JPS5815501B2 - Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing porous synthetic resin bodies, such as porous films or perforated plates, exhibiting high flux from synthetic resin emulsions.

The method for producing a synthetic resin perforated plate is to obtain a powdered resin in advance by emulsion polymerization, etc., form a powder layer with this resin, and then heat soften or heat press to fuse the powder particles appropriately. A method of forming a perforated plate having a continuous pore structure from one surface to another surface, that is, a capillary-type pore structure, is known.

However, the above method requires a drying process to obtain powdered resin, and the pore structure of the perforated plate varies depending on the selected particle size, heat softening, or heat compression conditions, making it easier to obtain the desired flux using simple operations. The disadvantage is that it is difficult to obtain a perforated plate as shown.

Therefore, the present invention does not use a dry powdered resin as in the conventional method described above, and therefore does not use heat softening or heat compression, but directly produces a high flux resin from a synthetic resin emulsion obtained by emulsion polymerization. It is an object of the present invention to provide a new and useful manufacturing method capable of obtaining a synthetic resin porous body exhibiting the following properties.

In other words, this invention cleverly utilizes the property of a synthetic resin emulsion to coagulate with an electrolyte, and also swells the emulsion particles by absorbing a medium that exhibits an appropriate swelling property and displaces the medium with water. This technique makes good use of volumetric shrinkage, and is made by contacting a synthetic resin emulsion with a metal salt that coagulates the synthetic resin emulsion with an electrolyte, dissolved in a medium that exhibits appropriate swelling properties for the polymer of the emulsion particles, and forming an emulsion. A part of the particles is fused to form a porous coagulate due to swelling of the particles, and then, by replacing at least the above-mentioned medium in this coagulate with water, the volume shrinkage of the fused emulsion particles makes the porous coagulate microscopic. It is characterized by producing large cracks and drying without collapsing the void structure.

The synthetic resin emulsion used in this invention can be easily produced by a conventionally known emulsion polymerization method.

For example, 0.05 to 5% of a polymerization decomposition agent such as ammonium persulfate or hydrogen peroxide;
A predetermined monomer is dispersed in an aqueous solution containing 0.05 to 10% of an emulsifier such as polyethylene glycol alkyl phenol ether, and polymerization is initiated by heating to usually 30 to 100°C, and the desired temperature is maintained at a predetermined temperature. The polymerization rate is

Thereafter, the resulting emulsion is filtered to remove some coagulated matter, and if necessary, a small amount of a surfactant is added as a storage stabilizer to obtain a synthetic resin emulsion.

The concentration of the polymer (solid content) in this emulsion is preferably about 10 to 60% by weight; if it is lower than about 10%, it is difficult to obtain a synthetic resin porous body exhibiting the desired flux; It becomes sensitive to high mechanical shearing forces, has poor storage stability, and tends to solidify early.

Since the particle size of the emulsion affects the quality, especially the pore diameter, of the porous synthetic resin, it is determined appropriately by changing the type and concentration of the emulsifier, the concentration of the initiator, the polymerization temperature, the stirring speed, etc.

Depending on the type of metal salt and medium used for electrolyte coagulation, the emulsion size will usually range from 0.01 to 1 μm to about 0.5 μm! A porous body having an arbitrary pore diameter of z or less can be obtained.

The monomer used in the production of this synthetic resin emulsion is preferably a polymer whose glass transition temperature is higher than room temperature, particularly preferably 50°C or higher, from the viewpoint of producing or using the porous body. Choose what you can give.

Specifically, monomers such as methacrylic acid ester (the alkyl group in the ester residue has 1 to 4 carbon atoms), styrene, vinyl chloride, vinylidene chloride, ethylene, and other copolymerizable monomers that can be used in combination with these monomers are used. Examples include saturated monomers.

In materials such as natural rubber, which has a glass transition temperature below room temperature, particles fuse together during the process of replacing the medium in the porous coagulate with water and the subsequent drying process in the series of manufacturing processes of this invention. This results in a transparent or translucent synthetic resin body, making it difficult to obtain the desired porous body.

Moreover, when used, the porous material easily fuses together, and when the porous material is used, for example, as a filtration membrane, it tends to become compacted by water pressure, gas pressure, etc. during use, and its permeability tends to decrease.

However, especially when the above manufacturing process is carried out at a temperature lower than the glass transition temperature and the use temperature is lower than the above temperature, such problems are rare, and even polymers with a glass transition temperature below the above room temperature are effective. Available for

In this invention, in the above synthetic resin emulsion,
A metal salt that coagulates the synthetic resin emulsion with an electrolyte is dissolved in a medium having an appropriate swelling property for the polymer of the emulsion particles and brought into contact with the polymer.

