JPH0774290B2 - Hydrophilic porous fluororesin material - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hydrophilic porous fluororesin material.

[0002]

2. Description of the Related Art Conventionally, a porous fluororesin material having a large number of fine pores has been known. Such materials are widely used as filters having excellent heat resistance and chemical resistance. However, this material has a large water repellency and does not allow water to smoothly pass therethrough, and therefore cannot be applied to the separation of particles dispersed in water. In order to obtain a porous fluororesin material that allows water to permeate, it is necessary to make the inner surfaces of the pores hydrophilic, and therefore various methods have been investigated.

As such a method, for example, (1)
After impregnating the material with a hydrophilic organic solvent such as alcohol,
Method of substituting with water, (2) Method of impregnating material with alcohol solution of surfactant, (3) Method of impregnating material with hydrophilic group-containing monomer and then polymerizing to compound hydrophilic polymer into material , (4) a method of graft-polymerizing a hydrophilic group-containing monomer into the material, (5) a method of impregnating an organic solvent solution of polyvinyl alcohol into a composite, and (6) a material after impregnating the hydrophilic group-containing monomer ,
There are methods such as treatment with a strong reducing agent or plasma gas, or irradiation with high energy rays such as gamma rays and electron rays.

However, these conventional methods have various drawbacks. For example, the method (1) is a general method, but has a drawback that the effect is lost once the material is dried. In the method of (2), when the obtained material is used as a filter, the surfactant is eluted, so that the durability of the material is poor, (3),
Each of (4) and (5) has the drawback that the pores are easily clogged, the polymer is easily eluted, and the durability is poor. Therefore, in the methods (2) to (5), in order to prevent the elution of the surfactant and the polymer, the impregnated surfactant and the polymer need to be crosslinked or crystallized. Regarding these treatments, JP-A-53-53
21270, JP-A-54-8669, JP-A-56-
157437 and JP-A-64-98640.

On the other hand, in the method (6), the mechanical properties of the material are impaired and it is difficult to prevent the polymerization of the monomer itself.

As described above, the conventional hydrophilization techniques for porous fluororesin materials have various problems and are not yet satisfactory.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above problems found in the conventional hydrophilization technology for a porous fluororesin material having a large number of fine pores, and does not use a cross-linking treatment but only impregnation treatment. It is an object of the present invention to provide a porous fluororesin material which has excellent hydrophilicity and whose hydrophilicity is stably maintained over a long period of time.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, in a porous fluororesin material having a large number of fine pores, a copolymer of a fluorine-containing monomer and a fluorine-free hydrophilic group-containing monomer is attached at least in the pores. Thus, there is provided a hydrophilic porous fluorine material characterized in that the copolymer has a fluorine content of 2 to 60% by weight.

The porous fluororesin material used as the substrate in the present invention may be any one having continuous fine pores (through holes), and the means for forming the pores is not particularly limited, and stretching, expansion, Foaming, extraction, etc. are adopted. Also,
The type of fluororesin is not particularly limited, and various types can be used. The preferred fluororesin for use in the present invention is polytetrafluoroethylene, but tetrafluoroethylene / hexafluoropropylene copolymer, polyvinyl fluoride, polyvinylidene fluoride, etc. may also be used. In the present invention, it is preferable to use porous polytetrafluoroethylene, particularly stretched porous polytetrafluoroethylene.

The porous fluororesin material preferably used as the substrate in the present invention comprises a stretched product of polytetrafluoroethylene and has a porosity of 15 to 95%, preferably 50 to 95%.
With 95%. For such base materials, Japanese Patent Publication No. 56-45773 and Japanese Patent Publication No. 56-1721.
No. 6, U.S. Pat. No. 4,187,390.

In the present invention, the hydrophilic fluorocopolymer to be adhered and bonded in the pores of the porous fluororesin material is
A copolymer of a fluorine-containing ethylenically unsaturated monomer and a fluorine-free hydrophilic group-containing vinyl monomer,
It can be obtained by copolymerizing those monomers. Examples of the fluorine-containing monomer include tetrafluoroethylene, vinyl fluoride, vinylidene fluoride, monochlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene and the like.

