 2 μm · 1 / m ² · hr · 0.5 kg · cm ^−2. 9.9 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 10 The cast membrane produced in Example 1 was stretched at 160 ° C. at a deformation rate of 100% / min to a stretching ratio of 6 times, and heat-set at 165 ° C. for 3 minutes at a constant length to form a porous flat membrane. Got

The obtained porous film had a film thickness of 20 μm. As a result of observing the surface of the porous film with an SEM, slit-like micropores having an average width of 1.3 μm and an average length of 28 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 8.1 × 10 ^7.
The maximum pore size determined by the bubble point method is 1.5 μm, the average pore size determined by the air flow method is 1.3 μm, and the water permeation rate is 3 μm · 1 / m ² · hr · 0.5 kg · cm ^−2. 6.6 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 11 Polycaprolactone (PLACCEL H-7, trade name, manufactured by Daicel Chemical Industries, Ltd., Tm = 60 ° C., Tg = -6)
0 ° C.) 80 parts by weight, polymethylmethacrylate polymer (Acrypet VH, trade name, manufactured by Mitsubishi Rayon Co., Ltd.,
Tg of about 100 ° C.) 20 parts by weight was dissolved in 700 parts by weight of chloroform to prepare a mixed solution, which was cast on a glass substrate to prepare a cast film. After drying, the cast film separated from the substrate was stretched at 45 ° C. at a deformation rate of 100% / min to a stretching ratio of 6 times, and heat set at 50 ° C. for 3 minutes at a constant length to obtain a porous flat film.

The obtained porous film had a film thickness of 35 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 4.8 μm and an average length of 30 μm are oriented in the direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 2.1 × 10 ⁸
μm · 1 / m ² · hr · 0.5 kg · cm ⁻² , the maximum pore size determined by the bubble point method is 2.7 μm, the average pore size determined by the air flow method is 2.1 μm, and the water permeation rate is 1 0.0 × 10 ⁴ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 12 Aliphatic polyester (Bionol # 3010, trade name,
Showa Highpolymer Co., Ltd., Tm = 95 ° C, Tg = -45 ° C)
80 parts by weight, 20 parts by weight of polymethylmethacrylate polymer (Acrypet VH, trade name, manufactured by Mitsubishi Rayon Co., Ltd., Tg about 100 ° C.) are dissolved in 700 parts by weight of chloroform to prepare a mixed solution, and a glass substrate is prepared. A cast film was prepared by casting on top. After drying, the cast film separated from the substrate was stretched at 70 ° C. at a deformation rate of 100% / min to a stretching ratio of 6 times, and heat-set at 75 ° C. for 3 minutes at a constant length to obtain a porous flat film.

The obtained porous film had a film thickness of 30 μm. As a result of observing the surface of the porous membrane with an SEM, slit-shaped micropores having an average width of 2.4 μm and an average length of 21 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 9.4 × 10 ^7.
The maximum pore size determined by the bubble point method is 1.8 μm, the average pore size determined by the air flow method is 1.5 μm, and the water permeation rate is 6 μm · 1 / m ² · hr · 0.5 kg · cm ^−2. 0.0 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 13 Poly-DL-lactic acid (weight average molecular weight 22.0 × 10 ⁴ ,
Tg = 60 ° C.) 80 parts by weight, polymethylmethacrylate polymer (Acrypet VH, trade name, Mitsubishi Rayon
Co., Ltd., Tg: about 100 ° C.) 20 parts by weight was dissolved in 700 parts by weight of chloroform to prepare a mixed solution, which was cast on a glass substrate to prepare a cast film. After drying, the cast film peeled from the substrate was deformed at 60 ° C at a deformation rate of 100% /
The film was stretched to a draw ratio of 6 times in minutes to obtain a porous flat membrane.

The resulting porous film had a film thickness of 20 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 1.1 μm and an average length of 16 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 3.6 × 10 ^7.
μm · 1 / m ² · hr · 0.5 kg · cm ⁻² , maximum pore size determined by bubble point method is 0.9 μm, average pore size determined by air flow method is 0.7 μm, water permeation rate is 1 0.7 × 10 ³ μm ・ 1 / m ²・ hr ・ mmHg
Met.

