Resin composition for optical wave guide and dry film and optical waveguide using said composition

Abstract

This resin composition for an optical waveguide contains an epoxy compound (A). The epoxy compound (A) contains a first epoxy compound (a1) having a norbornane structure and a second epoxy compound (a2) having a silicon structure having 1 to 6 Si. The content of the second epoxy compound (a2) is 5 to 60 parts by mass per 100 parts by mass of the first epoxy compound (a1).

Description

Resin composition for optical waveguide, and dry film and optical waveguide using the same

[0001] The present invention relates to a resin composition for an optical waveguide, and a dry film and an optical waveguide using the same.

[0002] Optical fiber has traditionally been the mainstream transmission medium in the fields of FTTH (Fiber to the Home) and long-distance and medium-distance communications in the automotive field. In recent years, high-speed optical transmission over short distances of less than 1 meter has become necessary. In this area, optical waveguide-type optical wiring boards are suitable because they offer high-density wiring (narrow pitch, branching, crossing, multilayering, etc.), surface mountability, integration with electrical substrates, and small-diameter bending capabilities that are not possible with optical fiber.

[0003] An optical waveguide can be obtained by forming a clad portion and a core portion using two types of ultraviolet (UV) curable optical waveguide resin compositions that are highly transparent and have different refractive indices. Generally, such optical waveguide resin compositions contain a resin such as an epoxy resin, an acrylic resin, or a silicone resin, and a curing agent.

[0004] Furthermore, in an optical waveguide-type optical wiring board, an electrical circuit is preferably formed on a substrate on which an optical waveguide is formed, in order to utilize light input and output from the optical waveguide, and for example, a light-emitting element, a photoelectric conversion element, a semiconductor element, or the like is mounted. When an electrical circuit is formed on a substrate, the substrate is subjected to a reflow treatment using, for example, lead-free solder. Since such a reflow treatment is performed at high temperatures, an epoxy resin, which has the highest heat resistance among the above-mentioned resins, is preferably used as the resin material for the optical waveguide to be subjected to the reflow treatment. Furthermore, in recent years, in order to further mass-produce optical wiring boards on which such optical elements are mounted, many resin compositions for optical waveguides containing epoxy resins with higher heat resistance have been developed (see, for example, Patent Document 1).

[0005] Patent No. 6960616

[0006] An object of the present invention is to provide a resin composition for an optical waveguide that can suppress optical loss in the 1310 nm wavelength band before and after reflow treatment and has good film handling properties.

[0007] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.

[0008] A resin composition for an optical waveguide according to a first aspect of the present invention contains an epoxy compound (A), wherein the epoxy compound (A) comprises a first epoxy compound (a1) having a norbornane structure and a second epoxy compound (a2) having a silicone structure in which the number of Si atoms is 1 or more and 6 or less, and the content of the second epoxy compound (a2) is 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the first epoxy compound (a1).

[0009] A dry film according to a second aspect of the present invention has a layer containing an uncured or semi-cured product of the resin composition for an optical waveguide according to the first aspect.

[0010] An optical waveguide according to a third aspect of the present invention is an optical waveguide comprising a core portion and a clad portion having a refractive index lower than that of the core portion and formed to cover the core portion, wherein the core portion is formed using the resin composition for an optical waveguide according to the first aspect (or the dry film according to the second aspect).

[0011] FIG. 1 is a cross-sectional schematic diagram illustrating an example of a method for forming an optical waveguide using a dry film according to the present embodiment. Specifically, FIG. 1( a) is a schematic diagram illustrating a step in which a clad dry film is laminated onto a surface of a substrate. FIG. 1( b) is a schematic diagram illustrating a step in which the clad dry film is cured by ultraviolet light irradiation or the like, thereby forming an underclad. FIG. 1( c) is a schematic diagram illustrating a step in which a core dry film is exposed to a core pattern. FIG. 1( d) is a schematic diagram illustrating a step in which a core portion is formed on the surface of the underclad. FIG. 1( e) is a schematic diagram illustrating a step in which a clad dry film is laminated to cover the underclad and core portion. FIG. 1( f) is a schematic diagram illustrating a step in which the clad dry film laminated to cover the underclad and core portion is cured by ultraviolet light irradiation or the like, thereby forming an overclad.

[0012] Epoxy resins, particularly bisphenol A epoxy resins, which have traditionally been widely used as materials for optical waveguides, contain aromatic and aliphatic structures containing many OH groups, CH groups, and epoxy groups. When optical waveguides are formed using such epoxy resins, optical loss in the 1310 nm wavelength band increases. This loss can exceed 0.40 dB / cm. In addition, it is generally known that high-temperature reflow treatment of a substrate on which an optical waveguide and an electrical circuit are formed increases the optical loss of the optical waveguide in the 1310 nm wavelength band. Therefore, a resin composition for optical waveguides that is improved not only in terms of heat resistance but also in terms of the optical loss of the optical waveguide after high-temperature reflow treatment is needed.

[0013] As a result of research conducted by the present inventors, it was found that by incorporating an epoxy compound having a norbornane structure, rather than a cyclohexane structure, as the epoxy resin in a resin composition for optical waveguides, the optical loss at a wavelength of 1310 nm can be suppressed not only before reflow treatment but also after reflow treatment at high temperatures. However, because epoxy compounds having a norbornane structure have rigidity, depending on the content, handling during film formation may become difficult.

[0014] Therefore, as a result of further intensive research by the present inventors, it has been found that by incorporating an epoxy compound having a norbornane structure and an epoxy compound having a silicone structure in which the Si number is 1 or more and 6 or less in a predetermined content ratio in a resin composition for an optical waveguide, it is possible to suppress light loss in the 1310 nm wavelength band before and after reflow treatment, and to obtain a resin composition for an optical waveguide which has good film handleability.

[0015] As described above, the present invention can provide a resin composition for an optical waveguide that can suppress optical loss in the 1310 nm wavelength band before and after reflow treatment and has good film handling properties.

[0016] In this specification, the term "epoxy compound" also includes the meaning of "epoxy resin." Specifically, the term "epoxy compound" is intended to encompass both epoxy resins as polymers and epoxy compound monomers capable of forming epoxy resins. In this specification, an epoxy compound having a norbornane structure refers to an epoxy compound having a norbornane structure in its monomer structure. In this specification, an epoxy compound having a silicone structure with an Si number of 1 to 6 refers to an epoxy compound having a silicone structure with an Si element of 1 to 6 in its monomer structure.

