JP2016029638A - Conductive paste for laser machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste for laser machining which has a viscosity suitable for printing and can form a coating with a smooth surface, thereby facilitating formation of, e.g., fine signal wiring.SOLUTION: A conductive paste for laser machining comprises a binder resin, conductive particles, and a dispersant. The D10 average particle diameter of the conductive particles is 0.3 to 1 μm, and the D90 average particle diameter is 2-5 times the D10 average particle diameter. The viscosity measured using an E-type viscometer at a temperature of 25°C and a rotor rotation number of 5 rpm is 10 Pa s to 150 Pa s, and the thixotropic index is 1.2 to 2.4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a conductive paste capable of forming signal wiring and the like by laser ablation.

  Etching methods are widely used as means for forming electronic parts, electromagnetic wave shielding thin film forming means, or signal wiring. The etching method is a method of obtaining a signal wiring having a desired shape by removing a part of the metal film with an etching solution. However, since the process is generally complicated and a waste liquid treatment is separately required, the cost and There was a problem that caused an environmental load. Further, since the signal wiring formed by the etching method is formed of a metal material such as aluminum or copper, there is a problem that it is weak against physical impact such as bending.

  Therefore, in order to solve the above problems and form signal wiring at a lower cost, a printing method using a conductive paste has attracted attention. Since the printing method does not require an etching process, it does not require large-scale equipment, waste liquid treatment, or the like, so that signal wiring can be easily formed at low cost. Furthermore, since it can contribute to the miniaturization of the entire wiring board, it is expected to reduce the size and weight of electronic components, improve productivity, and reduce costs.

In recent years, information terminals such as smartphones and tablet-type terminals have been increased in functionality while maintaining the size, and display resolution has been increased. In order to further improve these performances, electronic components are further added. It is necessary to mount with high density. For high-density mounting of electronic components, miniaturization of the electronic components themselves and miniaturization of signal wiring are required, and high-definition printing methods using conductive paste are also required accordingly.
For example, in capacitive touch panels, lines / spaces with a width of 100 μm or less (100 μm or less / 100 μm or less) (hereinafter abbreviated as “L / S”) are widely used. Furthermore, smartphones and tablets Although the L / S is strongly required to be 50 μm / 50 μm or less due to the multifunctional functions of the type terminal and the like and the high definition of the display, it is difficult to achieve further high definition by the printing method.

  Therefore, a laser processing method (laser ablation method) for forming a signal wiring by irradiating a conductive film with laser light has been studied. In the laser processing method, a conductive paste is printed to form a conductive film on an insulating substrate, and a part thereof is removed from the insulating substrate by laser light to form a signal wiring. This makes it possible to form high-definition signal wiring with an L / S of about 50 μm / 50 μm, which is difficult to form by the printing method. However, from the market, ultra-high-definition signal wiring with an L / S of 30 μm / 30 μm or less is stronger. It was sought after.

Patent Document 1 discloses conductive fine particles, inorganic fillers, resin binders, surfactants, and silane coupling agents as conductive pastes for forming ablation processing (hereinafter referred to as laser processing) by laser irradiation. And a conductive paste containing any of the organometallic compounds.
Patent Document 2 discloses a conductive paste containing a binder resin having a number average molecular weight of 5,000 to 60,000 and a glass transition temperature of 60 to 100 ° C., a metal powder, and an organic solvent.

JP 2014-29992 A WO2014 / 013899

  However, in order to form a fine signal wiring by laser processing, it is necessary to form the surface of the conductive film smoothly. However, in the conventional conductive paste, coarse particles are present in the conductive fine particles. . Further, the conventional conductive paste has a viscosity that is suitable for forming a conductive film with a film having high surface smoothness. For this reason, since the obtained conductive film has a variation in thickness, a variation in the amount of film that can be removed with the same output during laser processing has resulted in a fine signal wiring having a precise L / S. There was a problem that was difficult to form.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive paste for laser processing that has a viscosity suitable for printing and that can form a smooth surface to easily form fine signal wirings.

The conductive paste for laser processing of the present invention contains a binder resin, conductive fine particles, and a phosphoric acid dispersant,
The D10 average particle size of the conductive fine particles is 0.3 to 1 μm, and the D90 average particle size is 2 to 5 times the D10 average particle size,
Using an E-type viscometer, the viscosity measured at a temperature of 25 ° C. and a rotor rotation speed of 5 rpm is 10 Pa · s to 150 Pa · s, and the thixo index is 1.2 to 2.4.

  According to the present invention described above, the conductive paste has a viscosity with a relatively narrow particle size distribution, using conductive fine particles in which coarse particles are suppressed, and a thixo index (TI value) within a predetermined range. Thus, the surface smoothness of the formed conductive film could be improved. Since this conductive coating is excellent in surface smoothness, it is difficult for laser light to diffusely reflect during laser processing, and fine signal wiring can be formed.

  According to the present invention, it is possible to provide a conductive paste for laser processing in which fine signal wirings and the like can be easily formed by forming a coating film having a viscosity suitable for printing and a smooth surface.

It is a top view of the screen printing plate used by laser workability evaluation. It is a one part enlarged view of the circuit pattern after laser processing.

  First, terms are defined before describing the present invention. The signal wiring includes wiring for transmitting an electrical signal such as a wiring circuit and a circuit pattern, and wiring for ground connection such as a ground wiring. The viscosity of the conductive paste is a numerical value measured using an E-type (cone plate type) viscometer and rotor # 7 (θ3 ° x R7.7 mm) at a temperature of 25 degrees and a rotational speed of 5 rpm. The thixo index (hereinafter referred to as TI value) is a numerical value obtained by dividing the viscosity at a rotation speed of 2 rpm at a temperature of 25 ° C. by using a rotor # 7 with an E-type viscometer by the viscosity at a rotation speed of 20 rpm. Each viscosity is a value 2 minutes after the start of measurement.

The conductive paste for laser processing of the present invention (hereinafter sometimes simply referred to as a conductive paste) includes a binder resin, conductive fine particles, and a phosphoric acid dispersant.
The D10 average particle size of the conductive fine particles is 0.3 to 1 μm, and the D90 average particle size is 2 to 5 times the D10 average particle size,
Using an E-type viscometer, the viscosity measured at a temperature of 25 ° C. and a rotor rotation speed of 5 rpm is 10 Pa · s to 150 Pa · s, and the thixo index is 1.2 to 2.4.

  In general, the signal wiring is formed by screen printing a conductive paste by a printing method. In order to print a high-definition signal wiring by screen printing of the conductive paste, the viscosity has been adjusted to thixotropic properties. For this reason, the conventional conductive paste has poor fluidity, and when the conductive film for laser processing is formed by printing, the unevenness derived from the screen printing plate remains on the surface, so the variation in film thickness is large. It was. When such a conductive film is subjected to laser processing for the purpose of, for example, L / S = 30 μm / 30 μm, it is difficult for laser ablation to occur in a thick part of the film, so that the film tends to remain. On the other hand, since the laser ablation is easy and the coating is easy to remove in the thin coating portion, the space width (S width) varies as a result, and the signal wiring with low linearity is formed. On the other hand, since the conductive paste of the present invention has good fluidity because the viscosity is close to Newtonian, the formed conductive film has few surface irregularities and good smoothness. Since this conductive film has little variation in the thickness of the film, for example, when laser processing is performed for the purpose of L / S = 30 μm / 30 μm, it is easy to uniformly remove the conductive film, so that signal wiring with high linearity can be formed. .

  This conductive paste for laser processing preferably forms a conductive film by screen printing or the like and forms a desired signal wiring by laser light irradiation.

