JPH08132454A - Production of polyvinyl alcohol type porous sheet - Google Patents

Abstract

PURPOSE: To efficiently and continuously produce a PVA type porous sheet relatively large in surface voids by laying a fabric or nonwoven fabric on the metal plate of which the surface is coated with fluoroplastic of a belt conveyor. CONSTITUTION: The fabric 11 trained over rotary drums 12a, 12b, 12c to be rotated is arranged above a belt conveyor 1 so as to cover the upper surface of the reaction soln. spread over the belt conveyor l in a sheet form and moved and rotated at the same speed as the moving speed of the belt conveyor 1. The belt conveyor 1 is composed of a metal plate 1a of which the surface is coated with fluoroplastic. Further, a fabric 1c composed of an extremely fine fiber is laid and fixed on the fabric. The projected parts 14 for limiting the spreading of the reaction soln. so as to prevent the overflow of the reaction soln. are provided in the vicinity of both side end parts of the surface of the belt conveyor 1 over the entire periphery of the conveyor 1. A reaction product 20 is peeled from the fabric 11 and the belt conveyor 1 and, after cooling, a void forming material is removed by washing to obtain a PVC type porous sheet.

Description

Detailed Description of the Invention

[0001]

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

[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 type porous sheet is prepared by adding starch as a pore-forming material, aldehydes as a cross-linking agent, and acids as a cross-linking catalyst to an aqueous solution of polyvinyl alcohol (hereinafter abbreviated as "PVA"). After casting this in a predetermined mold, it is heated to a temperature of 50 to 70 ° C. to cause a crosslinking reaction to form a reaction product, which is washed with water to remove the pore-forming material to form a block-shaped porous body, Then, the obtained porous body was manufactured by slicing it into a sheet having a predetermined thickness.

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.
It required more than one day and was a very inefficient method of production. Therefore, in order to improve the production efficiency, if the temperature of the cross-linking reaction is raised to reduce the reaction time, the reaction time is shortened, but the resulting porous body has a non-uniform pore size distribution, and thus the central portion There is a problem that there is a large difference in the size of the pores from the outer peripheral portion, and in some cases, the reaction product is released from the mold and thermally contracts.

Further, according to the conventional method, since the block-shaped porous body is sliced into a sheet, many parts of the block-shaped porous body which are not used for the sheet-shaped product are generated in the peripheral portion, resulting in poor product yield. There was a problem that
Further, since each mold is made to react in batches, if the production amount increases, it cannot be dealt with unless the space of the reaction bath is widened, which is inconvenient for mass production in limited equipment, resulting in poor production efficiency. Was the way.

Therefore, a method of producing a sheet-like PVA-based porous body by spreading the reaction solution into a sheet and heating it is conceivable. The sheet-like reaction product obtained by this method is The surface becomes an extremely dense structure, and only those having a small surface porosity can be obtained, and it is extremely difficult to obtain a surface having a large porosity.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have conducted extensive studies in view of the above problems, and as a result, by using a heated belt conveyor, PVA-based porous sheets can be continuously produced, The present invention has been completed by finding that the above-mentioned problems can be solved by further designing the heating plate for heating with a specific structure or by adding a specific device in the course of the crosslinking reaction. An object of the present invention is to provide a method for producing a PVA-based porous sheet that can efficiently and continuously produce a PVA-based porous sheet having a relatively large surface porosity.

[0008]

The first method of the present invention for achieving the above-mentioned object is to continuously react a reaction liquid comprising PVA, a pore-forming material, a cross-linking agent and a cross-linking catalyst on a belt conveyor heated to a predetermined temperature. Of the PVA-based porous sheet, the surface of the belt conveyor is coated with a fluororesin. It is characterized by comprising a woven or non-woven fabric on the top.

In the second method of the present invention, a reaction liquid composed of 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, and the reaction liquid is sheeted. A method for producing a PVA-based porous sheet by spreading in a sheet shape and heating to carry out a crosslinking reaction, wherein the upper surface of the reaction solution is contact-coated with a woven or non-woven fabric when the reaction solution undergoes a crosslinking reaction. After that, the woven or non-woven fabric is peeled off after completion of the crosslinking reaction.

