JP2015206933A - Liquid photosensitive resin composition for forming optical waveguide core, and optical waveguide, flexible printed wiring board and touch sensor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid photosensitive resin composition for forming an optical waveguide core, which has both of a high absorptivity to light at a wavelength of 300 to 500 nm used for exposure of the photosensitive resin and a low absorptivity to light at a wavelength near 850 nm used for optical signals, and an optical waveguide, a flexible printed wiring board and a touch sensor using the above resin composition.SOLUTION: An optical waveguide is formed by using the following photosensitive resin composition as a material for forming an optical waveguide core. The composition comprises a cationic polymerizable compound, a photoacid generator, and a photosensitizer, in which the photosensitizer is a compound showing a change rate ΔG of Gibbs free energy of -41.86 kJ/mol or less and having a light absorption wavelength in a wavelength range from 300 to 500 nm.

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, a flexible printed wiring board including the optical waveguide, and a touch sensor.

  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, an optical touch sensor, or the like. Is used. The core is formed by applying a liquid resin composition (varnish) obtained by adding a solvent to the resin composition, and using ultraviolet light (UV) or the like through a photomask having an opening having a desired pattern shape. “Photolithography” is used in which actinic rays are irradiated to cure the irradiated area, 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. For the purpose of imparting photosensitivity (photocurability) to the material forming the cured body, a photoacid generator (photocation polymerization initiator) or the like is appropriately blended and cured (patterning using the photolithography). ) Is an actinic ray such as I-ray (ultraviolet light having a wavelength of 365 nm).

  Photoacid generator (photocation polymerization initiator) used in a liquid photosensitive resin composition (hereinafter referred to as “liquid photosensitive resin composition for forming an optical waveguide core”) used for forming the core of an optical waveguide as described above ), In the case of using a cationically polymerizable compound as a resin, in consideration of patterning properties such as accuracy (fineness and sharpness of edges) and stability of a molded shape by photocuring (photolithography), A sulfonium salt-based photocationic polymerization initiator having a cationic skeleton having a wide π-conjugated system (for example, a triphenylsulfonium salt-based photoacid generator) is used.

  However, when the above-described sulfonium salt photoacid generator is used as a photopolymerization initiator of a cationic polymerizable compound, there are the following problems. That is, in the sulfonium salt photoacid generator, the wide π-conjugated skeleton as described above is deteriorated (colored) by a by-product (π-conjugated expansion factor) generated by photolysis during photoacid generation. Originally, the light absorption band which was originally included only in the short wavelength (ultraviolet) band is expanded (broadened) to the long wavelength (infrared) band. Therefore, in an optical signal transmission optical waveguide that uses near-infrared light having a wavelength of about 850 nm for transmission of an optical signal or the like in the core, a part of the optical signal is absorbed and the optical propagation loss in the optical waveguide increases. There was a problem of doing.

  Accordingly, the present inventors use an iodonium salt-based (diphenyliodonium salt-based) photoacid generator as a photopolymerization initiator for a cationically polymerizable compound in place of the sulfonium salt-based color causing the core. Has already been made (Japanese Patent Application No. 2013-231730). According to this proposal, a flexible printed wiring board for optical signal transmission that has high transparency (low light propagation loss) without coloring the core of the optical waveguide even when cured by irradiation with actinic rays (ultraviolet rays), etc. An optical waveguide suitable for the above can be produced.

JP 2010-230944 A JP2011-237645A

  By the way, the photosensitive resin composition containing the iodonium salt-based photocationic polymerization initiator as described above has a coloring by-product as in the sulfonium salt-based upon photopolymerization curing (photoacid generation). Although an object (cause of light propagation loss) is not generated, it has almost no absorption band with respect to the exposure wavelength (I-line: ultraviolet light having a wavelength of 365 nm) mainly used in this type of photopolymerization curing process, and exposure light It has the feature that the sensitivity to is low. Therefore, in order to obtain sufficient photocuring of the photosensitive resin composition, it is necessary to irradiate ultraviolet rays having a wider wavelength range and stronger than before, and thus the production efficiency of the optical waveguide is improved compared to the conventional case. There was a problem of being lowered.

  Therefore, from the viewpoint of optical waveguide production, it can be manufactured using existing equipment that balances optical waveguide performance (low propagation loss with respect to signal light) and productivity (high sensitivity with respect to exposure light). Development of photosensitive materials is desired.

  The present invention has been made in view of such circumstances, and has a high absorption rate for light having a wavelength of 300 to 500 nm used for exposure of a photosensitive resin, and a low absorption rate for light having a wavelength of about 850 nm used for an optical signal. An object of the present invention is to provide a liquid photosensitive resin composition for forming an optical waveguide core that combines the above, an optical waveguide using the same, a flexible printed wiring board, and a touch sensor.

〔式（１）において、Ｅ(1/2)oxは光増感剤の酸化電位を、Ｅ(1/2)redは光酸発生剤の還元電位を、Ｅ(p)＊は光増感剤の励起エネルギーを示す。〕 In order to achieve the above object, the present invention includes a cationically polymerizable compound, a photoacid generator, and a photosensitizer, wherein the photosensitizer is represented by the following formula (1). A liquid photosensitive resin composition for forming an optical waveguide core, which is a compound having a free energy change ΔG of −41.86 kJ / mol or less and a light absorption wavelength in a wavelength range of 300 to 500 nm, is a first gist. .

[In Formula (1), E (1/2) ox is the oxidation potential of the photosensitizer, E (1/2) red is the reduction potential of the photoacid generator, and E (p) * is the photosensitization. The excitation energy of the agent is shown. ]

  In the present invention, the core of the optical waveguide is formed of a cured body obtained by irradiating the liquid photosensitive resin composition for forming an optical waveguide core according to the first aspect with ultraviolet rays in a wavelength range of 300 to 500 nm. Let the optical waveguide currently made be the 2nd summary.

  And this invention makes a flexible printed wiring board provided with the optical waveguide of the said 2nd summary a 3rd summary, and makes a touch sensor provided with the optical waveguide of the said 2nd summary a 4th summary.

  The inventors of the present invention have made extensive studies in order to obtain a photosensitive resin composition that achieves both low loss of signal propagation light and high sensitivity during pattern exposure using photolithography. As a result, a photosensitizer that satisfies specific conditions and has the property of easily transmitting photoexcitation energy to the photoacid generator is referred to as a photoacid generator of the above type (iodonium salt-based photocation polymerization initiator). It has been found that the intended purpose can be achieved when used in combination, and the present invention has been achieved.

〔式（１）において、Ｅ(1/2)oxは光増感剤の酸化電位を、Ｅ(1/2)redは光酸発生剤の還元電位を、Ｅ(p)＊は光増感剤の励起エネルギーを示す。〕 Thus, the liquid photosensitive resin composition for forming an optical waveguide core of the present invention has a Gibbs free energy change ΔG represented by the following formula (1) of −41.86 kJ / mol or less and a wavelength of 300 to 500 nm. The photosensitizer which has a light absorption wavelength in the range is contained.

[In Formula (1), E (1/2) ox is the oxidation potential of the photosensitizer, E (1/2) red is the reduction potential of the photoacid generator, and E (p) * is the photosensitization. The excitation energy of the agent is shown. ]

  Therefore, when the liquid photosensitive resin composition for forming an optical waveguide core is irradiated with actinic rays such as ultraviolet rays (UV), the photosensitizer absorbs ultraviolet rays having a wavelength of 300 to 500 nm, and the excitation energy thereof is The photoacid generator is transmitted to the photoacid generator, and a cationic polymerization reaction by the photoacid generator and its catalytic action is efficiently generated. Therefore, when producing an optical waveguide by a photocuring process such as photolithography using the liquid photosensitive resin composition for forming an optical waveguide core, the exposure time due to the ultraviolet rays and the like is shortened, and after curing, A cured product (optical waveguide core) having high transparency and low light propagation loss can be obtained. In addition, if the liquid photosensitive resin composition for forming an optical waveguide core of the present invention is used, there is no lot-to-lot fluctuation in performance, and a high-quality optical waveguide with uniform dimensions and quality can be efficiently obtained in a short processing time, It becomes possible to manufacture at low cost.

  In addition, the photosensitizer used in the liquid photosensitive resin composition for forming an optical waveguide core is preferably a photosensitizer having at least one peak in the range of 300 to 500 nm among the maximum value in the light absorption spectrum. Can be adopted. Thereby, ultraviolet rays such as I-line (wavelength 365 nm) used in a normal photolithography process are absorbed more efficiently, and the curing efficiency of the photocuring process can be further increased.

  Further, an optical waveguide formed of a cured body obtained by irradiating the liquid photosensitive resin composition for forming an optical waveguide core with ultraviolet rays in a wavelength range of 300 to 500 nm and cured, a flexible printed wiring board including the optical waveguide, and a touch The sensor also has few troubles caused by the optical waveguide, and can construct a highly reliable device or system.

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

〔式（１）において、Ｅ(1/2)oxは光増感剤の酸化電位を、Ｅ(1/2)redは光酸発生剤の還元電位を、Ｅ(p)＊は光増感剤の励起エネルギーを示す。〕
以下、各種成分について順に説明する。 << 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 ) Containing a photosensitizer and the like. (C) The photosensitizer has a Gibbs free energy change ΔG represented by the following formula (1) of −41.86 kJ / mol or less and a wavelength of 300 It is a compound having a light absorption wavelength in a range of ˜500 nm.

[In Formula (1), E (1/2) ox is the oxidation potential of the photosensitizer, E (1/2) red is the reduction potential of the photoacid generator, and E (p) * is the photosensitization. The excitation energy of the agent is shown. ]
Hereinafter, various components will be described in order.

<Cationically polymerizable compound>
Examples of the cationic polymerizable compound include an epoxy compound, an oxetane compound, an episulfide compound, a vinyl ether compound, and the like.
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.).

  Furthermore, a vinyl ether compound can be used as the cationic polymerizable compound. Examples of vinyl ether compounds include ethyl vinyl ether, isobutyl vinyl ether, hydroxybutyl vinyl ether, butanediol divinyl ether, cyclohexyl vinyl ether, N-butyl vinyl ether, tert.-butyl vinyl ether, triethylene glycol divinyl ether octadecyl vinyl ether, cyclohexane dimethanol divinyl ether, diethylene glycol divinyl ether. Examples include vinyl ether and cyclohexanedimethanol monovinyl ether (both manufactured by BASF Japan Ltd.).

<Photo acid generator> (photo cationic polymerization initiator)
The photoacid generator is used for imparting curability to the photosensitive resin composition by light irradiation (for example, ultraviolet irradiation). As the photoacid generator, sulfonium salt-based and iodonium salt-based onium salt-based photoacid generators (photocation polymerization initiators) can be used. From the viewpoint of “coloring of the core”, an iodonium salt-based photocationic polymerization initiator is preferably used.

  Specifically, diphenyliodonium salt light such as WPI-116, WPI-113, WPI-169, WPI-170, WPI-116 (all manufactured by Wako Pure Chemical Industries, Ltd.) and IRGACURE205 (BASF Japan). Examples thereof include cationic polymerization initiators.

  The content of the photoacid generator is preferably set to 0.1 to 3 parts by weight, more preferably 0.5 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.

〔式（１）において、Ｅ(1/2)oxは光増感剤の酸化電位を、Ｅ(1/2)redは光酸発生剤の還元電位を、Ｅ(p)＊は光増感剤の励起エネルギーを示す。〕 <Photosensitizer>
The said photosensitizer increases the sensitivity of the photocuring reaction by ultraviolet irradiation with respect to the photosensitive resin composition. As described above, this photosensitizer has a Gibbs free energy change ΔG represented by the following formula (1) of −41.86 kJ / mol or less and absorbs light in a wavelength range of 300 to 500 nm. A compound having a wavelength. The Gibbs free energy change ΔG of the photosensitizer is preferably −41.86 kJ / mol or less, more preferably −60 kJ / mol or less, and even more preferably −80 kJ / mol or less. It is desirable that the compound has at least one peak in the range of 300 to 500 nm among the maximum values in the light absorption spectrum.

[In Formula (1), E (1/2) ox is the oxidation potential of the photosensitizer, E (1/2) red is the reduction potential of the photoacid generator, and E (p) * is the photosensitization. The excitation energy of the agent is shown. ]

  The above formula (1) is known as the Rehm-Weller equation, and when the “Gibbs free energy change ΔG” when combined with a photoacid generator is −41.86 kJ / mol or less, a system of these combinations Is sensitive to photosensitization reaction (high sensitivity) and is considered to be a system suitable for photocuring. (Reference: Zaza Gomurashvili and James V. Crivello, Journal of Polymer Science Part A: Polymer Chemistry, Volume 39, Issue 8, pages 1187-1197, 15 April (2001), “Phenothiazine photosensitizers for onium salt photoinitiated cyclic polymerization”)

  As a photosensitizer used for the photosensitive resin composition of the present invention, for example, when combined with a diphenyliodonium salt photocationic polymerization initiator (WPI-116 or the like), thioxaton (ΔG = about −93.7 kJ / mol, maximum of light absorption wavelength = 380 nm), anthracene (ΔG = about −193.8 kJ / mol, maximum of light absorption wavelength = 241 nm, 357 nm, 376 nm), phenothiazine (ΔG = about −162.0 kJ / mol, light absorption) Wavelength maxima = 250 nm, 318 nm) and perylene (ΔG = about −170.7 kJ / mol, optical absorption wavelength maxima = 436 nm, 460 nm) and the like can be used. Incidentally, acetophenone (ΔG = about −8.8 kJ / mol, maximum of light absorption wavelength = 246 nm) and benzophenone (ΔG = about −10.0 kJ / mol, light absorption wavelength) commonly used as a photosensitizer. Is not suitable for combination with the diphenyliodonium salt-based photocationic polymerization initiator.

  The content of the suitable photosensitizer is preferably set to 0.01 to 3.0 parts by weight, more preferably 0.05 to 100 parts by weight of the solid content of the varnish (liquid resin composition). -1.0 part 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 abnormal shape during patterning of the core. There is also a tendency for required physical properties such as propagation loss to deteriorate.

<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.

<Liquid photosensitive resin composition>
The liquid photosensitive resin composition for forming an optical waveguide core of the present invention comprises the components (A) a cationic polymerizable compound, (B) a photoacid generator, (C) a photosensitizer and the above components of the photosensitive resin composition. Preparing a “photosensitive varnish” that is a material for forming the core of the optical waveguide of the present invention by stirring and mixing a solvent and, if necessary, other additives in a predetermined mixing ratio. Can do. Moreover, in order to prepare the said photosensitive resin composition as a varnish for coating, you may stir and dissolve in a solvent, heating (for example, about 60-90 degreeC). Although the usage-amount of the said solvent (organic solvent) is adjusted suitably, it sets to 20-80 weight part with respect to 100 weight part of resin components (photopolymerizable resin) of the photosensitive resin composition, for example. It is preferably 30 to 50 parts by weight. That is, if the amount of solvent used is too small, the viscosity becomes high when prepared as a coating varnish, and the coating property tends to decrease. If the amount of solvent used is too large, the coating varnish is used. Therefore, it tends to be difficult to form a thick film.

<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 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 within a wavelength range of 300 to 500 nm is performed. Examples of the ultraviolet light source in the ultraviolet irradiation include a low pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, an ultraviolet LED light source, and an excimer laser. 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 photosensitive varnish W2 for forming the clad layer include ethyl lactate, methyl ethyl ketone, cyclohexanone, ethyl lactate, 2-butanone, N, N-dimethylacetamide, diglyme, diethylene glycol methyl ethyl ether. Propylene glycol methyl 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 for an optical waveguide for a flexible printed wiring board for optical signal transmission and for an optical touch sensor of 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 filtered with heating and pressure 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) 1.0 part, photosensitizer (2-isopropylthioxanthone, manufactured by Kanto Chemical Co.) 0.1 part, ethyl lactate (Showa Denko Co., Ltd.) 40 parts The mixture is mixed and completely dissolved under heating at 85 ° C., and then cooled to room temperature (25 ° C.), followed by heating and pressure filtration using a membrane filter having a diameter of 1.0 μm, thereby providing a photosensitivity as a core forming material. Varnish W1 was prepared. The Gibbs free energy change ΔG of the photosensitizer (2-isopropylthioxanthone) in this compounding system is −93.7 kJ / mol, and the maximum light absorption wavelength (peak) of the photosensitizer is 380 nm (ie, 2-isopropylthioxanthone meets the set conditions of the present invention).

(Preparation of underclad layer)
The photosensitive varnish W2 for the cladding layer was applied on the back surface of the FPC base material having a total thickness of 22 μm with a spin coater, and the solvent was dried (130 ° C. × 10 minutes) on a hot plate, and then 5000 mJ / Mask pattern exposure of cm ² (I-line filter) 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 photosensitive varnish W1 was coated on the obtained underclad layer with a spin coater, and the solvent was dried on a hot plate (130 ° C. × 5 minutes). The obtained uncured core layer (film or film) is irradiated with ultraviolet light having a wavelength of 365 nm (I-line filter) through a line and space pattern mask to 1000 to 20000 mJ / cm ² and 1000 mJ / cm 2. Exposure is performed in ² steps (1000, 2000, 3000, ... 18000, 19000, 20000 total 20 exposure conditions), and prebaked at 130 ° C for 10 minutes for each sample obtained for each exposure. Was given. Thereafter, each sample was developed in γ-butyrolactone (at room temperature for 4 minutes), washed with water, and dried on a hot plate (120 ° C. × 10 minutes) in order, thereby forming a longitudinal layer on the undercladding layer. A set (20 sets) of samples in which a plurality of cores having a predetermined linear pattern (thickness: 50 μm, design core width: 50 μm) extending in the direction was formed.

[Example 2]
In the “adjustment of the core forming material”, an optical waveguide core was prepared in the same manner as in Example 1 except that 0.1 part of anthracene (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a photosensitizer. . The Gibbs free energy change ΔG of the photosensitizer (anthracene) in this compounding system is −193.8 kJ / mol, and the maximum light absorption wavelength (peak) of the photosensitizer is 376 nm (that is, anthracene is This matches the setting conditions of the present invention).

[Example 3]
In the “adjustment of core-forming material”, an optical waveguide core was prepared in the same manner as in Example 1 except that 0.1 part of phenothiazine (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a photosensitizer. . The Gibbs free energy change ΔG of the photosensitizer (phenothiazine) in this compounding system is −162.0 kJ / mol, and the maximum light absorption wavelength (peak) of the photosensitizer is 318 nm (that is, phenothiazine is This matches the setting conditions of the present invention).

[Comparative Example 1]
In the “adjustment of core forming material”, a core of an optical waveguide was prepared in the same manner as in Example 1 except that no photosensitizer was used. Although exposure was performed by irradiating with ultraviolet rays in increments of 1000 mJ / cm ² (total 20 exposure conditions) up to 20000 mJ / cm ² , sufficient curing could not be obtained.

[Comparative Example 2]
In the “adjustment of the core forming material”, an optical waveguide core was prepared in the same manner as in Example 1 except that 0.1 part of acetophenone (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a photosensitizer. . The Gibbs free energy change ΔG of the photosensitizer (acetophenone) in this compounding system is −8.8 kJ / mol, and the maximum light absorption wavelength (peak) of the photosensitizer is 246 nm (that is, acetophenone is , ΔG and the maximum light absorption wavelength do not meet the setting conditions of the present invention. In addition, exposure was performed by irradiating with ultraviolet rays in increments of 1000 mJ / cm ² up to 20000 mJ / cm ² (total 20 exposure conditions), but sufficient curing was not obtained.

<Evaluation of pattern formability of core forming material>
The optical waveguide samples (underclad layer + multiple cores, each exposure amount) obtained in each example and each comparative example were observed using an optical microscope, and a cured body (core) pattern (each viewed from above) The one whose core line width was closest to the design value (50 μm) was determined as the “optimal exposure amount” (mJ / cm ² ) in the blending system. In addition, even if exposure was performed by irradiating ultraviolet rays up to 20000 mJ / cm ² , those that could not obtain sufficient curing were described as “20,000 or more”.

<Evaluation of optical propagation loss>
Next, among the above Examples and Comparative Examples, a sample [sample corresponding to “optimum exposure amount” (under clad layer + core)] obtained with sufficient curing was used. In the same manner as in “Production”, an over clad layer covering the core was formed on the core (layer).
(Prism coupler method)
Light having a wavelength of 850 nm was incident on the core of a test sample having an obtained three-layer structure (under clad layer + core + over clad layer) by prism coupling and propagated through the core. Then, changing the propagation length, measuring the light intensity at that length with an optical measurement system (Optical Multi Power Meter Q8221, manufactured by Advantest), plotting the optical loss against the propagation length, performing linear approximation, The light propagation loss (dB / cm) of each sample (the “optimum exposure dose” equivalent product) was calculated from the slope of the straight line.

The results of the above test are shown in “Table 1” below.

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. It was also found that the performance (light propagation loss) was good and the transparency was high (no coloration). On the other hand, the cores (cured bodies) of Comparative Examples 1 and ² were not sufficiently cured by the ultraviolet irradiation of 20000 mJ / cm ² , and the light propagation loss could not be measured. From this, it is estimated that Comparative Examples 1 and 2 have low production efficiency of the photocuring process and the entire manufacturing process using the photocuring process, and increase the manufacturing cost.

  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 or an optical touch sensor. 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, an optical touch sensor, etc.

Claims (7)

A cationic polymerizable compound, a photoacid generator, and a photosensitizer are included. The photosensitizer has a Gibbs free energy change ΔG represented by the following formula (1) of −41.86 kJ / mol or less. And the liquid photosensitive resin composition for optical waveguide core formation characterized by being a compound which has a light absorption wavelength in the wavelength range of 300-500 nm.

[In Formula (1), E (1/2) ox is the oxidation potential of the photosensitizer, E (1/2) red is the reduction potential of the photoacid generator, and E (p) * is the photosensitization. The excitation energy of the agent is shown. ]   2. The liquid photosensitive resin composition for forming an optical waveguide core according to claim 1, wherein at least one peak in the light absorption spectrum of the photosensitizer is in the range of 300 to 500 nm.   3. The liquid photosensitive resin composition for forming an optical waveguide core according to claim 1, wherein the cationic polymerizable compound is at least one selected from the group consisting of an epoxy compound, an oxetane compound, an episulfide compound, and a vinyl ether compound.   The liquid photosensitive resin composition for forming an optical waveguide core according to any one of claims 1 to 3, wherein the photoacid generator is an iodonium salt-based photocationic polymerization initiator.   The core of the optical waveguide is a cured product obtained by irradiating the liquid photosensitive resin composition for forming an optical waveguide core according to any one of claims 1 to 4 with ultraviolet rays having a wavelength in the range of 300 to 500 nm. An optical waveguide characterized by being formed.   A flexible printed wiring board comprising the optical waveguide according to claim 5.   A touch sensor comprising the optical waveguide according to claim 5.