Hot melt compositions, adhesives, and coatings

Abstract

This invention provides technology for adhesives and coatings that exhibit excellent adhesion in wet conditions and a softening temperature suitable for hot melting. [Solution] The hot melt composition comprises gelatin, polyethyleneimine, and at least one polycation of polylysine, and an aromatic compound which includes at least one of the following: an aromatic compound having two or three phenolic hydroxyl groups in the same molecule, an aromatic compound having a guaiacol skeleton, and an aromatic compound having a syringyl skeleton, wherein the number average molecular weight of the polycation is 4,000 or more and 10,000 or less, and in terms of solid content, the gelatin is 50% by mass or more and 80% by mass or less, the polycation is 10% by mass or more and 40% by mass or less, and the aromatic compound is 2% by mass or more and 10% by mass or less.

Description

Technical Field

[0001] The present disclosure relates to hot-melt compositions, adhesives, and coating agents.

Background Art

[0002] In recent years, for the purpose of reducing environmental impact, the use of natural-derived adhesives has been attracting attention. Gelatin has been used since ancient times as a natural-derived wood adhesive. In a dry state without gelatin water, it has poor thermoplasticity and the softening temperature is around 220°C. Since the softening temperature serves as a guide for the working temperature, for example, in a hot press for plywood, it exceeds 180°C which is the decomposition start temperature of wood, so there is a problem that it cannot be used. When the water content of gelatin is high, thermoplasticity can be obtained at a lower temperature, but there is a problem that the water in the adhesive becomes steam during hot pressing and expands during unloading, causing "swelling" and resulting in poor adhesion. A technique of adding a plasticizer (such as glycerin, stearic acid, etc.) to gelatin to exhibit thermoplasticity at a lower temperature and creating a thermoplastic foam has been reported (Non-Patent Document 1). Although it is possible to lower the working temperature of the gelatin adhesive by adding such a plasticizer, gelatin has the problem of low water resistance. To solve this problem, Non-Patent Document 2 discloses a technique of blending either hydroquinone or catechin with gelatin.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

[0004] However, the inventors discovered that while the non-patent literature technologies improve the thermoplasticity and water resistance of gelatin, their adhesive properties when wet are insufficient. Therefore, there is a need for a gelatin-based hot-melt adhesive that exhibits excellent adhesive properties when wet. Furthermore, adhesives used in hot-melt applications must have a softening temperature at least below the heat resistance temperature of the adherend. These challenges are common not only to adhesives but also to coatings and other materials using gelatin. [Means for solving the problem]

[0005] This disclosure can be implemented in the following forms:

[0006] (1) According to one embodiment of the present disclosure, a hot melt composition is provided. This hot melt composition comprises gelatin, a polycation of polyethyleneimine and polylysine, and an aromatic compound comprising at least one of the following: an aromatic compound having two or three phenolic hydroxyl groups in the same molecule, an aromatic compound having a guaiacol skeleton, and an aromatic compound having a syringyl skeleton, wherein the number average molecular weight of the polycation is 4,000 or more and 10,000 or less, and in terms of solid content, the gelatin is 50% or more by mass and 80% or less by mass, the polycation is 10% or more by mass and 40% or less by mass, and the aromatic compound is 2% or more by mass and 10% or less by mass. According to this embodiment of the hot melt composition, it exhibits excellent adhesion when wet and a softening temperature suitable for hot melting. Furthermore, water resistance is significantly improved by crosslinking between the amino groups of the gelatin and polycation and the aromatic compound.

[0007] (2) In the hot melt composition described in (1) above, the aromatic compound may include at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, 3,4-dihydroxyphenylacetic acid, 3,5-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, tannic acid, green tea polyphenol, vanillic acid, and syringaldehyde. This form of composition exhibits excellent adhesion when wet and a softening temperature more suitable for hot melting.

[0008] (3) In the hot melt composition described in (1) above, the aromatic compound may include at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, tannic acid, green tea polyphenol, vanillic acid, and syringaldehyde. This form of composition exhibits excellent adhesion when wet and a softening temperature more suitable for hot melting.

[0009] (4) In other forms of the present disclosure, an adhesive is provided comprising the hot melt composition described in any one of paragraphs (1) to (3) above.

[0010] (5) In other forms of the present disclosure, a coating agent comprising the hot melt composition described in any one of paragraphs (1) to (3) above is provided.

[0011] Furthermore, the present invention can be realized in various forms, for example, as a solution consisting of the composition, a sheet molded body obtained by processing the composition into a sheet, a powder obtained by processing the composition into granules or powder, a cured body obtained by curing the composition, a coated body covered with the composition, or a joined body joined with the composition. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the temperature dependence of the elastic modulus in adhesives with different PEI formulations. [Figure 2]This figure shows the temperature dependence of the elastic modulus in adhesives with different molecular weights of PEI (polyethylene oxide) added. [Figure 3] This figure shows the temperature dependence of the elastic modulus in adhesives with different proportions of PEI in which crosslinking is promoted by the addition of an oxidizing agent. [Figure 4] This figure shows the temperature dependence of the elastic modulus in adhesives with different proportions of εPL. [Figure 5] This figure shows the temperature dependence of the elastic modulus in adhesives with different proportions of εPL in which crosslinking is promoted by the addition of an oxidizing agent. [Figure 6] This figure shows the temperature dependence of adhesives containing aromatic compounds having two or three phenolic hydroxyl groups within the same molecule. [Figure 7] This figure shows the temperature dependence of an adhesive containing an aromatic compound having a guaiacol skeleton or a syringyl skeleton. [Figure 8] This figure shows the temperature dependence of adhesives containing aromatic compounds having two or three phenolic hydroxyl groups within the same molecule, with crosslinking promoted by the addition of an oxidizing agent. [Figure 9] This figure shows the temperature dependence of an adhesive containing an aromatic compound having a guaiacol or syringyl skeleton, in which crosslinking is promoted by the addition of an oxidizing agent. [Figure 10] This figure shows the temperature dependence of the elastic modulus in adhesives containing only gelatin, gelatin with 10% glycerin added, and adhesives containing 10% by weight of PEI. [Modes for carrying out the invention]

