JP6376551B2 - Liquid photosensitive resin composition for forming optical waveguide core, optical waveguide using the same, and flexible printed wiring board - Google Patents

Description

  The present invention relates to a liquid photosensitive resin composition constituting a core of an optical waveguide in a flexible printed wiring board for optical signal transmission widely used in optical communication, optical information processing, and other general optics, and light formed using the same. The present invention relates to a waveguide and a flexible printed wiring board.

  A liquid photosensitive resin composition (photo-curable resin composition) is used as a material for forming a core of a film-like optical waveguide (polymer optical waveguide) used for a flexible printed wiring board for optical signal transmission. . The core is formed by applying a liquid resin composition (varnish) obtained by adding a solvent to the resin composition, and irradiating ultraviolet rays (UV) through a photomask having an opening having a desired pattern shape. "Photolithography" is used in which the irradiated portion is cured to form a core, and then uncured unnecessary portions are removed.

  The optical waveguide core forming material (resin composition) used in the above applications is a cured product after molding (hereinafter referred to as “cured product”) such as refractive index, transparency, resolution patterning property, and heat resistance after curing of the material. ) In consideration of various physical properties, and in order to satisfy the required characteristics according to the application, selection of various raw materials constituting the composition, examination of the blending balance, etc. Many proposals have been made (see Patent Documents 1 and 2).

  In particular, in the core of the optical waveguide used for the flexible printed wiring board, cation polymerization such as an epoxy compound is used as a base of a material (photosensitive resin composition) for forming a cured body in consideration of required characteristics. A suitable compound is selected. At that time, for the purpose of imparting photosensitivity (photocurability), a photoacid generator or the like is appropriately blended in the forming material, and further, in order to ensure the optical temporal stability of the produced optical waveguide core. In addition, various antioxidants and the like are added. In some cases, two or more kinds of antioxidants are used at the same time in order to increase the effect of the combined use (synergistic effect).

JP 2010-230944 A JP2011-237645A

  By the way, in the optical waveguide manufacturing process (formation process) by photolithography, a liquid whose viscosity is adjusted by dispersing a forming material (composition) in a solvent (solvent) for both the core and each cladding layer constituting the optical waveguide. The photosensitive resin composition (varnish or coating solution) is applied in a layer (or film) using a wet coating process such as spin coating or roll coating, and an uncured liquid resin composition layer (light (Before irradiation) is once formed. Therefore, depending on the composition of the composition, the viscosity (viscosity) of the coating liquid (liquid resin composition) varies with time (thickening with time), and the thickness of the liquid resin composition layer (uncured) after coating is It may vary.

  Even in the production of an optical waveguide core using a liquid photosensitive resin composition to which two kinds of antioxidants are added as described above, this coating liquid (liquid The viscosity of the resin composition) increases with time, and there is a problem that the thickness of the cured body (core) obtained after curing becomes thicker than the initial set value (design value), and an improvement is desired. .

  The present invention has been made in view of such circumstances. Even when two antioxidants having different functions are used in combination, the liquid for forming an optical waveguide core can suppress an increase in the viscosity of the liquid resin composition with time. The objective is to provide a photosensitive resin composition, and an optical waveguide and a flexible printed wiring board using the same.

In order to achieve the above object, the present invention contains the following components (A) to (E), and the water content X in the entire liquid resin composition after mixing each component is 0.005% by weight or more and 0.0. 5 wt% der less is, the addition ratio of the following components (C) and (D), by weight, (C) :( D) = 1: 3~3: 1 der Ruhikarishirube waveguide core forming liquid Let the photosensitive resin composition be the 1st summary.
(A) Cationic polymerizable compound (B) Photoacid generator (C) Primary antioxidant comprising a hindered phenol compound (D) Secondary antioxidant comprising a phosphite compound (E) solvent

  Further, the present invention provides a second optical waveguide in which the core of the optical waveguide is formed of a cured product obtained by curing the liquid photosensitive resin composition for forming an optical waveguide core according to the first aspect by irradiating with ultraviolet rays. A flexible printed wiring board including the optical waveguide according to the second aspect is referred to as a third aspect.

