Resin composition, cured product, and optical fiber array

Abstract

This invention provides a resin composition having low viscosity and high transparency.　The resin composition comprises (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, wherein the (C) inorganic particles include inorganic particles which have a median diameter (D50) of 0.05-3.0 μm and for which D90 / D10 is 1-4, D90 / D10 being the ratio of a cumulative volume 90% value (D90) to a cumulative volume 10% value (D10) in particle size distribution. It is preferable that the (C) inorganic particles include silica particles.

Description

Resin composition, cured product, and optical fiber array

[0001] The present invention relates to a resin composition, a cured product, and an optical fiber array.

[0002] In recent years, the increasing speed of information and communications technology and the rapid increase in communication volume have become problems. One solution to these problems is silicon photonics, which combines conventional electrical communication technology with optical communication technology.

[0003] Silicon photonics is a technology that integrates elements such as optical waveguides, optical switches, optical modulators, and photodetectors on a silicon substrate, and by integrating optical devices and electronic circuits into optical integrated circuits, it is possible to realize small, highly functional optical devices.

[0004] Conventionally, optical adhesives have been required to have optical properties such as low refractive index and high transparency. Generally, methods for lowering the refractive index include methods for lowering the glass transition temperature of a resin composition and methods for lowering the crosslinking density of a polymer. Another known method for lowering the refractive index is the use of fluorine compounds. However, fluorine compounds have a very stable structure and are difficult to decompose in the environment, raising environmental concerns, and their use is being restricted.

[0005] For example, Patent Document 1 describes a low refractive index adhesive containing an acrylic matrix resin and porous hollow resin particles. The technology of Patent Document 1 focuses on the porous hollow resin particles from the viewpoints of adhesiveness and transparency.

[0006] JP 2011-037978 A

[0007] In a situation where resin compositions are used in a wide variety of applications, such as for adhesives, there has been a demand for resin compositions with excellent injectability and optical properties. For example, there has been a demand for resin compositions for adhesives that have low viscosity and high transparency. In particular, optical adhesives for silicon photonics have been required to have low viscosity from the viewpoint of injectability and high transparency from the viewpoint of optical properties. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a resin composition and a cured product that have low viscosity and high transparency. Another object of the present invention is to provide an optical fiber array using a resin composition that has a low refractive index, low viscosity, and high transparency.

[0008] The present invention relates to a resin composition for adhesives, a cured product, and an optical fiber array, as shown below. [1] A resin composition comprising: (A) an organic substance; (B) a polymerization initiator; and (C) inorganic particles, wherein the (C) inorganic particles have a median diameter (D50) of 0.05 to 3.0 μm and a particle size distribution ratio (D90 / D10) of 1 to 4, i.e., a ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10). [2] The resin composition according to [1] above, wherein the (C) inorganic particles comprise silica particles. [3] The resin composition according to [1] or [2] above, wherein the (C) inorganic particles are substantially free of inorganic particles having a maximum particle size of 5 μm or more. [4] The resin composition according to any one of [1] to [3] above, wherein the (C) inorganic particles are substantially free of inorganic particles having a minimum particle size of less than 0.01 μm in the cumulative volume 10% value (D10) of the inorganic particles. [5] The resin composition according to any one of [1] to [4] above, wherein the sphericity of the (C) inorganic particles is 0.9 or more. [6] The resin composition according to any one of [1] to [5] above, wherein the amount of the (C) inorganic particles is 10 to 80 parts by weight, when the total amount of the resin composition is 100 parts by weight. [7] The resin composition according to any one of [1] to [6] above, wherein the viscosity measured at 25°C and 10 rpm using an E-type viscometer is 12 Pa s or less. [8] The resin composition according to any one of [1] to [7] above, wherein the thixotropic index value, which is the viscosity at 5 rpm / viscosity at 50 rpm measured at 25°C using an E-type viscometer, is 3 or less. [9] The resin composition according to any one of [1] to [8] above, comprising the (A) organic substance and a siloxane compound having a reactive functional group.

[10] The resin composition according to [9] above, wherein the siloxane compound having a reactive functional group comprises (A1) a cyclic siloxane compound having a reactive functional group, and (A2) a linear siloxane compound having a reactive functional group.

[11] The resin composition according to any one of [1] to

[10] above, further comprising (A3) an oxetane.

[12] A cured product of the resin composition according to any one of [1] to

[11] above.

[13] The cured product according to

[12] above, wherein the cured product has a thickness of 100 μm and a transmittance of 90% or more at a wavelength of 1,310 nm.

[14] The cured product according to

[12] or

[13] above, wherein the cured product has a refractive index of 1.47 or less at a wavelength of 1310 nm.

[15] The resin composition according to any one of [1] to

[11] above, used for fixing an optical fiber in a groove formed in an optical waveguide element.

[16] The resin composition according to any one of [1] to

[11] above, used for optically coupling an optical fiber to an optical waveguide element.

[17] The resin composition according to any one of [1] to

[11] above, used for simultaneously fixing an optical fiber in a groove formed in an optical waveguide element and optically coupling the optical fiber to the optical waveguide element.

[18] An optical fiber array comprising the resin composition according to any one of [1] to

[17] above, an optical fiber, and an optical waveguide element, wherein the optical fiber is optically coupled to the optical waveguide element via the resin composition.

[0009] According to the present invention, it is possible to provide a resin composition having low viscosity and high transparency, a cured product of the resin composition, and an optical fiber array using the resin composition having low viscosity and high transparency.

[0010] 3 is an exploded perspective view of the optical waveguide module, an enlarged view of the vicinity of the connection portion, a side view showing a state in which an optical fiber is fixed to an optical waveguide element, and a cross-sectional view taken along the line AA in FIG.

[0011] An embodiment of the present invention (hereinafter, the present embodiment) will be described below. The present embodiment relates to a resin composition for adhesives, a cured product of the resin composition, and an optical fiber array. Note that the present invention is not limited to the present embodiment. Also, the drawings are schematic, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0012] [Definitions] In this specification, ○ to △ (for example, ○ parts by mass to △ parts by mass) means ○ or more and △ or less (○ parts by mass or more and △ parts by mass or less). In addition, in this specification, the terms "comprise" or "comprises" mean that the specified component is included, but do not exclude the presence of other components.

[0013] [Resin Composition] The resin composition of the present embodiment includes (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, wherein the inorganic particles (C) have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4.

[0014] (A) Organic Material The resin composition of this embodiment contains (A) an organic material (hereinafter also referred to as "component (A)"). Various synthetic resins can be used as component (A). Examples of synthetic resins that can be used include thermosetting resins such as epoxy resins, (meth)acrylic resins, phenolic resins, and silicone resins, and thermoplastic resins such as polyester resins and polyamide resins. When using a thermosetting resin, there are no particular limitations as long as it is a resin component (polymerizable compound) that can be polymerized and cured by heating and / or light irradiation. It is preferable that component (A) contains a thermosetting resin that is liquid at room temperature (25°C). Examples include, but are not limited to, silicone resins, epoxy resins, (meth)acrylic resins, maleimide resins, polyamide resins, and polyimide resins. From the viewpoint of optical properties, it is preferable to use epoxy resins, (meth)acrylic resins, and silicone resins. It is preferable that component (A) contains a siloxane compound having a reactive functional group (A) from the viewpoints of injectability, transparency, low refractive index, and high heat resistance.

[0015] (A) Siloxane Compound Having a Reactive Functional Group The siloxane compound having a reactive functional group (A) that is preferably contained in the resin composition of this embodiment is not particularly limited, but preferably contains (A1) a cyclic siloxane compound having a reactive functional group or (A2) a linear siloxane compound having a reactive functional group. Hereinafter, the siloxane compound having a reactive functional group (A) may be simply referred to as "siloxane compound (A)" or "component (A)."

[0016] (A1) Cyclic siloxane compound having a reactive functional group The resin composition of this embodiment may contain (A1) a cyclic siloxane compound having a reactive functional group (hereinafter also referred to as "(A1) component" or "(A1) cyclic siloxane compound"). The (A1) component is not particularly limited as long as it is a cyclic siloxane compound having one or more reactive functional groups per molecule. As the (A1) component, one type may be used alone, or two or more types may be used in combination.

[0017] The reactive functional group refers to a functional group that can react with a functional group possessed by a compound contained in the resin composition of the present embodiment. The reactive functional group is not particularly limited, but examples thereof include an epoxy group, an oxetanyl group, a glycidyl group, an alkoxysilyl group, and a vinyl ether group.

[0018] There are no particular limitations on the number of reactive functional groups per molecule in the component (A1), as long as it is one or more. From the standpoints of optical properties, heat resistance, availability of raw materials, reactivity, and the like, it is desirable for the number to be two or more, and the number is preferably 2 to 10, more preferably 2 to 6, even more preferably 2 to 4, and particularly preferably 2 or 4.

[0019] The cyclic siloxane compound refers to a compound having a cyclic siloxane skeleton based on siloxane bonds (—Si—O—Si—). The number of Si—O units forming the cyclic siloxane skeleton (equal to the number of silicon atoms forming the siloxane ring) is not particularly limited, but from the viewpoints of optical properties, heat resistance, availability of raw materials, reactivity, etc., it is preferably 2 to 15, more preferably 3 to 10, even more preferably 3 to 8, and particularly preferably 3 to 6.

