Adhesives and bonding methods

Abstract

The purpose of the present invention is to provide an adhesive agent which is safe and has low environmental impact, and an adhering method which uses the adhesive agent. An adhesive agent according to the present invention is characterized by comprising, as active components, poly-γ-glutamic acid and a specific pyridinium compound. A method according to the present invention for adhering two adhesion targets is characterized by comprising: a step for either softening the adhesive agent according to the present invention on the surface of at least one of the adhesion targets, or adhering, onto the surface of at least one of the adhesion targets, the adhesive agent according to the present invention which has been softened; and a step for press-bonding, onto the softened adhesive agent on the surface of one of the adhesion targets, the other one of the adhesion targets.

Description

[Technical Field]

[0001] This invention relates to a safe and environmentally friendly adhesive and a bonding method using the adhesive. [Background technology]

[0002] Adhesives are substances used to join two objects, and in addition to natural adhesives such as starch paste, casein, and gum arabic, many synthetic adhesives have been developed for various purposes. Natural adhesives are generally applied to the objects to be bonded in the form of an aqueous solution or dispersion in water, and exhibit adhesive properties upon drying, making them highly safe. On the other hand, natural adhesives have the problem of low adhesive strength.

[0003] Synthetic adhesives generally exhibit high adhesive strength, such as curing through reactions that form covalent bonds. However, many require organic solvents as solvents, such as being used as solutions or dispersions of organic solvents, raising concerns about their environmental impact.

[0004] Therefore, there is a need for adhesives that exhibit sufficient bonding properties while being safe and having a low environmental impact.

[0005] For example, Patent Document 1 discloses surgical adhesives containing polyvalent metal salts of proteins and polycarboxylic acids, and Patent Document 2 discloses Ca of polyaspartic acid and polyglutamic acid. 2+ -Na + Adhesive formulations containing mixed salts and quaternary ammonium cationic salts have been disclosed. However, given that Patent Document 1 is for surgical use, the adhesive strength per unit area is only a few Pa, and the adhesive strength of Patent Document 2 is several grams to more than ten grams, the adhesive strength of these adhesives is considered insufficient.

[0006] Incidentally, the present inventors have developed a PGA ion complex containing poly-γ-glutamic acid (PGA) and a quaternary ammonium ion compound (Patent Document 3) and fibers composed of the PGA ion complex (Patent Document 4) as plastic materials exhibiting antibacterial and biodegradable properties. The PGA ion complex can inactivate not only bacteria and fungi but also viruses (Non-Patent Documents 1 and 2).

[0007] In recent years, the problem of microplastics, in which plastic materials are miniaturized without being decomposed and pollute the environment, has attracted attention. In contrast, the above-mentioned PGA ion complex is decomposed into PGA and a quaternary ammonium ion compound in an environment with a high ionic strength at the seawater level (Non-Patent Document 3). PGA is originally biodegradable, and some of the quaternary ammonium ion compounds exhibit antibacterial properties. However, since the concentration thereof rapidly decreases by being separated from PGA, it is considered to be biodegradable in the environment. Therefore, it can be said that the environmental load of the PGA ion complex is extremely low.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

[0010] Under the circumstances described above, the present invention aims to provide a safe and environmentally friendly adhesive and a bonding method using the adhesive. [Means for solving the problem]

[0011] The inventors diligently conducted research to solve the above problems. As a result, they discovered that the PGA ion complex, which they had already developed, is soluble in certain organic solvents but insoluble in water. However, it softens not only under heating but also, surprisingly, under hydrothermal conditions, and exhibits excellent adhesive properties, thus making it usable as an adhesive. This led to the completion of the present invention. The present invention is described below.

