Curable resin composition and sealant for display element

Abstract

The present invention provides: a curable resin composition in which the bending resistance of a cured product is excellent and the surface tackiness of the cured product is suppressed; and a sealant for a display element, the sealant comprising the curable resin composition. The present invention is a curable resin composition containing: a polythiol compound (A) having a plurality of thiol groups in one molecule; a polyene compound (B) having a plurality of polymerizable unsaturated double bonds in one molecule and having a weight average molecular weight of less than 20,000; a polyene compound (C) having a plurality of polymerizable unsaturated double bonds in one molecule and having a weight average molecular weight of 20,000 or more; and a polymerization initiator (D). A cured product obtained by applying the curable resin composition on a substrate so as to have a thickness of 500 μm and curing under curing conditions of irradiation with light having a wavelength of 365 nm and an irradiance of 100 mW / cm2 has a storage elastic modulus at -20°C of 500 MPa or less.

Description

Curable resin composition and encapsulant for display elements

[0001] The present invention relates to a curable resin composition. Furthermore, the present invention relates to a encapsulant for a display element comprising a curable resin composition.

[0002] In recent years, liquid crystal displays and organic EL displays have been widely used as display elements that are thin, lightweight, and have low power consumption. For example, a liquid crystal display is usually manufactured by placing two transparent substrates with electrodes opposite each other at a predetermined distance apart, sealing the periphery with a sealant to form a cell, and injecting liquid crystal into the cell through a liquid crystal injection port provided in a part of the cell. Curable resin compositions are used for sealing liquid crystals in this way.

[0003] As a technology relating to curable resin compositions, for example, Patent Document 1 discloses a photocurable adhesive for polarizing plates that contains a polythiol compound having two or more thiol groups in one molecule, a polyene compound having two or more carbon-carbon double bonds in one molecule, and a photopolymerization initiator.

[0004] Patent Document 2 contains a polythiol monomer having two or more thiol groups in one molecule, a polyene monomer having two or more carbon-carbon double bonds in one molecule, and a photopolymerization initiator, with a volume resistivity of 5.0 × 10 at 30°C. １０ A encapsulant for display elements is disclosed, having a viscosity of Ω or more, and a viscosity of 0.4 to 8 Pa·s measured using a cone-rotor viscometer at 20°C and 20 rpm.

[0005] Patent Document 3 discloses a photocurable resin composition comprising a polyene compound having two or more carbon-carbon double bonds in one molecule, a polythiol compound having two or more thiol groups in one molecule, and a photopolymerization initiator, wherein the acid value is 3 or less.

[0006] Patent Document 4 discloses a crosslinked coating film obtained by crosslinking a crosslinkable resin composition, wherein the crosslinked coating film has a glass transition temperature of -30 to 60°C, a storage modulus in a dynamic viscoelasticity test of 0.1 to 1,000 MPa in the range of -30 to -10°C and 0.01 to 5 MPa in the range of 80 to 150°C, and an elongation of 30% or more in an atmosphere of 25°C.

[0007] Patent Document 5 discloses a photocurable composition comprising a thiol compound (A) having two or more specific groups in its molecule and an allyl monomer (B).

[0008] Japanese Patent Publication No. 2005-139401, Japanese Patent Publication No. 2016-074784, Japanese Patent Publication No. Hei 6-306172, International Publication No. 2017 / 056141, Japanese Patent Publication No. 2017-206572

[0009] In recent years, with the widespread use of foldable smartphones, it has become necessary for the encapsulant itself to not crack or peel when bent. Furthermore, if tack remains on the surface of the encapsulant, it poses a risk of foreign matter adhesion, so it is also required to reduce surface tackiness. Although curable resin compositions described in Patent Documents 1 to 5 were known, there was room for improvement in further enhancing the bending resistance of the cured product and suppressing the surface tackiness of the cured product. The present invention aims to provide a curable resin composition that has excellent bending resistance and suppressed surface tackiness of the cured product, and an encapsulant for display elements made from the curable resin composition.

[0010] Disclosure 1 is a curable resin composition comprising: a polythiol compound (A) having multiple thiol groups in one molecule; a polyene compound (B) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000; a polyene compound (C) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of 20,000 or more; and a polymerization initiator (D), and not containing a colorant (E). The curable resin composition is applied to a substrate to a thickness of 500 μm, and the illuminance is 365 nm and 100 mW / cm². ２The cured product obtained by a first curing condition of irradiating with light for 30 seconds has a storage modulus of 500 MPa or less at -20°C. Disclosure 2 is a curable resin composition comprising a polythiol compound (A) having a plurality of thiol groups in one molecule, a polyene compound (B) having a plurality of polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000, a polyene compound (C) having a plurality of polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of 20,000 or more, a polymerization initiator (D), and a colorant (E), wherein the curable resin composition is applied to a substrate to a thickness of 500 μm, and irradiated with a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ The present invention relates to a curable resin composition in which the cured product obtained by a second curing condition, in which light is irradiated from the front side for 30 seconds and from the back side for 30 seconds, has a storage modulus of 500 MPa or less at -20°C. Disclosure 3 is the curable resin composition of Disclosure 1 or 2 in which the cured product obtained by the first curing condition or the second curing condition has a tensile elongation at 25°C of 80% or more. Disclosure 4 is the curable resin composition of Disclosure 1, 2 or 3 in which the content of the polyene compound (C) in the curable resin composition is 10% by mass or more and 30% by mass or less. Disclosure 5 is the curable resin composition of Disclosure 1, 2, 3 or 4 in which the mass ratio (C / B) of the polyene compound (C) to the polyene compound (B) is 0.25 or more. Disclosure 6 is a encapsulant for display elements made from the curable resin composition of Disclosure 1, 2, 3, 4 or 5. The present invention will be described in detail below.

