JP7548012B2 - Photocurable adhesive composition - Google Patents

Description

The present invention relates to a photocurable adhesive composition.

Adhesive compositions containing 2-cyanoacrylate compounds rapidly initiate polymerization when exposed to minute amounts of moisture near the surface of the adherend, and bond almost all adherends made of various materials in an extremely short time of just a few seconds to a few minutes. In addition, because of their strong adhesive strength, they are used as the main component of instant adhesives in a wide range of fields, including electrical, electronic, mechanical parts, precision machinery, household goods, and medical applications.

Also known is a photocurable adhesive composition that can be easily cured by light without impairing the excellent characteristic of instant adhesives, that is, a room temperature one-liquid type.
As conventional photocurable adhesive compositions, for example, compositions described in Patent Documents 1 to 4 are known.
Patent Document 1 describes a photocurable composition characterized by comprising, as essential components, (A) an α-cyanoacrylate and (B) a metallocene compound of a transition metal of Group VIII of the periodic table containing an aromatic electron system ligand.

Furthermore, Patent Document 2 describes a photocurable composition characterized by containing, as essential components, (A) an α-cyanoacrylate, (B) a lower alkyl-substituted ferrocene compound, and (C) a photocuring accelerator.

Furthermore, Patent Document 3 describes a photocurable composition characterized by comprising, as essential components, (A) α-cyanoacrylate, (B) a transition metal metallocene compound of Group VIII of the periodic table having an aromatic electron system ligand, and (C) a photocuring accelerator having the structure shown in the following general formula (1).

(In the formula, R is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen group, or an alkylthio group having 1 to 8 carbon atoms, and each R may be the same or different.)

Furthermore, Patent Document 4 describes a moisture-curable and light-curable cyanoacrylate adhesive composition that contains as essential components (A) α-cyanoacrylate, (B) a polyfunctional compound having a (meth)acryloyl group, (C) a peroxide, (D) a periodic group 8 transition metal metallocene compound containing an aromatic electron system ligand, and (E) an intramolecular cleavage-type photoradical initiator.

Patent Document 1: JP-A-9-249708 Patent Document 2: JP-A-11-166006 Patent Document 3: JP-A-2003-277422 Patent Document 4: JP-A-2007-217484

The problem that the present invention aims to solve is to provide a photocurable adhesive composition that has excellent storage stability.

Means for solving the above problems include the following aspects.
<1> A photocurable adhesive composition containing a Group 8 transition metal metallocene compound and a 2-cyanoacrylate compound, and containing no compound having a benzoquinone structure, or containing a compound having a benzoquinone structure in an amount of more than 0 ppm and less than 4 ppm.
<2> The photocurable adhesive composition according to <1>, wherein the Group 8 transition metal metallocene compound is at least one compound selected from the group consisting of ferrocene and ruthenocene.
<3> The photocurable adhesive composition according to <1> or <2>, wherein the Group 8 transition metal metallocene compound is ferrocene.
<4> The photocurable adhesive composition according to any one of <1> to <3>, further comprising a photoradical generator.
<5> The photocurable adhesive composition according to <4>, wherein the photoradical generator is at least one compound selected from the group consisting of an acylgermane compound, an acylphosphine oxide compound, and an alkylphenone compound.
<6> The photocurable adhesive composition according to any one of <1> to <5>, further comprising a polymerization inhibitor.
<7> The photocurable adhesive composition according to <6>, wherein the polymerization inhibitor includes a phenol-based radical polymerization inhibitor.
<8> The photocurable adhesive composition according to <6> or <7>, wherein the polymerization inhibitor includes a radical polymerization inhibitor having a hydroquinone structure.
<9> The photocurable adhesive composition according to <7> or <8>, wherein the content of the polymerization inhibitor is 10 ppm or more and 1,000 ppm or less.

According to the present invention, it is possible to provide a photocurable adhesive composition having excellent storage stability.

The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.
In the present invention, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.
In the present invention, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.
In the present invention, "mass %" and "weight %" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
Also, in the present invention, a combination of two or more preferred embodiments is a more preferred embodiment.
In addition, in this specification, "(meth)acryloyl" refers to both or either of acryloyl and methacryloyl, and "(meth)acryloxy" refers to both or either of acryloxy and methacryloxy.
Furthermore, in some of the compounds in this specification, the hydrocarbon chain may be represented by a simplified structural formula in which the symbols for carbon (C) and hydrogen (H) are omitted.
The present invention will be described in detail below.

(Photocurable adhesive composition)
The photocurable adhesive composition of the present invention contains a Group 8 transition metal metallocene compound and a 2-cyanoacrylate compound, and does not contain a compound having a benzoquinone structure, or the content of the compound having a benzoquinone structure is more than 0 ppm and less than 4 ppm.

In conventional methods for producing 2-cyanoacrylate compounds, a compound having a hydroquinone structure, such as hydroquinone, is often used as a polymerization inhibitor during depolymerization or the like.
However, the present inventors have found that when a compound having a hydroquinone structure is used in the production of a 2-cyanoacrylate compound, the compound having a hydroquinone structure is oxidized by the action of impurities and decomposition products, and a trace amount of a compound having a benzoquinone structure is produced, that the compound having a benzoquinone structure in the 2-cyanoacrylate compound cannot be completely removed even by distillation or the like, and that the presence of the compound having a benzoquinone structure greatly contributes to the storage stability of the photocurable adhesive composition.
As a result of intensive research, the present inventors have found that a 2-cyanoacrylate-based photocurable adhesive composition that does not contain a compound having a benzoquinone structure, or that contains a compound having a benzoquinone structure in an amount of more than 0 ppm and less than 4 ppm, can provide a photocurable adhesive composition with excellent storage stability.

