JP2623494B2 - Method for producing polyvinyl alcohol-based porous sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously and efficiently producing a sheet-shaped polyvinyl alcohol-based porous material.

[0002]

2. Description of the Related Art A polyvinyl alcohol-based porous sheet is a continuous porous structure having a high porosity, and has excellent hydrophilicity and favorable rubber elasticity when wet. Widely used for various applications such as filtration media.

Conventionally, a polyvinyl alcohol-based porous sheet has been generally manufactured as follows. That is, a starch as a pore-forming material, an aldehyde as a cross-linking agent, and an acid as a cross-linking catalyst are added to an aqueous solution of polyvinyl alcohol (hereinafter abbreviated as “PVA”), and the mixture is cast into a predetermined mold. The mixture is heated to a temperature of 50 to 70 ° C. to form a reaction product by a cross-linking reaction, and then the pore-forming material is removed by washing with water to form a block-shaped porous body, which is sliced into a desired thickness to form a sheet. How to

By the way, the above-mentioned method requires 15 minutes for the crosslinking reaction.
It takes up to 25 hours and usually takes 2 to 2 hours to obtain a sheet.
More days were required, and the production efficiency was extremely low. Therefore, if the reaction time is shortened by raising the temperature of the cross-linking reaction in order to improve the production efficiency, the reaction time is certainly shortened, but the obtained porous body has a nonuniform pore diameter distribution, and the There is a problem that a large difference occurs in the size of the pores between the portion and the outer peripheral portion, and in some cases, the reaction product is released from the mold and tends to thermally shrink.

Further, in the conventional method, since a block-shaped porous body is sliced into a sheet, many portions of the block-shaped porous body which are not used for a sheet-shaped product are generated in a peripheral portion, and if the product yield is low, the block-shaped porous body is not used. There was a problem. In addition, since the reaction is carried out in batches for each mold, if the production volume increases, it is not possible to cope without increasing the space of the reaction bath,
There was a problem with mass production in limited facilities, and this was a method with poor production efficiency.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have conducted intensive studies in view of the above problems, and as a result, by using a heated belt conveyor, a PVA-based porous sheet can be continuously produced. The inventors have found that the above problems can be solved and completed the present invention. The purpose of the present invention is
It is an object of the present invention to provide a method for producing a PVA-based porous sheet, which can efficiently and continuously produce a PVA-based porous sheet and can greatly increase the production amount per production facility area.

[0007]

According to a first method of the present invention for achieving the above object, a reaction solution comprising PVA, a pore-forming material, a crosslinking agent and a crosslinking catalyst is placed on a belt conveyor heated to a predetermined temperature. The reaction solution is continuously supplied, and the reaction solution is heated to cause a crosslinking reaction.

In the second method of the present invention, a reaction solution comprising PVA, a pore-forming material, a cross-linking agent and a cross-linking catalyst is continuously supplied onto a belt conveyor heated to a predetermined temperature. The mixture is heated to perform a primary crosslinking reaction (hereinafter, may be abbreviated as “primary reaction”), and then the obtained primary reactant is continuously transferred into a hot water bath, and is heated in the hot water bath to perform secondary crosslinking. (Hereinafter sometimes abbreviated as “secondary reaction”). Further, the third method of the present invention is characterized in that the crosslinking reaction on the belt conveyor in the second method is performed in a steam atmosphere.

In the method of the present invention, PVA is completely saponified with an average degree of polymerization of 1500 to 3800 (98% saponification).
Is preferred to be used alone, but an average degree of polymerization of 50
A mixture of the completely saponified product of 0 to 1500 and the completely saponified product at a ratio of, for example, 10 to 50% by weight may be used. Since fully saponified PVA tends to have a shorter crosslinking reaction time than partially saponified PVA, it is preferable to use completely saponified PVA for the purpose of the present invention.

