JPH11255949A - Microporous film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a microporous film having about 10-300 μm thickness in which space between silica primary particles which function as unit for chemical reaction in an impermeable film which functions as a support. SOLUTION: In this microporous film, an aggregate 3 obtained by aggregating primary particles of silica 2 through voids is dispersed in island-like state and voids of the aggregate are made to communicate in the cross sectional direction to impart permeability to the film. This method for producing microporous film comprises casting a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer solution in which silica aggregate particles are dispersed. In this case, the porosity of the microporous film can be controlled by impregnating a liquid preparation having limited properties into silica aggregate particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to applications such as removal of particles present in a liquid, such as water treatment, and chemical reaction, such as secondary batteries and enzyme purification, through micropores forming voids in a membrane. The present invention relates to a microporous membrane used and a method for producing the same.

[0002]

2. Description of the Related Art Generally, to remove particles in a liquid medium,
Microfiltration membranes (pore size is 10 ⁻⁶ m to 10 ⁻⁴ m), and ultrafiltration membranes (pore size is 10 ⁻⁷ ), in which the mechanism based on the so-called “sieve effect” is such that particles larger than the membrane pore size cannot pass through the membrane. separation membrane 10 ^-6 m), such as from m (microporous membrane) and,
Porous foams having pores in the same range as these membranes have been used. When the microporous membrane is used as a filter, it is reinforced by applying a liquid pressure to the module, etc., and in the case of a separator, the microporous membrane is left as it is because no liquid pressure is applied. I'm using

[0003] Most of the microporous membranes are provided in a polymer matrix. To obtain this, (1) sintering a powder containing a polymer matrix as a main component in a partially fused state. (2) a stretching method obtained by stretching a sheet from a polymer matrix composed of two or more compounds,
Representative examples include (3) a method obtained by subjecting a sheet to mechanical or physical treatment, and (4) an extraction method obtained by extracting a polymer matrix mixed with a compound that dissolves or decomposes. These manufacturing methods are basic configurations,
Pre-processing or post-processing is performed depending on the material of the matrix.

[0004] Since the structure of the voids formed by the above-mentioned production methods affects the separation performance, it is necessary to select a production method of the microporous membrane according to the purpose. For example, when used in applications such as water purification where the resistance of the cake attached to the microporous membrane is dominant, the void structure is simplified so that the permeation resistance of the microporous membrane itself is reduced. Therefore, in this case, a stretching method or a mechanical / physical method is suitable. On the other hand, when used in secondary batteries or enzymatic purification where a chemical reaction occurs between the two liquid phases through the microporous membrane, the void inside the microporous membrane is a unit of the chemical reaction. Therefore, it is better that the structure of the void is complicated.

[0005] Therefore, in this case, the sintering method and the extraction method capable of forming voids having a complicated structure are suitable, but the extraction method is more suitable for mass production than the sintering method. Based microporous membranes are widely used industrially. For example, a polyethylene-based microporous membrane is prepared by mixing a liquid agent 30 to 500 selected from a compound compatible with polyethylene, such as a plasticizer such as paraffin or DOP (dioctyl phthalate), based on 100 parts by weight of polyethylene.
Parts by weight and silica 20 to 200 for imparting hydrophilicity
The parts by weight are mixed and molded in a temperature range of 130 to 250 ° C., and then immersed in an organic solvent to extract a liquid agent, thereby obtaining a microporous film having a porosity of 20 to 70%.

At present, in applications where a chemical reaction is carried out via a microporous membrane such as a secondary battery or enzyme purification, the size of the internal voids having a more complicated internal structure and functioning as a unit of the chemical reaction is as follows. In addition, miniaturization of about several tens of nanometers (hereinafter referred to as nm) is required. However, the current polyethylene-based microporous membrane is that the polyethylene and the liquid agent are compatible with each other during kneading and molding, and that the secondary or tertiary silica particles that are agglomerated during mixing or molding are at the level of the primary particles. The size of the unit is about several hundreds of nanometers, and it is not possible to reduce the size to about several tens of nanometers without sacrificing the entire porosity.

