Photocurable liquid silicone composition, cured product thereof, optical filler containing the same, and display device including layer made of the cured product

Abstract

[Problem] To provide: a photocurable liquid silicone composition which has low viscosity so as to be easily injectable into small gaps, cures quickly upon being irradiated with high energy rays such as ultraviolet rays, has a high refractive index after curing not only in the visible region but also in the infrared region, and is particularly useful as a material for a device which uses an infrared LED light source; a cured article thereof; an optical filler containing said composition; and a display device containing a layer comprising the cured article thereof. [Solution] A photocurable liquid silicone composition which contains (A) an organosilane or low-molecular-weight organosiloxane which has a silicon atom number of 1-5, and in each molecule thereof has two or more alkenyl groups, and has two or more monovalent functional groups selected from an aromatic group and an aralkyl group, (C) a compound having two or more mercapto groups per molecule thereof, and (D) a photo-radical initiator, wherein the refractive index of the liquid composition overall before curing is 1.48 or higher. Also, a cured article thereof, an optical filler containing said composition, and a display device containing a layer comprising the cured article thereof.

Description

[Technical field]

[0001] The present invention relates to a curable liquid silicone composition that can be cured by actinic rays, such as ultraviolet rays or electron beams, and that has a low viscosity suitable for use in injection molding and a cured product with a high refractive index, the cured product, and uses thereof. The photocurable liquid silicone composition of the present invention has a high refractive index and transparency, and is suitable as a material for forming a light-transmitting layer for electronic / electrical devices and optical devices. [Background technology]

[0002] Electronic / electrical devices and optical devices using white and ultraviolet LEDs as light sources have been widely put to practical use. Silicone materials are being actively studied as peripheral materials because of the need for high transparency and reliability. As a liquid sealing material that directly seals a light source, for example, a high refractive index liquid silicone composition as disclosed in Patent Document 1 has already been put to practical use. In addition, infrared LED light sources and devices using them are being actively developed with an eye on the large market for various sensors, surveillance cameras, infrared data communications, etc. Meanwhile, in addition to these conventional LEDs, micro LED technology that takes advantage of its high energy efficiency has been rapidly researched and developed, and is beginning to be applied to various uses.

[0003] Here, in the case of micro LEDs, which have been studied in recent years, the size of the light source substrate is very small, so the surrounding materials are often required to be small in area and thin. In this case, the injection molding method, in which a curable composition is injected into the gap between the light source substrate and the transparent substrate and cured, is considered to be a promising method for forming a sealing layer between the light source substrate and the transparent substrate. As a material suitable for this processing method, a low-viscosity liquid silicone material that can be photocured and has high transparency after curing is required. Furthermore, a material with a high refractive index is desired to reduce interface reflection and increase light extraction efficiency.

[0004] For example, Patent Document 2 proposes an ultraviolet-curable silicone composition consisting of a branched organopolysiloxane containing an alkenyl group and a phenyl group, an organosiloxane containing a mercaptoalkyl group bonded to a silicon atom, and a photoreaction initiator. However, such an ultraviolet-curable silicone composition has a low refractive index because the content of phenyl groups in the organopolysiloxane is low (less than 2 mol% of the total number of substituents). Patent Document 3 also proposes an ultraviolet-curable silicone composition consisting of a linear organopolysiloxane containing an alkenyl group and a phenyl group, an organosiloxane containing a mercaptoalkyl group bonded to a silicon atom, a silane compound containing an aliphatic unsaturated group, and a photoreaction initiator. However, this ultraviolet-curable silicone composition also has a low refractive index because the content of phenyl groups in the organopolysiloxane is not high enough (5 to 33 mol% of the total number of substituents), and the composition has a high viscosity of 1,800 cP or more, making it unsuitable for injection molding.

[0005] Furthermore, Patent Document 4 discloses an ultraviolet-curable silicone composition consisting of a linear organopolysiloxane containing an alkenyl group and a phenyl group, a polyether compound containing an alkenyl group, a compound containing a mercaptoalkyl group, a phosphorus-containing photoreaction initiator, and a hindered phenol compound. Such an ultraviolet-curable silicone composition has a high refractive index because of the high content of phenyl groups in the organopolysiloxane (47 mol% of the total number of substituents). On the other hand, the composition has a very high viscosity of 3,000 mPas or more, making it unsuitable for injection molding. The curable liquid silicone composition disclosed in Patent Document 1 above has a very high overall viscosity of 3,000 mPas or more at 25°C, making it unsuitable for injection molding.

[0006] Thus, in the liquid silicone material having a low refractive index of the cured product as in Patent Document 2, sufficient light extraction efficiency cannot be achieved in devices using micro LEDs and the like. Furthermore, when the overall viscosity of the composition is high as in Patent Documents 1, 3, and 4 and it is applied to an injection molding method, it may not be possible to inject it into a minute gap (hereinafter, sometimes referred to as a "small gap") between members, or sufficient gap filling may not be achieved. Specifically, even if a high-viscosity curable liquid silicone composition is injected between a light source substrate and a transparent substrate to seal them, it is difficult to inject it so as to sufficiently fill the gap between them, which may cause defects and sealing failures in the process, and this is undesirable as it causes a decrease in production efficiency and yield, a decrease in quality, and a breakdown of the final display device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-008996 A (Patent No. 5392805 A) [Patent Document 2] Japanese Patent Application Publication No. 11-60953 [Patent Document 3] International Publication No. 2012 / 86402 [Patent Document 4] Special Publication No. 2019-507813 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a photocurable liquid silicone composition which has a low viscosity enabling it to be easily injected into small gaps, which cures quickly when irradiated with high-energy rays such as ultraviolet rays, and which has a high refractive index after curing not only in the visible region but also in the infrared region, and which is particularly useful as a material for devices using infrared LED light sources; a cured product thereof; and uses of the same. [Means for solving the problem]

