JP7794873B2 - adhesive composition - Google Patents

Description

The present disclosure relates to adhesive compositions. In particular, the present disclosure relates to two-component acrylic adhesive compositions.

Two-component acrylic adhesives are known as two-component reactive adhesives that harden in a short time at room temperature and bond materials together (Patent Document 1).

Japanese Patent Application Laid-Open No. 2019-156992

Conventionally, adhesive compositions that can produce flame-retardant cured products have not been given much importance, as the proportion of the cured product in the bonded product is small. However, in recent years, there has been a demand for adhesive compositions that can produce flame-retardant cured products for products that require a high level of flame retardancy.

Conventionally, a flame retardant has been added to a composition as a means of imparting flame retardancy to the composition. For example, additive-type phosphorus-based flame retardants, which exert their flame retardant effect by forming a carbonized layer in the solid phase, are widely used as flame retardants. Generally, flame retardancy improves as the amount of flame retardant added increases, but increasing the amount of flame retardant added can also reduce the performance of the adhesive composition (e.g., adhesive strength and stability of the adhesive composition). Therefore, there is a demand for adhesive compositions that can produce cured products that exhibit flame retardancy and have suitable performance as adhesive compositions.

This disclosure was made in light of these problems. That is, the primary objective of this disclosure is to provide an adhesive composition that has suitable performance as an adhesive composition and is capable of forming a flame-retardant cured adhesive product.

In order to achieve the above object, the present disclosure provides a coating composition comprising a first agent containing an organic peroxide and a second agent containing a reducing agent,
(a) a monofunctional (meth)acrylic monomer;
(b) (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate; and (c) a thickener are each contained in at least one of the first agent and the second agent,
An adhesive composition is provided in which at least one of the first part and the second part further comprises a reactive flame retardant.

The adhesive composition according to the present disclosure has suitable properties as an adhesive composition and is capable of forming a flame-retardant cured adhesive product.

Embodiments of this disclosure are described in detail below.

Features or benefits of the present disclosure are illustrated with reference to preferred embodiments. These embodiments are described in sufficient detail to enable one skilled in the art to practice the present disclosure. It should be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. While the embodiments may be presented separately for convenience, partial substitution or combination of features shown in different embodiments is possible. Therefore, the present disclosure is not expressly limited to preferred embodiments (alone or in combination with other features) that illustrate non-limiting combinations of possible features. In the embodiments described below, descriptions of matters common to those described above will be omitted, and only differences will be described. In particular, similar actions and effects resulting from similar configurations will not be mentioned in each embodiment.

The adhesive composition disclosed herein may be a second-generation acrylic adhesive (SGA), which undergoes reactive curing by mixing a peroxide and its decomposition accelerator (reducing agent). Specifically, the adhesive composition contains a radical-generating peroxide and a reducing agent that reacts with the peroxide, stored separately in a first and second part. Upon use, the first and second parts are brought into contact with each other to initiate a radical reaction, polymerizing the polymerizable (meth)acrylic monomer contained in the first and/or second parts. Such SGAs primarily include two-part base acrylic adhesives, base-primer acrylic adhesives, and base-curing agent acrylic adhesives. Two-part base acrylic adhesives contain a first part containing a peroxide and a second part containing a reducing agent, with both the first and second parts containing polymerizable (meth)acrylic monomers. In base-primer type acrylic adhesives and base-curing agent type acrylic adhesives, either the first or second part contains a polymerizable (meth)acrylic monomer, and the other functions as a primer liquid or a curing agent. As described in detail below, the adhesive composition of the present disclosure may be either a two-part base type or a base-primer type. In this specification, (meth)acrylic means acrylic or methacrylic.

The adhesive composition of the present disclosure comprises a first agent containing an organic peroxide and a second agent containing a reducing agent. At least one of the first and second agents further comprises a (meth)acrylic monomer as component (a), (meth)acrylic acid and/or a hydroxyalkyl (meth)acrylate as component (b), and a thickener as component (c). A characteristic of the adhesive composition of the present disclosure relates to the fact that at least one of the first and second agents having such a composition further comprises a reactive flame retardant.

