Resin composition for metal bonding and pre-coated metal sheet

Abstract

This invention provides a water-based metal adhesive that exhibits low tackiness after pre-drying and excellent adhesion after curing. [Solution] A resin composition for metal bonding comprising a water-soluble carboxyl group-containing phenol resin, an amine, and water, wherein the resin composition is in the form of an aqueous solution, and the water-soluble carboxyl group-containing phenol resin has a structural unit represented by formula (1) and a specific phenol structural unit. TIFF2026046769000010.tif56153

Description

[Technical Field]

[0001] The present invention relates to a resin composition for metal bonding and a pre-coated metal sheet in which the resin composition is applied to a metal sheet. [Background technology]

[0002] Phenolic resins are widely used as molding materials for various substrates, as binders for friction materials, binders for abrasive materials, adhesives for wood, binders for laminated materials, binders for molds, coating agents, and epoxy resin curing agents, taking advantage of their excellent heat resistance, adhesive properties, mechanical properties, electrical properties, and cost advantages. In particular, phenolic resin compositions are used as adhesives for metals in fields such as building materials, home appliances, general merchandise, and automotive parts.

[0003] Furthermore, from the perspective of reducing environmental impact and occupational safety and health, there is a demand for phenolic resin materials that do not use organic solvents or use organic solvents with low amounts. Therefore, there is a need for highly water-dilutable resins that can be provided as water-soluble resins using water as a solvent or water-dispersible resins using water-based dispersants.

[0004] For example, Patent Document 1 discloses an aqueous vulcanizing adhesive for metal and nitrile butadiene rubber, comprising a phenol resin emulsion prepared from a methyl ethyl ketone solution of a water-insoluble phenol resin and an unmodified polyvinyl alcohol solution, and hexamethylenetetramine. Patent Document 1 provides an aqueous adhesive composition by using a methyl ethyl ketone solution and an aqueous solution of unmodified polyvinyl alcohol as solvents. As a technology using water as a solvent, Patent Document 2 describes an aqueous vulcanization adhesive for metal and nitrile butadiene rubber, comprising a water-soluble phenolic resin, a mercaptosilane coupling agent, a surfactant, and water. Patent Document 2 discloses an aqueous adhesive that uses water as a solvent, which suppresses environmental pollution and is superior in terms of workplace hygiene and safety. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-052051 [Patent Document 2] Japanese Patent Publication No. 2024-052040 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Adhesives for metals require good adhesion after curing and low tack after pre-drying if pre-drying is performed. Furthermore, in recent years, there has been a demand for water-based adhesives due to environmental concerns. However, all of the compositions described in the above-mentioned patent documents had room for improvement in terms of the balance between adhesion, low tack, and water-based properties.

[0007] The object of the present invention is to provide a water-based adhesive for metals that exhibits low tackiness after pre-drying and excellent adhesion after curing. [Means for solving the problem]

[0008] According to the present invention, the following resin compositions are provided. [1] A resin composition for metal bonding comprising a water-soluble carboxyl group-containing phenol resin, an amine, and water, The resin composition is in the form of an aqueous solution, The water-soluble carboxyl group-containing phenol resin has a structural unit represented by formula (1) and a structural unit represented by formula (2), [ka] In equation (1), X is an alkylene group having 1 to 6 carbon atoms. R 1 These are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or -CH2OH. [ka] In equation (2), R 2 The resin composition is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or -CH2OH. [2] The resin composition according to [1], wherein the proportion of the structural unit represented by formula (1) in the carboxyl group-containing phenol resin is 5 mol% or more and 90 mol% or less with respect to the entire carboxyl group-containing phenol resin. [3] The resin composition according to [1] or [2], wherein the amine comprises a tertiary amine. [4] The resin composition according to any one of [1] to [3], further comprising a water-soluble plasticizer. [5] The resin composition according to "4", wherein the water-soluble plasticizer comprises at least one selected from polyvinyl alcohol, polyvinyl acetal, gum arabic, hydroxyethylcellulose, and carboxymethylcellulose. [6] The resin composition according to [4], wherein the water-soluble plasticizer is in an amount of 1% by mass or more and 40% by mass or less with respect to the water-soluble phenolic resin solids. A resin composition according to any of [7] [1] to [6], When the resin composition is prepared as a B-stage resin film under the following conditions, the resin film dissolves in methanol, according to the following resin composition: Condition: The resin composition is applied to a substrate and dried at 110°C to produce a B-stage resin film with a thickness of 100 μm. [8] A pre-coated metal plate comprising a metal plate and a coating film provided on at least one surface of the metal plate, The aforementioned coating film is a coating film formed from any of the resin compositions described in [1] to [7]. Pre-coated metal sheet. [9] The pre-coated metal plate according to [8], wherein the coating film has a thickness of 1 μm or more and 50 μm or less.

