JPH02175736A - Production of porous film - Google Patents

Abstract

PURPOSE:To obtain a porous film having a fine and uniform cellular structure and improved properties by dissolving a resin system based on a polyurethane in an organic solvent, heating the solution, adding a specified coagulating system to the heated solution, applying the resultant solution to a substrate and cooling it. CONSTITUTION:A resin system (a) based on a polyurethane and optionally containing a PVC or polyacrylate resin is dissolved in an organic solvent (b) (e.g. DMF) and heated near the b.p. of component (b) to obtain a high- temperature solution. A coagulating system (c) which is a nonsolvent and/or a poor solvent for component (a) (e.g. water) is slowly added to this high- temperature solution to obtain a solution in a high-temperature region and coagulates near room temperature or in a low-temperature region below that. This solution is applied in the form of a film at high temperatures to a substrate (d) such as a knit or woven fabric, a nonwoven fabric, paper or a film and coagulated by cooling by, for example, immersion in a cooling medium, and the whole is immersed in an extractant (e) to remove the remaining component (b) and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a porous membrane that can be used for synthetic leather, microfilters, and the like.

(Prior Art) A method for manufacturing porous membranes used for synthetic leather and filter media by a wet film forming method is described in Japanese Patent Publication No. 37-2489 and the like. In particular, as a manufacturing method for improving the fineness and homogeneity of the porous membrane cell structure, a method of wet coagulation in which a surfactant and various additives are added to a polyurethane solution as a main ingredient (Japanese Patent Publication No. 4B-43475) , Special Public Service Showa 4B-759
5 etc.) and a method of coagulating in a coagulation bath containing an inorganic salt etc. (Japanese Patent Publication No. 45-39636 etc.) are known.

(Problems to be Solved by the Invention) In conventional technology, a coating film is usually formed by using a resin system mainly composed of polyurethane as a solution of water-soluble N N'-dimethylformamide (hereinafter referred to as rDMFJ). After that, DMF was gradually extracted by immersion in water, and the resin system was gradually solidified as the DMF extraction progressed.

This extraction process usually takes about 5 minutes, although it depends on the coating thickness. The solidification process that determines the cell structure depends on such an extraction process that progresses gradually over a relatively long period of time, and therefore it has been difficult to obtain a homogeneous and fine porous membrane.

The cell structure of porous membranes made mainly of polyurethane manufactured using conventional technology is the most dense and fine, and the fourth
As shown in the figure, the pore diameter was 100 microns or more.

When such a porous membrane is used as a synthetic leather, it lacks density compared to the grain layer of natural leather, so it cannot be said to be satisfactory in terms of wrinkle resistance and texture. In addition, because the cell structure is coarse and non-uniform, the delamination strength of this porous membrane is at most 8 under practical usage conditions.
The physical properties were also not necessarily satisfactory, such as about Kg/3 cm.

As a filter material, the use of porous membranes having a pore size of 100 microns or more is limited to general filtration, and does not extend to the area of microfiltration, which has been in high demand in recent years.

In view of the problems of the conventional techniques as described above, the present invention aims to provide a manufacturing method that can easily obtain a porous membrane having a finer and more homogeneous cell structure and high physical properties. .

(Means for Solving the Problems) A method for producing a porous membrane according to the present invention is to heat a solution in which a resin system mainly composed of polyurethane is dissolved in an organic solvent to form a high-temperature solution, and to add the high-temperature solution to the resin system. Gradually add a coagulating system selected from the group consisting of non-solvents and poor solvents, thereby converting the solution into a solution that remains in a solution state at high temperatures but solidifies at low temperatures near or below room temperature; The process consists of applying a film on a substrate at a high temperature, cooling and solidifying it, immersing it in an extraction bath to extract and remove the organic solvent remaining in the solidified film, and drying it.

The resin system is mainly composed of polyurethane,
It is also possible to use in combination resins such as polyvinyl chloride and polyacrylate that are compatible with polyurethane.

The organic solvent used to dissolve the resin system is D.
MF is most preferred, but dimethyl sulfoxide, dioxane, etc. can also be used or used in combination.

The solution obtained by dissolving the resin system in an organic solvent is preferably heated to a temperature at or near the boiling point of the solvent used.

The coagulation system includes water, normal propyl alcohol,
Isopropyl alcohol, ethylene glycol, etc. can be used. It is advantageous to add the coagulation system diluted with a strong solvent such as DMF in order to prevent the formation of partial agglomerates.