  In the present invention, the binder resin preferably has a number average molecular weight of 10,000 to 50,000, more preferably 20,000 to 40,000. When the number average molecular weight is 10,000 or more, the environmental reliability of the signal wiring formed is improved, and in particular, the moisture and heat resistance is further improved. Further, when the number average molecular weight is 50,000 or less, an appropriate cohesive force can be imparted to the conductive film, so that ablation at the time of laser processing is facilitated and fine signal wiring is easily obtained. The number average molecular weight is a value in terms of polystyrene measured by GPC (gel permeation chromatography). The environmental reliability of the signal wiring is that the adhesiveness of the conductive coating to the base material (for example, ITO film) is not easily deteriorated, specifically, 80 ° C., −40 ° C., and 60 ° C. 90 °, respectively. % Time, as well as a cycle test from 85 ° C to -40 ° C.

  The binder resin preferably has a glass transition temperature (hereinafter referred to as Tg) of 5 to 100 ° C, more preferably 10 to 95 ° C. When Tg is 5 ° C. or higher, the adhesion between the signal wiring and the substrate after 90 ° C. and 90% aging (hereinafter referred to as “moisture and heat resistance”) is further improved. Further, when Tg is 100 ° C. or lower, the adhesion between the signal wiring and the base material is further improved, and laser processing is facilitated, so that a fine L / S can be easily obtained. Tg is a numerical value measured with a DSC (Differential Scanning Calorimeter) measuring device “DSC-220C” (manufactured by Seiko Instruments Inc.).

  When the binder resin satisfies the number average molecular weight and Tg at the same time, the environmental reliability of the signal wiring is further improved and the laser processability is further improved.

The binder resin is, for example, polyester resin, urethane-modified polyester resin, epoxy-modified polyester resin, (meth) acrylic resin, styrene resin, styrene- (meth) acrylic resin, styrene-butadiene resin, epoxy resin, modified epoxy resin, phenoxy resin, Vinyl chloride-vinyl acetate copolymer, butyral resin, acetal resin, phenol resin, polycarbonate resin, polyether resin, polyurethane resin, polyurethane urea resin, polyamide resin, polyimide resin, polyamideimide resin, alkyd resin, polyolefin resin, fluorine resin , Ketone resin, benzoguanamine resin, melamine resin, urea resin, silicone resin, nitrocellulose, cellulose acetate butyrate (CAB) resin, cellulose acetate Propionate (CAP) resins, rosin, rosin esters, and maleic acid resins. Among these, the binder resin is polyester resin, polyurethane resin, polyurethane urea resin in terms of adhesion to a substrate, for example, solubility in a solvent used in screen printing, and mechanical strength of a coating film necessary for signal wiring. , And an epoxy resin are preferably selected as appropriate.
Binder resins can be used alone or in combination of two or more.

  The polyester resin preferably has at least one of a hydroxyl group and a carboxyl group. The polyester resin can be synthesized by a known synthesis method such as a known reaction such as a reaction between a polybasic acid and a polyol or a transesterification reaction between a polybasic acid ester and a polyol. In addition, as a method for imparting a carboxyl group to a polyester resin, a known method can be used. For example, after polymerization of a polyester resin, a cyclic ester such as ε-caprolactone is post-added (ring-opening addition) at 180 to 230 ° C. Examples thereof include a method of blocking or a method of adding an acid anhydride such as trimellitic anhydride or phthalic anhydride. The polyester resin is preferably a saturated polyester.

The polybasic acid is preferably, for example, an aromatic dicarboxylic acid, a linear aliphatic dicarboxylic acid, a cyclic aliphatic dicarboxylic acid, or the like, or a trifunctional or higher functional carboxylic acid. The polybasic acid includes an acid anhydride group-containing compound.
Examples of the aromatic dicarboxylic acid include, but are not limited to, terephthalic acid and isophthalic acid. Examples of the linear aliphatic dicarboxylic acid include, but are not limited to, adipic acid, sebacic acid, and azelaic acid. Examples of the cycloaliphatic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, dicarbonoxy hydrogenated bisphenol A, dimer acid, 4-methylhexahydrophthalic anhydride, and 3-methylhexahydrophthalic anhydride. It is not limited to these. Examples of the tri- or higher functional carboxylic acid include, but are not limited to, trimellitic anhydride and pyromellitic anhydride. Other carboxylic acids include, but are not limited to, unsaturated dicarboxylic acids such as fumaric acid, sulfonic acid metal salt-containing dicarboxylic acids such as sodium 5-sulfoisophthalate, and the like.
Polybasic acids can be used alone or in combination of two or more.

The polyol is preferably a diol and a compound having 3 or more hydroxyl groups.
Examples of the diol include, but are not limited to, ethylene glycol, propylene glycol, 1,4-butanediol, and neopentyl glycol.
Examples of the compound having three or more hydroxyl groups include, but are not limited to, tolmethylolpropane, glycerin, and pentaerythritol.
Polyols can be used alone or in combination of two or more.

  The polyurethane resin is a compound having a hydroxyl group at the terminal, obtained by reacting a polyol, diisocyanate, and a chain extender diol compound. A polyurethane resin can extend a molecular chain using a chain extender. The chain extender is generally preferably a diol. The polyurethane resin can be synthesized by a known synthesis method.

Polyols used for the synthesis of the polyurethane resin are preferably polyether polyols, polyester polyols, polycarbonate polyols, and polybutadiene glycols. Polyols can be used alone or in combination of two or more.
The polyether polyol is a polymer such as ethylene oxide, propylene oxide, and tetrahydrofuran, and a copolymer thereof.
The polyester polyol is an ester of a polyol and a polybasic acid described in the polyester resin.
The polycarbonate polyol is preferably 1) a compound obtained by reacting a diol or bisphenol with a carbonic ester, and 2) a compound obtained by reacting a diol or bisphenol with phosgene in the presence of an alkali.
Examples of the carbonate ester include, but are not limited to, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, and propylene carbonate.

  The diisocyanate is preferably an aromatic diisocyanate, an aliphatic diisocyanate, an alicyclic isocyanate, or the like. Diisocyanate can be used alone or in combination of two or more.

The polyurethane urea resin is a compound obtained by reacting a polyol and diisocyanate to synthesize a urethane prepolymer having an isocyanate group at a terminal and further reacting with a polyamine. In addition, the polyurethane urea resin can be reacted with a reaction terminator as necessary to adjust the molecular weight. As the polyol and diisocyanate, it is preferable to use the compounds described for the polyurethane resin. The polyamine is preferably a diamine.
The reaction terminator is preferably a dialkylamine, monoalcohol or the like. The polyurethane urea resin can be synthesized by a known synthesis method.

  The polyurethane resin and the polyurethane urea resin preferably have a carboxyl group in addition to the hydroxyl group. Specifically, a method of synthesizing by synthesizing a part of the diol with a diol having a carboxyl group at the time of synthesis can be mentioned. The diol is preferably dimethylolpropionic acid, dimethylolbutanoic acid, or the like.

  When the conductive paste contains a polyurethane resin or a polyurethane urea resin, the hardness of the conductive film to be formed is further improved.

