Photocurable silicone composition and its cured products, laminates, and optical devices or optical displays

Abstract

This invention provides a photocurable silicone composition and its applications, which is photocurable, exhibits excellent transparency of the cured product, and shows high adhesion and adhesive strength even to difficult-to-adhere substrates. [Solution] A photocurable silicone composition and its uses, comprising (A) an organopolysiloxane having at least two alkenyl groups in one molecule, (B) a compound having at least two mercapto groups in one molecule, (C) a photoradical initiator, and (D) an adhesion promoter containing (d1) an organosilicon compound having a boiling point of 100°C or higher at 1 atm and containing at least one nitrogen atom and an alkoxysilyl group in the molecule, and (d2) an organosilicon compound having at least one trialkoxysilyl group in the molecule, not containing a nitrogen atom, and containing 1 to 3 silicon atoms, in a mass ratio of 1:9 to 9:1, wherein the refractive index of the cured product is less than 1.42 at 25°C and a wavelength of 365 nm.

Description

[Technical Field]

[0001] The present invention relates to a photocurable silicone composition and its cured product, laminate, and optical device or optical display. [Background technology]

[0002] Highly transparent, curable silicone compositions with high elongation of the cured product are used as adhesives or sealants to improve the visibility of optical displays. Optical displays require the use of thermally unstable materials such as display units like liquid crystals and organic ELs, and display forming components such as touch panels and cover lenses. There is a demand for materials that cure at relatively low temperatures. Furthermore, in recent years, from the perspective of energy conservation, compositions that cure by ultraviolet irradiation without requiring a heating process have attracted attention. For example, the applicant of this case has proposed a curable silicone composition (Patent Document 1) that uses a photoactive hydrosilylation reaction catalyst to provide UV-delayed curing, high transparency after curing, and excellent adhesive strength to glass and difficult-to-bond polarizing plates, making it usable as an adhesive or sealant for optical displays or touch panels. However, this curable silicone composition is designed for UV-delayed curing and has the drawback of being difficult to use in applications or processes that require rapid curing and adhesion in a short time.

[0003] On the other hand, compositions that do not require a heating process and harden by ultraviolet irradiation are known, specifically compositions having a so-called thiol-ene type curing system. For example, the applicants of this case have proposed a photocurable liquid silicone composition that hardens rapidly by irradiation with high-energy rays such as ultraviolet light and has a high refractive index (RI) after hardening (Patent Document 2), and thiol-ene type photocurable silicone compositions with excellent rapid hardening properties have also been proposed (Patent Documents 3-5).

[0004] However, in recent years, there has been a growing demand for fast-curing applications and processes that require relatively low refractive indices and quick curing and adhesion. These thiol-ene type photocurable silicone compositions may not adequately provide optical adhesives (especially optical transparent resins, OCRs) that yield cured products with low refractive indices, particularly those with a refractive index of less than 1.42 for visible light. Furthermore, from the standpoint of diversifying optical materials, functional coatings, and eliminating environmentally harmful substances, optical devices and optical displays are increasingly using substrates that are even more difficult to adhere to than before. Conventional thiol-ene type photocurable silicone compositions have insufficient adhesion and adhesive strength of their cured products to difficult-to-adhere substrates. There is a strong market demand for a photocurable silicone composition that cures rapidly upon irradiation with high-energy rays such as ultraviolet light, and that provides a low refractive index cured product / adhesive layer that achieves sufficient adhesion and adhesive strength even to difficult-to-adhere substrates without impairing the physical properties of the resulting cured product, such as transparency, desired hardness, flexibility, and adhesive strength (especially shear adhesive strength). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Patent Publication No. 2024 / 057924 Brochure [Patent Document 2] Brochure for International Patent Publication No. 2021 / 167051 [Patent Document 3] Japanese Patent Publication No. 2021-134329 [Patent Document 4] Japanese Patent Publication No. 2016-150958 (Japanese Patent Registration No. 6426023) [Patent Document 5] Japanese Patent Publication No. 2005-171189 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention has been made to solve the problems of the above-mentioned prior art, and aims to provide a photocurable silicone composition and its cured product, particularly laminates, optical devices, optical displays, etc., that can be used as an adhesive for optical transparent resins with a low refractive index, usable in optical devices such as optical displays or touch panels, and that can be rapidly cured by irradiation with high-energy rays such as ultraviolet rays, exhibiting high adhesion and adhesive strength even to substrates that are difficult to adhere to. [Means for solving the problem]

[0007] The inventors of this invention have diligently studied the above problems and arrived at the present invention. That is, the object of the present invention is (A) Organopolysiloxanes having at least two alkenyl groups with 2 to 12 carbon atoms in one molecule, (B) Compounds having at least two mercapto groups in one molecule, (C) Photoradical initiator, and (D) This is achieved by a photocurable silicone composition comprising (d1) an organosilicon compound having a boiling point of 100°C or higher at 1 atmosphere and containing at least one nitrogen atom and an alkoxysilyl group in its molecule, and (d2) an organosilicon compound having at least one trialkoxysilyl group in its molecule, lacking a nitrogen atom, and containing 1 to 3 silicon atoms, in a mass ratio of 1:9 to 9:1, wherein the refractive index of the cured product at 25°C and a wavelength of 365 nm is less than 1.42.

[0008] The aforementioned component (A) includes (A1) a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain, It is preferable that component (B) contains (B1) a linear organopolysiloxane having at least two mercapto groups in the side chain portion of its molecular chain. Furthermore, it is more preferable that component (A) is (A1-1) a linear organopolysiloxane having alkenyl groups having 2 to 12 carbon atoms at both ends of its molecular chain and optionally having alkenyl groups having 2 to 12 carbon atoms in the side chain portion, and that component (B) is (B1-1) a linear organopolysiloxane having at least two mercapto groups only in the side chain portion of its molecular chain. Furthermore, it is preferable that the content of component (B) is such that the amount of mercapto groups in component (B) is 0.5 moles to 4 moles and 0.75 moles to 2 moles per mole of the total amount of aliphatic unsaturated carbon-carbon bonds, specifically alkenyl groups, in component (A).

[0009] The composition according to the present invention is preferably a one-component composition, and preferably has a viscosity of 100,000 mPa·s or less before irradiation with high-energy rays at 25°C.

[0010] The component (d1) constituting the aforementioned component (D) is preferably one or more organosilicon compounds selected from (d1-1) organosilicon compounds having a carbasilatran structure in the molecule and (d1-2) aminoalkyltrialkoxysilanes, and (d1-1-1) has the following structural formula: [ka] (In the formula, Rc is a group selected from a methoxy group, an ethoxy group, a vinyl group, an allyl group, and a hexenyl group.) It is more preferable that the molecule represented by is one or more carbasilatran derivatives having a silicon atom-bonded alkoxy group or a silicon atom-bonded alkenyl group, and one or more organosilicon compounds selected from (d1-2)aminoalkyltrialkoxysilanes.

[0011] The (d2) component constituting the (D) component described above is preferably one or more organosilicon compounds selected from (d2-1) organosilicon compounds having two or more alkoxysilyl groups in one molecule, and (d2-2) organosilicon compounds having an alkoxysilyl group and an epoxy group in one molecule, and more preferably one or more organosilicon compounds selected from (d2-1-2) disilaalkane compounds having alkoxysilyl groups at both ends of the molecular chain and (d2-2-2) 3-glycidoxyalkyltrialkoxysilane.

[0012] The content of component (D) is preferably in the range of 0.01 to 5% by mass, more preferably in the range of 0.01 to 2.5% by mass or 0.01 to 1.0% by mass, relative to the total amount of non-volatile components of the photocurable silicone composition. Furthermore, components (d1) and (d2) (or compounds corresponding to their preferred forms) may be used in a mass ratio of 2:8 to 8:2, more preferably in a mass ratio of 3:7 to 7:3 or 6:4 to 4:6.

[0013] The photocurable silicone composition of the present invention is preferably an optical adhesive or optical tack. These applications explicitly include low refractive index optical transparent resins (OCRs).

[0014] The present invention also relates to cured products of the curable silicone composition of the present invention.