[0020] It is preferable that the component (A1) has a cationically polymerizable group as the reactive functional group bonded to the cyclic siloxane skeleton. The cationically polymerizable group refers to a functional group that undergoes chain polymerization in the presence of cations. By having the component (A1) have a cationically polymerizable group bonded to the cyclic siloxane skeleton, it is possible to provide heat resistance while reducing cure shrinkage. Examples of the cationically polymerizable group include an epoxy group, a glycidyl group, an oxetanyl group, and a vinyl ether group. Although not particularly limited, from the viewpoint of reducing the refractive index, it is preferable that the cationically polymerizable group is a functional group that does not have an aromatic ring.

[0021] From the viewpoints of optical properties, heat resistance, availability of raw materials, and storage stability of the composition, it is preferable that the cationically polymerizable group of component (A1) is an epoxy group. The epoxy group is a group having an oxirane structure, and is a substituent having a three-membered ring (oxirane ring) consisting of two carbon atoms and one oxygen atom. When the cationically polymerizable group is an epoxy group, the epoxy group may be an alicyclic epoxy group or a non-alicyclic epoxy group. From the viewpoint of achieving excellent transparency, it is preferable that the epoxy group be an alicyclic epoxy group.

[0022] The alicyclic epoxy group has a cycloalkene oxide structure as an alicyclic skeleton. The cycloalkene oxide structure is a structure having an aliphatic ring and an epoxy group that constitutes the aliphatic ring and is composed of two adjacent carbon atoms and oxygen atoms. The cycloalkene oxide structure can be obtained, for example, by epoxidizing a cycloalkene with an oxidizing agent such as a peroxide. The alicyclic skeleton of the alicyclic epoxy group is not particularly limited, but examples include a cyclopropane skeleton, a cyclobutane skeleton, a cyclopentane skeleton, a cyclohexane skeleton, a cycloheptane skeleton, and a cyclooctane skeleton, and preferably a cyclohexane skeleton.

[0023] The non-alicyclic epoxy group is an epoxy group other than the above-mentioned alicyclic epoxy groups. Examples of groups containing a non-alicyclic epoxy group include a glycidyl group and a glycidoxypropyl group (preferably a 3-glycidoxypropyl group).

[0024] In the component (A1), the epoxy group may be bonded directly to the cyclic siloxane skeleton, or may be bonded via a linking group. The linking group may be any divalent group, such as an alkylene group (-(CH ２ ) ｎ Examples of such bonds include - (n is an integer of 0 or more), ether bonds (-O-), and combinations thereof. Although the epoxy group and the cyclic siloxane skeleton are close to each other, a dense cured product tends to be obtained when the resin composition is cured, and the cured product has excellent heat resistance (reflow resistance). Therefore, when the epoxy group is bonded to the cyclic siloxane skeleton via a linking group, the number of atoms between the epoxy group and the cyclic siloxane skeleton is preferably 4 or less, and more preferably 2 or less.

[0025] The weight-average molecular weight of component (A1) is preferably 200 to 3,000, more preferably 300 to 2,000, and particularly preferably 400 to 1,000. When the weight-average molecular weight of component (A1) is within the above range, the viscosity of the resin composition becomes appropriate, and the optical properties and heat resistance of the cured product are well balanced. Note that the weight-average molecular weight in this specification refers to a value calculated by gel permeation chromatography (GPC) using a calibration curve based on standard polystyrene.

[0026] There are no particular limitations on the functional group equivalent weight (g / mol) of component (A1), but from the standpoint of reactivity, it is preferably 50 to 1,000, more preferably 100 to 500, and particularly preferably 150 to 400. In this specification, the epoxy equivalent weight refers to a value measured in accordance with JIS K7236.

[0027] The content of component (A1) in the resin composition is not particularly limited, but from the viewpoint of improving reflow resistance, it is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 5 parts by mass or more, when the total amount of the resin composition is 100 parts by mass. Also, from the viewpoint of achieving a low refractive index and high transparency, the content of component (A1) in the resin composition is preferably 95 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 15 parts by mass or less, when the total amount of the resin composition is 100 parts by mass.

[0028] Component (A1) is preferably a liquid at 25°C, but may be a solid at room temperature. From the viewpoint of preparation and dispensability of the resin composition, component (A1) preferably has a viscosity at 25°C of 10 to 10,000 mPa·s, more preferably 20 to 8,000 mPa·s, and particularly preferably 50 to 5,000 mPa·s. In this specification, viscosity is expressed as a value measured in accordance with Japanese Industrial Standard JIS K6833, unless otherwise specified. Specifically, it can be determined by measuring using an E-type viscometer at a rotation speed of 10 rpm.

[0029] As the component (A1), for example, a compound represented by the following general formula (1) can be used.

[0030] [In general formula (1), R １ or R ２ represents a glycidyl group, an epoxy group, or a hydrocarbon group having 1 to 6 carbon atoms, and n represents an integer of 3 to 10. １ , R ２ may be the same or different. １ or R ２ At least two of them are organic groups containing a glycidyl group or an epoxycyclohexylethyl group.

[0031] Examples of compounds in which the component (A1) is a cyclic siloxane compound having an epoxy group include 2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8,8-hexamethyl-cyclotetrasiloxane, 4,8-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,2,4,6,6,8-hexamethyl-cyclotetrasiloxane, 2,4-di[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6,8-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane, 4,8-di[2-(3-{oxabicyclo[ 4.1.0]heptyl})ethyl]-2,6-dipropyl-2,4,6,8-tetramethyl-cyclotetrasiloxane, 2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,6,8-pentamethyl-cyclotetrasiloxane, 2,4,8-tri[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-6-propyl-2,4,6,8-tetramethyl-cyclotetrasiloxane, and 2,4,6,8-tetra[2-(3-{oxabicyclo[4.1.0]heptyl})ethyl]-2,4,6,8-tetramethyl-cyclotetrasiloxane.

[0032] When component (A1) is a cyclic siloxane compound having an epoxy group, commercially available products include, but are not limited to, cyclic siloxane compounds having an alicyclic epoxy group such as KR-470 (functionality 4), X-40-2670 (functionality 4), and X-40-2678 (functionality 2) (all manufactured by Shin-Etsu Chemical Co., Ltd.), and cyclic siloxane compounds having a glycidyl group, which is a non-alicyclic epoxy group such as X-40-2701 (functionality 4) (manufactured by Shin-Etsu Chemical Co., Ltd.), X-40-2728 (functionality 2) (manufactured by Shin-Etsu Chemical Co., Ltd.), and EP-3400L (functionality 4) (manufactured by ADEKA Corporation). It is preferable that component (A1) be one of these epoxy-modified cyclic siloxane compounds having two or four epoxy groups. Component (A1) may be any one of these compounds, or two or more of these compounds may be used in combination.

[0033] The epoxy equivalent (g / mol) of the (A1) cyclic siloxane compound is not particularly limited, but from the viewpoint of reactivity, it is preferably 50 to 1,000, more preferably 100 to 500, and even more preferably 150 to 400. In this specification, the epoxy equivalent can be measured in accordance with JIS K7236.

[0034] The weight-average molecular weight of the (A1) cyclic siloxane compound is not particularly limited, but is preferably 200 to 3,000, more preferably 300 to 2,000, and even more preferably 400 to 1,000. When the weight-average molecular weight of the (A1) cyclic siloxane compound is within the above range, the viscosity of the composition becomes appropriate and workability is improved. Note that, in this specification, the weight-average molecular weight can be calculated by gel permeation chromatography (GPC) using a calibration curve based on standard polystyrene.

[0035] The (A1) cyclic siloxane compound is preferably a liquid at room temperature (25°C), but may also be a solid. From the viewpoint of workability, the viscosity of the (A1) cyclic siloxane compound at 25°C is preferably 10 to 30,000 mPa·s. In this specification, viscosity can be measured in accordance with Japanese Industrial Standard JIS K6833. Specifically, viscosity can be determined by measuring using an E-type viscometer at a rotation speed of 10 rpm. The measurement is not particularly limited by the equipment, rotor, or measurement range used.

[0036] (A2) Linear siloxane compound having a reactive functional group The resin composition of this embodiment may contain (A2) a linear siloxane compound having a reactive functional group (hereinafter also referred to as "(A2) component" or "(A2) linear siloxane compound") as (A) a siloxane compound having a reactive functional group. The (A2) component is not particularly limited as long as it is a linear siloxane compound having one or more reactive functional groups per molecule. As the (A2) component, one type may be used alone, or two or more types may be used in combination.

[0037] The reactive functional group of component (A2) is the same as that of component (A1) and is not particularly limited, but examples thereof include epoxy groups, glycidyl groups, oxetanyl groups, alkoxysilyl groups, vinyl ether groups, and alkoxyl groups. Furthermore, it is preferable that component (A2) has a cationically polymerizable group as the reactive functional group. A cationically polymerizable group refers to a functional group that undergoes chain polymerization in the presence of cations. By including a cationically polymerizable group bonded to a linear siloxane skeleton in component (A2), it is possible to achieve low refractive index while also reducing cure shrinkage. Examples of cationically polymerizable groups include epoxy groups, glycidyl groups, oxetanyl groups, and vinyl ether groups. Although not particularly limited, from the perspective of lowering the refractive index, it is preferable that the cationically polymerizable group is a functional group that does not have an aromatic ring.

