Optical fiber array, optical waveguide module, method for reducing refractive index of adhesive layer, and method for manufacturing optical fiber array

Abstract

Provided is an optical fiber array (1) comprising an adhesive layer (20) that exhibits a low refractive index and excellent transparency.　This optical fiber array comprises an optical fiber (10) and an adhesive layer (20), wherein the optical fiber (10) is optically coupled to an optical waveguide element (30) by the adhesive layer (20) and the content of the adhesive layer (20) in terms of the element Si is at least 10%. The adhesive layer (20) preferably has a transmittance of at least 90% at a wavelength of 1310 nm. The adhesive layer (20) preferably has a refractive index of not greater than 1.47 at a wavelength of 1310 nm. The adhesive layer (20) preferably contains a cured product of (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator.

Description

Optical fiber array, optical waveguide module, method for reducing refractive index of adhesive layer, and method for manufacturing optical fiber array

[0001] The present invention relates to an optical fiber array, an optical waveguide module, a method for reducing the refractive index of an adhesive layer, and a method for manufacturing 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] Furthermore, Patent Document 2 describes the use of a compound having an aromatic ring and a reactive silicon-containing group in an adhesive composition for optical communications that has excellent adhesion, moisture resistance, and a low refractive index. However, the use of a large amount of a resin material having an aromatic ring increases the refractive index, and the refractive index obtained is only higher than the refractive index of 1.46 of quartz glass, which is a common raw material for optical fibers.

[0007] JP 2011-037978 A JP 2017-061599 A

[0008] In light of these circumstances, there has been a demand for an optical fiber array using an adhesive with excellent optical properties. For example, there has been a demand for an optical fiber array having an adhesive layer with a low refractive index and excellent transparency. The present invention has been made in view of the above-mentioned problems, and its object is to provide an optical fiber array having an adhesive layer with a low refractive index and excellent transparency, an optical waveguide module including such an optical fiber array, a method for lowering the refractive index of an adhesive layer, and a method for manufacturing an optical fiber array.

[0009] The present invention relates to the following optical fiber arrays, optical waveguide modules, methods for reducing the refractive index of an adhesive layer, and methods for manufacturing optical fiber arrays. [1] An optical fiber array comprising an optical fiber and an adhesive layer, wherein the optical fiber is optically coupled to an optical waveguide element by the adhesive layer, and the adhesive layer has a Si content of 10% or more. [2] The optical fiber array according to [1] above, further comprising: a substrate having a groove for accommodating the optical fiber; and a pressure plate adhesively fixed to the surface of the optical fiber, wherein the optical fiber is adhesively fixed to the groove by the adhesive layer, and the adhesive layer bonds the optical fiber to the optical waveguide element and also bonds the substrate with the optical fiber accommodated in the groove to the pressure plate. [3] The optical fiber array according to [2] above, wherein the substrate is a semiconductor substrate. [4] The optical fiber array according to [3] above, wherein one surface of the semiconductor substrate has a ball grid array electrode. [5] The optical fiber array according to any one of [1] to [4] above, wherein the adhesive layer has a transmittance of 90% or more at a wavelength of 1310 nm. [6] The optical fiber array according to any one of [1] to [5] above, wherein the adhesive layer has a refractive index of 1.49 or less at a wavelength of 1310 nm. [7] The optical fiber array according to any one of [1] to [6] above, wherein the adhesive layer contains a cured product of (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator. [8] The optical fiber array according to [7] above, wherein the (A) siloxane compound having a reactive functional group contains (A1) a cyclic siloxane compound having a reactive functional group and (A2) a linear siloxane compound having a reactive functional group. [9] The optical fiber array according to any one of [1] to [8] above, wherein the adhesive layer further contains (C) an inorganic filler.

[10] The optical fiber array according to [9] above, wherein the content of the inorganic filler (C) is 0.1 to 80 parts by weight when the total amount of the components contained in the adhesive layer is 100 parts by weight.

[11] The optical fiber array according to [9] or

[10] above, wherein the average particle size of the inorganic filler (C) is 0.1 μm to 5.0 μm.

