Composition, adhesive, and coating agent

Abstract

To provide a technology for an adhesive and a coating agent that exhibit superior adhesion in a wet state.SOLUTION: A composition contains: gelatin; at least one polycation selected from polyethyleneimine and polylysine; and an aromatic compound having two phenolic hydroxyl groups within the same molecule, where the positional relationship of the phenolic hydroxyl groups is ortho-position or para-position. Based on solid content, the gelatin is 50 mass% or more and 80 mass% or less, the polycation is 10 mass% or more and 35 mass% or less, and the aromatic compound is 2 mass% or more and 10 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to compositions, adhesives and coatings. [Background technology]

[0002] In recent years, the use of biomass-derived adhesives has been attracting attention in order to reduce environmental impact. Gelatin has long been used as a biomass-derived wood adhesive. However, gelatin has a problem of low water resistance. To solve this problem, Non-Patent Document 1 discloses a technique of blending gelatin with either hydroquinone or catechin. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Gelatin adhesive using oxidative cross-linking of polyphenols" Science and Industry, Vol. 86, 223-228 (2012) Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have discovered that while the techniques described in the non-patent literature improve water resistance, they do not provide sufficient adhesiveness when wet. Therefore, there is a need for a technique related to an adhesive that uses gelatin and has excellent adhesiveness when wet. Furthermore, this problem is not limited to adhesives, but is also a common problem in coating agents and the like that use gelatin. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, there is provided a composition comprising gelatin, at least one polycation selected from the group consisting of polyethyleneimine and polylysine, and an aromatic compound having two phenolic hydroxyl groups in the same molecule, the phenolic hydroxyl groups being ortho or para positions, wherein the gelatin accounts for 50% to 80% by mass, the polycation for 10% to 35% by mass, and the aromatic compound for 2% to 10% by mass, calculated on a solids basis. The composition of this aspect exhibits excellent adhesiveness in a wet state.

[0007] (2) In the composition according to (1) above, the gelatin may be present in an amount of 60% by mass or more and 70% by mass or less in terms of solid content. This composition has superior adhesiveness in a wet state.

[0008] (3) In the composition according to (1) or (2), the aromatic compound may comprise at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)-L-alanine, 3-(3,4-dihydroxyphenyl)propionic acid, 3,4-dihydroxyphenylacetic acid, and 2,5-dihydroxybenzoic acid. This composition has superior adhesiveness in a wet state.

[0009] (4) In the composition according to any one of (1) to (3), the aromatic compound may comprise at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, and 3,4-dihydroxyphenylacetic acid. This composition has even better adhesiveness in a wet state.

[0010] (5) According to another aspect of the present disclosure, there is provided an adhesive comprising the composition according to any one of (1) to (4) above.

[0011] (6) According to another aspect of the present disclosure, there is provided a coating agent comprising the composition according to any one of (1) to (4) above.

[0012] The present invention can be realized in various forms, such as a cured body obtained by curing the composition, a coated body coated with the composition, or a bonded body bonded with the composition. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing the relationship between the mass fraction of PEI and adhesive strength in a hot water resistance test. [Figure 2] FIG. 1 is a graph showing the relationship between the mass fraction of polylysine and the adhesive strength in a hot water resistance test. [Figure 3] FIG. 1 is a graph showing the relationship between the type of polyphenol and adhesive strength in a hot water resistance test. DETAILED DESCRIPTION OF THE INVENTION

[0014] According to one aspect of the present disclosure, there is provided a composition comprising (i) gelatin, (ii) at least one polycation selected from the group consisting of polyethyleneimine and polylysine, and (iii) an aromatic compound having two phenolic hydroxyl groups in the same molecule, the hydroxyl groups being in the ortho or para positions. This composition contains, in terms of solid content, (i) 50% to 80% by mass of gelatin, (ii) 10% to 35% by mass of polycation, and (iii) 2% to 10% by mass of aromatic compound. This composition exhibits excellent adhesive properties in a wet state when used in adhesives, coatings, and the like that use gelatin.