As the substrate, a woven fabric, a nonwoven fabric, a film, etc. can be used.

Cooling for solidifying the coated film can be performed by using a cooling device or by contacting or immersing it in a refrigerant. As the cooling device, a chilled cylinder cooled by a refrigerator is suitable.

As a refrigerant for performing immersion cooling, liquid preon cooled to about 20° C. or less, methanol, water, etc. can be used, and water is particularly preferred.

As the extraction bath, methanol, water, etc., which are non-solvents for the resin system, can be used. Extraction can be accelerated by heating the extraction bath to near the boiling point of the bath. Further, at the stage where the extraction has progressed and the resin system has completely solidified, it is also possible to further accelerate the removal of the remaining solvent by using reduced pressure suction, squeezing operation, etc.

(Function) In the present invention, rather than gradually coagulating the resin solution by solvent extraction, the solubility of the resin solution in an organic solvent varies depending on the temperature, and the coagulation system is added to the resin solution. By adding it, it imparts low-temperature coagulation properties, and after forming a coating film at a high temperature, instantaneous coagulation is achieved by cooling. Since the solvent extraction process takes place after the membrane has solidified, the membrane, once solidified, is not affected by the extraction process, even if the extraction takes time.

In the present invention, when the amount of organic solvent for dissolving the resin system is increased in proportion to the resin system, the concentration of the resin system decreases;
The stability of the solution is increased and it becomes possible to add a larger amount of the coagulation system. Increased organic solvent and resin systems mean increased extractables, which results in larger pore sizes in the cell structure.

On the other hand, when the organic solvent and coagulation system are reduced, the pore size becomes finer. It is also possible to slightly adjust the pore diameter by adding fiber-based or inorganic fillers.

The pores of the porous membrane obtained by the present invention are always substantially uniform regardless of the size of the pores. This is thought to be because the solidification of the coating film layer occurs almost simultaneously throughout the thickness direction, and the entire coating layer is uniformly fixed. In the present invention, it is possible to obtain a porous membrane having a fine and homogeneous cell structure on the order of several microns.

(Example) Example 1 Softening temperature 180°C, 100% modulus 80 to 9/cr
j 20% DMF solution of polyurethane elastomer 20
Kg was heated to 80℃ and while stirring, gradually added 12.5Kg of a mixed solution of DMF/water with a ratio of 3/2 heated to <80℃. Although it is a solution, it has the property of solidifying at temperatures below 40°C, and the ratio of polyurethane/DMF/water is 4/23.5/
A solution of No. 5 was prepared, and while keeping the temperature at 70°C or higher, a yarn with a thickness of 0.8711111. Coat it on a woven fabric with a width of 970# at R1000'j/rrt, immerse it in a coagulation bath with methanol as a coolant at 10°C for 10 seconds to solidify it, and then extract DMF for 60 minutes in an extraction bath with a water temperature of 20°C. 1
It was dried for a total of 10 minutes in a drying oven equipped with a cylinder dryer at 20°C and a tenter at 120°C.

The resulting membrane had a thickness of about 0.8 m, and the porous layer of polyurethane had a uniform cell structure with pore diameters of about 10 microns as shown in FIG. This cell structure was so minute that the presence of the cell could not be recognized with the naked eye. Synthetic leather finished using this as a base has a rich texture and fine wrinkle properties, and has an interlayer peel strength of 10% in the porous layer.
It exceeded b/3cm.

Example 2 Softening temperature 190°C, 100% modulus LO5 9/c
27% DMF solution of tA polyurethane elastomer 1
While heating 5Ky to 80℃ and stirring, 9 was gradually added to a mixed solution 10 of DMF/water/methanol with a ratio of 6/3/1 heated to <80℃. A solution with a ratio of polyurethane/DMF/water/methanol of 4/17/3/1, which is a good stable solution but has the property of solidifying at temperatures below 40°C, was prepared and heated at 70°C or higher. It was applied on nylon taffeta (thickness: approximately 0.125. r111200) using denier thread at a coating amount of 300 g/bottom, and was brought into contact from the back side with a chilled cylinder with a diameter of 600 mm that had been cooled to 8°C by a refrigerator. The mixture was further immersed in a coagulation bath using water at 10°C as a refrigerant for 5 seconds to complete solidification, and then DMF was extracted for 30 minutes in a divided extraction bath with a temperature gradient from 10°C to 45°C. , 110℃ cylinder dryer and 1
It was dried for a total of 6 minutes in a drying oven with a tenter at 10°C.