[0015] The cured product of the curable silicone composition of the present invention preferably has a penetration degree in the range of 5 to 70 at 25°C. The penetration degree of the cured product can be designed as desired, and may be in the range of 5 to 20, 20 to 50, or 50 to 70. The curable silicone composition of the present invention has the advantage that even cured products with relatively low penetration degrees can be easily designed.

[0016] Similarly, the cured product of the curable silicone composition of the present invention preferably forms a cured layer with a thickness of 200 μm, and the shear adhesive strength of the cured layer, as measured by the method specified in JIS K 6850, is preferably 0.4 MPa or higher.

[0017] The present invention also, The present invention also relates to a laminate comprising a first transparent or opaque optical member and an adhesive layer made of a cured product of the present invention disposed between a second transparent or opaque optical member.

[0018] Furthermore, the present invention also relates to an optical device comprising a substrate, an optical element disposed on the substrate, and a cured product of the present invention that encapsulates at least a portion of the optical element.

[0019] Furthermore, the present invention also relates to an optical display comprising the laminate of the present invention. [Effects of the Invention]

[0020] The photocurable silicone composition of the present invention can be rapidly cured by irradiation with high-energy rays such as ultraviolet light, and after curing, it can provide a cured product that is highly transparent, has a low refractive index in the visible light region, and exhibits excellent adhesion and adhesive strength to difficult-to-bond substrates. Furthermore, it has the advantage that the physical properties (hardness, etc.) of the cured product can be designed as desired. For this reason, the photocurable silicone composition is extremely useful as an optical adhesive or optical bonding agent used in optical displays or touch panels, including optical transparent resin (OCR) applications for bonding low refractive index and difficult-to-bond substrates. [Modes for carrying out the invention]

[0021] [Curing silicone composition] The ultraviolet-curable silicone composition of the present invention (hereinafter sometimes referred to as "this composition") will be described in detail below.

[0022] Component (A) is an organopolysiloxane having at least two alkenyl groups with 2 to 12 carbon atoms in one molecule. Examples of alkenyl groups in component (A) include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl groups, and vinyl, allyl, hexenyl, and octenyl groups are preferred from the viewpoint of economy and reactivity.

[0023] Furthermore, examples of other groups that bond to the silicon atom in component (A) include alkyl groups having 1 to 12 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl groups; aralkyl groups having 7 to 12 carbon atoms such as benzyl and phenethyl groups; halogen-substituted alkyl groups having 1 to 12 carbon atoms such as 3-chloropropyl and 3,3,3-trifluoropropyl groups; aryl groups having 6 to 20 carbon atoms such as phenyl, tolyl, and xylyl groups; and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine, chlorine, and bromine atoms. From the viewpoint of economy and heat resistance, the methyl group is preferred. Furthermore, the silicon atoms in component (A) may have small amounts of alkoxy groups such as methoxy groups, ethoxy groups, n-propoxy groups, i-propoxy groups, n-butoxy groups, sec-butoxy groups, and tert-butoxy groups, or hydroxyl groups, bonded to them, to the extent that it does not impair the objectives of the present invention. It is particularly preferable that component (A) substantially does not contain aryl groups such as phenyl groups or aralkyl groups, from the viewpoint of designing the refractive index of the cured product according to the present invention to be less than 1.42.

[0024] The molecular structure of component (A) is not limited and may include, for example, linear, partially branched linear, branched, cyclic, or three-dimensional network structures. Component (A) may be a single organopolysiloxane having one of these molecular structures, or a mixture of two or more organopolysiloxanes having one of these molecular structures.

[0025] Preferably, the component (A) contains the following component (A1) and may optionally contain the component (A2): (A1) A linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain (A2) Average unit formula: (R 1 3SiO 1 / 2 ) a (R 1 2SiO 2 / 2 ) b (R 1 SiO 3 / 2 ) c (SiO 4 / 2 ) d (In the formula, each R 1 is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and at least 1 mol% of R 1 is an alkenyl group having 2 to 12 carbon atoms, and a, b, c, and d all satisfy the following conditions: a + b + c + d = 1, 0 ≦ a ≦ 0.8, 0 ≦ b ≦ 0.4, 0 ≦ c ≦ 0.8, 0 ≦ d ≦ 0.6, 0.2 ≦ c + d ≦ 0.8), an organopolysiloxane having an alkenyl group

[0026] (A1) component is a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain, which may be linear or branched, but is more preferably a linear organopolysiloxane. In the present invention, the component (A) particularly preferably contains (A1-1) a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain and optionally having alkenyl groups with 2 to 12 carbon atoms at the side chain sites. From the viewpoint of designing the refractive index of the cured product according to the present invention to be less than 1.42, at least 95 mol% or more, 95 to 100 mol% of the substituents bonded to silicon atoms other than alkenyl groups in the component (A1) or (A1-1) are alkyl groups such as methyl groups, and it is particularly preferable that the molecule does not substantially contain an aryl group or an aralkyl group.

[0027] Examples of such component (A) include dimethylpolysiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain, methylvinylpolysiloxane with trimethylsiloxy groups sealed at both ends of the molecular chain, dimethylsiloxane-methylvinylsiloxane copolymer with trimethylsiloxy groups sealed at both ends of the molecular chain, partially branched polydimethylsiloxane with methylsilsesquioxane units (T units) containing methylsilsesquioxane units (T units), polydimethylsiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain containing silica units (Q units), and mixtures of two or more organopolysiloxanes thereof. Particularly preferred as component (A) is dimethylpolysiloxane with dimethylvinylsiloxy groups sealed at both ends of the molecular chain or dimethylsiloxane-methylvinylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends of the molecular chain.

[0028] In component (A2), in the formula, R 1 Each of these is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and examples include alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine, chlorine, and bromine. However, R 1 At least 1 mol% of the component is an alkenyl group having 2 to 12 carbon atoms. However, from the standpoint of designing the refractive index of the cured product according to the present invention to be less than 1.42, it is preferable that component (A2) substantially does not contain an aryl group or an aralkyl group.

[0029] Such (a2) components include tetrakis(dimethylvinylsiloxy)silane, hexa(dimethylvinylsiloxy)disiloxane, and organopolysiloxane resins represented by the following average unit formula: (ViMe2SiO 1 / 2 ) 0.1 (Me3SiO 1 / 2 ) 0.4 (SiO 4 / 2 ) 0.5 (ViMe2SiO 1 / 2 ) 0.1(Me3SiO 1 / 2 ) 0.5 (SiO 4 / 2 ) 0.4 (ViMe2SiO 1 / 2 ) 0.05 (Me3SiO 1 / 2 ) 0.55 (SiO 4 / 2 ) 0.4 (ViMe2SiO 1 / 2 ) 0.046 (Me3SiO 1 / 2 ) 0.394 (SiO 4 / 2 ) 0.56 This is an example. In the above formula, Me is a methyl group and Vi is a vinyl group.

[0030] The use of component (A2) is optional, and its content is in the range of 0 to 10.0% by mass relative to the solid content of the photocurable silicone composition, preferably in the range of 0 to 5.0% by mass. Here, the solid content refers to the sum of the components that form non-volatile solids through the curing reaction, and particularly includes components (A) to (D) and optional non-volatile components that constitute this composition.

[0031] Particularly preferred as component (A) is (A1) a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain, and especially preferred is (A1-1) a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain, and optionally having alkenyl groups with 2 to 12 carbon atoms in the side chain portion. Such component (A) can impart elongation and flexibility to the resulting cured product and achieve excellent mechanical strength.

[0032] Furthermore, a portion of component (A) may be the aforementioned component (A2), and having T units or Q units may improve the mechanical strength of the cured product, particularly hardness and toughness. On the other hand, if the content of component (A2) is high, the curing rate of the composition after irradiation with high-energy rays may slow down. Therefore, from the viewpoint of maintaining a practical curing rate, component (A) may consist only of component (A1) or component (A1-1), and is preferable. In addition, to satisfy the required properties such as hardness, component (A1) and component (A2) may be used in combination as component (A) in a mass ratio such as 100:0 to 80:20, thereby improving the mechanical strength of the resulting cured product while maintaining a practical curing rate.