The present invention is described in detail below.

<Compounds Having a Benzoquinone Structure>
The photocurable adhesive composition of the present invention does not contain a compound having a benzoquinone structure, or the content of a compound having a benzoquinone structure is more than 0 ppm and less than 4 ppm.
Furthermore, from the viewpoint of storage stability, the photocurable adhesive composition of the present invention preferably does not contain a compound having a benzoquinone structure or the content of a compound having a benzoquinone structure is more than 0 ppm and 3 ppm or less, more preferably does not contain a compound having a benzoquinone structure or the content of a compound having a benzoquinone structure is more than 0 ppm and 2 ppm or less, and more preferably does not contain a compound having a benzoquinone structure or the content of a compound having a benzoquinone structure is more than 0 ppm and 1.5 ppm or less.
When the photocurable adhesive composition of the present invention contains two or more compounds having a benzoquinone structure, the above content is the total content of the compounds having two or more benzoquinone structures.

The compound having a benzoquinone structure in the present invention may be a compound having a 1,4-benzoquinone structure or a compound having a 1,2-benzoquinone structure.
Examples of compounds having a benzoquinone structure include 1,4-benzoquinone, 1,2-benzoquinone, 1,4-naphthoquinone, 1,2-naphthoquinone, and 9,10-anthraquinone.

There are no particular limitations on the method for reducing the content of the compound having a benzoquinone structure in the photocurable adhesive composition of the present invention, but a preferred example is a method in which a 2-cyanoacrylate compound that does not contain or contains a small amount of a compound having a benzoquinone structure is used as the 2-cyanoacrylate compound to be used.
As a method for producing a 2-cyanoacrylate compound, for example, a method is known in which a 2-cyanoacrylate polycondensate, which is a condensate of a cyanoacetic acid ester compound and a formaldehyde compound, is depolymerized, and the resulting crude 2-cyanoacrylate compound is distilled to obtain a purified 2-cyanoacrylate compound.
In the depolymerization, conventionally, at least a compound having a hydroquinone structure is often used as a polymerization inhibitor, and many commercially available 2-cyanoacrylate compounds contain a compound having a benzoquinone structure.
Specific examples of the method for reducing the content of the compound having a benzoquinone structure in the 2-cyanoacrylate compound include a method in which a polymerization inhibitor not having a hydroquinone structure is used during the depolymerization, and a method in which a polymerization inhibitor not having a hydroquinone structure is used during the depolymerization and the distillation is more preferable.

From the viewpoint of storage stability, the polymerization inhibitor not having a hydroquinone structure preferably contains a compound having a phenolic hydroxy group, more preferably a compound represented by the following formula (1), and particularly preferably a compound represented by the following formula (2).

In formula (1) and formula (2), R ₁ to R ₅ each independently represent a hydrogen atom or a substituent other than a hydroxy group (excluding a phenolic hydroxy group) which may be bonded to each other to form a ring; R ₆ represents a hydrogen atom or an alkyl group; R ₇ to R ₁₀ each independently represent an alkyl group, a cycloalkyl group, or an alkenyl group; and R ₁₁ represents a hydrogen atom or a (meth)acryloyl group.

In formula (1), from the viewpoint of storage stability, it is preferable that at least one of R ₁ to R ₅ is the above-mentioned substituent, it is more preferable that at least R ₁ and R ₅ are the above-mentioned substituent, and it is particularly preferable that at least R ₁ , R ₃ and R ₅ are the above-mentioned substituent.
In formula (1), from the viewpoint of storage stability, it is preferable that R ₁ and R ₅ are each independently a linear or branched alkyl group, a cycloalkyl group, an alkyl group having a structure having a phenolic hydroxy group, or an alkyl group having a (meth)acryloxyphenyl structure, it is more preferable that R ₁ is a linear or branched alkyl group and R ₅ is an alkyl group having a structure having a phenolic hydroxy group or an alkyl group having a (meth)acryloxyphenyl structure, and it is particularly preferable that R ₁ is a linear or branched alkyl group and R ₅ is an alkyl group having a (meth)acryloxyphenyl structure.
In terms of storage stability, _R3 in formula (1) is preferably a hydrogen atom, an alkyl group, or an alkoxy group, more preferably a linear or branched alkyl group, a cycloalkyl group, or an alkoxy group, and further preferably a linear or branched alkyl group, or an alkoxy group.
The alkyl group in R ₁ , R ₃ and R ₅ is preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, further preferably a linear or branched alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 1 to 6 carbon atoms, a t-butyl group or a 2-methyl-2-butyl group, and particularly preferably a methyl group, a t-butyl group or a 2-methyl-2-butyl group.
The alkyl group may be linear, branched, or have a ring structure, and may have a substituent.
The substituent may be any group that does not lose its polymerization-inhibiting ability, and examples of the substituent include a halogen atom, an alkoxy group, an aryl group, etc. The substituent may be further substituted with at least one group selected from the group consisting of the above-mentioned substituents and alkyl groups.
In formula (1), _R2 and _R4 each independently preferably represent a hydrogen atom or an alkyl group, and more preferably a hydrogen atom.

From the viewpoint of storage stability, R ₆ in formula (2) is preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and more preferably a hydrogen atom or a methyl group.
In terms of storage stability, R ₇ and R ₁₀ in formula (2) are preferably a tertiary alkyl group, more preferably a tertiary alkyl group having 4 to 8 carbon atoms, and particularly preferably a t-butyl group or a 2-methyl-2-butyl group.
From the viewpoint of storage stability, _R8 and _R9 in formula (2) are preferably an alkyl group or an alkoxy group having 1 to 8 carbon atoms, and more preferably a methyl group, a t-butyl group, a 2-methyl-2-butyl group, a methoxy group, an ethoxy group, a propoxy group, or a butoxy group.
In terms of storage stability, R ₁₁ in formula (2) is preferably a hydrogen atom or a (meth)acryloyl group.

