Photocurable resin composition

Abstract

The present invention provides a photocurable resin composition that exhibits less shrinkage stress during curing, that applies less stress on an adherend during curing, and that can produce a cured product which has superior adhesiveness, and in which fogging due to moisture is reduced and yellowing occurring in a high-temperature atmosphere is reduced. A photocurable resin composition according to the present invention is characterized by comprising: a (meth)acrylic monomer (A) that is water‐insoluble and that has a glass transition temperature Tg of 50°C or higher; and a polyfunctional (meth)acrylic oligomer (B) that has a polydiene-based skeleton having a hydrogenation rate of 90% or more.

Description

Photocurable resin composition

[0001] The present invention relates to a photocurable resin composition.

[0002] Photocurable resin compositions have been used as adhesives for glass and synthetic resins. Photocurable resin compositions are cured by irradiation with light to develop adhesive properties. Photocurable resin compositions generate shrinkage stress during photocuring.

[0003] If the shrinkage stress during photocuring of a photocurable resin composition is large, stress is applied to the adherend bonded using the photocurable resin composition, causing distortion. In the optical field, such as optical lenses, if optical distortion occurs in the adherend, it will result in a decrease in product quality, so there is a need to reduce the stress applied to the adherend and thereby reduce the occurrence of optical distortion.

[0004] Furthermore, in recent years, the use of optical lenses in in-vehicle applications has increased with the spread of automatic driving of automobiles and their management function systems. The interior of an automobile is greatly affected by temperature and humidity, and it is particularly required that the quality of the cured product of the photocurable resin composition does not deteriorate even under harsh humid and hot environments.

[0005] Patent Document 1 discloses a photocurable adhesive composition containing (a) an oligomer having a photocurable functional group, (b) a long-chain hydrocarbon-based (meth)acrylate monomer, and (c) a cyclic (meth)acrylate monomer.

[0006] JP 2012-1648 A

[0007] However, the photocurable adhesive composition has problems such as a large shrinkage stress during curing, which causes a large stress on the adherend during curing, and poor adhesion of the cured product. Furthermore, when used for a long period of time in a harsh environment such as the interior of an automobile, the cured product of the photocurable adhesive composition becomes cloudy. In addition, when exposed to high temperatures in summer, the cured product becomes yellow.

[0008] The present invention provides a photocurable resin composition that has low shrinkage stress during curing and imparts low stress to an adherend during curing, and further has excellent adhesive properties, is resistant to fogging due to moisture, and is capable of producing a cured product with reduced yellowing due to high-temperature atmospheres.

[0009] The photocurable resin composition of the present invention contains a water-insoluble (meth)acrylic monomer (A) having a glass transition temperature Tg of 50°C or higher, and a polyfunctional (meth)acrylic oligomer (B) having a polydiene skeleton and a hydrogenation rate of 90% or higher.

[0010] The photocurable resin composition of the present invention has a small shrinkage stress during curing, and therefore exerts a small stress on an adherend during curing. The photocurable resin composition of the present invention can produce a cured product having excellent adhesive properties.

[0011] The photocurable resin composition of the present invention can produce a cured product that is less susceptible to moisture absorption, less prone to fogging due to moisture, and less prone to yellowing due to high-temperature atmospheres.

[0012] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. In this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits.

[0013] The photocurable resin composition of the present invention contains a water-insoluble (meth)acrylic monomer (A) having a glass transition temperature Tg of 50°C or higher, and a polyfunctional (meth)acrylic oligomer (B) having a polydiene skeleton and a hydrogenation rate of 90% or higher.

[0014] In the present invention, "(meth)acrylic" refers to a compound having an acryloyl group [formula (1)] or a methacryloyl group [formula (2)] in the molecule. In formulas (1) and (2), *1 represents a bond and means a single bond.

[0015]

[0016] [(Meth)acrylic Monomer (A) Having a Glass Transition Temperature Tg of 50°C or Higher and Being Water-Insoluble] The photocurable resin composition contains a (meth)acrylic monomer (A) having a glass transition temperature Tg of 50°C or higher and being water-insoluble (hereinafter, may be simply referred to as "(meth)acrylic monomer (A)").

[0017] The photocurable resin composition contains a (meth)acrylic monomer (A). The photocurable resin composition uses the (meth)acrylic monomer (A) in combination with a polyfunctional (meth)acrylic oligomer (B) described below, so that the photocurable resin composition produces a cured product having excellent adhesiveness, and further, the cured product of the photocurable resin composition has reduced cloudiness due to moisture and reduced yellowing due to a high-temperature atmosphere.