[0033] Furthermore, the viscosity of component (A) at 25°C (or the overall viscosity in the case of a mixture) is not limited, but is preferably 100,000 mPa·s or less, within the range of 100 to 100,000 mPa·s, within the range of 100 to 50,000 mPa·s, or within the range of 100 to 10,000 mPa·s. This is because if the viscosity of component (A), particularly component (a1), is above the lower limit of the above range, the mechanical properties of the resulting cured product are improved, while if it is below the upper limit of the above range, the handling workability of the resulting composition is improved.

[0034] Component (B) is a compound having at least two mercapto groups in one molecule, and is a component for curing the composition by reacting with the alkenyl group in component (A) under irradiation with high-energy rays such as ultraviolet light. Preferred embodiments of component (B) are (B1) a linear organopolysiloxane having at least two mercapto groups in the side chain portion of its molecular chain, or (B2) an organic compound containing a mercapto group but not containing a silicon atom. Furthermore, from the viewpoint of designing the refractive index of the cured product according to the present invention to be less than 1.42, it is preferable that component (B) substantially does not contain aryl groups or aralkyl groups. Components (B1) and (B2) will be described in detail below.

[0035] (B1) A linear organopolysiloxane having at least two mercapto groups in the side chain region of its molecular chain: In component (B1), mercaptoalkyl groups are common as mercapto group-containing organic groups, with 3-mercaptopropyl, 4-mercaptobutyl, and 6-mercaptohexyl groups being examples. In addition, in component (B1), groups other than mercaptoalkyl groups that bond to silicon atoms include C1-C1 alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl groups; C6-C12 aryl groups such as phenyl, tolyl, and xylyl groups; C7-C12 aralkyl groups such as benzyl and phenethyl groups; and halogen-substituted C1-C12 alkyl groups such as 3-chloropropyl and 3,3,3-trifluoropropyl groups. From the viewpoint of economy and heat resistance, methyl groups are preferred. Furthermore, the silicon atoms in component (B1) may have small amounts of alkoxy groups or hydroxyl groups attached to them, such as methoxy groups, ethoxy groups, n-propoxy groups, i-propoxy groups, n-butoxy groups, sec-butoxy groups, and tert-butoxy groups.

[0036] The viscosity of component (B1) at 25°C is in the range of 5 to 1,000 mPa·s, preferably in the range of 5 to 500 mPa·s or 10 to 500 mPa·s. This is because if the viscosity of component (B1) is above the lower limit of the above range, the mechanical properties of the resulting cured product are improved, while if it is below the upper limit of the above range, the transparency and coatability of the resulting composition are improved.

[0037] Preferably, such a (B1) component is (B11) general formula: R3SiO(R2SiO) n SiR3 Linear organopolysiloxanes represented by and / or (B12) average unit formula: (R3SiO 1 / 2 ) a (R2SiO 2 / 2 ) b (RSiO 3 / 2 ) c (SiO 4 / 2 ) d Examples include branched-chain organopolysiloxanes represented by [formula].

[0038] In the formula, R is the same or different mercaptoalkyl group or a monovalent organic group having 1 to 12 carbon atoms that does not have an aliphatic unsaturated bond. Examples of this mercaptoalkyl group are the same groups as described above. Examples of monovalent hydrocarbon groups that do not have an aliphatic unsaturated bond are the same as described above, alkyl groups having 1 to 12 carbon atoms, aryl groups having 6 to 12 carbon atoms, aralkyl groups having 7 to 12 carbon atoms, and halogen-substituted alkyl groups having 1 to 12 carbon atoms. However, at least two of the total R are the mercaptoalkyl groups.

[0039] Furthermore, in the formula, n is an integer of 1 or more such that the viscosity of (B11) at 25°C is between 5 and 1,000 mPa·s.

[0040] Furthermore, in the formula, a, b, c, and d are each numbers between 0 and 1, and the sum of a, b, c, and d is 1. However, c or d can be a number greater than 0.

[0041] The component (B) according to the present invention is particularly preferably (B1-1) a linear organopolysiloxane having at least two mercapto groups only in the side chain portion of its molecular chain. More specifically, the following general formula: Me3SiO(Me2SiO) n1 (MeThiSiO) n2 SiMe3 Examples include one or a mixture of two or more organopolysiloxanes represented by the formula. In the formula, Me and Thi represent a methyl group and a 3-mercaptopropyl group, respectively, n1 is an integer of 1 or more such that the viscosity at 25°C is in the range of 5 to 1,000 mPa·s, and n2 is an integer of 2 or more such that the viscosity at 25°C is in the range of 5 to 1,000 mPa·s.

[0042] As the (B12) component, one or a mixture of two or more kinds of organopolysiloxanes represented by the following average unit formula is exemplified. In the formula, Me and Thi represent a methyl group and a 3-mercaptopropyl group, respectively, and a', b’, b’’, c’, and d’ are numbers from 0 to 1 (excluding 0), provided that the sum of a', b’, b’’, c’, and d’ is 1. (Me3SiO 1 / 2 ) a’ (Me2SiO 2 / 2 ) b’ (MeThiSiO 2 / 2 ) b’’ (MeSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeThiSiO 2 / 2 ) b’ (MeSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeThiSiO 2 / 2 ) b’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (Me2SiO 2 / 2 ) b’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (ThiSiO 3 / 2 ) c’ (Me2SiO 2 / 2 ) b’ (MeThiSiO 2 / 2 ) b’’ (MeSiO 3 / 2 ) c’ (MeThiSiO 2 / 2 ) b’ (MeSiO 3 / 2 ) c’ (Me2SiO 2 / 2 ) b’(ThiSiO 3 / 2 ) c’ (Me2SiO 2 / 2 ) b’ (MeThiSiO 2 / 2 ) b’’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeThiSiO 2 / 2 ) b’ (SiO 4 / 2 ) d’

[0043] (B2) An organic compound containing a mercapto group and not containing a silicon atom It is not particularly limited as long as it has at least two mercapto groups in one molecule, and examples include ester compounds of mercapto carboxylic acids and polyhydric alcohols such as trimethylolpropane-tris(3-mercaptopropionate), trimethylolpropane-tris(3-mercaptobutyrate), trimethylolethane-tris(3-mercaptobutyrate), pentaerythritol-tetrakis(3-mercaptopropionate), tetraethylene glycol-bis(3-mercaptopropionate), dipentaerythritol-hexakis(3-mercaptopropionate), pentaerythritol-tetrakis(3-mercaptobutyrate), 1,4-bis(3-mercaptobutyryloxy)butane; aliphatic or aromatic thiol compounds such as ethanedithiol, propanedithiol, hexamethylenedithiol, decamethylenedithiol, 3,6-dioxa-1,8-octanedithiol, 1,4-benzenedithiol, toluene-3,4-dithiol, xylylenedithiol; and others, 1,3,5-tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, 1,3,5-tris[(3-mercaptobutyryloxy)-ethyl]-isocyanurate, and mixtures of two or more of these are exemplified.

[0044] The molecular weight of the mercapto-containing compound is not particularly limited, but is preferably in the range of 100 to 2,000, 100 to 1,500, or 100 to 1,000. This is because if the molecular weight is above the lower limit of the above range, the volatility of the mercapto-containing compound itself decreases, reducing odor problems, while if it is below the upper limit of the above range, the solubility in component (A) improves.

[0045] Component (B) can be one or more selected from the above-mentioned components (B1) and (B2), or a mixture thereof. However, from the viewpoint of designing an optical adhesive or optical tack suitable for low refractive index optical transparent resin (OCR) applications, it is preferable that component (B) includes at least component (B1), a linear organopolysiloxane having at least two mercapto groups in the side chain portion of its molecular chain. From the viewpoint of improving the adhesion and adhesive strength of the resulting cured product to difficult-to-adhere substrates, it is more preferable that component (B) is (B1-1), a linear organopolysiloxane having at least two mercapto groups only in the side chain portion of its molecular chain. On the other hand, from the viewpoint of efficiently designing and manufacturing a uniform photocurable silicone composition, components (B1) and (B2) may be used in combination.

