Adhesive materials

Abstract

To provide an adhesive material having high stability over time.SOLUTION: An adhesive material includes (A) a polymer which includes a structural unit (a1) having a catechol skeleton with all or some of hydroxy groups protected by protecting groups, and a structural unit (a2) having an epoxy group, and (B) a deprotection agent which protects a protecting group. The adhesive material is suitable for a primer and also suitable for an adhesive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive material preferably used as a primer or adhesive in the bonding of articles, an article bonded using this adhesive material, and a polymer preferably applied to the adhesive material. [Background technology]

[0002] Attempts have been made to use polymers containing a catechol skeleton as constituent materials for adhesives and primers. Although the detailed mechanism is still under discussion, it is thought that the two hydroxyl groups in the catechol skeleton interact with the substrate (such as a metal substrate) to contribute to improved adhesion.

[0003] For example, Non-Patent Document 1 describes the evaluation of metal adhesion using a copolymer of glycidyl methacrylate and N-(3,4-dihydroxyphenethyl)methacrylamide (containing a catechol skeleton).

[0004] As another example, Patent Document 1 describes a polymer in which at least three types of side chains (first, second, and third side chains) are bonded to a main chain made of polyacrylate, which is useful as an underwater adhesive. The first side chain has a structure derived from the monomer constituting the polyacrylate. Hydrophilic or hydrophobic functional groups or atomic groups may be bonded to the end of this side chain via a linker moiety. The second side chain has a catecholic hydroxyl group at its end, which may be modified. Furthermore, the third side chain has a functional group or atomic group that modifies the polymer or imparts a predetermined function to the polymer.

[0005] As yet another example, Patent Document 2 describes an adhesive hydrogel comprising a water-soluble main chain monomer, a crosslinking agent, a polymerization initiator, and an adhesive monomer having a catechol group in its side chain. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2020-011923 [Patent Document 2] International Publication No. 2016 / 190400 [Non-Patent Document]

[0007] [Non-Patent Document 1] ACS Appl. Polym. Mater. 2020, 2, 4, 1500-1507 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] The catechol structure is easily oxidized in air. Therefore, an adhesive material using a material having a catechol skeleton has poor stability over time, and the pot life of the adhesive material tends to be short.

[0009] The present invention has been made in view of such circumstances. One object of the present invention is to provide an adhesive material having good stability over time. [Means for Solving the Problems]

[0010] The inventors of the present invention have completed the invention provided below and solved the above problems.

[0011] According to the present invention, a polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxy groups are protected by a protecting group and a structural unit (a2) having an epoxy group, a deprotecting agent for deprotecting the protecting group, and an adhesive material containing the same is provided.

[0012] Also, according to the present invention, an adhesive material containing a polymer having a structural unit represented by the following general formula (1') It will be provided. In general formula (1'), R 1 'and R 2 Each of these is independently a protecting group for a hydrogen atom or a hydroxyl group. L' is a single bond, alkylene group, arylene group, carbonyl group, ether group, or a divalent group consisting of two or more of these. R is either a hydrogen atom or a methyl group.

[0013] [ka]

[0014] Furthermore, according to the present invention, An article in which a first member and a second member are bonded together using the above-mentioned adhesive material. It will be provided.

[0015] Furthermore, according to the present invention, A polymer having a structural unit represented by the following general formula (1') and a structural unit having an epoxy group. It will be provided. In general formula (1'), R 1 'and R 2 Each of these is independently a protecting group for a hydrogen atom or a hydroxyl group. L' is a single bond, alkylene group, arylene group, carboxyl group, carbonyl group, ether group, or a divalent group consisting of two or more of these. R is either a hydrogen atom or a methyl group.

[0016] [ka] [Effects of the Invention]

[0017] According to the present invention, an adhesive material with good long-term stability is provided. [Brief explanation of the drawing]

[0018] [Figure 1] This is the 1H-NMR spectrum measured in the example. [Figure 2] This is the 1H-NMR spectrum measured in the example. [Figure 3] This is the 1H-NMR spectrum measured in the example. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0020] In this specification, the notation "X~Y" in descriptions of numerical ranges means "X or greater and Y or less" unless otherwise specified. For example, "1~5 mass%" means "1 mass% or greater and 5 mass% or less".

[0021] In this specification, when a group (atomic group) is not specified as substituted or unsubstituted, it includes both unsubstituted and substituted groups. For example, "alkyl group" includes not only unsubstituted alkyl groups but also substituted alkyl groups. In this specification, unless otherwise specified, the term "organic group" refers to an atomic group obtained by removing one or more hydrogen atoms from an organic compound. For example, "monovalent organic group" refers to an atomic group obtained by removing one hydrogen atom from any organic compound.

[0022] <Adhesive material> The adhesive material of this embodiment is A polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, and a structural unit (a2) having epoxy groups, • Deprotecting agents that remove the protecting group, Includes.