[0013] According to one embodiment of the present disclosure, there is provided a hot-melt composition (hereinafter, also simply referred to as "composition") containing (i) gelatin, (ii) at least one polycation of polyethyleneimine and polylysine, and (iii) an aromatic compound. The aromatic compound includes at least one of an aromatic compound having two or three phenolic hydroxyl groups in the same molecule, an aromatic compound having a guaiacol skeleton, and an aromatic compound having a syringyl skeleton. The number average molecular weight of the polycation is 4,000 or more and 10,000 or less. In terms of solid content, (i) gelatin is 50% by mass or more and 80% by mass or less, (ii) the polycation is 10% by mass or more and 40% by mass or less, and (iii) the aromatic compound is 2% by mass or more and 10% by mass or less. According to the composition of this embodiment, in adhesives, coating agents, etc. using gelatin, it has excellent adhesiveness when wet and shows a softening temperature suitable for hot-melt.

[0014] The gelatin of the present disclosure is not particularly limited, but is extracted after solubilizing collagen, which is the main component of animal skins, bones, tendons, etc. In the present disclosure, gelatin obtained by a known production method can be used. For example, gelatin produced by extracting from raw materials obtained by solubilizing and purifying skins, bones, tendons, etc. of cows, pigs, chickens, fish, etc. with acid or alkali and then extracting with warm water can be used. Further, the gelatin of the present disclosure may be a hydrolyzate, an enzymatically decomposed product, a gelatin derivative (e.g., acylated gelatin, etc.).

[0015] The polycation of the present disclosure is at least one of polyethyleneimine and polylysine. Polyethyleneimine may be linear or branched. The number average molecular weight of polyethyleneimine is 4,000 or more and 10,000 or less, and preferably 4,000 or more and 8,000 or less. Polylysine may be ε-poly-L-lysine (hereinafter, also referred to as "ε-polylysine") or α-polylysine. As polylysine, ε-poly-L-lysine is preferable from the viewpoint of improving adhesiveness when wet.

[0016] The aromatic compounds of the present disclosure (hereinafter, also simply referred to as "aromatic compounds") include at least one of an aromatic compound having two or three phenolic hydroxyl groups in the same molecule, an aromatic compound having a guaiacol skeleton, and an aromatic compound having a syringyl skeleton. In the present specification, the "phenolic hydroxyl group" means a hydroxyl group bonded to an aromatic ring. The aromatic ring is not particularly limited, and examples thereof include a condensed aromatic ring, a heteroaromatic ring, and the like. The condensed aromatic ring is not particularly limited, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, a pyrene ring, and the like. The heteroaromatic ring is not particularly limited, and examples thereof include a pyridine ring, a pyrrole ring, and the like.

[0017] In the present specification, the "aromatic compound having a guaiacol skeleton" means a compound having the chemical structure of the following formula (1). Examples of the aromatic compound having a guaiacol skeleton include vanillin, vanillic acid, ferulic acid, and the like.

Chemical formula

[0018] In the present specification, the "aromatic compound having a syringyl skeleton" means a compound having the chemical structure of the following formula (2). Examples of the aromatic compound having a syringyl skeleton include syringaldehyde, sinapyl aldehyde, sinapic acid, and the like. Among the aromatic compounds having a syringyl skeleton, syringaldehyde is preferred.

Chemical formula

[0019] Aromatic compounds are not particularly limited, but examples include caffeic acid, hydroxycaffeic acid (hereinafter also called "DHCA"), 2,5-dihydroxybenzoic acid (hereinafter also called "25DHBA"), 3,5-dihydroxybenzoic acid (hereinafter also called "35DHBA"), 3,4-dihydroxyphenylacetic acid (hereinafter also called "DOPAC"), 3-(3,4-dihydroxyphenyl)propionic acid (hereinafter also called "DHCA"), 3-(3,4-dihydroxyphenyl)-L-alanine (hereinafter also called "LDOPA"), tannic acid, epicatechin, epicatechin gallate, green tea polyphenols which are mixtures of epicatechin and epicatechin gallate, vanillin, vanillic acid, ferulic acid, syringaldehyde, cinapyraldehyde, cinnapic acid, etc. As aromatic compounds, caffeic acid, DHCA, DOPAC, 35DHBA, 25DHBA, tannic acid, green tea polyphenols, vanillic acid, and syringaldehyde are preferred from the viewpoint of improving adhesion when wet, and caffeic acid, DHCA, tannic acid, green tea polyphenols, vanillic acid, and syringaldehyde are more preferred.

[0020] The composition of this disclosure preferably contains 50% by mass or more and 80% by mass or less of gelatin on a solid content basis, more preferably 55% by mass or more and 75% by mass or less, more preferably 60% by mass or more and 70% by mass or less.

