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

Abstract

An aspect of the present invention pertains to a resin composition that is for an optical waveguide and that contains an epoxy resin and a curing agent. In the resin composition for an optical waveguide, the number of aliphatic compound-derived CH groups included in the epoxy resin per unit volume is at most 0.055 × Avogadro's number (NA)( / cm3).

Description

[Technical Field]

[0001] The present invention relates to a resin composition for optical waveguides. Furthermore, the present invention relates to a dry film and an optical waveguide core using such a resin composition. [Background technology]

[0002] Traditionally, optical fibers have been the dominant transmission medium in FTTH (Fiber to the Home) and long-distance and medium-distance communications in the automotive sector. In recent years, however, there has been a growing need for high-speed transmission using light even over short distances of less than 1 meter. For 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, which are not possible with optical fibers.

[0003] Conventionally, it is known that optical waveguides are formed by creating cladding and core layers using highly transparent resin materials, exposing them to ultraviolet (UV) irradiation, developing them, and then curing the resin. As such optical waveguide materials, it has been reported that resin compositions containing liquid epoxy resin and solid epoxy resin are used to suppress stickiness and improve productivity and processability (for example, Patent Document 1).

[0004] The aforementioned Patent Document 1 discloses a film material for optical waveguides, which has a compound composition of epoxy-based raw materials and an ultraviolet curing initiator (photoacid generator) as described above. However, our research has shown that with the aforementioned composition of optical waveguide film materials and other conventional materials, light in the 1.3 μm wavelength band used in optical communication is absorbed, resulting in an optical loss of approximately 0.50 dB / cm. Therefore, there is a need for an optical waveguide material that can achieve even lower loss, especially for light in the 1.3 μm band.

[0005] Therefore, the present invention aims to provide a resin composition for optical waveguides that can improve upon the above problems and further suppress optical loss (particularly optical loss in the 1.3 μm band) compared to conventionally used materials. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-128360 [Overview of the Initiative]

[0007] As a result of diligent research to solve the aforementioned problems, the inventors have found that the problems can be solved by the following means.

[0008] In other words, a resin composition for optical waveguides according to one aspect of the present invention comprises an epoxy resin and a curing agent, wherein the number of aliphatic CH groups in the epoxy resin per unit volume is 0.055 × Avogadro's number (N A )( / cm 3 ) is characterized by being less than or equal to the following. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional diagram illustrating one embodiment of a method for forming an optical waveguide using the resin composition of this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing the configuration of the slab waveguide created in the example. [Modes for carrying out the invention]

[0010] The inventors conducted extensive research to further reduce optical loss and discovered that the functional group that absorbs harmonics for 1.3 μm wavelength light used in optical communication is an aliphatic CH group. Based on this finding, the inventors discovered that by reducing the number of aliphatic CH groups in the epoxy resin in an optical waveguide composition, the absorption of 1.3 μm wavelength light can be reduced, and consequently, optical loss can be suppressed, thus completing the present invention. It was also found that a similar effect is observed with aromatic CH groups, but the effect is very small. This is presumed to be because even the same functional group has different light-absorbing capabilities depending on its environment.

[0011] The following describes specific embodiments for carrying out the present invention, but the present invention is not limited to these embodiments.

[0012] [Resin composition for optical waveguide] The optical waveguide resin composition of this embodiment (hereinafter sometimes simply referred to as the resin composition) comprises an epoxy resin and a curing agent. Furthermore, in the optical waveguide resin composition, the number of aliphatic CH groups in the epoxy resin per unit volume is 0.055 × Avogadro's number (N A )( / cm 3 ) is characterized by being less than or equal to the following.

[0013] The above configuration makes it possible to provide a resin composition for optical waveguides that can further suppress optical loss (particularly optical loss in the 1.3 μm band) compared to conventional methods. Furthermore, by using the above optical waveguide composition, it is possible to provide a dry film and an optical waveguide with excellent performance.

[0014] First, we will explain how to calculate the number of aliphatic-derived CH groups.

[0015] In this embodiment, the number of CHs per unit volume (unit: cells × Avogadro's number / cm³) 3 ) is calculated using the following formula. Number of CH molecules per unit volume = (Number of CH molecules in the structure) / (Volume per molecule) Here, the (volume per molecule) is determined by the following formula. (Volume per molecule) = (Molecular weight) / (Specific gravity of the molecule)

[0016] An example calculation will be given for explanation. The bisphenol A type liquid epoxy resin used in the examples described later (the structure of "850S" manufactured by DIC Corporation) is as follows in the chemical formula.

