JP7331840B2 - conductive paste - Google Patents

Description

An object of the present invention is to provide a conductive paste suitably used for forming fine wiring formed in proximity to a transparent conductive thin film, which is used in touch panels and the like, and is also used in printed electronics. Another object of the present invention is to provide a conductive paste that enables the production of electrode circuit wiring having high surface smoothness without any problem when forming a TFT base electrode.

2. Description of the Related Art In recent years, electronic devices equipped with a transparent touch panel, such as mobile phones, laptop computers, and electronic books, have been rapidly increasing in performance and miniaturization. In order to increase the performance and reduce the size of these electronic devices, it is necessary to reduce the size, improve the performance, and improve the degree of integration of the electronic components to be mounted, as well as increase the density of the electrode circuit wiring that connects these electronic components. It is In addition to the resistive film method, which has a small number of electrode circuit wiring, as a transparent touch panel method, the electrostatic capacitance method, which has a large number of electrode circuit wiring, has rapidly spread in recent years. There is a strong demand for higher densities. In addition, in order to make the display screen larger and due to product design requirements, there is a demand for a narrower frame portion where the electrode circuit wiring is arranged. transformation is required. In order to meet the above demands, there is a need for a technique capable of arranging the electrode circuit wiring at a higher density than in the past.

The arrangement density of the electrode circuit wiring in the frame portion of the resistive transparent touch panel is such that the widths of lines and spaces in the plane direction are each about 200 μm (hereinafter abbreviated as L/S=200/200 μm) or more, Conventionally, this has been formed by screen-printing a conductive paste. In capacitive touch panels, the required L/S is about 100/100 μm or less, and in some cases L/S is required to be 50/50 μm or less. The situation is becoming difficult to deal with.

Photolithography is an example of a candidate electrode circuit wiring formation technique that can replace screen printing. By using the photolithography method, it is sufficiently possible to form fine lines with L/S of 50/50 μm or less. However, the photolithographic method also has problems. The most typical example of the photolithography method is the method using a photosensitive resist. Generally, a photosensitive resist is applied to the copper foil portion of the surface substrate on which the copper foil layer is formed, and a photomask or laser light is applied. A desired pattern is exposed by a method such as direct writing, the photosensitive resist is developed, and then the copper foil portions other than the desired pattern are dissolved and removed with a chemical to form a thin line pattern of the copper foil. For this reason, the waste liquid treatment has a large environmental load, the process is complicated, and there are many problems including the viewpoint of production efficiency and cost.

In Patent Document 1, a coating step of applying a paste composed of an inorganic powder, a carboxyl group-containing resin, a glass frit, and a solvent on a substrate, and drying the applied paste to form a dry coating film. a laser irradiation step of drawing a pattern on the dry coating film by laser irradiation; and a developing step of developing the pattern using an alkaline solution. This proposal differs from general photolithography in that patterning is performed by removing the resin component in the paste resin component with a laser. I can't say it's resolved.

In Patent Document 2, a coating step of applying a paste containing AlN powder, glass frit and a solvent on a substrate, a drying step of drying the applied paste to form a dry coating film, and a laser beam irradiation , a laser drawing step of drawing a conductive pattern on the dry coating film, and a developing step of removing a portion of the dry coating film that has not been irradiated with the laser light using a developer A patterning method is disclosed. This invention is similar to the above technology in that it uses a laser for patterning, and in that it requires cleaning, it cannot be said that it eliminates the drawbacks of the conventional photolithography method.

Furthermore, in the recent printed electronics technology, a technology for fabricating active elements such as transistors by printing is being realized. In such applications, uniformity of film thickness and thinning are required at the same time as fine wiring. In terms of printing technology, instead of conventional screen printing and gravure printing, reversal printing, microcontact printing, screen offset printing, inkjet printing, inkjet offset printing, pad printing, etc. have been applied. It is becoming difficult to apply conventional conductive pastes to such new printing methods.

JP 2010-237573 A JP 2011-181338 A

An object of the present invention is to provide a conductive paste that is suitably used for forming fine wiring formed in proximity to a transparent conductive thin film for use in touch panels and the like, and also for forming a TFT base electrode. The object of the present invention is to provide a conductive paste that can be used to manufacture electrode circuit wiring having high surface smoothness without any problem when printing, and that is widely compatible with new printing techniques used in printed electronics technology. To provide a sexual paste.

