WO2025023263A1 - Resin composition for optical waveguide, and dry film and optical waveguide using said resin composition - Google Patents

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

The present invention relates to a resin composition for optical waveguides, and a dry film and optical waveguide using the same.

Optical fiber has traditionally been the mainstream transmission medium in the fields of long-distance and medium-distance communications in the FTTH (Fiber to the Home) and in-vehicle fields. In recent years, high-speed transmission using light has become necessary even over short distances of less than 1m. In this area, optical waveguide-type optical wiring boards are suitable because they allow high-density wiring (narrow pitch, branching, crossing, multi-layering, etc.), surface mounting, integration with electrical boards, and small-diameter bending, which are not possible with optical fiber.

The optical waveguide is obtained by forming a clad and a core using two types of ultraviolet (UV) curable optical waveguide resin compositions with high transparency and different refractive indexes. In general, 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 preferably used from the viewpoints of heat resistance and optical signal transmission. For example, Patent Documents 1 and 2 also list many types of epoxy resins. Of these epoxy resins, bisphenol A type epoxy resins have traditionally been more preferably used from the viewpoints of being able to form optical waveguide resin compositions with high transparency and being able to easily cure with ultraviolet light.

International Publication No. 2020/203366 JP 2020-166107 A

The objective of the present invention is to provide a resin composition for optical waveguides that can suppress optical loss (particularly at a wavelength of 1,310 nm) and has good film handling properties.

The inventors conducted extensive research to solve the above problems and arrived at the present invention. That is, the present invention includes the following preferred aspects.

The resin composition for an optical waveguide according to a first aspect of the present invention comprises an epoxy resin (A),
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,
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).

The dry film according to the second aspect of the present invention includes a layer made of an uncured or semi-cured optical waveguide resin composition according to the first aspect.

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,
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).

FIG. 1 is a schematic cross-sectional view for explaining 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 showing a stage in which a clad dry film is laminated on a surface of a substrate. FIG. 1(b) is a schematic view showing a stage in which an underclad is laminated. FIG. 1(c) is a schematic view showing a stage in which a core dry film is exposed with a core pattern. FIG. 1(d) is a schematic view showing a stage in which a core is formed on the surface of the underclad. FIG. 1(e) is a schematic view showing a stage in which a clad dry film is laminated so as to cover the underclad and the core. FIG. 1(f) is a schematic view showing a stage in which an optical waveguide is formed.

However, bisphenol A type epoxy resins that have traditionally been used in resin compositions for optical waveguides generally contain a normal amount or more of hydroxyl groups (specifically secondary hydroxyl groups) in their molecular structure. When optical waveguides are formed using such bisphenol A type epoxy resins, a problem arises in that the optical loss at a wavelength of 1310 nm becomes large.

As a result of the inventors' research, it was found that the optical loss at a wavelength of 1,310 nm can be suppressed by including a fluorene-type epoxy resin that does not contain a hydroxyl group in its molecular structure as the resin in the resin composition for optical waveguides. However, it was also found that the handling properties during film formation can be deteriorated depending on the content of the fluorene-type epoxy resin.

The inventors then conducted further intensive research and found that by containing, as the epoxy resin in the resin composition for optical waveguides, a bisphenol A type epoxy resin having an epoxy equivalent of 1500 g/eq or less and a fluorene type epoxy resin that does not contain a hydroxyl group in its molecular structure, and by setting the content of the fluorene type epoxy resin within a specified range, it is possible to obtain a resin composition for optical waveguides that can suppress optical loss (particularly at a wavelength of 1310 nm) and has good film handleability.

In this way, the present invention can provide a resin composition for optical waveguides that can suppress optical loss (particularly at a wavelength of 1,310 nm) and has good film handling properties.

In this specification, "epoxy resin" refers to the form of an epoxy compound, including not only epoxy resin as a polymer, but also monomers that can form epoxy resin.