[12] The optical fiber array according to any one of [1] to

[11] above, wherein the adhesive layer comprises a cured product of (A) a siloxane compound having a reactive functional group, (B) a polymerization initiator, and (C) an inorganic filler, and wherein the adhesive layer has a Si element content of 5% or more derived from the siloxane compound having a reactive functional group (A).

[13] An optical waveguide module comprising the optical fiber array according to any one of [1] to

[12] above.

[14] A method for reducing the refractive index of an adhesive layer in an optical fiber array in which optical fibers are optically coupled to an optical waveguide element by an adhesive layer, the adhesive layer having a Si element content of 10% or more.

[15] A method for manufacturing an optical fiber array in which optical fibers are optically coupled to an optical waveguide element by an adhesive layer, the adhesive layer having a Si element content of 10% or more.

[16] A method for manufacturing an optical fiber array according to

[15] above, wherein the step of fixing the optical fiber to a groove formed in the optical waveguide element and the step of optically coupling the optical fiber to the optical waveguide element are carried out simultaneously.

[0010] According to the present invention, it is possible to provide an optical fiber array having an adhesive layer with a low refractive index and excellent transparency, an optical waveguide module having the optical fiber array, a method for reducing the refractive index of the adhesive layer, and a method for manufacturing an optical fiber array.

[0011] 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.

[0012] An embodiment of the present invention (hereinafter, the present embodiment) will be described below. The present embodiment relates to an optical fiber array, an optical waveguide module, a method for reducing the refractive index of an adhesive layer, and a method for manufacturing 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.

[0013] [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.

[0014] 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.

[0015] 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).

[0016] 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.

[0017] In the optical fiber array 1 of this embodiment, the adhesive layer 20 has a Si element content of 10% or more, which gives the adhesive layer 20 a low refractive index and excellent transparency. Here, the Si element content of the adhesive layer 20 is the sum of the Si element content of each component contained in the adhesive composition that forms the adhesive layer 20. The Si element content of each component contained in the adhesive composition is a value calculated by the formula: Si atomic weight / molecular weight x number of Si atoms in one molecule x 100 (%).

[0018] The adhesive layer 20 may be formed, for example, using the adhesive composition of the present embodiment described below. The adhesive composition of the present embodiment that forms the adhesive layer 20 is not particularly limited as long as it has an Si element content of 10% or more. From the viewpoint of achieving a low refractive index and high transparency, the Si element content of the adhesive layer 20 is 10% or more, preferably 12% or more, more preferably 15% or more, even more preferably 20% or more, particularly preferably 30% or more, or even 35% or more. The Si element content of the adhesive layer 20 is preferably in the range of 10 to 50%, more preferably 15 to 45%, even more preferably 20 to 45%, and particularly preferably 30 to 40%.

[0019] [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. 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.

[0020] [Adhesive Composition] The adhesive composition forming the adhesive layer 20 included in the optical fiber array 1 of this embodiment preferably contains (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator. Specifically, the adhesive layer 20 is preferably formed from a cured product of the adhesive composition containing (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator. In this case, from the viewpoint of achieving a low refractive index and high transparency, it is preferable that the Si element content derived from the siloxane compound having the reactive functional group (A) in the adhesive layer 20 be 5% or more. Here, the Si element content derived from the siloxane compound having the reactive functional group (A) in the adhesive layer 20 refers to the sum of the Si element content of the siloxane compound having the reactive functional group (A) contained in the adhesive composition forming the adhesive layer 20.

[0021] The content of the adhesive layer 20 derived from the siloxane compound having a reactive functional group (A) in terms of Si element is 5% or more, preferably 7% or more, more preferably 8% or more, even more preferably 9% or more, and particularly preferably 10% or more. The range of the content of the adhesive layer 20 derived from the siloxane compound having a reactive functional group (A) in terms of Si element is preferably 5 to 40%, more preferably 7 to 30%, even more preferably 8 to 20%, and particularly preferably 9 to 20%.

[0022] (A) Siloxane Compound Having a Reactive Functional Group The siloxane compound having a reactive functional group (A) contained in the adhesive 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)."

[0023] (A1) Cyclic Siloxane Compound Having a Reactive Functional Group The adhesive 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.

