JP2010195950A - Aqueous composition of graft modified starch, and curable composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous composition of a graft modified starch obtained by a series of processes of gelatinization, addition reaction and graft reaction of a starch without the need of refinement, the aqueous composition obtaining a colorless film with a preferable viscosity stability in an aqueous solution state and a high water resistance even if a composition derived from a starch is included by a large amount. <P>SOLUTION: The aqueous composition of a graft modified starch with the crystallinity derived from the starch remaining is obtained by cutting the starch chain by dropping a monomer-emulsified product made of one or more ethylenically unsaturated monomers and an oxidizing agent in the presence of a starch with its α (gelatinization) degree controlled, and carrying out graft polymerization reaction of the ethylenically unsaturated monomer to the starch at the same time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aqueous composition of graft-modified starch that can be used as a plastic, paint, or adhesive, using starch, which is a renewable natural resource, as a main raw material as an alternative to various petroleum-derived resins.

At present, chemical synthetic resin products such as plastics, paints, and adhesives are materials used in every field of life and industry, and their production is enormous. However, most of these chemical synthetic resins are incinerated or disposed of in the soil after use, and in recent years it has become a problem to adversely affect the global environment due to the release of CO ₂ and harmful substances. Yes. In addition, petroleum, which is a raw material for chemically synthesized resins, is a finite resource, and there are growing concerns about depletion in the future. Therefore, building a recycling-oriented society by switching from depleted resources to renewable resources has attracted attention.

Therefore, it is necessary to actively use natural resources from the viewpoint of reducing the impact on the global environment, such as improving the disposal of waste and reducing CO ₂ emissions, and from the viewpoint of switching to renewable resources. It has been demanded.

  Naturally-occurring raw materials include polysaccharide starch. Starch can be easily isolated from plants and is available at a relatively low cost. In addition to edible materials, starch paste or plasticizer blended is conventionally processed (casting, extrusion molding, mold molding, foam molding, etc.), film, food container, packaging material, cushioning material, etc. Has been used. However, due to problems such as an aging phenomenon, low film formability, and low water resistance, it is difficult to use as a substitute for synthetic resin products.

  As a method for solving this problem, a modified starch in which the hydroxyl group of starch is substituted with another functional group has been proposed. For example, thermoplastic modified starch in which long chain and short chain hydrocarbon groups are added to starch by an esterifying agent in DMSO is disclosed (see Patent Document 1). Modified starch can greatly change the properties of starch, but a high degree of substitution is required to obtain sufficient water resistance. In order to obtain a high degree of substitution, a large excess of a modifier and a catalyst is required, and there is a problem that the cost for purification increases.

  On the other hand, a graft-modified starch obtained by grafting another type of polymer has been proposed. For example, a papermaking additive comprising a water-soluble polymer substance such as starch, a water-soluble cationic monomer, an α, β-unsaturated dicarboxylic acid, and a water-soluble polymer having acrylamide and / or methacrylamide as essential components is disclosed. (See Patent Document 2). Also manufactured using a free radical initiator that forms three or more free radical sites per molecule when free radical polymerizing hydrophilic monomers in the presence of starch and / or chemically modified starch A water-swellable hydrophilic polymer composition is disclosed (see Patent Document 3). In addition, a temperature-responsive material is disclosed in which a polysaccharide skeleton and a segment having cohesiveness are bonded by heating (see Patent Document 4). In Patent Document 4, polymerization of polysaccharide and a carboxylic acid having a polymerizable group such as a vinyl group or a reactive derivative thereof (anhydrous (meth) acrylic acid, maleic anhydride, (meth) acrylic acid chloride, etc.) is started. It is described that a side chain of a cohesive polymer can be introduced into a polysaccharide by reacting in the presence of an agent, introducing a polymerizable group by an ester bond, and subjecting it to polymerization with a monomer. However, in order to obtain a graft-modified starch having a high graft ratio, it is necessary to use an expensive cerium (IV) catalyst or a highly dangerous irradiation method. Starch could not be obtained, and various physical properties such as water resistance of the obtained film were not sufficient.

  Also, at least one kind of decomposition with respect to a monomer comprising (a) styrene and / or methylstyrene, (b) butadiene-1,3 and / or isoprene and (c) other ethylenically unsaturated copolymerizable monomer An aqueous polymer dispersion obtained by radical-initiated copolymerization in the presence of 10 to 40% by weight of the starch and a water-soluble redox catalyst is disclosed (see Patent Document 5). However, since the amount of starch used is 40% by mass or less based on the ethylenically unsaturated copolymerizable monomer, the object of using a renewable natural raw material as an alternative to a petroleum raw material cannot be achieved.