  The inventors of the present invention have made extensive studies to solve the above-mentioned problems. As a result, for the purpose of increasing the effect of the combined use, a primary antioxidant (hindered phenol compound) for scavenging peroxy radicals and primary oxidation are used. In the liquid resin composition added with the secondary antioxidant (phosphite compound) for peroxide decomposition generated from the inhibitor, the phosphite compound used as the secondary antioxidant is: Although it itself does not exhibit acidity, the hydrolysis reaction proceeds in the presence of water (moisture) to produce “phosphorous acid groups” that are acidic compounds. It was found that an increase in viscosity was caused. Then, the inventors obtained an idea from the above knowledge, and by suppressing or removing “residual moisture in the composition” which is one cause of the formation of the acidic compound in the liquid resin composition having the above composition. The inventors have found that the formation of the acidic compound can be suppressed to suppress the thickening over time, and the present invention has been achieved.

Thus, the liquid photosensitive resin composition for forming an optical waveguide core of the present invention comprises (A) a cationically polymerizable compound, (B) a photoacid generator, and (C) a primary antioxidant comprising a hindered phenol compound. In a liquid resin composition containing an agent, (D) a secondary antioxidant composed of a phosphite compound, and (E) a solvent, the ratio of moisture (moisture content X) in the total composition after mixing the components is 0.005 wt% or more and 0.5 wt% or less of (C) a primary antioxidant composed of a hindered phenol compound and (D) a secondary antioxidant composed of a phosphite compound ratio, by weight, (C) :( D) = 1: 3~3: Ru 1 der. Therefore, when the core of an optical waveguide is formed by wet coating using this liquid photosensitive resin composition, thickening of the liquid resin composition during storage or coating can be suppressed, and the core can be formed as originally designed. The core thickness can be formed. In addition, if the liquid photosensitive resin composition for forming an optical waveguide core of the present invention is used, a high-quality optical waveguide having the same size and quality can be obtained at low cost with high efficiency (yield) without performance fluctuation between lots. It becomes possible to manufacture with.

  In addition, it is preferable that the (E) solvent used for the liquid photosensitive resin composition for optical waveguide core formation of this invention is the thing whose water content Y is 0.001 to 1.0 weight%. . Thereby, mixing of the water | moisture content derived from a solvent can be reduced significantly, and the thickening of the liquid resin composition in storage or coating can be suppressed more reliably.

  In addition, an optical waveguide formed of a cured product obtained by irradiating the liquid photosensitive resin composition for forming an optical waveguide core with ultraviolet rays and cured, and a flexible printed wiring board provided with the optical waveguide also have problems caused by the optical waveguide. There are few and highly reliable apparatuses or systems, etc. can be constructed.

  Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

<< Liquid photosensitive resin composition for optical waveguide core formation >>
The liquid photosensitive resin composition for forming an optical waveguide core of the present invention (hereinafter sometimes simply referred to as “liquid resin composition”) includes (A) a cationic polymerizable compound, (B) a photoacid generator, (C ) A hindered phenol compound, (D) a phosphite compound, and (E) a solvent. The water content X in the entire liquid resin composition after mixing each component is 0.005% by weight. The addition ratio of (C) hindered phenol compound and (D) phosphite compound is (C) :( D) = 1: 3 based on weight. 3: characterized by one der Rukoto.
Hereinafter, various components will be described in order.

<Cationically polymerizable compound>
Examples of the cationic polymerizable compound include epoxy compounds, oxetane compounds, and episulfide compounds.
Examples of the epoxy compound include polyfunctional aliphatic epoxy resins such as 1,2-epoxy-4- (2-oxiranyl) cyclohexane adduct of 2,2-bis (hydroxymethyl) -1-butanol. Examples thereof include aliphatic epoxy resins such as' -epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate. Furthermore, examples of the resin that acts as a binder resin include hydrogenated bisphenol A type epoxy resins and hydrogenated bisphenol F type epoxy resins that do not have an aromatic ring. These may be used alone or in combination of two or more.