[0038] There are no particular limitations on the number of reactive functional groups per molecule of the component (A2), so long as it is one or more. From the standpoints of optical properties, heat resistance, ease of raw material availability, reactivity, and the like, it is preferable for the number to be two or more, and the number is preferably 2 to 10, more preferably 2 to 6, even more preferably 2 to 4, and particularly preferably 2.

[0039] The linear siloxane compound refers to a compound having a linear siloxane skeleton based on siloxane bonds (—Si—O—Si—). The number of Si—O units forming the linear siloxane skeleton (equal to the number of silicon atoms forming the siloxane chain) is not particularly limited, but is preferably 2 to 50, more preferably 3 to 40, even more preferably 5 to 30, and particularly preferably 10 to 20, from the viewpoints of optical properties, heat resistance, availability of raw materials, reactivity, etc.

[0040] From the viewpoints of optical properties, heat resistance, and adhesiveness, it is preferable that the cationically polymerizable group of component (A2) is an epoxy group. It is preferable that component (A2) has one or more epoxy groups in the molecule. When the cationically polymerizable group is an epoxy group, the epoxy group may be an alicyclic epoxy group or a non-alicyclic epoxy group, as with component (A1). From the viewpoint of achieving excellent transparency, it is preferable that the epoxy group is an alicyclic epoxy group.

[0041] In the component (A2), the epoxy group may be bonded directly to the linear siloxane skeleton, or may be bonded via a linking group. The linking group may be any divalent group, such as an alkylene group (-(CH ２ ) ｎ Examples of such bonds include - (n is an integer of 0 or more), ether bonds (-O-), and combinations thereof. Although the epoxy group and the linear siloxane skeleton are close to each other, a dense cured product tends to be obtained when the resin composition is cured, and the cured product has excellent heat resistance (reflow resistance). Therefore, when the epoxy group is bonded to the linear siloxane skeleton via a linking group, the number of atoms between the epoxy group and the linear siloxane skeleton is preferably 4 or less, and more preferably 2 or less.

[0042] The weight-average molecular weight of component (A2) is preferably 200 to 10,000, more preferably 200 to 8,000, and particularly preferably 400 to 6,000. When the weight-average molecular weight of component (A2) is within this range, the viscosity of the resin composition becomes appropriate, and the cured product has a good balance of optical properties and heat resistance.

[0043] There are no particular limitations on the amount of functional groups (g / mol) in the component (A2), but from the standpoint of reactivity, it is preferably 300 to 5,000, more preferably 350 to 3,000, even more preferably 400 to 2,700, and particularly preferably 400 to 1,500.

[0044] The content of component (A2) in the resin composition is not particularly limited, but from the viewpoint of achieving a low refractive index and high transparency, it is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 20 parts by mass or more, when the total amount of the resin composition is 100 parts by mass. Also, from the viewpoint of improving reflow resistance, the content of component (A2) in the resin composition is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less, when the total amount of the resin composition is 100 parts by mass.

[0045] The component (A2) is preferably a liquid at 25° C., but may be a solid at room temperature. From the viewpoint of preparation and dispensability of the resin composition, the component (A2) preferably has a viscosity at 25° C. of 1 to 500 mPa s, more preferably 2 to 300 mPa s, and particularly preferably 5 to 100 mPa s.

[0046] Examples of when component (A2) is a linear siloxane compound having an epoxy group include a linear siloxane compound having an epoxy group at its terminal. A linear siloxane compound having an epoxy group at its terminal means a compound having an alicyclic epoxy group or a non-alicyclic epoxy group at the terminal of a main chain formed by siloxane bonds. While component (A2) may have an epoxy group at at least one terminal of the main chain, it is preferable that it has an epoxy group at all terminals of the main chain (or at both terminals of the main chain if the main chain is not branched). Component (A2) may have epoxy groups on side chains in addition to the terminals of the main chain, but it is preferable that it has epoxy groups only at the terminals of the main chain. From the viewpoints of optical properties and adhesiveness, it is particularly preferable that component (A2) has a glycidyl ether structure at both terminals.

[0047] As the component (A2), for example, a compound represented by the following general formula (2) can be used.

[0048] [In general formula (2), R ４ ~R ７ and R ９ ~R １２ R each independently represents an organic group containing a hydrocarbon group or a glycidyl group. ３ and R ８ each independently represents an organic group containing a glycidyl group; m represents -[Si(R ５ ) (R １１ n represents the number of moles of siloxane units represented by —[Si(R )O]— in one molecule, and is a number from 0 to 3000. ６ ) (R １０ )O]— in one molecule, and is a number from 0 to 3000.

[0049] When the component (A2) is a linear siloxane compound having an alicyclic epoxy group or a non-alicyclic epoxy group at its terminal, examples of the compound include, but are not limited to, modified silicone oil. Commercially available modified silicone oils include, but are not limited to, modified silicone oils having alicyclic epoxy groups at both ends such as X-22-169B and X-22-169AS, modified silicone oils having epoxy groups at both ends such as X-22-163, KF-105, X-22-163A, X-22-163B, and X-22-163C, modified silicone oils having alicyclic epoxy groups in the side chain such as X-22-2046 and KF-102, modified silicone oils having epoxy groups in the side chain such as X-22-343, KF-101, KF-1001, and X-22-2000, modified silicone oils having epoxy groups in the side chain, and X-22-9002, modified silicone oil having epoxy groups at both ends and in the side chain (all manufactured by Shin-Etsu Chemical Co., Ltd.). It is preferred that component (A2) is a modified silicone oil. The component (A2) may be any one of these, or two or more of them may be used in combination.

[0050] The epoxy equivalent (g / mol) of the linear siloxane compound (A2) is not particularly limited, but from the viewpoint of reactivity, it is preferably 100 to 4,000, more preferably 120 to 2,000, and even more preferably 150 to 1,000.

[0051] The weight-average molecular weight of the linear siloxane compound (A2) is not particularly limited, but is, for example, preferably 200 to 10,000, more preferably 200 to 8,000, and even more preferably 400 to 6,000. When the weight-average molecular weight of the linear siloxane compound (A2) is within the above range, the viscosity of the composition becomes appropriate, and workability is improved.

[0052] The linear siloxane compound (A2) is preferably a liquid at room temperature (25°C), but may also be a solid. From the viewpoint of workability, the viscosity of the linear siloxane compound (A2) at 25°C is preferably 1 to 500 mPa·s, more preferably 2 to 300 mPa·s, and even more preferably 5 to 100 mPa·s.

[0053] Blending ratio of component (A1) and component (A2) Among the siloxane compounds (A) contained in the resin composition, the cyclic siloxane compound (A1) having a reactive functional group contributes to lowering the refractive index and improving heat resistance. Furthermore, the linear siloxane compound (A2) having a reactive functional group contributes to lowering the refractive index and improving transparency by reducing the crosslink density of the cured product. Therefore, the siloxane compound (A) contains both component (A1) and component (A2). In this case, the ratio (mass ratio) of the siloxane compound (A), component (A1) to component (A2) is preferably 100:0 to 0:100, 90:10 to 10:90, 85:15 to 5:95, 75:25 to 15:85, 70:25 to 25:75, 65:35 to 35:65, 60:40 to 30:70, 55:45 to 25:75, or 50:50 to 20:80.

[0054] The content of component (A) in the resin composition of this embodiment is preferably 5 to 99 parts by mass, more preferably 10 to 70 parts by mass, even more preferably 20 to 60 parts by mass, and particularly preferably 30 to 50 parts by mass, when the total amount of the resin composition is 100 parts by mass. By setting the content of component (A) within the above range, it is possible to reduce the refractive index, achieve high transparency, and improve adhesion.

[0055] (A3) Oxetane Compound The component (A) in the resin composition of this embodiment may contain an oxetane compound as (A3). The oxetane compound (A3) is not particularly limited as long as it is a compound containing an oxetane ring. When the resin composition contains an oxetane compound, the initial adhesion can be improved. However, it is preferable not to contain compounds that may increase the refractive index of the resin composition, such as oxetane compounds having aromatic rings. The blending ratio of the oxetane compound is not particularly limited, but is preferably 1 to 5 parts by mass when the total amount of the resin composition is 100 parts by mass.