[10] The pre-coated metal sheet according to [8] or [9], wherein the metal sheet is an iron sheet, a steel sheet, an iron alloy sheet, a stainless steel sheet, an aluminum sheet, an aluminum alloy sheet, a magnesium alloy sheet, a titanium sheet, a titanium alloy sheet, a copper sheet, or a copper alloy sheet.

Advantages of the Invention

[0009] According to the present invention, there is provided a resin composition for metal adhesion, which is excellent in low tackiness after preliminary drying and adhesiveness after curing and is aqueous.

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described. In this specification, the notation "a to b" in the description of a numerical range means "a or more and b or less" unless otherwise specified. For example, "5 to 90% by mass" means "5% by mass or more and 90% by mass or less".

[0011] [Resin Composition] The resin composition of this embodiment is a carboxyl group-containing phenol resin having a structural unit represented by formula (1) and a structural unit represented by formula (2); amine; and water.

[0012]

Chemical formula

[0013] In formula (1), X is an alkylene group having 1 to 6 carbon atoms, R 1 is independently a hydrogen atom (H), an alkyl group having 1 to 20 carbon atoms, a hydroxyl group (-OH), or a methylol group (-CH2OH).

[0014]

Chemical formula

[0015] In formula (2), R 2 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or -CH2OH.

[0016] In the resin composition of this embodiment, the carboxyl group-containing phenol resin has structural units represented by formula (1) and structural units represented by formula (2). Carboxyl group-containing phenol resins having such structural units have excellent curability and adhesion, and the resulting cured product has excellent heat resistance and excellent mechanical strength. Furthermore, since the carboxyl group-containing phenol resin has low tackiness in the B-stage state after pre-drying, when the resin composition is provided as a pre-coated metal sheet, problems such as the resin composition adhering to and contaminating equipment and transport parts that handle the pre-coated metal sheet do not occur, resulting in excellent handling. Generally, pre-drying (B-stage) of an adhesive reduces its tackiness, but it can also decrease its adhesive strength. The carboxy-containing phenol resin used in this embodiment achieves both low tackiness after pre-drying and excellent adhesiveness after curing.

[0017] In the resin composition of this embodiment, the carboxyl group-containing phenol resin, through interaction with the amine contained in the resin composition, has its carboxyl group neutralized and exists as a water-soluble oil. Therefore, the resin composition of this embodiment is an aqueous resin composition using water as a solvent, and since it does not substantially use organic solvents, the environmental burden is reduced. The following describes each component that makes up the resin composition of this embodiment.

[0018] (Water-soluble carboxyl group-containing phenolic resin) The carboxyl group-containing phenol resin used in the resin composition of this embodiment has a structural unit represented by formula (1) and a structural unit represented by formula (2). This phenol resin is characterized by having a structure in which a carboxyl group is introduced into the side chain, as represented by formula (1). In this specification, the carboxyl group-containing phenol resin having the above structure may be simply referred to as "phenol resin".

[0019] [ka]

[0020] In equation (1), X is an alkylene group having 1 to 6 carbon atoms. R 1 These are independently a hydrogen atom (H), an alkyl group having 1 to 20 carbon atoms, a hydroxyl group (-OH), or a methylol group (-CH2OH).

[0021] [ka]

[0022] In equation (2), R 2 These are independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or -CH2OH.

[0023] The alkylene group having 1 to 6 carbon atoms that can constitute X in formula (1) may be linear, branched, or cyclic. Examples include linear or branched alkylenes having 1 to 6 carbon atoms such as methylene, ethylene, propylene, and butylene groups. From the viewpoint of ease of production, a methylene or ethylene group is preferred. The structure of X in formula (1) can be adjusted by selecting the type of carboxylic acid compound used in the production of the carboxyl group-containing phenol resin, which will be described in detail below.

[0024] R in equations (1) and (2) 1 and R 2 The C1-C20 alkyl groups that can constitute the alkyl group may be linear, branched, or cyclic. Examples of linear or branched alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Examples of cyclic alkyl groups include adamantyl, cyclopentyl, cyclohexyl, and cyclooctyl groups.

[0025] The structures of the structural unit represented by formula (1) and the structural unit represented by formula (2) can be controlled by selecting the types of raw material monomers used in the production of the carboxyl group-containing phenol resin, which will be detailed below, or by selecting the production conditions.

[0026] In one embodiment, the carboxyl group phenol resin has R in the structural unit represented by formula (1) 1 being a methylol group, and R in the structural unit represented by formula (2) 2 being a methylol group, and is a resol type phenol resin. In one embodiment, the phenol resin has R in the structural unit represented by formula (1) 1 being a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, and R in the structural unit represented by formula (2) 2 being a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a hydroxyl group, and is a novolak type phenol resin.

