JPH0121174B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a formal sponge with improved water retention, water return properties, and texture. Formal sponges made from polyvinyl alcohol are widely used, but they tend to be extremely hard when dried, do not always return smoothly when brought into contact with water, and have some problems with the texture when soaked with water. There are problems such as a lack of smoothness. In order to improve this point, it has been proposed to incorporate polyhydric alcohol into the formal sponge, but the effect of this is temporary and not sustainable. Japanese Patent Publication No. 38-9428 also discloses an attempt to formalize using modified polyvinyl alcohol into which acid groups or acid ester groups have been introduced as a raw material, but the improvement effect cannot be said to be sufficient. However, as a result of extensive research, the present inventors have found that a sponge obtained by formalizing modified polyvinyl alcohol (or a mixture of polyvinyl alcohol and polyvinyl alcohol) modified with an unsaturated carboxylic acid compound in the presence of a strong acid can be used in an alkaline aqueous solution. It has been discovered that when immersed in a medium, a formal sponge with significantly superior water retention properties, water return properties, and texture can be obtained, leading to the completion of the present invention. A sponge obtained by formalizing the above modified polyvinyl alcohol in the presence of a strong acid (untreated sponge) and a sponge obtained by immersing it in an alkaline aqueous medium (alkaline treated sponge)
(1) When immersed in water, the volume of the treated sponge is approximately 2 to 8 when the untreated sponge is 1. (2) When a dry sponge is put into water, the treated sponge returns water faster than the untreated sponge. (3) Treated sponges are much more flexible when immersed in water (soaked in water) and have a better texture. That is, when it touches the skin, it does not have a rough feel and gives an extremely smooth feeling. There are differences in effectiveness, such as: The alkali immersion treatment in the present invention is different from simple neutralization. In other words, the desired purpose cannot be achieved simply by neutralizing the strong acid catalyst remaining in the sponge after formalization, and the unsaturated carboxylic acid in the modified polyvinyl alcohol that constitutes the sponge must be made alkaline (especially at pH 9 or higher). At least a portion of the compound components must be in the form of an alkali salt. Because this component is formalized in the presence of a strong acid, it is in a free acid form or forms a lactone ring with an adjacent vinyl alcohol group, but its chemical structure can be changed by immersion treatment in an alkaline aqueous medium. It is converted into an alkali salt form by As the modified polyvinyl alcohol as a raw material in the present invention, polyvinyl alcohol modified with an unsaturated carboxylic acid compound is used. Such modified polyvinyl alcohol includes acrylic acid,
Unsaturated monocarboxylic acids or their salts such as methacrylic acid and crotonic acid; unsaturated dicarboxylic acids or their salts such as maleic acid, fumaric acid, and itaconic acid;
It can be obtained by copolymerizing an unsaturated carboxylic acid compound such as an anhydride or partially alkyl ester with vinyl acetate or other vinyl ester, and then saponifying the vinyl ester component in the copolymer. The copolymerization ratio of unsaturated carboxylic acid compound is 0.1 to 20 mol%,
In particular, it is appropriate to set it at 0.1 to 10 mol%,
When its content is too low, it lacks improvement effect,
On the other hand, if the amount is too high, the elastic recovery power is lost and a good sponge cannot be obtained. Although the degree of saponification of the vinyl ester component can vary widely, it is appropriate to set it to 70 mol% or more; if it is less than 70 mol%, it tends to lack elasticity and become too flexible. The above-mentioned modified polyvinyl alcohol can be used alone or mixed with ordinary polyvinyl alcohol for formalization. When polyvinyl alcohol is used in combination, the weight ratio of modified polyvinyl alcohol/polyvinyl alcohol is 0.1 or more, preferably 0.2.
or more, and the ratio of the unsaturated carboxylic acid compound to the total amount of both is 0.1 to 20 mol%,
In particular, it should be between 0.1 and 10 mol%. Formalization is carried out by reacting formaldehyde, polyoxymethylene, hexamethylenetetramine, etc. in an aqueous solution using a strong acid as a catalyst according to a known method. Other aldehydes can also be used in small amounts. As the strong acid catalyst, hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid, trichloroacetic acid, organic sulfonic acid, etc. are used. Foaming methods include mechanical stirring and foaming, using soluble substances, mixing fibers and other binding substances, using substances that give high viscosity, using pressurized gas, and foaming. Any known method, such as a method using a chemical agent, can be employed. For example, a soluble substance such as starch is added to the above-mentioned aqueous solution of modified polyvinyl alcohol, formalin and a strong acid are added to carry out a formalization reaction, and the resulting solid is thoroughly washed with water to remove the soluble substance. Just remove it. The sponge thus obtained does not necessarily have sufficient water retention properties, water return properties, and texture when used as is. Therefore, in the present invention, this sponge is treated by immersing it in an alkaline aqueous medium. As the alkali, caustic soda, caustic potash, soda carbonate, tribasic sodium phosphate, calcium hydroxide, etc. are used, and the pH of the alkaline aqueous solution is usually set to 9 or higher, preferably 10 or higher. The alkaline aqueous solution may be heated. It may also contain an organic solvent such as alcohol. If the pH is too low, the desired effect cannot be obtained. After performing the above treatment, wash the sponge,
After dehydration and drying, it becomes a product. In the present invention, the sponge may have any shape including a thin film shape. Alternatively, the sponge may be formed on a base material such as a woven fabric, a non-woven fabric, or a mesh body, and the sponge may have a laminated structure with these base materials. The sponge thus obtained can be used for household use (cosmetic,
It can be used for a wide range of purposes, including baths, kitchens), industrial uses, interior decoration, personal items, and agricultural and horticultural uses. Next, the method of the present invention will be further explained with reference to Examples. Hereinafter, "parts" and "%" are expressed on a weight basis unless otherwise specified. Example 1 90 parts of modified polyvinyl alcohol obtained by saponifying 98 mol% of the vinyl acetate component of a monomethyl maleate-vinyl acetate copolymer with a monomethyl maleate content of 3.0 mol% was dissolved in 810 parts of water to give a 10%
Prepare an aqueous solution and add 45% of horse starch to this aqueous solution.
124.2 parts of 37% formalin and 180 parts of 50% sulfuric acid, and further water was added to make the total 1500 parts. This mixed aqueous solution was allowed to react in a mold at 50° C. for 24 hours, and then the solid matter was taken out and thoroughly washed in water to obtain a sponge. This will be referred to as an untreated sponge. Next, when the untreated sponge was immersed in a 1/5 normal aqueous solution of caustic soda, it expanded rapidly, so it was repeatedly squeezed and water-absorbed in this state, and then thoroughly washed in water and dried. The sponge thus obtained will be referred to as a treated sponge. In addition, as a control example, the degree of polymerization was 1400 and the degree of saponification was 98 mol%.
An untreated sponge and a treated sponge were obtained in the same manner as in Example 1, except that polyvinyl alcohol was used as the raw material. The above results are shown in Table 1.