A solvent can be used when synthesizing a polyurethane resin or a polyurethane urea resin.
The solvent is preferably an ester solvent, a ketone solvent, a glycol ether solvent, an aliphatic solvent, an aromatic solvent, a carbonate solvent, or the like.
Examples of the ester solvent include, but are not limited to, ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, and ethyl lactate.
Examples of the ketone solvent include, but are not limited to, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, diacetone alcohol, isophorone, and cyclohexanenone.
Examples of the glycol ether solvent include monoethers such as ethylene glycol monoethyl ether, ethylene glycol monoisopropyl, and ethylene glycol monobutyl ether, and acetates thereof; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, Propylene glycol monomethyl ether, propylene glycol monoethyl ether, and the like, and acetic acid esters thereof are exemplified, but not limited thereto.
Examples of the aliphatic solvent include, but are not limited to, n-heptane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, and the like.
Examples of the aromatic solvent include, but are not limited to, toluene and xylene.
Examples of the carbonate solvent include, but are not limited to, dimethyl carbonate and diethyl carbonate.
The solvent can be used alone or in combination of two or more.

The epoxy resin is a compound having an epoxy group and a hydroxyl group, and a known compound can be used. The epoxy resin is preferably a polyglycidyl ether obtained by reacting an aromatic diol represented by bisphenol A and bisphenol F with epichlorohydrin. As the epoxy resin, it is also preferable to use a so-called phenoxy resin which is a polymer epoxy resin.
Binder resins can be used alone or in combination of two or more.

  The binder resin is preferably blended in an amount of 5 to 40% by weight, more preferably 5 to 15% by weight, out of a total of 100% by weight of the binder resin and conductive fine particles. By being 5% by weight or more, the conductive film is further improved in adhesion to the substrate, and the mechanical strength of the film is also improved. Moreover, the electroconductivity of a conductive film improves more by becoming 40 weight% or less.

  In the present invention, the conductive fine particles have a small particle size, a sharp particle size distribution, and few coarse particles. For example, when screen printing is performed, unevenness on the surface of the coating can be suppressed. However, it is difficult to scatter on the surface of the conductive coating, and fine signal wiring is easy to form. In addition, since the thickness of the conductive coating does not vary easily, it is easy to obtain good processing accuracy by laser processing, and a highly linear signal wiring can be formed. In addition, since the conductive fine particles have a sharp particle size distribution, the TI value of the conductive paste is easily brought close to Newtonian.

  In order to obtain the above characteristics, the conductive fine particles have a D10 average particle size of 0.3 to 1 μm and a D90 average particle size of 2 to 5 times the D10 average particle size. As for D10 average particle diameter, 0.3-0.8 micrometer is more preferable. The D90 average particle size is more preferably 2 to 4 times the D10 average particle size. When the conductive fine particles satisfy these numerical ranges, the laser processability is further improved. The D10 average particle size and the D90 average particle size are numerical values obtained by measuring the cumulative particle size (D10 and D90) of the volume particle size distribution using a laser diffraction particle size distribution measuring device “SALAD-3000” (manufactured by Shimadzu Corporation).

The conductive fine particles include, for example, metal powders such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, platinum, alloys thereof, and composite powders thereof. Can be mentioned.
In addition, there are nuclei and composite fine particles in which the nuclei surface is coated with a substance different from the nuclei substance, for example, so-called silver-coated copper powder in which copper is used as a nuclei and the surface is coated with silver. In addition, the conductive fine particles may be metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide). And powders that are surface-coated with these metal oxides.
Among these, silver is preferable because it is low in cost, high in conductivity, and hardly oxidizes, so that the change in electrical resistivity is small. The conductive fine particles can be used alone or in combination of two or more.

  As the shape of the conductive fine particles, known shapes such as a spherical shape, a flake shape, a dendritic shape, a rod shape, and a linear shape can be used.

  The conductive fine particles are preferably blended in an amount of 60 to 95% by weight, more preferably 85 to 95% by weight, out of a total of 100% by weight of the binder resin and the conductive fine particles. Conductivity improves more by becoming 60 weight% or more. In addition, when the content is 95% by weight or less, the conductive film has more improved adhesion to the base material, and mechanical strength is also improved.

  The conductive paste for laser processing of the present invention can contain a laser photosensitizer in order to further improve laser processing properties. The laser photosensitizer is preferably a dye, pigment, filler or the like having absorption at the wavelength of the laser beam, and more preferably carbon powder of the pigment. Examples of the carbon powder include carbon black, furnace black, channel black, lamp black, acetylene black, ketjen black, carbon nanotube, and graphite. The laser photosensitizer is preferably blended in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the total of the binder resin and the conductive fine particles.

  In the present invention, the dispersant is used to disperse the conductive fine particles that are difficult to disperse in the conductive paste. In addition, when the conductive paste contains a phosphoric acid dispersant, the binder resin and the conductive fine particles are easily mixed and the dispersibility is improved, so that the TI value is lowered and the viscosity is likely to approach Newtonian. Since the conductive paste of the present invention has a low viscosity and a viscosity close to Newtonian, it has good fluidity. For this reason, for example, a coating formed by screen printing has a smooth surface and is unlikely to vary in film thickness. Therefore, the processability in laser processing is good, and a signal wiring with good linearity can be formed.

  Moreover, the electroconductive paste of this invention also improved the storage stability because the dispersibility improved by including a phosphoric acid type dispersing agent. On the other hand, the conductive paste containing no phosphoric acid dispersant has a low TI value and good fluidity immediately after preparation, but when the conductive paste is stored at 25 ° C., the viscosity and TI value change over time. Fluidity may decrease. However, the conductive paste of the present invention has the effect of increasing the affinity between the binder resin and the conductive fine particles, so that the change in viscosity and TI value is small over time, and the storage stability of the conductive paste is improved. Are better.

  The phosphate dispersant is preferably a dispersant having a phosphate group, a phosphate ester, and a phosphate. The basic skeleton of the phosphoric acid dispersant is preferably polyphosphoric acid, and a phosphoric acid ester composed of a polyester unit, a polyether unit, a polyester ether unit, a polyurethane unit, and the like.

  The phosphoric acid dispersant preferably has an acid value of 10 to 250 mgKOH / g, and more preferably 50 to 200 mgKOH / g.

  The phosphoric acid group and the unit derived from the phosphoric acid group possessed by the phosphoric acid-based dispersant may be present randomly in the molecule of the dispersing agent, but by taking the molecular structure of a block structure or a graft structure, the unit Is preferably present at the terminal portion of the molecule. The presence of the unit at the molecular terminal portion increases the affinity for the conductive fine particles and improves dispersibility. Therefore, the conductive paste for laser processing of the present invention has a viscosity suitable for printing and can form a coating film having a smooth surface.

The phosphate dispersant is more preferably a dispersant in which an amine salt is formed by a phosphate group and an amine compound. Amine salts can modify some or all of the phosphate groups. When the phosphoric acid dispersant has an amine salt, compatibility with the binder resin is improved. At the same time, since the acidity of the phosphoric acid dispersant is lowered, the binder resin, the conductive fine particles and the phosphoric acid dispersant are easily mixed, and the dispersibility is further improved. The compound that forms an amine salt is preferably a low molecular amine or a polymer amine.
Examples of low molecular amines include ethanolamine, diethanolamine, 2- (2-aminoethoxy) ethanol, triethanolamine, N, N-dimethylethanolamine, N, N-diethylethanolamine, N, N-dibutylethanolamine, and oleylamine. Etc.
Examples of the polymer amine include polyamines, amine-based (meth) acrylate copolymers, and polyallylamine.
Phosphoric acid dispersants can be used alone or in combination of two or more.

