Biodegradable adhesive composition and biodegradable adhesive composition kit

Abstract

Provided is a biodegradable adhesive composition capable of forming a gelatin-based adhesive having good water resistance, good preservability against mold and the like, and higher safety.　Provided is a biodegradable adhesive composition containing: gelatin; a polyhydric alcohol; water; and at least one crosslinking agent selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols. This biodegradable adhesive composition has a gelatin content of 5%-40% by mass, a polyhydric alcohol content of 7%-55% by mass, a water content of 20%-80% by mass, and a crosslinking agent content of 0.005%-3% by mass.

Description

Biodegradable adhesive composition and biodegradable adhesive composition kit

[0001] The present invention relates to a biodegradable adhesive composition and a biodegradable adhesive composition kit.

[0002] Gelatin and glue have long been used as adhesives. When a composition containing gelatin or glue is used as an adhesive, for example, gelatin and / or glue is mixed with water to prepare a gel-like composition, which is then heated to form a sol. The liquid solubilized composition is then applied to an object (adherend) as an adhesive. Gelatin and glue are extracted by applying heat to collagen, a major component of connective tissues such as animal skin, bones, and tendons. Generally, highly purified gelatin, which is primarily used in foods and pharmaceuticals, is referred to as gelatin, while less purified glue, which is used as an adhesive for art supplies and crafts, is referred to as glue. In this specification, gelatin and glue may be collectively referred to as gelatin.

[0003] Because gelatin is a natural material, adhesives using gelatin can be constructed as environmentally and human-friendly adhesives by using natural materials for other components as well. For example, Patent Document 1 discloses a water-soluble adhesive containing predetermined amounts of gelatin and / or glue, glycerin, a polyhydric alcohol and / or a derivative thereof that is solid or highly viscous at room temperature, and water, and having a viscosity of 500 to 100,000 mPa·s / 60°C. Furthermore, Patent Document 2 proposes an adhesive containing predetermined amounts of glue, purified wood vinegar, glutinous rice flour, hiba oil, and wasabi oil as a coating agent made from natural materials so as not to generate environmental pollutants.

[0004] However, conventional adhesives that use gelatin (glue) generally have poor water resistance and absorb water and swell when immersed in water or placed in a humid environment, resulting in a decrease in adhesive strength and easy peeling. For example, Patent Document 3 proposes an adhesive that uses tung oil to improve the water resistance of gelatin-based adhesives, and is composed of glue, water, water-soluble sugars, and tung oil blended in a specified ratio. Furthermore, an adhesive has been proposed that uses wood vinegar or bamboo vinegar instead of water to prevent the glue from gelling, making it easier to work with and also inhibiting mold growth.

[0005] Japanese Patent Laid-Open No. 7-070543 Japanese Patent Laid-Open No. 2000-355675 Japanese Patent Laid-Open No. 2007-039514

[0006] In addition to the technology disclosed in Patent Document 3, it has also been proposed to add formaldehyde to gelatin-based adhesives to improve their water resistance. Patent Document 3 also describes that the wood vinegar and bamboo vinegar disclosed in Patent Documents 2 and 3 have the effect of inhibiting mold growth in gelatin-based adhesives. However, the above-mentioned formaldehyde, wood vinegar, and bamboo vinegar are irritating, and wood vinegar and bamboo vinegar may also contain benzopyrene and formaldehyde, raising safety concerns. In addition, adhesives that do not use aldehydes, such as those using aqueous polymers and isocyanates, are widely used in the production of structural laminated lumber. However, there are concerns about skin irritation and sensitization due to exposure to isocyanates before the bonding reaction and to unreacted materials remaining after the reaction.

[0007] Furthermore, adhesives using gelatin are generally inferior in terms of adhesive performance to petrochemical adhesives such as vinyl acetate resin, epoxy resin, resorcinol resin, and cyanoacrylate resin, and are therefore difficult to popularize.

[0008] Therefore, the present invention aims to provide a biodegradable adhesive composition that uses gelatin and has good water resistance and storage stability against mold and mildew, etc., and can form an adhesive that is even safer.

[0009] That is, the present invention provides a biodegradable adhesive composition comprising gelatin; a polyhydric alcohol; water; and at least one crosslinking agent selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols, wherein the gelatin content is 5 to 40% by mass, the polyhydric alcohol content is 7 to 55% by mass, the water content is 20 to 80% by mass, and the crosslinking agent content is 0.005 to 3% by mass.

[0010] According to the present invention, it is possible to provide a biodegradable adhesive composition that can form an adhesive using gelatin that has good water resistance and storage stability against mold and the like, and is also able to form an adhesive that is safer.

[0011] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0012] <Biodegradable Adhesive Composition> In light of the above-described current situation regarding conventional adhesives using gelatin, the present inventors investigated adhesive compositions using safer materials that can form adhesives with good water resistance and good shelf life against mold and decay. As a new approach to providing such an adhesive composition, the present inventors attempted to improve the water resistance of gelatin by crosslinking it with enzymes, metals, or sugars, and to suppress the occurrence of mold and decay by reducing the water activity with polyhydric alcohols such as glycerin. As a result, they found that it was possible to almost completely eliminate the performance drawbacks of conventional gelatin-based adhesives. This led to the completion of an invention related to a biodegradable adhesive composition that can form environmentally friendly adhesives derived from biological resources and can be used in everyday products that require low toxicity, such as building materials, toys, and furniture.

[0013] A biodegradable adhesive composition according to one embodiment of the present invention (hereinafter sometimes simply referred to as the "adhesive composition") contains gelatin, a polyhydric alcohol, water, and at least one crosslinking agent selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols. In this adhesive composition, the gelatin content is 5 to 40% by mass, the polyhydric alcohol content is 7 to 55% by mass, the water content is 20 to 80% by mass, and the crosslinking agent content is 0.005 to 3% by mass.

[0014] The adhesive composition configured as described above has good water resistance and good preservation properties against mold, decay, etc., and can form a biodegradable adhesive (hereinafter, sometimes simply referred to as "adhesive") that is safer. In this specification, the term "adhesive composition" refers to the composition before it is applied to an object (adherend) by coating or the like. The term "adhesive" also refers to the composition after it has been applied to an adherend.

[0015] The adhesive composition contains gelatin, polyhydric alcohol, water, and the specific crosslinking agent in the specific proportions, making it possible to form a practical adhesive that is highly biodegradable and has minimal impact on living organisms and the natural environment. Therefore, even if various waste materials using this adhesive are discarded in nature, it is possible to form an adhesive that is easily decomposed and rendered harmless over time. Furthermore, scraps and sawdust generated by processing wood with this adhesive can be reused as mushroom beds, etc.