JP 2000-159802 A JP-A-8-246388 Japanese Patent Laid-Open No. 10-330433 JP 2003-252936 A JP 2005-528478 A

  Therefore, the present invention has been made to solve the above-described problems, and does not require purification, and can be obtained by performing starch gelatinization, addition reaction, and graft reaction in a series of steps. An object of the present invention is to provide an aqueous composition of a graft-modified starch that has a good viscosity stability in an aqueous solution state and has a high water resistance even when a large amount of starch-derived components are contained, and a film having no color can be obtained. To do.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention added dropwise a monomer emulsion composed of one or more ethylenically unsaturated monomers and an oxidizing agent in the presence of starch with a controlled degree of gelatinization. An aqueous composition of graft-modified starch that retains the crystallinity derived from starch, obtained by simultaneously performing starch chain scission and graft polymerization reaction of ethylenically unsaturated monomer onto starch. The present invention has been found to be useful for solving the problems, and the present invention has been completed.

  That is, the present invention is an emulsion polymerization of an ethylenically unsaturated monomer in an aqueous medium in the presence of starch to which a dicarboxylic anhydride compound having a linear or branched alkyl group or alkenyl group having 4 to 30 carbon atoms is added. It is an aqueous composition of graft-modified starch obtained by, and the graft-modified starch has 40 to 2000% by mass of a starch-derived component with respect to a polymer component comprising an ethylenically unsaturated monomer, and is a starch-derived component The present invention relates to an aqueous composition of graft-modified starch having a gelatinization degree of 80% or less.

  The aqueous composition of graft-modified starch is an anhydrous dicarboxylic acid having a linear or branched alkyl or alkenyl group having 4 to 30 carbon atoms in at least one (A) pregelatinized starch having a pregelatinization degree of 80% or more. It is preferably obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of a modified starch to which an acid compound has been added and at least one (B) starch having a degree of alpha conversion of 20% or less.

  The ratio of (A) pregelatinized starch having a pregelatinization degree of 80% or more and (B) starch having a pregelatinization degree of 20% or less is preferably 10:90 to 90:10.

  The amount of the ethylenically unsaturated monomer used is 5% by mass to 250% by mass with respect to the total amount of (A) pregelatinized starch having a pregelatinization degree of 80% or more and (B) starch having a pregelatinization degree of 20% or less. Preferably there is.

  The amount of the dicarboxylic anhydride compound (A) added to the pregelatinized starch having a pregelatinization degree of 80% or more is preferably 0.1% by mass to 30% by mass.

  The dicarboxylic anhydride compound is preferably octenyl succinic anhydride.

  The aqueous composition of graft-modified starch is preferably obtained by emulsion polymerization of an ethylenically unsaturated monomer using a redox initiator.

  The reducing agent of the redox initiator is preferably thiourea dioxide or sodium dithionite.

  The ethylenically unsaturated monomer preferably includes an ethylenically unsaturated monomer having a reactive group capable of reacting with a starch hydroxyl group.

  The present invention also relates to a curable composition characterized in that it is a mixture of an aqueous composition of graft-modified starch and a curing agent having a functional group capable of reacting with a hydroxyl group or a carboxyl group.

  According to the present invention, purification is not required and starch is modified in a series of steps. The viscosity is good in the state of an aqueous dispersion, and the polymer component is composed of an ethylenically unsaturated monomer. On the other hand, even if the starch-derived component is contained in an amount of 40% by mass or more, it is possible to provide an aqueous composition of graft-modified starch that can be obtained without coloring and having good water resistance.

  Hereinafter, the present invention will be described in detail.

