JPS61233026A - Production of porous film - Google Patents

Abstract

PURPOSE:To obtain a porous film, having improved heat resistance without deterioration in performance at high temperatures, and suitable for microfilters, etc., by incorporating a crystalline thermoplastic resin with inorganic fine powder, etc., melt molding the resultant mixture, annealing the molded film while heating, and extracting the inorganic fine powder. CONSTITUTION:(A) A crystalline thermoplastic resin, e.g. ethylene-tetrafluo roethylene copolymer, is melt incorporated with (B) inorganic fine powder having preferably 50-500m<2>/g specific surface area and 0.005-0.5mu average primary particle diameter, e.g. fine powdery silicic acid, and (C) a plasticizer in a pre ferred proportion of 15-40vol% component (A), 10-20vol% component (B) and 50-70vol% component (C) and the resultant mixture is then molded into for example hollow fibers, etc. The component (C) is then extracted and the above-mentioned molded article is annealed preferably at the melting point of the component (A) - the melting point -100 deg.C. The component (B) is further extracted to afford the aimed porous film.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a porous membrane with excellent heat resistance, particularly to a method for producing a porous membrane suitable for microfilter use.

<Prior art> Sintering methods, nonwoven fabric methods, stretching methods, phase separation methods, extraction methods, etc. are known as methods for producing porous organic polymers, but methods that have uniform pores and high permeability are known. The best methods for producing porous membranes include phase separation and extraction methods.

These seven excellent methods for producing porous membranes are as follows: After melt-mixing thermoplastic resin, inorganic fine powder, and plasticizer and molding, the plasticizer is extracted, and the inorganic fine powder is further extracted to obtain a porous membrane. A method is known (Japanese Unexamined Patent Publication No. 1986-64)
2/≦7, JP-A-63-790//, JP-A-Sho! ! -/79297 publication, etc.).

Problems to be Solved by the Present Invention> When a porous membrane is exposed to high temperatures when modularized, or when hot filtration is performed at high temperatures, changes in the pore diameter of the porous membrane and a decrease in permeability are observed. This is often a problem.

In order to solve such problems, it is conceivable to anneal the film made only of crystalline thermoplastic resin under heating conditions in advance. There is no means to restrict shrinkage, deformation, etc. in the thickness direction, and therefore it has been difficult to obtain a film with desired performance with good reproducibility.

Means for Solving Problems〉 The present inventors believe that the 1 strain I generated in the crystalline thermoplastic resin constituting the porous membrane during the porous membrane molding process is the cause of the performance deterioration of the porous membrane at high temperatures. It is believed that the main cause is that 1 strain I exists and the cancellation of that 1 strain I occurs when heated.
As a result of intensive study on a method for producing porous membranes that minimizes the strain 1 and minimizes performance deterioration under high temperatures, we found that annealing under heating conditions is usually necessary to eliminate the strain 1 described above. However, when a porous film made only of a crystalline thermoplastic resin is annealed, its physical properties change significantly. Further, the physical properties do not change uniformly in each part of the film, and the resulting film is non-uniform, and reproducibility is often not achieved. In order to prevent such non-uniform changes in physical properties, the film shape can be restrained in some way, but in general it is difficult to restrain the film from the outside, and even if it is a flat film, it is difficult to restrain it from the outside. Although restraint is possible, restraint in the thickness direction of the film is difficult.

Furthermore, it is difficult to constrain a hollow fiber-like porous membrane in any direction other than the longitudinal direction, and it is difficult to obtain a uniform membrane by annealing.

The present inventors have found that by annealing a porous membrane filled with inorganic fine powder, the inorganic fine powder itself constrains the shape of the porous membrane from within, and as a result, a uniform membrane can be obtained with good reproducibility. This discovery led to the completion of the present invention.

That is, in the present invention, a mixture of a crystalline thermoplastic resin, an inorganic fine powder, and a plasticizer is melt-molded, and after only the plasticizer is extracted, heat annealing is performed to eliminate resin termite distortion, and then the inorganic fine powder is melt-molded. This is a method for producing a porous membrane characterized by extraction.

The crystalline thermoplastic resin in the present invention may basically be any resin that can be formed into a film, but preferably polyethylene, polypropylene, polybutene, poly-
Goo-methylpentene-7 and mixtures thereof, or ethylene, propylene, butene, goo-methylpentene-7
/, polyolefins such as copolymers of two or more types of hexene, ethylene-tetrafluoroethylene copolymers, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymers, tetrafluoroethylene-hexafluoropropene Examples include crystalline thermoplastic fluororesins such as copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, and polyvinylidene fluoride. Ethylene-tetrafluoroethylene copolymer and polychlorotrifluoroethylene are particularly preferred because they have excellent heat resistance, chemical resistance, thermal creep, strength, etc., and have a large annealing effect.