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0018] 1. Resin Composition for Optical Waveguides The resin composition for optical waveguides according to this embodiment (hereinafter also referred to as the "resin composition") primarily contains an epoxy compound (A). The epoxy compound (A) includes a first epoxy compound (a1) having a norbornane structure (hereinafter also referred to as the "first epoxy compound (a1)") and a second epoxy compound (a2) having a silicone structure containing 1 to 6 silicon atoms (hereinafter also referred to as the "second epoxy compound (a2)"). In the resin composition according to this embodiment, the content (parts by mass) of the second epoxy compound (a2) relative to 100 parts by mass of the first epoxy compound (a1) (hereinafter also referred to as "{(a2) / (a1)}×100 (parts by mass)") is within a predetermined range.

[0019] The components contained in the resin composition will be described in detail below.

[0020] [Epoxy Compound (A)] The epoxy compound (A) includes a first epoxy compound (a1) and a second epoxy compound (a2). In addition, the epoxy compound (A) may further include other epoxy compounds.

[0021] These epoxy compounds (A) may be liquid epoxy compounds or solid epoxy compounds. In this specification, with respect to epoxy compounds, "liquid" means that they are liquid at room temperature, and "solid" means that they are solid at room temperature. Each epoxy compound will be described in detail below.

[0022] (First Epoxy Compound (a1) Having a Norbornane Structure) When the epoxy compound (A) according to this embodiment contains the first epoxy compound (a1), it is possible to obtain a resin composition that can suppress optical loss in the 1310 nm wavelength band not only before reflow treatment but also after reflow treatment at high temperatures. This is thought to be because the inclusion of a rigid norbornane structure in the epoxy compound suppresses the broadening of the spectrum in the 1310 nm wavelength band that is derived from cyclohexane in the epoxy compound, resulting in the formation of a sharp peak.

[0023] The first epoxy compound (a1) is not particularly limited, but preferably contains a solid epoxy compound having a norbornane structure. By containing the solid epoxy compound having a norbornane structure, a resin composition can be obtained that can more reliably suppress optical loss in the 1310 nm wavelength band before and after reflow treatment.

[0024] Specifically, the first epoxy compound (a1) preferably contains one or more compounds having structural formulae represented by the following formulas (1) and (2).

[0025]

[0026]

[0027] In the above formula (1) and formula (2), R １（a１） ~R ３６（a１） are each independently selected from the group consisting of hydrogen, an alkyl group having from 1 to 10 carbon atoms, and an alkoxy group having from 1 to 10 carbon atoms.

[0028] R in the above formula (1) and formula (2) １（a１） ~R ３６（a１）In the case where an alkyl group and / or an alkoxy group is selected, it is preferably an alkyl group and / or an alkoxy group having 1 to 5 carbon atoms, more preferably an alkyl group and / or an alkoxy group having 1 to 3 carbon atoms. The alkyl group and the alkoxy group may be linear or branched. １（a１） ~R ３６（a１） are more preferably each independently selected from hydrogen, and R １（a１） ~R ３６（a１） It is particularly preferred that all of are hydrogen.

[0029] Although such a first epoxy compound (a1) is not particularly limited, it is preferable that the first epoxy compound (a1) contains, for example, one or more compounds having structural formulas represented by the following formulas (1-1) and (2-1).

[0030]

[0031] The first epoxy compound (a1) may be synthesized by a known method, or a commercially available product may be used. For example, a compound having the structural formula represented by the above formula (1-1) may be "DE102" manufactured by ENEOS Corporation. For example, a compound having the structural formula represented by the above formula (2-1) may be "DE103" manufactured by ENEOS Corporation. Other examples of the first epoxy compound (a1) include "EPICLON HP-7200" manufactured by DIC Corporation and "DCPD-DE" manufactured by Japan Material Technology Co., Ltd.

[0032] The first epoxy compound (a1) may be used alone or in combination of two or more.

[0033] The content of the first epoxy compound (a1) is not particularly limited as long as it satisfies the condition of {(a2) / (a1)}×100 (parts by mass) described below, but is preferably 40% by mass or more and 95% by mass or less relative to the total amount of the epoxy compound (A). When the content of the first epoxy compound (a1) is 40% by mass or more, optical loss in the 1310 nm wavelength band before and after reflow treatment can be more effectively suppressed. When the content of the first epoxy compound (a1) is 95% by mass or less, difficulty in forming a film can be reliably prevented.

[0034] The content of the first epoxy compound (a1) is more preferably 55% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. The content of the first epoxy compound (a1) is more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0035] (Second Epoxy Compound (a2) Having a Silicone Structure) The epoxy compound (A) according to this embodiment contains not only the first epoxy compound (a1) but also the second epoxy compound (a2). By including the second epoxy compound (a2), it is possible to suppress optical loss in the 1310 nm wavelength band before and after reflow treatment. Furthermore, it is possible to suppress the rigidity derived from the norbornane structure and impart flexibility to the dry film produced. As a result, it is possible to improve the film's handleability. When an epoxy compound having a silicone structure with an Si number of more than 6 is used, it becomes difficult to uniformly mix the epoxy compound having a silicone structure in the resin composition, which results in difficulty in film formation.

[0036] The second epoxy compound (a2) is not particularly limited, but preferably contains a liquid epoxy compound having a silicone structure. By containing a liquid epoxy compound having a silicone structure, it is possible to more reliably suppress light loss in the 1310 nm wavelength band before and after reflow treatment and to reliably improve film handleability.

[0037] Specifically, the second epoxy compound (a2) preferably contains one or more compounds having structural formulas represented by the following formulas (3), (4), and (5). Each formula will be explained below.

[0038] Equation (3) is as follows:

[0039]

[0040] In the above formula (3), R １（a２） ~R ４（a２） are each independently an alkyl group having 1 to 10 carbon atoms. １ and X ２ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a group represented by the following formula (3A), and a group represented by the following formula (3B). １ and X ２ At least one of the groups is a group represented by the following formula (3A) or (3B).

[0041]

[0042] In the above formula (3A) and formula (3B), R ５（ａ２） and R ６（ａ２） is a bond or an alkylene group having 1 to 6 carbon atoms.