  Specifically, EHPE3150, EHPE3150CE (all manufactured by Daicel Corporation), YX-8040, YX-8000, YX-8034 (all manufactured by Mitsubishi Chemical Corporation), ST-4000D (manufactured by Nippon Steel Chemical Co., Ltd.), Celoxide 2021P (Manufactured by Daicel Corporation). In the present invention, the aliphatic epoxy resin includes an alicyclic epoxy resin. And as said aliphatic resin, it is preferable to show solid, The solid in this case means exhibiting a solid state under normal temperature (25 degreeC) temperature.

  Next, as the oxetane compound, specifically, OXT-101 (3-ethyl-3-hydroxymethyloxetane (oxetane alcohol), OXT-212 (2-ethylhexyloxetane), OXT-121 (xylylenebisoxetane) , OXT-221 (3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane) (all manufactured by Toagosei Co., Ltd.), ETERNACOLL OXBP, EHO, OXTP, OXMA (all Ube Industries In addition, you may mix and use the said epoxy compound and the said oxetane compound.

  Moreover, an episulfide compound can also be used as a cationically polymerizable compound. Examples of the episulfide compound include SR100H (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.).

<Photoacid generator> (photopolymerization initiator)
The photoacid generator is used for imparting curability to the photosensitive resin composition by light irradiation (for example, ultraviolet irradiation). Examples of the photoacid generator include photoacid generators such as benzoins, benzoin alkyl ethers, acetophenones, aminoacetophenones, anthraquinones, thioxanthones, ketals, benzophenones, xanthones, and phosphine oxides ( Photocationic curing initiator).

  Specifically, triphenylsulfonium hexamonium fluoride, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl- 1-phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane, 2-hydroxy-1- {4- [4- ( 2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2 -Methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, bis (2,4,6-trimethylbenzoyl) -phenylphenol Sphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis (η5-2,4-cyclopentadien-1-yl) -bis [2,6-difluoro-3 (1H-pyrrol-1-yl ) -Phenyl] titanium, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one, and the like. These may be used alone or in combination of two or more. Among them, from the viewpoint of fast curing speed and thick film curability, triphenylsulfonium hexafluoromonium salt, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl-phenyl- The ketone, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one, is preferably used.

  The content of the photoacid generator is preferably set to 0.1 to 3 parts by weight, more preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the solid content of the varnish (liquid resin composition). It is. If the content of the photoacid generator (photopolymerization initiator) is too small, it is difficult to obtain photocurability by satisfactory light irradiation (ultraviolet irradiation), and if it is too large, the photosensitivity increases, and when patterning the core, There is a tendency to cause shape abnormalities, and there is also a tendency to deteriorate required physical properties such as initial loss.

  Moreover, you may use a photosensitizer together in order to improve the acid generation efficiency of said photoacid generator. As the photosensitizer, 2-isopropylthioxanthone, diethylthioxanthone, chlorothioxanthone, anthracene, dimethoxyanthracene, dibutoxyanthracene, perylene, phenothiazine, acetophenone, benzophenone, Michler ketone, ketocoumarin, eosin and the like can be used.

  The content of the photosensitizer is preferably set to 0.01 to 1.0 part by weight, more preferably 0.05 to 0, based on 100 parts by weight of the solid content of the varnish (liquid resin composition). .5 parts by weight. If the content of the photosensitizer is too small, satisfactory photo-curing property by light irradiation (ultraviolet irradiation) is difficult to obtain, and if it is too large, there is a tendency to cause an abnormal shape during patterning of the core. There is also a tendency for the required physical properties such as loss to deteriorate.

<Hindered phenol-based compound> Primary antioxidant The primary antioxidant is a compound that captures a highly active peroxy radical in the initial stage of the oxidation reaction of the resin and gives a somewhat stable hydroperoxide. For that purpose, a hindered phenol compound is preferably used.