The inventor of the present invention applied an extraction method to perform a crush prevention treatment by including a liquid agent that is not compatible with the polymer in the aggregated particles of silica, and dispersed the resultant in a polymer as a binder. A porous foam obtained by molding into an arbitrary shape by means such as extrusion or pressing and extracting the liquid agent by extraction has been proposed. (Japanese Patent Application No. 8-14
No. 2633, Japanese Patent Application No. 9-108323, Japanese Patent Application No. 9-3
No. 28458). In this foam, the gap between the primary particles of silica forms a unit of several tens of nm without sacrificing the porosity, and in the field of batteries, enzyme purification, etc., it is higher than the conventional polyethylene-based microporous membrane. Has also demonstrated high performance.

[0008]

However, the thickness is conventionally 10
There is a demand for a microporous membrane having a pore size of about １００100 nm and a pore diameter of about several tens of nanometers. However, the porous foam devised by the inventor described above has a 300 μm
It is difficult to obtain a thickness less than m, and the above-mentioned needs cannot be met. Therefore, the problem to be solved by the present invention is that a non-permeable membrane functioning as a support has a thickness of 10 to 3 in which a gap between primary particles of silica is a unit.
An object of the present invention is to obtain a microporous film of about 00 μm.

[0009]

The inventor of the present invention uses a gap between primary particles of silica as a unit.
In order to create a microporous membrane of about 300 μm, a method (casting method) of dissolving a matrix and coating it on a substrate was adopted. Then, the particles are selected from silica which is rich in cohesiveness, and the conditions for selecting a polymer for obtaining the above microporous membrane are that the polymer is soluble and that the surface energy has a large difference from that of silica. After various studies, it was found that a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride-based terpolymer (hereinafter referred to as THV) was suitable,
The present invention has been reached.

[0010] That is, the invention according to claim 1 is a polymer film comprising a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer and silica particles, wherein the terpolymer is a non-permeable membrane. Is formed, the silica forms an aggregate through voids between the particles, and the aggregate is dispersed and disposed in a state where the aggregate protrudes from the front and back with the non-permeable membrane as a support. The present invention relates to a microporous membrane characterized in that the front and back sides are permeable through a gap between them.

[0011] The invention according to claim 2 relates to a method for producing the above microporous membrane, comprising tetrafluoroethylene.
-A liquid mixture is prepared by dispersing silica in the form of secondary particles or aggregated tertiary particles in a solution of a terpolymer of hexafluoropropylene-vinylidene fluoride, and the liquid mixture is applied to a substrate and dried. And obtained by peeling off from the substrate.

[0012] In the above-mentioned formulation of claim 2, unexpectedly, silica is extremely unevenly distributed in an island shape due to a high effect of promoting the aggregation of silica. As a result, as shown in FIG.
The non-permeable membrane 1 made of THV functions as a support, in which silica particles 2 are protruded from the front and back using the non-permeable membrane 1 as a support with the silica particles 2 interposed with voids between the particles. A microporous membrane (invention of claim 1) which is dispersed and present in a number of islands, and in which the aggregate is permeable so that the front and back sides thereof communicate with each other via voids between particles, can be easily obtained. It is. And, since this microporous film is manufactured by a so-called casting method, it has become possible to easily provide a microporous film having a thickness of about 10 to 300 μm.

The invention according to claim 3 is a preferred embodiment of the invention according to claim 2 for adjusting the porosity and improving the water absorption as a microporous membrane. The solvent to be used is liquid A, and in a state where the liquid B is incompatible with the liquid A and has a higher boiling point than the liquid A, impregnated into the aggregated particles of silica, the dispersion is dispersed in a solution in which the terpolymer is dissolved. To produce a liquid mixture.

In the case of the third aspect, since the aggregated silica particles have a bulk specific gravity of 50 to 300 g / l and thus have voids of 80 to 98%, in the present invention, when dispersed in a THV solution, the liquid agent enters. Most voids are lost. In order to secure the lost space, it is necessary to prevent the liquid material in the THV solution from entering, and to do so, a liquid material incompatible with the liquid material may be previously impregnated. In addition, when this formulation is applied, the liquid material impregnated in the aggregated particles opens the surface, so that the water absorption of the microporous film is improved.

