Adhesive composition, bonded body, and method for producing adhesive composition

Abstract

An adhesive composition which contains a polymerizable monomer that has a (meth)acryloyl group, a radical polymerization initiator and polymer particles that are swellable with an organic solvent, wherein with respect to the particle size distribution of secondary particles, which are aggregates of the polymer particles, in the adhesive composition as determined by a laser diffraction / scattering method, the proportion of the secondary particles having a diameter of 1 μm to 200 μm is 30% by volume or more.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition, a bonded body, and a method for producing the adhesive composition. [Background technology]

[0002] Known adhesive compositions include epoxy adhesives, acrylic adhesives, urethane adhesives, etc. Among these, acrylic adhesives are generally superior in terms of adhesion to oily surfaces and ease of work.

[0003] An example of an acrylic adhesive is Patent Document 1. Patent Document 1 describes an acrylic adhesive composition containing (1) a (meth)acrylic acid derivative monomer, (2) a polymerization initiator, (3) a reducing agent, and (4) a diene-based core-shell polymer. In this composition, the diene-based core-shell polymer is an MBS resin (methyl methacrylate-acrylonitrile-butadiene-styrene copolymer), which is swellable in the (meth)acrylic acid derivative monomer and has a swelling index of 9.5 or higher in toluene at 25°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4707320 Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of investigations, the present inventors have completed an adhesive composition that shows improvements in terms of storage stability compared to the adhesive composition described in Patent Document 1. Specifically, the present invention has completed an adhesive composition that can obtain a desired adhesive strength even after a long period of time has passed since production. [Means for solving the problem]

[0006] The inventors have completed the invention provided below.

[0007] According to the present invention, a polymerizable monomer having a (meth)acryloyl group; a radical polymerization initiator; and polymer particles having a property of swelling with an organic solvent, An adhesive composition in which the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less is 30% by volume or more in the particle size distribution of secondary particles, which are aggregates of the polymer particles, in the adhesive composition as determined by a laser diffraction / scattering method. is provided.

[0008] Further, according to the present invention, a first structural member; a second structural member; and a bonded body comprising the cured product of the adhesive composition for bonding the first structural member and the second structural member; is provided.

[0009] Further, according to the present invention, A method for producing the adhesive composition, comprising: a dispersing step of adding the polymer particles to a container containing the polymerizable monomer and stirring the mixture to disperse the polymer particles in the polymerizable monomer, The temperature of the polymerizable monomer when added is 0°C or higher and 40°C or lower. is provided. [Effects of the Invention]

[0010] According to the present invention, an adhesive composition is provided which has good storage stability and can provide high adhesive strength. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] In this specification, unless otherwise specified, the expression "X to Y" in the description of a numerical range means at least X and at most Y. For example, "1 to 5% by mass" means "at least 1% by mass and at most 5% by mass." In this specification, the amount used preferably represents the amount relative to the total amount of the first and second agents.

[0013] In the description of groups (atomic groups) in this specification, when a notation does not specify whether the group is substituted or unsubstituted, it encompasses both groups having no substituents and groups having a substituent. For example, the term "alkyl group" encompasses not only alkyl groups having no substituents (unsubstituted alkyl groups) but also alkyl groups having a substituent (substituted alkyl groups). In this specification, the term "(meth)acrylic" represents a concept that encompasses both acrylic and methacrylic. The same applies to similar terms such as "(meth)acrylate." Unless otherwise specified, the term "organic group" as used herein means an atomic group obtained by removing one or more hydrogen atoms from an organic compound. For example, a "monovalent organic group" refers to an atomic group obtained by removing one hydrogen atom from any organic compound.

[0014] <Adhesive composition> The adhesive composition of the present embodiment contains a polymerizable monomer having a (meth)acryloyl group, a radical polymerization initiator, and polymer particles that have the property of swelling in an organic solvent. In the particle size distribution of the secondary particles, which are aggregates of the polymer particles, in the adhesive composition of this embodiment, determined by a laser diffraction / scattering method, the proportion of secondary particles with diameters of 1 μm to 200 μm is 30% by volume or more, preferably 40% by volume or more, and more preferably 50% by volume or more. This value may be 100% by volume or 99.5% by volume or less.

[0015] The present inventors have conducted various studies to improve the storage stability of adhesive compositions. As described above, the present inventors have determined that the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less in the particle size distribution of secondary particles, which are aggregates of polymer particles, is 30% by volume or more. This has enabled them to provide an adhesive composition that has good storage stability and provides high adhesive strength.