  Specific examples of hindered phenol compounds include IRGANOX 1010, IRGANOX 1035, IRGANOX 1076, IRGANOX 1098, IRGANOX 1135, IRGANOX 1330, IRGANOX 1726, IRGANOX 1425 WL, IRGANOX 1520 L, IRGANOX 245, IRGANOX 245, IRGANOX 245 , IRGANOX 565, IRGAMOD 295 (manufactured by BASF Japan Ltd.), ADK STAB AO-20, AO-30, AO-40, AO-50, AO-60, AO-80, AO-330 (manufactured by ADEKA), Sumilyzer GA-80, MDP-S, WX-R, WX-RC (manufactured by Sumitomo Chemical Co., Ltd.), Antage BHT, DAH, D BH, W-300, W-400, W-500, SP (made by Kawaguchi Chemical Industry Co., Ltd.), etc. are mention | raise | lifted.

  The amount of the hindered phenol compound added is preferably 0.1 to 3.0% by weight, more preferably 0.2 to 1.0% by weight, based on the solid content of the varnish (liquid resin composition). It is. If the addition amount is lower than this range, the effect of preventing loss reduction cannot be expected because the antioxidant effect is low. If the addition amount is higher than this range, the antioxidant acts as a plasticizer and the core (resin layer) is cured. This is not desirable because

<Phosphorus ester compound> Secondary antioxidant The secondary antioxidant is a compound added to decompose the peroxide generated by the primary antioxidant added to prevent the oxidation reaction of the resin. It is. A combination of the two provides a high antioxidant effect. Secondary antioxidants include phosphorus compounds and sulfur compounds. From the viewpoint of the antioxidant effect, among the phosphorus compounds, phosphite compounds are particularly preferably used in the present invention.

  Specific examples of the phosphite compound include JP-360 (triphenyl phosphite), JP-351 (trisnonylphenyl phosphite), JP-3CP (tricresyl phosphite), JP-302 (triethyl). Phosphite), JP-308E (tris (2-ethylhexyl phosphite), JP-310 (tridecyl phosphite), JP-312L (trilauryl phosphite), JP-333 (tris (tridecyl) phosphite), JP -318-O (trioleyl phosphite), JPM-308 (diphenyl mono (2-ethylhexyl) phosphite), JPM-311 (diphenyl monodecyl phosphite), JPM-313 (diphenyl mono (tridecyl) phosphite), JPS-312 (Trilaurylchi Phosphite), JPP-613M, JA-805, JPP-88, JPE-10 (bis (decyl) pentaerythritol diphosphite), JP-318E (tristearyl phosphite), JPP-2000PT (distearyl pentaerythritol diphosphite) Phosphite), JP-650 (tris (2,4-di-tert-butylphenyl) phosphite), JPH-3800 (hydrogenated bisphenol A / pentaerythritol phosphite polymer), HBP (hydrogenated bisphenol A phosphite polymer) (Songoku Chemical Industry Co., Ltd.), SANKO-HCA, SANKO-EPOCLEAN (Sanko Co., Ltd.), and the like.

  The addition amount of the phosphite compound is preferably 0.1 to 3.0% by weight, more preferably 0.2 to 1.0% by weight, based on the solid content of the varnish (liquid resin composition). It is. If the addition amount is lower than this range, the anti-oxidation effect is low, so the loss reduction prevention effect cannot be expected. If the addition amount is higher than this range, the antioxidant acts as a plasticizer and the core (resin layer) This is not preferable because it prevents curing.

The addition ratio (weight basis) of the hindered phenol compound (primary antioxidant) and the phosphite compound (secondary antioxidant) is 1 for primary antioxidant: secondary antioxidant. : 3 to 3: 1 is necessary .

<Solvent>
Examples of the solvent used in the liquid resin composition (varnish) of the present invention include glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol alkyl ether acetates such as methyl cellosolve acetate, diethylene glycols such as diethylene glycol monomethyl ether, and propylene. Propylene glycol alkyl ether acetates such as glycol methyl ether acetate, amides such as dimethylformamide, dimethylacetamide, dimethylimidazolidinone, aromatic hydrocarbons such as toluene, ketones such as cyclohexanone and cyclopentanone, gamma butyrolactone, etc. Lactones, 2-hydroxypropionic acid, ethyl lactate and the like. These may be used alone or in combination of two or more.

  The content of the solvent is preferably set to 10 to 90 parts by weight, and more preferably 30 to 80 parts by weight with respect to 100 parts by weight of the solid content of the varnish (liquid resin composition). Since the solvent is used for adjusting the viscosity of the varnish, it may be added additionally after the varnish is prepared.