  Examples of commercially available phosphoric acid dispersants include Disperbyk (registered trademark) -110, -111, and -180 (all manufactured by Big Chemie Japan Co., Ltd.), TEGO (registered trademark) Dispers 651, and the like. Dispers655 (all manufactured by Evonik Japan Co., Ltd.), Prisurf (registered trademark) A212C, A215C, A208F, A208N, A208B, A219B, A210D, DB-01, AL, Known dispersing agents such as AL12H, DBS, DOM (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), DISPARLON (registered trademark) -DA325, and -375 (all manufactured by Enomoto Kasei Co., Ltd.) Can be mentioned.

  The phosphoric acid-based powder is preferably blended in an amount of 0.1 to 20 parts by weight, more preferably 0.1 to 15% by weight, based on 100 parts by weight of the total of the binder resin and the conductive fine particles. The dispersibility of electroconductive fine particles improves more because a dispersing agent will be 0.1 weight part or more. Moreover, the electroconductivity of a conductive film improves more because a dispersing agent will be 20 weight or less.

  Further, the conductive paste of the present invention can be used in combination with a dispersant such as a resin-type dispersant and a surfactant as long as the problem can be solved.

The conductive paste for laser processing of the present invention can further contain a solvent. By blending the solvent, the dispersion of the conductive fine particles is facilitated, and the viscosity suitable for printing can be easily adjusted.
The solvent can be selected depending on the solubility of the resin used, the type of printing method, and the like. The solvent is preferably an ester solvent, a ketone solvent, a glycol ether solvent, an aliphatic solvent, an alicyclic solvent, an aromatic solvent, an alcohol solvent, water, or the like.
Examples of the ester solvent include, but are not limited to, ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and dimethyl carbonate.
Examples of the cyclic ester solvent include, but are not limited to, ε-caprolactone and γ-butyrolactone.
Examples of the ketone solvent include, but are not limited to, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, diacetone alcohol, isophorone, and cyclohexanone.
Examples of glycol ether solvents include monoethers such as ethylene glycol monoethyl ether, ethylene glycol monoisopropyl, and ethylene glycol monobutyl ether, and their acetates, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, Examples thereof include propylene glycol monomethyl ether, propylene glycol monoethyl ether, and acetates thereof, but are not limited thereto.
Examples of the aliphatic solvent include, but are not limited to, n-heptane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, and the like.
Examples of the aromatic solvent include, but are not limited to, toluene, xylene, tetralin and the like.
The solvent can be used alone or in combination of two or more.

  The solvent is about 5 to 50% by weight out of the total 100% by weight of the nonvolatile content of the conductive paste and the solvent.

The conductive paste of the present invention can further contain a curing agent. The curing agent has a plurality of functional groups capable of reacting with the reactive functional group (for example, hydroxyl group or carboxyl group) of the binder resin, and heat resistance, solvent resistance, chemical resistance, or adhesion of the cured conductive film. Etc. can be improved. The curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, an oxazoline compound, a carbodiimide compound, an amine compound, an acid anhydride group-containing compound, or the like.
Specifically, when the binder resin has a hydroxyl group, an isocyanate compound or the like is preferable. Moreover, when a binder resin has a carboxyl group, an isocyanate compound, an epoxy compound, an aziridine compound, an oxazoline compound, a carbodiimide compound, etc. are preferable. Furthermore, when a binder resin has an epoxy group, an amine compound, an acid anhydride group-containing compound, and the like are preferable.

The isocyanate compound is preferably an aromatic polyisocyanate, an aliphatic polyisocyanate, an alicyclic polyisocyanate, or the like.
Examples of the aromatic polyisocyanate include a trimethylolpropane adduct of tolylene diisocyanate, an isocyanurate of tolylene diisocyanate, and an oligomer of 4,4′-diphenylmethane diisocyanate.
Aliphatic polyisocyanates include, for example, hexamethylene diisocyanate biuret, hexamethylene diisocyanate isocyanurate, hexamethylene diisocyanate trimethylolpropane adduct, hexamethylene diisocyanate oligomer, hexamethylene diisocyanate uretdione, and tolylene diisocyanate. Examples thereof include isocyanurate bodies of copolymers made of hexamethylene diisocyanate.
Examples of the alicyclic polyisocyanate include an isocyanurate of isophorone diisocyanate, an oligomer of isophorone diisocyanate, and the like.
Moreover, the blocked isocyanate which blocked these compounds is also preferable. As the blocking agent, for example, ε-caprolactam, butanone oxime, phenol, and an active methylene compound are preferable.

  The epoxy compound is a compound having an epoxy group. The properties of the epoxy compound include liquid and solid. The epoxy compound is preferably an epoxy resin such as a glycidyl ether type epoxy resin, a glycidyl amine type epoxy resin, a glycidyl ester type epoxy resin, and a cyclic aliphatic (alicyclic type) epoxy resin.

  Examples of glycidyl ether type epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AD type epoxy resins, cresol novolac type epoxy resins, phenol novolac type epoxy resins, and cresol novolak type epoxy resins. Epoxy resin having biphenyl structure between cresol structure and cresol structure (manufactured by Nippon Kayaku Co., Ltd .: NC-3000, etc.), epoxy resin having dicyclopentadiene skeleton structure between cresol structure and cresol structure of cresol novolac type epoxy resin (Nippon Kayaku Co., Ltd .: XD-1000, etc.), α-naphthol novolak type epoxy resin, bisphenol A type novolak type epoxy resin, dicyclopentadiene type epoxy resin, bif Sulfonyl type epoxy resins, tris (glycidyloxy) methane, and tetrakis (glycidyloxyphenyl) ethane and the like.

  Examples of the glycidylamine type epoxy resin include tetraglycidyldiaminodiphenylmethane, triglycidylparaaminophenol, triglycidylmetaaminophenol, and tetraglycidylmetaxylylenediamine.

Examples of the glycidyl ester type epoxy resin include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl tetrahydrophthalate.

  Examples of the cycloaliphatic (alicyclic) epoxy resin include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate and bis (epoxycyclohexyl) adipate.

  Examples of the aziridine compound include trimethylolpropane-tri-β-aziridinylpropionate, tetramethylolmethane-tri-β-aziridinylpropionate, N, N-hexamethylene-1,6-bis-1 -Aziridinecarboxamide, 4, 4-bis (ethyleneimino carboxyamino) diphenylmethane etc. are mentioned.

  Examples of the oxazoline compound include 2,2 '-(1,3-phenylene) -bis (2-oxazoline).

  Examples of the carbodiimide compound include dicyclohexyl carbodiimide, carbodilite (manufactured by Nisshinbo Co., Ltd., polycarbodiimide resin), and the like.

  Examples of the amine compound include diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

Examples of the acid anhydride group-containing compound include tetrahydrophthalic anhydride, dodecenyl succinic anhydride, methyl nadic anhydride, trimellitic anhydride, and pyromellitic anhydride.
A hardening | curing agent can be used individually or in combination of 2 or more types.

  It is preferable to mix 0.5-20 weight part of hardening | curing agents with respect to 100 weight part of binder resin. When the curing agent is used within the above range, the adhesion and heat resistance of the conductive film are further improved.

  The conductive paste of the present invention can contain additives such as a curing accelerator in order to accelerate the curing reaction. As the curing accelerator, dicyandiamide, tertiary amine compound, phosphine compound, imidazole compound, carboxylic acid hydrazide, dialkylurea such as aliphatic or aromatic dimethylurea, acid anhydride and the like can be used. The additive is effective for promoting the curing of the epoxy resin.

