JPS61152739A - Production of porous membrane of ethylene-tetrafluoroethylene copolymer - Google Patents

Abstract

PURPOSE:To produce the titled porous membrane having excellent heat- resistance and filtration property, by mixing inorganic fine powder and a chlorotrifluoroethylene oligomer to an ethylene-tetrafluoroethylene copolymer, melting and forming the mixture, and extracting the inorganic fine powder and the oligomer from the formed article. CONSTITUTION:(A) 10-60(vol)% ethylene-tetrafluoroethylene copolymer is mixed with a mixture of (B) 7-42% inorganic fine powder which is fine particles or porous particles having a specific surface area of 50-500m<2>/g and an average primary particle diameter of 0.005-0.5mu, preferably fine silica and (C) 30-75% chlorotrifluoroethylene oligomer (preferably 4-15-mer) or a mixture of said oligomer and other heat-resistant organic substance having an sp value of 5-11 (preferably silicon oil). The obtained mixture is formed under melting, and the component C and then the component B is extracted from the formed article to obtain a porous membrane of the component A having uniform porous structure.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is an ethylene-tetrafluoroethylene copolymer that has excellent chemical resistance, excellent filtration performance, excellent mechanical properties, and has fine particles. The present invention relates to a method for producing a porous membrane having a uniform porous structure consisting of pores. In particular, the present invention provides a porous membrane suitable for a microfilter with excellent heat resistance and excellent filtration performance, and a porous membrane suitable for a microfilter for purifying chemicals such as strong acids and strong alkalis with 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 with excellent chemical resistance and heat resistance, but among these fluorine-based resins, it is one with excellent mechanical properties. It is a resin with very good creep properties (long-term deformation resistance under load), especially at high temperatures, and has excellent chemical resistance, heat resistance,
It is expected to be a material for porous membranes with high mechanical properties.

As a method for producing a porous membrane made of this ethylene-tetrafluoroethylene copolymer, 4I Kasho 5O-136
No. 354, 4I Publication No. 158465/1983, and Japanese Patent Publication No. 147030/1989 are known. JP-A-50-136354 discloses a method of preparing a porous membrane by preparing a slurry mixture of ethylene-tetrafluoroethylene copolymer fine powder and styrene monomer, polymerizing the ethylene-tetrafluoroethylene copolymer, forming a membrane, and eluating the styrene polymer. However, the porous membrane obtained by this method has a large pore diameter of 10 μm and has very low permeability, making it unsuitable for microfilters. Japanese Patent Publication No. 54-158
Publication No. 465 (c) is a method of making a porous membrane by etching an ethylene-tetrafluoroethylene copolymer film with an aqueous soda solution irradiated with loaded particles. There are problems in that a filamentous membrane cannot be obtained, and since a nuclear reactor is used, it is not suitable for mass production. JP-A-59-147030 discloses ethylene-
This method creates a porous film by coating a tetrafluoroethylene copolymer film with resist to form a perforated resist pattern, and then performing sputter etching to form through holes corresponding to the resist pattern, but the film is thin. Therefore, the mechanical properties are poor, it is difficult to obtain a uniform hollow fiber state, and furthermore, a long sputter etching process is required, resulting in problems in productivity. As a method for improving the problems of the above manufacturing method, Japanese Patent Application Laid-Open No. 55-79011,
JP-A-56-159128, JP-A-57-281
No. 39, JP-A No. 58-93798, JP-A No. 58-179297, etc. Ethylene-tetrafluoroethylene copolymer, finely powdered silicic acid, and dioctyl phthalate are mixed and melt-molded, and then fine powder is obtained from the molded product. A method of producing a porous membrane by extracting silicic acid and dioctyl phthalate is known. However, this method has problems in that pinholes (abnormally large holes) occur frequently, the quality of the membrane is unstable (performance is uneven), and productivity (receiving good products) is poor.

