JPH05230270A - Production of polyvinyl acetal sponge sheet - Google Patents

Abstract

PURPOSE:To efficiently produce the title sheet which has a relief or engraving pattern formed on its surface. CONSTITUTION:A liq. raw material mixture contg. polyvinyl acetal, an aldehyde, an acid, and a pore-forming agent is reacted in the form of layers formed by dividing the mixture with a separator paper. After the reaction, unreacted acid, aldehyde, and pore-forming agent are removed and then the paper is removed, giving the title sheet. At least a part of the surface of the paper is pretreated with a starch deriv.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a desired character on a surface,
The present invention relates to a method for producing a polyvinyl acetal-based sponge sheet in which a design such as a design is formed in a relief shape or an engraved shape.

[0002]

2. Description of the Related Art Conventionally, polyvinyl acetal (hereinafter referred to as
A sheet of sponge (hereinafter abbreviated as “PVAt”) or a sheet of composite in which reinforcing fabrics are interleaved with the PVAt sponge is a product that absorbs moisture well and has relatively high smoothness. It is used as a wiping material to wipe off and remove water drops, dust, etc. on the surface. For example, it is commercially available as a sheet for removing water drops on the surface of a car body after car washing, a waste cloth for cleaning the surface of precision machinery, parts or instruments.

Further, in recent years, due to its flexibility, good texture and high water absorption, it is often applied to sports applications, and above all, it is used as a wet body wipe for swimming and a sweat wipe. It has increased. Therefore, the PVAt-based porous sheet is desired to have an appearance that is excellent not only as a wiping material but also as a fashionable item.

The PVAt type sponge sheet as described above is
In general, by separating the reaction stock solution with paper as a separator and stacking several sheets to produce a layered form, the shape of the paper itself is transferred to the surface, so a uniform and flat surface is obtained. is there.

As a method of forming designs such as characters and patterns on the surface of such a PVAt type sponge sheet, a method of coloring by print printing is known. However, in this method, the colored portion is covered with a pigment or the like, and the surface of the porous structure is closed. As a result, the characteristic water absorption is reduced, and there is a problem that the performance as a wiping material is reduced.

Therefore, a method of forming a desired design by applying a slight uneven pattern to the surface is conceivable, instead of coloring the surface of the PVAt sponge sheet.
Examples of the method for producing such a PVAt-based porous sheet include (a) a method of producing a sheet and then heat-compressing and shaping it, and (b) a separator obtained by preliminarily forming uneven embossing paper. However, the method (a) has inferior quality, and the method (a) has a drawback that the operability is poor and a clear design cannot be obtained.

Therefore, the present inventors proposed the following method in Japanese Patent Application No. 3-285613 in order to solve the above-mentioned drawbacks.

That is, when reacting a reaction stock solution containing polyvinyl alcohol, an aldehyde, an acid, and a pore-forming material, the reaction is carried out with at least a part of the surface being in contact with a paper coated with a printing paste. After the completion of the reaction, the unreacted aldehydes, acids, and pore-forming material are removed, and the paper is removed.
It is a method for producing an At-based porous body.

However, in obtaining a paper coated with a printing paste used in the above-mentioned method, when a general printing paste is dyed by roller printing, the viscosity of the printing paste having a high density is However, there are problems such as unstable physical properties, a slow drying speed after dyeing, and poor surface smoothness of the printing paste after application, and it is not easy to apply efficiently by roller printing.

The present inventors have completed the present invention as a result of intensive studies in view of the above-mentioned problems, and the object of the present invention is to emboss a design such as letters and patterns on the surface or Another object of the present invention is to provide a method for efficiently producing a PVAt-based sponge sheet formed in an engraved shape.

[0011]

[Means for Solving the Problems] The above-mentioned object is to react a reaction stock solution containing polyvinyl alcohol, aldehydes, acids and a pore-forming material in a state of being partitioned into layers by a separator paper, and after the reaction is completed, unreacted Aldehydes,
A PVAt system characterized in that a starch derivative is applied to at least a part of the surface of the separator paper when the PVAt sponge sheet is produced by removing the paper and the acid and the pore-forming material. This is achieved by the method of manufacturing a sponge sheet.