The metal salts used here include a wide range of conventionally known electrolyte coagulants, such as monovalent or divalent coagulants such as sodium acetate, zinc acetate, calcium nitrate, magnesium chloride, sodium sulfate, and zinc ethylenediaminetetraacetate.
Typical examples include metal salts with higher valences.

Further, the medium having an appropriate degree of swelling for the polymer is one whose degree of swelling is in the range of about 1.01 to 50, preferably 2 to 10.

However, the above swelling degree is obtained by cutting 1.5 g of the polymer obtained by drying the synthetic resin emulsion into approximately 0.1 g pieces and placing them in an Erlenmeyer flask, adding 50 g of medium to this, and keeping it at room temperature for 5 hours. After standing, the contents were poured onto a NO4 Whatman filter paper and filtered, and the weight of the swollen polymer on the filter paper was measured to determine the ratio of the weight of the swollen polymer to the weight of the original sampled polymer. It is expressed.

Specific examples of media with such characteristics include organic polar media that dissolve at least one weight class or more in water, such as acetone, methyl ethyl ketone, methanol, isopropanol, butanol, dimethylformamide, tetrahydrofuran, and a portion of ethylene glycol. Examples include one or a mixture of two or more of the above, or a mixture of the above-mentioned medium and water. For organic polar media with a strong swelling effect, increase the proportion of water used to adjust the degree of swelling of the medium as a whole to within the above range. used.

The metal salt is brought into contact with the synthetic resin emulsion in a state in which it is dissolved in a concentration range of 0.5 weight to saturated solubility in the medium.

When obtaining a porous filtration membrane using a synthetic resin porous body, the contacting means is, for example, a roll coater after adding various thickeners to the synthetic resin emulsion as necessary.
, cast onto a glass plate or other sheet-like material with a smooth or rough surface by a conventional coating method such as knife caulk, spray coater, extrusion or dipping,
This may be immediately immersed for a short time in a medium bath in which the metal salt is dissolved.

The medium absorbed into the emulsion in the above contacting step swells the emulsion particles and causes some of the particles to fuse together.

The emulsion is then solidified under the action of the metal salt in the above state.

In the end, a porous solidified product is formed in which a portion of the emulsion particles are appropriately fused.

In the present invention, it is necessary to form a porous coagulate by appropriately fusing a portion of the emulsion particles as described above, and this coagulate can be obtained by using a medium exhibiting the above swelling degree and a metal salt.

In other words, if a medium that dissolves the emulsion polymer well is used, most of the emulsion particles will essentially fuse together, making it impossible to obtain the desired porous body; Again, the degree of fusion would be too large, and in the subsequent step of replacing the absorbed medium with water, the volume of the emulsion particles would shrink too much, resulting in large cracks in the coagulate, which is not what is desired from both points of view. Porous bodies cannot be obtained.

On the other hand, if the swelling property is too low, the degree of fusion will be low, resulting in a mere porous solidified material, and the product obtained in the final drying step will be granulated or a discontinuous porous material.

In this invention, the medium contained in the above-mentioned porous coagulum is then replaced with water.

The replacement method may be carried out by immersion in water or spraying with water.

During this substitution, the metal salts contained in the porous coagulate will also be removed, but the purpose of this step is to replace the medium with water, and the medium in the coagulate is usually in an equilibrium state. Do this until

The equilibrium state is considered to be when the content of the organic polar medium having a swelling effect contained in the immersion water or the water after spraying reaches a certain level.

When the medium is removed, the emulsion particles that were fused and swelled due to the replacement of the medium and water contract in volume, and as a result of this contraction, small cracks occur between the particles or inside the particles. However, in the end, the porous solidified product as a whole has a void structure consisting of a porous structure between particles and the above-mentioned crack structure, resulting in a porous body exhibiting a higher flux than a mere porous structure between particles.

Moreover, since the above-mentioned minute cracks mainly occur between the fused particles which are limited to the appropriate ratio, there is no fear that the crack structure will become too large and deviate from the original role of the porous body.

Next, the porous solidified material having the above-mentioned pore structure is washed with water as necessary to remove residual metal salts, and then the above-mentioned pore structure is disintegrated at room temperature or at a temperature lower than the glass transition temperature of the polymer. When a porous coagulated material is formed on a glass plate as described above for the purpose of obtaining a filtration membrane that dries quickly, it may be peeled off from the glass plate and dried before or after washing with water.

The above peeling can be easily performed.

The synthetic resin porous body thus obtained is an opaque white porous body, and in the case of a thin film filter, it exhibits a high water permeation flux of about 0.1 m, 17 min.atm-i or more.

As detailed above, the present invention does not use dry powdered resin as in the conventional method, but instead obtains a synthetic resin porous body exhibiting high flux directly from a synthetic resin emulsion obtained by emulsion polymerization. This method makes good use of the properties of a synthetic resin emulsion that coagulates with an electrolyte, the swelling of the emulsion particles by absorbing a medium that exhibits appropriate swelling properties, and the volumetric contraction of the emulsion particles by replacing the medium with water. be.