Generally, flame retardants are materials that make flammable materials, such as resins, less flammable. Such flame retardants are broadly divided into inorganic flame retardants, halogen-based flame retardants, and phosphorus-based flame retardants. Among these, additive-type phosphorus-based flame retardants are widely used as phosphorus-based flame retardants. Here, "additive-type" refers to a flame retardant that is blended into the composition and exists without being chemically bonded to other components.

The present inventors have discovered that the use of additive-type flame retardants to impart flame retardancy to adhesive compositions poses several challenges. Specifically, the addition of additive-type flame retardants can reduce the adhesive strength of the adhesive composition. Furthermore, insufficient compatibility with the resin can lead to separation and precipitation of components contained in the adhesive composition, potentially reducing the storage stability of the adhesive composition. Furthermore, when additive-type flame retardants are used, the flame retardant is physically mixed into the adhesive composition, which can result in uneven distribution of the flame retardant depending on the degree of mixing between the first and second parts. This can lead to variations in the flame retardancy of the adhesive cured product (hereinafter simply referred to as the "cured product") obtained from the adhesive composition, reducing the reproducibility of the flame retardancy of the cured product. Furthermore, adhesives containing additive-type flame retardants can suffer from a bleed-out phenomenon, in which low-molecular-weight phosphorus compounds leak from the surface of the adhesive composition into the atmosphere over time, potentially posing a health hazard.

The present inventors have newly discovered that the use of a reactive flame retardant can address the issues encountered when using the aforementioned additive flame retardants. In this specification, a reactive flame retardant refers to a compound that has a reactive group capable of reacting with at least one compound contained in a material to which the reactive flame retardant is added, thereby imparting flame retardancy to the material. In other words, the reactive flame retardant introduces the flame retardant skeleton into the polymer by chemically bonding with at least one component contained in the adhesive composition. After extensive research, the present inventors have discovered that adding a reactive flame retardant to an adhesive composition containing at least a (meth)acrylic monomer (component (a)), (meth)acrylic acid and/or a hydroxyalkyl (meth)acrylate (component (b)), and a thickener (component (c)) results in the introduction of the flame retardant skeleton into the polymer backbone in the cured product of the adhesive composition obtained by copolymerization induced by mixing the first and second components. Because reactive flame retardants are introduced into the molecules of the resin backbone of the adhesive composition, they can have better compatibility with the adhesive composition than when additive-type flame retardants are used. Furthermore, because the flame retardant chemically bonds with the components of the adhesive composition, the occurrence of bleed-out can also be suppressed. Furthermore, it has been newly discovered that by using reactive flame retardants, a cured product with suitable flame retardancy can be obtained with a smaller content compared to when additive-type flame retardants are used.

When considering environmental impact, the reactive flame retardant used in the adhesive composition of the present disclosure is preferably a non-halogen-based reactive flame retardant that does not contain halogen. For example, the reactive flame retardant may be a phosphorus-based reactive flame retardant that contains a phosphorus atom in the molecule. When a phosphorus-based reactive flame retardant is used, it may be possible to impart suitable flame retardancy to the adhesive composition with a small content, thereby imparting flame retardancy to the cured product without excessively reducing the adhesive strength of the adhesive composition.

The reactive flame retardant may have at least one polymerizable unsaturated group as a reactive group that chemically reacts with the components of the adhesive composition. When the reactive flame retardant has a polymerizable unsaturated group, the (meth)acrylic monomer, (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate contained in the adhesive composition copolymerize with the reactive flame retardant, and the molecular skeleton of the reactive flame retardant is introduced into the polymer main chain of the cured product of the adhesive composition. In other words, by using the adhesive composition of the present disclosure, a flame-retardant cured product can be obtained as a flame-retardant polymer copolymerized with the reactive flame retardant.

For example, the polymerizable unsaturated group can be a vinyl group, an acrylic group, or a methacrylic group. The reactive flame retardant may contain at least one functional group selected from the group consisting of a vinyl group, an acrylic group, or a methacrylic group.

For example, the reactive flame retardant used in the adhesive composition of the present disclosure can be a compound represented by the following general formula (I):
In the formula, _R1 is a reactive group capable of chemically bonding to a (meth)acrylic monomer contained in the adhesive composition, and is preferably a polymerizable unsaturated group. _R2 and _R3 each independently represent an alkyl group having 1 to 15 carbon atoms, an alkoxy group having 1 to 15 carbon atoms, or an aryl group having 6 to 14 carbon atoms.

