Resin composition for optical waveguide, and dry film and optical waveguide using said resin composition

Abstract

This resin composition for an optical waveguide contains an epoxy resin (A) and a curing agent (B). The epoxy resin (A) contains a bisphenol A-type epoxy resin (a-1) having an epoxy equivalent of 1,500 g / eq or less, and a fluorene-type epoxy resin (a-2) containing no hydroxyl group in the molecular structure thereof. The content of the fluorene-type epoxy resin (a-2) is 15-80 mass% with respect to the total amount of the epoxy resin (A).

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 is obtained by forming a cladding and a core using two types of ultraviolet (UV)-curable optical waveguide resin compositions with high transparency and 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 (see, for example, Patent Documents 1 and 2). Of these resins, epoxy resins are preferred from the viewpoints of heat resistance and optical signal transmission. Patent Documents 1 and 2 also list many types of epoxy resins. Among these epoxy resins, bisphenol A epoxy resins have traditionally been more preferred from the viewpoints of their ability to form highly transparent optical waveguide resin compositions and facilitate UV curing.

[0004] International Publication No. 2020 / 203366 Japanese Patent Application Laid-Open No. 2020-166107

[0005] An object of the present invention is to provide a resin composition for an optical waveguide that can suppress optical loss (particularly at a wavelength of 1310 nm) and has good film handling properties.

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention includes the following preferred embodiments.

[0007] A resin composition for optical waveguides according to a first aspect of the present invention comprises an epoxy resin (A) and a curing agent (B), wherein the epoxy resin (A) comprises a bisphenol A type epoxy resin (a-1) having an epoxy equivalent of 1500 g / eq or less and a fluorene type epoxy resin (a-2) which does not contain a hydroxyl group in its molecular structure, and the content of the fluorene type epoxy resin (a-2) is 15 mass % or more and 80 mass % or less based on the total amount of the epoxy resin (A).

[0008] A dry film according to a second aspect of the present invention includes a layer made of an uncured or semi-cured product of the resin composition for an optical waveguide according to the first aspect.

[0009] An optical waveguide according to a third aspect of the present invention is an optical waveguide including a core layer and a clad layer having a refractive index lower than that of the core layer, wherein the core layer is formed using the resin composition for an optical waveguide according to the first aspect (or the dry film according to the second aspect).

[0010] FIG. 1 is a cross-sectional view illustrating an example of a method for forming an optical waveguide using the dry film according to the present embodiment. Specifically, FIG. 1( a) is a schematic view illustrating a step in which a clad dry film is laminated onto a surface of a substrate. FIG. 1( b) is a schematic view illustrating a step in which an underclad is formed. FIG. 1( c) is a schematic view illustrating a step in which a core dry film is exposed with a core pattern. FIG. 1( d) is a schematic view illustrating a step in which a core is formed on the surface of the underclad. FIG. 1( e) is a schematic view illustrating a step in which a clad dry film is laminated to cover the underclad and the core. FIG. 1( f) is a schematic view illustrating a step in which an optical waveguide is formed.

[0011] However, bisphenol A epoxy resins conventionally used in resin compositions for optical waveguides generally contain a normal or greater amount of hydroxyl groups (specifically, secondary hydroxyl groups) in their molecular structure, and when optical waveguides are formed using such bisphenol A epoxy resins, a problem arises in that optical loss at a wavelength of 1310 nm becomes large.

[0012] As a result of research by the present inventors, it was found that the optical loss at a wavelength of 1310 nm can be suppressed by including a fluorene-type epoxy resin that does not contain a hydroxyl group in the molecular structure as the resin for an optical waveguide resin composition. However, it was also found that the handling property during film formation becomes poor depending on the content of the fluorene-type epoxy resin.

[0013] Therefore, as a result of further intensive research by the present inventors, it has been found that a resin composition for optical waveguides can be obtained which can suppress optical loss (particularly at a wavelength of 1310 nm) and has good film handleability by containing, as epoxy resins, a bisphenol A type epoxy resin having an epoxy equivalent of 1500 g / eq or less and a fluorene type epoxy resin which does not contain a hydroxyl group in its molecular structure, and by setting the content of the fluorene type epoxy resin within a predetermined range.

[0014] As described above, the present invention can provide a resin composition for an optical waveguide that can suppress optical loss (particularly at a wavelength of 1310 nm) and has good film handling properties.

[0015] In this specification, the term "epoxy resin" refers to not only epoxy resin as a polymer but also the form of an epoxy compound, including a monomer capable of forming an epoxy resin.