As mentioned above, there has been no conventional method for producing a porous membrane made of an ethylene-tetrafluoroethylene copolymer that has 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 comprises 10 to 60% by volume of ethylene-tetrafluoroethylene copolymer, 7 to 42% by volume of inorganic fine powder,
Heat-resistant organic liquid that is liquid at melt molding temperature 30-75
After mixing and melt-molding, heat-resistant organic liquid and inorganic fine powder are extracted from the molded product and ethylene-
In the method for producing a porous tetrafluoroethylene copolymer membrane, chlorotrifluoroethylene orisimer or chlorotrifluoroethylene orisimer and chlorotrifluoroethylene orisimer are excluded as the heat-resistant organic liquid <sp' value 5 to 11 This is a method for producing a porous ethylene-tetrafluoroethylene copolymer membrane, characterized by using a mixture of the above and a heat-resistant organic substance.

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, making molding easier, and it is further extracted to form pores.III+1! It is something that has. The inorganic fine powder is microparticles or porous particles having an average diameter of 50 to SOO bi/9 and an average particle size of 0,000 to 0.5μ. Even more no 4! The powder is preferably capable of absorbing at least ⅔ volume, preferably 3 times or more of the heat-resistant organic liquid.

Examples of the inorganic fine powder used in the present invention include fine silicic acid,
Examples include 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 into the molded product to impart porosity to the molded product. The heat-resistant organic liquid must have a boiling point at 1 atm of at least 200°C or higher, preferably 250°C or higher, be heat resistant to melt molding, be liquid at the melt molding temperature, and be substantially inert to the polymer. is necessary.

First, we investigated various heat-resistant organic liquid single components.
It has been discovered that only by doing so can a porous membrane with excellent permeability and a uniform pore structure be manufactured with good productivity and stable membrane quality with less occurrence of pinholes (abnormally large pores). Furthermore, it is possible to use a mixture of chlorotrifluoroethylene oligomer and a specific heat-resistant organic substance as a heat-resistant organic liquid.
I got better results. That is, as the heat-resistant organic liquid used in the present invention, chlorotrifluoroethylene oligomer and chlorotrifluoroethylene oligomer are used.
It has been found that a porous membrane with even better mechanical properties can be obtained by removing the mer and using a mixture with a heat-resistant organic substance having an sp value of 5 to 11.

Here, Kurohi silyfluoroethylene oligomer and sp.
When a mixture with a heat-resistant organic substance with an MP value of 11 or more is used as a heat-resistant organic liquid (currently no heat-resistant organic substance with an MP value of 5 or less is found), chlorotrifluoroethylene oligomer: P''
The compatibility between f- and a heat-resistant organic substance having an sp value of 11 or more is poor, and the resulting membrane has too large a pore diameter, has a nonuniform pore structure, and has many cipin holes (abnormally large pores), which is undesirable.

On the other hand, /l rotosilyloethylene ori! Remove mar(a
When a heat-resistant organic substance with a p-value of 5 to 11 is used alone as a heat-resistant organic liquid, the resulting film has too large a pore diameter, has a non-uniform pore structure, and has many pinholes (abnormally large pores). Undesirable.

That is, by using a mixture of chlorotrifluoroethylene oryzmer and a heat-resistant organic substance with an sp value of 5 to 11 as a heat-resistant organic liquid, it has excellent permeability, has a uniform pore structure, and has excellent mechanical properties. It is possible to manufacture excellent porous membranes with low pinholes (abnormally large pores), stable membrane quality, and high productivity.

Furthermore, by selecting the heat-resistant organic substance and the mixing ratio, it is possible to widen the pore size adjustment range of the porous membrane.

The chlorotrifluoroethylene oligomer as the heat-resistant organic liquid used in the present invention is preferably a chlorotrifluoroethylene tetramer or monomer, but
In view of resistance, workability, extractability, etc., octamer or 11-mer are more preferable.

SP value 5 as a heat-resistant organic substance used in the present invention
-11 include silicone oil, perfluoro polyether oligo i-, phthalic acid esters, trimellitic acid esters, henananodic acid esters, adipic acid esters, azelaic acid esters, phosphoric acid Examples include esters.

Among these, silicone oil, fluorocarbon polyether 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.

Excluding the chlorotrifluoroethylene oligomer, the chlorotrifluoroethylene oligomer (mixing ratio with a heat-resistant organic substance with an MP value of 5 to 11) The heat-resistant organic material preferably has a capacity of 0.05 to 1 G, more preferably 0.1 to 4. If the heat-resistant organic material is less than 0.05 volume, the obtained film will have low toughness and will not be suitable. Moreover, if the capacity exceeds 10, the fF obtained is undesirable because the pore diameter of the membrane is too large, the membrane has a non-uniform pore structure, and there are many occurrences of pinholes (abnormally large pores).