[0015] To realize this, TH
After the solution V loses the solvent and forms a non-permeable membrane as a support, a process of volatilizing the liquid material impregnated in the aggregated particles is required. Therefore, the liquid material for dissolving THV and the aggregated particles are impregnated. Make the solution incompatible.
Two essential properties, such as the fact that the boiling point of the liquid agent for impregnating the aggregated particles is higher than that of the liquid agent for dissolving THV, are essential requirements.

Further, particularly preferred embodiments of the invention described in claim 2 or 3 include the following requirements. (1) It is preferable to mix 10 to 200 parts by weight of aggregated silica particles with respect to 100 parts by weight of THV. (2) It is desirable that the boiling point of the liquid agent A is 90 ° C. or lower, while the boiling point of the liquid agent B is 90 ° C. or higher. Particularly, as the liquid agent B, water is most preferable because it can be removed by drying without extraction.

(3) As a prescription for extracting and removing the liquid to be impregnated into the aggregated particles, it is preferable to apply the liquid mixture to a substrate, volatilize the liquid A, and then extract or dry the liquid B. . (4) It is preferable to appropriately add a surfactant and an alkyl silane to the liquid agent A or the liquid agent B, since the system in which the two liquid agents are incompatible with each other is stabilized. (5) In order to modify the microporous film according to the present invention, it is preferable to apply an electron beam after applying the liquid mixture to the substrate. The effects of the modification by the present formulation include an improvement in heat resistance and a hydrophilicity imparted by crosslinking of THV.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the materials used in the present invention will be described. Silica includes synthetic silica such as wet silica or dry silica and fine powder of natural silica such as silica sand. Silica is rich in cohesiveness if there are many silanol groups present on the surface of the particles, but in the present invention, synthetic silica, which has more silanol groups and has a property of easily aggregating, is suitable. Synthetic silica with many silanol groups is usually
Primary particles of about several nm to several tens nm are aggregated to form several tens of μ.
Aggregated particles of m to several hundred μm are formed. The aggregated particles have voids, and the present invention is characterized in that the voids are used as a flow path of a liquid medium or a unit of a chemical reaction. In order to obtain an aggregated structure in which the primary particles of the silica in the present invention are aggregated via voids, wet silica having a high cohesiveness is desirable. On the other hand, if the particle size of the primary particles exceeds 1 μm, the formation of voids is not complicated, which is not preferable. On the other hand, there is no particular limitation on the lower limit of the particle size, and smaller one is more preferable. However, primary particles of commercially available silica have an average particle size of several nm to 100 n.
m, which should be used.

The THV used in the present invention is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer, which belongs to a fluoropolymer and has excellent chemical resistance. It can be used for a wide range of applications like olefin polymers such as polyethylene. The characteristics of THV vary depending on the constitutional ratio of the three types of monomers, and there are various grades depending on the constitutional ratio, but not all of them show solubility in organic solvents. In the present invention, there is no limitation on the constitutional ratio of the monomer as long as it is soluble THV.

At present, as a THV exhibiting solubility, a product having a composition of about 40% tetrafluoroethylene, about 20% hexafluoropropylene, and about 40% vinylidene fluoride has been commercialized (trade name, manufactured by Sumitomo 3M Ltd.). : T
HV200G, THV200P). The above-mentioned THV showing solubility is acetone, methyl ethyl ketone,
Since these solvents are dissolved in organic solvents such as ethyl acetate and butyl acetate, these solvents are preferably used as the liquid agent A for dissolving THV in the present invention. In the present invention, a step of drying the liquid agent A for dissolving THV is performed. In consideration of the rationality of this step, it is preferable that the boiling point does not exceed 90 ° C. There's a problem. Therefore, the boiling point is optimally 70 to 85 ° C., and the liquid agent A for dissolving THV in the present invention is:
Most suitable are methyl ethyl ketone (boiling point 79 ° C.) and ethyl acetate (boiling point 77 ° C.).