[0016] 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.

[0017] 1. Resin Composition for Optical Waveguide The resin composition for optical waveguide according to this embodiment (hereinafter also simply referred to as "resin composition") contains an epoxy resin (A) and a curing agent (B). The epoxy resin (A) contains a bisphenol A-type epoxy resin (a-1) and a fluorene-type epoxy resin (a-2).

[0018] The components contained in the resin composition will be described in detail below.

[0019] [Epoxy Resin (A)] The epoxy resin (A) contains a bisphenol A type epoxy resin (a-1) and a fluorene type epoxy resin (a-2). In addition, the epoxy resin (A) may further contain a multifunctional epoxy resin (a-3).

[0020] These epoxy resins (A) may be liquid epoxy resins or solid epoxy resins. In this specification, with respect to epoxy resins, "liquid" means that the epoxy resin is liquid at room temperature, and "solid" means that the epoxy resin is solid at room temperature. Each epoxy resin will be described in detail below.

[0021] (Bisphenol A-type epoxy resin (a-1)) When the resin composition contains the bisphenol A-type epoxy resin (a-1) as the epoxy resin (A), it is possible to obtain a resin composition that is highly transparent and easily curable by ultraviolet light.

[0022] The epoxy equivalent of the bisphenol A epoxy resin (a-1) is 1500 g / eq or less. When the epoxy equivalent of the bisphenol A epoxy resin (a-1) is 1500 g / eq or less, the content of hydroxyl groups derived from the epoxy resin (A) can be reduced, thereby suppressing optical loss at a wavelength of 1310 nm.

[0023] The epoxy equivalent of the bisphenol A epoxy resin (a-1) is preferably 1300 g / eq or less, more preferably 1200 g / eq or less, even more preferably 1100 g / eq or less, and particularly preferably a value selected from the group consisting of 900 g / eq, 700 g / eq, 600 g / eq, 500 g / eq, 400 g / eq, and 300 g / eq or less. The lower limit of the epoxy equivalent of the bisphenol A epoxy resin (a-1) is not particularly limited as long as the effects of suppressing light loss and improving film handleability in this embodiment are exhibited. For example, the epoxy equivalent of the bisphenol A epoxy resin (a-1) may be 150 g / eq or more, and preferably 170 g / eq or more.

[0024] The bisphenol A epoxy resin (a-1) 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, for example, 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.

[0025] The bisphenol A epoxy resin (a-1) may be used alone or in combination of two or more. From the viewpoints of adjusting the tack of the film and film handling, it is preferable to use a combination of at least one solid bisphenol A epoxy resin and at least one liquid bisphenol A epoxy resin.

[0026] The content of the bisphenol A epoxy resin (a-1) is not particularly limited as long as it satisfies the requirements for the content of the fluorene epoxy resin (a-2) described below and does not impair the effects of suppressing light loss and improving film handleability in this embodiment. For example, the content of the bisphenol A epoxy resin (a-1) may be 20% by mass or more and 85% by mass or less based on the total amount of the epoxy resin (A). With this content, a resin composition that is highly transparent and easily UV-curable can be obtained.

[0027] The content of the bisphenol A epoxy resin (a-1) is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more, based on the total amount of the epoxy resin (A). The content of the bisphenol A epoxy resin (a-1) is preferably 65% ​​by mass or less, more preferably 55% by mass or less, even more preferably 45% by mass or less, and particularly preferably 40% by mass or less, based on the total amount of the epoxy resin (A).

[0028] (Fluorene-type epoxy resin (a-2)) When the resin composition contains a predetermined amount of a fluorene-type epoxy resin (a-2) that does not contain a hydroxyl group in its molecular structure, light loss can be suppressed and good film handleability can be maintained. The fluorene-type epoxy resin (a-2) preferably contains a liquid fluorene-type epoxy resin. By containing a liquid fluorene-type epoxy resin, cracking, powder falling, and the like are more unlikely to occur, and a dry film with better film handleability can be obtained. The content of the liquid fluorene-type epoxy resin is preferably 65% ​​by mass or more based on the total amount of the fluorene-type epoxy resin (a-2). By containing a larger amount of the liquid fluorene-type epoxy resin, a dry film that is more reliably less likely to crack, powder falling, and the like can be produced. The upper limit of the content of the liquid fluorene-type epoxy resin is not particularly limited, but the content of the liquid fluorene-type epoxy resin is preferably 100% by mass based on the total amount of the fluorene-type epoxy resin (a-2).