[0018] The glass transition temperature Tg of the (meth)acrylic monomer (A) is 50°C or higher, preferably 90°C or higher, more preferably 120°C or higher, more preferably 150°C or higher, more preferably 160°C or higher, and more preferably 170°C or higher. The glass transition temperature Tg of the (meth)acrylic monomer (A) is preferably 250°C or lower, more preferably 230°C or lower, more preferably 210°C or lower, more preferably 200°C or lower, and more preferably 190°C or lower. When the glass transition temperature Tg of the (meth)acrylic monomer (A) is 50°C or higher, the photocurable resin composition produces a cured product with superior adhesive properties. Furthermore, the cured product of the photocurable resin composition exhibits reduced cloudiness due to moisture and reduced yellowing due to high-temperature atmospheres. When the glass transition temperature Tg of the (meth)acrylic monomer (A) is 250°C or lower, the stress applied to the adherend during curing of the photocurable resin composition is reduced, which is preferable. The glass transition temperature Tg of the (meth)acrylic monomer (A) refers to a temperature measured in accordance with JIS K7121:1987.

[0019] The (meth)acrylic monomer (A) is water-insoluble. Because the (meth)acrylic monomer (A) is water-insoluble, the photocurable resin composition produces a cured product having excellent adhesiveness, and further, the cured product of the photocurable resin composition has reduced cloudiness due to moisture.

[0020] The phrase "the (meth)acrylic monomer (A) is water-insoluble" means that when the same volume of the (meth)acrylic monomer (A) is added to 100 g of pure water at 20°C and mixed at a stirring speed of 100 rpm, and the mixture is allowed to stand for 1 hour, the (meth)acrylic monomer (A) and water separate into two layers.

[0021] The (meth)acrylic monomer (A) may be any monomer having a glass transition temperature Tg of 50°C or higher and being water-insoluble, and examples thereof include (meth)acrylate monomers having a monocyclo ring, (meth)acrylate monomers having a bicyclo ring, and (meth)acrylate monomers having a tricyclo ring. The (meth)acrylic monomers (A) may be used alone or in combination of two or more. In the present invention, (meth)acrylate means acrylate or methacrylate.

[0022] In the (meth)acrylic monomer (A), the cyclic skeleton such as a monocyclo ring, a bicyclo ring, or a tricyclo ring is preferably a saturated alicyclic skeleton. When the (meth)acrylic monomer (A) has a saturated alicyclic skeleton, the photocurable resin composition produces a cured product with better adhesiveness, and further, the cured product of the photocurable resin composition exhibits less cloudiness due to moisture and less yellowing due to a high-temperature atmosphere. The alicyclic structure refers to a structure in which carbon atoms are bonded in a ring and does not have aromaticity.

[0023] Examples of the (meth)acrylate having a monocyclo ring include cyclohexyl (meth)acrylate, morpholine (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and 4-tert-butylcyclohexyl (meth)acrylate, with 4-tert-butylcyclohexyl (meth)acrylate being preferred.

[0024] Examples of (meth)acrylate monomers having a bicyclo ring include dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and isobornyl (meth)acrylate. As the (meth)acrylate monomer having a bicyclo ring, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate are more preferred, and isobornyl methacrylate and dicyclopentanyl methacrylate are more preferred. This is because the photocurable resin composition produces a cured product with superior adhesiveness, and further, the cured product of the photocurable resin composition exhibits reduced cloudiness due to moisture and reduced yellowing due to high-temperature atmospheres.

[0025] Examples of the (meth)acrylate monomer having a tricyclo ring include a (meth)acrylate compound having an adamantane skeleton.

[0026] The (meth)acrylic monomer (A) is preferably a (meth)acrylate monomer having a bicyclo ring. The bicyclo ring preferably has an alicyclic skeleton, more preferably a saturated alicyclic skeleton. This is because the photocurable resin composition produces a cured product having superior adhesiveness, and further, the cured product of the photocurable resin composition exhibits reduced cloudiness due to moisture and reduced yellowing due to high-temperature atmospheres.

[0027] The (meth)acrylic monomer (A) may be polyfunctional. When the (meth)acrylic monomer (A) is polyfunctional, the photocurable resin composition has low shrinkage stress during curing, and the stress applied to the adherend is reduced. Examples of the polyfunctional (meth)acrylic monomer (A) include tricyclodecane dimethanol di(meth)acrylate and ethoxylated bisphenol A di(meth)acrylate. The polyfunctional (meth)acrylic monomer (A) preferably has two or more (meth)acryloyl groups in the molecule. The (meth)acryloyl group refers to an acryloyl group (CH2=CHCO-) ​​or a methacryloyl group (CH2=C(CH3)CO-).

[0028] [Polyfunctional (meth)acrylic oligomer (B) having a polydiene skeleton with a hydrogenation rate of 90% or more] The photocurable resin composition contains a polyfunctional (meth)acrylic oligomer (B) having a polydiene skeleton with a hydrogenation rate of 90% or more (hereinafter, may be simply referred to as "polyfunctional (meth)acrylic oligomer (B)").

[0029] Since the photocurable resin composition contains the polyfunctional (meth)acrylic oligomer (B), the photocurable resin composition has low shrinkage stress during curing and exerts low stress on the adherend. Furthermore, the photocurable resin composition produces a cured product with excellent adhesiveness, and the cured product of the photocurable resin composition has reduced cloudiness due to moisture and reduced yellowing due to high-temperature atmospheres.

