JPS5830335B2 - Manufacturing method of microporous resin membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a microporous resin membrane having an asymmetric porous structure.

In general, microporous membranes have unique uses that utilize micropores, such as ultrafiltration membranes and electrolytic diaphragms.

The following three points are particularly required for the performance of these membranes.

(1) It has a uniform pore diameter of several tens of microns or less.

(2) Has high permeability (water permeability, air permeability).

(3) It has strength, stability (water resistance, heat resistance, chemical resistance), and has a long membrane life.

The conventional manufacturing method for microporous membranes involves dissolving resin in a mixed solvent of a good solvent and a poor solvent, and then pouring this mixed solution and drying it to generate micropores (hereinafter referred to as the "drifting method"). ) are the most common.

The membrane obtained by this flowing method has a felt-like network structure and has uniform pore diameters.

However, the porosity of the membrane is usually 50-80 vo1%
The transmission performance is not sufficient.

The purpose of the present invention is to provide a sufficiently useful resin membrane that is free from such drawbacks, that is, has a uniform pore distribution, and has improved porosity and permeability due to its asymmetric porous structure. However, by dissolving vinyl chloride resin and polyalkylene glycol in one or more kinds of solubilizers I),
It has an asymmetric porous structure characterized in that after the obtained solution is poured out, it is immediately immersed in a solution (ml) that is a poor solvent for vinyl chloride resin and a good solvent for polyalkylene glycol without going through a drying process. It consists in a method for manufacturing a microporous resin membrane.

The vinyl chloride resin (hereinafter abbreviated as rVcRJ) of the present invention includes polyvinyl chloride (PVC), vinyl chloride copolymer, and blends of these and other resins. As the vinyl chloride copolymer, For example, there are binary or ternary copolymers of vinyl chloride and vinyl acetate, vinylidene chloride, ethylene, acrylic acid, etc.

In addition, polyalkylene glycol (hereinafter abbreviated as IPAGj) includes polyethylene glycol (PEG).
, polypropylene glycol (PPG), or copolymers thereof.

Examples of the solvent (1) include dimethylformamide, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, and a mixed solvent of acetone and benzene. Examples of the solvent include water, alcohol, ester, aldehyde,
Mixed solvents of these are used.

Note that in order to control the solubility of PAG, it is also effective to add a metal salt or an inorganic acid.

Furthermore, regarding the manufacturing conditions of the method of the present invention, VCRlPAG
Although the molecular weight of PEG is not particularly limited, for example, when PVC with a polymerization degree of 1000 is used, the molecular weight of PEG is preferably 200 to 100.

Preferred PAG depending on the type of matrix and degree of polymerization
The type, molecular weight, solvent, etc. of each are different.

For example, the mixing ratio of PvC and PEG can be arbitrarily changed within a range that allows sufficient dissolution in the solvent.

However, in order to obtain practically meaningful permeation performance, a certain level of porosity is required in the membrane, and for this reason, PEG/PV
There is a minimum limit on the ratio of C.

In addition, in order to have practical film strength, the matrix (p
vc) content needs to be increased, and for this reason, PEG
There is a maximum limit for the ratio of /PVC.

Therefore, micropores can be generated by changing the PEG/PVC ratio under conditions that allow film formation, but preferably PEG/PVC
/PVC ratio is 1/10 to 10/1.

The solvent for immersion has been described above, but water is preferred from a practical standpoint.

The immersion temperature is suitably below the softening point of the matrix.

The membrane obtained as described above has an asymmetric porous structure, as shown in FIGS. 2 and 4 (cross-sectional structure by scanning electron micrograph, magnified at 250 times).

The corresponding surface structures of these membranes are shown in Figures 1 and 3, respectively.
As shown in the photo (2500 times magnification), a membrane having fine pores with a pore diameter of 10 μm or less is obtained.

The asymmetric porous structure referred to here refers to the anisotropic membrane used in reverse osmosis membranes.
(anisotropic membrane or asymmetric membrane).

That is, the membrane surface has a dense layer (usually 5 kin 1 aye
r ), the inside of the membrane is a porous layer (usually porous
1ayer).

At this time, the porous layer has a cylindrical structure as shown in FIGS. 2 and 4.

When observed in more detail, the cylindrical structure collapses in areas closer to the surface and shifts to a nearly mesh-like structure, which is connected into a dense layer.

Conventionally obtained membranes have a network porous structure over the entire surface, as described in Japanese Patent Application No. 48-139379, and do not have the above-mentioned asymmetric porous structure.

This difference is due to the difference in the polymer aggregation process in the solution, depending on whether the prepared solution is immersed in the solvent without going through the drying process or after the drying process as described above. .

Hereinafter, the features of the present invention will be specifically explained using an example in which PvC and PEG are dissolved in a dimethylformamide solvent, aborted, and immersed in water.

First, PVC and PEG as a matrix are dispersed in a relatively microscopic manner through the immersion treatment process.

This is the most basic and important point of the invention.

That is, it means that the diameter of the generated micropores is uniform and fine.

Second, membrane formation can be easily performed by miscarriage, and industrial membrane formation is possible.

By changing the miscarriage conditions, membranes with arbitrary predetermined structures can be obtained, and the reproducibility of membrane performance is good.

Third, since PEG is water-soluble, P
The vC is solidified and the PEG is extracted.