[0046] The content of component (B) may be in the range of 0.5 moles to 4 moles of mercapto groups in component (B) per mole of the total amount of aliphatic unsaturated carbon-carbon bonds, specifically alkenyl groups, in component (A), preferably in the range of 0.75 moles to 2 moles, and particularly preferably in the range of 0.75 moles to 1.5 moles. This is because if the content of component (B) is above the lower limit of the above range, the resulting composition will harden sufficiently and, when used in combination with component (D) described later, will exhibit practically sufficient adhesive strength even to substrates that are difficult to adhere to. On the other hand, if the content of component (B) is below the upper limit of the above range, there is the advantage that the mechanical properties of the resulting cured product tend to improve. The ratio of the amount of substance (number of moles) of mercapto groups in component (B) to 1 mole of aliphatic unsaturated carbon-carbon bonds in component (A) will be simply referred to as the "SH / Vi ratio" below.

[0047] Component (C) is a photoradical initiator that promotes the curing of the composition. Examples of component (C) include α-hydroxyketone initiators, benzyldimethylketal initiators, phosphine oxide initiators, etc. Specifically, 1-hydroxycyclohexylphenyl ketone (BASF trade name Irgacure 184), 2-hydroxy-2-methyl-1-phenylpropanone (BASF trade name Darocur 1173), α,α-dimethoxy-α-phenylacetophenone (BASF trade name Irgacure 651), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (BASF trade name Darocur TPO), ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (BASF trade name Irgacure Examples include TPO-L), a 50 / 50 (by weight) mixture of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenylpropanone (BASF trade name Darocur 4265), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BASF trade name Irgacure 819), and a mixture of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BASF trade name Irgacure 2100).

[0048] The content of component (C) is in the range of 0.01 to 3.0 parts by mass, preferably in the range of 0.05 to 1.0 parts by mass, or 0.05 to 0.5 parts by mass, relative to 100 parts by mass of the total of components (A) to (D). This is because if the content of component (C) is above the lower limit of the above range, the resulting composition will have good curability, while if it is below the upper limit of the above range, the resulting cured product will have good heat resistance and light resistance.

[0049] Component (D) contains, in a mass ratio of 1:9 to 9:1, an organosilicon compound having a boiling point of 100°C or higher at 1 atmosphere and containing at least one nitrogen atom and an alkoxysilyl group in its molecule, and (d2) an organosilicon compound having at least one trialkoxysilyl group in its molecule, lacking a nitrogen atom, and containing 1 to 3 silicon atoms. This component acts as an adhesion promoter to improve the adhesion and adhesive strength of the photocurable silicone composition according to the present invention to difficult-to-adhere substrates. If the above two components are not used in combination, and a single adhesion-improving component or a combination of adhesion-improving components that do not meet the above requirements is used instead of component (D), it may not be possible to obtain the technical effects intended by the present invention and a photocurable silicone composition suitable for low refractive index optical transparent resin (OCR) applications, and in particular, the adhesion and adhesive strength to difficult-to-adhere substrates may be insufficient. Furthermore, if component (d1) is used alone, not only will its action as an adhesion promoter be insufficient, but the cured product may become cloudy or discolored, impairing its transparency. In particular, if the transparency decreases, the photocurable silicone composition according to the present invention may not be applicable to optical applications.

[0050] Examples of alkoxysilyl groups in component (D) include trimethoxysilyl, methyldimethoxysilyl, triethoxysilyl, methyldiethoxysilyl, and triisopropoxysilyl groups, which are common to components (d1) and (d2).

[0051] Component (d1) is the first adhesion-enhancing component, and is an organosilicon compound having a boiling point of 100°C or higher at 1 atmosphere and containing at least one nitrogen atom and an alkoxysilyl group in its molecule. Since such component (d1) is substantially non-volatile, it does not volatilize during storage of the composition or during photocuring, thus preventing a decrease in adhesion-enhancing properties. Furthermore, because it contains a condensation-reactive alkoxysilyl group and a polar nitrogen atom in its molecule, when used in combination with component (d2), it can significantly improve adhesion and adhesive strength to difficult-to-bond substrates.

[0052] The alkoxysilyl group in component (d1) is preferably a trialkoxysilyl group, and industrially, it is particularly preferably a trimethoxysilyl group or a triethoxysilyl group. Furthermore, the nitrogen atom in component (d1) may, and is preferred, originate from a cyclic structure formed by cyclization via an alcohol exchange reaction when reacting an alkoxysilane having an amino group-containing organic group with an alkoxysilane having an epoxy group-containing organic group, as exemplified by an alkylamino group bonded to a silicon atom or a carbasilatran derivative.

[0053] More specifically, preferably, the (d1) component constituting the (D) component is one or more organosilicon compounds selected from (d1-1) organosilicon compounds having a carbasilatran structure in the molecule and (d1-2) aminoalkyltrialkoxysilanes.

[0054] (d1-1) Organosilicon compounds having a carbasilatran structure within the molecule can be obtained by reacting an alkoxysilane having an amino group-containing organic group with an alkoxysilane having an epoxy group-containing organic group, particularly by cyclization via an alcohol exchange reaction, as described in Japanese Patent Publication No. 10-195085. Examples of such carbasilatran derivatives include carbasilatran derivatives having a silicon atom-bonded alkoxy group or a silicon atom-bonded alkenyl group in one molecule, represented by the following structure. [ka] (In the formula, Rc is a group selected from a methoxy group, an ethoxy group, a vinyl group, an allyl group, and a hexenyl group.)

[0055] Examples of (d1-2) aminoalkyltrialkoxysilanes include aminomethyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)aminomethyltributoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-anilinopropyltriethoxysilane. Industrially, 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane are preferred.

[0056] Component (d2) is an organosilicon compound having at least one trialkoxysilyl group in its molecule, lacking a nitrogen atom, and containing 1 to 3 silicon atoms, and is distinguished from component (d1) by the presence or absence of a nitrogen-containing structure. By using such a component in combination with component (d1) in a certain quantitative ratio, the adhesion and adhesive strength to difficult-to-bond substrates are significantly improved.

[0057] Component (d2) has one or more trialkoxysilyl groups in its molecule and is therefore highly reactive in condensation reactions by hydrolysis. In particular, from the viewpoint of improving adhesion to difficult-to-bond substrates when used in combination with component (d1), component (d2) may preferably have two or more trialkoxysilyl groups in its molecule, or it may have one or more trialkoxysilyl groups and other reactive functional groups (excluding reactive functional groups containing nitrogen atoms), and it is especially preferable that it has a trialkoxysilyl group and an epoxy group in its molecule.

[0058] More specifically, component (d2) may be one or more organosilicon compounds selected from (d2-1) organosilicon compounds having two or more trialkoxysilyl groups in one molecule, and (d2-2) organosilicon compounds having a trialkoxysilyl group and an epoxy group in one molecule.