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. And this inorganic fine powder has a specific surface area! O-! 00 Shishi and average particle diameter of 0.00j~
0. -tμ range (: certain microparticles or porous particles. Furthermore, the inorganic fine powder is preferably capable of absorbing at least % volume, preferably 3 times the volume 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, diatomaceous earth, and the like. Among these, finely divided silicic acid is particularly effective.

The plasticizer used in the present invention is extracted from the molded product,
It is used to impart porosity to the molded product. The plasticizer must have a boiling point at least 7 atmospheres above the molding temperature, be liquid at the molding temperature, and be substantially inert to the polymer. For example, polyolefins such as polyethylene and polypropylene (preferred examples include phthalic acid derivatives such as diptyl phthalate and di-(2-ethylhexyl) phthalate; sepacic acid derivatives such as di-(2-ethylhexyl) sepacic acid; and adipic acid. G (,
Examples include adipic acid derivatives such as nitrimellitic acid tri(2-ethylhexyl), trimellitic acid derivatives such as nitrimellitic acid tri(2-ethylhexyl), and mixtures of two or more of these.

In addition, suitable fluorine-based thermoplastic resins such as ethylene-tetrafluoroethylene copolymer and polychlorotrifluoroethylene include chlorotrifluoroethylene oligomer, hexafluoropropylene oxytide oligomer, and hexafluoroethylene oligomer. Fluorine-based oligomer: Fluorine-based silicone oil or a mixture of two or more of these, or silicone oil such as dimethyl-based silicone oil or phenylmethyl-based silicone oil: Di(2-ethylhexyl phthalate)
, low volatility phthalic acid derivatives such as dinonyl phthalate and dicredecyl phthalate; trimellitic acid 1-! Mixed systems with low-volatile trimellitic acid derivatives such as (J-C2-edelhexyl) and the like can be mentioned.

In the manufacturing method of the present invention (:), first, three types of crystalline thermoplastic resin, inorganic fine powder, and plasticizer are mixed.The composition ratio of each is 10 to 60% by volume of crystalline thermoplastic resin,
Preferably /j-4tO capacity 1, inorganic fine powder 2~X! Capacity factor, preferably lO~20 capacity, plasticizer 30~7!
Capacity Shig, preferably! θ to 7θ capacity Chi.

If the crystalline thermoplastic resin is less than the /θ capacity coefficient, the resin is too small and the resulting porous membrane has low strength and poor moldability. On the other hand, if the volume ratio exceeds 60, a porous membrane with a high porosity cannot be obtained and the permeability becomes low, which is not preferable.

If the inorganic fine powder has a volume of less than 7, it will not be able to adsorb the plasticizer necessary to create an effective porous membrane, making molding difficult.

If the volume ratio exceeds 1A2, the fluidity during melting will be poor and the resulting molded product will be brittle and cannot be put to practical use. If the plasticizer is less than 30% by volume, the contribution rate of the plasticizer to liquid pore formation decreases, the porosity of the resulting porous membrane is small, and a porous membrane that is substantially not effective is obtained. If the capacity exceeds 1, it will be difficult to mold, and the mechanical strength will also be low.
A desirable porous membrane cannot be obtained.

These three components are mixed by a conventional mixing method using a mixer such as a Henschel mixer, a -blender, a ribbon blender, or the like. There is no special C2 regulation regarding the mixing order of the three components, but first the inorganic fine powder and the plasticizer are mixed, and after the inorganic fine powder (two plasticizers have been adsorbed), the crystalline thermoplastic resin is added and mixed again. It is preferable.

The obtained mixture is melt-kneaded and molded using an extruder or the like. In this case, although it is possible to directly knead and mold the mixture, it is preferable to perform melt mixing once to form pellets, and then mold the mixture.

The plasticizer is extracted from the three-component mixture molded product thus obtained. The extraction solvent must be capable of dissolving the plasticizer and must not substantially dissolve or modify the crystalline thermoplastic resin and inorganic fine powder used under the extraction conditions.

Next, after the plasticizer extraction is completed, the molded article made of the crystalline thermoplastic resin and the inorganic fine powder is subjected to heat annealing treatment. In principle, the annealing treatment temperature may be any temperature higher than the glass transition point of the crystalline thermoplastic resin, but considering the time required for annealing treatment and productivity, the melting point Preferably, the temperature is in the range of -700°C. Further, it is more effective and preferable to perform the treatment at a temperature higher than the expected usage temperature (including heating conditions in the assembly process, etc.). The treatment time depends on the treatment temperature, but is usually in the range of several minutes to several days.

After the annealing process, the inorganic fine powder is extracted, but the extraction (:
The chemical used is not particularly limited as long as it dissolves the inorganic fine powder under the extraction conditions (2) without substantially dissolving or modifying the crystalline thermoplastic resin used.

