JPH03174455A - Preparation of porous article of polyvinyl acetal - Google Patents

Abstract

PURPOSE:To prepare the title article having fine and uniform open cells by adding a polyvinyl alcohol, starch, a defoamer, a crosslinker, and an acid catalyst to an aq. dispersion of a glass fiber with specified sized, conducting the acetalization of the polyvinyl alcohol, and then removing the starch. CONSTITUTION:A polyvinyl alcohol having an average degree of polymn. of 300-3000, a fine particle starch pref. extracted from rice, a defoamer in an amt. of 0.5wt.% or higher (based on the polyvinyl alcohol), a crosslinker comprising an aldehyde, and an acid catalyst comprising an org. or inorg. acid are added to an aq. dispersion contg. 3-20wt.% (based on the polyvinyl alcohol) glass fiber with a diameter of 0.1-1.2mum and a length of 10-200mum. Then the dispersion is kept heated for 2-5hr at a temp. at which the starch does not turn into its alpha-form, thus carrying out the acetalization of the polyvinyl alcohol. The resulting product is washed water, and from the product the starch is removed, giving the title article having a mean pore diameter of 30-50mum, a pore content of 70-93vol.%, and a degree of acetalization of 60-70mol%.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a polyvinyl acetal porous material, and more particularly to a polyvinyl acetal porous material having uniform, fine, continuous pores and suitable for various filter media. Regarding the manufacturing method.

(Prior art) Polyvinyl acetal (hereinafter abbreviated as rPVAt)-based porous materials have a uniform pore diameter and a continuous pore structure with high porosity, which makes them effective in removing dust in gases and impurities in liquids. It is often used as a filter material to trap and remove.

Conventionally, PVAt-based porous bodies have been manufactured by approximately the following method. That is, polyvinyl alcohol (rP
(abbreviated as VA) starch as a pore-forming material in an aqueous solution,
Aldehydes as a crosslinking agent and acids as a catalyst are added and mixed with stirring, poured into a prescribed mold, heated to cause an acetalization reaction, and the resulting reaction product is taken out from the mold and washed with water. This method removes the pore-forming material, unreacted crosslinking agent, and catalyst to obtain a PVAt-based porous material having continuous pores.

In the above method, the porosity can be adjusted to suit the purpose by appropriately selecting the type and amount of the pore-forming material.

However, the starch used as the pore-forming material is dispersed in a sufficiently swollen state in the heated reaction stock solution, and even if rice starch with the smallest particle size is used, The average pore diameter of the resulting PVAt-based porous material was usually larger than 50 μm. Also, PVAt
When the pore size of a porous material becomes small, it tends to become soft and elastic, and if it lacks rubber elasticity, it tends to have poor shape retention, and during manufacturing, especially during squeezing during the washing process, it does not return to its original shape and deforms. The removal efficiency of the pore-forming material decreases, and the quality also tends to deteriorate.
It has been extremely difficult to efficiently and stably produce a porous material based on the following.

By the way, in order to perform high-precision filtration, a material with small pore diameter and small variation in pore diameter is required. For example, a high-precision filter medium called submicron has a nominal accuracy of 1
It has the ability to capture 90% or more of particles with a particle size smaller than 10 μm, but in order to achieve this accuracy with a PVAt-based porous material, the average pore size must be 50 μm or less, preferably 40 μm or less. It is necessary to do so. However, as mentioned above, it is difficult to obtain fine pores with an average pore size of 50 μm or less using conventional methods. Therefore, in order to obtain a porous material with a fine pore size, cross-linking is carried out at a low temperature that does not cause the starch to swell. A reaction method is also considered, but this method has a slow reaction rate and requires a long time for the crosslinking reaction, so it is not practical.Also, there is a lot of starch in an aggregated state, resulting in non-uniform pore size, resulting in unstable quality. It is not easy to obtain such a porous material, and no satisfactory method has yet been proposed for efficiently and stably producing a PVAt-based porous material suitable for high-precision filter media.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a PVAt-based porous body having fine and uniform continuous pores and suitable for various filter media. is to provide.

(Means for Solving the Problems) The object of the present invention is to have a fiber diameter of 0.1 to 1.2 μm and a fiber length of 1 μm.
Pv
A. A PVAt-based porous material characterized by adding IQ powder, an antifoaming agent, and a crosslinking agent, adding an acid catalyst thereto, causing an acetalization reaction, and washing the resulting reaction product with water to remove starch. This is achieved by a manufacturing method.

The method of the present invention uses PVA with a uniform and fine continuous pore structure.
In order to obtain a t-based porous material, the first feature is that it is produced by dispersing specific glass fibers.