The inventors of the present invention have extensively studied a conductive paste for arranging electrode circuit wiring having high surface smoothness, and found a conductive paste suitable for forming a conductive film. That is, the present invention consists of the following configurations.
[1] A conductive paste containing at least a conductive filler, an organic solvent, and a binder resin, wherein the binder resin is a diol compound having a bisphenol structure,
A conductive paste characterized by using a carboxyl group-containing dihydroxy compound and a carboxyl group-containing polyurethane resin which is a polyaddition reaction product of an isocyanate compound.
[2] The content of the organic solvent is 5 to 100 parts by mass with respect to 100 parts by mass of the conductive filler, and the content of the binder resin is 5 to 25 parts by mass with respect to 100 parts by mass of the conductive filler. The conductive paste according to [1], characterized in that it is a part.
[3] The conductive paste according to [1] or [2], wherein the diol compound having a bisphenol structure is an alkylene oxide adduct of bisphenol A.
[4] The conductive paste according to any one of [1] to [3], wherein the diol compound having a bisphenol structure has a molecular weight of 500 or less.
[5] Any one of [1] to [4], wherein the conductive filler is a metal powder having a center diameter D50 of 0.8 μm or more and less than 2.0 μm as measured by a laser diffraction method. conductive paste.

In the conductive paste of the present invention, a coating film formed by screen printing has a small surface roughness Ra by using a carboxyl group-containing polyurethane resin containing a diol compound having a bisphenol structure in its skeleton as a binder resin. It is a conductive paste that has an Ra of 0.4 μm or less and can form a conductive film having excellent adhesion to the substrate after a wet heat test. It is possible to form a conductive film suitable for fine wiring required for touch panels and TFT gate electrodes for printed electronics, as well as base, collector, and emitter electrodes.

The conductive paste of the present invention contains a binder resin, a conductive filler and an organic solvent as essential components.
<Binder resin>
As the binder resin in the present invention, a carboxyl group-containing polyurethane resin obtained by polyaddition reaction of a diol compound having a bisphenol structure, a dihydroxy compound containing a carboxyl group, and an isocyanate compound is used.
The binder resin of the present invention has a number average molecular weight of 3,000 to 100,000 and an acid value of 20 to 500 meq. /kg is preferred.
The diol compound having a bisphenol structure in the present invention includes bisphenol A, bisphenol F, bisphenol S, alkylene oxide adducts of bisphenol A, alkylene oxide adducts of bisphenol F, alkylene oxide adducts of bisphenol S, mixtures thereof, and polycondensation. can use objects.
In the present invention, bisphenol A/F copolymerization type, bisphenol S type, and bisphenol A/S copolymerization type can be used. Among these, from the viewpoint of substrate adhesion, the flexibility of the resulting film, and from the viewpoint of transferability through a blanket in reverse printing, microcontact printing, and other printing techniques including offset processes, bisphenol It is preferable to use an alkylene oxide adduct of A. The acid value of the binder resin in the present invention is 20 meq. / kg or more 500 meq. /kg or less, and 30 meq. /kg or more 200 meq. /kg or less is more preferable. The acid value in the organic component improves the adhesion to the substrate, especially after the wet heat test, but if it is too high, the hydrolysis of the organic component may be accelerated and the electrical conductivity and adhesion to the substrate may be impaired. Moreover, there is a possibility that the migration resistance may be adversely affected.

A dihydroxy compound containing a carboxyl group is used to keep the acid value of the binder resin within a predetermined range.
Dihydroxy compounds containing a carboxyl group include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, N,N-bishydroxyethylglycine, N,N-bishydroxyethylalanine and the like.

Isocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, m-phenylene diisocyanate, 3,3'-dimethoxy-4,4' - biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, isophorone diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate and the like.

The content ratio of each of the diol compound having a bisphenol structure, the dihydroxy compound containing a carboxyl group, and the isocyanate compound is 3 parts per 100 parts by mass of the diol compound having a bisphenol structure. ~10 parts by mass, preferably 60 to 80 parts by mass. Adhesion and heat resistance effects can be exhibited by setting it as the former range.

