JPH06313064A - Gel-strengthening agent for natural polysaccharide and method for increasing gel strength - Google Patents

Abstract

PURPOSE:To obtain a gel-strengthening agent capable of remarkably improving the gel strength of a natural polysaccharide such as agar useful as a binder for the injection molding of ceramic powder and metallic powder and to provide a method for increasing the gel strength. CONSTITUTION:The gel strength of a natural polysaccharide exhibiting sol-gel transition is remarkably improved by adding a gel-strengthening agent having sol form and composed of a polymer modified by substituting a part of groups with at least one kind of hydrophilic reactive groups selected from carboxyl group (COOH), carbonyl group (C=O), amino group (NH2) and sulfo group (SO3H), a polymer having these reactive groups, a powdery resin having functional groups and composed of an aqueous solution of the polymer or an aqueous solution of the resin powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel strengthening agent for improving the gel strength of a natural polysaccharide in a gel state, which is a resin powder having a specific functional group in the natural polysaccharide which causes a sol-gel transformation or an aqueous solution thereof. A gel strengthening agent for natural polysaccharides and a method for strengthening gel strength, characterized by increasing the strength in a gel state by adding a gel strengthening agent comprising

[0002]

2. Description of the Related Art Generally, natural polysaccharides that undergo sol-gel transformation are in a sol state at a temperature of 80 to 100 ° C. when they contain water, but are in a semi-solid gel state when the temperature is lowered to 30 to 40 ° C. Has the property of causing transformation. In recent years, the use of natural polysaccharides that undergo sol-gel transformation has spread, such as utilizing these properties in the fields of food, medical care, and biotechnology, and using them as a binder for injection molding of ceramic powder, metal powder, and the like.

[0003]

For example, when agar, which is a natural polysaccharide, is used as a binder for injection molding of ceramic powder, metal powder, etc., the powder, agar and water are usually mixed to form a binder. About 80 in the binder
% Or more is water. Therefore, compared to ordinary organic binders and the like, there is an advantage that the degreasing step is unnecessary because water in the binder is easily vaporized and evaporated, but the strength of the molded body is weak, so There are problems such as breakage and difficulty in molding large-sized products having a large molding weight and complicated-shaped products.

These problems are due to the weak gel strength of natural polysaccharides in a gel state, and it has been desired to improve the gel strength of natural polysaccharides in a gel state.
Therefore, in order to improve the gel strength, a method of using magnetically treated water instead of normal water as a binder has been proposed (Japanese Patent Application No. 4-88101), but in the method,
Since a device for producing the magnetically treated water has to be separately installed, the structure of the device becomes complicated, the workability deteriorates, the cost becomes high, and the remarkable improvement in gel strength cannot be expected.

The present invention aims to improve the gel strength of a natural polysaccharide in a gel state, and particularly in a gel state of a natural polysaccharide such as agar used as a binder for injection molding of ceramic powder or metal powder. An object of the present invention is to provide a gel enhancer for natural polysaccharides capable of remarkably improving the gel strength and a method for strengthening the gel strength.

[0006]

Means for Solving the Problems The inventors of the present invention have improved the gel strength of natural polysaccharides in the gel state, particularly in the gel state of agar used as a binder when molding the above-mentioned ceramic powder or metal powder. As a result of various studies on improving the gel strength, by adding a resin powder having a functional group or an aqueous solution thereof in a sol state, it was found that the gel strength of the agar gel state is significantly improved.
Completed this invention.

Namely, the present invention is a carboxyl group portions of the groups of the polymer is hydrophilic (-COOH), carbonyl group (> C = O), amino group (-NH _2), a sulfo group (-SO ₃ H) a polymer which is substituted with at least one reactive group, a polymer having the reactive group and a resin powder having a functional group consisting of an aqueous solution thereof, or an aqueous solution thereof, which is a gel enhancer for natural polysaccharides. .

Further, according to the present invention, in a natural polysaccharide which undergoes a sol-gel transformation, a part of the groups of the polymer is a hydrophilic carboxyl group (-COOH) or carbonyl group (> C =).
O), amino group (—NH ₂ ), sulfo group (—SO ₃ H), a polymer substituted with at least one reactive group, a polymer having the reactive group, and a resin powder having a functional group consisting of an aqueous solution thereof. A method for strengthening gel strength of natural polysaccharides, characterized by increasing the strength in a gel state by adding a gel strengthening agent composed of an aqueous solution. Furthermore, the present invention is the method for strengthening gel strength of natural polysaccharides, characterized in that, in the above-mentioned constitution, the natural polysaccharide is a binder for injection molding of ceramic powder or metal powder.