[0027] In this embodiment, the resin composition is in the form of an aqueous solution in which the carboxyl group-containing phenol resin exists in a state dissolved in water, and the carboxyl group-containing phenol resin is preferably a resol type phenol resin.

[0028] In one embodiment, the carboxyl group-containing phenol resin has a structure in which the proportion of structural units containing carboxyl groups represented by formula (1) is 5 to 90 mol% of the total carboxyl group-containing phenol resin. Preferably, the proportion of structural units represented by formula (1) in the carboxyl group-containing phenol resin is 5 to 70 mol%, more preferably 5 to 50 mol%, and even more preferably 5 to 30 mol%. The carboxyl group-containing phenol resin having a proportion of structural units represented by formula (1) within the above range has excellent water solubility, and the resulting resin composition has excellent handling properties. The proportion of structural units represented by formula (1) in the carboxyl group-containing phenol resin can be changed by adjusting the blending ratio of raw materials used or by adjusting the manufacturing conditions in the production of the carboxyl group-containing phenol resin described below.

[0029] Carboxylate-containing phenolic resins can typically be produced by reacting a carboxylic acid compound with a reaction product obtained by reacting phenols with aldehydes (Step 1). In detail, when producing a novolac-type carboxyl group-containing phenol resin, step 1 includes a step of condensing phenols and aldehydes in the presence of an acid catalyst to obtain a novolac-type phenol resin (step 1-1a), and a step of reacting the novolac-type phenol resin obtained in step 1-1a with a carboxylic acid compound in the presence of a basic catalyst to obtain a novolac-type carboxyl group-containing phenol resin (step 1-2a). When producing a resol-type carboxyl group-containing phenol resin, step 1 includes a step of condensation polymerization of phenols, aldehydes, and carboxylic acid compounds under a basic catalyst (step 1b). Alternatively, when producing a resol-type carboxyl group-containing phenol resin, step 1 includes a step of condensation polymerization of phenols and aldehydes in the presence of an acid catalyst to obtain a novolac-type phenol resin (step 1-1b), a step of reacting the novolac-type phenol resin obtained in step 1-1b with a carboxylic acid compound in the presence of a basic catalyst to obtain a novolac-type carboxyl group-containing phenol resin (step 1-2b), and a step of reacting the novolac-type carboxyl group-containing phenol resin obtained in step 1-2b with aldehydes in the presence of a basic catalyst to introduce methylol groups into the novolac-type carboxyl group-containing phenol resin to obtain the desired resol-type carboxyl group-containing phenol resin (step 1-3b).

[0030] Phenols that can be used in the production of carboxyl group-containing phenolic resins include phenols; cresols such as o-cresol, m-cresol, and p-cresol; ethylphenols such as o-ethylphenol, m-ethylphenol, and p-ethylphenol; butylphenols such as isopropylphenol, butylphenol, and p-tert-butylphenol; alkylphenols such as p-tert-amylphenol, p-octylphenol, p-nonylphenol, and p-cumylphenol; halogenated phenols such as fluorophenol, chlorophenol, bromophenol, and iodophenol; monovalent phenol-substituted compounds such as p-phenylphenol, aminophenol, nitrophenol, dinitrophenol, and trinitrophenol; monovalent phenols such as 1-naphthol and 2-naphthol; and polyvalent phenols such as resorcinol, alkylresorcinol, pyrogallol, catechol, alkylcatechol, hydroquinone, alkylhydroquinone, phloroglucin, bisphenol A, bisphenol F, bisphenol S, and dihydroxynaphthalene. These can be used individually or in combination of two or more. In particular, from the standpoint of manufacturing costs, it is preferable to use phenol.

[0031] Examples of aldehydes that can be used in the production of carboxyl group-containing phenolic resins include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, hexamethylenetetramine, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxymethylene, phenylacetaldehyde, o-tolualdehyde, and salicylaldehyde. These may be used individually or in combination of two or more. Precursors of these aldehydes or solutions of these aldehydes can also be used. Among these, from the viewpoint of production cost, it is preferable to use an aqueous formaldehyde solution.

[0032] The carboxylic acid compounds used in the production of carboxyl group-containing phenolic resins are used to derive the structural unit represented by formula (1) above, in which a -X-COOH group is bonded to the oxygen atom of a phenolic hydroxyl group. Here, "X" in the -X-COOH group is synonymous with "X" in formula (1) and represents an alkylene group having 1 to 6 carbon atoms. Examples of such carboxylic acid compounds include the compound represented by formula (CA). LX-COOH (CA) In formula (CA), L represents a halogen, and X represents an alkylene group having 1 to 6 carbon atoms. Specific examples of carboxylic acid compounds represented by formula (CA) include, but are not limited to, 1-chloroacetic acid, 1-bromoacetic acid, 1-iodoacetic acid, 2-chloropropionic acid, 3-chlorobutyric acid, or their alkali metal salts (e.g., sodium 1-chloroacetate).