[0023] As mentioned above, conventional adhesive materials using materials with a catechol skeleton have poor stability over time. Therefore, the inventors have improved the stability over time by using a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, and by using this in combination with a deprotecting agent. When using adhesive materials, it is believed that good adhesion is obtained when the catechol skeleton portion, which has been deprotected by the protecting groups, interacts with the substrate (typically a metal substrate).

[0024] The following provides a more detailed explanation of polymers, deprotecting agents, and other related topics.

[0025] (polymer) • Structural unit (a1) The protecting group that protects the hydroxyl group of the catechol skeleton in structural unit (a1) is not particularly limited as long as it can be deprotected with a deprotecting agent. From the perspective of ease of synthesis, balance between stability before deprotection and ease of deprotection, the protecting group is preferably at least one selected from the group consisting of acyl groups and alkoxycarbonyl groups. The acyl group is a group represented as Rx-CO-, where Rx can preferably be an alkyl group, an alicyclic group, an aryl group, an aralkyl group, etc. The number of carbon atoms in Rx is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. The alkoxycarbonyl group is a group represented as Rx-O-CO-, and the specific form of Rx is the same as that of the acyl group described above.

[0026] The structural unit (a1) preferably includes a structural unit represented by the following general formula (1).

[0027] [ka]

[0028] In general formula (1), R 1 and R 2 These are, independently, protecting groups for hydroxyl groups. L is a single bond or a divalent linking group, R is a hydrogen atom or a methyl group.

[0029] R 1 and R 2 Specific examples of the protecting groups for the hydroxy groups of R and R are, as described above, preferably at least any one selected from the group consisting of an acyl group and an alkoxycarbonyl group. R 1 and R 2 At least one of them is usually a protecting group for a hydroxy group, preferably both R 1 and R 2 are protecting groups for hydroxy groups. -OR 1 and -OR 2 are preferably present at positions ortho to each other. The divalent linking group of L can be, for example, a single bond, an alkylene group, an arylene group, a carbonyl group, an ether group, an imino group, and a divalent group formed by combining two or more of these. L is preferably a single bond. When L is a single bond, the distance between the hydroxy group interacting with the substrate and the polymer main chain becomes closer, and it is considered that the polymer can interact more strongly with the substrate. R is preferably a hydrogen atom.

[0030] The ratio of the structural unit (a1) in the polymer is, from the viewpoint of the balance of various properties such as adhesion and storage stability, for example, 50 mol% or more, preferably 60 to 95 mol%, more preferably 75 to 80 mol%.

[0031] · Structural unit (a2) The structural unit (a2) is not particularly limited as long as it has an epoxy group. Specifically, the structural unit (a2) can include a structural unit represented by the following general formula (2).

[0032]

Chemical formula

[0033] In general formula (2), R' represents a hydrogen atom or a methyl group. B represents a direct bond or a divalent group. Ep represents a monovalent group containing an epoxy group.

[0034] Examples of divalent groups of B include divalent groups having 0 to 30 carbon atoms, preferably 1 to 20 carbon atoms, and more preferably 1 to 10 carbon atoms. Specifically, divalent groups can include linear or branched alkylene groups, cycloalkylene groups, polycyclic aliphatic groups, arylene groups, -O-, -CO-, -COO-, -OCO-, -S-, -SO2-, -NH-, -NR- (where R is a monovalent organic group), and groups formed by combining two or more of these. Ep preferably comprises a glycyryl group or a 3,4-epoxycyclohexyl group.

[0035] In general formula (2), preferred structural examples of the -B-Ep portion include structures represented by the following formulas (E1) and (E2).

[0036] [ka]

[0037] In equation (E1), R 22 These are directly bonded, alkylene groups having 1 to 18 carbon atoms, or oxyalkylene groups having 1 to 18 carbon atoms.

[0038] [ka]

[0039] In equation (E2), R 23 These are directly bonded, alkylene groups having 1 to 18 carbon atoms, or oxyalkylene groups having 1 to 18 carbon atoms.

[0040] The ratio of structural units (a1) in the polymer is, from the viewpoint of balancing various properties such as curability and storage stability, for example, 50 mol% or more, preferably 60-95 mol%, and more preferably 75-80 mol%.

[0041] Incidentally, the ratio of structural units (a1) to structural units (a2) in the polymer (structural unit (a1):structural unit (a2)) is, in molar ratio, for example, 50:50 to 1:99, preferably 40:60 to 5:95, and more preferably 25:75 to 20:80. By adjusting the ratio of structural units (a1) to structural units (a2), it is possible to further improve the balance of various properties.