[0011] The inventors investigated the composition of a curable resin composition in order to obtain a cured product with excellent bending resistance and suppressed surface tack, and focused on a composition containing a polythiol compound (A) having multiple thiol groups in one molecule and a polyene compound having multiple polymerizable unsaturated double bonds (also referred to as "aliphatic carbon-carbon double bonds") in one molecule. As a result of further diligent investigation, the inventors found that by using a polyene compound (B) with a weight-average molecular weight of less than 20,000 and a polyene compound (C) with a weight-average molecular weight of 20,000 or more in combination, and by adjusting the storage modulus of the cured product at -20°C to 500 MPa or less under specific conditions, a cured product with excellent bending resistance and suppressed surface tack can be obtained, thus completing the present invention.

[0012] The curable resin composition of this disclosure contains a polythiol compound (A) having multiple thiol groups in one molecule, a polyene compound (B) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000, a polyene compound (C) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of 20,000 or more, and a polymerization initiator (D). The curable resin composition is applied to a substrate to a thickness of 500 μm, and the illuminance is 365 nm and 100 mW / cm². ２ The storage modulus at -20°C of the cured product obtained by irradiation with light is 500 MPa or less. Here, the curable resin composition of this disclosure may or may not contain a colorant (E). If it does not contain a colorant (E), when obtaining the cured product, a wavelength of 365 nm and an illuminance of 100 mW / cm ２ The first curing condition is applied, which involves irradiating with light for 30 seconds. If a coloring agent (E) is included, when obtaining the cured product, a wavelength of 365 nm and an irradiance of 100 mW / cm are applied. ２ A second curing condition is applied, in which light is irradiated from the front side for 30 seconds and from the back side for 30 seconds. The following describes the polythiol compound (A), polyene compound (B), polyene compound (C), polymerization initiator (D), colorant (E), and other components in order.

[0013] The curable resin composition of this disclosure contains a polythiol compound (A) having multiple thiol groups in one molecule. The curable resin composition of this disclosure contains a polythiol compound (A) together with a polyene compound (B) and a polyene compound (C), resulting in a curable resin composition with excellent surface reactivity. As a result, the surface tackiness of the cured product of the curable resin composition can be reduced.

[0014] Furthermore, when a curable resin composition is used as a encapsulant for a display element, surface reactivity under atmospheric conditions becomes important when the coating-like curable resin composition is cured with one side of the coating exposed to air. Since the curable resin composition of this disclosure exhibits excellent surface reactivity under atmospheric conditions, the surface tackiness of the cured product can be reduced even when the curable resin composition of this disclosure is used as a encapsulant for a display element.

[0015] The polythiol compound (A) is a compound having multiple thiol groups in one molecule. Preferably, the thiol groups in the polythiol compound (A) are secondary thiol groups. The fact that the thiol groups in the polythiol compound (A) are secondary thiol groups results in a curable resin composition with excellent storage stability.

[0016] From the viewpoint of curability of the curable resin composition and flexibility of the cured product, the polythiol compound (A) preferably has two to six thiol groups per molecule, more preferably two to four thiol groups, even more preferably two to three thiol groups, and particularly preferably two thiol groups. Furthermore, from the viewpoint of reducing the storage modulus at -20°C, the content of the polythiol compound having two thiol groups in the curable resin composition is preferably 80 parts by mass or more, more preferably 85 parts by mass or more, and even more preferably 90 parts by mass or more, per 100 parts by mass of the total polythiol compound (A).

[0017] Examples of polythiol compounds (A) having two thiol groups in one molecule include 1,4-bis(3-mercaptobutyryloxy)butane, butanediol bisthiopropionate, ethylenebis(3-mercaptopropionate), 1,2-bis(2-mercaptoethoxy)ethane, and ethylenebis(thioglycolate). These polythiol compounds having two thiol groups in one molecule may be used individually or in combination of two or more.

[0018] Examples of polythiol compounds (A) having three or more thiol groups in one molecule include 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione, pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), and dipentaerythritol hexakis(3-mercaptopropionate). These polythiol compounds having three or more thiol groups in one molecule may be used individually or in combination of two or more types.

[0019] The preferred lower limit for the content of polythiol compound (A) in the above curable resin composition is 20% by mass, and the preferred upper limit is 80% by mass. When the content of polythiol compound (A) is within this range, the resulting curable resin composition exhibits excellent surface reactivity, and the surface tackiness of the cured product can be further reduced. A more preferred lower limit for the content of polythiol compound (A) is 35% by mass, and a more preferred upper limit is 65% by mass.

[0020] The curable resin composition of this disclosure contains a polyene compound (B) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000. The inclusion of polyene compound (B) in the curable resin composition of this disclosure increases the flexibility of the cured product, resulting in a cured product with high bending resistance. Thus, because the cured product of this disclosure has high bending resistance (flexibility), it can be suitably used as a peripheral sealing agent for casings of foldable smartphones and the like.