In the present invention, in order to adjust the porosity and hydrophilicity, it is preferable to impregnate the silica particles with a liquid agent in advance (claim 3). In this case, the silica particles are coagulated with the liquid agent A for dissolving THV. It is incompatible with the liquid agent B for impregnating the particles. The boiling point of the liquid agent B for impregnating the aggregated particles is higher than that of the liquid agent A for dissolving THV. As described above, these two properties are essential requirements. It is also important that it has a high affinity for silica. According to these selection criteria, the liquid agent B is water or a highly polar compound. Highly polar compounds such as higher alcohols, ethylene glycol,
When the boiling point is higher than the melting point of THV (125 ° C.) such as carbitol acetate and polyethylene glycol, it is reasonable to immerse the solvent in a solvent or the like to remove it. On the other hand, water whose boiling point is lower than the melting point of THV has a boiling point of T
Since it is lower than the melting point of HV, it can be removed by a simple method such as natural drying without extraction, and can be further streamlined.

Next, it is preferable to appropriately add a surfactant or an alkyl silane to the solution A or the solution B in order to stabilize a system in which two incompatible solutions are present. For example, when ethyl acetate is selected as the liquid agent A for dissolving THV and water is selected as the liquid agent B for impregnating the aggregated particles, the inventors have studied and found that anionic surfactants such as fatty acid soaps and metal salts of alkyl benzene sulfonic acids were used. It is clear that mixing can be facilitated by adding agents, nonionic surfactants such as ether-type and alkylphenol-type, cationic surfactants such as methyl-type and benzyl-type, and alkyl-based silanes. In order to realize the ratio, it is essential to add a surfactant and an alkyl silane.

Next, the amounts of the materials used in the present invention will be described. The microporous membrane according to the present invention basically comprises
It consists of an aggregate of THV and silica. With respect to the composition, if the amount of silica is less than 10 parts by weight based on 100 parts by weight of THV, the silica does not function as a microporous film, and if it is 150 parts by weight or more, it becomes brittle. Therefore, the amount of silica is desirably 30 to 120 parts by weight based on 100 parts by weight of THV. On the other hand, TH
The amount of the liquid agent A for dissolving V is not particularly limited and can be arbitrarily selected depending on conditions at the time of casting. Is desirable.

Further, even if the amount of the liquid agent B for impregnating the aggregated particles of silica is 0 parts by weight with respect to 100 parts by weight of silica, the microporous membrane according to the present invention can be obtained, and there is no lower limit. If it exceeds 500 parts by weight, processing becomes difficult. Therefore, it is desirably added in a range of 300 parts by weight or less in order to adjust porosity and water absorption. Further, when the amount of the surfactant and the alkyl-based silane is not more than 0.1 part by weight with respect to 100 parts by weight of the total amount of the liquid agent, there is no effect, and when the amount exceeds 10 parts by weight, the cost is increased more than necessary. Therefore, 1 to 5 parts by weight is optimal.

The present invention essentially produces a liquid mixture by dispersing aggregated silica particles in a solution of THV, casting, drying, and peeling the mixture to produce a microporous membrane. . This manufacturing method includes the following steps. The first step is to prepare a THV solution, in which THV in powder or pellet form is dissolved in a soluble solvent A such as methyl ethyl ketone or ethyl acetate. In the present invention, the production method in this step is not particularly limited and is optional. The solvent A to be used is not limited to the above-mentioned compounds alone but may be a mixture.

In the second step, the aggregated silica particles are
This is a step of obtaining a liquid mixture by dispersing in a solution of the above. First, a predetermined amount of a THV solution and silica are respectively weighed and mixed and dispersed by a disperser, a kneader, or the like. However, in the present invention, there is no particular limitation on equipment used or conditions. If dispersion is difficult due to conditions or the like, silica may be wetted in advance with the liquid agent A used for the THV solution. Further, as described above, when the second liquid agent B is impregnated into the aggregated silica particles in order to adjust the porosity and hydrophilicity, TH is used.
Before dispersing in the solution V, the solution B is impregnated.
This impregnation may be performed by mixing and dispersing with a disperser, a kneader, or the like, as described above. It is difficult to mix and disperse the impregnated silica agglomerated particles with the THV solution. Therefore, the surfactant A or the liquid agent A used in the solution of the alkyl-based silane and the THV is simultaneously added and mixed and dispersed. It is advisable to disperse in a THV solution in a state where the property is enhanced.