[0042] Other structural units The polymer may or may not have structural units other than structural units (a1) and (a2). The other structural units are not particularly limited. When a polymer has other structural units, the ratio of these other structural units in the polymer is, for example, 1 to 30 mol%, preferably 1 to 10 mol%, from the viewpoint of not excessively degrading other properties and fully obtaining the effects derived from these other structural units.

[0043] Incidentally, polymers may contain structural units in which the protecting group has been deprotected at the structural unit (a1) due to changes over time.

[0044] The number-average molecular weight of the polymer is, from the viewpoint of appropriate viscosity and applicability as an adhesive material, for example, 1000 to 10000, preferably 2000 to 5000, and more preferably 2500 to 3500. The degree of dispersion of the polymer is typically 1 to 2, preferably 1.2 to 1.8, more preferably 1.2 to 1.5, and even more preferably 1.2 to 1.3. The number-average molecular weight and dispersion of polymers can be determined, for example, by gel permeation chromatography using poly(methyl methacrylate) as a standard substance.

[0045] (Methods for polymer synthesis) The method for synthesizing polymers is not particularly limited. Typically, a desired polymer can be obtained by polymerizing a monomer corresponding to structural unit (a1) with a monomer corresponding to structural unit (a2) using polymerization methods such as radical polymerization, cationic polymerization, or anionic polymerization. Knowledge from the field of polymer synthesis can be appropriately utilized for the synthesis and purification of polymers.

[0046] A preferred method for synthesizing polymers is reversible addition-cleavage chain transfer polymerization (RAFT polymerization), a type of living radical polymerization. In RAFT polymerization, thiocarbonyl compounds are typically used as chain transfer agents to carry out radical polymerization. RAFT polymerization allows for the synthesis of polymers with relatively low dispersibility while controlling the molecular weight (while suppressing high molecular weight formation).

[0047] Incidentally, the monomer corresponding to structural unit (a1) can be synthesized by referring to, for example, the description in ACS Sustainable Chem. Eng. 2018, 6, 13681-13686. Incidentally, the monomer "Ac2VC" shown in the examples below is shown as compound 5 in the above-mentioned document.

[0048] (Deprotecting agent) The deprotecting agent is not particularly limited as long as it is capable of deprotecting protecting groups in the polymer. However, the deprotecting agent preferably has a reactive group that reacts with and forms a bond with the epoxy group. More preferably, the reactive group of the deprotecting agent is a group that has the function of deprotecting protecting groups. In other words, by using a compound that possesses both the property of being able to deprotect protecting groups in polymers and the property of being able to react with epoxy groups as a deprotecting agent, it is possible to simplify the composition of the adhesive material while improving its long-term stability. Even if the deprotecting agent and the epoxy curing agent are separate components, the effect of improving stability over time can still be obtained. However, deprotecting agents typically do not directly contribute to the development of adhesive strength. Therefore, by using a compound that possesses both deprotecting and epoxy curing properties, the adhesive strength can be further enhanced.

[0049] The deprotecting agent preferably has two or more reactive groups per molecule, more preferably two to six, and even more preferably two to four. Having two or more reactive groups per molecule allows for crosslinking between polymers, resulting in better adhesion.

[0050] As an example of a preferred deprotective agent, a polyfunctional amine can be mentioned in which the total number of primary and secondary amino groups in one molecule is two or more (more preferably 2 to 6, and even more preferably 2 to 4). Primary or secondary amino groups can deprotect protecting groups in the polymer (by appropriate heating, etc.) and can also react with epoxy groups in the polymer to form bonds.

[0051] Specific examples of preferred deprotecting agents include ethylenediamine, N-alkylethylenediamine, propylenediamine, 2,2-dimethyl-1,3-propanediamine, N-alkylpropylenediamine, butylenediamine, N-alkylbutylenediamine, pentanediamine, hexamethylenediamine, N-alkylhexamethylenediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, dodecanediamine, hexadecanediamine, tolylenediamine, xylylenediamine, diaminodiphenylmethane, diaminodicyclohexylmethane, and phenylenediamine. Examples include cyclohexylenediamine, bis(aminomethyl)cyclohexane, diaminodiphenylsulfone, isophoronediamine, 2-butyl-2-ethyl-1,5-pentamethylenediamine, 2,2,4-or 2,4,4-trimethyl-1,6-hexamethylenediamine, 2-aminopropylcyclohexylamine, 3(4)-aminomethyl-1-methylcyclohexylamine, 1,4-diamino-4-methylpentane, amine-terminated polyoxyalkylene polyols (known as the "Jeffamine" series), and amine-terminated polytetramethylene glycol. These can function as deprotective agents and are also reactive with epoxy groups.

[0052] (Combination of protecting group and deprotecting agent) In this embodiment, the combination of the protecting group and the deprotecting agent is preferably as follows: • Protecting group: At least one selected from the group consisting of acyl groups and alkoxycarbonyl groups. • Deprotecting agent: A compound having at least one group selected from the group consisting of primary amino groups and secondary amino groups, more preferably a polyfunctional amine in which the total number of primary and secondary amino groups in one molecule is two or more.