As the pore-forming material used in the present invention, starch and other fine powders of organic substances can be used, and starch granules extracted from plants are preferred. Plants of origin include, for example, grains such as rice, wheat, corn, and the like.
Potatoes such as potato, sweet potato, taro and the like can be mentioned. Since the starch granules have different particle sizes depending on the type of plant, the type of starch to be used may be appropriately selected according to the desired pore size. By changing the type and amount of the pore-forming material, the pore diameter and porosity of the porous body can be adjusted.

The crosslinking agent used in the present invention is an aldehyde, for example, an aliphatic aldehyde such as formaldehyde, acetaldehyde, butyraldehyde, acrylaldehyde, an aliphatic dialdehyde such as glyoxal, or an aromatic aldehyde such as benzaldehyde. Can be mentioned.

The crosslinking catalyst used in the present invention is an acid,
For example, inorganic acids or organic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and maleic acid can be exemplified. In the present invention, sulfuric acid is preferred.

The belt conveyor used in the present invention is preferably formed by coating a metal plate or a heat-resistant woven fabric having no water permeability with a fluororesin or a heat-resistant acid-resistant resin. By coating with a resin, corrosion by a strongly acidic reaction liquid can be prevented, and the release property of the reaction product can be enhanced.

The first method of the present invention is, for example, shown in FIGS.
It can be carried out by an apparatus as shown in FIG. FIG.
FIG. 2 is a configuration explanatory view showing an example of an apparatus applied to the first method, FIG. 2 is a plan explanatory view showing a structure of a belt conveyor section of the apparatus, and FIG. 3 shows a belt conveyor section of the apparatus. It is a principal part enlarged sectional explanatory view.

This device comprises a rotating belt conveyor 1
A reaction solution discharge unit 2 for flowing a reaction solution into the belt conveyor 1; and rotating drums 3a, 3b, 3c for stretching the belt conveyor 1 and applying a rotational force to the belt conveyor 1.
A plurality of heating rollers 4 for horizontally supporting the belt conveyor 1 and heating the belt conveyor 1; a heating drum 5 for heating the belt conveyor 1;
And a water absorption roller 7 for wiping the surface of the belt conveyor 1 with water. Further, the belt conveyor 1 has a heat-resistant woven fabric 1a coated with a fluororesin 1b on the surface thereof, and restricts the flow of the reaction solution so that the reaction solution does not spill near both ends of the surface of the belt conveyor. Protruding portion 8 is provided over the entire circumference of the belt conveyor.

To produce a PVA-based porous sheet by the first method of the present invention using the above-described apparatus, for example, the following method may be used. First, PVA is dissolved in warm water,
A PVA aqueous solution of about 20% by weight is prepared. A liquid in which starch serving as a pore-forming material is dispersed in water is added thereto, and a crosslinking agent and a crosslinking catalyst are further added. After that, the mixture is sufficiently stirred and mixed to form a uniform slurry reaction liquid. The PVA concentration of this reaction solution is preferably adjusted to 6 to 10% by weight based on the weight of the reaction solution. The reaction liquid is preferably a viscous liquid having a viscosity of, for example, about 1000 to 3000 cps.

The reaction solution is continuously supplied from the reaction solution discharge section 2 to the upper surface of the rotating belt conveyor 1. The supplied reaction solution is spontaneously cast and spreads in a sheet shape.
The reaction solution on the belt conveyor is heated by the heated belt conveyor 1 and a crosslinking reaction proceeds, and eventually the reaction solution gradually loses fluidity and becomes a sheet-like reaction product on the belt conveyor. The belt conveyor 1 is previously heated to 70 to 95 ° C. by a heating drum 5 and additionally heated by a heating roller 4. The thickness of the obtained reaction product sheet can be changed by adjusting the discharge amount of the reaction liquid, the rotation speed of the belt conveyor, and the like. In addition, you may enable each heating roller 4 to set a temperature individually, respectively.

The above-mentioned belt conveyor moves at a speed of, for example, several tens of centimeters per minute to about 1 meter, and the reaction time on the belt conveyor varies depending on the temperature of the belt conveyor, the supply amount of the reaction liquid, and the like. Usually, about 10 to 20 minutes is sufficient. The sheet-like reaction product 31 obtained as described above is separated from the belt conveyor, the pore-forming material is removed by cooling and then washing with water, and a PVA-based porous sheet having rubber elasticity in a wet state is formed. Is done.