[0043] In the above formula (3), R １（a２） ~R ４（a２） are each independently preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. １ or X ２ When each of the groups is an alkyl group, it is preferable that each of them independently has 1 to 5 carbon atoms, and more preferably has 1 to 3 carbon atoms. The alkyl group may be linear or branched.

[0044] In addition, in the above formula (3A) and formula (3B), R ５（ａ２） and R ６（ａ２） is preferably an alkylene group having 1 to 3 carbon atoms, and more preferably a dimethylene group or a trimethylene group.

[0045] Equation (4) is as follows:

[0046]

[0047] In the above formula (4), R ７（ａ２） ~R １２（ａ２） are each independently an alkyl group having 1 to 10 carbon atoms. ３ and X ４ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a group represented by the above formula (3A), and a group represented by the above formula (3B). ３ and X ４ At least one of the groups is a group represented by the above formula (3A) or (3B), and n is an integer of 1 or more and 4 or less.

[0048] In the above formula (4), R ７（ａ２） ~R １２（ａ２） are each independently preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. ３ and X ４ When each of the groups is an alkyl group, it is preferable that each of them independently has 1 to 5 carbon atoms, and more preferably has 1 to 3 carbon atoms. The alkyl group may be linear or branched.

[0049] Equation (5) is as follows:

[0050]

[0051] In the above formula (5), R １３（ａ２） and R １４（ａ２） are each independently selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, a group represented by the above formula (3A), and a group represented by the above formula (3B) for each repeating unit k, provided that all R １３（ａ２） and R １４（ａ２） At least one of the groups is a group represented by the above formula (3A) or (3B), and k is an integer of 3 or more and 6 or less.

[0052] In the above formula (5), R ７（ａ２） ~R １２（ａ２） When is an alkyl group, each repeating unit k is independently preferably an alkyl group having 1 to 5 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms.

[0053] Although such a second epoxy compound (a2) is not particularly limited, it is preferable that the second epoxy compound (a2) contains, for example, one or more compounds having structural formulas represented by the following formulas (3-1) and (5-1).

[0054]

[0055] (In formula (5-1), R １５（ａ２） and R １６（ａ２） are each independently selected from the group consisting of alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 10 carbon atoms.

[0056] R １５（ａ２） and R １６（ａ２） The alkyl group or alkoxy group in may be linear or branched.

[0057] The second epoxy compound (a2) may be synthesized by a known method, or a commercially available product may be used. For example, an example of a compound having the structural formula represented by the above formula (3-1) is "X-40-2669" manufactured by Shin-Etsu Chemical Co., Ltd. For example, an example of a compound having the structural formula represented by the above formula (5-1) is "X-40-2678" manufactured by Shin-Etsu Chemical Co., Ltd. Other examples of the second epoxy compound (a2) include "X-22-163", "X-40-2728", and "KR470" manufactured by Shin-Etsu Chemical Co., Ltd.

[0058] The second epoxy compound (a2) may be used alone or in combination of two or more.

[0059] In the resin composition according to this embodiment, the content of the second epoxy compound (a2) is 5 parts by mass or more and 60 parts by mass or less relative to 100 parts by mass of the first epoxy compound (a1). That is, {(a2) / (a1)}×100 (parts by mass) is 5 parts by mass or more and 60 parts by mass or less. In the resin composition according to this embodiment, {(a2) / (a1)}×100 (parts by mass) satisfies this condition, so that a resin composition can be obtained that can suppress optical loss in the 1310 nm wavelength band not only before reflow treatment but also after reflow treatment at high temperatures, and maintain good film handleability.

[0060] {(a2) / (a1)} x 100 (parts by mass) is preferably 5.3 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably a value selected from the group consisting of 17.6 parts by mass, 20 parts by mass, 23 parts by mass, and 25 parts by mass or more. Also, {(a2) / (a1)} x 100 (parts by mass) is preferably 58 parts by mass or less, more preferably 55 parts by mass or less, even more preferably 53.8 parts by mass or less, and particularly preferably a value selected from the group consisting of 50 parts by mass, 42.9 parts by mass, 40.0 parts by mass, 35 parts by mass, and 33.3 parts by mass or less.

[0061] The content of the second epoxy compound (a2) relative to the total amount of epoxy compound (A) is not particularly limited as long as the above condition of {(a2) / (a1)}×100 (parts by mass) is satisfied. For example, the content of the second epoxy compound (a2) is preferably 5% by mass or more and 35% by mass or less relative to the total amount of epoxy compound (A). When the content of the second epoxy compound (a2) is 5% by mass or more, the optical loss in the 1310 nm wavelength band before and after the reflow treatment can be effectively suppressed and the film handleability can be further improved. When the content of the second epoxy compound (a2) is 35% by mass or less, it is possible to prevent the epoxy compounds from being difficult to mix uniformly in the resin composition and to reliably obtain a resin composition having good film handleability.

[0062] (Other Epoxy Compounds) The resin composition may contain epoxy compounds other than the above-described epoxy compounds, as long as the effects of suppressing optical loss before and after the reflow treatment and improving film handleability according to the present embodiment are not impaired. The other epoxy compounds may be either liquid epoxy compounds or solid epoxy compounds.

[0063] Examples of epoxy compounds include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, bisphenol F type epoxy resins, polyfunctional epoxy resins, bisphenol E type epoxy resins, brominated epoxy resins, fluorinated epoxy resins, aromatic epoxy resins, novolac type epoxy resins, biphenyl type epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins.

[0064] Among the other epoxy compounds, it is preferable to use a bisphenol A type epoxy resin from the viewpoints of high transparency and ease of UV curing. The epoxy equivalent of the bisphenol A type epoxy resin is not particularly limited, but is preferably, for example, about 170 g / eq to 1200 g / eq.

[0065] The bisphenol A epoxy resin may be synthesized by a known method, or a commercially available product may be used. For example, commercially available solid bisphenol A epoxy resins include "1001," "1002," "1003," "1055," "1004," "1004AF," "1003F," "1004F," "1005F," "1004FS," "1006FS," and "1007FS" manufactured by Mitsubishi Chemical Group Corporation. Furthermore, commercially available liquid bisphenol A epoxy resins include "Epiclon (registered trademark) 850S" manufactured by DIC Corporation and "JER (registered trademark) 825" manufactured by Mitsubishi Chemical Corporation.

