JPS6311370B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is made of an ethylene-tetrafluoroethylene copolymer that has excellent chemical resistance, excellent filtration performance, and excellent mechanical properties, and has a uniform porous structure consisting of fine pores. The present invention relates to a method for producing a porous membrane having the following. In particular, the present invention provides a porous membrane suitable for microfilters with excellent heat resistance and excellent filtration performance, and a porous membrane suitable for microfilters for purifying chemicals such as strong acids and strong alkalis, and furthermore, has excellent chemical resistance. The present invention relates to a manufacturing method. (Prior art and its problems) Ethylene-tetrafluoroethylene copolymer is a type of fluorine-based resin that has excellent chemical resistance and heat resistance. It is a resin with very good creep properties (long-term deformation resistance under load), especially at high temperatures, and is expected to be used as a material for porous membranes with chemical resistance, heat resistance, and high mechanical properties. Ru. A method for producing a porous membrane made of this ethylene-tetrafluoroethylene copolymer was already developed in Japanese Patent Application Laid-Open No.
Publication No. 136354, Japanese Patent Application Laid-open No. 158465, Japanese Patent Application Publication No. 1987-158465,
No. 59-147030 is known. Japanese Patent Publication 1973-
Publication No. 136354 discloses a method of making a porous membrane by making a slurry mixture of ethylene-tetrafluoroethylene copolymer fine powder and styrene monomer, styrene polymerization, forming a membrane, and eluting the styrene polymer. The resulting porous membrane has a large pore diameter of 10μ and has very low permeability, making it unsuitable for microfilters. JP-A-54-158465 discloses a method of making a porous film by irradiating an ethylene-tetrafluoroethylene copolymer film with loaded particles and then etching it with an aqueous solution of caustic soda, but the film is thin and has poor mechanical properties. However, since a uniform hollow fiber membrane cannot be obtained and a nuclear reactor is used, it is not suitable for mass production. JP-A-59-147030 discloses ethylene-
In this method, a resist is applied to a tetrafluoroethylene copolymer film to form a perforated resist pattern, and then sputter etching is performed to form through holes corresponding to the resist pattern to create a porous film. Since it is thin, it has poor mechanical properties, it is difficult to obtain a uniform hollow fiber state, and it also requires a long sputter etching process, which poses a problem in productivity. As a method for improving the problems of the above manufacturing method, Japanese Patent Application Laid-Open Nos. 55-79011, 159128-1980, 28139-1980,
JP-A-58-93798, JP-A-58-179297, etc. Ethylene-tetrafluoroethylene copolymer, finely powdered silicic acid, and dioctyl phthalate are mixed and melt-molded, and then finely powdered silicic acid and dioctyl phthalate are melt-molded from the molded product. A method of extracting it to make a porous membrane is known. However, this method has problems in that pinholes (abnormally large holes) occur frequently, the quality of the membrane is unstable (variation in performance), and the productivity (yield of good products) is poor. As described above, there has been no conventional method for producing a porous membrane made of an ethylene-tetrafluoroethylene copolymer with excellent membrane performance and productivity. (Means for Solving the Problems) The present inventors have discovered that an ethylene-tetrafluoroethylene copolymer has excellent chemical resistance, excellent heat resistance, excellent filtration properties, and excellent mechanical properties. As a result of extensive research into a method for producing a porous membrane having a uniform porous structure consisting of fine pores with good productivity, the present invention was completed. That is, the present invention uses 10 to 60% by volume of ethylene-tetrafluoroethylene copolymer and 7 to 42% by volume of inorganic fine powder.
% by volume, 30 to 75% by volume of a heat-resistant organic liquid that is liquid at the melt-molding temperature is melt-molded, and then the heat-resistant organic liquid and inorganic fine powder are extracted from the molded product to form ethylene-tetrafluorocarbon. In the method for producing an ethylene copolymer porous membrane, a chlorotrifluoroethylene oligomer or a chlorotrifluoroethylene oligomer and a heat-resistant organic substance with an sp value of 5 to 11 excluding the chlorotrifluoroethylene oligomer are used as the heat-resistant organic liquid. This is a method for producing an ethylene-tetrafluoroethylene copolymer porous membrane, characterized by using a mixture. The inorganic fine powder used in the present invention holds a heat-resistant organic liquid and functions as a carrier. That is, it prevents the release of the heat-resistant organic liquid during melt molding and facilitates molding, and also has the function of being extracted and forming pores. This inorganic fine powder has a specific surface area of 50 to 500.
