Starch-containing curable composition and coating agent using the same

Abstract

To provide a starch-containing curable composition allowing formation of a coating film (cured article) having high water resistance.SOLUTION: A starch-containing curable composition including starch, a hydroxycarboxylic acid, a water-soluble polymer different from the starch, a water-containing solvent, and a crosslinking agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a starch-containing curable composition and a coating agent using the same. [Background technology]

[0002] Currently, synthetic resin products such as plastics, paints, and adhesives are used in all areas of daily life and industry, and their production volume is enormous. However, the majority of these synthetic resins are incinerated or disposed of in the ground after use, which has recently become a problem due to their negative impact on the global environment due to the release of carbon dioxide and toxic substances. Furthermore, petroleum, the raw material for synthetic resins, is a finite resource, and there are growing concerns about its future depletion. Therefore, the creation of a recycling-oriented society by shifting from exhaustible resources to renewable resources has attracted attention. In other words, there is a need to actively utilize natural resources from the perspective of reducing the impact on the global environment, such as improving waste disposal and reducing carbon dioxide emissions, as well as from the perspective of shifting to renewable resources.

[0003] One example of a naturally derived raw material is the polysaccharide starch. Starch can be easily isolated from plants and is relatively inexpensive. In addition to being used as food, it has also been used as starch paste or mixed with plasticizers for molding (casting, extrusion, molding, foam molding, etc.) to make films, food containers, packaging materials, cushioning materials, etc.

[0004] In order to expand the applications that utilize the various properties of starch and to improve its ease of handling, efforts are being made to develop aqueous solutions of uniformly dissolved unmodified starch (starch-containing aqueous compositions). For example, Patent Document 1 proposes a method for dissolving starch in water to prepare an aqueous solution by adding a surfactant to the starch, or by adding fats and / or oils and / or free fatty acids and an alkaline substance to the starch, and then heating and dissolving the starch.

[0005] Furthermore, developments are also being made to modify starch to impart properties according to the purpose. For example, Patent Document 2 discloses a melt containing starch modified by thermal treatment and a water-insoluble synthetic thermoplastic polymer, and states that the melt of the composition can be molded to obtain an article. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-345802 [Patent Document 2] Japanese Patent Application Publication No. 2-14228 Summary of the Invention [Problem to be solved by the invention]

[0007] From the viewpoint of more widely utilizing natural resources, the demand for starch-containing aqueous compositions is increasing. In order to expand the applications of starch-containing aqueous compositions, the present inventors have attempted to form a coating film (cured product) by curing the starch-containing aqueous composition. However, it has been found that when a coating film is simply formed using a starch-containing aqueous composition, there is a problem in that the coating film has low water resistance due to the high hydrophilicity of starch.

[0008] Therefore, an object of the present invention is to provide a starch-containing curable composition that can form a coating film (cured product) that has high water resistance. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by further adding a hydroxycarboxylic acid, a water-soluble polymer other than starch, and a crosslinking agent to an aqueous composition containing starch and water, thereby completing the present invention.

[0010] That is, according to one aspect of the present invention, there is provided a starch-containing curable composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, a solvent containing water, and a crosslinking agent. [Effects of the Invention]

[0011] According to the present invention, there is provided a starch-containing curable composition capable of forming a coating film (cured product) having high water resistance. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes in detail the embodiments of the present invention. The embodiments described herein are merely illustrative examples for embodying the technical concept of the present invention and are not intended to limit the scope of the present invention. Therefore, all other possible embodiments, methods of use, and operational techniques conceivable by those skilled in the art without departing from the spirit of the present invention are within the scope and spirit of the present invention, as well as within the scope of the claims and their equivalents. The embodiments described herein can be arbitrarily combined to produce other embodiments. Furthermore, in this specification, the range "X to Y" means "X or more and Y or less," and "weight," "weight %," "mass %," and "parts by weight" and "parts by mass" are treated as synonyms. Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C) and a relative humidity of 40-60% RH.

[0013] As used herein, the term "(meth)acrylic" encompasses both acrylic and methacrylic. Thus, for example, the term "(meth)acrylic acid" encompasses both acrylic acid and methacrylic acid. Similarly, the term "(meth)acrylate" encompasses both acrylate and methacrylate, and the term "(meth)acrylamide" encompasses both acrylamide and methacrylamide.

[0014] <Starch-containing hardenable composition> One aspect of the present invention is a starch-containing curable composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, a solvent containing water, and a crosslinking agent.

[0015] According to the starch-containing curable composition of the present invention, a cured product with high water resistance can be formed by incorporating a hydroxycarboxylic acid, a water-soluble polymer other than starch, and a crosslinking agent into an aqueous composition containing starch and water. It is believed that the crosslinking agent increases hydrophobicity and improves water resistance by reacting with the hydroxyl groups (OH groups) of starch. However, because starch forms particulate aggregates in the aqueous composition, the compatibility between the starch and the crosslinking agent in the aqueous composition is poor. The present invention discovered that a hydroxycarboxylic acid and a water-soluble polymer other than starch act as solubilizers and dispersants, helping to dissolve starch in water while also improving the compatibility between the starch and the crosslinking agent. Therefore, it is believed that the combination of a hydroxycarboxylic acid, a water-soluble polymer other than starch, and a crosslinking agent in the starch-containing curable composition improves water resistance. Furthermore, coating films (cured products) formed using the starch-containing curable composition of the present invention also have the advantage of excellent transparency. The above mechanism is speculative, and the scope of the present invention is not limited thereby. The components of the starch-containing curable composition according to this embodiment will be described in detail below.

[0016] In the following, as one embodiment of the present invention, a starch-containing curable composition containing starch, a hydroxycarboxylic acid, a water-soluble polymer other than starch, a solvent containing water, and a crosslinking agent will be described. According to one embodiment of the present invention, the starch-containing curable composition can be obtained by adding a crosslinking agent to a starch-containing aqueous composition containing starch, a hydroxycarboxylic acid, the water-soluble polymer other than starch, and a solvent containing water. Therefore, according to one embodiment of the present invention, the starch-containing curable composition contains a starch-containing aqueous composition containing starch, a hydroxycarboxylic acid, the water-soluble polymer other than starch, and a solvent containing water; and a crosslinking agent. Details of the starch-containing aqueous composition are the same as those of the starch-containing curable composition described below, except for the crosslinking agent (content ratios of each component and physical properties). Hereinafter, the starch-containing curable composition will be referred to as the "curable composition," and the starch-containing aqueous composition will be referred to as the "aqueous composition." Furthermore, in the present invention, the "aqueous composition" refers to a composition containing water in an amount of 10% by mass or more relative to the total mass (100% by mass) of the solvent. In the present invention, the solvent means a substance that is liquid at 25° C., excluding water-soluble polymers other than starch, which will be described later.

[0017] [Starch] As noted above, the starch-containing settable composition comprises starch.

[0018] "Starch" has the molecular formula (C6H 10 O5) nStarch is a carbohydrate (polysaccharide) and refers to a natural polymer formed by the polymerization of numerous α-glucose molecules through glycosidic bonds. The term "starch granules" includes starch crystals (starch granules) found in the cells of higher plants, as well as the collected starch. Starch forms a micellar structure within its molecules, making it difficult to dissolve in water. However, when starch is suspended in water and heated, it absorbs water molecules into its molecules, gradually expanding. Continued heating eventually causes the starch's micellar structure to collapse and transform into a gel (gelatinization). When gelatinized starch is cooled, the water molecules absorbed within the molecules are expelled (synthesis), the micellar structure is reformed, and the starch becomes cloudy (aging). The starch-containing curable composition of this embodiment preferably contains a high concentration of starch (e.g., 5 mass % or more). Even when such a high concentration of starch is contained, the presence of hydroxycarboxylic acid improves the solubility of starch, and the composition does not gel at temperatures above -10°C, resulting in a highly transparent, homogeneous liquid composition. In other words, the composition is free from gelation, syneresis, cloudiness, etc., and is therefore highly stable and easy to handle.

[0019] Examples of starches include corn starch, waxy cornstarch (waxy corn), high-amylose cornstarch (high-amylose corn), wheat starch, rice starch, starch produced from beans (broad beans, mung beans, adzuki beans, etc.), potato starch, sweet potato starch, tapioca starch, and waste starch, as well as modified starches thereof, etc. One type of starch may be used alone, or two or more types may be used in combination.

[0020] In the starch-containing curable composition according to the present embodiment, the starch used may have a hot water solubility of less than 30% or 30% or more. In this specification, the "hot water solubility" of starch is calculated according to the following measurement method.

[0021] "Method for measuring hot water solubility" 6 g of starch was immersed in 94 g of hot water (80°C) for 5 hours with stirring, and the starch that did not dissolve into the aqueous phase was separated by filtration and dried for 90 minutes at 130°C. The weight W [g] of the dried starch was measured, and the hot water solubility was calculated using the following formula 1: (Formula 1) Hot water solubility [%] = (6-W) / 6 x 100.

[0022] According to one embodiment, the starch has a hot water solubility of less than 30%. There are no particular limitations on the specific form of starch that exhibits a hot water solubility of less than 30%. In this embodiment, the starch may be unmodified starch (natural starch) or may be modified starch that has been chemically or physically modified, but most starches that exhibit a hot water solubility of less than 30% are modified starches. Therefore, in this embodiment, the starch is preferably modified starch.

[0023] According to one embodiment, the starch has a hot water solubility of 30% or more. There are no particular limitations on the specific form of starch that exhibits a hot water solubility of 30% or more. In this form, the starch may be unmodified starch (natural starch) or may be modified starch that has been chemically or physically modified, but most starches that exhibit the above hot water solubility of 30% or more are unmodified starches. Therefore, according to one embodiment, the starch is preferably unmodified starch.

[0024] Here, modified starch refers to natural starch that has been treated with heat, acid, alkali, enzyme, etc. to physically (morphologically) or chemically change its structure, and the modification method is not particularly limited. For example, the modified starch used in the starch-containing curable composition according to this embodiment may be a chemically modified (modified) starch in which a functional group is introduced into the hydroxyl group of the anhydroglucose residue of starch to modify (modify) chemical properties such as water solubility and reactivity, or a physically modified (modified) starch in which starch is heated, if necessary, with an additive such as acid, alkali, enzyme, etc. to modify (modify) physical properties such as gelatinization temperature.

[0025] Functional groups introduced into modified starch by chemical modification include, but are not limited to, acetyl groups, phosphate groups, hydroxypropyl groups, etc. Examples of chemically modified starches include acetylated adipate cross-linked starch, acetylated oxidized starch, oxidized starch, hydroxypropyl starch, hydroxypropylated phosphate cross-linked starch, urea phosphate esterified starch, phosphate cross-linked starch, and starch acetate. Examples of physically modified starches include starches whose heat absorption at 80 to 180°C is eliminated by heating (for example, heating at a temperature higher than the gelatinization temperature of the starch).

[0026] Generally, modified starch is obtained by changing the crystal structure by heat treatment or the like, physical modification such as condensation or decomposition, chemical modification by introducing functional groups, modification by enzymes, blending with glycerin, glycol, sorbitol, etc., or a combination thereof. The modified starch used in the present invention is obtained by changing the hydrated crystal structure mainly by heat treatment or the like, and is thought to have undergone or been chemically modified only to a limited extent, and has thermoplastic properties due to the change in crystal structure.

[0027] On the other hand, unmodified starch has a micellar structure (crystalline structure) formed by hydrogen bonding between amylopectin and amylose, and therefore forms micellar starch particles in water and is not thermoplastic. Furthermore, unmodified starch undergoes gelatinization (gelatinization) due to swelling of starch particles caused by hydration in water at around 80°C, and gelation occurs at concentrations of 6% or higher, making it impossible to obtain a liquid composition. Furthermore, when unmodified starch is cooled after gelatinization, retrogradation (beta-conversion) rapidly progresses, causing separation of water and starch and cloudiness.

[0028] According to the present invention, by combining starch with a hydroxycarboxylic acid in a curable composition, a stable liquid composition in water can be formed. As a result, the starch-containing curable composition according to this embodiment can contain a high concentration of starch (e.g., 5% by weight or more). Here, according to one embodiment, the starch-containing curable composition according to this embodiment is prepared by adding a crosslinker after obtaining a starch-containing aqueous composition. Thus, according to one embodiment, by combining starch with a hydroxycarboxylic acid in an aqueous composition, a stable liquid composition in water can be formed. As a result, the aqueous composition can contain a high concentration of starch (e.g., 10% by weight or more).

[0029] Although the detailed reason why combining starch with a hydroxycarboxylic acid in a curable composition and / or aqueous composition allows a stable liquid composition to be formed in water is unknown, it is speculated as follows: Starch forms hydrogen bonds with the hydroxycarboxylic acid in water, and these hydrogen bonds are thought to improve the solubility of starch in water, allowing the starch to maintain its dissolved state in water. It is also thought that the hydroxycarboxylic acid and the water-soluble polymer other than starch reduce the aggregation structure associated with hydration of starch and impart a dispersing effect, thereby improving the compatibility of the starch-containing aqueous composition with the crosslinking agent. Note that the above mechanism is merely speculation, and the scope of the present invention is not limited thereby.

[0030] In the present invention, the term "liquid (liquid state)" means that the entire composition has fluidity and is not gelled. For example, the term "liquid (liquid state)" means that the viscosity (25°C) measured in the examples is 10,000 mPa s or less.

[0031] In the starch-containing curable composition according to this embodiment, when the starch has a hot water solubility of less than 30%, the dissolved content of the starch in the starch-containing curable composition is preferably 5% by mass or more relative to 100% by mass of the curable composition. This is because a dissolved content of 5% by mass or more of the starch ensures sufficient storage stability. The "dissolved content" refers to the amount of starch dissolved in the composition. Here, "dissolved" refers to a state in which the starch is not precipitated as a solid, and includes, for example, a state in which the starch is hydrated and swollen. From the viewpoint of improving the handleability of the starch-containing curable composition, the higher the dissolved content of the starch in the curable composition, the better. Therefore, in the starch-containing curable composition according to this embodiment, the dissolved starch content is preferably 5% by mass or more, more preferably 6% by mass or more, even more preferably 8% by mass or more, even more preferably 10% by mass or more, particularly preferably 12% by mass or more, and most preferably 15% by mass or more, based on 100% by mass of the curable composition. According to one embodiment, the dissolved starch content in the starch-containing curable composition according to this embodiment is 17% by mass or more, 18% by mass or more, or 20% by mass or more, based on 100% by mass of the curable composition. There is no particular upper limit to the dissolved starch content in the starch-containing curable composition according to this embodiment, but it is usually 50% by mass or less, based on 100% by mass of the curable composition. The higher the dissolved starch content in the starch-containing curable composition, the higher the biomass content of the starch-containing curable composition, which can effectively contribute to reducing carbon dioxide emissions.