[0030] The hydrogenation rate of the polyfunctional (meth)acrylic oligomer (B) is 90% or more, preferably 91% or more, more preferably 92% or more, more preferably 93% or more, and even more preferably 94% or more. When the hydrogenation rate of the polyfunctional (meth)acrylic oligomer (B) is 90% or more, yellowing due to a high-temperature atmosphere can be reduced in the cured product of the photocurable resin composition. The hydrogenation rate of the polyfunctional (meth)acrylic oligomer (B) is the proportion of hydrogen added to unsaturated bonds contained in the molecule, and when all unsaturated bonds are hydrogenated, the hydrogenation rate is 100%.

[0031] The polyfunctional (meth)acrylic oligomer (B) having a hydrogenated polydiene skeleton refers to a (meth)acrylate having a hydrogenated conjugated diene skeleton in the molecule. The hydrogenated conjugated diene refers to, for example, a compound obtained by hydrogenating a conjugated diene. Examples of the hydrogenated conjugated diene include hydrogenated polybutadiene and hydrogenated polyisoprene, with hydrogenated polybutadiene being preferred.

[0032] The polyfunctional (meth)acrylic oligomer (B) has a hydrogenated polydiene skeleton in the molecule. Therefore, the photocurable resin composition has reduced shrinkage stress during curing, and the stress applied to the adherend is reduced. Furthermore, the photocurable resin composition produces a cured product with excellent adhesiveness, and the cured product of the photocurable resin composition has reduced cloudiness due to moisture and reduced yellowing due to high-temperature atmospheres.

[0033] The polyfunctional (meth)acrylic oligomer (B) is polyfunctional, so that the photocurable resin composition has reduced shrinkage stress during curing, and the stress applied to the adherend is reduced. The polyfunctional (meth)acrylic oligomer (B) preferably has two or more (meth)acryloyl groups in the molecule.

[0034] The (meth)acrylate having a hydrogenated conjugated diene skeleton in the molecule is preferably a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups at the terminal or side chain of the molecule. The polyfunctional (meth)acrylate refers to a compound having two or more (meth)acryloyl groups in the molecule. The (meth)acryloyl group refers to an acryloyl group (CH2=CHCO-) ​​or a methacryloyl group (CH2=C(CH3)CO-).

[0035] The polyfunctional (meth)acrylic oligomer (B) having a hydrogenated polydiene skeleton preferably does not have a conjugated diene structure (a conjugated diene structure in which a double bond is separated by one single bond).

[0036] The polyfunctional (meth)acrylic oligomer (B) having a hydrogenated polydiene skeleton is preferably a urethane (meth)acrylate.

[0037] Examples of urethane (meth)acrylate include terminal urethane (meth)acrylate of hydrogenated 1,2-polybutadiene (for example, "TEAI-1000" manufactured by Nippon Soda Co., Ltd.).

[0038] Here, the urethane (meth)acrylate refers to a urethane (meth)acrylate having a urethane bond in the molecule, which is obtained by reacting (for example, by polycondensation reaction) a polyol compound, an organic polyisocyanate compound, and a hydroxy (meth)acrylate.

[0039] Examples of polyol compounds include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, 1,4-butanediol, polybutylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 2,2-butylethyl-1,3-propanediol, neopentyl glycol, cyclohexanedimethanol, hydrogenated bisphenol A, polycaprolactone, trimethylolethane, trimethylolpropane, polytrimethylolpropane, pentaerythritol, polypentaerythritol, sorbitol, mannitol, glycerin, polyglycerin, poly Examples of suitable polyols include polyhydric alcohols such as tetramethylene glycol, polyether polyols having at least one structure of polyethylene oxide, polypropylene oxide, or block or random copolymerization of ethylene oxide / propylene oxide, polyester polyols which are condensates of polyhydric alcohols or polyether polyols with polybasic acids such as maleic anhydride, maleic acid, fumaric acid, itaconic anhydride, itaconic acid, adipic acid, and isophthalic acid, caprolactone-modified polyols such as caprolactone-modified polytetramethylene polyol, polyolefin polyols, polycarbonate polyols, polybutadiene polyols, polyisoprene polyols, and hydrogenated conjugated diene polyols (hydrogenated polybutadiene polyols, hydrogenated polyisoprene polyols, etc.), and silicone polyols such as polydimethylsiloxane polyols. Polydiene polyols are preferred because they have a hydrogenated conjugated diene skeleton.

[0040] Among polydiene polyols, hydrogenated conjugated diene polyols are preferred because they have a hydrogenated conjugated diene skeleton. As hydrogenated conjugated diene polyols, hydrogenated polybutadiene polyols and hydrogenated polyisoprene polyols are more preferred, and hydrogenated polybutadiene polyols (hydrogenated polybutadiene polyols) are more preferred. As hydrogenated polybutadiene polyols, hydrogenated 1,2-polybutadiene polyols are preferred.