[0016] The method for producing the adhesive composition of this embodiment is not limited, but from the viewpoint of appropriately controlling the particle size distribution of the secondary particles, which are aggregates of polymer particles, it is preferable to adopt appropriate production methods and conditions. Key points regarding the production methods and conditions include, for example, appropriately controlling the temperature when mixing the polymerizable monomer and the polymer particles, the stirring speed (stirring peripheral speed) during mixing, and the like. Details of the production methods and conditions will be explained later.

[0017] The components that can be contained in the adhesive composition of this embodiment, the physical properties of the adhesive composition of this embodiment, and other matters related to the adhesive composition of this embodiment will be described below.

[0018] (polymerizable monomer) The adhesive composition of the present embodiment contains a polymerizable monomer having a (meth)acryloyl group. In this specification, the polymerizable monomer having a (meth)acryloyl group is also referred to simply as a "polymerizable monomer."

[0019] Specific examples of the polymerizable monomer include the following: (i) General formula ZO-R1 A monomer represented by In the general formula, Z represents a (meth)acryloyl group, CH2=CHCOOCH2CH2- group, CH2=C(CH3)COOCH2-CH2CH2- group, CH2=CHCOOCH2-CH(OH)- group, CH2=C(CH3)COOCH2-CH(OH)- group, CH2=CHCOOCH2-CH(OH)CH2- group, or CH2=C(CH3)COOCH2-CH(OH)CH2- group; R1 represents hydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, a benzyl group, a phenyl group, a tetrahydrofurfuryl group, a glycidyl group, a dicyclopentyl group, a dicyclopentenyl group, a (meth)acryloyl group, or an isobornyl group.

[0020] Examples of such monomers include methyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, glycerol (meth)acrylate, glycerol di(meth)acrylate, isobornyl (meth)acrylate, and (meth)acrylic acid.

[0021] (ii) General formula ZO-(R2O) p -R1 A monomer represented by In the general formula, Z and R1 are as defined above. R2 is -C2H4-, -C3H6-, -CH2CH(CH3)-, -C4H8-, or -C6H 12 -, and p represents an integer of 1 or more and 25 or less.

[0022] Examples of such monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethoxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate.

[0023] (iii) General formula [ka] A monomer represented by In the general formula, Z and R2 are as defined above. R3 represents hydrogen or an alkyl group having 1 to 4 carbon atoms, and q represents an integer of 0 to 8. Z, R2, R3, and q may be the same or different.

[0024] Examples of such monomers include 2,2-bis(4-(meth)acryloxyphenyl)propane, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane, and ethoxylated bisphenol A di(meth)acrylate.

[0025] (iv) (meth)acrylic acid esters of polyhydric alcohols not included in (i), (ii), or (iii) above.

[0026] Examples of such monomers include trimethylolpropane tri(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate and dipentaerythritol hexa(meth)acrylate, tripropylene glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate.

[0027] (v) Urethane prepolymer having a (meth)acryloyloxy group. Such a monomer can be obtained, for example, by reacting a (meth)acrylic acid ester having a hydroxyl group, an organic polyisocyanate, and a polyhydric alcohol.

[0028] Examples of the (meth)acrylic acid ester having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0029] Examples of organic polyisocyanates include toluene diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate. Examples of polyhydric alcohols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyester polyols.

[0030] (vi) An acidic phosphoric acid compound represented by general formula (I).

[0031] [ka]

[0032] In the above general formula, R is CH2=CR4CO(OR5) m - group (wherein R4 is hydrogen or a methyl group, and R5 is -C2H4-, -C3H6-, -CH2CH(CH3)-, -C4H8-, -C6H 12 -or-C2H4-OCO-C5H 10 -, and m represents an integer of 1 or more and 10 or less. ) and n represents an integer of 1 or 2.

[0033] Examples of the acidic phosphoric acid compound represented by general formula (I) include acid phosphooxyethyl (meth)acrylate, acid phosphooxypropyl (meth)acrylate, bis(2-(meth)acryloyloxyethyl)phosphate, and 2-(meth)acryloyloxyethyl acid phosphate.