[0024] The reactive functional group refers to a functional group that can react with a functional group possessed by a compound contained in the adhesive composition of this 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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, when the adhesive composition is cured, a dense cured product tends to be obtained, and the adhesive composition 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.

[0032] 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 adhesive 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.

[0033] 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.

[0034] The content of component (A1) in the adhesive 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 adhesive composition is 100 parts by mass. Furthermore, from the viewpoint of achieving a low refractive index and high transparency, the content of component (A1) in the adhesive 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 adhesive composition is 100 parts by mass.

[0035] 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 adhesive 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, 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.

[0036] As the component (A1), for example, a compound represented by the following general formula (1) can be used.

[0037] (In the formula, 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] (A2) Linear siloxane compound having a reactive functional group The adhesive 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"). 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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, when the adhesive composition is cured, a dense cured product tends to be obtained, and the adhesive composition 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.

[0049] 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 adhesive composition becomes appropriate, and the cured product exhibits a good balance between the optical properties and heat resistance.

[0050] 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.

[0051] The content of component (A2) in the adhesive 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 adhesive composition is 100 parts by mass. Furthermore, from the viewpoint of improving reflow resistance, the content of component (A2) in the adhesive 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 adhesive composition is 100 parts by mass.

[0052] 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 adhesive composition, the viscosity of the component (A2) at 25° C. is preferably 1 to 500 mPa s, more preferably 2 to 300 mPa s, and particularly preferably 5 to 100 mPa s.

[0053] 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.

[0054] As the component (A2), for example, a compound represented by the following general formula (2) can be used.

[0055] [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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Blending ratio of component (A1) and component (A2) Among the siloxane compounds (A) contained in the adhesive 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 crosslink density of the cured product, thereby lowering the refractive index and providing excellent transparency. 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.

[0061] The content of component (A) in the adhesive 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 adhesive composition is 100 parts by mass. By setting the content of component (A) within the above range, it is possible to lower the refractive index and improve adhesion.

[0062] (B) Polymerization Initiator The adhesive composition of this embodiment contains (B) a polymerization initiator (hereinafter also referred to as "component (B)"). There are no particular limitations on the component (B) as long as it is capable of initiating 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.

[0063] 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 components (A1) and (A2) 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.

[0064] 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.

[0065] 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).

[0066] 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.

[0067] The onium gallate salt is not particularly limited, but an onium salt represented by the following general formula (3) can be used.

[0068] [In formula (3), R １３ ~R １６each independently represents an alkyl group having 1 to 18 carbon atoms, an aryl group, or a group having a heterocycle, and 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.]

[0069] 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.

[0070] 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.

[0071] The onium borate salt is not particularly limited, but an onium salt represented by the following general formula (4) can be used.

[0072] [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 R ２２ 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.]

[0073] 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.

[0074] 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.

[0075] The content of component (B) in the adhesive composition is not particularly limited, but from the viewpoint of polymerizability and achieving a low refractive index and high transparency of the cured product, 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 siloxane compound (A) having a reactive functional group. The content of component (B) can be appropriately determined 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 the thickness of the adhesive composition, and is not limited to the above range.

[0076] [Other Optional Components] The adhesive composition of the present embodiment may contain optional components other than the above-described component (A) and component (B), such as the components described below, as needed, within the scope of the present embodiment.

[0077] (C) Inorganic Filler The adhesive composition of the present embodiment may contain (C) an inorganic filler (hereinafter also referred to as "component (C)") as an optional component. 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.

[0078] The component (C) may be used alone or in combination of two or more. From the viewpoint of refractive index, silica particles are preferably used as the component (C). Furthermore, amorphous silica is preferred. The component (C) may be surface-treated with a coupling agent such as a silane coupling agent to prevent aggregation. The shape of the component (C) is not particularly limited and may be spherical, scaly, needle-like, irregular, or the like. However, when a scaly or needle-like inorganic filler is used as an adhesive composition for an optical adhesive, light may be scattered if the orientation of the inorganic filler is disordered. Therefore, from the viewpoint of refractive index and transmittance, the silica particles are preferably spherical, with a sphericity of 0.8 or more, and more preferably a substantially spherical shape with a sphericity of 0.9 or more.