The fluorine-containing monomer used in the present invention can be represented by the following general formula. CXY = CFZ (1) In the formula, Z is a fluorine or hydrogen, X and Y are hydrogen, fluorine, chlorine and trifluoromethyl _(-CF 3)
Chosen from among.

The other fluorine-containing monomer used in the present invention can be represented by the following general formula. In the above formula, R is hydrogen, fluorine, a methyl group, an ethyl group, a trifluoromethyl group (CF ₃ ) or a pentafluoroethyl (C ₂ F ₅ ). Rf represents a perfluoroalkyl group having 4 to 21 carbon atoms.

On the other hand, as the hydrophilic group-containing monomer, hydroxyl group, carboxyl group, sulfone group, phosphoric acid group,
Examples thereof include those having an N-substituted amide group, an N-substituted amino group and the like. A monomer in which an alkylene oxide such as ethylene oxide or propylene oxide is subjected to an addition reaction with active hydrogen of the hydrophilic group is also preferable. Also used are those which give a hydrophilic group-containing copolymer by hydrolysis after copolymerization, such as vinyl acetate. Specific examples of the hydrophilic monomer containing no fluorine include unsaturated carboxylic acids such as vinyl alcohol, acrylic acid and methacrylic acid, and alkylene oxide adducts of acrylic acid and methacrylic acid as shown below. In the above formula, R is hydrogen or a methyl group, and n and m are 1
It is an integer above the above. Both the fluorine-containing monomer and the fluorine-free hydrophilic group-containing monomer may be one kind or two or more kinds. In addition, the fluorine-containing monomer and the fluorine-free hydrophilic group-containing monomer may further include other vinyl monomers, for example, an alkyl ester of acrylic acid or methacrylic acid, a polyhydric alcohol such as trimethylolpropane, and an acrylic resin. An acid or an ester with methacrylic acid can be used in combination.

The copolymer of vinyl alcohol and a fluorine-containing monomer used in the present invention can be obtained by saponifying a copolymer of vinyl acetate and a fluorine-containing monomer and converting an acetate group contained in the copolymer into a hydroxyl group. In this case, it is not always necessary to convert all the acetate groups contained in the copolymer into hydroxyl groups, and conversion of the acetate groups into hydroxyl groups may be carried out to the extent that the copolymer has hydrophilicity. The fluorine content of the fluorine-containing hydrophilic copolymer used in the present invention is usually 2% to 60%, preferably 10% to 60%, and more preferably 20% to 60% on a weight basis. When the fluorine content of the fluorine-containing hydrophilic copolymer is too high, the heat resistance is improved but the hydrophilicity of the polymer is lowered. On the other hand, when the fluorine content is too low, the adhesiveness of the fluorine-containing hydrophilic copolymer to the substrate becomes small and the heat resistance also becomes small. In the fluorine-containing hydrophilic copolymer used in the present invention, the hydrophilic group equivalent is generally 45 to 700, preferably 60 to 50.
It is 0, more preferably 60 to 450. When the hydrophilic group equivalent is less than 45, the solubility of the fluorine-containing hydrophilic copolymer becomes very large, and the fluorine-containing copolymer is easily eluted from the substrate with water, while the hydrophilic group equivalent is 700.
If it becomes larger, the hydrophilicity becomes too small, and it becomes impossible to make the substrate hydrophilic.

Tables 1 and 2 show some copolymers in terms of mol% of fluorine-containing monomer units, weight% of fluorine (F-wt%) and equivalent of hydrophilic group (Eq).
-W) is shown. VOH is vinyl alcohol.

The hydrophilic group equivalent (Eq
-W) is the molecular weight of the copolymer divided by the number of hydrophilic groups. The hydrophilic group equivalent shown below is calculated by the following formula. In the formula, A · x is a value obtained by multiplying the molecular weight of the fluorine-containing monomer by its mole number x, while B · y is a value obtained by multiplying the molecular weight of the hydrophilic group-containing monomer by its mole number y.

[0018]

[Table 1]

[0019]

[Table 2]

Further, in Table 3, the copolymer [(CF ₂ = C
F ₂ ) x / (VOH) y] is attached to the inside of the pores of the porous fluorine membrane in the same manner as in Example 1 described later, and the hydrophilicity evaluation is shown. The content of the criteria for hydrophilicity evaluation in this case is shown in the section of Examples below.