[0015] The gelatin of the present disclosure is not particularly limited, but is obtained by applying heat to collagen, a main component of animal skin, bones, tendons, etc., and extracting it. In the present disclosure, gelatin obtained by a known production method can be used, and for example, gelatin produced by treating raw materials such as skin, bones, tendons, etc. of cows, pigs, chickens, fish, etc. with acid or alkali to obtain crude collagen and then heat-extracting it can be used. Furthermore, the gelatin of the present disclosure may be a hydrolysate, an enzymatic decomposition product, a gelatin derivative (e.g., acylated gelatin, etc.), etc.

[0016] The polycation of the present disclosure is at least one of polyethyleneimine and polylysine. The polyethyleneimine may be linear or branched. The number-average molecular weight of the polyethyleneimine is not particularly limited, but is preferably 1,000 or more and 100,000 or less, and more preferably 2,500 or more and 70,000 or less. The polylysine may be ε-poly-L-lysine or α-polylysine. As the polylysine, ε-poly-L-lysine is preferred from the viewpoint of improving adhesiveness in a wet state.

[0017] The aromatic compound of the present disclosure (hereinafter also simply referred to as "aromatic compound") refers to a compound having two phenolic hydroxyl groups in the same molecule, where the phenolic hydroxyl groups are located at the ortho or para positions. In this specification, "phenolic hydroxyl group" refers to a hydroxyl group bonded to an aromatic ring. Examples of aromatic rings include, but are not limited to, fused aromatic rings and heteroaromatic rings. Examples of fused aromatic rings include, but are not limited to, benzene rings, naphthalene rings, anthracene rings, pyrene rings, and the like. Examples of heteroaromatic rings include, but are not limited to, pyridine rings and pyrrole rings.

[0018] The aromatic compound is not particularly limited, but examples thereof include caffeic acid, 2,5-dihydroxybenzoic acid (hereinafter also referred to as "25DHBA"), 3,4-dihydroxyphenylacetic acid (hereinafter also referred to as "DOPAC"), 3-(3,4-dihydroxyphenyl)propionic acid (hereinafter also referred to as "DHCA"), 3-(3,4-dihydroxyphenyl)-L-alanine (hereinafter also referred to as "LDOPA"), etc. From the viewpoint of improving adhesiveness in wet conditions, caffeic acid, LDOPA, DHCA, DOPAC, and 25DHBA are preferred, and caffeic acid, DHCA, and DOPAC are more preferred.

[0019] In the composition of the present disclosure, the gelatin content, calculated as solid content, is 50% by mass or more and 80% by mass or less, preferably 55% by mass or more and 75% by mass or less, more preferably 60% by mass or more and 75% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less.

[0020] The composition of the present disclosure contains, in terms of solid content, 10% by mass or more and 35% by mass or less, preferably 15% by mass or more and 35% by mass or less, more preferably 20% by mass or more and 35% by mass or less, and even more preferably 25% by mass or more and 35% by mass or less.

[0021] The composition of the present disclosure contains, in terms of solid content, 2% by mass or more and 10% by mass or less of aromatic compounds, 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.

[0022] In the composition of the present disclosure, the mass ratio of gelatin to aromatic compound (gelatin / aromatic compound), calculated as solid content, 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.

[0023] In the composition of the present disclosure, the mass ratio of polycation to aromatic compound (polycation / aromatic compound), calculated as solid content, is preferably 2 or more and 7 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.

[0024] In the composition of the present disclosure, the mass ratio of gelatin to polycation (polycation / aromatic compound), calculated as solid content, is preferably 1.5 or more and 3.0 or less, more preferably 1.7 or more and 2.5 or less, even more preferably 2.0 or more and 2.5 or less, and even more preferably 2.0 or more and 2.4 or less.