[0033] Examples of acid catalysts that can be used in the production of carboxyl group-containing phenolic resins include organic acids such as acetic acid, formic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, benzoic acid, salicylic acid, sulfonic acid, phenolsulfonic acid, and p-toluenesulfonic acid; or inorganic acids such as hydrochloric acid, sulfuric acid, sulfuric acid esters, phosphoric acid, and phosphoric acid esters.

[0034] Basic catalysts that can be used in the production of carboxyl group-containing phenolic resins include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; carbonates such as sodium carbonate and calcium carbonate; oxides such as lime; sulfites such as sodium sulfite; phosphates such as sodium phosphate; and amines such as ammonia, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, hexamethylenetetramine, and pyridine.

[0035] In the reaction between phenols and aldehydes in step 1-1a above, the molar ratio of aldehydes to phenols (F / P) is, for example, 0.5 or more, preferably 0.55 or more, and more preferably 0.6 or more. The upper limit of the molar ratio of aldehydes to phenols (F / P) is, for example, 1.2 or less, preferably 1.1 or less, and more preferably 1.0 or less. By carrying out the reaction under conditions where the molar ratio of aldehydes to phenols (F / P) is within the above range, a novolac-type carboxyl group-containing phenol resin having a desired weight-average molecular weight can be obtained.

[0036] In step 1-1a, the step of reacting phenols and aldehydes in the presence of an acid catalyst is preferably carried out at a temperature of, for example, 60°C to 120°C, preferably 80°C to 100°C, for a reaction time of, for example, 10 to 100 minutes. This allows the reaction to proceed efficiently and sufficiently. In step 1-2a, the step of reacting a novolac-type phenol resin and a carboxylic acid compound in the presence of a basic catalyst is preferably carried out by adding the basic catalyst to the reaction mixture obtained in step 1-1a, followed by adding the carboxylic acid compound, and at a temperature of, for example, 60°C to 120°C, preferably 80°C to 100°C, for a reaction time of, for example, 10 to 180 minutes. By carrying out the above process under heating, the starting materials are uniformly mixed, and the molecular weight of the resulting novolac-type carboxyl group-containing phenolic resin can be made uniform through intermolecular entanglement and interaction. There are no particular restrictions on the reaction time, and it should be determined appropriately depending on the type of starting materials, the molar ratio of the mixture, the amount and type of catalyst used, and the reaction conditions.

[0037] Water is commonly used as the reaction solvent for the production of novolac-type carboxyl group-containing phenolic resins in steps 1-1a and 1-2a, but organic solvents may also be used. Specific examples of such organic solvents include alcohols, ketones, and aromatics. Specific examples of alcohols include methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerin. Specific examples of ketones include acetone and methyl ethyl ketone. Specific examples of aromatics include toluene and xylene.

[0038] The weight-average molecular weight of the novolac-type carboxyl group-containing phenol resin obtained through steps 1-1a and 1-2a is, for example, 100 to 8,000, preferably 400 to 7,000, and more preferably 500 to 6,000. The novolac-type carboxyl group-containing phenol resin having the above weight-average molecular weight range is preferred because it is soluble in water. Furthermore, the cured product obtained by curing it is preferred because it has high mechanical strength and heat resistance.

[0039] The novolac-type carboxyl group-containing phenol resin produced by the above method may be subjected to post-treatment to remove unreacted free phenols as needed. For post-treatment, a method of atmospheric distillation up to 150°C followed by reduced-pressure distillation at 500 Pa up to 250°C can be used. The novolac-type carboxyl group-containing phenol resin obtained by the above method has a reduced content of unreacted free phenols to 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less. Furthermore, the novolac-type carboxyl group-containing phenol resin obtained by the above method has a reduced content of unreacted free aldehydes to 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

[0040] If the carboxyl group-containing phenol resin used in the resin composition of this embodiment is of the resol type, the basic catalyst used in its production will be present in the reaction product. When a metal hydroxide such as sodium hydroxide is used as the basic catalyst, the metal hydroxide will remain in the cured phenol resin, which will lead to a decrease in the water resistance of the cured product. Therefore, it is preferable that the basic catalyst used in step 1-2 be a non-metallic catalyst such as an amine.