[0021]

[Table 3]

The fluorinated hydrophilic copolymer of the present invention, which is adhered and bound in the pores, can be prepared by dissolving the fluorinated hydrophilic copolymer in an organic solvent such as alcohol, ketone, ester, amide or hydrocarbon. Then, it is manufactured by immersing it in the solution, or by impregnating the solution with the solution by a coating method using a spray or a roller and then drying. In this way, the fluorinated hydrophilic copolymer adheres to the inner surface of the material and allows water to pass through the micropores. The amount of the fluorine-containing hydrophilic copolymer attached to the material may be an amount sufficient to increase the hydrophilicity of the material, and it varies depending on the porosity of the material used, etc. , 1.5 to 10% by weight, preferably 2 to 6% by weight.

The hydrophilic porous fluororesin material of the present invention is
This is impregnated with an organic solvent solution of a copolymer of a fluorine-containing monomer and a hydrophobic monomer such as vinyl acetate that can be converted into a hydrophilic group, the substrate is dried, and at least a part of the acetate group is converted into a hydrophilic group. It can also be manufactured by

The porous fluororesin material used in the present invention is
It can be in any form such as a film, tape, plate, tube thread, fiber, fabric. The hydrophilic porous fluororesin material of the present invention has a structure in which the fluorine-containing hydrophilic copolymer is bonded to the surface of the material forming the pores of the material. This allows water to permeate the pores and makes them hydrophilic. Elution of the copolymer itself from the material can be prevented by defining the hydrophilic group equivalent of the copolymer within an appropriate range and controlling the solubility of the copolymer in water. The adhesive force of the fluorine-containing hydrophilic copolymer to the porous fluororesin material becomes strong due to the action of fluorine atoms in the hydrophilic copolymer, and its durability can be maintained in a stable state for a long time. Therefore, in the present invention, the troublesome crosslinking treatment after impregnating the fluorine-containing copolymer with the material, which is performed in the conventional method, is unnecessary.

[0025]

INDUSTRIAL APPLICABILITY The hydrophilic porous fluororesin material of the present invention has excellent water permeability and can be advantageously used as a water-permeable filter, a gas / liquid separation membrane, an oxygen-immobilized carrier and the like. The technique of the present invention has excellent heat resistance and chemical resistance because it is entirely made of a fluororesin material.

[0026]

EXAMPLES Next, the present invention will be described in more detail by way of examples. (Experimental procedure) (1) Thickness Thickness was measured with a dial thickness gauge having an accuracy of 1/1000 mm. (2) Ethanol broth point (EBP) Ethanol was spread on the surface of a sample of material (membrane), and the sample was placed horizontally on a fixing device to evaluate EBP.
In this case, air was blown from the bottom. EBP is the initial pressure (kg) when air bubbles continuously emerge from the opposite surface.
/ Cm ² ). (3) Porosity The porosity of the material before impregnation was obtained by measuring the density of the material.
The density of the material (polyteftrafluoroethylene) is 2.2
It is g / cm ³ . The porosity was calculated using the following formula. Porosity = (2.2-sample density) ÷ 2.2 in the calculation of × 100 porosity after impregnation of the material adopts 2.1 g / cm ³ instead of 2.2 g / cm ³ as the density did.

(4) Flow time The flow time is 35 mm under vacuum of 1 atm of 200 ml of water.
The time required to pass through a thick sample.
Fix the sample horizontally and pour water from above. Then suction from the bottom. In the case of measuring the material before impregnation, the sample is first impregnated with ethanol to render the material hydrophilic. (5) Durability The durability of the material after the impregnation treatment was evaluated by the flow time test (1
10 times after each time) or using a flow tester and method
Shown by hydrophilicity after circulation of 1 liter of water. (6) Fluorine content and hydroxyl content The fluorine content and hydroxyl content are calculated. (7) Water permeability (WP) WP is calculated by the following formula. WP = 200 ÷ (flow time-60 × (1.75) ² ×
3.14) (8) Heat resistance The heat resistance is determined by fixing the film to a frame, placing the material in an air oven controlled at a test temperature for a predetermined time, and then measuring the hydrophilicity according to the following. (9) Gurley value (GN) GN is determined by measuring the time required for 100 cm ³ of air to pass through a sample area of 6.45 cm ² under a water pressure of 12.4 cm. (10) Acid resistance, alkali resistance, and solvent resistance Samples are immersed in the liquid for the time shown in the examples. After drying, hydrophilicity is measured according to the following. (11) Hydrophilicity The initial hydrophilicity is determined by dropping a water droplet from a height of 5 cm on the sample surface and measuring the time required for the water droplet to be absorbed. The hydrophilicity is evaluated as follows. A: Absorbed within 1 second B: Absorbed naturally C: Absorbed only by pressurizing D: Not absorbed but contact angle decreased E: Not absorbed That is, it repels water. This E rating is unique to porous fluororesin materials.