Below, an embodiment 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 embodiment described here, and various modifications can be made without departing from the spirit of the present invention.

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).

The components contained in the resin composition are described in detail below.

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

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 in a liquid state at room temperature, and "solid" means that the epoxy resin is in a solid state at room temperature. Each epoxy resin will be described in detail below.

(Bisphenol A type epoxy resin (a-1))
By containing the bisphenol A type epoxy resin (a-1) as the epoxy resin (A) in the resin composition, it is possible to obtain a resin composition which is highly transparent and easily curable with ultraviolet light.

The epoxy equivalent of the bisphenol A type epoxy resin (a-1) is 1500 g/eq or less. When the epoxy equivalent of the bisphenol A type 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.

The epoxy equivalent of the bisphenol A type 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 type epoxy resin (a-1) is not particularly limited as long as it exhibits the effects of suppressing light loss and film handleability in this embodiment. For example, the epoxy equivalent of the bisphenol A type epoxy resin (a-1) may be 150 g/eq or more, and is preferably 170 g/eq or more.

Bisphenol A type 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 type 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 type epoxy resins include "Epicron (registered trademark) 850S" manufactured by DIC Corporation and "JER (registered trademark) 825" manufactured by Mitsubishi Chemical Corporation.

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

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

The content of bisphenol A type 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 epoxy resin (A). The content of bisphenol A type 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 epoxy resin (A).

(Fluorene-type epoxy resin (a-2))
By containing a predetermined amount of the fluorene type epoxy resin (a-2) that does not contain a hydroxyl group in the molecular structure, the resin composition can suppress light loss and maintain good film handleability. The fluorene type epoxy resin (a-2) preferably contains a liquid fluorene type epoxy resin. By containing the liquid fluorene type epoxy resin, cracks, powder fall, etc. 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 fall, etc. 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).

In this specification, fluorene-type epoxy resin (a-2) refers to 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.

［式（１）中、Ｒ_１～Ｒ_４は、水素原子または炭素数１～６のアルキル基であり、同じであっても異なっていてもよい。また、Ｒ_５およびＲ_６は、水素原子またはメチル基であり、同じであっても異なっていてもよい。ｎは、各々独立して０～１０の整数を示す。］ 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 to R ₄ are hydrogen atoms or alkyl groups having 1 to 6 carbon atoms and may be the same or different. R 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.]

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).

［式（３）中、Ｒ_１～Ｒ_４は、水素原子または炭素数１～６のアルキル基であり、同じであっても異なっていてもよい。また、Ｒ_５およびＲ_６は、水素原子またはメチル基であり、同じであっても異なっていてもよい。ｎは、各々独立して０～１０の整数を示す。］ 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 to R ₄ are hydrogen atoms or alkyl groups having 1 to 6 carbon atoms and may be the same or different. R 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.]

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

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.

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

The content of fluorene-type epoxy resin (a-2) is 15% by mass or more and 80% by mass or less based on the total amount of epoxy resin (A). By including 15% by mass or more of fluorene-type epoxy resin (a-2) based on the total amount of epoxy resin (A), the content of hydroxyl groups derived from epoxy resin (A) can be reduced, and light loss at a wavelength of 1310 nm can be suppressed. In addition, by including 80% by mass or less of fluorene-type epoxy resin (a-2) based on the total amount of epoxy resin (A), a resin composition that can maintain good film handling properties can be obtained.

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 especially preferably 65% by mass or less, based on the total amount of the epoxy resin (A).

(Multifunctional epoxy resin (a-3))
The optionally contained 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 type epoxy resin, and the like. The polyfunctional epoxy resin (a-3) may be synthesized by a known method, but a commercially available product 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.

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

By further including a polyfunctional epoxy resin (a-3) as the epoxy resin (A) in the resin composition, the glass transition temperature Tg of the cured product can be improved, and therefore good heat resistance can be imparted 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 from the peak temperature of tan δ calculated by attaching the dry film to a dynamic viscoelasticity measuring device.