[0032] According to one embodiment, a crosslinker is added to the starch-containing curable composition of this embodiment after the starch-containing aqueous composition is obtained. A high dissolved starch content in the starch-containing aqueous composition can more effectively exhibit the water resistance effect of the starch-containing curable composition of this embodiment. Therefore, when the starch has a hot water solubility of less than 30%, the dissolved starch content in the starch-containing aqueous composition is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most preferably 30% by mass or more, based on 100% by mass of the aqueous composition. There is no particular upper limit for the dissolved starch content in the starch-containing aqueous composition, but it is usually 50% by mass or less, based on 100% by mass of the aqueous composition.

[0033] According to the starch-containing curable composition of this embodiment, when the starch has a hot water solubility of less than 30%, the viscosity of the starch-containing curable composition at 25°C is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, even more preferably 2,500 mPa·s or less, particularly preferably 2,000 mPa·s or less, and most preferably 1,500 mPa·s or less in the shear rate range of production processes such as stirring, viscosity adjustment, and pigment dispersion. According to the starch-containing curable composition of this embodiment, when the starch has a hot water solubility of less than 30%, the lower limit of the viscosity of the starch-containing curable composition at 25°C is not particularly limited, but is preferably 50 mPa·s or more, more preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more. Furthermore, the starch-containing curable composition of this embodiment remains liquid even at high temperatures (e.g., 80°C), thereby providing excellent handleability. The starch-containing curable composition according to this embodiment has a viscosity at 80°C of preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, even more preferably 2,500 mPa·s or less, particularly preferably 2,000 mPa·s or less, and most preferably 1,500 mPa·s or less, in the shear rate range of production processes such as stirring, viscosity adjustment, and pigment dispersion. When the starch has a hot water solubility of less than 30%, the lower limit of the viscosity of the starch-containing curable composition at 80°C is not particularly limited, but is preferably 50 mPa·s or more, more preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more.

[0034] According to one embodiment, the viscosity at 25°C of a starch-containing curable composition according to this aspect, which contains 5% by mass or more of starch exhibiting a hot water solubility of less than 30%, is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less). According to one embodiment, the viscosity at 25°C of a starch-containing curable composition according to this aspect, which contains 10% by mass or more of starch exhibiting a hot water solubility of less than 30%, is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less). According to one embodiment, the viscosity of the starch-containing curable composition containing 15% by mass or more of starch having a hot water solubility of less than 30% at 25°C is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less).

[0035] In the starch-containing curable composition according to this embodiment, the starch may have a hot water solubility of 30% or more. In this case, the dissolved starch content in the starch-containing curable composition is preferably 7% by mass or more relative to 100% by mass of the curable composition.

[0036] In the starch-containing curable composition according to this embodiment, when the starch has a hot water solubility of 30% or more, the dissolved starch content in the starch-containing curable composition is preferably 7% by mass or more relative to 100% by mass of the curable composition. This is because a dissolved starch content of 7% by mass or more ensures sufficient storage stability. From the viewpoint of improving the handleability of the starch-containing curable composition, a higher dissolved starch content in the curable composition is preferable. Therefore, in the starch-containing curable composition according to this embodiment, the dissolved starch content is preferably 8% by mass or more, more preferably 9% by mass or more, even more preferably 10% by mass or more, even more preferably 12% by mass or more, particularly preferably 13% by mass or more, and most preferably 15% by mass or more relative to 100% by mass of the curable composition. There is no particular upper limit to the dissolved starch content in the starch-containing curable composition according to this embodiment, but it is usually 50% by mass or less relative to 100% by mass of the curable composition.

[0037] According to one embodiment, a crosslinker is added to the starch-containing curable composition of this embodiment after the starch-containing aqueous composition is obtained. By ensuring that the dissolved starch content in the starch-containing aqueous composition is appropriate, the water resistance of the starch-containing curable composition of this embodiment can be more effectively achieved. Therefore, when the starch has a hot water solubility of 30% or more, the dissolved starch content in the starch-containing aqueous composition is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most preferably 30% by mass or more, based on 100% by mass of the aqueous composition. There is no particular upper limit for the dissolved starch content in the starch-containing aqueous composition, but it is usually 50% by mass or less, based on 100% by mass of the aqueous composition.

[0038] According to the starch-containing curable composition of this embodiment, when the starch has a hot water solubility of 30% or more, the viscosity of the starch-containing curable composition at 25°C is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, even more preferably 2,500 mPa·s or less, particularly preferably 2,000 mPa·s or less, and most preferably 1,500 mPa·s or less. According to the starch-containing curable composition of this embodiment, when the starch has a hot water solubility of 30% or more, the lower limit of the viscosity of the starch-containing curable composition at 25°C is not particularly limited, but is preferably 50 mPa·s or more, more preferably 100 mPa·s or more, and even more preferably 200 mPa·s or less. Furthermore, the starch-containing curable composition of this embodiment remains liquid even at high temperatures (e.g., 80°C), thereby providing excellent handleability. The viscosity of the starch-containing curable composition according to this embodiment at 80°C is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, even more preferably 2,500 mPa·s or less, particularly preferably 2,000 mPa·s or less, and most preferably 1,500 mPa·s or less. When the starch has a hot water solubility of 30% or more, the lower limit of the viscosity of the starch-containing curable composition at 80°C is not particularly limited, but is preferably 50 mPa·s or more, more preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more.

[0039] According to one embodiment, the viscosity at 25°C of a starch-containing curable composition according to this aspect, which contains 5% by mass or more of starch exhibiting a hot water solubility of 30% or more, is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less). According to one embodiment, the viscosity at 25°C of a starch-containing curable composition according to this aspect, which contains 10% by mass or more of starch exhibiting a hot water solubility of 30% or more, is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less). According to one embodiment, the viscosity of the starch-containing curable composition containing 15% by mass or more of starch having a hot water solubility of 30% or more at 25°C is 10,000 mPa·s or less (preferably 5,000 mPa·s or less, more preferably 1,000 mPa·s or less).

[0040] [Hydroxycarboxylic acids] The starch-containing curable composition according to this embodiment is characterized by the inclusion of a hydroxycarboxylic acid. The presence of the hydroxycarboxylic acid can improve the water resistance of coating films formed by the starch-containing curable composition. The mechanism by which the water resistance of coating films formed by the starch-containing curable composition is improved is believed to be that the hydroxycarboxylic acid reacts with the crosslinking agent described below to form a crosslinked structure between the starch and the water-soluble polymer, thereby transforming the starch-containing curable composition into a polymer network. Furthermore, the hydroxycarboxylic acid can improve the compatibility of the crosslinking agent in the starch-containing curable composition, thereby improving the uniformity and transparency of the composition. The hydroxycarboxylic acid can also suppress an increase in viscosity in the starch-containing curable composition.

[0041] The hydroxycarboxylic acid is not particularly limited, but examples thereof include aliphatic hydroxycarboxylic acids such as lactic acid, citric acid, tartaric acid, glycolic acid, malic acid, ricinoleic acid, isocitric acid, curtronic acid, tartronic acid, glyceric acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid (hydroxyisobutyric acid), 4-hydroxyacetic acid, leucinic acid, mevalonic acid, quinic acid, pantoic acid, and dimethylolpropionic acid; and aromatic hydroxycarboxylic acids such as shikimic acid, salicylic acid (orthohydroxybenzoic acid), parahydroxybenzoic acid, metahydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 2-hydroxy-3-naphthoic acid, 1-hydroxy-4-naphthoic acid, 4-hydroxy-4'-carboxydiphenyl ether, 2,6-dichloro-parahydroxybenzoic acid, 2-chloro-parahydroxybenzoic acid, 2,6-difluoro-parahydroxybenzoic acid, and 4-hydroxy-4'-biphenylcarboxylic acid. Among these, aliphatic hydroxycarboxylic acids are preferred, lactic acid, citric acid, tartaric acid, glycolic acid, malic acid, ricinoleic acid, isocitric acid, curtronic acid, tartronic acid, or glyceric acid is more preferred, lactic acid, citric acid, tartaric acid, glycolic acid, malic acid, ricinoleic acid, or isocitric acid is even more preferred, lactic acid, citric acid, tartaric acid, glycolic acid, or isocitric acid is particularly preferred, and lactic acid, citric acid, or tartaric acid is most preferred. The use of these hydroxycarboxylic acids is thought to reduce the aggregation structure associated with starch hydration, thereby achieving the effects described above.

[0042] The hydroxycarboxylic acid in the starch-containing aqueous composition according to this embodiment preferably has a molecular weight of 350 or less, more preferably 250 or less, even more preferably 220 or less, and particularly preferably 200 or less. The molecular weight of the hydroxycarboxylic acid is preferably 30 or more, more preferably 40 or more, even more preferably 50 or more, and particularly preferably 70 or more. The use of these hydroxycarboxylic acids is thought to reduce the aggregation structure associated with hydration of starch, thereby achieving the effects described above. The molecular weight of the hydroxycarboxylic acid is the sum of the atomic weights of the atoms constituting the compound.

[0043] The content of hydroxycarboxylic acid in the starch-containing curable composition according to this embodiment is not particularly limited, but is preferably 2 to 40 mass %, more preferably 2.5 to 30 mass %, particularly preferably 3 to 20 mass %, particularly preferably 3.5 to 10 mass %, and most preferably 4 to 7 mass %, relative to 100 mass % of the starch content.

[0044] [solvent] The starch-containing curable composition according to this embodiment contains a solvent, and the solvent essentially contains water. The proportion of water in the solvent is preferably 10 to 100% by mass, more preferably 12 to 98% by mass, even more preferably 15 to 95% by mass, still more preferably 18 to 90% by mass, particularly preferably 20 to 88% by mass, and most preferably 27 to 86% by mass.

[0045] When the solvent for the starch-containing curable composition contains components other than water, the components other than water are not particularly limited, but are preferably one or more selected from the group consisting of polyhydric alcohols or glycol ethers. When these components are added at a relatively low temperature during aqueous solution formation, they can contribute to improving the uniformity and storage stability of the resulting composition. On the other hand, when aqueous solution formation is performed at a relatively high temperature, it is also a preferred embodiment to obtain the composition without using these components (for example, using only water as the solvent). Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, tripropylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol, 1,3-butylene glycol, polyethylene glycol, glycerin, diglycerin, polyglycerin, pentanediol, and hexamethylene glycol. Examples of glycol ethers include methyl glycol (ethylene glycol monomethyl ether), methyl diglycol, methyl triglycol, ethyl glycol (ethylene glycol monoethyl ether), ethyl diglycol (diethylene glycol monoethyl ether), dipropylene glycol dimethyl ether, isopropyl glycol, isopropyl diglycol, butyl glycol, butyl diglycol, butyl triglycol, isobutyl glycol, isobutyl diglycol, hexyl glycol, hexyl diglycol, 2-ethylhexyl glycol, 2-ethylhexyl diglycol, aryl glycol, phenyl glycol, phenyl diglycol, benzyl glycol, methyl propylene glycol, methyl propylene diglycol, methyl propylene triglycol, propyl propylene glycol, propyl propylene diglycol, butyl propylene glycol, butyl propylene diglycol, and phenyl propylene glycol.

[0046] The starch-containing curable composition according to this embodiment preferably contains water as a solvent and one or more selected from polyhydric alcohols, polyhydric alcohol ethers, and alkyl ethers thereof. As polyhydric alcohols, polyhydric alcohol ethers, and alkyl ethers thereof, preferred are glycerin, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and diethylene glycol mono-2-ethylhexyl, and more preferred are glycerin, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and dipropylene glycol dimethyl ether.

[0047] The content of the solvent in the starch-containing curable composition according to this embodiment is not particularly limited, but is preferably 20 to 99 mass%, more preferably 22 to 98 mass%, particularly preferably 24 to 97 mass%, particularly preferably 26 to 90 mass%, and most preferably 28 to 85 mass%, relative to 100 mass% of the total mass of the curable composition.

[0048] In the starch-containing curable composition according to this embodiment, the water content is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 100% by mass or more, and most preferably 120% by mass or more, based on the total mass (100% by mass) of the starch. There is no particular upper limit for the water content in the starch-containing curable composition, but it is usually 500% by mass or less, preferably 400% by mass or less, and more preferably 300% by mass or less, based on the total mass (100% by mass) of the starch.

[0049] In the starch-containing curable composition according to this embodiment, the solvent content is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 100% by mass or more, particularly preferably 120% by mass or more, and most preferably 150% by mass or more, based on the total mass (100% by mass) of the starch. There is no particular upper limit to the solvent content in the starch-containing curable composition, but it is usually 2000% by mass or less, preferably 1500% by mass or less, and more preferably 1000% by mass or less, based on the total mass (100% by mass) of the starch.

[0050] According to one embodiment, the starch-containing curable composition of this aspect is prepared by adding a crosslinking agent after obtaining the starch-containing aqueous composition. According to one embodiment, the content of the solvent in the starch-containing aqueous composition of this aspect is preferably 20 to 95 mass %, more preferably 25 to 92.5 mass %, particularly preferably 30 to 90 mass %, particularly preferably 35 to 87.5 mass %, and most preferably 40 to 85 mass %, relative to the total mass (100 mass %) of the aqueous composition.

[0051] The water content in the starch-containing aqueous composition according to this embodiment is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 100% by mass or more, and most preferably 120% by mass or more, based on the total mass (100% by mass) of the starch. There is no particular upper limit for the water content in the starch-containing aqueous composition, but it is usually 400% by mass or less, preferably 300% by mass or less, and more preferably 200% by mass or less, based on the total mass (100% by mass) of the starch.

[0052] The content of the solvent in the starch-containing aqueous composition according to this embodiment is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 100% by mass or more, and most preferably 120% by mass or more, relative to the total mass (100% by mass) of the starch. There is no particular upper limit to the content of the solvent in the starch-containing aqueous composition, but it is usually 500% by mass or less, preferably 400% by mass or less, more preferably 300% by mass or less, relative to the total mass (100% by mass) of the starch.

[0053] [Water-soluble polymer] The starch-containing curable composition according to the present invention is also characterized by the inclusion of a water-soluble polymer other than starch. The water-soluble polymer can improve the compatibility of the crosslinker in the starch-containing curable composition, improve the uniformity of the composition, and improve the water resistance of the coating film formed by the starch-containing curable composition. The mechanism by which the water-soluble polymer improves the water resistance of the coating film formed by the starch-containing curable composition is believed to be that the water-soluble polymer induces the starch-containing curable composition into a polymer network through a crosslinking reaction with the crosslinker and hydroxycarboxylic acid described below. Furthermore, the water-soluble polymer can improve the compatibility of the crosslinker in the starch-containing curable composition, improve the uniformity of the composition, and improve transparency. Furthermore, the inclusion of a water-soluble polymer in the starch-containing curable composition has the advantage of increasing the dissolved starch content in the starch-containing curable composition.