As described above, the film obtained by the manufacturing method including the step of annealing has better film physical properties during heating compared to the film obtained by the manufacturing method (2) that does not include the annealing treatment. The changes will be significantly smaller.

<Examples> Examples are shown below to clarify the present invention, but the present invention is not limited by these Examples.

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

Composition ratio (capacity) Calculated from the value obtained by dividing the added heavy electricity of each composition by the true specific gravity.

Porosity (ch)〉 Porosity = (pore volume / porous membrane volume) x 100 pore volume =
Water-containing weight - absolute dry weight, maximum pore diameter (μ)〉(bubble point method) 8TM? 3
Measured by 7o-70 and E/, 2♂-6no.

Water permeability (27 m”h・atm at 2 j ℃)
>2♂℃, differential pressure/Measured at private inspection.

<Average pore diameter (μ)> Measured using a mercury intrusion method poron meter.

Example/ Fine powder silicic acid [Aerosil R-972 (trade name)] //,
/Capacity Ch, Chlorotrifluoroethylene Oligomer [Dyfroil #, 20 (trade name)] Kufta.

Capacity section, silicone oil (KF qt-3so (
Product name) ) / 2. % was mixed in a Henschel mixer, 2g of this (niethylene-tetrafluoroethylene copolymer (770yCOP Z-(5'♂Coθ (trade name)), 7 volumes of H was added, and the mixture was mixed again with a Henschel mixer. Mixed at .

The resulting mixture was mixed in a 30 ttas twin screw extruder,
After forming pellets, they were molded into hollow fibers using a hollow fiber manufacturing device equipped with a 3L twin-screw extruder equipped with a hollow spinneret. From molded hollow fiber /, /, /-)! Silicone oil and chlorotrifluoroethylene oligomer were extracted using J chloroethane and dried.

A hollow fiber made of finely divided silicic acid and an ethylene-tetrafluoroethylene copolymer was annealed at 200° C. for 7 hours. Thereafter, fine powder silicic acid was extracted using an aqueous sodium hydroxide solution, washed with water, and dried to obtain a hollow fiber-like porous membrane.

The physical properties of the obtained porous membrane are as follows: maximum pore diameter θ, 36 (μ),
Water permeability/g3θ (t//・h-atm at 2 j
℃), porosity ≦2, and average pore diameter 0.2j (μ).

After leaving this film in a 170°C atmosphere (1=,
When physical properties were evaluated, the maximum pore diameter was 0.3 (μ), water permeability/3θ0 (tAr? h-atm at 2 r
℃), the porosity decreased by 2 inches, and the rate of change with respect to the original physical properties was the maximum pore diameter θ, the water permeability width decreased, the porosity decreased by 2 inches, and the average pore size decreased by 0.

Comparative Example/Example/A hollow fiber-like porous membrane was obtained in the same manner as in Example/, except that the annealing treatment was performed at 200° C. for 7 hours.

The physical properties of the obtained porous membrane were as follows: maximum pore diameter of 0.36 (μ);
Water permeability // 00 (L/rr?・h・atm
2 j °C) porosity g/% and average pore diameter 0.23μ.

Next, this membrane was left to stand for a period of time at l♂O℃, and the physical properties were evaluated. As a result, the maximum pore diameter was 0.29 (I
t), water permeability! A O (27m”h・atm
2 j ℃) Porosity! ! h, average pore diameter θ, 20(μ
), and the rate of change with respect to the original physical properties was as follows: maximum pore size decreased by 19 degrees, water permeability decreased by 1 inch, porosity/θ decreased by 3 degrees, and average pore diameter decreased by 3 degrees. This is significantly larger than in Example 7.

Example λ Fine powder silicic acid [ICI Zil R-cp7s (trade name)] 7
3.3 volume and 60.0 volume of chlorotrifluoroethylene oligomer [Daifloil #100 (trade name)] were mixed in a Henschel mixer, and to this was added ethylene-tetrafluoroethylene copolymer [Aflon COP Z-♂
26.7 volumes of ♂2θ (trade name) was added and mixed again using a Henschel mixer.

The resulting mixture was mixed in a 30-order twin-screw extruder to form pellets, which were then molded into hollow fibers in a hollow fiber manufacturing device equipped with a jOfls twin-screw extruder C and a hollow spinner. i,/,,2-) from the formed hollow fiber! The chlorotrifluoroethylene oligomer was extracted using J chlorotrifluoroethane and dried.

Hollow fibers made of finely divided silicic acid and ethylene-tetrafluoroethylene copolymer were annealed at 200°C for 7 hours, and then the finely divided silicic acid was extracted using an aqueous sodium hydroxide solution, washed with water, and dried to form hollow fibers. A porous membrane was obtained.

The physical properties of the obtained porous membrane were as follows: maximum pore diameter 0.3/(μ);
Water permeability/72θ (t/m'・h・atm at, 2
j °C), porosity 32 cm, average pore diameter 0. , :20(μ)
Met.