The glass fiber used in the present invention has a fiber diameter of O0l to 1.2
μm, and those with a smaller fiber diameter tend to have finer pores, and those with a fiber diameter larger than 1.2 μm cannot obtain fine pores, and the fiber diameter is 0.1 μm.
Glass fibers smaller than μm are difficult to obtain industrially. In addition, the PVAt-based porous body of the present invention may contain two or more types of glass fibers of different sizes, large and small, dispersed therein, and those with large fiber diameters have the effect of improving material recovery properties, Specifically, the effect becomes remarkable when the thickness is 0.6 μm or more. Therefore, for example, fiber diameter 0.1~
0.6 am and 2 of fiber II diameter 0.6~1.2 am
If different types of glass fibers are used in combination, a porous body having fine pore diameters and excellent restorability can be obtained. Furthermore, the glass fiber used in the present invention has a fiber length of 10 to 200 IJm.
If the fiber length is too long, the fibers will become entangled with each other and it will be difficult to disperse them uniformly.If the fiber length is too short, the fibers will fall off more easily than the PVAt-based porous material, which is not preferable. The glass fiber is used in an amount of 3% by weight or more based on the weight of PVA, which will be described later. If it is less than 3% by weight, the effect of making the pore size finer is poor, and the larger the amount of glass fiber, the finer the pore size is. However, if there are too many glass fibers, it becomes difficult to disperse the glass fibers uniformly in the viscous PVA solution, and if the PVA solution is made low in concentration, the PVAt obtained
Since the porous material has low strength, the glass fiber is preferably used in an amount of 20% by weight or less based on the weight of PVA.

The above-mentioned fine glass fibers used in the present invention are not obtained by a general melt-spinning method, but are made by, for example, blowing glass that has been brought into a melt-flowing state with a jet stream, and then using a fine fiber mass that is made into a filament yarn as a raw material. It can be obtained by pulverizing this using a jet mill, turbo mill, or other means.

The PVA used in the method of the present invention is completely saponified, partially saponified, or a mixture thereof,
Preferably, the average degree of polymerization is from 300 to 3,000.

The starch used in the method of the present invention can be granular-structured starch extracted and purified from various plants, such as rice, wheat, corn, etc., and if necessary, pulverized and classified starch is used. . In order to obtain a porous material with a smaller pore size, it is preferable that the particle size is small.
R powder extracted from rice is preferably used.

Examples of the antifoaming agent used in the present invention include carboxylate-based antifoaming agents. In the method of the present invention, the antifoaming agent removes air bubbles in the high viscosity PVA aqueous solution, and
This has the unexpected effect of improving the resilience of the material after it has been deformed. Therefore, it is desirable to select the mixing amount taking into consideration not only the defoaming effect but also the restoring effect.
For example, in higher fatty acid carboxylate antifoaming agents, PVA
It is preferably mixed in an amount of 0.5% by weight or more based on the weight of the solid content.

The crosslinking agent used in the present invention refers to aldehydes, such as formaldehyde, acetaldehyde, butyraldehyde, and the like. Further, as the acid catalyst, inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, and organic acids such as oxalic acid, formic acid, and acetic acid can be used.

In order to produce a PVAt-based porous body by the method of the present invention, first the glass fibers are uniformly dispersed in water, the PVA is added thereto and dissolved by heating, and then the liquid temperature is lowered to 60°C or less. Add the starch and stir to mix, if necessary.
Practice precepts for 5 hours. It is also suitable to carry out the aging at a temperature at which the added starch does not gelatinize, and to carry out the aging while stirring slowly.

Next, the antifoaming agent is added to the obtained mixture, aldehydes as a crosslinking agent and acids as a catalyst are added and stirred thoroughly, and then poured into a mold and heated to perform a crosslinking reaction. Here, stirring is preferably performed using a vacuum stirrer in order to remove air bubbles in the reaction stock solution.

Subsequently, the obtained reaction product is sufficiently washed with water to remove unreacted crosslinking agent, acid catalyst, remaining starch, etc., to obtain a PVAt-based porous body having uniform, fine, continuous pores. The PVAt-based porous material obtained by the above method usually has an average pore diameter of 30 to 50 μm.

Porosity: 70-93% by volume 2 Degree of acetalization: 60-7
It is 0 mol%.

If the degree of acetalization is 60 to 70 mol%, the physical properties will be flexible when wet and the mechanical strength will be weak. It is preferable to carry out a chemical reaction to obtain an acetalized product with a concentration of preferably 80 mol % or more, or to impregnate a thermosetting resin such as a melamine resin and heat-cure it.

(Effects of the Invention) According to the method of the present invention, a PVAt-based porous body having a finer pore diameter can be easily and stably produced compared to conventional methods. In addition, the reaction product obtained by the method of the present invention has excellent shape recovery properties despite its fine pore size, so there is almost no deformation during removal from the mold or washing process, making it easy to handle. Therefore, a PVAt-based porous body having uniform, fine, continuous pores can be efficiently produced.

The PVAt-based porous body produced by the method of the present invention is
It usually has uniform and fine continuous pores with an average pore diameter of 50 μm or less, has a high porosity, and can be easily formed into a desired shape, making it suitable as a filter medium for liquids and gases. It is suitable as a filter medium for high-precision filtration called medium submicron. Further, following the method of the present invention, the acetalization reaction is further advanced to obtain a highly acetalized product, and the product impregnated with a thermosetting resin and cured has excellent water resistance, chemical resistance, dimensional stability, and mechanical properties. It has excellent strength, etc., and is extremely suitable as a variety of high-precision filter media.

