JPS63245447A - Production of porous article - Google Patents

Abstract

PURPOSE:To obtain a uniform porous article having no closed cell in a high yield, by curing a resin soln. contg. a curing agent, a catalyst and a cell forming agent uniformly dispersed therein under pressure and then removing the cell forming agent. CONSTITUTION:A curing agent (e.g., formaldehyde), a catalyst (e.g., sulfuric acid) and a cell forming agent (e.g., wheat starch) are added to an aq. soln. of a synthetic resin such as a polyvinyl formal resin, a phenolic resin, etc. The mixture is stirred to disperse them uniformly, thus obtaining a resin soln. The resin soln. is cast into a desired mold, placed in a high-pressure reactor such as an autoclave and pressurized to at least 1.0kg/cm<2> through air or steam to obtain a cured product. The product is washed with water or shower to remove the cell forming agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a porous body that suppresses the generation of bubbles other than those caused by a pore-forming agent and obtains a homogeneous porous body.

[Conventional technology]

In various porous material manufacturing industries, manufacturing methods using pore-forming agents produce more homogeneous and finer pores than other foaming methods, and the resulting pores are continuous, so they can be used as mere cushioning materials, It is widely used not only as a buffer material, but also as a filter material, liquid absorbent material, and research material.

Although the above production methods differ depending on the type of resin used as the base material, the basic reaction format is as shown below.

That is, a resin solution (undiluted solution) of a synthetic resin in which fine powder or emulsion as a crosslinking agent, a catalyst, and a pore-forming agent are uniformly dispersed is heated to complete the reaction, and then the above-mentioned process is carried out by washing with water, mechanical washing, etc. This removes pore-forming agents such as fine powder and emulsions.

[Problem that the invention seeks to solve]

In the conventional method described above, a stock solution and a crosslinking agent are used.

When mixing the catalyst or pore-forming agent, mechanical stirring is used, which tends to entrain air, which becomes air bubbles in the reaction system liquid and remains as air bubbles in the product even after the reaction, but the volume ratio is high. Product quality.

This method has the drawback of decreasing yield or performance. In particular, when applied to filtration or polishing applications, this could lead to serious defects as a product, placing a great burden on the inspection process.

In order to prevent the above-mentioned adverse effects, when pouring the stock solution into the mold, slit-shaped casting holes are used to eliminate the pores.
Alternatively, methods such as using a means of depressurization to float and eliminate internal air bubbles have been taken, but this method is less effective and extremely insufficient if the solution has a high viscosity or the liquid tank is deep. Furthermore, large-diameter pores are relatively easy to eliminate, but small-diameter bubbles are difficult to eliminate.
For example, bubbles smaller than l*m are extremely difficult to eliminate.

The present invention was made in view of the above circumstances, and its purpose is to provide a method for producing a porous body in which closed cells other than continuous pores caused by a pore-forming agent, especially small-diameter cells, do not remain. do.

[Means for solving problems]

In order to achieve the above object, the present invention prepares a resin liquid of a synthetic resin in which a curing agent, a catalyst, and a pore-forming agent are uniformly dispersed, and hardens this resin liquid to create a cured body. This is a method for producing a porous body in which a pore-forming agent is removed and the residue left behind is made into pores, and the resin liquid is cured under pressure.

In other words, as a result of a series of studies conducted by the present inventors to achieve the above object, in manufacturing a porous body,
During the process of pouring the prepared synthetic resin liquid into a predetermined mold and allowing it to undergo a curing reaction, it is placed in a high-pressure reaction vessel such as an autoclave and pressurized, creating a porous structure in which closed cells other than open pores caused by the pore-forming agent remain. This invention was achieved by discovering that the body can be improved.

Next, this invention will be explained in detail.

The porous body to which this invention is applied refers to porous bodies made from polyvinyl formal resins, phenol resins, epoxy resins, vinyl acetate resins, acetate resins, etc., and porous bodies obtained by combining them. do. In other words, fine particles,
emulsion.

Specifically, a method of adding an emulsion of starch and its derivatives, polyethylene glycol 2 polypropylene glycol and its derivatives, stirring uniformly, curing the resin, and then removing the pore forming agent by means such as washing;
In other words, it means a porous body produced by a pore-forming agent extraction method. The porous body of the present invention has the following advantages (a) to (c) in terms of its properties compared to porous bodies manufactured by other manufacturing methods, that is, foaming methods.

(a) The pore diameter is uniform.

(b) Continuous pores.