[0056] Examples of the oxetane compound include 3,3'-(oxybismethylene)bis(3-ethyloxetane), 3-ethyl-3-hydroxymethyloxetane, 3-(meth)allyloxymethyl-3-ethyloxetane, (3-ethyl-3-oxetanylmethoxy)methylbenzene, 4-fluoro-[1-(3-ethyl-3-oxetanylmethoxy)methyl]benzene, [1-(3-ethyl-3-oxetanylmethoxy)ethyl]phenyl ether, and isobutyl ether. 2-ethylhexyl (3-ethyl-3-oxetanylmethyl) ether, ethyl diethylene glycol (3-ethyl-3-oxetanylmethyl) ether, tetrahydrofurfuryl (3-ethyl-3-oxetanylmethyl) ether, tetrabromophenyl (3-ethyl-3-oxetanylmethyl) ether, 2-tetrabromophenoxyethyl (3-ethyl-3-oxetanylmethyl) ) ether, pentachlorophenyl (3-ethyl-3-oxetanylmethyl) ether, pentabromophenyl (3-ethyl-3-oxetanylmethyl) ether, ethylene glycose bis(3-ethyl-3-oxetanylmethyl) ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl) ether, tetraethylene glycol bis(3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tris(3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis(3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol tetrakis(3-ethyl-3-oxetanylmethyl) ether, ditrimethylolpropane tetrakis(3-ethyl-3-oxetanylmethyl) ether, and the like, but are not limited thereto.

[0057] Commercially available oxetane compounds include, for example, OXT-212, OX-221, OXT-213, and OXT-101 (manufactured by Toagosei Co., Ltd.).

[0058] (B) Polymerization Initiator The resin composition of this embodiment contains (B) polymerization initiator (hereinafter also referred to as "component (B)"). The component (B) is not particularly limited as long as it can initiate the polymerization reaction of component (A). As component (B) of this embodiment, an appropriate compound may be used depending on the type of reactive functional group possessed by component (A). As component (B), one type may be used alone, or two or more types may be used in combination.

[0059] In this embodiment, a photopolymerization initiator is preferably used as component (B). The photopolymerization initiator is not particularly limited as long as it is a compound that generates an acid, base, radical, or the like that cures component (A) upon irradiation with active energy rays. Here, active energy rays include all light in the broad sense, such as radiation such as α-rays and β-rays, electromagnetic waves such as γ-rays and X-rays, electron beams (EB), ultraviolet rays of about 100 to 400 nm, and visible light of about 400 to 800 nm, and preferably ultraviolet rays.

[0060] When the reactive functional group of component (A) is a cationically polymerizable group, it is preferable to use a photoacid generator as the photopolymerization initiator. The photoacid generator is a compound that generates an acid upon irradiation with active energy rays. Cationic polymerization proceeds between the cationically polymerizable groups of component (A) due to the catalytic effect of the acid generated from the photoacid generator. The photoacid generator is not particularly limited, and examples thereof include compounds that generate an acid upon exposure to radiation, such as onium salts, halogen-containing compounds, diazomethane compounds, sulfone compounds, and sulfonic acid compounds.

[0061] From the viewpoint of achieving a low refractive index and high transparency, it is preferable to use an onium salt as the photoacid generator. The onium salt is a salt compound of an onium ion and an anion. The onium salt reacts with light to release a Lewis acid or a Bronsted acid (protonic acid).

[0062] The onium salt is not particularly limited, but is preferably at least one onium salt selected from the group consisting of onium borates and onium gallates, and in this case, it is preferable that the onium salt contains at least one cation selected from the group consisting of iodonium and sulfonium.

[0063] The onium gallate salt is not particularly limited, but an onium salt represented by the following general formula (3) can be used.

[0064] [In general formula (3), R １３ ~R １６ each independently represents an alkyl group having 1 to 18 carbon atoms, an aryl group, or a group having a heterocycle, R １３ ~R １６ at least one of is an aryl group, the number of carbon atoms in the aryl group (excluding the number of carbon atoms in the substituent) is 6 to 14, and the aryl group may have a substituent; E represents an element of Group 15 to 17 (IUPAC notation) with a valence of n, and n is an integer of 1 to 3; R １７ is an organic group bonded to E, and R １７ The number of R is n+1, and (n+1) R １７ may be the same or different, and two or more R １７ are directly connected to each other or -O-, -S-, -SO-, -SO ２ A ring structure containing the element E may be formed via -, -NH-, -CO-, -COO-, -CONH-, an alkylene group, or a phenylene group.]

[0065] The onium gallate salt may contain an anion having a tetraphenyl gallate skeleton, and a hydrogen atom of a phenyl group of the tetraphenyl gallate skeleton may be substituted with at least one halogen atom selected from the group consisting of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The anion having a tetraphenyl gallate skeleton is preferably tetrakis(pentafluorophenyl)gallate. The onium gallate salt can be synthesized, for example, based on the method described in JP 2017-048325 A.

[0066] Examples of onium gallate salts include 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)gallate, triarylsulfonium tetrakis(pentafluorophenyl)gallate, diphenyl[4-(phenylthio)phenyl]sulfonium tetrakis(pentafluorophenyl)gallate, and 4-isopropylphenyl(p-tolyl)iodonium tetrakis(pentafluorophenyl)gallate, but are not limited to these compounds.

[0067] The onium borate salt is not particularly limited, but an onium salt represented by the following general formula (4) can be used.

[0068] [In general formula (4), R １８ ~R ２１ are each independently an alkyl group having 1 to 18 carbon atoms or Ar, provided that at least one is Ar, and Ar is an aryl group having 6 to 14 carbon atoms (not including the carbon atoms of the following substituents), and some of the hydrogen atoms in the aryl group are replaced with an alkyl group having 1 to 18 carbon atoms, an alkyl group having 1 to 8 carbon atoms substituted with a halogen atom, an alkenyl group having 2 to 18 carbon atoms, an alkynyl group having 2 to 18 carbon atoms, an aryl group having 6 to 14 carbon atoms, a nitro group, a hydroxyl group, a cyano group, or -OR ２３ an alkoxy group or an aryloxy group represented by R ２４ an acyl group represented by CO—, R ２５ an acyloxy group represented by COO-; ２６ an alkylthio group or an arylthio group represented by the formula: ２７ R ２８ or a halogen atom, ２３ ~R ２６ is an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 14 carbon atoms, R ２７ and R ２８ is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 14 carbon atoms; E represents an element of Group 15 to 17 (IUPAC notation) with a valence of n, n is an integer of 1 to 3, and R ２２ is an organic group bonded to E, and R２２ The number of R is n+1, and (n+1) R ２２ may be the same or different, and two or more R ２２ are directly connected to each other or -O-, -S-, -SO-, -SO ２ A ring structure containing the element E may be formed via -, -NH-, -CO-, -COO-, -CONH-, an alkylene group, or a phenylene group.]

[0069] The onium borate salt may contain an anion having a tetraphenylborate skeleton, and a hydrogen atom of a phenyl group of the tetraphenylborate skeleton may be substituted with at least one halogen atom selected from the group consisting of fluorine, chlorine, bromine, and iodine. The anion having a tetraphenylborate skeleton is preferably tetrakis(pentafluorophenyl)borate. The onium borate salt can be synthesized, for example, based on the method described in JP 2014-205624 A.

[0070] Specific examples of onium borate salts include 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate, triarylsulfonium tetrakis(pentafluorophenyl)borate, diphenyl[4-(phenylthio)phenyl]sulfonium tetrakis(pentafluorophenyl)borate, and 4-isopropylphenyl(p-tolyl)iodonium tetrakis(pentafluorophenyl)borate, but are not limited to these compounds.

[0071] The content of the component (B) in the resin composition is not particularly limited, but from the viewpoint of polymerizability and from the viewpoint of providing a cured product with a low refractive index and high transparency, it is 0.05 to 20.0 parts by mass, preferably 0.1 to 15 parts by mass, more preferably 0.3 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the organic substance (A). Note that the content of the component (B) can be appropriately designed taking into consideration various factors such as the type and properties of the polymerizable compound, the type and dose of active energy rays (if active energy rays are used), heating temperature, curing time, humidity, and thickness of the resin composition, and is not limited to the above range.

[0072] (C) Inorganic Particles The resin composition of the present embodiment contains (C) inorganic particles (hereinafter also referred to as "component (C)"), and the (C) inorganic particles have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4.

[0073] Component (C) is not particularly limited as long as it is a granular material formed from an inorganic material. Examples of inorganic materials that can be used include silica, talc, alumina, aluminum nitride, calcium carbonate, aluminum silicate, magnesium silicate, magnesium carbonate, barium sulfate, barium carbonate, lime sulfate, aluminum hydroxide, calcium silicate, potassium titanate, titanium oxide, zinc oxide, silicon carbide, silicon nitride, and boron nitride. Component (C) may be used alone or in combination of two or more.

[0074] As component (C), silica particles are preferably used from the viewpoint of reducing the refractive index. Furthermore, the silica is preferably amorphous silica. To prevent aggregation, component (C) may be surface-treated with a coupling agent such as a silane coupling agent.

[0075] The shape of component (C) is not particularly limited and may be spherical, scaly, needle-like, irregular, or the like. However, when scaly or needle-like inorganic particles are used in a resin composition for an optical adhesive, light may be scattered if the inorganic particles are randomly oriented. Therefore, from the viewpoints of refractive index and transmittance, the inorganic particles of component (C) are preferably spherical, with a sphericity of 0.8 or more, and more preferably a nearly spherical shape of 0.9 or more. Furthermore, a nearly spherical shape with a sphericity of 0.8 or more is preferred from the viewpoints of improving the dispersibility of the inorganic particles in the resin composition and the injectability of the resin composition. In this specification, "sphericity" is defined as "the ratio of the minimum diameter to the maximum diameter of a particle." For example, the ratio of the minimum diameter to the maximum diameter observed as a result of observation with a scanning electron microscope (SEM) may be 0.8 or more. Preferably, component (C) is silica particles with a sphericity of 0.9 or more.