[0021] The compositions of this disclosure, on a solid content basis, preferably contain 10% to 40% by mass of polycations, more preferably 15% to 35% by mass, more preferably 20% to 35% by mass, and even more preferably 25% to 35% by mass.

[0022] The compositions of this disclosure preferably contain 2% by mass or more and 10% by mass or less of aromatic compounds on a solid content basis, more preferably 3% by mass or more and 8% by mass or less, more preferably 4% by mass or more and 7% by mass or less, and even more preferably 4.5% by mass or more and 6% by mass or less.

[0023] In the compositions of this disclosure, the mass ratio of gelatin to aromatic compound (gelatin / aromatic compound) on a solid content basis is preferably 10 or more and 18 or less, more preferably 11 or more and 15 or less, even more preferably 12 or more and 15 or less, and even more preferably 12 or more and 14 or less.

[0024] In the compositions of this disclosure, the mass ratio of polycations to aromatic compounds (polycation / aromatic compound) on a solid content basis is preferably 2 or more and 8 or less, more preferably 3 or more and 7 or less, even more preferably 4 or more and 7 or less, and even more preferably 5 or more and 7 or less.

[0025] In the compositions disclosed herein, the mass ratio of gelatin to polycation (gelatin / polycation) on a solid content basis is preferably 1.4 or more and 9.0 or less, more preferably 1.7 or more and 3.0 or less, even more preferably 2.0 or more and 2.8 or less, and even more preferably 2.0 or more and 2.5 or less.

[0026] The method for preparing the compositions of this disclosure is not particularly limited. For example, one method is to prepare an aqueous solution by mixing gelatin and a polycation, and then mix an aromatic compound into this aqueous solution. An oxidizing agent may be added when preparing the composition. The oxidizing agent is not particularly limited, but an example is sodium periodate.

[0027] The compositions of this disclosure can be used, for example, as adhesives or coatings. The compositions of this disclosure may contain other materials to the extent that they exhibit performance. Other materials are not particularly limited, but include, for example, oils and fats, polyhydric alcohols, polyvinyl alcohols, fillers, pigments, etc. Oils and fats are not particularly limited, but include, for example, drying oils, semi-drying oils, non-drying oils, etc. Drying oils are not particularly limited, but include, for example, linseed oil, perilla oil, sardine oil, tung oil, sunflower oil, etc. Semi-drying oils are not particularly limited, but include, for example, soybean oil, herring oil, cottonseed oil, sesame oil, rice oil, rapeseed oil, etc. Non-drying oils are not particularly limited, but include, for example, castor oil, olive oil, palm oil, coconut oil, etc. Polyhydric alcohols are not particularly limited, but include, for example, glycerin and its derivatives, propylene glycol, sugar alcohols (sorbitol, xylitol, etc.), polyethylene glycol, etc. The fillers are not particularly limited, but examples include organic fillers and inorganic fillers. Examples of organic fillers are not particularly limited, but examples include wood flour, cellulose, bark flour, walnut flour, wheat flour, coconut shell powder, starch, etc. Examples of inorganic fillers are not particularly limited, but examples include calcium carbonate, silica, diatomaceous earth, kaolin, gypsum, clay, aluminum hydroxide, etc. Examples of pigments are not particularly limited, but examples include inorganic pigments such as metal oxides, sulfides, and chromates. Examples of metals in metal oxides are not particularly limited, but examples include titanium, zinc, chromium, iron, cobalt, and copper. Other pigments are not particularly limited, but examples include carbon black, metal powder, gold and silver nano(colloidal) particles, and lake pigments. Examples of metals in metal powders are not particularly limited, but examples include aluminum and copper.

[0028] (Explanation of effects) As described above, the composition of the above form comprises gelatin, polyethyleneimine, and at least one polycation of polylysine, and an aromatic compound, wherein the number-average molecular weight of the polycation is 4,000 or more and 10,000 or less, and in terms of solid content, gelatin is 50% or more by mass and 80% or less by mass, polycation is 10% or more by mass and 40% or less by mass, and aromatic compound is 2% or more by mass and 10% or less by mass. Such a composition provides excellent adhesion when wet and exhibits a softening temperature suitable for hot melting, thus making it possible to provide adhesives and coatings.

[0029] The following describes the tests conducted to confirm adhesion in wet conditions.

[0030] (Test 1) This test investigated the relationship between the mass of polyethyleneimine (hereinafter also referred to as "PEI") and its softening temperature. The number-average molecular weight (Mn) of the PEI used in this test was 10,000. First, an aqueous solution containing gelatin and PEI, with 75% by mass of water, was prepared and mixed for 15 minutes using a rotation-revolution type mixer. After that, caffeic acid was added and mixed for 10 minutes, followed by a 2-minute defoaming treatment to remove air bubbles. In the above aqueous solution, the proportions of gelatin, PEI, and caffeic acid, in terms of solid content, were as follows. Gelatin: 85% by mass, PEI: 10% by mass, Caffeic acid: 5% by mass Gelatin: 80% by mass, PEI: 15% by mass, Caffeic acid: 5% by mass Gelatin: 75% by mass, PEI: 20% by mass, Caffeic acid: 5% by mass Gelatin: 65% by mass, PEI: 30% by mass, Caffeic acid: 5% by mass Gelatin: 55% by mass, PEI: 40% by mass, Caffeic acid: 5% by mass

[0031] Dry adhesives were obtained by freeze-drying each aqueous solution. Subsequently, the softening onset temperature of each adhesive was calculated. Specifically, dynamic viscoelasticity measurements were performed using a thermomechanical analyzer (with stress-strain measurement function, manufactured by Seiko Instruments Inc.) with a load of 300 mN, amplitude of 100 mN, frequency of 0.03 Hz, heating rate of 2 °C / min, and a temperature range of 50 to 200 °C. For the obtained elastic modulus curve, the intersection point of the extension of the baseline of the elastic modulus (the tangent to the elastic modulus curve before the decrease in elastic modulus due to softening) and the tangent at the point of maximum slope of the curve due to softening (inflection point) was evaluated as the onset temperature at which softening occurs (= softening onset temperature).