[0016] The adhesive composition is capable of forming the above-mentioned practical adhesive, specifically, it can form an adhesive having practical adhesive performance with any adherend material (e.g., wood, paper, cloth, plastic, metal, glass, etc.). Furthermore, it is possible to form an adhesive that has water resistance and strength sufficient to not immediately disintegrate even when exposed to rain or immersed in water such as the sea, lake, or river. In addition, it can also contribute to providing an adhesive that is heat-resistant enough to withstand the temperatures (approximately 50 to 70°C) inside automobiles, which are the main means of transportation, transport, and storage of products using adhesives during the Japanese summer.

[0017] Hereinafter, from the viewpoint of easily achieving the above-mentioned effects, a preferred configuration of the adhesive composition will be described.

[0018] The adhesive composition contains gelatin. Gelatin is a natural polymer generally obtained by hydrolysis of collagen, a protein component present in animal hide, bone, cartilage, tendons, etc. The adhesive composition may contain one or more types of gelatin.

[0019] The content of gelatin in the adhesive composition is 5 to 40% by mass, based on the total mass of the adhesive composition. Therefore, it is possible to obtain an adhesive composition and adhesive with excellent biodegradability. The content of gelatin is more preferably 10 to 30% by mass.

[0020] The origin of gelatin is not particularly limited, and examples include pigskin, pig bone, cowhide, cow bone, fish scales, fish skin, and combinations thereof. Gelatin may be pretreated with any pretreatment, such as acid treatment or alkali treatment, and its molecular weight is not particularly limited. Gelatin having a gel strength (Bloom value) of 200 or more as measured in accordance with JIS K6503:2001 is preferred. Commercially available gelatin and glue can be used due to their ease of availability. Among these, food-grade gelatin is preferred from the viewpoint of easily increasing gel strength, and industrial-grade gelatin is preferred from the viewpoint of easily reducing the production cost of the adhesive composition.

[0021] Generally, gelatin colloidal aqueous solutions have the property of reversibly changing with temperature: they dissolve and become a sol when heated, and solidify and become a gel when cooled. Gelatin generally absorbs water and swells and disintegrates in water in a short time, and because it has low heat resistance, it easily melts when temperatures rise in summer. Therefore, the adhesive composition of this embodiment contains a crosslinking agent, as described below, to impart practical levels of water resistance and heat resistance. Furthermore, by adjusting the amounts of gelatin, crosslinking agent, polyhydric alcohol, and water within specific ranges, it is possible to adjust the physical properties of the adhesive composition and adhesive, such as hardness, elasticity, tactile feel, and flexibility.

[0022] The gelatin content is preferably 7% by mass or more, more preferably 10% by mass or more, and even more preferably 14% by mass or more, from the viewpoint of easily increasing the mechanical strength, and is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of easily increasing the adhesive strength and ensuring the content of a crosslinking agent, etc., described later, so as to easily impart practically sufficient water resistance and heat resistance.

[0023] The adhesive composition contains a polyhydric alcohol. A polyhydric alcohol is an alcohol having two or more hydroxyl groups in one molecule. In the adhesive composition, the polyhydric alcohol is a component that can constitute a liquid medium (a dispersion medium in the gel described above) together with water, which will be described later.

[0024] The content of the polyhydric alcohol in the adhesive composition is 7 to 55% by mass, based on the total mass of the adhesive composition. Adjusting the content of the polyhydric alcohol in the adhesive composition within this range facilitates adjustment of physical properties such as hardness, elasticity, tactile feel, and flexibility of the adhesive composition and adhesive. Furthermore, because the adhesive composition contains the polyhydric alcohol in the above-mentioned specific proportion, improvements in strength, heat resistance, water resistance, and antiseptic properties of the adhesive composition and adhesive can be expected compared to when the dispersion medium is water alone. Furthermore, because polyhydric alcohols generally have a higher boiling point than water, evaporation of the dispersion medium from the adhesive composition and adhesive is suppressed compared to when the dispersion medium is water alone, resulting in less change in shape and physical properties and longer-term quality maintenance. From the above perspectives, the content of the polyhydric alcohol is more preferably 10 to 40% by mass.

[0025] The content of the polyhydric alcohol is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoints of imparting flexibility and easily suppressing the occurrence of mold and decay. On the other hand, the content of the polyhydric alcohol is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, from the viewpoints of easily increasing adhesive strength and ensuring a water content sufficient to dissolve gelatin, which is a water-soluble molecule, in water.

[0026] Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,2-butylene glycol, 1,3-butylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, hexylene glycol, erythritol, pentaerythritol, dipentaerythritol, glycerin, diglycerin, triglycerin, polyglycerin, and sugar alcohols (e.g., sorbitol, mannitol, xylitol, reduced maltose, reduced lactose, reduced starch syrup, etc.). The adhesive composition can contain one or more polyhydric alcohols. Among polyhydric alcohols, at least one selected from the group consisting of glycerin, 1,3-butylene glycol, and sugar alcohols is preferred.

[0027] The adhesive composition is an aqueous composition containing water. In the adhesive composition, water is a component that can constitute a dispersion medium in the gel together with the polyhydric alcohol. As the water, deionized water or ion-exchanged water is preferred.

[0028] The water content in the adhesive composition is 20 to 80% by mass, based on the total mass of the adhesive composition. By adjusting the water content within this range, it becomes easier to adjust the hardness, elasticity, tactile feel, drying time (curing time), flexibility, etc. of the adhesive composition and adhesive. Furthermore, because the adhesive composition contains water in the above-mentioned specific proportion, improvements in the flexibility, etc. of the adhesive composition and adhesive, as well as antibacterial and antifungal effects, can be expected compared to when the dispersion medium is only a polyhydric alcohol, and production costs can be reduced. From the above-mentioned perspectives, the water content is more preferably 40 to 70% by mass.

[0029] The water content is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more from the viewpoint of dissolving gelatin, which is a water-soluble molecule. On the other hand, the water content is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less from the viewpoint of ensuring the polyhydric alcohol content and thereby easily improving storage stability, and from the viewpoint of ensuring mechanical strength.