[0009] The photocurable liquid silicone composition of the present invention comprises: (A) an organosilane or organopolysiloxane having 1 to 5 silicon atoms, at least two alkenyl groups having 2 to 12 carbon atoms in one molecule, and at least two monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms; (C) a compound having at least two mercapto groups per molecule {an amount such that the number of mercapto groups in this component is 0.2 to 3 moles per mole of alkenyl groups in component (A)}, and (D) Photoradical initiator The composition is characterized in that, relative to 100 parts by mass of the total of components (A), (C), and (D), the content of component (A) is in the range of 10 to 99 parts by mass and the content of component (D) is in the range of 0.01 to 3.0 parts by mass, and the refractive index of the entire liquid composition before curing at 25°C and a wavelength of 847 nm is 1.48 or more. Furthermore, the viscosity of the entire liquid composition before curing, measured at 25°C using an E-type viscometer, is preferably 500 mPa s or less, and more preferably 200 mPa s or less.

[0010] The cured product of the present invention is obtained by irradiating the above-mentioned photocurable liquid silicone composition with light and curing it.

[0011] The cured product of the present invention preferably has a refractive index at 25° C. and a wavelength of 847 nm of 1.50 or more, particularly preferably 1.54 or more.

[0012] The optical filler of the present invention is characterized by containing the above-mentioned photocurable liquid silicone composition.

[0013] The display device of the present invention is characterized by including a layer made of a cured product of the above-mentioned photocurable liquid silicone composition. In particular, the display device is preferably a display device using an infrared LED light source.

[0014] The method for producing a display device of the present invention is characterized by comprising the steps of injecting the above-mentioned photocurable liquid silicone composition between a light source substrate and a transparent substrate, and curing the injected photocurable liquid silicone composition by irradiating it with high-energy rays. Effect of the Invention

[0015] The photocurable liquid silicone composition of the present invention has a low viscosity that allows it to be easily injected into small gaps, and it cures quickly when irradiated with high-energy rays such as ultraviolet rays. In addition, the refractive index after curing is high not only in the visible region but also in the infrared region, making it useful as a material for devices using infrared LED light sources. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] First, the photocurable liquid silicone composition of the present invention will be described in detail. Component (A) is one of the characteristic components of the present composition, and is a component that reduces the viscosity of the curable liquid silicone composition without impairing its curability. It is an organosilane or organopolysiloxane having 1 to 5 silicon atoms, at least two alkenyl groups having 2 to 12 carbon atoms in one molecule, and at least two monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms. Component (A) is characterized by its low volatility and does not inhibit the photocuring of the composition of the present invention. In addition, component (A) is a component that improves the refractive index of the entire composition and the cured product because it has an aromatic group or an aralkyl group in the molecule.

[0017] Since the number of silicon atoms in such component (A) is 5 or less, it is a silane or siloxane oligomer (organopolysiloxane with a degree of siloxane polymerization of 5 or less) with a small molecular weight, and since it has at least two alkenyl groups with 2 to 12 carbon atoms in the molecule that participate in the curing reaction, a crosslinking reaction proceeds with component (C) described below. Meanwhile, component (A) has the property of being a relatively low molecular weight and low viscosity component, yet being low in volatility and unlikely to inhibit the curing reaction. Therefore, the composition of the present invention containing component (A) has excellent curing reactivity, reduces the viscosity of the entire composition suitable for injection molding, and significantly improves gap filling properties.

[0018] Examples of alkenyl groups in component (A) include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl groups, with the vinyl, allyl, 5-hexenyl, and 7-octenyl groups being preferred from the standpoints of economy and reactivity.

[0019] In addition to the alkenyl group, component (A) has at least two monovalent functional groups in the molecule selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms. Examples of these functional groups include aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl, and xylyl, and aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl, with phenyl and phenethyl being preferred from the standpoint of economy.

[0020] On the other hand, examples of other groups bonded to silicon atoms in component (A) (specifically, groups other than monovalent functional groups selected from the above-mentioned alkenyl groups, aromatic groups having 6 to 12 carbon atoms, and aralkyl groups having 7 to 12 carbon atoms) include alkyl groups having 1 to 12 carbon atoms, such as methyl groups, ethyl groups, propyl groups, butyl groups, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, and dodecyl groups; and halogen-substituted alkyl groups having 1 to 12 carbon atoms, such as 3-chloropropyl groups and 3,3,3-trifluoropropyl groups, with methyl groups being preferred from the standpoints of economy and heat resistance. In addition, 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, and hydroxyl groups may be bonded to silicon atoms in component (A).

[0021] Specifically, the following compounds A-1 to A-13 are exemplified as the component (A) in the present invention. A-1: Divinyldiphenylsilane A-2: 1,3-divinyl-1,3-dimethyl-1,3-diphenyldisiloxane A-3: 1,5-divinyl-3,3-diphenyl-1,1,5,5-tetramethyltrisiloxane A-4: 1,5-divinyl-1,5-diphenyl-1,3,3,5-tetramethyltrisiloxane A-5: 1,5-diphenyl-3,3-divinyl-1,1,5,5-tetramethyltrisiloxane A-6: 1,5-diphenethyl-3,3-divinyl-1,1,5,5-tetramethyltrisiloxane A-7: 1,7-divinyl-3,3,5,5-tetraphenyl-1,1,7,7-tetramethyltetrasiloxane A-8: 1,7-divinyl-1,7-diphenyl-1,3,3,5,5,7-hexamethyltetrasiloxane A-9: 1,7-divinyl-3,3-diphenyl-1,1,5,5,7,7-hexamethyltetrasiloxane A-10: 1,7-divinyl-3,5-diphenyl-1,1,3,5,7,7-hexamethyltetrasiloxane A-11: 1,3-divinyl-5,7-diphenyl-1,3,5,7-tetramethylcyclotetrasiloxane A-12: 1,5-divinyl-3,7-diphenyl-1,3,5,7-tetramethylcyclotetrasiloxane A-13: Phenyl-tris(dimethylvinylsiloxy)silane

[0022] The number of silicon atoms in the component (A) is 5 or less, and more preferably 2 or 3. This can increase the contribution to lowering the viscosity of the curable composition. Specifically, among the above compound group, the compounds A-2 to A-6 can be preferably used.