[0054] Examples of water-soluble polymers include gelatin, agar, semi-synthetic polymers such as hydroxypropylmethylcellulose, carboxymethylcellulose, and hydroxyethylcellulose, as well as synthetic polymers such as polyvinyl alcohol, polyacrylic acid polymers, polyacrylamide, polyethylene oxide, and polyvinylpyrrolidone. Water-soluble polymers such as polyoxyalkylene adducts and arylsulfonic acid-formalin condensates may also be used. The use of these water-soluble polymers is believed to improve dispersibility and thereby increase the dissolved starch content in the curable composition. Specific examples of polyoxyalkylene adducts include, but are not limited to, polyoxyalkylene alkyl ethers, polyoxyalkylene aryl ethers, polyoxyalkylene alkylamines, polyoxyalkylene fatty acid esters, polyoxyalkylene glycerin ether fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, and sulfates thereof (e.g., polyoxyalkylene alkyl ether sulfates, polyoxyalkylene aryl ether sulfates, etc.). Examples of arylsulfonic acid-formalin condensates include formalin condensates of alkylbenzenesulfonic acid, formalin condensates of naphthalenesulfonic acid, formalin condensates of alkylnaphthalenesulfonic acid, and salts thereof (e.g., sodium salts, potassium salts, etc.). Among these, polyacrylic acid polymers are preferably used. As the polyacrylic acid polymer, it is preferable to use a polyacrylic acid polymer having a degree of neutralization of 40 mol% or less, preferably 20 mol% or less, and more preferably 10 mol% or less.

[0055] Thus, according to one embodiment, the water-soluble polymer is at least one selected from the group consisting of polyacrylic acid polymers, polyoxyalkylene adducts, and arylsulfonic acid-formalin condensates. Also, according to one embodiment, the water-soluble polymer is at least one selected from the group consisting of polyacrylic acid polymers, polyoxyalkylene adducts and sulfate ester salts thereof, and arylsulfonic acid-formalin condensates and salts thereof.

[0056] There are no particular restrictions on the average molecular weight of the water-soluble polymer, but the weight average molecular weight (Mw) measured by GPC is preferably 1,000 to 30,000, more preferably 3,000 to 20,000, even more preferably 5,000 to 15,000, and particularly preferably 7,000 to 12,000.

[0057] Commercially available water-soluble polymers include AQUALIC® HL415 (Mw = 10,000, manufactured by Nippon Shokubai Co., Ltd.), a polyacrylic acid polymer with a degree of neutralization of approximately 0 mol %, NYCOL® 1545 (Mw = approximately 3,000, manufactured by Nippon Nyukazai Co., Ltd.), a polyoxyethylene castor oil ether, NYCOL® 2399-S (Mw = approximately 4,500, manufactured by Nippon Nyukazai Co., Ltd.), a polyoxyethylene alkyl (C12, C13 mixed) ether, NYCOL® 780 (Mw = approximately 5,000, manufactured by Nippon Nyukazai Co., Ltd.), a polyoxyethylene polycyclic phenyl ether, NYCOL® 707-SF (Mw = approximately 1,000, manufactured by Nippon Nyukazai Co., Ltd.), a polyoxyethylene polycyclic phenyl ether sulfate, and DISLOR® SH (Mw = approximately 1,000, manufactured by Nippon Nyukazai Co., Ltd.), a naphthalenesulfonic acid formalin condensate sodium salt.

[0058] The content of the water-soluble polymer in the starch-containing curable composition according to this embodiment is not particularly limited, but is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, particularly preferably 1 to 10% by mass, particularly preferably 1.5 to 8% by mass, and most preferably 2 to 5% by mass, relative to 100% by mass of the starch content.

[0059] [Crosslinking agent] The starch-containing curable composition according to this embodiment contains a crosslinking agent. The crosslinking agent is thought to react with the hydroxyl groups (OH groups) of the starch, reducing the hydrophilicity of the starch and improving its water resistance. The crosslinking agent is preferably a compound having a reactive functional group that reacts with the hydroxyl groups (OH groups), such as an isocyanate group, an epoxy group, an alkoxysilyl group, a carboxyl group, a carboxylic acid anhydride, a carbodiimide group, a methylol group, an oxazoline group, or a vinyl group. More preferably, the crosslinking agent is a compound having a carboxyl group, an isocyanate group, an epoxy group, or an alkoxysilyl group as the reactive functional group. Therefore, the crosslinking agent is preferably one or more compounds selected from the group consisting of carboxyl group-containing compounds, isocyanate group-containing compounds, epoxy group-containing compounds, and alkoxysilyl group-containing compounds. Considering the reactivity with starch and the water resistance and transparency of the coating film, the crosslinking agent is preferably one or more selected from the group consisting of a carboxyl group-containing compound, an isocyanate group-containing compound, and an epoxy group-containing compound. Furthermore, considering the reactivity with starch and the water resistance, transparency (coloration), and oil resistance of the coating film, the crosslinking agent is preferably a carboxyl group-containing compound. A single crosslinking agent may be used, or two or more crosslinking agents may be used in combination. According to one embodiment, the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound. This further improves the reactivity with starch and the water resistance, transparency (coloration), and oil resistance of the coating film.

[0060] The starch-containing curable composition according to this embodiment has the advantage of a high biomass ratio due to the starch being naturally derived, but the use of a naturally derived crosslinking agent can further increase the biomass ratio, making one of the advantages of the present invention even more significant. The biomass ratio in a starch-containing curable composition refers to the ratio (mol %) of the solid content of naturally derived materials when the total number of moles of solids contained in the curable composition is taken as 100 mol %.

[0061] "Crosslinking agent content" The content of the crosslinking agent in the starch-containing curable composition according to this embodiment is preferably from 1 to 80% by mass, more preferably from 3 to 70% by mass, particularly preferably from 5 to 65% by mass, particularly preferably from 10 to 60% by mass, and most preferably from 15 to 55% by mass, relative to 100% by mass of the starch-containing curable composition.

[0062] In the starch-containing curable composition according to this embodiment, the reactive groups of the crosslinking agent are preferably from 0.1 mol % to 1000 mol % relative to the hydroxyl groups (OH) (100 mol %) of the starch, more preferably from 0.2 mol % to 300 mol %, even more preferably from 0.3 mol % to 200 mol %, particularly preferably from 0.4 mol % to 120 mol %, and most preferably from 0.5 mol % to 100 mol %. According to one embodiment, in the starch-containing curable composition according to this aspect, the reactive groups of the crosslinker are 0.5 mol % to 150 mol %, 0.5 mol % to 100 mol %, 0.5 mol % to 95 mol %, 0.5 mol % to 90 mol %, 0.8 mol % to 150 mol %, 0.8 mol % to 120 mol %, 0.8 mol % to 100 mol %, 0.8 mol % to 95 mol %, or 0.8 mol % to 90 mol % of the hydroxyl groups (OH) of the starch (100 mol %). In one embodiment, the reactive groups of the crosslinking agent in the starch-containing curable composition according to this embodiment are 10 mol% to 1000 mol%, 15 mol% to 300 mol%, 20 mol% to 200 mol%, 25 mol% to 120 mol%, or 28 mol% to 70 mol% of the hydroxyl groups (OH) of the starch (100 mol%). In another embodiment, the reactive groups of the crosslinking agent in the starch-containing curable composition according to this embodiment are 10 mol% to 150 mol%, 20 mol% to 120 mol%, or 25 mol% to 100 mol% of the hydroxyl groups (OH) of the starch (100 mol%). Having the molar amount of reactive groups of the crosslinking agent within this range has the advantage of ensuring good curing reactivity of the starch-containing curable composition. When two or more crosslinking agents are used, the molar amount of the reactive group is the total amount of reactive groups possessed by the crosslinking agents contained therein.

[0063] According to one embodiment, the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and the reactive groups of the crosslinking agent account for more than 6 mol % relative to the hydroxyl groups (100 mol %) of the starch.

[0064] According to one embodiment, the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and the reactive groups of the crosslinking agent account for more than 6 mol% of the hydroxyl groups (100 mol%) of the starch. When the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, the reactive groups of the crosslinking agent account for preferably 8 mol% to 200 mol%, more preferably 10 mol% to 150 mol%, even more preferably 12 mol% to 120 mol%, particularly preferably 13 mol% to 100 mol%, and most preferably 15 mol% to 90 mol%, of the hydroxyl groups (100 mol%) of the starch.

[0065] "Compounds having reactive functional groups" The compound having the reactive functional group is not particularly limited as long as it has the reactive functional group. Preferred embodiments of the compound having each reactive group are described below.

[0066] "Carboxyl group-containing compounds" A compound having a carboxyl group as a reactive functional group (carboxyl group-containing compound) is a compound having one or more carboxyl groups in one molecule. The starch-containing curable composition according to this embodiment comprises a starch-containing aqueous composition and a crosslinking agent containing a carboxyl group-containing compound, thereby increasing the hardness and improving the water resistance of the coating film obtained by applying the curable composition.

[0067] When a carboxyl group-containing compound is used as a crosslinking agent, the carboxyl group-containing compound is preferably a polymer produced from a monomer having a carboxyl group (carboxyl group-containing monomer). In this case, the polymer produced from the carboxyl group-containing monomer is preferably in a form that is easily miscible with water, from the viewpoint of compatibility with the starch-containing aqueous composition. Therefore, the crosslinking agent is preferably in the form of a polymer polymerized from the carboxyl group-containing monomer dispersed in water. Therefore, according to one embodiment, the crosslinking agent is a polymer emulsion in which a polymer polymerized from the carboxyl group-containing monomer exists as an emulsion.

[0068] Examples of polymers (carboxyl group-containing compounds) obtained by polymerizing carboxyl group-containing monomers include acrylic resins, acrylic styrene resins, polylactic acid, etc. As a crosslinking agent, it is preferable that these polymers (carboxyl group-containing compounds) are contained in an emulsion as a base resin.

[0069] The carboxyl group-containing monomer is preferably a compound containing a hydroxyl group and / or a vinyl group in addition to a carboxyl group, more preferably a compound containing a carboxyl group and a vinyl group (an ethylenically unsaturated carboxyl group-containing compound), and even more preferably a (meth)acrylic group-containing compound (an acrylic resin). Thus, according to one embodiment, the carboxyl group-containing compound has structural units derived from an ethylenically unsaturated carboxyl group-containing compound (preferably a (meth)acrylic group-containing compound). According to one embodiment, the carboxyl group-containing compound is an acrylic resin or a styrene-acrylic resin (more preferably an ammonium salt of a styrene-acrylic acid resin), and the acrylic resin or the styrene-acrylic resin is contained in the form of an emulsion.

[0070] Examples of the carboxyl group-containing monomer include saturated or alicyclic compounds containing a carboxyl group and a hydroxyl group, such as glycolic acid, lactic acid, ε-caprolactone, and lactide; unsaturated compounds containing a carboxyl group, such as (meth)acrylic acid, itaconic acid, and maleic acid; alkyl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; and (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxycyclohexyl (meth)acrylate, and hydroxydecyl (meth)acrylate. Examples of suitable carboxyl group-containing monomers include hydroxyalkyl acrylates; (poly)oxyethylene (meth)acrylates such as ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, and dipropylene glycol (meth)acrylate; (meth)acrylamides such as (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and diacetone acrylamide; epoxy group-containing acrylates such as glycidyl (meth)acrylate; vinyl carboxylate esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl versatate; vinyl cyanides such as (meth)acrylonitrile; and fluorine-containing (meth)acrylates such as trifluoroethyl (meth)acrylate and pentafluoropropyl (meth)acrylate. These carboxyl group-containing monomers can be used alone or in combination of two or more, and therefore the carboxyl group-containing compound may be a homopolymer or a copolymer.

[0071] The carboxyl group-containing compound may be a copolymer of a carboxyl group-containing monomer and another monomer (a monomer other than the carboxyl group-containing monomer).

[0072] The other monomer is preferably a compound having a vinyl group. Examples of the compound having a vinyl group include ethylene, propylene, vinyl acetate, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, and pn-dodecylstyrene. Among these, styrene is preferred as the other monomer to be used in combination with the carboxyl group-containing monomer. These other monomers can be used alone or in combination of two or more.

[0073] The carboxyl group-containing compound may be any of the following: a polymer formed using the (meth)acrylic acid; a polymer formed using the (meth)acrylic acid ester monomer; a copolymer formed using the (meth)acrylic acid and the (meth)acrylic acid ester monomer; a copolymer formed using the (meth)acrylic acid and two or more of the (meth)acrylic acid ester monomers; a copolymer formed using the (meth)acrylic acid and the styrene monomer; a copolymer formed using the (meth)acrylic acid ester monomer and the styrene monomer; a copolymer formed using two or more of the (meth)acrylic acid ester monomers and the styrene monomer; a copolymer formed using the (meth)acrylic acid, the (meth)acrylic acid ester monomer, and the styrene monomer; a copolymer formed using the (meth)acrylic acid, two or more of the (meth)acrylic acid ester monomers, and the styrene monomer; or a polymer formed using the lactic acid.

[0074] Here, when the carboxyl group-containing compound contains structural units derived from an ethylenically unsaturated carboxyl group-containing compound (preferably a (meth)acrylic group-containing compound) and the carboxyl group-containing compound is in the form of a polymer emulsion, the polymer (the carboxyl group-containing compound having structural units derived from the ethylenically unsaturated carboxyl group-containing compound) is more preferably in the form of core-shell resin particles containing a core polymer and a shell polymer coating the core polymer. According to one embodiment, the core-shell resin particles may be a copolymer of an ethylenically unsaturated carboxyl group-containing compound (preferably a (meth)acrylic group-containing compound) and another monomer, for example, a copolymer of an ethylenically unsaturated carboxyl group-containing compound (monomer) and a compound (monomer) having a vinyl group. Thus, according to one embodiment, the core-shell resin particles contain a styrene-acrylic resin. In this case, the styrene-acrylic resin or the monomer of the structural unit constituting the styrene-acrylic resin may be modified. For example, the core-shell resin particles contain a styrene-acrylic resin and / or a modified styrene-acrylic resin. Here, methods for modifying styrene-acrylic resin include RC emulsions using styrene-acrylic resin oligomers synthesized using SGO technology in a styrene-acrylic resin solution containing a large amount of crosslinking components such as -COOH derived from acrylic acid, and methods for modifying the monomers that make up the structural units that make up styrene-acrylic resin include copolymerization with vinyl compounds such as butadiene.