After leaving this membrane in an atmosphere at / and 0°C for Z hours, we evaluated its physical properties and found that the maximum pore diameter was 0.37 (μ), and the water permeability was 0θ (A/m”・h・atm at 2 j °C). )
, the porosity is 6%, the average pore diameter θ is 20 (μ), and the rate of change with respect to the original physical properties is the maximum pore diameter θ.

Water permeation rate decreased by 7%, porosity decreased by 3 cm, and average pore diameter decreased by θ.

Comparative Example λ A hollow fiber-like porous membrane was obtained in the same manner as in Example 1 except that the annealing treatment was performed at θ0° C. for 7 hours.

The physical properties of the obtained porous membrane were as follows: maximum pore diameter of 0.37 (μ);
Water permeability/! ♂0 (A/m"h-atm at 23-
C), porosity 67%, average pore diameter θ, 20Cμ).

After leaving this membrane in an atmosphere at 170°C for a period of time, physical properties were evaluated, and the maximum pore diameter θ, 2≦(/f), water permeability ♂3θ (A/m”h・atm at 2 j 'C)
, porosity 5♂chi, average pore diameter 0. /♂ (μ), and the rate of change with respect to the original physical properties is maximum pore diameter / Otsuchi decrease, water permeability / 7chi decrease, porosity / 3chi decrease, average pore diameter 10%
It was a decrease. The change is significantly larger than in the example case.

Example 3 Fine powder silicic acid [Aerosil R-972 (trade name)] //,
/ Capacity section, Lifluoroethylene oligomer [Guifluoroyl #20 (product name)], 2 capacity, silicone oil (KF5'Otsu-3!0 (product name)) i
s, mix Otsukaichi with Hensiel Mikichi, and add this (
: Polychlorotrifluoroethylene [Daiflon M-
300 (trade name)) by volume of 26.7 was added and mixed again using the Henschel mixer.

The resulting mixture was mixed in a 30 mm twin screw extruder to form pellets, and then molded into hollow fibers in a hollow fiber manufacturing apparatus in which a hollow spinneret was attached to a 30 ttm twin screw extruder.

From molded hollow fibers /, /, /-to! Silicone oil and chlorotrifluoroethylene oligomer were extracted using chloroethane and dried.

A hollow fiber made of finely divided silicic acid and polychlorotrifluoroethylene was annealed at θθ°C for 7 hours.

Thereafter, fine powder silicic acid was extracted using an aqueous sodium hydroxide solution, washed with water, and dried to obtain a hollow fiber-like porous membrane.

The physical properties of the obtained porous membrane are as follows: maximum pore diameter θ, λ (μ),
Water permeability/θ90 (t/r?・hlatm at 2
j ℃), porosity! !壬、Average pore diameter θ...? , 2(μ
)Met.

After leaving this membrane in an atmosphere of /♂θ℃ for 7 hours, we evaluated its physical properties and found that the maximum pore diameter was 0.3 mm (μ) and the water permeability was J' j O (t/i h atm at 2 j ℃
), porosity 30%, average pore diameter O1,2θ (μ), and the rate of change with respect to each original physical property is the maximum pore diameter 7
The amount of water permeation decreased by 7%, the porosity decreased by 9%, and the average pore diameter decreased by 9%.

Comparative Example 3 A hollow fiber-like porous membrane was obtained in the same manner as in Example 3, except that it was annealed at 200° C. for 7 hours.

The physical properties of the obtained porous membrane were as follows: maximum pore diameter of 0.32 (μ);
Water permeability j 70 (t/m”・h・atm at 2
j °C), porosity jj'l, average pore diameter 0. /♂(μ).

After leaving this membrane in an atmosphere of /♂θ℃ for 7 hours, we evaluated the physical properties and found that the maximum pore diameter was 01.2≦(μ), the water permeability / g O (A/i・h・atm at 2 j °C
), porosity is 32 cm, average pore diameter o, /s (μ), and the rate of change with respect to the original physical properties is: maximum pore diameter/tall decrease, water permeation rate decrease by 75 cm, porosity decrease by 3 cm, average The pore diameter was reduced by 2 inches. Compared to the case of Example 3, the change is significantly large.

<Effects of the Invention> Conventionally, crystalline thermoplastic resins constituting porous membranes themselves have a high operating temperature (despite this, physical properties of porous membranes change at high temperatures and are often unsuitable for use). However, the present invention has made it possible to stably supply a porous membrane with little change in membrane properties even when used at high temperatures.

Claims (1)

[Claims] A method for producing a porous membrane, which comprises melt-molding a mixture of a crystalline thermoplastic resin, an inorganic fine powder, and a plasticizer, extracting the plasticizer, performing a heat annealing treatment, and further extracting the inorganic fine powder.