[0029] In this specification, the fluorene-type epoxy resin (a-2) means an epoxy resin that contains a fluorene skeleton in its monomer structure and does not contain a hydroxyl group (secondary hydroxyl group) in the skeleton of its molecular structure.

[0030] The liquid fluorene-type epoxy resin is not particularly limited, but an example thereof is a fluorene-type epoxy resin having a monomer structure represented by the following structural formula (1). [In formula (1), R １ ~R ４ are hydrogen atoms or alkyl groups having 1 to 6 carbon atoms, and may be the same or different. ５ and R ６ are hydrogen atoms or methyl groups and may be the same or different. Each n is independently an integer of 0 to 10.

[0031] An example of the liquid fluorene-type epoxy resin is a fluorene-type epoxy resin having a monomer structure represented by the following structural formula (2).

[0032] The solid fluorene-type epoxy resin is not particularly limited, but an example thereof is a fluorene-type epoxy resin having a monomer structure represented by the following structural formula (3). [In formula (3), R １ ~R ４ are hydrogen atoms or alkyl groups having 1 to 6 carbon atoms, and may be the same or different. ５ and R ６ are hydrogen atoms or methyl groups and may be the same or different. Each n is independently an integer of 0 to 10.

[0033] An example of a solid fluorene-type epoxy resin is a fluorene-type epoxy resin having a monomer structure represented by the following structural formula (4).

[0034] The fluorene-type epoxy resin (a-2) may be synthesized by a known method, or a commercially available product may be used. Commercially available liquid fluorene-type epoxy resins include, for example, "OGSOL-EG200" (epoxy equivalent: 290 g / eq) and "OGSOL-EG280" manufactured by Osaka Gas Chemicals Co., Ltd. Commercially available solid fluorene-type epoxy resins include, for example, "OGSOL-PG100" and "OGSOL-CG500" (epoxy equivalent: 310 g / eq) manufactured by Osaka Gas Chemicals Co., Ltd.

[0035] The fluorene-type epoxy resin (a-2) may be used alone or in combination of two or more.

[0036] The content of the fluorene-type epoxy resin (a-2) is 15% by mass or more and 80% by mass or less, based on the total amount of the epoxy resin (A). By including 15% by mass or more of the fluorene-type epoxy resin (a-2) based on the total amount of the epoxy resin (A), the content of hydroxyl groups derived from the epoxy resin (A) can be reduced, thereby suppressing optical loss at a wavelength of 1,310 nm. Furthermore, by including 80% by mass or less of the fluorene-type epoxy resin (a-2) based on the total amount of the epoxy resin (A), a resin composition that can maintain good film handleability can be obtained.

[0037] The content of the fluorene type epoxy resin (a-2) is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 35% by mass or more, particularly preferably 47.5% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, based on the total amount of the epoxy resin (A). The content of the fluorene type epoxy resin (a-2) is preferably 75% by mass or less, more preferably 73% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less, based on the total amount of the epoxy resin (A).

[0038] (Polyfunctional Epoxy Resin (a-3)) The optionally included polyfunctional epoxy resin (a-3) has three or more epoxy groups. Specific examples of the polyfunctional epoxy resin (a-3) include 2-[4-(2,3-epoxypropoxy)phenyl]-2-[4-[1,1-bis[4-([2,3-epoxypropoxy]phenyl)]ethyl]phenyl]propane, cresol novolac epoxy resin, and the like. The polyfunctional epoxy resin (a-3) may be synthesized by a known method, or a commercially available product may 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.

[0039] The polyfunctional epoxy resin (a-3) may be used alone or in combination of two or more.

[0040] By further including a polyfunctional epoxy resin (a-3) as the epoxy resin (A), the resin composition can improve the glass transition temperature Tg of the cured product, thereby imparting good heat resistance to the cured product. The glass transition temperature Tg of the cured product is preferably 145°C or higher, and more preferably 148°C or higher. In this specification, the glass transition temperature Tg is defined as the temperature measured by attaching a dry film to a dynamic viscoelasticity measuring device and calculating the peak temperature of tan δ.

[0041] The epoxy equivalent of the polyfunctional epoxy resin (a-3) is not particularly limited, but is, for example, 250 g / eq or less. The lower limit of the epoxy equivalent of the polyfunctional epoxy resin (a-3) is also not particularly limited, but is preferably 150 g / eq or more from the viewpoint of improving film handleability.