[0012] [1] An adhesive characterized by containing poly-γ-glutamic acid and a pyridinium compound represented by the following formula (I) as active ingredients. [ka] [In the formula, X may have a substituent α and represents a heteroaromatic ring group containing a pyridinium ring. R 1 C 6-20 This refers to a monovalent aliphatic hydrocarbon group, or a group represented by the following formula (II): [ka] (In the formula, Y represents a heteroaromatic ring group which may have a substituent β and contains a pyridinium ring, and R 2 represents a divalent aliphatic hydrocarbon group, and the substituent β represents one or more substituents selected from the group consisting of a C 6-20 alkyl group, a C 1-6 alkoxy group, a hydroxyl group, an amino group, a halogeno group, a cyano group, and a nitro group.) The substituent α represents one or more substituents selected from the group consisting of a C 1-6 alkyl group, a C 1-6 alkoxy group, a hydroxyl group, an amino group, a halogeno group, a cyano group, and a nitro group.) [2] The adhesive according to [1] above, wherein R 1 is a monovalent aliphatic hydrocarbon group, and the molar ratio of the pyridinium compound represented by the above formula (I) to glutamic acid constituting poly-γ-glutamic acid is 0.8 or more and 1.2 or less. [3] The adhesive according to [1] above, wherein R 1 is a group represented by the above formula (II), and the molar ratio of the pyridinium compound represented by the above formula (I) to glutamic acid constituting poly-γ-glutamic acid is 0.4 or more and 0.6 or less. [4] The adhesive according to any one of [1] to [3] above, wherein X is a pyridinium group which may have a substituent α. [5] The adhesive according to any one of [1] to [4] above, wherein X is a quinolinium group which may have a substituent α, and Y is a quinolinium group which may have a substituent β.

[0013] [6] A method for bonding two adherends, comprising: a step of softening an adhesive on the surface of at least one of the adherends or attaching a softened adhesive onto the surface of at least one of the adherends, and a step of pressing the other adherend against the softened adhesive on the surface of one of the adherends, wherein the adhesive contains poly-γ-glutamic acid and a pyridinium compound represented by the above formula (I) as active ingredients. ​​​[7] R 1 C 10-20 The method according to [6], wherein the monovalent aliphatic hydrocarbon group has a molar ratio of the pyridinium compound represented by formula (I) to glutamic acid constituting poly-γ-glutamic acid of 0.8 or more and 1.2 or less. [8] R 1 The method according to [6], wherein is a group represented by formula (II) above, and the molar ratio of the pyridinium compound represented by formula (I) above to glutamic acid constituting poly-γ-glutamic acid is 0.4 or more and 0.6 or less. [9] The method according to any one of the above [6] to [8], wherein X is a pyridinium group which may have a substituent α.

[10] The method according to any one of the above [6] to [9], wherein X is a quinolinium group which may have a substituent α and Y is a quinolinium group which may have a substituent β.

[11] The method according to any of the above [6] to

[10] , wherein the adhesive is softened by hydrothermal conditions.

[12] The method according to

[11] , wherein the adhesive is softened by water vapor or steam.

[0014] In this disclosure, "C 6-20 A "monovalent aliphatic hydrocarbon group" refers to a linear or branched monovalent aliphatic hydrocarbon group having 6 to 20 carbon atoms, for example, C 6-20 Alkyl alkyl group, C 6-20 Alkenyl group, and C 6-20 An example is the alkynyl group. 6-20 Examples of alkyl groups include n-hexyl, isohexyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, and n-icosyl. Preferably C 8-18 It is an alkyl group, and a linear alkyl group is preferred. 6-20 Examples of alkenyl groups include hexenyl, octenyl, decenyl, dodecenyl, tetradecenyl, hexadecenyl, octadecenyl, and icocenyl. 8-18 An alkenyl group is preferred. 6-20Examples of alkynyl groups include hexynyl, octinyl, desinyl, dodecinyl, tetradecinyl, hexadesinyl, octadecinyl, and icosinyl. 8-18 Alkynyl groups are preferred.

[0015] "C 6-20 The "divalent aliphatic hydrocarbon group" is the above C 6-20 This refers to a divalent group corresponding to a monovalent aliphatic hydrocarbon group, for example, C 6-20 Alkanediyl group, C 6-20 Alkenediyl group, and C 6-20 One example is the alkynediyl group. 6-20 Examples of alkanediyl groups include n-hexanediyl, isohexanediyl, n-octanediyl, n-decanediyl, n-dodecanediyl, n-tetradecanediyl, n-hexadecanediyl, n-octadecanediyl, and n-icosanediyl. Preferably C 8-18 It is an alkanediyl group, and a linear alkanediyl group is preferred. 6-20 Examples of alkenediyl groups include hexendiyl, octendiyl, decendiyl, dodecendiyl, tetradecendiyl, hexadecendiyl, octadecendiyl, icosendiyl, etc. 8-18 Alkenediyl group is preferred. 6-20 Examples of alkynediyl groups include hexindiyl, octindiyl, decindiyl, dodecindiyl, tetradecindiyl, hexadecindiyl, octadecindiyl, icosindiyl, and C 8-18 Alkynediyl groups are preferred.