  And each component of the liquid photosensitive resin composition for optical waveguide core formation (A) cation polymerizable compound, (B) photoacid generator, (C) hindered phenol compound, (D) phosphite ester After mixing the compound and the solvent (E), for example, complete stirring and heating under heating at 85 ° C., and then cooling to room temperature (25 ° C.) followed by heating and pressure filtration using a filter or the like. Thus, a “photosensitive varnish” that is a material for forming a core of an optical waveguide according to the present invention can be prepared.

  In addition, in the state of the liquid resin composition after the addition of the solvent, in order to keep the water content (water content X) low, from the “solvent” considered to contain the most water in the composition, before mixing, It is desirable to remove moisture in advance. For this reason, as the solvent used in the present invention, a solvent having a water content Y of 0.001 wt% (10 ppm) or more and 1.0 wt% (10000 ppm) or less is preferably used.

  In addition, as a method of removing moisture from the solvent, for example, a method of distilling under reduced pressure with a desiccant (diphosphorus pentoxide, sodium sulfate, etc.) present in the system, or a desiccant (molecular sieve 4A, etc.) is packed. Drying treatment such as passing through a column. Further, a commercially available dehydrated solvent from which moisture has been sufficiently removed (low moisture content) may be used. For example, as a typical example, dry DMF, DMAc, NMP manufactured by Kanto Chemical Co., Ltd. (all of which water content is 50 ppm or less), or ethyl lactate for electronic industry (water content of 100 ppm or less) manufactured by Showa Denko Co., Ltd. is used. be able to.

<Liquid photosensitive resin composition>
As described above, the cationic polymerizable compound, the photoacid generator, the primary antioxidant (hindered phenol compound), the secondary antioxidant (phosphite compound), and the moisture content The water content X in the entire liquid resin composition after mixing Y with 0.001% by weight or more and 1.0% by weight or less of the above solvent becomes 0.005% by weight or more and 0.5% by weight or less. Yes. The water content X in the composition can be measured by Karl Fischer titration or the like.

  In addition, when the moisture content X in the said composition exceeds 0.5 weight%, you may give a drying process (heat drying) to a composition. A drying process is performed by the method of heat-drying for 8 to 24 hours at 30-90 degreeC using the vacuum dryer decompressed to 10-20 mmHg, for example.

<Optical waveguide>
Next, an optical waveguide using the liquid photosensitive resin composition of the present invention as a core forming material will be described.

  The optical waveguide obtained by the present invention is, for example, a base material, a clad layer (under clad layer) formed in a predetermined pattern on the base material, and a predetermined optical path for transmitting an optical signal on the clad layer. It consists of a core formed by a pattern and a clad layer (over clad layer) formed on the core (layer). And the optical waveguide obtained by this invention is characterized by the said core being formed with the above-mentioned liquid photosensitive resin composition.

  Moreover, regarding the under clad layer forming material and the over clad layer forming material, a liquid resin composition for forming a clad layer having the same component composition may be used, or a liquid resin composition having a different component composition may be used. . In the optical waveguide obtained by the present invention, the cladding layer needs to be formed so that the refractive index is smaller than that of the core.

  In the present invention, the optical waveguide can be manufactured through the following processes, for example. That is, a base material is prepared, and a photosensitive varnish W2 made of a liquid photosensitive resin composition, which is a cladding layer forming material, is applied onto the base material. The photosensitive varnish W2 is cured by irradiating the coated surface of the varnish W2 with light such as ultraviolet rays and further performing a heat treatment as necessary. In this manner, an under cladding layer (a lower portion of the cladding layer) is formed.

  Next, an uncured resin layer for core formation is formed by applying a core forming material (photosensitive varnish W1) made of the liquid photosensitive resin composition of the present invention on the undercladding layer. At this time, after coating the core forming material (photosensitive varnish W1), the organic solvent (solvent) is dried by heating to remove an uncured optical waveguide core forming resin layer (liquid). It can be formed into a film (film). Then, a photomask for exposing a predetermined pattern (core pattern) is disposed on the surface of the core-forming uncured layer, irradiated with light such as ultraviolet rays through the photomask, and further heated as necessary. Process. Then, the core of a predetermined pattern is formed by dissolving and removing the unexposed part of the uncured core forming layer using a developer.

