JP7615528B2 - Curable composition, cured product and adhesive - Google Patents

Description

The present invention relates to a curable composition that has excellent moisture and heat resistance, good flexibility and toughness in the cured product, and is suitable for use as an adhesive, as well as to the cured product and adhesive.

In recent years, from the viewpoint of energy saving, lightweight materials such as aluminum, magnesium, and plastics are increasingly being used as structural materials, and adhesives are increasingly being used in place of welding in assembly. Adhesives for automobiles and other structural members are required to have good adhesion between different materials and to be able to withstand changes in temperature and humidity in the environment in which they are used. In order to meet these requirements, for example, adhesives that combine bisphenol-type epoxy resins with urethane-modified epoxy resins or rubber-modified epoxy resins have been provided from the viewpoint of maintaining adhesiveness by improving conformity to the substrate (see, for example, Patent Document 1). However, when a flexible skeleton is introduced by modifying the epoxy resin, there is an upper limit to the amount of the flexible skeleton that can be introduced, and it may not be possible to fully meet the increasingly advanced requirements. Furthermore, from the viewpoint of moisture and heat resistance, improvements are also required in the point that moisture can easily enter the interface between the substrate and the cured product due to the hydrophobicity of the cured product (adhesive layer), which easily causes interfacial peeling.

JP 2010-185034 A

The problem that the present invention aims to solve is to provide a curable composition and its cured product, as well as an adhesive, that have excellent moisture and heat resistance, good flexibility and toughness, and can be suitably used in adhesive applications.

As a result of intensive research into solving the above problems, the inventors discovered that the above problems could be solved by using an isocyanate prepolymer made from a specific polyol as a raw material in combination with an epoxy resin, and thus completed the present invention.

That is, the present invention provides a curable composition characterized by containing an isocyanate prepolymer (A) whose essential raw materials are a polyol (a1) containing a polyoxyethylene unit, a polyoxypropylene unit, and a polyoxytetramethylene unit, and a polyisocyanate (a2), an epoxy resin (B), and a curing agent or curing accelerator (C), a curable product thereof, and an adhesive comprising the curable composition.

The present invention provides a curable composition and its cured product, as well as an adhesive, that have good flexibility and toughness in the cured product and excellent resistance to moisture and heat, and are suitable for use as adhesives.

The present invention will be described in detail below.
The present invention is characterized by containing an isocyanate prepolymer (A) containing, as essential raw materials, a polyol (a1) containing a polyoxyethylene unit, a polyoxypropylene unit, and a polyoxytetramethylene unit, and a polyisocyanate (a2), an epoxy resin (B), and a curing agent or curing accelerator (C).

The present invention is characterized in that polyoxyethylene units, polyoxypropylene units, and polyoxytetramethylene units coexist in polyol (a1) as described above. By including polyoxyethylene units, when used as an adhesive, it is possible to incorporate a certain amount of moisture into the adhesive layer (cured product), and as a result, even if peeling occurs, interfacial peeling is suppressed, and due to high cohesive failure, it is possible to fully function as an adhesive. In addition, compared to when only polyoxytetramethylene units are used as raw materials, which have excellent moist heat resistance but tend to lack flexibility and are prone to interfacial peeling, by including the polyoxyethylene units and polyoxypropylene units, the adhesive has an excellent balance of performance.

The polyoxyethylene units, polyoxypropylene units, and polyoxytetramethylene units contained in the polyol (a1) do not need to be present in the same molecule. For example, a polyol containing only polyoxyethylene units, a polyol containing only polyoxypropylene units, and a polyol containing only polyoxytetramethylene units may be used in combination to react with the polyisocyanate (a2) described below.

In particular, from the viewpoint of ease of adjusting the content of each unit, it is preferable to use a mixture of polyol (a1-1) containing polyoxyethylene units and polyoxypropylene units and polyoxytetramethylene polyol (a1-2), and it is particularly preferable to use a polyoxyethylene-polyoxypropylene copolymer as polyol (a1-1).

The polyoxyethylene-polyoxypropylene copolymer is preferably a copolymer having three or more functionalities from the viewpoint of superior adhesiveness. The polyoxytetramethylene polyol is preferably a copolymer having two or more functionalities from the viewpoint of superior adhesiveness.

When polyol (a1-1) is a copolymer of polyoxyethylene and polyoxypropylene, it is preferable that the number of repeating oxyethylene units in the polyoxyethylene is in the range of 2 to 10, from the viewpoint of excellent adhesion to a substrate when used as an adhesive, and an excellent balance between mechanical strength and moist heat resistance.

