Photocurable resin composition

Abstract

The present invention provides a photocurable resin composition which has a small shrinkage stress at the time of curing and thus exerts a small stress on an adherend at the time of curing, and which is capable of producing a cured product having excellent adhesion, a cured product in which fogging caused by moisture is reduced, and a cured product in which yellowing caused by a high-temperature atmosphere is reduced. The photocurable resin composition of the present invention contains a (meth)acrylic monomer (A) having a glass transition temperature Tg of 50°C or higher and being non-water-soluble, and a multifunctional (meth)acrylic oligomer (B) having a polydiene skeleton and a hydrogenation rate of 90% or higher.

Description

Technical Field

[0001] This invention relates to photocurable resin compositions. Background Technology

[0002] Previously, photocurable resin compositions have been used as adhesives for glass and synthetic resins. Photocurable resin compositions cure upon exposure to light and exhibit adhesive properties. However, photocurable resin compositions generate shrinkage stress during their photocuring process.

[0003] If the shrinkage stress of the photocurable resin composition is high during photocuring, it will apply stress and cause strain to the adhered objects bonded with the photocurable resin composition. In optical fields such as optical lenses, if the adhered objects experience optical strain, it will lead to a decrease in the quality of the product. Therefore, it is necessary to reduce the stress applied to the adhered objects to reduce the generation of optical strain.

[0004] Furthermore, in recent years, with the increasing prevalence of autonomous driving or its management systems in automobiles, the use of optical lenses in automotive applications is growing. The interior of a car is significantly affected by temperature and humidity; in particular, there is a requirement that the quality of cured photocurable resin compositions not degrade even in harsh, hot and humid environments.

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

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2012-1648 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] However, the aforementioned photocurable adhesive compositions have the following problems: high shrinkage stress during curing, high stress applied to the adhered object during curing, and low adhesion of the cured product. Furthermore, in harsh environments such as inside a car, in addition to the problem of haziness appearing in the cured product, long-term use also results in yellowing when exposed to high summer temperatures.

[0011] The present invention provides a photocurable resin composition that has low shrinkage stress during curing, thus exerting low stress on the adherend during curing, and can produce a cured product with excellent adhesion, less susceptibility to moisture-induced haze, and reduced yellowing caused by high-temperature atmosphere.

[0012] Problem Solving Methods

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

[0014] The effects of the invention

[0015] The photocurable resin composition of the present invention exhibits low shrinkage stress during curing, thus resulting in low stress exerted on the adherend during curing. The photocurable resin composition of the present invention can produce cured products with excellent adhesion.

[0016] The photocurable resin composition of the present invention can produce a cured product that reduces moisture absorption and is less prone to moisture-induced haze, and also reduces yellowing caused by high-temperature atmosphere. Detailed Implementation

[0017] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain stage's numerical range can be arbitrarily combined with the upper or lower limits of other stages' numerical ranges. The upper or lower limit of the numerical range described in this specification can also be replaced with the values ​​shown in the embodiments or values ​​that can be unambiguously derived from the embodiments. In this specification, numerical values ​​connected by "~" refer to a numerical range including the values ​​before and after "~" as both the lower and upper limits.

[0018] The photocurable resin composition of the present invention contains a (meth)acrylic monomer (A) with a glass transition temperature (Tg) of 50°C or higher and which is non-water-soluble, and a polyfunctional (meth)acrylic oligomer (B) with a hydrogenation rate of 90% or higher and having a polydiene-based backbone.

[0019] In this invention, "(meth)acrylic acid" refers to a molecule containing an acryloyl group [Formula (1)] or a methacryloyl group [Formula (2)]. It should be noted that in formulas (1) and (2), 1 represents a bonding arm and indicates a single bond.

[0020] [Chemical Formula 1]

[0021] [A (meth)acrylic acid monomer with a glass transition temperature (Tg) above 50°C and which is non-water-soluble]

[0022] The photocurable resin composition contains a (meth)acrylic monomer (A) with a glass transition temperature (Tg) of 50°C or higher and which is non-water-soluble (hereinafter, sometimes simply referred to as "(meth)acrylic monomer (A)").

[0023] The photocurable resin composition contains a (meth)acrylic monomer (A). By combining the (meth)acrylic monomer (A) with the polyfunctional (meth)acrylic oligomer (B) described later, the photocurable resin composition produces a cured product with excellent adhesion. Furthermore, the curing of the photocurable resin composition is lessened due to moisture-induced haze and lessened due to yellowing caused by high-temperature atmospheres.