[0034] Particularly preferred polymerizable monomers (monofunctional and polyfunctional) are as follows: Monofunctional Methyl (meth)acrylate, ethylhexyl (meth)acrylate, lauryl (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and (meth)acrylic acid ·Multifunctional Ethylene oxide modified di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, and ethoxylated pentaerythritol tetra(meth)acrylate

[0035] The adhesive composition of this embodiment may contain only one of the monomers (i) to (vi), or may contain two or more of them. Among these, one or two or more of (i), (ii), and (vi) are preferred, and a combination of (i), (ii), and (vi) is more preferred, in terms of high adhesiveness and small adhesive strain on the adherend after adhesion. When (i) and (ii) are used in combination, the composition ratio by mass of (i):(ii) is preferably 50-95:5-50, more preferably 60-80:20-40. When (vi) is used, the amount used is preferably 0.05 parts by mass or more and 10 parts by mass or less, more preferably 0.1 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the total of (i) and (ii).

[0036] (Radical polymerization initiator) The adhesive composition of this embodiment contains a radical polymerization initiator, which polymerizes the polymerizable carbon-carbon double bonds of the polymerizable monomer, thereby enabling adhesion of articles.

[0037] The radical polymerization initiator is preferably a thermal radical polymerization initiator. Preferred examples of the thermal radical polymerization initiator include organic peroxides. Examples of organic peroxides include cumene hydroperoxide, paramenthane hydroperoxide, tertiary butyl hydroperoxide, diisopropylbenzene dihydroperoxide, methyl ethyl ketone peroxide, tertiary butyl peroxybenzoate, and benzoyl peroxide. Among these, cumene hydroperoxide is preferred from the viewpoint of stability. Incidentally, by using a radical polymerization initiator in combination with a reducing agent, which will be described later, it is possible to further enhance the curability and achieve room temperature curing.

[0038] The amount of radical polymerization initiator is preferably 0.1 to 20 parts by mass, more preferably 0.4 to 10 parts by mass, per 100 parts by mass of polymerizable monomer. By using a moderately large amount of radical polymerization initiator, the curing rate can be sufficiently increased. On the other hand, by not using too much radical polymerization initiator, storage stability can be further improved.

[0039] (polymer particles) The adhesive composition of this embodiment contains polymer particles that have the property of swelling in an organic solvent. "Swelling in an organic solvent" means that when the polymer particles are brought into contact with a liquid such as an organic solvent, the polymer particles have the property of absorbing the liquid and swelling. Specifically, the swelling degree is preferably 5 times or more, more preferably 7 times or more, even more preferably 9.5 times or more, and particularly preferably 10 times or more. The upper limit of the swelling degree is, for example, 15 times.

[0040] The degree of swelling can be measured as described in paragraph 0049 of the aforementioned Patent Document 1. Specifically, 1 g of a sample is left to stand in 100 mL of toluene at 25°C for 24 hours, and then the gel that has swollen in the toluene is filtered through a 100-mesh wire mesh (mass A). After 1 minute, the mass B of the swollen gel and wire mesh is measured. The sample is air-dried overnight at room temperature, and then vacuum-dried, and the mass C of the dried gel and wire mesh is measured. The degree of swelling can then be calculated using the formula: swelling (times) = (BA) / (CA).

[0041] Since the polymer particles are swellable, the polymerizable monomers enter the polymer particles, causing polymerization within the polymer particles, which is expected to result in a further increase in adhesive strength and the like. In this specification, polymer particles that have the property of swelling with an organic solvent are also referred to simply as "polymer particles."

[0042] Just to be clear, the numerical values ​​relating to the particle sizes and particle size distributions of the polymer particles in this specification represent the numerical values ​​of the polymer particles in the adhesive composition (in the case where the polymer particles are swollen, the particle size in the swollen state, etc.) unless otherwise specified.

[0043] In one aspect, the polymer particles preferably include core-shell type polymer particles, which can be obtained by the methods described in International Publication No. 2005 / 028546 and Japanese Patent Application Laid-Open No. 2016-104834. From another perspective, the polymer particles preferably contain a diene-based polymer, and more preferably, the polymer constituting the polymer particles contains a (meth)acrylonitrile-butadiene-styrene copolymer and / or a methyl (meth)acrylate-(meth)acrylonitrile-butadiene-styrene copolymer.