The polymerizable unsaturated group R ₁ can be, for example, a vinyl group, an acrylic group, or a methacrylic group.

The alkyl group can be a straight-chain or branched alkyl group. The number of carbon atoms in the alkyl group may be, for example, 1 to 15, 1 to 10, 1 to 5, or 1 to 3. Although merely exemplary, examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, neopentyl, n-hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, and pentadecyl groups.

The alkoxy group can be a straight-chain or branched alkoxy group. The number of carbon atoms in the alkoxy group can be, for example, 1 to 15, 1 to 10, 1 to 5, or 1 to 3. Although merely exemplary, examples of alkoxy groups include methoxy, ethoxy, propyloxy, butoxy, pentyloxy, and hexyloxy groups.

The number of carbon atoms in the aryl group may be, for example, 6 to 14, 6 to 10, or 6 to 8. The aryl group may be, for example, a substituted or unsubstituted phenyl group. The substituent on the phenyl group may be, for example, a linear or branched alkyl group. The number of carbon atoms in the alkyl group may be, for example, 1 to 8. Although merely exemplary, examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, neopentyl, n-hexyl, heptyl, and octyl groups. For example, the aryl group may be a phenyl group.

When a high phosphorus content in the reactive flame retardant is important, it is particularly preferable that the functional groups _R2 and _R3 in the phosphorus-based reactive flame retardant represented by general formula (1) be alkyl groups having 1 to 3 carbon atoms or alkoxy groups having 1 to 3 carbon atoms, which have a smaller number of molecules. By using such a reactive flame retardant, an adhesive composition capable of forming a cured product exhibiting suitable flame retardancy can be obtained by incorporating a small amount of the reactive flame retardant. A small amount of the reactive flame retardant in the adhesive composition allows the adhesive composition to contain higher proportions of components that contribute to adhesion, such as (meth)acrylate monomers and (meth)acrylic acid and/or hydroxyalkyl (meth)acrylates. Therefore, the deterioration of adhesive performance due to the inclusion of a flame retardant can be mitigated. Therefore, according to the present disclosure, an adhesive composition capable of forming a flame-retardant solidified product while maintaining suitable adhesive strength can be obtained.

Commercially available reactive flame retardants may be used as the reactive flame retardant. Specific reactive flame retardants having a vinyl group as the reactive group include, for example, dimethyl vinyl phosphonate (VHP-1, manufactured by Koatsu Gas Kogyo Co., Ltd.), diethyl vinyl phosphonate (VHP-2, manufactured by Koatsu Gas Kogyo Co., Ltd.), diphenyl vinyl phosphonate (VHP-3, manufactured by Koatsu Gas Kogyo Co., Ltd.), and diphenyl vinyl phosphine oxide (VHP-4, manufactured by Koatsu Gas Kogyo Co., Ltd.). Specific reactive flame retardants having a methacrylic group as the reactive group include, for example, diethoxyphosphinylmethyl methacrylate (MC-2, manufactured by Katayama Chemical Industry Co., Ltd.) and diphenylphosphinylmethyl methacrylate (MC-4, manufactured by Katayama Chemical Industry Co., Ltd.).

The reactive flame retardant contained in the adhesive composition of the present disclosure may be a single type, or may be a combination of two or more different reactive flame retardants. For example, at least one of the first and second agents may contain a single reactive flame retardant, or may contain a combination of two or more different reactive flame retardants. Furthermore, when both the first and second agents contain a reactive flame retardant, the reactive flame retardants contained in each of the first and second agents may be the same, or may contain different reactive flame retardants.

The total content of the reactive flame retardants contained in the first and second parts of the adhesive composition is preferably 7 to 50 parts by weight, and more preferably 7 to 30 parts by weight, per 100 parts by weight of the total of (a) (meth)acrylic monomer, (b) (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate, and (c) thickener contained in the first and second parts. For example, when the total content of the reactive flame retardants is 7 parts by weight or more per 100 parts by weight of the total of components (a), (b), and (c), the cured product obtained by curing the adhesive composition can exhibit more favorable flame retardancy. Furthermore, when the total content of the reactive flame retardants is 50 parts by weight or less per 100 parts by weight of the total of components (a), (b), and (c), the adhesive composition can more favorably maintain its performance, such as its adhesive strength.