The polyvinyl alcohol used in the present invention is a completely or partially saponified polymer having a degree of polymerization of 300 to 2000, and may be one in which a part of the hydroxyl groups is substituted with some other functional group, These may be used alone or in combination.

The aldehyde used in the present invention is a cross-linking agent for converting polyvinyl alcohol into a PVAt resin, which is an aliphatic or aromatic type, monovalent or polyvalent. But it's okay. In particular, formaldehyde and acetaldehyde are suitable for exhibiting physical properties as a PVAt-based porous body.

The acids used in the present invention are those which act as a catalyst, and are composed of, for example, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, organic acids such as oxalic acid, citric acid, maleic acid, or strong acids and weak bases. It is also possible to use salts that exhibit acidity in an aqueous solution.

The pore-forming material used in the present invention may be a fine powder of starch or other organic substances, but is preferably starch granules extracted from plants. Examples of the plant from which it is derived include grains such as rice, wheat and corn, and potatoes such as potato, sweet potato and taro. Since the starch granules have different particle diameters depending on the type of plant, they may be appropriately selected according to the target pore diameter. Further, so-called modified starch in which a hydrophobic functional group is introduced into the hydroxyl group of these starch granules to modify may be used. Further, in order to obtain a large pore size, it is also possible to use a processed starch in which the starch is once gelatinized, dried, pulverized and then classified if necessary.

The pore diameter and porosity can be adjusted by changing the kind and addition amount of the pore forming material.

Since the paper used in the present invention is used as a separator and is completely loosened and removed after the reaction, it does not contain a binder or additives, and has a low beating degree. It is preferable to use a product, that is, a product having properties almost similar to pulp.

The starch derivative used in the present invention is an anhydroglucose residue of starch to which various highly reactive functional groups are bound. Examples thereof include etherified starch in which a hydrophobic group or hydrophilic group such as carboxymethyl group, hydroxyalkyl group, cation group or the like is introduced into starch, organic acid such as acetic acid group, phosphoric acid group, methyl group, allyl group and the like. Examples thereof include esterified starch obtained by reacting starch with an inorganic acid or a salt thereof, and crosslinked starch having a polyfunctional group bonded between hydroxyl groups of two or more starches.

In the present invention, the starch derivative is applied to a separator paper to close the fine porous structure on the surface of the paper to make the surface relatively flat.

In order to apply the above-mentioned starch derivative to paper, a liquid in which the starch derivative is dispersed or dissolved in water or a solvent is applied to the surface of the paper, then dried and fixed on the surface of the paper. The method of applying is not particularly limited, but a method by mechanical printing such as roller printing or screen printing is preferable in that a good design can be stably obtained, and even by a method by hand printing Good. Above all, the method of roller printing is preferable because of high printing speed and high production efficiency.

In order to apply the starch derivative to the paper by mechanical printing, the viscous liquid (printing paste) in which the starch derivative is dispersed or dissolved needs to be stable. In this respect, when the starch derivative used in the present invention is dispersed or dissolved in water or a solvent, a liquid having a viscosity to some extent even at room temperature is obtained, and there is almost no change in physical properties such as viscosity with the passage of temperature and time, and therefore it is stable. It is possible to obtain a viscous liquid in such a state.

For example, the method of roller printing is generally performed as follows. That is, the printing paste is attached to a rotating copper engraving roller (the pattern is engraved on the roller). Next, when the printing paste on the surface of the roller is removed with a doctor, the printing paste remains only on the dented portion of the roller. This roller is pressed against the paper that is moving along a large cylinder (drum), and the printing paste of the dented portion is transferred to the paper to give a pattern.

In the present invention, since the above-mentioned starch derivative is used, in the roller printing step, the liquid in which the starch derivative as the printing paste is dispersed or dissolved efficiently moves from the engraving roller to the paper. Therefore, it is possible to form a design such as a clear pattern and characters without bleeding or flowing on the surface of the paper, and the surface flatness of the design portion is also excellent.

In the present invention, when ordinary starch is used in place of the above-mentioned starch derivative, the viscous liquid as the printing paste does not have stable physical properties such as viscosity and a good design for paper as a separator. Cannot be formed.