In addition, it is preferable that the polymerization inhibitor not having a hydroquinone structure contains a compound whose 5% weight loss temperature under a nitrogen atmosphere is in the range of -150°C to +50°C relative to the boiling point of the 2-cyanoacrylate compound contained in the photocurable adhesive composition of the present invention.

Among them, from the viewpoint of storage stability, it is preferable that the polymerization inhibitor not having a hydroquinone structure is at least one compound selected from the group consisting of 2,2'-methylenebis(6-tert-butyl-p-cresol) (221°C), 2,2'-methylenebis(4-ethyl-6-tert-butyl-phenol) (229°C), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) monoacrylate (234°C), 2,2'-ethylenebis(4,6-di-tert-amylphenol) monoacrylate (253°C) and 2,2'-methylenebis(6-(1-methylcyclohexyl)-p-cresol) (285°C). The temperatures listed in parentheses are all 5% weight loss temperatures.

The polymerization inhibitor not having a hydroquinone structure may be removed from the 2-cyanoacrylate compound used in the depolymerization and distillation, or may not be completely removed from the 2-cyanoacrylate compound and may be included in the photocurable adhesive composition of the present invention.

<Group 8 Transition Metal Metallocene Compound>
The photocurable adhesive composition of the present invention contains a Group 8 transition metal metallocene compound.
It is presumed that the Group 8 transition metal metallocene compound functions as a photopolymerization initiator. Furthermore, since the light absorption wavelength of the Group 8 transition metal metallocene compound is also on the long wavelength side of wavelengths of 500 nm or more, the photocurable adhesive composition of the present invention can be photocured with light in a wider wavelength range, i.e., the ultraviolet range and the visible range.

Examples of the Group 8 transition metal metallocene compound include metallocene compounds having a Group 8 transition metal element of the periodic table, such as a ferrocene compound in which the transition metal is iron, an osmocene compound in which the transition metal is osmium, a ruthenocene compound in which the transition metal is ruthenium, a cobaltocene compound in which the transition metal is cobalt, and a nickelocene compound in which the transition metal is nickel.
Among these, from the viewpoints of photocurability and storage stability, at least one compound selected from the group consisting of ferrocene compounds and ruthenocene compounds is preferred.

Specific examples of the Group 8 transition metal metallocene compound include ferrocene, ethylferrocene, n-butylferrocene, benzoylferrocene, acetylferrocene, t-amylferrocene, 1,1'-dimethylferrocene, 1,1'-di-n-butylferrocene, 1,1'-dibenzoylferrocene, 1,1'-di(acetylcyclopentadienyl)iron, bis(pentamethylcyclopentadienyl)iron, bis(cyclopentadienyl)osmium, bis(pentamethylcyclopentadienyl)osmium, ruthenocene (bis(cyclopentadienyl)ruthenium), and bis(pentamethylcyclopentadienyl)ruthenium.
As the Group 8 transition metal metallocene compound, a metallocene compound of a transition metal of Group 8 of the periodic table having an aromatic electron system ligand, which is described in JP-A-2003-277422, can be preferably used.
Among these, the Group 8 transition metal metallocene compound is preferably at least one compound selected from the group consisting of ferrocene, ethylferrocene, n-butylferrocene, benzoylferrocene, and ruthenocene, and particularly preferably at least one compound selected from the group consisting of ferrocene, benzoylferrocene, and ruthenocene, from the viewpoints of photocurability, adhesion speed, cost-effectiveness, and storage stability.

The photocurable adhesive composition of the present invention may contain one type of Group 8 transition metal metallocene compound alone, or may contain two or more types.
From the viewpoints of photocurability and storage stability, the content of the Group 8 transition metal metallocene compound in the photocurable adhesive composition of the present invention is preferably 1 ppm to 50,000 ppm, more preferably 10 ppm to 10,000 ppm, and particularly preferably 20 ppm to 2,000 ppm.

<2-Cyanoacrylate Compound>
The photocurable adhesive composition of the present invention contains a 2-cyanoacrylate compound.
The 2-cyanoacrylate compound used in the present invention is not particularly limited, but is preferably a compound represented by the following formula (C).

In formula (C), R represents a saturated or unsaturated linear hydrocarbon group, branched chain hydrocarbon group or cyclic hydrocarbon group having 1 to 20 carbon atoms which may have a halogen atom, or an aromatic hydrocarbon group having 1 to 20 carbon atoms which may have a halogen atom.
However, when R contains an ether bond, one or both of the ether-linked hydrocarbon residual chains are a saturated or unsaturated linear hydrocarbon group, branched chain hydrocarbon group or cyclic hydrocarbon group having 5 to 20 carbon atoms which may have a halogen atom, or an aromatic group having 5 to 20 carbon atoms which may have a halogen atom.