The molecular weight of the diol compound having a bisphenol structure is preferably 500 or less, more preferably 400 or less, still more preferably 350 or less. Although the lower limit is not particularly limited, it is preferably 200 or more, more preferably 300 or more, and still more preferably 300 or more. Within the above range, the urethane group concentration is optimized, and excellent adhesion can be achieved.

The content of the binder resin is preferably 5 to 25 parts by mass, more preferably 5 to 15 parts by mass based on 100 parts by mass of the conductive filler. By setting it within the above range, the conductivity and the adhesion to the substrate are improved.

In the present invention, other resins may be added as a binder resin. The type of the binder resin is preferably a thermoplastic resin, and is not particularly limited, but polyester resin, epoxy resin, phenoxy resin, polyamide resin, polyamideimide resin, polycarbonate resin, polyurethane resin, phenol resin, acrylic resin, polystyrene, styrene resin. -Acrylic resin, styrene-butadiene copolymer, phenolic resin, polyethylene resin, polycarbonate resin, phenolic resin, alkyd resin, styrene-acrylic resin, styrene-butadiene copolymer resin, polysulfone resin, polyethersulfone resin, vinyl chloride -vinyl acetate copolymer resin, ethylene-vinyl acetate copolymer resin, polystyrene, silicone resin, fluororesin, etc., can be mentioned, and these resins can be used alone or as a mixture of two or more. It is preferably one or a mixture of two or more selected from the group consisting of polyester resins, polyurethane resins, epoxy resins, phenoxy resins, vinyl chloride resins, and cellulose derivative resins.

Although the number average molecular weight of the binder resin in the present invention is not particularly limited, the number average molecular weight is preferably from 3,000 to 100,000, more preferably from 8,000 to 50,000. If the number average molecular weight is too low, it is not preferable in terms of durability and moist heat resistance of the formed conductive film. On the other hand, if the number average molecular weight is too high, the cohesive force of the resin increases, and although the durability of the conductive film is improved, the surface smoothness may be significantly deteriorated.

The glass transition temperature of the binder resin in the invention is preferably 60° C. or higher, more preferably 65° C. or higher. If the glass transition temperature is low, there is a risk that the reliability as a conductive film after wet heat will decrease, and the surface hardness will decrease, and the tackiness will cause migration of the components contained in the paste to the contact partner during use. The reliability of the conductive film may deteriorate. On the other hand, the glass transition temperature of the binder resin is preferably 150° C. or lower, more preferably 120° C. or lower, and even more preferably 100° C. or lower, in consideration of printability, adhesion, solubility and paste viscosity.

<Conductive filler>
As the conductive filler in the present invention, metal powders, carbon-based particles, metal-coated inorganic or organic particles, conductive polymers, hybrid materials containing conductive polymers, and the like can be used. The conductive filler mainly used in the present invention is metal powder. Metal powders include precious metals such as gold, silver, platinum, rhodium and ruthenium; base metals such as copper, nickel and aluminum; base metal particles coated with precious metals such as silver-coated copper powder and silver-coated nickel powder; , cupronickel, phosphor bronze, monel, invar, nickel silver, silver-copper alloy, and other alloy powders can be used.
Silver powder is generally the most commonly used metal powder for conductive paste, and silver powder can be preferably used in the present invention as well. The shape of the silver powder used in the present invention is not particularly limited. Examples of conventionally known shapes include flake-like (flaky), spherical, dendrite-like, and three-dimensional spherical primary particles described in JP-A-9-306240. There is an aggregated shape (aggregate) etc.

The median diameter (D50) of the silver powder used in the present invention is preferably 0.6 μm or more. More preferably, it is 0.8 μm or more. Moreover, the preferable upper limit of the center diameter is less than 2.0 μm. It is more preferably 1.5 μm or less, and still more preferably 1 μm or less. If the center diameter deviates from the predetermined range, a conductive path may not be formed satisfactorily, resulting in poor conductivity. On the other hand, if the particle size is too small, it tends to aggregate, and as a result, it may become difficult to disperse. On the other hand, when the upper limit is exceeded, the smoothness of the printed film may deteriorate.

The median diameter (D50) in the present invention is determined from the cumulative particle size distribution measured in the total reflection mode using a laser diffraction/scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., MICROTRAC HRA).

The silver powder used in the present invention preferably has a tap density of 2.0 g/cm ³ or more. If the tap density is low, the degree of silver filling in the coating film is low, resulting in poor surface smoothness. Although the upper limit of the tap density is not particularly limited, it is preferably 9.0 g/cm ³ , more preferably 7.5 g/cm ³ , still more preferably 5.5 g/cm ³ .

