JPH0693982B2 - Polychlorotrifluoroethylene-based porous membrane and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention provides excellent chemical resistance, excellent heat resistance, excellent filtration performance, which is made of a polychlorotrifluoroethylene-based resin,
The present invention relates to a porous membrane having excellent mechanical properties and a uniform porous structure composed of fine pores, and a method for producing the same. In particular, the present invention is a porous film suitable for a microfilter having excellent heat resistance and excellent filtration performance, and further, by utilizing its excellent chemical resistance, a porous film suitable for a microfilter for chemical purification such as strong acid or strong alkali. And a manufacturing method thereof.

(Prior art and its problems) Fluorocarbon resin is a resin with excellent chemical resistance and heat resistance,
Polychlorotrifluoroethylene and ethylene-chlorotrifluoroethylene copolymers are selected as the fluorine resin that also has excellent mechanical properties. Porous membranes made of these fluorine resins have heat resistance, chemical resistance,
Expected as a porous film with excellent durability.

However, as the porous membrane made of polychlorotrifluoroethylene, JP-A-47-34081 and JP-A-48-25065 are known to be electrolytic diaphragms, but these membranes are intended to be electrolytic diaphragms. Therefore, the transparency is extremely low,
It cannot be used for micro filters. That is, no satisfactory porous membrane made of polychlorotrifluoroethylene and a method for producing the same have hitherto been available.

Further, the porous membrane made of the ethylene-chlorotrifluoroethylene copolymer and the method for producing the same have not been studied at all.

(Means for Solving Problems) The inventors of the present invention have excellent chemical resistance made of polychlorotrifluoroethylene-based resin, excellent heat resistance, excellent filtration characteristics, excellent mechanical properties, and The present invention has been completed as a result of intensive studies on a method capable of producing a porous membrane having a uniform porous structure composed of fine pores with high productivity.

That is, the present invention provides the porous membrane described in the claims and a method for producing the same.

The features of the porous membrane of the present invention will be described below.

In the present invention, polychlorotrifluoroethylene or ethylene-chlorotrifluoroethylene copolymer is selected as the porous membrane material because of its excellent chemical resistance, heat resistance and mechanical properties. Also, mixtures of these resins are possible.

In the porous membrane of the present invention, the average pore size is preferably 0.01 to 5 µ, more preferably 0.05 to 1 µ. If it is less than 0.01 μ, the permeability is too low, and if it exceeds 5 μ, the removability of fine particles is poor and neither is preferable. Porosity is preferably 40-90%,
If it is less than 40%, the permeability is too low, and if it exceeds 90%, the mechanical properties are remarkably deteriorated, and neither is preferable.

The porous membrane of the present invention preferably has a three-dimensional network structure. The three-dimensional network structure is a porous structure in which a resin network structure is observed on the surface of the porous membrane and the cross section in each direction, and it means a so-called sponge structure having communication holes. Such a three-dimensional network structure is excellent in strength as a porous film, and when this porous film is used for a filter, it is excellent in fine particle removability due to the same effect as that of laminating a large number of screens. Further, the fiber constituting the network structure is a network resin portion surrounding the hole, and is expressed as a fiber for convenience, but its shape is not particularly limited, and it may form a three-dimensional network structure. For example, in addition to fibrous materials, thin films, nodules, and irregular shapes can be used.

In the present invention, the number N of fibers constituting the network structure is preferably N ≧ 2 P / D, and more preferably N ≧ 5 P / D per 1 mm in the thickness direction of the film. However, P is the porosity (%) and D is the average pore diameter (μ). When N <2P / D, it is not preferable because it is inferior in the effect of removing fine particles when used as a filter.

Further, the ratio of the maximum pore diameter to the average pore diameter is preferably 4 or less.
If it exceeds 4, the fine particle removing effect tends to be poor. The maximum pore size is measured by the bubble point method (ASTM F316-70).

The thickness of the porous film is preferably 0.025 to 2.5 mm, and if it is less than 0.025 mm, the mechanical properties are poor, and if it exceeds 2.5 mm, the permeability tends to be poor, which is not preferable in some cases.