[0021] In this specification, the "weight-average molecular weight" can be determined, for example, by measuring the molecular weight distribution in terms of polystyrene using gel permeation chromatography (GPC). Specifically, it can be determined, for example, by measuring using gel permeation chromatography (Waters, "2690 Separations Module," etc.) under the following conditions: Solvent: Tetrahydrofuran Sample flow rate: 1 mL / min Detector: Differential refractive index RI Column: GPC KF-806L (Showa Denko Corporation) Column temperature (measurement temperature): 40°C Injection volume: 20 μL

[0022] Examples of polyene compound (B) include (meth)allyl compound (B1) and (meth)acrylic compound (B2). Among these, (meth)allyl compound (B1) is preferred. These polyene compounds (B) may be used individually or in combination of two or more. In this specification, "(meth)allyl" means allyl or methallyl, and "(meth)acrylic" means acrylic or methacrylic.

[0023] Examples of (meth)allyl compounds (B1) having two polymerizable unsaturated double bonds in one molecule include di(meth)allyl isophthalate, di(meth)allyl terephthalate, diallyl tetrabromophthalate, diallyl satinate, diallyl glutariate, diallyl adipate, diallyl fumarate, diallyl maleate, trimethylolpropane diallyl ether, and glycerin diallyl ether. Among these, di(meth)allyl isophthalate is preferred.

[0024] Examples of (meth)allyl compounds (B1) having three or more polymerizable unsaturated double bonds in one molecule include tri(meth)allyl cyanurate, tri(meth)allyl isocyanurate, tri(meth)allyl trimellitate, tetra(meth)allyl pyromelitate, 1,3,4,6-tetra(meth)allyl glycoluryl, 1,3,4,6-tetra(meth)allyl-3a-methylglycoluryl, 1,3,4,6-tetra(meth)allyl-3a,6a-dimethylglycoluryl, trimethylolpropane trialyl ether, glycerin trialyl ether, pentaerythritol trialyl ether, and pentaerythritol tetraallyl ether. Among these, tri(meth)allyl isocyanurate is preferred.

[0025] Examples of the above (meth)acrylic compound (B2) include (meth)acrylic acid ester compounds, epoxy (meth)acrylates, and urethane (meth)acrylates. In this specification, "(meth)acrylate" means acrylate or methacrylate, and "epoxy (meth)acrylate" means a compound obtained by reacting all epoxy groups in an epoxy compound with (meth)acrylic acid.

[0026] Examples of the (meth)acrylic acid ester compounds having two polymerizable unsaturated double bonds in one molecule include 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 2-n-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. Examples include rilate, neopentyl glycol di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, ethylene oxide-modified bisphenol F di(meth)acrylate, dimethylol dicyclopentadienyl di(meth)acrylate, ethylene oxide-modified isocyanurate di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl(meth)acrylate, carbonate diol di(meth)acrylate, polyether diol di(meth)acrylate, polyester diol di(meth)acrylate, polycaprolactone diol di(meth)acrylate, polybutadiene diol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and the like.

[0027] Examples of the (meth)acrylic acid ester compounds having three or more polymerizable unsaturated double bonds in one molecule include trimethylolpropane tri(meth)acrylate, ethylene oxide-added trimethylolpropane tri(meth)acrylate, propylene oxide-added trimethylolpropane tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, ethylene oxide-added isocyanuric acid tri(meth)acrylate, glycerin tri(meth)acrylate, propylene oxide-added glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(meth)acryloyloxyethyl phosphate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0028] Examples of the epoxy (meth)acrylates mentioned above include those obtained by reacting an epoxy compound with (meth)acrylic acid in the presence of a basic catalyst according to a conventional method.

[0029] Examples of epoxy compounds that can be used as raw materials for synthesizing the above epoxy (meth)acrylate include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol E type epoxy compounds, bisphenol S type epoxy compounds, 2,2'-diallylbisphenol A type epoxy compounds, hydrogenated bisphenol type epoxy compounds, propylene oxide-added bisphenol A type epoxy compounds, resorcinol type epoxy compounds, biphenyl type epoxy compounds, sulfide type epoxy compounds, diphenyl ether type epoxy compounds, dicyclopentadiene type epoxy compounds, naphthalene type epoxy compounds, phenol novolac type epoxy compounds, orthocresol novolac type epoxy compounds, dicyclopentadiene novolac type epoxy compounds, biphenyl novolac type epoxy compounds, naphthalene phenol novolac type epoxy compounds, glycidylamine type epoxy compounds, alkyl polyol type epoxy compounds, rubber-modified epoxy compounds, glycidyl ester compounds, and the like.

[0030] The above-mentioned urethane (meth)acrylate can be obtained, for example, by reacting an isocyanate compound with a (meth)acrylic acid derivative having a hydroxyl group in the presence of a catalytic amount of a tin-based compound.

[0031] Examples of isocyanate compounds that serve as raw materials for the above-mentioned urethane (meth)acrylate include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, norbornane diisocyanate, tollidine diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, lysine diisocyanate, triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, tetramethylxylylene diisocyanate, and 1,6,11-undecane triisocyanate.

[0032] Furthermore, as the isocyanate compound used as a raw material for the above-mentioned urethane (meth)acrylate, a chain-extended isocyanate compound obtained by the reaction of a polyol with an excess isocyanate compound can also be used. Examples of the above-mentioned polyols include ethylene glycol, propylene glycol, glycerin, sorbitol, trimethylolpropane, carbonate diol, polyether diol, polyester diol, and polycaprolactone diol.

[0033] Examples of (meth)acrylic acid derivatives having a hydroxyl group include hydroxyalkyl mono(meth)acrylate, mono(meth)acrylate of a dihydric alcohol, mono(meth)acrylate or di(meth)acrylate of a trihydric alcohol, and epoxy(meth)acrylate. Examples of hydroxyalkyl mono(meth)acrylate include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate. Examples of dihydric alcohol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and polyethylene glycol. Examples of trihydric alcohol include trimethylolethane, trimethylolpropane, and glycerin. Examples of epoxy(meth)acrylate include bisphenol A type epoxy(meth)acrylate.