[0017]

Chemical formula

[0018] Since the epoxy resin has an epoxy equivalent of 188, it is estimated that n = 0.13. Therefore, in the chemical formula, the molecular weight derived from the structure outside the parentheses is 340.4, the total number of CH is 24, the number of CH derived from aliphatic (hereinafter also referred to as "ACH number") is 16, the molecular weight derived from the structure inside the parentheses is 284.3, the total number of CH is 19, and the ACH number is 11.

[0019] Therefore, when calculated as a whole, Molecular weight: 340.4 + 284.3×0.13 = 377.4 Total number of CH in one molecule: 24 + 19×0.13 = 26.47 Number of aliphatic CH in one molecule: 16 + 11×0.13 = 17.43 It becomes like this.

[0020] Since the specific gravity of the epoxy resin "850S" is 1.15, Total number of CH per unit volume = 26.47÷(377.4 / 1.15) = 0.081 × Avogadro's number / cm 3 ; Number of aliphatic CH per unit volume = 17.43÷(377.4 / 1.15) = 0.053 × Avogadro's number / cm 3 It becomes like this.

[0021] In this way, after obtaining the number of CHs derived from aliphatic groups in each raw material (epoxy resin), when the resin composition contains a plurality of epoxy resins, the number of aliphatic CHs in the entire epoxy resin is obtained as follows.

[0022] Specifically: Let the blending ratio (weight) of epoxy resin A be a, the number of CHs in A be a ACH , and the specific gravity be a specific gravity; Let the blending ratio (weight) of epoxy resin B be b, the number of CHs in B be b ACH , and the specific gravity be b specific gravity; Let the blending ratio (weight) of epoxy resin C be c, the number of CHs in C be c ACH , and the specific gravity be c specific gravity. When the number of aliphatic CHs (ACH number) in all epoxy resins is given by the following formula:

Equation

[0023] (Epoxy resin) The epoxy resin contained in the resin composition of the present embodiment is an epoxy resin in which the number of CH groups derived from aliphatic groups possessed by the epoxy resin per unit volume is 0.055 × Avogadro's number (N A )( / cm 3 ) or less, and it can be used without particular limitation. The resin composition of the present embodiment may contain one kind of epoxy resin that satisfies the above ACH number, or when it contains two or more kinds of epoxy resins, as described above, it is only necessary that the ACH number of the entire epoxy resin composed of a plurality of epoxy resins satisfies the above value.

[0024] More specifically, the epoxy resin used in the present embodiment may be a liquid epoxy resin or a solid epoxy resin. In the present embodiment, "liquid" means liquid at room temperature, and "solid" means solid at room temperature.

[0025] Examples of liquid epoxy resins that can be used in this embodiment include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, brominated epoxy resin, and alicyclic epoxy resin.

[0026] Examples of solid epoxy resins that can be used in this embodiment include bisphenol A type epoxy, hydrogenated bisphenol A type epoxy resin, bisphenol F type epoxy resin, brominated epoxy resin, fluorinated epoxy resin, aromatic epoxy resin, novolac type epoxy resin, biphenyl skeleton epoxy resin, and alicyclic epoxy resin.

[0027] These can be used individually, or in combination of two or more types.

[0028] In preferred embodiments, it is desirable to use mainly aromatic epoxy resins as the epoxy resin in this embodiment. This effectively reduces the amount of aliphatic-derived CH groups. Specifically, for example, it is preferable that the epoxy resin in this embodiment contains at least one epoxy resin selected from bisphenol A type epoxy resins having two or more epoxy groups, or bisphenol F type epoxy resins having two or more epoxy groups. These epoxy resins may be solid epoxy resins or liquid epoxy resins. By including such epoxy resins, low loss to 1.3 μm light can be more reliably achieved.

[0029] Furthermore, it is preferable to include both a liquid epoxy resin and a solid epoxy resin as the epoxy resin, which allows the material to be formed into a solid film at room temperature, and is thought to improve handling in the optical waveguide manufacturing process. When including both a liquid epoxy resin and a solid epoxy resin in this way, it is preferable that the difference between the refractive index of the liquid epoxy resin and the refractive index of the solid epoxy resin is 0.05 or less.