In producing the porous membrane of the present invention, first, ethylene-
Tetrafluoroethylene copolymer, inorganic fine powder, and heat-resistant organic liquid are mixed. The mixing ratio is ethylene-
Tetrafluoroethylene co-electrolyte 10-60% by volume, preferably 15-40% by volume, inorganic fine powder 7-42% by volume
, preferably 10 to 20% by volume, heat-resistant organic liquid 30
-75 capacity, preferably 50-70 capacity.

If the amount of ethylene-tetrafluoroethylene copolymer is less than 10 volumes, the resin content will be too small, resulting in low strength and poor moldability (
If the amount exceeds 60, a porous membrane with a high porosity cannot be obtained, which is not preferable. If the volume of the inorganic fine powder is less than 7%, it will not be able to adsorb the organic liquid necessary to create an effective porous membrane, making molding difficult. In addition, the resulting molded product is brittle and cannot be put to practical use. When the volume of the heat-resistant organic liquid is less than 30%, 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%.
Substantially no effective porous membrane can be obtained, and if the volume exceeds 75, molding becomes difficult and a porous membrane with high mechanical strength cannot be obtained.

A conventional mixing method using a mixer such as a Henschel mixer, 1-blender, Risen blender, etc. is sufficient for mixing the three components. As for the mixing order of the three components, although it is possible to mix the three components at the same time, first mix the inorganic fine powder and the heat-resistant organic liquid so that the heat-resistant organic liquid is sufficiently adsorbed on the inorganic fine powder, and then add the ethylene. It is preferable to blend and mix a tetrafluoroethylene copolymer. This mixture is kneaded using a melt mixing device such as an extruder, a nine-way mixer, a two-roll mixer, a kneader, or the like. The resulting mixed material is molded by a melt molding method, and the melt molding methods used in the method of the present invention include extrusion molding such as T-die method and inflation method, calendar molding, compression molding,
There are injection molding, etc. It is also possible to directly mold the mixture using an extruder, kneader-ruder, or other device having both kneading and extrusion functions.

With these molding methods, ternary mixtures with 0.025 to λ
It is formed into a film with a wall thickness of sm. The shape of the membrane can be hollow fiber, tube, flat membrane, etc., but hollow fiber is preferable for reasons such as the 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. The solvent used for extraction is 1,1.1-
Halogenated hydrocarbons such as trictetraloethane 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 several 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 finely divided 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 size of the cis-pores 4 having a larger pore diameter, the porous membrane obtained by extracting one or both of the heat-resistant organic liquid and the 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 by these Examples.

The physical properties shown in the present invention were determined by the following measurement method.

0 composition ratio (answer amount 1 Calculated from the value obtained by dividing the added weight of each composition by the true specific gravity.

0 porosity-) Porosity (capital) = (pore volume/porous membrane volume) xlo.

Pore volume = water content – bone dry weight O average pore diameter ψ) Measured using an electron microscope.

O maximum pore diameter ω) () pull point method) ASTM 83
Measured by 16-TO and [12B-61.

osp value (solubility parameter) d: specific gravity, G: molar traction constant, M: molecular weight 0 water permeability (1
Measured at 25°C, differential pressure 1 to 2/-.

0 pinhole occurrence m degrees (ke/m) 1 of the uniformity of the porous structure, which evaluates the number of abnormally coarse pores
There are two evaluation items. A 150 m continuous hollow fiber porous membrane was immersed in ethyl alcohol, and a pressure 0.5 to 1/- lower than the pull 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 in the state and calculate from the following Example 1 Fine powder silicic acid [Aerosil A-S7Z (trade name), specific surface area 120 FIL''/i, average particle size 1a22.μ
)il, i volume %, chlorotrifluoroethylene oligomer [Guifluoroyl #20 (trade name)) 62.2 volume percent were mixed in a Henschel mixer, and ethylene-tetrafluoroethylene and 14i1c Aphron C0PZ-
8820 (trade name) 126.7 volumes tqb'ftfA was added and mixed in a shell mixer.