[0041] The organic polyisocyanate compound is not particularly limited, and examples thereof include aromatic, aliphatic, alicyclic, and alicyclic polyisocyanates. Examples of the organic polyisocyanate compound include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hydrogenated diphenylmethane diisocyanate (H-MDI), polyphenylmethane polyisocyanate (crude MDI), modified diphenylmethane diisocyanate (modified MDI), hydrogenated xylylene diisocyanate (H-XDI), xylylene diisocyanate (XDI), and hexamethylene diisocyanate (HM Suitable examples of the polyisocyanates include polyisocyanates such as tolylene diisocyanate (TDI), trimethylhexamethylene diisocyanate (TMXDI), tetramethylxylylene diisocyanate (m-TMXDI), isophorone diisocyanate (IPDI), norbornene diisocyanate (NBDI), and 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), trimer compounds of these polyisocyanates, and reaction products of these polyisocyanates with polyols. Among these, tolylene diisocyanate (TDI), hydrogenated xylylene diisocyanate (H-XDI), and isophorone diisocyanate (IPDI) are preferred, with tolylene diisocyanate (TDI) and isophorone diisocyanate (IPDI) being more preferred, and isophorone diisocyanate (IPDI) being even more preferred.

[0042] The hydroxy(meth)acrylate refers to a (meth)acrylate having a hydroxyl group. Examples of the hydroxy(meth)acrylate include hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, and 2-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acryloylphosphate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, glycerin di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl(meth)acrylate, caprolactone-modified 2-hydroxyethyl(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and caprolactone-modified 2-hydroxyethyl(meth)acrylate, with hydroxyalkyl(meth)acrylates being preferred. The hydroxyalkyl (meth)acrylate is preferably 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, or 2-hydroxybutyl (meth)acrylate, and more preferably 2-hydroxyethyl (meth)acrylate.

[0043] The average molecular weight of the polyfunctional (meth)acrylic oligomer (B) is preferably 6,000 or more, more preferably 10,000 or more, more preferably 15,000 or more, and more preferably 20,000 or more. The average molecular weight of the polyfunctional (meth)acrylic oligomer (B) is preferably 50,000 or less, more preferably 40,000 or less, and more preferably 30,000 or less. When the average molecular weight of the polyfunctional (meth)acrylic oligomer (B) is 6,000 or more, stress applied to the adherend during curing of the photocurable resin composition is reduced, which is preferable.

[0044] The average molecular weight of the polyfunctional (meth)acrylic oligomer (B) refers to a value measured as follows. The average molecular weight of the polyfunctional (meth)acrylic oligomer (B) is measured by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent under the following conditions, with a calibration curve prepared using commercially available standard polystyrene. For example, the measurement can be performed using the following measuring device and under the following measuring conditions.

[0045] Measurement equipment: ACQUITY APC system manufactured by Waters Measurement conditions: Column: HSPgel™ HR MB-M manufactured by Waters Mobile phase: Tetrahydrofuran used at 0.5 mL / min Detector: RI detector Standard material: Polystyrene SEC temperature: 40°C

[0046] The content of the polyfunctional (meth)acrylic oligomer (B) in the photocurable resin composition is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and more preferably 50 parts by mass or more, per 100 parts by mass of the (meth)acrylic monomer (A). The content of the polyfunctional (meth)acrylic oligomer (B) in the photocurable resin composition is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, more preferably 110 parts by mass or less, and more preferably 90 parts by mass or less, per 100 parts by mass of the (meth)acrylic monomer (A). When the content of the polyfunctional (meth)acrylic oligomer (B) is 40 parts by mass or more, the shrinkage stress during curing of the photocurable resin composition is reduced, the stress applied to the adherend is reduced, and the cloudiness due to moisture of the cured product of the photocurable resin composition and yellowing in a high-temperature atmosphere are further reduced. When the content of the polyfunctional (meth)acrylic oligomer (B) is 150 parts by mass or less, the adhesiveness of the cured product of the photocurable resin composition is improved.

[0047] [(Meth)acrylic Monomer (C) Having a Glass Transition Temperature Tg of 0° C. or Lower] The photocurable resin composition preferably contains a (meth)acrylic monomer (C) having a glass transition temperature Tg of 0° C. or lower (hereinafter, may be simply referred to as "(meth)acrylic monomer (C)"). The glass transition temperature Tg of the (meth)acrylic monomer (C) is measured in the same manner as that of the (meth)acrylic monomer (A).

[0048] When the photocurable resin composition contains the (meth)acrylic monomer (C) having a glass transition temperature Tg of 0°C or lower, the shrinkage stress during curing of the photocurable resin composition is further reduced, and the stress applied to the adherend is further reduced.

[0049] The glass transition temperature Tg of the (meth)acrylic monomer (C) is preferably 0°C or lower, more preferably -10°C or lower, more preferably -20°C or lower, more preferably -30°C or lower, more preferably -40°C or lower, more preferably -50°C or lower, and more preferably -60°C or lower. The glass transition temperature Tg of the (meth)acrylic monomer (C) is preferably -80°C or higher, more preferably -70°C or higher. When the glass transition temperature Tg of the (meth)acrylic monomer (C) is 0°C or lower, the shrinkage stress during curing of the photocurable resin composition is further reduced, and the stress applied to the adherend is further reduced.