[0025] The method for preparing the composition of the present disclosure is not particularly limited. For example, a method may be used in which an aqueous solution of gelatin and a polycation is prepared, and then an aromatic compound is mixed with the aqueous solution. An oxidizing agent may be added when preparing the composition. The oxidizing agent is not particularly limited, but may be, for example, sodium periodate.

[0026] The composition of the present disclosure can be used, for example, in adhesives and coatings. Other materials may be added to the composition of the present disclosure as long as the composition exhibits its performance. Examples of other materials include, but are not limited to, fats and oils, polyhydric alcohols, polyvinyl alcohol, fillers, pigments, etc. Examples of fats and oils include, but are not limited to, drying oils, semi-drying oils, and non-drying oils. Examples of drying oils include, but are not limited to, linseed oil, perilla oil, sardine oil, tung oil, and sunflower oil. Examples of semi-drying oils include, but are not limited to, soybean oil, menhaden oil, cottonseed oil, sesame oil, rice bran oil, and rapeseed oil. Examples of non-drying oils include, but are not limited to, castor oil, olive oil, palm oil, and coconut oil. Examples of polyhydric alcohols include, but are not limited to, glycerin and its derivatives, propylene glycol, sugar alcohols (sorbitol, xylitol, etc.), and polyethylene glycol. Examples of fillers include, but are not limited to, organic fillers, inorganic fillers, and the like. Examples of organic fillers include, but are not limited to, wood flour, cellulose, bark flour, walnut flour, wheat flour, coconut shell powder, starch, and the like. Examples of inorganic fillers include, but are not limited to, calcium carbonate, silica, diatomaceous earth, kaolin, gypsum, clay, aluminum hydroxide, and the like. Examples of pigments include, but are not limited to, inorganic pigments such as metal oxides, sulfides, and chromates. Examples of metals in metal oxides include, but are not limited to, titanium, zinc, chromium, iron, cobalt, copper, and the like. Examples of other pigments include, but are not limited to, carbon black, metal powders, gold or silver nano (colloidal) particles, lake pigments, and the like. Examples of metals in metal powders include, but are not limited to, aluminum, copper, and the like.

[0027] (Explanation of effect) As explained above, the composition of the above form contains gelatin, at least one polycation selected from polyethyleneimine and polylysine, and an aromatic compound having two phenolic hydroxyl groups in the same molecule, the hydroxyl groups being in the ortho or para positions, and the gelatin accounts for 50% to 80% by mass, the polycation for 10% to 35% by mass, and the aromatic compound for 2% to 10% by mass, calculated as solid content. Such a composition can provide an adhesive or coating agent with excellent adhesiveness in a wet state.

[0028] The test for checking the adhesiveness in a wet state will be described below.

[0029] (Test 1) In this test, the relationship between the mass of polyethyleneimine (hereinafter also referred to as "PEI") and adhesiveness in a wet state was investigated. First, an aqueous solution containing gelatin and PEI, with a water content of 75% by mass, was prepared and mixed for 15 minutes using a rotation-revolution mixer. Caffeic acid was then added, and the mixture was mixed for 10 minutes, after which it was degassed for 2 minutes to remove air bubbles. The gelatin, PEI, and caffeic acid concentrations were 75%, 20%, and 5% by mass, respectively, calculated as solids.

[0030] In addition, aqueous solutions containing 5% by mass of caffeic acid, 10%, 15%, and 40% by mass of PEI, and the remainder being gelatin, were prepared by the above method. Specifically, the aqueous solutions were prepared with the following blending ratios, calculated as solid content: Aqueous solution of caffeic acid: 5% by mass, PEI: 10% by mass, and gelatin: 85% by mass Aqueous solution of caffeic acid: 5% by mass, PEI: 15% by mass, and gelatin: 80% by mass Aqueous solution of caffeic acid: 5% by mass, PEI: 40% by mass, and gelatin: 55% by mass

[0031] The resulting compositions were all brownish, transparent solutions at temperatures above 37°C, and brownish, transparent jelly-like at temperatures below room temperature. No mold growth was observed in these compositions even after storage for one month.