The reactive flame retardant is contained in at least one of the first and second components. For example, in the case of a two-component adhesive composition, the reactive flame retardant may be contained in only one of the first and second components, or in both the first and second components. When prioritizing the prevention of a decrease in the content of components other than the reactive flame retardant contained in each of the first and second components, it is more preferable for the reactive flame retardant to be contained in both the first and second components. This more effectively prevents a decrease in adhesive strength due to the addition of the flame retardant, allowing the adhesive composition to exhibit more favorable adhesive performance. Furthermore, it is more preferable that the reactive flame retardant be contained in approximately the same amount in the first and second components. This allows the reactive flame retardant to be more evenly distributed when the first and second components are mixed.

Alternatively, the reactive flame retardant may be contained in either the first or second part. For example, in a base-primer type or base-cure type adhesive composition, the reactive flame retardant may be contained only in the base part.

The adhesive composition of the present disclosure contains a small amount of reactive flame retardant, making it possible to obtain a cured product of the adhesive composition that exhibits suitable flame retardancy. The small amount of reactive flame retardant does not excessively reduce the content of other components in the adhesive composition, thereby more appropriately maintaining the performance of the adhesive composition, such as adhesive strength. For example, if the reactive flame retardant is a phosphorus-based reactive flame retardant, the phosphorus content derived from the reactive flame retardant contained in the first and second parts that make up the adhesive composition can be, for example, 0.5% by weight or more and 5% by weight or less, 0.7% by weight or more and 4% by weight or less, or 1% by weight or more and 3% by weight or less.

In one embodiment, the adhesive composition of the present disclosure may be free of additive flame retardants. Specifically, additive flame retardants may not be added to either the first or second part of the adhesive composition. In such an embodiment, the adhesive composition of the present disclosure may also be considered an additive-flame retardant-free flame retardant adhesive composition. However, trace amounts of additive flame retardants that are unavoidably or accidentally mixed in during the manufacturing process or use of the adhesive composition may be acceptable. For example, it is acceptable for such unavoidable or accidental additive flame retardants to be present in an amount of 0.01% by weight or less of the adhesive composition, as long as the desired effects of the present disclosure are achieved.

As described above, the adhesive composition of the present disclosure contains at least (a) a (meth)acrylic monomer, (b) (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate, and (c) a thickener as components contributing to adhesion. When the adhesive composition is a two-part main component type, components (a), (b), and (c) are contained in both the first and second components. On the other hand, when the adhesive composition is a main component-primer type or a main component-curing agent type, components (a), (b), and (c) are contained in either the first or second component. In other words, when the adhesive composition is a main component-primer type or a main component-curing agent type, either the first or second component is a main component containing at least components (a), (b), and (c), and the other is a primer or a curing agent. For example, components (a), (b), and (c) may be contained in a first component containing an organic peroxide. That is, the first part containing the organic peroxide may be the main part, while the second part containing the reducing agent may be the primer. Alternatively, components (a), (b), and (c) may be contained in a second part containing a reducing agent. That is, the second part containing the reducing agent may be the main part, while the first part containing the organic peroxide may be the curing agent.

The (meth)acrylic monomer (component (a)) contained in the adhesive composition of the present disclosure may be a monofunctional (meth)acrylate monomer. Examples of monofunctional (meth)acrylate monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-lauryl (meth)acrylate, and tridecyl (meth)acrylate. Examples of suitable acrylates include alicyclic (meth)acrylates such as (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, cyclohexyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; and heterocyclic ring-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and glycidyl (meth)acrylate. These may be used alone or in combination of two or more. For example, the first and second agents may contain different types of (meth)acrylic monomers, or the same types of (meth)acrylic monomers.

The adhesive composition of the present disclosure further contains (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate as component (b). Examples of (meth)acrylic acid include acrylic acid and methacrylic acid. Given the ease of adjusting the reactivity when mixing the first and second components, methacrylic acid is preferred. Examples of hydroxylalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyisobutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, and hydroxylauryl (meth)acrylate. Given the ease of adjusting the reactivity when mixing the first and second components, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are preferred. The adhesive composition of the present disclosure may contain one or more types of (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate. For example, the first and second parts may contain different types of (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate, or may contain the same type.