They are microparticles or porous particles having a particle size of m ² /g and an average primary particle size in the range of 0.005 to 0.5μ. Furthermore, the inorganic fine powder contains at least 2/3 of the heat-resistant organic liquid.
It is preferable that it is capable of absorbing a capacity, preferably three times the capacity or more. Examples of the inorganic fine powder used in the present invention include finely divided silicic acid, calcium silicate, aluminum silicate, magnesium oxide, alumina, calcium carbonate, magnesium carbonate, kaolin, clay, diatomaceous earth, and the like. Among these, finely divided silicic acid is particularly effective. The heat-resistant organic liquid used in the present invention is extracted from the molded product and is used to impart porosity to the molded product. The heat-resistant organic liquid has a boiling point of at least 200°C or higher at 1 atm, preferably 250°C.
It needs to be heat resistant to melt molding above 0.degree. C., be liquid at the melt molding temperature, and be substantially inert to the polymer. First, we investigated various heat-resistant organic liquid single components and found that only chlorotrifluoroethylene oligomer had excellent permeability and a porous membrane with a uniform pore structure that was stable with few pinholes (abnormally large pores). We have discovered that it can be manufactured with high quality and productivity. Furthermore, improved results were obtained by using a mixture of a chlorotrifluoroethylene oligomer and a specific heat-resistant organic substance as the heat-resistant organic liquid. That is, by using a mixture of a chlorotrifluoroethylene oligomer and a heat-resistant organic substance with an sp value of 5 to 11 excluding the chlorotrifluoroethylene oligomer as the heat-resistant organic liquid used in the present invention, the mechanical properties are further improved. It was found that a porous membrane can be obtained. Here, if a mixture of chlorotrifluoroethylene oligomer and a heat-resistant organic substance with an sp value of 11 or more is used as the heat-resistant organic liquid (currently no heat-resistant organic substance with an sp value of 5 or less has been found), chlorotrifluoroethylene oligomer It has poor compatibility with a heat-resistant organic substance having an sp value of 11 or more, and the resulting film has too large a pore size, has a non-uniform pore structure, and has many pinholes (abnormally large pores), which is undesirable. On the other hand, when a heat-resistant organic substance with an sp value of 5 to 11, excluding chlorotrifluoroethylene oligomer, is used alone as a heat-resistant organic liquid, the resulting film has too large a pore size and a non-uniform pore structure. There are also many holes (abnormally large holes), which is not desirable. That is, by using a mixture of a chlorotrifluoroethylene oligomer and a heat-resistant organic substance with an sp value of 5 to 11 as a heat-resistant organic liquid, it has excellent permeability, a uniform pore structure, and excellent mechanical properties. Porous membranes can be manufactured with high productivity and stable membrane quality with less occurrence of pinholes (abnormally large pores). Furthermore, the range of pore size adjustment of the porous membrane can be expanded by selecting the heat-resistant organic substance and the mixing ratio. The chlorotrifluoroethylene oligomer used as the heat-resistant organic liquid used in the present invention is preferably a tetramer or a 15-mer of chlorotrifluoroethylene, but from the viewpoint of heat resistance, workability, extractability, etc. A mer to a 11-mer is more preferable. Also, as a heat-resistant organic substance used in the present invention
Those with an sp value of 5 to 11 include silicone oil, perfluoropolyether oligomer, phthalate esters, trimellitate esters, sebacate esters, adipate esters, azelaic esters, phosphoric esters, etc. Can be mentioned. Among these, silicone oil, perfluoropolyether oligomer, and trimellitic acid esters are particularly preferred. Particularly, silicone oil is more preferable from the viewpoint of thermal stability during melt molding, cost, etc. Silicone oil is a heat-resistant organic substance with a siloxane structure, such as dimethyl silicone oil and methylphenyl silicone oil. sp value 5 excluding chlorotrifluoroethylene oligomer and chlorotrifluoroethylene oligomer
The mixing ratio with a heat-resistant organic substance of ~11 is per volume of chlorotrifluoroethylene oligomer.