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

(Example 1) Glass fiber with a fiber diameter of 0.3μ (average fiber length 20 to 40μ
m) Disperse IKg and 0.5 Kg of glass fibers with a fiber diameter of 0.8 μm (average fiber length 40 to 70 μm) in 5 μl of water using a homogenizer, and add a polymerization degree of 17 to this dispersion.
8 kg of fully saponified PVA with a degree of polymerization of 500 and 2 kg of completely saponified PVA with a degree of polymerization of 500 were added, heated to 90°C, stirred thoroughly to dissolve the PVA, and then the liquid temperature was lowered to 50°C.

Next, 3.2 kg of rice starch was dispersed in 10 f water, mixed with the PVA aqueous solution in which the glass fibers were dispersed, and heated at 50°C.
After stirring for 3 hours at
80g of was added, and water was further added to adjust the total amount to 10,042 g.

Next, 37% formaldehyde aqueous solution 137! and 5
0% sulfuric acid 111 was added and mixed by stirring uniformly, and the reaction stock solution was poured into a cylindrical mold and heated at 60°C for about 20 hours to obtain a reaction product. The obtained reaction product had extremely good restorability, and was taken out from the mold and washed with water to remove remaining formaldehyde, sulfuric acid and starch, to obtain a PVAt-based porous body.

The obtained PVAt-based porous material had fine continuous pores with an average pore diameter of 3 μm, a porosity of 90% by volume, and an acetalization degree of 65 mol%, and could be suitably used as a filter medium. .

(Examples 2 to 9) Reaction products were obtained in the same manner as in Example 1, except that glass fibers with a fiber diameter of 0.3 to 1.0 pm were used in the types and amounts shown in Table 1. A PVAt-based porous body was produced. Both had good restorability, and the obtained PV
The At-based porous material had a porosity of about 90% by volume and fine pores as shown in Table 1, and was suitable as a filter medium for high-precision filtration. The larger the amount of glass fiber blended, the larger the pore diameter.
Furthermore, the smaller the fiber diameter, the more fine the fibers tended to be. On the other hand, the recovery properties tended to improve as the fiber diameter increased.

(Comparative Example 1) P was prepared in the same manner as in Example 1 except that glass fiber was not used.
A VAt-based porous body was manufactured. The obtained PVAt-based porous material had a large average pore diameter of 50 to 60 μm, and was not suitable for high-precision filtration.

(Comparative Example 2) A PVAt-based porous body was produced in the same manner as in Example 1, except that 1 kg of glass fiber with a fiber diameter of 1.5 μm (average fiber length 100 to 160 μm) was used as the glass fiber. The average pore diameter of the obtained PVAt-based porous material was 50 to 60 μm, which was comparable to that produced without using glass fibers, and was not suitable for high-precision filtration.

(Comparative Example 3) 0.2 kg of glass fiber with a fiber diameter of 0°3 μm
(2% by weight based on the weight of PVA) A PVAt-based porous body was produced in the same manner as in Example 1 except that the amount was used. The obtained PVAt-based porous material had an average pore diameter of 50 to 55 μm, and almost no effect of incorporating glass fiber was observed.

(Comparative Example 4) 0.2 kg of glass fiber with a fiber diameter of 0.8 μm
Example 1 except that (2% by weight based on PVA weight) was used.
A PVAt-based porous body was produced in the same manner as in the above.

The obtained PVAt-based porous material has an average pore diameter of 50 to 6 μm, which is the same as that without using glass fiber (Example 10). Addition of 140 g of antifoaming agent, which was 80 g in Example 1.
A PVAt-based porous body was produced in the same manner as in Example 1, except for the following. The obtained PVAt-based porous material had an average pore diameter of 30 μm, similar to Example 1, but its restorability was slightly inferior to that of Example 1.

(Comparative Example 5) A PVAt-based porous body was produced in the same manner as in Example 1 except that the antifoaming agent used in Example 1 was not used. Obtained P
The VAt-based porous material has many air bubbles in its micropores, and lacks uniformity in pore size, making it unsuitable for high-precision filter media.Also, this material has no shape recovery, and is difficult to wash with water. I transformed it. In the method of the present invention, the antifoaming agent not only has the effect of removing air bubbles, but also has the effect of improving restorability.

Claims (1)

[Claims] (1) Fiber diameter 0.1-1.2 μm, fiber length 10-200
Polyvinyl alcohol, starch, antifoaming agent, and crosslinking agent are added to a solution in which μm glass fibers are dispersed in water, and an acid catalyst is added to the solution to cause an acetalization reaction. The resulting reaction product is washed with water to remove starch. A method for producing a polyvinyl acetal porous body, characterized by: