wiring board

Abstract

The purpose of the present invention is to provide a wiring board on which an opaque wiring electrode is less visible. The wiring board comprises a transparent substrate, an opaque wiring electrode patterned on at least one surface of the transparent substrate, and a transparent protective layer formed on the transparent substrate and the opaque wiring electrode. The part where the opaque wiring electrode is formed has an internal reflectivity R1 of 0.1% or less, which is measured from the transparent protective layer of the wiring board, and a refractive index n1 of the transparent substrate and a refractive index n2 of the transparent protective layer satisfy the following formula (1). 0.97 ≤ n2 / n1 ≤ 1.03 (1)

Description

[Technical Field]

[0001] The present invention relates to a wiring board. [Background technology]

[0002] In recent years, touch panels have become widely used as an input device. A touch panel consists of a display unit such as a liquid crystal panel and a touch panel sensor that detects information input at a specific position. Touch panel types are broadly classified into resistive, capacitive, optical, electromagnetic induction, and ultrasonic types depending on how they detect the input position. Of these, capacitive touch panels are widely used due to their excellent design, simple structure, and excellent functionality.

[0003] A capacitive touch panel sensor has a second electrode that is perpendicular to a first electrode via an insulating layer, and outputs a signal representing the contact position obtained by applying a voltage to the electrodes on the touch panel surface and detecting a change in capacitance when a conductive object such as a finger touches the electrode. Known examples of capacitive touch panel sensors include a structure in which electrodes and external connection terminals are formed on a pair of opposing transparent substrates, and a structure in which electrodes and external connection terminals are formed on both sides of a single transparent substrate.

[0004] Transparent wiring electrodes have generally been used as wiring electrodes in touch panel sensors in order to make them less visible, but in recent years, opaque wiring electrodes made of metallic materials have become more common due to increased sensitivity and larger screen sizes. Touch panel sensors with opaque wiring electrodes made of metallic materials have had the problem of the opaque wiring electrodes being visible due to their metallic luster. As a method for making opaque wiring electrodes less visible, a method has been proposed in which an opaque wiring electrode is formed on a transparent substrate, and then a black positive-type photosensitive composition is applied, and the positive-type photosensitive composition is exposed and developed using the opaque wiring electrode as a mask, thereby forming a light-shielding layer on the opaque wiring electrode (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 168325 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology of forming a light-shielding layer on the opaque wiring electrode and suppressing the metallic luster of the opaque wiring electrode portion, as described in Patent Document 1, alone had the problem that the opaque wiring electrode was visible due to the difference in reflectance between the opaque wiring electrode on which the light-shielding layer was formed and the transparent substrate.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a wiring board in which opaque wiring electrodes are less visible. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention mainly has the following configuration.

[0009] A wiring substrate having a transparent substrate, an opaque wiring electrode patterned on at least one surface of the transparent substrate, and a transparent protective layer formed on the transparent substrate and the opaque wiring electrode, wherein the internal reflectance R1 at the opaque wiring electrode formation portion measured from the transparent protective layer side of the wiring substrate is 0.1% or less, and the refractive index n1 of the transparent substrate and the refractive index n2 of the transparent protective layer satisfy the following formula (1): 0.97≦n2 / n1≦1.03 (1) [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a wiring board in which the opaque wiring electrodes are difficult to see. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a schematic diagram illustrating an example of a wiring board according to the present invention. [Figure 2] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing an opaque wiring electrode formation region of the first reflectance evaluation substrate. [Figure 4] FIG. 2 is a schematic diagram showing an area where an opaque wiring electrode is not formed on the first reflectance evaluation substrate. [Figure 5] FIG. 2 is a schematic diagram showing a second reflectance evaluation substrate. [Figure 6] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 7] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 8] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 9] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 10] FIG. 1 is a schematic diagram of a mask used in the examples. [Figure 11] FIG. 1 is a schematic diagram of a mesh pattern of a mask used in an example. [Figure 12] FIG. 2 is a schematic view showing another example of the wiring board of the present invention. [Figure 13] FIG. 1 is a schematic diagram of a mesh pattern of a mask used in an example. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the wiring board of the present invention will be described in detail with reference to the drawings. Note that the drawings are schematic. Furthermore, the present invention is not limited to the embodiments described below.

[0013] 1 is a schematic diagram showing an example of a wiring board 5 of the present invention. The wiring board 5 has a transparent substrate 1, an opaque wiring electrode 2 patterned on at least one surface of the transparent substrate 1, and a transparent protective layer 4 formed on the transparent substrate 1 and the opaque wiring electrode 2. Each of these will be described below.

[0014] <Transparent substrate> The transparent substrate is transparent in the visible light region. In this specification, "transparent" means that the transmittance at a wavelength of 550 nm is 80% or more. The transmittance at a wavelength of 550 nm can be measured using an ultraviolet-visible spectrophotometer (U-3310, manufactured by Hitachi High-Technologies Corporation).

[0015] Examples of transparent substrates include inflexible and flexible transparent substrates. Examples of inflexible transparent substrates include quartz glass, soda glass, chemically strengthened glass, Pyrex (registered trademark) glass, synthetic quartz plates, epoxy resin substrates, polyetherimide resin substrates, polyetherketone resin substrates, and polysulfone resin substrates. Examples of flexible transparent substrates include transparent films and optical resin plates made of resins such as polyethylene terephthalate film (hereinafter referred to as "PET film"), cycloolefin polymer film, polyimide film, polyester film, and aramid film. A plurality of these may be used in layers; for example, multiple transparent substrates may be bonded together using an adhesive layer.

[0016] The surface of the transparent substrate preferably has an inorganic film with a thickness of 5 to 50 nm.

[0017] Examples of inorganic films include silicon dioxide and niobium pentoxide. By having an inorganic film on a transparent substrate, the adhesion between the transparent substrate and the transparent protective layer can be improved. By making the thickness of the inorganic film 50 nm or less, the contribution of the inorganic film to reflection can be minimized. The thickness of the inorganic film is more preferably 30 nm or less. On the other hand, from the viewpoint of adhesion, the thickness of the inorganic film is preferably 5 nm or more.

[0018] The thickness of the transparent substrate is appropriately selected depending on the material, as long as it can stably support the opaque wiring electrode and has the aforementioned transparency. For example, from the viewpoint of more stably supporting the opaque wiring electrode, a thickness of 300 μm or more is preferable for an inflexible transparent substrate such as glass, and a thickness of 25 μm or more is preferable for a flexible transparent substrate such as PET film. On the other hand, from the viewpoint of improving the transparency of exposure light, a thickness of 1500 μm or less is preferable for an inflexible transparent substrate such as glass, and a thickness of 300 μm or less is preferable for a flexible transparent substrate such as PET film.

[0019] <Opaque wiring electrode> The opaque wiring electrode is patterned on at least one surface of the transparent substrate. Here, "opaque" refers to a material having a transmittance of 25% or less at a wavelength of 550 nm.

[0020] Examples of materials constituting the opaque wiring electrode include metals such as silver, gold, copper, platinum, lead, tin, nickel, aluminum, tungsten, molybdenum, chromium, titanium, and indium, as well as alloys thereof. Among these, silver, copper, and gold are preferred from the viewpoint of electrical conductivity. The opaque wiring electrode may also be formed by curing a conductive composition containing conductive particles. In this case, the conductive particles are preferably spherical, and the aforementioned metals and alloys can be used as the material.

[0021] The average particle size of the conductive particles is preferably 0.01 μm or more, more preferably 0.03 μm or more, 0.05 μm or more, or even 0.10 μm or more, from the viewpoint of improving the dispersibility of the conductive particles. On the other hand, from the viewpoint of sharpening the edges of the pattern of the opaque wiring electrode, the average particle size is preferably 1.5 μm or less, more preferably 1.0 μm or less. The average particle size of the conductive particles can be determined by observing the conductive particles at a magnification of 15,000 times using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), measuring the major axis length of each of 100 randomly selected conductive particles, and calculating the number average value.

[0022] The conductive composition preferably contains an alkali-soluble resin. By including the alkali-soluble resin, fine opaque wiring electrodes can be formed by patterning through development. Examples of alkali-soluble resins include resins having hydroxyl groups and / or carboxyl groups.

[0023] Examples of resins having a hydroxy group include novolac resins such as phenol novolac resins and cresol novolac resins having a phenolic hydroxy group, polymers of monomers having a hydroxy group, and copolymers of monomers having a hydroxy group with styrene, acrylonitrile, acrylic monomers, or the like.

[0024] Examples of monomers having a hydroxy group include monomers having a phenolic hydroxy group, such as 4-hydroxystyrene and hydroxyphenyl (meth)acrylate; and monomers having a non-phenolic hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and polyethylene glycol mono(meth)acrylate.