[0041] In step 1b above, the step of reacting phenols, aldehydes, and carboxylic acid compounds is carried out by charging these starting materials into a reaction vessel in a ratio such that the molar ratio of aldehydes to phenols (F / P) is, for example, 0.7 or more, preferably 1.0 to 2.0, and more preferably 1.2 to 1.9, and then adding the above-mentioned basic catalyst as a polymerization catalyst, and refluxing for an appropriate time. By carrying out the reaction under conditions where the molar ratio of aldehydes to phenols (F / P) is within the above range, gelation is suppressed, and a resol-type carboxyl group-containing phenol resin having the desired weight-average molecular weight can be obtained.

[0042] In the production of resol-type carboxyl group-containing phenolic resin in step 1b, the step of reacting phenols, aldehydes, and carboxylic acid compounds in the presence of a basic catalyst is preferably carried out at a temperature of, for example, 60°C to 120°C, preferably 80°C to 100°C, for a reaction time of, for example, 10 to 100 minutes. This allows the reaction to proceed efficiently and sufficiently. Furthermore, by carrying out the reaction under heating, the starting materials are uniformly mixed, and the molecular weight of the resulting resol-type carboxyl group-containing phenolic resin can be made uniform through intermolecular entanglement and interaction. The reaction time is not particularly limited and should be appropriately determined according to the type of starting materials, the molar ratio of the blending, the amount and type of catalyst used, and the reaction conditions.

[0043] Water is commonly used as the reaction solvent for the synthesis of the resol-type carboxyl group-containing phenolic resin in step 1b, but organic solvents may also be used. Specific examples of such organic solvents include alcohols, ketones, and aromatics. Specific examples of alcohols include methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerin. Specific examples of ketones include acetone and methyl ethyl ketone. Specific examples of aromatics include toluene and xylene.

[0044] The weight-average molecular weight of the resol-type carboxyl group-containing phenol resin obtained through step 1b is, for example, 100 to 2,000, preferably 200 to 1,500, and more preferably 500 to 1,000. A resol-type carboxyl group-containing phenol resin having a weight-average molecular weight within the above range is preferred because it is easily emulsified. Furthermore, the cured product obtained by curing it is preferred because it has high mechanical strength and heat resistance.

[0045] When the production of resol-type carboxyl group-containing phenol resin is carried out using the method of steps 1-1b to 1-3b, the step of reacting phenols and aldehydes in the presence of an acid catalyst in step 1-1b can be carried out under the same conditions as in step 1-1a. The subsequent steps 1-2b can also be carried out under the same conditions as steps 1-2a. In the subsequent step 1-3b, a predetermined amount of aldehydes and a basic catalyst are added to the reaction mixture containing the novolac-type carboxyl group-containing phenol resin obtained in step 1-2b, and the mixture is heated, for example, at a temperature of 60°C to 120°C, preferably 80°C to 100°C, for a period of 10 to 100 minutes. This introduces methylol groups into the aromatic rings of the novolac-type carboxyl group-containing phenol resin obtained in step 1-2b, thereby yielding a resol-type carboxyl group-containing phenol resin.

[0046] The weight-average molecular weight of the resol-type carboxyl group-containing phenol resin obtained through steps 1-1b to 1-3b is, for example, 100 to 8,000, preferably 400 to 7,000, and more preferably 500 to 6,000. Resol-type carboxyl group-containing phenol resins having a weight-average molecular weight within the above range are preferred because they are easily emulsified. Furthermore, the cured product obtained by curing them is preferred because it has high mechanical strength and heat resistance.

[0047] The resol-type carboxyl group-containing phenol resin obtained by the above-described step 1b or the method of steps 1-1b to 1-3b has a reduced content of unreacted free phenols to 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less. Furthermore, the resol-type carboxyl group-containing phenol resin obtained by the above-described method has a reduced content of unreacted free aldehydes to 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

[0048] (amine) The resin composition of this embodiment contains an amine. In the resin composition, the amine interacts with the carboxyl group of the carboxyl group-containing phenol resin (the carboxyl group possessed by the structural unit represented by formula (1)), thereby neutralizing the carboxyl group, and the carboxyl group-containing phenol resin exists as a water-soluble oil.

[0049] The amine used in the resin composition of this embodiment is preferably a tertiary amine that has appropriate basicity for neutralizing the carboxyl group-containing phenol resin and is also water-soluble. Examples of such tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, trioctylamine, diisopropylethylamine, quinuclidine, 1,4-diazabicyclo[2.2.2]octane (DABCO), triethanolamine, triisopropanolamine, N-dimethylaminoethanol, N-diethylaminoethanol, pyridine, 2,6-lutidine, 4-dimethylaminopyridine, quinoline, isoquinoline, and the like. Among these, N-dimethylaminoethanol is preferred because it has appropriate basicity, is water-soluble, and is readily available.