The belt conveyor 1 from which the sheet-like reaction product has been peeled off is washed off the remaining unreacted raw materials, cross-linking catalysts and other deposits by a water washing device 6, the surface is cleaned thoroughly, and then adhered by a water absorbing roller 7. After the cleaning water thus wiped off, the above-mentioned crosslinking step is repeated.

In the second method of the present invention, after the primary reaction is performed by a belt conveyor, the obtained primary reactant 32 is continuously transferred into a hot water bath, and then immersed in hot water to perform the secondary reaction. Is applied. This method can be performed by, for example, an apparatus as shown in FIG. This apparatus is similar to the apparatus shown in FIG. 1 except that a hot tub 10 is connected. The hot tub 10 is provided with a plurality of rotating drums 12 different from each other, and the hot tub is filled with hot water 11. Further, a rotary drum 13 for taking out a sheet-like reaction product after the completion of the secondary reaction is disposed outside the hot tub 10. The sheet-like reaction product 31 obtained by performing the secondary reaction is a PVA-based porous sheet having a rubber elasticity in a wet state in which the pore-forming material is removed by cooling and washing with water in the same manner as in the first method. It is said.

The temperature of the hot water in the hot tub used in this method is set at 80 to 100 ° C., preferably 90 to 100 ° C. The time required for the secondary reaction in the hot water bath depends on the thickness of the primary reactant 32, but usually about 5 minutes is sufficient. Since the sheet during the secondary reaction is activated by high temperature, it is highly possible to cause tissue destruction, blockage of pores, and decrease of porosity when a strong tension is applied. It is preferable to hold and move the sheet in a state where strong tension is not applied. In addition, the said hot water in this invention may contain the said crosslinking agent and a crosslinking catalyst.

In the second method, since the crosslinking reaction can proceed in a hot water bath, the crosslinking reaction (primary reaction) by the belt conveyor loses the fluidity of the reaction solution and is necessary for the secondary reaction step. The reaction time by the belt conveyor can be shortened to, for example, about 2 to 8 minutes. Therefore, the length of the belt conveyor can be made shorter than in the first method, and the entire manufacturing apparatus can be made smaller. A reaction time of the primary reaction and the secondary reaction in combination of about 5 to 15 minutes is sufficient.

The PV obtained by the first and second methods described above
The A-based porous sheet has a three-dimensional network-like continuous pore structure and a high porosity, but the surface layer tends to have a film-like structure with few pores and low porosity.
Such a PVA-based porous sheet is suitable for, for example, a puff for cosmetics.

Next, in a third method of the present invention, a crosslinking reaction by a belt conveyor is performed in a steam atmosphere in the above-mentioned second method. This method can be performed by, for example, an apparatus as shown in FIGS. FIG. 5 is a structural explanatory view showing an example of an apparatus applied to the third method of the present invention, and FIG. 6 is an enlarged sectional explanatory view of a main part showing a structure of a belt conveyor section of this apparatus. In this apparatus, a box 20 is disposed above the belt conveyor 1 of the apparatus shown in FIG. The box body 20 is provided such that the bottom is opened toward the belt conveyor 1 and covers the entire part where the primary reaction is caused. A steam injection pipe 22 provided with a large number of nozzles 21 for ejecting steam is provided above the inside of the box 20.
Is arranged. By supplying steam from the nozzle 21 to the inside of the box 20, the inside of the box is filled with steam.

The inside of the box 20 is partitioned by a partition plate 23. By partitioning the inside of the box, the inside of the box can be temperature-controlled for each partitioned room. However, if it is not necessary to control the temperature inside the box in a particularly fine manner, the partition plate may not be provided.