Specific examples of 2-cyanoacrylate compounds include 2-cyanoacrylic acid, methyl, ethyl, chloroethyl, n-propyl, i-propyl, allyl, propargyl, n-butyl, i-butyl, n-pentyl, n-hexyl, amyl, 2-methyl-3-butenyl, 3-methyl-3-butenyl, 2-pentenyl, 6-chlorohexyl, cyclohexyl, phenyl, tetrahydrofurfuryl, 2-hexenyl, 4-methylpentenyl, 3-methyl-2-cyclohexenyl, norbornyl, heptyl, cyclohexanemethyl, cycloheptyl, 1-methylcyclohexyl, 2-methylcyclohexyl, 3-methyl-cyclohexyl, 2-ethylhexyl, n-octyl, 2-octyl, cyclooctyl, cyclopentanemethyl, Examples of ester compounds include ethyl, 2,3-dimethylcyclohexyl, n-nonyl, isononyl, oxononyl, n-decyl, isodecyl, n-dodecyl, 2-methoxyethyl, 2-ethoxyethyl, 2-ethoxy-2-ethoxyethyl, butoxyethoxyethyl, 1-(2-methoxy-1-methylethoxy)propyl, 2,2,2-trifluoroethyl, hexafluoroisopropyl, lauryl, isotridecyl, myristyl, cetyl, stearyl, oleyl, behenyl, hexyldecyl, octyldodecyl, benzyl, chlorophenyl, 2-pentyloxyethyl, 2-hexyloxyethyl, 2-cyclohexyloxyethyl, 2-(2-ethylhexyloxy)ethyl, and 2-phenoxyethyl.

Among these, preferred 2-cyanoacrylate compounds include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, cyclohexyl, phenyl, tetrahydrofurfuryl, 2-ethylhexyl, n-octyl, 2-octyl, 2-methoxyethyl, 2-ethoxyethyl ester, and 1-(2-methoxy-1-methylethoxy)propyl of 2-cyanoacrylic acid.

The photocurable adhesive composition of the present invention may contain one type of 2-cyanoacrylate compound alone, or may contain two or more types.
The content of the 2-cyanoacrylate compound in the photocurable adhesive composition of the present invention is preferably 40% by mass or more, and more preferably 60% by mass or more, from the viewpoints of curability, adhesion speed, and adhesion strength.

<Photoradical generator>
From the viewpoint of photocurability, the photocurable adhesive composition of the present invention preferably further contains a photoradical generator.
As the photoradical generator, a known photoradical generator used for photopolymerizing a radically polymerizable compound can be used.
Examples of photoradical generators include acylgermane compounds, acylphosphine oxide compounds, acetophenone compounds having no hydroxyl group, nitrogen atom, or thioether bond, and benzoin compounds having no hydroxyl group, nitrogen atom, or thioether bond.
Among these, as the photoradical generator, acylgermane compounds are preferred from the viewpoints of photocurability, adhesion speed, and storage stability.

Preferred examples of the acylgermane compound include monoacylgermane compounds and bisacylgermane compounds, and more preferred examples include bisacylgermane compounds.
A preferred example of the acylgermane compound is Ivocerin (manufactured by Ivoclar Vivadent).

Preferred examples of the acylphosphine oxide compound include monoacylphosphine oxide compounds and bisacylphosphine oxide compounds, and more preferred examples include bisacylphosphine oxide compounds.
Preferred examples of the monoacylphosphine oxide compounds include compounds represented by the following formula (A-1).

In formula (A-1), R ^A1 and R ^A2 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a phenyl group, or a phenyl group substituted with 1 to 3 alkyl groups having 1 to 8 carbon atoms or alkoxy groups having 1 to 8 carbon atoms, and R ^A3 represents a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms that is unsubstituted or substituted with an acetyloxy group; an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an aryl group that is unsubstituted or substituted with a halogen atom; or a group represented by the following formula (A-2):

In formula (A-2), R ^A4 and R ^A5 each independently represent an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a phenyl group, or a phenyl group substituted with 1 to 3 alkyl groups having 1 to 8 carbon atoms or alkoxy groups having 1 to 8 carbon atoms, and X ^A1 represents a p-phenylene group.

Examples of acylphosphine oxide compounds include methyl isobutyroyl methylphosphinate, methyl isobutyroyl phenylphosphineate, methyl pivaloyl phosphinate, methyl 2-ethylhexanoyl phosphinate, isopropyl 2-ethylhexanoyl phenylphosphonate, methyl p-tolyl phenylphosphinate, methyl o-tolyl phenylphosphinate, methyl 2,4-dimethylbenzoyl phenylphosphineate, methyl acyloyl phenylphosphonate, isobutyroyl diphenylphosphine oxide, 2-methylhexanoyl diphenylphosphine oxide, o-toluyl diphenylphosphine oxide, p-t-butyl benzoyl diphenylphosphine oxide, 3-polyzylcarbonyl diphenylphosphine oxide, acryloyl diphenylphosphine oxide, benzoyl diphenylphosphine oxide, and adiboyl bis(diphenylphosphine oxide).

Preferred examples of bisphosphine oxides include compounds represented by the following formula (A-3):

In formula (A-3), R ^p is unsubstituted or represents an alkyl group having 1 to 12 carbon atoms, an alkylthio group having 1 to 8 carbon atoms, or a halogen atom, and each R ^p may be the same or different.

The alkyl group having 1 to 12 carbon atoms in R ^p in formula (A-3) may be linear or branched, and is, for example, a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, heptyl, octyl, nonyl, decyl, or dodecyl group, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms.
The alkylthio group having 1 to 8 carbon atoms in R ^p in formula (A-3) may be linear or branched, and examples thereof include methylthio, ethylthio, propylthio, isopropylthio, butylthio, tert-butylthio, hexylthio, and octylthio. Of these, methylthio is preferable.
Examples of halogen atoms include a chlorine atom, a bromine atom, and an iodine atom. Among these, a chlorine atom is preferable.

Examples of bisacylphosphine oxide compounds include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Examples of the acetophenone compounds include 4-phenoxydichloroacetophenone, 4-t-butyldichloroacetophenone, 4-t-butyltrichloroacetophenone, and diethoxyacetophenone.
Examples of the benzoin compounds include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and benzyl methyl ketal.