[0034] The preferred lower limit of the number of polymerizable unsaturated double bonds contained in one molecule of the polyene compound (B) is 2. When the polyene compound (B) has 2 or more polymerizable unsaturated double bonds in one molecule, it can efficiently react with the polythiol compound. The preferred upper limit of the number of polymerizable unsaturated double bonds contained in one molecule of the polyene compound (B) is 6. When the polyene compound (B) has 6 or less polymerizable unsaturated double bonds in one molecule, it can have excellent ultraviolet curability. It is more preferable that the polyene compound (B) has 2 polymerizable unsaturated double bonds in one molecule. When the polyene compound (B) has 2 polymerizable unsaturated double bonds in one molecule, the cured product can have high bending resistance (flexibility).

[0035] The preferred lower limit of the weight average molecular weight of the polyene compound (B) is 200, and the preferred upper limit is 5000. When the weight average molecular weight of the polyene compound (B) falls within this range, the resulting curable resin composition is liquid and has excellent handleability. A more preferred lower limit of the weight average molecular weight of the polyene compound (B) is 300, a more preferred upper limit is 1000, and a still more preferred upper limit is 500.

[0036] The preferred lower limit of the content ratio of the polyene compound (B) in the curable resin composition of the present disclosure is 10% by mass, and the preferred upper limit is 60% by mass. When the content ratio of the polyene compound (B) falls within this range, the resulting curable resin composition becomes more excellent in low viscosity. In addition, the cured product of the obtained curable resin composition becomes more excellent in flexibility (bending resistance). A more preferred lower limit of the content ratio of the polyene compound (B) is 25% by mass, and a more preferred upper limit is 45% by mass.

[0037] The curable resin composition of the present disclosure contains a polyene compound (C) having a plurality of polymerizable unsaturated double bonds in one molecule and a weight average molecular weight of 20000 or more. When the curable resin composition of the present disclosure contains the polyene compound (C), the content of crosslinked polymer in the cured product increases. Therefore, according to the curable resin composition of the present disclosure containing the polyene compound (C), the surface tackiness of the cured product can be suppressed.

[0038] As the polyene compound (C), resins obtained by polymerizing allyl esters, allyl ethers, etc., can be used. These polyene compounds (C) may be used individually or in combination of two or more types.

[0039] Examples of allyl esters that can be used in polymerization include tri(meth)allyl isocyanurate, tri(meth)allyl cyanurate, diallyl phthalate, diallyl isophthalate, diallyl tetrabromophthalate, and triallyl phthalate.

[0040] Examples of allyl ethers that can be used for polymerization include ethylene glycol monoallyl ether, diethylene glycol monoallyl ether, triethylene glycol monoallyl ether, polyethylene glycol monoallyl ether, propylene glycol monoallyl ether, dipropylene glycol monoallyl ether, tripropylene glycol monoallyl ether, polypropylene glycol monoallyl ether, 1,2-butylene glycol monoallyl ether, 1,3-butylene glycol monoallyl ether, hexylene glycol monoallyl ether, octylene glycol monoallyl ether, trimethylolpropanediallyl ether, glycerin diallyl ether, pentaerythritol triallyl ether, and the like.

[0041] Examples of polyene compounds (C) include diallyl phthalate resin and polyalkylene oxide-modified allyl ether. For diallyl phthalate resin, see, for example, Japanese Patent Application Publication No. 2018-172480.

[0042] The preferred lower limit for the number of polymerizable unsaturated double bonds in one molecule of polyene compound (C) is three. Having three or more polymerizable unsaturated double bonds in one molecule of polyene compound (C) allows for an effective increase in the molecular weight of the cured product through crosslinking during the curing of the curable resin composition. A more preferred lower limit for the number of polymerizable unsaturated double bonds in one molecule of polyene compound (C) is five.

[0043] The preferred upper limit for the number of polymerizable unsaturated double bonds in one molecule of polyene compound (C) is 20. Having 20 or fewer polymerizable unsaturated double bonds in one molecule of polyene compound (C) helps maintain the flexibility of the cured product of the curable resin composition. A more preferred upper limit for the number of polymerizable unsaturated double bonds in one molecule of polyene compound (C) is 10.

[0044] The preferred lower limit for the weight-average molecular weight of polyene compound (C) is 5,000, and the preferred upper limit is 100,000. Having the weight-average molecular weight of polyene compound (C) within this range allows for an effective increase in the molecular weight of the cured product during the curing of the curable resin composition. A more preferred lower limit for the weight-average molecular weight of polyene compound (C) is 20,000, and a more preferred upper limit is 50,000.

[0045] The preferred lower limit for the content of polyene compound (C) in the above curable resin composition is 10% by mass, and the preferred upper limit is 30% by mass. By having the polyene compound (C) content within this range, it is possible to effectively suppress the surface tackiness of the cured product. A more preferred lower limit for the polyene compound (C) content is 12% by mass, and a more preferred upper limit is 25% by mass.