Example 14 Polycaprolactone (PLACCEL H-7, trade name, manufactured by Daicel Chemical Industries, Tm = 60 ° C., Tg = -60 ° C.)
80 parts by weight, poly-L-lactic acid (weight average molecular weight 28.0
(× 10 ⁴ , Tm = 179 ° C., Tg = 59 ° C.) 20 parts by weight was dissolved in 700 parts by weight of chloroform to prepare a mixed solution, which was cast on a glass substrate to prepare a cast film. After drying, the cast film separated from the substrate was stretched at 45 ° C. at a deformation rate of 100% / min to a stretching ratio of 6 times, and heat set at 50 ° C. for 3 minutes at a constant length to form a porous flat film (14). Obtained.

The obtained porous film had a film thickness of 30 μm. As a result of observing the surface of the porous film with an SEM, slit-shaped micropores having an average width of 4.5 μm and an average length of 33 μm are oriented in a direction perpendicular to the thickness direction and penetrate in the thickness direction, and almost in the thickness direction. It was found to have a uniform structure. The air permeation rate of this porous membrane is 1.8 × 10 ⁸
μm · 1 / m ² · hr · 0.5 kg · cm ⁻² , the maximum pore diameter determined by the bubble point method is 2.6 μm, the average pore diameter determined by the air flow method is 2.0 μm, and the water permeation rate is 1 0.0 × 10 ⁴ μm ・ 1 / m ²・ hr ・ mmHg
Met.

[0085]

EFFECTS OF THE INVENTION According to the present invention, a porous membrane having slit-shaped micropores oriented in a direction perpendicular to the thickness direction is laminated and penetrates in the thickness direction and has a substantially uniform structure in the thickness direction. can get.

Further, the porous membrane of the present invention has a high membrane flux such as air permeation rate and water permeation rate, is excellent in pressure resistance and mechanical strength, and has a porous structure obtained by adding ordinary inorganic fine particles to form a stretched porous film. Since there is almost no drop of particles as seen in the quality membrane, it can be used in a wide range of fields such as household water purifiers, air purification, industrial wastewater treatment and other industrial fields, medical applications, food-related fields, and other filtration and separation applications. Can be used.

Furthermore, according to the method for producing a porous membrane of the present invention, it is possible to obtain a porous membrane using various polymers in which the orientation of molecular chains is not so easy as a substrate.

Claims (7)

[Claims] 1. 50 to 90% by weight of a polymer (A), 50 to 10% of a polymer (B) which is incompatible with the polymer (A) and has a glass transition temperature higher than that of the polymer (A) by 20 ° C. or more. A porous membrane consisting of wt.%,
The fibrils made of the polymer (A) oriented in the direction perpendicular to the thickness direction of the porous membrane and the slit-shaped micropores are laminated in the thickness direction, and the slit-shaped micropores penetrate in the thickness direction, and the polymer A porous film in which (B) is dispersed and present in the porous film. 2. The average width of the slit-shaped micropores is 0.01 to.
The porous membrane according to claim 1, which has a thickness of 10 µm and an average length of 0.05 to 50 µm. 3. The porous membrane according to claim 1, wherein the polymer (B) is present in the form of particles having an average particle diameter of 0.01 to 10 μm dispersed in the porous membrane. 4. A thin film made of a saponification product of an ethylene-vinyl acetate copolymer is held on at least a part of the pore wall surface of the slit-shaped fine pores of the porous film. Or the porous membrane as described in 3. 5. A hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linking monomer is held on at least a part of the pore wall surface of the slit-like fine pores of the porous membrane. Claim 1, characterized in that
The porous membrane according to 2 or 3. 6. The polymer (A) in an amount of 50 to 90% by weight.
And a polymer (B) in an amount of 50 to 10 wt% is stretched, and the method for producing a porous membrane according to claim 1, wherein the shaped product is stretched. 7. The production method according to claim 8, wherein the stretching temperature is not lower than the glass transition temperature of the polymer (A).