[0079] The average particle size of component (C) is preferably 5.0 μm or less, more preferably 3.0 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, average particle size refers to the volume-based median diameter (D50) measured by a laser diffraction scattering method in accordance with ISO-13320 (2020). By setting the average particle size of component (C) to the upper limit or less, transmittance can be increased. While there is no particular lower limit for the average particle size of component (C), from the viewpoint of the viscosity of the adhesive composition, it is preferably 0.1 μm or more, and more preferably 0.2 μm or more. The average particle size of component (C) is preferably 0.1 μm to 5.0 μm, more preferably 0.2 μm to 2.0 μm. Inorganic fillers with different average particle sizes may be used in combination. For example, an inorganic filler with an average particle size of 0.1 μm or more and less than 0.5 μm may be used in combination with an inorganic filler with an average particle size of 0.5 μm to 5.0 μm.

[0080] In addition, when silica is used as an inorganic filler, its manufacturing method is not particularly limited.For example, spherical silica powder obtained by reacting metal silicon with oxygen, spherical silica powder obtained by melting pulverized silica, silica filler obtained by the sol-gel method, precipitation method, aqueous solution wet method can be exemplified.Among these, from the viewpoint of optical properties, silica particles obtained by the sol-gel method, that is, sol-gel silica particles, which have high sphericity and a relatively sharp particle size distribution, are particularly preferred.

[0081] The content of component (C) in the adhesive composition of this embodiment is preferably 0.1 to 80 parts by mass, more preferably 5 to 70 parts by mass, and even more preferably 10 to 60 parts by mass, when the total amount of the adhesive composition is 100 parts by mass. By setting the content of component (C) within this range, it is possible to improve reflow resistance and lower the refractive index.

[0082] Furthermore, silica particles are preferably contained as the inorganic filler (C) in order to make the Si element content of the adhesive layer 20 10% or more. By containing silica particles, the Si element content of the adhesive layer 20 can be increased and the refractive index of the adhesive layer can be lowered. The content of the silica particles is preferably 0.1 to 80 parts by mass, more preferably 5 to 70 parts by mass, and even more preferably 10 to 60 parts by mass, when the total amount of the adhesive composition is 100 parts by mass.

[0083] (D) Oxetane Compound The adhesive composition of this embodiment may contain an oxetane compound (D) (hereinafter also referred to as "component (D)") as an optional component. The component (D) is not particularly limited as long as it is a compound containing an oxetane ring. When the adhesive composition contains component (D), it can improve initial adhesion. However, it is preferable not to contain compounds that may increase the refractive index of the adhesive composition, such as oxetane compounds having aromatic rings. The blending ratio of component (D) is not particularly limited, but it is preferably 1 to 5 parts by mass when the total amount of the adhesive composition is 100 parts by mass.

[0084] 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.

[0085] Commercially available oxetane compounds include, for example, OXT-212, OX-221, OXT-213, and OXT-101 (manufactured by Toagosei Co., Ltd.).

[0086] (E) Other Additives If desired, the adhesive composition of the present embodiment may further contain other additives, such as coupling agents, stabilizers, ion trapping agents, leveling agents, antioxidants, antifoaming agents, viscosity modifiers, solvents, etc., within the scope of the present embodiment. The content of each additive can be selected appropriately.

[0087] The method for producing the adhesive composition of this embodiment is not particularly limited. For example, the adhesive composition of this embodiment can be obtained by simultaneously or separately introducing component (A), component (B), and, if necessary, component (C), component (D), and component (E) 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, Henschel mixer, three-roll mill, ball mill, planetary mixer, and bead mill equipped with a stirring device and a heating device. These devices may also be used in appropriate combination. The adhesive composition obtained in this manner is photocurable and thermosetting.

[0088] [Viscosity of Adhesive Composition] The viscosity of the adhesive 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 adhesive 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 adhesive composition at 25°C is preferably 0.05 Pa·s to 200 Pa·s, preferably 0.1 Pa·s to 100 Pa·s, more preferably 0.1 Pa·s to 50 Pa·s, and even more preferably 0.1 Pa·s to 20 Pa·s. If the viscosity of the adhesive composition is too low, it may not maintain its shape when applied and may flow. If the viscosity of the adhesive composition is too high, the injectability may be poor or unevenness may occur when the adhesive composition is applied.