[0053] (Hardening agent: A separate component from the deprotecting agent) The above mainly describes an embodiment in which the deprotecting agent and the curing agent are the same component (the deprotecting agent is reactive with epoxy groups). On the other hand, in the adhesive material of this embodiment, the deprotecting agent and the curing agent may be different components. Even if the deprotecting agent and the curing agent are different components, the hydroxyl groups of the catechol structure remain protected, and therefore the effect of improving the long-term stability of the adhesive material can be obtained.

[0054] (Regarding the ratio of polymer to deprotectant) The polymer content and deprotectant content in the adhesive material of this embodiment are not limited. These contents are appropriately determined based on the desired adhesiveness, long-term stability, curability, etc.

[0055] From the viewpoint of ensuring that the deprotection of the deprotecting group proceeds sufficiently quickly, the content of the deprotecting agent is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and particularly preferably 23 parts by mass or more, per 100 parts by mass of polymer. There is no particular upper limit on the amount of deprotecting agent, but from the viewpoint of balancing various performance aspects, the amount of deprotecting agent is, for example, 100 parts by mass or less, preferably 75 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of polymer.

[0056] Furthermore, if the deprotecting agent has a reactive group that reacts with epoxy groups to form a bond, it is preferable that the amount of the deprotecting agent be determined considering the number of moles of epoxy groups in the adhesive material. Specifically, the amount of reactive groups that react with epoxy groups to form bonds is, for example, 0.1 to 2 moles, preferably 0.5 to 1.5 moles, per mole of epoxy groups in the adhesive material.

[0057] (Other ingredients) The adhesive material of this embodiment may or may not contain components other than the polymer and the deprotecting agent (optional components).

[0058] Examples of optional components include polymers other than those having the above-mentioned structural units (a1) and (a2).

[0059] Another example of an optional component is an epoxy resin (EP) that does not contain a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups. Specific examples of epoxy resins (EP) include, for example, glycidyl ethers of bisphenol A, F, S, and AD types, phenol novolac type glycidyl ethers, cresol novolac type glycidyl ethers, bisphenol A type novolac type glycidyl ethers, naphthalene type glycidyl ethers, biphenol type glycidyl ethers, dihydroxypentadiene type glycidyl ethers, triphenylmethane type epoxy resins, phenol novolac type epoxy resins, and cresol novolac type epoxy resins. Furthermore, alicyclic epoxy compounds can also be cited as epoxy resins (EP). Specifically, hydrogenated bisphenol A diglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-1-methylcyclohexyl-3,4-epoxy-1-methylhexanecarboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexanecarboxylate, 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5-methylcyclohexanecarboxylate, 2- Examples include (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-methadioxane, bis(3,4-epoxycyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexylcarboxylate, methylenebis(3,4-epoxycyclohexane), dicyclopentadienediepoxide, ethylenebis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate, di-2-ethylhexyl epoxyhexahydrophthalate, 1-epoxyethyl-3,4-epoxycyclohexane, and 1,2-epoxy-2-2-epoxyethylcyclohexane. Commercially available alicyclic epoxy compounds include, for example, the "Celoxide" series manufactured by Daicel Corporation.

[0060] As shown in the examples below, the adhesive material of this embodiment can be preferably used as an adhesive by using epoxy resin (EP) in combination with a polymer having structural units (a1) and (a2). Although the details are unclear, it is likely that good adhesion can be expected due to the combination of the curing reaction of the normal epoxy group and the adhesion of catechol to the substrate. When epoxy resin (EP) is used in combination with a polymer having structural units (a1) and structural units (a2), the mass ratio (polymer having structural units (a1) and structural units (a2) / epoxy resin (EP)) is, for example, 5 / 95 to 60 / 40, preferably 10 / 90 to 50 / 50, and more preferably 20 / 80 to 40 / 60. By adjusting this ratio, a better balance can be achieved between the normal curing reaction of epoxy groups and the adhesion of catechol to the substrate, resulting in even better adhesion.

[0061] The adhesive material of this embodiment may be a polymer or deprotecting agent dispersed or dissolved in a solvent. In other words, the adhesive material of this embodiment may contain a solvent. The solvents are typically organic solvents. Examples of organic solvents include ketones such as acetone, methyl ethyl ketone (MEK), and cyclohexanone; acetic acid esters such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbons such as toluene and xylene; and dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone, and tetrahydrofuran. For the sake of clarity, the adhesive material of this embodiment does not need to contain substantially any solvent, as long as it is usable as an adhesive material.

[0062] Other optional components include, for example, inorganic particles such as silica and alumina, fiber fillers such as glass fibers and carbon fibers, thermoplastic elastomers, flame retardants, and defoaming agents.