[0030] Furthermore, it is preferable that the epoxy resin of this embodiment contains a bisphenol AF type epoxy resin. Although the bisphenol AF type epoxy resin is a fluorine-containing epoxy resin, the aliphatic-derived CH groups can be effectively reduced by using an epoxy resin in which some of the CH groups are replaced with CF groups. Similarly, it is also preferable to use a brominated epoxy resin in which some of the CH groups are replaced with CBr groups.

[0031] Furthermore, it is preferable that the epoxy resin of this embodiment includes a solid aromatic epoxy resin having three or more epoxy groups. Including such a polyfunctional epoxy resin has the advantage of improving the heat resistance of the dry film and optical waveguide obtained from the resin composition of this embodiment.

[0032] The epoxy resins of the preferred embodiments described above can be used individually or in combination of two or more types.

[0033] Furthermore, when the resin composition of this embodiment contains both liquid epoxy resin and solid epoxy resin, the proportion of liquid epoxy resin is preferably about 5 to 35% by mass of the entire resin composition. Such a ratio has the advantage of excellent handling properties when manufacturing dry films for optical waveguides, etc. On the other hand, the proportion of solid epoxy resin is preferably about 65 to 95% by mass of the entire resin composition. Such a ratio has the advantage of keeping the tackiness of the film before curing low and suppressing powder shedding during handling.

[0034] Furthermore, in the resin composition of this embodiment, the number of OH groups in the epoxy resin per unit volume is 0.01 × Avogadro's number (N A )( / cm 3 It is preferable that the ratio is less than or equal to the above. In addition to reducing the CH groups as described above, by also reducing the OH groups present in the epoxy resin, it is possible to suppress the 1.3 μm optical loss due to OH group vibration, and thus provide waveguide materials with even lower optical loss.

[0035] (Hardening agent) The resin composition of this embodiment further contains a curing agent in addition to the epoxy resin described above. As the curing agent, for example, a photocuring agent that can be initiated by light (such as a photoacid generator that generates acid when exposed to light, or a photobase generator that generates a base when exposed to light) can be used. A thermosetting agent that can be initiated by heat (such as a thermoacid generator that generates acid when exposed to heat, or a thermobase generator that generates a base when exposed to heat), or a photo-thermosetting agent that can be initiated by both light and heat, may be used in combination.

[0036] More specifically, antimony-based curing agents, phosphorus-based curing agents, special phosphorus-based curing agents, borate-based curing agents, etc., can be used as photoacid generators. These can be used individually or in combination of two or more types.

[0037] In this embodiment, by using antimony-based and special phosphorus-based curing agents among the curing agents mentioned above, curability and transparency can be further enhanced, and light loss can be reliably reduced.

[0038] Furthermore, if the epoxy resin described above contains a brominated epoxy resin, it is preferable to include a borate-based curing agent because brominated epoxy resins are difficult to cure with ordinary curing agents. Due to the principle of diffusion, during the heat treatment process after exposure, liquid resins and low-molecular-weight solid resins diffuse to the exposed area. Because borate-based curing agents have strong curing properties, they harden sufficiently during diffusion, making it easy for refractive index distributions to occur inside the core. In that case, for example, it is more preferable that the brominated epoxy resin contains a brominated epoxy resin A that is liquid at room temperature and a brominated epoxy resin B that is solid at room temperature, and that the difference between the refractive index of brominated epoxy resin A and the refractive index of brominated epoxy resin B is 0.005 or less.

[0039] In this embodiment, the blending ratio of the curing agent described above is preferably in the range of 0.05% by mass or more and 5% by mass or less, relative to the total amount of resin components in the resin composition. Having a curing agent content in this range has the advantage of obtaining sufficient resin curing and keeping the strength of residual acid in the cured product low. A more preferable curing agent content is 0.2% by mass or more and 1.5% by mass or less.

[0040] (others) Furthermore, the optical waveguide resin composition according to this embodiment may optionally contain other additives, such as sensitizers, antioxidants, curing accelerators, flame retardants, flame retardant aids, leveling agents, etc., to the extent that they do not impair the effects of the present invention.

[0041] (Method for manufacturing resin compositions) The resin composition for optical waveguides of the present invention is typically prepared and used in the form of a varnish. Such a varnish can be prepared, for example, as follows.