[0042] The content of the polyfunctional epoxy resin (a-3) is not particularly limited, as long as it satisfies the requirements for the content of the fluorene-type epoxy resin (a-2) described above and does not impair the effects of suppressing light loss and improving film handleability in this embodiment. For example, the content of the polyfunctional epoxy resin (a-3) can be within a range selected from the group consisting of 0% by mass or more and 20% by mass or less, 0% by mass or more and 15% by mass or less, 5% by mass or more and 20% by mass or less, and 5% by mass or more and 15% by mass or less, based on the total amount of the epoxy resin (A).

[0043] (Other Epoxy Resins) The resin composition may contain epoxy resins other than the epoxy resins described above, as long as the effects of suppressing light loss and providing good film handleability in this embodiment are not impaired. Examples of other epoxy resins include "NER-1202" and "NER-1302" manufactured by Nippon Kayaku Co., Ltd., and "EPOX-MK R1710" manufactured by Printec Co., Ltd.

[0044] In the resin composition for optical waveguide according to this embodiment, the content of hydroxyl groups derived from the epoxy resin (A) is preferably 0.0013 mol / g or less. When the content of hydroxyl groups is 0.0013 mol / g or less, optical loss at a wavelength of 1310 nm can be reliably suppressed, and therefore the resin composition can be suitably used particularly as a resin composition for cores.

[0045] In this specification, the "content of hydroxyl groups derived from the epoxy resin (A)" means the amount of hydroxyl groups (mol / g) calculated from the blending amounts, molecular weights, and number of hydroxyl groups in the skeleton of the bisphenol A epoxy resin (a-1) and the optionally contained polyfunctional epoxy resin (a-3) (and optionally contained other epoxy resins).

[0046] The content of hydroxyl groups derived from the epoxy resin (A) is more preferably 0.0010 mol / g or less, further preferably 0.0009 mol / g or less, and particularly preferably 0.0007 mol / g or less.

[0047] [Curing agent (B)] The curing agent (B) is not particularly limited as long as it can promote the photocuring of the resin composition containing the epoxy resin (A). For example, the curing agent (B) is a polymerization initiator that causes ring-opening polymerization of the epoxy group of each epoxy resin, and an example thereof is a photoacid generator that can initiate a reaction by light such as ultraviolet light.

[0048] Specific examples of the curing agent (B) include antimony-based curing agents, phosphorus-based curing agents, special phosphorus-based curing agents, borate-based curing agents, etc. These curing agents may be used alone or in combination of two or more.

[0049] Among these, the curing agent (B) is preferably an antimony-based curing agent. By using an antimony-based curing agent, it is possible to further improve curability and transparency, and to reliably reduce optical loss at a wavelength of 1310 nm. Commercially available antimony-based curing agents can be used. Examples of commercially available antimony-based curing agents include "CPI-101A" manufactured by San-Apro Co., Ltd. and "SP-170" manufactured by ADEKA Corporation.

[0050] The content of the curing agent (B) is not particularly limited as long as it does not impair the effects of suppressing light loss and improving film handleability in this embodiment. For example, the content of the curing agent (B) is preferably 0.1% by mass or more and 0.9% by mass or less, and more preferably 0.25% by mass or more and 0.75% by mass or less, based on the total amount of the epoxy resin (A).

[0051] [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 and improving film handleability in this embodiment are not impaired.

[0052] In particular, from the viewpoint of improving the heat resistance of the cured product, it is preferable that the resin composition further contains an antioxidant (C). The antioxidant (C) is not particularly limited, and a phenol-based antioxidant, a phosphite-based antioxidant, a sulfur-based antioxidant, etc. can be used. Among these, the antioxidant (C) is preferably a phenol-based antioxidant.

[0053] Commercially available phenolic antioxidants can be used, including, for example, "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.

[0054] The content of the antioxidant (C) is not particularly limited, but is preferably (0 mass % or more) 5 mass % or less based on the total amount of the epoxy resin (A).

[0055] The resin composition for an optical waveguide according to this embodiment is used in the form of a cured product when used in an optical waveguide, which will be described later. The refractive index of the cured product of the resin composition is preferably greater than 1.5700. When the refractive index of the cured product is greater than 1.5700, the resin composition can be suitably used as a resin composition for a core.

[0056] In this specification, the "refractive index of the cured product" means the refractive index of the cured product at a temperature of 25°C and a wavelength of 1310 nm, as measured using an Abbe refractometer.

[0057] The refractive index of the cured product is more preferably 1.575 or more, and even more preferably 1.580 or more.

[0058] As described above, the resin composition for an optical waveguide according to this embodiment can suppress optical loss at a wavelength of 1,310 nm and has good film handling properties, and therefore, the resin composition can be suitably used as a material for a dry film according to an embodiment described below that is used when producing an optical waveguide.