[0025] Examples of resins having a carboxyl group include carboxylic acid-modified epoxy resins, carboxylic acid-modified phenolic resins, polyamic acid resins, carboxylic acid-modified siloxane resins, polymers of monomers having a carboxyl group, and copolymers of monomers having a carboxyl group with styrene, acrylonitrile, acrylic monomers, etc.

[0026] Examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, and cinnamic acid.

[0027] Examples of resins having a hydroxy group and a carboxyl group include copolymers of a monomer having a hydroxy group and a monomer having a carboxyl group, and copolymers of a monomer having a hydroxy group, a monomer having a carboxyl group, and styrene, acrylonitrile, an acrylic monomer, etc. Two or more of these may be contained.

[0028] The conductive composition may contain a pigment and / or a dye. By including a pigment and / or a dye in the conductive composition, the metallic luster of the opaque wiring electrode can be suppressed, making the opaque wiring electrode less visible, without the need for a separate light-shielding layer, which will be described later. A light-shielding layer may also be provided, further suppressing the metallic luster of the opaque wiring electrode.

[0029] When no separate light-shielding layer is provided, the content of the pigment and / or dye in the conductive composition is preferably 0.5 to 2.5% by mass. From the viewpoint of further suppressing the metallic luster of the opaque wiring electrode, the content of the pigment and / or dye is preferably 0.5% by mass or more. On the other hand, from the viewpoint of improving conductivity, the content of the pigment and / or dye is preferably 2.5% by mass or less.

[0030] Examples of pigments include lactam pigments, perylene pigments, phthalocyanine pigments, isoindoline pigments, diaminoanthraquinone pigments, dioxazine pigments, indanthrone pigments, carbon black, and inorganic pigments.

[0031] Examples of dyes include ferrocene-based dyes, fluorenone-based dyes, perylene-based dyes, triphenylmethane-based dyes, coumarin-based dyes, diphenylamine-based dyes, quinacridone-based dyes, quinophthalone-based dyes, phthalocyanine-based dyes, and xanthene-based dyes.

[0032] The conductive composition is preferably a photosensitive conductive composition containing a photopolymerization initiator in addition to the conductive particles and alkali-soluble resin described above. By using the photosensitive conductive composition, it is possible to form a fine opaque wiring electrode by photolithography.

[0033] Examples of the photopolymerization initiator include 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyloxime)], 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, ethanone, 1-[9-ethyl-6-2(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), benzophenone, methyl o-benzoylbenzoate, 4,4'-bis(dimethylamino)benzophenone, 4,4'- Bis(diethylamino)benzophenone, 4,4'-dichlorobenzophenone, 4-benzoyl-4'-methyldiphenyl ketone, dibenzyl ketone, fluorenone, 2,2'-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, pt-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, benzil, benzil dimethyl ketal, benzil- β-Methoxyethyl acetal, benzoin, benzoin methyl ether, benzoin butyl ether, anthraquinone, 2-t-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, anthrone, benzanthrone, dibenzosuberone, methyleneanthrone, 4-azidobenzalacetophenone, 2,6-bis(p-azidobenzylidene)cyclohexanone, 6-bis(p-azidobenzylidene)-4-methylcyclohexanone, 1-phenyl-1,2-butanedione-2-(o-methoxycarbonyl)o Oxime, 1-phenyl-propanedione-2-(o-ethoxycarbonyl)oxime, 1-phenyl-propanedione-2-(o-benzoyl)oxime, 1,3-diphenyl-propanetrione-2-(o-ethoxycarbonyl)oxime, 1-phenyl-3-ethoxy-propanetrione-2-(o-benzoyl)oxime, Michler's ketone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, naphthalenesulfonyl chloride, quinolinesulfonyl chloride, N-phenylthioacridone, 4,Examples of suitable photoreducible dyes include 4'-azobisisobutyronitrile, diphenyl disulfide, benzthiazole disulfide, triphenylphosphine, camphorquinone, 2,4-diethylthioxanthone, isopropylthioxanthone, carbon tetrabromide, tribromophenyl sulfone, benzoin peroxide, eosin, and combinations of photoreducible dyes such as methylene blue with reducing agents such as ascorbic acid or triethanolamine.

[0034] The conductive composition may further contain, as necessary, a dispersant, a monomer having an unsaturated double bond, a photoacid generator, a thermal acid generator, a sensitizer, an adhesion improver, a surfactant, a heat curing agent, a polymerization inhibitor, etc.

[0035] Examples of the monomer having an unsaturated double bond include methyl acrylate, ethyl acrylate (hereinafter referred to as "EA"), acrylic acid (hereinafter referred to as "AA"), 2-ethylhexyl acrylate, n-butyl acrylate, i-butyl acrylate, i-propane acrylate, glycidyl acrylate, N-methoxymethyl acrylamide, N-ethoxymethyl acrylamide, Nn-butoxymethyl acrylamide, N-isobutoxymethyl acrylamide, butoxytriethylene glycol acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, 2-hydroxypropyl acrylate, acrylate, isodexyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methoxyethyl acrylate, methoxyethylene glycol acrylate, methoxydiethylene glycol acrylate, octafluoropentyl acrylate, phenoxyethyl acrylate, stearyl acrylate, trifluoroethyl acrylate, acrylamide, aminoethyl acrylate, phenyl acrylate, phenoxyethyl acrylate, 1-naphthyl acrylate, 2-naphthyl acrylate, thiophenol acrylate, benzyl mercaptan acrylate, allylated cyclohexyl diacrylate, 1,4-butanediol diacrylate, 1,Examples of the diacrylate include 3-butylene glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane tetraacrylate, glycerol diacrylate, methoxylated cyclohexyl diacrylate, neopentyl glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, bisphenol A diacrylate, bisphenol F diacrylate, diacrylate of a bisphenol A-ethylene oxide adduct, diacrylate of a bisphenol F-ethylene oxide adduct, or diacrylate of a bisphenol A-propylene oxide adduct, or compounds in which the acrylic group is substituted with a methacrylic group.

[0036] Examples of the pattern shape of the opaque wiring electrode include a mesh shape and a stripe shape. Among these, a mesh shape is preferred from the viewpoint of uniform conductivity of the pattern. The opaque wiring electrode is more preferably a metal mesh made of the above-mentioned metal and having a mesh-like pattern. Examples of the mesh shape include a lattice shape in which the unit shapes are triangular, rectangular, polygonal, or circular, or a combination of these unit shapes.

[0037] From the viewpoint of visibility, the area of ​​the portion where the opaque wiring electrode is formed is preferably 20% or less, more preferably 15% or less, of the transparent substrate. The opaque wiring electrode can be formed in two or more layers with a transparent protective layer interposed therebetween. By forming the opaque electrode in two layers, it is possible to reduce the area of ​​the portion where the opaque wiring electrode is formed.

[0038] From the viewpoint of electrical conductivity, the thickness of the opaque wiring electrode is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more, while from the viewpoint of forming fine wiring, the thickness of the opaque wiring electrode is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0039] The line width of the opaque wiring electrode is preferably 1 to 10 μm. When the line width of the opaque wiring electrode is 1 μm or more, the conductivity can be improved. The line width of the opaque wiring electrode is more preferably 1.5 μm or more, and even more preferably 2 μm or more. On the other hand, when the line width of the opaque wiring electrode is 10 μm or less, the opaque wiring electrode can be made less visible. The line width of the opaque wiring electrode is more preferably 7 μm or less, and even more preferably 6 μm or less. The line width of the opaque wiring electrode can be measured using an optical microscope (VHX-6000 manufactured by Keyence Corporation).

[0040] <Light blocking layer> As shown in FIG. 2, it is preferable to have a light-shielding layer 3 on the opaque wiring electrode 2. By having a light-shielding layer on the opaque wiring electrode, reflection due to the metallic luster of the opaque wiring electrode can be suppressed, making the opaque wiring electrode less visible. Examples of the light-shielding layer include black sputtered films of alloys such as nickel, titanium, and copper, plating, and cured films of resin compositions containing black pigments. Among these, a cured film of a resin composition containing a black pigment is preferable from the viewpoint of suppressing reflection in the region where the opaque wiring electrode is formed. Furthermore, the light-shielding layer may be conductive, and the conductivity of the opaque wiring electrode can be improved by having a light-shielding layer that is conductive.

[0041] The plating can be formed on the surface of the opaque wiring electrode, for example, by contacting the opaque wiring electrode with a hydrochloric acid solution containing palladium, tellurium, and / or compounds thereof. The hydrochloric acid solution containing palladium, tellurium, and / or compounds thereof preferably has a pH of 3 or less, more preferably 2 or less, from the viewpoint of effectively forming plating by oxidation-reduction reaction between the palladium and / or tellurium and the metal in the opaque wiring electrode.

[0042] When the light-shielding layer is a cured film of a resin composition containing a black pigment, the resin composition may contain an alkali-soluble resin, a dispersant, a monomer having an unsaturated double bond, a photopolymerization initiator, a photoacid generator, a thermal acid generator, a sensitizer, an adhesion improver, a surfactant, a thermal curing agent, a polymerization inhibitor, a leveling agent, etc. For each component, those exemplified in the description of the opaque wiring electrode can be used.