[0032] Figure 1 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows. Assuming that wood materials are hot-pressed at around 180°C, the results in Figure 1 show that the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot-melt applications. The softening start temperature of an adhesive (labeled "PEI10k10CF5_GEL" in the figure) consisting of gelatin: 85% by mass, PEI: 10% by mass, and caffeic acid: 5% by mass was 171°C. The softening start temperature of an adhesive (labeled "PEI10k15CF5_GEL" in the figure) consisting of gelatin: 80% by mass, PEI: 15% by mass, and caffeic acid: 5% by mass was 162°C. The softening start temperature of the adhesive (labeled "PEI10k20CF5_GEL" in the figure), consisting of gelatin: 75% by mass, PEI: 20% by mass, and caffeic acid: 5% by mass, was 151°C. The softening start temperature of the adhesive (labeled "PEI10k30CF5_GEL" in the figure), consisting of gelatin: 65% by mass, PEI: 30% by mass, and caffeic acid: 5% by mass, was 141°C. The softening start temperature of an adhesive (labeled "PEI10k40CF5_GEL" in the figure) consisting of gelatin: 55% by mass, PEI: 40% by mass, and caffeic acid: 5% by mass was 137°C.

[0033] (Exam 2) This study investigated the relationship between the number-average molecular weight (Mn) of PEI and its softening temperature. This study was conducted using the same method as Study 1, except for a difference in composition. Gelatin, PEI, and caffeic acid were present in solid content amounts of 80% by mass, 15% by mass, and 5% by mass, respectively. The number-average molecular weights of the PEI used were 1,800, 10,000, and 70,000, respectively.

[0034] Figure 2 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 2, the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "PEI70k15_CF5_GEL" in the figure) consisting of gelatin: 80% by mass, PEI (Mn=70,000): 15% by mass, and caffeic acid: 5% by mass was 161°C. The softening start temperature of an adhesive (labeled "PEI10k15_CF5_GEL" in the figure) consisting of gelatin: 80% by mass, PEI (Mn=10,000): 15% by mass, and caffeic acid: 5% by mass was 162°C. The softening start temperature of an adhesive (labeled "PEI1.8k15_CF5_GEL" in the figure) consisting of gelatin: 80% by mass, PEI (Mn=1,800): 15% by mass, and caffeic acid: 5% by mass was 162°C.

[0035] Although not shown in Figure 2, the following adhesive compositions were also prepared as dried samples and subjected to dynamic viscoelasticity measurements. Their softening onset temperatures were as follows. When the PEI content was the same, no significant difference in softening onset temperature was observed based on the molecular weight of PEI. In all of the following compositions, the softening onset temperature was below 180°C, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive containing 65% gelatin, 30% PEI (Mn=70,000), and 5% caffeic acid was 139°C. The softening start temperature of an adhesive containing 65% gelatin, 30% PEI (Mn=10,000), and 5% caffeic acid was 141°C.

[0036] (Exam 3) This test investigated the relationship between the mass of PEI and the softening temperature when an oxidizing agent was added. This test was similar to Test 1, except that an oxidizing agent was used. The number-average molecular weight (Mn) of the PEI used in this test was 10,000. First, aqueous solutions of gelatin, PEI, and caffeic acid were prepared with the following solid content ratios. Gelatin: 85% by mass, PEI: 10% by mass, Caffeic acid: 5% by mass Gelatin: 70% by mass, PEI: 25% by mass, Caffeic acid: 5% by mass Gelatin: 65% by mass, PEI: 30% by mass, Caffeic acid: 5% by mass Gelatin: 55% by mass, PEI: 40% by mass, Caffeic acid: 5% by mass

[0037] Subsequently, to an aqueous solution containing 0.5 g of gelatin, PEI, and caffeic acid in terms of solid content, 200 μL of 5% by mass sodium periodate aqueous solution was added as an oxidizing agent and stirred, and then freeze-dried to obtain a dried adhesive.

[0038] Figure 3 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 3, even when quinone crosslinking was promoted by adding an oxidizing agent, the softening onset temperature was below 180°C, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "PEI10k10CF5_GEL_ox" in the figure) consisting of gelatin: 85% by mass, PEI: 10% by mass, and caffeic acid: 5% by mass was 177°C. The softening start temperature of the adhesive (labeled "PEI10k25CF5_GEL_ox" in the figure), consisting of gelatin: 65% by mass, PEI: 25% by mass, and caffeic acid: 5% by mass, was 141°C. The softening start temperature of the adhesive (labeled "PEI10k30CF5_GEL_ox" in the figure), consisting of gelatin: 65% by mass, PEI: 30% by mass, and caffeic acid: 5% by mass, was 140°C. The softening start temperature of the adhesive (labeled "PEI10k40CF5_GEL_ox" in the figure), consisting of gelatin: 55% by mass, PEI: 40% by mass, and caffeic acid: 5% by mass, was 124°C.