[0024] 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 adhesion, and the haze caused by moisture and yellowing caused by high-temperature atmosphere are further reduced. When the glass transition temperature (Tg) of the (meth)acrylic monomer (A) is 250°C or lower, the stress exerted on the adherend during the curing of the photocurable resin composition is reduced, which is preferable. It should be noted that the glass transition temperature Tg of (meth)acrylic acid monomer (A) refers to the temperature measured according to JIS K7121:1987.

[0025] The (meth)acrylic acid monomer (A) is water-insoluble. By making the (meth)acrylic acid monomer (A) water-insoluble, the photocurable resin composition produces a cured product with excellent adhesion, and the turbidity caused by moisture in the cured product of the photocurable resin composition is reduced.

[0026] "(Meth)acrylic monomer (A) is not water-soluble" means that when an equal volume of (meth)acrylic monomer (A) is added to 100g of pure water at 20°C and mixed at a stirring speed of 100rpm, after standing for 1 hour, the (meth)acrylic monomer (A) and water separate into two layers.

[0027] As a (meth)acrylate monomer (A), any monomer that has a glass transition temperature (Tg) of 50°C or higher and is not water-soluble can be used. Examples include (meth)acrylate monomers with monocyclic rings, (meth)acrylate monomers with bicyclic rings, and (meth)acrylate monomers with tricyclic rings. It should be noted that (meth)acrylate monomer (A) can be used alone or in combination of two or more. In this invention, (meth)acrylate refers to acrylate or methacrylate.

[0028] In (meth)acrylic acid monomers (A), monocyclic, bicyclic, and tricyclic cyclic skeletons are preferably saturated alicyclic skeletons. When (meth)acrylic acid monomers (A) have a saturated alicyclic skeleton, the photocurable resin composition produces a cured product with superior adhesion. Furthermore, the turbidity caused by moisture and the yellowing caused by high-temperature atmospheres in the cured product are further reduced. An alicyclic structure refers to a structure in which carbon atoms are bonded in a ring and do not possess aromaticity.

[0029] Examples of monocyclic (meth)acrylates 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.

[0030] Examples of bicyclic (meth)acrylate monomers include dicyclopentenoxyethyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and isobornyl (meth)acrylate. More preferably, isobornyl (meth)acrylate and dicyclopentyl (meth)acrylate are bicyclic monomers, and even more preferably, isobornyl methacrylate and dicyclopentyl methacrylate are bicyclic monomers. This is because the photocurable resin composition produces a cured product with superior adhesion, and the turbidity caused by moisture and yellowing caused by high-temperature atmospheres are further reduced.

[0031] Examples of tricyclic (meth)acrylate monomers include (meth)acrylate compounds having an adamantane backbone.

[0032] The (meth)acrylic monomer (A) is preferably a (meth)acrylate monomer having a bicyclic structure. The bicyclic structure is preferably an alicyclic skeleton, more preferably a saturated alicyclic skeleton. This is because the photocurable resin composition produces a cured product with better adhesion, and the turbidity caused by moisture and the yellowing caused by high temperature atmosphere are further reduced.

[0033] The (meth)acrylic monomer (A) can also be multifunctional. When the (meth)acrylic monomer (A) is multifunctional, the shrinkage stress of the photocurable resin composition during curing is small, and the stress exerted on the adherend is reduced. Examples of multifunctional (meth)acrylic monomers (A) include tricyclodecanediethanol di(meth)acrylate and ethoxylated bisphenol A di(meth)acrylate. The multifunctional (meth)acrylic monomer (A) preferably has two or more (meth)acryloyl groups within its molecule. It should be noted that (meth)acryloyl group refers to acryloyl group (CH2=CHCO-) ​​or methacryloyl group (CH2=C(CH3)CO-).

[0034] [Polyfunctional (meth)acrylic acid oligomers (B) with a hydrogenation rate of over 90% and a polydiene backbone]

[0035] The photocurable resin composition contains a polyfunctional (meth)acrylic oligomer (B) with a polydiene backbone having a hydrogenation rate of 90% or higher (hereinafter sometimes simply referred to as "polyfunctional (meth)acrylic oligomer (B)").

[0036] By incorporating polyfunctional (meth)acrylic acid oligomers (B) into the photocurable resin composition, the shrinkage stress during curing is low, resulting in less stress on the adhered substrate. Furthermore, the photocurable resin composition produces a cured product with excellent adhesion, and the turbidity caused by moisture and yellowing caused by high-temperature atmospheres are reduced.