(c) Porous bodies having micropores can be manufactured.

An example of an application that takes advantage of the above advantages is as a filtration material.

There are many pure industrial uses such as water-absorbing materials or abrasive materials with abrasive grains dispersed within the structure. However, in such industrial applications, closed cells other than the continuous pores inherent in the porous material tend to affect its properties. That is, in the case of continuous pores, the pores are continuous up to the surface of the porous body, whereas in the case of closed pores, the pores are distributed in the form of bubbles in the porous body. The presence of such closed cells disrupts the filtration characteristics in filter media applications, and in abrasive applications, the closed cell portion becomes a drawback and not only changes the polishing performance, but also impairs the overall strength of hard materials. Significantly lower.

According to the method of this invention, closed air bubbles mixed into the stock solution system are absorbed into the solution under pressure and are completely eliminated. Then, after the stock solution has passed the initial 1υ1 hardening period,
When the pressure is released at an appropriate stage, the closed cells that disappeared under the pressure will regenerate, but the air in these cells will be replaced by the already formed porous structure (which has undergone initial hardening and has rigidity). will not be destroyed. As described above, if the reaction system is kept under pressure for a short period of time after the start of the reaction until the initial curing, the residual air bubbles can be completely eliminated. Moreover,
Even if the depth of the formwork is greater than the surface area, the effect extends to the deeper layers.

The above pressurization method is performed by pouring the stock solution into a mold, placing it in a high-pressure container such as an autoclave, and pressurizing it using a gas such as enclosing compressed air or pressurized steam. The reaction is carried out at least until initial curing occurs. In this case, the pressurization condition is 1.0 kg/c
J or higher is preferable, especially 1.5 from the viewpoint of effectiveness.
It is preferable to set it between kg/ad and 15 kg/CIl+. If the pressure is less than 1.0 kg/cIA, the effect may be small and closed cells may not be sufficiently absorbed into the liquid. In addition, if mechanical pressure is applied, for example, using an extrusion press machine, instead of the above-mentioned pressure using gas, particles such as starch, which is a pore-forming agent, may be destroyed and the physical properties may differ from the intended ones. This is not preferable in some cases.

Next, examples will be described together with comparative examples.

[Example 1] Completely saponified polyvinyl alcohol 95 with a degree of polymerization of 1700
Dissolve 0g in warm water to make 15% by weight (hereinafter abbreviated as "%")
An aqueous solution of was prepared, and formaldehyde as a curing agent and sulfuric acid as a catalyst were added thereto, and the entire amount was converted into ION to prepare a reaction stock solution.

This is maintained at 55℃, inner diameter 3Qmmφ, depth 30Q
It was cast into a cylindrical mold of mm.

Next, place the cylindrical mold containing the reaction stock solution into a pressure cooker.
After heating and holding at 60°C for 2 hours under a pressure of 7 kg/cnl, the reaction was continued for 18 hours at a temperature of 60°C and normal pressure. After the reaction is complete, remove the reaction product from the mold and wash with water to remove excess formaldehyde.
Sulfuric acid and starch were extracted and removed to obtain a sponge-like porous elastic body.

[Example 2] The pressurization conditions were changed to 1.2 kg/ctA. A spongy porous elastic body was obtained in the same manner as in Example 1 except for the above.

[Comparative Example 1] The reaction was carried out for 200 hours in an atmosphere of 60° C. without applying pressure. A spongy porous elastic body was obtained in the same manner as in Example 1 except for the above.

The sponge-like porous elastic bodies obtained in Examples 1 and 2 and Comparative Example 1 were cut at the center, and the number of closed cells other than the continuous pores inherent in the porous bodies was measured. The results are shown in Table 1.

From Table 1: The porous material of Example 1 obtained under pressurized conditions has no closed cells and is extremely excellent. However, as in Example 2, the effect is insufficient under the low pressure condition of about 1.2 kg/cnl, but it is still superior to the comparative example product in which no pressurization is applied. In addition, Example 1
The porous body obtained in Example 2 was the same as that of Comparative Example 1 with no difference in other properties.

[Example 3] Water-soluble phenol resin aqueous solution (manufactured by Sumitomo Bakelite Co., Ltd.,
PR-961A,), completely saponified polyvinyl alcohol (hereinafter abbreviated as rPVAJ) with an average degree of polymerization of 1700
were added at a ratio of 1/10 to prepare a liquid. Next, formalin as a hardening agent, sulfuric acid as a catalyst, and wheat starch as a pore-forming agent were added to this, and the mixture was mixed and poured into the same mold as used in Example 1.