The membrane may have a hollow shape, a tube shape, a flat membrane shape, or the like, but in a microfilter application, the hollow shape is preferable because of the compactness of the device when it is modularized.

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

In the present invention, polychlorotrifluoroethylene, or a polychlorotrifluoroethylene-based resin comprising an ethylene-chlorotrifluoroethylene copolymer, an inorganic fine powder, a chlorotrifluoroethylene oligomer or a chlorotrifluoroethylene oligomer and chlorotrifluoroethylene. A mixture of heat-resistant organic substances having an SP value of 5 to 11 excluding oligomers is used.

The inorganic fine powder is preferably a fine particle having a specific surface area of 50 to 500 m ² / g and an average primary particle size of 0.005 to 0.5 μ, and the material is silicic acid, calcium silicate, aluminum silicate, magnesium oxide, alumina, calcium carbonate, kaolin. , Clay, diatomaceous earth, etc. are used. Of these, finely divided silicic acid is particularly preferable. The average primary particle diameter is the average value of the diameters of the fine powder single particles, and is not the diameter of the aggregate (secondary particles) of the single particles. The average primary particle diameter can be measured by an electron microscope.

In the present invention, it is essential to use a chlorotrifluoroethylene oligomer, and by using this, it is possible to produce a porous film having a uniform pore structure and excellent in fine particle removal with stable film quality and high productivity. It was possible. The chlorotrifluoroethylene oligomer is preferably a 4- to 20-mer of chlorotrifluoroethylene, and 8 to
The 15-mer is more preferable, and the 9- to 12-mer is most preferable.
If it is a trimer or less, it is not preferable because the heat resistance is low, the evaporation at the time of melt molding is large, and the permeability of the porous membrane is small, and if it is 21 or more, the mixing workability is poor and the extractability is poor. The number of chlorotrifluoroethylene oligomers in the present invention is an average number of chlorotrifluoroethylene oligomers composed of a mixture of various chlorotrifluoroethylene oligomers.

In the present invention, the use of a mixture of a chlorotrifluoroethylene oligomer and a heat resistant organic substance having an SP value of 5 to 11 excluding the chlorotrifluoroethylene oligomer facilitates the adjustment of the pore size of the porous membrane. That is, the pore diameter can be easily controlled to a desired pore diameter by selecting the heat-resistant organic material and / or adjusting the mixing ratio of the chlorotrifluoroethylene oligomer and the heat-resistant organic material. In particular, in the method for producing a polychlorotrifluoroethylene porous film, it is preferable to use a mixture of a chlorotrifluoroethylene oligomer and a heat-resistant organic substance because the chlorotrifluoroethylene oligomer alone has a small pore size and low permeability. When a mixture of chlorotrifluoroethylene oligomer and heat-resistant organic substance with sp value over 11 is used (no heat-resistant organic substance with sp value less than 5 is currently found), chlorotrifluoroethylene oligomer with heat resistance over sp value 11 is used. The compatibility with the organic substance is poor, and the pore size of the obtained film is too large and has a non-uniform pore structure, which is not preferable.

The heat-resistant organic substance in the present invention is an organic substance having a heat resistance such that the boiling point at 1 atm is at least 200 ° C. or higher, preferably 250 ° C. or higher, and is a liquid when melt-molding the porous membrane of the present invention. Examples of the heat-resistant organic substance having an sp value of 5 to 11 include silicone oil, perfluoropolyether oligomer, phthalic acid ester, trimellitic acid ester, sebacic acid ester, adipic acid ester, azelaic acid ester, and phosphoric acid ester.

Of these, silicone oil, perfluoropolyether oligomer and trimellitate ester are particularly preferable.

In particular, silicone oil is more preferable from the viewpoints of thermal stability during melt molding, price, and the like. Silicon oil is a heat-resistant organic substance with a siloxane structure, dimethyl silicone,
Methyl phenyl silicon diphenyl silicon and the like.