  The aqueous composition of graft-modified starch of the present invention comprises (A) pregelatinized starch having a degree of pregelatinization of 80% or more (hereinafter referred to as (A) pregelatinized starch), linear or branched chain having 4 to 30 carbon atoms. Modified starch having an alkyl group or an alkenyl group added thereto, and (B) starch having a degree of alpha conversion of 20% or less (hereinafter referred to as (B) starch), It is obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of starch. By using such a method, even if the graft-modified starch has a starch-derived component of 40% by mass or more based on the total amount of the polymer component composed of the ethylenically unsaturated monomer, a film having high water resistance can be obtained. It is possible to produce an aqueous composition of the resulting graft-modified starch. The starch-derived component has a solid content of 40 to 2000% by mass and preferably 40 to 1000% by mass with respect to the polymer component composed of the ethylenically unsaturated monomer. If the starch-derived component is greater than 2000% by mass, the effects of improving water resistance and imparting flexibility due to grafting of the ethylenically unsaturated monomer cannot be obtained. Further, the viscosity stability tends to decrease due to aging of starch.

  The (A) pregelatinized starch used in the present invention contributes to the dispersion stability of the graft-modified starch in an aqueous medium. (A) Specific examples of pregelatinized starch include natural carbohydrates composed of amylose and / or amylopectin and derivatives thereof, more specifically corn starch, potato starch, tapioca starch, wheat starch, sweet potato starch , Rice starch, waxy starch, and modified starch based on these starches are alpha-treated, and the degree of alpha-ization is 80% or more, more preferably 90% or more, and is transparent when dissolved in an aqueous medium. An aqueous starch solution can be obtained. When the degree of pregelatinization is less than 80%, the dispersion stability of the graft-modified starch in an aqueous medium is lowered, and the graft-modified starch tends to settle. Especially, it is more preferable that the weight average molecular weight of (A) pregelatinized starch is 500,000 or more. When the weight average molecular weight is less than 500,000, a very large amount of very short starch chains are generated by the cleavage of starch chains by an oxidizing agent during the grafting reaction, and the water resistance tends to be lowered. The method for the alpha treatment is not particularly limited, and known methods such as hot water treatment, alkali treatment, and wet heat treatment can be used.

  The starch (B) used in the present invention contributes to improving the water resistance of the graft-modified starch. (B) Specific examples of starch include natural carbohydrates composed of amylose and / or amylopectin, and derivatives thereof, more specifically corn starch, potato starch, tapioca starch, wheat starch, sweet potato starch, rice Starch, waxy starch, and modified starch based on these starches, with a degree of gelatinization of 20% or less, more preferably 10% or less. When the degree of pregelatinization exceeds 20%, the crystallinity remaining in the obtained graft-modified starch is low, and the water resistance tends to be lowered. Especially, it is more preferable that the weight average molecular weight of (B) starch is 500,000 or more. When the weight average molecular weight is less than 500,000, a very large amount of very short starch chains are generated by the cleavage of starch chains by an oxidizing agent during the grafting reaction, and the water resistance tends to be lowered.

  In addition, the aqueous composition of the graft-modified starch of the present invention is obtained by adding (A) a dicarboxylic acid anhydride compound having an alkyl group or an alkenyl group to pregelatinized starch, and (B) adding the starch, and then adding these starches. As described above, it can be obtained by emulsion polymerization of an ethylenically unsaturated monomer. However, as long as the α-degree of the starch-derived component in the graft-modified starch is 80% or less, the α-degree is 20%. After adding a dicarboxylic anhydride compound having a linear or branched alkyl or alkenyl group having 4 to 30 carbon atoms to -80% starch, an ethylenically unsaturated monomer in the presence of the modified starch Can also be produced by emulsion polymerization.

  The dicarboxylic anhydride compound for modifying (A) the pregelatinized starch used in the present invention is an addition reaction with the hydroxyl group of starch, and starch is introduced with a hydrophobic alkyl group or alkenyl group and a hydrophilic carboxyl group. Improves emulsifying power. In the case of a linear alkyl group or an alkenyl group, the viscosity of the starch aqueous solution is greatly reduced by forming a complex with the starch chain and inhibiting the formation of the double helical structure of the starch chain, and further aging. There is an effect to prevent. Specific examples include octenyl succinic anhydride, decenyl succinic anhydride, dodecenyl succinic anhydride, tetradecenyl succinic anhydride, hexadecenyl succinic anhydride, octadecenyl succinic anhydride, and the like. The alkyl group or alkenyl group of the dicarboxylic anhydride compound preferably has 4 to 30 carbon atoms, and more preferably a straight chain having 6 to 22 carbon atoms. When the carbon number is less than 4, the hydrophobicity of the alkyl group or alkenyl group added to the starch is weak, so that the emulsifying power of the starch is weak and the water resistance is also lowered. When the number of carbon atoms is larger than 30, the dicarboxylic anhydride compound has strong hydrophobicity and low affinity with starch, so that the efficiency of the addition reaction is lowered and the effect cannot be obtained. Of these, linear octenyl succinic anhydride and decenyl succinic anhydride are preferable in terms of addition efficiency and emulsifying power.