[0066] Among the other epoxy compounds, it is preferable to contain a polyfunctional epoxy resin, from the viewpoint that the glass transition temperature Tg of the dry film can be improved, thereby imparting good heat resistance to the optical waveguide. The epoxy equivalent of the polyfunctional epoxy resin is not particularly limited, but is preferably, for example, about 150 g / eq to 250 g / eq.

[0067] Examples of polyfunctional epoxy resins include 2-[4-(2,3-epoxypropoxy)phenyl]-2-[4-[1,1-bis[4-([2,3-epoxypropoxy]phenyl)]ethyl]phenyl]propane, cresol novolac epoxy resins, and the like. The polyfunctional epoxy resins may be synthesized by known methods, but commercially available products may also be used. Examples of commercially available products include "VG3101M80" manufactured by Printec Co., Ltd., "EHPE-3150" manufactured by Daicel Corporation, and "EPPN-502" manufactured by Nippon Kayaku Co., Ltd.

[0068] These other epoxy compounds may be used singly or in combination of two or more.

[0069] The content of the other epoxy compound is not particularly limited as long as it satisfies the above-mentioned condition of {(a2) / (a1)}×100 (parts by mass) and does not impair the effects of suppressing light loss before and after the reflow treatment and good film handleability according to this embodiment. For example, the content of the other epoxy compound relative to the total amount of epoxy compound (A) is preferably 0% by mass or more and 30% by mass or less. Furthermore, the content of the other epoxy compound is more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0070] [Curing Agent] The resin composition according to the present embodiment may generally contain a curing agent. The type of curing agent is not particularly limited as long as it can promote photocuring of the resin composition containing the epoxy compound (A).

[0071] As the curing agent, for example, a polymerization initiator that causes ring-opening polymerization of the epoxy group of each epoxy compound (A) can be used. An example of the polymerization initiator is a photoacid generator that can initiate a reaction by light such as ultraviolet light.

[0072] Specific examples of the curing agent include antimony-based curing agents, gallate-based curing agents, phosphorus-based curing agents, special phosphorus-based curing agents, and borate-based curing agents. Commercially available products can be used for these curing agents. Examples of commercially available curing agents include "CPI-310FG" manufactured by San-Apro Co., Ltd., which is a gallate-based curing agent, "CPI-101A" manufactured by San-Apro Co., Ltd., and "SP-170" manufactured by ADEKA Corporation, which are antimony-based curing agents. These curing agents may be used alone or in combination of two or more.

[0073] The content of the curing agent is not particularly limited as long as it does not impair the effects of suppressing light loss before and after the reflow treatment according to the present embodiment and good film handleability. For example, the content of the curing agent is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.5 mass % or more and 3 mass % or less, based on the total amount of the epoxy compound (A).

[0074] [Other Additives] In addition to the components described above, the resin composition may further contain other additives such as antioxidants, leveling agents, coupling agents (silane coupling agents), flame retardants, and inorganic fillers, as long as the effects of suppressing light loss before and after the reflow treatment and providing good film handleability according to this embodiment are not impaired.

[0075] In particular, from the viewpoint of improving the heat resistance of the optical waveguide, it is preferable that the resin composition further contains an antioxidant. The antioxidant is not particularly limited, and phenol-based antioxidants, phosphite-based antioxidants, sulfur-based antioxidants, etc. can be used. Of these, the antioxidant is preferably a phenol-based antioxidant.

[0076] Commercially available phenolic antioxidants can be used, such as "AO-20," "AO-30," "AO-40," "AO-50," "AO-60," and "AO-80" manufactured by Adeka Corporation, and "SUMILIZER GA-80" manufactured by Sumitomo Chemical Co., Ltd.

[0077] The content of the antioxidant (C) is not particularly limited, but is preferably (0 mass % or more) and 5 mass % or less, and more preferably (0 mass % or more) and 1 mass % or less, based on the total amount of the epoxy compound (A).

[0078] As described above, the resin composition for an optical waveguide according to this embodiment can suppress optical loss in the 1310 nm wavelength band not only before reflow treatment but also after reflow treatment at high temperatures. Furthermore, the resin composition for an optical waveguide according to this embodiment also has good film handling properties. Therefore, this resin composition can be suitably used as a material for a dry film according to an embodiment described below, which is used in the manufacture of an optical waveguide, particularly an optical waveguide on which an electric circuit is also formed and on which optical elements and the like are mounted.

[0079] The resin composition for an optical waveguide according to this embodiment may be used for both the core and the cladding. However, since the optical loss at a wavelength of 1,310 nm occurs mainly in the core, the resin composition for an optical waveguide according to this embodiment can be more effective when used to produce a dry film for the core.

[0080] 2. Dry Film The dry film according to this embodiment is not particularly limited as long as it has a layer containing the resin composition for optical waveguides according to the above-described embodiment. Specifically, the dry film has a layer containing an uncured or semi-cured product of the resin composition for optical waveguides according to the above-described embodiment (hereinafter also referred to as an "optical waveguide resin composition layer" or "resin composition layer"). The resin composition for optical waveguides according to the above-described embodiment has good film handleability, and therefore the dry film according to this embodiment has excellent film handleability and excellent adhesion to a film base, a film substrate, etc.

[0081] In this specification, the term "uncured product" or "semi-cured product" refers to a resin composition layer in an uncured or semi-cured state obtained by applying a resin composition in the form of a varnish as described below, and then heating and / or drying at an appropriate temperature and time as necessary to reduce or remove the solvent, etc. In other words, the "uncured product" or "semi-cured product" is in a state where the epoxy resin in the resin composition layer can be further cured.

[0082] In this specification, the term "cured product" refers to a resin layer that does not melt even when heated due to the curing reaction of an uncured or semi-cured resin composition layer that has progressed due to irradiation with light such as ultraviolet light, causing the resin to crosslink. The optical waveguide finally obtained in the embodiments described below has a core and / or clad that are cured products of the resin composition for an optical waveguide.

[0083] The dry film may include a film substrate laminated on at least one surface of the resin composition layer. Furthermore, a protective film may be laminated on the other surface of the resin composition layer. The dry film may also include other layers in addition to the resin composition layer, the film substrate, and / or the protective film. However, the dry film may also be composed of a resin composition layer containing an uncured and / or semi-cured product of the resin composition for optical waveguides according to the above-described embodiment.

[0084] The film substrate is not particularly limited, but examples thereof include polyethylene terephthalate (PET) film, biaxially oriented polypropylene film, polyethylene naphthalate film, polyimide film, etc. Among these, PET film is preferred. The protective film is not particularly limited, but examples thereof include polypropylene film, etc.