Among the above-mentioned starch derivatives, those having a high hydrophobicity can be dispersed and dissolved in a non-aqueous solvent, which makes it easy to dry after printing on paper, and rolls after printing on paper. It is advantageous in the case of being wound up on the sheet, and it is possible to prevent undesired phenomena such as deterioration and sticking due to humidity after application and the growth of mold. Further, when printing is carried out after being dispersed and dissolved in a water solvent, partial contraction and shrinkage of the paper, which are likely to occur after drying, do not occur, so that a clearer design can be formed.

The PVAt sponge sheet can be produced by the method of the present invention, for example, as follows.

That is, first, polyvinyl alcohol is dissolved in warm water to prepare a polyvinyl alcohol aqueous solution of about 5 to 15% by weight. A liquid in which starch as a pore-forming material is dispersed in water is added thereto, and an aqueous solution of sulfuric acid and formaldehyde is further added, followed by sufficiently stirring and mixing to obtain a uniform slurry-like stock solution.

The stock solution is heated to a temperature near the gelatinization temperature of starch and cast in a predetermined mold in a predetermined amount. A paper to which the starch derivative has been applied is placed thereon by the method of roller printing, and then a predetermined amount of the stock solution is poured again. Further, when the paper is placed and the stock solution is repeatedly cast in the same manner, the paper functions as a separator, and the layers separated from the paper are stacked in multiple layers.

The reaction is carried out at about 60 ° C. for 10 hours or more, and after the reaction is completed, the unreacted aldehydes, acids and starches are removed by squeezing and washing with water, and the paper is removed and peeled off at this portion. Thus, a PVAt sponge sheet can be manufactured.

The separator paper used in the above-mentioned method is printed with a viscous liquid in which the starch derivative is dispersed or dissolved in a desired shape such as letters or designs according to a roller printing method, and then dried. Those immobilized are preferable. If it is desired to form a design on both sides of the PVAt sponge sheet, after forming the design with the starch derivative on one side of the paper, the starch derivative is similarly printed and fixed on the other side to form the design. The one that has been used may be used.

Further, when the stock solution is cast, the cloths are placed, and the stock solution is poured again, the sheet-like article having the cloths as a reinforcing material can be obtained. The cloth used at this time is preferably cloth having a coarse mesh and capable of being firmly integrated with the PVAt sponge, such as a ginseng cloth.

[0032]

FUNCTION The reaction between polyvinyl alcohol and aldehydes is a dehydration cross-linking reaction, and the volume thereof usually shrinks as the reaction proceeds.

As described above, the paper used in the present invention has a property close to that of pulp, and its surface looks smooth at first glance, but microscopically it is an aggregate of fibers and has a three-dimensional network structure. None, the PVAt resin is firmly held in an adhered state with the surface of the paper. For this reason, the contraction due to the crosslinking reaction is suppressed in the portion in contact with the paper.

The essential point of the method of the present invention is that the behavior of the above-mentioned paper for a separator is well applied, and a sponge-like PVAt resin which is usually a reaction product is adhered to the paper as a separator. Is partially peeled off to cause a difference in surface condition.

That is, in the portion of the surface of the paper to which the starch derivative has been applied, the PVAt resin as the reaction product is peeled off without adhering to the paper. The part peeled from the paper shrinks along with the crosslinking reaction, and the surface state is significantly different from that of the part that is adhered to the paper and does not shrink. In particular,
The part to which the starch derivative has been applied has a concave surface.

[0036]

EXAMPLES The method of the present invention will be specifically described below with reference to examples.

A viscous liquid having a concentration of 15% was prepared by dispersing hydroxypropyl etherified starch (trade name: Abelex # 2530, manufactured by Matsutani Chemical Industry Co., Ltd.) modified based on potato starch as a starch derivative in water. did.
This viscous liquid was continuously printed on a roll-wound paper which did not undergo any surface treatment by using additives, by a roller printing method. The pattern printed is 3 straight lines with a width of 30 mm.
It was a striped pattern diagonally arranged with 0 mm intervals.

Next, the printed paper, on which the starch derivative was immobilized by heating and drying the paper, was once wound up on a roll and then cut into a predetermined length to prepare a separator paper. The amount of starch derivative applied is about 0.38 mg /
It was cm ² .

The hydroxypropyl etherified starch used in the roller printing step had a low viscosity even at a high concentration, and the physical properties such as the viscosity of the viscous liquid were extremely stable. Therefore, printing was carried out stably and continuously. Was broken. Further, in the above drying step, the viscous liquid printed on the paper was quickly dried, and the starch derivative was immobilized.