[0059] Specifically, (d2-1) organosilicon compounds having two or more trialkoxysilyl groups in one molecule include 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(methyldimethoxysilyl)ethane, 1,2-bis(methyldiethoxysilyl)ethane, 1,3-bis(trimethoxysilyl)propane, 1,4-bis(trimethoxysilyl)butane, 1,4-bis(triethoxysilyl)butane, 1-methyldimethoxysilyl-4-trimethoxysilylbutane, and 1-methyldiethoxysilyl-4-triethoxysilyl Sisilylbutane, 1,4-bis(methyldimethoxysilyl)butane, 1,4-bis(methyldiethoxysilyl)butane, 1,5-bis(trimethoxysilyl)pentane, 1,5-bis(triethoxysilyl)pentane, 1,4-bis(trimethoxysilyl)pentane, 1,4-bis(triethoxysilyl)pentane, 1-methyldimethoxysilyl-5-trimethoxysilylpentane, 1-methyldiethoxysilyl-5-triethoxysilylpentane, 1,5-bis(methyldimethoxysilyl)pentane, 1,5-bis(methyldiethoxysilyl)pentane, 1,6-Bis(trimethoxysilyl)hexane, 1,6-Bis(triethoxysilyl)hexane, 1,4-Bis(trimethoxysilyl)hexane, 1,5-Bis(trimethoxysilyl)hexane, 2,5-Bis(trimethoxysilyl)hexane, 1-Methyldimethoxysilyl-6-trimethoxysilylhexane, 1-Phenyldiethoxysilyl-6-triethoxysilylhexane, 1,6-Bis(methyldimethoxysilyl)hexane, 1,7-Bis(trimethoxysilyl)heptane, 2,5-Bis(trimethoxysilyl)heptane, 2,6-Bis(trimethoxysilyl) Alkane compounds having trialkoxysilyl groups at both ends of the molecular chain, such as xysilyl)heptane, 1,8-bis(trimethoxysilyl)octane, 1,8-bis(methyldimethoxysilyl)octane, 2,5-bis(trimethoxysilyl)octane, 2,7-bis(trimethoxysilyl)octane, 1,9-bis(trimethoxysilyl)nonane, 2,7-bis(trimethoxysilyl)nonane, 1,10-bis(trimethoxysilyl)decane, and 3,8-bis(trimethoxysilyl)decane, 1,3-bis{2-(trimethoxysilyl)ethyl}-1,1,3,Examples of disiloxane compounds having trialkoxysilyl groups at both ends of the molecular chain include 3-tetramethyldisiloxane, 1,3-bis{2-(methyldimethoxysilyl)ethyl}-1,1,3,3-tetramethyldisiloxane, 1,3-bis{2-(triethoxysilyl)ethyl}-1,1,3,3-tetramethyldisiloxane, 1,3-bis{2-(methyldiethoxysilyl)ethyl}-1,1,3,3-tetramethyldisiloxane, 1,3-bis{6-(trimethoxysilyl)hexyl}-1,1,3,3-tetramethyldisiloxane, and 1,3-bis{6-(triethoxysilyl)hexyl}-1,1,3,3-tetramethyldisiloxane. Furthermore, examples of organic compounds having three alkoxysilyl groups include trisiloxane compounds having three alkoxysilyl groups, such as 1,3,5-tris{2-(trimethoxysilyl)ethyl}-1,1,3,5,5-pentamethyltrisiloxane, 1,3,5-tris{2-(methyldimethoxysilyl)ethyl}-1,1,3,5,5-tetramethyldisiloxane, 1,3,5-tris{2-(triethoxysilyl)ethyl}-1,1,3,5,5-tetramethyldisiloxane, and 1,3,5-tris{6-(trimethoxysilyl)hexyl}-1,1,3,5,5-tetramethyldisiloxane. An example of its structure is, (MeO)3SiCH2CH2(Me)2Si-O-SiMe(CH2CH2Si(OMe)3)-O-Si(Me)2CH2CH2Si(OMe)3 (In the above formula, Me is a methyl group.)

[0060] In particular, component (d2) may and is preferred to be a disilaalkane compound having trialkoxysilyl groups at both ends of the (d2-1-2) molecular chain.

[0061] Similarly, (d2-2) organosilicon compounds having a trialkoxysilyl group and an epoxy group in one molecule include, specifically, 3-glycidoxyalkyltrialkoxysilanes such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane; and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0062] In particular, the (d2) component is preferably the (d2-2-2)3-glycidoxyalkyltrialkoxysilane described above.

[0063] The (D) component, which consists of the aforementioned (d1) and (d2) components, may consist of one or more components, and it is preferable to select them from the compounds corresponding to the preferred forms thereof. Furthermore, in order to improve adhesion and adhesive strength to substrates that are difficult to adhere to, the (D) component of the present invention must be used in a mass ratio of 1:9 to 9:1 between the (d1) and (d2) components, and these components may be used in a mass ratio of 2:8 to 8:2, and it is more preferable to use them in a mass ratio of 3:7 to 7:3 or 6:4 to 4:6. In the photocurable silicone composition according to the present invention, a particularly preferred (D) component is one or more of the preferred components as the aforementioned (d1) and (d2) components, in a mass ratio in the range of 6:4 to 4:6 (including cases where both are used in approximately the same mass ratio).

[0064] To achieve the technical effects of the present invention, particularly to realize a photocurable silicone composition that provides a cured product with the curing speed required for low refractive index optical transparent resins (OCRs), a low refractive index in the visible light region, and excellent adhesion and adhesive strength to difficult-to-adhere substrates, it is essential to use a specific component (D) in combination with the aforementioned components (A), (B), and (C), and it is preferable that the SH / Vi ratio of components (A) and (B) in the composition satisfies a predetermined range. Simply adding an adhesion promoter may result in reduced adhesive strength due to curing failure in difficult-to-adhere substrates, and if an adhesion promoter other than the above-mentioned component (D) is used, sufficient adhesive strength may not be obtained, or compatibility with components (A), (B), etc. may decrease, the transparency of the resulting cured product may deteriorate, or practical performance as an OCR or adhesive for optical components may not be achieved.

[0065] The content of component (D) can be selected as appropriate, but it is preferably in the range of 0.01 to 5% by mass, more preferably in the range of 0.01 to 2.5% by mass or 0.01 to 1.0% by mass, relative to the total amount of nonvolatile components of the photocurable silicone composition. If the amount of component (D) is below the lower limit, the improvement of adhesion and adhesive strength to difficult-to-adhere substrates may be insufficient, and if it exceeds the upper limit, it may affect the curing characteristics and physical properties such as the transparency and hardness / penetration of the cured product.

[0066] [Optional ingredients] This composition contains the above-mentioned components (A) to (D), and may also contain the following optional components as long as they do not impair the technical effects of the present invention. Furthermore, from the standpoint of achieving a low refractive index of the cured product, it is preferable to avoid using large amounts of raw material components that contain aryl groups or aralkyl groups and increase the refractive index of the cured product.

[0067] This composition may contain (E) a hindered phenol compound to maintain good storage stability of the composition and to impart heat resistance to the cured product. Examples of such (E) components include 2,6-bis(hydroxymethyl)-p-cresol, 2,6-ditterbutyl-4-methylphenol, 2,6-ditterbutyl-4-hydroxymethylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 2,4-dimethyl-6-(1-methylpentade Examples include sil(phenol), diethyl[{3,5-bis(1,1-di-tert-butyl-4-hydroxyphenyl)methyl}phosphonate, 3,3',3”,5,5',5”-hexane-tert-butyl-4-a,a',a”-(mesitylene-2,4,6-tolyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], and hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0068] The content of component (E) is in the range of 0 to 1 part by mass, preferably in the range of 0.01 to 1 part by mass, or 0.01 to 0.5 parts by mass, when the total amount of the photocurable silicone composition is 100 parts by mass. This is because if the content of component (E) is above the lower limit of the above range, the storage stability of the resulting composition is good, while if it is below the upper limit of the above range, the heat resistance and light resistance of the resulting cured product are good.

[0069] Furthermore, the composition may contain (F), an organic compound having one aliphatic unsaturated bond and no siloxane bond per molecule, in order to reduce the crosslinking density of the resulting cured product and, as a result, improve its mechanical properties or tackiness. Such a (F) component is preferably an organic compound with a boiling point of, for example, 200°C or higher at one atmosphere, as it exhibits good compatibility with components (A) to (D) and has good storage stability. Examples of such a (F) component include linear aliphatic olefins such as dodecene, tetradecene, hexadecene, and octadecene; cyclic aliphatic olefins such as 4-phenyl-1-cyclohexene; and unsaturated alcohols such as 9-decen-1-ol, oleyl alcohol, and terpene-4-ol.

[0070] The content of component (F) is not limited, but from the viewpoint of the curability and mechanical properties of the photocurable silicone composition according to the present invention, it is preferably in the range of 0 to 10 parts by mass or 0 to 5 parts by mass when the total photocurable silicone composition is 100 parts by mass.

[0071] Furthermore, the composition may optionally contain metal oxide fine powders such as fumed silica and wet silica; alkenyl group-containing low molecular weight siloxanes as reactive diluents such as 1,1,3,3-tetramethyl-1,3-divinyldisiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; and conventionally known additives such as heat resistance improvers such as N-nitrosophenylhydroxylamine aluminum salts, as long as the objectives of the present invention are not impaired. Furthermore, the composition according to the present invention may optionally contain additives selected from leveling agents, silane coupling agents not included in the adhesion-imparting agents listed above, dyes, pigments, flame retardants, solvents, organic resin fine powders such as polymethacrylate, phosphors, ultraviolet absorbers, antioxidants, polymerization inhibitors, insulating fillers, and functional fillers such as thermal conductive fillers. In addition, the composition according to the present invention may optionally contain thixotropic agents, especially when used as a potting agent or sealing material.