[0039] (Exam 4) This test investigated the relationship between the mass of PEI and its adhesive properties when wet. Specifically, adhesives were prepared using an oxidizing agent in the same manner as in Test 3. Aqueous solutions of gelatin, PEI, and caffeic acid were prepared with the following solid content ratios. Gelatin: 85% by mass, PEI (Mn=10,000): 10% by mass, Caffeic acid: 5% by mass Gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, Caffeic acid: 5% by mass Gelatin: 65% by mass, PEI (Mn=10,000): 30% by mass, Caffeic acid: 5% by mass Gelatin: 55% by mass, PEI (Mn=10,000): 40% by mass, Caffeic acid: 5% by mass

[0040] For the adhesion test, we used cedar heartwood pieces with the fiber direction oriented longitudinally and dimensions of 25mm x 30mm x 10mm, which had been pre-dried to a state of complete dryness at 105°C using a forced-air dryer. The obtained adhesive was applied to the 25mm x 30mm surface of the wood piece for the adhesion test, so that it covered an area of ​​25mm x 25mm. Two wood pieces coated with the adhesive solution were bonded together with the adhesive-coated surfaces facing each other, and then temporarily bonded by applying a pressure of approximately 7.8kPa to the bonded surface. After bonding, the pieces were acclimatized for at least 3 days in a constant temperature and humidity chamber at 60% humidity and 20°C, and then bonded at 10kg / cm². 2 Hot-melt bonding was performed by hot compression (hot press) at 150°C for 20 minutes under the specified load.

[0041] Furthermore, a hot water resistance test was conducted using a method compliant with JIS K6852:1994. This hot water resistance test is equivalent to the hot and cold water immersion test for plywood in the Japanese Agricultural Standards. After immersing the test specimens in water at 60±3℃ for 3 hours, they were cooled in water at room temperature (25℃), and then, while the test specimens were still wet, a shear, compression, and peel test was performed using a method compliant with JIS K6852:1994.

[0042] In normal conditions, the adhesive strength was 6.1–7.7 MPa, and the average wood fracture rate was 100%. The results of the hot water resistance test are as follows, and all adhesives showed an average wood fracture rate of 0%. From these results, it can be seen that even when an oxidizing agent was added, the softening initiation temperature was good, and the adhesive strength in wet conditions was also good. When the PEI content was higher than 40% by mass, a tendency for the adhesive strength in wet conditions to decrease was observed, which was undesirable. The adhesive strength of the bonded material consisting of gelatin (85% by mass), PEI (Mn=10,000) (10% by mass), and caffeic acid (5% by mass) was 0.79 MPa. The adhesive strength of the bonded material consisting of gelatin (70% by mass), PEI (Mn=10,000) (25% by mass), and caffeic acid (5% by mass) was 1.27 MPa. The adhesive strength of a material consisting of gelatin (65% by mass), PEI (Mn=10,000) (30% by mass), and caffeic acid (5% by mass) was 1.43 MPa. The adhesive strength of a material consisting of gelatin (55% by mass), PEI (Mn=10,000) (40% by mass), and caffeic acid (5% by mass) was 0.77 MPa.

[0043] (Exam 5) This experiment investigated the relationship between the mass of polylysine and its softening temperature. In this experiment, ε-polylysine (hereinafter also referred to as "εPL") was used as the polylysine. The number-average molecular weight (Mn) of εPL used in this experiment and subsequent experiments is 4,000. This experiment is similar to Experiment 1, except that εPL is used instead of PEI. Aqueous solutions of gelatin, εPL, and caffeic acid were prepared with the following solid content ratios. Gelatin: 85% by mass, εPL: 10% by mass, Caffeic acid: 5% by mass Gelatin: 75% by mass, εPL: 20% by mass, Caffeic acid: 5% by mass Gelatin: 65% by mass, εPL: 30% by mass, Caffeic acid: 5% by mass

[0044] Figure 4 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 4, it can be seen that the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of the adhesive (labeled "εPL10_CF5_GEL" in the figure) consisting of gelatin: 85% by mass, εPL: 10% by mass, and caffeic acid: 5% by mass was 167°C. The softening start temperature of the adhesive (labeled "εPL20_CF5_GEL" in the figure) consisting of gelatin: 75% by mass, εPL: 20% by mass, and caffeic acid: 5% by mass was 163°C. The softening start temperature of the adhesive (labeled "εPL30_CF5_GEL" in the figure) consisting of gelatin: 65% by mass, εPL: 30% by mass, and caffeic acid: 5% by mass was 150°C.

[0045] (Exam 6) This test investigated the relationship between the mass of εPL and the softening temperature when an oxidizing agent was added. This test was similar to Test 3, except that εPL was used instead of PEI. Aqueous solutions of gelatin, εPL, and caffeic acid were prepared with the following solid content ratios. Gelatin: 85% by mass, εPL: 10% by mass, Caffeic acid: 5% by mass Gelatin: 75% by mass, εPL: 20% by mass, Caffeic acid: 5% by mass Gelatin: 65% by mass, εPL: 30% by mass, Caffeic acid: 5% by mass

[0046] Figure 5 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 5, it can be seen that the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "εPL10CF5_GEL_ox" in the figure) consisting of gelatin: 85% by mass, εPL: 10% by mass, and caffeic acid: 5% by mass was 119°C. The softening start temperature of the adhesive (labeled "εPL20CF5_GEL_ox" in the figure) consisting of gelatin: 75% by mass, εPL: 20% by mass, and caffeic acid: 5% by mass was 152°C. The softening start temperature of an adhesive (labeled "εPL30CF5_GEL_ox" in the figure) consisting of gelatin: 65% by mass, εPL: 30% by mass, and caffeic acid: 5% by mass was 133°C.