The mass ratio of the polyoxyethylene units to the polyoxypropylene units in the polyol (a1) is preferably in the range of 40/60 to 1/99 from the viewpoints of suppressing interfacial peeling, ensuring adhesion to the substrate, and achieving a better balance between flexibility and toughness of the cured product, and is particularly preferably in the range of 30/70 to 1/99 from the viewpoint of moisture and heat resistance.

Furthermore, when a mixture of polyol (a1-1) containing polyoxyethylene units and polyoxypropylene units and polyoxytetramethylene polyol (a1-2) is used, the mass ratio of (a1-1)/(a1-2) is preferably in the range of 10/90 to 60/40 from the viewpoint of excellent balance of performance.

The polyol (a1) may contain units other than polyoxyethylene, polyoxypropylene, and polyoxytetramethylene, as long as the effects of the present invention are not impaired. Examples of other units include aliphatic dihydric alcohols such as neopentane glycol; glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3,4-pentanetriol, pentamethylglycerin, Examples of repeating units include trihydric alcohols such as pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, and trimethylolpropane; tetrahydric alcohols such as erythritol, pentaerythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,3,5-pentanetetrol, and 1,3,4,5-hexanetetrol; pentahydric alcohols such as adonite, arabitol, and xylitol; and hexahydric alcohols such as sorbitol, mannitol, and idit, either alone or in combination.

The polyol (a1) used in the present invention may be any polyol containing a polyoxyethylene unit, a polyoxypropylene unit, or a polyoxytetramethylene unit, and other structures are not particularly limited. For example, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol, both of which have hydroxyl groups at both ends, may be used as is, or polyester polyols, which are reaction products of these glycols with polycarboxylic acids, or alkylene oxide adducts of castor oil, may be used.

In order to adjust the content of polyoxyethylene units, it is also preferable to mix a polyoxyethylene-polyoxypropylene copolymer with a polyoxypropylene polyol and further mix with polyoxytetramethylene polyol.

The polyol (a1) preferably contains a difunctional component, a tetrafunctional component, and a trifunctional component in particular, from the viewpoint of superior adhesion to the substrate. The number average molecular weight of the polyol (a1) is preferably in the range of 1,000 to 7,000, and more preferably in the range of 2,000 to 5,000.

The polyisocyanate (a2) used in the present invention may be any compound having two or more isocyanate groups in one molecule, and is preferably a compound having 2 to 4 isocyanate groups in particular from the viewpoint of facilitating molecular weight adjustment of the isocyanate prepolymer (A), and is most preferably a diisocyanate.

Examples of the polyisocyanate (a2) include propane-1,2-diisocyanate, 2,3-dimethylbutane-2,3-diisocyanate, 2-methylpentane-2,4-diisocyanate, octane-3,6-diisocyanate, 3,3-dinitropentane-1,5-diisocyanate, octane-1,6-diisocyanate, 1,6-hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, lysine diisocyanate, and tolylene diisocyanate. (TDI), xylylene diisocyanate, metatetramethylxylylene diisocyanate, isophorone diisocyanate (3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate), 1,3- or 1,4-bis(isocyanatemethyl)cyclohexane, diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), hydrogenated tolylene diisocyanate, and mixtures thereof.

Among these, from the viewpoints of ease of controlling the reaction with the polyol (a1) and ease of raw material availability, it is preferable to use hexamethylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, and it is particularly preferable to use isophorone diisocyanate.

In the present invention, a blocked isocyanate prepolymer obtained by blocking a polyurethane obtained by using a polyisocyanate (a2) so that there are excess isocyanate groups relative to the hydroxyl groups in the polyol (a1) with a blocking agent (a3) is particularly preferred from the viewpoint of better storage stability when made into a curable composition.

The reaction between the polyol (a1) and the polyisocyanate (a2) is not particularly limited, and may be carried out as a normal urethane reaction. For example, the reaction temperature is 40 to 140°C, preferably 60 to 130°C, and various urethane polymerization catalysts can be used to promote the reaction, such as organometallic compounds such as dioctyltin dilaurate, dibutyltin dilaurate, stannous octoate, stannous octoate, lead octoate, lead naphthenate, and zinc octoate, and tertiary amine compounds such as triethylenediamine and triethylamine.

The excess amount of isocyanate groups relative to hydroxyl groups in the polyol (a1) is preferably in the range of 2.05 to 3.50 moles of isocyanate groups per mole of hydroxyl groups, from the viewpoints of making it easier to adjust the molecular weight of the resulting prepolymer and reducing unreacted polyisocyanate.