[0085] The method for producing the dry film is not particularly limited, but examples thereof include the following method. First, a solvent or the like is added to the resin composition for optical waveguides according to the above-described embodiment to form a varnish-like resin composition, and the varnish is then applied to a film substrate. This application can be performed using a comma coater or the like. The applied varnish is then dried at an appropriate temperature and for an appropriate time, thereby forming a resin composition layer on the film substrate. Furthermore, a protective film is laminated on this resin composition layer. Examples of methods for laminating the protective film include thermal lamination.

[0086] The dry film having the resin composition layer thus produced is used as a material for an optical waveguide according to the embodiment described below. The dry film may be used when producing a core portion of the optical waveguide or when producing a clad portion. However, as described above, optical loss at a wavelength of 1310 nm occurs mainly in the core portion, so the dry film is preferably used when producing the core portion of the optical waveguide.

[0087] It should be noted that the resin composition for an optical waveguide according to the above-described embodiment does not necessarily need to be used after forming the dry film according to this embodiment when manufacturing an optical waveguide. For example, the resin composition for an optical waveguide according to the above-described embodiment may be made into a varnish-like resin composition and used directly when manufacturing the core and / or clad of an optical waveguide. For the same reasons as above, it is preferable to use the varnish-like resin composition when manufacturing the core.

[0088] The optical waveguide according to this embodiment is formed using the resin composition or dry film according to the above-described embodiment. Because the optical waveguide is formed using the resin composition or dry film according to the above-described embodiment, it is possible to suppress optical loss at a wavelength of 1310 nm before and after reflow treatment, making it very useful for industrial applications.

[0089] Specifically, the optical waveguide according to this embodiment is an optical waveguide including a core portion and a clad portion having a lower refractive index than the core portion and formed to cover the core portion, and the core portion or the clad portion is formed using the resin composition or dry film according to the above-described embodiment. As described above, it is preferable that the core portion of the optical waveguide is formed using the resin composition or dry film according to the above-described embodiment.

[0090] In this specification, "the cladding portion is formed so as to cover the core portion" means that the undercladding and / or overcladding formed by, for example, hardening a dry cladding film is formed so as to embed the core portion (or substantially cover or surround the periphery of the core portion).

[0091] An example of a method for forming an optical waveguide on a substrate using the dry film according to the above-described embodiment will be described below with reference to Fig. 1. In Fig. 1(a) to Fig. 1(f), the reference characters respectively represent a cladding dry film 1, a core dry film 2, a cladding portion 3, an undercladding 3a, an overcladding 3b, a core portion 4, a substrate 10, an electric circuit 11, a slit 12, a mask 13, and an optical waveguide A.

[0092] 1, a clad dry film and a core dry film are used to form the core and clad portions, respectively. In the example shown in FIG. 1, the core dry film is made of the dry film according to the above-described embodiment, and the clad dry film is made of a dry film having a lower refractive index than the core film. The clad dry film and the core dry film may both be made of the dry film according to the above-described embodiment.

[0093] First, as shown in Fig. 1(a), a cladding dry film 1 is laminated onto the surface of a substrate 10 on which an electric circuit 11 has been formed, and then the cladding dry film 1 is cured by irradiation with light such as ultraviolet light, heating, or the like. The substrate 10 may be, for example, a flexible printed wiring board in which an electric circuit has been formed on one side of a transparent substrate such as a polyimide film, or a printed wiring board made of glass epoxy. Through this process, an undercladding 3a is formed and laminated on the surface of the substrate 10, as shown in Fig. 1(b).

[0094] 1(c), a core dry film 2 is laminated on the surface of the undercladding 3a, and then a mask 13 having slits 12 of a core pattern is placed over it. Then, photo-curable light such as ultraviolet light is irradiated through the slits 12, thereby exposing the core dry film 2 to the core pattern. The exposure method may be a selective exposure method using a mask 13, or a direct writing method in which a laser beam is scanned and irradiated along the pattern shape.

[0095] After the exposure, the core dry film 2 is developed using a developer such as an aqueous flux cleaner to remove the resin from the unexposed and uncured portions of the core dry film 2. As a result, a core portion 4 of a predetermined core pattern is formed on the surface of the underclad 3a, as shown in FIG.

[0096] Next, as shown in Fig. 1(e), a clad dry film 1 is laminated to cover the underclad 3a and the core 4. Then, the clad dry film 1 is cured by irradiation with light, heating, etc., to form an overclad 3b as shown in Fig. 1(f). In this way, an optical waveguide A is formed on the surface of the substrate 10, with the core 4 embedded in the clad 3 consisting of the underclad 3a and the overclad 3b.

[0097] The optical waveguide A obtained in this manner uses the dry film according to the embodiment described above, and therefore can suppress optical loss at a wavelength of 1310 nm not only before reflow treatment but also after reflow treatment at high temperatures. Therefore, even if a reflow treatment at high temperatures is performed with the optical waveguide A provided for mounting an optical element, etc., excellent optical communication can be achieved while suppressing optical loss. Therefore, the substrate 10 on which such an optical waveguide A is formed is preferably used as an optical transmission printed wiring board that is subjected to reflow treatment, and is preferably used for, for example, a mobile phone, a personal digital assistant, etc.

[0098] As described above, this specification discloses various aspects of the technology, the main aspects of which are summarized below.

[0099] The resin composition for optical waveguides according to a first aspect of the present invention contains an epoxy compound (A), wherein the epoxy compound (A) comprises a first epoxy compound (a1) having a norbornane structure and a second epoxy compound (a2) having a silicone structure in which the number of Si atoms is 1 or more and 6 or less, and the content of the second epoxy compound (a2) is 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the first epoxy compound (a1).

[0100] A resin composition for optical waveguides according to a second aspect of the present invention is the resin composition for optical waveguides of the first aspect, wherein the first epoxy compound (a1) includes one or more compounds having structural formulas represented by the following formulas (1) and (2):

[0101]

[0102]

[0103] (In formula (1) and formula (2), R １（a１） ~R ３６（a１） are each independently selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, and an alkoxy group having 1 to 10 carbon atoms.