[0047] (Exam 7) This test investigated the relationship between the mass of εPL and its adhesive properties when wet. Specifically, adhesives were prepared using an oxidizing agent in the same manner as in Test 4. Aqueous solutions of gelatin, εPL, and caffeic acid were prepared with the following solid content ratios. Gelatin: 65% by mass, εPL: 30% by mass, Caffeic acid: 5% by mass

[0048] In the normal condition test, the adhesive strength was 7.3 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the adhesive strength was 0.86 MPa, and the average wood fracture rate was 0%, indicating good adhesive strength even when wet.

[0049] (Exam 8) This experiment investigated the relationship between aromatic compounds and softening temperature. This experiment was similar to Experiment 1, except that instead of caffeic acid, 25DHBA, 35DHBA, green tea polyphenols (hereinafter also referred to as "GTP"), tannic acid (hereinafter also referred to as "TA"), vanillin (hereinafter also referred to as "VAN"), vanillic acid (hereinafter also referred to as "VANAc"), and syringaldehyde (hereinafter also referred to as "SylAld") were used as aromatic compounds. Gelatin, PEI, and aromatic compounds were present in solid content amounts of 70% by mass, 25% by mass, and 5% by mass, respectively.

[0050] Figure 6 shows the temperature dependence of the elastic modulus in the dried form of adhesives containing aromatic compounds with two or three phenolic hydroxyl groups in the same molecule. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 6, the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "PEI10k25_25DHBA5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and 25DHBA: 5% by mass was 129°C. The softening start temperature of an adhesive (labeled "PEI10k25_35DHBA5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and 35DHBA: 5% by mass was 137°C. The softening start temperature of an adhesive (labeled "PEI10k25TA5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and TA: 5% by mass was 142°C. The softening start temperature of an adhesive (labeled "PEI10k25GTP5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and GTP: 5% by mass was 141°C.

[0051] Figure 7 shows the temperature dependence of the elastic modulus in the dried form of adhesives containing aromatic compounds having a guaiacol or syringyl skeleton. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 7, it can be seen that the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "PEI10k25VAN5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and VAN: 5% by mass was 127°C. The softening start temperature of an adhesive (labeled "PEI10k25VANAc5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and VANAc: 5% by mass was 143°C. The softening start temperature of an adhesive (labeled "PEI10k25SylAld5_GEL" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and SylAld: 5% by mass was 129°C.

[0052] (Exam 9) This test investigated the relationship between aromatic compounds and softening temperature when an oxidizing agent was added. This test was similar to Test 8, except that an oxidizing agent was used. The method of using the oxidizing agent was the same as in Test 3.

[0053] Figure 8 shows the temperature dependence of the elastic modulus in the dried form of adhesives containing aromatic compounds with two or three phenolic hydroxyl groups in the same molecule. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 8, the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and 25DHBA: 5% by mass (labeled "PEI10k25_25DHBA5_GEL_ox" in the figure) was 138°C. The softening start temperature of an adhesive (labeled "PEI10k25_35DHBA5_GEL_ox" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and 35DHBA: 5% by mass was 143°C. The softening start temperature of an adhesive (labeled "PEI10k25TA5_GEL_ox" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and TA: 5% by mass was 152°C. The softening start temperature of an adhesive (labeled "PEI10k25GTP5_GEL_ox" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and GTP: 5% by mass was 147°C.

[0054] Figure 9 shows the temperature dependence of the elastic modulus in the dried adhesive containing aromatic compounds with a guaiacol skeleton. The relationship between each adhesive and its softening onset temperature is as follows. From the results in Figure 9, the softening onset temperature was below 180°C for all compositions, indicating a softening temperature suitable for hot melting. The softening start temperature of an adhesive (labeled "PEI10k25VAN5_GEL_ox" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and VAN: 5% by mass was 144°C. The softening start temperature of an adhesive (labeled "PEI10k25VANAc5_GEL_ox" in the figure) consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and VANAc: 5% by mass was 119°C. The softening start temperature of the adhesive (labeled "PEI10k25SylAld5_GEL_ox" in the figure), consisting of gelatin: 70% by mass, PEI (Mn=10,000): 25% by mass, and SylAld: 5% by mass, was 129°C.

[0055] (Test 10) This test investigated the relationship between the type of aromatic compound and its adhesion when wet. The aromatic compounds used were the same as in Test 9.

[0056] The adhesive strength of each adhesive in the normal state test was 6.6 to 7.8 MPa, and the average base fracture rate was 100%. The results of the hot water resistance test are as follows: PEI10k25_25DHBA5_GEL_ox showed an adhesive strength of 1.28 MPa, PEI10k23_35DHBA5_GEL_ox showed an adhesive strength of 1.45 MPa, PEI10k25GTP5_GEL_ox showed an adhesive strength of 1.37 MPa, PEI10k25TA5_GEL_ox showed an adhesive strength of 1.21 MPa, PEI10k25VAN5_GEL_ox showed an adhesive strength of 0.93 MPa, PEI10k25VANAc5_GEL_ox showed an adhesive strength of 1.21 MPa, and PEI10k25SylAld5_GEL_ox showed an adhesive strength of 1.20 MPa. In all test specimens using any of the adhesives, the average wood fracture rate was 0%. This result indicates that adhesives containing various aromatic compounds exhibited good softening initiation temperatures and good adhesive strength in the wet state, even when oxidizing agents were added to promote quinone crosslinking.