[0042] In other words, the varnish is obtained by dissolving the epoxy resin described above in a predetermined ratio in a solvent, further adding a curing agent and other additives as needed, and then drying it to remove the solvent, selecting a formulation that becomes solid at room temperature. The mixing ratio of the resin component and the solvent in the varnish is not particularly limited and can be adjusted as appropriate to achieve a viscosity suitable for coating (filling) the substrate surface in varnish form.

[0043] The aforementioned organic solvent is not particularly limited, and examples include aromatic hydrocarbons such as benzene and toluene, amides such as N,N-dimethylformamide (DMF), and ketones such as acetone and methyl ethyl ketone. These may be used individually or in combination of two or more.

[0044] The temperature at which it is dissolved in the solvent is approximately 50-80°C.

[0045] Furthermore, to form an optical waveguide using the resin composition described above, a cured layer may be formed by applying varnish directly to the substrate surface and then drying it in a coating process. However, from the viewpoint of productivity, it is preferable to use a dry film that has been formed in advance from the resin composition described above. When such a dry film is used, a complicated coating process is not required, and optical waveguides can be manufactured with high productivity. In addition, when using a dry film, there is also the advantage that optical waveguides can be formed with uniform thickness accuracy.

[0046] (Dry film) The dry film according to this embodiment is formed by applying the resin composition of this embodiment to the surface of a film substrate, such as a PET film, using a multi-coater with a comma coater head, and then drying it. Furthermore, a dry film with a thickness of approximately 10 to 100 μm can be obtained by heat laminating a polypropylene film or the like as a release film.

[0047] (optical waveguide) Next, an embodiment of forming an optical waveguide on a substrate using such a dry film will be described in detail with reference to Figure 1. In this specification, the reference numerals in the drawings indicate the following: 1 cladding film, 2 optical film for the core, 3 cladding, 3a undercladding, 3b overcladding, and 4 core.

[0048] To form an optical waveguide, a cladding film and a core film are used to form the core and cladding, respectively. The resin composition of this embodiment can be used as both a cladding material and a core material, but the refractive index of the cladding film is adjusted to be lower than that of the core film.

[0049] First, as shown in Figure 1(a), a cladding film 1 is laminated onto the surface of a substrate 10 on which the electrical circuit 11 is formed, and then the cladding film 1 is cured by irradiation with light such as ultraviolet light or by heating. As the substrate 10, for example, a flexible printed circuit board with an electrical circuit formed on one side of a transparent substrate such as a polyimide film, or a printed circuit board such as glass epoxy, can be used. Through this process, an undercladding 3a is laminated onto the surface of the substrate 10, as shown in Figure 1(b).

[0050] Next, as shown in Figure 1(c), the core film 2 is laminated onto the surface of the underclad 3a, a mask with slits for the core pattern is placed on top, and the core film 2 is exposed to the core pattern by irradiating it with light that can be photocured, such as ultraviolet light, through the slits. In addition to selective exposure using a mask, the exposure method may also be a direct writing method in which laser light is scanned and irradiated along the pattern shape.

[0051] Next, after exposure, the core light film 2 is developed using a developing solution such as an aqueous flux cleaning agent to remove the unexposed, uncured resin from the core light film 2. As a result, a core 4 with a predetermined core pattern is formed on the surface of the underclad 3a, as shown in Figure 1(d).

[0052] Next, as shown in Figure 1(e), the cladding film 1 is laminated to cover the undercladding 3a and the core 4. Then, by curing the cladding film 1 with light irradiation or heating, the overcladding 3b shown in Figure 1(f) is formed. In this way, an optical waveguide A is formed on the surface of the substrate 10, in which the core 4 is embedded within the cladding 3 consisting of the undercladding 3a and the overcladding 3b.

[0053] In the optical waveguide A obtained in this manner, the use of the resin composition of this embodiment reduces the 1.3 μm light loss, enabling superior optical communication. Therefore, the substrate 10 on which such an optical waveguide A is formed is preferably used as a printed circuit board for optical transmission, and is preferably used in, for example, mobile phones and personal information terminals.

[0054] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way by the following examples. [Examples]

[0055] First, the raw materials used in preparing the resin composition in this example are summarized below.