[0104] A resin composition for optical waveguides according to a third aspect of the present invention is the resin composition for optical waveguides according to the first or second aspect, wherein the first epoxy compound (a1) includes one or more compounds having structural formulas represented by the following formulas (1-1) and (2-1):

[0105]

[0106] A resin composition for optical waveguides according to a fourth aspect of the present invention is the resin composition for optical waveguides according to any one of the first to third aspects, wherein the second epoxy compound (a2) includes one or more compounds having structural formulas represented by the following formulas (3), (4), and (5):

[0107]

[0108] (In formula (3), R １（a２） ~R ４（a２） are each independently an alkyl group having 1 to 10 carbon atoms, and X １ and X ２ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a group represented by the following formula (3A), and a group represented by the following formula (3B), and X １ and X ２ At least one of the groups is a group represented by the following formula (3A) or formula (3B):

[0109]

[0110] (In formula (3A) and formula (3B), R ５（ａ２） and R ６（ａ２） is a bond or an alkylene group having 1 to 6 carbon atoms.

[0111]

[0112] (In formula (4), R ７（ａ２ ) ~R １２（ａ２） are each independently an alkyl group having 1 to 10 carbon atoms, and X ３ and X ４ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a group represented by the above formula (3A), and a group represented by the above formula (3B), ３and X ４ At least one of the groups is a group represented by the above formula (3A) or formula (3B), and n is an integer of 1 or more and 4 or less.

[0113]

[0114] (In formula (5), R １３（ａ２） and R １４（ａ２） are each independently selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, a group represented by the above formula (3A), and a group represented by the above formula (3B), for each repeating unit k, １３（ａ２） and R １４（ａ２） At least one of the groups is a group represented by the above formula (3A) or formula (3B), and k is an integer of 3 or more and 6 or less.

[0115] A resin composition for optical waveguides according to a fifth aspect of the present invention is the resin composition for optical waveguides according to any one of the first to fourth aspects, wherein the second epoxy compound (a2) includes one or more compounds having structural formulas represented by the following formulas (3-1) and (5-1):

[0116]

[0117] (In formula (5-1), R １５（ａ２） and R １６（ａ２） are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms.

[0118] A dry film according to a sixth aspect of the present invention has a layer containing an uncured or semi-cured product of the resin composition for an optical waveguide according to any one of the first to fifth aspects.

[0119] The optical waveguide according to the seventh aspect of the present invention is an optical waveguide comprising a core portion and a clad portion having a refractive index lower than that of the core portion and formed to cover the core portion, wherein the core portion is formed using the resin composition for an optical waveguide according to any one of the first to fifth aspects (or the dry film according to the sixth aspect).

[0120] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0121] In this example, various resin compositions for optical waveguides were prepared using epoxy compounds having various norbornane structures and epoxy compounds having silicone structures, and the content ratios of these compounds were varied. Dry films were then manufactured using these compositions. Furthermore, the handleability of the manufactured dry films was evaluated, and the glass transition temperature (Tg) of some of the dry films was measured. Various waveguide samples were also manufactured, and the optical loss at a wavelength of 1310 nm before and after reflow treatment was measured and evaluated.

[0122] First, the raw materials used in preparing the resin compositions for optical waveguides in the examples are summarized below.

[0123] [First epoxy compound (a1) having a norbornane structure] "DE102": alicyclic epoxy resin (solid epoxy resin), manufactured by ENEOS Corporation "DE103": alicyclic epoxy resin (solid epoxy resin), manufactured by ENEOS Corporation "EPICLON HP-7200": ordinary epoxy resin containing dicyclopentadiene (solid epoxy resin), manufactured by DIC Corporation [Second epoxy compound (a2) having a silicone structure having 1 to 6 Si atoms] "X-40-2669": alicyclic epoxy resin (liquid epoxy resin) having a linear silicone structure (Si=1), manufactured by Shin-Etsu Chemical Co., Ltd. (epoxy equivalent 190 g / eq) "X-22-163": ordinary epoxy resin (liquid epoxy resin) having a linear silicone structure (Si=1), manufactured by Shin-Etsu Chemical Co., Ltd. (epoxy equivalent 200 g / eq) "X-40-2678": alicyclic epoxy resin (liquid epoxy resin) having a cyclic silicone structure (Si=4), manufactured by Shin-Etsu Chemical Co., Ltd. (epoxy equivalent: 290 g / eq) "X-40-2728": ordinary epoxy resin (liquid epoxy resin) having a cyclic silicone structure (Si=4), manufactured by Shin-Etsu Chemical Co., Ltd. (epoxy equivalent: 280 g / eq) [epoxy compound having a silicone structure with more than 6 Si atoms] "X-22-169AS": alicyclic epoxy resin (liquid epoxy resin) having a linear silicone structure (Si=8), manufactured by Shin-Etsu Chemical Co., Ltd. (epoxy equivalent: 500 g / eq) [other epoxy compounds (BisA type epoxy resin)] "1006FS": BisA type epoxy resin (solid epoxy resin), manufactured by Mitsubishi Chemical Corporation (epoxy equivalent: 900 to 1100 g / eq) "VG3101M80": BisA type trifunctional epoxy resin (solid epoxy resin), manufactured by Printec Co., Ltd. (epoxy equivalent: 205 to 215 g / eq) "850S": BisA type epoxy resin (liquid epoxy resin), manufactured by DIC Corporation (epoxy equivalent: 183 to 193 g / eq) [Antioxidant] "AO-60": Phenol-based antioxidant, manufactured by ADEKA Corporation [Curing agent] "CPI-310FG": Gallate-based curing agent, manufactured by San-Apro Co., Ltd. [Leveling agent] "BYK3560": BYK Japan Co., Ltd.

[0124] "DE102" is the first epoxy compound (a1) having the structural formula represented by the above formula (1-1). "DE103" is the first epoxy compound (a1) having the structural formula represented by the above formula (2-1). "EPICLON HP-7200" is the first epoxy compound (a1) having the structural formula represented by the following formula (6). In the following formula (6), m is an integer of 0 to 5.

[0125]

[0126] "X-40-2669" is the second epoxy compound (a2) having the structural formula represented by the above-mentioned formula (3-1). "X-40-2678" is the second epoxy compound (a2) having the structural formula represented by the above-mentioned formula (5-1).

[0127] Next, the methods for preparing the resin compositions (resin varnishes) for optical waveguides and the methods for producing dry films in each Example and Comparative Example are described below. Furthermore, the methods for evaluating film handleability, measuring the glass transition temperature Tg, and measuring and evaluating the optical loss in the 1310 nm wavelength band using waveguide samples before and after reflow treatment are also described below.