Further, in the third method of the present invention, a reaction liquid 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, and the reaction liquid is sheeted. A method for producing a PVA-based porous sheet by spreading and heating to perform a cross-linking reaction, characterized in that a pore-forming material is uniformly dispersed on the upper surface of the reaction solution during the cross-linking reaction. It is a thing.

The PVA used in the present invention has an average degree of polymerization of 15
Completely saponified product of 00 to 3800 (saponification degree 98% or more)
Is preferably used alone, but the average degree of polymerization is 500 to 1
It is also possible to use a mixture of 500 fully saponified products or partially saponified products with the fully saponified product at a ratio of, for example, 10 to 50% by weight. Fully saponified PVA is partially saponified PVA
It is preferable to use the completely saponified PVA for the purpose of the present invention because the crosslinking reaction time tends to be shorter than that.

As the pore-forming material used in the present invention, starch and fine powders of other organic substances can be used, but starch granules extracted from plants are preferable. 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, it becomes possible to adjust the pore diameter and porosity of the porous body.

The cross-linking agent used in the present invention is an aldehyde, for example, an aliphatic aldehyde such as formaldehyde, acetaldehyde, butyraldehyde and acrylaldehyde, an aliphatic dialdehyde such as glyoxal, and 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 first method of the present invention is one in which a woven cloth or a non-woven cloth is laid and fixed on the surface of a metal plate coated with a fluororesin. 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 woven or non-woven fabric used here is preferably made of ultrafine fibers.

The belt conveyor used in the second and third methods of the present invention may be the belt conveyor used in the above-mentioned first method, but it may be a metal plate or a heat resistant woven fabric having no water permeability. You may use what was coated with the fluororesin or the heat-resistant and acid-resistant resin.

The first and second methods of the present invention can be carried out by an apparatus as shown in FIGS. 1 to 3, for example. 1 is a configuration explanatory view showing an example of a manufacturing apparatus applied to the first method, FIG. 2 is a plan explanatory view showing a structure of a belt conveyor section of this apparatus, and FIG. 3 is a belt conveyor of this apparatus. It is a principal part expanded sectional explanatory view which shows a part.

This apparatus 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 heating plate 4 for horizontally supporting the belt conveyor 1 and heating the belt conveyor 1, a water washing device 5 for washing the belt conveyor 1, and a water absorbing roller 6 for wiping the surface of the belt conveyor 1 ing.

Above the belt conveyor 1, the woven cloth 11 stretched around the rotating drums 12a, 12b, 12c and rotated so as to cover the upper surface of the reaction solution spread on the belt conveyor 1 in the form of a sheet. And is moving and rotating at the same speed as the moving speed of the belt conveyor 1. In the belt conveyor 1, the surface of the metal plate 1a is coated with the fluororesin 1b, and the woven cloth 1c made of ultrafine fibers is further laid and fixed so that the reaction solution does not spill around the both end portions of the surface of the belt conveyor. A protrusion 14 for limiting the flow of the reaction solution is provided over the entire circumference of the belt conveyor. The woven fabric 11 is made of ultrafine fibers.

The first and second aspects of the present invention using the above apparatus
In order to produce a PVA-based porous sheet by the above method, for example, the following may be performed. That is, first, PVA is dissolved in warm water to prepare a PVA aqueous solution of about 10 to 20% by weight. A liquid in which starch, which is a pore-forming material, is dispersed in water is added thereto, a crosslinking agent and a crosslinking catalyst are further added, and the mixture is sufficiently stirred and mixed to obtain a uniform slurry reaction liquid. PV of this reaction solution
A concentration is preferably 6 to 10% by weight based on the weight of the reaction solution.
Is prepared. The reaction solution is, for example, 1000 to 3000.
A viscous liquid having a viscosity of about cps is preferable.