[0043] The resin composition containing the black pigment is preferably a positive-type photosensitive resin composition containing an alkali-soluble resin and a photoacid generator. Here, "positive photosensitivity" refers to the property that a chemical structure changes upon irradiation with actinic rays, making the composition soluble in an alkaline developer. When the resin composition containing the black pigment is a positive-type photosensitive resin composition, a light-shielding layer of the same pattern can be easily formed on the opaque wiring electrode by the method described below.

[0044] Examples of the photoacid generator include diazonium salts, diazoquinonesulfonic acid amides, diazoquinonesulfonic acid esters, diazoquinonesulfonic acid salts, nitrobenzyl esters, onium salts, halides, halogenated isocyanates, halogenated triazines, bisarylsulfonyldiazomethanes, and disulfones.

[0045] Examples of black pigments include organic pigments and inorganic pigments, and two or more of these pigments may be contained.

[0046] Examples of organic pigments include soluble azo pigments, insoluble azo pigments, metal complex azo pigments, phthalocyanine pigments, and condensed polycyclic pigments.

[0047] Examples of inorganic pigments include carbon black, graphite, pine soot, iron oxides such as iron black, hematite, goethite, and magnetite, titanium, chromium, lead, and composites of these metals. Among these, carbon black is preferred because of its high light-shielding properties.

[0048] The content of the black pigment is preferably 5 to 30% by mass of the solid content of the resin composition. When the content of the black pigment is 5% by mass or more, the light-blocking properties can be further improved. On the other hand, when the content of the black pigment is 30% by mass or less, the sensitivity to light exposure is improved, and the solubility is improved. The content of the black pigment is more preferably 15% by mass or less. Here, "solubility" refers to the ease with which the exposed area dissolves in a developer, and the better the solubility, the shorter the time it takes for the exposed area to dissolve in the developer.

[0049] The light-shielding layer may be formed directly on the opaque wiring electrode, or may be formed on the opaque wiring electrode via a transparent protective layer.

[0050] <Transparent protective layer> The transparent protective layer is transparent in the visible light region. The definition of "transparent" is as described above. When it is difficult to measure the transparent protective layer alone because it is a thin film, the transparent protective layer can be formed on alkali-free glass "AN Wizus (registered trademark)" (manufactured by AGC Inc.) and the transmittance of the obtained sample can be measured to determine the transmittance.

[0051] The transparent protective layer may be ion migration resistant and adhesive, and may be a multilayer structure containing two or more identical or different layers. Among these, an insulating layer having ion migration resistance is preferred, from the viewpoint of preventing short circuits caused by ion migration between adjacent opaque wiring electrodes. Here, ion migration resistance refers to resistance to short circuits caused by ion migration between electrodes that occur when positive and negative electrical terminals are connected to two electrically unconnected electrodes and a voltage is applied.

[0052] Furthermore, since the transparent protective layer is an adhesive layer having adhesive properties, it can be attached to a cover material such as a cover glass or a cover plastic.

[0053] If the transparent protective layer is only an insulating layer, it cannot be attached to a cover material, and if it is only an adhesive layer, short circuits due to ion migration are likely to occur, but by laminating an insulating layer and an adhesive layer in this order on a transparent substrate, it is possible to achieve both ion migration resistance and adhesiveness. If the opaque wiring electrode is formed in two or more layers with a transparent protective layer interposed between them, from the viewpoint of ion migration resistance, it is preferable that the same number of insulating layers be laminated as the number of layers of the opaque wiring electrode, and if the opaque wiring electrode is formed in two layers with a transparent protective layer interposed between them, it is preferable that the insulating layer, insulating layer, adhesive layer be laminated in this order on the transparent substrate.

[0054] In particular, it is preferable that two or more transparent protective layers are laminated, at least one of which is an insulating layer having ion migration resistance and at least one of which is an adhesive layer having adhesive properties, and that the transparent substrate, the insulating layer, and the adhesive layer are laminated in this order, and that the refractive index n2a of the insulating layer and the refractive index n2b of the adhesive layer satisfy the following formula (2). 0.97≦n2a / n2b≦1.03 (2).

[0055] By satisfying the above formula (2), the reflectance can be further suppressed.

[0056] In the case where the transparent substrate has resistance to ion migration, insulating resin materials such as polyimide resin, acrylic resin, cardo resin, epoxy resin, melamine resin, urethane resin, silicone resin, and fluorine resin, as well as inorganic materials such as glass, are preferably used. Two or more of these may be used. Among these, insulating resin materials are preferred from the viewpoint of strength against bending and flexing of the transparent substrate.

[0057] When adhesiveness is required, for example, acrylic resin, silicone resin, urethane resin, polyamide resin, polyvinyl ether oil, vinyl acetate / vinyl chloride copolymer, modified polyolefin resin, fluorine-based resin, natural rubber, synthetic rubber, etc. Two or more of these may be used.

[0058] Commercially available adhesive transparent protective layers can be used, and examples of such commercially available products include transparent adhesive films such as "LUCIACS (registered trademark)" CS9867US, "LUCIACS (registered trademark)" CS9824T, and "LUCIACS (registered trademark)" CS9827US (all manufactured by Nitto Denko Corporation).

[0059] The transparent protective layer may be formed on the transparent substrate and the opaque wiring electrode using a transparent resin composition by the transparent protective layer forming method described below. The transparent resin composition may contain an alkali-soluble resin, a dispersant, a monomer having an unsaturated double bond, a photopolymerization initiator, a photoacid generator, a thermal acid generator, a sensitizer, an adhesion improver, a surfactant, a heat curing agent, a polymerization inhibitor, a leveling agent, etc. Among these, it is preferable to exhibit photosensitivity by containing an alkali-soluble resin and a photopolymerization initiator. For each component, those exemplified in the description of the opaque wiring electrode can be used.

[0060] <Wiring board> In the wiring board of the present invention, the internal reflectance R1 of the opaque wiring electrode formation portion measured from the transparent protective layer side is 0.1% or less, and preferably 0.01% or more and 0.1% or less, thereby suppressing the metallic luster of the opaque wiring electrode and making the opaque wiring electrode less visible.

[0061] The internal reflectance R1 can be calculated as follows. First, as shown in FIG. 3, a first reflectance evaluation substrate is prepared by attaching an anti-reflection film 6 to the surface of the transparent protective layer 4 of the wiring substrate 5 and a black film 7 to the surface of the transparent substrate 1 to reduce reflection at the interface between the transparent protective layer 4 and the air and at the interface between the transparent substrate 1 and the air. Next, the reflectance R3 is measured from the transparent protective layer 4 side in the region of the first reflectance evaluation substrate 8 where the opaque wiring electrode is formed. Then, as shown in FIG. 4, the reflectance R4 is similarly measured in the region of the first reflectance evaluation substrate 8 where the opaque wiring electrode is not formed. From the obtained reflectances R3 and R4, R3-R4 is calculated, and this value is defined as the internal reflectance R1. By calculating the internal reflectance R1 in this manner, even if the reflectances at the interface between the transparent protective layer 4 and the air and the interface between the transparent substrate 1 and the air are high, the influence of this can be suppressed, and the internal reflectance R1 can be calculated with a small error. Each reflectance can be measured using a spectrophotometer.

[0062] In addition, when a transparent substrate has opaque wiring electrodes and transparent protective layers on both sides, as in the wiring substrate of an embodiment shown in Figure 9 described later, and the internal reflectances at the opaque wiring electrode formation portion measured from each transparent protective layer side are different, the internal reflectance R1 can be determined by preparing a first reflectance evaluation substrate by attaching an anti-reflection film 6 to the surface of the transparent protective layer 4 on the side with the lower reflectance R3 and a black film 7 to the surface of the other transparent protective layer 4.

[0063] Methods for reducing the internal reflectance R1 to 0.1% or less include incorporating a pigment and / or dye into the opaque wiring electrode, and providing a light-shielding layer on top of the opaque wiring electrode.

[0064] In the wiring board of the present invention, the refractive index n1 of the transparent substrate and the refractive index n2 of the transparent protective layer satisfy the following formula (1): When the refractive index n1 and the refractive index n2 satisfy the following formula (1), reflection at the interface between the transparent protective layer and the transparent substrate is suppressed, and the difference with the reflection at the portion where the opaque wiring electrode is formed is reduced, making it possible to make the opaque wiring electrode less visible. 0.97≦n2 / n1≦1.03 (1).

[0065] The refractive index n1 of the transparent substrate and the refractive index n2 of the transparent protective layer can be determined by measuring the refractive index at a wavelength of 550 nm using a prism coupler (Metricon PC-2000). If it is difficult to measure the transparent protective layer alone due to its thinness, the refractive index can be determined by forming a transparent protective layer on a silicone wafer and then measuring the refractive index of the transparent protective layer on the silicone wafer. If two or more transparent protective layers are stacked, the refractive index of the transparent protective layer in contact with the transparent substrate is taken as n2.