[0076] In addition, when silica is used as inorganic particles, its manufacturing method is not particularly limited.For example, the spherical silica powder obtained by reacting metal silicon with oxygen (deflagration method (VMC method)), the spherical silica powder obtained by melting pulverized silica, the silica particles obtained by sol-gel method, precipitation method, aqueous solution wet method can be exemplified.Among these, from the viewpoint of optical properties, the silica particles obtained by sol-gel method, that is, sol-gel silica particles, are particularly preferred, because they have high sphericity and a relatively sharp particle size distribution.

[0077] The average particle size of component (C) is preferably 3.0 μm or less, more preferably 2.0 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less. In this specification, unless otherwise specified, the average particle size refers to the volume-based median diameter (D50) measured by a laser diffraction scattering method in accordance with ISO-13320 (2020) (JIS Z 8825:2022).

[0078] In this specification, D10 refers to the particle size of inorganic particles when the cumulative volume distribution curve obtained by laser diffraction scattering is 10% from the small particle size side, and D90 refers to the particle size of inorganic particles when the cumulative volume distribution curve obtained by laser diffraction scattering is 90% from the small particle size side.

[0079] The D10 / D90 of inorganic particles means the ratio of the particle diameter (D10) of inorganic particles when the cumulative total from the small particle size side is 10% to the particle diameter (D90) of inorganic particles when the cumulative total from the small particle size side is 90% in a volume cumulative distribution curve obtained by a laser diffraction scattering method. Note that, like the above-mentioned D50, D10 / D90 can be measured using a laser diffraction particle size distribution analyzer.

[0080] By setting the average particle size of component (C) to the upper limit or less, transmittance can be increased. Furthermore, from the viewpoint of transparency, it is preferable that component (C) is substantially free of inorganic particles with a maximum particle size of 5 μm or more. In this specification, "substantially free" means that the content in component (C) is 0.1% or less, preferably 0.01% or less. The lower limit of the average particle size of component (C) is not particularly limited, but from the viewpoint of the viscosity of the resin composition, it is preferably 0.05 μm or more, more preferably 0.06 μm or more. Furthermore, from the viewpoint of reducing viscosity, it is preferable that component (C) is substantially free of inorganic particles having a D10 value of less than 0.01 μm.

[0081] From the viewpoint of reducing transmittance, the smaller the average particle size of the inorganic particles, the better. However, if the average particle size is too small, the viscosity of the resin composition increases, resulting in poor injectability. Furthermore, if inorganic particles with a large average particle size are included, the transmittance of the cured resin composition will be low. Therefore, the average particle size of component (C) is preferably 0.05 μm to 3.0 μm, more preferably 0.06 μm to 2.0 μm, even more preferably 0.07 μm to 1.5 μm, and particularly preferably 0.07 μm to 1.0 μm.

[0082] As mentioned above, from the viewpoint of reducing transmittance, the smaller the average particle size of the inorganic particles, the better. However, if the average particle size is too small, the viscosity of the resin composition increases, resulting in poor injectability. Furthermore, if inorganic particles with a large average particle size are included, the transmittance of the cured resin composition decreases. Therefore, the D10 of component (C) is preferably 0.01 to 2.0 μm, more preferably 0.02 to 1.0 μm, and even more preferably 0.05 to 0.5 μm. Furthermore, the D90 of component (C) is preferably 0.01 to 5.0 μm, more preferably 0.05 to 3.0 μm, and even more preferably 0.07 to 2.0 μm.

[0083] For example, inorganic particles having an average particle size of 0.05 μm or more and less than 2.0 μm may be used in combination with inorganic particles having an average particle size of 0.5 μm to 1.0 μm. When a plurality of inorganic particles are used in combination, the above-mentioned D50, D10, and D90 values ​​may be within the above-mentioned ranges for the entire inorganic particles when the plurality of inorganic particles are mixed.

[0084] From the viewpoint of reducing the viscosity of the resin composition and increasing its transparency, it is preferable to use inorganic particles with a sharp (narrow) particle size distribution. As an indicator of this, the ratio (D10 / D90) of the particle size at 10% cumulative volume (D10) from the small particle size side to the particle size at 90% cumulative volume (D90) from the small particle size side in the particle size distribution based on laser diffraction / scattering method can be used. A low D90 / D10 value indicates a narrow particle size distribution (a sharp particle size distribution with uniform particle diameters). When all inorganic particles have the same particle size, the value of D90 / D10 is 1; conversely, the wider the particle size distribution, the larger the value of D90 / D10. In the resin composition of this embodiment, component (C) contains inorganic particles having a D90 / D10, which is the ratio of the 90% cumulative volume value (D90) to the 10% cumulative volume value (D10) in the particle size distribution, of 1 to 4. The D90 / D10 value of the inorganic particles contained in component (C) may be 1 to 4, preferably 1.1 to 3.8, more preferably 1.2 to 3.5, even more preferably 1.3 to 3.3, and particularly preferably 1.4 to 3.0. When the D90 / D10 value is within the above range, it becomes possible to uniformly disperse the inorganic particles in the resin composition, and a resin composition having low viscosity and excellent transparency can be obtained.

[0085] Furthermore, from the viewpoint of reducing the viscosity of the resin composition and increasing the transparency, it is preferable that the (C) component contains inorganic particles having a D50 / D10 ratio, which is the ratio of the cumulative volume 50% value (D50) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 2. The D50 / D10 value of the inorganic particles contained in the (C) component is sufficient as long as it is 1 to 2, preferably 1.1 to 1.9, and more preferably 1.2 to 1.8. Furthermore, from the viewpoint of reducing the viscosity of the resin composition and increasing the transparency, it is preferable that the (C) component contains inorganic particles having a D90 / D50 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 50% value (D50) in the particle size distribution, of 1 to 2. The D90 / D50 value of the inorganic particles contained in the (C) component is sufficient as long as it is 1 to 2, preferably 1.1 to 1.9, and more preferably 1.2 to 1.8.

[0086] The content of component (C) in the resin composition of this embodiment is preferably 0.1 to 80 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 10 to 80 parts by mass, and particularly preferably 20 to 80 parts by mass, 30 to 80 parts by mass, 35 to 75 parts by mass, or 40 to 70 parts by mass, when the total amount of the resin composition is 100 parts by mass. By setting the content of component (C) within the above range, reflow resistance is improved, and high transparency and a low refractive index can be achieved.

[0087] [Other Optional Components] The resin composition of the present embodiment may contain optional components other than the above-described components (A), (B), and (C), such as the components described below, as necessary, within the scope of the present embodiment.

[0088] (D) Other Additives If desired, the resin composition of the present embodiment may further contain other additives, such as a coupling agent, a stabilizer, an ion trapping agent, a leveling agent, an antioxidant, an antifoaming agent, a viscosity modifier, a solvent, etc., within the scope of the present embodiment. The content of each additive can be appropriately selected.

[0089] The method for producing the resin composition of this embodiment is not particularly limited. For example, the resin composition of this embodiment can be obtained by simultaneously or separately introducing component (A), component (B), and, if necessary, component (C), (D), and other additives into an appropriate mixer, and stirring and mixing them while melting them by heating if necessary, to form a homogeneous composition. The mixer is not particularly limited, but examples include a Raikai mixer, a Henschel mixer, a three-roll mill, a ball mill, a planetary mixer, and a bead mill equipped with a stirring device and a heating device. These devices may also be used in appropriate combination. The resin composition obtained in this manner is photocurable and thermosetting.

[0090] [Viscosity of Resin Composition] The viscosity of the resin composition of this embodiment is not particularly limited and may be adjusted appropriately depending on the application. For example, the components may be selected and their blending ratios adjusted appropriately so that the viscosity of the resin composition at 25°C is in the range of 0.01 to 1,000 Pa·s. In this specification, unless otherwise specified, viscosity is expressed as a value measured in accordance with Japanese Industrial Standard JIS K6833. Specifically, it can be determined by measuring using an E-type viscometer at a rotation speed of 10 rpm. From the viewpoint of improving injectability, the viscosity of the resin composition at 25°C is preferably 0.05 Pa·s to 50 Pa·s, preferably 0.1 Pa·s to 20 Pa·s, more preferably 0.1 Pa·s to 15 Pa·s, and even more preferably 0.1 Pa·s to 12 Pa·s. A resin composition having a viscosity at 25°C of 12 Pa·s or less provides particularly good injectability. If the viscosity of the resin composition is too low, it may not be able to maintain its shape when applied and may flow, whereas if the viscosity of the resin composition is too high, it may be difficult to inject or may become uneven when applied.