The mixture was mixed in a 30-mole screw extruder and made into pellets. The pellets were molded into a hollow fiber shape using a hollow fiber manufacturing apparatus comprising an Aomp twin-screw extruder equipped with a hollow spinneret. The formed hollow fibers were immersed in 1°1.1-)lichloroethane at 50° C. 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 m, inner diameter 0.52 m, pores $601% average pore diameter O, OS μ, maximum pore diameter 0.1 μ,
Water permeability was 1501/m''·hr@atm*25°C.

The frequency of pinhole occurrence was as low as 0 holes/m, and even when the membrane was manufactured repeatedly under the same conditions, there was little variation in membrane performance.

Examples 2 to 8 Example 1 except that a mixture of chlorotrifluoroethylene and a heat-resistant organic substance shown in Table 1 was used instead of the chlorotrifluoroethylene oligomer as the heat-resistant organic liquid.
An ethylene-tetrafluoroethylene copolymer porous membrane was obtained in the same manner as above.

As a heat-resistant organic liquid, dimethyl silicone oil (KPO3 (trade name), IP value s,
3) o, 17-0.25 volume or methylphenyl silicone oil [KF54 (trade name), IIp value 8.2
) 0.25 volume or trioctyl trimellitate Cap
value 8.9] was carried out on a mixture of 0.25 to 0.5 volume.

Table 1 shows the performance of each of the obtained ethylene-tetrafluoroethylene copolymer porous membranes. The frequency of pinhole occurrence was good at 0 pcs/m in all cases, and even when repeated production was performed under the same conditions, there was little variation in membrane performance.

Below is a margin Comparative Example 1 Fine powder silicic acid [Aerosil 20G (trade name), specific surface area 200 f/9, average particle size 16 mp) 1a, a volume %, dioctyl phthalate SO, O volume percentage were mixed in a Henschel mixer, 26.7 volumes of ethylene-tetrafluoroethylene copolymer [Afron COPZ-8820 (trade name)] was added and mixed again using a Henschel mixer.

The mixture was mixed in a 30 mg twin screw extruder and pelletized. The pellets were molded into a hollow fiber shape using a hollow fiber manufacturing device equipped with a 30 M$ twin-screw extruder and a hollow spinneret. The formed hollow fibers were immersed in 1.1.1-trichloroethane at 50°C for 1 hour to extract dioctylph and Tare-F, and then dried.

Then, it was immersed in a 40% caustic soda aqueous solution at 70°C for 1 hour to extract fine powder silicic acid, washed with water, and dried. m″shrsatm*25°C.

Pinholes occur in this porous film! The yield of non-defective products was very low, with a high value of 0.3 pieces/m. 1 more under the same conditions 5
When manufacturing a multi-porous membrane, the maximum pore diameter of the obtained porous membrane was 0.6 to 1.0μ, and the water permeability was 650 to 22,001μ.
/f*hreatm1125°C, the membrane performance varied greatly 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 2
00m''/J'% Average particle size tzmpHλ5 Volume%
, chlorotrifluoroethylene oligomer [Gui 7-day Il #20 (trade name)] and trioctyl trimelite) C
A mixture with an Ip value of 8.9] was mixed in a 56.2 volume capacity mixer, and ethylene-tetrafluoroethylene copolymer [Afro 7COP Z-8820 (trade name): 131.3 volume tst- was added to the mixture. Then, the mixture was mixed again using a Henschel mixer.

Thereafter, in the same manner as in Example 1, an ethylene-tetrafluoroethylene copolymer porous membrane was obtained.

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.

Comparative Example 3: An ethylene-tetrofluoroethylene copolymer porous membrane was produced in the same manner as in Example 1, except that dimethyl silicone oil [KF96 (trade name)] was used instead of the chlorotrifluoroethylene oligomer. However, the processability was poor and it was not possible to form a film.

(Effects of the Invention) According to the present invention, a porous ethylene-tetrafluoroethylene copolymer membrane having a uniform porous structure with excellent chemical resistance, excellent filtration performance, and excellent durability can be produced with high productivity and low cost. It became K so that it could be obtained with.

As a result, by using this porous membrane, deliberation (11
It becomes possible to carry out high-precision filtration and purification under strict conditions in terms of heat resistance and chemical resistance, such as EAL filtration, at low cost.

Claims (1)

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