Examples of the tertiary amine compound include triethylamine, benzyldimethylamine, 1,8-diazabicyclo (5.4.0) undecene-7, 1,5-diazabicyclo (4.3.0) nonene-5, and the like.
Examples of the phosphine compound include triphenylphosphine and tributylphosphine.
Examples of the imidazole compound include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 2,4-dimethylimidazole, 2-phenylimidazole, and the like, and these and an epoxy resin. And a latent curing accelerator having improved storage stability, such as a compound insolubilized in a solvent and a type in which these are encapsulated in microcapsules.

Examples of the carboxylic acid hydrazide include succinic acid hydrazide and adipic acid hydrazide. Examples of the acid anhydride include tetrahydrophthalic anhydride, dodecenyl succinic anhydride, methyl nadic anhydride, trimellitic anhydride, and pyromellitic anhydride. The additives may be used alone or in combination of two or more.

  The additive is preferably blended in an amount of 0.1 to 30 parts by weight with respect to 100 parts by weight of the binder resin.

  The conductive paste of the present invention includes a friction improver, an infrared absorber, an ultraviolet absorber, a fragrance, an antioxidant, an organic pigment, an inorganic pigment, an antifoaming agent, a plasticizer, a flame retardant, and a moisturizing agent as necessary. Agents and the like.

  The conductive paste of the present invention can be produced by blending the raw materials described above in a predetermined ratio and mixing with a stirrer. As the stirrer, a known apparatus such as a planetary mixer and a desper can be used. In addition to the stirrer, the conductive fine particles can be dispersed more finely by dispersing. Examples of the disperser include a ball mill, a bead mill, and a three roll.

  The conductive paste of the present invention has a viscosity close to Newtonian. Specifically, the viscosity is 10 Pa · s to 150 Pa · s measured with a rotor # 7 (θ3 ° x R 7.7 mm) at a temperature of 25 ° C. and a rotor rotational speed of 5 rpm, and a TI value is 1. 2 to 2.4. The TI value is more preferably 1.2-2.

  The electroconductive sheet of this invention is equipped with the base material and the electroconductive film formed from the electroconductive paste for laser processing. If an example of the manufacturing method of an electroconductive sheet is given, an electroconductive film can be formed by printing an electroconductive paste on a base material, for example. Since the obtained conductive film has a smooth surface, it has good laser processability. The surface smoothness of the conductive film is preferably a surface roughness Ra of 0.3 μm or less, and more preferably 0.25 μm or less. The lower limit of Ra is preferably 0 μm, but is actually about 0.1 μm because it is technically difficult in practice. When Ra is 0.3 μm or less, there are few irregularities on the surface, so that it becomes difficult to form a circuit pattern with high rectilinearity because it is difficult for laser light to be irregularly reflected. Ra is an arithmetic average height, and can be measured with a contact-type surface shape roughness measuring machine Talysurf 60 (manufactured by Ametech).

For example, screen printing, flexographic printing, offset printing, gravure printing, and gravure offset printing are preferable, and screen printing is more preferable. The screen plate used in the screen printing is preferably a fine mesh screen, particularly preferably a fine mesh screen of about 400 to 650 mesh, in order to cope with high definition of the conductive circuit pattern and smoothness of the conductive film. . At this time, the open area of the screen is preferably 20 to 50%. The screen wire diameter is preferably about 10 to 70 μm. After printing, a drying step is preferably performed. Examples of the drying step include known drying apparatuses such as a hot air oven, an infrared oven, a microwave oven, and a composite oven in which these are combined.

  The substrate is not particularly limited. For example, polyimide film, polyparaphenylene terephthalamide film, polyether nitrile film, polyether sulfone film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polycarbonate Examples include films, polyvinyl chloride films, and polyacrylic films. Moreover, the ITO film which formed the ITO (tin dope indium oxide) layer on these films and the ITO glass which formed the ITO layer on the glass plate are also mentioned. In addition, examples of the substrate include ITO ceramics in which an ITO layer is formed on a ceramic plate. The ITO layer does not need to be formed on the entire surface of the film or plate and may be formed partially.

  Although the thickness of a base material is not specifically limited, It is about 30-350 micrometers, and 50-250 micrometers is more preferable. The mechanical properties, shape stability, dimensional stability, handling surface and the like of the substrate are likely to be appropriate depending on the thickness within the above range.

  The thickness of the conductive coating is usually preferably 3 to 30 μm and more preferably 4 to 10 μm. When the thickness is 3 to 30 μm, the influence of the laser beam on the non-irradiated portion of the laser beam is suppressed, and the adhesion to the substrate is further improved.

A method for manufacturing a signal wiring using the conductive paste of the present invention will be described.
On the base material, a conductive paste for laser processing containing a binder resin, conductive fine particles, and a dispersant is printed to form a conductive coating, and the conductive coating is irradiated with a laser to form the conductive coating. A step of forming a signal wiring by removing a part is provided.
Here, the conductive paste for laser processing has a temperature of 25 ° C., a viscosity at a rotor rotation speed of 5 rpm is 10 Pa · s to 150 Pa · s, and a thixo index is 1.2 to 2.4,
The conductive fine particles have a D10 average particle size of 0.3 to 1 μm and a D90 average particle size of 2 to 5 times the D10 average particle size.

  The steps up to the previous step (formation of the conductive film) have already been described.

  Next, in the latter stage of the process, the obtained conductive film is irradiated with laser light to form a signal wiring. The part of the conductive film irradiated with laser light absorbs the laser energy and the temperature rapidly rises to several thousand degrees, so that the part melts and evaporates, or instantly becomes plasma, and the conductive film becomes conductive. Is thought to be removed. The signal wiring may be a wiring circuit having a desired L / S, or may be a ground wiring or the like.

The laser beam preferably has a fundamental wavelength in the range of 193 to 10600 nm. Specifically, excimer laser (wavelength of fundamental wave: 193 to 308 nm), YVO ₄ laser (wavelength of fundamental wave: 1064 nm), YAG laser (wavelength of fundamental wave: 1064 nm), fiber laser (wavelength of fundamental wave: 1060 nm) , CO ₂ laser (wavelength of fundamental wave: 10600 nm), semiconductor laser, and the like.
In the present invention, a YAG laser is particularly preferable because it causes little damage to the substrate.

The output, scanning speed, and frequency when using the laser beam are not limited as long as the conductive film can be removed. Generally, the output is 1 to 50 W, and the scanning speed is 1,000 to 4. , 000 mm / s, and the frequency is about 10 to 400 kHz.
In addition, laser beam scanning (irradiation) can be repeated a plurality of times.

  The signal wiring obtained by the manufacturing method of the present invention can be used as a constituent member of a touch panel in which visibility is important because an ultrahigh-definition pattern having an L / S of 30 μm / 30 μm or less is easily obtained. Moreover, you may use for the use of wiring, such as a flat panel display and a solar cell.

  The electronic device of the present invention includes a signal wiring formed using a conductive paste for laser processing. Electronic devices are mobile phones, smartphones, and tablet devices. Examples of the electronic device include a touch panel display such as a notebook PC, an electronic book, and a car navigation system. Moreover, even if there is no display, it can be preferably used for an electronic device having a signal wiring formed by laser processing, for example, a digital camera, a video camera, a CD / DVD player, and the like.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited only to a following example. “Parts” means “parts by weight” and “%” means “% by weight”.

(Binder resin solution 1)
40 parts of JER1256 (bisphenyl A type epoxy resin, number average molecular weight (Mn) 25,000, Tg 95 ° C., epoxy equivalent 7,500, hydroxyl value 190, manufactured by Mitsubishi Chemical Corporation) in 30 parts of isophorone and 30 parts of γ-butyrolactone It melt | dissolved and the binder resin solution (1) of 40% of non volatile matters was obtained.