[0044] The median diameter D of secondary particles calculated from the particle size distribution of secondary particles 50 is preferably 1 μm or more and 200 μm or less, more preferably 5 μm or more and 180 μm or less, and even more preferably 10 μm or more and 150 μm or less. The cumulative 90% diameter of secondary particles D obtained from the particle size distribution of secondary particles 90 is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 400 μm or less, and even more preferably 30 μm or more and 300 μm or less. These values ​​define the relatively small amount of coarse secondary particles from a different perspective than the proportion of secondary particles with diameters of 1 μm or more and 200 μm or less. Adjusting these values ​​can further improve the performance of the adhesive composition. Median diameter of secondary particles D 50 and the cumulative 90% diameter of secondary particles D 90 The adjustment of is carried out, for example, by appropriately controlling the temperature when mixing the polymerizable monomer and the polymer particles, the shear force during mixing, etc. The shear force is adjusted, for example, by appropriately selecting the rotation speed of the stirring blade, the diameter of the stirring blade, the stirring speed (stirring peripheral speed), etc.

[0045] Incidentally, the volume average particle diameter of the "primary particles" of the polymer particles is preferably 0.01 μm or more and 1 μm or less, more preferably 0.02 μm or more and 0.8 μm or less, and even more preferably 0.03 μm or more and 0.6 μm or less. By appropriately selecting the volume average particle diameter of the primary particles, the performance of the adhesive composition can be further improved. For example, the volume average particle size of the "primary particles" can be adjusted by subjecting the polymer particles to a pulverization process and a sieve classification process after the pulverization process. The volume average particle size of the "primary particles" can also be adjusted by using polymer particles having an appropriate particle size distribution.

[0046] Polymer particles that can be preferably used are available from, for example, Denka Company Ltd. and Kaneka Corporation.

[0047] The amount of polymer particles is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of polymerizable monomer. By using a moderate amount of polymer particles, the toughness of the cured film can be further improved. On the other hand, by not using too many polymer particles, sufficient amounts of polymerizable monomer and polymerization initiator can be used, which tends to further improve curability.

[0048] (Elastomer) The adhesive composition of this embodiment preferably contains one or more elastomers. The elastomer preferably does not include the polymer particles described above. By using an elastomer, the cured product of the adhesive composition has appropriate elasticity, which can further improve, for example, toughness.

[0049] Examples of the elastomer component include (meth)acrylonitrile-butadiene-(meth)acrylic acid copolymer, (meth)acrylonitrile-butadiene-methyl(meth)acrylate copolymer, styrene-based thermoplastic elastomers such as (meth)acrylonitrile-butadiene copolymer, styrene-butadiene copolymer, chlorosulfonated polyethylene, and styrene-polybutadiene-styrene synthetic rubber, as well as polybutadiene whose ends are (meth)acrylic-modified, and urethane-based elastomers.

[0050] Among these, in terms of solubility and adhesiveness, one or more selected from the group consisting of (meth)acrylonitrile-butadiene-(meth)acrylic acid copolymers and (meth)acrylonitrile-butadiene copolymers (such as NBR) are preferred.

[0051] When an elastomer is used, the amount thereof, in total with the polymer particles, is preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the polymerizable monomer.

[0052] (reducing agent) The adhesive composition of this embodiment preferably contains one or more reducing agents. By using a radical polymerization initiator and a reducing agent in combination, the curability can be further improved and room temperature curing can be achieved. The reducing agent may be any known reducing agent that reacts with the polymerization initiator to generate radicals. The reducing agent is preferably at least one selected from the group consisting of tertiary amines, thiourea derivatives, and transition metal salts, and more preferably transition metal salts. Examples of thiourea derivatives include acetylthiourea and ethylenethiourea. Examples of transition metal salts include cobalt naphthenate, cobalt octoate, copper naphthenate, and vanadyl acetylacetonate. Among the transition metal salts, vanadyl acetylacetonate is preferred.

[0053] When a reducing agent is used, the amount used is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 100 parts by mass of polymerizable monomer. Using 0.01 part by mass or more will sufficiently increase the curing rate, and using 10 parts by mass or less will improve storage stability.

[0054] (paraffin) The adhesive composition of this embodiment may contain paraffin. Specifically, various paraffins can be used to accelerate curing of the portion exposed to air. Examples of paraffins include paraffin wax, microcrystalline wax, carnauba wax, beeswax, lanolin, spermaceti, ceresin, and candelilla wax.