Among these, from the viewpoints of photocuring property, adhesion speed, and storage stability, the photoradical generator is preferably at least one compound selected from the group consisting of dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)dimethylgermanium, bis(4-methoxybenzoyl)diethylgermanium, ferrocenyl acylgermanium, benzoyldimethylgermanium, bis(4-methylbenzoyl)diethylgermanium, bis(4-methylbenzoyl)dimethylgermanium, and dibenzoyldibutylgermanium, and more preferably at least one compound selected from the group consisting of dibenzoyldiethylgermanium, bis(4-methoxybenzoyl)dimethylgermanium, bis(4-methoxybenzoyl)diethylgermanium, bis(4-methylbenzoyl)diethylgermanium, bis(4-methylbenzoyl)dimethylgermanium, and dibenzoyldibutylgermanium.

The photocurable adhesive composition of the present invention may contain one type of photoradical generator alone, or may contain two or more types.
From the viewpoints of photocurability, adhesion speed, and storage stability, the content of the photoradical generator in the photocurable adhesive composition of the present invention is preferably 0.01 mass % to 5 mass %, more preferably 0.05 mass % to 2 mass %, and particularly preferably 0.05 mass % to 1 mass %, relative to the total mass of the photocurable adhesive composition.

<Polymerization inhibitor>
From the viewpoint of storage stability, the photocurable adhesive composition of the present invention preferably further contains a polymerization inhibitor.
As the polymerization inhibitor, a known polymerization inhibitor can be used.

Preferred examples of the polymerization inhibitor include anionic polymerization inhibitors that do not have a hydroquinone structure, such as diphosphorus pentoxide, SO ₂ , p-toluenesulfonic acid, methanesulfonic acid, propane sultone, and BF ₃ complex.

From the viewpoint of storage stability, a phenol-based radical polymerization inhibitor is preferably used as the polymerization inhibitor.

Preferred examples of the phenol-based radical polymerization inhibitor include the above-mentioned radical polymerization inhibitors not having a hydroquinone structure, such as the compounds represented by formula (1) or (2).
As the radical polymerization inhibitor not having a hydroquinone structure, from the viewpoint of storage stability, mequinol, butyl hydroxyanisole, dibutyl hydroxytoluene, di-tert-butyl hydroxytoluene, 6-tert-butyl-4-xylenol, 2,6-di-tert-butylphenol, 2,2'-methylenebis(6-tert-butyl-p-cresol), 2,2'-methylenebis(4-ethyl-6-tert-butyl-phenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) monoacrylate, 2,2'-ethylenebis(4,6-di-tert-amylphenol) monoacrylate and 2,2'-methylenebis(6-(1-methylcyclohexyl)-p-cresol) are preferably at least one selected from the group consisting of monoacrylate.

From the viewpoint of storage stability, the phenol-based radical polymerization inhibitor preferably contains a radical polymerization inhibitor having a hydroquinone structure, and more preferably contains a radical polymerization inhibitor having a 1,4-hydroquinone structure.
As the radical polymerization inhibitor having a hydroquinone structure, from the viewpoint of storage stability, at least one compound selected from the group consisting of 1,4-hydroquinone, 1,2-hydroquinone, methylhydroquinone, 2,6-dimethylhydroquinone, 2,6-di-tert-butylhydroquinone, 1,4-dihydroxynaphthalene, 1,2-dihydroxynaphthalene, and 9,10-dihydroxyanthracene is preferable, at least one compound selected from the group consisting of 1,4-hydroquinone, 1,2-hydroquinone, methylhydroquinone, methoxyhydroquinone, 2,6-dimethylhydroquinone, and 2,6-di-tert-butylhydroquinone is more preferable, and at least one compound selected from the group consisting of hydroquinone, methylhydroquinone, and methoxyhydroquinone is particularly preferable.

It is more preferable that the radical polymerization inhibitor having a hydroquinone structure is added during the preparation of the photocurable adhesive composition or after distillation purification during the production of the raw material 2-cyanoacrylate compound, and more preferably during the preparation of the photocurable adhesive composition.

The photocurable adhesive composition of the present invention may contain one type of polymerization inhibitor alone or two or more types. Among them, from the viewpoint of storage stability, it is preferable to contain an anionic polymerization inhibitor that does not have a hydroquinone structure, more preferable to contain a radical polymerization inhibitor that does not have a hydroquinone structure and an anionic polymerization inhibitor that does not have a hydroquinone structure, and particularly preferable to contain a radical polymerization inhibitor that has a hydroquinone structure, a radical polymerization inhibitor that does not have a hydroquinone structure, and an anionic polymerization inhibitor that does not have a hydroquinone structure.
The content of the polymerization inhibitor is preferably 50 ppm to 1 mass %, and more preferably 20 ppm to 5,000 ppm, based on the total mass of the photocurable adhesive composition.
The content of the radical polymerization inhibitor having a hydroquinone structure is preferably 10 ppm or more and 1000 ppm or less, and more preferably 20 ppm or more and 500 ppm or less.

<Other additives>
The photocurable adhesive composition of the present invention may contain additives other than the above-mentioned components.
The other additives are not particularly limited, and known additives can be used.
Other additives include, for example, anionic polymerization accelerators, plasticizers, thickeners, fumed silica, particles, fillers, colorants, fragrances, solvents, strength improvers, etc., which can be blended in appropriate amounts depending on the purpose, etc., within ranges that do not impair the curability, adhesive strength, etc. of the photoadhesive adhesive composition.
The content of the other additives is not particularly limited, but is preferably 20 mass % or less, and more preferably 10 mass % or less, based on the total mass of the photocurable adhesive composition.