[0030] The adhesive composition contains at least one crosslinking agent (sometimes referred to herein as a "specific crosslinking agent") selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols. In the adhesive composition, transglutaminase can crosslink gelatin through enzymatic crosslinking, alum through metal salt crosslinking, monosaccharides through reductive action, and polyphenols through redox action. Enzymatic crosslinking, sugar crosslinking, and polyphenol crosslinking are thought to be caused by covalent bonds with amino groups in gelatin as crosslinking points. On the other hand, alum crosslinking is thought to be caused by non-covalent crosslinking via an aluminum complex. The crosslinking reaction with the specific crosslinking agent tends to insolubilize gelatin and suppress sol-gel transformation as the degree of crosslinking increases, while the degree of crosslinking decreases as the degree of crosslinking decreases, resulting in a certain degree of thermal reversibility (thermal reversibility of sol-gel). The specific crosslinking agent has significantly lower cytotoxicity and environmental impact than chemical crosslinking agents such as aldehydes and epoxy compounds, and therefore the adhesive composition has less impact on living organisms and the natural environment and is safer than conventional techniques. Among the above crosslinking agents, it is preferable to use transglutaminase.

[0031] The content of the crosslinking agent in the adhesive composition, i.e., the total content of transglutaminase, alum, monosaccharides, and polyphenols, is 0.005 to 3% by mass relative to the total mass of the adhesive composition. This makes it possible to obtain an elastic adhesive composition and adhesive, and also to obtain an adhesive composition and adhesive having practically sufficient strength, water resistance, heat resistance, shape retention, and the like. By adjusting the content of the crosslinking agent within the above range, it becomes easier to adjust the physical properties of the adhesive composition and adhesive, such as hardness, elasticity, tactile feel, and flexibility. From the viewpoint of easily increasing the water resistance and adhesive strength of the adhesive, the content of the crosslinking agent is more preferably 0.05 to 1% by mass.

[0032] The content of the crosslinking agent is preferably 0.008% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.05% by mass or more, from the viewpoints of strength, water resistance, heat resistance, etc. On the other hand, the content of the crosslinking agent is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, from the viewpoints of facilitating accurate bonding work within an appropriate drying time (curing time) range and facilitating increased adhesive strength.

[0033] The transglutaminase used as a cross-linking agent is an enzyme that cross-links through an enzymatic reaction and has the activity of catalyzing an acyl transfer reaction in which a glutamine residue in a protein or peptide serves as a donor and a lysine residue serves as an acceptor. The origin of the transglutaminase is not particularly limited, and examples thereof include those derived from mammals, fish, and microorganisms. One or more of these can be used. Furthermore, commercially available transglutaminases can be used due to their ease of availability.

[0034] Alum used as a cross-linking agent is a sulfate salt of a monovalent cation (M ２ Ｉ (SO ４ )) and sulfates of trivalent metal ions (M ２ III (SO ４ ) ３) double salt. Suitable alums include aluminum potassium sulfate dodecahydrate (AlK(SO ４ ) ２ ・12H ２ O; also known as potassium alum.), anhydrous aluminum potassium sulfate (AlK(SO ４ ) ２ ; also known as burnt alum.), aluminum sodium sulfate dodecahydrate (AlNa(SO ４ ) ２ ・12H ２ O; also known as sodium alum.), anhydrous sodium aluminum sulfate (AlNa(SO ４ ) ２ ; also known as calcined sodium alum.), aluminum ammonium sulfate dodecahydrate (AlNH ４ (SO ４ ) ２ ・12H ２ O; also known as ammonium alum.), and anhydrous aluminum ammonium sulfate (AlNH ４ (SO ４ ) ２ (also called burnt ammonium alum).) and the like can be mentioned. One or more of these can be used. Furthermore, commercially available alum can be used because of its easy availability. When alum hydrate is used, the content of the crosslinking agent (alum) refers to the content converted into anhydrous alum (alum).

[0035] Examples of monosaccharides used as cross-linking agents include glucose, fructose, galactose, and ribose. One or more of these can be used. These exhibit reducing properties in aqueous solutions and react with proteins, etc., to form intramolecular and intermolecular cross-linking points. Cross-linking reactions using monosaccharides can occur in foods, etc., making them an extremely safe cross-linking method.

[0036] Examples of polyphenols used as cross-linking agents include catechins, persimmon tannins, tannic acid, and lignin. One or more of these can be used. Polyphenols obtained primarily from plants are preferred. These polyphenols undergo oxidation reactions in the air, producing oxidized polyphenols that react with proteins, and the resulting products act as the starting point for cross-linking between proteins. Similar to cross-linking reactions using monosaccharides, cross-linking reactions using polyphenols can also occur in foods, making them a highly safe cross-linking method.

[0037] The essential components of the adhesive composition described above, gelatin, polyhydric alcohol, water, and the specific crosslinking agent, all pose little harm to living organisms and the natural environment. Therefore, by using these components as the main components, it is possible to obtain an adhesive composition and adhesive that are even more biodegradable and can be evaluated as having almost no ecotoxicity. From this perspective, the total content of the gelatin, polyhydric alcohol, water, and specific crosslinking agent in the adhesive composition is preferably 80 to 100% by mass, based on the total mass of the adhesive composition. The total content of the gelatin, polyhydric alcohol, water, and specific crosslinking agent in the adhesive composition is more preferably 90% by mass or more, and even more preferably 95% by mass or more. Furthermore, the total content of the gelatin, polyhydric alcohol, water, and specific crosslinking agent in the adhesive composition may be 100% by mass, i.e., the adhesive composition may be composed of gelatin, polyhydric alcohol, water, and the specific crosslinking agent.

[0038] The adhesive composition may contain optional components other than the gelatin, polyhydric alcohol, water, and specific crosslinking agent. Examples of optional components include light stabilizers, UV absorbers, colorants, plasticizers, dispersants, antifoaming agents, leveling agents, tackifiers, pH adjusters, viscosity adjusters, reducing agents, preservatives, antifungal agents, bactericides, flame retardants, antioxidants, and antioxidants. One or more of the optional components may be contained in the adhesive composition.

[0039] From the viewpoint of ensuring the amounts of the aforementioned essential components, the content of the optional components in the adhesive composition is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to the total mass of the adhesive composition.

[0040] <Method for Producing Adhesive Composition> The adhesive composition can be produced, for example, by the following production method. A preferred method for producing the adhesive composition includes first mixing gelatin, a polyhydric alcohol, and water. These components are preferably mixed in a ratio such that, when a crosslinking agent, described below, is mixed, the content (mass %) of each component in the adhesive composition falls within the specific range described above. When dissolving gelatin in a polyhydric alcohol and water, more specifically, it is more preferable to impregnate the gelatin with water, add the polyhydric alcohol, heat to dissolve them, and then mix uniformly. The temperature during mixing is preferably 30 to 80°C, and more preferably 40 to 60°C.