[0016] "C 1-6 An "alkyl group" refers to a linear or branched monovalent saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, and n-hexyl. Preferably C 1-4 It is an alkyl group, more preferably C 1-2 It is an alkyl group, and more preferably a methyl group.

[0017] "C 1-6 An "alkoxy group" refers to a linear or branched saturated aliphatic hydrocarbon oxy group having 1 to 6 carbon atoms. Examples include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, t-butoxy, n-pentoxy, n-hexoxy, etc., preferably C 1-4 It is an alkoxy group, more preferably C 1-2 It is an alkoxy group.

[0018] The "amino group" includes an unsubstituted amino group (-NH2) as well as one of the above C 1-6 Mono-C substituted with alkyl groups 1-6 Alkylamino group and two above C 1-6 diC substituted with alkyl group 1-6 The molecule shall contain an alkylamino group. Such amino groups include unsubstituted amino acids; mono-C amino acids such as methylamino, ethylamino, n-propylamino, isopropylamino, n-butylamino, isobutylamino, t-butylamino, n-pentylamino, and n-hexylamino. 1-6 Alkylaminos; such as dimethylamino, diethylamino, di(n-propyl)amino, diisopropylamino, di(n-butyl)amino, diisobutylamino, di(n-pentyl)amino, di(n-hexyl)amino, ethylmethylamino, methyl(n-propyl)amino, n-butylmethylamino, ethyl(n-propyl)amino, n-butylethylamino, etc. 1-6 Examples include alkylamino groups. Preferably, they are unsubstituted amino groups.

[0019] When a heteroaromatic ring group containing a pyridinium ring has substituent α or substituent β, the number of substituents is not particularly limited as long as they are substituted, but for example, it can be 1 or more and 10 or less, preferably 5 or less or 3 or less, and more preferably 1 or 2. When there are 2 or more substituents, the multiple substituents α or β may be the same or different from each other. [Effects of the Invention]

[0020] The active ingredient of the adhesive according to the present invention is a complex of poly-γ-glutamic acid, which constitutes the threads of natto (fermented soybeans), and a pyridinium compound, which is used as an antibacterial agent, and therefore can be said to be extremely safe. Furthermore, the adhesive according to the present invention, while composed of naturally derived ingredients, exhibits excellent adhesive properties, and its adhesive strength can be adjusted by selecting the pyridinium compound. Furthermore, the adhesive according to the present invention decomposes into poly-γ-glutamic acid and pyridinium compounds under high ionic strength conditions at seawater levels. Since poly-γ-glutamic acid is an amino acid polyester, it exhibits biodegradability, and although pyridinium compounds are used as antibacterial agents, they cannot exert antibacterial properties when released into the environment at low concentrations and are also biodegradable. In addition, since the adhesive according to the present invention softens under hydrothermal conditions, there is no need to use organic solvents. Therefore, it can be said that the environmental impact of the adhesive according to the present invention is small. As described above, the adhesive according to the present invention is safe and has a low environmental impact, making it highly advantageous from an industrial perspective. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a photograph showing that a cut porcelain mortar can be used without any problems after being bonded together with the adhesive according to the present invention. [Figure 2] Figure 2 is a graph showing the adhesive durability of commercially available cyanoacrylate-based general-purpose adhesives. [Figure 3] Figure 3 is a graph showing the adhesive durability of the PGA-DEQ ion complex according to the present invention. [Figure 4] Figure 4 is a graph showing the adhesive durability of the PGA-HDP ion complex according to the present invention. [Modes for carrying out the invention]

[0022] The adhesive according to the present invention contains poly-γ-glutamic acid and a pyridinium compound represented by formula (I) as active ingredients. Hereinafter, poly-γ-glutamic acid will be abbreviated as "PGA," the pyridinium compound represented by formula (I) will be abbreviated as "pyridinium compound (I)," and the complex of PGA and pyridinium compound (I) may be abbreviated as "PGA ion complex."

[0023] Unlike typical polypeptides, PGA has a unique chemical structure in which the α-carboxyl group and α-amino group form an amide bond, rather than the α-carboxyl group and α-amino group forming a peptide bond, as shown in the formula below. It is known as the main component of the threads found in natto (fermented soybeans).