The mixing ratio of the chlorotrifluoroethylene oligomer and the heat-resistant organic substance having an sp value of 5-11 excluding the chlorotrifluoroethylene oligomer varies depending on the type of the heat-resistant organic substance. The heat-resistant organic substance is preferably 10 volumes or less,
More preferably, it is 4 volumes or less. If it exceeds 10 volumes, the resulting membrane tends to have a larger pore size, and tends to have a non-uniform pore structure, and pin holes (abnormally large continuous pores) tend to occur. When the heat-resistant organic substance is silicone oil, it is preferably 2 volumes or less.

In producing the porous membrane of the present invention, first, polychlorotrifluoroethylene-based resin consisting of polychlorotrifluoroethylene or ethylene-chlorotrifluoroethylene copolymer, inorganic fine powder, chlorotrifluoroethylene oligomer or chlorotrifluoroethylene. Sp value 5 excluding fluoroethylene oligomer and chlorotrifluoroethylene oligomer
Mix a mixture of ~ 11 refractory organic materials. The mixing ratio is 10 to 60% by volume of polychlorotrifluoroethylene resin, preferably 15 to 40% by volume, 7 to 42% by volume of fine inorganic powder, preferably 10 to 20% by volume, chlorotrifluoroethylene oligomer or heat resistance. 30 to 75% by volume, preferably 50 to 70% by volume, of the mixture with the organic substance.

If the polychlorotrifluoroethylene-based resin is less than 10% by volume, the amount of the resin is too small and the strength is low and the moldability is poor. If it exceeds 60% by volume, a porous membrane having a large porosity cannot be obtained, which is not preferable. If the inorganic fine powder is less than 7% by volume, molding becomes difficult, and if it exceeds 42% by volume, the fluidity at the time of melting is poor, and the obtained molded product is brittle and cannot be put to practical use. If the content of the chlorotrifluoroethylene oligomer or a mixture of the chlorotrifluoroethylene oligomer and the heat-resistant organic substance is less than 30% by volume, the porosity of the obtained porous membrane is less than 40%, and a porous membrane having excellent permeability cannot be obtained. If it exceeds the capacity%, molding becomes difficult,
A porous film with high mechanical strength cannot be obtained.

The mixing of the above components is carried out by a mixer such as a Henschel mixer, a V-blender, a ribbon blender, or the like. The order of mixing is to mix the inorganic fine powder and the chlorotrifluoroethylene oligomer or the heat-resistant organic substance first, and then mix and mix the polychlorotrifluoroethylene-based resin, rather than mixing the respective components at the same time. Is preferred. It is preferable that this mixture is further kneaded by a melt-kneading device such as an extruder. The obtained kneaded product is crushed by a crusher as necessary, and then melt-molded into a flat film shape, a hollow film shape or the like by an extruder or the like. It is also possible to directly mold the mixture with a device having both functions of kneading and extrusion, such as a kneader ruder.

Then, the mixture of the chlorotrifluoroethylene oligomer or the heat-resistant organic substance is extracted from the formed film-like substance with a solvent. The extraction is performed by a general method for extracting a membranous substance such as a batch method or a Mukaioki multistage method. The solvent used for the extraction is preferably a halogenated hydrocarbon such as 1,1,1-trichloroethane or tetrachloroethylene.

The semi-extracted porous membrane on which the extraction of the mixture with the chlorotrifluoroethylene oligomer or the heat-resistant organic substance has been completed is then subjected to extraction of the inorganic fine powder with a solvent for the inorganic fine powder. The extraction is completed within a few seconds to a few tens of hours by a general extraction method such as a batch method or a countercurrent multistage method. Solvents used for extracting inorganic fine powder include calcium carbonate, magnesium carbonate, magnesium oxide, calcium silicate, magnesium silicate, etc., such as hydrochloric acid, sulfuric acid, hydrofluoric acid, etc., and silicic acid, etc., such as caustic soda, caustic potash. An aqueous solution is used. There is no particular limitation as long as it does not substantially dissolve the polychlorotrifluoroethylene-based resin and dissolves the inorganic fine powder.