[0075] According to one embodiment, the core-shell resin particles contain an ammonium salt of a styrene-acrylic resin or an ammonium salt of a modified styrene-acrylic resin. According to one embodiment, the shell polymer is a styrene-acrylic polymer (oligomer) obtained by bulk polymerization or a modified styrene-acrylic polymer (oligomer). According to one embodiment, the core-shell resin particles contain a structural unit derived from a quaternary ammonium salt-containing monomer as a structural unit constituting the shell polymer. According to another embodiment, the emulsion containing the core-shell resin particles contains a structural unit derived from a nonionic hydrophilic monomer. According to yet another embodiment, the core-shell resin particles contained in the emulsion as a base resin have a glass transition temperature of 10 to 95°C, 10 to 50°C, 10 to 40°C, 10 to 30°C, 60 to 95°C, 65 to 95°C, or 70 to 95°C.

[0076] The aqueous solvent (dispersion medium for polymer emulsion) for dispersing the carboxyl group-containing compound may contain water and, if necessary, an organic solvent. Examples of the organic solvent include butyl acetate, xylene, toluene, methyl isobutyl ketone, propylene glycol, dipropylene glycol dimethyl ether, methyl ether acetate, tetrahydrofuran, ethanol, methanol, propanol, isopropanol, 2-butanol, t-butyl alcohol, dioxane, methyl ethyl ketone, ethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate (butyl cellosolve acetate), propylene glycol monomethyl ether acetate, 2-methoxypropanol, 2-butoxypropanol, diethylene glycol monobutyl ether, butyl diglycol, N-methylpyrrolidone, ethylene carbonate, and propylene carbonate.

[0077] When the carboxyl group-containing compound is in the form of a polymer emulsion, the polymer emulsion may further contain other components within the range that does not impair the effects of the present invention. Examples of other components include nonionic surfactants such as alcohol ethoxylates, alkylphenol ethoxylates, polyalkylene glycols, polyalkylene glycol alkyl ethers, polyalkylene glycol fatty acid esters, alkyl polyglycosides, and alkanolamides; and anionic surfactants such as alkyl benzene sulfonates, alkyl sulfates, alkyl ether sulfates, α-olefin sulfonates, fatty acid soaps, and alkyl ether carboxylates.

[0078] In addition to the surfactants described above, the other components may include, depending on the purpose and application, pigments, resin particles, resin components, dispersants, curing catalysts, viscosity agents, film-forming aids, and additives commonly used in coating compositions (e.g., ultraviolet absorbers, light stabilizers, antioxidants, antifoaming agents, surface conditioners, pinhole prevention agents, rust inhibitors, etc.).

[0079] The carboxyl group-containing compound (polymer emulsion containing a carboxyl group-containing compound) may be produced by a known method, or a commercially available product may be used.

[0080] Commercially available carboxyl group-containing compounds (polymer emulsions containing carboxyl group-containing compounds) include, for example, Acroal (registered trademark) 742, Joncryl (registered trademark (hereinafter, omitted)) PDX-7326, Joncryl 70J, Joncry PDX-7741, Joncryl PDX-7780, Joncryl PDX-7326, Joncryl PDX-7356, Joncryl PDX-7787, Joncryl PDX-7182, Joncryl PDX-7734, Joncryl PDX-7615, Joncryl PDX-7692, Joncryl PDX-7630A, Joncryl PDX-7358, Joncryl PDX-7696, Joncryl PDX-7667, and Joncryl PDX-7177, all manufactured by BASF Japan Ltd.

[0081] In the starch-containing curable composition according to this embodiment, when the carboxyl group-containing compound has a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the carboxyl group (COO - or COOH) is preferably more than 6 mol% and not more than 100 mol%, more preferably more than 6 mol% and not more than 80 mol%, even more preferably more than 6 mol% and not more than 70 mol%, particularly preferably more than 6 mol% and not more than 60 mol%, and most preferably more than 6 mol% and not more than 50 mol% relative to the hydroxyl groups (OH) (100 mol%) of the starch. According to one embodiment, in the starch-containing curable composition according to this aspect, the carboxyl groups (COO -or COOH) relative to the hydroxyl groups (OH) (100 mol%) of the starch, is more than 6 mol% and 45 mol% or less, more than 6 mol% and 40 mol% or less, more than 6 mol% and 35 mol% or less, more than 6 mol% and 30 mol% or less, 7 mol% to 50 mol%, 7 mol% to 45 mol%, 7 mol% to 40 mol% or less, 7 mol% to 35 mol% or less, or 7 mol% to 30 mol%. According to one embodiment, in the starch-containing curable composition according to this aspect, the carboxyl groups (COO - or COOH) relative to the hydroxyl groups (OH) (100 mol%) of the starch, is 8 mol% to 50 mol%, 8 mol% to 45 mol%, 8 mol% to 40 mol%, 10 mol% to 50 mol%, 10 mol% to 45 mol%, 10 mol% to 40 mol%, 12 mol% to 50 mol%, 12 mol% to 40 mol%, 12 mol% to 30 mol%, 15 mol% to 50 mol%, 15 mol% to 40 mol%, or 15 mol% to 30 mol%. The carboxyl groups (COO) of the carboxyl group-containing compound (carboxyl group-containing compound having a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound) - When the molar amount of the carboxyl group (COO or COOH) is within this range, the hardening reactivity of the starch-containing composition can be advantageously ensured within a favorable range. When two or more types of carboxyl group-containing compounds are used, - or COOH) is determined based on the molar amount of the carboxyl group (COO - or COOH).

[0082] According to one embodiment, the crosslinking agent comprises at least one compound selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and when the carboxyl group-containing compound has a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the carboxyl groups account for more than 6 mol % relative to the hydroxyl groups (100 mol %) of the starch.

[0083] In the case of a carboxyl group-containing compound that does not have a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the reactive group (carboxyl group) of the crosslinker (carboxyl group-containing compound) may be 0.1 mol% to 1000 mol%, 0.2 mol% to 300 mol%, 0.3 mol% to 200 mol%, 0.4 mol% to 120 mol%, 0.5 mol% to 100 mol%, 0.5 mol% to 150 mol%, 0.5 mol% to 100 mol%, 0.5 mol% to 95 mol%, 0.5 mol% to 90 mol%, 0.8 mol% to 150 mol%, 0.8 mol% to 120 mol%, 0.8 mol% to 100 mol%, 0.8 mol% to 95 mol%, or 0.8 mol% to 90 mol% relative to the hydroxyl groups (OH) (100 mol%) of the starch. In the case of a carboxyl group-containing compound that does not have a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the reactive group (carboxyl group) of the crosslinker (carboxyl group-containing compound) may be 1 mol% to 100 mol%, 1 mol% to 80 mol%, 1 mol% to 60 mol%, 2 mol% to 100 mol%, 2 mol% to 80 mol%, 2 mol% to 60 mol%, 3 mol% to 100 mol%, 3 mol% to 80 mol%, 3 mol% to 60 mol%, more than 6 mol% to 100 mol%, more than 6 mol% to 80 mol%, more than 6 mol% to 70 mol%, more than 6 mol% to 60 mol%, or more than 6 mol% to 50 mol%, relative to the hydroxyl groups (OH) (100 mol%) of the starch.

[0084] In the starch-containing curable composition according to this embodiment, when the carboxyl group-containing compound has a structural unit derived from a carboxyl group- and hydroxyl group-containing saturated or alicyclic compound (for example, when the carboxyl group-containing compound is polylactic acid), the carboxyl group (COO - or COOH) is preferably 0.1 mol % or more and 100 mol % or less, more preferably 0.2 mol % or more and 80 mol % or less, even more preferably 0.5 mol % or more and 70 mol % or less, particularly preferably 0.8 mol % or more and 60 mol % or less, and most preferably 0.9 mol % or more and 50 mol % or less, relative to the hydroxyl groups (OH) (100 mol %) of the starch. According to one embodiment, in the starch-containing curable composition according to this aspect, the carboxyl groups (COO - or COOH) is 0.1 mol% or more and 45 mol% or less, 0.1 mol% or more and 40 mol% or less, 0.1 mol% or more and 35 mol% or less, 0.1 mol% or more and 30 mol% or less, 0.5 mol% or more and 50 mol% or less, 0.5 mol% or more and 45 mol% or less, 0.5 mol% or more and 40 mol% or less, 0.5 mol% or more and 35 mol% or less, or 0.5 mol% or more and 30 mol% or less, relative to the hydroxyl groups (OH) (100 mol%) of the starch. - When the molar amount of the carboxyl group (COO or COOH) is within this range, the hardening reactivity of the starch-containing composition can be advantageously ensured within a favorable range. When two or more types of carboxyl group-containing compounds are used, - or COOH) is determined based on the molar amount of the carboxyl group (COO - or COOH).

[0085] According to one embodiment, the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound. When the carboxyl group-containing compound has structural units derived from a carboxyl group- and a hydroxyl group-containing saturated or alicyclic compound, the carboxyl groups of the carboxyl group-containing compound account for more than 0.5 mol % relative to the hydroxyl groups (100 mol %) of the starch. When the reactive groups of the crosslinking agent are at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound that do not have structural units derived from a carboxyl group- and a hydroxyl group-containing saturated or alicyclic compound, the reactive groups of the crosslinking agent account for more than 6 mol % relative to the hydroxyl groups (100 mol %) of the starch.

[0086] According to one embodiment, the starch-containing curable composition according to this aspect also has excellent oil resistance, for example, when a carboxyl group-containing compound having a glass transition temperature of 10 to 50°C (preferably 10 to 30°C) is used in the starch-containing curable composition according to this aspect, the oil resistance is particularly excellent.

[0087] Alternatively, when a carboxyl group-containing compound having a glass transition temperature of 60 to 95°C (preferably 65 to 95°C) is used as the carboxyl group-containing compound in the starch-containing curable composition according to this embodiment, excellent oil resistance can be achieved by using it in combination with an epoxy group-containing compound. According to one embodiment, the starch-containing curable composition according to this embodiment has a crosslinking agent that includes a carboxyl group-containing compound having a glass transition temperature of 60 to 95°C (preferably 65 to 95°C) and an epoxy group-containing compound, and the reactive groups of the crosslinking agent account for 10 mol% to 60 mol% (preferably 15 mol% to 50 mol%) of the hydroxyl groups (OH) of the starch (100 mol%).

[0088] According to one embodiment, the starch-containing curable composition according to this embodiment contains a crosslinker comprising a carboxyl group-containing compound having a glass transition temperature of 60 to 95°C (preferably 65 to 95°C) and an epoxy group-containing compound, and the carboxyl groups of the carboxyl group-containing compound account for 1 mol% or more and 10 mol% or less (preferably 1 mol% or more and less than 9 mol%, more preferably 1 mol% or more and 8 mol% or less) of the hydroxyl groups (OH) of the starch (100 mol%).

[0089] "Isocyanate group-containing compounds" The compound having an isocyanate group as a reactive functional group (isocyanate group-containing compound) is preferably a compound having two or more isocyanate groups in one molecule (polyisocyanate compound). The isocyanate group-containing compound may be a blocked isocyanate that becomes an isocyanate group-containing compound by deblocking or the like.

[0090] In the isocyanate group-containing compound, some of the isocyanate groups may be modified, and a crosslinked structure due to multiple isocyanate groups may exist between multiple isocyanate group-containing compounds or within a single isocyanate group-containing compound. Since a polymeric isocyanate group-containing compound is trifunctional or higher, at least one of the multiple isocyanate groups may be modified, and at least two isocyanate groups may contribute to the formation of a crosslinked structure.

[0091] Specific examples of isocyanate group-containing compounds include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, undecane diisocyanate-(1,11), 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, lysine diisocyanate, and diethylene glycol. Diisocyanate, dipropylene glycol diisocyanate, triethylene glycol diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate, thiodipropyl diisocyanate, and other linear or branched aliphatic polyisocyanates (aliphatic polyisocyanates); toluene diisocyanate (TDI), 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, Phenylmethane diisocyanate (MDI), 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, xylylene diisocyanate (XDI), meta-xylylene diisocyanate (MXDI), tris(4-isocyanatophenyl)methane, 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-trimethyl-2,4-bis(ω-isocyanatoethyl)benzene, 1,3,5-trimethyl-2,4-bis(ω-isocyanatoethyl)benzene aromatic polyisocyanates (aromatic polyisocyanates), such as ethyl-2,4-bis(isocyanatomethyl)benzene, 1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene, 2,4- and / or 2,6-toluene diisocyanate, 1,4-diisocyanatoisopropylbenzene, α,α,α',α'-tetramethylxylylene diisocyanate, 4,4'-dibenzyl diisocyanate, tolidine diisocyanate, and 1,5-naphthalene diisocyanate;Examples of the polyisocyanate include alicyclic polyisocyanates such as isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), norbornane diisocyanate (NBDI), hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and dicyclohexylmethane diisocyanate (H12MDI); isocyanurate-modified products of the various diisocyanate compounds mentioned above; biuret-modified products of the various diisocyanate compounds mentioned above; allophanate-modified products of the various diisocyanate compounds mentioned above; difunctional or higher isocyanate-terminated urethane prepolymers (adducts) obtained by reacting the various diisocyanate compounds mentioned above with polyols having two or more hydroxyl groups per molecule; and deblocked products of blocked isocyanates. These isocyanurate group-containing compounds can be used alone or in combination of two or more.

[0092] The number of carbon atoms contained in the isocyanate group-containing compound is preferably 5 to 24, more preferably 6 to 18. The isocyanate group-containing compound is preferably an aliphatic diisocyanate and / or an alicyclic polyisocyanate, more preferably hexamethylene diisocyanate (HDI) and / or isophorone diisocyanate (IPDI). Aliphatic diisocyanates and alicyclic polyisocyanates have lower reactivity than aromatic polyisocyanates, and can suppress side reactions with aqueous solvents such as water.

[0093] In the starch-containing curable composition according to this embodiment, the isocyanate group-containing compound is preferably added to the composition in a state dissolved or dispersed in a solvent, more preferably in a state dissolved or dispersed in an aqueous solvent. Therefore, the isocyanate group-containing compound is preferably a water-soluble or water-dispersible compound having two or more isocyanate groups per molecule, and is preferably a compound that can be dissolved without separation when added to an aqueous solvent (water-soluble isocyanate group-containing compound) or a compound that can be dispersed (water-dispersible isocyanate group-containing compound). The water-soluble isocyanate group-containing compound may be modified with a hydrophilic compound having a hydrophilic group, if necessary. The hydrophilic group may be an ionic hydrophilic group or a nonionic hydrophilic group.

[0094] Examples of the water-dispersible isocyanate group-containing compound include polyisocyanate compounds that have been modified with a hydrophilic group such as polyethylene oxide, a carboxyl group, or a sulfonic acid group to make them self-emulsifiable (self-emulsifying polyisocyanate compounds); and compounds that have been emulsified with a surfactant or the like to make them water-dispersible (forced emulsifying polyisocyanate compounds).