  (A) The addition amount of the dicarboxylic anhydride compound to the pregelatinized starch is preferably 0.1% by mass to 30% by mass, and more preferably 1% by mass to 20% by mass. When the amount of dicarboxylic anhydride added is less than 0.1% by mass, the emulsifying power of starch is low, the graft reaction becomes unstable, and the aging resistance tends to decrease. When the amount of dicarboxylic anhydride added exceeds 30% by mass, the alkali resistance tends to decrease.

  In addition, in calculation of the mass ratio of each raw material of this invention and starch, the dry mass which dried starch for 3 hours at 110 degreeC is used as the mass of starch. The same applies hereinafter.

  In the present invention, the addition reaction of the dicarboxylic anhydride compound to starch is preferably performed at 60 to 95 ° C, more preferably 80 to 95 ° C. When the temperature is lower than 60 ° C., starch gelatinization is insufficient, and the addition of dicarboxylic anhydride to starch tends to be uneven.

  The ethylenically unsaturated monomer graft-polymerized to starch used in the present invention has the effect of improving the water resistance of starch and imparting flexibility by grafting to starch. Specific examples include methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, cyclohexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid Examples include 2-hydroxypropyl, 2-hydroxypropyl methacrylate, acrylonitrile, methacrylonitrile, methoxyethyl acrylate, methoxyethyl methacrylate, butoxyethyl acrylate, butoxyethyl methacrylate, styrene, vinyl acetate, and vinyl propionate. Of these, butyl acrylate, ethyl acrylate, butyl methacrylate, and methyl methacrylate are preferred from the viewpoint of grafting efficiency to starch.

  The amount of the ethylenically unsaturated monomer used in the emulsion polymerization is preferably 5% by mass to 250% by mass and more preferably 20% by mass to 200% by mass with respect to the total amount of starch. When the amount is less than 5% by mass, the effect of improving water resistance and imparting flexibility by grafting cannot be obtained. When it is more than 250% by mass, the graft polymerization tends to become unstable. In addition, the amount of starch used is reduced, and the use of renewable natural raw materials as an alternative to petroleum raw materials is deviated.

  Moreover, it is preferable to contain the ethylenically unsaturated monomer which has a reactive group which can react with the hydroxyl group of starch as an ethylenically unsaturated monomer graft-polymerized to the starch used by this invention. The ethylenically unsaturated monomer having a reactive group improves the grafting frequency of the monomer to starch, and has effects of preventing aging and improving water resistance. Specific examples include 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, trimethoxysilylpropyl methacrylate, and glycidyl methacrylate. The amount of the ethylenically unsaturated monomer having a reactive group capable of reacting with the hydroxyl group of starch is preferably 0.1% by mass to 30% by mass with respect to the total amount of (A) pregelatinized starch and (B) starch. It is more preferable that it is 0.5 mass%-15 mass%. If it is less than 0.1% by mass, the effects of preventing aging and improving water resistance cannot be obtained. When it is more than 30% by mass, the graft polymerization tends to be unstable and the storage stability tends to be lowered.

  In the present invention, the ratio of (A) pregelatinized starch to (B) starch and the crystallinity remaining in the graft-modified starch are controlled by the reaction temperature of the graft polymerization of the ethylenically unsaturated monomer. The ratio of (A) pregelatinized starch and (B) starch used in the present invention is 10:90 to 90:10, more preferably 20:80 to 80:20. (A) When the ratio of pregelatinized starch is less than 10%, the dispersion stability of the resulting graft-modified starch in an aqueous medium is lowered, and the graft-modified starch tends to settle. (A) When the ratio of pregelatinized starch exceeds 90%, the crystallinity remaining in the obtained graft-modified starch is low, and the water resistance tends to decrease.

  In the present invention, the polymerization reaction of the ethylenically unsaturated monomer is preferably performed at a reaction temperature of 30 ° C to 60 ° C, more preferably 40 to 60 ° C. When the temperature is lower than 30 ° C., aging of the starch proceeds during the reaction, and the graft tends to become non-uniform. When the temperature is higher than 60 ° C., gelatinization of the starch proceeds, the crystallinity remaining in the obtained graft-modified starch is low, and the water resistance tends to decrease.