[0050] The (meth)acrylic monomer (C) having a glass transition temperature Tg of 0°C or lower is not particularly limited, and examples thereof include normal octyl (meth)acrylate, isooctyl (meth)acrylate, dodecyl (meth)acrylate, isodecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isostearyl (meth)acrylate, butyl (meth)acrylate, ethoxy-diethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxy-polyethylene glycol (meth)acrylate. Normal octyl (meth)acrylate, dodecyl (meth)acrylate, isodecyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, normal octyl (meth)acrylate is more preferred, and normal octyl acrylate is more preferred. The (meth)acrylic monomer (C) may be used alone or in combination of two or more.

[0051] The content of the (meth)acrylic monomer (C) in the photocurable resin composition is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, more preferably 8 parts by mass or more, more preferably 10 parts by mass or more, and more preferably 12 parts by mass or more, per 100 parts by mass of the (meth)acrylic monomer (A). The content of the (meth)acrylic monomer (C) in the photocurable resin composition is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and more preferably 25 parts by mass or less, per 100 parts by mass of the (meth)acrylic monomer (A). When the content of the (meth)acrylic monomer (C) is 3 parts by mass or more, the stress applied to the adherend during curing of the photocurable resin composition is further reduced. When the content of the (meth)acrylic monomer (C) is 35 parts by mass or less, the cloudiness due to moisture of the cured product of the photocurable resin composition is further reduced, and yellowing in a high-temperature atmosphere can be further reduced.

[0052] [Photopolymerization initiator] The photocurable resin composition may contain a photopolymerization initiator. When the photocurable resin composition contains a photopolymerization initiator, the photocurable resin composition can be easily photopolymerized and cured.

[0053] The photopolymerization initiator is not particularly limited, and for example, an α-hydroxyketone-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, a thioxanthone-based photopolymerization initiator, or a triazine-based photopolymerization initiator is preferred. An α-hydroxyketone-based photopolymerization initiator and an acylphosphine oxide-based photopolymerization initiator are preferred, with an α-hydroxyketone-based photopolymerization initiator being more preferred, because they have excellent compatibility with the (meth)acrylic monomer (A) and the polyfunctional (meth)acrylic oligomer (B), excellent curing properties of the photocurable resin composition, and can reduce shrinkage stress during curing of the photocurable resin composition, thereby reducing stress on the adherend. The photopolymerization initiator may be used alone or in combination of two or more types.

[0054] The α-hydroxyketone photopolymerization initiator is not particularly limited, and examples thereof include 1-hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one, and 2-hydroxy-2-methyl-1-phenyl-propan-1-one.

[0055] Examples of the acylphosphine oxide photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0056] Examples of thioxanthone-based photopolymerization initiators include 2,4-diethylthioxanthone.

[0057] Examples of the triazine-based photopolymerization initiator include 2-[2-(furan-2-yl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-[2-(5-methylfuran-2-yl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-[(4-methoxyphenyl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine, and 2-[(3,4-dimethoxyphenyl)vinyl]-4,6-bis(trichloromethyl)-1,3,5-triazine.

[0058] The content of the photopolymerization initiator in the photocurable resin composition is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, per 100 parts by mass of the (meth)acrylic monomer (A). The content of the photopolymerization initiator in the photocurable resin composition is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the (meth)acrylic monomer (A). When the content of the photopolymerization initiator is within the above range, the shrinkage stress during curing of the photocurable resin composition can be further reduced, thereby reducing the stress applied to the adherend.

[0059] [Additives] The photocurable resin composition may contain a silane coupling agent, a thixotropic agent, an adhesion-imparting resin, a plasticizer, non-thermally expandable fine particles, a dye, a pigment, a flame retardant, a surfactant, and the like, within the range that does not impair the physical properties of the composition.

[0060] The photocurable resin composition preferably contains a silane coupling agent. The silane coupling agent is not particularly limited and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, (3-acryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)triethoxysilane, (3-methacryloxyoctyl)trimethoxysilane, and (3-mercaptopropyl)trimethoxysilane. Alkoxysilanes are preferred, trialkoxysilanes are more preferred, trimethoxysilane and triethoxysilane are more preferred, and vinyltriethoxysilane, (3-acryloxypropyl)trimethoxysilane, and (3-methacryloxypropyl)trimethoxysilane are preferred.

[0061] The content of the silane coupling agent in the photocurable resin composition is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of the (meth)acrylic monomer (A). The content of the silane coupling agent in the photocurable resin composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of the (meth)acrylic monomer (A).

[0062] [Photocurable Resin Composition] The method for producing the photocurable resin composition is not particularly limited, and the photocurable resin composition can be produced, for example, by uniformly mixing the (meth)acrylic monomer (A), the polyfunctional (meth)acrylic oligomer (B), and compounds contained as necessary in a general manner, preferably under reduced pressure.