[0095] In a composition containing a water-soluble or water-dispersible isocyanate group-containing compound, the aqueous solvent for dissolving the water-soluble or water-dispersible isocyanate group-containing compound may contain water and, if necessary, an organic solvent. Examples of organic solvents include butyl acetate, xylene, toluene, methyl isobutyl ketone, propylene glycol, dipropylene glycol dimethyl ether, methyl ether acetate, tetrahydrofuran, ethanol, methanol, propanol, isopropanol, 2-butanol, t-butyl alcohol, dioxane, methyl ethyl ketone, ethylene glycol, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate (butyl cellosolve acetate), propylene glycol monomethyl ether acetate, 2-methoxypropanol, 2-butoxypropanol, diethylene glycol monobutyl ether, butyl diglycol, N-methylpyrrolidone, ethylene carbonate, and propylene carbonate.

[0096] In addition to the aqueous solvent, a composition containing a water-soluble isocyanate group-containing compound or a water-dispersible isocyanate group-containing compound may contain other components, such as pigments, resin particles, resin components, dispersants, curing catalysts, viscosity agents, film-forming aids, and additives commonly used in coating compositions (e.g., ultraviolet absorbers, light stabilizers, antioxidants, antifoaming agents, surface conditioners, pinhole inhibitors, rust inhibitors, etc.), depending on the purpose and application.

[0097] The isocyanate group-containing compound may be produced by a known method, or a commercially available product may be used.Furthermore, the composition containing the water-soluble isocyanate group-containing compound or the water-dispersible isocyanate group-containing compound may be produced by a known method, or a commercially available product may be used.

[0098] Commercially available isocyanurate-modified products include, for example, Duranate (registered trademark (hereinafter omitted)) TPA-100 and Duranate TKA-100 (manufactured by Asahi Kasei Corporation); and Coronate (registered trademark (hereinafter omitted)) HX (manufactured by Tosoh Corporation).

[0099] Commercially available biuret-modified products include, for example, Duranate 24A-100 and Duranate 22A-75P (manufactured by Asahi Kasei Corporation).

[0100] Commercially available tri- or higher functional isocyanate group-terminated urethane prepolymers include, for example, Coronate L, Coronate L-55E, and Coronate L-45E (manufactured by Tosoh Corporation).

[0101] Commercially available water-dispersible isocyanate group-containing compounds (compositions containing water-dispersible isocyanate group-containing compounds) include, for example, Duranate WB40-100, Duranate WB40-80D, Duranate WT20-100, Duranate WT30-100, Duranate WL70-100, Duranate WE50-100, and Duranate WR80-70P (manufactured by Asahi Kasei Corporation); Aquanate (registered trademark (hereinafter, omitted)) 105, Aquanate 130, Aquanate 140 (AQ-140), Aquanate 200, and Aquanate (registered trademark (hereinafter, omitted)) 105, Aquanate 130, Aquanate 140 (AQ-140), and Aquanate 200. Takenate 210 (manufactured by Tosoh Corporation); Takenate (registered trademark (hereinafter omitted)) WD series (Takenate WD-720, Takenate WD-725, Takenate WD-220, Takenate XWD-HS7, Takenate XWD-HS30, etc.) (manufactured by Mitsui Chemicals, Inc.); Bayhydur (registered trademark (hereinafter omitted)) 3100, Bayhydur XP2487 / 1 (manufactured by Bayer MaterialScience); Basonat (registered trademark (hereinafter omitted)) HW100, Basonat HA100 (manufactured by BASF), etc.

[0102] Commercially available blocked isocyanates include, for example, SU-268A, NBP-211, Meikanate (registered trademark (hereinafter omitted)) CX, Meikanate TP-10, DM-6400 (manufactured by Meisei Chemical Industry Co., Ltd.); Duranate WM44-L70G (manufactured by Asahi Kasei Corporation); Aqua BI200, Aqua BI220 (manufactured by Baxenden Chemicals); Takelac (registered trademark (hereinafter omitted)) W, Takelac WPB (manufactured by Mitsui Chemicals, Inc.); Burnock (registered trademark (hereinafter omitted)) (manufactured by DIC Corporation); Elastron (registered trademark (hereinafter omitted)) (manufactured by Daiichi Kogyo Co., Ltd.); and the like.

[0103] From the viewpoint of easy mixing with other components of the starch-containing curable composition, the viscosity of the isocyanate group-containing compound at 25°C is preferably 10,000 mPa·s or less, more preferably 7,000 mPa·s or less, even more preferably 5,000 mPa·s or less, and is preferably 20 mPa·s or more, more preferably 100 mPa·s or more, even more preferably 200 mPa·s or more. The viscosity of the isocyanate group-containing compound at 25°C can be measured with an E-type viscometer.

[0104] In the starch-containing curable composition according to this embodiment, the isocyanate groups (NCO) of the isocyanate group-containing compound are preferably from 10 mol % to 1000 mol % relative to the hydroxyl groups (OH) (100 mol %) of the starch, more preferably from 15 mol % to 300 mol %, even more preferably from 20 mol % to 200 mol %, particularly preferably from 25 mol % to 150 mol %, and most preferably from 28 mol % to 120 mol %. According to one embodiment, in the starch-containing curable composition, the isocyanate groups of the isocyanate group-containing compound are 10 mol% to 150 mol%, 20 mol% to 120 mol%, 25 mol% to 100 mol%, 30 mol% to 100 mol%, 35 mol% to 100 mol%, 40 mol% to 100 mol%, or 50 mol% to 100 mol% relative to the hydroxyl groups (OH) of the starch (100 mol%). Having the molar amount of isocyanate groups (NCO) of the isocyanate group-containing compound within this range has the advantage of ensuring good curing reactivity of the starch-containing composition. When two or more isocyanate group-containing compounds are used, the molar amount of the isocyanate groups (NCO) refers to the total amount of isocyanate groups (NCO) of the isocyanate group-containing compounds.

[0105] According to one embodiment, in the starch-containing curable composition of this embodiment, the crosslinking agent contains a carboxyl group-containing compound and an isocyanate group-containing compound, and the reactive groups of the crosslinking agent account for more than 6 mol % and not more than 60 mol % (preferably 8 mol % to 50 mol %, more preferably 10 mol % to 40 mol %) of the hydroxyl groups (OH) of the starch (100 mol %).

[0106] According to one embodiment, in the starch-containing curable composition of this embodiment, the crosslinking agent comprises a carboxyl group-containing compound and an isocyanate group-containing compound, and the carboxyl groups of the carboxyl group-containing compound account for 1 mol % or more and 10 mol % or less (preferably 2 mol % or more and less than 9 mol %, more preferably 5 mol % or more and less than 9 mol %, and even more preferably more than 6 mol % and 8 mol % or less) of the hydroxyl groups (OH) of the starch (100 mol %).

[0107] According to one embodiment, in the starch-containing curable composition of this embodiment, the crosslinking agent contains a carboxyl group-containing compound and an isocyanate group-containing compound, and the isocyanate groups of the isocyanate group-containing compound account for 1 mol % or more and 30 mol % or less (preferably 2 mol % or more and less than 20 mol %, more preferably 3 mol % or more and 15 mol % or less) of the hydroxyl groups (OH) of the starch (100 mol %).

[0108] According to one embodiment, the starch-containing curable composition according to this aspect includes a crosslinking agent comprising a carboxyl group-containing compound and an isocyanate group-containing compound, wherein the carboxyl groups of the carboxyl group-containing compound account for 1 mol % or more and 10 mol % or less (preferably 2 mol % or more and less than 9 mol %, more preferably 5 mol % or more and less than 9 mol %, and even more preferably more than 6 mol % and 8 mol % or less) of the hydroxyl groups (OH) (100 mol %) of the starch; and the isocyanate groups of the isocyanate group-containing compound account for 1 mol % or more and 30 mol % or less (preferably 2 mol % or more and less than 20 mol %, more preferably 3 mol % or more and 15 mol %) of the hydroxyl groups (OH) (100 mol %) of the starch.

[0109] "Epoxy group-containing compound" Compounds having an epoxy group as a reactive functional group (epoxy group-containing compounds) are preferably compounds having two or more epoxy groups per molecule. Examples of epoxy group-containing compounds include glycidyl ether-type epoxy compounds obtained from a compound having a hydroxyl group and epichlorohydrin, glycidyl amine-type epoxy compounds obtained from a compound having an amino group and epichlorohydrin, glycidyl ester-type epoxy compounds obtained from a compound having a carboxyl group and epichlorohydrin, alicyclic epoxy compounds obtained by oxidizing a compound having a double bond, and epoxy compounds in which two or more types selected from these are present in the molecule. These epoxy group-containing compounds can be used alone or in combination.

[0110] Specific examples of glycidyl ether type epoxy compounds include alkylene glycol type epoxy resins obtained by reacting alkylene glycol or its polymer with epichlorohydrin, polyhydric alcohol type epoxy resins obtained by reacting polyhydric alcohol or its polymer with epichlorohydrin, bisphenol A type epoxy resins obtained by reacting bisphenol A with epichlorohydrin, bisphenol F type epoxy resins obtained by reacting bisphenol F with epichlorohydrin, bisphenol S type epoxy resins obtained by reacting 4,4'-dihydroxydiphenyl sulfone with epichlorohydrin, biphenyl type epoxy resins obtained by reacting 4,4'-biphenol with epichlorohydrin, resorcinol type epoxy resins obtained by reacting resorcinol with epichlorohydrin, phenol novolac type epoxy resins obtained by reacting phenol with epichlorohydrin, polyethylene glycol type epoxy resins, polypropylene glycol type epoxy resins, and positional isomers and alkyl group or halogen substituted products thereof.

[0111] Examples of alkylene glycol type epoxy resins include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and polypropylene diglycidyl ether.

[0112] Examples of alkylene glycol epoxy resins include Denacol (registered trademark (hereinafter omitted)) EX-810, Denacol EX-811, Denacol EX-850, Denacol EX-851, Denacol EX-821, Denacol EX-830, Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-920, Denacol EX-931, Denacol EX-211, and Denacol EX-212 (manufactured by Nagase ChemteX Corporation); Glycier (registered trademark (hereinafter omitted)) PP-300P (manufactured by Sanyo Chemical Industries, Ltd.); and the like.

[0113] Examples of polyhydric alcohol-type epoxy resins include glycerol diglycidyl ether, glycerol triglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and sorbitol polyglycidyl ether.

[0114] Examples of polyhydric alcohol-type epoxy resins include Denacol EX-313, Denacol EX-314, Denacol EX-321, Denacol EX-412, Denacol EX-512, Denacol EX-521, EX-612, Denacol EX-614, Denacol EX-614B, and Green Denacol GEX-614B (manufactured by Nagase ChemteX Corporation). Of these, Green Denacol GEX-614B is an epoxy crosslinking agent that uses naturally derived (plant-derived) carbon. By using Green Denacol GEX-614B as a crosslinking agent, the biomass content of the starch-containing curable composition according to this embodiment can be further improved.

[0115] Commercially available bisphenol A epoxy resins include jER (registered trademark (hereinafter omitted)) 825, jER826, jER827, and jER828 (manufactured by Mitsubishi Chemical Corporation); Epiclon (registered trademark (hereinafter omitted)) 850 (manufactured by DIC Corporation); Epototo (registered trademark (hereinafter omitted)) YD-128 (manufactured by Nippon Steel Chemical & Material Co., Ltd.); DER-331 (trademark) (manufactured by The Dow Chemical Company); and Bakelite (registered trademark (hereinafter omitted)) EPR154, Bakelite EPR162, Bakelite EPR172, Bakelite EPR173, and Bakelite EPR174 (manufactured by AG).

[0116] Commercially available bisphenol F epoxy resins include jER806, jE807, and jER1750 (manufactured by Mitsubishi Chemical Corporation); Epicron 830 (manufactured by DIC Corporation); Epototo YD-170 and Epototo YD-175 (manufactured by Nippon Steel Chemical & Material Co., Ltd.); Bakelite EPR169 (manufactured by AG); and Araldite (registered trademark (hereinafter omitted)) GY281, Araldite GY282, and Araldite GY285 (manufactured by Huntsman Advanced Materials).

[0117] Commercially available biphenyl type epoxy resins include jER YX4000, jER YX4000K, jER YX4000H, and jER YX4000HK (manufactured by Mitsubishi Chemical Corporation).

[0118] Commercially available resorcinol-type epoxy resins include Denacol EX-201 (manufactured by Nagase ChemteX Corporation).

[0119] Commercially available phenol novolac epoxy resins include jER152 and jER154 (manufactured by Mitsubishi Chemical Corporation); Epiclon 740 (manufactured by DIC Corporation); and EPN179 and EPN180 (manufactured by Huntsman Advanced Materials).

[0120] From the viewpoint of easy mixing with other components of the starch-containing curable composition, the viscosity of the epoxy group-containing compound at 25°C is preferably 10,000 mPa·s or less, more preferably 7,000 mPa·s or less, even more preferably 6,000 mPa·s or less, and is preferably 20 mPa·s or more, more preferably 100 mPa·s or more, even more preferably 200 mPa·s or more. The viscosity of the epoxy group-containing compound at 25°C can be measured with an E-type viscometer.

[0121] In the starch-containing curable composition according to this embodiment, the epoxy groups contained in the epoxy group-containing compound preferably account for 10 mol % or more and 1000 mol % or less, more preferably 15 mol % or more and 300 mol % or less, even more preferably 20 mol % or more and 200 mol % or less, particularly preferably 25 mol % or more and 150 mol % or less, and most preferably 28 mol % or more and 120 mol % or less, relative to the hydroxyl groups (OH) (100 mol %) contained in the starch. According to one embodiment, in the starch-containing curable composition, the epoxy groups of the epoxy group-containing compound are present in an amount of 10 mol% to 150 mol%, 20 mol% to 120 mol%, 25 mol% to 100 mol%, 28 mol% to 100 mol%, 28 mol% to 98 mol%, 28 mol% to 95 mol%, or 28 mol% to 90 mol% relative to the hydroxyl groups (OH) of the starch (100 mol%). Having the molar amount of epoxy groups of the epoxy group-containing compound within this range has the advantage of ensuring good curing reactivity of the starch-containing curable composition. When two or more epoxy group-containing compounds are used, the molar amount of epoxy groups refers to the total amount of epoxy groups of the epoxy group-containing compounds.