It is preferable to block the excess isocyanate groups using a blocking agent (a3) as described above. Examples of blocking agents (a3) include active methylene compounds such as malonic acid diesters (diethyl malonate, etc.), acetylacetone, and acetoacetate esters (ethyl acetoacetate, etc.); oxime compounds such as acetoxime, methyl ethyl ketoxime (MEK oxime), and methyl isobutyl ketoxime (MIBK oxime); monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, heptyl alcohol, hexyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol, and stearyl alcohol, or isomers thereof; methyl glycol, ethyl glycol derivatives such as ethyl glycol, ethyl diglycol, ethyl triglycol, butyl glycol, and butyl diglycol; amine compounds such as dicyclohexylamine; monohydric phenol compounds such as phenol, cresol, ethylphenol, n-propylphenol, isopropylphenol, butylphenol, tertiary butylphenol, octylphenol, nonylphenol, dodecylphenol, cyclohexylphenol, chlorophenol, and bromophenol; dihydric phenol compounds such as resorcin, catechol, hydroquinone, bisphenol A, bisphenol S, bisphenol F, and naphthol; ε-caprolactone, ε-caprolactam, and the like, which may be used alone or in combination of two or more.

Among these, monohydric phenol compounds are preferred from the viewpoint of being less likely to affect the reaction when preparing the curable composition and obtaining the cured product, and alkylphenols having an alkyl group with 1 to 8 carbon atoms are particularly preferred, and p-t-butylphenol is most preferred from the viewpoint of safety.

The blocking reaction can be carried out by a known reaction method, and the amount of blocking agent (a3) used is usually 1 to 2 equivalents, preferably 1.05 to 1.5 equivalents, relative to the free isocyanate groups.

The blocking reaction with the blocking agent (a3) is usually carried out by adding the blocking agent (a3) in the final reaction of the polyurethane polymerization, but the blocking agent (a3) can also be added and reacted at any stage of the polyurethane polymerization to obtain a blocked isocyanate prepolymer.

The blocking agent (a3) can be added at the end of the polymerization, at the beginning of the polymerization, or partially at the beginning of the polymerization and the remainder at the end of the polymerization. It is preferably added at the end of the polymerization. In this case, the isocyanate % can be used as a standard for the end of the polymerization. The reaction temperature when the blocking agent is added is usually 50 to 150°C, preferably 60 to 120°C. The reaction time is usually about 1 to 7 hours. The reaction can be accelerated by adding the urethane polymerization catalyst during the reaction. A plasticizer can also be added in any amount during the reaction.

The weight average molecular weight of the isocyanate prepolymer (A) in the present invention is preferably in the range of 4,000 to 15,000 from the viewpoint of easy handling when the curable composition is used as an adhesive, and is particularly preferably in the range of 5,000 to 10,000.

In the present invention, the number average molecular weight (Mn) of the polyol is a value calculated from the hydroxyl value and the number of functional groups, and the other weight average molecular weights (Mw) are values measured by gel permeation chromatography (GPC) under the following conditions.

Measuring device: Tosoh Corporation HLC-8220GPC
Column: TSK-GUARD COLUMN SuperHZ-L manufactured by Tosoh Corporation
+ Tosoh Corporation TSK-GEL Super HZM-M x 4
Detector: RI (differential refractometer)
Data processing: Multistation GPC-8020 model II manufactured by Tosoh Corporation
Measurement conditions: Column temperature: 40°C
Solvent Tetrahydrofuran
Flow rate: 0.35 ml/min. Standard: Monodisperse polystyrene Sample: 100 μl of a tetrahydrofuran solution containing 0.2% by mass of resin solids filtered through a microfilter

The epoxy resin (B) used in the present invention is not particularly limited, and various types can be used. When used as an adhesive, it is preferable that the epoxy resin is liquid at room temperature, and examples thereof include bisphenol-type or biphenol-type epoxy resins such as tetramethylbiphenol-type epoxy resins, bisphenol A-type epoxy resins, and bisphenol F-type epoxy resins; aliphatic polyol polyglycidyl ethers such as butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerin triglycidyl ether; ring-structure-containing polyglycidyl compounds such as diglycidyl aniline, resorcinol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether; ring-structure-containing monofunctional glycidyl compounds such as alkylphenol monoglycidyl ether; and polyglycidyl ester compounds such as neodecanoic acid glycidyl ester. Among these, it is preferable to use bisphenol-type or biphenol-type epoxy resins because they provide cured products with excellent flexibility, toughness, etc., and bisphenol-type epoxy resins are preferred from the viewpoint of industrial availability. In particular, the ratio of bisphenol-type epoxy resins to the total mass of epoxy resin (B) is preferably 50 mass% or more, and more preferably 70 mass% or more.