[0046] The preferred lower limit for the mass ratio (C / B) of polyene compound (C) to polyene compound (B) is 0.25. A mass ratio (C / B) of 0.25 or higher effectively suppresses the surface tackiness of the cured product. A more preferred lower limit for the mass ratio (C / B) of polyene compound (C) to polyene compound (B) is 0.3, and an even more preferred lower limit is 0.5. The preferred upper limit for the mass ratio (C / B) of polyene compound (C) to polyene compound (B) is 1.5. A mass ratio (C / B) of 1.5 or lower effectively increases the flexibility (bending resistance) of the cured product. A more preferred upper limit for the mass ratio (C / B) of polyene compound (C) to polyene compound (B) is 1.2, and an even more preferred upper limit is 1.0.

[0047] Furthermore, it is preferable that polyene compound (B) is not a residual monomer or low-molecular-weight component (such as an oligomer) generated during the production of polyene compound (C). For this reason, it is preferable that polyene compound (B) is different from the raw material monomer used in the production of polyene compound (C), in addition to its molecular weight. It is also preferable that the content of polyene compound (B) in the above curable resin composition is greater than the content of polyene compound (C).

[0048] The curable resin composition of this disclosure contains a polymerization initiator (D). The polymerization initiator (D) is a compound that initiates the polymerization of a polymerizable compound. Examples of the polymerization initiator include photopolymerization initiators and thermal polymerization initiators, with photopolymerization initiators being preferably used.

[0049] Examples of the above-mentioned photopolymerization initiators include benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, oxime ester compounds, benzoin ether compounds, and thioxanthone compounds. Examples of the above-mentioned photopolymerization initiators include, specifically, 1-hydroxycyclohexylphenyl ketone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, 2-(dimethylamino)-2-((4-methylphenyl)methyl)-1-(4-(4-morpholinyl)phenyl)-1-butanone, 2,2-dimethoxy-1,2-diphenylethane-1-one, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 1-(4-(2-hydroxyethoxy)-phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 1-(4-(phenylthio)phenyl)-1,2-octanedione 2-(O-benzoyloxime), and 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO). The above photopolymerization initiators may be used alone or in combination of two or more.

[0050] Examples of the thermal polymerization initiators include those composed of azo compounds and organic peroxides. Examples of the azo compounds include those having a structure in which multiple units such as polyalkylene oxide or polydimethylsiloxane are bonded via an azo group. As for polymer azo compounds having a structure in which multiple units such as polyalkylene oxide are bonded via an azo group, those having a polyethylene oxide structure are preferred. Specific examples of the azo compounds include polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polyalkylene glycol, and polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polydimethylsiloxane having terminal amino groups. Examples of the organic peroxides include ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, and peroxydicarbonates.

[0051] The preferred lower limit for the content of polymerization initiator (D) in the above curable resin composition is 0.1% by mass, and the preferred upper limit is 5% by mass. Having the content of polymerization initiator (D) within this range allows for excellent UV curability. A more preferred lower limit for the content of polymerization initiator is 0.5% by mass, and a more preferred upper limit is 2% by mass.

[0052] The curable resin composition of this disclosure preferably further contains a coloring agent (E). By containing a coloring agent (E), the curable resin composition of this disclosure can, for example, impart light-shielding properties or design properties to the cured product.

[0053] The coloring agent (E) may be a pigment or a dye. Specific examples of coloring agents (E) include ultraviolet-transmitting dyes, titanium black, zirconium nitride, carbon black, iron oxide, aniline black, cyanine black, and the like.

[0054] The above-mentioned ultraviolet-transmitting dye, titanium black, and zirconium nitride are pigments with low light transmittance in the visible light region and high light transmittance near the ultraviolet region. That is, the above-mentioned ultraviolet-transmitting dye, titanium black, and zirconium nitride absorb all or part of the wavelengths of light in the visible light region, thereby imparting light-shielding properties and design properties to the curable resin composition of this disclosure, while allowing sufficient transmission of light with wavelengths near the ultraviolet region. Therefore, by using the above-mentioned ultraviolet-transmitting dye, titanium black, or zirconium nitride as a colorant (E), and then using a photopolymerization initiator that has excellent reactivity to light at wavelengths in which the light transmittance of the above-mentioned ultraviolet-transmitting dye, titanium black, or zirconium nitride is high, the curable resin composition of this disclosure will have superior light-shielding properties, design properties, and photocurability.

[0055] The preferred lower limit for the content of the colorant (E) in the curable resin composition of this disclosure is 0.1% by mass, and the preferred upper limit is 7% by mass. Having the colorant (E) content within this range makes it easier to increase the optical density of the resulting curable resin composition. A more preferred lower limit for the colorant (E) content is 0.3% by mass, and a more preferred upper limit is 5% by mass.

[0056] The curable resin composition of this disclosure may contain an antifoaming agent from the viewpoint of improving coatability, etc. Examples of the antifoaming agent include silicone-based antifoaming agents, acrylic polymer-based antifoaming agents, vinyl ether polymer-based antifoaming agents, olefin polymer-based antifoaming agents, and the like.

[0057] The curable resin compositions of this disclosure may further contain various known additives, such as plasticizers, silane coupling agents, sensitizers, thermosetting agents, curing retarders, antioxidants, storage stabilizers, and dispersants, to the extent that they do not impede the objectives of the present invention.

[0058] From the viewpoint of preventing a decrease in curability (reactivity), the curable resin composition of this disclosure preferably contains substantially no solvent, and more specifically, the solvent content in the curable resin composition is preferably 1.5% by mass or less. More preferably, the curable resin composition of this disclosure contains no solvent, and more specifically, the solvent content in the curable resin composition is 0% by mass. That is, the viscosity of the curable resin composition of this disclosure is preferably adjusted not by the solvent, but by the type and physical properties of the polythiol compound (A), polyene compound (B), polyene compound (C), and polymerization initiator (D) used.