In the present invention, when a porous film having a high degree of heat resistance is desired, the inorganic fine powder is annealed in the state of a semi-extracting porous film present in the film and then the inorganic fine powder is extracted and removed as described below. It is valid.

When the porous membrane is exposed to a high temperature when it is converted to a module, or when filtration is performed at a high temperature, a change in the pore diameter of the porous membrane and a decrease in the permeability are often observed.

As a cause of the performance deterioration of the porous membrane at high temperature, the inventors have found that "strain" generated during the porous membrane molding process exists inside the resin forming the porous membrane, and the "strain" is eliminated when heated. It was thought that this was the main factor, and the inventors studied earnestly on a method for producing a porous membrane that minimizes the "strain" and has little performance degradation at high temperatures. Usually, an annealing treatment is performed to eliminate the above-mentioned “strain”, but when the annealing treatment is performed on a porous film made only of a resin, which is a usual method, the physical properties change greatly, and The physical properties do not change uniformly at each part of the film, and the film obtained as a result of the change in the film shape becomes non-uniform, and reproducibility is often not obtained. In order to prevent such non-uniform changes in physical properties, it is sufficient to restrain the shape of the membrane so that it does not change, but it is generally difficult to restrain the membrane from the outside, and even if it is a flat membrane. Although it is possible to restrain in the vertical and horizontal directions, it is difficult to restrain in the thickness direction of the film. Furthermore, in the hollow fiber porous membrane, it is difficult to constrain it in a direction other than the length direction, and it is difficult to perform an annealing treatment to obtain a uniform membrane.

The present inventors annealed the porous film filled with the inorganic fine powder, whereby the inorganic fine powder itself restrains the shape of the porous film from the inside, and as a result, a uniform film can be obtained with good reproducibility. I found a thing.

The annealing temperature may be a temperature equal to or higher than the glass transition point of the resin, but it is preferably in the range of the melting point of the resin to the melting point minus 100 ° C. in consideration of productivity such as the time required for the annealing treatment. Further, it is more effective and preferable to carry out the treatment at a temperature higher than the expected use temperature (including heating conditions in the module assembling process and the like).
The treatment time depends on the treatment temperature, but is usually in the range of several minutes to several days.

The annealing treatment is usually a batch treatment or a continuous treatment in a hot air oven.

Although the heat resistance of the porous film is improved by the above-mentioned method, when this is still insufficient, it is further improved by extracting and removing the inorganic fine powder after annealing and reannealing it.

In the present invention, in order to increase the pore size of the porous membrane, increase the porosity, and improve the mechanical properties, a chlorotrifluoroethylene oligomer or a mixture of this and a heat-resistant organic substance, an inorganic fine powder The porous membrane obtained by extracting one or both of them can be uniaxially or uniaxially stretched under known conditions.

The physical properties shown in the specification of the present application depend on the measuring methods.

○ Average Pore Size (μ) The pore size was measured with an electron microscope on the surface and cross section of the sample and averaged (number average).

Averaging is carried out by taking electron micrographs of the film surface, the film front and back, and the film cross section for 10 or more samples randomly sampled from the porous film manufactured under the same conditions, and randomly selecting from each electron micrograph. It is carried out by actually measuring the average diameter of the 10 or more holes, and averaging the diameters of the measurement points of 300 or more. It is necessary to increase the number of measurement points for a porous film having a non-uniform pore structure.
The average pore size can be calculated from the electron microscope photograph by subjecting the photograph to an image processing device and subjecting it to a computer process.

○ Porosity (%) Obtained by the following formula.

However, the pore volume was obtained by subtracting the weight of only the pore body from the weight of the pore body in which the pores were filled with water.