The epoxy equivalent of the multifunctional 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 multifunctional epoxy resin (a-3) is also not particularly limited, but from the viewpoint of improving the film handling properties, it is preferably 150 g/eq or more.

The content of the polyfunctional epoxy resin (a-3) is not particularly limited as long as it satisfies the conditions for the content of the fluorene-type epoxy resin (a-2) described above and does not impair the effects of suppressing light loss and film handleability in this embodiment. For example, the content of the polyfunctional epoxy resin (a-3) can be in 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).

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

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

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

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

[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 start a reaction by light such as ultraviolet light.

Specific examples of the hardener (B) include antimony-based hardeners, phosphorus-based hardeners, special phosphorus-based hardeners, borate-based hardeners, etc. These hardeners may be used alone or in combination of two or more.

Among these, it is preferable that the curing agent (B) is an antimony-based curing agent. By using an antimony-based curing agent, it is possible to further increase the curability and transparency, and to reliably reduce the 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.

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).

[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.

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. Of these, it is preferable that the antioxidant (C) is a phenol-based antioxidant.

Commercially available phenolic antioxidants can be used. Examples of commercially available phenolic antioxidants include "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.

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

The resin composition for optical waveguides 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, it can be suitably used as a resin composition for cores.

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

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

In this way, the resin composition for optical waveguides according to this embodiment can suppress optical loss at a wavelength of 1310 nm and has good film handling properties. Therefore, this resin composition can be suitably used as a material for the dry film according to the embodiment described below that is used when manufacturing optical waveguides.

The resin composition for optical waveguides according to this embodiment may be used for both the core and the cladding. However, since the optical loss at a wavelength of 1310 nm occurs mainly in the core, the resin composition for optical waveguides according to this embodiment can be more effective when used to manufacture a dry film for the core.

2. Dry Film The dry film according to this embodiment is not particularly limited as long as it has a layer made of the resin composition for optical waveguide according to the above-mentioned embodiment. Specifically, the dry film includes a layer made of an uncured or semi-cured product of the resin composition for optical waveguide according to the above-mentioned embodiment (hereinafter also referred to as "resin composition layer for optical waveguide" or "resin composition layer"). Since the resin composition for optical waveguide according to the above-mentioned embodiment has good film handling properties, the dry film according to this embodiment has excellent film handling properties and excellent adhesion to the film base, film substrate, etc.

In this specification, "uncured material" or "semi-cured material" refers to a resin composition layer in an uncured or semi-cured state, in which a varnish-like resin composition as described below is applied and then heated and/or dried at an appropriate temperature and time as necessary, so that the solvent and the like are reduced or removed. In other words, an "uncured material" or "semi-cured material" is in a state in which the epoxy resin in the resin composition layer can be further cured.

In addition, in this specification, the term "cured product" refers to a resin layer in which the curing reaction of an uncured or semi-cured resin composition layer progresses due to irradiation with light such as ultraviolet light, causing the resin to crosslink, resulting in a resin layer that does not melt even when heated. In the embodiment described below, the optical waveguide finally obtained comprises a core layer and/or a clad layer that is a cured product of the resin composition for optical waveguides.

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, the film substrate and/or the protective film. However, the dry film may be composed of a resin composition layer made of an uncured and/or semi-cured product of the resin composition for optical waveguide according to the above-mentioned embodiment.

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. Of these, PET film is preferable. The protective film is not particularly limited, but examples thereof include polypropylene film, etc.

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

The dry film containing the resin composition layer produced in this manner is used as a material for an optical waveguide according to an embodiment described below. The dry film may be used when producing a core layer of an optical waveguide, or may be used when producing a cladding layer. However, as mentioned above, optical loss at a wavelength of 1310 nm occurs mainly in the core layer, so it is preferably used when producing a core layer of an optical waveguide.