[0063] Generally, when a photocurable resin composition is cured, and the flexibility of the cured product of the photocurable resin composition is improved in order to reduce the stress applied to the adherend during curing, the adhesiveness of the cured product of the photocurable resin composition decreases and the cured product of the photocurable resin composition becomes more susceptible to fogging due to moisture. Thus, reducing the stress applied to the adherend during curing of the photocurable resin composition and improving the adhesiveness and reducing fogging due to moisture in the cured product of the photocurable resin composition are contradictory goals, and it is difficult to achieve both goals at the same time.

[0064] However, the photocurable resin composition contains both the (meth)acrylic monomer (A) and the polyfunctional (meth)acrylic oligomer (B), and therefore can achieve the above-mentioned conflicting objectives, namely, reducing the stress applied to the adherend when the photocurable resin composition is cured, while improving the adhesion of the cured product of the photocurable resin composition and reducing cloudiness due to moisture. Furthermore, the photocurable resin composition is characterized in that it can also reduce yellowing of the cured product of the photocurable resin composition due to a high-temperature atmosphere.

[0065] The tensile modulus of the cured product of the photocurable resin composition is preferably 50 MPa or more, more preferably 100 MPa or more, more preferably 150 MPa or more, and more preferably 200 MPa or more. The tensile modulus of the cured product of the photocurable resin composition is preferably 900 MPa or less, more preferably 800 MPa or less, more preferably 700 MPa or less, and more preferably 600 MPa or less. When the tensile modulus of the cured product of the photocurable resin composition is 50 MPa or more, the adhesiveness of the cured product of the photocurable resin composition can be improved, and clouding due to moisture in the cured product of the photocurable resin composition can be further reduced, and yellowing due to a high-temperature atmosphere can be further reduced. When the tensile modulus of the cured product of the photocurable resin composition is 900 MPa or less, the shrinkage stress during curing of the photocurable resin composition can be further reduced. The tensile modulus of elasticity of the cured product of the photocurable resin composition is a value measured in accordance with JIS K7161-1 under conditions of a dumbbell thickness of 1.0 mm and a pulling speed of 10 mm / min.

[0066] In the cured product of the photocurable resin composition, the maximum stress is preferably 5 MPa or more, more preferably 6 MPa or more, and more preferably 7 MPa or more. In the cured product of the photocurable resin composition, the maximum stress is preferably 20 MPa or less, more preferably 16 MPa or less, and even more preferably 15 MPa or less. In the cured product of the photocurable resin composition, when the maximum stress is 5 MPa or more, the adhesiveness of the cured product of the photocurable resin composition can be improved, and clouding due to moisture in the cured product of the photocurable resin composition can be further reduced, and further yellowing due to high-temperature atmospheres can be reduced. In the cured product of the photocurable resin composition, when the maximum stress is 20 MPa or less, the shrinkage stress during curing of the photocurable resin composition can be further reduced, and the stress applied to the adherend can be reduced. The maximum stress of the cured product of the photocurable resin composition refers to the value measured in accordance with JIS K7161-1 under conditions of a dumbbell thickness of 1.0 mm and a tensile speed of 10 mm / min.

[0067] In the cured product of the photocurable resin composition, the curing shrinkage stress is preferably 0.06 MPa or less, more preferably 0.05 MPa or less. When the curing shrinkage stress is 0.06 MPa or less, the shrinkage stress during curing of the photocurable resin composition is small, reducing the stress applied to the adherend and reducing the occurrence of optical distortion in the adherend. The curing shrinkage stress of the photocurable resin composition is a value measured at room temperature of 23°C in accordance with JIS K6941. For example, it can be measured by curing under the following conditions using an apparatus commercially available from Acroedge Co., Ltd. under the trade name "Custron". Light source: LED-Aicure (wavelength: 365 nm) manufactured by Panasonic Corporation Irradiation intensity: 65 mW / cm 2 Irradiation time: 300 seconds

[0068] [Method for bonding adherends using photocurable resin composition] The photocurable resin composition can be suitably used to bond and integrate adherends. The adherend is not particularly limited, and examples thereof include thin-layer glass, optical glass, optical lenses, prisms, lenses, silicon wafers, semiconductor mounting components, and synthetic resin molded products (e.g., synthetic resin sheets), with optical lenses being preferred. The material of the optical lens is not particularly limited, and may be glass or synthetic resin, with glass being preferred. The photocurable resin composition can be suitably used as an adhesive for optical adherends, particularly thin-layer glass, optical glass, prisms, and optical lenses. The adherends may be of the same type or different types.

[0069] The procedure for bonding and integrating adherends using a photocurable resin composition will now be described. First, a laminate is produced by placing the adherends in a state in which the photocurable resin composition is interposed between opposing surfaces of the adherends (lamination step). The laminate may also be produced by laminating three or more adherends with the photocurable resin composition interposed between the opposing surfaces of the adherends.

[0070] Since the photocurable resin composition is a one-component type, the production of a laminate does not require the complicated operation of mixing two components, and the laminate can be easily produced.