[0128] <Method of Preparing Resin Composition for Optical Waveguide (Resin Varnish)> In each Example and Comparative Example, the components were blended according to the blending compositions (parts by mass) shown in Tables 1 and 2 below, and the mixed solvent of MEK and toluene was adjusted to 55 parts by mass per 100 parts by mass of the epoxy compound, and these were mixed while heating to 50° C. to 60° C. Next, the mixture was filtered through a membrane filter with a pore size of 1.0 μm and then degassed, thereby preparing resin compositions for optical waveguides (resin varnishes) of Examples 1 to 15 and Comparative Examples 1 to 6.

[0129] <Method for manufacturing dry film> The resin composition for optical waveguides (resin varnish) of each example and comparative example was applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a K control coater manufactured by Matsuo Sangyo Co., Ltd. The PET film was then dried at 130°C for 10 minutes to a predetermined thickness, and a release film, OPP-MA420 manufactured by Oji Specialty Paper Co., Ltd., was thermally laminated to obtain a dry film having a thickness of 40 to 50 μm.

[0130] <Method for Evaluating Film Handling Efficiency> The dry films of each Example and Comparative Example prepared as described above were used to evaluate film handling. Specifically, when the dry film was cut with a cutter, the edges were checked for cracks or powder shedding. Furthermore, when the protective film was peeled off from the dry film, the dry film was checked for traces of peeling. If no cracks or powder shedding occurred and no traces of peeling remained upon peeling, the dry film was evaluated as having "good" film handling. On the other hand, if cracks or powder shedding occurred or traces of peeling remained upon peeling, the dry film was evaluated as having "poor" film handling (poor film handling). The evaluation results of film handling in each Example and Comparative Example are summarized in Tables 1 and 2 below.

[0131] <Method for Measuring Glass Transition Temperature Tg> The dry films of each Example and Comparative Example produced as described above were cut to a size of 10 mm x 40 mm and attached to a dynamic viscoelasticity measuring device (Seiko Instruments Inc., "DMS6100"). Tests were conducted under conditions of a strain amplitude of 10 μm, a frequency of 10 Hz (sine wave), and a temperature rise rate of 5°C / min, and the calculated peak temperature of tan δ was used as the glass transition temperature Tg (°C). The higher the glass transition temperature Tg of the dry film, the more suitable it can be evaluated as a resin composition for optical waveguides to be subjected to reflow treatment, also from the standpoint of heat resistance. The glass transition temperature Tg was measured in some Examples and Comparative Examples. The measurement results are summarized in Tables 1 and 2 below.

[0132] <Method for measuring and evaluating optical loss in the 1310 nm wavelength band before and after reflow treatment> (Manufacturing of waveguide samples) In measuring and evaluating optical loss in the 1310 nm wavelength band before and after reflow treatment, first, the dry films of each example and comparative example manufactured as described above were used as core films to manufacture waveguide samples.

[0133] The clad film of the waveguide sample was produced using the same first epoxy compound (a1) and second epoxy compound (a2) as the base epoxy compounds used in the core films of each example and comparative example. However, out of 100 parts by mass of the epoxy compound, the amount (parts by mass) of the first epoxy compound (a1) was half the amount of the core film, and the amount (parts by mass) of the second epoxy compound (a2) was the remaining amount. 100 parts by mass of the epoxy compound thus blended, 1 part by mass of a curing agent, 1 part by mass of an antioxidant, and 0.2 parts by mass of a leveling agent were dissolved in a mixed solvent of MEK, toluene, and PGMEA in an amount of 50 parts by mass per 100 parts by mass of the epoxy compound. The mixture was then filtered through a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 1.0 μm and degassed to prepare a resin varnish. The prepared resin varnish was applied to a PET film (product number A4100) manufactured by Toyobo Co., Ltd. using a multi-coater with a comma coater head manufactured by Hirano Tecseed Co., Ltd. The film was then dried to obtain a dry film for cladding having a thickness of 40 to 50 μm.

[0134] The resulting clad film was then laminated onto a substrate as an underclad. The core film of each example and comparative example was then laminated on top of the clad film. The laminated film was exposed to light and heat-treated, and then an overclad was laminated using the clad film to produce a slab waveguide sample.

[0135] (Measurement of Optical Loss at 1310 nm Wavelength Band Before Reflow Treatment) Using the manufactured slab waveguide sample, the optical loss at a wavelength of 1310 nm before reflow treatment was measured using the following method. Light from a 1310 nm LED light source was passed through an optical fiber with a core diameter of 9 μm and NA of 0.12 and incident on the end of the manufactured waveguide sample via matching oil (silicone oil). Furthermore, an optical fiber with a core diameter of 50 μm and NA of 0.21 was passed through the same matching oil, and the other end of the waveguide sample was connected to a power meter to measure the power (P1) when an optical circuit was inserted. In addition, the power (P0) measured by butting two similar optical fibers together without an optical circuit was also measured. From the measured value, the optical loss (dB / cm) at a wavelength of 1310 nm was calculated using the formula -10 log (P1 / Po). The calculation results of the optical loss (dB / cm) at a wavelength of 1310 nm for each example and each comparative example are summarized in Tables 1 and 2. When the optical loss was 0.400 dB / cm or less, the optical loss was evaluated as being well suppressed, and when the optical loss exceeded 0.400 dB / cm, the optical loss was evaluated as being large.

[0136] (Measurement of Optical Loss in the 1310-nm Wavelength Band After Reflow Treatment) The manufactured slab waveguide samples of each Example and Comparative Example were subjected to reflow treatment five times (five passes) under the reflow conditions for lead-free solder, and the optical loss in the 1310-nm wavelength band for each slab waveguide sample was calculated using the same method as above. In addition, the optical loss value (dB / cm) at a wavelength of 1310 nm after reflow treatment relative to the optical loss value (dB / cm) at a wavelength of 1310 nm before reflow treatment was calculated as the loss increase rate (%).

[0137] The evaluation, measurement, and calculation results for each of the above examples and comparative examples, along with the formulation, are summarized in the following Tables 1 and 2. In the following Tables 1 and 2, "-" means that the component in that item is not formulated in the composition, that the item cannot be calculated, or that the item has not been measured.