Fourth, since PEG is a polymer (including oligomers), it has a moderate viscosity, and it is thought that a "fluctuation phenomenon" between a dissolved state and an agglomerated state occurs at the interface between PVC and PEG. It will be done.

This facilitates the formation of a stable PVC matrix that cannot be obtained simply by using poor solvents.

Fifth, PVC is useful as a material with high strength and stability.

Sixth, the asymmetric porous structure, unlike the conventional mesh-like structure, can have an extremely high porosity, thereby aligning the conventional maze-like permeation path and improving permeability.

Seventh, unlike conventional filtration membranes, it has a high porosity, so it is useful as a new membrane material in which the micropores are filled with a desiccant or the like.

Applications include, in addition to filtration membranes, packaging materials that take advantage of their air permeability, membranes filled with desiccant materials that take advantage of their high porosity, battery separators, and diffusion dialysis membranes for use in artificial kidneys.

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

In the examples, the membrane pore diameter was calculated from a scanning electron micrograph of the surface structure, and the permeation amount was calculated based on a differential pressure of 0.5 kg/cr.
In the case of A, the values are expressed per unit time and unit area.

The porosity was calculated from the amount of water contained in the membrane and expressed as a volume percentage of space.

In the following examples, parts expressed as percentages are by weight.

Example 1 7 parts of PVC (degree of polymerization 1000), PEG (molecular weight 600)
) and 72 parts of dimethylformamide to prepare a homogeneous solution.

This solution was poured onto a 40×40 CrrL glass plate in a 20° C. constant temperature bath, and immediately immersed in 50° C. water to obtain a film.

The obtained membrane has a thickness of 300 μm and a water permeability of 1.1 cc 7 mm.
/ crti, the porosity was 89%, and when observed with a scanning electron microscope, the membrane pore diameter was less than o, iμ, and the surface structure was as shown in Figure 1.
The cross-sectional structure was as shown in FIG.

This membrane separated an NBR emulsion with a particle size of 0.05μ.

In addition, if the solvent is volatilized at 20°C for 30 minutes under the same conditions, the cross-sectional structure becomes a network, and the porosity becomes 8.
This decreases to 1%, and the water permeability also decreases.

Example 2 9 parts of PVC (degree of polymerization 1000), PEG (molecular weight 600)
) and 55 parts of dimethylformamide to prepare a homogeneous solution.

This solution was poured onto a 40×40 (m) glass plate in a constant temperature bath at 20° C., and immediately immersed in water at 50° C. to obtain a film.

The obtained membrane has a thickness of 250μ and a water permeability of 0.7cc 7m1
yt/crii, porosity was 85%, and when observed with a scanning electron microscope, the membrane pore diameter was 0.1 μ or less, the surface structure was as shown in FIG. 3, and the cross-sectional structure was as shown in FIG. 4.

This membrane separated an NBR emulsion with a particle size of 0.5μ.

If the solvent is evaporated for 30 minutes under the same conditions after a miscarriage, the cross-sectional structure becomes a network, the porosity decreases to 55%, and the amount of water permeation decreases.

Example 3 A miscarriage was carried out in the same manner as in Example 1, and the membrane was immediately immersed in ice water at 0° C. to obtain a membrane.

The obtained membrane had a thickness of 300μ, a pore diameter of 0.5μ, and a water permeability of 1.
．． It had a performance of 7 cc/f/cni and a porosity of 91%.

Example 4 In the same manner as in Example 1, the membrane was poured into a 50° C. constant temperature bath and immediately immersed in room temperature water to obtain the membrane.

The obtained membrane had a thickness of 150μ, a pore diameter of 0.7μ, and a water permeability of 2.
．． It had the performance of Qcc/Y/crrt and porosity of 93%.

Example 5 In the same manner as in Example 1, abortion was carried out in a 5° C. constant temperature bath, and the membrane was immediately immersed in room temperature water to obtain a membrane.

The obtained membrane had a thickness of 200μ, a pore diameter of 0.1μ or less, a water permeability of 0.2CC/acid/crA, and a porosity of 90%.

Example 6 A membrane was obtained in the same manner as in Example 1 except that PEG with a molecular weight of 10,000 was used.

The obtained membrane had a thickness of 350μ, a pore diameter of 0.1μ or less, a water permeability Q of 3 cc/min/c4, and a porosity of 87%.

Example 7 A membrane was obtained in the same manner as in Example 1, except that a vinyl chloride-vinyl acetate copolymer (manufactured by Nippon Zeon) having a vinyl acetate content of 20% was used instead of pvcO.

The obtained membrane had a thickness of 400μ, a pore diameter of 0.1μ or less, a water permeability of 2 cc/cm/crA, and a porosity of 88%.

[Brief explanation of the drawing]

Figures 1 and 3 are scanning electron micrographs (2500x) of the surface structure of the microporous resin film obtained by the method of the present invention;
2 and 4 each show the cross-sectional structure of the corresponding film taken in the same photograph (250x magnification).

Claims (1)

[Claims] 1. After dissolving vinyl chloride resin and polyalkylene glycol in one or more solvents and licking the resulting solution, immediately dissolve the vinyl chloride resin in a poor solvent and the polyalkylene glycol in a good manner without going through a drying process. A method for producing a microporous resin membrane having an asymmetric porous structure, which comprises immersing the membrane in a solvent.