[Table] As is clear from the table above, sponges made from polyvinyl alcohol are somewhat unsatisfied with water retention, water return properties, and texture, and these properties hardly change even after treatment with an alkaline aqueous solution. . On the other hand, the quality of the sponge obtained using monomethyl maleate-modified polyvinyl alcohol as a raw material is also unsatisfactory, but it can be seen that the quality is significantly improved by treating it with an alkaline aqueous solution. Examples 2-3 Untreated and treated sponges were produced in the same manner as in Example 1, except that the following modified polyvinyl alcohols were used. Example 2 98 of the vinyl acetate component of an itaconic acid-vinyl acetate copolymer with an itaconic acid content of 2.5 mol%
Example 3 Modified polyvinyl alcohol obtained by saponifying mol% of vinyl acetate component of crotonic acid-vinyl acetate copolymer with crotonic acid content of 1.0 mol%
Modified polyvinyl alcohol obtained by saponifying mol% The results are shown in Table 2.

[Table] Examples 4 to 5 25 parts of modified polyvinyl alcohol obtained by saponifying 98 mol% of the vinyl acetate component of a fumaric acid-vinyl acetate copolymer with a fumaric acid content of 5.0 mol% and a degree of polymerization of 1400, saponified Dissolve 50 parts of 98 mol% polyvinyl alcohol in water to prepare a 10% aqueous solution. To this aqueous solution, add 40 parts of horse starch, 105 parts of 37% formalin, and 180 parts of 50% sulfuric acid, and further add water to make a whole. 1500 copies. This mixed aqueous solution was allowed to react in a mold at a temperature of 65° C. for 8 hours, and then the solid matter was taken out and thoroughly washed in water to obtain a sponge. (Untreated sponge) When this untreated sponge was immersed in a 1/10 normal aqueous solution of caustic soda, it expanded rapidly, so it was repeatedly squeezed and water-absorbed in this state, and then thoroughly washed in water and then dried. (Treated sponge) In addition, the vinyl acetate component of an acrylic acid-vinyl acetate copolymer with an acrylic acid content of 6.0 mol% is used as a raw material.
A sponge was produced in the same manner as above, except that 25 parts of acrylic acid-modified polyvinyl alcohol obtained by saponifying 98 mol% and 50 parts of polyvinyl alcohol with a degree of polymerization of 1400 and a degree of saponification of 98 mol% were used. The above results are shown in Table 3.

【table】

Claims (1)

[Claims] 1. An improved method characterized by immersing a sponge obtained by formalizing modified polyvinyl alcohol modified with an unsaturated carboxylic acid compound or a mixture of this and polyvinyl alcohol in the presence of a strong acid in an alkaline aqueous medium. Method for manufacturing formal sponge.