0.05 to 10 volumes of the heat-resistant organic material having an sp value of 5 to 11 is preferred, and more preferably 0.1 to 4 volumes. If the volume of the heat-resistant organic substance is less than 0.05, the resulting film will have low toughness, which is not preferable. Moreover, if the volume exceeds 10, the pore diameter of the obtained membrane is too large, the pore structure is non-uniform, and pinholes (abnormally large pores) occur frequently, which is not preferable. In producing the porous membrane of the present invention, first, an ethylene-tetrafluoroethylene copolymer, an inorganic fine powder, and a heat-resistant organic liquid are mixed. The mixing ratio is 10 to 60% by volume of ethylene-tetrafluoroethylene copolymer, preferably 15 to 40% by volume,
Inorganic fine powder 7-42% by volume, preferably 10-20% by volume, heat-resistant organic liquid 30-75% by volume, preferably
It is 50-70% by volume. Ethylene-tetrafluoroethylene copolymer
If it is less than 10% by volume, the resin content is too small, resulting in low strength and poor moldability, and if it exceeds 60% by volume, a porous film with high porosity cannot be obtained, which is not preferred. If the inorganic fine powder is less than 7% by volume, it will not be able to adsorb the organic liquid necessary to create an effective porous membrane, making it difficult to mold, and if it exceeds 42% by volume, the fluidity during melting will be poor. Moreover, the molded product obtained is brittle and cannot be put to practical use. When the heat-resistant organic liquid is less than 30% by volume, the contribution rate of the heat-resistant organic liquid to pore formation decreases, and the porosity of the resulting porous membrane is less than 40%, making it virtually ineffective as a porous membrane. If the amount exceeds 75% by volume, molding becomes difficult and a porous membrane with high mechanical strength cannot be obtained. For mixing the three components, a Henschel mixer, V
- Conventional mixing methods using a mixer such as a blender or ribbon blender are sufficient. Rather than mixing the three components at the same time, the order of mixing the three components is to first mix the inorganic fine powder and the heat-resistant organic liquid so that the inorganic fine powder sufficiently adsorbs the heat-resistant organic liquid, and then add the ethylene-tetra It is preferable to blend and mix a fluoroethylene copolymer. This mixture is kneaded using a melt kneading device such as an extruder, Banbury mixer, two rolls, or a kneader. The obtained kneaded product is molded by a melt molding method, and the melt molding method used in the method of the present invention is T.
-Extrusion molding such as die method and inflation method, calendar molding, compression molding, injection molding, etc. It is also possible to directly mold the mixture using a device having both kneading and extrusion functions, such as an extruder or a kneader-ruder. With these forming methods, the ternary mixture is 0.025
Formed into a ~2.5mm thick membrane. The shape of the membrane can be hollow fiber, tube, flat membrane, etc., but hollow fiber is preferred for reasons such as compactness of the device when modularized in microfilter applications. A heat-resistant organic liquid is extracted from the obtained membrane using a solvent. The solvent used for extraction must be capable of dissolving the heat-resistant organic liquid and must not be capable of substantially dissolving the ethylene-tetrafluoroethylene copolymer. Extraction is easily carried out using common extraction methods for membrane-like materials, such as a batch method or a countercurrent multi-stage method. As the solvent used for extraction, halogenated hydrocarbons such as 1,1,1-trichloroethane and tetrachloroethylene are preferred. After the extraction of the organic liquid has been completed, the semi-extracted porous membrane is then subjected to extraction of the inorganic fine powder using a solvent for the inorganic fine powder. Extraction can be easily completed within a few seconds to several tens of hours by a general extraction method such as a batch method or a countercurrent multistage method. Solvents used to extract inorganic fine powder include acids such as hydrochloric acid, sulfuric acid, and hydrofluoric acid for calcium carbonate, magnesium carbonate, magnesium oxide, calcium silicate, and magnesium silicate, and acids such as caustic soda and caustic potash for fine silicic acid. An alkaline aqueous solution is used. Other materials are not particularly limited as long as they do not substantially dissolve the ethylene-tetrafluoroethylene copolymer and dissolve the inorganic fine powder. Further, in order to increase