[0056] <Liquid epoxy> • "Celoxide 2021P (CEL2021P)": Alicyclic epoxy resin, manufactured by Daicel Corporation (ACH number: 0.093, specific gravity: 1.17) • "Epiclon 850S": Bisphenol A type epoxy resin, manufactured by DIC Corporation (ACH number: 0.056, specific gravity: 1.15) • "EPOX MK R1710": Bisphenol E type epoxy resin, manufactured by Printec Co., Ltd. (ACH number: 0.051, specific gravity: 1.2) • "BROC" brominated epoxy resin, manufactured by Nippon Kayaku Co., Ltd. (ACH number: 0.043, specific gravity: 1.75, refractive index: 1.6052)

[0057] <Solid epoxy> • "VG3101M80": Multifunctional epoxy resin, manufactured by Printec Co., Ltd. (ACH number: 0.048, specific gravity: 1.19) • "jER1001": Bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.050, specific gravity: 1.19) • "NC3000": Bisphenyl-type epoxy resin, manufactured by Nippon Kayaku Co., Ltd. (ACH number: 0.034, specific gravity: 1.2) • "YX7760" bisphenol AF type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.032, specific gravity: 1.47) • "Epicote 1006FS": Bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.048, specific gravity: 1.19) • "4005P": Bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation (ACH number: 0.035, specific gravity: 1.19) • "Epiclon 153": Brominated epoxy resin, manufactured by DIC Corporation (ACH number: 0.042, specific gravity: 1.8, refractive index: 1.6031)

[0058] <Hardening agent> • "CPI-200K": Special phosphorus-based cationic curing agent, manufactured by Sunapro Co., Ltd. • "CPI-210S": Special phosphorus-based cationic curing agent, manufactured by Sunapro Co., Ltd. • "CPI-310B": Borate-based cationic curing agent, manufactured by Sunapro Co., Ltd. • "SP-170": Antimony-based cationic curing agent (manufactured by ADEKA Corporation)

[0059] <Additives> • "UVS-1331": Sensitizer, Kawasaki Chemical Industries, Ltd. • "AO-60": Antioxidant, manufactured by ADEKA Corporation • "PEP36": Antioxidant, manufactured by ADEKA Corporation • "PF636": Leveling agent, manufactured by OMNOVA. • "BYK3560": Leveling agent, manufactured by BYK Japan Co., Ltd.

[0060] <Preparation of resin composition> (Examples 1-12 and Comparative Examples) The components were blended according to the formulations (parts by mass) shown in Table 1 below, and the mixed solvent of MEK and toluene was adjusted to 70 parts by mass per 100 parts by mass of resin. The mixture was then mixed while heating to 50-80°C. Next, the epoxy resin varnish for each example and comparative example was prepared by filtering through a membrane filter with a pore size of 1 μm and then degassing.

[0061] Table 1 also lists the refractive index n (1.3 μm wavelength), ACH number, and OH number of the epoxy resins used in each example and comparative example.

[0062] Furthermore, the resin composition was prepared by adjusting the formulation based on the refractive index n shown below.

[0063] (Refractive index n) For each example and comparative example resin composition, the refractive index (n) of the liquid component and the refractive index (n) of the entire core layer were determined as follows.

[0064] The refractive index of each resin individually at a wavelength of 1.3 μm was measured using an Abbe refractometer. For the epoxy resins BROC (Nippon Kayaku Co., Ltd.) and Epiclon 153 (DIC Corporation), resin cured with CPI310B (Sun Apro Co., Ltd.) as the curing agent was used as the refractive index measurement sample. For the other resins, resin cured with CPI101A (Sun Apro Co., Ltd.) as the curing agent was used as the refractive index measurement sample. Using the refractive index values ​​of each resin measured in this way, the refractive index (n) of the liquid component and the refractive index (n) of the entire core layer were estimated using the following equations 1 and 2. For the resin compositions of the examples, the resin formulation was adjusted so that the difference between the refractive index (n) of the liquid epoxy resin and the refractive index of the entire optical waveguide resin composition (core layer resin composition) was 0.05 or less.