Examples of anionic polymerization accelerators include polyalkylene oxides, crown ethers, silacrown ethers, calixarenes, cyclodextrins, and pyrogallol-based cyclic compounds. Polyalkylene oxides are polyalkylene oxides and their derivatives, such as those disclosed in JP-B-60-37836, JP-B-1-43790, JP-A-63-128088, JP-A-3-167279, U.S. Pat. No. 4,386,193, and U.S. Pat. No. 4,424,327. Specific examples of the polyalkylene oxide include (1) diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and the like, and (2) derivatives of polyalkylene oxides such as polyethylene glycol monoalkyl esters, polyethylene glycol dialkyl esters, polypropylene glycol dialkyl esters, diethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, dipropylene glycol monoalkyl ethers, dipropylene glycol dialkyl ethers, and the like. Examples of the crown ethers include those disclosed in JP-B-55-2236 and JP-A-3-167279. Specific examples thereof include 12-crown-4, 15-crown-5, 18-crown-6, benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, dibenzo-18-crown-6, dibenzo-24-crown-8, dibenzo-30-crown-10, tribenzo-18-crown-6, asym-dibenzo-22-crown-6, dibenzo-14-crown-4, dicyclohexyl-24-crown-8, cyclohexyl-12-crown-4, 1,2-decalyl-15-crown-5, 1,2-naphtho-15-crown-5, 3,4,5-naphthyl-16-crown-5, 1,2-methylbenzo-18-crown-6, 1,2-tert-butyl-18-crown-6, and 1,2-vinylbenzo-15-crown-5. Examples of silacrown ethers include those disclosed in JP-A-60-168775 etc. Specific examples include dimethylsila-11-crown-4, dimethylsila-14-crown-5, dimethylsila-17-crown-6 etc. Examples of calixarenes include those disclosed in JP-A-60-179482, JP-A-62-235379, JP-A-63-88152 etc. Specifically, 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexahydroxycalix[6]arene, 37,38,39,40,41,42-hexahydroxycalix[6]arene, 37,38,39,40,41,42-hexa-(2-oxo-2-ethoxy)-ethoxycalix[6]arene, 25,26,27,28-tetra-(2-oxo-2-ethoxy)-ethoxycalix[4]arene, tetrakis(4-t-butyl-2-methylenephenoxy)ethyl acetate, etc. Examples of cyclodextrins include those disclosed in JP-A-5-505835 and the like. Specific examples include α-, β-, and γ-cyclodextrin. Examples of pyrogallol-based cyclic compounds include the compounds disclosed in JP-A-2000-191600 and the like. Specific examples include 3,4,5,10,11,12,17,18,19,24,25,26-dodecaethoxycarbomethoxy-C-1,C-8,C-15,C-22-tetramethyl[14]-metacyclophane and the like. These anionic polymerization accelerators may be used alone or in combination of two or more.

A plasticizer can be contained within a range that does not impair the effects of the present invention.
Examples of the plasticizer include triethyl acetyl citrate, tributyl acetyl citrate, dimethyl adipate, diethyl adipate, dimethyl sebacate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisodecyl phthalate, dihexyl phthalate, diheptyl phthalate, dioctyl phthalate, bis(2-ethylhexyl) phthalate, diisononyl phthalate, diisotridecyl phthalate, dipentadecyl phthalate, dioctyl terephthalate, diisononyl isophthalate, decyl toluate, bis(2-ethylhexyl) camphorate, 2-ethylhexyl cyclohexyl carboxylate, diisobutyl fumarate, diisobutyl maleate, triglyceride caproate, 2-ethylhexyl benzoate, and dipropylene glycol dibenzoate. Among these, acetyl tributyl citrate, dimethyl adipate, dimethyl phthalate, 2-ethylhexyl benzoate, and dipropylene glycol dibenzoate are preferred because they have good compatibility with 2-cyanoacrylic acid esters and high plasticizing efficiency. These plasticizers may be used alone or in combination of two or more. The content of the plasticizer is not particularly limited, but is preferably 3 to 50 parts by mass, more preferably 10 to 45 parts by mass, and even more preferably 20 to 40 parts by mass, based on 100 parts by mass of the 2-cyanoacrylate compound. If the content of the plasticizer is 3 to 50 parts by mass, the retention rate of the adhesive strength after a thermal cycle test can be improved.

Further examples of thickeners include polymethyl methacrylate, copolymers of methyl methacrylate and acrylic esters, copolymers of methyl methacrylate and other methacrylic esters, acrylic rubber, polyvinyl chloride, polystyrene, cellulose ester, polyalkyl-2-cyanoacrylate, and ethylene-vinyl acetate copolymers. These thickeners may be used alone or in combination of two or more.

The photocurable adhesive composition of the present invention may also contain fumed silica.
The fumed silica is anhydrous silica in the form of ultrafine powder (preferably with a primary particle size of 500 nm or less, particularly preferably 1 nm to 200 nm), which is produced, for example, from silicon tetrachloride as a raw material by oxidation in a gas phase in a high-temperature flame, and includes hydrophilic silica with high hydrophilicity and hydrophobic silica with high hydrophobicity. Either type of fumed silica can be used, but hydrophobic silica is preferred from the viewpoint of good dispersibility in 2-cyanoacrylate compounds.

As the hydrophilic silica, various commercially available products can be used, such as Aerosil 50, 130, 200, 300 and 380 (all trade names, manufactured by Nippon Aerosil Co., Ltd.). The specific surface areas of these hydrophilic silicas are 50±15 m ² /g, 130±25 m ² /g, 200±25 m ² /g, 300±30 m ² /g and 380±30 m ² /g, respectively. In addition, as commercially available hydrophilic silica, Reolosil QS-10, QS-20, QS-30 and QS-40 (all trade names, manufactured by Tokuyama Corporation) can be used. The specific surface areas of these hydrophilic silicas are 140±20 m ² /g, 220±20 m ² /g, 300±30 m ² /g, and 380±30 m ² /g, respectively. In addition, commercially available hydrophilic silica manufactured by CABOT Corporation or the like can also be used.