[0072] This composition may preferably contain a non-reactive organopolysiloxane as a plasticizer or viscosity modifier for the cured product. Specifically, examples include linear or branched organopolysiloxanes or organopolysiloxane resins that do not contain functional groups such as alkenyl groups. Specifically, polydimethylsiloxane having a trimethylsiloxy group terminus is preferred. In particular, using this component may allow the hardness (penetration) and fluidity (viscosity) in the cured or semi-cured state to be adjusted to a desired range.

[0073] The viscosity of this composition at 25°C is not limited, but is preferably 100,000 mPa·s or less, within the range of 100 to 100,000 mPa·s, or within the range of 100 to 30,000 mPa·s. This is because if the viscosity of this composition is above the lower limit of the above range, the mechanical properties of the resulting cured product are good, while if it is below the upper limit of the above range, the resulting composition is easy to handle and less likely to entrain air in the cured product. These viscosities can be measured using a rotational viscometer.

[0074] This composition can be prepared by uniformly mixing components (A) to (D), and optionally any other components. The composition can be prepared using various stirrers or kneaders at room temperature, or under heating if necessary. There are no restrictions on the order in which the components are added; they can be mixed in any order. However, to avoid affecting the curing process during preparation, it is recommended to prepare the composition in a location free from light below 450 nm, or in a location with as little light exposure as possible.

[0075] Furthermore, this composition can be a one-component composition in which all components are blended in the same container, or it can be a two-component composition that is mixed at the time of use, taking storage stability into consideration.

[0076] This composition has the property of photocuring by irradiation with visible light to high-energy rays. The light used to cure this composition is preferably high-energy rays, such as ultraviolet rays, gamma rays, X-rays, alpha rays, and electron beams. In particular, ultraviolet rays, X-rays, and electron beams irradiated from commercially available electron beam irradiation devices are preferred, and among these, ultraviolet rays are preferred from the viewpoint of the efficiency of the photocuring reaction, with wavelengths in the range of 250 to 450 nm, preferably 400 nm or less, and particularly ultraviolet rays in the range of 280 to 380 nm being preferred from the viewpoint of industrial use. Furthermore, the irradiation dose of high-energy rays (especially ultraviolet rays) varies depending on the type and amount of component (C) used in this composition and the SH / Vi ratio of the composition, but in the case of ultraviolet rays, it is preferable that the integrated irradiation dose at a wavelength of 365 nm is in the range of 100 mJ / cm2 to 10 J / cm2.

[0077] [Use of this composition] This composition is useful as a potting agent, sealant, adhesive, or bonding agent for various applications, and is particularly useful as an optical sealant, optical adhesive, or bonding agent for displays. This composition hardens even at low temperatures when exposed to high-energy rays such as ultraviolet light. The cured product exhibits high elongation, excellent flexibility and adhesive strength, and is less prone to clouding. Therefore, it is suitable as a material for forming an intermediate layer between the image display area and the protective area of ​​a display. Such applications are sometimes referred to as optically clear resins (OCR). Furthermore, it hardens by light irradiation alone without the need for a heating process and exhibits excellent adhesion and adhesive strength even to difficult-to-bond components. This shortens the bonding process between components, making it suitable for energy-saving processes and improving industrial production efficiency.

[0078] This composition is not limited to liquid crystal displays, but can be used in the entire field of display displays, such as organic EL displays, electronic paper displays, and plasma displays.

[0079] This composition can be cured without a heating process, making it applicable to coating substrates with poor heat resistance. Typical substrates include glass, synthetic resin films / sheets, transparent electrode coatings, and other transparent substrates.

[0080] The coating method for this composition is not particularly limited, and examples include dispensing, gravure coating, microgravure coating, slit coating, slot die coating, screen printing, stencil printing, and comma coating. When this composition is used as an OCR for bonding components such as optical displays, optionally, a resin component, so-called dam material, can be formed in a frame shape on the display module, or the composition can be applied to the inside without a dam, and the front panel can be bonded on top of it. Alternatively, depending on the injection or placement area, the curable silicone composition according to the present invention may be injected and filled using a dispenser such as a syringe or cartridge, and the OCR may be placed. These processes can be carried out in the same manner as the OCR placement or injection process disclosed in, for example, Patent Document 1 (International Patent Publication WO2020 / 080348, pamphlet), and are preferred.

[0081] The composition of the present invention can be cured by irradiation with ultraviolet light. Suitable ultraviolet light sources include high-pressure mercury lamps, medium-pressure mercury lamps, Xe-Hg lamps, deep UV lamps, and UV-LED light sources. In particular, irradiation with ultraviolet light at wavelengths of 280 to 405 nm, preferably 300 to 405 nm, is preferred, and a light source having multiple emission bands may be used. Furthermore, when curing the composition of the present invention, ultraviolet light may be irradiated directly onto the arranged composition, or through a translucent member to irradiate with ultraviolet light, or deep curing may be performed by irradiating with ultraviolet light from the gaps between members. The irradiation method can be appropriately selected depending on the bonding and curing process.

[0082] The amount of ultraviolet light irradiated to cure the composition of the present invention can be appropriately designed according to the amount of coating, coating thickness, curing process, desired cycle time, etc., but the cumulative light amount is 100 mJ / cm². 2~20,000 mJ / cm 2 More preferably 1,000 mJ / cm² 2 ~15,000 mJ / cm 2 More preferably 2,000 mJ / cm² 2 ~10,000 mJ / cm 2 That is the case.

[0083] [Cured product] The cured product of the present invention (hereinafter sometimes referred to as "the cured product") is characterized by being obtained by curing the above-mentioned UV-delayed curing silicone composition.

[0084] As described above, this composition is suitably used as an optically clear resin ("OCR (Optically Clear Resin)") having functions such as protection, sealing, and adhesion. It is preferable that it hardens to form an elastomer (elastic) resin member or a gel-like resin member. In the case of the hardened silicone resin member, at 25°C, its penetration degree (hereinafter simply referred to as "penetration degree") as defined in JIS K2220 can be designed as desired within the range of 5 to 70, and may be in the range of 5 to 20, 20 to 50, or 50 to 70. The curable silicone composition of the present invention has the advantage that even cured products with relatively low penetration degrees can be easily designed. Such cured products (=silicone resin members) have appropriate flexibility and durability, and excellent adhesion / tightness retention and followability between members. Therefore, when used as an interlayer adhesive or gap sealant composition for display devices, a strong adhesive structure can be formed between optical and electronic components, and a reliable sealing effect can be achieved as needed.

[0085] The photocurable silicone composition according to the present invention is characterized by forming a cured product having a relatively low refractive index, with a refractive index of less than 1.42 at 25°C and a wavelength of 365 nm in the visible light region, upon curing. The refractive index of the cured product is preferably less than 1.42, 1.415 or less, and preferably in the range of 1.410 or less, 1.390 to 1.410, or 1.395 to 1.410. In addition, such a refractive index of the cured product can be achieved by selecting components (A) to (D) above, where each component is substantially free of aryl groups or aralkyl groups, and the content of aryl groups or aralkyl groups in each component is preferably 2% by mass or less, 1% by mass or less, and below the detection limit in the raw materials to 0.5% by mass or less. In particular, if the content of aryl groups such as phenyl groups or aralkyl groups such as benzyl groups in each raw material component is high, the cured product obtained by photocuring the composition according to the present invention may exhibit a refractive index greater than 1.42.

[0086] Preferably, the cured product of the present invention is light-transmitting, and more preferably transparent. Light-transmitting, and especially transparent, cured products can be suitably used for optical applications. Preferably, the cured product of the present invention has a parallel light transmittance of 90% or more at 25°C with an optical path length of 6 mm, as measured in accordance with JIS K 7105, and a parallel light transmittance of 99% or more at 200°C compared to the parallel light transmittance at 25°C.