  The redox initiator used in the present invention is a combination of an oxidizing agent that is water-soluble and cleaves to generate radicals, and a reducing agent that promotes cleavage of the oxidizing agent. By using a redox initiator, the graft reaction can be carried out at a temperature lower than the gelatinization temperature of starch, and the decrease in crystallinity remaining in the graft-modified starch obtained can be prevented.

  Specific examples of the oxidizing agent include persulfates such as hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate, and organic peroxides such as t-butyl hydroperoxide and disuccinic acid peroxide. These may be used individually by 1 type and may be used in combination of 2 or more type. The oxidizing agent is preferably used in the range of 0.1% by mass to 20% by mass with respect to the total amount of (A) pregelatinized starch and (B) starch. When the amount of the oxidizing agent used is less than 0.1% by mass, the degree of starch cutting is low, the viscosity of the system increases, and the aging resistance may decrease. When the usage-amount of an oxidizing agent exceeds 20 mass%, the molecular weight of graft-modified starch will become low and water resistance may fall.

  Specific examples of the reducing agent include thiourea dioxide, sodium dithionite, acidic sodium sulfite, Rongalite, L-ascorbic acid, tartaric acid, oxalic acid, and ferrous sulfate. Of these, thiourea dioxide and sodium dithionite are more preferred because of their high reducing power and difficulty in coloring. These may be used individually by 1 type and may be used in combination of 2 or more type. The amount of the reducing agent used is an amount necessary for cleaving the oxidizing agent, and is preferably used in an amount of 0.1 mol equivalent to 2 mol equivalent with respect to the oxidizing agent.

  The surfactant used in the present invention emulsifies the ethylenically unsaturated monomer composition and adjusts the monomer concentration in the aqueous medium during the reaction, thereby allowing the non-grafted copolymer of the ethylenically unsaturated monomer in the aqueous medium. Suppresses the formation of polymer and improves the graft ratio. Specific examples include anionic emulsifiers such as alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, alkyl allyl sulfosuccinate, styrene sulfonate, alkyl benzene sulfonate, glycerin alkyl ether, polyoxyethylene alkylphenyl, etc. Nonionic emulsifiers such as ether, polyoxyethylene alkyl ether, polyoxyethylene carboxylic acid ester, polyoxyalkylene alkyl ether, water-soluble polymers such as octenyl succinic acid starch, hydroxyethyl cellulose, polyvinyl alcohol, and the like. These may be used individually by 1 type and may be used in combination of 2 or more type. Among these, those having a long-chain alkyl group having an antiaging effect are preferable. The surfactant is preferably used in the range of 0.1% by mass to 5% by mass with respect to the ethylenically unsaturated monomer composition. When the amount of the surfactant used is less than 0.1% by mass, the graft ratio may be decreased. On the other hand, when the amount of the surfactant used exceeds 5% by mass, the water resistance may be decreased. .

  The curing agent used in the present invention reacts with the hydroxyl group or carboxyl group of the graft-modified starch to crosslink between the graft-modified starch molecules, thereby improving water resistance and alkali resistance. Examples of the functional group capable of reacting with the hydroxyl group or carboxyl group of the graft-modified starch include an isocyanate group, an acid anhydride, a carbodiimide group, and an epoxy group. Specific examples of the compound having a functional group (curing agent) include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, xylene diisocyanate, ethylene glycol bisanhydro trimellitate, glycerin bis anhydro trimellitate monoacetate, 3, 3 ′ 4,4′-diphenylsulfonetetracarboxylic dianhydride, polycarbodiimide, neopentyl glycol diglycidyl ether, glycerin triglycidyl ether, and the like. Of these, hexamethylene diisocyanate is preferred because it has a relatively fast crosslinking reaction and is well dispersed in an aqueous medium.

  It is preferable to use a hardening | curing agent in 1 mass%-50 mass% with respect to the total amount of (A) pregelatinized starch and (B) starch. When the amount of the curing agent used is less than 1% by mass, the crosslinking density between the graft-modified starch molecules is low, and the water resistance and alkali resistance may not be improved. When the usage-amount of a hardening | curing agent exceeds 50 mass%, a pot life is very short and workability | operativity may fall.