[0063] (Regarding two-drug prescriptions) The adhesive material of this embodiment may be a two-part system, that is, in which components that react easily with each other are placed in separate containers and mixed immediately before use. As an example, the adhesive material in this embodiment may be a two-component system as described below (i) and (ii). (i) A first agent comprising a polymer having structural unit (a1) and structural unit (a2), but without a deprotecting agent. (ii) A second agent that contains a deprotecting agent but does not contain a polymer having structural unit (a1) and structural unit (a2).

[0064] Furthermore, in cases where the adhesive material is an adhesive, as will be described later, the epoxy resin (EP) and the other components may be housed in separate containers.

[0065] <Another embodiment> Several embodiments different from those described above are described below.

[0066] Polymers having a structural unit represented by the following general formula (1'), and adhesive materials containing this polymer, are also industrially useful.

[0067] [ka]

[0068] In general formula (1'), R 1 'and R 2 Each of these is independently a protecting group for a hydrogen atom or a hydroxyl group. L' is a single bond, alkylene group, arylene group, carboxyl group, carbonyl group, ether group, or a divalent group consisting of two or more of these. R is either a hydrogen atom or a methyl group.

[0069] R 1 'and R 2 As a protecting group for the hydroxyl group of ', R in general formula (1) 1 and R 2 It can be similar to a protecting group for the hydroxyl group. 1 'and R 2 At least one of the ' is usually a protecting group for a hydroxyl group, preferably R 1 'and R 2 Both of these are protecting groups for the hydroxyl group. -OR1 'and -OR 2 It is preferable that the elements ' are located in ortho positions relative to each other. L' is preferably a single bond.

[0070] Furthermore, the various physical properties, characteristics, copolymerization components, and methods for producing the polymer described here can be the same as those of the polymer described above (preferably including the structural unit represented by general formula (1)). For example, the polymer described here preferably also has a structural unit having an epoxy group (as described above as structural unit (a2)), similar to the polymer described above. Furthermore, the components and their quantities that can be included in the polymer-containing adhesive material described here can be the same as those of the adhesive material described above.

[0071] <Regarding applications / bonding of materials> An article can be obtained in which a first member and a second member are bonded together using the adhesive material described above in <Adhesive Material> or <Another Embodiment>.

[0072] For example, when using an adhesive material as a primer, articles can be bonded by following the procedure below. (1) The members to be bonded are immersed in an adhesive material that is liquid and contains an organic solvent. After immersion, heating is preferably performed. The heating temperature is, for example, 30 to 100°C, preferably 40 to 70°C. The heating time is, for example, 1 to 200 minutes, preferably 10 to 120 minutes. In this way, the polymer is adsorbed onto the surface of the members while promoting the deprotection of catechol. (2) The member that was immersed in the adhesive material is removed. Then, the polymer that did not adsorb to the member is removed by washing, for example, with an organic solvent. In this way, a primer-treated member is obtained. (3) The primer-treated members are bonded together, or the primer-treated members are bonded to other members, with an adhesive. Preferably, an epoxy adhesive, and more preferably an epoxy-amine adhesive, can be used as the adhesive.

[0073] Furthermore, when using adhesive materials as an adhesive, articles can be bonded together by following the procedure below. (1) Apply an adhesive material, prepared for application to the components, to one or both surfaces of the two components to be bonded. (2) The two members to be bonded are brought into contact with each other on the surfaces coated with the adhesive material and heated. The heating is preferably carried out in two stages: a first stage at a relatively low temperature that promotes the deprotection of catechol but does not substantially advance the curing of the adhesive material itself, and a second stage at a relatively high temperature that advances the curing of the adhesive material itself. The temperature for the first stage is, for example, 60 to 90°C, preferably 70 to 80°C. The temperature for the second stage is, for example, 100 to 180°C, preferably 105 to 150°C.

[0074] Incidentally, when using adhesive materials as adhesives, it is preferable to use epoxy resin (EP) and a polymer having structural units (a1) and (a2), as mentioned above. In other words, when using an adhesive material as an adhesive, the adhesive material preferably comprises (i) an epoxy resin (EP) that does not contain a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, (ii) a polymer having structural units (a1) and (a2), and (iii) a deprotecting agent (preferably one having reactive groups that react with epoxy groups to form bonds). The ratio of (ii) the polymer having structural units (a1) and (a2) in the whole adhesive material (adhesive) is, for example, 5 to 50% by mass, preferably 10 to 40% by mass, and more preferably 10 to 30% by mass. By adjusting this ratio, it is expected that the balance between the curing reaction of the epoxy groups and the adhesion of catechol to the substrate will be optimized, thereby increasing the adhesive strength.