The bisphenol- or biphenol-type epoxy resins include, for example, those obtained by using various bisphenol compounds or biphenol compounds and epihalohydrin as resin raw materials, specifically, those represented by the following structural formula (1):

［式中Ｘはそれぞれ独立に下記構造式（２－１）～（２－８）

[wherein X is independently any one of the following structural formulas (2-1) to (2-8)]

（式中、Ｒ^２はそれぞれ独立に水素原子、炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基の何れかであり、Ｒ^３はそれぞれ独立に炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基の何れかである。）
の何れかで表される構造部位であり、ｎは繰り返し数を表す。］
で表されるものが挙げられる。これらはそれぞれ単独で用いても良いし、２種類以上を併用しても良い。

(In the formula, each R ² is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms, and each R ³ is independently any one of an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms.)
and n represents the number of repetitions.
These may be used alone or in combination of two or more kinds.

X in the structural formula (1) is a structural moiety represented by any one of the structural formulae (2-1) to (2-8), and multiple Xs present in a molecule may be the same structural moiety or different structural moieties. Among these, the structural moiety represented by the general formula (2-1) or (2-2) is preferred because it provides excellent flexibility and toughness in the cured product.

The epoxy equivalent of the bisphenol- or biphenol-type epoxy resin is preferably in the range of 150 to 250 g/eq, and more preferably in the range of 160 to 200 g/eq, as this provides excellent flexibility and toughness in the cured product.

As described above, the bisphenol- or biphenol-type epoxy resin can be produced by a method using various bisphenol compounds or biphenol compounds and epihalohydrin as resin raw materials. Specific production methods include, for example, a method of reacting a bisphenol compound or biphenol compound with epihalohydrin to obtain a diglycidyl ether compound, which is then reacted with a bisphenol compound or biphenol compound (Method 1), and a method of reacting a bisphenol compound or biphenol compound with epihalohydrin to directly obtain an epoxy resin (Method 2). Among these, the above-mentioned Method 1 is preferred because the reaction is easy to control and it is easy to control the epoxy equivalent of the resulting epoxy resin (B) to the preferred value.

The bisphenol or biphenol compound used in the above method 1 or 2 is, for example, one of the following structural formulas (3-1) to (3-8):

（式中、Ｒ^２はそれぞれ独立に水素原子、炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基の何れかであり、Ｒ^３はそれぞれ独立に炭素原子数１～４のアルキル基、炭素原子数１～４のアルコキシ基の何れかである。）
の何れかで表される化合物などが挙げられる。これらはそれぞれ単独で用いても良いし、２種類以上を併用しても良い。中でも、硬化物における柔軟性と靱性に優れることから、前記一般式（３－１）又は（３－２）で表される化合物が好ましい。

(In the formula, each R ² is independently any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms, and each R ³ is independently any one of an alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4 carbon atoms.)
These may be used alone or in combination of two or more. Among them, the compounds represented by the general formula (3-1) or (3-2) are preferred because they provide excellent flexibility and toughness in the cured product.

In the above-mentioned method 1, the reaction ratio of the bisphenol compound or biphenol compound to these diglycidyl ether compounds is preferably in the range of 50/50 to 5/95 by mass. The reaction temperature is preferably about 120 to 160°C, and a reaction catalyst such as tetramethylammonium chloride may be used.

In the present invention, in order to further improve the flexibility and toughness of the resulting cured product, it is preferable to use, as the epoxy resin (B), a bisphenol-type or biphenol-type epoxy resin in combination with a flexible epoxy resin such as a urethane-modified epoxy resin or a rubber-modified epoxy resin.

The urethane-modified epoxy resin is not particularly limited in structure, so long as it is a resin having a urethane bond and two or more epoxy groups in the molecule. In terms of being able to efficiently introduce a urethane bond and an epoxy group into one molecule, it is preferable that the resin is obtained by reacting a urethane bond-containing compound having an isocyanate group obtained by reacting a polyhydroxy compound with a polyisocyanate, with a hydroxy group-containing epoxy compound.

Examples of polyhydroxy compounds used in producing urethane-modified epoxy resins include polyether polyols, polyester polyols, adducts of hydroxycarboxylic acids and alkylene oxides, polybutadiene polyols, polyolefin polyols, etc. The molecular weight of the polyhydroxy compound is preferably in the range of 300 to 5,000, particularly 500 to 2,000, in terms of weight average molecular weight, because it provides an excellent balance between flexibility and curability.