(Binder resin solution 2)
40 parts of JER4250 (mixture of bisphenyl A type epoxy resin and bisphenol F type epoxy resin, Mn 24,000, Tg 70 ° C., epoxy equivalent 8,500, hydroxyl value 180, manufactured by Mitsubishi Chemical) 30 parts isophorone, 30 gamma-butyrolactone 30 A binder resin solution (2) having a nonvolatile content of 40% was obtained.

(Binder resin solution 3)
40 parts of JER1009 (bisphenyl A type epoxy resin, Mn 5,200, Tg 79 ° C., epoxy equivalent 2500, hydroxyl value 220, manufactured by Mitsubishi Chemical Corporation) are dissolved in 30 parts of isophorone and 30 parts of γ-butyrolactone to give a nonvolatile content of 40 % Binder resin solution (3) was obtained.

(Binder resin solution 4)
Byron 650 (polyester resin, Mn 23,000, Tg 10 ° C., hydroxyl value 5, acid value 1, manufactured by Toyobo Co., Ltd.) 40 parts was dissolved in isophorone 30 parts and γ-butyrolactone 30 parts, and a binder resin solution (non-volatile content 40%) 4) was obtained.

(Binder resin solution 5)
Byron 550 (polyester resin, Mn 28,000, Tg-15 ° C., hydroxyl value 4, acid value 1, manufactured by Toyobo Co., Ltd.) 40 parts dissolved in isophorone 30 parts and γ-butyrolactone 30 parts, binder resin 40% non-volatile content A solution (5) was obtained.

(Binder resin solution 6)
Polyester polyol synthesized with isophthalic acid and 3-methyl-1,5-pentanediol (Kuraray Polyol P-2030, Mn 2033, manufactured by Kuraray Co., Ltd.) in a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction pipe 127.4 parts, dimethylolbutanoic acid 1.9 parts, isophorone diisocyanate 15.9 parts, dibutyltin dilaurate 0.04 parts and diethylene glycol monoethyl ether acetate 43 parts were charged and reacted at 90 ° C. for 5 hours under a nitrogen stream. I let you. Subsequently, 102 parts of diethylene glycol monoethyl ether acetate was added to obtain a polyurethane resin solution having a Mn of 19,000, a Tg of 17 ° C., a hydroxyl value of 3, and an acid value of 5. 25 parts of isophorone was added to 100 parts of a polyurethane resin solution to obtain a binder resin solution (6) of a polyurethane resin having a nonvolatile content of 40%.

(Binder resin solution 7)
In a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 90.9 parts of Kuraray polyol P-2030, 1.5 parts of dimethylolbutanoic acid, 17.1 parts of isophorone diisocyanate, dibutyltin dilaurate 0 0.03 part and 23 parts of diethylene glycol monoethyl ether acetate were charged and reacted at 90 ° C. for 3 hours under a nitrogen stream. Subsequently, 72 parts of diethylene glycol monoethyl ether acetate was added to obtain a urethane prepolymer solution having an isocyanate group. Next, a urethane prepolymer having an isocyanate group was added to a mixture of 3.18 parts of isophoronediamine, 0.36 parts of di-n-butylamine, 17.9 parts of diethylene glycol monoethyl ether, and 56.7 parts of diethylene glycol monoethyl ether acetate. After adding 204.5 parts of polymer solution and reacting at 50 ° C. for 3 hours, reacting at 90 ° C. for 2 hours, the polyurethane urea resin having Mn of 17,000, Tg of 19 ° C., acid value of 5 and nonvolatile content of 40% A binder resin solution (7) was obtained.

  The Mn, Tg, epoxy equivalent, acid value and hydroxyl value of the binder resins (1) to (7) were determined according to the following method.

<Measurement of number average molecular weight (Mn)>
Apparatus: GPC (gel permeation chromatography)
Model: Shodex GPC-101 manufactured by Showa Denko
Column: GPC KF-G + KF805L + KF803L + KF802 manufactured by Showa Denko KK
Detector: Differential refractive index detector Shodex RI-71 manufactured by Showa Denko KK
Eluent: THF
Flow rate: Sample side: 1 mL / min Reference side: 0.5 mL / min Temperature: 40 ° C
Sample: 0.2% THF solution (100 μL injection)
Calibration curve: A calibration curve was prepared using 12 standard polystyrenes with the following molecular weights manufactured by Tosoh Corporation.
F128 (1.09 X10 ⁶ ), F80 (7.06 X10 ⁵ ), F40 (4.27 X10 ⁵ ), F20 (1.90 X10 ⁵ ), F10 (9.64 X10 ⁴ ), F4 (3.79 X10 ⁴ ), F2 ( 1.81 × 10 ⁴ ), F1 (1.02 × 10 ⁴ ), A5000 (5.97 × 10 ³ ), A2500 (2.63 × 10 ³ ), A1000 (1.05 × 10 ³ ), A500 (5.0 × 10 ² ).
Baseline: Except for binder (3), the starting point of the first peak of the GPC curve was the starting point, and no peak was detected at a retention time of 25 minutes (molecular weight 3,150). The molecular weight was calculated using the line connecting both points as the baseline.
In the binder resin (3), the main peak was still detected at the retention time of 25 minutes. Therefore, a baseline was set in the same way as for other binder resins, with a retention time of 30 minutes (molecular weight 250), where a plurality of small peaks continuous to the low molecular weight side of the main peak were almost not detected, and the molecular weight Asked.

<Measurement of Tg>
Apparatus: Differential scanning calorimeter DSC-220C (manufactured by Seiko Instruments Inc.)
-Sample: about 10 mg (weigh to 0.1 mg)
・ Temperature increase rate: Measured up to 200 ° C at 10 ° C / min. ・ Tg temperature: Draw at the point where the gradient is maximized on the low temperature side of the straight line and the melting peak on the low temperature side of the curve. It was set as the temperature of the intersection of a broken line.

<Measurement of epoxy equivalent>
It measured based on JISK7236.
<Measurement of hydroxyl value and acid value>
Measurement was performed in accordance with JIS K 0070.

<Conductive fine particles>
[Silver powder A] Flake silver powder (D10 average particle diameter 0.8 μm, D90 / D10 average particle diameter ratio 2.3, tap density 3.9 g / cm ³ , specific surface area 1.46 m ² / g) manufactured by Metallo Technologies Japan
[Silver powder B] Agglomerated silver powder (D10 average particle diameter 0.5 μm, D90 / D10 average particle diameter ratio 3.4, tap density 2.9 g / cm ³ , specific surface area 1.50 m ² / g) manufactured by Metallo Technologies Japan
[Silver powder C] Spherical silver powder manufactured by DOWA Electronics Co., Ltd. (D10 average particle size 0.7 μm, D90 / D10 average particle size ratio 4.4, tap density 3.8 g / cm ³ , specific surface area 0.97 m ² / g)
[Silver powder D] Spherical silver powder manufactured by DOWA Electronics Co., Ltd. (D10 average particle size 1.3 μm, D90 / D10 average particle size ratio 2.6, tap density 5.2 g / cm ³ , specific surface area 0.43 m ² / g)
[Silver powder E] Spherical silver powder manufactured by DOWA Electronics Co., Ltd. (D10 average particle size 0.4 μm, D90 / D10 average particle size ratio 6.5, tap density 4.9 g / cm ³ , specific surface area 1.0 m ² / g)

<D10 average particle size and D90 average particle size determination>
The cumulative particle size (D10 and D19) of the volume particle size distribution was measured using a laser diffraction particle size distribution measuring device “SALAD-3000” (manufactured by Shimadzu Corporation).