[0041] A preferred method for producing an adhesive composition includes subsequently adding a crosslinking agent to a mixed solution containing the above-mentioned gelatin, water, and polyhydric alcohol (more preferably a mixed solution in a dissolved state by heating), and mixing the mixture to carry out a crosslinking reaction. When adding the crosslinking agent, a crosslinking agent composition containing the crosslinking agent may be used. The crosslinking agent composition may contain a polyhydric alcohol and / or water. The crosslinking agent is preferably mixed in a ratio such that the content (mass %) of each component in the adhesive composition falls within the above-mentioned specific ranges when the crosslinking agent is mixed. The temperature when the crosslinking agent is added to the mixed solution and mixed is preferably 30 to 63°C, more preferably 50 to 60°C.

[0042] A crosslinking agent is added to the above-mentioned mixed solution, and after the crosslinking reaction has occurred, the mixture is cooled and solidified at room temperature (20±15°C) to form a gel, thereby obtaining a solid (gel) adhesive composition. In this case, the adhesive composition that is solid at room temperature is preferably stored at about room temperature until use, and when used (when the adhesive composition is applied to an adherend), the adhesive composition is preferably heated to melt and sol (liquid) before use. The temperature for solization is preferably 60 to 110°C, and more preferably 70 to 100°C.

[0043] Another preferred method for producing an adhesive composition involves adding a crosslinking agent to the above-mentioned mixed liquid before applying the adhesive composition to an adherend to obtain a liquid adhesive composition. In this case, it is more preferable to apply the adhesive composition to an adherend and allow the crosslinking reaction to proceed on the adherend before the crosslinking reaction has fully proceeded. In this method, before adding the crosslinking agent, the above-mentioned mixed liquid is cooled and solidified at room temperature (20±15°C) to gel it once, and the gelled mixed composition can be stored at approximately room temperature until use of the adhesive composition. Then, when applying the adhesive composition to an adherend, the above-mentioned gelled mixed composition is heated to form a sol, and then a crosslinking agent is added to the sol mixed liquid and mixed uniformly to obtain a liquid adhesive composition. As described above, adding a crosslinking agent immediately before applying the adhesive composition to an adherend allows the crosslinking reaction to continue for a long time, making it easier to achieve a stronger crosslinked state, which in turn increases the adhesive strength, water resistance, and warm water resistance.

[0044] As described above, the adhesive composition may be in a liquid or paste form that is easy to apply to an adherend during use. A preferred embodiment is a hot-melt adhesive composition that is solid (including gel) at room temperature and becomes liquid or paste upon heating during use. Preferred shapes of the adhesive composition at room temperature include a block, a sheet, and a rod.

[0045] The adhesive composition that undergoes the above-mentioned sol-gel transition exhibits initial adhesive strength when applied to an adherend as it cools to room temperature and gels, then gradually loses moisture, and when the moisture content reaches equilibrium with the ambient air, further adhesive strength can be exhibited. In this way, when applied to an adherend, the adhesive composition is used as a heated solution dissolved in water, and after application to the adherend, it returns to room temperature and undergoes a sol-gel transition, which makes it easy to work with and allows it to form a coating with excellent heat resistance when dried.

[0046] <Biodegradable adhesive composition kit> The adhesive composition may be configured in the form of a biodegradable adhesive composition kit (hereinafter, sometimes simply referred to as an "adhesive composition kit"). An adhesive composition kit according to one embodiment of the present invention is used for the biodegradable adhesive composition described above. This adhesive composition kit includes a base composition containing gelatin, a polyhydric alcohol, and water, and a crosslinker composition containing a crosslinker. The crosslinker composition may further contain a polyhydric alcohol and / or water.

[0047] When using the adhesive composition kit, the adhesive composition can be obtained by mixing the base composition and the crosslinker composition. In this case, it is preferable to adopt the manufacturing method of the adhesive composition described above. By using the adhesive composition kit, the base composition and the crosslinker composition can be mixed immediately before applying the adhesive composition to the adherend. Therefore, the crosslinking reaction is likely to continue after the adhesive composition is applied to the adherend, and a stronger crosslinked state is likely to be achieved, which tends to further increase the adhesive strength, water resistance, and warm water resistance.

[0048] In the adhesive composition kit, the contents of gelatin, polyhydric alcohol, and water in the base composition, and the contents of the crosslinker in the crosslinker composition, and the polyhydric alcohol and / or water contained as needed, are preferably amounts such that when the base composition and the crosslinker composition are mixed in a predetermined ratio, the contents (mass %) of each component in the adhesive composition are within the above-mentioned specific ranges. In one embodiment, to facilitate the preparation of an adhesive composition in which the contents of each component are within the above-mentioned specific ranges using the adhesive composition kit, the gelatin content is preferably 5 to 40 mass %, the polyhydric alcohol content is 7 to 55 mass %, the water content is 20 to 80 mass %, and the crosslinker content is 0.005 to 3 mass %, relative to the total mass of the mixture of the base composition and the crosslinker composition.

[0049] A biodegradable adhesive can be formed by applying the adhesive composition described above to an adherend by coating or the like. Specifically, as described above, the adhesive can be formed by applying a heated and melted adhesive composition to an adherend and then cooling it to about room temperature. Examples of the material of the adherend include wood, paper, cloth, plastic, metal, and glass. By using the adhesive composition described above, it is possible to form an adhesive that has good water resistance and storage stability, is highly biodegradable, and is highly safe in that it has less impact on living organisms and the natural environment, and has practical adhesive performance for any adherend material.

[0050] As described above, one embodiment of the present invention can have the following configurations. [1] A biodegradable adhesive composition comprising gelatin, a polyhydric alcohol, water, and at least one crosslinking agent selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols, wherein the gelatin content is 5 to 40% by mass, the polyhydric alcohol content is 7 to 55% by mass, the water content is 20 to 80% by mass, and the crosslinking agent content is 0.005 to 3% by mass. [2] The biodegradable adhesive composition according to [1] above, wherein the gelatin content is 10 to 30% by mass, based on the total mass of the biodegradable adhesive composition. [3] The biodegradable adhesive composition according to [1] or [2] above, wherein the polyhydric alcohol content is 10 to 40% by mass, based on the total mass of the biodegradable adhesive composition. [4] The biodegradable adhesive composition according to any one of [1] to [3] above, wherein the content of the water is 40 to 70% by mass, based on the total mass of the biodegradable adhesive composition. [5] The biodegradable adhesive composition according to any one of [1] to [4] above, wherein the content of the crosslinking agent is 0.05 to 1% by mass, based on the total mass of the biodegradable adhesive composition. [6] The biodegradable adhesive composition according to any one of [1] to [5] above, wherein the polyhydric alcohol is at least one selected from the group consisting of glycerin, 1,3-butylene glycol, and sugar alcohols. [7] The biodegradable adhesive composition according to any one of [1] to [6] above, wherein the crosslinking agent is transglutaminase. [8] The biodegradable adhesive composition according to any one of [1] to [7] above, wherein the total content of the gelatin, the polyhydric alcohol, the water, and the crosslinking agent is 80 to 100% by mass, based on the total mass of the biodegradable adhesive composition. [9] A biodegradable adhesive composition kit for use with the biodegradable adhesive composition according to any one of [1] to [8] above, the biodegradable adhesive composition kit comprising: a base composition containing the gelatin, the polyhydric alcohol, and the water; and a crosslinker composition containing the crosslinker.