[0023] The content of the (A) component is 10 to 99 parts by mass, preferably 10 to 80 parts by mass, and more preferably 15 to 75 parts by mass, relative to 100 parts by mass of the curable composition. This is because, when the content of the (A) component is equal to or more than the lower limit of the above range, the viscosity of the obtained curable composition is easily reduced, whereas, when the content is equal to or less than the upper limit of the above range, the mechanical properties of the obtained cured product are improved.

[0024] Component (B) is an optional component that is added to the photocurable liquid silicone composition of the present invention as necessary, and is an organopolysiloxane having an average of more than 5 silicon atoms per molecule, at least one alkenyl group having 2 to 12 carbon atoms, and at least 34 mol% of the number of substituents on the silicon atoms being monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms. Since component (B) contains many aromatic groups or aralkyl groups in the molecule, it efficiently improves the refractive index of the entire composition and its cured product. Component (B) also preferably has at least two alkenyl groups having 2 to 12 carbon atoms in the molecule, and particularly preferably has alkenyl groups having 2 to 12 carbon atoms at both ends of the molecular chain.

[0025] Examples of the alkenyl group in component (B) include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl groups, with vinyl, allyl, hexenyl, and octenyl being preferred from the standpoint of economy and reactivity. Examples of groups bonded to silicon atoms other than the alkenyl group in component (B) 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; and halogen-substituted alkyl groups having 1 to 12 carbon atoms, such as 3-chloropropyl and 3,3,3-trifluoropropyl groups, with methyl being preferred from the standpoint of economy and heat resistance. On the other hand, examples of monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms include aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl, and xylyl, and aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl, with phenyl and phenethyl being preferred from the viewpoint of economy. A small amount of alkoxy groups, such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, sec-butoxy, and tert-butoxy, or hydroxyl groups may be bonded to the silicon atoms in component (B).

[0026] There is no limitation on the viscosity of component (B) at 25°C, but it is within the range of 50 to 100,000 mPa·s, and preferably within the range of 100 to 100,000 mPa·s, 100 to 50,000 mPa·s, or 100 to 10,000 mPa·s. This is because when the viscosity of component (B) is at or above the lower limit of the above range, the mechanical properties of the resulting cured product are improved, whereas when it is at or below the upper limit of the above range, it is easy to reduce the viscosity of the resulting curable composition.

[0027] A preferred embodiment of the component (B) is a linear polysiloxane represented by the following formula (1). [ka] (1) In the formula, R1 are the same or different alkenyl groups (terminal alkenyl groups) having 2 to 12 carbon atoms, examples of which include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, and dodecenyl groups, of which vinyl, allyl, 5-hexenyl, and 7-octenyl groups are preferred from the standpoints of economy and reactivity. R 2 and R 3 each independently represents an unsubstituted or fluorine-substituted monovalent alkyl group having 1 to 12 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a 3-chloropropyl group, and a 3,3,3-trifluoropropyl group. From the viewpoints of economy and heat resistance, a methyl group is preferred. R 4 are each independently a monovalent functional group selected from unsubstituted or fluorine-substituted aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms, and examples thereof include a phenyl group, a tolyl group, a xylyl group, a benzyl group, and a phenethyl group, with a phenyl group and a phenethyl group being preferred from the viewpoint of economy. R 5 and R 6 are each independently a monovalent functional group selected from an unsubstituted or fluorine-substituted monovalent alkyl group having 1 to 10 carbon atoms, an aromatic group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and each is exemplified by the same groups as those exemplified above, but examples thereof include a methyl group, a phenyl group, a tolyl group, a xylyl group, a benzyl group, and a phenethyl group, and from the viewpoint of economy, a group selected from a methyl group, a phenyl group, and a phenethyl group is preferred. However, in one molecule, the substituents on the silicon atoms, i.e., all R 1 ~R 6 At least 34% of the number of monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms. Additionally, m and n in the formula are numbers that satisfy 0≦m<1,000, 0≦n<500, and 3≦m+n<1,500.

[0028] Examples of such component (B) include one or a mixture of two or more organopolysiloxanes represented by the following general formula: In the formula, Me, Vi, and Ph represent methyl, vinyl, and phenyl groups, respectively, and a and b are each preferably an integer of 1 or greater such that the viscosity at 25°C is in the range of 50 to 100,000 mPa s. Here, the value of a+b is 3 or greater, and c is a number of 3 or greater such that the viscosity at 25°C is in the range of 50 to 100,000 mPa s. Me2ViSiO(Me2SiO) a (MePhSiO) b SiMe2Vi Me2ViSiO(Me2SiO) a (Ph2SiO) b SiMe2Vi Me2ViSiO(MePhSiO) a (Ph2SiO) b SiMe2Vi Me2ViSiO(MePhSiO) c SiMe2Vi Me2ViSiO(Me(PhCH2CH2)SiO) c SiMe2Vi Me2ViSiO(Ph2SiO) c SiMe2Vi

[0029] The blending amount of the (B) component is an amount such that the content of the (B) component falls within the range of 1 to 75 parts by mass, and more preferably an amount in the range of 1 to 70 parts by mass, when the total amount of the above (A) and the below-described (C), (D), and (B) components is taken as 100 parts by mass.