  In the reaction step of the graft-modified starch of the present invention, starch chain cleavage by acid or enzyme may be used in combination.

  The aqueous composition of the graft-modified starch of the present invention includes resins, colorants, plasticizers, anti-aging agents, antiseptics, bactericides, antifoaming agents, wetting agents, UV absorbers, and light stabilizers other than those described above. You may add suitably well-known usual additives, such as an agent, in the range which does not impair the effect of this invention.

  In addition, the gelatinization degree (alpha-ization degree) of the starch in this invention measured the enthalpy of the gelatinization endothermic peak detected in the following conditions on the following conditions using a differential scanning calorimeter, and the following It is calculated by equation (1).

Sample: An aqueous solution prepared by adding distilled water to starch to a solid content concentration of 20%, or a suspension in which the suspension was allowed to stand for 1 hour.
Sample container: Silver sealed container Reference: Distilled water Measurement temperature: 5 ° C to 105 ° C
Temperature increase rate: 4 ° C / min

In formula (1), ΔHg ₁ is the gelatinized endothermic enthalpy detected in the sample starch, and ΔHg ₂ is the gelatinized endothermic enthalpy detected in the raw starch in the untreated state of the sample starch.

  The gelatinization degree (alpha degree) of the starch-derived component in the graft-modified starch in the present invention is determined by using a differential scanning calorimeter, and the enthalpy of the gelatinization endothermic peak detected at around 50 ° C. to 90 ° C. under the following conditions. Is calculated by the following equation (2).

Sample: An aqueous dispersion prepared by adding distilled water to graft-modified starch to a solid content concentration of 20% and allowing to stand for 1 hour.
Sample container: Silver sealed container Reference: Distilled water Measurement temperature: 5 ° C to 105 ° C
Temperature increase rate: 4 ° C / min

In formula (2), ΔHg ₃ is the gelatinized endothermic enthalpy detected in the aqueous dispersion of the sample-grafted modified starch, and ΔHg ₄ is the starch (and in the untreated state) used to obtain the graft-modified starch. The gelatinized endothermic enthalpy detected in an aqueous suspension of raw starch), C ₁ is the concentration of the starch-derived component in the aqueous dispersion of the sample graft modified starch, and C ₂ is used to obtain the graft modified starch. Concentration of the aqueous suspension of the raw starch (and raw starch in the untreated state).

  In the aqueous composition of the graft-modified starch of the present invention, the pregelatinization degree of the starch-derived component present in the graft-modified starch is 80% or less, more preferably 50 to 75%. When the pregelatinization degree of the starch-derived component is higher than 80%, the water resistance tends to decrease. When the degree of pregelatinization of the starch-derived component is lower than 50%, the stability of the obtained graft-modified starch in an aqueous medium is lowered and tends to settle.

  The use of the aqueous composition of the graft-modified starch of the present invention is not particularly limited, and examples thereof include plastics, paint binders, adhesives, laundry glue, sizing agents, and coating agents.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the part and% in an example are "mass part" and "mass%" unless there is particular notice. Moreover, the mass of starch is a mass as a hydrate.

[Example 1]
In a reaction vessel equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, 100 parts by mass of ion-exchanged water and oxidized starch (made by Oji Cornstarch Co., Ltd., trade name “Oji Ace A”, water content 12.5% by mass) 57.1 parts by mass were charged and stirred to obtain a starch slurry. The temperature was raised to 95 ° C. and stirred for 30 minutes to make the starch slurry into a transparent gelatinized starch aqueous solution (degree of gelatinization 99%). After cooling the temperature to 55 ° C., 57.1 parts by mass of oxidized starch (0% gelatinization) and 350 parts by mass of ion-exchanged water were added. A monomer emulsion in which 100 parts by mass of butyl acrylate, 0.4 part by mass of a surfactant (“ADEKA rear soap SR-10” manufactured by ADEKA Co., Ltd.) and 60 parts by mass of ion-exchanged water are mixed for 5 hours. And dripped. At the same time, an oxidizing agent aqueous solution in which 5 parts by mass of 35% hydrogen peroxide water and 20 parts by mass of ion-exchanged water are mixed, and an aqueous reducing agent solution in which 5.6 parts by mass of thiourea dioxide are dissolved in 300 parts by mass of ion-exchanged water are taken for 5 hours. Then, it was dropped into the reaction vessel. After completion of dropping, the mixture was further stirred at 55 ° C. for 2 hours and then cooled to room temperature to obtain an aqueous dispersion of graft-modified starch.