[0032] The resulting composition, which contained 0.5 g of caffeic acid, PEI, and gelatin in total solids, was added with 200 μL of a 5% by mass aqueous solution of sodium periodate to promote oxidation, yielding a dark brown adhesive solution. For the adhesion test, pieces of cedar heartwood measuring 25 mm x 30 mm x 10 mm with the fiber direction aligned longitudinally were used, which had been dried in advance in a fan dryer at 105°C.

[0033] The resulting adhesive solution was applied to a 25mm x 30mm surface of a wood piece for adhesion testing, so that it measured 25mm x 25mm. Two wood pieces for adhesion testing, each coated with the adhesive solution, were then joined together with the coated surfaces facing each other, and a pressure of approximately 7.8kPa was applied to the bonding surfaces. After bonding, the pieces were allowed to acclimate for at least three days in a constant temperature and humidity chamber at 60% humidity and 20°C, after which a shear compression peel test (normal condition test) was conducted using a method in accordance with JIS6852. In all cases, the adhesive strength was 6MPa or more, and the average wood fracture rate was 60% or more.

[0034] Furthermore, a hot water resistance test was conducted using a method conforming to JIS 6852. This hot water resistance test is equivalent to the hot and cold water immersion test for plywood specified in the Japanese Agricultural Standards. The test specimens were immersed in water at 60±3°C for 3 hours, then cooled in water at room temperature (25°C). Then, while still wet, a shear compression peel test was conducted using a method conforming to JIS 6852.

[0035] In this test, the following examples (i) to (iv) were used as comparative examples. In Test 2 described later, the following examples (i) to (iv) were also used as comparative examples. These examples were prepared by the same method as above, except for the ratios of caffeic acid, PEI, and gelatin.

[0036] (i) An example was prepared in which caffeic acid was 5% by mass and gelatin was 95% by mass (calculated as solid content) (referred to as "gelatin + caffeic acid 5%" in the figures below). Furthermore, 1M aqueous sodium hydroxide was added to achieve an equimolar amount with caffeic acid. The composition used in the test was prepared so that the combined moisture content of the 1M aqueous sodium hydroxide solution was 75% by mass. The resulting composition, which contained 0.5 g of caffeic acid and gelatin in solid content, was accelerated by adding 200 μL of 5% by mass aqueous sodium periodate solution at 60°C to promote oxidation, yielding a dark brown adhesive solution. In normal conditions, this example exhibited an adhesive strength of 6 MPa or more and an average wood fracture rate of 30% or more. In hot water resistance tests, the adhesive strength was 0.14 MPa or more and an average wood fracture rate of 0%.

[0037] (ii) As an example of an adhesive containing 100% gelatin by mass (solids), an aqueous solution containing 25% gelatin by mass and 75% water by mass was prepared and mixed for 15 minutes in a rotation-revolution mixer. The mixture was then degassed for 2 minutes to remove air bubbles. The resulting composition was a pale yellow, transparent solution at temperatures above 37°C and became a pale yellow, transparent jelly at temperatures below room temperature. This example is referred to as "Gelatin" in the figures described below. In normal conditions, this example exhibited an adhesive strength of 6 MPa or more and an average wood fracture rate of 80% or more. In hot water resistance tests, peeling occurred on all test pieces, making it impossible to measure adhesive strength. Furthermore, mold growth was observed on the surface of this composition after approximately two weeks of storage at 4°C.

[0038] (iii) Test pieces for the normal test and hot water resistance test were prepared using a commercially available gelatin adhesive (product name: Nikawa Shokunin, manufactured by LOHAS Material Co., Ltd.). In the normal test, this example showed an adhesive strength of 5 MPa or more, and an average wood fracture rate of 30% or more. In the hot water resistance test, peeling occurred in all test pieces, so the adhesive strength could not be measured. As with Example (ii) above, this example did not show adhesive strength in the hot water resistance test, so it is not shown in the figures described below.