Separately from this, completely saponified polyvinyl alcohol (trade name: PVA-117, Kuraray Co., Ltd.)
750 g) was dissolved in warm water to make the total volume 8 l. Next, 700 g of corn starch was dispersed in water, and this was added to the above polyvinyl alcohol aqueous solution with stirring to make the total amount 10 l.

A mixed solution of 1 l of 37% formaldehyde aqueous solution and 1 l of 50% sulfuric acid was added to the mixed solution of polyvinyl alcohol and starch to form a homogeneous mixed solution, which was used as a reaction stock solution.

780 mm long x 490 mm wide x 100 depth
Prepare a mm stainless steel container, pour 300 ml of the reaction stock solution into it, and then place the reinforcing cloth on it, and then pour 300 ml of the reaction stock solution, and then pour it on top of it. The prepared separator paper was placed to almost completely separate the reaction stock solution layer. This procedure was repeated many times to form multiple layers. As the reinforcing cloth, a vinyl cloth made of vinylon fiber was used.

After the completion of stacking in the container, the container was placed in a heat treatment machine adjusted to 60 ° C., and the reaction was carried out for about one day and night. After the reaction was completed, the contents were taken out of the container and washed thoroughly with water to remove unreacted formaldehyde and sulfuric acid,
The starch was removed, the paper was further removed, and the reaction product was divided at this portion to obtain a sheet-shaped PVAt sponge.

The obtained PVAt sponge sheet had a striped pattern formed by depressions on the surface, and had a very high-grade appearance as compared with the ordinary one. The thickness of the sheet-like material was 1.6 mm, and the depth of the recessed portion was about 0.3 mm. The recessed portion had an excellent surface smoothness as compared with the normal portion, and the overall feeling of touch was also good.

Further, the obtained PVAt sponge sheet has a reinforcing cloth firmly inserted in the center portion in the thickness direction, so that it is strong even when used for a vehicle cleaning cloth, sports towel, etc. There was no problem at all and the usability was good. Furthermore, it was excellent in abrasion resistance and durability.

[0046]

According to the method of the present invention, desired designs such as designs and letters can be formed in relief or engraved on the surface of the PVAt type sponge sheet. Since the design formed by the method of the present invention is not formed by pressing a colored or heated mold, it does not impair the characteristics of the PVAt sponge sheet. In addition, it is possible to impart fashionability to a cleaning material such as a waste cloth and a towel, or a water absorbing material, and to give a high-class feeling.

The PVAt sponge sheet obtained by the method of the present invention has a design formed by the difference in surface smoothness and unevenness. The design is not lost by use and the design is excellent in durability. ing. Further, the uneven portion formed on the surface has an effect of capturing and holding the minute contaminant particles. Therefore, it is extremely excellent not only in appearance but also in performance as a cleaning material.

In the present invention, since the starch derivative is used, it is possible to perform the step of applying it to the paper for the separator by roller printing. That is, since the viscous liquid to which the starch derivative has been added has stable physical properties such as viscosity over time and the passage of time, the viscous liquid of the starch derivative smoothly moves from the engraving roller to the paper. A clear design can be obtained, and paper for a separator can be efficiently produced with stable quality.

Claims (2)

[Claims] 1. Polyvinyl alcohol, aldehydes,
A reaction stock solution containing acids and a pore-forming material is reacted in a state of being partitioned into layers with a paper for a separator, and after the reaction is completed,
At the time of removing unreacted aldehydes, acids, and pore-forming material and removing the paper to produce a polyvinyl acetal-based sponge sheet, a starch derivative was applied to at least a part of the surface of the separator paper. A method for producing a polyvinyl acetal-based sponge sheet, comprising: 2. Polyvinyl alcohol, aldehydes,
A reaction stock solution containing acids and a pore-forming material is reacted in a state of being partitioned into layers with a paper for a separator, and after the reaction is completed,
In addition to removing unreacted aldehydes, acids and pore-forming materials, in producing a polyvinyl acetal-based sponge sheet by removing the paper, when forming a design by roller printing on the surface of the paper for the separator, printing is performed. A method for producing a polyvinyl acetal-based sponge sheet, characterized in that a starch derivative is used as an adhesive paste.