[Example 2]
In Example 1, when the starch slurry was heated to 95 ° C., 7 parts by mass of octenyl succinic anhydride was added to the reaction vessel, and an addition reaction was performed simultaneously with gelatinization of the starch slurry. Otherwise in the same manner as in Example 1, an aqueous dispersion of the graft-modified starch of Example 2 was obtained.

Example 3
The water of the graft-modified starch of Example 3 was the same as Example 2 except that 100 parts by mass of butyl acrylate in Example 2 was a mixture of 90 parts by mass of butyl acrylate and 10 parts by mass of trimethoxysilylpropyl methacrylate. A dispersion was obtained.

Example 4
An aqueous dispersion of the graft-modified starch of Example 4 was obtained in the same manner as in Example 2 except that 5.6 parts by mass of thiourea dioxide in Example 2 was changed to 4.5 parts by mass of ascorbic acid.

[Comparative Example 1]
The same operation as in Example 2 was performed except that the temperature of the starch slurry in Example 2 was changed to 65 ° C. However, due to polymerization of the monomer emulsion, precipitation separation occurred in the reaction product, and an aqueous dispersion of graft-modified starch could not be obtained.

[Comparative Example 2]
The grafted graft of Comparative Example 2 was prepared in the same manner as in Example 2, except that the oxidized starch charged after cooling to a temperature of 55 ° C in Example 2 was charged at a temperature of 60 ° C, stirred for 30 minutes at 60 ° C and then cooled to 55 ° C. An aqueous dispersion of modified starch was obtained.

[Comparative Example 3]
In Example 2, 190 parts by mass of ion-exchanged water and 108.6 parts by mass of oxidized starch were charged in a reaction vessel and stirred to obtain a starch slurry. The temperature was raised to 95 ° C., and 13.3 parts by mass of octenyl succinic anhydride was added to the reaction vessel. After stirring at 95 ° C. for 30 minutes, the temperature was cooled to 55 ° C., and 5.7 parts by mass of oxidized starch and 260 parts by mass of ion-exchanged water were added. Otherwise in the same manner as in Example 2, an aqueous dispersion of the graft-modified starch of Comparative Example 3 was obtained.

[Comparative Example 4]
In Example 2, 10 parts by mass of ion-exchanged water and 5.7 parts by mass of oxidized starch were charged into a reaction vessel and stirred to obtain a starch slurry. The temperature was raised to 95 ° C., and 0.7 part by mass of octenyl succinic anhydride was added to the reaction vessel. After stirring at 95 ° C. for 30 minutes, the temperature was cooled to 55 ° C., and 108.6 parts by mass of oxidized starch and 440 parts by mass of ion-exchanged water were added. Otherwise, the same operation as in Example 2 was performed. However, due to polymerization of the monomer emulsion, precipitation separation occurred in the reaction product, and an aqueous dispersion of graft-modified starch could not be obtained.

[Comparative Example 5]
An aqueous dispersion of the graft-modified starch of Comparative Example 5 was obtained in the same manner as in Example 2 except that octenyl succinic anhydride in Example 2 was changed to succinic anhydride.

[Comparative Example 6]
Except that the monomer emulsion in Example 2 was a monomer emulsion in which 4 parts by mass of butyl acrylate, 0.016 parts by mass of a surfactant, and 2.4 parts by mass of ion-exchanged water were mixed, An aqueous dispersion of the graft-modified starch of Comparative Example 6 was obtained.

[Comparative Example 7]
In Example 2, 200 parts by mass of ion-exchanged water and 114.2 parts by mass of oxidized starch were charged in a reaction vessel and stirred to obtain a starch slurry. The temperature was raised to 60 ° C. to obtain a gelatinized starch aqueous solution (gelatinization degree 58%), and octenyl succinic anhydride was added at a temperature of 60 ° C. to carry out an addition reaction. After cooling to a temperature of 55 ° C., the same operation as in Example 2 was performed, except that oxidized starch having a gelatinization degree of 0% was not used and only 250 parts by mass of ion-exchanged water was added. However, due to polymerization of the monomer emulsion, precipitation separation occurred in the reaction product, and an aqueous dispersion of graft-modified starch could not be obtained.

  The aqueous solutions of the graft-modified starches of Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated according to the following methods. The results are shown in Tables 1 and 2.