○ The number of fibers constituting the network structure N (pieces / mm) Electron micrographs of cross-sections of 10 or more samples randomly sampled from the porous film produced under the same conditions were taken, and each electron micrograph was taken. Count the number of fibers in the thickness direction of the film at 30 or more points selected at random and convert it to the number of fibers in a film thickness of 1 mm, and measure a total of 3 points.
Average the number of fibers of 00 points or more. The average value of the number of fibers from the electron micrograph can be calculated by subjecting the photograph to an image processing device and subjecting it to a computer process.

○ sp value (dissolution parameter) Calculated by the following formula (Small formula).

d: Specific gravity, G: Molar traction constant, M: Molecular weight. (J.BRANDRUP e
t al, Polymer Handbook, IV−344,1966, INTERSCIENCE PU
BLISHERS a division of John Wiley & Sous) ".

○ Three-dimensional network structure Judged by electron microscopic observation ○ Fine particle removal rate (%) Dow Chemical Company UNIFORM LATEX PARTICLES solid concentration
The liquid diluted to 0.01% by weight is filtered through a porous membrane and LATEX PAR
Calculated from the removal rate of TICLES.

○ Frequency of pinholes (ke / m) Evaluate the number of abnormally large holes. Porosity uniformity 1
It is one evaluation item. A continuous hollow fiber porous membrane of 150 m was immersed in ethyl alcohol and a pressure lower than the bubble point pressure of the porous membrane by 0.5 kg / cm ² was applied to one side of the hollow fiber (the other side was closed). Check the number of foams generated and calculate from the following (Examples) Next, examples will be shown to clarify the present invention, but the present invention is not limited to these examples.

Examples 1 to 4 Finely powdered silicic acid [Aerosil R-972 (trade name), specific surface area 120
m ² / g, average primary particle size 16 mμ] 13.3% by volume and the following compound were mixed with a Henschel mixer, and polychlorotrifluoroethylene [Daiflon M300 (trade name)] 26.7
Volume% was added and mixed again with the Henschel mixer.

Example 1 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name) about octamer] 60.0% by volume Example 2 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 30.0% by volume and dimethyl silicone [ Shin-Etsu Silicone KF-96 (trade name) (sp value 6.3)] 3
Mixture consisting of 0.0 vol% Example 3 Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 30.0 vol% and tri- (2-
Ethylhexyl) trimellitate (sp value 9.0) 30.0 vol% mixture Example 4 Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 15.0 vol% and tri- (2-
Ethylhexyl) trimellitate 45.0% by volume of the mixture The mixture was mixed in a 30 mmφ twin-screw extruder at 250 ° C. to form a pellet. This pellet was molded into a hollow fiber at 250 ° C. by a hollow fiber manufacturing apparatus in which a hollow spinneret was attached to a 30 mmφ twin-screw extruder. The molded hollow fiber was immersed in 1,1,1-trifluoroethane at 50 ° C for 1 hour to remove chlorotrifluoroethylene Each of the obtained porous membranes has a three-dimensional network structure, and the performance is shown in Table 1.

Example 8 Finely powdered silicic acid [Aerosil R-972 (trade name)] 11.1% by volume, chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 46.7% by volume, dimethyl silicone [Shin-Etsu Silicone KF-96 (trade name)] 15.6% by volume was mixed with a Hensiel mixer, 26.6% by volume of polychlorotrifluoroethylene [Daiflon M-300 (trade name)] was added thereto, and the mixture was again mixed with the Henschel mixer.

Then, in the same manner as in Example 2, a polychlorotrifluoroethylene porous film having a three-dimensional network structure was obtained. The performance is shown in Table 1.

Example 9 In Example 8, the chlorotrifluoroethylene oligomer and dimethyl silicon were extracted and dried, then 20
Annealing treatment was performed at 0 ° C. for 1 hour. After that, 70
After immersing in 40% caustic soda aqueous solution at ℃ for 1 hour to extract finely divided silicic acid, it was washed with water and dried.

The obtained polychlorotrifluoroethylene porous film has a three-dimensional network structure, and its performance is shown in Table 1.

When this film was left in an atmosphere of 180 ° C for 1 hour and evaluated for its physical properties, the rate of change from the original physical properties was 21
%, Porosity 9%, average pore size 9%.