[0030] Component (C) is a compound having at least two mercapto groups in one molecule, and reacts with alkenyl groups in component (A) and optional component (B) under light irradiation to cure the composition. A preferred embodiment of component (C) is a mercaptoalkyl-functional polysiloxane (C1) or an organic compound (C2) that contains a mercapto group and does not contain a silicon atom. In particular, in the composition according to the present invention, it is preferable to use an organic compound (C2) that does not contain a silicon atom. These components will be described below.

[0031] (C1) Mercaptoalkyl-functional polysiloxane: Examples of the mercaptoalkyl group in the (C1) component include 3-mercaptopropyl, 4-mercaptobutyl, and 6-mercaptohexyl groups. Examples of groups bonded to silicon atoms other than the mercaptoalkyl group in the (C1) component 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; aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl, and xylyl groups; aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl groups; and halogen-substituted alkyl groups having 1 to 12 carbon atoms, such as 3-chloropropyl and 3,3,3-trifluoropropyl groups. From the standpoint of economy and heat resistance, methyl and phenyl groups are preferred. Furthermore, 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 may be bonded to silicon atoms in component (C1).

[0032] The viscosity of component (C1) at 25°C is within the range of 5 to 1,000 mPa s, and preferably within the range of 5 to 500 mPa s, or within the range of 10 to 500 mPa s. When the viscosity of component (C1) is at or above the lower limit of the above range, the mechanical properties of the resulting cured product are improved, whereas when it is below the upper limit of the above range, the transparency and coatability of the resulting composition are improved.

[0033] Examples of such a component (C1) include a compound represented by the general formula (C11): R3SiO(R2SiO) n SiR3 Linear organopolysiloxanes and / or (C12) having the average unit formula: (R3SiO 1 / 2 ) a (R2SiO 2 / 2 ) b (RSiO 3 / 2 ) c (SiO 4 / 2 ) d Examples of branched-chain organopolysiloxanes include those represented by the following formula:

[0034] In the formula, R is the same or different and is a mercaptoalkyl group or a monovalent organic group having 1 to 12 carbon atoms and no aliphatic unsaturated bonds. Examples of the mercaptoalkyl group include the same groups as above. Examples of the monovalent hydrocarbon group having no aliphatic unsaturated bonds include, as above, an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, and a halogen-substituted alkyl group having 1 to 12 carbon atoms. However, at least two of all R are the mercaptoalkyl groups.

[0035] Furthermore, in the formula, n is an integer of 1 or greater such that the viscosity of (C11) at 25° C. is 5 to 1,000 mPa·s.

[0036] In the formula, a, b, c, and d are each a number from 0 to 1, and the sum of a, b, c, and d is 1. However, c or d is a number exceeding 0.

[0037] Examples of component (C11) include one or a mixture of two or more organopolysiloxanes represented by the following general formula: In the formula, Me, Ph, and Thi represent methyl, phenyl, and 3-mercaptopropyl groups, respectively, n1 and n2 are integers of 1 or greater that result in a viscosity at 25°C in the range of 5 to 1,000 mPa s, and n3 is an integer of 2 or greater that results in a viscosity at 25°C in the range of 5 to 1,000 mPa s. Me3SiO(Me2SiO) n1 (MeThiSiO) n3 SiMe3 Me3SiO(MePhSiO) n1 (MeThiSiO) n3 SiMe3 Me3SiO(Me2SiO) n1 (Ph2SiO) n2 (MeThiSiO) n3 SiMe3

[0038] Examples of component (C12) include one or a mixture of two or more organopolysiloxanes represented by the following average unit formula: In the formula, Me, Ph, and Thi represent a methyl group, a phenyl group, and a 3-mercaptopropyl group, respectively, and a', b', b'', c', and d' are each numbers from 0 to 1 (but do not include 0), with the proviso that the sum of a', b', b'', c', and d' is 1. (Me3SiO 1 / 2 ) a’ (MeSiO 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’ (MeSiO 2 / 2 ) b’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeSiO2 / 2 ) b’ (Ph2SiO 2 / 2 ) b’’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeThiSiO 2 / 2 ) b’ (PhSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (ThiSiO 3 / 2 ) c’ (MeSiO 2 / 2 ) b’ (MeThiSiO 2 / 2 ) b’’ (MeSiO 3 / 2 ) c’ (MeThiSiO 2 / 2 ) b’ (MeSiO 3 / 2 ) c’ (MeSiO 2 / 2 ) b’ (ThiSiO 3 / 2 ) c’ (MeSiO 2 / 2 ) b’ (MeThiSiO 2 / 2 ) b’’ (ThiSiO 3 / 2 ) c’ (Me3SiO 1 / 2 ) a’ (MeThiSiO 2 / 2 ) b’ (SiO 4 / 2 ) d’

[0039] (C2) Organic compounds containing a mercapto group and no silicon atom There are no particular limitations on the mercapto group as long as it has at least two mercapto groups in one molecule, and examples thereof include 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-mercaptobutyrate), Examples of the mercaptocarboxylic acid include ester compounds of polyhydric alcohols such as mercaptocarboxylic acid (e.g., 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, and xylylenedithiol; and other examples include 1,3,5-tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, 1,3,5-tris[(3-mercaptobutyryloxy)-ethyl]-isocyanurate, and mixtures of two or more of these.

[0040] The molecular weight of this mercapto-containing compound is not particularly limited, but is preferably within the range of 100 to 2,000, 100 to 1,500, or 100 to 1,000. This is because, when the molecular weight is equal to or greater than the lower limit of the above range, the volatility of the mercapto-containing compound itself decreases, reducing odor problems, while, when the molecular weight is equal to or less than the upper limit of the above range, the solubility in components (A) and (B) is improved.