The adhesive composition of the present disclosure further contains a thickener as component (c). The thickener may be a polymer such as a thermoplastic resin or rubber. The inclusion of a thickener can improve the impact strength and peel strength of the adhesive. Specific examples of thickeners contained in the adhesive composition of the present disclosure include thermoplastic resins such as (meth)acrylic acid ester copolymers, methyl methacrylate-butadiene-styrene copolymers (MBS resins), methyl methacrylate-butadiene-acrylonitrile-styrene copolymers (MBAS resins), styrene-butadiene copolymers (SBS resins), and acrylonitrile-butadiene-styrene copolymers (ABS resins), as well as synthetic rubbers such as styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), ethylene-acrylic rubber, and epichlorohydrin rubber. These may be used alone or in combination of two or more. For example, the first and second agents may contain different types of thickeners, or may contain the same type of thickener.

Of the total 100 parts by weight of components (a), (b), and (c) contained in the adhesive composition, the content of component (a) may be 1 part by weight or more and 50 parts by weight or less. Of the total 100 parts by weight of components (a), (b), and (c) contained in the adhesive composition, the content of component (b) may be 1 part by weight or more and 50 parts by weight or less, and more preferably 5 parts by weight or more and 30 parts by weight or less. Of the total 100 parts by weight of components (a), (b), and (c) contained in the adhesive composition, the content of component (c) may be 1 part by weight or more and 50 parts by weight or less, and more preferably 1 part by weight or more and 30 parts by weight or less. Note that, in this specification, "content in the adhesive composition" refers to the total amount of the same component contained in the first and second agents. When the same component is contained in both the first and second agents, the content of the same component in the first and second agents may be the same or different from each other.

The first agent of the adhesive composition of the present disclosure contains an organic peroxide. Examples of organic peroxides include hydroperoxides such as t-butyl hydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide, and diisopropylbenzene hydroperoxide, and diacyl peroxides such as t-butyl peroxybenzoate, t-butyl peroxydecanoates, dibenzoyl peroxide, and diisobutyl peroxide. Of these, hydroperoxides are preferred from the standpoint of reactivity. These may be used alone or in combination of two or more types.

The content of organic peroxide contained in the first agent may be 0.1 parts by weight or more and 10 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less, per 100 parts by weight of the total of components (a), (b), and (c) contained in the first agent. When the content of organic peroxide is within the above range, polymerization can be carried out at a suitable reaction rate, while the first agent can be stably stored before being mixed with the second agent.

The second part of the adhesive composition of the present disclosure contains a reducing agent. The reducing agent forms a redox catalyst system with the organic peroxide contained in the first part. Examples of such reducing agents include thiourea compounds such as ethylene thiourea, trimethylthiourea, tetramethylthiourea, benzoylthiourea, and acetylthiourea; metal soaps such as vanadyl octenate, vanadyl naphthenate, and vanadyl stearate; vanadium compounds such as vanadyl acetylacetonate, vanadium acetylacetonate, vanadium pentoxide, and vanadyl stearate; cobalt compounds such as cobalt octoate, cobalt naphthenate, and cobalt acetylacetonate; and aromatic tertiary amines such as N,N-dimethylaniline, N,N-dimethyl-p-toluidine, and p-tolyldiethanolamine. Of these, thiourea compounds and vanadium compounds are preferred in terms of reactivity. These may be used alone or in combination of two or more.

When the adhesive composition is a two-part main component type, the content of the reducing agent in the second component may be 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total of components (a), (b), and (c) contained in the second component. A reducing agent content within the above range enables polymerization at an appropriate reaction rate while allowing the second component to be stably stored before being mixed with the first component.

When the adhesive composition is a base-primer type, the content of the reducing agent contained in the second agent as a primer may be 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total of components (a), (b), and (c) contained in the first agent as the base.

When the adhesive composition is a base-curing agent type, the content of the organic peroxide contained in the first agent as the curing agent may be 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total of components (a), (b), and (c) contained in the second agent as the base agent.