  Next, the photosensitive varnish W2 made of the liquid photosensitive resin composition, which is the above-described cladding layer forming material, is applied again on the core (layer), and then irradiated with light such as ultraviolet irradiation, and further required. By performing heat treatment according to the above, an over clad layer (upper part of the clad layer) is formed. By going through such a process, the target optical waveguide can be manufactured.

  Examples of the base material used for the production of the optical waveguide include a silicon wafer, a metal substrate, a polymer film, and a glass substrate. Examples of the metal substrate include stainless steel plates such as SUS. Specific examples of the polymer film include a polyethylene terephthalate (PET) film, a polyethylene naphthalate film, and a polyimide film. And the thickness is normally set in the range of 10 micrometers-3 mm.

In the light irradiation, specifically, ultraviolet irradiation is performed. Examples of the ultraviolet light source in the ultraviolet irradiation include a low pressure mercury lamp, a high pressure mercury lamp, and an ultrahigh pressure mercury lamp. The irradiation amount of ultraviolet rays is usually, 10~20000mJ / cm ^2, preferably 100~15000mJ / cm ^2, more preferably 500~10000mJ / cm ² approximately.

  After the exposure by the ultraviolet irradiation, a heat treatment may be further performed in order to complete the curing by the photoreaction. The heat treatment conditions are usually 80 to 250 ° C., preferably 100 to 150 ° C., for 10 seconds to 2 hours, preferably 5 minutes to 1 hour.

  Examples of the material for forming the cladding layer include various liquid epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, fluorinated epoxy resin, and epoxy-modified silicone resin. Examples of the resin composition include the solid epoxy resin and the above-described various photoacid generators as appropriate, and the compounding design is appropriately performed so as to have a low refractive index as compared with the core forming material. Furthermore, since a clad layer forming material is prepared and applied as a varnish (W2) as necessary, various conventionally known organic solvents and the above core forming material so as to obtain a viscosity suitable for coating. Appropriate amounts of various additives (antioxidants, adhesion-imparting agents, leveling agents, UV absorbers) that do not deteriorate the function of the optical waveguide using the above may be used.

  Examples of the organic solvent used for preparing the varnish W2 for the cladding layer include ethyl lactate, methyl ethyl ketone, cyclohexanone, ethyl lactate, 2-butanone, N, N-dimethylacetamide, diglyme, diethylene glycol methyl ethyl ether, propylene glycol methyl. Examples include acetate, propylene glycol monomethyl ether, tetramethylfuran, dimethoxyethane and the like. These organic solvents are used alone or in combination of two or more in an appropriate amount so as to obtain a viscosity suitable for coating.

  In addition, as a coating method using the forming material of each layer on the substrate, for example, a spin coater, a coater, a circular coater, a bar coater, or a coating method, screen printing, a gap using a spacer, or the like. And a method of injecting by capillarity, a method of coating continuously by roll-to-roll with a coating machine such as a multi-coater, and the like can be used. The optical waveguide can also be made into a film-like optical waveguide (polymer optical waveguide) by peeling and removing the substrate.

  The optical waveguide thus obtained is used as an optical waveguide for a flexible printed wiring board for optical signal transmission according to the present invention.

  Next, the present invention will be described based on examples. However, the present invention is not limited to these examples. In the examples, “parts” means weight basis unless otherwise specified.

[Example 1]
First, prior to the production of the optical waveguide as an example, a photosensitive varnish W2 as a cladding layer forming material and a photosensitive varnish W1 as a core (layer) forming material of the present invention were prepared.