Comparison difference, the film of Example 8 which was not annealed was similarly left for 1 hour in an atmosphere of 180 ° C., and the physical properties were evaluated. The rate of change with respect to the original physical properties was 75%.
It decreased, the porosity decreased 38%, and the average pore size decreased 17%.

Examples 10 to 14 Finely divided silicic acid [Aerosil R-972 (trade name)] 14.4% by volume
The following compounds were mixed in a Henschel mixer, and 26.7% by volume of an ethylene-chlorotrifluoroethylene copolymer [Halar 920 (trade name)] was added to the mixture and mixed again in the Henschel mixer.

Example 10 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name) about octamer] 58.9% by volume Example 11 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 50 (trade name) about 9mer] 58.9 volume% Example 12 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 100 (trade name) about 11-mer] 58.9% by volume Example 13 ... Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 44.2% by volume and dimethyl silicone [ Shin-Etsu Silicone KF96 (trade name)] 14.7% by volume mixture Example 14: Chlorotrifluoroethylene oligomer [Daifloyl ^# 20 (trade name)] 29.5 volume% and dimethyl silicone [Shin-Etsu Silicone KF96 (trade name)] 29.4 volume% The mixture was mixed with a 30 mmφ twin-screw extruder at 250 ° C. to form a pellet. This pellet was molded into a hollow fiber at 230 ° C. by a hollow fiber manufacturing apparatus in which a hollow spinneret was attached to a 30 mmφ twin-screw extruder. The molded hollow fiber was immersed in 1,1,1-trichloroethane at 50 ° C. for 1 hour to extract a chlorotrifluoroethylene oligomer and dimethylsilicon, and then dried. Then 1 at 70 ℃, 40% caustic soda solution
After soaking for a while to extract finely divided silicic acid, it was washed with water and dried.

Each of the obtained ethylene-chlorotrifluoroethylene copolymer porous membranes has a three-dimensional network structure, and its performance is shown in Table 2.

(Effects of the Invention) According to the present invention, a polychlorotrifluoroethylene-based porous membrane having a uniform porous structure with excellent chemical resistance, excellent heat resistance, excellent filtration performance, and excellent durability can be obtained. By using this porous membrane, it is possible to carry out high-precision filtration and purification under heat-resistant and chemical-resistant conditions such as hot concentrated sulfuric acid filtration.

Claims (4)

[Claims] 1. A polychlorotrifluoroethylene or ethylene-chlorotrifluoroethylene copolymer,
A polychlorotrifluoroethylene-based porous membrane having a network structure having an average pore diameter of 0.01 to 5 µ and a porosity of 40 to 90%. 2. The polychlorotriene according to claim 1, wherein the number N of fibers constituting the network structure has a three-dimensional network structure in which N ≧ 2 P / D per 1 mm in the thickness direction of the film. Fluoroethylene-based porous membrane. However, P is the porosity (%) and D is the average pore diameter (μ). 3. Polychlorotrifluoroethylene or ethylene-chlorotrifluoroethylene copolymer 10-60% by volume, inorganic fine powder 7-42% by volume, and chlorotrifluoroethylene oligomer 30-75% by volume are mixed, A method for producing a polychlorotrifluoroethylene-based porous membrane, comprising melt-molding, then extracting and removing a chlorotrifluoroethylene oligomer from the molded product, and further extracting and removing an inorganic fine powder. 4. Polychlorotrifluoroethylene or ethylene-chlorotrifluoroethylene copolymer 10 to 60% by volume, inorganic fine powder 7 to 42% by volume, SP value excluding chlorotrifluoroethylene oligomer and chlorotrifluoroethylene oligomer Mixtures of 5-11 heat-resistant organic substances 30-75
A method for producing a polychlorotrifluoroethylene-based porous membrane in which, after mixing by volume, the mixture is melt-molded, the chlorotrifluoroethylene oligomer and the heat-resistant organic substance are extracted and removed from the molded product, and further the inorganic fine powder is extracted and removed.