[0041] As the component (C), one or more types selected from the above components (C1) and (C2) or a mixture thereof can be used. From the viewpoint of efficiently designing and producing a homogeneous curable composition, the use of component (C2) is preferred.

[0042] The content of component (C) is an amount in which the mercapto groups in this component are in the range of 0.2 to 3 moles, preferably in the range of 0.5 to 2 moles, or in the range of 0.5 to 1.5 moles, per mole of the total amount of alkenyl groups in component (A) and any alkenyl groups in component (B). This is because, when the content of component (C) is equal to or greater than the lower limit of the above range, the obtained composition is cured sufficiently, whereas, when the content is equal to or less than the upper limit of the above range, the mechanical properties of the obtained cured product are improved.

[0043] Component (D) is a photoradical initiator that promotes the curing of the composition. Examples of component (D) include α-hydroxyketone initiators, benzyl dimethyl ketal initiators, and phosphine oxide initiators. Specific examples of component (D) include 1-hydroxycyclohexyl phenyl ketone (BASF product name: Irgacure 184), 2-hydroxy-2-methyl-1-phenylpropanone (BASF product name: Darocur 1173), α,α-dimethoxy-α-phenylacetophenone (BASF product name: Irgacure 651), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (BASF product name: Darocur TPO), ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (BASF product name: Irgacure 651), and the like. Examples of such photocatalysts include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenylpropanone (TPO-L), a 50 / 50 (weight ratio) mixture of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenylpropanone (BASF's product name Darocur 4265), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BASF's product name Irgacure 819), and a mixture of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BASF's product name Irgacure 2100).

[0044] The content of component (D) is within the range of 0.01 to 3.0 parts by mass, and preferably within the range of 0.05 to 1.0 part by mass, or within the range of 0.05 to 0.5 part by mass, relative to 100 parts by mass of the total of components (A) to (D). This is because, when the content of component (D) is equal to or greater than the lower limit of the above range, the curability of the resulting composition is good, whereas, when the content is equal to or less than the upper limit of the above range, the heat resistance and light resistance of the resulting cured product are good.

[0045] The composition may contain a hindered phenol compound (E) in order to maintain the storage stability of the composition and to impart heat resistance to the cured product. Examples of such a component (E) include 2,6-bis(hydroxymethyl)-p-cresol, 2,6-ditertiary butyl-4-methylphenol, 2,6-ditertiary butyl-4-hydroxymethylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,4-dimethyl-6-(1-methylpentadecyl)propionate, and 1,2-dimethyl- ... 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, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], and hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are examples.

[0046] The content of the (E) component is within the range of 0 to 1 part by mass, and preferably within the range of 0.01 to 1 part by mass, or within the range of 0.01 to 0.5 parts by mass, relative to 100 parts by mass of the total curable composition. This is because, when the content of the (E) component is equal to or greater than the lower limit of the above range, the storage stability of the resulting composition is good, whereas, when the content is equal to or less than the upper limit of the above range, the heat resistance and light resistance of the resulting cured product are good.

[0047] In addition, the composition may contain (F) an organic compound having one aliphatic unsaturated bond and no siloxane bond in one molecule in order to reduce the crosslink density of the resulting cured product and thereby improve mechanical properties or adhesion. As such an (F) component, an organic compound having a boiling point of, for example, 200°C or higher at one atmospheric pressure is preferable because it shows good compatibility with the (A) to (D) components and has good storage stability. Examples of such (F) components 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.

[0048] The content of the (F) component is not limited, but in order to ensure good curability of the composition and good mechanical properties of the resulting cured product, it is preferable that the content be in the range of 0 to 10 parts by mass, or in the range of 0 to 5 parts by mass, per 100 parts by mass of the total curable composition.

[0049] Furthermore, the present composition may further contain, within the scope of the present invention, a compound represented by the formula (G): R 7 SiO 3 / 2 and / or a siloxane unit represented by the formula: SiO2, and has a monovalent functional group selected from an aromatic group having 6 to 12 carbon atoms and an aralkyl group having 7 to 12 carbon atoms, and does not have a mercaptoalkyl group. 7is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a hydroxyl group, or an alkoxy group having 1 to 6 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group. Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, and a dodecenyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. In addition, the formula: R 7 SiO 3 / 2 When the siloxane unit represented by the formula (I) does not have an alkenyl group, the other siloxane units include R 8 3SiO 1 / 2 Siloxane units represented by the formula: R 8 2SiO 2 / 2 In the formula, R 8 is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a hydroxyl group, or an alkoxy group having 1 to 6 carbon atoms, and examples thereof include the same groups as those described above. However, at least one R 8 is the alkenyl group.

[0050] Examples of component (G) include one or a mixture of two or more organopolysiloxanes represented by the following average unit formula: In the formula, Me, Vi, and Ph represent a methyl group, a vinyl group, and a phenyl group, respectively, and i, i', j, k, and l are numbers from 0 to 1 (but do not include 0) that represent the ratio of the structural units, with the proviso that the sum of i, i', j, k, and l is 1. (Me3SiO 1 / 2 ) i (Me2ViSiO 1 / 2 ) i’ (PhSiO 3 / 2 ) k (Me3SiO 1 / 2 ) i (Me2ViSiO 1 / 2 ) i’(PhSiO 3 / 2 ) k (SiO 4 / 2 ) l (Me3SiO 1 / 2 ) i (PhSiO 3 / 2 ) k (Me2ViSiO 1 / 2 ) i (PhSiO 3 / 2 ) k (Me2ViSiO 1 / 2 ) i (Me2SiO 2 / 2 ) j (PhSiO 3 / 2 ) k (Me2ViSiO 1 / 2 ) i (Me2SiO 2 / 2 ) j (PhSiO 3 / 2 ) k (SiO 4 / 2 ) l (Me2ViSiO 1 / 2 ) i (MePhSiO 2 / 2 ) j (MeSiO 3 / 2 ) k (Me2ViSiO 1 / 2 ) i (MePhSiO 2 / 2 ) j (PhSiO 3 / 2 ) k (Me3SiO 1 / 2 ) i (MeViSiO) 2 / 2 ) j (PhSiO 3 / 2 ) k (Me3SiO 1 / 2 ) i (MeViSiO) 2 / 2 ) j (PhSiO 3 / 2 ) k (SiO 4 / 2 ) l (Me3SiO 1 / 2 ) i (MeSiO 2 / 2 ) j (PhSiO 3 / 2 ) k (Me3SiO 1 / 2 ) i (MeSiO 2 / 2 ) j (PhSiO 3 / 2 ) k (SiO 4 / 2 ) l