The polyisocyanate used in producing the urethane-modified epoxy resin is not particularly limited as long as it is a compound having two or more isocyanate groups. Examples include aliphatic polyisocyanates, aromatic polyisocyanates, and polyisocyanates having aromatic hydrocarbon groups. Among these, aromatic polyisocyanates are preferred. Examples of aromatic polyisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate.

The above reaction produces a urethane prepolymer containing free isocyanate groups at its terminals. By reacting this with an epoxy resin that has at least one hydroxyl group per molecule (such as diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of aliphatic polyhydric alcohol, and glycidol), a urethane-modified epoxy resin is obtained.

The urethane-modified epoxy resin preferably has an epoxy equivalent of 200 to 250 g/eq.

There are no particular limitations on the rubber-modified epoxy resin, so long as it is an epoxy resin that has two or more epoxy groups and has a rubber skeleton. Examples of rubber that forms the skeleton include polybutadiene, acrylonitrile butadiene rubber (NBR), and carboxyl-terminated NBR (CTBN). The rubber-modified epoxy resins can be used alone or in combination of two or more.

The rubber-modified epoxy resin preferably has an epoxy equivalent of 200 to 500 g/eq. There are no particular limitations on the production of the rubber-modified epoxy resin. For example, it can be produced by reacting rubber and epoxy in a large amount of epoxy. There are no particular limitations on the epoxy (e.g., epoxy resin) used when producing the rubber-modified epoxy resin.

In the present invention, the curable composition further contains a curing agent or curing accelerator (C).

The curing agent or curing accelerator (C) may be any of a wide variety of agents commonly used for curing epoxy resins, including, for example, polyamine compounds, amide compounds, acid anhydrides, phenolic hydroxyl group-containing resins, phosphorus compounds, imidazole compounds, imidazoline compounds, urea compounds, organic acid metal salts, Lewis acids, and amine complex salts.

The polyamine compounds include, for example, aliphatic amine compounds such as trimethylenediamine, ethylenediamine, N,N,N',N'-tetramethylethylenediamine, pentamethyldiethylenetriamine, triethylenediamine, dipropylenediamine, N,N,N',N'-tetramethylpropylenediamine, tetramethylenediamine, pentanediamine, hexamethylenediamine, trimethylhexamethylenediamine, N,N,N',N'-tetramethylhexamethylenediamine, N,N-dimethylcyclohexylamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminopropylamine, diethylaminopropylamine, dibutylaminopropylamine, 1,4-diazabicyclo(2,2,2)octane(triethylenediamine), polyoxyethylenediamine, polyoxypropylenediamine, bis(2-dimethylaminoethyl)ether, dimethylaminoethoxyethoxyethanol, triethanolamine, and dimethylaminohexanol;

Alicyclic and heterocyclic amine compounds such as piperidine, piperazine, menthanediamine, isophoronediamine, methylmorpholine, ethylmorpholine, N,N',N"-tris(dimethylaminopropyl)hexahydro-s-triazine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxyspiro(5,5)undecane adduct, N-aminoethylpiperazine, trimethylaminoethylpiperazine, bis(4-aminocyclohexyl)methane, N,N'-dimethylpiperazine, and 1,8-diazabicyclo-[5.4.0]-undecene (DBU);

Aromatic amine compounds such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, benzylmethylamine, dimethylbenzylamine, m-xylylenediamine, pyridine, picoline, and α-methylbenzylmethylamine;

Examples of modified amine compounds include epoxy compound-added polyamines, Michael addition polyamines, Mannich addition polyamines, thiourea addition polyamines, ketone-blocked polyamines, dicyandiamide, guanidine, organic acid hydrazides, diaminomaleonitrile, aminimides, boron trifluoride-piperidine complexes, and boron trifluoride-monoethylamine complexes.

Examples of the amide compound include dicyandiamide and polyamidoamine. Examples of the polyamidoamine include those obtained by reacting an aliphatic dicarboxylic acid such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, or azelaic acid, or a carboxylic acid compound such as a fatty acid or dimer acid, with an aliphatic polyamine or a polyamine having a polyoxyalkylene chain.