[0075] The material of the articles to be bonded (the "first member" and "second member" described above) is not particularly limited, but the material of the articles is preferably metal. The adhesive material described above exhibits strong adhesive strength, particularly in bonding aluminum-containing metal materials such as duralumin. According to our findings, the adhesive material can specifically bond aluminum alloys such as Al-Cu alloys and Al-Zn alloys. For the record, the adhesive material described above can also be used to bond metal materials other than aluminum-containing materials, such as iron-containing materials like stainless steel. Furthermore, it may be used to bond various inorganic and organic materials, provided that good adhesion can be achieved.

[0076] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. Reference embodiments of the present invention are described below. 1. A polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, and a structural unit (a2) having epoxy groups, A deprotecting agent for deprotecting the aforementioned protecting group, Adhesive materials containing [the specified element]. 2. The adhesive material described in 1. The aforementioned protecting group is at least one selected from the group consisting of acyl groups and alkoxycarbonyl groups in the adhesive material. 3. The adhesive material described in 1. or 2., An adhesive material in which the structural unit (a1) includes a structural unit represented by the general formula (1) shown above. In general formula (1), R 1 and R 2 These are, independently, protecting groups for hydroxyl groups. L is a single bond or a divalent linking group. R is either a hydrogen atom or a methyl group. 4. An adhesive material described in any one of 1. to 3., The deprotecting agent is an adhesive material having a reactive group that reacts with and forms a bond with an epoxy group. 5. The adhesive material described in 4. The reactive group is an adhesive material having the function of deprotecting the protecting group. 6. The adhesive material described in 4. or 5., The deprotective agent is an adhesive material having two or more of the reactive groups in one molecule. 7. An adhesive material described in any one of 1. to 6., The deprotective agent is an adhesive material containing a polyfunctional amine in which the total number of primary and secondary amino groups in one molecule is two or more. 8. An adhesive material described in any one of 1. to 7., The protecting group is at least one selected from the group consisting of acyl groups and alkoxycarbonyl groups. The deprotective agent is an adhesive material having at least one group selected from the group consisting of primary amino groups and secondary amino groups. 9. An adhesive material described in any one of 1. to 8., The protecting group is at least one selected from the group consisting of acyl groups and alkoxycarbonyl groups. The deprotective agent is an adhesive material containing a polyfunctional amine in which the total number of primary and secondary amino groups in one molecule is two or more. 10. An adhesive material described in any one of 1. to 9., An adhesive material used as a primer in the bonding of articles. 11. An adhesive material described in any one of 1. to 9., Adhesive materials used as adhesives. 12. An adhesive material comprising a polymer having a structural unit represented by the general formula (1') shown above. In general formula (1'), R 1 'and R 2 Each of these is independently a protecting group for a hydrogen atom or a hydroxyl group. L' is a single bond, alkylene group, arylene group, carbonyl group, ether group, or a divalent group consisting of two or more of these. R is either a hydrogen atom or a methyl group. 13. The adhesive material described in 12. An adhesive material in which L' is a single bond. 14. The adhesive material described in 12. or 13. The polymer is an adhesive material having structural units that have epoxy groups. 15. An article in which a first member and a second member are bonded together using an adhesive material described in any one of 1. to 14. 16. A polymer having a structural unit represented by the above-mentioned general formula (1') and a structural unit having an epoxy group. In general formula (1'), R 1 'and R 2 Each of these is independently a protecting group for a hydrogen atom or a hydroxyl group. L' is a single bond, alkylene group, arylene group, carboxyl group, carbonyl group, ether group, or a divalent group consisting of two or more of these. R is either a hydrogen atom or a methyl group. 17. The polymer described in 16. A polymer in which L' is a single bond. [Examples]

[0077] Embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted that the present invention is not limited to these examples.

[0078] <Preparation of materials for polymer synthesis> The following materials were prepared.

[0079] (monomer) • GMA: Monomer with the following structure

[0080] [ka]

[0081] • Ac2VC: Monomer with the following structure

[0082] [ka]

[0083] Incidentally, Ac2VC was synthesized based on the description in ACS Sustainable Chem. Eng. 2018, 6, 13681-13686.

[0084] (Radical initiator) 2,2'-azobis(2,4-dimethylvaleronitrile) (abbreviation: ADVN)

[0085] (RAFT agent) 2-cyano-2-propyl benzodithioate (abbreviation: CPDB)

[0086] <Polymer synthesis> Based on knowledge of reversible addition-cleavage chain transfer polymerization (RAFT polymerization), a type of living radical polymerization, the polymer was synthesized using the following procedure. (1) GMA 2.202 g, Ac2VC 4.254 g, radical initiator 0.497 g, and RAFT agent 0.442 g were dissolved in toluene 8.67 g to obtain a solution. This solution was subjected to freeze-degassing four times to sufficiently reduce the amount of dissolved gas in the solution. (2) The solution that had been thoroughly degassed in (1) above was heated and stirred overnight at 55°C under a nitrogen atmosphere. This polymerized the monomer. (3) After the heating and stirring described in (2) above was completed, the polymer in the polymerization solution, which had been allowed to cool naturally to room temperature, was reprecipitated with methanol.