[0059] 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.

[0060] 2. Dry Film The dry film according to this embodiment is not particularly limited as long as it includes a layer made of the resin composition for optical waveguides according to the above-described embodiment. Specifically, the dry film includes a layer made of 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.

[0061] 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.

[0062] 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 progressing by irradiation with light such as ultraviolet light, causing the resin to crosslink. The optical waveguide finally obtained in the embodiments described below includes a core layer and / or a clad layer that is a cured product of the resin composition for an optical waveguide.

[0063] The dry film may include a film substrate laminated on at least one side of the resin composition layer. Furthermore, a protective film may be laminated on the other side of the resin composition layer. The dry film may also include other layers in addition to the resin composition layer, film substrate, and / or protective film. However, the dry film may also be composed of a resin composition layer made of an uncured and / or semi-cured product of the resin composition for optical waveguides according to the above-described embodiment.

[0064] 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.

[0065] 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.

[0066] The dry film containing 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 layer of the optical waveguide or when producing a cladding layer. However, as mentioned above, optical loss at a wavelength of 1310 nm occurs mainly in the core layer, so the dry film is preferably used when producing the core layer of the optical waveguide.

[0067] 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 producing 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 producing the core layer and / or clad layer of the optical waveguide. For the same reasons as above, it is preferable to use the varnish-like resin composition when producing the core layer.

[0068] 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, making it extremely useful for industrial applications.

[0069] Specifically, the optical waveguide according to this embodiment is an optical waveguide including a core layer and a clad layer having a refractive index lower than that of the core layer, and the core layer or the clad layer is formed using the resin composition or the dry film according to the above-described embodiment. As described above, it is preferable that the core layer of the optical waveguide is formed using the resin composition or the dry film according to the above-described embodiment.

[0070] 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 symbols respectively represent a cladding dry film 1, a core dry film 2, a cladding 3, an undercladding 3a, an overcladding 3b, a core 4, a substrate 10, an electric circuit 11, a slit 12, a mask 13, and an optical waveguide A.

[0071] 1, a clad dry film and a core dry film are used to form the core and clad, 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.

[0072] 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).

[0073] 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.

[0074] 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 4 having a predetermined core pattern is formed on the surface of the underclad 3a, as shown in FIG.

[0075] Next, as shown in Fig. 1(e), a clad dry film 1 is laminated so as 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, in which the core 4 is embedded in the clad 3 consisting of the underclad 3a and the overclad 3b.

[0076] In the optical waveguide A obtained in this manner, the use of the dry film according to the above-described embodiment makes it possible to suppress optical loss at a wavelength of 1310 nm, thereby realizing excellent optical communication. Therefore, the substrate 10 on which such an optical waveguide A is formed is preferably used as an optical transmission printed wiring board, and is preferably used in, for example, a mobile phone, a personal digital assistant, etc.

[0077] As described above, this specification discloses various aspects of the technology, the main aspects of which are summarized below.

[0078] The resin composition for optical waveguides according to a first aspect of the present invention contains an epoxy resin (A) and a curing agent (B), wherein the epoxy resin (A) contains a bisphenol A type epoxy resin (a-1) having an epoxy equivalent of 1500 g / eq or less and a fluorene type epoxy resin (a-2) having no hydroxyl group in its molecular structure, and the content of the fluorene type epoxy resin (a-2) is 15 mass % or more and 80 mass % or less based on the total amount of the epoxy resin (A).

[0079] A resin composition for optical waveguides according to a second aspect of the present invention is the resin composition for optical waveguides according to the first aspect, wherein the fluorene-type epoxy resin (a-2) includes a liquid fluorene-type epoxy resin.

[0080] A resin composition for an optical waveguide according to a third aspect of the present invention is the resin composition for an optical waveguide according to the first or second aspect, wherein the epoxy resin (A) further contains a polyfunctional epoxy resin (a-3).

[0081] 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 content of hydroxyl groups derived from the epoxy resin (A) is 0.0013 mol / g or less.

[0082] A resin composition for an optical waveguide according to a fifth aspect of the present invention is the resin composition for an optical waveguide according to any one of the first to fourth aspects, wherein the refractive index of the cured product is greater than 1.5700.

[0083] A resin composition for an optical waveguide according to a sixth aspect of the present invention is the resin composition for an optical waveguide according to any one of the first to fifth aspects, further comprising an antioxidant (C).

[0084] A dry film according to a seventh aspect of the present invention includes a layer made of an uncured or semi-cured product of the resin composition for an optical waveguide according to any one of the first to sixth aspects.