Examples of the acid anhydride include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

Examples of the phenolic hydroxyl group-containing resin include polyhydric phenol compounds such as phenol novolac resin, cresol novolac resin, aromatic hydrocarbon formaldehyde resin-modified phenol resin, dicyclopentadiene phenol addition type resin, phenol aralkyl resin (Zylok resin), naphthol aralkyl resin, trimethylolmethane resin, tetraphenylolethane resin, naphthol novolac resin, naphthol-phenol co-condensed novolac resin, naphthol-cresol co-condensed novolac resin, biphenyl-modified phenol resin (a polyhydric phenol compound in which the phenol nucleus is linked by a bismethylene group), biphenyl-modified naphthol resin (a polyhydric naphthol compound in which the phenol nucleus is linked by a bismethylene group), aminotriazine-modified phenol resin (a polyhydric phenol compound in which the phenol nucleus is linked by melamine, benzoguanamine, etc.), and alkoxy group-containing aromatic ring-modified novolac resin (a polyhydric phenol compound in which the phenol nucleus and the alkoxy group-containing aromatic ring are linked by formaldehyde).

Examples of the phosphorus compound include alkyl phosphines such as ethylphosphine and butylphosphine, primary phosphines such as phenylphosphine, dialkyl phosphines such as dimethylphosphine and dipropylphosphine, secondary phosphines such as diphenylphosphine and methylethylphosphine, and tertiary phosphines such as trimethylphosphine, triethylphosphine, and triphenylphosphine.

The imidazole compound is, for example, imidazole, 1-methylimidazole, 2-methylimidazole, 3-methylimidazole, 4-methylimidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 3-ethylimidazole, 4-ethylimidazole, 5-ethylimidazole, 1-n-propylimidazole, 2-n-propylimidazole, 1-isopropylimidazole, 2-isopropylimidazole, isopropylimidazole, 1-n-butylimidazole, 2-n-butylimidazole, 1-isobutylimidazole, 2-isobutylimidazole, 2-undecyl-1H-imidazole, 2-heptadecyl-1H-imidazole, 1,2-dimethylimidazole, 1,3-dimethylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-phenylimidazole, 2-phenyl-1H-imidazole imidazole, 4-methyl-2-phenyl-1H-imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole Socyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 1-benzyl-2-phenylimidazole hydrochloride, etc.

Examples of the imidazoline compound include 2-methylimidazoline and 2-phenylimidazoline.

Examples of the urea compound include p-chlorophenyl-N,N-dimethylurea, 3-phenyl-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-N,N-dimethylurea, and N-(3-chloro-4-methylphenyl)-N',N'-dimethylurea.

In the present invention, the ratio of the isocyanate prepolymer (A) to the epoxy resin (B) is usually in the range of 5/95 to 40/60, and more preferably in the range of 10/90 to 30/70, as a mass ratio represented by (A)/(B), from the viewpoint of obtaining a better balance between the flexibility, toughness, and moisture and heat resistance of the cured product obtained. In addition, when a curing agent having a functional group capable of reacting with an epoxy group is used, the amount of the epoxy resin (B) and the curing agent or curing accelerator (C) is preferably mixed in such a ratio that the functional group in the curing agent is in the range of 0.5 to 1.1 moles per mole of epoxy group in the epoxy resin (B). In addition, when a curing accelerator is used, it is preferably mixed in a ratio of 0.5 to 10 parts by mass per 100 parts by mass of the epoxy resin (B).

The curable composition of the present invention may also contain organic solvents, ultraviolet absorbers, antioxidants, silicon-based additives, fluorine-based additives, flame retardants, plasticizers, silane coupling agents, organic beads, inorganic fine particles, inorganic fillers, rheology control agents, defoamers, anti-fogging agents, colorants, etc. These various components may be added in any amount depending on the desired performance.

The curable composition of the present invention can be prepared by uniformly mixing the isocyanate prepolymer (A), the epoxy resin (B), the curing agent or curing accelerator (C), and the various optional components using a pot mill, ball mill, bead mill, roll mill, homogenizer, super mill, homodisper, universal mixer, Banbury mixer, kneader, etc.

The use of the curable composition of the present invention is not particularly limited, and it can be used for various applications such as paints, coating agents, molding materials, insulating materials, sealants, sealing agents, and fiber binders. In particular, by taking advantage of the excellent flexibility and toughness of the cured product, it can be suitably used as an adhesive for structural members in the fields of automobiles, trains, civil engineering and construction, electronics, aircraft, and the space industry. The adhesive of the present invention can maintain high adhesion without being affected by changes in the temperature environment, even when used to bond different materials such as metal and non-metal, and peeling is unlikely to occur. In addition to structural member applications, the adhesive of the present invention can also be used as an adhesive for general office use, medical use, carbon fiber, electronic materials, etc. Examples of adhesives for electronic materials include interlayer adhesives for multilayer substrates such as build-up substrates, adhesives for bonding optical components, adhesives for bonding optical disks, adhesives for mounting printed wiring boards, die bonding adhesives, adhesives for semiconductors such as underfills, underfills for reinforcing BGAs, and mounting adhesives such as anisotropic conductive films and anisotropic conductive pastes.