[0087] By following the above procedure, a polymer represented by the following chemical formula (PGMA-co-P(Ac2VC)) was obtained. The obtained polymer was dissolved in tetrahydrofuran and subjected to GPC measurement. The number-average molecular weight of the polymer was 3000 and the degree of dispersion was 1.27 when poly(methyl methacrylate) was used as the standard substance. Furthermore, in the following chemical formula, x=0.77 and y=0.23 ( 1 (Based on the analysis results of the peak area ratio of 1H-NMR.)

[0088] [ka]

[0089] <Evaluation of temporal stability and deprotection> A solution was prepared by dissolving 20 mg of the polymer obtained above and 19.5 mg of the diamine compound in 1.1 g of dimethyl sulfoxide. As the diamine compound, a compound having -NH2 at both ends of polyoxypropylene glycol (manufactured by Mitsui Chemicals, trade name: JEFFAMINE D-230) was used. The solution was allowed to stand for 3 hours at 20°C, 50°C, or 80°C. The solution was then measured at the start of standing and every hour thereafter. 1 The 1H-NMR spectrum was measured.

[0090] The above 1 The 1H-NMR spectra are shown in Figures 1, 2, and 3. Figure 1 shows the spectra obtained when the solution is left standing at 20°C. 1 H-NMR spectrum, Figure 2 shows the result when the solution is left standing at 50°C. 1 Figure 3 shows the H-NMR spectrum and the results when the solution is left standing at 80°C. 1 This is an H-NMR spectrum. As shown in Figure 1, when the solution was allowed to stand at 20°C, a peak around 6.8 ppm, indicating the presence of acyl groups, was still present even after 3 hours of standing. On the other hand, as shown in Figures 2 and 3, when the solution was left to stand at 50°C or 80°C, the peak around 6.8 ppm indicating the presence of acyl groups almost disappeared over time.

[0091] From the results, the following (1) and (2) can be understood. (1) The polymer obtained above is relatively stable at temperatures of 20°C or below, even in the presence of amines, with deprotection suppressed; in other words, it has good temporal stability before being used as an adhesive material. (2) The polymer obtained above undergoes a deprotection reaction upon heating in the presence of an amine; that is, when used for bonding articles, a catechol skeleton is produced upon heating.

[0092] <Evaluation as a primer> First, the following (i) to (iii) were prepared as substrates to be bonded. (i) SUS304 with a thickness of 0.2 mm (ii) Al-Zn alloy with a thickness of 1.0 mm (A-7075 (super duralumin) as defined in JIS H 4040) (iii) Al-Cu alloy (duralumin) with a thickness of 2.0 mm For reference, the table below shows the results of the elemental composition analysis of these substrates based on X-ray fluorescence analysis. In the table below, % represents atomic percentage.

[0093] [Table 1]

[0094] The above substrates were treated with a primer according to the following procedure, and then bonded together using an adhesive to obtain a joint. (1) 0.5 g of the above polymer was dissolved in 27.5 g of dimethyl sulfoxide (DMSO) to prepare a solution. 0.49 g of JEFFAMINE D-230 was added to this solution and stirred to obtain a primer solution. (2) The substrate was immersed in the primer solution obtained in (1) above and heated at 50°C for 90 minutes. (3) After heating as described in (2) above, the substrate was removed. The substrate was then washed with tetrahydrofuran (THF) to remove any polymers that had not been adsorbed onto the substrate. This prepared a primer-treated substrate. Multiple primer-treated substrates were prepared for adhesion evaluation in (4) and beyond. Incidentally, the water contact angle (static contact angle) of the substrate was measured before and after treatment (3). This was used to evaluate the degree of surface modification.

[0095] (4) The primer-treated substrates obtained in (3) above were bonded together with an epoxy-amine adhesive. A joint was obtained. As the epoxy-amine adhesive, a mixture of 3.8 g (20 mmol epoxy groups) of bisphenol A diglycidyl ether (DGEBA) and 1.2 g (5 mmol) of JEFFAMINE D-230 was used. The coating thickness of the epoxy-amine adhesive was 0.2 mm. For comparison, substrates that had not undergone primer treatment were also bonded together using the epoxy-amine adhesive described above. This resulted in comparative bonded structures.

[0096] (5) The shear strength of the joint obtained in (4) above and the comparative joint was measured. A Shimadzu Corporation "EZ Graph" testing machine was used for the measurement. The tensile speed was set to 1 mm / min.