[0051] Hereinafter, one embodiment of the present invention will be specifically described based on examples, but one embodiment of the present invention is not limited to these examples.

[0052] <Preparation of Materials> The following gelatin and cross-linking agents were prepared: Gelatin: trade name "FGL250SP" (cross-linking agent) manufactured by Nitta Gelatin Co., Ltd. Transglutaminase powder: trade name "Activa TG-S" manufactured by Ajinomoto Co., Inc. Alum: trade name "burnt alum" manufactured by Kenei Pharmaceutical Co., Ltd. Glucose: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Fructose: manufactured by Nissin Sugar Co., Ltd. Ribose: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Tannic acid: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0053] The polyhydric alcohols used were glycerin, 1,3-butylene glycol, and reduced starch syrup (water content 30% by mass; product name "SE 600" manufactured by Bussan Food Science Co., Ltd.), and deionized water was used. In the comparative examples, formaldehyde, resorcinol, ethanol, polyvinyl alcohol (hereinafter also referred to as PVA; product name "Poval 4-88" manufactured by Kuraray Co., Ltd.), and polymethylene polyphenyl polyisocyanate (hereinafter also referred to as PMDI) were used.

[0054] <Preparation of adhesive composition> (Comparative Example 1) 20 parts by mass of gelatin was impregnated with 80 parts by mass of water, and then heated at 75°C until completely dissolved, and the resulting composition was used as the adhesive composition of Comparative Example 1. The adhesive composition of Comparative Example 1 is used in a typical way as a gelatin adhesive.

[0055] Example 1: 20 parts by weight of gelatin was impregnated with a predetermined amount of water (46.91 parts by weight, including the small amount of water used to disperse the transglutaminase described below). 33 parts by weight of glycerin was then added, heated to 50°C, dissolved, and mixed until homogenous to obtain a mixed solution, which was then heated to 60°C. 0.09 parts by weight of transglutaminase dispersed in a small amount of water was added to the mixed solution, and stirring was continued to carry out a crosslinking reaction. When a clear increase in viscosity was observed, the temperature was raised to 80°C to inactivate the transglutaminase. The resulting mixture was then poured into a tray and cooled to room temperature (approximately 25°C; the same applies below to room temperature), resulting in the adhesive composition of Example 1, which was solid at room temperature. The prepared adhesive composition was stored at room temperature until use, and was heated to 75°C until completely dissolved.

[0056] (Comparative Example 2) 20 parts by mass of gelatin was impregnated with 47 parts by mass of water, and then 33 parts by mass of glycerin was added, heated to 50°C to dissolve, and mixed until homogenous to obtain a mixed solution. The mixed solution was then poured into a tray and cooled to room temperature to solidify, obtaining an adhesive composition of Comparative Example 2 that was solid at room temperature. The prepared adhesive composition was stored at room temperature until use, and at the time of use, it was heated to 75°C until completely dissolved.

[0057] (Examples 2, 3, and Comparative Example 3) The amounts of glycerin and water used in Example 1 (33 parts by mass and 46.91 parts by mass, respectively) were changed to 10 parts by mass and 69.91 parts by mass in Example 2, 50 parts by mass and 29.91 parts by mass in Example 3, and 5 parts by mass and 74.91 parts by mass in Comparative Example 3, respectively. Except for these, adhesive compositions of Examples 2, 3, and Comparative Example 3, which are solid at room temperature, were prepared using the same procedure as in Example 1. The prepared adhesive compositions were stored at room temperature until use, and were heated at 75°C until completely dissolved before use.

[0058] (Examples 4, 5, and Comparative Example 4) The amounts of gelatin and water used in Example 1 (20 parts by mass and 46.91 parts by mass, respectively) were changed to 10 parts by mass and 56.91 parts by mass in Example 4, 35 parts by mass and 31.91 parts by mass in Example 5, and 1 part by mass and 65.91 parts by mass in Comparative Example 4, respectively. Otherwise, adhesive compositions of Examples 4, 5, and Comparative Example 4, which were solid at room temperature, were prepared using the same procedure as in Example 1. Each of the prepared adhesive compositions was stored at room temperature until use, and was heated at 75°C until completely dissolved before use.

[0059] (Examples 6 and 7) In Examples 6 and 7, adhesive compositions of Examples 6 and 7, which are solid at room temperature, were prepared by the same procedure as in Example 1, except that the glycerin used in Example 1 was changed to 1,3-butylene glycol and reduced starch syrup, respectively. Each of the prepared adhesive compositions was stored at room temperature until use, and was heated to 75°C until completely dissolved before use.

[0060] (Examples 8 to 10) The amounts of transglutaminase and water used in Example 1 (0.09 parts by mass and 46.91 parts by mass, respectively) were changed to 0.005 parts by mass and 46.995 parts by mass in Example 8, 0.14 parts by mass and 46.86 parts by mass in Example 9, and 3 parts by mass and 44 parts by mass in Example 10. Otherwise, adhesive compositions of Examples 8 to 10, which were solid at room temperature, were prepared using the same procedure as in Example 1. Each prepared adhesive composition was stored at room temperature until use, and was heated at 75°C until completely dissolved before use.

[0061] Example 11: 20 parts by weight of gelatin was impregnated with a predetermined amount of water (46.995 parts by weight, including the small amount of water used for the alum described below). 33 parts by weight of glycerin was then added, heated to 50°C to dissolve, and mixed until homogenous to obtain a mixed solution, which was then heated to 60°C. 0.005 parts by weight of alum supersaturated in a small amount of water was added to the mixed solution, and stirring was continued to induce a crosslinking reaction. When a clear increase in viscosity was observed, the mixture was poured into a tray and cooled to room temperature to solidify. In this way, the adhesive composition of Example 11, which was solid at room temperature, was prepared. The prepared adhesive composition was stored at room temperature until use, and was heated to 75°C until completely dissolved.