<Tap density>
Measured based on JIS Z 2512: 2006 method.

<BET specific surface area>
The value calculated by the following calculation formula from the surface area measured using the flow type specific surface area measuring device “Flowsorb II” (manufactured by Shimadzu Corporation) was defined and described as the specific surface area.
Specific surface area (m ² / g) = surface area (m ² ) / powder mass (g)
[Dispersant A] DISPERBYK-180 (amine salt of polyester ether copolymer containing a phosphate group, acid value 94 KOH mg / g, amine value 94 KOH mg / g, nonvolatile content 81%, manufactured by Big Chemie Japan)
[Dispersant B] TEGO Dispers 655 (phosphate ester of specially modified polyether polymer, acid value 190 KOH mg / g, non-volatile content 100% manufactured by Evonik Japan)
[Dispersant C] DISPERBYK-111 (block copolymer containing a phosphate group, acid value: 129 KOH mg / g, non-volatile content: 95%, manufactured by Big Chemie Japan)
[Dispersant D] BYK-104P (unsaturated polycarboxylic acid polymer, acid value 180 KOH mg / g, nonvolatile content 50%, manufactured by Big Chemie Japan)
[Dispersant E] DISPERBYK-182 (block copolymer of polyurethane and polyether containing tertiary amino group, amine value 13 KOHmg / g, nonvolatile content 43%, manufactured by Big Chemie Japan)
[Carbon Black A] Carbon black # 3030B (D50: 55nm, specific surface area 32m ² / g, oil absorption of 130 cm ^3/100 g, manufactured by Mitsubishi Chemical Corporation)
[Curing Agent A] Duranate MF-K60X (Block type hexamethylene diisocyanate curing agent, non-volatile content 60%, manufactured by Asahi Kasei Chemicals Corporation)

<Example 1>
Binder resin solution (1): 100 parts, Dispersant A: 2.5 parts, Silver powder A: 370 parts, Diethylene glycol monobutyl ether acetate: 37 parts are mixed in a planetary mixer, and then three rolls are used. Then, a conductive paste was prepared by dispersing.
The obtained conductive paste had a nonvolatile content of about 81% by weight. In the nonvolatile content, the silver powder was about 90% by weight and the epoxy resin was about 10% by weight.

<Examples 2 to 17, Comparative Examples 1 to 5>
Examples 2 to 17 and Comparative Example 1 were carried out in the same manner as in Example 1 except that the binder resin solution, silver powder, dispersant, carbon black, and curing agent were changed to the blending ratios shown in Tables 1 and 2. -5 conductive pastes were prepared. Carbon black was mixed with a binder resin solution, silver powder, a dispersant and a solvent, and dispersed using a three roll.

<Measurement of viscosity and TI value>
The viscosity and TI value of the obtained conductive paste were measured under the following conditions.
・ Viscometer: E-type viscometer TVE-25H (manufactured by Toki Sangyo Co., Ltd.)
Rotor: Cone rotor # 7 (θ3 ° x R7.7mm)
・ Measurement temperature: 25 ℃
・ Sample: 0.1 ml
Viscosity measurement: The value after 2 minutes at a rotation speed of 5 rpm was taken as the viscosity.
-TI value measurement: Measured 2 minutes after 2 rpm and 2 minutes after 20 rpm TI value = (2 minutes after 2 rpm) / (2 minutes after 20 rpm) Number)

<Storage stability>
100 g of the obtained conductive paste was put into an 80 ml mayonnaise bottle and stored in a sealed state at 25 ° C. for 3 months. After storage, the viscosity and TI value were measured by the same method as described above to evaluate the storage stability.
Evaluation criteria ○: Change in viscosity or TI value is less than 20% Good Δ: Change in viscosity or TI value is 20% or more and less than 40% (no problem in practical use)
X: Change in viscosity or TI value is 40% or more (not practical)

[Creation of conductive sheet]
The conductive ink obtained on a 75 μm thick polyethylene terephthalate film (hereinafter referred to as “PET film”) is screen-printed in a pattern shape of 15 mm in length × 30 mm in width and dried in an oven at 135 ° C. for 30 minutes to form a conductive film A conductive sheet having a thickness of about 5 μm was obtained. In addition, the thickness of the electroconductive sheet was measured using MH-15M type | mold measuring device (made by Nikon Corporation).

<Represented resistance value>
The surface resistance value of the obtained conductive sheet was measured using a series 4 probe (ASP) of a Loresta GPMCP-T610 measuring instrument (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) at 25 ° C. and a humidity of 50%. .

<Calculation of volume resistivity>
The volume resistivity of the conductive sheet was calculated by substituting the surface resistance value and the film thickness measured by the above method into the following equations.
Volume resistivity (Ω · cm) = (Surface resistivity: Ω / □) x (Film thickness: cm)
The evaluation criteria are as follows.
Good: 50 μΩ · cm or less Practical range: Over 50 μΩ · cm, 150 Ω · cm or less Impractical use: Over 150 μΩ · cm

<Adhesion>
1. The adhesion was evaluated using an ITO laminated film and an ITO laminated etching film as a base material. The adhesion was evaluated by initial adhesion and adhesion after a time test.
The conductive paste obtained on the ITO layer of the ITO laminated film was screen-printed so that the film thickness after drying was about 6 μm to form a pattern of 15 mm length × 30 mm width, and then in a 135 ° C. oven for 30 minutes A printed matter was obtained by drying. Separately, a printed material was obtained by printing a conductive paste in the same manner as described above on the surface of the ITO laminated etching film where the ITO layer and the PET film substrate were exposed. These printed materials were used to evaluate the adhesion of the conductive film.
-ITO laminated film: V150L-OFME (thickness: 175 μm, manufactured by Nitto Denko Corporation)
ITO laminated etching film: A film in which a part of the ITO laminated film is etched with hydrochloric acid to remove the ITO layer to expose the substrate (PET film).

Evaluation method Tape adhesion test: A tape adhesion test was performed in accordance with JIS K5600.
Put a total of 100 squares of 10 squares x 10 squares at intervals of 1 meter into the conductive paste on the ITO remaining part and ITO etched part, and use cellophane tape (25 mm wide, manufactured by Nichiban Co.) on the printing surface. After pasting, the cellophane tape was rapidly peeled by hand to evaluate the state of the remaining cells.
・ Evaluation criteria ○: No peeling (good)
Δ: Slightly chipped edges (no problem in practical use)
×: Peeling over 1 square is observed (not practical)

-Adhesiveness after time test After leaving the printed matter of the ITO laminated film and the ITO laminated etching film separately prepared by the above method in an atmosphere of 60 ° C and 90% for 240 hours, the adhesiveness was evaluated by the same method as above. did. Evaluation was performed according to the same evaluation criteria as above.

2. Adhesion was evaluated using a polyimide film as the substrate.
On the polyimide film (Kapton 100H, 25 μm thickness, manufactured by Toray DuPont), the conductive paste was screen-printed so that the film thickness after drying was about 8 μm to form a pattern of 15 mm length × 30 mm width. Subsequently, the printed matter was obtained by drying in an oven at 180 ° C. for 30 minutes. The printed matter was used to evaluate the adhesion of the conductive coating.
Cellophane tape (25 mm width) was affixed on the conductive film of the printed matter, and the cellophane tape was rapidly peeled by hand to evaluate the adhesion.
○: No peeling at all (good)
Δ: Slight peeling (no problem in practical use)
X: Exfoliated entirely (not practical)

[Evaluation of laser processability]
The conductive paste is printed on a PET film having a thickness of 75 μm using a high-precision screen printing apparatus (SERIA, manufactured by Tokai Seiki Co., Ltd.) and dried at 135 ° C. for 30 minutes to have a conductive film having a thickness of about 6 μm. A conductive sheet was obtained. As the screen printing plate, as shown in FIG. 1, a plate having four window frame image portions having a width of 6 mm, a length of 115 mm, and a width of 65 mm in an area of 205 mm in length and 340 mm in width was used. The printing conditions are as follows.