[0138]

[0139]

[0140] <Discussion> As shown in Tables 1 and 2 above, the waveguide samples of Examples 1 to 15, in which the epoxy compound (A) contained a first epoxy compound (a1) and a second epoxy compound (a2) and in which {(a2) / (a1)}×100 (parts by mass) was in the range of 5 parts by mass or more and 60 parts by mass or less, were able to suppress light loss before and after reflow treatment and had good film handleability. This is thought to be because both the first epoxy compound (a1) and the second epoxy compound (a2) suitably suppressed light loss in the waveguide before and after reflow treatment, and an appropriate amount of the second epoxy compound (a2) imparted appropriate flexibility to the film.

[0141] On the other hand, in the waveguide samples of Comparative Examples 1 and 2, which did not contain both the first epoxy compound (a1) and the second epoxy compound (a2), not only was the optical loss before the reflow treatment large, but the rate of increase in loss after the reflow treatment was also high, resulting in a significant increase in optical loss. This is thought to be because the spectral shape of a typical bisphenol A epoxy resin in the 1310 nm wavelength band is broad, resulting in a large optical loss.

[0142] In the waveguide sample of Comparative Example 3, which contained the first epoxy compound (a1) but not the second epoxy compound (a2) as the epoxy compound (A), the optical loss before the reflow treatment was suppressed, but the loss increase rate after the reflow treatment was significantly high, resulting in a large increase in optical loss. This suggests that in order to appropriately suppress the optical loss after the reflow treatment, it is necessary to contain not only the first epoxy compound (a1) but also the second epoxy compound (a2) as the epoxy compound (A).

[0143] In the waveguide sample of Comparative Example 4, which contained a large amount of the second epoxy compound (a2), the tackiness of the film was poor, and peeling marks remained when the protective film was peeled off, making it impossible to properly form a dry film. This is thought to be due to the fact that the content of the second epoxy compound (a2) was too high. As a result, the amount of liquid components in the resin composition increased, which increased the adhesion to the protective film, making it impossible to properly form a film.

[0144] The waveguide sample of Comparative Example 5, which used an epoxy compound having a silicone structure with an Si number of 8, also had poor film tackiness, leaving traces of peeling when the protective film was peeled off, and was unable to properly form a dry film, as in Comparative Example 4. This is also thought to be due to the fact that the amount of Si element in the epoxy compound having a silicone structure was too high. As a result, the amount of liquid components in the resin composition increased, the melting point of the entire composition was too low, the tackiness at room temperature was poor, and the adhesion to the protective film was too high, which is thought to have prevented the film from being properly formed.

[0145] In the waveguide sample of Comparative Example 6, which used only the first epoxy compound (a1) as the epoxy compound (A), cracks and powder fall occurred, and a dry film could not be formed. This is thought to be because the resin composition contained too many solid components at room temperature, which reduced the flexibility of the resin film before curing and made it weak to bending.

[0146] This application is based on Japanese Patent Application No. 2023-221011 filed on December 27, 2023, the contents of which are incorporated herein by reference.

[0147] The embodiments and examples disclosed herein should be understood to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0148] According to the present invention, it is possible to provide a resin composition for optical waveguides that can suppress optical loss in the 1,310 nm wavelength band before and after reflow treatment and has good film handleability. The resin composition for optical waveguides can be suitably used as a material for optical waveguides used in the manufacture of optical transmission printed wiring boards for mobile phones, personal digital assistants, etc.

Claims

1. A resin composition for an optical waveguide, which contains an epoxy compound (A), wherein the epoxy compound (A) includes a first epoxy compound (a1) having a norbornane structure and a second epoxy compound (a2) having a silicone structure with 1 to 6 Si atoms, and the content of the second epoxy compound (a2) is 5 to 60 parts by mass with respect to 100 parts by mass of the first epoxy compound (a1).

2. The resin composition for an optical waveguide according to claim 1, wherein the first epoxy compound (a1) contains one or more of compounds having structural formulas represented by the following formulas (1) and (2). (In formulas (1) and (2), R １（a１） to R ３６（a１） are each independently selected from the group consisting of hydrogen, an alkyl group having 1 or more and 10 or less carbon atoms, and an alkoxy group having 1 or more and 10 or less carbon atoms.) 3. The resin composition for an optical waveguide according to claim 2, wherein the first epoxy compound (a1) contains one or more of compounds having structural formulas represented by the following formulas (1-1) and (2-1).

4. The resin composition for an optical waveguide according to claim 1, wherein the second epoxy compound (a2) contains one or more of compounds having structural formulas represented by the following formulas (3), (4), and (5). (In formula (3), R １（a２） ~R ４（a２） are each independently an alkyl group having 1 to 10 carbon atoms, and X １ and X ２ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, a group represented by the following formula (3A), and a group represented by the following formula (3B), and at least one of X １ and X ２ is a group represented by the following formula (3A) or formula (3B).) (In formulas (3A) and (3B), R ５（ａ２） and R ６（ａ２） are a bond or an alkylene group having 1 to 6 carbon atoms.) (In formula (4), R ７（ａ２ )~R １２（ａ２） are each independently an alkyl group having 1 to 10 carbon atoms, and X ３ and X ４ are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, the group represented by the above formula (3A), and the group represented by the above formula (3B), at least one of X ３ and X ４ is a group represented by the above formula (3A) or formula (3B), and n is an integer of 1 or more and 4 or less.) (In formula (5), R １３（ａ２） and R １４（ａ２） are each independently selected from the group consisting of hydrogen, an alkyl group having 1 to 10 carbon atoms, the group represented by the above formula (3A), and the group represented by the above formula (3B) for each repeating unit k, and at least one of all R １３（ａ２） and R １４（ａ２） of the repeating unit k is a group represented by the above formula (3A) or formula (3B), and k is an integer of 3 or more and 6 or less.) 5. The resin composition for an optical waveguide according to claim 4, wherein the second epoxy compound (a2) contains one or more of compounds having structural formulas represented by the following formulas (3-1) and (5-1). (In formula (5-1), R １５（ａ２） and R １６（ａ２） are each independently selected from the group consisting of an alkyl group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms.) 6. A dry film having a layer containing an uncured or semi-cured product of the resin composition for an optical waveguide according to any one of claims 1 to 5.

7. An optical waveguide including a core portion and a clad portion that has a refractive index lower than that of the core portion and is formed so as to cover the core portion, wherein the core portion is formed using the resin composition for an optical waveguide according to any one of claims 1 to 5.

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