[0091] In addition, the thixotropic index value (TI (Thixotropic Index) value) of the resin composition is preferably 0.5 to 3.0. In this specification, the TI value is the ratio of the viscosity at 5 rpm and 50 rpm measured at 25 °C using an E-type viscometer, and is calculated as the viscosity at 5 rpm / the viscosity at 50 rpm. The TI value measures the dependency of viscosity on shear rate (the rotation speed of the viscometer) and is an index representing thixotropy. A Newtonian fluid such as water, whose viscosity does not change even when the shear rate changes, has a TI value of 1. A TI value smaller than 1 indicates that a smaller shear force results in a smaller viscosity than a larger shear force, and a TI value greater than 1 indicates that a smaller shear force results in a larger viscosity than a larger shear force. The larger the TI value, the more thixotropic the resin composition. A TI value of 0.5 to 3.0 improves workability when injecting the resin composition. The resin composition may have thixotropy close to that of a Newtonian fluid with a TI value of 0.8 to 1.2, or may have thixotropy of a non-Newtonian fluid with a thixotropic index value of more than 1.2.

[0092] [Cured Product of Resin Composition] The resin composition of this embodiment can be easily cured into a cured product by irradiating it with the above-mentioned active energy rays, preferably light having a wavelength of 10 nm to 600 nm, more preferably ultraviolet light having a wavelength of 100 nm to 500 nm, even more preferably ultraviolet light having a wavelength of 250 nm to 450 nm, and particularly preferably ultraviolet light having a wavelength of 300 nm to 400 nm. When the resin composition of this embodiment is cured by ultraviolet irradiation, the irradiation amount (cumulative light amount) of the ultraviolet light used is 500 to 30,000 mJ / cm. ２ The device used for irradiating ultraviolet light is not particularly limited, and examples thereof include conventionally known devices.

[0093] [Refractive Index, Transmittance, and Reflow Resistance of Cured Product] (Refractive Index of Cured Product) The resin composition of this embodiment comprises (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, wherein the (C) inorganic particles have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4. This results in excellent optical properties when the cured product is formed. In this case, when the resin composition comprises (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator, and the (B) polymerization initiator contains at least one onium salt selected from the group consisting of onium borate salts and onium gallate salts, the cured product will have excellent optical properties and heat resistance. Specifically, the cured product of the resin composition of this embodiment has a low refractive index, high transparency, and a small weight loss rate after the reflow process. In this case, if the resin composition contains, as the siloxane compound (A), both the cyclic siloxane compound (A1) having a reactive functional group and the linear siloxane compound (A2) having a reactive functional group, the optical properties and heat resistance of the cured product will be more excellent.

[0094] The cured product of this embodiment may have a refractive index of 1.49 or less at a wavelength of 1310 nm and / or 589 nm at 25°C, preferably 1.48 or less, more preferably 1.47 or less, even more preferably 1.46 or less, or 1.45 or less. The refractive index of the cured product of this embodiment may have a refractive index of 1.40 or more but less than 1.49 at a wavelength of 1310 nm and / or 589 nm at 25°C, preferably 1.41 or more but less than 1.49, more preferably 1.42 to 1.48, and even more preferably 1.43 to 1.47. Unless otherwise specified, the refractive index herein is expressed as a value measured in accordance with JIS K7142:2014 Method A.

[0095] (Transmittance of Cured Product) The cured product of this embodiment has a transmittance of 85% or more at a thickness of 100 μm and a wavelength of 1310 nm and / or 589 nm at 25° C., preferably 90% or more, more preferably 91% or more, even more preferably 92% or more, and particularly preferably 94% or more. The transmittance of the cured product at a thickness of 100 μm and a wavelength of 1310 nm and / or 589 nm at 25° C. is in the range of 85 to 99%, preferably 90 to 95%, more preferably 91 to 95%, even more preferably 92 to 95%, and particularly preferably 93 to 95%.

[0096] (Reflow Resistance of Cured Product) The cured product of the resin composition of this embodiment has excellent heat resistance, particularly excellent reflow resistance, and exhibits a small weight loss rate after the reflow process. In this specification, reflow resistance refers to the ability to withstand thermal shock at a maximum temperature of 260°C for 1 minute. In other words, the cured product of the resin composition of this embodiment has the property of showing little change in physical properties before and after the reflow process (maximum temperature of approximately 260°C) in which electronic components are soldered when mounted. For example, the resin composition of this embodiment has the property of showing little change in adhesive strength before and after the reflow process when cured.

[0097] The reflow resistance of a cured resin composition can be evaluated by the rate of decrease in evaluated adhesive strength. The adhesive strength of the cured product can be measured by any method, as long as it is the same before and after the reflow process. For example, it can be measured by die shear measurement. The die shear strength is measured as follows: (1) A resin composition (sample) is applied to a glass substrate. (2) A Si chip is placed on the applied sample to prepare a test piece. (3) The test piece is irradiated with UV light from the glass substrate side to cure the sample. (4) After the sample is photocured, the die shear strength is immediately measured using a bond tester. This value is taken as the adhesive strength before reflow. (5) Next, the test piece is subjected to a 6-minute heat treatment. The heat treatment involves raising the temperature from room temperature to 170°C, 160°C, 160°C, 260°C, 255°C, and cooling, with each step consisting of 6 steps of 1 minute each. This heat treatment is repeated three times. After the heat treatment, the die shear strength is immediately measured in the same manner as before reflow. This value is the adhesive strength after reflow. (6) The rate of decrease in adhesive strength before and after the reflow process is calculated using the following formula (1). The heat treatment in (5) above simulates the reflow process carried out in the mounting process. The sample before the heat treatment is labeled "before the reflow process," and the sample after the heat treatment is labeled "after the reflow process."

[0098] The smaller the absolute value of the rate of decrease in adhesive strength before and after the reflow process represented by formula (1), the smaller the fluctuation due to heat treatment, and therefore the more preferable. The cured product of the resin composition of this embodiment preferably has an absolute value of the rate of decrease in adhesive strength before and after the reflow process represented by formula (1) of 74% or less, preferably 65% ​​or less, more preferably 55% or less, even more preferably 50% or less, and particularly preferably 40% or less. The lower limit of the absolute value of the rate of decrease in adhesive strength is not particularly limited, but is, for example, 0% or more.

[0099] [Uses of Resin Composition] The resin composition of this embodiment has excellent optical properties and heat resistance, and therefore can be used for a variety of applications, including but not limited to optical adhesives for bonding optical components. For example, the resin composition of this embodiment can be used as an adhesive or sealant for fixing, bonding, or protecting optical components, electronic components, and semiconductor components, or as a raw material thereof. Examples of optical components that can be used with the resin composition of this embodiment include, but are not limited to, optical fibers, fiber arrays, optical waveguide elements, lenses, filters, diffraction gratings, and optically active elements. Furthermore, the resin composition of this embodiment has excellent optical properties and heat resistance, and therefore can be suitably used, particularly as an optical adhesive for silicon photonics.

[0100] As described below, the resin composition of this embodiment can be used to fix the optical fiber 10 in a groove (V-groove 33) formed in the optical waveguide element 30, or to optically couple the optical fiber 10 to the optical waveguide 32 of the optical waveguide element 30. It is also preferable to use the resin composition of this embodiment to simultaneously fix the optical fiber 10 in the V-groove 33, which is a groove formed in the optical waveguide element 30, and optically couple the optical fiber 10 to the optical waveguide 32 of the optical waveguide element 30.

[0101] For example, the resin composition of the present embodiment may be used in a method for fixing an optical fiber to a groove formed in an optical waveguide element, or a method for optically coupling an optical fiber to an optical waveguide element. The resin composition of the present embodiment may also be used in a method for simultaneously fixing an optical fiber to a groove formed in an optical waveguide element and optically coupling the optical fiber to an optical waveguide element.

[0102] [Optical Fiber Array] The resin composition of this embodiment is preferably used for bonding optical fibers and optical waveguide elements. Specifically, it is preferable to construct an optical fiber array 1 using the resin composition of this embodiment. As shown in FIGS. 1 to 4 , the optical fiber array 1 of this embodiment includes optical fibers 10 and an adhesive layer 20. The optical fibers 10 are covered with a coating 11 and are shown in the form of ribbon fibers 12. In the optical fiber array 1, the optical fibers 10 are optically coupled to the optical waveguides 32 of the optical waveguide element 30 by the adhesive layer 20.

[0103] 1 to 4, the optical fiber array 1 of this embodiment includes a substrate 31 having a V-groove 33 formed therein for accommodating the optical fibers 10, and a presser plate 40 adhesively fixed to the surface of the optical fibers 10, and the optical fibers 10 are adhesively fixed to the V-groove 33 by an adhesive layer 20 (FIGS. 3 and 4). The adhesive layer 20 bonds the optical fibers 10 to the optical waveguide element 30 (FIG. 3), and also bonds the substrate 31 with the optical fibers 10 accommodated in the V-groove 33 to the presser plate 40 (FIG. 4).

[0104] The substrate 31 may be made of, for example, glass, a semiconductor, an organic resin, or the like, with a semiconductor substrate being preferred. The substrate may also have a ball grid array electrode (not shown) on one surface. Providing a ball grid array electrode on one surface of the substrate allows for a high density of multiple electrical interfaces, thereby enabling the miniaturization of silicon photonics devices. The ball grid array electrode is positioned with the expectation that it will be mounted and fixed to another substrate or the like by a reflow process. Therefore, the adhesive layer in the optical fiber array of this embodiment is required to be heat resistant so as to withstand the temperatures and time required during reflow heating.