<Organic solvent>
The organic solvent that can be used in the present invention is not particularly limited, but from the viewpoint of keeping the volatilization rate of the organic solvent within an appropriate range, it preferably has a boiling point of 100° C. or more and less than 300° C., more preferably a boiling point of It is 150°C or more and less than 280°C. The conductive paste of the present invention is typically prepared by dispersing a thermoplastic resin, silver powder, an organic solvent and, if necessary, other components using a three-roll mill or the like. If too much is used, the solvent may volatilize during dispersion, and there is a concern that the ratio of components constituting the conductive paste may change. On the other hand, if the boiling point of the organic solvent is too high, a large amount of the solvent may remain in the coating film depending on the drying conditions, and there is a concern that the reliability of the coating film may be lowered.

Moreover, as the organic solvent that can be used in the present invention, one in which the binder is soluble and the conductive filler can be well dispersed is preferable. Specific examples include ethyl diglycol acetate (EDGAC), butyl glycol acetate (BMGAC), butyl diglycol acetate (BDGAC), cyclohexanone, toluene, isophorone, γ-butyrolactone, benzyl alcohol, Solvesso 100, 150, manufactured by Exxon Chemical Co., Ltd. 200, propylene glycol monomethyl ether acetate, adipic acid, a mixture of dimethyl esters of succinic acid and glutaric acid (for example, DBE manufactured by DuPont Co.), terpineol, etc. Among these, binder resin dissolution EDGAC, BMGAC, BDGAC, and mixed solvents thereof are preferred from the viewpoints of excellent properties, moderate solvent volatility during continuous printing, and good suitability for printing by screen printing or the like.

The content of the organic solvent is preferably 5-100 parts by mass, more preferably 10-50 parts by mass, with respect to 100 parts by mass of the conductive filler. If the content of the organic solvent is too high, the viscosity of the paste becomes too low, and sagging tends to occur during fine line printing. On the other hand, if the content of the organic solvent is too low, the viscosity of the paste will be extremely high, and the screen printability, for example, in forming a conductive film may be remarkably lowered.

A carbon-based filler can be added to the conductive paste of the present invention. Examples include carbon-based fillers such as carbon black, graphite powder, ketjen black, carbon nanotube, graphene, fullerene, and carbon nanohorn. The content of the carbon-based filler is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2 parts by weight, with respect to 100 parts by weight of the silver powder.

The following inorganic substances can be added to the conductive paste of the present invention. Inorganic substances include various carbides such as silicon carbide, boron carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, niobium carbide, tungsten carbide, chromium carbide, molybdenum carbide, calcium carbide, diamond carbon lactam; boron nitride , various nitrides such as titanium nitride and zirconium nitride, various borides such as zirconium boride; titanium oxide (titania), calcium oxide, magnesium oxide, zinc oxide, copper oxide, aluminum oxide, silica, fumed silica (for example, Japan Various oxides such as Aerosil colloidal silica manufactured by Aerosil; various titanic acid compounds such as calcium titanate, magnesium titanate, and strontium titanate; sulfides such as molybdenum disulfide; various types such as magnesium fluoride and carbon fluoride Fluorides; various metal soaps such as aluminum stearate, calcium stearate, zinc stearate and magnesium stearate; talc, bentonite, talc, calcium carbonate, bentonite, kaolin, glass fiber, mica, etc. can be used. By adding these inorganic substances, it may be possible to improve printability, heat resistance, mechanical properties and long-term durability. Among these, fumed silica is preferable in the conductive paste of the present invention from the viewpoint of imparting durability and printability, particularly screen printability.

The conductive paste of the present invention may contain additives such as a dispersant, a surface conditioner, an antifoaming agent, and a rheology control agent. Furthermore, carbodiimide, epoxy, and the like can be appropriately blended. These can be used alone or in combination. When these are added to the paste, they may change the rheology of the paste and improve the surface smoothness.