[0071] Next, the entire laminate obtained is irradiated with radiation from the stacking direction of the laminate to cure the photocurable resin composition interposed between the opposing surfaces of the adherends constituting the laminate, thereby producing a cured product (polymer) (curing step). This cured product can bond and integrate the adherends together.

[0072] Since the photocurable resin composition has a small shrinkage stress when cured, it is possible to reduce the stress applied to two adherends bonded via the photocurable resin composition, thereby reducing distortion of the adherends.

[0073] The cured product produced by curing the photocurable resin composition has excellent adhesive properties, and two adherends can be firmly bonded together via the cured product.

[0074] The peak wavelength of the radiation is preferably 500 nm or less, as this provides excellent curing properties for the photocurable resin composition. The radiation is preferably light with a peak wavelength of 320 nm or more. By using radiation with a peak wavelength of 320 nm or more, the photocurable resin composition can be cured to a deep portion to produce a cured product.

[0075] Furthermore, the cured product of the photocurable resin composition that bonds and integrates the adherends has low water absorption, reducing the occurrence of cloudiness due to humidity and reducing yellowing due to high-temperature atmospheres.

[0076] Therefore, the cured product of the photocurable resin composition can maintain a state in which adherends are firmly bonded together for a long period of time without discoloration such as cloudiness or yellowing, even in harsh environments such as the interior of an automobile.

[0077] The present invention will be described in more detail below using examples, but the present invention is not limited thereto. Specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or greater than") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of the Invention."

[0078] The following compounds were used in the examples and comparative examples.

[0079] [(Meth)acrylic monomer (A)] Isobornyl methacrylate (glass transition temperature Tg: 180°C, average molecular weight: 222) Dicyclopentanyl methacrylate (glass transition temperature Tg: 175°C, average molecular weight: 220)

[0080] [Polyfunctional (meth)acrylic oligomer (B)] Polyfunctional urethane acrylate oligomer having a 1,2-polybutadiene skeleton with a hydrogenation rate of 95% (polyfunctional urethane acrylate oligomer having a hydrogenated 1,2-polybutadiene skeleton) A first reactant was obtained by reacting isophorone diisocyanate with 2-hydroxyethyl acrylate in a molar ratio of 1:1. This was produced by reacting a diol compound (weight average molecular weight: 25,000) terminated at both ends of hydrogenated 1,2-polybutadiene with the first reactant in a molar ratio of 1:2. - Urethane acrylate oligomer having a polyester skeleton (manufactured by Negami Chemical Industrial Co., Ltd., product name "UN-7600", does not have a polydiene skeleton) - Methacrylate oligomer 1 having an unhydrogenated polyisoprene skeleton (manufactured by Kuraray Co., Ltd., product name "UC-102M", does not have a hydrogenated polydiene skeleton) - Methacrylate oligomer 2 having an unhydrogenated polyisoprene skeleton (manufactured by Kuraray Co., Ltd., product name "UC-203M", does not have a hydrogenated polydiene skeleton)

[0081] [(Meth)acrylic monomer (C)] Normal octyl acrylate

[0082] [Photopolymerization initiator] 1-hydroxycyclohexyl phenyl ketone (peak wavelength: 330 nm)

[0083] [Silane coupling agent] (3-methacryloxypropyl)trimethoxysilane

[0084] (Examples 1 to 3, Comparative Examples 1 to 4) The (meth)acrylic monomer (A), the polyfunctional (meth)acrylic oligomer (B), the (meth)acrylic monomer (C) and the silane coupling agent in the predetermined amounts shown in Table 1 were respectively supplied into a reaction vessel and mixed uniformly to prepare a mixed solution.

[0085] Next, a predetermined amount of a photopolymerization initiator shown in Table 1 was added to the mixed liquid, and the mixture was mixed until the photopolymerization initiator was completely dissolved in the mixed liquid, to obtain a photocurable resin composition.

[0086] The photocurable resin compositions thus obtained were measured for tensile modulus, maximum stress, cure shrinkage stress, water absorption, and yellowing index in the following manner. The results are shown in Table 1.

[0087] (Tensile Modulus of Elasticity) Using the obtained photocurable resin composition, a dumbbell-shaped test piece (Type 3 specified in JIS K6251) measuring 50 mm in length, 25 mm in width, and 1.0 mm in thickness was prepared. The test piece was irradiated with ultraviolet light having a peak wavelength of 365 nm at an intensity of 65 mW / cm. 2 The test piece was then irradiated with light at 1000 kJ / min for 2 minutes to cure the photocurable resin composition.

[0088] The tensile modulus of the cured test specimen was measured in accordance with JIS K7161-1 under conditions of a dumbbell thickness of 1.0 mm and a pulling speed of 10 mm / min.

[0089] (Maximum stress) A dumbbell-shaped test piece (Type 3 specified in JIS K6251) measuring 50 mm in length, 25 mm in width, and 1.0 mm in thickness was prepared using the obtained photocurable resin composition. The test piece was irradiated with ultraviolet light having a peak wavelength of 365 nm at an intensity of 65 mW / cm. 2 The test piece was then irradiated with light at 1000 kJ / min for 2 minutes to cure the photocurable resin composition.