[0066] The ratio of the reflectance R2 to the R1 at the interface between the transparent protective layer and the transparent substrate is preferably R1:R2=1:3 to 3:1. By increasing the ratio of R1 from R1:R2=1:3, the opaque wiring electrodes appear dark, which can further prevent the opaque wiring electrodes from being visible. On the other hand, by increasing the ratio of R2 from R1:R2=3:1, the opaque wiring electrodes appear bright, which can further prevent the opaque wiring electrodes from being visible. It is more preferable that R1:R2 is 1:2 to 2:1.

[0067] Here, the reflectance R2 can be calculated as follows. First, as shown in FIG. 5, a second reflectance evaluation substrate 9 is prepared by attaching an anti-reflection film 6 to one surface of a transparent substrate 1 and a black film 7 to the other surface of the transparent substrate 1 to reduce reflection at the interfaces between both surfaces of the transparent substrate 1 and air. For the obtained second reflectance evaluation substrate 9, the reflectance R5 is measured from the anti-reflection film 6 side. R4-R5 is calculated from the obtained reflectance R5 and the above-mentioned reflectance R4, and this value is used as the reflectance R2 at the interface between the transparent protective layer and the transparent substrate. By calculating the reflectance R2 in this manner, even if the reflectances at the interface between the transparent protective layer 4 and air and the interface between the transparent substrate 1 and air are high, the influence of this can be suppressed, and the reflectance R2 can be calculated with a small error.

[0068] The ion migration resistance of a wiring substrate can be evaluated, for example, by the following method. First, an opaque wiring electrode pattern with a line width of 10 μm and a line spacing of 10 μm as shown in FIG. 13 is formed, and a transparent protective layer is formed on the wiring portion of the opaque wiring electrode to prepare a substrate for evaluating ion migration resistance. Positive and negative electrical terminals are connected to the terminal portions of the obtained substrate for evaluating ion migration resistance, and the substrate is placed in a constant temperature and humidity chamber at 85°C and 85% RH while a direct current of 5 V is applied. The time when the electrical resistance reaches 15,630 Ω or less is defined as the short-circuit time. A shorter short-circuit time indicates lower ion migration resistance, while a longer short-circuit time indicates higher ion migration resistance.

[0069] 6 to 9 and 12 are schematic diagrams showing other examples of the configuration of the wiring board of the present invention.

[0070] FIG. 6 is a schematic diagram of a wiring board having a first opaque wiring electrode 2 on a transparent substrate 1, a first transparent protective layer 4 on the first opaque wiring electrode 2, and a second opaque wiring electrode 2 and a second transparent protective layer 4 on the first transparent protective layer 4.

[0071] FIG. 7 is a schematic diagram of a wiring board having a first opaque wiring electrode 2 on a transparent substrate 1, a first transparent protective layer 4 on the first opaque wiring electrode 2, a second opaque wiring electrode 2 on the first transparent protective layer 4, and a light-shielding layer 3 and a second transparent protective layer 4 on the second opaque wiring electrode 2.

[0072] FIG. 8 is a schematic diagram of a wiring board having opaque wiring electrodes 2 on both sides of a transparent substrate 1, and transparent protective layers 4 on the opaque wiring electrodes 2 on both sides of the transparent substrate 1, respectively.

[0073] Figure 9 is a schematic diagram of a wiring board having opaque wiring electrodes 2 on both sides of a transparent substrate 1, a light-shielding layer 3 on the opaque wiring electrodes 2 on one side, and transparent protective layers 4 on the opaque wiring electrodes 2 and the light-shielding layer 3 on both sides of the transparent substrate 1.

[0074] Figure 12 is a schematic diagram of a wiring board having an opaque wiring electrode 2 on one side of a transparent substrate 1, a first transparent protective layer 4 on the opaque wiring electrode 2, and a second transparent protective layer 4 on the first transparent protective layer 4.

[0075] <Method of manufacturing wiring board> Next, a method for manufacturing a wiring board according to the present invention will be described.

[0076] First, an opaque wiring electrode is formed on at least one surface of a transparent substrate. The opaque wiring electrode may be formed on both surfaces of the transparent substrate. Furthermore, the step of forming the opaque wiring electrode on at least one surface of the transparent substrate may include the steps of forming a first opaque wiring electrode on one surface of the transparent substrate, forming a transparent protective layer on the first opaque wiring electrode, and forming a second opaque wiring electrode on the transparent protective layer.

[0077] Examples of methods for forming opaque wiring electrodes include a method of forming a pattern by photolithography using the above-mentioned photosensitive conductive composition, a method of forming a pattern by screen printing, gravure printing, inkjet printing, or the like using a conductive composition (conductive paste), and a method of forming a film of metal, metal composite, composite of metal and metal compound, metal alloy, or the like, and then forming it by photolithography using a resist. Among these, the method of forming by photolithography using a photosensitive conductive composition is preferred because it allows for the formation of fine wiring. Note that when opaque wiring electrodes are formed on both sides of a transparent substrate, or when two or more layers of opaque wiring electrodes are formed via a transparent protective layer, each opaque wiring electrode may be formed by the same method, or different methods may be combined.

[0078] The method for forming a pattern by photolithography using a photosensitive conductive composition includes a coating step of applying the photosensitive conductive composition onto a transparent substrate to obtain a coating film, a photolithography step of exposing and developing the coating film to obtain a pattern, and a curing step of heating the pattern at 100 to 300°C to obtain a conductive pattern.

[0079] The coating step is a step of applying the photosensitive conductive composition to a transparent substrate to obtain a coating film. Examples of methods for applying the photosensitive conductive composition to a transparent substrate include spin coating using a spinner, spray coating, roll coating, screen printing, or coating using a slit coater, blade coater, die coater, calendar coater, meniscus coater, or bar coater.

[0080] When the photosensitive conductive composition contains a solvent, the resulting coating film may be dried to remove the solvent. Methods for drying the coating film include, for example, heat drying in an oven, on a hot plate, or by infrared irradiation, or vacuum drying. The heat drying temperature is generally 50 to 120°C, and the heat drying time is generally one minute to several hours.

[0081] The photolithography process is a process of exposing and developing the coating film obtained in the coating process to obtain a pattern. The light source used to expose the coating film is preferably a mercury lamp or an LED lamp with i-line (365 nm), h-line (405 nm), or g-line (436 nm). A conductive pattern is obtained by exposing the coated surface of the photosensitive conductive composition on the transparent substrate through an exposure mask and removing the unexposed areas with a developer.

[0082] Examples of developers for alkaline development include aqueous solutions of tetramethylammonium hydroxide, diethanolamine, diethylaminoethanol, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, triethylamine, diethylamine, methylamine, dimethylamine, dimethylaminoethyl acetate, dimethylaminoethanol, dimethylaminoethyl methacrylate, cyclohexylamine, ethylenediamine, and hexamethylenediamine. To these aqueous solutions, a polar solvent such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or γ-butyrolactone, an alcohol such as methanol, ethanol, or isopropanol, an ester such as ethyl lactate or propylene glycol monomethyl ether acetate, a ketone such as cyclopentanone, cyclohexanone, isobutyl ketone, or methyl isobutyl ketone, or a surfactant may be added.

[0083] Examples of the developer for organic development include polar solvents such as N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and hexamethylphosphortriamide, and mixed solutions of these polar solvents with methanol, ethanol, isopropyl alcohol, xylene, water, methyl carbitol, or ethyl carbitol.

[0084] Examples of the development method include a method in which the developer is sprayed onto the surface of the coating film while the substrate is left standing or rotated, a method in which the substrate is immersed in the developer, or a method in which ultrasonic waves are applied to the substrate while the substrate is immersed in the developer.

[0085] The pattern obtained in the development step may be subjected to a rinse treatment with a rinse solution, such as water or an aqueous solution of water to which an alcohol such as ethanol or isopropyl alcohol, an ester such as ethyl lactate or propylene glycol monomethyl ether acetate, or a surfactant has been added.

[0086] When a light-shielding layer is provided on the opaque wiring electrode, a positive-type photosensitive resin composition containing a black pigment is applied to the opaque wiring electrode formed on a transparent substrate, and then the positive-type photosensitive resin composition containing the black pigment is exposed from the side opposite to the coated side using the opaque wiring electrode as a mask, followed by development, to form a light-shielding layer having the same pattern as the opaque wiring electrode. If necessary, for example, when it is necessary to ensure electrical continuity with an external element, such as a terminal portion, and the light-shielding layer is removed from a portion where the opaque wiring electrode is to be exposed, a step of exposing the positive-type photosensitive resin composition from the coated side using an exposure mask may be included.