As a gel strengthening agent for strengthening the gel of natural polysaccharides, water and a resin powder having a functional group which causes a hydrogen bond or an ionic bond with the natural polysaccharide or an aqueous solution thereof is effective. That is, the carboxyl group portions of the groups of the polymer is hydrophilic (-COOH), carbonyl group (> C = O), amino group (-NH _2), at least the reactive group of a sulfo group (-SO ₃ H) A methacrylic resin having a functional group of polymethylmethacrylate (PMMA) or polymethylacrylate (PMA), which is a resin powder having a functional group consisting of a polymer substituted with one kind or a polymer having the reactive group and an aqueous solution thereof. Powder, acrylic aqueous solution having a functional group, polyethylene glycol or the like is preferable for improving gel strength,
In addition, a thermoplastic resin powder having a hydrophilic functional group is also effective. When substituting a part of the groups of the polymer with the above-mentioned reactive groups, it can be substituted with a plurality of reactive groups, but in order to keep the pH of the aqueous solution in the sol state as neutral as possible, each of the acidic and alkaline reactive groups Is preferably used in combination as appropriate, and each reactive group can be used in combination as appropriate to adjust the required pH.

When a resin powder having a functional group is used as the gel strengthening agent, a fine powder having a particle size of 0.5 μm or less is used in order to maximize the number of the functional group responsible for binding the resin powder per unit weight. Is effective. Also, it has been confirmed that the sol-gel transformation of natural polysaccharides is reversible with temperature regardless of the presence or absence of functional groups in the polymer and the addition amount thereof.

As a method for strengthening the gel strength, for example, a method in which agar, which is one of natural polysaccharides, is added with warm water heated to 60 ° C. and the above-mentioned gel strengthening agent and the mixture is stirred, etc.
If the agar with enhanced gel strength is used as a binder for injection molding of metal powder,
The metal powder is put into a mixture of agar, a gel strengthening agent and warm water, and further kneaded to form a kneaded product. The kneaded product is pelletized and then molded by an injection molding apparatus.

As mentioned above, when agar is used as a binder for injection molding of metal powder, the amount of agar powder added is about 2 to 4 wt% of the metal powder, and the amount of gel strengthening agent added is injection. Depending on the type of metal powder used for molding, the particle size and the amount of water added, 3 wt% of water
% Or less, or 0.5w with respect to the weight of the metal powder
Since the gel strength of agar is greatly improved by adding about t% or less, compared with conventional injection molding using an organic binder (when using an organic binder, about 10 wt% is usually added to the weight of the metal powder). The total amount of carbon in the binder can be reduced,
The residual carbon amount of the sintered body after the sintering as the subsequent step can be significantly reduced, and the use of agar as the binder has an advantage that the degreasing step as the subsequent step can be omitted.

[0013]

In the present invention, a part of the groups is a hydrophilic reactive group such as carboxyl group (-COOH) or carbonyl group (>).
C = O), amino group (-NH ₂₎ and a sulfo group (-SO ₃
H) a polymer substituted with at least one of them, a polymer having the reactive group and a resin powder having a functional group consisting of an aqueous solution thereof, or a gel toughening agent consisting of an aqueous solution thereof is added in a sol state to obtain a sol-gel transformation. It is possible to remarkably improve the gel strength of the natural polysaccharide that causes the above-mentioned problem.

That is, since the natural polysaccharide which causes the sol-gel transformation is water-soluble, a resin powder of a polymer having a functional group having hydrophilicity and its aqueous solution are most suitable as a gel strengthening agent, and they are most suitable for water. Since the strength is improved by about 1.5 times with the addition of 1 wt%, for example, a binder containing agar, which is one of the natural polysaccharides added with a gel strengthening agent, is used for injection molding of ceramic powder or metal powder. In this case, since the addition amount of the gel strengthening agent is extremely small, the mold release characteristic of the binder containing agar and the mold releasing property at the time of molding, without omitting the degreasing step, etc. The green strength can be remarkably improved, and the addition of a gel strengthening agent can reduce the amount of expensive agar powder used, so that it is possible to provide a cheaper product.

[0015]

[Example] Agar powder (MA20 manufactured by Shimizu Foods Co., Ltd.) was added to ordinary water.
No. 00) was added in an amount of 2.0 wt% and stirred, and then 0.5 wt% or 1.0 wt% of 0.5 μm polymethylmethacrylate (PMMA) powder was added as an additive. 0.5 parts by weight of (PMA) powder, 1.0 μm polyethylene glycol powder, and gel strengthening agent of acrylic aqueous solution in terms of solid content.
In each case where wt% was added, the mixture was heated to 96 ° C. with stirring and then cooled to gel. The gel strength was measured for each of the various additives mixed. The results are shown in Table 1.