Furthermore, as the hydrophobic silica, a product can be used which is produced by contacting hydrophilic silica with a compound capable of reacting with hydroxyl groups present on the surface of hydrophilic silica to form a hydrophobic group, or a compound capable of being adsorbed on the surface of hydrophilic silica to form a hydrophobic layer on the surface, in the presence or absence of a solvent, and preferably heating the resulting product to treat the surface of the hydrophilic silica.

Compounds used to surface treat hydrophilic silica to make it hydrophobic include various alkyl, aryl, and aralkyl silane coupling agents having hydrophobic groups such as n-octyltrialkoxysilane, silylating agents such as methyltrichlorosilane, dimethyldichlorosilane, and hexamethyldisilazane, silicone oils such as polydimethylsiloxane, higher alcohols such as stearyl alcohol, and higher fatty acids such as stearic acid. As hydrophobic silica, products that have been hydrophobized using any of these compounds may be used.

Examples of commercially available hydrophobic silica include Aerosil RY200 and R202 which have been surface-treated with silicone oil and hydrophobized, Aerosil R974, R972, and R976 which have been surface-treated with a dimethylsilylation agent and hydrophobized, Aerosil R805 which has been surface-treated with n-octyltrimethoxysilane and hydrophobized, Aerosil R811 and R812 which have been surface-treated with a trimethylsilylation agent and hydrophobized (all of these are trade names, manufactured by Nippon Aerosil Co., Ltd.), and Reolosil MT-10 which has been surface-treated with methyltrichlorosilane and hydrophobized (trade name, manufactured by Tokuyama Corporation). The specific surface areas of these hydrophobic silicas are 100±20 m ² /g, 100±20 m ² /g, 170±20 m ² /g, 110±20 m ² /g, 250±25 m ² /g, 150±20 m ² /g, 150±20 m ² /g, 260±20 m ² /g, and 120±10 m ² /g, respectively.

The preferred content of fumed silica in the photocurable adhesive composition of the present invention is 1 to 30 parts by mass when the content of the 2-cyanoacrylate compound is 100 parts by mass. The preferred content of this fumed silica, depending on the type of 2-cyanoacrylate compound and the type of fumed silica, is 1 to 25 parts by mass, and a particularly preferred content is 2 to 20 parts by mass. If the content of fumed silica is 1 to 30 parts by mass, the curability and adhesive strength of the photocurable adhesive composition are not impaired, and an adhesive composition with good workability can be obtained.

The method for curing the photocurable adhesive composition of the present invention is not particularly limited as long as it is possible to polymerize and cure the composition using the 2-cyanoacrylate compound. The composition may be cured using light or moisture such as humidity.
When the photocurable adhesive composition of the present invention is cured by light, it can be cured by irradiating it with ultraviolet light or visible light using a high-pressure mercury lamp, a halogen lamp, a xenon lamp, an LED (light-emitting diode) lamp, sunlight, or the like.

The photocurable adhesive composition of the present invention may be stored by any known method. For example, it is preferable to mix the composition in an atmosphere free of moisture and oxygen or with little moisture and oxygen (for example, 0.01% by volume or less), and it is more preferable to mix the composition in an inert gas atmosphere.
The inert gas includes nitrogen, argon, and the like.
The photocurable adhesive composition of the present invention is preferably stored in a light-shielded state.

The photocurable adhesive composition of the present invention can be used in applications as a known 2-cyanoacrylate composition or a photocurable adhesive composition.
For example, it can be used as a so-called instant adhesive, and also as a photocurable instant adhesive.
The photocurable adhesive composition of the present invention has photocurability and moisture curability, and also has excellent storage stability, and therefore can be used in a wide range of fields, including general, industrial, and medical applications.
Specifically, the adhesive can be suitably used for bonding or fixing between similar or different articles or coating, such as sealing of electronic components, attachment of reel seats or threading guides on fishing rods, fastening of wire such as coils, fastening of magnetic heads to bases, filling agents used in dental treatment, adhesion or decoration of artificial nails, etc.

The present invention will be specifically described below based on examples. Note that the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

Example 1
_BF3 ·methanol complex (polymerization inhibitor) was added to the composition at 20 ppm.
Sumilizer MDP-S (polymerization inhibitor, compound shown below) is added to the composition at 1,000 ppm.
Ferrocene (FeCp ₂ , Group 8 transition metal metallocene compound, manufactured by Wako Pure Chemical Industries, Ltd.) was added to the composition at 600 ppm.
Ivocerin (photoradical generator, the following compound, manufactured by Ivoclar Vivadent) was added to the composition at 3,000 ppm.
The photocurable adhesive composition of Example 1 was obtained by mixing with 2-octyl ester of 2-cyanoacrylic acid (2-OctCA) in an amount equivalent to an acid content (acid content) of 0.20 μg.

<Viscosity>
The measurement was carried out using an E-type viscometer at 25° C. and at an arbitrary rotation speed.

<Storage stability evaluation>
1.5 g of the obtained photocurable adhesive composition was placed in a light-shielding sealed container and stored in a temperature-controlled room at 60° C., and the initial viscosity and the viscosity at each of the elapsed times shown in Table 1 were measured. The smaller the viscosity change, the more excellent the storage stability.
The evaluation results are shown in Table 1.