[0065] (Formula 1) Refractive index of liquid components = {(Refractive index of liquid resin a) × (Parts of mass of liquid resin a) + (Refractive index of liquid resin b) × (Parts of mass of liquid resin b) + ...} / (Parts of mass of liquid resin a + Parts of mass of liquid resin b + ...) (Formula 2) Refractive index of the entire core layer = {(Refractive index of liquid resin a) × (Parts of mass of liquid resin a) + (Refractive index of liquid resin b) × (Parts of mass of liquid resin b) + ... + (Refractive index of solid resin A) × (Parts of mass of solid resin A) + (Refractive index of solid resin B) × (Parts of mass of solid resin B) + ...} / {(Parts of mass of liquid resin a + Parts of mass of liquid resin b + ...) + (Parts of mass of solid resin A + Parts of mass of solid resin B + ...)}

[0066] <Loss measurement> (Examples 1-10 and Comparative Examples) The resin composition varnishes of each example and comparative example were applied to Toyobo PET film (product number A4100) using a Hirano Texseed comma coater head multi-coater, dried to a predetermined thickness, and then heat-laminated with Oji Specialty Paper's OPP-MA420 release film to obtain a dry film with a resin layer thickness of 25 μm. This was used as the core film.

[0067] As cladding material for optical waveguides, we fabricated the following dry films for cladding.

[0068] An epoxy resin varnish was prepared by dissolving 14 parts by mass of Celoxide 2021P (manufactured by Daicel Chemical Industries), 25 parts by mass of 1006FS (manufactured by Mitsubishi Chemical), a solid bisphenol A type resin, 38 parts by mass of YX8040 (manufactured by Mitsubishi Chemical), a hydrogenated bisphenol A type resin, 23 parts by mass of trifunctional epoxy resin VG3101L (manufactured by Printec), 1 part by mass of SP-170 (manufactured by Adeka) as a curing agent, 1.4 parts by mass of AO-60 (manufactured by Adeka) as an antioxidant, and 0.1 parts by mass of PF-636 (manufactured by OMNOVA) as a leveling agent in a solvent, filtering the mixture through a membrane filter with a pore size of 1 μm, and then degassing. This varnish was applied to a PET film (product number A4100) manufactured by Toyobo using a multi-coater with a comma coater head manufactured by Hirano Texseed, and dried to obtain a film of the specified thickness.

[0069] Using the core film and cladding film described above, the undercladding was first laminated onto the substrate. Then, the core film was laminated on top of that, and after exposure and heat treatment using a mask capable of forming a 25μm wide pattern, the unexposed core material was removed by development, and then the overcladding was laminated to create a 25μm core-sized multimode waveguide sample.

[0070] Then, light from a 1310 nm LED light source was injected through an optical fiber with a core diameter of 9 μm and an NA of 0.12, and silicone oil was injected into the end of the optical waveguide created above, via matching oil (refractive index 1.505). From the opposite side, an optical fiber with a core diameter of 50 μm and an NA of 0.21 was connected to a power meter via the same matching oil, and the power (P1) with the optical circuit inserted was measured. The power (P0) without the optical circuit was measured by striking the two fibers together, and the insertion loss of the optical circuit was calculated using the formula -10log(P1 / Po). The results are shown in Table 1 as material losses.

[0071] (Example 11) Using the resin composition varnish of Example 11, a dry film with a resin layer thickness of 50 μm was obtained in the same manner as in Example 1. This was used as the core film. As a cladding material with a lower refractive index than the core, the same resin composition as in Example 1 was used to prepare a cladding film with a thickness of 35 μm.

[0072] Then, a slab waveguide, as shown in Figure 2, was fabricated on a substrate 10 ("R1515W," manufactured by Panasonic Corporation), with a core 4 sandwiched between two cladding layers 3.

[0073] Light from a 1310 nm LED light source was then introduced through a 9 μm core diameter, NA 0.12 optical fiber into the end of a slab waveguide via silicone oil and matching oil (refractive index 1.505), and the light was received from the opposite side with a power meter. The power (P1) with the optical circuit inserted was measured, and the power (P0) without the slab waveguide was measured, and the insertion loss of the optical circuit was calculated using the formula -10log(P1 / Po). The results are shown in Table 1 as material losses.

[0074] (Example 12) Using the resin composition varnish of Example 12, dry films were prepared for the core material and cladding material of μm each by the method described, and then the cladding material was laminated onto the substrate as an undercladding. Furthermore, the core film was laminated on top of that, and after exposure and heat treatment using a mask capable of forming a pattern with a width of 6-7 μm, the unexposed core was removed by development, and then the overcladding was laminated to obtain a waveguide sample.