[0024] [ka]

[0025] The type of PGA is not particularly limited. For example, it can consist only of L-glutamic acid, only of D-glutamic acid, or contain both, and any of these can be used. However, a higher proportion of one component results in superior stereoregularity and higher strength, and if thoroughly dried, it will also exhibit a melting point (approximately 150°C). This melting point becomes more clearly defined by forming an ionic complex by ionically bonding it with a pyridinium compound, as described in the present invention. Furthermore, since the L-glutamic acid-based PGA has superior biodegradability, it is preferable to use one with an L-glutamic acid content of 90 mol% or more. Preferably, this percentage is 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more or 99.5 mol% or more. The upper limit of this percentage is 100 mol%, in which case the PGA consists only of L-glutamic acid.

[0026] While there are no particular restrictions on the molecular size of the PGA used, those with an average molecular mass of 10 kD or more are preferred. Generally, the larger the molecular size, the higher the performance, such as strength. On the other hand, excessively large molecular sizes of PGA are expensive to manufacture and can be technically difficult to produce, so they are usually kept below 1,000 kD. The average molecular mass can be determined by referring to the catalog value of the PGA product being used, if available, but if there is no catalog value, it can be measured by a standard method such as size exclusion chromatography.

[0027] PGA can be used if it is commercially available, or it can be manufactured separately. However, since polymerizing glutamic acid under normal conditions yields poly-α-glutamic acid, it is preferable to biosynthesize it using microorganisms. One microorganism capable of producing PGA with a large molecular size is the hyperhalophilic archaeon Natrialba aegyptiaca.

[0028] The pyridinium compound (I) used in this invention has a hydrophilic pyridinium group and a hydrophobic long-chain alkyl group in its molecule, and is commonly used as a surfactant, as well as an antibacterial agent, antifungal agent, and antiviral agent. The pyridinium group of pyridinium compound (I) ionically bonds with the carboxyl group of PGA, forming a PGA ion complex, which is a complex that is insoluble in water at least.

[0029] In pyridinium compound (I), examples of heteroaromatic ring groups containing a pyridinium ring include the pyridinium group itself, as well as heteroaromatic ring groups in which a benzene ring, pyridine ring, or pyridinium ring is fused to a pyridinium ring, such as a quinolinium group, isoquinolinium group, naphthyridinium group, phenantridinium group, and acridinium group. A pyridinium group or a quinolinium group is preferred.

[0030] In the adhesive according to the present invention, the adhesive strength can be adjusted by selecting the pyridinium compound (I). For example, R 1 C 6-20Adhesives containing an ionic complex of a monovalent aliphatic hydrocarbon group, pyridinium compound (I), and PGA as active ingredients have relatively weak adhesive strength, making them suitable for bonding packaging bags that are intended to be opened, or as disassemblable adhesives that can be peeled off as needed. For example, since the adhesive according to the present invention is safe, it can be used to bond food packaging bags. Furthermore, because it can be decomposed in high-salt environments such as high-brine water, it can also be applied to industrial uses such as the manufacturing of products intended for recycling or the temporary fixing of processed objects. 1 In adhesives that use an ionic complex of a pyridinium compound (I) with (II) as the base and PGA as the active ingredient, the adhesive strength is relatively high, probably because the PGA is crosslinked two-dimensionally and three-dimensionally.

[0031] R 1 C 6-20 Examples of pyridinium compounds (I) that have a monovalent aliphatic hydrocarbon group include n-hexylpyridinium, isohexylpyridinium, n-octylpyridinium, n-decylpyridinium, n-dodecylpyridinium, n-tetradecylpyridinium, n-hexadecylpyridinium, n-octadecylpyridinium, and n-icosylpyridinium. In particular, hexadecylpyridinium (cetylpyridinium) is used as an antibacterial agent.

[0032] R 1 Examples of pyridinium compounds (I) in which group (II) are decalinium(1,1'-decamethylenebis(4-aminoquinaldinium)) and N,N'-hexamethylenebis(4-carbamoyl-1-decylpyridinium).