Next, put the mold containing the above reaction stock solution into a pressure cooker, and then
The reaction was carried out for 2 hours while maintaining the temperature at 50°C under a pressure of kg/cJ, and the obtained reaction product was taken out from the pressure cooker, and the reaction was continued for 18 hours at a temperature of 50°C and normal pressure. After the reaction was completed, the reaction product was washed with a shower to remove acid, formalin, and starch. After drying the reaction product, it was heated at 150°C under a nitrogen stream.
A synthetic resin porous body was obtained by curing.

[Comparative example 2] The reaction was carried out at 50°C for 20 hours without applying pressure.

A synthetic resin porous body was obtained in the same manner as in Example 2 except for the above.

From the synthetic resin porous bodies obtained in Example 3 and Comparative Example 2, 20 samples each with a cross section of 1 cm square and length of 1 Q cm were collected, and the number of bubbles per length of 1 Q cm and bending strength were measured. did. The results are shown in Tables 2 and 3.

(Margin below) *: Value of (highest value - lowest value).

Compared to Comparative Example 2, the synthetic resin porous body obtained in Example 3 has fewer bubbles and less variation in bending strength. That is, it is clear that the synthetic resin porous body obtained in Comparative Example 2 has a considerable decrease in strength because of the presence of many air bubbles.

[Example 4] In a 10% aqueous solution of completely saponified PVA with a degree of polymerization of 1700,
Abrasive grains made of fine silicon carbide powder having an average particle diameter of 5 μm were uniformly dispersed, and wheat starch as a pore-forming agent, a 37% formaldehyde aqueous solution as a crosslinking agent, and an appropriate amount of hydrochloric acid as a catalyst were added. Next, a phenolic resin initial condensate (manufactured by Sumitomo Bakelite Co., Ltd., PR-961A) was added to this to form a refined steel slurry stock solution, which was uniformly stirred and mixed using a stirrer.

The blending ratio of each of the above components is 30% PVA, 20% phenol resin, and 50% abrasive grains.

Example 1 The stock solution uniformly stirred and mixed in this way was
After pouring into a mold similar to that of
The reaction was continued for 2 hours while maintaining the temperature at 60°C under a pressure of nl. Furthermore, the pressure was returned to normal and the reaction was carried out at 60°C for 10 hours. Next, the reaction product was taken out from the mold and washed with running water to remove starch, excess acid and formaldehyde, and an initial product of a synthetic grindstone was obtained. The initial product of this synthetic whetstone was heated and cured at 130° C. for 5 hours to accelerate the curing reaction of the phenol resin, and a synthetic whetstone was obtained.

[Comparative Example 3] Reaction was carried out for 12 hours without applying pressure. A synthetic grindstone was obtained in the same manner as in Example 4 except for the above.

As a result of measuring the number of closed air bubbles on the cut surface of the synthetic whetstones obtained in Example 4 and Comparative Example 3, it was found that the synthetic whetstone obtained in Comparative Example 3 had air bubbles mixed in at a rate of 12/10 clr. However, no bubbles were observed in the synthetic grindstone obtained in Example 4.

〔Effect of the invention〕

As described above, in the present invention, a porous body is manufactured by curing a resin liquid under pressure, so that the resulting porous body has homogeneous properties without remaining closed cells. That is, according to the present invention, since the number of defective products due to residual closed cells is reduced, the production yield of porous bodies can be improved, and there is an advantage that the overall quality of the product is improved. As a result of being able to obtain a product free of residual closed cells in this way, it becomes possible to omit the 100% inspection process that was conventionally installed for the purpose of excluding pore contaminants from the product.

Claims (5)

[Claims] (1) Prepare a synthetic resin liquid in which a curing agent, a catalyst, and a pore-forming agent are uniformly dispersed, cure this resin liquid to create a cured body, and remove the pore-forming agent from this cured body. 1. A method for producing a porous body in which marks are made into pores, the method comprising curing the resin liquid under pressure. (2) The method for producing a porous body according to claim 1, wherein the pressurization is performed using gas. (3) The method for producing a porous body according to claim 2, wherein the pressurization using gas is performed by enclosing compressed air. (4) The method for producing a porous body according to claim 2, wherein the pressurization using gas is performed by steam pressurization. (5) The method for producing a porous body according to any one of claims 1 to 4, wherein the pressurization is performed under a pressure condition of 1.0 kg/cm^2 or more.