[0122] "Alkoxysilyl group-containing compound" Examples of compounds having an alkoxysilyl group as a reactive functional group (alkoxysilyl group-containing compounds) include alkoxysilane, bis(methyldimethoxysilyl)polypropylene glycol, bis(methyldimethoxysilyl)polyisobutylene, and silane coupling agents having an alkoxysilyl group. Examples of the alkoxysilane include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, trimethoxysilane, methyltrimethoxysilane, triethoxysilane, and ethyltriethoxysilane. Specific examples of the silane coupling agent having the alkoxysilyl group include glycidyl group-containing silane coupling agents such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane; vinyl group-containing silane coupling agents such as vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, and vinyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane (γ-methacryloyloxypropyltrimethoxysilane); amino group-containing silane coupling agents such as 3-(2-aminoethyl)aminopropylmethoxysilane, 3-aminopropyltriethoxysilane, and trimethoxy[3-(phenylamino)propyl]silane; and others such as γ-mercaptopropyltrimethoxysilane and γ-chloropropyltrimethoxysilane. These may be used alone or in combination of two or more. In the starch-containing curable composition according to the present invention, from the viewpoint of water resistance of the cured product, it is preferable to use two or more alkoxysilyl group-containing compounds as the crosslinking agent, and it is preferable to use a combination of an alkoxysilane and a silane coupling agent having an alkoxysilyl group. Furthermore, from the viewpoint of water resistance of the cured product, it is preferable that the silane coupling agent having an alkoxysilyl group is a silane coupling agent containing an epoxy group (glycidyl group) or a (meth)acryloyl group.In this specification, even if a silane coupling agent having an alkoxysilyl group has a reactive group such as an epoxy group (glycidyl group) or a vinyl group, if it has an alkoxysilyl group, it is considered to be a compound having an alkoxysilyl group (an alkoxysilyl group-containing compound).

[0123] In the starch-containing curable composition according to this embodiment, the alkoxysilyl groups of the alkoxysilyl group-containing compound are preferably from 10 mol% to 1000 mol%, more preferably from 15 mol% to 300 mol%, even more preferably from 20 mol% to 200 mol%, particularly preferably from 30 mol% to 120 mol%, and most preferably from 30 mol% to 70 mol%, relative to the hydroxyl groups (OH) (100 mol%) of the starch. According to one embodiment, in the starch-containing curable composition, the alkoxysilyl groups of the alkoxysilyl group-containing compound are from 10 mol% to 150 mol%, 20 mol% to 120 mol%, or 30 mol% to 100 mol%, relative to the hydroxyl groups (OH) (100 mol%) of the starch. The molar amount of the alkoxysilyl groups in the alkoxysilyl group-containing compound within this range has the advantage of ensuring the curing reactivity of the starch-containing curable composition within a good range. When two or more alkoxysilyl group-containing compounds are used, the molar amount of the alkoxysilyl groups refers to the total amount of alkoxysilyl groups in the alkoxysilyl group-containing compounds contained therein.

[0124] According to one embodiment, in the starch-containing curable composition according to this aspect, the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and in this case, the carboxyl group (COO) of the carboxyl group-containing compound having a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound is at least one selected from the group consisting of a carboxyl group (COO) of the carboxyl group-containing compound having a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound. -or COOH) is more than 6 mol % and not more than 100 mol % (preferably more than 6 mol % and not more than 60 mol %, more preferably more than 6 mol % and not more than 50 mol %, and even more preferably 7 mol % or more and not more than 50 mol %) relative to the hydroxyl groups (OH) (100 mol %) of the starch. That is, according to one embodiment, in the starch-containing curable composition according to this aspect, the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound (with the proviso that the carboxyl groups (COO) of the carboxyl group-containing compound having a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound - or COOH) is 6 mol % or less (preferably less than 7 mol %) relative to the hydroxyl groups (OH) (100 mol %) of the starch).

[0125] According to one embodiment, in the starch-containing curable composition according to this aspect, the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound. According to one embodiment, in the starch-containing curable composition according to this aspect, the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, wherein the carboxyl group (COO) possessed by the carboxyl group-containing compound having a structural unit derived from the ethylenically unsaturated carboxyl group-containing compound is at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound. - or COOH) is more than 6 mol % and not more than 100 mol % (preferably more than 6 mol % and not more than 60 mol %, more preferably more than 6 mol % and not more than 50 mol %, and even more preferably 7 mol % or more and not more than 50 mol %) relative to the hydroxyl groups (OH) (100 mol %) of the starch.

[0126] [catalyst] The starch-containing curable composition according to this embodiment preferably contains a catalyst, which further improves the reactivity of the starch-containing curable composition and further improves the water resistance of the coating film.

[0127] When a carboxyl group-containing compound or an epoxy group-containing compound is used as the crosslinking agent, the catalyst may be a compound known as a catalyst for epoxy resins. Examples of the tetrafluoroboric acid or its salts include tetrafluoroborates of alkali metals (e.g., sodium or potassium), tetrafluoroborates of alkaline earth metals (e.g., calcium or magnesium), zinc tetrafluoroborate, and ammonium tetrafluoroborate; diazabicycloalkenes and derivatives thereof such as 1,8-diazabicyclo[5,4,0]undecene-7; amine compounds such as tributylamine and benzyldimethylamine; imidazole compounds such as 2-methylimidazole; organic phosphines such as triphenylphosphine and methyldiphenylphosphine; tetra-substituted phosphonium salts such as tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetrabenzoic acid borate, tetraphenylphosphonium tetranaphthoic acid borate, tetraphenylphosphonium tetranaphthoyloxyborate, tetraphenylphosphonium tetranaphthyloxyborate, and tetraphenylphosphonium 4,4'-sulfonyldiphenolate; and triphenylphosphine adducted with benzoquinone. Of these, zinc tetrafluoroborate is preferred. These curing catalysts can be used alone or in combination of two or more.

[0128] Commercially available catalysts include Zn(BF4)2 (zinc tetrafluoroborate, manufactured by Sigma-Aldrich).

[0129] When an epoxy resin catalyst is used, the amount of the catalyst is, for example, 0.1 to 40 parts by mass, and preferably 0.5 to 20 parts by mass, relative to 100 parts by mass of the epoxy group-containing compound.

[0130] When a carboxyl group-containing compound or an isocyanate group-containing compound is used as a crosslinking agent, the catalyst may be a compound known as a catalyst for urethane resins. For example, zirconium-containing compounds (zirconium-based catalysts) such as zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, zirconium octylate, n-propyl zirconate, n-butyl zirconate, zirconium stearate, zirconium tetraacetylacetonate, zirconyl chloride compounds, and zirconium lactate ammonium salt; tin (Sn)-containing compounds (tin-based catalysts) such as dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, and butyltin oxide; aluminum sec-butoxide, aluminum trisacetylacetonate, and aluminum bicarbonate. Examples of the curing catalyst include aluminum-containing compounds (aluminum catalysts) such as aluminum trisethylacetoacetate and aluminum trisethylacetoacetate; iron-containing compounds (iron catalysts) such as ferric naphthem; titanium-containing compounds (titanium catalysts) such as tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate and titanium lactate ammonium salt; and organometallic catalysts such as zirconium-containing compounds (zirconium catalysts) such as normal propyl zirconate, normal butyl zirconate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate and zirconium tetraacetylacetonate. These curing catalysts can be used alone or in combination of two or more.

[0131] Commercially available catalysts include Neostan U-100 (organotin catalyst; dibutyltin dilaurate, manufactured by Nitto Kasei Co., Ltd.); Orgatix T-300 (titanium-based catalyst; titanium lactate ammonium salt, manufactured by Matsumoto Fine Chemical Co., Ltd.); and Orgatix ZC-300 (zirconium-based catalyst; zirconium lactate ammonium salt, manufactured by Matsumoto Fine Chemical Co., Ltd.).

[0132] When a catalyst for a urethane resin is used, the amount of the catalyst is, for example, 0.1 to 20 parts by mass, and preferably 0.2 to 10 parts by mass, relative to 100 parts by mass of the isocyanate group-containing compound.

[0133] When a catalyst is contained in the starch-containing curable composition according to this embodiment, the content of the catalyst is preferably from 0.1 to 5% by mass, more preferably from 0.1 to 3% by mass, even more preferably from 0.2 to 3% by mass, particularly preferably from 0.2 to 2% by mass, and most preferably from 0.2 to 1.5% by mass, relative to the total mass of the starch-containing curable composition.

[0134] When a carboxyl group-containing compound is used as the crosslinking agent, the catalyst may be a compound known as an acid catalyst. Examples of the acid catalyst include nonylnaphthalene disulfonic acid, dinonylnaphthalene (mono)sulfonic acid, p-toluenesulfonic acid, and methanesulfonic acid. These curing catalysts may be used alone or in combination of two or more.

[0135] Commercially available acid catalysts include p-toluenesulfonic acid (manufactured by Konan Chemical Co., Ltd.); methanesulfonic acid (manufactured by Toyobo Co., Ltd.); and the like.

[0136] When an acid catalyst is used, the amount of the catalyst is, for example, 0.1 to 20 parts by mass, and preferably 0.2 to 10 parts by mass, relative to 100 parts by mass of the crosslinking agent (for example, a carboxyl group-containing compound).

[0137] [Additives] The starch-containing curable composition according to this embodiment may contain other known additives as needed, such as pigments, solvents, plasticizers, dispersants, thickeners, antifoaming agents, preservatives, UV absorbers, fragrances, etc. The content of these additives is not particularly limited, but is preferably 0.01 to 30% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.1 to 5% by mass, relative to 100% by mass of the curable composition.

[0138] [pH] The pH of the starch-containing curable composition according to this embodiment is not particularly limited, but is preferably 1 to 11, more preferably 1 to 10, particularly preferably 1.5 to 9, and most preferably 1.5 to 8. According to one embodiment, the pH of the starch-containing curable composition according to this embodiment is 1.5 to 7.5, or 2 to 7.5. When the pH of the starch-containing curable composition is within the above range, the desired effects of the present invention can be more effectively exhibited. The pH is measured in an aqueous solution (25°C) obtained by diluting the starch-containing curable composition with water to a starch concentration of 10% by mass.

[0139] According to one embodiment, a crosslinking agent is added to the starch-containing setting composition according to this embodiment after obtaining the starch-containing aqueous composition. The pH of the starch-containing aqueous composition according to this embodiment is preferably 1 to 11, more preferably 1 to 10, particularly preferably 1.5 to 9, and most preferably 1.5 to 8. According to one embodiment, the pH of the starch-containing aqueous composition according to this embodiment is 1.5 to 7.5 or 2 to 7.5. When the pH of the starch-containing aqueous composition is within the above range, the desired effects of the present invention can be more effectively achieved. The pH is measured in an aqueous solution (25°C) obtained by diluting the starch-containing aqueous composition with water to a starch concentration of 10% by mass.

[0140] [Method for producing starch-containing hardenable composition] The starch-containing curable composition according to this embodiment can be obtained by mixing its essential components and, if necessary, a catalyst at 0 to 80°C. In this case, the crosslinking agent may be added in the form of a composition dissolved or dispersed in a solvent. For example, when the crosslinking agent is an epoxy group-containing compound or an isocyanate group-containing compound, the crosslinking agent is preferably in the form of a composition dissolved or dispersed in a solvent. Furthermore, when the crosslinking agent is an epoxy group-containing compound or an isocyanate group-containing compound, the starch-containing curable composition preferably contains a catalyst. When the crosslinking agent is an alkoxysilyl group-containing compound, the starch-containing curable composition preferably contains two or more alkoxysilyl group-containing compounds.

[0141] In the method for producing a starch-containing hardenable composition according to one embodiment of the present invention, for example, when pH adjustment is performed using a pH adjuster, it is preferable to adjust the pH after obtaining a homogenized mixture.

[0142] In the above-mentioned production method, there are no particular limitations on the various devices used for mixing and stirring the components, and conventionally known knowledge can be used as appropriate.

[0143] In one preferred embodiment, the starch-containing curable composition of this embodiment is prepared by first preparing a starch-containing aqueous composition containing starch, a hydroxycarboxylic acid, a water-soluble polymer other than starch, and a solvent containing water, and then adding a crosslinker (and a catalyst) to the aqueous composition. In this case, a solution temperature of approximately 70 to 150°C is preferably used to obtain the starch-containing aqueous composition, from the viewpoint of increasing the dissolved starch content while maintaining the starch properties. The temperature is preferably 100 to 150°C, more preferably 110 to 150°C, even more preferably 115 to 150°C, particularly preferably 120 to 140°C, and most preferably 135 to 140°C, from the viewpoint of increasing the starch concentration in the aqueous composition. In this case, the amounts of the components are preferably adjusted so that the dissolved starch content in the starch-containing aqueous composition is 5% by mass or more, or 7% by mass or more. In a preferred embodiment of the above production method, it is preferable to further carry out an aging step in which the mixture is heated to 70 to 150° C. and then aged for 10 minutes to 10 hours, 10 minutes to 8 hours, or 10 minutes to 6 hours at a temperature of 70 to 150° C. From the viewpoint of increasing the starch concentration in the aqueous composition, the aging step time is also preferably 1 to 6 hours, more preferably 2 to 6 hours, and even more preferably 3 to 6 hours.

[0144] Furthermore, when producing a starch-containing aqueous composition, if the starch has a hot water solubility of less than 30%, the starch with a hot water solubility of less than 30% may be pre-mixed with the solvent when preparing a mixture containing the starch, a hydroxycarboxylic acid, and a solvent containing water. In this case, the solvent combined with the starch with a hot water solubility of less than 30% may be one or more of the solvents other than water listed above, but glycerin is preferred. Therefore, it is also preferable to obtain a starch-containing aqueous composition by heating a mixture containing a starch with a hot water solubility of less than 30%, a hydroxycarboxylic acid, water, and a solvent to 70 to 150°C while stirring to homogenize the mixture. Furthermore, it is also preferable to obtain a starch-containing aqueous composition by heating a mixture containing a starch mixture containing a starch with a hot water solubility of less than 30% and a solvent, a hydroxycarboxylic acid, water, and a solvent to 70 to 150°C while stirring to homogenize the mixture.

[0145] In one embodiment of the method for producing a starch-containing aqueous composition, when the hot water solubility of the starch is less than 30%, a water-soluble polymer may be added as needed when obtaining a mixture containing starch, a hydroxycarboxylic acid, and a solvent containing water. Therefore, it is also preferable to obtain the starch-containing aqueous composition by heating a mixture containing starch having a hot water solubility of less than 30%, a hydroxycarboxylic acid, a water-soluble polymer, and water to 70 to 150°C while stirring to homogenize the mixture.

[0146] [Uses of starch-containing hardenable compositions] The starch-containing curable composition provided by the present invention can be used in various applications that utilize the physical properties of starch, such as antistatic agents, plasticizers, fillers, surfactants, inks, paints, inkjet inks, adhesives, pressure-sensitive adhesives, and release agents.

[0147] Although the embodiments of the present invention have been described in detail, it is clear that this is by way of illustration and example only and not of limitation, and that the scope of the present invention should be interpreted by the appended claims.

[0148] The present invention encompasses the following aspects and configurations.