[0051] The content of the (G) component is not limited, but is within the range of 0 to 20 parts by mass, and preferably within the range of 0 to 10 parts by mass, or within the range of 0 to 5 parts by mass, relative to 100 parts by mass of the total curable composition. This is because if the content of the (G) component is equal to or greater than the upper limit of the above range, the viscosity of the obtained curable composition becomes high.

[0052] Other Additives In addition to the above components, further additives may be added to the composition of the present invention as desired. Examples of additives include, but are not limited to, the following:

[0053] [Adhesion imparting agent] An adhesion promoter can be added to the composition of the present invention in order to improve adhesion or adhesion to a substrate in contact with the composition. When the curable composition of the present invention is used for applications requiring adhesion or adhesion to a substrate, such as a coating agent or a sealing material, it is preferable to add an adhesion imparting agent to the curable composition of the present invention. As the adhesion promoter, any known adhesion promoter can be used as long as it does not inhibit the curing reaction of the composition of the present invention.

[0054] Examples of adhesion promoters that can be used in the present invention include organosilanes having a trialkoxysiloxy group (e.g., trimethoxysiloxy group, triethoxysiloxy group) or a trialkoxysilylalkyl group (e.g., trimethoxysilylethyl group, triethoxysilylethyl group) and a hydrosilyl group or an alkenyl group (e.g., vinyl group, allyl group), or organosiloxane oligomers having a linear, branched or cyclic structure with about 4 to 20 silicon atoms; organosilanes having a trialkoxysiloxy group or a trialkoxysilylalkyl group and a methacryloxyalkyl group (e.g., 3-methacryloxypropyl group); organosilanes, or organosiloxane oligomers having a linear, branched, or cyclic structure with about 4 to 20 silicon atoms; organosilanes having a trialkoxysiloxy group or a trialkoxysilylalkyl group and an epoxy group-bonded alkyl group (e.g., 3-glycidoxypropyl group, 4-glycidoxybutyl group, 2-(3,4-epoxycyclohexyl)ethyl group, 3-(3,4-epoxycyclohexyl)propyl group), or organosiloxane oligomers having a linear, branched, or cyclic structure with about 4 to 20 silicon atoms; organic compounds having two or more trialkoxysilyl groups (e.g., trimethoxysilyl group, triethoxysilyl group);Examples of the reaction product of aminoalkyltrialkoxysilane and epoxy group-bonded alkyltrialkoxysilane, and epoxy group-containing ethyl polysilicate include vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, hydrogentriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 1,6-bis(trimethoxysilane), silyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,3-bis[2-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyldisiloxane, reaction product of 3-glycidoxypropyltriethoxysilane and 3-aminopropyltriethoxysilane, condensation reaction product of silanol group-blocked methylvinylsiloxane oligomer and 3-glycidoxypropyltrimethoxysilane, condensation reaction product of silanol group-blocked methylvinylsiloxane oligomer and 3-methacryloxypropyltriethoxysilane, and tris(3-trimethoxysilylpropyl)isocyanurate.

[0055] The amount of adhesion promoter added to the curable composition of the present invention is not particularly limited, but in order not to promote the curing characteristics of the curable composition or discoloration of the cured product, it is preferably within the range of 0 to 5 parts by mass, or within the range of 0 to 2 parts by mass, relative to 100 parts by mass of the total of the components (A), (C), and (D).

[0056] [Other additives] In addition to the adhesion promoter described above, or instead of the adhesion promoter, other additives may be added to the composition of the present invention as desired. Examples of additives that can be used include leveling agents, silane coupling agents not included in the adhesion promoters described above, ultraviolet absorbers, antioxidants, polymerization inhibitors, fillers (functional fillers such as reinforcing fillers, insulating fillers, and thermally conductive fillers), and the like. If necessary, appropriate additives can be added to the composition of the present invention. In addition, if necessary, a thixotropic agent may be added to the composition of the present invention, especially when the composition is used as a potting agent or a sealing material.

[0057] The refractive index of the curable composition of the present invention is 1.48 or more as a value of the entire liquid composition before curing at 25°C and a wavelength of 847 nm. The refractive index value under these conditions is preferably 1.50 or more, and more preferably 1.52 or more. Due to this characteristic, the refractive index of the cured product obtained by curing the composition is sufficiently high, and in various devices using infrared LEDs as a light source, the interfacial reflection between optical glass and other light transmitting layers can be reduced, and the light extraction efficiency can be increased.

[0058] The viscosity of the curable composition is not particularly limited, but in order to enable application to injection molding, it is preferably 500 mPa·s or less, in the range of 10 to 200 mPa·s, or in the range of 10 to 100 mPa·s, as measured using an E-type viscometer at 25° C. This is because when the viscosity of the composition is at or above the lower limit of the above range, the mechanical properties of the obtained cured product are good, whereas when the viscosity is at or below the upper limit of the above range, the obtained composition can be injection molded.