[0050] (Water-soluble plasticizer) In another embodiment, the resin composition of the present invention may contain a water-soluble plasticizer. Examples of usable water-soluble plasticizers include polyvinyl alcohol, polyvinyl acetal, gum arabic, hydroxyethylcellulose, and carboxymethylcellulose. More specific examples of water-soluble plasticizers include polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyethylene oxide, polyacrylamides, gelatin, casein, cellulose derivatives, methylcellulose, carboxymethylcellulose, carboxyethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, polysaccharides and their derivatives, starch, gum arabic, and guar gum. A single water-soluble plasticizer may be used, or two or more may be used in combination.

[0051] The amount of water-soluble plasticizer is, for example, 1% by mass or more and 40% by mass or less, preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, relative to the water-soluble phenolic resin solids.

[0052] (Method for manufacturing resin compositions) The resin composition of this embodiment can be produced by mixing the carboxyl group-containing phenol resin and the amine described above in water. The carboxyl group-containing phenol resin can be blended in an amount such that the solid content of the resulting resin composition is 10 to 90% by mass. The solid content can be changed by adjusting the amount of water used, and can be adjusted to a desired range depending on the application of the resin composition. The amount of amine blended is, for example, 0.3 moles to 2.0 moles, preferably 0.5 moles to 1.5 moles, per mole of carboxyl groups in the carboxyl group-containing phenol resin. A resin composition containing the carboxyl group-containing phenol resin and the amine in such blending amounts has excellent handling properties and excellent adhesive properties.

[0053] The resin composition of this embodiment may further contain additives depending on its intended use. Examples of additives that can be used include thixotropes, toughness modifiers, thickeners, and curing accelerators.

[0054] (Properties of resin compositions) When the resin composition of this embodiment is formed into a resin film in the B stage under the following conditions, the resin film dissolves in methanol. Conditions: The resin composition is applied to a substrate and dried at 110°C to produce a B-stage resin film with a thickness of 100 μm. The resin composition of this embodiment has low tackiness in the B-stage state (after pre-drying).

[0055] [Pre-coated metal sheet] The pre-coated metal sheet of this embodiment comprises a metal sheet and a coating film formed from the resin composition of this embodiment, which is provided on at least one surface of the metal sheet. The pre-coated substrate of this embodiment is manufactured by applying the resin composition of this embodiment to a metal plate, and then pre-drying the resin film to form a coating in the B-stage state. The application method can include spray coating, roll coating, etc. Next, the applied resin composition is heated, for example, at 100°C for 20 minutes to dry out the water, which is the solvent. The coating film thus formed preferably has a thickness of 1 μm to 50 μm.

[0056] The metal sheets used in the pre-coated metal sheets of this embodiment are iron sheets, steel sheets, iron alloy sheets, stainless steel sheets, aluminum sheets, aluminum alloy sheets, magnesium alloy sheets, titanium sheets, titanium alloy sheets, copper sheets, or copper alloy sheets.

[0057] (Application) The pre-coated metal sheet of this embodiment is used for bonding metal to dissimilar materials, or for bonding metal to metal. As a metal sheet with an adhesive layer, it is used, for example, for bonding dissimilar materials such as rubber components, friction materials, plastic molded products, and fiber-reinforced plastics to metal, or for bonding structural steel, high-tensile steel, electrical steel, and aluminum alloys. Specifically, it is used to bond a metal sheet that has been coated with an adhesive in the B-stage state and processed into a predetermined shape, by heating and pressurizing it at a temperature of about 150°C to cure the adhesive. The resin composition of this embodiment does not contain organic solvents, so no volatilization of organic solvents occurs during heating and drying. Therefore, it has a low environmental impact. Furthermore, since the resin composition of this embodiment is in the B-stage state after pre-drying, problems such as the resin composition adhering to conveyor rolls do not occur, and it does not stick when stacked, resulting in excellent workability.

[0058] The embodiments of the present invention have been described above, but these are merely examples, and various other configurations can also be adopted. [Examples]

[0059] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto. [Preparation Example: Preparation of Carboxyloid-Containing Phenolic Resin and Composition] (Synthesis Example 1: Synthesis of Unmodified Novolac-Type Phenolic Resin A) A mixture of 1000 parts phenol, 570 parts 37% formalin (F), and 10 parts oxalic acid was reacted at 100°C for 3 hours. The reaction mixture was then dehydrated by atmospheric distillation until its temperature reached 140°C. Further dehydration and demonomerization were carried out by vacuum distillation, gradually reducing the pressure to 0.9 kPa until the reaction mixture reached 220°C, yielding a novolac-type phenolic resin A with a hydroxyl equivalent of 106. The molar ratio of formalin to phenol was 0.77.