[0089] The adhesive composition preferably has a thixotropic index (TI) value of 0.5 to 3.0. In this specification, the TI value is the ratio of the viscosities measured at 5 rpm and 50 rpm using an E-type viscometer at 25°C, calculated as viscosity at 5 rpm / 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 with changes in shear rate, has a TI value of 1. A TI value smaller than 1 indicates that the viscosity is smaller when the shear force is small than when the shear force is large, and a TI value greater than 1 indicates that the viscosity is larger when the shear force is small than when the shear force is large. The larger the TI value, the more thixotropic the adhesive composition is. A TI value of 0.5 to 3.0 improves workability when injecting the adhesive composition. The adhesive 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 like that of a non-Newtonian fluid with a thixotropy index of greater than 1.2.

[0090] [Cured Product of Adhesive Composition] The adhesive 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 adhesive composition of this embodiment is cured by ultraviolet irradiation, the irradiation dose (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.

[0091] [Refractive Index, Transmittance, and Reflow Resistance of the Cured Product] The adhesive composition of this embodiment has an Si element content of 10% or more, which results in excellent optical properties when cured. Therefore, it is suitable for use as the adhesive layer 20 of the optical fiber array 1 of this embodiment. In this case, if the adhesive composition contains both (A1) a cyclic siloxane compound having a reactive functional group and (A2) a linear siloxane compound having a reactive functional group as the siloxane compound (A), the optical properties and heat resistance of the cured product will be even better. Specifically, the cured product of the adhesive composition of this embodiment has a low refractive index, high transparency, and good reflow resistance.

[0092] The cured product and adhesive layer 20 of this embodiment preferably 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, and even more preferably 1.45 or less. The refractive index of the cured product and adhesive layer 20 at a wavelength of 1310 nm and / or 589 nm at 25°C is preferably in the range of 1.40 or more and less than 1.49, preferably 1.41 or more and 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.

[0093] The cured product of this embodiment has a transmittance of 80% or more, preferably 85% or more, more preferably 90% or more, and even more preferably 92% or more at 25°C for a thickness of 100 μm and a wavelength of 1310 nm and / or 589 nm. The transmittance of the cured product of this embodiment has a thickness of 100 μm and a wavelength of 1310 nm and / or 589 nm at 25°C for a range of 80 to 99%, preferably 85 to 95%, more preferably 87 to 95%, and even more preferably 90 to 95%.

[0094] The adhesive layer 20 included in the optical fiber array 1 of this embodiment preferably has a transmittance of 75% or more at wavelengths of 1310 nm and / or 589 nm at 25°C, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The adhesive layer 20 included in the optical fiber array 1 of this embodiment preferably has a transmittance of 75 to 99% at wavelengths of 1310 nm and / or 589 nm at 25°C, preferably 80 to 95%, more preferably 85 to 95%, and even more preferably 90 to 95%. In this specification, transmittance is expressed as a value measured in accordance with JIS K7105, unless otherwise specified.

[0095] The cured product of the adhesive composition of this embodiment and the adhesive layer 20 have excellent heat resistance, particularly excellent reflow resistance. 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 adhesive composition of this embodiment and the adhesive layer 20 have the property that their physical properties change little before and after the reflow process (maximum temperature of approximately 260°C) used for soldering when mounting electronic components. For example, the adhesive composition of this embodiment has the property that, when cured, their adhesive strength changes little before and after the reflow process.

[0096] The reflow resistance of the cured adhesive 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) The adhesive 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."

[0097] 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 adhesive composition and the adhesive layer 20 of this embodiment preferably have an absolute value of the rate of decrease in adhesive strength before and after the reflow process represented by formula (1) above 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.

[0098] [Method for Manufacturing Optical Fiber Array] The method for manufacturing the optical fiber array 1 of this embodiment is a method for manufacturing the optical fiber array 1 in which the optical fibers 10 are optically coupled to the optical waveguide element 30 by the adhesive layer 20, and the adhesive layer 20 has an Si content of 10% or more. In this case, the step of fixing the optical fibers 10 in the V-grooves 33 that 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 be performed separately. Furthermore, in the method for manufacturing the optical fiber array 1 of this embodiment, it is preferable to simultaneously perform the step of fixing the optical fibers 10 in the V-grooves 33 that 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.