[0037] The hydrogenation rate of the polyfunctional (meth)acrylic acid oligomer (B) is 90% or more, preferably 91% or more, more preferably 92% or more, more preferably 93% or more, and more preferably 94% or more. When the hydrogenation rate of the polyfunctional (meth)acrylic acid oligomer (B) is 90% or more, it can reduce the yellowing of the cured product of the photocurable resin composition caused by a high-temperature atmosphere. The hydrogenation rate of the polyfunctional (meth)acrylic acid oligomer (B) is the proportion of hydrogen added to the unsaturated bonds contained in the molecule; when all unsaturated bonds are hydrogenated, the hydrogenation rate is 100%.

[0038] Polyfunctional (meth)acrylic acid oligomers (B) having a hydrogenated polydiene backbone refer to (meth)acrylates having a hydrogenated conjugated diene backbone in the molecule. Hydrogenated conjugated dienes are, for example, compounds obtained by hydrogenating a conjugated diene. Examples of hydrogenated conjugated dienes include hydrogenated polybutadiene and hydrogenated polyisoprene, with hydrogenated polybutadiene being preferred.

[0039] The multifunctional (meth)acrylic acid oligomer (B) has a hydrogenated polydiene backbone within its molecule. Therefore, the shrinkage stress during curing of the photocurable resin composition is reduced, as is the stress exerted on the adherend. Furthermore, the photocurable resin composition produces a cured product with excellent adhesion, and the moisture-induced haze and yellowing caused by high-temperature atmospheres are reduced.

[0040] By making the multifunctional (meth)acrylic oligomer (B) multifunctional, the shrinkage stress of the photocurable resin composition during curing is reduced, and the stress applied to the adherend is also reduced. The multifunctional (meth)acrylic oligomer (B) preferably has two or more (meth)acryloyl groups within its molecule.

[0041] As a (meth)acrylate having a hydrogenated conjugated diene skeleton in the molecule, a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups at the terminal or side chain within the molecule is preferred. A polyfunctional (meth)acrylate refers to a compound having two or more (meth)acryloyl groups within the molecule. It should be noted that (meth)acryloyl group refers to acryloyl (CH2=CHCO-) ​​or methacryloyl (CH2=C(CH3)CO-).

[0042] As a polyfunctional (meth)acrylic acid oligomer (B) with a hydrogenated polydiene backbone, it is preferable not to have a conjugated diene structure (a diene structure in which double bonds are separated by a single bond and thus conjugation occurs).

[0043] As a multifunctional (meth)acrylic oligomer (B) having a hydrogenated polydiene backbone, urethane (meth)acrylate is preferred.

[0044] Examples of urethane (meth)acrylates include hydrogenated 1,2-polybutadiene-terminated urethane (meth)acrylates (e.g., "TEAI-1000" manufactured by Nippon Soda Co., Ltd.).

[0045] Here, urethane (meth)acrylate refers to urethane (meth)acrylate having an intramolecular urethane bond, obtained by reacting a polyol compound, an organic polyisocyanate compound, and a hydroxy (meth)acrylate (e.g., a condensation reaction).

[0046] Examples of polyol compounds include: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, 1,4-butanediol, polybutanediol, 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, neopentanediol, cyclohexanediol, hydrogenated bisphenol A, polycaprolactone, trimethylolethane, trimethylolpropane, polytrimethylolpropane, pentaerythritol, polypentaerythritol, sorbitol, mannitol, glycerol, polyglycerol, and polytetramethylenediol. Polyols, etc.; polyether polyols having at least one structure of polyethylene oxide, polypropylene oxide, or ethylene oxide / propylene oxide block or random copolymers; polyester polyols as condensates of polyols or polyether polyols with maleic anhydride, maleic acid, fumaric acid, itaconic anhydride, itaconic acid, adipic acid, isophthalic acid, etc.; caprolactone-modified polyols such as caprolactone-modified polytetramethylene polyols; polyolefin polyols; polycarbonate polyols; polybutadiene polyols, polyisoprene polyols, hydrogenated conjugated diene polyols (hydrogenated polybutadiene polyols, hydrogenated polyisoprene polyols, etc.) and other polydiene polyols; organosilicon polyols such as polydimethylsiloxane polyols, etc. Polydiene polyols are preferred due to their hydrogenated conjugated diene backbone.