[0057] (Test 11) This test was similar to the previous one, except that an aluminum plate was used instead of a wooden block. The adhesive used was PEI10k25CF5_GEL_ox. An aluminum plate test specimen with dimensions of 100mm × 25mm × 1.5mm, conforming to JIS K6850:1999, was used as the adherend for the adhesion test. The adhesive solution was applied to the leading edge of one side of the aluminum specimen to create a shape conforming to JIS K6850:1999, resulting in a 25mm × 12.5mm area. Two aluminum specimens coated with the adhesive solution were bonded together with the adhesive-coated sides facing each other, and then compressed to approximately 7.8kPa. After bonding, the specimens were acclimatized for at least 3 days in a constant temperature and humidity chamber at 60% humidity and 20°C, and then bonded at 10kg / cm². 2The specimens were subjected to hot compression (hot pressing) at 150°C for 20 minutes under a load. A tensile shear bond strength test was performed on the obtained specimens in accordance with JIS K6850:1999. The tensile shear bond strength of the aluminum plate bond test specimens using the adhesive (PEI10k25CF5_GEL_ox) was 3.6 MPa. From these results, it was found that the adhesive of this embodiment, which is a mixture of 70% by mass gelatin, 25% by mass PEI, and 5% by mass caffeic acid with the addition of an oxidizing agent, showed good bond strength even when bonding metals together.

[0058] In subsequent tests, the properties of comparative adhesives were investigated.

[0059] (Exam 12) This test investigated the softening temperatures of additive-free gelatin, a composition of gelatin with added glycerin, and a compound of gelatin with only an aromatic compound (caffeic acid) added (without polycations). It also investigated the softening temperature of a composition of gelatin with added polycations (PEI) and catechol (caffeic acid) when the polycation content was low. This test was similar to Test 1, except for the use of a comparative adhesive. In this test, aqueous solutions with the following solid content ratios were prepared. • Gelatin: 100% by mass Gelatin: 90% by mass, Glycerin: 10% by mass Gelatin: 95% by mass, Caffeic acid: 5% by mass Gelatin: 90% by mass, PEI (Mn=70,000): 5% by mass, Caffeic acid: 5% by mass Gelatin: 90% by mass, εPL: 5% by mass, Caffeic acid: 5% by mass

[0060] Figure 10 shows the temperature dependence of the elastic modulus in the dried state of each adhesive. The relationship between each adhesive and its softening onset temperature is as follows: Gelatin alone did not show clear softening within the measurement range, and for compositions other than those with added glycerin, softening onset temperatures of 180°C or higher were observed, making them unsuitable for pot pressing of wood materials. With gelatin with added glycerin, the softening onset temperature decreased significantly, but as will be discussed later, the adhesive strength was insufficient. The softening start temperature of the adhesive (labeled "GL10_GEL" in the figure) consisting of 90% gelatin and 10% glycerin was 105°C. The softening start temperature of an adhesive containing 95% gelatin and 5% caffeic acid (labeled "CF5_GEL" in the figure) was 198°C. The softening start temperature of an adhesive (labeled "PEI70k5CF5_GEL" in the figure) consisting of gelatin: 90% by mass, PEI (Mn=70,000): 5% by mass, and caffeic acid: 5% by mass was 186°C. The softening start temperature of an adhesive (labeled "εPL5CF5_GEL" in the figure) consisting of gelatin: 90% by mass, εPL: 5% by mass, and caffeic acid: 5% by mass was 182°C.

[0061] Although not shown in Figure 10, dried samples were prepared for adhesives with the following compositions (without aromatic compounds) and dynamic viscoelasticity measurements were performed. The softening onset temperatures were as follows. Regardless of the presence or absence of aromatic compounds, compositions with low PEI content showed softening onset temperatures of 180°C or higher, which are unsuitable for pot pressing of wood materials. The softening start temperature of an adhesive containing 95% gelatin by mass and 5% PEI (Mn=70,000) by mass was 187°C.

[0062] (Exam 13) This test investigated the adhesive strength of an adhesive using only gelatin. An aqueous solution was prepared by adding water to gelatin so that the solid content was 25% by mass. Adhesion test specimens were prepared by hot pressing under the same conditions as in the previously described example, and normal condition tests and hot water resistance tests were conducted. In the normal condition test, the adhesive strength was 7.64 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the test specimen peeled off after immersion in hot water, and no adhesive strength was obtained.

[0063] (Exam 14) This test investigated the adhesive strength of adhesives containing glycerin. An adhesive solution (GL10_GEL) was prepared by adding 10% glycerin to 90% gelatin by mass to achieve a solid content of 25% by mass. Adhesion test specimens were prepared by hot pressing under the same conditions as in the previously described examples, and normal condition tests and hot water resistance tests were conducted. In the normal condition test, the adhesive strength was 8.5 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the adhesive strength of GL10_GEL was 0.40 MPa, and the average wood fracture rate was 0%. Gelatin adhesives with only glycerin added showed a good softening initiation temperature, but did not achieve sufficient adhesive strength when wet.