According to the third method of the present invention, the reaction solution is heated from the upper and lower surfaces by heating the lower surface of the reaction solution by the belt conveyor 1 and also from the upper surface by the steam. The cross-linking reaction proceeds faster and uniformly. For this reason, although it depends on the thickness of the reaction solution cast on the belt conveyor 1, the time required for the primary reaction is reduced to about 1 to 5 minutes, and the reaction time for the primary reaction and the secondary reaction is also 5 to 5. An extremely short time of about 10 minutes is sufficient. In addition, since the surface of the reaction solution is in contact with steam, the formation of a film layer is prevented, and the surface layer has a porous structure having a high porosity and a high porosity. Therefore, the obtained PVA-based porous sheet is excellent in water absorption.

[0027]

According to the method of the present invention, the reaction solution is cast on a belt conveyor and heated in a state spread in the form of a sheet to carry out a crosslinking reaction communicatively. And the crosslinking reaction time can be drastically reduced as compared with the conventional method. Further, since the slicing step required in the conventional method can be omitted, the production efficiency of the PVA-based porous sheet is significantly improved, and the product yield is also significantly improved. Further, in the case of the same production amount, the area occupied by the production equipment can be significantly reduced as compared with the conventional method, so that it is industrially extremely useful.

Further, in the second method of the present invention, since the crosslinking reaction is performed separately in the primary reaction by the belt conveyor and the secondary reaction in the hot water bath, the time required for the crosslinking reaction can be further reduced. Thus, the production efficiency is further improved, and the production equipment can be further downsized.

Further, in the third method of the present invention, the primary crosslinking reaction by the belt conveyor is performed in a steam atmosphere.
The time required for the primary reaction can be further reduced, and the production efficiency is further improved. In addition, since a film layer is not formed on the surface by the action of steam, a PVA-based porous sheet having high porosity, large surface porosity, and excellent water absorption can be stably obtained.

[0030]

【Example】

Example 1 400 g of completely saponified PVA having an average degree of polymerization of 1500 was poured into water to make the total amount 2000 ml, and this was heated to obtain PVA.
Was completely dissolved. Then, water was added to bring the total amount to 3100.
and cooled with stirring to prepare an aqueous PVA solution at a temperature of 84 ° C. Next, 150 g of corn starch was added to 500 g
The dispersion prepared by dispersing in 12 ml of water and adjusting the temperature to 12 ° C. was added to the previously prepared aqueous PVA solution, and sufficiently stirred and mixed until the whole became uniform.

When the mixture of PVA and starch is cooled to 50 ° C., a 37% formaldehyde aqueous solution 500%
ml and 900 ml of 50% sulfuric acid are added and uniformly mixed by stirring.
This was used as a reaction solution.

Next, using an apparatus as shown in FIG. 1, the obtained reaction solution was poured onto a belt conveyor 1 heated to 80 ° C. The reaction liquid was cast on a belt conveyor 1 in a sheet form. The reaction solution was heated on a belt conveyor for 10 minutes to perform a crosslinking reaction, thereby obtaining a sheet-shaped reaction product. Subsequently, the obtained reaction product was peeled off from the belt conveyor, and sufficiently washed with water to remove starch and the like to obtain a PVA-based porous sheet. The obtained PVA-based porous sheet is
It was a homogeneous porous structure having continuous pores having a thickness of 5 mm and a pore diameter of 40 to 50 mμ, and had favorable rubber elasticity when wet.

Example 2 Using a device as shown in FIG. 4, a PVA-based porous sheet was produced. The same reaction solution as that used in Example 1 was used, and the reaction solution was poured onto a belt conveyor 1 heated to 80 ° C. The reaction liquid was cast on a belt conveyor 1 in a sheet form. The reaction solution was heated on a belt conveyor for 5 minutes to perform a primary crosslinking reaction, thereby obtaining a sheet-shaped primary reaction product. Subsequently, the obtained primary reactant is peeled off from the belt conveyor 1, continuously transferred to a hot water bath 10, passed through hot water 11 set at a temperature of 90 to 100 ° C., and heated for 5 minutes to form a secondary reactant. A crosslinking reaction was performed to obtain a sheet-like reaction product. Subsequently, the reaction product is taken out of the hot water bath 10 and sufficiently washed with water to remove starch and the like.
A VA-based porous sheet was obtained. The obtained PVA-based porous sheet was a uniform porous structure having a thickness of 5 mm and continuous pores having a pore diameter of 40 to 50 μm, and had favorable rubber elasticity when wet.