When the adhesive composition is of the base-primer type or base-curing agent type, the primer or curing agent of the first or second parts may further contain a solvent. The solvent may be an organic solvent capable of dissolving the organic peroxide or reducing agent contained in the primer or curing agent, and is preferably a volatile organic solvent. Examples of solvents include toluene, xylene, ethyl acetate, ethyl propionate, acetone, methyl ethyl ketone, methyl butyl ketone, methanol, ethanol, isopropyl alcohol, and methylcyclohexane. These may be used alone or in combination of two or more.

The adhesive composition of the present disclosure may further contain a phosphate ester compound in at least one of the first and second parts. The inclusion of a phosphate ester compound can improve the adhesive strength of the adhesive composition. Specifically, the phosphate ester compound promotes curing when the first and second parts are mixed or contacted and a polymerization reaction begins, and can improve adhesion to the adherend.

Furthermore, the adhesive composition of the present disclosure may contain additional components added to the first and/or second parts as needed. Examples of additional components include various known additives such as silane coupling agents, polymerization inhibitors, antioxidants, paraffins, plasticizers, fillers, pigments, and/or colorants.

The above describes embodiments of the present disclosure, but the present disclosure is not limited to these. Various modifications based on the knowledge of those skilled in the art are possible, such as combining the above configurations, as long as they do not deviate from the spirit of the claims.

The present disclosure will be explained in more detail below with reference to examples. Note that all parts indicating the amount of each component used are parts by weight.

<Composition of the first and second agents>
(a) Monofunctional (meth)acrylate monomer: Methyl methacrylate (MMA, manufactured by Mitsubishi Gas Chemical Company, Inc.)
(b) (meth)acrylic acid/hydroxyalkyl (meth)acrylate 2-hydroxyethyl methacrylate (2-HEMA, manufactured by Mitsubishi Chemical Corporation)
-Methacrylic acid (MAa, manufactured by Mitsubishi Chemical Corporation)
(c) Thickener: Methacrylic resin (Delpet LP-1 (hereinafter also referred to as LP-1), manufactured by Asahi Kasei Chemicals Corporation)
Nitrile rubber (NBR) (Niopl DN219 (hereinafter also referred to as DN219), manufactured by Zeon Corporation)
(d) Reactive flame retardant: Dimethyl vinyl phosphonate (VHP-1, manufactured by Koatsu Gas Kogyo Co., Ltd.)
Diethyl vinylphosphonate (VHP-2, manufactured by Koatsu Gas Kogyo Co., Ltd.)
Diphenyl vinyl phosphonate (VHP-3, manufactured by Koatsu Gas Kogyo Co., Ltd.)
(d') Additive-type flame retardant (comparative example)
Organophosphorus compounds (Fireguard FCX-210 (hereinafter also referred to as FCX-210), manufactured by Teijin Limited)
Aromatic condensed phosphate ester (PX-200, manufactured by Daihachi Chemical Industry Co., Ltd.)
Aromatic phosphate amidate (DAIGUARD-850 (hereinafter also referred to as Daiguard), manufactured by Daihachi Chemical Industry Co., Ltd.)
(e) Organic peroxides: Cumene hydroperoxide (CHP, manufactured by NOF Corporation)
(f) Reducing agent: 1-benzoyl-2-thiourea (BTU, manufactured by Sanuki Chemical Industry Co., Ltd.)
Vanadyl acetylacetonate (hereinafter also referred to as VO(AA) ₂ ) (manufactured by Shinko Chemical Industry Co., Ltd.)
(g) Polymerization Inhibitor Furthermore, hydroquinone (HQ) was used as a polymerization inhibitor in the first agent.

<Phosphorus content>
From the phosphorus content of each flame retardant, the phosphorus content (wt %) relative to the total amount after addition was theoretically calculated.

In the following examples and comparative examples, flame retardancy and adhesive tests were carried out under the following conditions:

<Flame retardancy test>
Flame retardancy tests were conducted in accordance with UL94HB. Test pieces measuring 125 mm long x 13 mm x 3 mm were prepared from the cured product obtained by mixing the first and second parts of each adhesive composition in the Examples and Comparative Examples. Those that met the UL94HB test criteria were evaluated as ◯, and those that did not meet the criteria were evaluated as ×.