[0099] 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, an adhesive composition is dropped into the V-groove 33. Note that the presser plate 40 may be formed integrally with the substrate 31.

[0100] The adhesive 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 adhesive 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 adhesive composition needs to be injectable, and the viscosity and TI value of the adhesive composition need to be set to appropriate values.

[0101] Next, the adhesive composition is irradiated with ultraviolet light to cure, 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 coupling and the bonding for V-groove fixation. It is not necessary for the adhesive layer 20 to perform these bonding processes 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.

[0102] [Uses of Adhesive Composition] Because the adhesive composition of this embodiment has excellent optical properties and heat resistance, it can be used for a variety of purposes, not limited to optical adhesives for bonding optical components. For example, the adhesive composition of this embodiment can be used as an adhesive or sealant for fixing, bonding, or protecting optical components, electronic components, or semiconductor components, or as a raw material thereof. Examples of optical components that can be used with the adhesive 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, because the adhesive composition of this embodiment has excellent optical properties and heat resistance, it can be suitably used, particularly as an optical adhesive for silicon photonics.

[0103] The adhesive composition of the present embodiment can be used to fix the optical fiber 10 to 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 adhesive composition of the present embodiment to simultaneously fix the optical fiber 10 to 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.

[0104] For example, the adhesive 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 adhesive 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.

[0105] [Method] As will be shown in the examples described later, the adhesive composition of this embodiment has an Si element content of 10% or more, and therefore has excellent optical properties and heat resistance when cured. Therefore, this embodiment provides a method for reducing the refractive index of the adhesive layer 20 in an optical fiber array 1 in which optical fibers 10 are optically coupled to an optical waveguide element 30 by an adhesive layer 20, by adjusting the Si element content of the adhesive layer 20 to 10% or more.

[0106] Furthermore, as shown in the examples described below, the adhesive composition of this embodiment contains both (A1) a cyclic siloxane compound having a reactive functional group and (A2) a linear siloxane compound having a reactive functional group as the siloxane compound (A), and therefore has excellent optical properties and heat resistance when cured. Therefore, according to this embodiment, in an optical fiber array 1 in which optical fibers 10 are optically path-coupled to an optical waveguide element 30 by an adhesive layer 20, a method for reducing the refractive index of an adhesive layer 20 (a cured product of the adhesive composition) is provided, the method including the step of combining (A1) a cyclic siloxane compound having a reactive functional group, (A2) a linear siloxane compound having a reactive functional group, and (B) a polymerization initiator. Furthermore, according to the present embodiment, in an optical fiber array 1 in which optical fibers 10 are optically path-coupled to optical waveguide elements 30 via an adhesive layer 20, a method is provided for suppressing a decrease in adhesive strength due to heating of the adhesive layer 20 (cured product of the adhesive composition), the method including a step of combining (A1) a cyclic siloxane compound having a reactive functional group, (A2) a linear siloxane compound having a reactive functional group, and (B) a polymerization initiator.

[0107] 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.

[0108] [Examples 1 to 20, Comparative Example 1] Adhesive compositions were prepared by mixing predetermined amounts of each component using a three-roll mill according to the formulations shown in Tables 1 to 4. 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.

[0109] (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) A cyclic dimethylsiloxane compound represented by general formula (1) in which n is 4 and which has four 3-glycidoxypropyl groups in the molecule (product name: EP-3400L, manufactured by ADEKA Corporation, non-alicyclic epoxy group, number of epoxy functional groups: 4, viscosity at 25°C: 100 Pa s, epoxy equivalent: 174 g / mol). (A1-3) X-40-2678 represented by the following formula (manufactured by Shin-Etsu Chemical Co., Ltd., alicyclic epoxy group, number of epoxy functional groups: 2, viscosity at 25°C: 120 Pa s, epoxy equivalent: 290 g / mol). (A1-4) 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):

[0110] (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)

[0111] (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

[0112] (C) Inorganic particles (component (C)) (C-1) Spherical silica particles (product name: KE-S30HG, manufactured by Nippon Shokubai Co., Ltd., D50 is 0.3 μm, spherical sol-gel silica particles)

[0113] (D) Oxetane Compound (Component (D)) (D-1) 3,3'-(oxybismethylene)bis(3-ethyloxetane) (product name: OXT-221, manufactured by Toagosei Co., Ltd.)