[0055] When the adhesive composition of the present embodiment contains paraffin, it may contain only one paraffin, or may contain two or more paraffins. When the adhesive composition of this embodiment contains paraffin, the amount thereof is preferably 0.01 to 3 parts by mass, more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the polymerizable monomer. By using a relatively large amount of paraffin, the effect of accelerating curing can be sufficiently obtained. On the other hand, by not using too much paraffin, the effect of accelerating curing can be obtained while maintaining sufficient adhesiveness.

[0056] (Other ingredients) The adhesive composition of the present embodiment may or may not contain optional components other than those described above. For example, the adhesive composition of the present embodiment may contain spacers (particles) or the like to adjust the film thickness during use. The spacers are typically spherical particles made of a resin such as polyolefin.

[0057] As another example, the adhesive composition of this embodiment may contain various stabilizers to improve storage stability (suppress deterioration during storage). Examples of stabilizers include (i) compounds known as phenolic antioxidants, (ii) quinone compounds such as p-benzoquinone and hydroquinone monomethyl ether, (iii) compounds known as polymerization inhibitors such as amine-based polymerization inhibitors such as phenothiazine, and (iv) stable radical-type compounds having stable radicals. Among these, stable radical-type compounds are preferred because they improve storage stability without impairing adhesive performance (tensile shear adhesive strength and storage modulus).

[0058] The stable radical is preferably a nitroxide radical. Specific examples of stable radical compounds that are nitroxide radicals include 1-oxyl-2,2,6,6-tetramethylpiperidine, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, and 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine 1-oxyl. When a stable radical compound is used, it is preferable to use one or more of these.

[0059] When a stabilizer such as a stable radical compound is used, the content thereof is, for example, from 0.001 to 1 part by mass, preferably from 0.001 to 0.5 parts by mass, more preferably from 0.01 to 0.3 parts by mass, and even more preferably from 0.02 to 0.1 parts by mass, relative to 100 parts by mass of polymerizable monomer, in order to improve storage stability without impairing performance as an adhesive.

[0060] ( 1 Dosage form / 2 Dosage form) The adhesive composition of the present embodiment is a so-called 1 It may be in the form of 2 It may also be in a dosage form (an adhesive composition in which two components filled in separate containers are mixed immediately before use). 2 In the case of a dosage form, the radical polymerization initiator is preferably 1 The reducing agent is 2 However, tertiary amines are contained in the 1 It is preferable that the thiourea derivative and the transition metal salt are contained in the first 2 It is preferable that other ingredients are contained in the agent. 2 It can be mixed with the first 1 Agents and 2 The agent may be mixed and used. Incidentally, the adhesive composition of this embodiment 2 If it is a dosage form, 1 Agents and 2 The adhesive composition after mixing the additives is prepared by mixing the additives in the first step so that each component is contained in the preferred range of content. 1 Agents and 2 It is preferable to adjust the amount of each component in the agent.

[0061] <Method of manufacturing adhesive composition> The method for producing the adhesive composition of this embodiment is not limited. However, from the viewpoint of appropriately controlling the particle size distribution of the secondary particles, which are aggregates of polymer particles, it is preferable to adopt an appropriate production method and production conditions. Key points in the production method and production conditions include, for example, appropriately controlling the temperature when mixing the polymerizable monomer and the polymer particles, the stirring speed during mixing, and the like.

[0062] The method for producing an adhesive composition of this embodiment preferably includes a dispersing step of adding polymer particles to a container containing a polymerizable monomer and stirring the mixture to disperse the polymer particles in the polymerizable monomer. In this dispersing step, the temperature of the polymerizable monomer in the container when the polymer particles are added is preferably 0°C or higher and 40°C or lower, more preferably 15°C or higher and 35°C or lower. By setting the temperature of the polymerizable monomer at 0° C. or higher when the polymer particles are added, the polymer particles can be easily dispersed in the polymerizable monomer in a shorter time. Furthermore, by keeping the temperature of the polymerizable monomer at 40° C. or less when it is added, clumps of polymer particles (aggregates, splices) are less likely to form, making it easier to obtain a good polymer dispersion state.

[0063] In the dispersion step, the polymerizable monomer and the polymer particles are preferably mixed using a stirring blade. To sufficiently and uniformly disperse the polymer particles in the polymerizable monomer, the stirring peripheral speed of the stirring blade is preferably 300 mm / s or more, more preferably 500 mm / s or more. There is no particular upper limit to the stirring peripheral speed, but due to restrictions of the equipment, it is, for example, 300,000 mm / s or less.