[0047] Among polydiene polyols, hydrogenated conjugated diene polyols are preferred from the perspective of having a hydrogenated conjugated diene backbone. More preferably, hydrogenated polybutadiene polyols and hydrogenated polyisoprene polyols are preferred, and even more preferably, hydrogenated polybutadiene polyols (hydrogenated polybutadiene polyols). Among hydrogenated polybutadiene polyols, hydrogenated 1,2-polybutadiene polyols are preferred.

[0048] As organic polyisocyanate compounds, there are no particular limitations; examples include aromatic, aliphatic, cyclic aliphatic, and alicyclic polyisocyanates. As organic polyisocyanate compounds, suitable polyisocyanates include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hydrogenated diphenylmethane diisocyanate (H-MDI), polyphenylmethane polyisocyanate (crude MDI), modified diphenylmethane diisocyanate (modified MDI), hydrogenated diphenylmethylene diisocyanate (H-XDI), diphenylmethylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), trimethylhexamethylene diisocyanate (TMXDI), tetramethyldiphenylmethylene diisocyanate (m-TMXDI), isophorone diisocyanate (IPDI), norbornene diisocyanate (NBDI), 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), trimer compounds of these polyisocyanates, and reaction products of these polyisocyanates with polyols. Preferably, toluene diisocyanate (TDI), hydrogenated diphenylmethylene diisocyanate (H-XDI), or isophorone diisocyanate (IPDI) are used, more preferably toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and even more preferably isophorone diisocyanate (IPDI).

[0049] Hydroxy(meth)acrylates refer to (meth)acrylates having hydroxyl groups. Examples of hydroxy(meth)acrylates include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and other hydroxyalkyl (meth)acrylates; 2-hydroxyethyl (meth)acryloyl phosphate; 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate; glycerol di(meth)acrylate; 2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate; caprolactone-modified 2-hydroxyethyl (meth)acrylate; pentaerythritol tri(meth)acrylate; dipentaerythritol penta(meth)acrylate; caprolactone-modified 2-hydroxyethyl (meth)acrylate; and preferably hydroxyalkyl (meth)acrylates. 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate are more preferably hydroxyethyl (meth)acrylate.

[0050] The average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) is preferably 6,000 or more, more preferably 10,000 or more, more preferably 15,000 or more, and even more preferably 20,000 or more. The average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) is preferably 50,000 or less, more preferably 40,000 or less, and even more preferably 30,000 or less. When the average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) is 6,000 or more, the stress applied to the adhered object during the curing of the photocurable resin composition is reduced, which is preferable.

[0051] The average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) is the value determined according to the following points. The average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) was determined under the following conditions using tetrahydrofuran as a solvent and by gel permeation chromatography (GPC) with a standard curve prepared using commercially available standard polystyrene. For example, it can be determined using the following measuring apparatus and conditions.

[0052] Measuring apparatus: Waters ACQUITY APC system

[0053] Measurement conditions: Column: Waters HSPgel™ HR MB-M Mobile phase: Tetrahydrofuran 0.5 mL / min Detector: RI detector Standard material: polystyrene SEC temperature: 40℃ 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 even more preferably 50 parts by mass or more, relative to 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, even more preferably 110 parts by mass or less, and even more preferably 90 parts by mass or less, relative to 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 of the photocurable resin composition during curing becomes smaller, the stress exerted on the adhered object becomes smaller, and the haze caused by moisture in the cured product of the photocurable resin composition is further reduced, and the yellowing at high temperature is further reduced. When the content of polyfunctional (meth)acrylic oligomer (B) is less than 150 parts by mass, the adhesion of the cured product of the photocurable resin composition is improved.

[0054] [(Meth)acrylic acid monomers (C) with a glass transition temperature (Tg) below 0℃]

[0055] The photocurable resin composition preferably contains a (meth)acrylic monomer (C) with a glass transition temperature (Tg) below 0°C (hereinafter sometimes simply referred to as "(meth)acrylic monomer (C)"). It should be noted that the method for determining the glass transition temperature (Tg) of (meth)acrylic monomer (C) is the same as that for (meth)acrylic monomer (A).

[0056] By including (meth)acrylic monomers (C) with a glass transition temperature (Tg) below 0°C in the photocurable resin composition, the shrinkage stress of the photocurable resin composition during curing is further reduced, and the stress applied to the adherend is further reduced.

[0057] The glass transition temperature (Tg) of the (meth)acrylic monomer (C) is preferably below 0°C, more preferably below -10°C, more preferably below -20°C, more preferably below -30°C, more preferably below -40°C, more preferably below -50°C, and more preferably below -60°C. The glass transition temperature (Tg) of the (meth)acrylic monomer (C) is preferably above -80°C, more preferably above -70°C. When the glass transition temperature (Tg) of the (meth)acrylic monomer (C) is below 0°C, the shrinkage stress of the photocurable resin composition during curing is further reduced, and the stress applied to the adhered substrate is further reduced.