[0059] This composition can be prepared by uniformly mixing the components (A), (C) and (D), and, if necessary, any other components including the component (B). When preparing this composition, the components can be mixed at room temperature using various stirrers or kneaders, and if necessary, they can be mixed under heating. There is also no limitation on the order in which the components are mixed, and they can be mixed in any order. On the other hand, in order to avoid any effect on the curing during the preparation of this composition, it is recommended to prepare the composition in a place that is not contaminated by light of 450 nm or less, or in a place where the above light is contaminated as little as possible.

[0060] The present composition can be cured by irradiation with light. Examples of light used to cure the present composition include ultraviolet light and visible light, but in particular, high-energy light such as ultraviolet light is preferred, and the wavelength of the light is preferably within the range of 250 to 450 nm, and more preferably ultraviolet light of 400 nm or less.

[0061] The cured product obtained by curing the composition has a high refractive index, and the refractive index of the cured product is preferably 1.50 or more at 25°C and a wavelength of 847 nm. The refractive index of the cured product under these conditions is preferably 1.52 or more, and more preferably 1.54 or more. Due to this characteristic, the refractive index of the cured product obtained by curing the composition is sufficiently high, and in various devices using infrared LEDs as a light source, it is possible to reduce interface reflection between optical glass and other light transmitting layers and increase light extraction efficiency.

[0062] This composition is useful as various injection agents, potting agents, sealants, and adhesives, and is particularly useful as an optical filler for forming light-transmitting layers for various devices using infrared LEDs, particularly display devices. The cured product is less colored and less likely to become cloudy under high temperature or high temperature and high humidity conditions, making it suitable as a light-transmitting layer for display devices using infrared LEDs.

[0063] This composition cures at room temperature, so it can be used to coat substrates with poor heat resistance. Such substrates are generally transparent substrates such as glass, synthetic resin films, sheets, and coatings. In addition, injection molding is an example of a coating method for this composition, taking advantage of its low viscosity characteristics.

[0064] Next, the cured product of the present invention will be described in detail. The cured product of the present invention is characterized by being obtained by curing the above-mentioned photocurable liquid silicone composition by irradiating it with light. The shape of the cured product is not particularly limited, and examples thereof include a sheet, film, tape, and block shape. It may also be integrated with various substrates.

[0065] The present cured product can be formed, for example, by applying the present composition to a film-like substrate, a tape-like substrate, or a sheet-like substrate, and then curing the composition by light irradiation to form a cured film made of the present cured product on the surface of the substrate. The present composition can also be injected between two substrates, at least one of which is a transparent substrate, and cured by light irradiation from the transparent substrate side to form a cured product integrated with the substrate. The thickness of the cured film is not limited, but is preferably 1 to 3000 μm, more preferably 10 to 2000 μm.

[0066] The display device of the present invention is produced using the curable liquid silicone composition of the present invention, and examples thereof include passive display devices such as LCDs (liquid crystal displays) and ECDs (electrochromic displays), and light-emitting display devices such as ELDs (electroluminescent displays). In the display device of the present invention, the space between the display unit such as a liquid crystal or organic EL display and a display-forming member such as a touch panel or cover lens, or between the display-forming members, is filled with a cured product of the curable liquid silicone composition of the present invention, thereby reducing interfacial reflection and increasing light extraction efficiency.

[0067] A typical method for manufacturing the display device of the present invention is the injection molding method, taking advantage of the low viscosity characteristic of the curable liquid silicone composition of the present invention. Specifically, the composition is injected into a narrow gap between an infrared LED light source substrate and various transparent substrates, and cured by irradiating with ultraviolet light to manufacture the display device.

[0068] The present invention will be further described below based on examples, but the present invention is not limited to the following examples. EXAMPLES

[0069] The photocurable liquid silicone composition of the present invention and its cured product will be described in detail with reference to the following examples. In the formulas, Me, Vi, and Ph represent methyl, vinyl, and phenyl groups, respectively. Measurements and evaluations in the examples were performed as follows.

[0070] [Viscosity of the photocurable liquid silicone composition and each component] The viscosity (mPa·s) of the photocurable liquid silicone composition and each of its components at 25°C was measured using a VISCONIC EMD E-type viscometer manufactured by Tokimec Inc.

[0071] [Chemical structure of organopolysiloxane] The chemical structure of the organopolysiloxane was identified by nuclear magnetic resonance spectroscopy.

[0072] [Appearance of the photocurable liquid silicone composition and the cured product] The appearance of the photocurable liquid silicone composition and the cured product were visually observed and rated as follows. A:Transparent B: Slightly cloudy

[0073] [Transparency and haze of the cured product] The photocurable liquid silicone composition was filled between two glass plates (filling area: 40 × 40 mm) so that the thickness after curing was 200 microns. 2 ), 405 nm LED light with illuminance of 50 mW / cm 2The total light transmittance and haze of the cured sheet formed between the two glass plates were measured using a SH7000 haze meter manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7361-1.

[0074] [Hardness of cured product] The photocurable liquid silicone composition was placed in a glass cup with a diameter of 25 mm and a depth of 10 mm, and 405 nm LED light was irradiated in a nitrogen atmosphere with an illuminance of 50 mW / cm. 2 The cured product was exposed to light at room temperature for 40 seconds. The penetration strength of the resulting cured product was measured using a penetration tester in accordance with JIS K2207. For products with high hardness, the test was performed using a type A durometer or type 00 durometer in accordance with ASTM D 2240.

[0075] [Refractive index of cured product] Using the above-mentioned curable composition and the cured product prepared for hardness measurement, the refractive index at a wavelength of 847 nm was measured at room temperature with a Metricon Model 2010 / M prism coupler.

[0076] [Examples 1 to 7, Comparative Example 1] A solventless photocurable liquid silicone composition was prepared using the following components. At the time of preparation, components (D), (E), and (H) were mixed in advance to form a catalyst solution. This catalyst solution was mixed with components (A), (B), and (C) at room temperature using a planetary centrifugal mixer to form a curable composition. The mixing ratio of the components (parts by mass), the physical properties of the curable composition, and the characteristics of the cured product are summarized in Table 1.