<Tensile shear strength>
To evaluate adhesive strength, tensile shear strength was measured. SPHC sandblasted steel plates measuring 100 mm x 20 mm x 2.3 mm were used as the metal plates to be bonded with the adhesive composition. The metal plates were bonded together using each of the adhesive compositions of the Examples and Comparative Examples, and 24 hours after bonding, the tensile shear strength was measured at a tensile speed of 25 mm/min using a testing machine (Shimadzu Corporation, AG-50kNX). The measurement temperature was 23°C. The overlap area of the bonding surfaces was 10 mm x 20 mm.

<Storage stability test>
As a storage stability test for the adhesive composition, the adhesive composition was left to stand for 10 days at an ambient temperature of 40° C., and the state of the adhesive composition after standing was confirmed. When no changes such as separation of components and/or an increase in viscosity (thickening) were observed compared to before standing, the adhesive composition was evaluated as good.

<Results>
The compositions of the first and second parts and the evaluation results of various tests for each of the adhesive compositions of the Examples and Comparative Examples are shown in Table 1. The content of each component shown in the table is the number of parts blended in each of the first and second parts.

As shown in Table 1, in the adhesive compositions of Comparative Examples 2, 3, 5, and 7, which contain an additive flame retardant, adding the additive flame retardant until the flame retardancy met the UL94HB pass criteria reduced the tensile shear strength and prevented sufficient adhesive strength from being achieved. On the other hand, the adhesive composition of the present disclosure, which uses a reactive flame retardant, resulted in improved flame retardancy of the cured product obtained from the adhesive composition, without an excessive reduction in tensile shear strength, compared to the adhesive composition of Comparative Example 1, which does not contain a flame retardant.

Furthermore, in the storage stability test, the adhesive compositions of Comparative Examples 2 to 8, which used an additive flame retardant, exhibited separation and thickening in the adhesive composition due to poor compatibility between the additive flame retardant and the acrylic resin, and the adhesive composition exhibited poor stability. On the other hand, the adhesive compositions of Examples 1 to 16, which used a reactive flame retardant, did not exhibit separation or thickening in the adhesive composition in the storage stability test, and exhibited good storage stability.

As is clear from the above results, the adhesive composition of the present disclosure exhibits flame retardant effects in the resulting cured product, while the adhesive composition's performance, such as adhesive strength and storage stability, is not excessively reduced compared to a composition that does not contain a flame retardant (Comparative Example 1). Therefore, it has been found that the present disclosure provides an adhesive composition that has favorable performance as an adhesive composition and is capable of forming a flame-retardant cured adhesive product.

Furthermore, the adhesive compositions of Examples 2-5, 7-10, and 12 and Comparative Examples 4, 6, and 8 all had a phosphorus content of 1.5%. The cured products formed from the adhesive compositions of the Examples, which used a reactive flame retardant, obtained flame retardancy test results indicating flame retardancy, while the cured products formed from the adhesive compositions of the Comparative Examples, which used an additive flame retardant, did not exhibit sufficient flame retardancy. This demonstrates that when a flame retardant is used to achieve the same phosphorus content, the cured products formed from the adhesive compositions of the present disclosure, which use a reactive flame retardant, exhibit a higher flame retardancy effect. In other words, according to the present disclosure, an adhesive composition can be obtained that can form a cured product with suitable flame retardancy by containing a small amount of flame retardant.