[0114] (X) Epoxy Compound (X-1) Alicyclic Epoxy (Product Name: 2021P, manufactured by Daicel Chemical Industries, Ltd.)

[0115] [Evaluation of Properties] In the examples and comparative examples, the viscosity of the adhesive composition and the properties of the cured product obtained by curing the adhesive composition (adhesive strength, rate of strength reduction before and after reflow, refractive index, and transmittance) were measured as follows.

[0116] (Viscosity of Adhesive Composition) Using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. (model number: TVE-22H, rotor name: 1°34′×R24) (set to an appropriate measurement range (H, R or U)), the viscosity of the adhesive composition was measured within one hour after its preparation at 25° C. with a rotor rotation speed of 10 rpm, and the value was read one minute after the start of measurement.

[0117] (Curing of adhesive 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 ...

[0118] (Refractive Index) The refractive index at 589 nm of a 100 μm thick cured film prepared from the adhesive 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 adhesive composition formed into a film on a glass substrate was measured using a spectroscopic ellipsometer (SE-2000, manufactured by Semilab).

[0119] (Transmittance) The transmittance of a 100 μm thick cured product prepared from the adhesive composition was measured using an ultraviolet-visible spectrophotometer (V-670, manufactured by JASCO Corporation) at measurement wavelengths of 589 nm and 1310 nm.

[0120] (Reflow Resistance) The adhesive strength of the cured adhesive composition was measured by die shear measurement. The die shear strength was measured as follows. (1) The prepared adhesive 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 sheet was applied onto 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):

[0121] (Si element equivalent content) The Si element equivalent content of each component is shown in Table 5. The Si concentration was calculated by dividing the atomic weight of Si by the molecular weight. The Si element equivalent content of each component contained in the adhesive composition was calculated by dividing the atomic weight of Si by the molecular weight of Si by the number of Si atoms in one molecule by 100 (%). The atomic weight of Si was set to 28.09. Tables 1 to 4 show the results of calculating the Si element equivalent content derived from the siloxane compound (A) having a reactive functional group contained in the adhesive composition, and the Si element equivalent content of the entire adhesive composition.

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[0127] [Results] As can be seen from Tables 1 to 4, when the adhesive composition had a Si element content of 10% or more, the cured product (adhesive layer) had a low refractive index, high transmittance, and excellent optical properties. Specifically, Examples 1 to 20 had a low refractive index of 1.49 or less at 25°C at wavelengths of 1310 nm and 589 nm, and a high transmittance of 75% or more, indicating excellent transparency. Furthermore, the adhesive compositions of Examples 1 to 20 had low viscosity and therefore excellent injectability. In other words, it was found that by forming an adhesive layer using the adhesive compositions of Examples 1 to 20, it was possible to realize an optical fiber array 1 including an adhesive layer 20 with a low refractive index and excellent transparency.

[0128] A comparison of Examples 1 and 2 shows that the refractive index is low and the transparency is excellent, regardless of the type of component (A) (the structure of the siloxane compound, the type and number of functional groups).

[0129] A comparison of Examples 3 to 5 with Examples 4 to 6 shows that the inclusion of the oxetane compound (D) increases the adhesive strength before reflow.

[0130] A comparison of Examples 6 to 9 shows that the refractive index and reflow 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 reflow resistance, while increasing the ratio of the (A2) linear siloxane compound decreases the refractive index.

[0131] A comparison of Examples 6 and 10 to 12 shows that the refractive index is low and the transparency is excellent regardless of the type of (A1) cyclic siloxane compound (type and number of functional groups). Furthermore, a comparison of Examples 6 and 10 shows that when the functional group of the (A1) cyclic siloxane compound is an alicyclic epoxy group, the reflow resistance is superior to when the functional group is a non-alicyclic epoxy group. Furthermore, a comparison of Examples 6 and 11 shows that when the number of functional groups in the (A1) cyclic siloxane compound is large, the reflow resistance is excellent.