The resin composition for optical waveguide according to the above-mentioned embodiment does not necessarily have to be used after forming the dry film according to this embodiment when manufacturing an optical waveguide. For example, the resin composition for optical waveguide according to the above-mentioned embodiment may be made into a varnish-like resin composition and used directly when manufacturing 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 manufacturing the core layer.

The optical waveguide according to this embodiment is formed using the resin composition or dry film according to the above-mentioned embodiment. Since the optical waveguide is formed using the resin composition or dry film according to the above-mentioned embodiment, it is possible to suppress the optical loss at a wavelength of 1310 nm, and is very useful for industrial use.

Specifically, the optical waveguide according to this embodiment is an optical waveguide including a core layer and a clad layer having a lower refractive index than 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-mentioned embodiment. As mentioned 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-mentioned embodiment.

Below, an example of a method for forming an optical waveguide on a substrate using the dry film according to the above-mentioned embodiment will be described with reference to Figure 1. In Figures 1(a) to 1(f), the reference characters respectively indicate a clad dry film 1, a core dry film 2, a clad 3, an underclad 3a, an overclad 3b, a core 4, a substrate 10, an electric circuit 11, a slit 12, a mask 13, and an optical waveguide A.

In the example shown in FIG. 1, the optical waveguide is formed by using a clad dry film and a core dry film to form the core and clad, respectively. In the example shown in FIG. 1, the core dry film is a dry film according to the embodiment described above, and the clad dry film is a dry film with a lower refractive index than the core film. The clad dry film and the core dry film may both be dry films according to the embodiment described above.

First, as shown in FIG. 1(a), a clad dry film 1 is laminated onto the surface of a substrate 10 on which an electric circuit 11 is formed, and then the clad dry film 1 is cured by irradiation with ultraviolet light or other light, heating, or the like. The substrate 10 may be, for example, a flexible printed wiring board with an electric circuit formed on one side of a transparent base material such as a polyimide film, or a printed wiring board such as a glass epoxy. Through this process, an underclad 3a is laminated and formed on the surface of the substrate 10, as shown in FIG. 1(b).

Next, as shown in FIG. 1(c), the core dry film 2 is laminated onto the surface of the underclad 3a, and then a mask 13 with slits 12 of the core pattern is placed over it. Then, light capable of photocuring, 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.

After 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 parts of the core dry film 2. As a result, a core 4 with a specified core pattern is formed on the surface of the underclad 3a, as shown in Figure 1(d).

Next, as shown in FIG. 1(e), the clad dry film 1 is laminated so as to cover the underclad 3a and the core 4. The clad dry film 1 is then cured by irradiation with light, heating, etc., to form the 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 overclad 3b.

The optical waveguide A thus obtained uses the dry film according to the above-mentioned embodiment, thereby suppressing optical loss at a wavelength of 1310 nm and enabling excellent optical communication. Therefore, the substrate 10 on which such an optical waveguide A is formed is preferably used as a printed wiring board for optical transmission, and is preferably used in, for example, mobile phones, personal digital assistants, etc.

As mentioned above, this specification discloses various aspects of the technology, the main technologies of which are summarized below.

The resin composition for optical waveguides according to the first aspect of the present invention 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 1500 g/eq or less, and a fluorene type epoxy resin (a-2) that does not contain a hydroxyl group in its molecular structure, and 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).

The resin composition for optical waveguides according to the second aspect of the present invention is the resin composition for optical waveguides according to the first aspect, and the fluorene-type epoxy resin (a-2) includes a liquid fluorene-type epoxy resin.

The resin composition for optical waveguides according to the third aspect of the present invention is the resin composition for optical waveguides according to the first or second aspect, in which the epoxy resin (A) further contains a multifunctional epoxy resin (a-3).

The resin composition for optical waveguides according to the fourth aspect of the present invention is a resin composition for optical waveguides according to any one of the first to third aspects, in which the content of hydroxyl groups derived from the epoxy resin (A) is 0.0013 mol/g or less.