[0077] The following compound was used as component (A). (A1) 1,3-divinyl-1,3-dimethyl-1,3-diphenyldisiloxane (A2) 1,5-divinyl-3,3-diphenyl-1,1,5,5-tetramethyltrisiloxane

[0078] The following organopolysiloxane was used as component (B). A polymethylphenylsiloxane with a viscosity of 3,000 mPa s at 25°C and both ends of the molecular chain capped with dimethylvinylsiloxy groups, represented by the following formula: Me2ViSiO(MePhSiO) 25 SiMe2Vi

[0079] The following compound was used as component (C). (C1): Pentaerythritol-tetrakis(3-mercaptobutyrate) (C2): 3,6-dioxa-1,8-octanedithiol

[0080] The following compound was used as component (D). Ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide

[0081] The following compound was used as component (E). 2,6-Ditertiary Butyl-4-Methylphenol

[0082] As other components (H), the following compounds were used. 1,3,5,7-Tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

[0083] [Table 1] *The number of moles of the total amount of mercapto groups in components (C1) and (C2) per mole of the total amount of vinyl groups in components (A1), (A2), and (B).

[0084] From the results of Examples 1 to 7, the photocurable liquid silicone composition of the present invention has a very low viscosity and good transparency. It was also confirmed that the transparency of the cured product obtained by curing is high, and the refractive index, particularly in the infrared region, is high. It was also demonstrated that the hardness of the cured product can be adjusted over a wide range by appropriately changing the components used and their contents. On the other hand, from the results of Comparative Example 1, it was confirmed that the viscosity of the photocurable liquid silicone composition not containing component (A) is very high. [Industrial Applicability]

[0085] The photocurable liquid silicone composition of the present invention has a very low viscosity at room temperature and is suitable for injection molding. In addition, it is rapidly cured by irradiation with long wavelength light, for example, visible light with a wavelength of 405 nm and ultraviolet light, which contributes to improving productivity. Furthermore, the obtained cured product has excellent transparency and a high refractive index, especially in the infrared region (1.50 or more), so it is useful as a material for devices using infrared LED light sources.

Claims

1. (A) an organosilane or organopolysiloxane having 1 to 5 silicon atoms, at least two alkenyl groups having 2 to 12 carbon atoms in one molecule, and at least two monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms; (B) an organopolysiloxane having an average number of silicon atoms in one molecule greater than 5, having at least one alkenyl group having 2 to 12 carbon atoms, and in which 34 mol % or more of the substituents on the silicon atoms are monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms; (C) a compound having at least two mercapto groups per molecule (an amount such that the number of mercapto groups in this component is 0.2 to 3 moles per mole of alkenyl groups in component (A)), and (D) Photoradical initiator the content of the component (A) is in the range of 10 to 99 parts by mass, the content of the component (D) is in the range of 0.01 to 3.0 parts by mass, and the content of the component (B) is in the range of 1 to 75 parts by mass, relative to 100 parts by mass in total of the components (A), (C), (D), and (D); and A photocurable liquid silicone composition, wherein the refractive index of the entire liquid composition before curing is 1.48 or greater at 25° C. and a wavelength of 847 nm.

2. 2. The photocurable liquid silicone composition according to claim 1, wherein the viscosity of the entire liquid composition before curing, as measured at 25° C. using an E-type viscometer, is 500 mPa·s or less.

3. 3. The photocurable liquid silicone composition according to claim 1, wherein component (A) is an organopolysiloxane having at least two aromatic groups containing 6 to 12 carbon atoms and 2 or 3 silicon atoms in each molecule.

4. 2. The photocurable liquid silicone composition according to claim 1, wherein component (B) is a linear polysiloxane represented by the following formula (1): 【Chemistry 1】 （１） (In the formula, R １ is an alkenyl group having 2 to 12 carbon atoms, R ２ and R ３ are each independently an unsubstituted or fluorine-substituted monovalent alkyl group having 1 to 10 carbon atoms; R ４ are each independently a monovalent functional group selected from an unsubstituted or fluorine-substituted aromatic group having 6 to 12 carbon atoms and an aralkyl group having 7 to 12 carbon atoms; R ５ and R ６ are each independently a monovalent functional group selected from an unsubstituted or fluorine-substituted monovalent alkyl group having 1 to 10 carbon atoms, an aromatic group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and m and n are numbers that satisfy the relationships 0≦m<1,000, 0≦n<500, and 3≦m+n<1,500, and all of R １ ~R ６ At least 34 mol % of the number of monovalent functional groups selected from aromatic groups having 6 to 12 carbon atoms and aralkyl groups having 7 to 12 carbon atoms.

5. The photocurable liquid silicone composition according to any one of claims 1 to 4, wherein component (C) is a compound that does not contain a silicon atom in the molecule.

6. 6. The photocurable liquid silicone composition according to claim 1, which has a refractive index of at least 1.52 at 25° C. and a wavelength of 847 nm.

7. A cured product obtained by curing the photocurable liquid silicone composition according to any one of claims 1 to 6 through light irradiation.

8. The cured product according to claim 7, which has a refractive index of 1.50 or more at 25°C and a wavelength of 847 nm.

9. An optical filler comprising the photocurable liquid silicone composition of any one of claims 1 to 6.

10. A display device comprising a layer made of a cured product of the photocurable liquid silicone composition according to any one of claims 1 to 6.

11. 7. A method for producing a display device, comprising the steps of: injecting the photocurable liquid silicone composition according to any one of claims 1 to 6 between a light source substrate and a transparent substrate; and curing the injected curable liquid silicone composition by irradiating it with high-energy rays.

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