(Create film)
A polyethylene sheet was pasted on a glass plate, and a frame was made of silicon on the sheet. An aqueous dispersion of graft-modified starch was poured into the frame in such an amount that the film thickness of the dried film was about 0.4 mm and dried at 23 ° C. and humidity 65% RH for 7 days. The presence or absence of hue, cracks, and distortion was visually observed.

(Elution rate)
0.2 parts by mass of the prepared film was dried at 110 ° C. for 5 hours, and the dry mass of the film was measured. 0.2 parts by mass of the prepared film was immersed in 50 parts by mass of ion-exchanged water for 1 day. One day later, the film was taken out and dried at 110 ° C. for 5 hours, and the dry mass of the film after water immersion was measured. The water elution rate was calculated by the following formula (3).

(Starch-derived component in graft-modified starch)
The degree of gelatinization (degree of gelatinization) of the starch-derived component in the graft-modified starch is calculated by the equation (2) by measuring the enthalpy of the gelatinization endothermic peak using a differential scanning calorimeter under the conditions described above. did.

  As is apparent from the results of Tables 1 and 2, the aqueous dispersions of graft-modified starches of Examples 1 to 3 can form a film having no color and good water resistance, and Examples 2 and 3 are viscosity stable. Good properties.

[Example 5]
4 parts by mass of hexamethylene diisocyanate was added as a curing agent to 100 parts by mass (20 parts by mass in solid content) of the graft-modified starch aqueous dispersion obtained in Example 2 to obtain a curable composition. About the obtained curable composition, the film performance was measured by the method similar to the method described above. The color of the film was colorless, there was no crack or distortion, and the water elution rate was 4.0%, which was a very low value.

Claims (10)

Grafts obtained by emulsion polymerization of ethylenically unsaturated monomers in an aqueous medium in the presence of starch to which a dicarboxylic anhydride compound having a linear or branched alkyl group or alkenyl group having 4 to 30 carbon atoms is added. It is an aqueous composition of modified starch, and the graft-modified starch has 40 to 2000 mass% of starch-derived components with respect to the polymer component composed of ethylenically unsaturated monomer, and the starch-derived component has a degree of alpha of 80%. An aqueous composition of graft-modified starch which is: A modified starch obtained by adding a dicarboxylic anhydride compound having a linear or branched alkyl group or alkenyl group having 4 to 30 carbon atoms to at least one (A) pregelatinized starch having a pregelatinization degree of 80% or more, and The aqueous composition of graft-modified starch according to claim 1, which is obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of at least one (B) starch having a degree of pregelatinization of 20% or less. The ratio of (A) pregelatinized starch having a pregelatinization degree of 80% or more and (B) starch having a pregelatinization degree of 20% or less is 10:90 to 90:10. An aqueous composition of graft-modified starch. The amount of the ethylenically unsaturated monomer used is 5% by mass to 250% by mass with respect to the total amount of (A) pregelatinized starch having a degree of pregelatinization of 80% or more and (B) starch having a pregelatinization degree of 20% or less. The aqueous composition of graft-modified starch according to any one of claims 2 and 3. The graft-modified starch according to any one of claims 2, 3 and 4, wherein the addition amount of the dicarboxylic anhydride compound (A) to the pregelatinized starch having a pregelatinization degree of 80% or more is 0.1 mass% to 30 mass%. Aqueous composition. The aqueous composition of graft-modified starch according to any one of claims 1, 2, 3, 4 and 5, wherein the dicarboxylic anhydride compound is octenyl succinic anhydride. The aqueous composition of graft-modified starch according to any one of claims 1, 2, 3, 4, 5 and 6, obtained by emulsion polymerization of an ethylenically unsaturated monomer using a redox initiator. The aqueous composition of graft-modified starch according to claim 7, wherein the reducing agent of the redox initiator is thiourea dioxide or sodium dithionite. The ethylenically unsaturated monomer includes an ethylenically unsaturated monomer having a reactive group capable of reacting with a hydroxyl group of starch, according to any one of claims 1, 2, 3, 4, 5, 6, 7 and 8. An aqueous composition of the graft-modified starch described in 1. An aqueous composition of the graft-modified starch according to any one of claims 1, 2, 3, 4, 5, 6, 7, 8, or 9, and a curing agent having a functional group capable of reacting with a hydroxyl group or a carboxyl group A curable composition, which is a mixture.