The third step is a step of casting the obtained liquid mixture on a substrate. The substrate used in the present invention is optional, and there is no particular limitation on the material or form, but a film coated with a silicone-based or fluorine-based release agent, a smooth endless belt, a rotating drum, or the like is desirable. Further, the processing machine used for casting is not particularly limited and is optional. Also,
After the casting, removal of the liquid agent and peeling from the base material are performed, and this can also be performed by an arbitrary method.

Finally, in order to modify the microporous membrane according to the present invention, it is preferable to apply an electron beam after applying the liquid mixture to the substrate. Irradiation with an electron beam is performed after casting. In this processing, there are irradiation conditions such as a pressurized voltage, a beam current, and a dose, but in the present invention, the condition setting is arbitrary. The effect of modification by this formulation is to improve heat resistance and impart hydrophilicity by cross-linking THV, but if exposed in an oxygen-free state after irradiation, cross-linking will proceed preferentially, and exposure to air after irradiation. If this is the case, the imparting of hydrophilicity proceeds preferentially.

[0029]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. The various evaluation tests performed in the following examples were performed as follows.

(1) Method of Evaluating Pore Diameter Evaluation Test Each sample was cut into a disk having a diameter of 49 μm, and this was used as a test piece 5, which was incorporated into an apparatus shown in FIG. 2 and evaluated.
The details are as follows. The test piece 5 was incorporated into the holder 4 together with the filter paper 6. On the other hand, average particle size 0.5
μm silicone ball (trade name: Tospearl 105
10% dispersion water (manufactured by Toshiba Silicon Corporation) was poured from above, the passage of silicone balls and water was observed, and the evaluation was made according to the following criteria. -Only water remained in flask 7. Judgment A passed-Water and silicone balls stayed in flask 7. Judgment B rejection-Neither water nor silicone balls remain in the flask 7. Judgment C failed

(2) Method of heat resistance test Each sample was cut into 10 × 50 mm, and this was cut into 150 mm.
The sample was placed in an oven controlled at a temperature of ° C., taken out after 5 minutes, and observed for a test piece. (3) Evaluation Method of Water Absorption Test Each sample was cut into a disk having a diameter of 49 mm, and a drop of water was dropped to measure a time required for complete absorption.

Example 1 100 parts by weight of THV (trade name: THV-200P manufactured by 3M Co., Ltd.) and 400 parts by weight of ethyl acetate were mixed with a disper at room temperature to obtain a 25% THV solution. . Next, in 500 g of the above solution, the average particle size of the primary particles was 16%.
A liquid powder 1 is prepared by mixing and dispersing silica powder (trade name: Nip Seal LP, manufactured by Nippon Silica Kogyo Co., Ltd.) having an average particle diameter of 9 μm and a particle diameter of 9 μm (based on 100 parts by weight of THV) shown in Table 1. 1,1-2,1-3,1-
4,1-5,1-6,1-7,1-8 were obtained. Dispersers were used to obtain the above liquid mixture, but it took a day and night to completely disperse (all liquid mixtures).

Next, a silicone release-treated PET film having a thickness of 25 μm was selected as a base material, and the obtained eight liquid mixtures were cast thereon using an applicator. And after air drying, 1
-1, 1-2, 1-3, 1-4, 1-5, and 1-6 can be peeled from the substrate, and a white film having a thickness of about 30 μm was obtained.
1-7 and 1-8 could not be peeled. The porosity was calculated for the six films obtained by peeling from the weight, thickness, and the like, and a pore size evaluation test was performed using a silicone ball. The results are shown in Table 1. Then, 1-2, 1-3, 1-4, 1-4,1-
6 was observed with an electron microscope and found to have the structure shown in FIG. As a result, it was confirmed that the microporous membrane was obtained by the formulation of the present invention.