[0062] (Examples 12 and 13) The amounts of alum and water used in Example 11 (0.005 parts by mass and 46.995 parts by mass, respectively) were changed to 0.14 parts by mass and 46.86 parts by mass in Example 12, and 3 parts by mass and 44 parts by mass in Example 13. Otherwise, adhesive compositions of Examples 12 and 13, which were solid at room temperature, were prepared using the same procedure as in Example 11. Each prepared adhesive composition was stored at room temperature until use, and was heated at 75°C until completely dissolved before use.

[0063] Example 14: 20 parts by weight of gelatin was impregnated with a predetermined amount of water (44 parts by weight, including the small amount of water used to disperse the glucose described below). 33 parts by weight of glycerin was then added, heated to 50°C to dissolve, and mixed until homogenous to obtain a mixed solution, which was then heated to 60°C. 3 parts by weight of glucose dispersed in a small amount of water was added to the mixed solution, and stirring was continued to carry out a crosslinking reaction. When a clear increase in viscosity was observed, the mixture was poured into a tray and cooled to room temperature to solidify. In this way, the adhesive composition of Example 14, which was solid at room temperature, was prepared. The adhesive composition was stored at room temperature until use, and was heated to 75°C until completely dissolved.

[0064] (Examples 15 to 17) The 3 parts by mass of glucose used in Example 14 was changed to 1 part by mass of fructose in Example 15, 1 part by mass of ribose in Example 16, and 1 part by mass of tannic acid in Example 17, and accordingly the amount of water used in Example 14 was changed from 44 parts by mass to 46 parts by mass. Except for these changes, adhesive compositions of Examples 15 to 17, which were solid at room temperature, were prepared by the same procedure as in Example 14. Each of the prepared adhesive compositions was stored at room temperature until use, and was heated to 75°C until completely dissolved before use.

[0065] Example 18: 20 parts by weight of gelatin was impregnated with 46.91 parts by weight of water, followed by the addition of 32 parts by weight of glycerin (33 parts by weight, including the glycerin used to disperse the transglutaminase below). The mixture was heated to 50°C to dissolve and mixed until homogenous to obtain a mixed solution. The mixed solution was then poured into a tray and cooled to room temperature to solidify, obtaining a solid composition at room temperature. This composition was stored at room temperature until use. Upon use, the composition was heated to 60°C until completely dissolved, and then 0.09 parts by weight of transglutaminase dispersed in 1 part by weight of glycerin was added thereto. Further stirring was performed to homogenize the composition, obtaining the adhesive composition of Example 18, which was liquid at room temperature. This adhesive composition was applied to the adherend described below, bonded, and then the crosslinking reaction was accelerated at room temperature for 12 hours.

[0066] Comparative Example 5 Gelatin was immersed in water in the same manner as in Comparative Example 1, and then heated to dissolve the gelatin. Immediately before use, this was mixed with approximately ¼ of the mass of a 30% by mass aqueous formaldehyde solution to prepare a mixed liquid, which was used as the adhesive composition of Comparative Example 5. The final formaldehyde concentration of this adhesive composition was determined by high performance liquid chromatography (HPLC) and was found to be 5.56% by mass.

[0067] Comparative Example 6 A resorcinol-based resin adhesive composition, the adhesive composition of Comparative Example 6, was obtained with reference to Example 1 described in JP-A-11-199848. Specifically, 170 g of formaldehyde (37%), 440 g of resorcinol, and 160 g of ethanol were charged into a three-neck flask equipped with a reflux condenser and a stirrer, and the pH was adjusted to 5.6 to 6.0 with caustic soda. Immediately thereafter, an appropriate amount was applied to an adherend described below, and then the mixture was reacted at 65 to 70°C for 6 hours while being clamped to bond the adherend.

[0068] Comparative Example 7 A mixed liquid was prepared by mixing 85 g of a 15% by mass aqueous solution of polyvinyl alcohol (PVA) with 15 g of polymethylene polyphenyl polyisocyanate as a crosslinking agent immediately before use, and the mixed liquid was used as the adhesive composition of Comparative Example 7.

[0069] (Comparative Example 8) An adhesive composition of Comparative Example 8 was prepared with reference to Example 1 described in Patent Document 1 (JP-A-7-070543). Specifically, 31 g of gelatin was impregnated with 31 g of water, and then heated to 50°C to dissolve. 31 g of glycerin and 7 g of sucrose were added to the gelatin, and the mixture was mixed at 50°C until uniform, to obtain a mixed solution. This mixed solution was poured into a tray, cooled to room temperature, and solidified, thereby preparing the adhesive composition of Comparative Example 8. The prepared adhesive composition was stored at room temperature until use, and was heated to 75°C until completely dissolved.

[0070] The composition (unit: mass %) of each adhesive composition is shown in the upper part of Table 1 (Tables 1-1 to 1-3). Each adhesive composition was evaluated as described below. For each evaluation item, "AA," "A," and "B" were considered pass levels. The evaluation results are shown in the lower part of Table 1.

[0071]

[0072]

[0073]

[0074] <Evaluation> [Adhesion test] According to the "Test method for compressive shear bond strength of adhesives" described in JIS K 6852:1994, a compressive shear force was applied to the test piece, and the maximum stress until the bond of the test piece peeled off or the test piece broke was measured. Specifically, two cypress boards measuring 25 mm wide, 35 mm long, and 12 mm thick were prepared as adherends, which were the base materials of the test pieces. Then, the adhesive composition was applied to the adhesive surface 1 cm apart so that the flat surface along the width and length of the adherend was used as the adhesive surface, and the dimensions of the adhesive surface were 25 mm wide and 25 mm long. ２ The test piece was thinly spread with an application amount of 1 g per test piece. After that, the test piece was left at room temperature (25°C) for 12 hours while being tightly clamped with a woodworking clamp, and then the woodworking clamp was removed to obtain a test piece. Twelve such test pieces were prepared for each test area and subjected to the test. The test results were reported as the maximum pressure measured in N / mm ２ After converting the data into the average value of 12 pieces of data, the average value was used as the measurement result of adhesive strength (N / mm ２ The adhesive strength was measured for each of the following normal test, water resistance test, and hot water resistance test. Test pieces that peeled off during the test were not measured (shown as "0" in the adhesive strength column at the bottom of Table 1).

[0075] 1) Normal test: The test room environment was set at a temperature of 23±2°C and a relative humidity of 50±10%, and the test was conducted at a test speed of 2 mm / min. 2) Water resistance test: The test specimen was immersed in 30°C water for 3 hours, then left to stand in an environment at a temperature of 23±2°C and a relative humidity of 50±10% for 24 hours, and then tested at a test speed of 2 mm / min. 3) Hot water resistance test: The test specimen was immersed in 50°C water for 3 hours, then left to stand in an environment at a temperature of 23±2°C and a relative humidity of 50±10% for 24 hours, and then tested at a test speed of 2 mm / min.