[0058] The (meth)acrylic monomer (C) having a glass transition temperature (Tg) below 0°C is not particularly limited, and examples include n-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, phenoxy-ethyl (meth)acrylate, and phenoxy-polyethylene glycol (meth)acrylate. Preferably, it is n-octyl (meth)acrylate, dodecyl (meth)acrylate, isodecyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate; more preferably, it is n-octyl (meth)acrylate, and even more preferably, it is n-octyl acrylate. The (meth)acrylic monomer (C) can be used alone or in combination of two or more.

[0059] The content of (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, relative to 100 parts by mass of (meth)acrylic monomer (A). The content of (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, relative to 100 parts by mass of (meth)acrylic monomer (A). When the content of (meth)acrylic monomer (C) is 3 parts by mass or more, the stress exerted on the adhered object by the photocurable resin composition during curing is further reduced. When the content of (meth)acrylic monomer (C) is 35 parts by mass or less, the haze caused by moisture in the cured product of the photocurable resin composition is further reduced, and yellowing at high temperature is further reduced.

[0060] [Photopolymerization initiator]

[0061] The photocurable resin composition may contain a photopolymerization initiator. By including a photopolymerization initiator in the photocurable resin composition, it is possible for the photocurable resin composition to readily undergo photopolymerization and cure.

[0062] There are no particular limitations on the photopolymerization initiator. For example, α-hydroxyketone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, thioxanthone photopolymerization initiators, and triazine photopolymerization initiators are preferred. These are particularly suitable because they exhibit excellent compatibility with (meth)acrylic acid monomers (A) and polyfunctional (meth)acrylic acid oligomers (B), excellent curability of the photocurable resin composition, and the ability to reduce shrinkage stress during curing, thereby reducing stress on the adhered substrate. α-hydroxyketone photopolymerization initiators and acylphosphine oxide photopolymerization initiators are preferred, and α-hydroxyketone photopolymerization initiators are more preferred. It should be noted that the photopolymerization initiator can be used alone or in combination of two or more.

[0063] As an α-hydroxy ketone photopolymerization initiator, there are no particular limitations; examples include 1-hydroxycyclohexylphenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propanoyl)-benzyl]phenyl}-2-methyl-propane-1-one, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, etc.

[0064] Examples of acylphosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyl diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0065] Examples of thioxanthone photopolymerization initiators include 2,4-diethylthioxanthone.

[0066] Examples of triazine photopolymerization initiators 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.

[0067] 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, relative to 100 parts by mass of (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, relative to 100 parts by mass of (meth)acrylic monomer (A). When the content of the photopolymerization initiator is within the above range, the shrinkage stress of the photocurable resin composition during curing can be further reduced, thereby reducing the stress applied to the adhered substrate.

[0068] [additive]

[0069] The photocurable resin composition may contain silane coupling agents, thixotropic agents, adhesive resins, plasticizers, non-thermally expanding microparticles, dyes, pigments, flame retardants, surfactants, etc., without impairing its physical properties.

[0070] The photocurable resin composition preferably contains a silane coupling agent. There are no particular limitations on the silane coupling agent; examples include vinyltrimethoxysilane, vinyltriethoxysilane, (3-acryloyloxypropyl)trimethoxysilane, (3-methacryloyloxypropyl)trimethoxysilane, (3-methacryloyloxypropyl)triethoxysilane, (3-methacryloyloxyoctyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, etc. Alkoxysilanes are preferred, trialkoxysilanes are more preferred, trimethoxysilanes and triethoxysilanes are even more preferred, and vinyltriethoxysilane, (3-acryloyloxypropyl)trimethoxysilane, and (3-methacryloyloxypropyl)trimethoxysilane are particularly preferred.

[0071] 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 even more preferably 2 parts by mass or more, relative to 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 even more preferably 6 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic monomer (A).

[0072] [Photocurable resin composition]

[0073] The method for manufacturing the photocurable resin composition is not particularly limited. For example, it can be manufactured by mixing (meth)acrylic monomer (A) and polyfunctional (meth)acrylic oligomer (B) with compounds as needed, according to general principles, preferably under reduced pressure until homogeneous.