[0059] Methods for preparing the curable resin composition of this disclosure include, for example, a method of mixing a polythiol compound (A), a polyene compound (B), a polyene compound (C), and a polymerization initiator (D) with additives as needed using a mixer (stirrer). Examples of such mixers include homodispersers, homomixers, universal mixers, planetary mixers, kneaders, and three-roll mixers.

[0060] The curable resin composition of this disclosure is preferably curable by at least one of light irradiation and / or heating, and more preferably curable by light irradiation.

[0061] A method for curing the curable resin composition of this disclosure by light irradiation includes, for example, a wavelength of 315 nm to 480 nm and an illuminance of 10 mW / cm². ２ More than 1000mW / cm ２ Examples of methods include irradiating with the following light for more than 10 seconds but less than 10 minutes.

[0062] Examples of light sources for irradiating the curable resin composition of this disclosure include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, excimer lasers, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, sodium lamps, halogen lamps, xenon lamps, LED lamps, fluorescent lamps, sunlight, electron beam irradiation devices, and the like. These light sources may be used individually or in combination of two or more types.

[0063] Examples of means for irradiating the curable resin composition of the present disclosure with light include simultaneous irradiation using various light sources, sequential irradiation with a time difference, and combined irradiation of simultaneous irradiation and sequential irradiation, and any irradiation means may be used.

[0064] The curable resin composition of the present disclosure can prevent the occurrence of liquid crystal contamination when used in a liquid crystal display element and damage to the organic light-emitting material layer when used in an organic EL display element. A sealant for display elements formed from the curable resin composition of the present disclosure is also one aspect of the present invention.

[0065] The sealant for display elements of the present disclosure can be used as a sealant for sealing the entire surface, front surface, rear surface, or periphery of a display element, or as a sealing agent for sealing an opening provided in a display element, and among these, it is particularly suitably used for sealing the entire surface of a display element. In this specification, the above-mentioned "entire surface" does not necessarily mean 100% of the surface of the display element, but means the entire sealing surface required for the display element. Further, the above-mentioned "front surface" means the surface on the side from which light is extracted, that is, the viewing side surface.

[0066] The sealant for display elements of the present disclosure can be used, for example, in organic EL curable resin compositions, sealing agents for liquid crystal display elements, sealants for electrochromic substrates, sealants for electronic paper, and the like.

[0067] The curable resin composition of the present disclosure is applied onto a substrate to a thickness of 500 μm, and irradiated with light having a wavelength of 365 nm and an illuminance of 100 mW / cm ２ , the storage modulus at -20°C of the cured product obtained is 500 MPa or less. When the composition does not contain a colorant (E), the first curing condition of irradiating with light having a wavelength of 365 nm and an illuminance of 100 mW / cm ２ for 30 seconds is applied to obtain the cured product. When the composition contains a colorant (E), when obtaining the cured product, light having a wavelength of 365 nm and an illuminance of 100 mW / cm ２A second curing condition is applied, in which light is irradiated from the front side for 30 seconds and from the back side for 30 seconds. Because the storage modulus of the cured product of the curable resin composition of this disclosure is 500 MPa or less at -20°C, the cured product has high bending resistance (flexibility) even when used in cold regions, and can therefore be suitably used as a peripheral sealing agent for the housing of foldable smartphones and the like. The preferred upper limit of the storage modulus of the above cured product at -20°C is 300 MPa.

[0068] A preferred lower limit for the storage modulus of the cured product at -20°C is 0.1 MPa. A storage modulus of 0.1 MPa or higher at -20°C ensures the strength required for applications such as sealing agents for display elements. A more preferred lower limit for the storage modulus of the cured product at -20°C is 0.5 MPa.

[0069] The storage modulus of the cured product at -20°C can be measured by the following method. First, the curable resin composition is applied to a release PET film used as a base material. A 500 μm thick silicone rubber sheet is used to create a hole punched out in a shape of 5 mm wide and 45 mm long, so that the resin has a thickness of 500 μm. The top surface is then sealed with another release PET film and flattened by squeezing. After that, a light irradiation device is used to irradiate the surface at a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ The curable resin composition is cured by irradiating it with light for 30 seconds to obtain a cured product sandwiched between a pair of release PET films. For samples containing a coloring agent (E), such as a black sample, light irradiation is performed from both sides for 30 seconds each. The release PET films sandwiching the cured product are peeled off, and the dynamic viscoelastic spectrum of the obtained test piece is measured from -40 to 140°C using a viscoelastic spectrometer (e.g., DVA-200, manufactured by IT Measurement Control Co., Ltd.) under constant-speed heating tensile mode at 5°C / min, strain of 0.1%, and frequency of 10 Hz. The storage modulus at -20°C obtained as a result is taken as the storage modulus at -20°C of the cured product.

[0070] The storage modulus of the cured product at -20°C can be adjusted by changing the type and content of polyene compound (B), the type and content of polythiol compound (A) and polyene compound (C), and by adding fillers.

[0071] The preferred lower limit of the tensile elongation at 25°C for the cured product obtained by the first or second curing conditions described above is 80%. A tensile elongation at 25°C of 80% or more in the cured product provides higher bending resistance (flexibility), making it more suitable for use as a peripheral sealant for casings of foldable smartphones and the like. A more preferred lower limit of the tensile elongation at 25°C for the cured product is 90%. There is no particular preferred upper limit for the tensile elongation at 25°C of the cured product, but the practical upper limit is 400%.