<Adhesion speed>
The obtained photocurable adhesive composition was placed in a light-shielding sealed container and stored in a temperature-controlled room at 60°C. The adhesion speed of the photocurable adhesive composition was measured in an environment of 23°C and 60% RH in accordance with JIS K 6861 "Test methods for α-cyanoacrylate adhesives" at the initial stage and after the elapsed time shown in Table 1. The test specimens used are as follows:
Test piece: ABS resin manufactured by UMG ABS, product name "GSE"
The evaluation results are shown in Table 1.

<Photocuring evaluation>
The obtained photocurable adhesive composition was placed in a light-shielding sealed container and stored in a thermostatic chamber at 60°C. The photocurable adhesive composition was taken at the initial time and at the time when the elapsed time was as shown in Table 1, and a liquid film having a thickness of 1 mm was formed in a polyethylene container. This was irradiated at an intensity of 150 W/cm ² (value at wavelength 405 nm) using a spot-type UV irradiation device (Spot Cure UIS-25102 manufactured by Ushio Inc.) equipped with a long-pass filter (GG395 manufactured by Schott), and the irradiation time until the sample was completely cured was measured. In Example 7 and Comparative Example 5, taking into account the absorption wavelength of the photoradical initiator, the long-pass filter was not equipped and the sample was irradiated at the same intensity of 150 W/cm ² (UV-A: value at wavelength 320 nm to 390 nm). The smaller the value, the better the photocurability.
The evaluation results are shown in Table 1.

(Examples 2 to 5 and Comparative Examples 1 and 2)
Photocurable adhesive compositions were prepared in the same manner as in Example 1, except that 1,4-hydroquinone (HQ), 1,4-benzoquinone (BQ), and 2-hydroxy-1,4-naphthoquinone were added to the compositions in the amounts shown in Table 1.
Using the obtained photocurable adhesive composition, various evaluations were carried out in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Examples 6 to 8 and Comparative Examples 3 to 5)
Photocurable adhesive compositions were prepared in the same manner as in Example 1, except that 2-octyl ester of 2-cyanoacrylic acid (2-OctCA) with an acid content (acid content) of 0.62 μg equivalent was used, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by iGM, product name "Omnirad 819") or 2,2-dimethoxy-2-phenylacetone (manufactured by iGM, product name "Omnirad 651") was added to the composition in the amounts shown in Table 2 instead of Ivocerin.
Using the obtained photocurable adhesive composition, various evaluations were carried out in the same manner as in Example 1. The evaluation results are shown in Table 2.

(Examples 9 to 11 and Comparative Examples 6 and 7)
Each photocurable adhesive composition was prepared in the same manner as in Example 1, except that 2-OctCA was changed to 2-ethoxyethyl ester of 2-cyanoacrylic acid (EtOEtCA), the contents of ferrocene (FeCp ₂ , Group III transition metal metallocene compound) and Ivocerin (photoradical generator) were changed to the amounts shown in Table 3, and 1,4-hydroquinone (HQ) or 1,4-benzoquinone (BQ) was added to the composition in the amount shown in Table 3.
Using the obtained photocurable adhesive composition, various evaluations were carried out in the same manner as in Example 1. The evaluation results are shown in Table 3.

(Examples 12 to 14 and Comparative Examples 8 and 9)
Each photocurable adhesive composition was prepared in the same manner as in Example 1, except that 2-OctCA was changed to isobutyl ester of 2-cyanoacrylic acid (iBuCA), the contents of ferrocene (FeCp ₂ , Group 8 transition metal metallocene compound) and Ivocerin (photoradical generator) were changed to the amounts shown in Table 4, and 1,4-hydroquinone (HQ) or 1,4-benzoquinone (BQ) was added to the composition in the amount shown in Table 4.
Using the obtained photocurable adhesive composition, various evaluations were carried out in the same manner as in Example 1. The evaluation results are shown in Table 4.

As shown in Tables 1 to 4, the photocurable adhesive compositions of the examples, which are the photocurable adhesive compositions of the present invention, have superior storage stability compared to the photocurable adhesive compositions of the comparative examples.

The disclosure of Japanese Patent Application No. 2018-199572, filed on October 23, 2018, is incorporated herein by reference in its entirety.
All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims (7)

a Group 8 transition metal metallocene compound;
a 2-cyanoacrylate compound;
and one or more radical polymerization inhibitors selected from the compounds represented by the following formula (2):
does not contain a compound having a benzoquinone structure, or the content of a compound having a benzoquinone structure is more than 0 ppm and less than 4 ppm;
The content of the Group 8 transition metal metallocene compound in the photocurable adhesive composition is 1 ppm to 50,000 ppm.
A photocurable adhesive composition.

In formula (2), R ₆ represents a hydrogen atom or an alkyl group, R ₇ to R ₁₀ each independently represent an alkyl group, a cycloalkyl group or an alkenyl group, and R ₁₁ represents a hydrogen atom or a (meth)acryloyl group. The photocurable adhesive composition according to claim 1, wherein the Group 8 transition metal metallocene compound is at least one compound selected from the group consisting of ferrocene and ruthenocene. The photocurable adhesive composition according to claim 1 or 2, wherein the Group 8 transition metal metallocene compound is ferrocene. The photocurable adhesive composition according to any one of claims 1 to 3, further comprising a photoradical generator. The photocurable adhesive composition according to claim 4, wherein the photoradical generator is at least one compound selected from the group consisting of acylgermane compounds, acylphosphine oxide compounds, and alkylphenone compounds. The photocurable adhesive composition according to any one of claims 1 to 5 , further comprising a radical polymerization inhibitor having a hydroquinone structure. The photocurable adhesive composition according to claim 6 , wherein the content of the radical polymerization inhibitor having a hydroquinone structure is from 10 ppm to 1,000 ppm.