A known dispersant can be used as the dispersant. Furthermore, monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, margaric acid and stearic acid, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, oxalic acid, malonic acid, Dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid and azelaic acid, dibasic acids having 12 to 28 carbon atoms such as maleic acid and dimer acid, 1,4-cyclohexanedicarboxylic acid, 1, 3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy Hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalenedicarboxylic acid, alicyclic dicarboxylic acids such as tricyclodecanedicarboxylic acid, and hydroxycarboxylic acids such as hydroxybenzoic acid and lactic acid can be mentioned. Trivalent or higher carboxylic acids such as trimellitic anhydride and pyromellitic anhydride, unsaturated dicarboxylic acids such as fumaric acid, and carboxylic acid diols such as dimethylolbutanoic acid and dimethylolpropionic acid can also be mentioned.

Among these, aliphatic monocarboxylic acids and aliphatic dicarboxylic acids that are solid at 25° C. are preferably used as dispersants in the present invention. Specifically, dicarboxylic acids such as lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid, and maleic acid etc. can be exemplified.
Furthermore, among these solid fatty acids, compounds having a melting point of 60° C. to 150° C. are preferred as dispersants in the present invention. Such a dispersing agent evaporates and precipitates under the temperature conditions during paste hardening, but at the same time, it liquefies because it reaches its melting point, exhibiting the effect of smoothing the paste hardened film.

As other surface conditioners, antifoaming agents, leveling agents and rheology control agents in the present invention, known additives used in inks or pastes may be used as required.

<Curing agent>
The conductive paste of the present invention may contain a curing agent capable of reacting with the binder resin to an extent that does not impair the effects of the present invention. Adding a curing agent raises the curing temperature and may increase the load on the production process, but it is expected that the heat and humidity resistance of the coating film will improve due to cross-linking due to the heat generated during drying of the coating film.

Although the type of the curing agent that can react with the binder resin of the present invention is not limited, isocyanate compounds and/or epoxy resins are particularly preferable from the viewpoints of adhesion, bending resistance, curability, and the like. Furthermore, with respect to the isocyanate compound, it is preferable to use a blocked isocyanate group, since the storage stability is improved. Curing agents other than isocyanate compounds include known compounds such as methylated melamine, butylated melamine, benzoguanamine, amino resins such as urea resins, acid anhydrides, imidazoles, and phenol resins. These curing agents can be used in combination with known catalysts or accelerators selected according to their type. The amount of the curing agent to be blended is not particularly limited, as long as it does not impair the effects of the present invention. It is preferably 1 to 30 parts by mass, and even more preferably 2 to 20 parts by mass.

Examples of isocyanate compounds that can be blended in the conductive paste of the present invention include aromatic or aliphatic diisocyanates, trivalent or higher polyisocyanates, and the like, and may be either low-molecular-weight compounds or high-molecular-weight compounds. For example, aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate; aromatic diisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and isophorone diisocyanate; Alicyclic diisocyanates, trimers of these isocyanate compounds, and excess amounts of these isocyanate compounds, such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine or a terminal isocyanate group-containing compound obtained by reacting with a low-molecular-weight active hydrogen compound, such as polyester polyols, polyether polyols, polyamides, or the like. Examples of blocking agents for isocyanate groups include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol and chlorophenol; oximes such as acetoxime, methylethylketoxime and cyclohexanone oxime; alcohols such as methanol, ethanol, propanol and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol Lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propyrolactam, and other aromatic amines, imides, acetylacetone, acetoacetate, ethyl malonate, etc. Also included are active methylene compounds, mercaptans, imines, imidazoles, ureas, diaryl compounds, sodium bisulfite and the like. Among these, oximes, imidazoles, and amines are particularly preferred in terms of curability.

Epoxy compounds used as curing agents in the present invention include, for example, bisphenol A glycidyl ether, bisphenol S glycidyl ether, novolac glycidyl ether, glycidyl ether types such as brominated bis, hexahydrophthalic acid glycidyl ester, dimer acid glycidyl ester, and the like. Glycidyl ester type, triglycidyl isocyanurate, or alicyclic or aliphatic epoxides such as 3,4-epoxycyclohexylmethyl carboxylate, epoxidized polybutadiene, and epoxidized soybean oil. The above may be used in combination. Among these, bisphenol A glycidyl ether is most preferable from the viewpoint of curability, and among them, those having a molecular weight of less than 3000 and having two or more glycidyl ether groups in one molecule are more preferable.