[0087] The cured product of the present invention can have adhesive properties (pressure-sensitive adhesive properties), and more specifically, it can be used as an adhesive member or pressure-sensitive adhesive member with a certain shear adhesive strength. The adhesive strength or tackiness of the cured product is not particularly limited, but it is preferable that the shear adhesive strength of the cured product layer, measured by the method specified in JIS K 6850, when a 200 μm thick cured product layer made of the cured reactive silicone composition of the present invention is formed between two glass plates, is 0.4 MPa or higher. The peeling mode of the cured product of the present invention from the adherend may be interfacial peeling or cohesive failure of the adhesive layer (permanent adhesion). In particular, by selecting components (A) to (D) of the composition of the present invention, the adhesive strength and adhesion mode to the adherend of the adhesive layer made of the cured product can be designed as desired, and in particular, it is possible to adjust the adhesion to the adherend and adhesive strength, and it is also easy to design an adhesive layer that is less prone to cohesive failure when peeled from the adherend.

[0088] The cured product of the present invention can have a certain degree of elasticity or flexibility. Therefore, the cured product according to the present invention may be used as an elastic adhesive member.

[0089] As for the method of forming the cured product, for example, the composition can be applied to a film-like substrate, a tape-like substrate, or a sheet-like substrate, and then cured by irradiation with ultraviolet light (preferably with the above-mentioned light source and irradiation amount). Alternatively, the composition can be placed between two substrates first and cured to firmly bond the two substrates, or the composition can be smoothly applied to at least one surface of the substrates, the two substrates can be bonded together, and then cured by irradiation with ultraviolet light to firmly bond them. The film thickness of the cured product is not limited, but is preferably 1 to 100,000 μm, and more preferably 50 to 30,000 μm. When forming the cured product between components, as mentioned above, it is optional and preferable to either form a frame-shaped resin component, a so-called dam material, on the display module, or, without a dam, place the composition inside it, bond the front panel on top, and then cure it by irradiation with ultraviolet light from the side that transmits ultraviolet light. Such a curing process can be carried out in the same manner as, and is preferable to, the curing process after placement or injection of OCR disclosed in, for example, Patent Document 1 (International Patent Publication WO2020 / 080348).

[0090] [Laminated structure] The laminate according to the present invention is characterized by comprising a first optical member, a second optical member, and an adhesive layer made of the cured product disposed between these two optical members. Here, these optical members may be transparent or opaque, and one or both may be transparent depending on the desired structure and ultraviolet irradiation process. Suitable laminates, optical members used therein, and processes for forming such laminates are common to laminates disclosed in, for example, Patent Document 1 and International Patent Publication WO2020 / 080348 (hereinafter, "Patent Document 1, etc."), and some or all of the compositions and cured products used in the laminates disclosed in Patent Document 1, etc. can be replaced with the composition or cured product of the present invention, and can be referenced as suitable embodiments of the present invention. In that case, it goes without saying that the composition according to the present invention should be cured by ultraviolet irradiation in place of, or together with, the curing of the composition in Patent Document 1.

[0091] [Optical device] The optical device according to the present invention (hereinafter sometimes referred to as "the optical device") comprises a substrate, an optical element disposed on the substrate, and a cured product that seals at least a part of the optical element. Preferably, the optical device is an optoelectronic device. Suitable optical devices and their structures are common to optical devices disclosed in, for example, Patent Document 1, and some or all of the compositions and cured products used in various optical devices disclosed in Patent Document 1, etc., can be replaced with the composition or cured product of the present invention, and can be referenced as preferred embodiments of the present invention. Depending on the type of optical component, the substrate surface may be provided with irregularities or grooves, and a coating layer such as a hard coating may be provided on the surface of the component or substrate to be bonded. Furthermore, the type of substrate is not particularly limited and can be any of glass, metal, thermoplastic resin, etc. In particular, the photocurable silicone composition according to the present invention has excellent adhesion and adhesive strength between substrates / components having surfaces that are difficult to bond, thus providing the advantage of providing an optical device in which these components are firmly bonded.

[0092] [Optical display] The optical display according to the present invention (hereinafter sometimes referred to as "the optical display") comprises the above-mentioned laminate and preferably further comprises one or more image display panels, and may also comprise one or more touch panels. Suitable types and configurations of the optical display are common to optical displays disclosed in, for example, Patent Document 1, and some or all of the compositions and cured products used in the various optical displays disclosed in Patent Document 1 can be replaced with the compositions or cured products of the present invention and can be referred to as suitable embodiments of the present invention.

[0093] The photocurable silicone composition according to the present invention and the cured product obtained by photocuring the same can be used as a encapsulant layer, transparent resin layer, adhesive (layer), or adhesive (layer) in laminates such as known polarizers, optical components, and automotive components; and in optical displays such as (image) display devices, touch panels, large to small flat / curved surface displays, VR goggles, and head-mounted displays. It can be used to replace part or all of the adhesive layer of known laminates or optical displays. In this case, the thickness, application method, curing conditions, manufacturing process, etc. of the adhesive layer applied to known laminates or optical displays may be appropriately designed to reflect the photocurability, refractive index, transparency, adhesion, and adhesive strength of the composition according to the present invention. For example, the photocurable silicone composition according to the present invention and the cured product obtained by photocuring therefrom are published in Japanese Patent Publication No. 2022-533588, Japanese Unexamined Patent Publication No. 2019-015783, Japanese Unexamined Patent Publication No. 2024-068071, Japanese Patent Publication No. 2022-552505, Japanese Unexamined Patent Publication No. 2010-044220, Japanese Unexamined Patent Publication No. 2021-103209, International Publication WO2023 / 286315, Japanese Unexamined Patent Publication No. 2021-131567, International Publication 2014 / 038466, and International Publication 2015 / 129409. The present application expressly teaches the use of the compositions and cured products thereof in such known structures. The compositions may be used to replace some or all of the adhesive layers, tack layers, and transparent resin layers (including those functioning as adhesive and / or sealing layers; OCR) of various laminates or displays described in the brochure, Japanese Patent Publication No. 2018-005291, Japanese Patent Publication No. 2023-513863, brochure International Publication No. WO2018 / 179214, and Japanese Patent Publication No. 2024-016097. [Industrial applicability]

[0094] The curable silicone composition and its cured product of the present invention exhibit high transparency and excellent adhesive strength, making them suitable for use in optical displays and touch panels. Furthermore, because the reaction does not proceed until irradiated with ultraviolet light, and the reaction proceeds with a delay in areas not directly irradiated with ultraviolet light compared to the directly irradiated areas, it can be applied to a variety of processes. After curing, it exhibits sufficient adhesion not only to glass but also to difficult-to-bond substrates such as polarizing plates, making it useful as an adhesive or sealant for display devices such as optical displays (including touch panels) and optoelectronic devices (including Micro LEDs). Moreover, the composition of the present invention is expected to exhibit similar effects not only to surface-coated polarizing plates but also to substrates such as acrylic, which are materials similar to the surface coating material. Furthermore, the cured product according to the present invention has excellent heat resistance, cold resistance, and adhesive strength, as well as excellent transparency, making it extremely useful as an OCR layer or optical adhesive layer for display devices such as displays (particularly including, but not limited to, in-vehicle displays and displays in aircraft including curved surfaces). [Examples]

[0095] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, the measurements and evaluations in the examples were carried out as follows. The resulting cured product was confirmed to be transparent by visual inspection.

[0096] [Refractive index of hardened material] A 5mm thick curable silicone composition is filled into a petri dish and exposed to ultraviolet light at 1400mW / cm² using a V-LED UV irradiation device (manufactured by JATEC). 2 2000 mJ / cm 2 The material was cured by irradiation with ultraviolet light at a wavelength of 365 nm, and the refractive index of the cured material at 365 nm was measured using a digital refractometer (manufactured by Atago). The measurement was performed at 25°C.

[0097] [Viscosity of the composition] The photocurable silicone composition was placed on a rheometer (Anton Paar MCR301), and a 25mm diameter cone plate jig was used to set the gap to 0.05mm. The viscosity of the composition before UV irradiation was measured at a shear rate d(gamma) / dt = 10 / s.