[0149] [1] A starch-containing curable composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, a solvent containing water, and a crosslinking agent; [2] The starch-containing hardenable composition according to the above [1], which comprises: a starch-containing aqueous composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, and a solvent containing water; and a crosslinking agent; [3] The starch-containing hardenable composition according to the above [1] or [2], wherein the hydroxycarboxylic acid is at least one selected from the group consisting of lactic acid, citric acid, tartaric acid, glycolic acid, malic acid, and ricinoleic acid; [4] The starch-containing curable composition according to any one of the above [1] to [3], wherein the water-soluble polymer is at least one selected from the group consisting of polyacrylic acid polymers, polyoxyalkylene adducts and sulfate ester salts thereof, and arylsulfonic acid-formalin condensates and salts thereof; [5] The starch-containing hardenable composition according to any one of [1] to [4] above, wherein the starch has a hot water solubility of less than 30% as calculated according to the following measurement method: [Method for measuring hot water solubility] 6 g of starch was immersed in 94 g of hot water (80°C) with stirring for 5 hours, and the starch that did not dissolve into the aqueous phase was separated by filtration and dried at 130°C for 90 minutes. The weight W [g] of the starch after drying was measured, and the hot water solubility was calculated using the following formula 1: (Formula 1) Hot water solubility [%] = (6 - W) / 6 x 100 [6] The starch-containing curable composition according to any one of [1] to [4] above, wherein the starch has a hot water solubility of 30% or more as calculated according to the following measurement method: [Method for measuring hot water solubility] 6 g of starch was immersed in 94 g of hot water (80°C) with stirring for 5 hours, and the starch that did not dissolve into the aqueous phase was separated by filtration and dried at 130°C for 90 minutes. The weight W [g] of the starch after drying was measured, and the hot water solubility was calculated using the following formula 1: (Formula 1) Hot water solubility [%] = (6 - W) / 6 x 100 [7] The starch-containing curable composition according to any one of the above [1] to [6], wherein the crosslinking agent comprises at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound; [8] The starch-containing curable composition according to any one of the above [1] to [6], wherein the crosslinking agent comprises a carboxyl group-containing compound; [9] The starch-containing curable composition according to any one of the above [1] to [6], wherein the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound;

[10] The starch-containing curable composition according to any one of the above [1] to [9], wherein the reactive groups of the crosslinking agent are contained in an amount of 0.1 mol % to 1000 mol % based on the hydroxyl groups of the starch;

[11] The starch-containing curable composition according to any one of the above [1] to [7], wherein the crosslinking agent comprises at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and when the carboxyl group-containing compound has a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the carboxyl groups account for more than 6 mol% relative to the hydroxyl groups (100 mol%) of the starch.

[0150]

[12] The starch-containing curable composition according to any one of the above [1] to [7], wherein the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound, and when the carboxyl group-containing compound has a structural unit derived from a carboxyl group and a hydroxy group-containing saturated or alicyclic compound, the carboxyl groups of the carboxyl group-containing compound account for more than 0.5 mol % relative to the hydroxyl groups (100 mol %) of the starch; otherwise (when the reactive groups of the crosslinking agent are at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound that do not have a structural unit derived from a carboxyl group and a hydroxy group-containing saturated or alicyclic compound), the reactive groups of the crosslinking agent account for more than 6 mol % relative to the hydroxyl groups (100 mol %) of the starch.

[0151]

[13] The starch-containing curable composition according to any one of [1] to

[12] above, further comprising a catalyst;

[14] The starch-containing curable composition according to

[13] above, wherein the catalyst is contained in an amount of 0.1% by mass or more and 5% by mass or less, based on the total mass of the starch-containing curable composition;

[15] The starch-containing curable composition according to any one of [1] to

[14] above, for use as an antistatic agent, a plasticizer, a filler, a surfactant, an ink, a paint, an inkjet ink, an adhesive, a pressure-sensitive adhesive, or a release agent;

[16] A coating agent comprising the starch-containing curable composition according to any one of [1] to

[15] above;

[17] A method for producing a starch-containing curable composition, comprising the steps of obtaining a starch-containing aqueous composition containing starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, and a solvent containing water, and adding a crosslinking agent to the aqueous composition. [Example]

[0152] The effects of the present invention will be explained using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. In the following examples, unless otherwise specified, operations were performed at 25°C.

[0153] [Modified starch mixture] Modified starch was used as the starch in the following Examples 1 to 9 and Comparative Example 1. The modified starch used in Examples 1 to 9 and Comparative Example 1 was a pellet-shaped modified starch mixture containing 20% by mass of glycerin (Sankyo Golden Starch: SGS, manufactured by Sankyo Chemical Industry Co., Ltd.) (derived from corn starch) prepared by mixing modified starch A with glycerin. Starch-containing aqueous compositions (a-1) and (a-2) were prepared as starch-containing aqueous compositions containing modified starch A (Production Examples 1 and 2 below).

[0154] [Measurement of hot water solubility of modified starch] First, modified starch A was prepared by separating modified starch A from a modified starch mixture (Sankyo Golden Starch: SGS, manufactured by Sankyo Chemical Industry Co., Ltd.). Specifically, glycerin was extracted from the modified starch mixture into an aqueous phase at 40°C and separated, thereby separating modified starch A contained in the modified starch mixture to obtain modified starch A. The hot water solubility of this modified starch A was measured according to the following method.

[0155] [Method for measuring hot water solubility] 6 g of the modified starch A separated as starch from the above was immersed in 94 g of hot water (80°C) with stirring for 5 hours, and the starch that did not dissolve into the aqueous phase was separated by filtration and dried for 90 minutes at 130°C. The weight W [g] of the starch after drying was measured, and the hot water solubility was calculated using the following formula 1.

[0156] (Formula 1) Hot water solubility [%] = (6-W) / 6 x 100.

[0157] As a result, the hot water solubility of modified starch A was 20%.

[0158] [Unmodified starch] Cornstarch (Y-3P, manufactured by Nippon Corn Starch Co., Ltd.) was used as the unmodified starch. Starch-containing aqueous compositions (b-1) and (b-2) containing cornstarch (Y-3P, manufactured by Nippon Corn Starch Co., Ltd.) were prepared as starch-containing aqueous compositions (Production Examples 3 and 4 below).

[0159] [Measurement of hot water solubility of unmodified starch] The hot water solubility of cornstarch (Y-3P manufactured by Nippon Cornstarch Co., Ltd.) was measured according to the hot water solubility measurement method described below.

[0160] [Method for measuring hot water solubility] Six grams of cornstarch (Y-3P, manufactured by Nippon Cornstarch Co., Ltd.) was immersed in 94 grams of hot water (80°C) for 5 hours with stirring, and the starch that did not dissolve into the aqueous phase was separated by filtration and dried for 90 minutes at 130°C. The weight W [g] of the dried starch was measured, and the hot water solubility was calculated using the following formula 1.

[0161] (Formula 1) Hot water solubility [%] = (6-W) / 6 x 100.

[0162] As a result, the hot water solubility of cornstarch (Y-3P manufactured by Nippon Cornstarch Co., Ltd.) was found to be 30% or more.

[0163] Preparation of starch-containing aqueous composition [Manufacturing Example 1] Starch-containing aqueous composition (a-1): Modified starch-containing aqueous composition (acid type (unneutralized)) 42.5 parts by weight of modified starch mixture (Sankyo Golden Starch (SGS) manufactured by Sankyo Chemical Industry Co., Ltd.) (35 parts by weight of modified starch A, 7.5 parts by weight of glycerin), 46.8 parts by weight of water, 7.7 parts by weight of lactic acid, and 3 parts by weight of polyacrylic acid (100 parts by weight of AQUALIC (registered trademark) HL415 47% aqueous solution manufactured by Nippon Shokubai Co., Ltd.) were charged into an autoclave and heated to 120 ° C. over 2 hours with stirring, aged for another 1 hour, and then cooled to obtain 100.0 parts by weight of liquid starch-containing aqueous composition (a-1). The composition ratio of each component of the starch-containing aqueous composition (a-1) was 35% by weight of modified starch A, 0.8% by weight of polyacrylic acid, 2.2% by weight of lactic acid, 9% by weight of glycerin, and 53% by weight of water. The viscosity (25°C) of the resulting starch-containing aqueous composition (a-1) was 85 mPa·s (100 rpm). The viscosity was measured at 25°C using an E-type viscometer (1°34' x R24) at 1 to 100 rpm. The pH of a 10% aqueous solution of the resulting starch-containing aqueous composition (a-1) was 3.2.

[0164] [Manufacturing Example 2] Starch-containing aqueous composition (a-2): Modified starch-containing aqueous composition (neutralized type) A modified starch mixture (Sankyo Golden Starch: SGS manufactured by Sankyo Chemical Industry Co., Ltd.) of 42.5 parts by weight (35 parts by weight of modified starch A, 7.5 parts by weight of glycerin), 46.8 parts by weight of water, 7.7 parts by weight of lactic acid, and 3 parts by weight of polyacrylic acid (100 parts by weight of AQUALIC (registered trademark) HL415 manufactured by Nippon Shokubai Co., Ltd.) was charged into an autoclave and heated to 120 ° C. over 2 hours with stirring, and after aging for another 1 hour, cooled to obtain 100.0 parts by weight of a liquid starch-containing aqueous composition (a-2). The obtained starch-containing aqueous composition (a-2) was neutralized with a 48% aqueous solution of caustic soda, and the starch-containing aqueous composition (a-2) was diluted with water to prepare an aqueous solution with a modified starch A concentration of 10% by weight. The pH was adjusted to 7.

[0165] The composition ratio of each component of the starch-containing aqueous composition (a-2) was 35% by mass of modified starch A, 0.8% by mass of polyacrylic acid, 2.2% by mass of lactic acid, 9% by mass of glycerin, and 53% by mass of water. The viscosity (25°C) of the resulting starch-containing aqueous composition (a-2) was 83 mPa·s (100 rpm). The viscosity was measured at 25°C using an E-type viscometer (1°34' x R24) at 1 to 100 rpm.

[0166] [Manufacturing Example 3] Starch-containing aqueous composition (b-1): Corn starch-containing aqueous composition (acid type (unneutralized)) Cornstarch (Y-3P, manufactured by Nippon Cornstarch Co., Ltd.) 39.8 parts by weight, water 36.3 parts by weight, lactic acid 7.7 parts by weight, polyacrylic acid 3 parts by weight (AQUALIC® HL415, manufactured by Nippon Shokubai Co., Ltd., 100 parts by weight as a 47% aqueous solution), and glycerin (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) 13.2 parts by weight were charged into an autoclave and heated to 120 ° C over 2 hours with stirring. After aging for another 1 hour, the mixture was cooled to obtain 100.0 parts by weight of a liquid starch-containing aqueous composition (b-1). The composition ratio of each component of the starch-containing aqueous composition (b-1) was 35% by weight of modified starch A, 0.8% by weight of polyacrylic acid, 2.2% by weight of lactic acid, 13.2% by weight of glycerin, and 48.8% by weight of water. The viscosity (25°C) of the resulting starch-containing aqueous composition (b-1) was 128 mPa·s (100 rpm). The viscosity was measured at 25°C using an E-type viscometer (1°34' x R24) at 1 to 100 rpm.

[0167] [Manufacturing Example 4] Starch-containing aqueous composition (b-2): Cornstarch-containing aqueous composition (neutralized type) Cornstarch (Y-3P, manufactured by Nippon Cornstarch Co., Ltd.) 39.8 parts by weight, water 36.3 parts by weight, lactic acid 7.7 parts by weight, and polyacrylic acid 3 parts by weight (AQUALIC® HL415, manufactured by Nippon Shokubai Co., Ltd., 100 parts by weight as a 47% aqueous solution), glycerin (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) 13.2 parts by weight were charged into an autoclave and heated to 120 ° C. over 2 hours with stirring, and then aged for another 1 hour and cooled to obtain 100.0 parts by weight of liquid starch-containing aqueous composition (b-2). The obtained starch-containing aqueous composition (b-2) was neutralized with a 48% aqueous solution of caustic soda, and the starch-containing aqueous composition (b-2) was diluted with water to prepare an aqueous solution with a cornstarch concentration of 10% by weight. The pH was adjusted to 7.

[0168] The composition ratio of each component of the starch-containing aqueous composition (b-2) was 35% by mass of modified starch A, 0.8% by mass of polyacrylic acid, 2.2% by mass of lactic acid, 13.2% by mass of glycerin, and 48.8% by mass of water. The viscosity (25°C) of the resulting starch-containing aqueous composition (b-2) was 114 mPa·s (100 rpm). The viscosity was measured at 25°C using an E-type viscometer (1°34' x R24) at 1 to 100 rpm.

[0169] [Example 1] First, the starch-containing aqueous composition (a-1) (acid type (unneutralized)) obtained above was prepared.

[0170] 42.5 parts by weight of a modified starch mixture (Sankyo Golden Starch (SGS) manufactured by Sankyo Chemical Industry Co., Ltd.) (35 parts by weight of modified starch A, 7.5 parts by weight of glycerin), 46.8 parts by weight of water, 7.7 parts by weight of lactic acid, and 3 parts by weight of polyacrylic acid (100 parts by weight of AQUALIC® HL415 47% aqueous solution manufactured by Nippon Shokubai Co., Ltd.) were charged into an autoclave and heated to 120 ° C. over 2 hours with stirring, aged for another 1 hour, and then cooled to obtain 100.0 parts by weight of a liquid starch-containing aqueous composition (a-1). The composition ratio of each component of the starch-containing aqueous composition (a-1) was 35% by weight of modified starch A, 0.8% by weight of polyacrylic acid, 2.2% by weight of lactic acid, 9% by weight of glycerin, and 53% by weight of water. The viscosity of the resulting starch-containing aqueous composition (a-1) was 85 mPa·s (100 rpm) at 25°C. The viscosity was measured at 25°C using an E-type viscometer (1°34' x R24) at 1 to 100 rpm.

[0171] Next, 1 part by mass of the starch-containing aqueous composition (a-1) was mixed with 1 part by mass of an epoxy group-containing compound (Denacol EX-614B (epoxy equivalent = 173 g / eq.; viscosity (25°C) 5,000 mPa·s), manufactured by Nagase ChemteX Corporation) as a crosslinking agent and 0.02 parts by mass of an epoxy curing catalyst Zn(BF) (zinc tetrafluoroborate, manufactured by Sigma-Aldrich) as a catalyst using a stirring device (Homodisper, manufactured by PRIMIX) at 23°C for 1 minute at 500 rpm to prepare the starch-containing curable composition of Example 1 (viscosity (25°C) 1,400 mPa·s).