[0033] The PGA ion complex according to the present invention is preferably one in which the PGA is sufficiently modified with a pyridinium compound (I) in order to overcome the drawbacks of PGA, such as excessive hydrophilicity. More specifically, the pyridinium compound (I) is R 1 as C 6-20When a monovalent aliphatic hydrocarbon group is present, the proportion of pyridinium compound (I) in the PGA ion complex is preferably 0.5 molar times or more, more preferably 0.6 molar times or more, even more preferably 0.8 molar times or more, and preferably 1.0 molar time or less, relative to the glutamic acid constituting the PGA. 1 When the compound has group (II), the proportion of pyridinium compound (I) in the PGA ion complex is preferably 0.25 molar times or more, more preferably 0.3 molar times or more, even more preferably 0.4 molar times or more, and preferably 0.5 molar times or less, relative to the glutamic acid constituting the PGA.

[0034] In particular, a PGA ion complex containing equimolar or nearly equimolar amounts of glutamic acid constituting PGA and pyridinium rings constituting pyridinium compound (I) is preferred. PGA is inherently highly hydrophilic, continuously absorbing water without limit, gelling, and eventually becoming an aqueous solution. While techniques for modifying the side-chain carboxyl groups of PGA have been known in the past, it has been impossible to sufficiently modify the numerous carboxyl groups present in the structure, so gelation and aqueous solution formation were unavoidable even after modification. In contrast, the present invention allows for extremely simple and sufficient modification of the side-chain carboxyl groups of PGA, but naturally, if the amount of pyridinium compound (I) used is insufficient, PGA cannot be sufficiently modified. On the other hand, if the pyridinium rings constituting pyridinium compound (I) in the PGA ion complex are equimolar or nearly equimolar with the glutamic acid constituting PGA, i.e., the side-chain carboxyl groups, PGA can be sufficiently modified. Here, "approximately equimolar" means that the number of moles of both is approximately equal, but more specifically, it means that the pyridinium ring constituting pyridinium compound (I) is 0.8 molar times or more and 1.2 molar times or less relative to glutamic acid constituting PGA, and especially 0.9 molar times or more and 1.1 molar times or less. Specifically, pyridinium compound (I) is R 1 as C 6-20When a monovalent aliphatic hydrocarbon group is present, the proportion of pyridinium compound (I) in the PGA ion complex is preferably 0.8 or more and 1.2 or less relative to the glutamic acid constituting PGA, and pyridinium compound (I) is R 1 When the compound has group (II), it is preferable that the proportion of pyridinium compound (I) in the PGA ion complex is 0.4 or more and 0.6 or less relative to the glutamic acid that constitutes PGA.

[0035] Pyridinium compound (I) may be used alone or as a mixture of two or more types.

[0036] The PGA ion complex, which is the active ingredient of the adhesive according to the present invention, can be manufactured very easily by simply mixing PGA and pyridinium compound (I) in a solvent.

[0037] Water is preferred as the solvent used here. This is because it can dissolve the PGA, the starting material, well, and because the PGA ion complex is insoluble in water, it is convenient for isolating and purifying the target product after the reaction. However, depending on the water solubility of pyridinium compound (I), water-miscible organic solvents such as alcohols like methanol or ethanol; ethers like diethyl ether or THF; or amides like dimethylformamide or dimethylacetamide may be added to the reaction solution to increase their solubility. However, considering the separation of the PGA complex after the reaction is complete, it is preferable to use only water as the solvent.

[0038] As the raw material, PGA may be used in the form of its salts. Examples of such salts include alkali metal salts such as sodium salt and potassium salt; and alkaline earth metal salts such as calcium salt and magnesium salt. Furthermore, even when using salts, it is not necessary for all carboxyl groups to be salts; only some of them may be salts. However, since polyvalent metal salts such as alkaline earth metal salts may have low solubility in water, it is preferable to use free PGA or monovalent metal salts of PGA.

[0039] Pyridinium compound (I) usually exists as a halide salt. Therefore, in this invention, the salt of pyridinium compound (I) can be added directly to the reaction solution, or the salt can be dissolved in an aqueous solvent before being added. It is preferable to use a sufficient amount of pyridinium compound (I) relative to PGA in order to adequately modify PGA.

[0040] Since the PGA ion complex of the present invention is water-insoluble, it can be easily separated from the aqueous solvent, and therefore the concentrations of each component in the reaction solution are not particularly limited. For example, the concentration of PGA in the reaction solution can be approximately 0.5 w / v% or more and 10 w / v% or less, and the concentration of pyridinium compound (I) can be approximately 1.0 w / v% or more and 10 w / v% or less.