[0060] (Preparation Example 1) 250 parts of novolac-type phenolic resin A were melted and dissolved in 125 parts of butanol. 84 parts of 50% sodium hydroxide solution and 100 parts of pure water were added. 90 parts of sodium chloroacetate were added to the resulting mixture and reacted at 80°C for 2 hours. Then, 195 parts of 25% sulfuric acid aqueous solution were added to neutralize the mixture. Subsequently, the mixture was washed four times with 500 parts of pure water each time to remove the neutralized salts. Next, 120 parts of amino alcohol and 240 parts of water were added and neutralized to obtain an aqueous solution of novolac-type carboxyl group-containing phenolic resin (phenolic resin aqueous solution 1). The non-volatile content was 45% by mass.

[0061] (Preparation Example 2) 250 parts of novolac-type phenolic resin A were melted and dissolved in 125 parts of butanol. 84 parts of 50% sodium hydroxide solution and 100 parts of pure water were added. 90 parts of sodium chloroacetate were added to the resulting mixture and reacted at 80°C for 2 hours. Then, 195 parts of 25% sulfuric acid aqueous solution were added to neutralize the mixture. Subsequently, the neutralized salts were removed by washing four times with 500 parts of pure water each time. After that, 75 parts of dimethylaminoethanol and 80 parts of 37% formalin aqueous solution were added and reacted at 60°C for 1 hour to methylolate the mixture. 300 parts of pure water were added to obtain an aqueous solution of resol-type carboxyl group-containing phenolic resin (phenolic resin aqueous solution 2). The non-volatile content was 42% by mass.

[0062] (Preparation Example 3) 1000 parts of phenol and 1000 parts of 37% formalin were mixed with 20 parts of a 50% sodium hydroxide aqueous solution and reacted at 75°C for 2 hours to obtain an aqueous solution of a water-soluble resol-type phenolic resin (phenolic resin aqueous solution 3). The non-volatile content was 53% by mass.

[0063] (Preparation Example 4) 1000 parts by weight of phenol, 1510 parts by weight of a 37% formalin aqueous solution, and 50 parts by weight of triethylamine were added and reacted under reflux conditions for 40 minutes. Then, under reduced pressure of 91 kPa, dehydration was carried out, and when the temperature in the system reached 70°C, 400 parts by weight of methanol was added and the mixture was reacted at 80°C for 2 hours. 1200 parts by weight of methanol was added and mixed to obtain a methanol solution of a non-water-soluble resol-type phenolic resin (phenolic resin methanol solution 4). The non-volatile content was 55% by mass.

[0064] (Preparation Example 5) 250 parts of novolac-type phenolic resin A were melted, then 6 parts of calcium hydroxide and 115 parts of 37% formaldehyde were added, and the mixture was heated to 80°C and reacted for 2 hours. The pH was neutralized with sulfuric acid to 5.0, and then the mixture was distilled under reduced pressure at 15000 Pa to adjust the solid content to 75% by mass. Subsequently, 140 parts of polyacrylamide (Arakawa Chemical Industries, Polystrom 117, 15% by mass aqueous solution) were added, and 205 parts of water were added and stirred for 1 hour to obtain an aqueous dispersion of a water-insoluble resol-type phenolic resin (phenolic resin dispersion 5). The non-volatile content was 40% by mass.

[0065] [Examples 1-4, Comparative Examples 1-4] The components shown in Table 1 were mixed in the amounts shown in Table 1 to prepare the resin composition. Details of each component listed in Table 1 are shown below. (Phenolic resin) • Phenolic resin aqueous solution 1: Phenolic resin aqueous solution 1 obtained in Preparation Example 1 • Phenolic resin aqueous solution 2: Phenolic resin aqueous solution 2 obtained in Preparation Example 1 • Phenolic resin aqueous solution 3: Phenolic resin aqueous solution 3 obtained in Preparation Example 1 • Phenolic resin organic solvent solution 4: Phenolic resin methanol solution 4 obtained in Preparation Example 4 • Phenolic resin dispersion 5: Phenolic resin dispersion 5 obtained in Preparation Example 5 (Water-soluble plasticizer) • Polyvinyl alcohol aqueous solution: A 5% by mass aqueous solution of polyvinyl alcohol (manufactured by Kuraray, PVA117) was prepared. • Polyvinyl acetal aqueous solution: A polyvinyl acetal aqueous solution (manufactured by Sekisui Chemical Co., Ltd., KW-10) was diluted with water to prepare a 5% by mass solid content aqueous solution. • Polyvinyl acetal alcohol solution: A 5% by mass methanol aqueous solution of polyvinyl acetal (manufactured by Sekisui Chemical Co., Ltd., BX-L) was prepared.