[0064] <Applications of adhesive composition / joints> A bonded body including a cured product of the adhesive composition can be obtained by applying the adhesive composition of this embodiment to an article and curing it, etc. Specifically, by using the adhesive composition of this embodiment, a bonded body including a first structural member, a second structural member, and a cured product of the adhesive composition that bonds the first structural member and the second structural member can be obtained. The adhesive composition of the present embodiment, particularly when it contains a reducing agent, preferably cures without heating (at room temperature) and can bond articles together, although heating is not necessarily required to obtain a bonded structure.

[0065] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0066] The embodiments of the present invention will be described in detail based on Examples and Comparative Examples. However, it should be noted that the present invention is not limited to the Examples.

[0067] <Production of Adhesive Composition> Agent A (first agent) and agent B (second agent) of each of the examples and comparative examples were prepared as follows. (1) The monomers (unit: parts by mass, same for other components) shown in the "Polymerizable monomer" section of the table below and the NBR shown in the "Elastomer" section were placed in a temperature-controllable mixing container, and mixed by stirring using a stirring blade (anchor blade) at 60°C for 1 hour. (2) Polymer particles shown in the "Polymer particles" section of the table below were added to the container. The temperature at the time of adding the polymer particles is shown in the table below. The mixture was then mixed for 1 hour using a stirring blade. The rotation speed, diameter, and peripheral speed of the stirring blade were as shown in the table. (3) The remaining ingredients were added to the container and further stirred at room temperature for 24 hours to thoroughly mix.

[0068] In the tables below, commercially available polymerizable monomers, radical polymerization initiators, reducing agents, and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl were used as appropriate. Details of the polymer particles and elastomer are as follows: Product 1: Core-shell type particles, methyl methacrylate-acrylonitrile-butadiene-styrene copolymer, swelling degree measured as described in paragraph 0049 of Patent Document 1: 14.0 Product 2: Core-shell type particles, acrylonitrile-butadiene-styrene copolymer, swelling index measured as described in paragraph 0049 of Patent Document 1: 10.1 NBR: JSR Corporation "230S" (bound acrylonitrile content: 35%, Mooney viscosity: 56) The structure of ethoxylated bisphenol A dimethacrylate is:

[0069] [ka]

[0070] <Measurement of particle size distribution of polymer particles in adhesive composition> The measurement was carried out according to the following procedure. (1) 1 g of the adhesive composition was placed in a 10 mL glass vial, and 4 g of methyl methacrylate (Tokyo Chemical Industry Co., Ltd., >99.8%) was added thereto (methyl methacrylate was used to dilute the composition and make it easier to measure the particle size distribution). (2) The glass vial was capped and left to stand at 23°C for 24 hours without shaking. After standing, the supernatant was removed from the glass vial with a dropper, and the particle size distribution of the polymer particles contained in this supernatant was measured. The particle size distribution was measured in accordance with JIS Z 8825:2013 using a Shimadzu laser diffraction particle size distribution analyzer "SALD-2200," at a measurement temperature of 23°C and a measurement solvent of methyl methacrylate (Tokyo Chemical Industry, >99.8%). (3) From the measurement results, the following was determined: The proportion of secondary particles with a diameter of 1 μm or more and 200 μm or less in the particle size distribution of secondary particles ·Median diameter of secondary particles D 50 Cumulative 90% diameter of secondary particles D 90

[0071] It should be noted that, in general, when measuring particle size distribution, ultrasonic dispersion or the like is often performed to minimize secondary particles. However, in this case, in order to obtain information on particle size distribution that reflects the aggregation state of polymer particles in the adhesive composition, dispersion treatment such as ultrasonic dispersion was not performed, and only dilution treatment with methyl methacrylate was performed.

[0072] <Measurement of particle size distribution of polymer particles themselves (primary particles)> The measurement was carried out in the following manner. (1) 0.1 g of polymer particles (Product 1 or Product 2) was placed in a 10 mL glass vial, 4.9 g of a 0.2% by mass aqueous solution of sodium hexametaphosphate was added, and the mixture was dispersed using ultrasound (130 W) for 10 minutes. (2) The particle size distribution of the polymer particles contained in this dispersion was measured in accordance with JIS Z 8825:2013 using a Shimadzu laser diffraction particle size distribution analyzer "SALD-2200" at a measurement temperature of 23°C and in pure water as the measurement solvent. (3) Of the measurement results, the volume average particle size of the primary particles of the polymer particles was used.