The viscosity of the conductive paste of the present invention is not particularly limited, and may be appropriately adjusted according to the coating film forming method. For example, when applying the conductive paste to the substrate by screen printing, the viscosity of the conductive paste is preferably 100 dPa·s or more, more preferably 150 dPa·s or more at the printing temperature. Although the upper limit is not particularly limited, if the viscosity is too high, the surface smoothness may deteriorate.

The conductive paste of the present invention preferably has an F value of 60 to 95%, more preferably 75 to 95%. The F-value is a numerical value indicating the filler mass part relative to the total solid content of 100 mass parts contained in the paste, and is expressed by F value=(filler mass part/solid content mass part)×100. Here, the weight part of the filler means the weight part of the conductive filler, and the weight part of the solid content means the weight part of the components other than the solvent, including the conductive filler, organic components, other curing agents and additives. If the F value is too low, a conductive film showing good conductivity cannot be obtained, and if the F value is too high, the adhesion between the conductive film and the substrate and/or the surface hardness of the conductive film tend to decrease. There is an unavoidable decrease in printability.

It is essential that the conductive paste of the present invention has a degree of dispersion of 10 μm or less as determined by the grind gage specified in ISO 1524:2013. If the degree of dispersion exceeds this range, abnormal projections increase on the surface of the conductive film obtained from the paste, and sharpness of fine lines by laser etching becomes poor.

As described above, the conductive paste of the present invention can be prepared by dispersing the organic component, silver powder, organic solvent and, if necessary, other components using a triple roll or the like. Here, an example of a more specific manufacturing procedure will be shown. First, the binder resin is dissolved in an organic solvent. After that, silver powder, a dispersant, and other additives are added as necessary, and the mixture is dispersed by using a double planetary mixer, a dissolver, a planetary stirrer, or the like. After that, it is dispersed by a three-roll mill to obtain a conductive paste. The conductive paste thus obtained can be filtered if desired. Dispersion using other dispersing machines such as bead mills, kneaders, extruders, etc. does not pose any problem.
In the present invention, it is preferable to use a dispersant that is solid at 25° C., and to mix and disperse the silver powder, the solvent solution of the binder resin, and the dispersant all at once.

In the present invention, filtration is performed after the materials are mixed and dispersed. Although the mesh size of the filter for filtering the conductive paste is not particularly limited, it is preferably 25 μm or less, more preferably 20 μm or less, and most preferably 15 μm or less. When a filter with a mesh opening of more than 25 μm is used, undispersed conductive powder, coarse particles, foreign matter, etc. cannot be removed, and short circuits occur between fine lines after etching, resulting in a decrease in yield.
On the other hand, the mesh size is preferably 1 μm or more. As a result, the number of filter replacements increases, and the production efficiency drops significantly.

The conductive paste of the present invention is applied or printed onto a substrate to form a coating film, and then the organic solvent contained in the coating film is volatilized to dry the coating film, thereby forming the conductive film of the present invention. be able to. The method of applying or printing the conductive paste on the substrate is not particularly limited, and it can be applied to any printing method such as gravure printing, offset printing, letterpress printing, inkjet printing, reverse printing, and microcontact printing. In particular, the screen printing method is preferable because the process is simple and the technique is widely used in the industry of forming electric circuits using a conductive paste.

The step of volatilizing the organic solvent is preferably carried out at room temperature and/or under heating. In the case of heating, the heating temperature is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 110° C. or higher, because the conductivity, adhesion, and surface hardness of the dried conductive film are improved. From the viewpoint of heat resistance of the underlying transparent conductive layer and energy saving in the production process, the heating temperature is preferably 150° C. or lower, more preferably 135° C. or lower, and even more preferably 130° C. or lower. When the conductive paste of the present invention contains a curing agent, the curing reaction proceeds when the step of volatilizing the organic solvent is performed under heating.

The thickness of the conductive film of the present invention may be appropriately set according to the intended use. However, from the viewpoint that the conductivity of the conductive film after drying is good, the film thickness of the conductive film is preferably 0.5 μm or more and 30 μm or less, more preferably 0.8 μm or more and 20 μm or less. It is preferably 1.2 μm or more and 10 μm or less, and more preferably 1.6 μm or more and 7 μm or less. If the film thickness of the conductive film is too thin, there is a possibility that desired conductivity as a circuit cannot be obtained. Further, the thickness of the conductive film affects the line width and line spacing formed by laser etching, so it is better not to make the conductive film excessively thick especially when fine wiring is required.