[0098] [Penetration degree of hardened material] A photocurable silicone composition with a thickness of 10 mm or more is filled into a petri dish and exposed to ultraviolet light at 1300 mW / cm² using a UV-LED ultraviolet irradiation device (manufactured by JATEC). 2 4,000 mJ / cm² 2 The material was cured by irradiation with ultraviolet light at a wavelength of 365 nm, then cooled to 25°C, and the penetration at 25°C was measured using a penetration depth measuring device (RPM-201 manufactured by Rigosha).

[0099] [Appearance of the hardened material] The cured material was visually inspected, and its appearance, including transparency, was determined.

[0100] [Shear bonding strength and fracture mode of hardened material to glass / glass] Between two glass plates (Paltec float glass, 75mm long x 25mm wide x 2mm thick), the dimensions of the cured silicone material after hardening are 200mm. 2 A photocurable silicone composition is filled to a thickness of 200 μm, and then irradiated with UV-LED ultraviolet light at 1400 mW / cm² using a UV-LED ultraviolet irradiation device (manufactured by JATEC). 2 2000 mJ / cm 2 A test specimen was prepared by irradiating the hardened material with ultraviolet light at a wavelength of 365 nm and sandwiching it between two glass plates. A shear adhesion test was performed on this test specimen in accordance with the method specified in JIS K6850, and the shear adhesion strength of the hardened material was measured. The measurement was performed 3 days after the test specimen was prepared, and the sweeping speed was set to 100 mm / min. In the shear adhesion test, the fracture mode was classified as "AF" (=interfacial delamination) when delamination occurred at the interface between the hardened material and the glass, and as "CF" (=cohesive failure) when the hardened material itself was destroyed.

[0101] [Examples 1-5, Comparative Examples 1-5] A photocurable silicone composition was prepared by uniformly mixing the following components in the composition (parts by mass) shown in Table 1. In each structural formula, Me represents a methyl group and Vi represents a vinyl group.

[0102] <Ingredient (A)> A-1: Dimethylsiloxane polymer with dimethylvinylsiloxy groups sealed at both ends (viscosity = 12,000 mPa·s, vinyl group content = 0.14% by mass) A-2: Dimethylsiloxane-methyl(hexyl)siloxane copolymer with dimethylhexylsiloxy groups sealed at both ends (viscosity = 400 mPa·s, vinyl group content = 0.97% by mass) A-3: Dimethylsiloxane-diphenylsiloxane copolymer with dimethylvinylsiloxy groups sealed at both ends (viscosity = 4500 mPa·s, vinyl group content = 0.18% by mass) <Ingredient (B)> B-1: Dimethylmethyl(3-mercaptopropyl)siloxane copolymer with trimethylsiloxy groups sealed at both ends (viscosity = 130 mPa·s, mercapto group content = 4.0% by mass) B-2: Dimethylmethyl(3-mercaptopropyl)siloxane copolymer with trimethylsiloxy groups sealed at both ends (viscosity = 70 mPa·s, mercapto group content = 2.0% by mass) <Ingredient (C)> C-1:2-Hydroxy-2-methyl-1-phenyl-1-propanone (product name Omnirad 1173, manufactured by IGM Resins) <Ingredient (D)> D1-1: Silatran derivative shown in the following formula [ka] D1-2: Aminopropyltriethoxysilane D2-1: Glycidoxypropyltrimethoxysilane D2-2: 1,6-bis(trimethoxysilyl)hexane

[0103] Table 1 Composition of photocurable silicone composition (Examples) [Table 1]

[0104] [Summary] As shown in Examples 1 to 5 (Table 1), the cured products according to the present invention had a refractive index of less than 1.42 and excellent transparency in appearance. Furthermore, the shear adhesive strength of the cured products according to the present invention all exceeded 0.4 MPa, and their fracture mode was CF (cohesive failure) accompanied by the fracture of the cured product itself, achieving high adhesion and adhesive strength of the cured product to the substrate.

[0105] On the other hand, in comparative examples that did not use component (D) of the present invention, i.e., an adhesion promoter combining the two components, the technical effects of the present invention could not be achieved. Specifically, in the cured products that did not contain either component D1 or component D2 (Comparative Examples 1 and 4), and in Comparative Example 3 which contained only component D2, the shear adhesion strength to the substrate was extremely low, and sufficient adhesion and adhesive strength could not be achieved. Furthermore, in Comparative Example 2 which contained only component D1, the cured product had a semi-transparent appearance and insufficient transparency, making it unsuitable for use as an optical component. Furthermore, in Comparative Example 5 which contained component A3 containing a phenyl group, the refractive index increased, and it was not possible to obtain a cured product with a refractive index of less than 1.42.

Claims

1. (A) Organopolysiloxane having at least two alkenyl groups with 2 to 12 carbon atoms in one molecule, (B) A compound having at least two mercapto groups in one molecule, (C) Photoradical initiator, and A photocurable silicone composition comprising (D) (d1) an organosilicon compound having a boiling point of 100°C or higher at 1 atmosphere and containing at least one nitrogen atom and an alkoxysilyl group in its molecule, and (d2) an organosilicon compound having at least one trialkoxysilyl group in its molecule, not containing a nitrogen atom, and containing 1 to 3 silicon atoms, in a mass ratio of 1:9 to 9:1, wherein the refractive index of the cured product is less than 1.42 at 25°C and a wavelength of 365 nm.

2. The aforementioned component (A) includes (A1) a linear organopolysiloxane having alkenyl groups with 2 to 12 carbon atoms at both ends of its molecular chain, The photocurable silicone composition according to claim 1, characterized in that the (B) component comprises (B1) a linear organopolysiloxane having at least two mercapto groups in the side chain portion of its molecular chain.

3. The photocurable silicone composition according to claim 1, wherein it is a one-component composition and the viscosity of the composition before irradiation with high-energy rays at 25°C is 100,000 mPa·s or less.

4. The photocurable silicone composition according to claim 1, wherein the (d1) component is one or more organosilicon compounds selected from (d1-1) organosilicon compounds having a carbasilatran structure in the molecule and (d1-2) aminoalkyltrialkoxysilanes.

5. The photocurable silicone composition according to claim 1, wherein the (d2) component is one or more organosilicon compounds selected from (d2-1) organosilicon compounds having two or more trialkoxysilyl groups in one molecule, and (d2-2) organosilicon compounds having a trialkoxysilyl group and an epoxy group in one molecule.

6. The above-mentioned (d1) component has the following structural formula: (d1-1-1) 【Chemistry 1】 (In the formula, Rc is a group selected from a methoxy group, an ethoxy group, a vinyl group, an allyl group, and a hexenyl group.) The molecule represented by one or more carbasilatran derivatives having a silicon atom-bonded alkoxy group or a silicon atom-bonded alkenyl group, and one or more organosilicon compounds selected from (d1-2)aminoalkyltrialkoxysilanes, The photocurable silicone composition according to claim 1, wherein the (d2) component is one or more organosilicon compounds selected from disilaalkane compounds having trialkoxysilyl groups at both ends of the (d2-1-2) molecular chain and (d2-2-2)3-glycidoxyalkyltrialkoxysilane.

7. The photocurable silicone composition according to claim 1, wherein the content of component (D) is in the range of 0.01 to 5% by mass relative to the total amount of nonvolatile components of the photocurable silicone composition.

8. A photocurable silicone composition according to any one of claims 1 to 7, which is an optical adhesive or optical tack.

9. A cured product of a photocurable silicone composition according to any one of claims 1 to 7.

10. The cured product according to claim 9, wherein the degree of penetration at 25°C is in the range of 5 to 70.

11. The cured product according to claim 9, wherein a 200 μm thick cured layer made of a cured product of a photocurable silicone composition according to any one of claims 1 to 7 is formed between two glass plates, and the shear adhesive strength of the cured layer, as measured by the method specified in JIS K 6850, is 0.4 MPa or more.

12. A laminate comprising a first transparent or opaque optical member and an adhesive layer made of the cured product according to claim 9, disposed between the first transparent or opaque optical member and the second transparent or opaque optical member.

13. An optical apparatus comprising a substrate, an optical element disposed on the substrate, and a cured product according to claim 9 that seals at least a portion of the optical element.

14. An optical display comprising the laminate according to claim 12.

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