[0087] The manufacturing process of the light-shielding layer may include a curing step. The curing temperature is preferably 100 to 300° C. Examples of the curing method include heat drying using an oven, an inert oven, or a hot plate, heat drying using electromagnetic waves such as an infrared heater, and vacuum drying.

[0088] Next, a transparent protective layer is formed on the transparent substrate and the opaque wiring electrodes.

[0089] Examples of methods for forming the transparent protective layer include a method of applying a transparent resin composition and drying it, and a method of laminating a transparent adhesive film onto the surface on which the opaque wiring electrode is formed.

[0090] Examples of methods for applying the transparent resin composition include spin coating using a spinner, spray coating, roll coating, screen printing, offset printing, gravure printing, letterpress printing, flexographic printing, and methods using a blade coater, a die coater, a calendar coater, a meniscus coater, or a bar coater.

[0091] In the method of applying and drying a transparent resin composition, the dried film can be cured by ultraviolet treatment and / or heat treatment. The transparent resin composition may be photosensitive. For example, when it is necessary to ensure electrical continuity with an external element, such as a terminal portion, and the transparent protective layer is to be removed from a portion where an opaque wiring electrode is to be exposed, the transparent protective layer can be removed by a photolithography process, as in the case of the photosensitive conductive composition. [Example]

[0092] The present invention will be described in detail below with reference to examples and comparative examples. It is not limited to:

[0093] The materials used in each example and comparative example are as follows. The transmittance of the transparent substrate at a wavelength of 550 nm was measured using an ultraviolet-visible spectrophotometer (U-3310, manufactured by Hitachi High-Technologies Corporation). The refractive index at a wavelength of 550 nm was measured at room temperature of 23°C using a prism coupler (PC-2000, manufactured by Metricon).

[0094] (Transparent substrate) Soda glass (thickness: 1.1 mm, transmittance at 550 nm: 90%, refractive index at 550 nm: 1.52) (a-1) Tormed Type S (manufactured by IST Co., Ltd.) (thickness: 25 μm, transmittance at wavelength of 550 nm: 87%, refractive index at wavelength of 550 nm: 1.68) (a-2).

[0095] (monomer) "Light Acrylate (registered trademark)" HPP-A (manufactured by Kyoeisha Chemical Co., Ltd.), "Light Acrylate (registered trademark)" BP-4EAL (manufactured by Kyoeisha Chemical Co., Ltd.), "Light Acrylate (registered trademark)" BP-4PA (manufactured by Kyoeisha Chemical Co., Ltd.), "Light Acrylate (registered trademark)" BP-4EA (manufactured by Kyoeisha Chemical Co., Ltd.).

[0096] (epoxy resin) CG-500 (manufactured by Osaka Gas Chemicals Co., Ltd.).

[0097] (Photopolymerization initiator) N-1919 (manufactured by ADEKA Corporation).

[0098] (carbon black) MA100 (manufactured by Mitsubishi Chemical Corporation).

[0099] (zirconia dispersion) "Zircostar (registered trademark)" ZP-153 (manufactured by Nippon Shokubai Co., Ltd.).

[0100] (solvent) PGMEA (manufactured by Kuraray Co., Ltd.).

[0101] (anti-reflective film) MTAR-3 (manufactured by Mitate Imaging Co., Ltd.).

[0102] (black film) Black PET film with adhesive, Kakuri Miel (manufactured by Tomoegawa Paper Co., Ltd.).

[0103] (Transparent adhesive film) "LUCIACS (registered trademark)" CS9867US (manufactured by Nitto Denko Corporation) (thickness: 175 μm, transmittance at a wavelength of 550 nm: 92%, refractive index at a wavelength of 550 nm: 1.48) (b-1).

[0104] (PET film) "Lumirror (registered trademark)" T60 (manufactured by Toray Industries, Inc.).

[0105] (High refractive index particles) "Eposter (registered trademark)" MS (manufactured by Nippon Shokubai Co., Ltd.).

[0106] (Release film) "Therapeel (registered trademark)" (thickness 38 μm, manufactured by Toray Film Processing Co., Ltd.).

[0107] (Production Example 1: Carboxyl Group-Containing Acrylic Copolymer (C-1)) A reaction vessel under a nitrogen atmosphere was charged with 150 g of diethylene glycol monoethyl ether acetate (DMEA) and heated to 80°C using an oil bath. A mixture consisting of 20 g of EA, 40 g of 2-ethylhexyl methacrylate (2-EHMA), 20 g of styrene (St), 15 g of AA, 0.8 g of 2,2'-azobisisobutyronitrile, and 10 g of DMEA was added dropwise over 1 hour. After the addition was complete, the polymerization reaction was continued for an additional 6 hours. Then, 1 g of hydroquinone monomethyl ether was added to terminate the polymerization reaction. Subsequently, a mixture consisting of 5 g of glycidyl methacrylate (GMA), 1 g of triethylbenzylammonium chloride, and 10 g of DMEA was added dropwise over 0.5 hours. After the addition was complete, the addition reaction was continued for an additional 2 hours. The resulting reaction solution was purified with methanol to remove unreacted impurities, and then vacuum dried for 24 hours to obtain a carboxyl group-containing acrylic copolymer (C-1) with a copolymerization ratio (by mass): EA / 2-EHMA / St / GMA / AA = 20 / 40 / 20 / 5 / 15.

[0108] (Production Example 2: Carboxyl Group-Containing Acrylic Copolymer (C-2)) A carboxyl group-containing acrylic copolymer (C-2) having a copolymerization ratio (by mass): EA / 2-EHMA / St / GMA / AA = 20 / 40 / 10 / 5 / 15 was obtained in the same manner as in Production Example 1, except that the mass of styrene was changed from 20 g to 10 g.

[0109] (Production Example 3: Photosensitive Conductive Paste (D-1)) In a 100 mL clean bottle, 3.0 g of the carboxyl group-containing cellulose obtained in Production Example 1 was added. Acrylic copolymer (C-1), 0.3 g of photopolymerization initiator N-1919, 1.2 g of monomer "Light Acrylate (registered trademark)" BP-4EA, 0.5 g of dispersant BYK-LP21116 (manufactured by BYK-Chemie), 79.0 g of PGMEA, 0.7 g of MA100, and 15.3 g of silver microparticles (manufactured by Nisshin Engineering Inc.) with an average surface carbon coating layer thickness of 1 nm and a particle diameter of 40 nm were added and mixed in a rotation-revolution vacuum mixer "Awatori Rentaro ARE-310" (manufactured by Thinky Corporation) to obtain 100.0 g of photosensitive conductive paste (D-1).

[0110] (Production Example 4: Photosensitive Conductive Paste (D-2)) 100.0 g of photosensitive conductive paste (D-2) was obtained in the same manner as in Production Example 3, except that the weight of MA100 was changed from 0.7 g to 2.4 g and the mass of silver particles was changed from 15.3 g to 13.6 g.

[0111] (Production Example 5: Quinone diazide compound) Under a dry nitrogen stream, 21.22 g (0.05 mol) of α,α,-bis(4-hydroxyphenyl)-4-(4-hydroxy-α,α-dimethyldimethylbenzylethylbenzene (trade name TrisP-PA, manufactured by Honshu Chemical Industry Co., Ltd.) and 33.58 g (0.125 mol) of 5-naphthoquinone diazide sulfonyl chloride were dissolved in 450 g of 1,4-dioxane and the solution was brought to room temperature. To this solution, 15.18 g of triethylamine mixed with 50 g of 1,4-dioxane was added dropwise so that the temperature in the system did not exceed 35°C. After the dropwise addition, the mixture was stirred at 30°C for 2 hours. The triethylamine salt was filtered, and the filtrate was poured into water. The precipitate that formed was then collected by filtration. This precipitate was dried in a vacuum dryer to obtain a quinone diazide compound.

[0112] (Production Example 6: Light-blocking paste) A 100 mL clean bottle was charged with 3.1 g of WR-101 (DIC Corporation), 0.8 g of the quinone diazide compound obtained in Production Example 5, and 40.1 g of PGMEA, and mixed using a planetary centrifugal mixer (Awatori Rentaro ARE-310) to obtain 44.0 g of a resin solution. 44.0 g of the resulting resin solution, 0.6 g of MA100, 0.2 g of acrylic copolymer (C-1), and 0.4 g of BYK-LP21116 were mixed and kneaded using an Ultra Apex Mill (Kotobuki Industries Co., Ltd.) equipped with a centrifugal separator filled with 70% by volume of 0.05 mmφ zirconia beads (Toray Industries, Inc.), to obtain 45.2 g of a light-shielding paste.

[0113] (Production example 7: Aqueous solution for electrode blackening) 25.0 g of 36% by mass hydrochloric acid and 0.5 g of tellurium dioxide were mixed in water, and after the tellurium dioxide had dissolved, 10.0 g of acetic acid and 64.5 g of water were added and mixed to obtain a 100.0 g aqueous solution for electrode blackening with a pH of 0. The pH was measured at 25°C using a pH meter (AP-20, manufactured by A&D Co., Ltd.).

[0114] (Production Example 8: Photosensitive Insulating Paste (E-1)) A 100 mL clean bottle was charged with 15.5 g of acrylic copolymer (C-2), 5.2 g of "Light Acrylate®" HPP-A, 0.3 g of photopolymerization initiator N-1919, and 79.0 g of PGMEA, and mixed using a planetary centrifugal vacuum mixer (Awatori Rentaro ARE-310) to obtain 100.0 g of photosensitive insulating paste (E-1). The resulting photosensitive insulating paste (E-1) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (Metricon, PC-2000) at room temperature (23 °C), resulting in a value of 1.50.

[0115] (Production Example 9: Photosensitive Insulating Paste (E-2)) 100.0 g of photosensitive insulating paste (E-2) was obtained in the same manner as in Production Example 8, except that 5.2 g of "Light Acrylate (registered trademark)" HPP-A was changed to 5.2 g of "Light Acrylate (registered trademark)" BP-4EAL. The obtained photosensitive insulating paste (E-2) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (manufactured by Metricon, PC-2000) at room temperature of 23°C, resulting in a value of 1.53.

[0116] (Production Example 10: Photosensitive Insulating Paste (E-3)) Except for changing 15.5 g of acrylic copolymer (C-2) to 15.5 g of acrylic copolymer (C-1), 100.0 g of photosensitive insulating paste (E-3) was obtained in the same manner as in Production Example 9. The obtained photosensitive insulating paste (E-3) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (manufactured by Metricon, PC-2000) at room temperature of 23°C, resulting in a value of 1.55.

[0117] (Production Example 11: Photosensitive Insulating Paste (E-4)) A 100 mL clean bottle was charged with 12.4 g of acrylic copolymer (C-1), 4.1 g of "Light Acrylate®" BP-4EAL, 4.1 g of CG-500, 0.3 g of photopolymerization initiator N-1919, and 79.0 g of PGMEA, and mixed using a planetary centrifugal vacuum mixer (Awatori Rentaro ARE-310) to obtain 100.0 g of photosensitive insulating paste (E-4). The resulting photosensitive insulating paste (E-4) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (Metricon, PC-2000) at room temperature (23 °C), resulting in a value of 1.58.

[0118] (Production Example 13: Photosensitive Insulating Paste (E-5)) 100.0 g of photosensitive insulating paste (E-5) was obtained in the same manner as in Production Example 12, except that the mass of the acrylic copolymer (C-1) was changed to 10.4 g, the mass of BP-4EAL to 2.1 g, and the mass of CG-500 to 8.3 g. The obtained photosensitive insulating paste (E-5) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (Metricon, PC-2000) at room temperature of 23°C, resulting in a value of 1.61.

[0119] (Production Example 11: Photosensitive Insulating Paste (E-6)) 7.3 g of acrylic copolymer (C-1), 1.5 g of "Light Acrylate®" BP-4EAL, 5.9 g of CG-500, 0.3 g of photopolymerization initiator N-1919, 25.0 g of zirconia dispersion, and 60.1 g of PGMEA were placed in a 100 mL clean bottle and mixed using a planetary centrifugal vacuum mixer (Awatori Rentaro ARE-310) to obtain 100.0 g of photosensitive insulating paste (E-6). The resulting photosensitive insulating paste (E-6) was applied to a 4-inch silicone wafer, and the refractive index at a wavelength of 550 nm was measured using a prism coupler (Metricon, PC-2000) at room temperature (23 °C) and found to be 1.66.

[0120] (Production Example 12: Transparent adhesive film (b-2)) 70.7 g of acrylic copolymer SK2094 (Soken Chemical & Engineering Co., Ltd.), 6.1 g of high refractive index particles, 0.4 g of crosslinker KBM-403 (Shin-Etsu Chemical Co., Ltd.), and 22.9 g of PGMEA were placed in a 100 mL clean bottle and mixed using a planetary centrifugal vacuum mixer (Awatori Rentaro ARE-310) to obtain 100.0 g of adhesive composition. The adhesive composition was applied to a release film and dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. A release film was then laminated to the adhesive layer to obtain transparent adhesive film (b-2). The refractive index of the resulting transparent adhesive film at a wavelength of 550 nm was measured and found to be 1.51.

[0121] The evaluation methods used in each of the examples and comparative examples are as follows.

[0122] <Visibility evaluation> For the first wiring boards obtained in each example and comparative example, a black film was placed on the side opposite the opaque wiring electrode formation surface, and then light was projected onto the wiring board using a floodlight. 10 people visually inspected the wiring board from a distance of 30 cm to evaluate whether the mesh electrode portion was visible. If it was visible to 8 or more people, it was rated as "E," if it was visible to 5 to 8 people, it was rated as "D," if it was visible to 3 to 5 people, it was rated as "C," if it was visible to 1 to 3 people, it was rated as "B," and if it was invisible to 10 people, it was rated as "A," with D or higher being considered a pass.

[0123] <Reflectance R1 measurement> For the first wiring substrates obtained in each example and comparative example, an anti-reflection film was attached to the surface of the transparent protective layer using a rubber roller to suppress reflection at the interface between the transparent protective layer and the air. Furthermore, to suppress reflection at the interface between the transparent substrate and the air, a black film was attached to the surface of the transparent substrate using a rubber roller, producing a first reflectance evaluation substrate as shown in Figure 3. The reflectance R3 was measured from the transparent protective layer side in the region where the opaque wiring electrode was formed on the obtained first reflectance evaluation substrate. Furthermore, as shown in Figure 4, the reflectance R4 was similarly measured in the region where the opaque wiring electrode was not formed on the first reflectance evaluation substrate. From the obtained reflectances R3 and R4, R3-R4 was calculated, and this was defined as the reflectance R1. The reflectances R3 and R4 were determined by measuring the luminous reflectance (Y value) at a 10° field of view using a spectrophotometer (CM-2500d) manufactured by Konica Minolta Sensing, Inc., using a D65 light source.

[0124] <Reflectance R2 measurement> For the transparent substrates used in each example and comparative example, an anti-reflection film was attached to one side of the transparent substrate using a rubber roller. Furthermore, a black film was attached to the other side of the transparent substrate using a rubber roller to prepare a second substrate for reflectance evaluation as shown in FIG. 5 . The reflectance R5 of the obtained second substrate for reflectance evaluation was measured from the anti-reflection film side. From the obtained reflectance R5 and reflectance R4, R4-R5 was calculated, and this was designated as reflectance R2. Reflectance R5 was determined by measuring the luminous reflectance (Y value) under a D65 light source and a 10° field of view using a spectrophotometer (CM-2500d) manufactured by Konica Minolta Sensing, Inc.

[0125] <Evaluation of reflectance R in opaque wiring electrode formation area> For the first wiring substrates obtained in each example and comparative example, R3-R5 was calculated from the obtained reflectance R5 and reflectance R3, and this was taken as the reflectance R in the opaque wiring electrode formation region. Reflectance R of less than 0.12% was evaluated as "A," reflectance R of 0.12% or more but less than 0.16% was evaluated as "B," reflectance R of 0.16% or more but less than 0.26% was evaluated as "C," and reflectance R of 0.26% or more was evaluated as "D."

[0126] <Ion migration resistance evaluation> For the second wiring boards obtained in each example and comparative example, positive and negative electrical terminals were connected to the terminal portions, and the boards were placed in a constant temperature and humidity chamber at 85°C and 85% RH while a direct current of 5V was applied, and the transition of electrical resistance was evaluated. The time when the electrical resistance became 15,630 Ω or less was defined as the short circuit time, and cases where the short circuit time was 500 hours or more were rated as "A," cases where the short circuit time was 100 hours or more but less than 500 hours were rated as "B," and cases where the short circuit time was less than 100 hours were rated as "C."

[0127] <Adhesion evaluation> For the first wiring boards obtained in each example and comparative example, a PET film was attached to one surface of the transparent protective layer with a rubber roller, and adhesive strength was measured using an adhesive / film peeling analyzer VPA (manufactured by Kyowa Interface Science Co., Ltd.) at a peeling speed of 300 mm / min and a peeling angle of 180°. Adhesive strengths of 3.0 N / 25 mm or more were evaluated as "A," and adhesive strengths of less than 3.0 N / 25 mm were evaluated as "B."

[0128] <Adhesion evaluation> The opaque wiring electrode formation portion of the first wiring substrate obtained in each example and comparative example was subjected to an adhesion test according to the cross-cut method specified in JIS K 5600-5-6: 1999. Classification 0 was evaluated as "A," 1-2 as "B," and 3-5 as "C."

[0129] Example 1 [Fabrication of the first wiring board] <Formation of opaque wiring electrodes> The photosensitive conductive paste (D-1) obtained in Production Example 3 was applied to one surface of a transparent substrate (a-1) by spin coating so that the film thickness after drying would be 1 μm, and then dried for 8 minutes at 90° C. Next, as shown in FIGS. 10 and 11, an exposure dose of 100 mJ / cm was applied using an exposure device (PEM-6M; manufactured by Union Optical Co., Ltd.) through an exposure mask having a mesh portion and a mask light-shielding portion with a mesh pitch of 150 μm and a mesh angle of 90°. 2 The mask was exposed to light (equivalent to a wavelength of 365 nm). The mask opening width was 4 μm. Development was then carried out using a 0.1% aqueous solution of tetramethylammonium hydroxide as the developer for twice the time it took for the exposed areas to dissolve. The substrate was then rinsed with ultrapure water for 30 seconds and heated in a box oven at 240°C for 60 minutes to obtain a substrate with an opaque wiring electrode. The line width of the resulting opaque wiring electrode was measured using an optical microscope and found to be 4 μm.

[0130] <Formation of light-shielding layer> The opaque wiring electrode-formed surface of the obtained substrate with opaque wiring electrode was coated with the film obtained in Production Example 6. The light-shielding paste was applied by spin coating so that the thickness of the light-shielding layer after drying would be 0.5 μm, and dried at 80°C for 5 minutes. Using the opaque wiring electrode as a mask, the light-shielding paste was exposed to light from the side opposite the opaque wiring electrode-formed surface at an exposure dose of 500 mJ / cm. 2 The substrate was exposed to light (equivalent to a wavelength of 365 nm). The substrate was then immersed in a 2.38% aqueous solution of tetramethylammonium hydroxide for 50 seconds to form a light-shielding layer on the opaque wiring electrode. The substrate was then heated in a box oven at 240°C for 60 minutes to obtain a substrate with a light-shielding layer.

[0131] <Formation of transparent protective layer> The photosensitive insulating paste (E-1) obtained in Production Example 8 was applied by spin coating to the surface of the obtained substrate with a light-shielding layer on which the opaque wiring electrode and the light-shielding layer were formed, so that the film thickness after drying would be 1.5 μm, and then dried at 80° C. for 5 minutes. The paste was exposed to light at a dose of 100 mJ / cm using an exposure device (PEM-6M; manufactured by Union Optical Co., Ltd.) through an exposure mask. 2 The substrate was exposed to light (equivalent to a wavelength of 365 nm). Thereafter, development was performed for 30 seconds using a 0.1% aqueous solution of tetramethylammonium hydroxide as a developer, and after rinsing with ultrapure water for 30 seconds, it was heated in a box oven at 240°C for 60 minutes to obtain a first wiring substrate as shown in Figure 2. Using the obtained first wiring substrate, visibility evaluation, reflectance R1 measurement, reflectance R evaluation in the opaque wiring electrode formation region, adhesiveness evaluation, and adhesion evaluation were performed.

[0132] [Fabrication of the second wiring board] The exposure mask used in <Formation of opaque wiring electrodes> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13. In <Formation of light-shielding layer>, after exposure, only the wiring area was shielded from light, and the exposure dose was 500 mJ / cm from the film surface side. 2 A second wiring substrate was fabricated in the same manner as the first wiring substrate, except that the first wiring substrate was exposed again to light (equivalent to a wavelength of 365 nm) and the terminal portion was shielded from light during the exposure in <Formation of Transparent Protective Layer>. The obtained second wiring substrate was used to evaluate ion migration resistance.

[0133] Examples 2 to 7 A first wiring board and a second wiring board as shown in FIG. 2 were produced in the same manner as in Example 1, except that the transparent substrate, the photosensitive insulating paste used to form the transparent protective layer, and the pattern of the exposure mask used to form the opaque wiring electrode were changed as shown in Table 1.

[0134] Example 8 [Fabrication of the first wiring board] <Formation of opaque wiring electrodes> A substrate with an opaque wiring electrode was obtained in the same manner as in <Formation of opaque wiring electrode> in Example 1, except that the photosensitive conductive paste (D-1) was changed to photosensitive conductive paste (D-2), a mesh pattern with a pitch of 450 μm and an angle of 90 degrees was used, and the mask opening width was set to 12 μm. The line width of the obtained opaque wiring electrode was measured with an optical microscope and found to be 12 μm.

[0135] <Formation of transparent protective layer> A transparent protective layer was formed on the opaque wiring electrode-formed surface of the obtained substrate with opaque wiring electrode in the same manner as in <Formation of transparent protective layer> of Example 1, to obtain a first wiring substrate as shown in FIG.

[0136] [Fabrication of the second wiring board] A second wiring board was produced in the same manner as in Example 1 [Production of a second wiring board], except that the photosensitive conductive paste (D-1) was changed to a photosensitive conductive paste (D-2) and no light-shielding layer was formed.

[0137] Example 9 A first wiring board and a second wiring board as shown in FIG. 1 were produced in the same manner as in Example 8, except that the photosensitive insulating paste used to form the transparent protective layer was changed as shown in Table 1.

[0138] Example 10 [Fabrication of the first wiring board] <Formation of opaque wiring electrodes> A substrate with opaque wiring electrodes was obtained in the same manner as in Example 1, except that a mesh pattern with a pitch of 450 μm and an angle of 90 degrees was used and the mask opening width was set to 12 μm. The line width of the opaque wiring electrodes was measured with an optical microscope and found to be 12 μm.

[0139] <Formation of light-shielding layer> The obtained substrate with opaque wiring electrode was immersed in the electrode blackening aqueous solution obtained in Manufacturing Example 7 for 30 seconds, then washed with water and dried to obtain a substrate with a light-shielding layer formed on the surface of the opaque wiring electrode.

[0140] <Formation of transparent protective layer> The same procedure as in Example 1 was repeated, except that the photosensitive insulating paste (E-1) was changed to the photosensitive insulating paste (E-3), and a transparent protective layer was formed on the opaque wiring electrode and the light-shielding layer-forming surface of the obtained substrate with a light-shielding layer, thereby obtaining a first wiring substrate as shown in Figure 2.

[0141] [Fabrication of the second wiring board] A second wiring substrate was fabricated in the same manner as the first wiring substrate, except that the exposure mask used in <Formation of opaque wiring electrode> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13, and that the terminal portion was shielded from light during exposure in <Formation of transparent protective layer>.

[0142] Example 11 [Fabrication of the first wiring board] <Formation of the first opaque wiring electrode> A substrate with an opaque wiring electrode (hereinafter referred to as the first opaque wiring electrode in this example) was obtained in the same manner as in Example 1, except that a mesh pattern with a pitch of 300 μm and an angle of 90 degrees was used. The line width of the first opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0143] <Formation of the first transparent protective layer> A transparent protective layer (hereinafter referred to as the first transparent protective layer in this example) was formed on the first opaque wiring electrode forming surface of the obtained first opaque wiring electrode-equipped substrate in the same manner as in <Formation of transparent protective layer> of Example 1, except that the photosensitive insulating paste (E-1) was changed to photosensitive insulating paste (E-3), thereby obtaining a first transparent protective layer-equipped substrate.

[0144] <Formation of second opaque wiring electrode> A second opaque wiring electrode was formed on the first transparent protective layer-formed surface of the obtained first substrate with a transparent protective layer in the same manner as the formation of the first opaque wiring electrode, thereby obtaining a second substrate with an opaque wiring electrode. The line width of the second opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0145] <Formation of light-shielding layer> A light-shielding layer was formed on the second opaque wiring electrode-formed surface of the obtained substrate with the second opaque wiring electrode in a position corresponding to the opaque wiring electrode in the same manner as in <Formation of light-shielding layer> of Example 1. Further, the substrate was heated in a box oven at 240°C for 60 minutes to obtain a substrate with a light-shielding layer.

[0146] <Formation of second transparent protective layer> A second transparent protective layer was formed on the surface of the obtained substrate with a light-shielding layer on which the opaque wiring electrode and light-shielding layer were formed in the same manner as in <Formation of first transparent protective layer>, thereby obtaining a wiring substrate as shown in Figure 7.

[0147] [Fabrication of the second wiring board] The exposure mask used in <Formation of first opaque wiring electrode> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13 ; the terminal portion was shielded from light during exposure in <Formation of first transparent protective layer>; the exposure mask used in <Formation of second opaque wiring electrode> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13 ; the exposure mask was placed in a position that did not overlap with the first opaque wiring electrode during exposure; and the exposure amount of 500 mJ / cm 2 was applied from the film surface side after exposure in <Formation of light-shielding layer>. 2A second wiring board was fabricated in the same manner as the first wiring board, except that the first wiring board was exposed again to light (equivalent to a wavelength of 365 nm) and the terminal portion was shielded from light during exposure in <Formation of second transparent protective layer>.

[0148] Example 12 [Fabrication of the first wiring board] <Formation of the first opaque wiring electrode> A first substrate with an opaque wiring electrode was obtained in the same manner as in <Formation of opaque wiring electrode> in Example 1, except that the transparent substrate (a-1) was changed to a transparent substrate (a-2), a mesh pattern with a pitch of 300 μm and an angle of 90 degrees was used, and the mask opening width was set to 4 μm. The line width of the obtained first opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0149] <Formation of second opaque wiring electrode> A second opaque wiring electrode was formed on the surface of the resulting substrate opposite to the surface on which the first opaque wiring electrode was formed in the same manner as for the first opaque wiring electrode, thereby obtaining a second substrate with an opaque wiring electrode. The line width of the second opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0150] <Formation of light-shielding layer> The surface of the obtained second substrate with opaque wiring electrodes on which the first opaque wiring electrodes were formed was exposed to light at an exposure dose of 3000 mJ / cm 2 A light-shielding layer was formed in the area corresponding to the opaque wiring electrode in the same manner as in <Formation of light-shielding layer> in Example 1, except that the above-mentioned procedure was repeated. The substrate was then heated in a box oven at 240°C for 60 minutes to obtain a substrate with a light-shielding layer.

[0151] <Formation of the first transparent protective layer> A first transparent protective layer was formed on the first opaque wiring electrode and light-shielding layer forming surface of the obtained substrate with a light-shielding layer in the same manner as in <Formation of transparent protective layer> of Example 1, except that the photosensitive insulating paste (E-1) was changed to photosensitive insulating paste (E-6), thereby obtaining a first substrate with a transparent protective layer.

[0152] <Formation of second transparent protective layer> A second transparent protective layer was formed on the surface of the obtained substrate with the first transparent protective layer on which the second opaque wiring electrode was to be formed in the same manner as in <Formation of the first transparent protective layer>, thereby obtaining a wiring substrate as shown in Figure 9.

[0153] [Fabrication of the second wiring board] The exposure mask used in <Formation of first opaque wiring electrode> and <Formation of second opaque wiring electrode> was changed to that shown in FIG. 13, which has a line width of 10 μm and a line space of 10 μm. In <Formation of light-shielding layer>, after exposure, only the wiring portion was shielded from light, and an exposure dose of 500 mJ / cm was applied from the film surface side. 2 A second wiring board was produced in the same manner as the first wiring board, except that the first wiring board was exposed again at a wavelength of 365 nm (equivalent to a wavelength of 365 nm) and that the terminal portion was shielded from light during exposure in <Formation of the first transparent protective layer> and <Formation of the second transparent protective layer>.

[0154] Example 13 A first wiring board and a second wiring board as shown in FIG. 2 were produced in the same manner as in Example 1, except that silicon dioxide was sputtered onto one side of the transparent substrate (a-1) using a sputtering device to a thickness of 1 nm.

[0155] (Examples 14 to 17) A first wiring board and a second wiring board as shown in FIG. 2 were produced in the same manner as in Example 13, except that the thickness of the silicon dioxide was changed as shown in Table 2.

[0156] Example 18 [Fabrication of the first wiring board] <Formation of opaque wiring electrodes> A substrate with an opaque wiring electrode was obtained in the same manner as in Example 14. The line width of the obtained first opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0157] <Formation of light-shielding layer> A substrate with a light-shielding layer was obtained in the same manner as in Example 1 on the surface of the obtained substrate with an opaque wiring electrode on which the opaque wiring electrode had been formed.

[0158] <Formation of the first transparent protective layer> A first transparent protective layer was formed in the same manner as in <Formation of transparent protective layer> of Example 1, except that the photosensitive insulating paste (E-1) was changed to photosensitive insulating paste (E-3), and a substrate with a first transparent protective layer was obtained.

[0159] <Formation of second transparent protective layer> A transparent adhesive film (b-1) was attached to the first transparent protective layer-forming surface of the obtained substrate with the first transparent protective layer using a rubber roller to form a second transparent protective layer, thereby producing a first wiring substrate as shown in Figure 12.

[0160] [Fabrication of the second wiring board] The exposure mask used in <Formation of opaque wiring electrodes> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13. In <Formation of light-shielding layer>, after exposure, only the wiring area was shielded from light, and the exposure dose was 500 mJ / cm from the film surface side. 2 The second wiring board was produced in the same manner as the first wiring board, except that the first wiring board was exposed again at a wavelength of 365 nm (equivalent to a wavelength of 365 nm), the terminal portion was shielded from light during exposure in <Formation of the first transparent protective layer>, and a transparent adhesive film (b-1) was attached with a rubber roller only to the wiring portion on the surface on which the first transparent protective layer was formed in <Formation of the second transparent protective layer>.

[0161] Example 19 A first wiring board and a second wiring board as shown in FIG. 12 were produced in the same manner as in Example 18, except that the second transparent protective layer (b-1) was changed to (b-2).

[0162] Example 20 [Fabrication of the first wiring board] <Formation of opaque wiring electrodes> A substrate with an opaque wiring electrode was obtained in the same manner as in <Formation of opaque wiring electrode> in [Preparation of first wiring substrate] of Example 14. The line width of the obtained first opaque wiring electrode was measured with an optical microscope and found to be 4 μm.

[0163] <Formation of light-shielding layer> A substrate with a light-shielding layer was obtained on the surface of the obtained substrate with an opaque wiring electrode on which the opaque wiring electrode had been formed in the same manner as in <Formation of a light-shielding layer> in Example 14.

[0164] <Formation of transparent protective layer> A transparent adhesive film (b-2) was attached to the light-shielding layer-formed surface of the obtained substrate with a rubber roller to form a transparent protective layer, thereby producing a first wiring board as shown in FIG.

[0165] [Fabrication of the second wiring board] The exposure mask used in <Formation of opaque wiring electrodes> was changed to one with a line width of 10 μm and a line space of 10 μm as shown in FIG. 13. In <Formation of light-shielding layer>, after exposure, only the wiring area was shielded from light, and the exposure dose was 500 mJ / cm from the film surface side. 2 The second wiring board was produced in the same manner as the first wiring board, except that the first wiring board was exposed to light again at a wavelength of 365 nm (equivalent to a wavelength of 365 nm), and that in <Formation of transparent protective layer>, a transparent adhesive film (b-2) was attached using a rubber roller only to the wiring portion on the light-shielding layer-forming surface.

[0166] (Comparative Example 1) A first wiring board and a second wiring board as shown in Figure 1 were produced in the same manner as in Example 8, except that the photosensitive conductive paste used to form the opaque wiring electrode was changed as shown in Table 3.

[0167] (Comparative Examples 2 to 5) A first wiring board and a second wiring board as shown in FIG. 2 were produced in the same manner as in Example 1, except that the photosensitive insulating paste used to form the transparent substrate and the transparent protective layer was changed as shown in Table 3.

[0168] [Table 1]

[0169] [Table 2]

[0170] [Table 3] [Explanation of symbols]

[0171] 1: Transparent substrate 2: Opaque wiring electrode 3: Light blocking layer 4:Transparent protective layer 5: Wiring board 6: Anti-reflective film 7: Black film 8: First reflectance evaluation substrate 9: Second reflectance evaluation substrate 10: Mask light shielding part 11: Mask mesh part 12: Light blocking section 13: Opening 14: Mesh pitch 15: Mesh angle 16:Terminal section 17:Wiring section

Claims

1. A wiring substrate having a transparent substrate, an opaque wiring electrode patterned on at least one surface of the transparent substrate, and a transparent protective layer formed on the transparent substrate and the opaque wiring electrode, wherein the internal reflectance R1 in an opaque wiring electrode formation region measured from the transparent protective layer side of the wiring substrate is 0.1% or less, the ratio of the reflectance R2 at the interface between the transparent protective layer and the transparent substrate to the R1 is R1:R2=1:3 to 3:1, and the refractive index n1 of the transparent substrate and the refractive index n2 of the transparent protective layer satisfy the following formula (1): 0.97≦n2 / n1≦1.03 (1)

2. 2. The wiring board according to claim 1, further comprising a light-shielding layer on the opaque wiring electrode.

3. 3. The wiring board according to claim 2, wherein the light-shielding layer is a cured film of a resin composition containing a black pigment.

4. 4. The wiring board according to claim 1, wherein the opaque wiring electrode has a line width of 1 to 10 μm.

5. 5. The wiring board according to claim 1, wherein the transparent substrate has an inorganic film having a thickness of 5 to 50 nm on the surface on which the transparent protective layer is formed.

6. The wiring board according to any one of claims 1 to 5, wherein the transparent protective layer is a laminate of two or more layers, at least one of which is an insulating layer having ion migration resistance, and at least one of which is an adhesive layer having adhesiveness, and the transparent substrate, the insulating layer, and the adhesive layer are laminated in this order, and the refractive index n2a of the insulating layer and the refractive index n2b of the adhesive layer satisfy the following formula (2): 0.97≦n2a / n2b≦1.03 (2)

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