[0041] The reaction solution is preferably heated to a moderate temperature to promote the formation of the PGA complex. The heating temperature can be, for example, between 40°C and 80°C. The reaction time can be adjusted as appropriate, but is usually between 1 hour and 20 hours.

[0042] Since the PGA ion complex of the present invention is water-insoluble, it can be easily separated from the aqueous solvent by filtration or centrifugation. Furthermore, the separated PGA ion complex can be washed with water to remove excess PGA or pyridinium compound (I) and other salts. The aqueous solvent can also be easily removed by washing with acetone or the like.

[0043] The separated PGA ion complex is preferably dried by conventional methods such as vacuum drying or freeze-drying.

[0044] The PGA ion complex according to the present invention is useful as an active ingredient in adhesives. Specifically, the PGA ion complex according to the present invention is softened on the surface of the object to be bonded, or the softened PGA ion complex is applied to the surface of the object to be bonded.

[0045] The inventors of the present invention have discovered that, despite being insoluble in water, the PGA ion complex according to the present invention unexpectedly softens under hydrothermal conditions. For example, the PGA ion complex according to the present invention can be softened by immersing it in water at a temperature of approximately 60°C to 100°C, or by applying steam or vapor.

[0046] More specifically, the adhesive of the present invention can be placed on the surface of at least one of the objects to be bonded, and then softened by heating or by applying steam or hot air, or by heating or by applying hot water, steam or hot air, and then attached to the surface of at least one of the objects to be bonded. After that, the other object to be bonded can be pressed onto the softened adhesive and left to stand. Alternatively, the adhesive of the present invention can be placed on the surface of at least one of the objects to be bonded, the other object to be bonded can be placed on top of the adhesive, the adhesive can be softened by heating or the like, and then left to stand.

[0047] The material of the object to be bonded is not particularly limited and includes, for example, wood; ceramics such as pottery and porcelain; metals such as iron, copper, zinc, aluminum, gold, silver, and alloys; glass; and plastics such as polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP). Furthermore, the adhesive according to the present invention may be capable of bonding not only objects of the same type but also objects of different types.

[0048] The conditions for setting the bonded objects after pressing them together using the adhesive according to the present invention can be adjusted as appropriate. For example, the setting temperature can be 0°C or higher and 50°C or lower, or it may be room temperature. The setting time can be 1 hour or higher and 48 hours or lower, and preferably 12 hours or higher and 24 hours or lower.

[0049] The adhesive strength of the adhesive according to the present invention can be adjusted mainly by the selection of pyridinium compound (I). For example, R 1 C 6-20Adhesives containing an ionic complex of a monovalent aliphatic hydrocarbon group, pyridinium compound (I), and PGA as active ingredients have relatively weak adhesive strength, making them suitable for bonding packaging bags that are intended to be opened, or as disassemblable adhesives that can be peeled off as needed. 1 Adhesives containing a composite of a pyridinium compound (I) with (II) as the base and PGA as the active ingredient can be used as adhesives that exhibit high adhesive strength.

[0050] The PGA ion complex, the active ingredient of the adhesive according to the present invention, is a complex of PGA, which constitutes the threads of natto (fermented soybeans), and a pyridinium compound used as an antibacterial agent, making it extremely safe and suitable for use in food and its packaging, for example. Furthermore, the adhesive strength can be adjusted by selecting the pyridinium compound. Moreover, the adhesive according to the present invention decomposes in a high ionic strength environment at the level of seawater, with PGA exhibiting biodegradability, and the pyridinium compound at low concentrations can also be biodegraded. In addition, the adhesive according to the present invention softens under hydrothermal conditions, eliminating the need to use organic solvents. Therefore, the environmental impact of the adhesive according to the present invention is extremely low.