Example 1 Tetrafluoroethylene / vinyl alcohol copolymer (copolymerization molar ratio = 1/4) (saponified tetrafluoroethylene / vinyl acetate copolymer; degree of saponification 100%: fluorine content 27% by weight) ; Hydroxy machine content 14.5 mmol /
g, hydroxyl equivalent = 69 g / mol) was dissolved in 1 liter of methanol to prepare a 0.2 wt% methanol solution. A porous fluororesin membrane having a thickness of 40 μm and a porosity of 80% was dipped in the above methanol solution to impregnate it, fixed on a frame, and dried at 50 ° C. for 5 minutes. The same process was repeated 5 times to obtain a hydrophilic porous membrane having a hydrophilicity of A rating and a flow time of 60 seconds. This product has a thickness of 30 μm and a porosity of 7
0%, pore diameter 0.2 μm, WP 20 cm ³ / cm
It was ² minutes. At the heat resistance temperature of 120 ° C., this good hydrophilicity was maintained after 24 hours, but at 135 ° C., the hydrophilicity was lost.

When this membrane was immersed in water, the substance did not dissolve in water (no elution of the copolymer). No change was observed when immersed in boiling water. The above film shows high acid resistance against acids such as 12N hydrochloric acid (room temperature) and 1N hydrochloric acid (80 ° C).
It also showed high alkali resistance against alkali such as normal sodium hydroxide (room temperature) and 1 normal sodium hydroxide (80 ° C).

Example 2 Tetrafluoroethylene / vinyl acetate copolymer (copolymerization molar ratio = 1/4, precursor of tetrafluoroethylene / vinyl alcohol copolymer of Example 1) was dissolved in methyl ethyl ketone to prepare a 0.3 wt% solution. Was prepared. A porous polytetrafluoroethylene membrane having a thickness of 40 μm and a porosity of 80% was impregnated with the above solution, fixed on a frame, and dried at 60 ° C. for 5 minutes. The same process was repeated 5 times. The obtained acid was dipped in ethanol containing sodium methoxide and heat-treated for 30 minutes to perform saponification, and the saponified hydrophilic membrane was washed with water. This film exhibited similar properties to the film of Example 1.

Comparative Example 1 A porous stretched polytetrafluoroethylene film having a thickness of 40 μm and a porosity of 80% was impregnated with 5% by weight of isopropanol (FC-93 manufactured by 3M Co.) as a surfactant for 20 minutes, Then, it was dried at room temperature to obtain a hydrophilic film. The stability of this membrane was poor, and the hydrophilicity was lost only by passing 200 ml of water through the membrane 5 times.

Comparative Example 2 A porous stretched polytetrafluoroethylene film having a thickness of 40 μm and a porosity of 80% was impregnated with isopropanol to impart hydrophilicity, and then immersed in a 0.1% polyvinyl alcohol aqueous solution for 2 hours. It was dipped and then dried at 50 ° C. The obtained film exhibited hydrophilicity, but when immersed in 3N hydrochloric acid, the hydrophilicity gradually decreased and was completely lost after 24 hours. When immersed in 5N hydrochloric acid, the hydrophilicity was lost in 12 hours. The heat resistant temperature was 110 ° C. As can be seen from Examples 1 and 2 and Comparative Examples 1 and 2 described above, the impregnated film of the present invention is superior in thermal stability, acid and alkali stability and durability as compared with the polyvinyl alcohol impregnated film. .