The present invention will be explained in more detail below with examples and comparative examples.

Synthesis Example 1
Under a nitrogen atmosphere, 194 parts by mass of polyether polyol (Actocol EP-450, Mn: 3800, number of functional groups: 3), which is a polyoxyethylene (PE)-polyoxypropylene (PP) copolymer manufactured by Mitsui Chemical & SKC Polyurethanes (MCNS), 582 parts by mass of polytetramethylene glycol (PTMG-3000, Mn: 3000, number of functional groups: 2) manufactured by Mitsubishi Chemical Corporation, and 126 parts by mass of isophorone diisocyanate (IPDI) manufactured by Sumika Covestro Urethane Co., Ltd. were mixed, and 0.1 parts of Neostan U-820 was added as a catalyst and reacted at 80° C. for 5 hours. Next, 98 parts by mass of para-tertiary butylphenol (PTBP) was added as a blocking agent and reacted at 90° C. for 5 hours to obtain a blocked isocyanate resin (1).

Synthesis Examples 2 to 6
Using the same recipe as in Synthesis Example 1, blocked isocyanate prepolymers (2) to (6) were obtained from the blending compositions shown in Table 1.

Compound EP-450 in Table 1: PE-PP polyol manufactured by MCNS (Mn: 3800, number of functional groups: 3)
EP-551: PE-PP polyol manufactured by MCNS (Mn: 3800, number of functional groups: 3)
T-3000: PP polyol manufactured by MCNS (Mn: 3000, number of functional groups: 3)
EP-3033: PP polyol manufactured by MCNS (Mn: 6600, number of functional groups: 4)
PTMG-3000: Polytetramethylene glycol (Mn: 3000, functional group number: 2) manufactured by Mitsubishi Chemical Corporation
PTMG-4000: Polytetramethylene glycol (Mn: 4000, functional group number: 2) manufactured by Mitsubishi Chemical Corporation
IPDI: Isophorone diisocyanate manufactured by Sumika Covestro Urethane Co., Ltd. HMDI: Hexamethylene diisocyanate manufactured by Tosoh Corporation TDI: Tolylene diisocyanate T-80 manufactured by MCNS Corporation
DMP: 3,5-dimethylpyrazole manufactured by Otsuka Chemical Co., Ltd. BPF: Bisphenol F manufactured by DIC Corporation

Example 1
20 parts by mass of the blocked isocyanate resin (1) synthesized in Synthesis Example 1, 70 parts by mass of bisphenol A type epoxy resin EPICLON 850-S manufactured by DIC Corporation, 10 parts by mass of rubber modified epoxy resin EPICLON TSR-601 manufactured by DIC Corporation, 5 parts by mass of dicyandiamide (DICY) as a curing agent, 1 part by mass of 3,4-dichlorophenyl-N,N-dimethylurea (DCMU) as a curing accelerator, and 20 parts by mass of calcium carbonate (CaCO ₃ ) as a filler were mixed to obtain a curable composition (1). This curable composition (1) was cured at 170° C. for 30 minutes, and the cured product was subjected to an adhesion evaluation and a moist heat resistance test.

Adhesion evaluation <Tensile shear test>
The tensile shear strength was measured using an AUTOGRAPH AG-XPlus 100 kN manufactured by Shimadzu Corporation at 25° C. according to the JIS K6859 (adhesive creep fracture test) method. The state of failure was also evaluated in terms of the area ratio (%) of cohesive failure (CF).
<T-peel test>
The peel strength was measured according to JIS K6854-3 (peel adhesion strength test for adhesives) at 25° C. using an AUTOGRAPH AG-IS 1 kN manufactured by Shimadzu Corporation.

Moisture and heat resistance test The test pieces prepared by the above JIS K6859 <tensile shear test> method were stored for 2 weeks in an environment of temperature: 70°C and humidity: 90%, and then within 5 hours, the tensile shear strength was measured by the JIS K6859 (adhesive creep fracture test) method at 25°C using an AUTOGRAPH AG-XPlus 100kN manufactured by Shimadzu Corporation. The state of failure was also evaluated in terms of the area ratio of cohesive failure (CF).

Example 2-6
The same evaluation was carried out on curable compositions prepared in the same manner as in Example 1, except that the blocked isocyanates shown in Table 2 were used instead of the blocked isocyanate resin (1) in Example 1. The evaluation results are summarized in Table 2.