The resin composition for optical waveguides according to the fifth aspect of the present invention is a resin composition for optical waveguides according to any one of the first to fourth aspects, in which the refractive index of the cured product is greater than 1.5700.

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

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

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

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.

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

First, the raw materials used to prepare the resin composition for optical waveguides in this example are summarized below.

[Epoxy resin (A)]
(Bisphenol A type (BisA type) epoxy resin (a-1))
"Epiclon (registered trademark) 850S": manufactured by DIC Corporation (epoxy equivalent weight 183 to 193 g/eq)
"jER (registered trademark) 1001": manufactured by Mitsubishi Chemical Corporation (epoxy equivalent: 450 to 500 g/eq)
"Epicoat (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 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

The following describes the method for preparing the resin composition for optical waveguides, the method for calculating the content of hydroxyl groups derived from the epoxy resin, the method for producing the dry film, and the method for evaluating the optical loss (1310 nm) using a waveguide sample in each example and comparative example. In addition, the methods for evaluating and measuring the physical properties of the dry film and the cured product (film handleability, refractive index (1310 nm) and glass transition temperature Tg) are also described below.

<Method for 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, 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 having 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.

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

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

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

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 optical waveguides for cores. The calculation results of the hydroxyl group content for each example and comparative example are summarized in Table 1 below.

<Method of manufacturing dry film>
The resin composition varnish for optical waveguides 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 with a resin layer thickness of 20 μm.

<Method for evaluating optical loss at wavelength 1310 nm using a waveguide sample>
In evaluating the 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.

Epoxy resins were 14 parts by mass of alicyclic epoxy resin ("Celloxide 2021P", Daicel Corporation), 25 parts by mass of bisphenol A type epoxy resin ("Epicoat (registered trademark) 1006FS", Mitsubishi Chemical Corporation), 38 parts by mass of hydrogenated bisphenol A type epoxy resin ("JER (registered trademark) YX8040", Mitsubishi Chemical Corporation), and 38 parts by mass of multifunctional (trifunctional) epoxy resin ("VG3101M80 ", manufactured by Printec Co., Ltd.), 23 parts by mass of antimony-based curing agent as a curing agent ("SP-170", manufactured by ADEKA Co., Ltd.), 1 part by mass of antioxidant as an additive ("AO-60", manufactured by ADEKA Co., Ltd.), and 0.1 part by mass of leveling agent ("PF-636", manufactured by OMNOVA Co., Ltd.) were dissolved in a mixed solvent of MEK, toluene and PGMEA of 50 parts by mass per 100 parts by mass of epoxy resin. After that, the mixture was 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 clad of a predetermined thickness.

Then, the obtained clad film was laminated onto a substrate as an underclad. Furthermore, a core film was laminated on top of that. After the laminated film was exposed to light and heat treated, an overclad was laminated using the clad film to produce a slab waveguide sample.

The manufactured slab waveguide sample was used to measure the optical loss at a wavelength of 1310 nm 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 silicone oil was injected into the end of the manufactured waveguide sample via matching oil (refractive index 1.505). Furthermore, the other side of the waveguide sample was connected to a power meter through an optical fiber with a core diameter of 50 μm and NA of 0.21 via the same matching oil, and the power (P1) when an optical circuit was inserted was measured. In addition, the power (P0) was measured by butting two similar optical fibers in a state without an optical circuit. The optical loss (1310 nm) was calculated from the measured value using the formula -10 log (P1/P0). The calculation results of the optical loss (1310 nm) in each embodiment and each comparative example are summarized in Table 1 below. In addition, if the light loss was 0.400 or less, the light loss was evaluated as being well suppressed, if the light loss was greater than 0.400 and less than 0.440, the light loss was evaluated as being suppressed, and if the light loss was greater than 0.440, the light loss was evaluated as being large.