[0105] The adhesive layer 20 may be formed using the resin composition of this embodiment. That is, the optical fiber array 1 of this embodiment includes an optical fiber 10 and an adhesive layer 20, the optical fiber 10 is optically coupled to an optical waveguide element 30 by the adhesive layer 20, the adhesive layer 20 contains (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, and the (C) inorganic particles have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4. In other words, the optical fiber array 1 of this embodiment preferably includes a resin composition containing (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, wherein the inorganic particles (C) have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4; an optical fiber 10; and an optical waveguide element 30, wherein the optical fiber 10 is optically coupled to the optical waveguide element 30 via the resin composition.

[0106] In this case, the optical fiber array 1 has a substrate 31 in which a V-groove 33 for accommodating the optical fiber 10 is formed, and a pressure plate 40 adhesively fixed to the surface of the optical fiber 10, and the optical fiber 10 is adhesively fixed to the V-groove 33 by an adhesive layer 20, which bonds the optical fiber 10 to the optical waveguide element 30 and also bonds the substrate 31 with the optical fiber 10 accommodated in the V-groove 33 to the pressure plate 40.

[0107] [Optical Waveguide Module] An optical waveguide module 50 (optical waveguide device) may be constructed using the optical fiber array 1 of this embodiment ( FIG. 1 ). The optical waveguide module 50 of this embodiment includes the optical fiber array 1 described above. Specifically, the optical waveguide module 50 of this embodiment includes the optical fiber array 1, an adhesive layer 20, and an optical waveguide element 30, and the optical fiber array 1 is optically coupled to the optical waveguide 32 of the optical waveguide element 30 via the adhesive layer 20. The adhesive layer 20 may be formed using the resin composition of this embodiment. Note that the optical fiber array 1 and the optical waveguide element 30 in the optical waveguide module 50 of this embodiment are not particularly limited as long as they are used in optical integrated circuits. The optical waveguide module 50 of this embodiment may be incorporated as a silicon photonics device.

[0108] [Method for Manufacturing Optical Fiber Array] The method for manufacturing an optical fiber array 1 according to the present embodiment is a method for manufacturing an optical fiber array 1 in which optical fibers 10 are optically coupled to an optical waveguide element 30 via an adhesive layer 20, the adhesive layer 20 being formed from a cured product of a resin composition containing inorganic particles having a median diameter (D50) of 0.05 to 3.0 μm and a particle size distribution in which the ratio D90 / D10, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10), is 1 to 4. In this case, the step of fixing the optical fibers 10 in V-grooves 33, which are grooves formed in the optical waveguide element 30, and the step of optically coupling the optical fibers 10 to the optical waveguides 32 of the optical waveguide element 30, may each be performed separately. Furthermore, in the manufacturing method of the optical fiber array 1 of this embodiment, it is preferable to simultaneously perform the process of fixing the optical fiber 10 in the V-groove 33, which is a groove portion formed in the optical waveguide element 30, and the process of optically coupling the optical fiber 10 to the optical waveguide 32 of the optical waveguide element 30.

[0109] A method for fixing the optical fiber 10 to the optical waveguide element 30 will be described below. Note that this fixing method is merely exemplary, and the present disclosure can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. First, the optical fiber 10 is fitted into the V-groove 33, and the end of the optical fiber 10 is brought into contact with the side surface on the optical waveguide 32 side. Here, accurate alignment is performed to reduce loss at the connection point between the optical fiber 10 and the optical waveguide 32. Next, the presser plate 40 is placed on the optical fiber 10. Thereafter, a resin composition is dripped into the V-groove 33. Note that the presser plate 40 may be formed integrally with the substrate 31.

[0110] The resin composition dropped into the V-groove 33 permeates, by capillary action, into the gap between the optical fiber 10 and the V-groove 33, along the contact portion between the optical fiber 10 and the presser plate 40, and also into the gap between the optical fiber 10 and the optical waveguide 32. Therefore, in order to enable the resin composition to permeate both the gap between the optical fiber 10 and the V-groove 33 and the gap between the optical fiber 10 and the optical waveguide 32, the resin composition needs to be injectable, and the viscosity and TI value of the resin composition need to be set to appropriate values.

[0111] Next, the resin composition is irradiated with ultraviolet light to harden it, thereby bonding the optical fiber 10 to the optical waveguide 32, the optical fiber 10 to the V-groove 33, and the optical fiber 10 to the presser plate 40. A thermal curing process may be added after the ultraviolet curing process. That is, the adhesive layer 20 in this embodiment can also serve to optically couple the optical fiber 10 to the optical waveguide 32 of the optical waveguide element 30, fix the optical fiber 10 to the V-groove 33, which is a groove portion formed in the optical waveguide element 30, and fix the optical fiber 10 to the presser plate 40. That is, the adhesive layer 20 in this embodiment can simultaneously perform the bonding for optical path coupling and the bonding for V-groove fixation. It is not necessary for the adhesive layer 20 to perform these bonding functions simultaneously. The adhesive layer 20 may be used as an adhesive layer for optically coupling the optical fiber 10 to the optical waveguide 32 of the optical waveguide element 30, or as an adhesive layer for V-groove fixation for fixing the optical fiber 10 to the V-groove 33, which is a groove portion formed in the optical waveguide element 30.

[0112] [Method] As shown in the examples described later, the resin composition of this embodiment combines (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles having a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume at 90% (D90) to the cumulative volume at 10% (D10) in the particle size distribution, of 1 to 4, to thereby achieve low viscosity and excellent optical properties and heat resistance when formed into a cured product. Therefore, this embodiment provides a method for reducing the viscosity of a resin composition, which includes the steps of combining (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles having a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume at 90% (D90) to the cumulative volume at 10% (D10) in the particle size distribution, of 1 to 4. Furthermore, according to the present embodiment, there is provided a method for improving the transmittance of a resin composition, the method including the step of combining (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles having a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4.

[0113] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, parts and % represent parts by mass and % by mass unless otherwise specified.

[0114] [Examples 1 to 14, Comparative Examples 1 to 3] Resin compositions were prepared by mixing predetermined amounts of each component using a three-roll mill according to the formulations shown in Tables 1 to 3. In Tables 1 to 3, the amount of each component is expressed in parts by mass (unit: g). The components used in the examples and comparative examples are as follows.

[0115] (A1) Cyclic siloxane compound (component (A1)) (A1-1) KR-470 (manufactured by Shin-Etsu Chemical Co., Ltd., alicyclic epoxy group, epoxy functional group number 4, viscosity at 25°C 3 Pa s, epoxy equivalent 200 g / mol) represented by the following formula: (A1-2) X-40-2728 (manufactured by Shin-Etsu Chemical Co., Ltd., non-alicyclic epoxy group, epoxy functional group number 2, viscosity at 25°C 26 mPa s, epoxy equivalent 280 g / mol) represented by the following formula (R is an alkyl group):

[0116] (A2) Linear siloxane compound (component (A2)) (A2-1) Modified silicone oil having alicyclic epoxy groups at both ends, represented by the following formula (product name: X-22-169AS, manufactured by Shin-Etsu Chemical Co., Ltd., alicyclic epoxy group, number average molecular weight 1,000, viscosity at 25°C 25 Pa s, epoxy equivalent 500 g / mol): (A2-2) The following formula (m=0, R ａ = methyl group, R ｂ = organic group having an epoxy group) at both ends (product name: KF-105, manufactured by Shin-Etsu Chemical Co., Ltd., non-alicyclic epoxy group, number average molecular weight 980, viscosity at 25°C 15 Pa s, epoxy equivalent 490 g / mol)

[0117] (A3) Oxetane Compound (Component (A)) (A3-1) 3,3'-(oxybismethylene)bis(3-ethyloxetane) (product name: OXT-221, manufactured by Toagosei Co., Ltd.)

[0118] (B) Polymerization initiator (component (B)) (B-1) 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate as an onium borate salt (B-2) 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)gallate as an onium gallate salt

[0119] (C) Inorganic particles (component (C)) (C-1) Silica particles (C-2) Silica particles (C-3) Silica particles (C-4) Silica particles (C-X1) Silica particles (C-X2) Silica particles (C-X3) Silica particles The properties of each silica particle are summarized in Table 4 below.

[0120] [Evaluation of Properties] In the examples and comparative examples, the particle size of the inorganic particles, the viscosity of the resin composition, the TI value, and the properties of the cured product obtained by curing the resin composition (refractive index, transmittance, adhesive strength, and rate of strength reduction before and after reflow) were measured as follows.

[0121] (Particle size of inorganic particles) The average particle size (D50, median diameter), particle size (D10) at 10% cumulative volume from the small particle size side in the particle size distribution, and particle size (D90) at 90% cumulative volume of the inorganic particles were measured by a laser diffraction / scattering method using a laser scattering / diffraction particle size distribution measuring device (LS13320 manufactured by Beckman Coulter, Inc.). The maximum particle size was the maximum particle size in the particle size distribution on a volume basis measured by the laser diffraction / scattering method.