[0074] Typically, with respect to photocurable resin compositions, increasing the flexibility of the cured product to reduce stress on the substrate during curing leads to decreased adhesion and a higher likelihood of moisture-induced haze. Thus, reducing stress on the substrate during curing and improving adhesion and reducing moisture-induced haze become conflicting technical problems, making it difficult to simultaneously address these issues.

[0075] However, by simultaneously containing (meth)acrylic monomers (A) and polyfunctional (meth)acrylic oligomers (B), the aforementioned photocurable resin composition can simultaneously address the opposite technical problems mentioned above. That is, it can simultaneously reduce the stress exerted on the adherend by the photocurable resin composition during curing, improve the adhesion of the cured product to the photocurable resin composition, and reduce the haze caused by moisture. Furthermore, it can also mitigate the yellowing of the cured product of the photocurable resin composition caused by high-temperature atmospheres.

[0076] 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 adhesion of the cured product can be improved, and the haze caused by moisture can be further reduced, as well as the yellowing caused by high-temperature atmospheres can be reduced. When the tensile modulus of the cured product of the photocurable resin composition is 900 MPa or less, the shrinkage stress of the photocurable resin composition during curing can be further reduced. It should be noted that the tensile modulus of the cured product of the photocurable resin composition refers to the value measured according to JIS K7161-1 under the conditions of a dumbbell thickness of 1.0 mm and a stretching speed of 10 mm / min.

[0077] The maximum stress of the cured product of the photocurable resin composition is preferably 5 MPa or more, more preferably 6 MPa or more, and even more preferably 7 MPa or more. The maximum stress of the cured product of the photocurable resin composition is preferably 20 MPa or less, more preferably 16 MPa or less, and even more preferably 15 MPa or less. When the maximum stress of the cured product of the photocurable resin composition is 5 MPa or more, the adhesion of the cured product can be improved, and the haze caused by moisture can be further reduced, as well as the yellowing caused by high-temperature atmospheres can be reduced. When the maximum stress of the cured product of the photocurable resin composition is 20 MPa or less, the shrinkage stress of the photocurable resin composition during curing can be further reduced, thereby reducing the stress applied to the adhered object. It should be noted that the maximum stress of the cured product of the photocurable resin composition refers to the value measured according to JIS K7161-1 under the conditions of a dumbbell thickness of 1.0 mm and a tensile speed of 10 mm / min.

[0078] The curing shrinkage stress of the cured photocurable resin composition 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 of the photocurable resin composition during curing is reduced, which can reduce the stress applied to the adhered object and reduce optical strain on the adhered object. It should be noted that the curing shrinkage stress of the photocurable resin composition is a value measured at room temperature (23°C) according to JIS K6941. For example, it can be measured by curing the material under the following conditions using a device commercially available from AcroEdge under the trade name "Custron".

[0079] Light source: Panasonic LED-Aicure (wavelength: 365nm)

[0080] Irradiation intensity: 65mW / cm 2

[0081] Irradiation time: 300 seconds

[0082] [A bonding method for substrates using a light-curable resin composition]

[0083] Photocurable resin compositions are suitable for bonding materials together. The materials to be bonded are not particularly limited, and examples include thin-layer glass, optical glass, optical lenses, prisms, lenses, silicon wafers, semiconductor mounting components, and molded synthetic resin articles (e.g., synthetic resin sheets), with optical lenses being preferred. The material of the optical lens is not particularly limited; it can be glass or synthetic resin, but glass is preferred. Photocurable resin compositions are particularly suitable as adhesives for optical materials such as thin-layer glass, optical glass, prisms, and optical lenses. It should be noted that the materials to be bonded can be of the same type or different types.

[0084] The key points of bonding adherends together using a photocurable resin composition are explained. First, a laminate is manufactured by placing the adherends in a state where the photocurable resin composition is sandwiched between the opposing surfaces of the adherends (lamination process). A laminate can also be manufactured by laminating three or more adherends together with the photocurable resin composition sandwiched between the opposing surfaces of the adherends.

[0085] Because the photocurable resin composition is a single component, the tedious process of mixing the two components is not required when making laminates, making it easy to manufacture laminates.

[0086] Next, the resulting laminate is irradiated with radiation from the lamination direction, causing the photocurable resin composition sandwiched between the opposing surfaces of the adherends constituting the laminate to cure and generate a cured product (polymer) (curing process). This cured product can be used to bond the adherends together as a single unit.

[0087] The photocurable resin composition has low shrinkage stress during curing, thus reducing the stress applied to the two adhered objects bonded by the photocurable resin composition, thereby reducing strain on the adhered objects.

