JPS5935644B2 - Separation membrane manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a separation membrane.

The separation membrane in the present invention refers to a membrane-like material used to separate inorganic and organic solids contained in a liquid or gas.

Conventionally, porous structures have been created in thermoplastic resin membranes using various methods, and the pores communicating from one side to the other allow liquids or gases to pass through, thereby separating the inorganic and organic solids contained therein. Attempts are being made. Such separation membranes are mainly used to separate inorganic and organic solids dispersed in water, but thermoplastic resins are generally hydrophobic and therefore difficult to penetrate. There was a drawback that the separation effect was not sufficient. For this reason, conventional methods for imparting hydrophilic properties to separation membranes include, for example, incorporating surfactants into membrane-forming resins, impregnating membrane-like materials with surfactants, and adding hydrophilic resins to membrane-forming resins. kneading, impregnating a membrane-like material with a solution of hydrophilic resin,
Surface treatments such as corona discharge treatment and flame treatment are performed on film-like materials. However, when kneading a surfactant into a film-forming resin and molding a film-like product, the surfactant is easily decomposed by the heating during molding, and there is a risk that it will not be highly hydrophilic. It requires drying of the solvent used, and has the drawback that pores are likely to become clogged and thermal shrinkage occurs during heating for drying. Furthermore, toxicity due to leaching of the surfactant poses a sanitary problem, which has the disadvantage that its uses are limited. In addition, when a hydrophilic resin is kneaded into a film-forming resin, it has poor compatibility and tends to cause poor dispersion, and when it is impregnated into a film-like material, it has the same drawbacks as the surfactant described above. Ta. Furthermore, when a film-like material is subjected to corona discharge treatment, large pores are formed due to sparks, and when flame treatment is applied, mechanical strength decreases and thermal shrinkage tends to occur. The present invention aims to eliminate the above-mentioned drawbacks and provide a separation membrane that has excellent water permeability, high mechanical strength, and excellent separation performance for inorganic or organic solids in liquids or gases. .

The gist of the present invention is to stretch a film-like material molded from a mixture of a thermoplastic resin and a finely powdered inorganic material, to create a porous structure in the film-like material, and to treat it with a low-temperature prism of a gas containing oxygen. A method of manufacturing a separation membrane is provided.

Next, the method for manufacturing the separation membrane of the present invention will be explained in more detail.

The film-like material in the present invention is molded from a mixture consisting of a thermoplastic resin and a finely powdered inorganic substance.

Thermoplastic resins are mainly used to form films, such as olefin resins, styrene resins, polyamide resins,
Polyacetal resins, polyacrylate resins, vinyl chloride resins, vinyl acetate resins, polyester resins, thermoplastic urethane resins, thermoplastic epoxy resins, etc. are suitable, and these resins may be used alone or , may be used in combination. The finely powdered inorganic substance is a necessary component to create a porous structure when the film-like material is stretched, and includes, for example, silica powder, diatomaceous earth powder, calcium carbonate powder, mica powder, graphite powder, and barium sulfate powder. , calcium hydroxide powder, magnesium hydroxide powder, barium hydroxide powder, etc. are suitable, and these inorganic substances may be used alone or in combination.

The particle size of the finely powdered inorganic material is preferably 20μ or less, optimally 5μ or less. In addition, the amount used is 5 to 300 parts by weight per 100 parts by weight of the thermoplastic resin, since this does not cause any trouble in forming a membrane-like product and also improves the conditions for the formation of a porous structure by stretching. The amount is preferably from 10 to 200 parts by weight. For molding the film-like material, conventional molding methods such as extrusion molding, roll molding, inflation molding, hot press molding, etc. can be employed.

The thickness of the film-like material is preferably about 0.2 nm to 5.0 nm in relation to the next stretching step. In the present invention, the film-like material is stretched to create a porous structure in the film-like material.