The adhesive composition of the present disclosure includes the following preferred embodiments.
<1> A first agent containing an organic peroxide and a second agent containing a reducing agent,
(a) a monofunctional (meth)acrylic monomer;
(b) (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate; and (c) a thickener are each contained in at least one of the first agent and the second agent,
At least one of the first agent and the second agent further comprises a reactive flame retardant.
<2> The adhesive composition according to <1>, wherein, based on a total of 100 parts by weight of the component (a), the component (b), and the component (c) contained in the first agent and the second agent, the content of the component (a) is 30 to 80 parts by weight, the content of the component (b) is 1 to 50 parts by weight, and the content of the component (c) is 1 to 50 parts by weight.
<3> The adhesive composition according to <1> or <2>, wherein the reactive flame retardant is a phosphorus-based reactive flame retardant.
<4> The adhesive composition according to any one of <1> to <3>, wherein the reactive flame retardant is a reactive flame retardant containing a polymerizable unsaturated group.
<5> The reactive flame retardant is represented by the following general formula (I):
(In the formula, _R1 represents a polymerizable unsaturated group, and _R2 and _R3 each independently represent an alkyl group having 1 to 15 carbon atoms, an alkoxy group having 1 to 15 carbon atoms, or an aryl group having 6 to 14 carbon atoms.)
<4> The adhesive composition according to any one of <1> to <4>, wherein the phosphorus-based reactive flame retardant is represented by the formula:
<6> The adhesive composition according to <4> or <5>, wherein the polymerizable unsaturated group is a vinyl group or a (meth)acryloyl group.
<7> The adhesive composition according to any one of <1> to <6>, wherein the total content of the reactive flame retardant contained in the first agent and the second agent is 7 to 50 parts by weight, relative to a total of 100 parts by weight of the component (a), the component (b), and the component (c) contained in the first agent and the second agent.
<8> Each of the first agent and the second agent contains the component (a), the component (b), and the component (c),
The adhesive composition according to any one of <1> to <7>, wherein at least one of the first agent and the second agent contains the reactive flame retardant.
<9> The adhesive composition according to <8>, wherein each of the first agent and the second agent contains the reactive flame retardant.
<10> Either the first agent or the second agent contains the component (a), the component (b), the component (c), and the reactive flame retardant,
<7> The adhesive composition according to any one of <1> to <7>, wherein the other of the first agent and the second agent contains a solvent, and the organic peroxide or the reducing agent is dissolved or dispersed in the solvent.
<11> The adhesive composition according to any one of <1> to <10>, wherein the first agent and the second agent do not contain an additive-type flame retardant.
<12> A cured product of the adhesive composition according to any one of <1> to <11>.

The adhesive composition of the present disclosure can be used as an adhesive in a variety of fields, including electrical, mechanical, and construction, where bonding of objects together is required.

Claims (9)

The composition includes a first agent containing an organic peroxide and a second agent containing a reducing agent,
(a) a monofunctional (meth)acrylic monomer;
(b) (meth)acrylic acid and/or hydroxyalkyl (meth)acrylate; and (c) a thickener are each contained in at least one of the first agent and the second agent,
At least one of the first agent and the second agent further contains a reactive flame retardant,
The reactive flame retardant is represented by the following general formula (I):
(In the formula, R1 _represents a polymerizable unsaturated group, and R2 _and R3 _each independently represent an alkyl group having 1 to 15 carbon atoms, an alkoxy group having 1 to 15 carbon atoms, or an aryl group having 6 to 14 carbon atoms.)
is a phosphorus-based reactive flame retardant represented by
The adhesive composition , wherein the polymerizable unsaturated group is at least one selected from the group consisting of a vinyl group, a (meth)acrylic group, and a (meth)acryloyl group . The adhesive composition according to claim 1, wherein, out of a total of 100 parts by weight of the components (a), (b), and (c) contained in the first and second agents, the content of component (a) is 30 to 80 parts by weight, the content of component (b) is 1 to 50 parts by weight, and the content of component (c) is 1 to 50 parts by weight. The adhesive composition according to claim 1 , wherein the polymerizable unsaturated group is a vinyl group or a (meth)acryloyl group. The adhesive composition according to claim 1, wherein the total content of the reactive flame retardant contained in the first and second agents is 7 to 50 parts by weight per 100 parts by weight of the total of the (a), (b), and (c) components contained in the first and second agents. each of the first agent and the second agent contains the component (a), the component (b), and the component (c);
The adhesive composition according to claim 1 , wherein at least one of the first part and the second part contains the reactive flame retardant. The adhesive composition according to claim 1, wherein the first and second parts each contain the reactive flame retardant. one of the first agent and the second agent contains the component (a), the component (b), the component (c), and the reactive flame retardant;
The adhesive composition according to claim 1 , wherein the other of the first part and the second part contains a solvent, and the organic peroxide or the reducing agent is dissolved or dispersed in the solvent. The adhesive composition according to claim 1, wherein the first and second components do not contain an additive-type flame retardant. A cured product of the adhesive composition according to any one of claims 1 to 8 .