[0072] The tensile elongation at 25°C of the cured material can be measured by the following method. First, the curable resin composition is applied to a release PET film used as a base material. A 500 μm thick silicone rubber sheet is used to create a hole punched out in a shape of 5 mm wide and 45 mm long, and the resin is applied to the recessed portion. The top surface is then sealed with another release PET film and flattened by squeegees. After that, a light irradiation device is used to measure the elongation at a wavelength of 365 nm and an illuminance of 100 mW / cm². ２ The curable resin composition is cured by irradiating it with light for 30 seconds to obtain a cured product sandwiched between a pair of release PET films. For samples containing a coloring agent (E), such as a black sample, light irradiation is performed from both sides for 30 seconds each. The release PET films sandwiching the cured product are peeled off, and the tensile elongation at break of the obtained test piece is measured using a tensile testing machine (e.g., Shimadzu Corporation's "Autograph AG-XPlus") under the conditions of 25°C, grip distance of 25 mm, and tensile speed of 10 mm / min. The resulting tensile elongation at break is taken as the tensile elongation at break of the cured product at 25°C.

[0073] The tensile elongation at 25°C of the cured product can be adjusted by changing the type and content of polyene compound (B), the type and content of polythiol compound (A) and polyene compound (C), and by adding fillers.

[0074] A 500 μm thick rubber sheet is prepared with a 5 mm diameter through-hole, one side is sealed with tape, and the above-mentioned curable resin composition is filled into the hole. At a wavelength of 365 nm and an illuminance of 100 mW / cm², the test is performed. ２ The preferred lower limit for the thickness of the cured product obtained by irradiating it with light for 30 seconds (hereinafter also simply referred to as "cured product formed using a 500 μm thick rubber sheet") is 200 μm. By having a thickness of 200 μm or more of the cured product formed using the 500 μm thick rubber sheet, the curable resin composition can form a cured product with excellent deep curing properties. The more preferred lower limit for the thickness of the cured product formed using the 500 μm thick rubber sheet is 400 μm. The upper limit for the thickness of the cured product formed using the 500 μm thick rubber sheet is 500 μm.

[0075] The thickness of a cured product formed using a 500 μm thick rubber sheet can be measured by the following method: A 5 mm diameter through-hole is made in the 500 μm thick rubber sheet, one side is sealed with tape, and the hole is filled with the respective curable resin composition. Then, using a light irradiation device, the thickness is measured at a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ The curable resin composition is cured by irradiating it with light for 30 seconds to obtain a cured product. The cured product is removed and its thickness is measured using a micrometer (for example, Mitutoyo's "Soft Touch Micro CLM"). The resulting thickness is taken as the thickness of the cured product formed using a 500 μm thick rubber sheet.

[0076] The thickness (deep curing properties) of the cured product formed using a 500 μm thick rubber sheet can be adjusted by changing the type and content of the polythiol compound (A), the type and content of the polyene compound (C), etc.

[0077] According to the present invention, it is possible to provide a curable resin composition that has excellent bending resistance of the cured product and suppressed surface tackiness of the cured product, and a encapsulant for display elements made from the curable resin composition.

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0079] (Examples 1-8, Comparative Examples 1-4) Each material was mixed in a planetary agitator (Sinky Co., Ltd., "Awatori Rentaro") according to the mixing ratios (mass ratios) listed in Tables 1-2 to obtain the respective curable resin compositions of the Examples and Comparative Examples. Details of the materials indicated by abbreviations in the table are as follows.

[0080] <Polythiol Compounds (A)> ・Karenz MT BD1: 1,4-bis(3-mercaptobutyryloxy)butane (manufactured by Resonaq, a polythiol compound having two thiol groups in one molecule) ・Karenz MT NR1: 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinan-2,4,6-trione (manufactured by Resonaq, a polythiol compound having three thiol groups in one molecule) <Polyene Compounds (B)> ・Daiso Dap 100 monomer: diallyl isophthalate, molecular weight 246.3 (manufactured by Osaka Soda Co., Ltd., an allyl monomer having two polymerizable unsaturated double bonds in one molecule) ・TAIC: triallyl isocyanurate, molecular weight 249.3 (manufactured by Shinryo Co., Ltd., an allyl monomer having three polymerizable unsaturated double bonds in one molecule) <Polyene Compounds (C)>・Daiso Dap A: Diallyl phthalate resin, weight-average molecular weight 40,000-50,000 (manufactured by Osaka Soda Co., Ltd., iodine value (g / 100g) 50-60) ・Daiso Dap K: Diallyl phthalate resin, weight-average molecular weight 20,000-30,000 (manufactured by Osaka Soda Co., Ltd., iodine value (g / 100g) 50-60) <Polymerization initiator (D)> ・Omnirad TPO-N: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO-N, manufactured by IGM Resins B.V., photopolymerization initiator) <Coloring agent (E)> ・13M-C: Titanium black (manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd., pigment) ・Elixa black 850: UV-transmitting dye (manufactured by Orient Chemical Industry Co., Ltd.)