The stretching temperature is preferably selected to be lower than the melting temperature of the thermoplastic resin forming the membrane and suitable for producing molecular orientation; for example, when high-density polyethylene resin is used, A temperature of 110°C is preferred, and a temperature of 80 to 130°C is preferred when polypropylene resin is used. The stretching direction may be uniaxial or multiple axial directions, but if it is stretched in two axial directions, vertical and horizontal, the hole shape will have the same directionality as in uniaxial stretching. This is preferable because it eliminates the need for The stretching ratio is
In order to generate a porous structure uniformly throughout the membrane,
It is preferable that the area magnification is 1.2 times or more. The porous structure produced in a membrane-like material by stretching is a structure in which fine pores are densely formed throughout the surface and inside of the membrane-like material, and the resin forming the pore walls has fibrous structure. There are many things that exist. Such a structure can be confirmed by observation using an electron microscope. When the thermoplastic resins forming the film-like material are two or more resins that have low compatibility with each other, a structure in which many thin layers having a porous structure are laminated and integrated by stretching, that is, a porous laminate is formed. can produce a shaped structure.

This is caused by the low compatibility of two or more types of thermoplastic resins and the synergistic effect of the behavior of each component of the finely powdered inorganic substance when it is stretched, and can be observed using an electron microscope. It can be confirmed that a porous structure and a laminated structure are formed in the cross-sectional direction of the membrane-like material. A membrane material that has a porous structure due to stretching has the property of permeating liquid or gas because the pores that make up the porous structure communicate from one side of the membrane material to the other at various locations. The pore diameter also differs depending on the stretching ratio, and generally speaking, the pore diameter becomes larger as the stretching ratio increases.
The membrane has a pore size of approximately 0.01μ to 20μ, which has the property of blocking the passage of inorganic or organic solids larger than the pore diameter.Therefore, the membrane material has no performance as a separation membrane even as it is. However, because the membrane is made of thermoplastic resin, it has poor affinity for water, resulting in only low water permeability and poor separation membrane performance. .

For this reason, although separation membranes are often used to capture and remove fine inorganic or organic solids dispersed in water, their low water permeability makes them unsuitable for this purpose. Only those with certain defects are allowed.
In the present invention, in order to improve the water permeability of the membrane-like material, low-temperature plasma treatment is performed.

In the present invention, low-temperature plasma refers to highly ionized gas generated by high-frequency discharge, glow discharge, etc. under reduced pressure, and whose temperature is lower than that of electrons. The low-temperature plasma treatment is performed by supplying a film-like material that has a porous structure through stretching to a low-temperature plasma generator, placing it in a low-temperature plasma atmosphere, and bringing the film-like material into contact with the low-temperature plasma. In the present invention, the gas to be turned into low-temperature plasma is a gas containing oxygen.
A gas containing oxygen is a gas containing oxygen molecules or oxygen atoms, such as oxygen gas, air, carbon dioxide gas,
Water vapor, ozone, etc. are preferably used, and these may be used alone or in combination. The pressure of the gas that is turned into low-temperature plasma is 0.001 mmHg to 20 mmH.
g, optimally between 1 mmHg and 10 mmHg. Processing time is 1 to 10
Approximately one minute is suitable. The reason why the water permeability of the film-like material is improved by low-temperature plasma treatment is that the low-temperature plasma of oxygen-containing gas oxidizes the surface of the pores forming the porous structure, and carbonyl groups are , hydrophilic groups such as hydroxyl groups are introduced to improve water permeability, and the ashing effect of low-temperature plasma oxidizes the fibrous resin that forms the walls between adjacent pores in the porous structure. This is due to the fact that the pore diameter is increased by cutting, and the water permeability is improved by increasing the communication between the pores.

Such changes in the porous structure not only occur on the surface of the membrane but also occur almost uniformly throughout from one side to the other, so they greatly contribute to improving water permeability. It is something. According to the present invention, a separation membrane is produced which has high hydrophilicity and excellent water permeability, has high mechanical strength by stretching, and has excellent separation performance for inorganic or organic solids in liquid or gas. be able to.

Such a separation membrane is suitable for use in stream applications, storage battery separators, and the like. Examples of the present invention are described below.