[0073] <Measurement and evaluation of viscosity> In accordance with JIS K 6838, the viscosity (unit: mPa s) of each adhesive composition (component A, component B) was measured using a Brookfield viscometer at a rotor rotation speed of 20 rpm, a measurement time of 2 minutes, and an ambient temperature of 25°C. This viscosity measurement value was designated A1. Prior to measurement, each adhesive composition (component A, component B) was allowed to stand in an ambient temperature of 25°C for at least 24 hours to adjust the liquid temperature to 25°C. Furthermore, 500 g of each adhesive composition (agent A, agent B) was filled into a 500 mL polyethylene bottle and left to stand at 23°C for one week. The viscosity of agents A and B after standing was measured in the same manner. This viscosity measurement value was designated as A2. The viscosity retention rate A (%) was calculated using the following formula: A(%)=(A2 / A1)×100

[0074] Regarding viscosity, the thixotropic index (TI) was also measured. Specifically, TI was calculated by calculating A1' / A1 from the viscosity A1' measured in the same manner as A1, except that the rotation speed was changed from 20 rpm to 2 rpm.

[0075] <Evaluation of adhesive toughness> The evaluation was carried out as follows in accordance with JIS K 6854. The evaluation was carried out in an environment of a temperature of 23°C and a relative humidity of 50%. First, a mixture was prepared by mixing equal amounts of Agent A and Agent B of the adhesive composition of each Example and Comparative Example. This mixture was quickly applied to one side of a test piece (200 mm x 25 mm x 1.6 mm, SECC steel plate). Immediately afterwards, the other test piece (200 mm x 25 mm x 0.5 mm: SECC steel plate) was placed on top of the other test piece, which was then attached and secured with clips. The test piece was then left to cure at room temperature for 24 hours. In this way, an evaluation sample was obtained. The peel strength (unit: kN / m) was measured using the obtained evaluation samples. Peel strength (unit: kN / m) was measured at a pulling rate of 50 mm / min in an environment of 23°C temperature and 50% relative humidity. The measurement was performed three times, and the average value is shown in the table as the peel strength. The standard deviation of the three measurements is also shown in the table. The results of observing the state of failure are also shown in the table. For the state of failure, the area percentage of the type of failure was calculated. Generally, strong adhesive strength is obtained when cohesive failure occurs, so cohesive failure is the preferred state of failure.

[0076] The various pieces of information mentioned above are summarized in the table below. The amounts of polymerizable monomers, polymer particles, elastomers, radical polymerization initiators, reducing agents, and other components are all expressed in parts by mass.

[0077] [Table 1]

[0078] As shown in the table above, the viscosity retention rate A of adhesive compositions in which the proportion of secondary particles with a diameter of 1 μm or more and 200 μm or less of the polymer particles was 30% by volume or more was nearly 100%, meaning that the storage stability was good. Furthermore, by using an adhesive composition in which the proportion of secondary particles with diameters of 1 μm to 200 μm is 30% by volume or more, SECC steel sheets can be strongly bonded together, which means that high adhesive strength can be achieved.

[0079] The present inventors have conducted various studies to improve the storage stability of adhesive compositions. Through these studies, it was determined that in conventional adhesive compositions such as those described in Patent Document 1, polymer particles (such as diene-based core-shell polymers) in the composition excessively aggregate to form coarse secondary particles, which is believed to lead to a decrease in adhesive strength over time. Specifically, the adhesive composition described in Patent Document 1 has the problem that it may no longer be able to achieve the desired adhesive strength over time after production, and therefore it is preferable to use the composition promptly after production. Based on this assumption, the inventors determined that the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less in the particle size distribution of the secondary particles, which are aggregates of polymer particles, is 30% by volume or more, as described above, and thereby provided an adhesive composition that has good storage stability and provides high adhesive strength.

[0080] This specification has primarily described an "adhesive composition" that contains a polymerizable monomer having a (meth)acryloyl group, a radical polymerization initiator, and polymer particles that swell in an organic solvent, and that is characterized by the particle size distribution of secondary particles, which are aggregates of the polymer particles. However, the adhesive composition described in this specification can also be used in fields other than adhesion, such as coating materials and injection agents. In other words, the adhesive composition described in this specification can also be used as a composition with no limited use, a curable composition, or a resin composition.