(Screen printing conditions)
Screen: Stainless steel plate 400 mesh, wire diameter 18 μm
・ Emulsion thickness: 10 μm
・ Screen frame: 650x550mm
・ Squeegee angle: 70 °
・ Squeegee hardness: 80 °
・ Squeegee speed: 150 mm / sec ・ Squeegee printing pressure: 15 kgf
・ Squeegee push: 1.5mm
・ Clearance: 2.5mm
・ Solvent used: Diethylene glycol monobutyl ether acetate

<Measurement of film thickness>
The thickness of the conductive film in the obtained conductive sheet was measured using an MH-15M type measuring instrument (manufactured by Nikon Corporation).

<Measurement of surface roughness Ra>
The surface roughness Ra of the conductive film in the obtained conductive sheet was measured using a contact-type surface shape roughness measuring machine Talysurf 60 (manufactured by Ametech Co., Ltd.), and the analysis software “Tally Map Platinum ver. 5.0” (Ametech) For analysis. The definition of Ra conformed to “JIS B 0601-2001”.
The measurement conditions are as follows.
・ Measurement range: 5mm x 5mm
-Number: 51-Speed: 0.5 mm / s
In the analysis, parameters were calculated using data obtained by removing a wave by applying a 0.25 μm filter in a range of 4 mm × 4 mm.

<Laser processing evaluation>
As shown in the enlarged view of FIG. 2, with respect to the corner portion of the window frame handle-like conductive coating of the conductive sheet, 16 lines composed of a vertical line (length 70 mm), a horizontal line (length 30 mm), and a corner portion are formed. Laser processing was performed for the purpose of forming a wiring pattern with L / S of 20 μm / 20 μm. The laser processing conditions are as follows.
(Laser processing conditions)
・ Laser processing machine: Ag Laser Etching System (Suzhou Delphi Laser Co., Ltd.)
・ Laser light: YAG laser (fundamental wavelength of 1064 nm)
・ Maximum output: 20W
・ Beam diameter: 20μm
・ Output: 25%
・ Frequency: 300 kHz
・ Pulse width: 25nm
・ Scanning speed: 2000mm / s
・ Number of scans: 2 times

Using a conductive sheet after laser processing, a digital microscope (manufactured by VHX-900 Keyence) was used to evaluate the degree of variation in space width. The space width of the part from which the conductive coating was removed was read from the photographed enlarged photograph using a small general-purpose image analyzer “LUZEX AP” (manufactured by Nireco).
Arbitrary 8 spaces of the circuit pattern were selected, and the space width of 3680 locations in total, which was 460 locations, was measured, and the average value and standard deviation were obtained.
The average value of the space width was determined according to the following criteria. ○: Space width averaged 18-22 μm. Good.
Δ: Space width averaged 16 to 17 μm, or 23 to 24 μm. There is no problem in practical use.
X: The space width is less than 15 μm or exceeds 24 μm. Not practical.

The linearity of the space (the jaggedness / roughness degree of the boundary between the line portion 3 and the space portion 4 in FIG. 2) was evaluated by the standard deviation.
The linearity of the space was judged according to the following criteria.
○: Standard deviation is 0 to 1.5 μm. Good.
(Triangle | delta): A standard deviation is 1.6-2.4 micrometers. There is no problem in practical use.
X: Standard deviation is 2.5 μm or more. Not practical.
Tables 1 and 2 show the average value of space width, standard deviation, space width evaluation, and space linearity evaluation.

From the results of Table 1, the conductive pastes of Examples 1 to 17 exhibit good volume resistivity, laser processability, and adhesion to a substrate. Moreover, Example 10 to which the curing agent was added further improved the adhesion to the polyimide film.
On the other hand, as shown in Table 2, since Comparative Example 1 does not use a dispersant, the dispersion is poor and the fluidity is poor and the TI value is high. Therefore, Ra of the printed film is larger than 0.3 μm, the linearity of the space after laser processing is low, and the storage stability is also poor. Further, in Comparative Example 2, D10 of the used silver powder is larger than 1.0 μm, and it is difficult to perform laser processing, so that the space width is narrow and the linearity of the space portion is low. Further, in Comparative Example 3, D10 of the used silver powder is 0.4 μm, but the ratio of D90 / D10 is 6.5, and since it has a large particle size particle size distribution, it is difficult to perform laser processing and the straight line of the space portion. The nature is low. Moreover, since Comparative Examples 4 and 5 use a dispersant other than the phosphoric acid dispersant, the storage stability is poor.

The conductive paste for laser processing of the present invention can provide a conductive sheet that has good laser processability and maintains substrate adhesion and heat / humidity resistance reliability.
Moreover, the signal wiring formed by laser processing using the conductive paste for laser processing according to the present invention can be suitably used for touch panel displays such as mobile phones, smartphones, tablet terminals, and notebook PCs.

1 Screen printing plate 2 Window frame image part 3 Line part (L)
4 Space part (S)

Claims (10)

Including a binder resin, conductive fine particles, and a phosphoric acid dispersant,
The D10 average particle size of the conductive fine particles is 0.3 to 1 μm, and the D90 average particle size is 2 to 5 times the D10 average particle size,
A conductive paste for laser processing having a viscosity of 10 Pa · s to 150 Pa · s and a thixo index of 1.2 to 2.4 measured at 25 ° C. using a E-type viscometer at a rotor rotational speed of 5 rpm.   The conductive paste for laser processing according to claim 1, wherein the binder resin has a number average molecular weight of 10,000 to 50,000 and a glass transition temperature of 5 to 100 ° C.   The conductive paste for laser processing according to claim 1 or 2, wherein the binder resin is at least one selected from the group consisting of a polyester resin, a polyurethane resin, a polyurethane urea resin, and an epoxy resin.   The conductive paste for laser processing according to claim 2 or 3, wherein the epoxy resin is at least one of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin.   The conductive paste for laser processing according to any one of claims 1 to 4, wherein the phosphoric acid dispersant is an amine salt.   Furthermore, the electrically conductive paste for laser processing of any one of Claims 1-5 containing a laser photosensitizer.   The electroconductive sheet provided with the base material and the electroconductive film formed from the electroconductive paste for laser processing of Claims 1-6.   The conductive sheet according to claim 7, wherein the conductive coating has a surface roughness Ra of 0.1 to 0.3 μm. On the base material, a conductive paste for laser processing containing a binder resin, conductive fine particles, and a phosphoric acid-based dispersant is printed to form a conductive coating, and the conductive coating is irradiated with a laser so that the conductive A step of forming a signal wiring by removing a part of the conductive film,
The conductive paste for laser processing has a viscosity of 10 Pa · s to 150 Pa · s and a thixo index of 1.2 to 2.4 measured at a temperature of 25 ° C. and a rotor rotation speed of 5 rpm using an E-type viscometer. ,
The method for producing a signal wiring, wherein the conductive fine particles have a D10 average particle diameter of 0.3 to 1 μm and a D90 average particle diameter of 2 to 5 times the D10 average particle diameter.   The electronic device provided with the signal wiring formed from the electrically conductive paste for laser processing of any one of Claims 1-6.