[0122] (Viscosity of Resin Composition) Using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. (model number: TVE-22H, rotor name: 1°34' x R24) (set to an appropriate measurement range (H, R or U)), the viscosity of the resin composition was measured within 1 hour from its preparation at 25°C with a rotor rotation speed of 10 rpm, and the value was read 1 minute after the start of measurement.

[0123] (TI Value of Resin Composition) Using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. (model number: TVE-22H, rotor name: 1°34' x R24) (set to an appropriate measurement range (H, R, or U)), the viscosity of the resin composition was measured within 1 hour from its preparation at 25°C with rotor rotation speeds of 5 rpm and 50 rpm, and the value 1 minute after the start of measurement was read, and the TI value was calculated as the viscosity at 5 rpm / 50 rpm.

[0124] (Curing of Resin Composition) The curing conditions were a peak wavelength of 365 nm and 30,000 mJ / cm using a UV irradiator with a metal halide lamp light source. ２ After UV irradiation with an integrated light amount of 10 ...

[0125] (Refractive Index) The refractive index at 589 nm of a 100 μm thick cured film prepared from the resin composition was measured using an Abbe refractometer (NAR-2T, manufactured by Atago Co., Ltd.). In addition, the refractive index at 1310 nm of a cured product of the resin composition formed into a film on a glass substrate was measured using a spectroscopic ellipsometer (SE-2000, manufactured by Semilab).

[0126] (Transmittance) The transmittance of a 100 μm thick cured product prepared from the resin composition was measured using an ultraviolet-visible spectrophotometer (V-670, manufactured by JASCO Corporation) at measurement wavelengths of 589 nm and 1310 nm.

[0127] (Reflow Resistance) The adhesive strength of the cured resin composition was measured by die shear measurement. The die shear strength was measured as follows: (1) The prepared resin composition (sample) was applied as an adhesive onto a glass substrate. The application size was 1.5 mm length x 1.5 mm width x 0.5 mm thickness. (2) A 2 mm thick adhesive was applied to the applied sample. ２ A Si chip of 10000 was placed on the test piece to prepare a test specimen. (3) The test piece was irradiated with UV light from the glass substrate side under the above-mentioned curing conditions to cure the sample. (4) After the sample was photocured, the die shear strength was immediately measured using a universal bond tester (Dage, Series 4000). This value was used as the adhesive strength before reflow. (5) Next, the test piece was subjected to a 6-minute heat treatment. The heat treatment consisted of raising the temperature from room temperature to 170°C, 160°C, 160°C, 260°C, 255°C, and cooling, with each step consisting of 6 steps of 1 minute each. This heat treatment was repeated three times. After the heat treatment, the die shear strength was immediately measured in the same manner as before reflow. This value was used as the adhesive strength after reflow. (6) The rate of decrease in adhesive strength before and after the reflow process was calculated using the following formula (1):

[0128]

[0129]

[0130]

[0131]

[0132] [Results] As can be seen from Tables 1 to 3, resin compositions containing (A) an organic substance, (B) a polymerization initiator, and (C) inorganic particles, wherein the (C) inorganic particles have a median diameter (D50) of 0.1 to 0.35 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1.25 to 4.00, exhibited low viscosity, low refractive index, and excellent transparency. Specifically, the resin compositions of Examples 1 to 14 were found to have excellent injectability, as evidenced by their low viscosities of 10.2 Pa·s or less and TI values ​​of 2.6 or less. Furthermore, the cured products of the resin compositions of Examples 1 to 14 exhibited high transmittance of 90% or more at 25°C at wavelengths of 1310 nm and 589 nm, and excellent transparency. Furthermore, the cured products of the resin compositions of Examples 1 to 14 had low refractive indices of 1.47 or less at 25° C. at wavelengths of 1310 nm and 589 nm.

[0133] A comparison of Examples 1 to 4 revealed that, as long as the (C) inorganic particles have a predetermined median diameter (D50) and D90 / D10, the viscosity is low, the refractive index is low, and the transparency is high, regardless of the type of inorganic particles. Among Examples 1 to 4, Examples 1 and 2 showed that a smaller median diameter (D50) resulted in better transparency. A comparison of Examples 2 and 5 revealed that the viscosity is low, the refractive index is low, and the transparency is high, regardless of the type of (B) polymerization initiator. A comparison of Examples 2 and 6 revealed that the viscosity is low, the refractive index is low, and the transparency is high, regardless of the type of (A1) cyclic siloxane compound (type and number of functional groups). A comparison of Examples 2, 7, and 8 revealed that the viscosity is low, the refractive index is low, and the transparency is high when the content of (C) inorganic particles is 35 to 75 parts by weight. Comparison of Examples 2 and 9 revealed that the viscosity was low, the refractive index was low, and the transparency was high, regardless of the type of linear siloxane compound (A2) (type of functional group).

[0134] A comparison of Examples 10, 11, and 12 to 14 shows that the refractive index and heat resistance can be adjusted by adjusting the blending ratio of the (A1) cyclic siloxane compound and the (A2) linear siloxane compound. Increasing the ratio of the (A1) cyclic siloxane compound improves heat resistance, while increasing the ratio of the (A2) linear siloxane compound decreases the refractive index. A comparison of Examples 10 to 14 shows that the inclusion of the (A3) oxetane compound increases the adhesive strength before reflow.

[0135] In Comparative Example 1, the (C) inorganic particles had a large D90 / D10 of 4.44, but the transmittance was low and the transparency was poor. In Comparative Example 2, the (C) inorganic particles had a large median diameter (D50) of 3.15 μm, but the transmittance was low and the transparency was poor. In Comparative Example 3, the (C) inorganic particles had a small median diameter (D50) of 0.03 μm, but the viscosity was high at 14.0 Pa s and the injectability was poor.

[0136] The resin composition of the present invention has low viscosity and high transparency, and is therefore useful as an adhesive for optical components, particularly as an optical adhesive for silicon photonics. Furthermore, the resin composition of the present invention can achieve a low refractive index without containing a fluorine compound, and is therefore also useful as an optical adhesive from an environmental perspective.

[0137] REFERENCE SIGNS LIST 1 Optical fiber array 10 Optical fiber 11 Coating 12 Ribbon fiber 20 Adhesive layer 30 Optical waveguide element 31 Substrate 32 Optical waveguide 33 V-groove (groove portion) 40 Pressing plate 50 Optical waveguide module (optical waveguide device)

Claims

1. A resin composition comprising: (A) an organic substance; (B) a polymerization initiator; and (C) inorganic particles, wherein the inorganic particles (C) have a median diameter (D50) of 0.05 to 3.0 μm and a D90 / D10 ratio, which is the ratio of the cumulative volume 90% value (D90) to the cumulative volume 10% value (D10) in the particle size distribution, of 1 to 4.

2. The resin composition according to claim 1, wherein the inorganic particles (C) include silica particles.

3. The resin composition according to claim 1 or 2, wherein the inorganic particles (C) are substantially free of inorganic particles having a maximum particle size of 5 μm or more.

4. A resin composition according to any one of claims 1 to 3, which is substantially free of inorganic particles having a cumulative volume 10% value (D10) of the inorganic particles (C) of less than 0.01 μm.

5. The resin composition according to any one of claims 1 to 4, wherein the inorganic particles (C) have a sphericity of 0.9 or more.

6. The resin composition according to any one of claims 1 to 5, wherein the inorganic particles (C) are contained in an amount of 10 to 80 parts by weight when the total amount of the resin composition is 100 parts by weight.

7. A resin composition according to any one of claims 1 to 6, having a viscosity of 12 Pa·s or less as measured using an E-type viscometer at 25°C and 10 rpm.

8. A resin composition described in any one of claims 1 to 7, having a thixotropic index value, which is the viscosity at 5 rpm / the viscosity at 50 rpm, measured at 25°C using an E-type viscometer, of 3 or less.

9. The resin composition according to any one of claims 1 to 8, comprising the organic substance (A), a siloxane compound having a reactive functional group.

10. The resin composition according to claim 9, wherein the siloxane compound having a reactive functional group comprises (A1) a cyclic siloxane compound having a reactive functional group, and (A2) a linear siloxane compound having a reactive functional group.

11. The resin composition according to any one of claims 1 to 10, further comprising (A3) an oxetane.

12. A cured product of the resin composition according to any one of claims 1 to 11.

13. The cured product according to claim 12, wherein the cured product has a thickness of 100 μm and a transmittance of 90% or more at a wavelength of 1,310 nm.

14. The cured product according to claim 12 or 13, wherein the cured product has a refractive index of 1.47 or less at a wavelength of 1,310 nm.

15. The resin composition according to any one of claims 1 to 11, which is used for fixing an optical fiber in a groove formed in an optical waveguide element.

16. The resin composition according to any one of claims 1 to 11, which is used for optically coupling an optical fiber to an optical waveguide element.

17. A resin composition according to any one of claims 1 to 11, used for simultaneously fixing an optical fiber to a groove formed in an optical waveguide element and optically coupling the optical fiber to the optical waveguide element.

18. An optical fiber array comprising: a resin composition according to any one of claims 1 to 17; an optical fiber; and an optical waveguide element, wherein the optical fiber is optically coupled to the optical waveguide element via the resin composition.

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