[0081] This application claims priority based on Japanese Patent Application No. 2021-059627, filed on March 31, 2021, the disclosure of which is incorporated herein in its entirety.

Claims

1. a polymerizable monomer having a (meth)acryloyl group; a radical polymerization initiator; and polymer particles having a property of swelling with an organic solvent, an adhesive composition in which, in a particle size distribution of secondary particles, which are aggregates of the polymer particles, in the adhesive composition, the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less is 50 vol % or more, as determined by a laser diffraction / scattering method; the polymer constituting the polymer particles contains a (meth)acrylonitrile-butadiene-styrene copolymer and / or a methyl (meth)acrylate-(meth)acrylonitrile-butadiene-styrene copolymer; the median diameter D 50 of the secondary particles determined from the particle size distribution of the secondary particles is 1 μm or more and 200 μm or less; a cumulative 90% diameter D 90 of the secondary particles determined from the particle size distribution of the secondary particles is 10 μm or more and 500 μm or less; the volume average particle size of the primary particles of the polymer particles is 0.01 μm or more and 1 μm or less; When the adhesive composition is a two-component adhesive composition consisting of a first component and a second component, the first component contains the polymerizable monomer and the polymer particles, and the second component contains the polymerizable monomer and the polymer particles, In the particle size distribution of the secondary particles, which are agglomerates of the polymer particles, in the first agent, determined by a laser diffraction / scattering method, the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less is 50 vol % or more, and in the particle size distribution of the secondary particles, which are agglomerates of the polymer particles, in the second agent, determined by a laser diffraction / scattering method, the proportion of secondary particles having a diameter of 1 μm or more and 200 μm or less is 50 vol % or more, the median diameter D50 of the secondary particles obtained from the particle size distribution of the secondary particles of the first agent is 1 μm or more and 200 μm or less, and the median diameter D50 of the secondary particles obtained from the particle size distribution of the secondary particles of the second agent is 1 μm or more and 200 μm or less; a cumulative 90% diameter D 90 of the secondary particles obtained from the particle size distribution of the secondary particles of the first agent is 10 μm or more and 500 μm or less, and a cumulative 90% diameter D 90 of the secondary particles obtained from the particle size distribution of the secondary particles of the second agent is 10 μm or more and 500 μm or less, an adhesive composition, wherein the volume average particle diameter of the primary particles of the polymer particles in the first agent is 0.01 μm or more and 1 μm or less, and the volume average particle diameter of the primary particles of the polymer particles in the second agent is 0.01 μm or more and 1 μm or less.

2. 2. The adhesive composition of claim 1, The adhesive composition, wherein the polymer particles include core-shell type polymer particles.

3. The adhesive composition according to claim 1 or 2, The adhesive composition further comprises an elastomer.

4. The adhesive composition according to any one of claims 1 to 3, The adhesive composition further comprises a stable radical type compound having a stable radical.

5. The adhesive composition according to claim 4, An adhesive composition wherein the stable radical is a nitroxide radical.

6. The adhesive composition according to claim 4 or 5, The adhesive composition wherein the stable radical compound comprises at least one compound selected from the group consisting of 1-oxyl-2,2,6,6-tetramethylpiperidine, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, and 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine 1-oxyl.

7. The adhesive composition according to any one of claims 4 to 6, The adhesive composition has a stable radical compound content of 0.001 parts by mass or more and 0.5 parts by mass or less relative to 100 parts by mass of the polymerizable monomer.

8. The adhesive composition according to any one of claims 1 to 7, The adhesive composition further comprises a reducing agent.

9. 9. The adhesive composition according to claim 8, The adhesive composition is a two-part adhesive composition comprising a first part and a second part that are mixed together immediately before use, wherein the first part contains the radical polymerization initiator and the second part contains the reducing agent.

10. a first structural member; a second structural member; and A bonded body comprising a cured product of the adhesive composition according to any one of claims 1 to 9, which bonds the first structural member and the second structural member.

11. A method for producing the adhesive composition according to any one of claims 1 to 9, comprising the steps of: a dispersing step of adding the polymer particles to a container containing the polymerizable monomer and stirring the mixture to disperse the polymer particles in the polymerizable monomer, The method for producing an adhesive composition, wherein the temperature of the polymerizable monomer when being added is 0°C or higher and 40°C or lower.

12. The method of claim 11, The method for producing an adhesive composition, wherein the stirring is carried out using a stirring blade at a peripheral stirring speed of 300 mm / s or more.

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