Example 3 A PVA-based porous sheet was produced using an apparatus as shown in FIGS. The same reaction solution as that used in Example 1 was used, and the reaction solution was poured onto a belt conveyor 1 heated to 80 ° C. The reaction liquid was cast on a belt conveyor 1 in a sheet form. The reaction solution was heated by the belt conveyor 1 and steam filled in the box 20 for 3.5 minutes to perform a primary crosslinking reaction, thereby obtaining a sheet-shaped primary reaction product. Subsequently, the obtained primary reactant was peeled off from the belt conveyor, and was continuously transferred to the hot water bath 10 so as to be 90 to 90 hours.
The sheet was heated in hot water set at a temperature of 100 ° C. for 5 minutes to perform a secondary crosslinking reaction, thereby forming a sheet-like reaction product.

Subsequently, the reaction product was taken out of the hot water bath 10 and sufficiently washed with water to remove starch and the like to obtain a PVA-based porous sheet. The obtained PVA-based porous sheet is
It was a uniform porous structure having a thickness of 5 mm and continuous pores having a pore diameter of 40 to 50 mμ, and had rubber elasticity when wet. The pore structure of the surface layer was also high in porosity and large in porosity as in the internal structure.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an example of an apparatus applied to a first method of the present invention.

FIG. 2 is an explanatory plan view showing a belt conveyor section of the apparatus shown in FIG. 1;

FIG. 3 is an enlarged sectional explanatory view of a main part showing a belt conveyor unit of the apparatus of FIG. 1;

FIG. 4 is a configuration explanatory view showing an example of an apparatus applied to the second method of the present invention.

FIG. 5 is a configuration explanatory view showing an example of an apparatus applied to a third method of the present invention.

FIG. 6 is an enlarged sectional explanatory view showing a main part of a belt conveyor of the apparatus shown in FIG. 5;

[Description of Signs] 1 Belt Conveyor 1a Heat Resistant Woven Fabric 1b Fluororesin 2 Reaction Liquid Discharge Part 3a, 3b, 3c Rotary Drum 4 Heating Roller 5 Heating Drum 6 Washing Device 7 Water Absorbing Roller 8 Projection 10 Hot Water Bath 11 Hot Water 12 , 13 rotating drum 20 box 21 nozzle 22 pipe for steam injection 30 reaction liquid 31 reaction product 32 primary reactant

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 7:00 C08L 29:02

Claims (3)

(57) [Claims] 1. A reaction solution comprising polyvinyl alcohol, a pore-forming material, a crosslinking agent, and a crosslinking catalyst is continuously supplied onto a belt conveyor heated to a predetermined temperature, and the reaction solution is heated to cause a crosslinking reaction. A method for producing a polyvinyl alcohol-based porous sheet. 2. A reaction solution comprising a polyvinyl alcohol, a pore-forming material, a crosslinking agent and a crosslinking catalyst is continuously supplied onto a belt conveyor heated to a predetermined temperature, and the reaction solution is heated to perform a primary crosslinking reaction. Then, the obtained primary reactant is continuously transferred into a hot water bath, and heated in the hot water bath to cause a secondary crosslinking reaction, thereby producing a polyvinyl alcohol-based porous sheet. 3. A reaction solution comprising a polyvinyl alcohol, a pore-forming material, a crosslinking agent and a crosslinking catalyst is continuously supplied onto a belt conveyor heated to a predetermined temperature, and the reaction solution is heated in a steam atmosphere to form a primary solution. A method for producing a polyvinyl alcohol-based porous sheet, wherein a cross-linking reaction is performed, and then the obtained primary reactant is continuously transferred into a hot water bath and heated in the hot water bath to cause a secondary cross-linking reaction. .