the pore size or increase the porosity, a porous membrane obtained by extracting one or both of a heat-resistant organic liquid and an inorganic fine powder can be uniaxially or biaxially stretched. (Examples) Next, Examples will be shown to clarify the present invention, but the present invention is not limited to these Examples. The various physical properties shown in the present invention were measured using the following measurement method. Γ Composition ratio (volume %) Calculated from the value obtained by dividing the added weight of each composition by the true specific gravity. Γ Porosity (%) Porosity (%) = (pore volume / porous membrane volume) × 100 pore volume = water content - bone dry weight Γ Average pore diameter (μ) Measured by electron microscope. Γ Maximum pore diameter (μ) (bubble point method) Measured according to ASTM8316-70 and E128-61. Γ sp value (solubility parameter) Calculated using the following formula (Small's formula) sp value = d・ΣG/M d: specific gravity, G: molar traction constant, M: molecular weight. Γ Water permeability (l/m ² , hy.atm.25℃) Measured at 25℃ and differential pressure of 1Kg/cm ² . Γ Pinhole occurrence frequency (ke/m) This is one evaluation item of the uniformity of the pore structure, which evaluates the number of abnormally large pores. A 150 m continuous hollow fiber porous membrane was immersed in ethyl alcohol, and a pressure 0.5 kg/cm ² lower than the bubble point pressure of the porous membrane was applied inside one side of the hollow fiber (the other side was closed). Check the number of bubbles generated and calculate from the following Pinhole frequency (ke/m) = Number of bubbles generated/150 Example 1 Fine powder silicic acid [Aerosil R-972 (trade name), specific surface area 120 m ³ /g, average 11.1% by volume of primary particle diameter 16mmμ and 62.2% by volume of chlorotrifluoroethylene oligomer [Dyfloil #20 (trade name)] were mixed in a Henschel mixer, and this was mixed with ethylene-tetrafluoroethylene copolymer [Afron COPZ].
8820 (trade name)] 26.7% by volume was added and mixed again using a Henschel mixer. The mixture was mixed in a 30 mmφ twin-screw extruder and made into pellets. The pellets were molded into hollow fibers using a hollow fiber manufacturing apparatus comprising a 30 mmφ twin-screw extruder equipped with a hollow spinneret. The formed hollow fibers were heated to 1,1 at 50°C.
The sample was immersed in 1-trichloroethane for 1 hour to extract the chlorotrifluoroethylene oligomer, and then dried. Then, it was immersed in a 40% caustic soda aqueous solution at 70° C. for 1 hour to extract the finely divided silicic acid, and then washed with water and dried. The performance of the obtained ethylene-tetrafluoroethylene copolymer porous membrane was as follows: outer diameter 1.04 mm, inner diameter 0.52 mm.
mm, porosity 60%, average pore size 0.05μ, maximum pore size 0.1μ,
Water permeability was 150l/ ^m2・hr・atm・25℃. The frequency of pinhole occurrence was as low as 0 holes/m, and even if the film was manufactured repeatedly under the same conditions, the variation in film performance was small. Examples 2 to 8 Ethylene-tetrafluoroethylene was prepared in the same manner as in Example 1, except that a mixture of chlorotrifluoroethylene and the heat-resistant organic substance shown in Table 1 was used instead of the chlorotrifluoroethylene oligomer as the heat-resistant organic liquid. An ethylene copolymer porous membrane was obtained. As a heat-resistant organic liquid, dimethyl silicone oil [KF96 (trade name),
sp value 6.3] 0.17 to 0.25 volume or methyl phenyl silicone oil [KF54 (product name), sp value 8.2] 0.25 volume or trioctyl trimellitate [sp value 8.9]
Work was carried out on 0.25-0.5 volumes of mixtures. Table 1 shows the performance of each of the obtained porous ethylene-tetrafluoroethylene copolymer membranes. The frequency of pinhole occurrence was good at 0 pcs/m in all cases, and there was little variation in film performance even when repeated production was performed under the same conditions.

[Table] Comparative example 1 Finely divided silicic acid [Aerosil 200 (product name), specific surface area
200m ² /g, average primary particle diameter 16mμ] 13.3% by volume,
60.0% by volume of dioctyl phthalate was mixed in a Henschel mixer, 26.7% by volume of ethylene-tetrafluoroethylene copolymer [Afron COPZ-8820 (trade name)] was added thereto, and the mixture was mixed again in a Henschel mixer. The mixture was mixed in a 30 mmφ twin-screw extruder and made into pellets. The pellets were molded into hollow fibers using a hollow fiber manufacturing apparatus comprising a 30 mmφ twin-screw extruder equipped with a hollow spinneret. The formed hollow fibers were heated to 1,1 at 50°C.
The sample was immersed in 1-trichloroethane for 1 hour to extract dioctyl phthalate, and then dried. Then, it was immersed in a 40% caustic soda aqueous solution at 70° C. for 1 hour to extract the finely divided silicic acid, and then washed with water and dried. The performance of the obtained ethylene-tetrafluoroethylene copolymer porous membrane is as follows: outer diameter 1.00 mm, inner diameter 0.50 mm.
mm, porosity 68%, average pore size 0.3μ, maximum pore size 0.8μ,
Water permeability was 2000l/ ^m2・hr・atm・25℃. The frequency of pinholes in this porous membrane was as high as 0.3 holes/m, and the yield of good products was extremely low. Furthermore, when porous membrane production was carried out five times under the same conditions, the maximum pore diameter of the obtained porous membrane was 0.6 to 1.0μ, and the water permeability was 650 to
Membrane performance fluctuated greatly at 2200l/ ^m2・hr・atm・25℃, and the quality of the membrane was unstable. Examples 9 to 11, Comparative Example 2 Fine powder silicic acid [Aerosil 200 (trade name), specific surface area
200m ² /g, average primary particle diameter 12mμ〕12.5% by volume,
A mixture of 56.2% by volume of chlorotrifluoroethylene oligomer [Dyfluoroyl #20 (trade name)] and trioctyl trimellitate [sp value 8.9] was mixed in a Henschel mixer, and this was mixed with ethylene-tetrafluoroethylene copolymer [Afron]. COP Z-
8820 (trade name)] was added in an amount of 31.3% by volume, and mixed again using a Henschel mixer. Thereafter, a porous ethylene-tetrafluoroethylene copolymer membrane was obtained in the same manner as in Example 1. The mixing ratio of chlorotrifluoroethylene oligomer and trioctyl trimellitate is 1 to 15 volumes of trioctyl trimellitate per 1 volume of chlorotrifluoroethylene oligomer. Table 2 shows the performance of each of the obtained porous ethylene-tetrafluoroethylene copolymer membranes.

[Table] Comparative Example 3 An attempt was made to produce an ethylene-tetrafluoroethylene copolymer porous membrane in the same manner as in Example 1, except that dimethyl silicone oil [KF96 (trade name)] was used instead of the chlorotrifluoroethylene oligomer. However, it had poor moldability and could not be formed into a film. (Effects of the Invention) According to the present invention, an ethylene-tetrafluoroethylene copolymer porous membrane having a uniform porous structure with excellent chemical resistance, excellent filtration performance, and excellent durability can be obtained with good productivity and at a low price. I started to be able to do it. As a result, by using this porous membrane, it becomes possible to carry out high-precision filtration and purification under severe conditions in terms of heat resistance and chemical resistance, such as hot concentrated sulfuric acid filtration, at low cost.

Claims (1)

[Claims] 1. Ethylene-tetrafluoroethylene copolymer
After mixing 10 to 60% by volume, 7 to 42% by volume of inorganic fine powder, and 30 to 75% by volume of a heat-resistant organic liquid that is liquid at the melt-molding temperature, the molded product is melt-molded. and an ethylene-tetrafluoroethylene copolymer, characterized in that a chlorotrifluoroethylene oligomer is used as the heat-resistant organic liquid in a method for producing an ethylene-tetrafluoroethylene copolymer porous membrane by extracting an inorganic fine powder. Method for manufacturing porous membrane. 2 Ethylene-tetrafluoroethylene copolymer
After mixing 10 to 60% by volume, 7 to 42% by volume of inorganic fine powder, and 30 to 75% by volume of a heat-resistant organic liquid that is liquid at the melt-molding temperature, the molded product is melt-molded. In a method for producing an ethylene-tetrafluoroethylene copolymer porous membrane by extracting inorganic fine powder, the heat-resistant organic liquid has an SP value of 5 to 11, excluding chlorotrifluoroethylene oligomer and chlorotrifluoroethylene oligomer. 1. A method for producing an ethylene-tetrafluoroethylene copolymer porous membrane, the method comprising using a mixture with a synthetic organic substance.