Example 1 A mixture consisting of the above-mentioned components was kneaded for about 15 minutes while heating with an open roll to form a film-like product with a thickness of 500 μm.

Next, the film-like material was maintained at 90° C. and stretched in two axes (longitudinal and transverse directions) at an area magnification of 16 times. When the film-like material after stretching was observed with an electron microscope, it was found that 0.0
producing a porous structure consisting of pores with a pore size of 1 μ to 20 μ;
It was also found that many of the resins forming the pore walls were fibrous. The membrane was installed in a water permeability measurement device, and water pressure of 3k9/Cd was applied from one side of the membrane to measure water permeation. Low-temperature plasma treatment was performed for 5 minutes in an oxygen gas atmosphere of 0.3 m and 7 nHg at an output of 100 watts.

When the film-like material after the low-temperature plasma treatment was observed using an electron microscope, it was found that in many cases, the fibrous resin forming the pore walls had been cut and the pore diameter had expanded. When the water permeability of the film-like material was measured in the same manner as above,
It improved to 35g/CrA・min.

The membrane-like material was suitable for use as a separation membrane. Example 2'' A mixture consisting of the above components was kneaded with an oven roll heated to 170°C for about 15 minutes, and then put into the cylinder of an extruder and passed through a flat mold attached to the tip of the extruder. The mold then molds the film-like material into 1
The film was maintained at 05° C. and stretched in two axial directions, the longitudinal direction and the transverse direction, at an area magnification of 12 times.

When the film-like material after stretching was observed using an electron microscope, it was found that
It has a porous structure with a pore size of 0.01 to 10μ,
It was also found that many of the resins forming the pore walls were fibrous. The water permeability of the membrane material, measured in the same manner as in Example 1, was 0g/Cni·min under a pressure of 3 kg/CrA.

A plasma output of 100 watts and an oxygen gas of 0.5 watts were applied to the film-like material.
Low temperature plasma treatment was performed for 7 minutes in a 5 mmHg atmosphere. When the film-like material after the treatment was observed using an electron microscope, it was found that in many cases, the fibrous resin forming the pore walls had been cut and the pore diameter had expanded.

The water permeability of the membrane-like material was 28 m1/Cwl·min, and it was suitable for use as a separation membrane. Example 3 A mixture of the above components was heated to 180°C in an inflation molding machine, extruded into a cylindrical shape, and further blown to increase the stretching ratio in the vertical and horizontal directions to 3 times. It was molded to look like this.

The water permeability of the membrane obtained by cutting this open is 3 kg/Cd.
The pressure was 0 m1/Cni·min. To the film-like substance,
Plasma output 100 watts, oxygen gas 0.2 m7! LH
A low temperature plasma treatment was performed for 12 minutes in a g atmosphere. When the treated film was observed using an electron microscope, it was found that the fibrous resin forming the pore walls had been cut and the pore diameter had expanded in many cases. The water permeability of the membrane-like material was 30 m1/Cd·min, and it was suitable for use as a separation membrane.

Claims (1)

[Scope of Claims] 1. A film-like material formed from a mixture of a thermoplastic resin and a finely powdered inorganic substance is stretched to create a porous structure in the film-like material, and then a porous structure is created in the film-like material, and the film-like material is heated with a low-temperature plasma of a gas containing oxygen. A method for producing a separation membrane, the method comprising: 2. The method for producing a separation membrane according to claim 1, wherein the stretching ratio is 1.2 times or more in terms of area ratio. 3. The method for producing a separation membrane according to claim 1 or 2, wherein the oxygen-containing gas is oxygen gas. 4. The method for producing a separation membrane according to claim 1 or 2, wherein the oxygen-containing gas is air. 5. The method for producing a separation membrane according to claim 1 or 2, wherein the oxygen-containing gas is carbon dioxide. 6. The method for producing a separation membrane according to claim 1 or 2, wherein the oxygen-containing gas is water vapor. 7. The method for producing a separation membrane according to claim 1 or 2, wherein the oxygen-containing gas is ozone.