[0039] (iv) An aqueous solution containing 70% PEI by mass and 30% caffeic acid by mass, calculated as solids, was prepared and mixed for 15 minutes using a planetary centrifugal mixer. The water content of this aqueous solution was adjusted to 75% by mass. The solution was then degassed for 2 minutes to remove air bubbles. The resulting composition was a brownish, transparent solution. A dark brown adhesive solution was obtained by adding an aqueous sodium periodate solution to the resulting composition, which contained 0.5 g of caffeic acid and PEI in total, calculated as solids, in the same manner as in Test 1, to promote oxidation. This example exhibited an adhesive strength of 1.2 MPa in the normal test. In the hot water resistance test, the adhesive strength was 0.01 MPa and the average wood fracture rate was 0%. Furthermore, no mold growth was observed in this composition even after one month of storage.

[0040] Figure 1 shows the relationship between the mass fraction (%) of PEI and adhesive strength (MPa) in a hot water resistance test. In all cases, the average wood fracture rate was 0%, and peeling occurred in the area where the adhesive was applied. The adhesive strength in the hot water resistance test was 0.26 MPa when 10% by mass of PEI was added, and the adhesive strength increased as the amount of PEI added increased. When 25% by mass of PEI was added, the strength exceeded 0.7 MPa, the standard value for JAS Class 2 ordinary plywood.

[0041] (Test 2) In this test, the relationship between the mass of polylysine and adhesiveness in a wet state was investigated. In this test, ε-polylysine (hereinafter also referred to as "εPL") was used as the polylysine. Aqueous solutions containing 5 mass% caffeic acid, 10, 20, 30, and 40 mass% polylysine in solid content terms, and the remainder gelatin were prepared in the same manner as in Test 1. Specifically, aqueous solutions with the following blending ratios in solid content terms were prepared. Aqueous solution of caffeic acid: 5% by mass, polylysine: 10% by mass, gelatin: 85% by mass Aqueous solution of caffeic acid: 5% by mass, polylysine: 20% by mass, gelatin: 75% by mass Aqueous solution of caffeic acid: 5% by mass, polylysine: 30% by mass, gelatin: 65% by mass Aqueous solution of caffeic acid: 5% by mass, polylysine: 40% by mass, gelatin: 55% by mass

[0042] The resulting compositions were all brownish, transparent solutions at temperatures above 37°C, and turned into brownish, transparent jellies at temperatures below room temperature. A sodium periodate aqueous solution was added to the resulting compositions, each containing 0.5 g of caffeic acid, polylysine, and gelatin in terms of solid content, in the same manner as in Test 1 to promote oxidation, thereby obtaining dark brown adhesive solutions. Furthermore, no mold growth was observed in these compositions even after storage for one month.

[0043] The resulting adhesive solution was used to conduct a normal test and a hot water resistance test similar to Test 1. In the normal test, the adhesive strength was 5 MPa or more in both cases, and the average wood fracture rate was 80% or more.

[0044] In Test 2, the same comparative examples as in Test 1 were used except for Comparative Example (iv). Comparative Example (iv) in Test 2 was the same as Comparative Example (iv) in Test 1 except that polylysine was used instead of PEI. In this example, the adhesive strength was 0.87 MPa in the normal test. In the hot water resistance test, the adhesive strength was 0.017 MPa, and the average wood fracture rate was 0%.

[0045] Figure 2 shows the relationship between the mass fraction (%) of polylysine and the adhesive strength (MPa) in the hot water resistance test. In the hot water resistance test, the average wood fracture rate was 0% in all cases, and peeling occurred in the area where the adhesive was applied. The adhesive strength in the hot water resistance test was 0.17 MPa when 10% by mass of polylysine was added, and the adhesive strength increased as the amount of polylysine added increased. When 30% by mass of polylysine was added, the strength was greater than 0.7 MPa, the standard value for JAS ordinary plywood type 2.