８３０－Ｓ：ＤＩＣ株式会社製ビスフェノールＦ型液状エポキシ樹脂

830-S: Bisphenol F type liquid epoxy resin manufactured by DIC Corporation

Comparative Synthesis Examples 1 to 4
Using the same recipe as in Synthesis Example 1 and the blending compositions shown in Table 3, blocked isocyanate prepolymers (7) to (10) for comparison were obtained.

Ｄ－３０００：ＭＣＮＳ社製ＰＰポリオール（Ｍｎ：３０００ 官能基数：２）
Ｔ－１５００：ＭＣＮＳ社製ＰＰポリオール （Ｍｎ：１５００ 官能基数：３）
ＰＴＭＧ－２０００：三菱ケミカル社製ポリテトラメチレングリコール（Ｍｎ：２０００ 官能基数：２）

D-3000: PP polyol manufactured by MCNS (Mn: 3000, number of functional groups: 2)
T-1500: PP polyol manufactured by MCNS (Mn: 1500, number of functional groups: 3)
PTMG-2000: Polytetramethylene glycol (Mn: 2000, functional group number: 2) manufactured by Mitsubishi Chemical Corporation

Comparative Examples 1 to 4
The same evaluation was carried out on curable compositions prepared in the same manner as in Example 1, except that the blocked isocyanate prepolymers shown in Table 4 were used instead of the blocked isocyanate prepolymer (1) in Example 1. The evaluation results are summarized in Table 4.

Claims (9)

A polyol (a1) containing a polyoxyethylene unit, a polyoxypropylene unit, and a polyoxytetramethylene unit;
An isocyanate prepolymer (A) containing polyisocyanate (a2) as an essential raw material,
an epoxy resin (B) containing a bisphenol type epoxy resin;
A cured product comprising a curable composition containing an epoxy resin curing agent and/or an epoxy resin curing accelerator (C),
the polyol (a1) is a mixture of a polyol (a1-1) containing a polyoxyethylene unit and a polyoxypropylene unit, a polytetramethylene glycol (a1-2), and an optional polyoxypropylene polyol;
the polyol (a1-1) is a polyoxyethylene-polyoxypropylene copolymer,
the ratio of the isocyanate prepolymer (A) to the epoxy resin (B) is in the range of 10/90 to 30/70 in terms of a mass ratio represented by (A)/(B);
The cured product is a heat-cured product of the curable composition. The cured product according to claim 1, wherein the isocyanate prepolymer (A) is a blocked isocyanate prepolymer obtained by blocking polyurethane made of polyisocyanate (a2) with a blocking agent (a3) so that there is an excess of isocyanate groups relative to the total amount of hydroxyl groups in the polyol (a1). The cured product according to claim 2, wherein the blocking agent (a3) is a monohydric phenol compound. The cured product according to any one of claims 1 to 3, wherein the proportion of the polyol (a1-1) and the polytetramethylene glycol (a1-2) used is in the range of 10/90 to 60/40 as a mass ratio represented by (a1-1)/(a1-2). The cured product according to any one of claims 1 to 4, wherein the mass ratio of polyoxyethylene units to polyoxypropylene units in the polyol (a1) is in the range of 30/70 to 1/99. The cured product according to any one of claims 1 to 5, wherein the number average molecular weight of the polyol (a1) is in the range of 1,000 to 7,000. The cured product according to any one of claims 1 to 6, wherein the polyisocyanate (a2) is a diisocyanate. The cured product according to any one of claims 1 to 7, wherein the epoxy equivalent of the epoxy resin (B) is in the range of 150 to 250 g/eq. A polyol (a1) containing a polyoxyethylene unit, a polyoxypropylene unit, and a polyoxytetramethylene unit;
An isocyanate prepolymer (A) containing polyisocyanate (a2) as an essential raw material,
an epoxy resin (B) containing a bisphenol type epoxy resin;
An adhesive for structural members comprising a curable composition containing an epoxy resin curing agent and/or an epoxy resin curing accelerator (C),
the polyol (a1) is a mixture of a polyol (a1-1) containing a polyoxyethylene unit and a polyoxypropylene unit, a polytetramethylene glycol (a1-2), and an optional polyoxypropylene polyol ;
the polyol (a1-1) is a polyoxyethylene-polyoxypropylene copolymer,
the ratio of the isocyanate prepolymer (A) to the epoxy resin (B) is in the range of 10/90 to 30/70 in terms of a mass ratio represented by (A)/(B);
13. An adhesive for structural components, wherein the curable composition is a thermosetting composition.