[0051] This application claims the benefit of priority based on Japanese Patent Application No. 2021-59214, filed on March 31, 2021. The entire specification of Japanese Patent Application No. 2021-59214, filed on March 31, 2021, is incorporated herein by reference. [Examples]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0053] Example 1: Production of PGA-DEQ ion complex An aqueous solution of decalinium chloride (DEQ) was obtained by adding 1 g of decalinium chloride (DEQ) hydrate powder to 100 mL of distilled water and dissolving it by heating to approximately 80-100°C. 100 mL of a 0.5% by mass PGA aqueous solution was heated to approximately 80°C, and the DEQ aqueous solution was added while stirring. At this time, the amount of DEQ added was 1 / 2 mole relative to the carboxyl groups contained in the total amount of PGA. After confirming that a white substance, the PGA-DEQ ion complex, had formed in the mixed solution, the solution was filtered by suction, and the obtained PGA-DEQ ion complex was washed with warm water at approximately 80-100°C. The obtained PGA-DEQ ion complex was frozen overnight at -80°C, then transferred to a freeze-dryer and dried until there was no further weight loss.

[0054] Example 2: Production of PGA-HDP ion complex An aqueous solution of hexadecylpyridinium (HDP) bromide hydrate was obtained by adding 3 g of powder to 100 mL of distilled water and dissolving it by heating to approximately 60-100°C. 100 mL of 1% by mass PGA aqueous solution was heated to approximately 60°C, and the HDP aqueous solution was added while stirring. At this time, the amount of HDP added was equimolar to the carboxyl groups contained in the total amount of PGA. After confirming that a white substance, the PGA-HDP ion complex, had formed in the mixed solution, the mixture was filtered by suction, and the obtained PGA-DEQ ion complex was washed with warm water at approximately 60-100°C. The obtained PGA-DEQ ion complex was frozen overnight at -80°C, then transferred to a freeze-dryer and dried until there was no further weight loss.

[0055] Test Example 1: Adhesion Test to Wood The adhesive strength of the PGA-DEQ ion complex powder produced in Example 1 and the PGA-HDP ion complex powder produced in Example 2 was measured using a tensile testing machine. Specifically, the PGA-DEQ ion complex was softened by adding twice its mass of 90°C hot water and heating for 15 minutes. After that, it was applied to a wood material, stacked with other wood materials, and hot-pressed at 90°C and 0.1 MPa for 5 minutes. Then, it was left to stand for 48 hours. For the PGA-HDP ion complex, it was added in solid form to the bonding surface of the wood material, stacked with other wood materials, and then heat-pressed in the same manner. After that, it was left to stand for 48 hours. The wood materials bonded as described above were fixed to a tensile testing machine, and their adhesive strength was measured. The results are shown in Table 1.

[0056] [Table 1]

[0057] As shown in Table 1, the PGA-DEQ ion complex according to the present invention exhibited adhesive strength equivalent to that of commercially available synthetic adhesives, specifically vinyl acetate resin emulsion-type adhesives. On the other hand, since the adhesive strength of the PGA-HDP ion complex according to the present invention was relatively low, it is conceivable that it could be applied to adhesives where peeling is expected, such as in food packaging.

[0058] Test Example 2: Adhesion Test to Ceramics A porcelain pestle approximately 18 cm long (product number: 6-549-04, manufactured by AS ONE Corporation, SiO2: approximately 67%, Al2O3: approximately 21%) was cut in the middle by impact with a blunt object (Figure 1(1)). The PGA-DEQ ion complex powder (0.1 g) prepared in Example 1 was softened by exposing it to hot water for 30 seconds, and 20 mg / cm² was applied to one side of the fracture surface of the pestle. 2 The material was applied in the following proportions (Figure 1(1)). Next, the two fractured surfaces were pressed together manually and left to stand at room temperature for 24 hours (Figure 1(2)). When 5.0g of activated carbon was placed in a mortar and ground with a mortar and pestle attached to it, it was successfully finely ground without any problems (Figure 1(3)).

[0059] Test Example 3: Adhesion Durability Test Cross-section of the combined materials to be bonded, as shown in Figure 2 (approximately 1 cm). 230 mg of cyanoacrylate-based general-purpose adhesive ("Aron Alpha," manufactured by Toagosei Co., Ltd., JIS S 6040 Type 6A) was dropped onto the material and pressed into place. The adhesive was dropped or applied to the cross-section of X in the "X / Y" combination of materials to be bonded shown in Figures 2-4. Five bonding samples were prepared for each combination. The obtained adhesive samples were placed in a small environmental test chamber ("SH-262," manufactured by ESPEC Corporation) and incubated at 85°C and 95% humidity. They were removed daily and tested for durability. Specifically, one of the bonded materials was grasped and lifted, and the number of samples in which the other bonded material peeled off and fell was determined. The adhesion retention rate was then calculated using the following formula. The results are shown in Figure 2. Adhesion retention rate (%) = 100 - [(Number of detached samples) / 5] × 100