(Preparation of cladding layer forming material): Reference Under light-shielding conditions, 50 parts of liquid bifunctional fluorinated alkyl epoxy resin (H022, manufactured by Tosoh F-Tech), liquid bifunctional alicyclic epoxy resin (Celoxide 2021P, manufactured by Daicel) ) 50 parts, photoacid generator (Adekaoptomer SP-170, manufactured by ADEKA) 4.0 parts, phosphorus antioxidant (HCA, manufactured by Sanko) 0.54 parts, silane coupling agent (KBM-403) , Manufactured by Shin-Etsu Silicone Co., Ltd.), 1 part of the mixture was mixed and stirred to complete dissolution under heating at 80 ° C., then cooled to room temperature (25 ° C.), and then heated and pressure filtered using a membrane filter having a diameter of 1.0 μm Thus, a photosensitive varnish W2 serving as a cladding layer forming material was prepared.

<Preparation of core forming material>
Similarly, 80 parts of a solid polyfunctional aliphatic epoxy resin (EHPE3150, manufactured by Daicel), 20 parts of a solid hydrogenated bisphenol A type epoxy resin (YX-8040, manufactured by Mitsubishi Chemical) under light-shielding conditions, photoacid generation Agent (WPI-116, manufactured by Wako Pure Chemical Industries, Ltd.) 1.0 part, hindered phenol antioxidant (Songnox 1010, manufactured by Kyodo Yakuhin Co., Ltd.) 0.5 part, phosphite ester antioxidant (HCA, Sanko) 0.5 parts) is mixed with 40 parts of ethyl lactate [manufactured by Showa Denko Co., Ltd., water content 80 ppm (0.0080 wt%)] and stirred to complete dissolution under heating at 85 ° C., then room temperature After cooling to (25 ° C.), a photosensitive varnish W1 serving as a core forming material was prepared by heating and pressure filtration using a membrane filter having a diameter of 1.0 μm. When the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 0.02% by weight.

(Preparation of underclad layer)
The obtained clad varnish W2 was applied on the back surface of the FPC base material having a total thickness of 22 μm using a spin coater, and the solvent was dried (130 ° C. × 10 minutes) on a hot plate, and then 5000 mJ / cm. ² (I-line filter) mask pattern exposure was performed. Then, pre-baking at 130 ° C. × 10 minutes, developing in γ-butyrolactone (at room temperature, 3 minutes), washing with water, and drying water on a hot plate (120 ° C. × 10 minutes) in sequence, An underclad layer (thickness: 15 μm) was obtained.

<Fabrication of core>
Next, the core varnish W1 was coated on the obtained underclad layer by a spin coater, and the solvent was dried (130 ° C. × 5 minutes) on a hot plate. The resulting uncured core layer (film or film) was subjected to mask pattern exposure of 9000 mJ / cm ² (I-line filter) and pre-baked at 130 ° C. for 10 minutes. Thereafter, development in γ-butyrolactone (at room temperature for 4 minutes), washing with water, and drying of moisture on a hot plate (120 ° C. × 10 minutes) in order are performed on the undercladding layer to form a core with a predetermined pattern (Thickness: 50 μm) was obtained.

[Example 2]
In the “adjustment of the core-forming material”, an optical waveguide was prepared in the same manner as in Example 1 except that cyclohexanone [dehydration treatment, water content after dehydration treatment: 80 ppm (0.008 wt%)] was used. Created the core. In addition, when the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 0.02% by weight.

[Example 3]
In the “adjustment of core forming material”, propylene glycol monomethyl ether acetate [dehydration treatment, moisture content after dehydration treatment 120 ppm (0.012 wt%)] was used in the same manner as in Example 1 above. An optical waveguide core was created. In addition, when the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 0.03% by weight.

[Comparative Example 1]
In the “adjustment of core forming material”, an optical waveguide core was prepared in the same manner as in Example 1 except that ethyl lactate (water content 1.1% by weight) was used as a solvent. In addition, when the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 0.6% by weight.

[Comparative Example 2]
An optical waveguide core was prepared in the same manner as in Example 1 above, except that cyclohexanone (water content 1.1% by weight) was used as a solvent in the “adjustment of core forming material”. In addition, when the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 0.6% by weight.

[Comparative Example 3]
An optical waveguide core was prepared in the same manner as in Example 1 above, except that propylene glycol monomethyl ether acetate (water content 1.6% by weight) was used as a solvent in the “adjustment of core forming material”. In addition, when the varnish W1 after adjustment was analyzed by Karl Fischer moisture titration, the moisture content X was 1.0% by weight.