[0085] An optical waveguide according to an eighth aspect of the present invention is an optical waveguide comprising a core layer and a clad layer having a refractive index lower than that of the core layer, and the core layer is formed using the resin composition for an optical waveguide according to any one of the first to sixth aspects (or the dry film according to the seventh aspect).

[0086] 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.

[0087] In this example, various resin compositions for optical waveguides were prepared using various epoxy resins and varying the content of each epoxy resin, and then dry films and waveguide samples for evaluating optical loss were manufactured using these compositions. Furthermore, the content of hydroxyl groups derived from the epoxy resin in each resin composition for optical waveguides was calculated, and the physical properties of various dry films and cured products were also evaluated or measured.

[0088] First, the raw materials used in preparing the resin compositions for optical waveguides in the examples are summarized below.

[0089] [Epoxy resin (A)] (Bisphenol A type (BisA type) epoxy resin (a-1)) - "Epiclon (registered trademark) 850S": manufactured by DIC Corporation (epoxy equivalent 183 to 193 g / eq) - "jER (registered trademark) 1001": manufactured by Mitsubishi Chemical Corporation (epoxy equivalent 450 to 500 g / eq) - "Epikote (registered trademark) 1006FS": manufactured by Mitsubishi Chemical Corporation (epoxy equivalent 900 to 1100 g / eq) (Fluorene type epoxy resin (a-2)) - "OGSOL-EG200": liquid fluorene type epoxy resin, manufactured by Osaka Gas Chemicals Co., Ltd. (epoxy equivalent 290 g / eq) (Multifunctional epoxy resin (a-3)) "VG3101M80": manufactured by Printec Co., Ltd. (3 epoxy groups, epoxy equivalent weight 205 to 215 g / eq) [curing agent (B)] "CPI-101A": antimony-based curing agent, manufactured by San-Apro Co., Ltd. [antioxidant (C)] "AO-60": manufactured by ADEKA Corporation

[0090] Next, the methods for preparing the resin compositions for optical waveguides, the methods for calculating the content of hydroxyl groups derived from the epoxy resin, the methods for producing the dry films, and the methods for evaluating the optical loss (1310 nm) using waveguide samples for each Example and Comparative Example are described below. Furthermore, the methods for evaluating and measuring the physical properties of the dry films and cured products (film handleability, refractive index (1310 nm) and glass transition temperature Tg of the cured products) are also described below.

[0091] <Method of Preparing Resin Composition for Optical Waveguide> In each Example and Comparative Example, the components were blended according to the blending composition (parts by mass) shown in Table 1 below, and the mixed solvent of MEK and toluene was adjusted to 55 parts by mass per 100 parts by mass of the resin, and mixed while heating to 50° C. to 80° C. Next, the mixture was filtered through a membrane filter with a pore size of 1.0 μm and then degassed to prepare resin varnishes of the resin compositions for optical waveguides of Examples 1 to 10 and Comparative Examples 1 to 3.

[0092] <Method for calculating the content of hydroxyl groups derived from epoxy resin (A)> Fluorene-type epoxy resin (a-2) ("OGSOL-EG200", liquid fluorene-type epoxy resin, manufactured by Osaka Gas Chemicals Co., Ltd.) does not contain hydroxyl groups. Therefore, the content of hydroxyl groups derived from epoxy resin (A) was calculated by the following method based on the amount of hydroxyl groups in bisphenol A-type (BisA-type) epoxy resin (a-1).

[0093] Incidentally, "Epiclon (registered trademark) 850S" (epoxy equivalent weight: 183 to 193 g / eq) manufactured by DIC Corporation has a monomer structure represented by the following structural formula (5). When converted from the epoxy equivalent weight, n in the following structural formula is estimated to be about 0.13.

[0094] "Epiclon (registered trademark) 850S," represented by the above structural formula (5), has a significantly smaller amount of hydroxyl groups than other bisphenol A (BisA) epoxy resins. Therefore, its hydroxyl group content was set to 0 and not included in the calculation formula. Specifically, the number of molecules (mol) of each epoxy resin contained in the resin composition was calculated by first dividing "jER (registered trademark) 1001" (hereinafter also referred to simply as "1001") and "Epikote (registered trademark) 1006FS" (hereinafter also referred to simply as "1006FS") by their respective molecular weights. Here, 1001 contains 2.1 hydroxyl groups in its skeleton, and 1006FS contains 5.5 hydroxyl groups in its skeleton. Therefore, these values ​​were then multiplied by the previously calculated number of molecules of each epoxy resin, and the calculated values ​​were added together. The sum was then divided by the total amount of epoxy resin to calculate the hydroxyl group content (mol / g) contained in the resin composition. The specific calculation formula is as follows: Hydroxyl group content = ((1001 blend amount / 1001 molecular weight x 2.1) + (1006FS blend amount / 1006FS molecular weight x 5.5)) / (total epoxy resin blend amount)

[0095] If the hydroxyl group content is 0.0013 mol / g or less, it can be evaluated as being suitable for use as a resin composition for an optical waveguide for a core. The calculation results of the hydroxyl group content for each example and each comparative example are summarized in Table 1 below.