[0066] (Evaluation of physical properties of resin compositions) (form) The morphology of the resin composition in each example was observed visually. When the phenolic resin is dissolved in water, it is described as an "aqueous solution"; when the phenolic resin is dissolved in methanol, it is described as an "organic solvent solution"; and when the phenolic resin is insoluble in water and suspended, it is described as a "dispersion," as shown in Table 1. (Tuck-type) Each example resin composition was applied to a degreased pickled steel sheet (SPHC-P) measuring 100 mm in length, 25 mm in width, and 1.6 mm in thickness, so that a coating film of 80-120 μm would form after drying. Subsequently, the sheets were dried under drying conditions 1-3 to obtain coated steel sheet samples. - Drying conditions 1: 15 minutes at 110°C - Drying conditions 2: 110°C for 30 minutes - Drying conditions 3: 110°C for 60 minutes The tackiness of the coating on the obtained coated steel sheet samples was checked by touch. If the resin adhered to the finger, it was classified as "tacky," and if it did not adhere, it was classified as "not tacky," as shown in Table 1. "Not tacky" indicates that the coating has low tackiness and that the coated steel sheet is easy to handle.

[0067] (Methanol solubility) Coated steel sheet samples were obtained in the same manner as the tackiness evaluation described above. Each coated steel sheet sample was immersed in methanol for 30 minutes, stirred, and then wiped with a methanol-soaked cloth to check for remaining coating. Samples with less than 80% remaining coating were evaluated as "solubility present," and those with 80% or more remaining coating were evaluated as "non-solubility present." "Soluble" indicates good handling properties of the coated steel sheet.

[0068] (Adhesive strength) A coated steel sheet was obtained in the same manner as the tackiness evaluation described above. The coated surfaces of the pickled steel sheets were bonded together with an adhesive area of ​​150 mm². 2 The plates were bonded together in this manner and then heated and pressed at a surface pressure of 5 MPa and 160°C for 30 minutes. The bonded steel plates were then pressed at a head speed of 0.5 mm. 2 A shear tensile test was performed at MPa / min to measure the tensile strength, and the adhesive strength (MPa) was defined as the value obtained by dividing the tensile strength by the adhesive area. The results are shown in Table 1. A higher adhesive strength value indicates better adhesion of the coating film.

[0069] [Table 1]

Claims

1. A resin composition for metal bonding comprising a water-soluble carboxyl group-containing phenol resin, an amine, and water, The resin composition is in the form of an aqueous solution, The water-soluble carboxyl group-containing phenol resin has a structural unit represented by formula (1) and a structural unit represented by formula (2), 【Chemistry 1】 In equation (1), X is an alkylene group having 1 to 6 carbon atoms. R １ These are independently a hydrogen atom, a C1-C20 alkyl group, a hydroxyl group, or -CH ２ OH, 【Chemistry 2】 In equation (2), R ２ These are independently a hydrogen atom, a C1-C20 alkyl group, a hydroxyl group, or -CH ２ A resin composition containing OH.

2. The resin composition according to claim 1, wherein the proportion of the structural unit represented by formula (1) in the carboxyl group-containing phenol resin is 5 mol% or more and 90 mol% or less with respect to the entire carboxyl group-containing phenol resin.

3. The resin composition according to claim 1, wherein the amine includes a tertiary amine.

4. The resin composition according to claim 1, further comprising a water-soluble plasticizer.

5. The resin composition according to claim 4, wherein the water-soluble plasticizer comprises at least one selected from polyvinyl alcohol, polyvinyl acetal, gum arabic, hydroxyethylcellulose, and carboxymethylcellulose.

6. The resin composition according to claim 4, wherein the amount of the water-soluble plasticizer is 1% by mass or more and 40% by mass or less with respect to the water-soluble phenolic resin solids.

7. The resin composition according to claim 1, When the resin composition is prepared as a B-stage resin film under the following conditions, the resin film dissolves in methanol in the following resin composition: Condition: The resin composition is applied to a substrate and dried at 110°C to produce a B-stage resin film with a thickness of 100 μm.

8. A pre-coated metal plate comprising a metal plate and a coating film provided on at least one surface of the metal plate, The coating film is a coating film formed from the resin composition described in claim 1. Pre-coated metal sheet.

9. The pre-coated metal plate according to claim 8, wherein the coating film has a thickness of 1 μm or more and 50 μm or less.

10. The pre-coated metal plate according to claim 8, wherein the metal plate is an iron plate, a steel plate, an iron alloy plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a magnesium alloy plate, a titanium plate, a titanium alloy plate, a copper plate, or a copper alloy plate.

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