[0060] Furthermore, the same tests were conducted using PGA-DEQ ion complex or PGA-HDP ion complex instead of cyanoacrylate-based general-purpose adhesives. Specifically, 30 mg of each ion complex was mixed with hot water at 60-100°C and heated for 20-60 seconds until softened. After softening, a 1 cm cross-section of the bonded material X for bonded material combination X / Y shown in Figure 3 or Figure 4 was measured. 2 The adhesion retention rate was calculated in the same manner as above, except that the sample was applied to the substrate and brought into close contact with the substrate Y to obtain an adhesion sample. The results for the PGA-DEQ ion complex are shown in Figure 3, and the results for the PGA-HDP ion complex are shown in Figure 4. In Figures 2-4, "PET" represents polyethylene terephthalate, "PC" represents polycarbonate, and "wood" represents cypress (Chamaecyparis obtusa).

[0061] As shown in Figure 2, in the case of commercially available cyanoacrylate-based general-purpose adhesives, delamination of the bonded samples began to be observed in more than half of the bonded material combinations after 2 or 3 days from the start of the test, and in some cases, all five bonded samples had delaminated after 2 to 5 days. On the other hand, as shown in Figure 3, in the case of the PGA-DEQ ion complex, no delamination was observed in any of the bonded samples until the third day, and ultimately, only the stainless steel / wood combination showed complete delamination of all five bonded samples. As shown in Figure 4, no delamination was observed in any of the bonded samples using the PGA-HDP ion complex. From the results above, it has been clearly demonstrated that the adhesive according to the present invention has significantly superior adhesive durability compared to commercially available cyanoacrylate-based general-purpose adhesives.

Claims

1. A method for bonding two objects to be bonded, A step of softening the adhesive on the surface of at least one of the objects to be bonded by hydrothermal conditions, or applying the adhesive softened by hydrothermal conditions to the surface of at least one of the objects to be bonded, The process includes a step of pressing one of the objects to be bonded onto the softened adhesive on the surface of one of the objects to be bonded, A method characterized in that the above adhesive contains poly-γ-glutamic acid and a pyridinium compound represented by the following formula (I) as active ingredients. 【Chemistry 1】 [In the formula, X may have a substituent α and represents a heteroaromatic ring group containing a pyridinium ring. R 1 C 6-20 This indicates a monovalent aliphatic hydrocarbon group or a group represented by the following formula (II): 【Chemistry 2】 (In the formula, Y may have a substituent β and represents a heteroaromatic ring group containing a pyridinium ring, R 2 is C 6-20 It exhibits a divalent aliphatic hydrocarbon group, and the substituent β is C 1-6 alkyl group, C 1-6 (This represents one or more substituents selected from the group consisting of alkoxy groups, hydroxyl groups, amino groups, halogeno groups, cyano groups, and nitro groups.) The heteroaromatic ring group containing the pyridinium ring described above is selected from pyridinium, quinolinium, isoquinolinium, naphthyridinium, phenantridinium, and acridinium groups. The substituent α is C 1-6 alkyl group, C 1-6 This represents one or more substituents selected from the group consisting of alkoxy groups, hydroxyl groups, amino groups, halogeno groups, cyano groups, and nitro groups.

2. R 1 is C 10-20 a monovalent aliphatic hydrocarbon group, and the molar ratio of the pyridinium compound represented by the above formula (I) to glutamic acid constituting poly-γ-glutamic acid is 0.8 or more and 1.2 or less. The method according to claim 1.

3. R 1 The method according to claim 1, wherein is a group represented by formula (II) above, and the molar ratio of the pyridinium compound represented by formula (I) above to glutamic acid constituting poly-γ-glutamic acid is 0.4 or more and 0.6 or less.

4. The method according to any one of claims 1 to 3, wherein X is a pyridinium group which may have a substituent α.

5. The method according to any one of claims 1 to 4, wherein X is a quinolinium group which may have a substituent α, and Y is a quinolinium group which may have a substituent β.

6. The method according to any one of claims 1 to 5, wherein the adhesive is softened by water vapor or steam.

Images