[0088] Furthermore, the cured product generated by curing the photocurable resin composition has excellent adhesive properties, enabling two adhered objects to be strongly bonded together through the cured product.

[0089] To ensure excellent curability of the photocurable resin composition, the peak wavelength of the radiation is preferably below 500 nm. The radiation is preferably light with a peak wavelength of 320 nm or higher. By using radiation with a peak wavelength of 320 nm or higher, the photocurable resin composition can be cured to a deeper depth to form a cured product.

[0090] Furthermore, the cured product of the light-curing resin composition that bonds the adhered materials together has low water absorption, which reduces the occurrence of haze caused by moisture and yellowing caused by high temperature atmosphere.

[0091] Therefore, the cured product of the light-curing resin composition will not produce discoloration such as haze or yellowing even in harsh environments such as inside a car, and can maintain a strong bond between the adhered objects for a long time.

[0092] Example

[0093] The present invention will be described in more detail below using examples, but the invention is not limited thereto. The specific numerical values ​​of the proportions (including proportions), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(defined in the form of "less than" or "less than") or lower limit values ​​(defined in the form of "above" or "more than") of the corresponding proportions (including proportions), physical property values, parameters, etc. described in the "Detailed Description" section.

[0094] The following compounds were used in the examples and comparative examples.

[0095] [(Meth)acrylic monomer (A)]

[0096] Isobornyl methacrylate (glass transition temperature Tg: 180℃, average molecular weight: 222)

[0097] • Dicyclopentyl methacrylate (glass transition temperature Tg: 175℃, average molecular weight: 220)

[0098] [Multifunctional (meth)acrylic acid oligomer (B)]

[0099] • Polyfunctional urethane acrylate oligomers with a 1,2-polybutadiene backbone and a hydrogenation rate of 95% (polyfunctional urethane acrylate oligomers with a hydrogenated 1,2-polybutadiene backbone)

[0100] The first reactant was obtained by reacting isophorone diisocyanate with 2-hydroxyethyl acrylate in a molar ratio of 1:1. The first reactant was prepared by reacting a di-terminated diol compound (weight average molecular weight: 25000) of hydrogenated 1,2-polybutadiene with the first reactant in a molar ratio of 1:2.

[0101] • A urethane acrylate oligomer with a polyester backbone (trade name "UN-7600" manufactured by Nejo Kogyo Co., Ltd., which does not have a polydiene backbone)

[0102] • Methacrylate oligomer 1 with an unhydrogenated polyisoprene backbone (trade name "UC-102M" manufactured by Kuraray Co., Ltd., which does not have a hydrogenated polydiene backbone)

[0103] • Methacrylate oligomer 2 with an unhydrogenated polyisoprene backbone (trade name "UC-203M" manufactured by Kuraray Co., Ltd., which does not have a hydrogenated polydiene backbone)

[0104] [(Meth)acrylic monomers (C)]

[0105] · Octyl acrylate

[0106] [Photopolymerization initiator]

[0107] ·1-Hydroxycyclohexylphenyl ketone (peak wavelength: 330nm)

[0108] [Silane coupling agent]

[0109] ·(3-Methacryloxypropyl)trimethoxysilane

[0110] (Examples 1-3, Comparative Examples 1-4)

[0111] The given amounts of (meth)acrylic monomer (A), multifunctional (meth)acrylic oligomer (B), (meth)acrylic monomer (C), and silane coupling agent shown in Table 1 were supplied to the reaction vessel and mixed until homogeneous to prepare a mixture.

[0112] Next, the given amount of photopolymerization initiator shown in Table 1 is supplied to the mixture, and the mixture is mixed until the photopolymerization initiator is completely dissolved in the mixture to obtain a photocurable resin composition.

[0113] For the obtained photocurable resin composition, the tensile modulus, maximum stress, curing shrinkage stress, water absorption and yellowing degree were determined according to the following criteria, and the results are shown in Table 1.

[0114] (Tensive modulus)

[0115] A dumbbell-shaped test piece (model No. 3 as 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 an intensity of 65 mW / cm². 2 Irradiate the test piece with ultraviolet light with a peak wavelength of 365nm for 2 minutes to cure the photocurable resin composition.

[0116] Using the cured test piece, the tensile modulus of the test piece was determined according to JIS K7161-1 under the conditions of a dumbbell thickness of 1.0 mm and a tensile speed of 10 mm / min.