According to the method of the present invention, it is possible to easily obtain a synthetic resin porous body exhibiting a desired flux reliably with ease of operation, and it has many advantages as an industrial manufacturing method over the above-mentioned conventional methods.

The porous body thus obtained can be widely applied to materials such as filtration membranes and other films, and various porous plates requiring air permeability or water permeability by utilizing its properties.

Next, the present invention will be explained in more detail with reference to Examples.

In addition, in the following, the term ``related'' indicates the weight related.

Example 1 100 parts of a monomer mixture consisting of 55 parts of methyl methacrylate and 45 parts of ethyl acrylate was mixed with 0.5% of ammonium persulfate and 5% of an emulsifier (Neugen EA160, manufactured by Dai-Kogyo Seiyaku Co., Ltd.). Disperse in 150 parts of an aqueous solution, start polymerization at 70°C with stirring, and maintain at about 75°C for 5 hours to complete polymerization.

After completion of polymerization, some coagulates contained in the emulsion are removed by filtration to make the emulsion almost uniform in particle size.

The resulting synthetic resin emulsion has a nonvolatile solid content of 43
%, the average particle size of the particles was 0.05μ.

After this emulsion was cast onto a glass plate to a thickness of about 100 μm, it was immediately immersed in a medium made by dissolving 20% calcium acetate (water: methyl ethyl ketone - 7:3, degree of swelling: about 10) for about 5 minutes. The particles are partially fused to form a porous solidified product.

This coagulated material is immersed in pure water, and the absorbed medium is replaced with water until an equilibrium state is reached.

Next, the coagulated material is peeled off from the glass plate, washed repeatedly with water to sufficiently remove the metal salts, and then dried with warm air at room temperature or at a temperature below the glass transition temperature (50'C) of the polymer. The resulting synthetic resin porous body has a pore diameter of approximately 0.1μ or less, and is approximately 1.5ml! /min・atrrr7 water permeation flux is shown.

The pore structure of this porous material is also shown in the attached enlarged photo (magnification: 2
8800), it consists of a porous structure and a crack structure between particles.

Example 2 About 1 part of sodium alginate was added to the synthetic resin emulsion of Example 1, and then cast onto a polyester film to a thickness of about 80 μm.

Next, it is immediately immersed for 3 minutes in a medium prepared by dissolving approximately 20% calcium chloride (water: acetone - 8:2; degree of swelling: 7) to form a porous coagulate in which some of the particles are fused together. shall be.

The coagulated material is immersed in pure water and the absorbed medium is replaced with water until an equilibrium state is reached.

At this time, metal salts are also removed. After that, it is peeled off from the polyester film and dried at room temperature.

The synthetic resin porous body thus obtained is approximately 0.04μ
It has the following pore diameter, 0.5 to 1.0 mA/min・atm-
cr? i, shows the water permeation flux.

Example 3 Methyl meccrylate 80%, butyl acrylate 15%,
A monomer mixture consisting of hydroxyl ethyl acrylate and 5 parts was emulsion polymerized in the same manner as in Example 1 to obtain a synthetic resin emulsion with an average grain size of 0.1 μm and a nonvolatile solid content of 30%.

This emulsion was applied to a thickness of about 150μ on a glass plate, and immediately immersed in a medium (methanol, swelling degree 5) prepared by dissolving about 20% zinc acetate for about 5 minutes to remove some of the emulsion particles. to form a porous solidified product.

Water is sprayed onto the coagulated material to replace methanol in the coagulated material with water until an equilibrium state is reached, and at the same time, metal salts are also removed.

Finally, the coagulated material is peeled off from the glass plate and dried at room temperature to form a porous synthetic resin body.

The pore diameter of the obtained synthetic resin porous body was 0.02μ, and the water permeation flux was 0.02μ. i-~0.5 m17 min.atm-d.

[Brief explanation of the drawing]

The drawing is an enlarged photograph (magnification: 28,800) showing the pore structure of the synthetic resin porous body according to Example 1.

Claims (1)

[Claims] 1 A synthetic resin emulsion is brought into contact with a metal salt that coagulates the synthetic resin emulsion as an electrolyte, dissolved in a medium that exhibits an appropriate swelling property for the polymer of the emulsion particles,
The swelling of the emulsion particles results in a porous coagulation in which some of the particles are fused, and then at least the above-mentioned medium in the coagulated substance is replaced with water, whereby the volume of the fused emulsion particles shrinks to form a porous coagulation. A method for producing a synthetic resin porous body exhibiting a high flux from an emulsion, which is characterized by producing minute cracks and drying without disintegrating the pore structure.