[0034]

[Table 1]

Example 2 A three-part silica composition composed of the same silica as used in Example 1 and having the composition shown in Table 2 was obtained by dispersing. Formulation 2-1 was without Liquid B and Formulation 2-
2 impregnates silica with polyethylene glycol (trade name: PEG300, manufactured by NOF Corporation) as liquid agent B;
Formulation 2-3 is prepared by impregnating silica as water as liquid agent B. It should be noted that TH in the next step was added to all the formulations.
For the purpose of shortening the dispersion time with the V solution, ethyl acetate as the liquid agent A used in the THV solution was added. Then, these blends were added to the solution of THV obtained in Example 1 with a disper for 5 minutes so that the silica was equivalent to the amount of THV.
After mixing and dispersing for about a minute, three liquid mixtures were obtained.

Next, a PET film having a thickness of 25 μm and having been subjected to silicone release treatment was selected as a base material.
The resulting three liquid mixtures were cast using an applicator. The liquid mixtures obtained from Formulations 2-1 and 2-3 could be peeled off from the air-dried substrate, and two white films having a thickness of about 30 μm were obtained. On the other hand, all of the liquid mixture obtained from the formulation 2-2 was air-dried, immersed in hot water at 60 ° C. to remove the liquid agent B, air-dried again, and peeled off from the substrate to form a 30 μm thick white color. Was obtained. The porosity of each of the obtained three films was calculated from the weight and thickness, and the same pore size evaluation test as in Example 1 was performed. The results were as shown in Table 2.
Then, when the obtained three points of the film were observed with an electron microscope, the film had the structure shown in FIG. As a result, it was confirmed that the microporous membrane was obtained by the formulation of the present invention.

[0037]

[Table 2]

Example 3 A microporous film obtained from the liquid mixture 1-4 of Example 1 was applied with an acceleration voltage of 250 kV, a beam voltage of 15 mA and a dose of 3
An electron beam was irradiated under the condition of 0 [M read]. Physical properties before and after irradiation and a heat resistance test and a water absorption test described below were performed. The results are as shown in Table 3. From these results, it was confirmed that physical properties, heat resistance test, and water absorption were improved by irradiation with an electron beam.

[0039]

[Table 3]

[0040]

According to the present invention, an aggregate formed by aggregating primary particles of silica through voids is present in the non-permeable membrane functioning as a support in the form of islands. It is possible to provide a microporous membrane in which the voids of the body are permeable and communicate in the cross-sectional direction. The voids (gap between silicas) existing in the aggregate function as units of about several tens of nanometers, and furthermore, have been conventionally desired because they are very thin microporous membranes having a thickness of 10 to 300 μm. It is suitable for applications such as removal of particles existing in a liquid such as water quality treatment, and for performing a chemical reaction via a porous material such as a secondary battery and enzyme purification.

[Brief description of the drawings]

FIG. 1 is a partially enlarged cross-sectional view showing a microporous membrane of the present invention.

FIG. 2 is a longitudinal sectional view of an apparatus used for a hole diameter evaluation test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-permeable membrane 2 Silica 3 Aggregate of silica 4 Holder 5 Test piece 6 Filter paper 7 Flask

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04 B29L 7:00 C08K 3:36 C08L 27:18

Claims (3)

[Claims] 1. A polymer membrane comprising a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer and silica particles, wherein the terpolymer forms a non-permeable membrane, and the silica has Form an aggregate through voids, and the aggregate is dispersed and disposed in a state where the aggregate protrudes from the front and back with the non-permeable membrane as a support. A microporous membrane characterized by communicating permeability. 2. A liquid mixture is prepared by dispersing silica in the form of a secondary particle or an aggregate of tertiary particles in a solution of a terpolymer of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride. A method for producing a microporous membrane, wherein the method is applied to a substrate, and after drying, peeled off from the substrate. 3. A solvent used for dissolving the terpolymer is liquid A, and a liquid B which is incompatible with the liquid A and has a higher boiling point than the liquid A is impregnated into aggregated silica particles.
3. The method for producing a microporous membrane according to claim 2, wherein the liquid mixture is prepared by dispersing in a solution in which the terpolymer is dissolved.