Example 3 Thickness 48 μm, GN 6.1 seconds, EBP 1.15 kg / c
A porous polytetrafluoroethylene membrane with m ² , porosity of 76% and flow time of 36 seconds was prepared from the copolymer used in Example 1
% Methanol solution for 30 seconds, taken out, fixed to a frame, and dried at room temperature for 1 hour. The physical properties of the obtained film were as follows. Membrane Copolymer Content: 0.7
5 kg / m ² , film thickness: 39 μm, GN: 10.4 seconds, E
BP: 1.2 kg / cm ² , porosity: 71%, flow time: 56 seconds, WP speed: 20 cm ³ / m ² · minute.

(Durability test) 200 ml of water was passed through the impregnated membrane 5 times (drying once) (method 1) or 101 water was passed continuously (method 2), and then hydrophilic The test was conducted. The results are as follows. Durability test conditions Hydrophilicity test results Method 1 A Method 2 A

The impregnated membrane was subjected to a five-time flow time test. still,
Drying was performed for each test. Then, when a hydrophilicity test was conducted on this film, an evaluation of A was obtained. Further, another impregnated membrane sample was used in the flow time tester and test method, and 10 liters of water was continuously passed through. The hydrophilicity test result of this film was A.

(Heat resistance) After the impregnated film was heat-treated at the following temperature and time, a hydrophilicity test was conducted, and the following results were obtained. Temperature Time Results of hydrophilicity test 100 ° C. 30 hours A 120 ° C. 5 hours B (absorption after 60 seconds) 120 ° C. 24 hours B (absorption after 60 seconds) 120 ° C. 48 hours B (absorption after 120 seconds) 120 ° C. 2 hours C or D 150 ° C 4 hours D 200 ° C 1 hour D

(Oxidation resistance) When the impregnated film was immersed in the oxidizing conditions shown below for the time shown below and then subjected to a hydrophilicity test, the following results were obtained. Oxidizer temperature time hydrophilicity test result 1N hydrochloric acid 80 ° C 2 hours A 3N nitric acid room temperature 350 hours A 12N nitric acid room temperature 1 hour A

(Alkali resistance) When the impregnated film was immersed in the alkaline conditions shown below for the time shown below and then subjected to a hydrophilicity test, the following results were obtained. Alkali temperature Time hydrophilicity test result 1N sodium hydroxide 80 ° C 1 hour A 1N sodium hydroxide 80 ° C 5 hours D 6N sodium hydroxide room temperature 36 hours A

(Organic solvent resistance) The following results were obtained when the hydrophilicity test was conducted after passing the impregnated film through the solvents shown below. Solvent flow rate Hydrophilicity test result Methanol 300 ml A Ethanol 2000 ml A Acetone 5000 ml A

Despite methanol being a good solvent for the copolymer, the hydrophilicity after passing 300 ml of methanol was A. It should be noted that ethanol and acetone are not good solvents for the above copolymers.

Comparative Example 3 A porous PTFE membrane having a thickness of 40 μm and a porosity of 80% was placed in a 1% by weight ethanol solution of a perfluoro ion exchange resin having a sulfonic acid group (trade name: Nafion ^# 511, DuPont). It was dipped and then dried at 60 ° C. When the hydrophilicity of the obtained film was evaluated, the contact angle decreased, but
Water droplets were not absorbed even after 1 hour (that is, D evaluation of hydrophilicity evaluation standard).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuya Morimoto 123 south of Yoshinaga-cho, Wake-gun, Okayama Japan Gore-Tex Co., Ltd. (56) Reference JP-A-57-115424 (JP, A) JP 61-246394 (JP, A)

Claims (3)

[Claims] 1. A porous fluororesin material having a large number of fine pores, wherein a copolymer of a fluorine-containing monomer and a fluorine-free hydrophilic group-containing monomer is deposited in at least the pores thereof, The hydrophilic porous fluororesin material, wherein the copolymer has a fluorine content of 2 to 60% by weight. 2. The material according to claim 1, wherein the porous fluororesin material comprises polytetrafluoroethylene. 3. The material of claim 2 in which the polytetrafluoroethylene is expanded polytetrafluoroethylene.