[0117] (Maximum stress)

[0118] A dumbbell-shaped test piece (model No. 3 as 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 an intensity of 65 mW / cm². 2 Irradiate the test piece with ultraviolet light with a peak wavelength of 365nm for 2 minutes to cure the photocurable resin composition.

[0119] Using cured test pieces, the maximum stress of the test pieces was determined according to JIS K7161-1 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.

[0120] (Cure shrinkage stress)

[0121] The curing shrinkage stress of the obtained photocurable resin composition was measured according to JIS K6941 at room temperature (23°C) using a measuring apparatus commercially available from AcroEdge under the trade name "Custron". A lower curing shrinkage stress indicates lower shrinkage stress during curing of the photocurable resin composition.

[0122] (Water absorption rate)

[0123] Using the obtained photocurable resin composition, planar square test pieces with a side length of 20 mm and a thickness of 0.5 mm were prepared. The test pieces were then irradiated with an intensity of 65 mW / cm². 2 The photocurable resin composition was cured by irradiation with ultraviolet light at a peak wavelength of 365 nm for 2 minutes, thus curing the test piece. The mass W0 of the test piece was then determined.

[0124] A bottomed cylindrical water bath with a square base (side length 22.5 cm) and a height of 17 cm was prepared. Water was supplied to the water bath to a depth of 4 cm. A 200-mesh stainless steel wire mesh was horizontally positioned 11 cm vertically above the water surface within the water bath. A steam-permeable cloth was then placed over the wire mesh. The cured test specimen was then placed on this cloth.

[0125] Next, the top opening of the water bath was completely sealed 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, 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.

[0126] Water absorption rate (%) = 100 × (W1 - W0) / W0

[0127] (Yellowishness)

[0128] A plate-shaped test specimen, 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 specimen was irradiated with an intensity of 65 mW / cm². 2 Irradiate the test piece with ultraviolet light with a peak wavelength of 365nm for 2 minutes to cure the photocurable resin composition.

[0129] The initial transmittance T0 of the test pieces at wavelengths of 450 nm and 400 nm was determined using a UV-Vis spectrophotometer (SHIMADZU, trade name "UV-3600 Plus").

[0130] Next, the test piece was placed in an oven at 135°C and heated continuously for 100 hours. After being removed from the oven, the test piece was placed in an atmosphere at 25°C for 24 hours. The transmittance T1 of the heated test piece was measured using a UV-Vis spectrophotometer (SHIMADZU, trade name "UV-3600 Plus"). The rate of change of transmittance was calculated based on the following formula. A smaller rate of change indicates lower yellowing.

[0131] Rate of change (%) = 100 × (T0 - T1) / T0

[0132] (Cross-reference to related applications)

[0133] This application claims priority based on Japanese Patent Application No. 2024-57837, filed on March 29, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0134] Industrial applicability

[0135] The photocurable resin composition of the present invention exhibits low shrinkage stress during curing, thus exerting minimal stress on the adherends during curing. The photocurable resin composition of the present invention produces a cured product with excellent adhesion. Furthermore, the photocurable resin composition of the present invention produces a cured product that reduces moisture absorption, thus minimizing moisture-induced haze and yellowing caused by high-temperature atmospheres. Therefore, the cured product of the photocurable resin composition does not exhibit discoloration such as haze or yellowing even in harsh environments like inside a car, and can maintain a strong, integrated bond between the adhered products for a long period.

Claims

1. A photocurable resin composition comprising: A glass transition temperature (Tg) above 50°C and consisting of non-water-soluble (meth)acrylic acid monomers (A), and Polyfunctional (meth)acrylic acid oligomers (B) with a hydrogenation rate of over 90% and a polydiene backbone.

2. The photocurable resin composition according to claim 1, wherein, The weight-average molecular weight of the polyfunctional (meth)acrylic acid oligomer (B) is above 6000.

3. The photocurable resin composition according to claim 1 or 2, wherein the polyfunctional (meth)acrylic oligomer (B) comprises 40 to 150 parts by weight of the polyfunctional (meth)acrylic oligomer (B) relative to 100 parts by weight of the (meth)acrylic monomer (A).

4. The photocurable resin composition according to claim 1 or 2, wherein the (meth)acrylic monomer (C) has a glass transition temperature (Tg) of 3 to 30 parts by weight relative to 100 parts by weight of the (meth)acrylic monomer (A) and is below 0°C.

5. The photocurable resin composition according to claim 1 or 2, wherein the cured product has a maximum stress of 5-20 MPa and a tensile modulus of 50-900 MPa in a tensile test.

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

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