[0076] (Adhesion) Based on the results of measuring the adhesive strength in the normal test, the adhesive strength of each adhesive composition to wood was evaluated according to the following evaluation criteria: A: Adhesion strength of 9.0 N / mm ２ B: Adhesion strength was 2.0 N / mm or more. ２ 9.0N / mm or more ２ C: Adhesion strength was less than 2.0 N / mm ２Less than 100% peeling or peeling occurred during the test.

[0077] (Water Resistance) Based on the results of measuring each adhesive strength in the water resistance test, the water resistance of each adhesive composition was evaluated according to the following evaluation criteria: A: Adhesive strength of 3.0 N / mm ２ B: Adhesion strength was 2.0 N / mm or more. ２ 3.0N / mm or more ２ C: Adhesion strength was less than 2.0 N / mm ２ Less than 100% peeling or peeling occurred during the test.

[0078] (Warm Water Resistance) Based on the results of measuring each adhesive strength in the warm water resistance test, the warm water resistance of each adhesive composition was evaluated according to the following evaluation criteria: A: Adhesive strength of 3.0 N / mm ２ B: Adhesion strength was 1.0 N / mm or more. ２ 3.0N / mm or more ２ C: Adhesion strength was less than 1.0 N / mm ２ Less than 100% peeling or peeling occurred during the test.

[0079] In the normal test, all of the adhesives except for Examples 3, 5, 10, 11 and 13 and Comparative Examples 2, 4 and 8 had a viscosity of 9 N / mm, which is sufficient for use as a wood adhesive. ２ The adhesive strength was 9 N / mm or more. ２ For the Examples and Comparative Examples that did not reach this level, except for Comparative Example 4, the adhesive strength was 7 to 8 N / mm ２ On the other hand, it was difficult to use the adhesive of Comparative Example 4 as an adhesive.

[0080] In the water resistance test and hot water resistance test, the adhesive strength of Comparative Examples 1, 2, and 8 was significantly reduced by water, and all test pieces of Comparative Examples 2 and 8 peeled off during immersion, making the test impossible. Comparative Example 4 did not adhere at all. The other test pieces were shown to have good water resistance and hot water resistance.

[0081] (Peel Adhesion Strength Test for Metals and Plastics) For each of the adhesive compositions of Examples 1, 2, 12, 16, and 18, a peel adhesion strength test of the adhesive was performed in accordance with JIS K 6854-3:1999. Specifically, aluminum (Al) foils 25 μm thick and 25 mm wide were prepared and bonded using the adhesive composition so that they overlapped by 200 mm or more in the longitudinal direction. The test pieces were then left to stand at room temperature (25°C) for 12 hours to prepare test pieces. Similarly, test pieces were prepared using polypropylene (PP) films 25 μm thick and 25 mm wide. Tensile tests were performed on the Al foils at a peel rate of 100 mm / min, and on the PP films at a peel rate of 10 mm / min. The test was continued until at least 150 mm of the bonded section had peeled, and the stress at that time was recorded. Data from the beginning and end of peeling, where the stress was not stable, were excluded. The average peel force required to peel the test piece was calculated in N / 25 mm from the curve recording the minimum 100 mm peel. Three test pieces were prepared, and the average peel force was recorded. The results are shown in Table 2. As shown in Table 2, the adhesive compositions of Examples 1, 2, 12, 16, and 18 also exhibited good adhesive strength to aluminum and PP, demonstrating their practical applicability to metals and plastics in addition to wood.

[0082]

[0083] [Storage Test] Each adhesive composition in the Examples and Comparative Examples was melted by heat according to the method for using it as an adhesive, then cooled and solidified into a block to prepare a sample. Five grams of each sample was placed in the center of a sterilized plastic dish (#12-6004, manufactured by Thermo Fisher Scientific) and, with the lid open, placed in an accelerated tester at a temperature of 40±2°C and a relative humidity of 75±5%RH. Observations were made one month, three months, and six months later to determine the presence or absence of mold based on appearance and the presence or absence of spoilage based on odor, and the storage stability against mold and spoilage was evaluated according to the following evaluation criteria. AA: Neither mold nor spoilage was observed after six months. A: Neither mold nor spoilage was observed after three months, but at least one of mold and spoilage was observed after six months. B: Neither mold nor spoilage was observed after one month, but at least one of mold and spoilage was observed after three months. C: At least one of mold and decay was observed after one month.

[0084] [Ecotoxicity Test] An ecotoxicity test was carried out on each of the adhesive compositions of the Examples and Comparative Examples in accordance with OECD (Organization for Economic Cooperation and Development) Test Guideline 202 "Daphnia Acute Immobilization Test."

[0085] (Materials) Each adhesive composition was pulverized to prepare each sample. Furthermore, resting eggs of Daphnia magna, commercially available as food for small ornamental fish, were used as materials for the ecotoxicity test. The resting eggs were placed in dechlorinated water that was sufficiently aerated and temperature-controlled at 20±1°C to hatch, and then reared on dried chlorella for one week. Juveniles judged to be within 24 hours of birth based on their body size were selected and used for the test.

[0086] (Exposure conditions) Water that had been thoroughly aerated and adjusted to a temperature of 20±1°C was used as test water, to which a finely powdered sample was added to give a concentration of 0.1% by mass. Daphnia magna was cultured in the solution, and the activity of the Daphnia magna was measured every 24 hours. Culture was continued for a maximum of 48 hours. At the same time, a similar test was conducted using test water without the sample as a control.

[0087] Twenty Daphnia magna juveniles were used in each test plot, and the experiment was carried out in quadruplicate. That is, one test plot = 5 individuals / container x 4 containers. Waist-high Petri dishes with an inner diameter of 80 mm and a depth of 50 mm were used as containers. The test liquid volume was 1000 mL / test plot (250 mL / container), and the water temperature was set to 20±1°C. The test water was used after confirming that the dissolved oxygen level was 3 mg / L or higher at the start of exposure. No aeration, feeding, or pH adjustment was performed during the exposure period. The experiment was conducted under standard indoor lighting with 16 hours of light and 8 hours of dark. At the end of exposure, the dissolved oxygen level of the test water was confirmed to be 3 mg / L or higher.