<Method for evaluating film handling properties>
The dry films of each Example and Comparative Example manufactured as described above were used to evaluate the film handling properties. Specifically, in the first test, the dry film was folded 90° to check whether resin cracks occurred at the fold, and if no cracks occurred, the first test was deemed to have passed. Furthermore, in the second test, the dry film was cut with a cutter to check whether cracks or powder fall occurred from the end, and if no cracks or powder fall occurred, the second test was deemed to have passed. If both the first and second tests were passed, the film was rated as "remarkably good" (remarkably good film handling properties), if either the first or second test was passed, the film was rated as "good" (good film handling properties), and if both the first and second tests were failed, the film was rated as "poor" (poor film handling properties). The evaluation results of the film handling properties in each Example and Comparative Example are summarized in Table 1 below. In addition, the evaluation in the case where the dry film could not be formed was also recorded as "poor".

<Method for evaluating refractive index of cured product (wavelength 1310 nm)>
Two sheets of the dry film of each Example and Comparative Example produced as described above were laminated and bonded together using a vacuum laminator "V-130" under conditions of 50°C and 0.3 MPa. The bonded dry film was irradiated with ultraviolet light at 120°C for 10 minutes to be temporarily cured. Thereafter, the PET film of the dry film was peeled off, 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 obtained cured product at a wavelength of 1310 nm at a temperature of 25°C was measured using an Abbe refractometer. The measurement results of the refractive index in each Example and Comparative Example are summarized in Table 1 below.

<Method for measuring glass transition temperature Tg>
The dry films of each of the examples and comparative examples manufactured 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"). The test was performed 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 adopted 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, if the glass transition temperature Tg is 150 ° C., an optical waveguide having excellent heat resistance can be reliably obtained. The glass transition temperature Tg was measured in some of the examples. The measurement results are summarized in Table 1 below.

The measurement, calculation and evaluation results for each of the above examples and comparative examples are summarized in Table 1 below, along with the compounding compositions. In Table 1 below, "-" means that the results were not measured.

<Considerations>
As shown in Table 1 above, 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 within the range of 15% by mass to 80% by mass based on the total amount of the epoxy resin (A), it was found that 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 small, and it can be suitably used as a resin composition for a core.

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

Furthermore, as can be seen from the comparison between Example 7 and Example 8, or between Example 9 and Example 10, by including a multifunctional epoxy resin (a-3) in the resin composition, it is possible to improve the glass transition temperature Tg and improve the heat resistance of the optical waveguide.

On the other hand, in Comparative Example 1, in which only fluorene-type epoxy resin (a-2) was used as the epoxy resin (A), film handling was significantly poor and a film could not be formed. In Comparative Example 2, in which the content of fluorene-type epoxy resin (a-2) was high, a film could be formed, but the handling was poor. In Comparative Example 3, which did not contain fluorene-type epoxy resin (a-2), the light loss was large. This is thought to be due to the high content of hydroxyl groups derived from the epoxy resin (A), resulting in large light loss.

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.

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 indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

According to the present invention, it is possible to obtain a resin composition for optical waveguides that can suppress optical loss (particularly at a wavelength of 1,310 nm) and has good film handling properties. By producing an optical waveguide using such a resin composition for optical waveguides, the optical waveguides can be preferably used as optical transmission printed wiring boards for mobile phones, personal digital assistants, etc.

Claims (8)

An epoxy resin (A),
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,
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). The resin composition for optical waveguides according to claim 1, wherein the fluorene-type epoxy resin (a-2) includes a liquid fluorene-type epoxy resin. The resin composition for optical waveguides according to claim 1, wherein the epoxy resin (A) further contains a multifunctional epoxy resin (a-3). 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. The resin composition for optical waveguides according to claim 1, wherein the refractive index of the cured product is greater than 1.5700. The resin composition for optical waveguides according to claim 1, further comprising an antioxidant (C). 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. An optical waveguide comprising a core layer and a clad layer having a refractive index lower than that of the core layer,
An optical waveguide, wherein the core layer is formed using the optical waveguide resin composition according to any one of claims 1 to 6.

Images