[0096] <Method for manufacturing dry film> The resin composition varnish for an optical waveguide of each example and each 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 with a resin layer thickness of 20 μm.

[0097] <Method for Evaluating Optical Loss at a Wavelength of 1310 nm Using Waveguide Samples> For evaluating optical loss at a wavelength of 1310 nm, the dry films of the Examples and Comparative Examples prepared as described above were used as core films. The clad dry films for optical waveguides were prepared by the following method.

[0098] 14 parts by mass of an alicyclic epoxy resin ("Celloxide 2021P" manufactured by Daicel Corporation) as an epoxy resin, 25 parts by mass of a bisphenol A type epoxy resin ("Epikote (registered trademark) 1006FS" manufactured by Mitsubishi Chemical Corporation), 38 parts by mass of a hydrogenated bisphenol A type epoxy resin ("JER (registered trademark) YX8040" manufactured by Mitsubishi Chemical Corporation), and a multifunctional (trifunctional) epoxy resin ("VG3101M80") 23 parts by mass of an antimony-based curing agent ("SP-170" manufactured by ADEKA Corporation) as a curing agent, 1 part by mass of an antioxidant ("AO-60" manufactured by ADEKA Corporation) as an additive, and 0.1 parts by mass of a leveling agent ("PF-636" manufactured by OMNOVA) were dissolved in a mixed solvent of MEK, toluene, and PGMEA (50 parts by mass per 100 parts by mass of epoxy resin). The mixture was then filtered through a membrane filter with a pore size of 1 μm and degassed to prepare an epoxy 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 of a predetermined thickness.

[0099] The resulting cladding film was then laminated onto a substrate as an undercladding, followed by laminating a core film on top of it. The laminated film was exposed to light and heat-treated, and then an overcladding was formed using the cladding film to produce a slab waveguide sample.

[0100] The optical loss at a wavelength of 1310 nm was measured using the manufactured slab waveguide sample 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 an NA of 0.12, and silicone oil was introduced into the end of the manufactured waveguide sample via matching oil (refractive index 1.505). Furthermore, an optical fiber with a core diameter of 50 μm and an NA of 0.21 was passed through the same matching oil, and the other side 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) was measured by butting two similar optical fibers together in the absence of an optical circuit. From the measured value, the optical loss (1310 nm) was calculated using the formula -10 log (P1 / P0). The calculation results of the optical loss (1310 nm) for each example and each comparative example are summarized in Table 1 below. In addition, when the optical loss was 0.400 or less, the optical loss was evaluated as being well suppressed, when the optical loss was more than 0.400 and less than 0.440, the optical loss was evaluated as being suppressed, and when the optical loss was more than 0.440, the optical loss was evaluated as being large.

[0101] <Method for Evaluating Film Handling Efficiency> The dry films of each Example and Comparative Example manufactured as described above were used to evaluate film handling. Specifically, in the first test, the dry film was bent 90° to check for resin cracks at the fold. If no cracks or powder fall-off occurred, the first test was evaluated as passing. Furthermore, in the second test, the dry film was cut with a cutter to check for cracks or powder fall-off at the edges. If no cracks or powder fall-off occurred, the second test was evaluated as passing. If both the first and second tests were passed, the film was evaluated as "significantly good" (significantly good film handling). If either the first or second test was passed, the film was evaluated as "good" (good film handling). If both the first and second tests were failed, the film was evaluated as "poor" (poor film handling). The evaluation results of the film handling efficiency for each Example and Comparative Example are summarized in Table 1 below. Incidentally, cases where a dry film could not be formed were also evaluated as "poor."