[0075] Then, light from a 1310 nm LED light source was introduced through an optical fiber with a core diameter of 9 μm and an NA of 0.12, with silicone oil injected into the end of the optical waveguide via matching oil (refractive index 1.505). From the opposite side, an optical fiber with a core diameter of 50 μm and an NA of 0.21 was connected to a power meter via the same matching oil, and the power (P1) with the optical circuit inserted was measured. The power (P0) without the optical circuit was also measured by striking the two fibers together, and the insertion loss of the optical circuit was calculated using the formula -10log(P1 / Po).

[0076] The waveguide used for measurement was cut to a predetermined size, and the length was varied. Similar measurements were repeated, and a graph was created with the waveguide length on the X-axis and the loss on the Y-axis. The slope of the graph was defined as the waveguide propagation loss. The results, as cutback losses, are shown in Table 1.

[0077] [Table 1]

[0078] <Evaluation and Analysis> The results in Table 1 confirm that, according to the present invention, an optical waveguide can be obtained that can suppress the loss of light in the 1.3 μm band to a very low level (0.50 dB / cm or less). In particular, in Example 11, which used brominated epoxy resin, even lower losses were achieved.

[0079] On the other hand, in the comparative optical waveguide that did not satisfy the provisions of the present invention, an optical loss of more than 0.50 dB / cm was measured.

[0080] In addition, although the measurement methods differ between Examples 1-10 and Example 11, both measurement methods can be interpreted as losses originating from the transparency of the core material itself, and therefore the physical property values ​​(material losses) are considered to be at the same level. Furthermore, since the measurement method for Example 12 estimates the loss as a waveguide consisting of a core and cladding, the transparency of the cladding and the shape of the core's side surface also affect the loss value. Therefore, when measured with the same material, the cutback loss in Example 12 will be larger than the loss value in the measurement methods used in Examples 1 and 11. Considering these factors, although the measurement methods differ between Example 12 and the comparative examples, it is clear that Example 12 has lower losses.

[0081] This application is based on Japanese Patent Application No. 2021-107421, filed on June 29, 2021, the contents of which are included in this application.

[0082] In order to express the present invention, the invention has been adequately and sufficiently described above through embodiments with reference to specific examples and drawings, etc. However, those skilled in the art should recognize that it is easy to modify and / or improve the embodiments described above. Therefore, unless the modifications or improvements implemented by those skilled in the art fall outside the scope of the claims described in the claims, such modifications or improvements shall be interpreted as being included within the scope of the claims. [Industrial applicability]

[0083] The present invention has broad industrial applicability in technical fields such as optical waveguides, various electronic devices, and optical devices.

Claims

1. A resin composition for optical waveguide cores comprising an epoxy resin and a curing agent, The epoxy resin contains a liquid epoxy resin, a solid epoxy resin, and a bisphenol AF type epoxy resin, and the difference between the refractive index of the liquid epoxy resin and the refractive index of the entire optical waveguide core resin composition is 0.05 or less. In the resin composition for the optical waveguide core, the number of aliphatic CH groups in the epoxy resin per unit volume is 0.055 × Avogadro's number (N Ａ ) ( / cm ３ The following are resin compositions for optical waveguide cores.

2. The resin composition for optical waveguide cores according to claim 1, wherein the epoxy resin contains at least one epoxy resin selected from bisphenol A type epoxy resin having two or more epoxy groups, or bisphenol F type epoxy resin having two or more epoxy groups.

3. The resin composition for optical waveguide cores according to claim 1, wherein the epoxy resin contains a solid aromatic epoxy resin having three or more epoxy groups.

4. In the aforementioned resin composition for optical waveguide cores, the number of OH groups in the epoxy resin per unit volume is 0.01 × Avogadro's number (N Ａ ) ( / cm ３ The resin composition for optical waveguide cores according to claim 1, wherein the composition is as follows:

5. The resin composition for optical waveguide cores according to claim 1, wherein the epoxy resin contains a brominated epoxy resin, and the curing agent contains a borate-based curing agent.

6. The brominated epoxy resin contains a liquid brominated epoxy resin A and a solid brominated epoxy resin B. The resin composition for optical waveguide cores according to claim 5, wherein the difference between the refractive index of the liquid brominated epoxy resin A and the refractive index of the solid brominated epoxy resin B is 0.005 or less.

7. A dry film comprising a cured product of the resin composition for optical waveguide cores according to any one of claims 1 to 6 and a substrate film.

8. An optical waveguide comprising the resin composition for optical waveguide cores according to any one of claims 1 to 6.

9. An optical waveguide made of a dry film as described in claim 7.

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