[0046] (Test 3) This test investigated the relationship between the type of polyphenol and adhesiveness when wet. This test differed from Test 2 in that a polyphenol other than caffeic acid (hereinafter also referred to as "CA") was used instead of caffeic acid, but otherwise the test was the same. The polyphenols used other than caffeic acid were 2,5-dihydroxybenzoic acid (hereinafter also referred to as "25DHBA"), 3,4-dihydroxyphenylacetic acid (hereinafter also referred to as "DOPAC"), 3-(3,4-dihydroxyphenyl)propionic acid (hereinafter also referred to as "DHCA"), and 3-(3,4-dihydroxyphenyl)-L-alanine (hereinafter also referred to as "LDOPA"). Meanwhile, 3,5-dihydroxybenzoic acid (hereinafter also referred to as "35DHBA") and tannic acid (hereinafter also referred to as "TA") were used as comparative examples. All compositions prepared in the same manner as Test 1 were brownish, transparent solutions at temperatures above 37°C and brownish, transparent jelly-like at temperatures below room temperature. The resulting composition, which contained 0.5 g of polyphenol, polylysine, and gelatin in total solids, was added with an aqueous sodium periodate solution in the same manner as in Test 1 to promote oxidation, yielding a dark brown adhesive solution. As a comparative example, 2',3',4'-trihydroxyacetophenone (hereinafter also referred to as "THAP") was used. Because the resulting composition gelled without the addition of sodium periodate, sodium periodate was not added. The adhesive using THAP was tested by heating the gel to 90°C to soften it, and then applying it to a wooden piece for adhesion testing.

[0047] 3 is a diagram showing the relationship between the type of polyphenol and the adhesive strength (MPa) in the hot water resistance test. The relationship between the examples and the comparative examples is as follows. (Example) LDOPA DHCA ·DOPAC 25DHBA (Comparative Example) 35DHBA ·TA THAP CA (without PEI): Contains only gelatin and caffeic acid, without PEI

[0048] In CA, LDOPA, DHCA, and DOPAC, the hydroxyl groups are in the ortho position. In 25DHBA, the hydroxyl groups are in the para position. On the other hand, in the comparative example, 35DHBA, the hydroxyl groups are in the meta position. Furthermore, tannic acid and THAP are compounds having three phenolic hydroxyl groups in the same molecule. From the results in Figure 3, it was found that when an aromatic compound having two phenolic hydroxyl groups in the same molecule, where the hydroxyl groups are in the ortho or para position, was used, the adhesiveness in a wet state was superior compared to when other polyphenols were used.

[0049] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or 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 appropriately deleted. [Industrial Applicability]

[0050] The composition of the present invention can be used, for example, as an adhesive or a coating agent, and has excellent adhesiveness when wet, making it industrially applicable as an adhesive or a coating agent.

Claims

1. Gelatin and a polycation selected from the group consisting of polyethyleneimine and polylysine; an aromatic compound having two phenolic hydroxyl groups in the same molecule, the phenolic hydroxyl groups being located at ortho or para positions; In terms of solid content, The gelatin content is 50% by mass or more and 80% by mass or less, The polycation is 10% by mass or more and 35% by mass or less, The aromatic compound is contained in an amount of 2% by mass or more and 10% by mass or less. composition.

2. 10. The composition of claim 1 , The gelatin content is 60% by mass or more and 70% by mass or less in terms of solid content. composition.

3. 10. The composition of claim 1 , The aromatic compound includes at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)-L-alanine, 3-(3,4-dihydroxyphenyl)propionic acid, 3,4-dihydroxyphenylacetic acid, and 2,5-dihydroxybenzoic acid. composition.

4. 10. The composition of claim 1 , The aromatic compound includes at least one selected from the group consisting of caffeic acid, 3-(3,4-dihydroxyphenyl)propionic acid, and 3,4-dihydroxyphenylacetic acid. composition.

5. An adhesive comprising the composition of claim 1.

6. A coating comprising the composition of claim 1.

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