[0088] (Evaluation method) Individuals that showed abnormal behavior or symptoms, such as bleaching or floating on the water surface, or that did not swim for 15 seconds or more even after gentle shaking were counted as immobilized individuals. Based on the number of immobilized individuals, ecotoxicity was evaluated according to the following evaluation criteria. No immobilized individuals were observed in the control group during the exposure period. A: Even after 48 hours, the number of immobilized individuals was less than 2. B: The number of immobilized individuals was less than 2 after 24 hours, but was between 2 and 5 after 48 hours. C: The number of immobilized individuals was already between 2 and 10 after 24 hours. D: The number of immobilized individuals was already 10 or more after 24 hours.

[0089] In Comparative Examples 5 and 6, all individuals sank to the bottom 24 hours after the start of the test and did not move even when shaken. In Comparative Example 7, 4 individuals showed immobility after 24 hours and 12 individuals showed immobility after 48 hours. On the other hand, in Examples and Comparative Examples other than Comparative Examples 5 to 7, no clear indication of toxicity to Daphnia magna was observed.

[0090] [Biodegradability Test] A marine degradability test (seawater + sediment) was conducted on the adhesive composition of Example 1 in accordance with the provisions of ISO 19679:2020. Specifically, first, to calculate the theoretical amount of carbon dioxide generated in the adhesive composition, the amount of organic elements in the adhesive composition after freeze-drying was measured using a CHN-O analyzer (product name "Microcorder JM10 Type", manufactured by J Science Lab Co., Ltd.). The measurement conditions were as follows: Carbon dioxide absorption solution: 0.5 mol / L KOH solution (5 mL); Test container: 500 mL culture bottle; Amount of seawater: 200 mL; Amount of sediment: 100 g; Test material concentration: 250 mg / g; Test temperature: 25 ± 2°C; Number of repetitions: n = 3. The following equipment was used to measure the carbon dioxide generated. Measuring device: automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., AT-610, MCU-610, EBU-610, CHA-600-12) Electrode: composite glass electrode (Kyoto Electronics Manufacturing Co., Ltd., C-171) Titration reagent: 0.5 mol / L HCl solution

[0091] (Evaluation method) The test period was set to 60 days, and a sample was judged to be aerobically biodegradable at the seawater / sediment interface if the amount of carbon dioxide generated from the sample during the period reached 60% or more of the amount of carbon dioxide that could be generated from the sample, and if the amount of carbon dioxide generated from the sample during the test period showed a change of less than 10% for 10 consecutive days. ○: Decomposed in the ocean (seawater + sediment) within 60 days. ×: Not decomposed in the ocean (seawater + sediment) within 60 days.

[0092] The adhesive composition of Example 1 degraded in the ocean within 60 days (rating: ○). Additionally, a simple biodegradability test roughly following the provisions of ISO 19679:2020 was also conducted on each of the adhesive compositions of Examples 1 to 3, 5, 6, 9, 10, 13, 14, 17, and 18, and Comparative Examples 5 to 8. This simple biodegradability test differed from the biodegradability test conducted in Example 1 above in the location where the seawater and sediment (sand) were collected; total organic carbon (TOC) was measured using a total organic carbon meter (TOC-V CPH) to calculate the theoretical amount of carbon dioxide; no carbon dioxide absorbing liquid was used; and the amount of carbon dioxide generated was measured using a method in accordance with ISO 14855-2; but otherwise the tests were similar. As a result of the above-mentioned simple biodegradability test, it was confirmed that each of the adhesive compositions of Examples 1 to 3, 5, 6, 9, 10, 13, 14, 17, and 18, and Comparative Example 8, was also degraded in the marine environment within 60 days (around 30 days). Furthermore, Comparative Examples 5 to 7 were not determined to have degraded in the marine environment during the test period. From these results and the composition of each adhesive composition, it was considered that each of the adhesive compositions of Examples 4, 7, 8, 11, 12, 15, and 16, and Comparative Examples 1 to 4, was also degraded in the marine environment within 60 days (around 30 days).

[0093] [VOC Test] (Qualitative Analysis by HS-GC-MS) Each adhesive composition of the Examples and Comparative Examples was used as a sample. 4 g of each sample was placed in a 5 mL vial, heated at 100°C for 4 hours, and analyzed using a headspace gas chromatograph mass spectrometer (HS-GS-MS). It was examined whether or not peaks for restricted substances appeared as volatile organic compounds in the chromatograph. The presence or absence of VOCs was evaluated according to the following evaluation criteria: A: No peaks for restricted substances were observed. C: Peaks for restricted substances were observed.

[0094] As a result of the VOC test, peaks of formaldehyde were confirmed in Comparative Example 5, peaks of formaldehyde, resorcinol, and ethanol were confirmed in Comparative Example 6, and peaks of polymethylene polyphenyl polyisocyanate were confirmed in Comparative Example 7. No peaks of volatile organic compounds were detected in the Comparative Examples other than Comparative Examples 5 to 7 and in all Examples.

Claims

1. A biodegradable adhesive composition comprising gelatin, a polyhydric alcohol, water, and at least one crosslinking agent selected from the group consisting of transglutaminase, alum, monosaccharides, and polyphenols, the gelatin content being 5 to 40% by mass, the polyhydric alcohol content being 7 to 55% by mass, the water content being 20 to 80% by mass, and the crosslinking agent content being 0.005 to 3% by mass.

2. The biodegradable adhesive composition according to claim 1, wherein the gelatin content is 10 to 30% by mass based on the total mass of the biodegradable adhesive composition.

3. The biodegradable adhesive composition according to claim 1, wherein the content of the polyhydric alcohol is 10 to 40 mass % based on the total mass of the biodegradable adhesive composition.

4. The biodegradable adhesive composition according to claim 1, wherein the water content is 40 to 70 mass % based on the total mass of the biodegradable adhesive composition.

5. The biodegradable adhesive composition according to claim 1, wherein the content of the crosslinking agent is 0.05 to 1% by mass, based on the total mass of the biodegradable adhesive composition.

6. The biodegradable adhesive composition according to claim 1, wherein the polyhydric alcohol is at least one selected from the group consisting of glycerin, 1,3-butylene glycol, and sugar alcohols.

7. The biodegradable adhesive composition according to claim 1, wherein the crosslinking agent is transglutaminase.

8. The biodegradable adhesive composition according to claim 1, wherein the total content of the gelatin, the polyhydric alcohol, the water, and the crosslinking agent is 80 to 100% by mass, based on the total mass of the biodegradable adhesive composition.

9. A biodegradable adhesive composition kit for use in the biodegradable adhesive composition according to any one of claims 1 to 8, comprising: a base composition containing the gelatin, the polyhydric alcohol, and the water; and a crosslinking agent composition containing the crosslinking agent.

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