[0102] <Method for evaluating the refractive index (wavelength 1310 nm) of the cured product> Two dry films of each Example and Comparative Example produced as described above were laminated together using a vacuum laminator "V-130" at 50°C and 0.3 MPa. The bonded dry film was irradiated with ultraviolet light at 120°C for 10 minutes to temporarily cure. The PET film was then peeled off from the dry film, and the film was cured by heat treatment at 140°C for 30 minutes to obtain a cured dry film. The refractive index of the resulting cured product at a wavelength of 1310 nm at a temperature of 25°C was measured using an Abbe refractometer. The refractive index measurement results for each Example and Comparative Example are summarized in Table 1 below.

[0103] <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, the more excellent the heat resistance of the cured product can be evaluated. For example, a glass transition temperature Tg of 150°C ensures the production of an optical waveguide with excellent heat resistance. The glass transition temperature Tg was measured in some Examples. The measurement results are summarized in Table 1 below.

[0104] The measurement, calculation and evaluation results for each of the above examples and comparative examples, together with the compounding compositions, are summarized in the following Table 1. In the following Table 1, "-" indicates that no measurement was performed.

[0105]

[0106] <Discussion> As shown in Table 1 above, it was found that in a resin composition, when the epoxy resin (A) contains a bisphenol A-type epoxy resin (a-1) and a fluorene-type epoxy resin (a-2), and the content of the fluorene-type epoxy resin (a-2) is in the range of 15% by mass or more and 80% by mass or less based on the total amount of the epoxy resin (A), the light loss of the cured product can be suppressed and the film handleability can be improved. This is thought to be because the content of hydroxyl groups derived from the epoxy resin (A) is low, making it suitable for use as a resin composition for the core.

[0107] In particular, as shown in Examples 5 to 10 in Table 1 above, when the content of the fluorene-type epoxy resin (a-2) is in the range of 50 mass % or more and 70 mass % or less relative to the total amount of the epoxy resin (A), it is possible to effectively suppress light loss and obtain a resin composition having remarkably good film handleability.

[0108] Furthermore, as can be seen from the comparison between Example 7 and Example 8, or the comparison between Example 9 and Example 10, when the resin composition contains the polyfunctional epoxy resin (a-3), the glass transition temperature Tg can be improved, and the heat resistance of the optical waveguide can be improved.

[0109] On the other hand, in Comparative Example 1, in which only the fluorene-type epoxy resin (a-2) was used as the epoxy resin (A), film handling was significantly poor and no film could be formed. Furthermore, in Comparative Example 2, in which the content of the fluorene-type epoxy resin (a-2) was high, a film could be formed, but its handling was poor. Comparative Example 3, which did not contain the fluorene-type epoxy resin (a-2), exhibited high optical loss. This is thought to be due to the high content of hydroxyl groups derived from the epoxy resin (A), resulting in high optical loss.

[0110] This application is based on Japanese Patent Application No. 2023-120914 filed on July 25, 2023, the contents of which are incorporated herein by reference.

[0111] 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.

[0112] According to the present invention, a resin composition for an optical waveguide can be obtained which can suppress optical loss (particularly at a wavelength of 1310 nm) and has good film handleability. By producing an optical waveguide using such a resin composition for an optical waveguide, the optical waveguide can be preferably used as an optical transmission printed wiring board for, for example, a mobile phone, a personal digital assistant, etc.

Claims

1. A resin composition for optical waveguides comprising: an epoxy resin (A); and a curing agent (B); the epoxy resin (A) comprises a bisphenol A type epoxy resin (a-1) having an epoxy equivalent of 1500 g / eq or less, and a fluorene type epoxy resin (a-2) not containing a hydroxyl group in its molecular structure; and the content of the fluorene type epoxy resin (a-2) is 15 mass% or more and 80 mass% or less based on the total amount of the epoxy resin (A).

2. The resin composition for optical waveguides according to claim 1, wherein the fluorene-type epoxy resin (a-2) comprises a liquid fluorene-type epoxy resin.

3. The resin composition for optical waveguides according to claim 1, wherein the epoxy resin (A) further contains a multifunctional epoxy resin (a-3).

4. The resin composition for optical waveguides according to claim 1, wherein the content of hydroxyl groups derived from the epoxy resin (A) is 0.0013 mol / g or less.

5. The resin composition for optical waveguides according to claim 1, wherein the refractive index of the cured product is greater than 1.5700.

6. The resin composition for an optical waveguide according to claim 1, further comprising an antioxidant (C).

7. A dry film comprising a layer of an uncured or semi-cured product of the resin composition for optical waveguides according to any one of claims 1 to 6.

8. An optical waveguide comprising a core layer and a clad layer having a refractive index lower than that of the core layer, the core layer being formed using the resin composition for optical waveguides according to any one of claims 1 to 6.

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