[0064] (Exam 15) This test investigated the adhesive strength of an adhesive that does not contain polycations. A gelatin composition containing 95% by mass of gelatin and 5% by mass of caffeic acid was prepared, and water was added to create an aqueous solution with a solid content of 25% by mass. To a composition with a total solid content of 0.5 g, 200 μL of 5% by mass sodium periodate aqueous solution was added and stirred to prepare the adhesive (CF5_GEL_ox). Adhesion test specimens were prepared by hot pressing under the same conditions as in the above example, and normal condition tests and hot water resistance tests were performed. In the normal condition test, the adhesive strength was 8.0 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the adhesive strength of CF5_GEL_ox was 0.59 MPa, and the average wood fracture rate was 0%. The gelatin adhesive that does not contain polycations did not provide sufficient adhesive strength when wet.

[0065] (Exam 16) This test investigated the adhesive strength of adhesives with a low polycation content. A gelatin composition containing 5% by mass of PEI (number average molecular weight Mn=10,000 (10k)) and 5% by mass of caffeic acid was prepared by adding water to create an aqueous solution with a solid content of 25% by mass. To a composition with a total solid content of 0.5g, 200μL of 5% by mass sodium periodate aqueous solution was added and stirred to prepare the adhesive (PEI10k5CF5_GEL_ox). Adhesion test specimens were prepared by hot pressing under the same conditions as in the previously described example, and normal condition tests and hot water resistance tests were conducted. In the normal condition test, the adhesive strength was 7.3 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the adhesive strength of PEI10k5CF5_GEL_ox was 0.16 MPa, and the average wood fracture rate was 0%. Gelatin adhesives with insufficient polycation content did not achieve sufficient adhesive strength when wet.

[0066] (Exam 17) This test investigated the adhesive strength of a gelatin adhesive that does not contain aromatic compounds. A gelatin composition containing 30% by mass of PEI (number average molecular weight Mn=10,000(10k)) by dry weight was prepared, and water was added to make an adhesive (PEI10k30_GEL) with a solid content of 25% by mass. Adhesion test specimens were prepared by hot pressing under the same conditions as in the above example, and normal condition tests and hot water resistance tests were performed. In the normal condition test, the adhesive strength was 6.9 MPa, and the average wood fracture rate was 100%. In the hot water resistance test, the adhesive strength of PEI10k30_GEL was 0.64 MPa, and the average wood fracture rate was 0%. Even when polycations were included, sufficient adhesive strength in the wet state could not be obtained with gelatin adhesives that do not contain aromatic compounds.

[0067] (Exam 18) This test investigated the adhesive strength of adhesives with PEI molecular weights less than 4,000 or greater than 10,000. A gelatin composition containing 25% by mass of PEI (number-average molecular weight (Mn) = 1,800 (1.8k) or Mn = 70,000 (70k)) and 5% by mass of caffeic acid was prepared by adding water to create an aqueous solution with a solid content of 25% by mass. To a composition with a total solid content of 0.5g, 200 μL of 5% by mass sodium periodate aqueous solution was added and stirred to prepare adhesives (PEI1.8k25CF5_GEL_ox, PEI70k25CF5_GEL_ox). Adhesion test specimens were prepared by hot pressing under the same conditions as in the previously described examples, and normal condition tests and hot water resistance tests were performed. The adhesive strength in the normal condition test showed 6.4 to 7.7 MPa, and the average wood fracture rate showed 100%. In the hot water resistance test, the adhesive strength of PEI1.8k25CF5_GEL_ox was 0.45 MPa, and the adhesive strength of PEI70k25CF5_GEL_ox was 0.60 MPa, with both showing an average wood fracture rate of 0%. If the molecular weight of the polycation was not appropriate, sufficient adhesive strength in wet conditions could not be obtained.

[0068] The present invention is not limited to the embodiments described above, and can be realized in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Industrial applicability]

[0069] The composition of the present invention can be used, for example, as an adhesive or coating agent, and exhibits excellent adhesion when wet, as well as a softening temperature suitable for hot melting, thus having industrial applicability as an adhesive or coating agent.

Claims

1. Gelatin and, Polyethyleneimine and at least one polycation of polylysine, An aromatic compound comprising at least one of the following: an aromatic compound having two or three phenolic hydroxyl groups in the same molecule; an aromatic compound having a guaiacol skeleton; and an aromatic compound having a syringyl skeleton. Includes, The number-average molecular weight of the polycation is 4,000 or more and 10,000 or less. In terms of solid content, The gelatin is present in an amount of 50% by mass or more and 80% by mass or less. The polycation is present in an amount of 10% by mass or more and 40% by mass or less. The aromatic compound is present in an amount of 2% by mass or more and 10% by mass or less. Hot melt adhesive composition.

2. In the hot melt composition according to claim 1, The aforementioned aromatic compound comprises at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, 3,4-dihydroxyphenylacetic acid, 3,5-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, tannic acid, green tea polyphenols, vanillic acid, and syringaldehyde. Hot melt adhesive composition.

3. In the hot melt composition according to claim 1, The aforementioned aromatic compound comprises at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, tannic acid, green tea polyphenols, vanillic acid, and syringaldehyde. Hot melt adhesive composition.

4. An adhesive comprising the hot melt composition according to any one of claims 1 to 3.

5. A coating agent comprising the hot melt composition according to any one of claims 1 to 3.

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