[0081] (Storage modulus of cured material at -20°C) The obtained curable resin composition was applied to a release PET film used as a base material. A 500 μm thick silicone rubber sheet was used to create holes in the recessed areas, which were 5 mm wide and 45 mm long, so that the total thickness of the recessed area was 500 μm. The top surface was then sealed with another release PET film and flattened by squeegeeing. Subsequently, a light irradiation device (CCS Corporation, "UVS01-01") was used to irradiate the surface at a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ The curable resin composition was cured by irradiating it with light from the front side for 30 seconds, and a cured product was obtained sandwiched between a pair of release PET films. For the black sample containing the coloring agent (E), further irradiation was performed from the back side at a wavelength of 365 nm and an illuminance of 100 mW / cm². ２ The specimen was irradiated with light for 30 seconds. The two release PET films sandwiching the cured material were peeled off, and the dynamic viscoelastic spectrum of the obtained specimen was measured from -40 to 140°C using a viscoelastic spectrometer (DVA-200, manufactured by IT Measurement Control Co., Ltd.) under constant-speed heating tensile mode at 5°C / min, strain of 0.1%, and frequency of 10 Hz. The storage modulus at -20°C obtained as a result was defined as the storage modulus at -20°C of the cured material. The storage modulus at -20°C was evaluated as follows: "A" if the storage modulus at -20°C was 500 MPa or less, and "B" if it exceeded 500 MPa. The results are shown in Tables 1 and 2.

[0082] (Tensile elongation at 25°C of cured material) The tensile elongation at 25°C was measured using a tensile testing machine (Shimadzu Corporation, "Autograph AG-XPlus") obtained in the same manner as described above for "(Storage modulus of cured material at -20°C)". The tensile elongation at 25°C was evaluated as follows: "A" if the tensile elongation at 25°C was 80% or more, and "B" if it was less than 80%. The results are shown in Tables 1 and 2.

[0083] (Surface tackiness of cured material) The curable resin composition was applied to a glass substrate (AGC Fabretech Eagle XG) to a thickness of 50 μm using 50 μm thick Kapton tape as a dam. Then, the top surface was squeegeeed with glass, and with the coated surface exposed to air, light irradiation was performed using a light irradiation device (CCS Corporation, "UVS01-01") at a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ The curable resin composition was cured by irradiating it with light for 30 seconds to obtain a cured product. Tackiness was evaluated using Rhesca's "TAC-II" under the following conditions: probe diameter Φ5 mm, indentation speed 120 mm / min, release speed 5 mm / min, indentation pressure 200 gf, and indentation time 5 s. 200 gf / cm ２ If the following conditions are met, it will be classified as "A", 200 gf / cm². ２ The surface tackiness of the cured product was evaluated, with values ​​exceeding a certain threshold designated as "B". The results are shown in Tables 1 and 2. It should be noted that curable resin compositions with a surface tackiness rating of A have higher reactivity of the polymerizable compounds contained in the composition than curable resin compositions with a rating of B.

[0084] (Deep curing properties of the cured material) A 500 μm thick rubber sheet was prepared with a 5 mm diameter through-hole, and one side was sealed with tape. Each curable resin composition was then filled into the hole. Next, a light irradiation device (CCS Corporation, "UVS01-01") was used to irradiate the material at a wavelength of 365 nm and an irradiance of 100 mW / cm². ２ A cured material was obtained by irradiating it with light for 30 seconds. The cured material was then removed, and its thickness was measured using a micrometer (Mitutoyo Corporation, "Soft Touch Micro CLM"). Deep curing properties were evaluated, with "A" indicating a thickness of 200 μm or more, and "B" indicating a thickness of less than 200 μm. The results are shown in Tables 1 and 2.

[0085]

[0086]

[0087] The cured products of the curable resin compositions described in Examples 4 and 5 also exhibited light-shielding properties. Note that, in the absence of polyene compound (B), polythiol compound (A) and polyene compound (C) alone are not compatible; therefore, comparative examples without polyene compound (B) were not prepared.

[0088] According to the present invention, it is possible to provide a curable resin composition that has excellent bending resistance of the cured product and suppressed surface tackiness of the cured product, and a encapsulant for display elements made from the curable resin composition.

Claims

1. A curable resin composition comprising: a polythiol compound (A) having multiple thiol groups in one molecule; a polyene compound (B) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000; a polyene compound (C) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of 20,000 or more; and a polymerization initiator (D), without containing a colorant (E). The curable resin composition is applied to a substrate to a thickness of 500 μm, and the illuminance is 365 nm and 100 mW / cm². ２ A curable resin composition characterized in that the storage modulus of the cured product obtained by a first curing condition of irradiating with light for 30 seconds is 500 MPa or less at -20°C.

2. A curable resin composition comprising: a polythiol compound (A) having multiple thiol groups in one molecule; a polyene compound (B) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of less than 20,000; a polyene compound (C) having multiple polymerizable unsaturated double bonds in one molecule and having a weight-average molecular weight of 20,000 or more; a polymerization initiator (D); and a coloring agent (E), wherein the curable resin composition is applied to a substrate to a thickness of 500 μm, and the illuminance is 365 nm and 100 mW / cm². ２ A curable resin composition characterized in that the storage modulus of the cured product obtained by a second curing condition in which light is irradiated from the front side for 30 seconds and from the back side for 30 seconds each has a storage modulus of 500 MPa or less at -20°C.

3. The curable resin composition according to claim 1 or 2, wherein the tensile elongation at 25°C of the cured product obtained by the first curing condition or the second curing condition is 80% or more.

4. The curable resin composition according to claim 1 or 2, wherein the content of the polyene compound (C) in the curable resin composition is 10% by mass or more and 30% by mass or less.

5. The curable resin composition according to claim 1 or 2, wherein the mass ratio (C / B) of polyene compound (C) to polyene compound (B) is 0.25 or more.

6. A encapsulant for a display element, characterized by comprising the curable resin composition described in any one of claims 1 to 5.

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