This 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 liquid is naturally cast and spread into a sheet, and the spread reaction liquid 10 is heated by the belt conveyor 1 heated by the heating plate 4 and the upper surface thereof is covered with the woven cloth 11. The cross-linking reaction proceeds in the state of contact coating. Eventually, the reaction liquid gradually loses fluidity and becomes a sheet-shaped reaction product on the belt conveyor. The thickness of the 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.

The belt conveyor 1 moves at a speed of, for example, several tens of centimeters to 1 meter per minute, and the reaction time on the belt conveyor depends on the temperature of the belt conveyor,
It varies depending on the amount of the reaction solution supplied, etc., but is usually 10 to 20.
About a minute is enough. The sheet-shaped reaction product 20 obtained as described above is peeled from the woven fabric 11 and the belt conveyor 1, and after cooling, is washed with water to remove the pore-forming material and the like, so that the rubber elasticity in a wet state is obtained. Have PVA
It is a porous sheet.

The belt conveyor 1 from which the sheet-like reaction products have been peeled off is washed with a water washing device 5 to wash away the remaining unreacted raw materials, cross-linking catalyst, and other deposits, clean the surface, and then attach it with a water-absorbing roller 6. After the washing water is wiped off, the above crosslinking step is repeated.

In the first and second methods of the present invention, fine irregularities are formed on the surface of the reaction product in the form of a sheet, so that the surface structure maintains a pore structure close to the internal structure of the reaction product. Therefore, a porous structure having a large surface pore opening ratio can be obtained.

The third method of the present invention can be carried out by an apparatus as shown in FIGS. 4 and 5, for example. This device is different from the device used in the second method described above in that the rotating woven fabric 11 is replaced by pores for evenly distributing the pore-forming material 17 from above the reaction liquid spread on the belt conveyor 1 in the form of a sheet. A forming material spray nozzle 16 is provided. The pore-forming material is preferably sprayed during the crosslinking reaction of the reaction solution, for example, immediately before the fluidity is lost.

Further, in the third method of the present invention, since the pore-forming material is sprinkled, more pores are formed in the surface layer on the sprinkled side, so that the pore opening ratio of the surface is increased. You can

[0027]

EFFECTS OF THE INVENTION According to the method of the present invention, since the reaction solution is cast on the belt conveyor and spread in the form of a sheet, the reaction solution is heated to continuously perform the crosslinking reaction. Can be continuously produced, and the crosslinking reaction time can be dramatically shortened as compared with the conventional method.
Further, since the slicing step which is required in the conventional method can be omitted, the production efficiency of the PVA-based porous sheet is remarkably improved, and further the product yield is remarkably 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.

In particular, according to the method of the present invention, it becomes possible to efficiently manufacture a PVA type porous sheet having a large surface opening ratio.

[0029]

【Example】

Example 1 400 g of completely saponified PVA having an average degree of polymerization of 1500 was added to water to make the total amount 2000 ml, and this was heated to PV.
A was completely dissolved. Next, water was added to this to make the total amount 3100 ml, and the mixture was cooled with stirring. Furthermore, 150 g of corn starch is dispersed in 500 ml of water and the temperature is 12 ° C.
The dispersion liquid prepared in step 1 was added, and the mixture was sufficiently stirred and mixed until the whole became uniform.

When the mixed solution of PVA and starch was cooled to 50 ° C., a 37% aqueous formaldehyde solution 500 was added.
ml and 50% sulfuric acid 900 ml were added and uniformly stirred and mixed to obtain a reaction solution.

Next, using the apparatus shown in FIGS. 1 to 3, the obtained reaction solution was continuously poured onto the belt conveyor 1 heated to 80.degree. The reaction solution was cast on the belt conveyor 1 in a sheet form. Woven cloth 1 on top of the reaction solution
1 was contacted and coated, and the reaction solution was heated on a belt conveyor for 20 minutes to carry out a crosslinking reaction to obtain a sheet-shaped reaction product. Then, the obtained reaction product is peeled off from the belt conveyor and washed sufficiently with water to remove starch and the like,
It was a VA-based porous sheet. In addition, the woven fabric 1 used here
No. 1 was composed of ultrafine fibers (trade name: Berryma XK-8622, manufactured by Kanebo).