The resulting film has a thickness of approximately 0.25771111 mm, and the polyurethane porous layer has a uniform cell structure with a pore diameter of approximately 5 microns as shown in Figure 2, but the presence of cells cannot be recognized with the naked eye. I couldn't. When this is used as a filter material, the permeability of distilled water is 2 under a pressure of IK (j/cyr).
1000 i/TIt/hr, and could be used as a material for pre-filters of water purification equipment and pre-filters for sterilization filtration.

Example 3 Softening temperature 210°C, 100% modulus 190 K9/
While heating 10 kg of a 25% DMF solution of Ctd polyurethane elastomer to 80°C and stirring, gradually add 5KI of a mixed solution of DMF/water with a ratio of 3/2 that was also heated to <80°C. It is a stable solution with good fluidity, but has the property of solidifying at temperatures below 40°C.
A solution with a polyurethane/DMF/water ratio of 5/21/4 was prepared and coated at a coating weight of 5009/m onto a polyethylene terephthalate film with a thickness of 200 microns and a width of 1 ions while keeping the temperature above 70°C. After being immersed in a coagulation bath using water at 15°C as a refrigerant for 10 seconds to solidify,
Subsequently, DMF was extracted for 30 minutes in a divided extraction bath with a water temperature gradient of 15°C to 45°C, and dried for 10 minutes in a drying oven at 120°C. Next, the polyurethane porous membrane was peeled off from the polyethylene terephthalate film to obtain a porous membrane made of polyurethane alone and having a thickness of 0.2 mm.

This membrane has a uniform cell structure with a pore size of about 4 microns as shown in FIG. 3, but the cells were so fine that the presence of the cells could not be recognized with the naked eye. The permeability of distilled water of this membrane is 16009. ,
/Trt/hr, and could be used as a material for microfilters. It was also possible to laminate it onto various thick and thin substrates and use it as a base for a variety of synthetic leathers.

(Effects of the Invention) According to the present invention, it is possible to easily obtain a porous film having an extremely fine and homogeneous cell structure and strong physical properties that could not be obtained by conventional wet film forming methods. Therefore, the industrial utility value of the present invention is extremely large.

[Brief explanation of the drawing]

Fig. 1 shows Example 1 of the present invention, Fig. 2 shows Example 2, Fig. 3 shows Example 3, and Fig. 4 shows the finest cells among the porous films formed by the conventional wet film forming method. These are micrographs each showing the cell structure of a porous membrane having a structure, and the magnification is 150 times. Atsushi Ono, Commissioner of the Japan Patent Office, Kunio Onono, Commissioner of the Japan Patent Office, May 5, 1983, column of the "Detailed Description of the Invention" of the specification subject to the amendment. Contents 1) The expression "resin-based" in the case on page 7, line 7, 1° of the specification is corrected to "coagulation-based." Patent Application No. 082.764 of 1988 Address 85 Hanamen, Nagiura, Satoura-cho, Naruto-shi, Tokushima Prefecture Name Nankai Rubber Co., Ltd. 4゜ Agent address 71M 5, Hauraiya Building, 5-2-1 Roppongi, Minato-ku, Tokyo゜Date of amendment order Voluntary amendment/procedure) 17 Official document (method) Subject of amendment: ``Brief explanation of drawings'' column and drawings of July 1939 specification. 7. Contents of the correction 1>"Cell" on page 12, line 7 of the specification is corrected to "particle". The drawings of 1982 Patent Application No. 082.764 are amended as shown in the attached sheet. Address 85 Hanamen, Satoura-cho, Satoura-cho, Naruto-shi, Tokushima Prefecture Name Nankai Rubber Co., Ltd. 4゜ Agent address 7th floor, Hauraiya Pill, 5-2-1 Roppongi, Minato-ku, Tokyo Date: June 1939 (Shipping port)

Claims (1)

[Claims] A solution in which a resin system mainly composed of polyurethane is dissolved in an organic solvent is heated to form a high-temperature solution, and a coagulation system selected from the group consisting of a non-solvent and a poor solvent for the resin system is gradually added to the high-temperature solution, As a result, the solution is in a solution state in a high temperature range, but solidifies in a low temperature range near room temperature or lower, and this solution is applied in a film form on a substrate at a high temperature, and after cooling and solidifying. . A method for producing a porous membrane, which comprises extracting and removing the organic solvent remaining in the membrane solidified by immersion in an extraction bath, and drying the membrane.