[0172] [Examples 2 to 9] A starch-containing aqueous composition (a-1) was obtained in the same manner as in Example 1 above. Thereafter, starch-containing curable compositions (viscosity (25°C) 80 to 1200 mPa·s) of Examples 2 to 9 were prepared in the same manner as in Example 1, except that the types and amounts of the crosslinking agent and catalyst were changed as shown in Table 1. Details of each compound used in Examples 2 to 9 are as follows. Blank cells in Table 1 indicate that the corresponding material was not contained. Isocyanate group-containing compound: Duranate WM44-L70G (isocyanate group content = 5.3% by mass; solid content = 70% by mass; solvent = dipropylene glycol dimethyl ether; viscosity (25°C) 2,200 mPa·s) (manufactured by Asahi Kasei Corporation) Isocyanate catalyst: Neostan U100 (manufactured by Nitto Kasei Co., Ltd.) Alkoxysilyl group-containing compound: Tetraethoxysilane XIAMETER OFS-6697 (Dow Chemical Company) Alkoxysilyl group-containing compound: 3-(2-aminoethyl)aminopropylmethoxysilane XIAMETER OFS-6020 (manufactured by The Dow Chemical Company).

[0173] [Comparative Example 1] A starch-containing aqueous composition (a-1) was obtained in the same manner as in Example 1. The starch-containing aqueous composition (a-1) was used as the composition of Comparative Example 1 without adding a crosslinking agent or a catalyst to the starch-containing aqueous composition (a-1).

[0174] [Comparative Examples 2 to 5] The starch-containing aqueous compositions (a-1) obtained in the above Preparation Examples 1 to 4 were used as the compositions of each Comparative Example without adding a crosslinking agent or a catalyst. In Table 2, blank spaces indicate that the corresponding material was not contained. [Examples 10 to 23] A carboxyl group-containing compound as a crosslinking agent, and in Examples 14 and 15, a catalyst, were added to the starch-containing aqueous compositions obtained in Production Examples 1 to 4 in the amounts shown in Tables 2 and 3, and mixed at 23°C for 1 minute at a stirring speed of 500 rpm (Homodisper, manufactured by PRIMIX) to prepare the starch-containing curable compositions of Examples 10 to 23 (viscosity (25°C) 100 to 300 mmPa s). Note that blank cells in Tables 2 and 3 indicate that the corresponding material was not contained.

[0175] [Comparative Examples 6 and 7] A catalyst was added in the amount shown in Table 4 to the starch-containing aqueous composition (b-1) obtained in Production Example 3 above, and the mixture was mixed at 23°C for 1 minute at a stirring speed of 500 rpm (Homodisper, manufactured by PRIMIX) to prepare starch-containing curable compositions (viscosity (25°C) 80 to 300 mmPa s) of Comparative Examples 6 and 7. Note that blank cells in Table 4 indicate that the corresponding material was not contained.

[0176] [Examples 24 to 38] A carboxyl group-containing compound as a crosslinking agent, and in examples where a catalyst was added, a carboxyl curing catalyst, were added to the starch-containing aqueous compositions obtained in Preparation Examples 1 to 4 in the amounts shown in Tables 4 and 5. The mixture was mixed at 23°C for 1 minute at a stirring speed of 500 rpm (Homodisper, manufactured by PRIMIX) to prepare the starch-containing curable compositions of Examples 24 to 38 (viscosity (25°C) 200 to 400 mmPa s). Note that blank cells in Tables 4 and 5 indicate that the corresponding material was not contained.

[0177] Details of the compounds used in Comparative Examples 2 to 7 and Examples 10 to 38 are as follows.

[0178] Carboxyl group-containing compounds (1) Joncryl PDX7741 BASF (styrene-acrylic resin (ammonium salt of modified styrene-acrylic resin)-containing emulsion; resin is contained as core-shell resin particles) oleyl type nonionic surfactant 1.3% (resin content (solid content) 49% by mass) (2) Joncryl PDX7780 (BASF) (styrene-acrylic resin (ammonium salt of modified styrene-acrylic resin)-containing emulsion; resin is contained as core-shell resin particles) Tg 92°C (resin content (solid content) 48% by mass) (3) PLA emulsion (average particle size 0.23 μm, pH 3.9) A PLA emulsion with the above composition was obtained by phase inversion emulsification; 30% by mass of PLA (PLZ-R-002-PGL, manufactured by Nagase & Co., Ltd.), 4.5% by mass of styrenated phenolic ethoxylate (N-780, manufactured by Nippon Nyukazai Co., Ltd.), 0.5% by mass of polyalkylene oxide (ADEKA (registered trademark) Pluronic F-108, manufactured by ADEKA Corporation), 2.5% by mass of hydrophilic glycol ether (BDG), 20% by mass of solvent (20% by mass of hydrophobic glycol ether and 8% by mass of alkoxy fatty acid alkyl ester), 42.5% by mass of water (resin content (solid content) 30% by mass).

[0179] ·Epoxy group-containing compounds (1) Green Denacol EX-614B (epoxy equivalent = 173 g / eq.; viscosity (25°C) 5,000 mPa·s) manufactured by Nagase ChemteX Corporation Carboxylic curing catalyst (1) Orgatix T-300 (Matsumoto Fine Chemical Co., Ltd.): Titanium lactate ammonium salt (2) Orgatix ZC-300 (manufactured by Matsumoto Fine Chemical Co., Ltd.: zirconium lactate ammonium salt) (3) PTS p-toluenesulfonic acid (used as a 10% by weight aqueous solution in Tables 4 and 5) (4) Neostan U100 (manufactured by Nitto Kasei Co., Ltd.) (5) Zn(BF4)2 (zinc tetrafluoroborate, Sigma-Aldrich).

[0180] Evaluation of starch-containing hardenable compositions [Paint film formation] Each of the starch-containing curable compositions of the Examples and Comparative Examples obtained above was applied to a glass substrate (size: 50 mm length x 50 mm width x 2 mm thickness) with a bar coater to a thickness of 25 μm (thickness when wet), dried for 30 minutes at a predetermined temperature described below, and then cooled to room temperature to obtain a coating film of each of the starch-containing curable compositions of the Examples and Comparative Examples. The coating films were dried at 150°C for 30 minutes in Examples 1 to 9 and Comparative Example 1, and at the temperatures listed in Tables 2 to 5 for 30 minutes in Examples 10 to 38 and Comparative Examples 2 to 7.

[0181] The coating films of the starch-containing curable compositions of the Examples and Comparative Examples obtained above were evaluated as follows, and the results are shown in Tables 1 to 5 below.

[0182] [Evaluation by touch (presence or absence of tack)] The coating films of the starch-containing curable compositions of the Examples and Comparative Examples obtained above were evaluated by touching with a finger (presence or absence of tackiness). Specifically, the coating surface was lightly touched with an index finger, and visually checked whether tackiness (finger marks) remained on the coating surface, and evaluated according to the following criteria. Note that an evaluation of △ or higher was considered to be acceptable. "Evaluation Criteria" 〇: No tuck △: Slight (finger marks are barely visible, but there is a sticky feeling when touched) ×: Tucked.

[0183] [Transparency] The coating film of each starch-containing curable composition of the Examples and Comparative Examples obtained above was evaluated for transparency. Specifically, the coating film was placed on a black paper, and the coating film was visually checked for haze (cloudiness) and evaluated according to the following criteria. An evaluation of △ or higher was considered to be acceptable. "Evaluation Criteria" ○: Haze is less than 20% of the coating area △: Haze is 20% or more but less than 50% of the coating area ×: Haze is 50% or more of the coated area.

[0184] [water resistance] The water resistance of the coating films of the starch-containing curable compositions of the Examples and Comparative Examples obtained above was evaluated. Specifically, a drop of deionized water was dropped onto the coating film, and the water droplet on the coating film was left to dry at room temperature and normal pressure for 24 hours. The appearance of the area on the coating film where the water droplet had been was then visually observed and evaluated according to the following criteria. A rating of △ or higher was considered acceptable. "Evaluation Criteria" 〇: No change in the coating △: The coating has turned white ×: Part of the coating film has dissolved (if there are parts without the coating film).

[0185] [Miscibility] The coating films of the starch-containing curable compositions of the Examples and Comparative Examples obtained above were evaluated for compatibility. Specifically, the coatings were applied with a bar coater to a thickness of 25 μm (wet thickness), dried for 30 minutes at a predetermined temperature described below, and then cooled to room temperature. The appearance of the coatings was visually observed and evaluated according to the following criteria. A rating of △ or higher was considered acceptable. "Evaluation Criteria" ○: No aggregates △: Some aggregates ×: Agglomeration.

[0186] [Coloring] The coating films of the starch-containing curable compositions of the Examples and Comparative Examples obtained above were evaluated for coloration. Specifically, the coatings were applied with a bar coater to a thickness of 25 μm (thickness when wet), dried for 30 minutes at a predetermined temperature described below, and then cooled to room temperature. The appearance of the coatings was visually observed and evaluated according to the following criteria. A rating of △ or higher was considered acceptable. "Evaluation Criteria" 〇:Colorless to light yellow △:Yellow ×: Brown ××: Dark brown.

[0187] [Oil resistance] The oil resistance of the coating films of the modified starch-containing curable compositions of the Examples and Comparative Examples obtained above was evaluated. Specifically, a drop of salad oil was dropped onto the coating film, and the state of the coating film was visually observed after 1 minute and 60 minutes, and evaluated according to the following criteria. A rating of △ or higher was considered to be acceptable. "Evaluation Criteria" 〇: No change in the coating even after 60 minutes (Salad oil has not penetrated the coating) △: No change in the coating film after 1 minute, but after 60 minutes the coating film has dissolved (leaving some areas without the coating film) or turned white (after 1 minute the salad oil has not penetrated the coating film, but after 60 minutes the salad oil has penetrated the coating film) ×: After 1 minute, the coating film was dissolved (leaving some areas without the coating film) or whitened (after 1 minute, salad oil had penetrated the coating film).

[0188] [Biomass content per solid] The biomass ratio per solid content was calculated for each of the modified starch-containing curable compositions of the Examples and Comparative Examples obtained above. The biomass ratio per solid content was calculated by calculating the solid content of each raw material and expressing the proportion (mass %) of naturally occurring compounds relative to 100% by mass of the solid content.

[0189] In Tables 1 to 5, the number of moles (mol %) of reactive groups of the crosslinking agent relative to the OH groups of the starch is shown as "crosslinking agent reactive groups / starch OH groups (mol %)."

[0190] [Table 1]

[0191] [Table 2]

[0192] [Table 3]

[0193] [Table 4]

[0194] [Table 5]

[0195] The results shown in Tables 1 to 5 show that the reaction proceeded sufficiently to obtain stable coating films using the starch-containing curable compositions of Examples 1 to 38. It is also clear that the coating films obtained using the starch-containing curable compositions of Examples 1 to 38 were highly water-resistant and highly transparent.

Claims

1. A starch-containing hardenable composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, a solvent containing water, and a crosslinking agent.

2. 2. The starch-containing hardenable composition according to claim 1, comprising: a starch-containing aqueous composition comprising starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, and a solvent containing water; and a crosslinking agent.

3. 3. The starch-containing hardenable composition according to claim 1, wherein the hydroxycarboxylic acid is at least one selected from the group consisting of lactic acid, citric acid, tartaric acid, glycolic acid, malic acid and ricinoleic acid.

4. 3. The starch-containing curable composition according to claim 1, wherein the water-soluble polymer is at least one selected from the group consisting of polyacrylic acid polymers, polyoxyalkylene adducts and sulfate ester salts thereof, and arylsulfonic acid-formalin condensates and salts thereof.

5. 3. The starch-containing hardenable composition according to claim 1 or 2, wherein the starch has a hot water solubility of less than 30% calculated according to the following measurement method: [Method for measuring hot water solubility] 6 g of starch is immersed in 94 g of hot water (80° C.) with stirring for 5 hours, and the starch that did not dissolve into the aqueous phase is separated by filtration and dried for 90 minutes at 130° C. The weight W [g] of the starch after drying is measured, and the hot water solubility is calculated using the following mathematical formula 1. (Formula 1) Hot water solubility [%] = (6 - W) / 6 x 100

6. 3. The starch-containing hardenable composition according to claim 1 or 2, wherein the starch has a hot water solubility of 30% or more as calculated according to the following measurement method: [Method for measuring hot water solubility] 6 g of starch is immersed in 94 g of hot water (80° C.) with stirring for 5 hours, and the starch that did not dissolve into the aqueous phase is separated by filtration and dried for 90 minutes at 130° C. The weight W [g] of the starch after drying is measured, and the hot water solubility is calculated using the following mathematical formula 1. (Formula 1) Hot water solubility [%] = (6 - W) / 6 x 100

7. 3. The starch-containing curable composition according to claim 1, wherein the crosslinking agent comprises at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound.

8. 3. The starch-containing hardenable composition of claim 1, wherein the crosslinking agent comprises a carboxyl group-containing compound.

9. 3. The starch-containing curable composition according to claim 1, wherein the crosslinking agent comprises a carboxyl group-containing compound and at least one selected from the group consisting of an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound.

10. 3. The starch-containing curable composition according to claim 1, wherein the reactive groups of the crosslinking agent are contained in an amount of 0.1 mol % to 1000 mol % relative to the hydroxyl groups (100 mol %) of the starch.

11. the crosslinking agent includes at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound; 3. The starch-containing curable composition according to claim 1, wherein when the carboxyl group-containing compound is a carboxyl group-containing compound having a structural unit derived from an ethylenically unsaturated carboxyl group-containing compound, the carboxyl groups account for more than 6 mol% relative to the hydroxyl groups (100 mol%) of the starch.

12. the crosslinking agent is at least one selected from the group consisting of a carboxyl group-containing compound, an epoxy group-containing compound, an isocyanate group-containing compound, and an alkoxysilyl group-containing compound; When the carboxyl group-containing compound has a structural unit derived from a carboxyl group- and hydroxy group-containing saturated or alicyclic compound, the carboxyl groups of the carboxyl group-containing compound are more than 0.5 mol % relative to the hydroxyl groups (100 mol %) of the starch, 3. A starch-containing hardenable composition according to claim 1 or 2, wherein the reactive groups of the crosslinker are greater than 6 mol % relative to the hydroxyl groups of the starch (100 mol %).

13. 3. The starch-containing curable composition of claim 1, further comprising a catalyst.

14. 14. The starch-containing curable composition according to claim 13, wherein the catalyst is contained in an amount of 0.1% by weight to 5% by weight, based on the total weight of the starch-containing curable composition.

15. 3. The starch-containing curable composition according to claim 1 or 2 for use as an antistatic agent, plasticizer, filler, surfactant, ink, paint, inkjet ink, adhesive, pressure sensitive adhesive or release agent.

16. A coating agent comprising the starch-containing curable composition of claim 1 or 2.

17. A method for producing a starch-containing curable composition, comprising the steps of obtaining a starch-containing aqueous composition containing starch, a hydroxycarboxylic acid, a water-soluble polymer other than the starch, and a solvent containing water, and adding a crosslinking agent to the aqueous composition.

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