The PVA-based porous sheet obtained had a thickness of 5
It was a homogeneous porous structure having continuous pores having a pore size distribution of 80 to 150 μm in mm, and had preferable rubber elasticity when wet. The obtained PVA-based porous sheet had a surface pore structure that was substantially the same as the internal pore structure, and had a large surface pore opening ratio.

Example 2 A PVA type porous sheet was manufactured using the apparatus as shown in FIGS. The same reaction solution as used in Example 1 was used, and this reaction solution was poured onto the belt conveyor 1 heated to 80 ° C. The belt conveyor 1 is
The same structure as in Example 1 was used. The reaction solution was cast on the belt conveyor 1 in a sheet form. Immediately before the reaction solution was heated on a belt conveyor for about 2 minutes to lose its fluidity, potato starch was sprayed from a pore-forming material spray nozzle and sprayed uniformly on the upper surface of the reaction solution. Subsequently, after a crosslinking reaction for a further 8 minutes, the obtained reaction product is peeled from the belt conveyor 1, cooled and washed to remove the pore-forming material and the like, and a PVA-based porous sheet having rubber elasticity is obtained. Obtained.

The PVA-based porous sheet obtained had a thickness of 5
In mm, the pore size distribution was a homogeneous porous structure having continuous pores of 40 to 50 μm, and had a preferable rubber elasticity when wet. Further, the pore structure of the surface of the obtained PVA-based porous sheet on the side on which the pore forming material was sprayed was almost the same as the internal pore structure, and the surface pore opening ratio was large.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing an example of a manufacturing apparatus applied to first and second methods 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 cross-sectional explanatory view of essential parts showing a belt conveyor section of the apparatus of FIG.

FIG. 4 is a structural explanatory view showing an example of a manufacturing apparatus applied to a third method of the present invention.

5 is an enlarged cross-sectional explanatory view of essential parts showing a belt conveyor section of the apparatus shown in FIG.

[Explanation of symbols]

 1 Belt Conveyor 1a Metal Plate 1b Fluorocarbon Resin 1c Woven Fabric 2 Reaction Liquid Discharging Section 3a, 3b, 3c Rotating Drum 4 Hot Plate 5 Water Washing Device 6 Water Absorbing Roller 10 Reaction Liquid 11 Woven Fabric 12a, 12b, 12c Rotating Drum 14 Projection 16 Pore forming material spray nozzle 17 Pore forming material 20 Reaction product

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area B29L 7:00 C08L 29:00

Claims (3)

[Claims] 1. A reaction liquid comprising polyvinyl alcohol, 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, and the reaction liquid is spread into a sheet and heated. Then, a cross-linking reaction is performed to produce a polyvinyl alcohol-based porous sheet, wherein the surface of the belt conveyor is a woven or non-woven fabric laid on a metal plate coated with a fluororesin. A method for producing a polyvinyl alcohol-based porous sheet, which is characterized. 2. A reaction liquid comprising polyvinyl alcohol, 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, and the reaction liquid is spread into a sheet and heated. A method for producing a polyvinyl alcohol-based porous sheet by subjecting the reaction solution to a cross-linking reaction, the upper surface of the reaction solution is contact-coated with a woven or non-woven fabric, and then the cross-linking reaction is completed. A method for producing a polyvinyl alcohol-based porous sheet, characterized in that the woven or non-woven fabric is subsequently peeled off. 3. A reaction solution comprising polyvinyl alcohol, 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, and the reaction solution is spread into a sheet and heated. A method for producing a polyvinyl alcohol-based porous sheet by subjecting to a cross-linking reaction, wherein the pore-forming material is uniformly dispersed on the upper surface of the reaction solution during the cross-linking reaction. Manufacturing method.