[0097] The table below shows the water contact angle measured in (3) above and the shear strength measured in (5) above.

[0098] [Table 2]

[0099] The change in water contact angle before and after primer treatment suggests that the catechol structure, deprotected by heating at 50°C for 90 minutes, likely adsorbed onto the substrate, causing it to become hydrophilic. Furthermore, the shear strength of each substrate could be increased by applying a primer treatment. In other words, it was shown that an adhesive material comprising a polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, a structural unit (a2) having epoxy groups, and a deprotecting agent is useful as a primer for bonding articles.

[0100] The table above shows that the shear strength is particularly improved when the substrate is an aluminum-containing metal material. Therefore, the adhesive material of this embodiment is particularly suitable for bonding aluminum-containing metal materials.

[0101] <Evaluation as an adhesive> An adhesive was prepared using the polymer (PGMA-co-P(Ac2VC)) obtained above, and its performance was evaluated according to the following procedure.

[0102] (1) First, an epoxy-amine adhesive was prepared containing 1.5 g of bisphenol A diglycidyl ether (DGEBA) and 0.96 g of JEFFAMINE D-230. (2) 0.50 g of PGMA-co-P(Ac2VC) was added to the epoxy-amine adhesive described above and mixed uniformly to prepare an adhesive for evaluation.

[0103] (3) Using the evaluation adhesive obtained in (2) above, two SUS304 substrates with a thickness of 0.2 mm were bonded together. The adhesive was applied to a thickness of 0.2 mm. The heating conditions during bonding were first at 75°C for 3 hours, and then at 125°C for 3 hours (it is thought that the deprotection of catechol mainly progressed in the first heating stage, and the curing reaction of epoxy groups mainly progressed in the second heating stage). A bonded body was obtained in this manner. Furthermore, for comparison, two SUS304 substrates were bonded in the same manner as above, except that the epoxy-amine adhesive (without PGMA-co-P(Ac2VC)) described in (1) above was used. A comparative bond was then obtained. (4) The shear strength of the joint and the comparative joint was measured in the same manner as in (5) of <Evaluation as a primer> above.

[0104] The table below shows the results of the shear strength measurements taken in (4) above.

[0105] [Table 3]

[0106] As shown in the table above, the shear strength was improved by adding PGMA-co-P(Ac2VC) to the epoxy-amine adhesive containing JEFFAMINE D-230. Although the details are unclear, it is presumed that the improvement in shear strength was due to a combination of the curing of the normal epoxy-diamine and the adhesion of PGMA-co-P(Ac2VC), whose hydroxyl groups were exposed by deprotection, to the substrate. The above results demonstrate that an adhesive material comprising a polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, a structural unit (a2) having epoxy groups, and a deprotecting agent such as a diamine, is useful not only as a primer but also as an adhesive.

Claims

1. A polymer having a structural unit (a1) having a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups, and a structural unit (a2) having epoxy groups, A deprotecting agent for deprotecting the aforementioned protecting group, An adhesive material containing, The protecting group is at least one selected from the group consisting of acyl groups and alkoxycarbonyl groups. The deprotecting agent is an adhesive material having a reactive group that reacts with and forms a bond with an epoxy group.

2. The adhesive material according to claim 1, The aforementioned structural unit (a1) is an adhesive material comprising a structural unit represented by the following general formula (1). 【Chemistry 1】 In general formula (1), R １ and R ２ These are, independently, protecting groups for hydroxyl groups. L is a single bond or a divalent linking group. R is either a hydrogen atom or a methyl group.

3. The adhesive material according to claim 1 or 2, The reactive group is an adhesive material having the function of deprotecting the protecting group.

4. An adhesive material according to any one of claims 1 to 3, The deprotecting agent is an adhesive material having two or more of the reactive groups in one molecule.

5. An adhesive material according to any one of claims 1 to 4, The deprotective agent is an adhesive material containing a polyfunctional amine in which the total number of primary and secondary amino groups in one molecule is two or more.

6. An adhesive material according to any one of claims 1 to 5, The deprotective agent is an adhesive material having at least one group selected from the group consisting of primary amino groups and secondary amino groups.

7. An adhesive material according to any one of claims 1 to 6, The deprotective agent is an adhesive material containing a polyfunctional amine in which the total number of primary and secondary amino groups in one molecule is two or more.

8. An adhesive material according to any one of claims 1 to 7, An adhesive material used as a primer in the bonding of articles.

9. An adhesive material according to any one of claims 1 to 7, Adhesive materials used as adhesives.

10. The adhesive material according to claim 9, The polymer other than the aforementioned polymer includes epoxy resin (EP) which does not contain a catechol skeleton in which some or all of the hydroxyl groups are protected by protecting groups. An adhesive material having a mass-based ratio of polymer / epoxy resin (EP) of 5 / 95 to 60 / 40.

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