<Aging stability test of core forming material>
The varnish W1 of each example and each comparative example was measured for viscosity using an E-type viscometer (RE-80M manufactured by Toki Sangyo Co., Ltd.) immediately after its production, and this was used as the initial viscosity Bi. Further, the varnish W1 was stored at room temperature (20 ° C.) for 120 hours, and then the viscosity was measured. This is the viscosity Bs after time. Here, the rate of increase in viscosity with time of the varnish W1 was calculated by the following formula (1).
Viscosity increase rate with time ΔB (%) = (viscosity after aging Bs−initial viscosity Bi) / initial viscosity Bi × 100 (1)
The results are shown in “Table 1” below. Moreover, evaluation was described with the rate of increase in viscosity over time (%) as “◯” when the viscosity was 105% or less, and “X” when the viscosity was over 105%.

  From the above “Table 1”, the water content Y of the solvent used exceeds 1.0% by weight, and the water content X of the varnish (liquid resin composition) after adjustment exceeds 0.5% by weight. It was found that the liquid photosensitive resin composition of No. 3 increased in viscosity over time during storage or application, and caused problems when the core (layer) was wet coated. Also, the thickness of the obtained optical waveguide core tended to be thicker than the design value. On the other hand, the liquid photosensitive resin composition for forming an optical waveguide core of Examples 1 to 3 can be applied with a predetermined thickness even in wet coating of the core (layer), and the obtained optical waveguide core The thickness was also as designed.

<Evaluation of coatability of core>
In the “core preparation” step, the surface state of the coating layer (film) after coating the core varnish W1 by spin coating and drying (130 ° C. × 5 minutes) is measured for each sample using an optical microscope. And observed. In the coating layers (films) of Examples 1 to 3, it was confirmed that a uniform film surface with no unevenness was obtained. On the other hand, the coating layer (film | membrane) of Comparative Examples 1-3 showed some surface roughness.

<Evaluation of pattern formability of core forming material>
The pattern core obtained in the “preparation of core” step was observed for each sample using an optical microscope. It was confirmed that the cores (cured bodies) of the optical waveguides of Examples 1 to 3 had a sharp shape with high rectangularity (sharp edges or corners) as designed. On the other hand, in the coating layers (films) of Comparative Examples 1 to 3, the edges or corners of the core pattern tended to be slightly broad.

  The liquid photosensitive resin composition for forming an optical waveguide core of the present invention is particularly useful as a material for forming an optical waveguide core for a flexible printed wiring board for optical signal transmission. And the optical waveguide produced using the said liquid photosensitive resin composition for optical waveguide core formation is used for the said flexible printed wiring board.

Claims (6)

Containing the following components (A) ~ (E), the moisture content X in the total liquid resin composition after mixing each component state, and are 0.005 wt% to 0.5 wt% or less, the following components (C ) and the addition ratio of (D), by weight, (C) :( D) = 1: 3~3: 1 der Rukoto waveguide core forming liquid photosensitive resin composition characterized.
(A) Cationic polymerizable compound (B) Photoacid generator (C) Primary antioxidant comprising a hindered phenol compound (D) Secondary antioxidant comprising a phosphite compound (E) solvent   2. The liquid photosensitive resin composition for forming an optical waveguide core according to claim 1, wherein (A) the cationic polymerizable compound is at least one selected from the group consisting of an epoxy compound, an oxetane compound and an episulfide compound.   3. The liquid photosensitive resin composition for forming an optical waveguide core according to claim 1, wherein the photoacid generator is an onium salt compound.   The liquid photosensitive resin for forming an optical waveguide core according to any one of claims 1 to 3, wherein the solvent has a water content Y of 0.001 wt% or more and 1.0 wt% or less. Composition.   The core of the optical waveguide is formed of a cured product obtained by irradiating and curing the liquid photosensitive resin composition for forming an optical waveguide core according to any one of claims 1 to 4 with ultraviolet rays. Optical waveguide.   A flexible printed wiring board comprising the optical waveguide according to claim 5.