[0090] The maximum stress of the cured test specimen was measured in accordance with JIS K 7161-1 under the conditions of a dumbbell thickness of 1.0 mm and a tensile speed of 10 mm / min. The smaller the maximum stress, the smaller the shrinkage stress of the photocurable resin composition during curing.

[0091] (Curing shrinkage stress) The curing shrinkage stress of the obtained photocurable resin composition was measured at room temperature of 23° C. in accordance with JIS K6941 using a measuring device commercially available from Acroedge Co., Ltd. under the trade name "Custron". It can be determined that the smaller the curing shrinkage stress, the smaller the shrinkage stress of the photocurable resin composition during curing.

[0092] (Water Absorption Rate) Using the obtained photocurable resin composition, a planar square test piece having a side length of 20 mm and a thickness of 0.5 mm was prepared. The test piece was irradiated with ultraviolet light having a peak wavelength of 365 nm at an intensity of 65 mW / cm. 2 The test piece was then irradiated with light at 1000 kJ / cm² for 2 minutes to cure the photocurable resin composition, and the mass W0 of the test piece was measured.

[0093] A cylindrical water bath with a bottom and a square base measuring 22.5 cm on each side and 17 cm high was prepared, and water was poured into the water bath to a depth of 4 cm. A 200-mesh stainless steel wire mesh was placed horizontally in the water bath at a distance of 11 cm vertically above the water surface, and a steam-permeable cloth was placed on the wire mesh. The cured test specimen was placed on the cloth.

[0094] Next, the top opening of the water bath was completely closed with aluminum foil, and the water in the water bath was heated to 96°C and maintained at this temperature for 4 hours. After 4 hours had passed, the test piece was removed from the water bath and its mass W1 was measured. The water absorption rate (%) was calculated based on the following formula: Water absorption rate (%) = 100 × (W1 - W0) / W0

[0095] (Yellowing Degree) Using the obtained photocurable resin composition, a plate-shaped test piece having a length of 50 mm, a width of 25 mm, and a thickness of 1.0 mm was prepared. The test piece was irradiated with ultraviolet light having a peak wavelength of 365 nm at an intensity of 65 mW / cm. 2 The test piece was then irradiated with light at 1000 kJ / min for 2 minutes to cure the photocurable resin composition.

[0096] The initial transmittance T0 of the test piece at wavelengths of 450 nm and 400 nm was measured using an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation, trade name "UV-3600 Plus").

[0097] Next, the test piece was placed in an oven at 135°C and heated for 100 hours. The test piece was removed from the oven and left in an atmosphere at 25°C for 24 hours. The post-heating transmittance T1 of the test piece after heating was measured using an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation, trade name "UV-3600 Plus"). The rate of change in transmittance was calculated based on the formula shown below. The smaller the rate of change, the lower the degree of yellowing can be determined. Rate of change (%) = 100 x (T0 - T1) / T0

[0098]

[0099] (Cross-reference to related applications) This application claims priority to Japanese Patent Application No. 2024-57837, filed on March 29, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0100] The photocurable resin composition of the present invention has low shrinkage stress during curing and applies low stress to the adherend during curing. The photocurable resin composition of the present invention can produce a cured product with excellent adhesive properties. The photocurable resin composition of the present invention can produce a cured product that is less susceptible to moisture absorption, making it less susceptible to moisture-induced fogging, and that is less susceptible to yellowing due to high-temperature atmospheres. Therefore, the cured product of the photocurable resin composition can maintain a state in which adherends are firmly bonded together for a long period of time without discoloration such as fogging or yellowing, even in harsh environments such as the interior of an automobile.

Claims

1. A photocurable resin composition comprising (A) a water-insoluble (meth)acrylic monomer having a glass transition temperature Tg of 50°C or higher, and (B) a polyfunctional (meth)acrylic oligomer having a polydiene skeleton with a hydrogenation rate of 90% or higher.

2. The photocurable resin composition according to claim 1, wherein the weight average molecular weight of the polyfunctional (meth)acrylic oligomer (B) is 6,000 or more.

3. A photocurable resin composition according to claim 1 or claim 2, characterized in that the polyfunctional (meth)acrylic oligomer (B) is contained in an amount of 40 to 150 parts by mass per 100 parts by mass of the (meth)acrylic monomer (A).

4. A photocurable resin composition according to claim 1 or 2, characterized in that it contains 3 to 30 parts by mass of a (meth)acrylic monomer (C) having a glass transition temperature Tg of 0°C or lower per 100 parts by mass of the (meth)acrylic monomer (A).

5. A photocurable resin composition according to claim 1 or 2, characterized in that the cured product has a maximum stress of 5 to 20 MPa in a tensile test and a tensile modulus of elasticity of 50 to 900 MPa after curing.

6. The photocurable resin composition according to claim 1 or 2, which is used as an adhesive for optical glass.

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