Further, as comparative examples, under the same conditions, the one prepared by adding 0.5 wt% of 0.5 μm acrylic resin powder having no functional group and the one prepared by adding nothing were prepared and implemented. Table 1 shows the results of gel strength measurement performed by the same measurement method as in the examples. As is clear from Table 1, the agar according to the present invention to which the resin powder of the polymer having a functional group and the aqueous solution thereof are added has a markedly improved gel strength as compared with the agar without the addition and has no functional group. The gel strength is also improved as compared to the case where the polymer resin powder is added. This is because the functional group on the surface of the polymer resin powder is the nucleus, and in the case of an aqueous solution, the long linear polymer functional group is the nucleus, and the polymer functional group and the agar hydroxyl group (-OH) or hydroxymethylene group ( -CH ₂
OH) causes a cross-linking reaction, or
It is considered that the gel strength is improved by the hydrogen bond or ionic bond between the functional group of the polymer and the agar and water.

[0017]

[Table 1]

[0018]

Industrial Applicability According to the present invention, a polymer powder having a functional group consisting of a polymer having a partial group of reactive groups and an aqueous solution thereof or a gel toughening agent consisting of an aqueous solution thereof is added in a sol state of a natural polysaccharide. As a result, the gel strength of the natural polysaccharide that undergoes sol-gel transformation in the gel state can be significantly improved. In particular, when the natural polysaccharide added with the gel strengthening agent is used as a binder for injection molding of ceramic powder or metal powder, since the addition amount of the gel strengthening agent is extremely small, a binder containing agar is used. The green strength at the time of molding can be remarkably improved without impairing the mold releasability from the mold and the omission of the degreasing process, which is peculiar to the molding. Since it is possible to make a heavy and large product and to reduce the amount of expensive agar powder used, it is possible to provide a cheaper product.

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[Procedure amendment]

[Submission date] November 8, 1993

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Delete

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

[0015]

[Example] Agar powder (MA20 manufactured by Shimizu Foods Co., Ltd.) was added to ordinary water.
00) was added at 2.0 wt% and stirred, and then 0.5 wt% or 1.0 wt% of 0.5 μm polymethylmethacrylate (PMMA) powder was added as an additive, and 0.5 μm polymethyl acrylate was added. 0.5 parts by weight of (PMA) powder, 1.0 μm polyethylene glycol powder, and gel strengthening agent of acrylic aqueous solution in terms of solid content.
In each case where wt% was added, the mixture was heated to 96 ° C. with stirring and then cooled to gel. The gel strength was measured for each of the various additives mixed. The results are shown in Table 1. The gel strength is
Water type (Japan Agar Fisheries Industry Association), release at 20 ℃ for 15 hours
The maximum that can stand up to 20 seconds per cm ² after being set and solidified
The weight (gr) is used for evaluation.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of front page (71) Applicant 593102770 Yoshihisa Noro 3-11-1-401 Namiki, Kanazawa-ku, Yokohama-shi, Kanagawa (72) Inventor Osamu Yamashita 5-44, Kasugaoka, Ibaraki-shi, Osaka (72) Invention Person Masahiro Asano 262-4 Nagao, Toma Town, Kita Katsuragi-gun, Nara Prefecture (72) Inventor Hironori Nakayama 290-88 Shimono, Shimizu City, Shizuoka Prefecture (72) Inventor Hiroyuki Suzuki 138, Miho 138 Shimizu City, Shizuoka Prefecture 202 (72) Inventor Ryota Hashimoto 3-2, Kusanagi, Shimizu City, Shizuoka Prefecture (72) Inventor Yoshihisa Noro 3-11-1-401 Namiki, Kanazawa-ku, Yokohama-shi, Kanagawa

Claims (3)

[Claims] 1. A part of the polymer is a hydrophilic carboxyl group (—COOH) or carbonyl group (> C =).
O), amino group (—NH ₂ ), sulfo group (—SO ₃ H), a polymer substituted with at least one reactive group, a polymer having the reactive group, and a resin powder having a functional group consisting of an aqueous solution thereof. A gel enhancer for natural polysaccharides, which is an aqueous solution. 2. A natural polysaccharide which undergoes sol-gel transformation,
Some of the groups of the polymer are hydrophilic carboxyl groups (-
COOH), carbonyl group (> C = O), amino group (-
NH ₂ ), a polymer substituted with at least one reactive group of a sulfo group (—SO ₃ H) or a polymer having the reactive group and a resin powder having a functional group consisting of an aqueous solution thereof or a gel strengthening agent comprising an aqueous solution thereof. A method for strengthening gel strength of natural polysaccharides, which comprises adding to enhance the strength in a gel state. 3. The method for strengthening gel strength of natural polysaccharide according to claim 2, wherein the natural polysaccharide is a binder for injection molding of ceramic powder or metal powder.