[0132] A comparison of Examples 6 and 13 shows that the refractive index is low and the transparency is excellent regardless of the type (type of functional group) of the linear siloxane compound (A2). Also, a comparison of Examples 6 and 13 shows that when the functional group of the linear siloxane compound (A2) is an alicyclic epoxy group, the reflow resistance is superior to when the functional group is a non-alicyclic epoxy group.

[0133] A comparison of Examples 14 and 15 shows that the refractive index is low and the transparency is excellent regardless of the content of (C) inorganic filler. A comparison of Examples 16 and 17 shows that the refractive index is low and the transparency is excellent regardless of the type of (B) polymerization initiator. Examples 18 to 20 show that the refractive index is low and the transparency is excellent even when no (C) inorganic filler is contained.

[0134] Comparative Example 1 did not contain component (A) but contained epoxy compound (X), and the adhesive composition had a high refractive index due to the Si element content being less than 10%.

[0135] The optical fiber array of the present invention has a low refractive index and an adhesive layer with excellent transparency, making it particularly useful in silicon photonics technology. Furthermore, the resin composition of the present invention can achieve a low refractive index without containing a fluorine compound, making it useful as an optical adhesive from an environmental perspective.

[0136] 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. An optical fiber array comprising: an optical fiber; and an adhesive layer, wherein the optical fiber is optically coupled to an optical waveguide element by the adhesive layer, and the adhesive layer has a silicon content of 10% or more.

2. The optical fiber array according to claim 1, comprising: a substrate having grooves formed therein for accommodating the optical fibers; and a pressure plate adhesively fixed to the surface of the optical fibers, the optical fibers being adhesively fixed in the grooves by the adhesive layer, the adhesive layer bonding the optical fibers to the optical waveguide element, and bonding the substrate with the optical fibers accommodated in the grooves to the pressure plate.

3. The optical fiber array according to claim 2, wherein said substrate is a semiconductor substrate.

4. The optical fiber array according to claim 3, further comprising a ball grid array electrode on one surface of said semiconductor substrate.

5. The optical fiber array according to any one of claims 1 to 4, wherein the adhesive layer has a transmittance of 90% or more at a wavelength of 1,310 nm.

6. The optical fiber array according to any one of claims 1 to 5, wherein the adhesive layer has a refractive index of 1.49 or less at a wavelength of 1310 nm.

7. The optical fiber array according to any one of claims 1 to 6, wherein the adhesive layer contains a cured product of (A) a siloxane compound having a reactive functional group and (B) a polymerization initiator.

8. The optical fiber array according to claim 7, wherein the (A) siloxane compound having a reactive functional group includes (A1) a cyclic siloxane compound having a reactive functional group, and (A2) a linear siloxane compound having a reactive functional group.

9. The optical fiber array according to any one of claims 1 to 8, wherein the adhesive layer further comprises (C) an inorganic filler.

10. The optical fiber array according to claim 9, wherein the content of said inorganic filler (C) is 0.1 to 80 parts by weight, when the total amount of the components contained in said adhesive layer is 100 parts by weight.

11. The optical fiber array according to claim 9 or 10, wherein the inorganic filler (C) has an average particle size of 0.1 μm to 5.0 μm.

12. An optical fiber array as described in any one of claims 1 to 11, wherein the adhesive layer contains a cured product of (A) a siloxane compound having a reactive functional group, (B) a polymerization initiator, and (C) an inorganic filler, and the content of silicon element derived from the (A) siloxane compound having a reactive functional group in the adhesive layer is 5% or more.

13. An optical waveguide module comprising an optical fiber array according to any one of claims 1 to 12.

14. A method for reducing the refractive index of an adhesive layer in an optical fiber array in which an optical fiber is optically coupled to an optical waveguide element by an adhesive layer, the adhesive layer having a silicon content of 10% or more.

15. A method for manufacturing an optical fiber array in which optical fibers are optically coupled to an optical waveguide element by an adhesive layer, wherein the adhesive layer has a silicon content of 10% or more.

16. The method for producing an optical fiber array according to claim 15, wherein the step of fixing the optical fiber in a groove formed in the optical waveguide element and the step of optically coupling the optical fiber to the optical waveguide element are carried out simultaneously.

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