It is essential that the surface roughness Ra of the conductive film of the present invention is 0.40 μm or less. If the surface roughness Ra is too high, the scattering of laser light becomes noticeable in the laser etching process, and the sharpness of fine lines (linearity of edges) decreases.

In the present invention, laser etching makes it possible to form conductive fine wiring having a line width of 100 μm or less and a line-to-line width of 100 μm or less. In the present invention, the line width of the conductive fine wiring is preferably 50 μm or less, and the line width can be four times or less the thickness of the conductive film. Further, in the present invention, the line width of the conductive fine wiring is 35 μm or less, and the line width can be 3.5 times or less the thickness of the conductive film.

Examples and comparative examples are given below to describe the present invention in more detail, but the present invention is not limited by the examples. Each measured value described in Examples and Comparative Examples was measured by the following method.

<Number average molecular weight>
The sample resin was dissolved in tetrahydrofuran so that the resin concentration was about 0.5% by weight, filtered through a polytetrafluoroethylene membrane filter with a pore size of 0.5 μm, and used as a GPC measurement sample. Using tetrahydrofuran as a mobile phase, using a gel permeation chromatograph (GPC) Prominence manufactured by Shimadzu Corporation, using a differential refractometer (RI meter) as a detector, GPC measurement of a resin sample at a column temperature of 30 ° C. and a flow rate of 1 ml / min. did The number-average molecular weight was converted to a standard polystyrene equivalent, and was calculated by omitting the portion corresponding to a molecular weight of less than 1,000. Showa Denko shodex KF-802, 804L, and 806L GPC columns were used.

<Acid value>
0.2 g of sample resin was precisely weighed and dissolved in 20 ml of chloroform. Then, using a phenolphthalein solution as an indicator, titration was performed with 0.01N potassium hydroxide (ethanol solution). The unit of acid value is eq. /10 ⁶ g, i.e. equivalent weight per metric ton of sample.

<Glass transition temperature (Tg)>
5 mg of the sample resin was placed in an aluminum sample pan, sealed, and measured using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc. up to 200° C. at a heating rate of 20° C./min. and the temperature at the intersection of the extended line of the baseline below the glass transition temperature and the tangent line showing the maximum slope at the transition.

<Dispersion degree>
Measured by Grind Gage specified in ISO 1524:2013.
<Preparation of conductive laminate test piece 1>
An annealed PET film (Lumirror S manufactured by Toray Industries, Inc.) having a thickness of 100 μm is printed with a conductive paste by a screen printing method using a 400-mesh stainless screen to form a solid pattern with a width of 25 mm and a length of 45 mm. Then, it was heated at 130° C. for 30 minutes in a hot air circulating drying oven to obtain a conductive laminate test piece. The coating thickness during printing was adjusted so that the dry film thickness was 5 to 10 μm.

<Adhesion>
According to JIS K-5400-5-6:1990, the conductive laminate test piece 1 was evaluated by a peeling test using Sellotape (registered trademark) (manufactured by Nichiban Co., Ltd.). However, the number of cuts in each direction of the grid pattern was 11, and the cut interval was 1 mm. 100/100 indicates good adhesion without peeling, and 0/100 indicates that all have been peeled off.

<Moisture heat test>
The sample was exposed for 240 hours in a high-temperature, high-humidity chamber adjusted to 85°C, 85% RH, and 1 atm, and then allowed to stand in a room under standard conditions for 24 hours or more.

<Resistivity>
The sheet resistance and film thickness of the conductive laminate test piece 1 were measured, and the specific resistance was calculated. The thickness of the cured coating film was measured at 5 points using a thickness gauge manufactured by Ono Sokki Co., Ltd. with the thickness of the PET film as the zero point, and the average value was used. The sheet resistance was measured by sandwiching the long side of the test piece with a width of 25 mm and a length of 45 mm between electrodes with a width of 10 mm, and measuring the resistance value of a square pattern of 25 mm × 25 mm as a measurement range. (manufactured by HEWLETT PACKARD), four test pieces were measured, and the average value was used.

<Surface roughness>
The surface roughness Ra of the conductive laminate test piece 1 was measured using a surface roughness meter (Handy Surf E-35B, manufactured by Tokyo Seimitsu Co., Ltd., calculated based on JIS-1994).

<Laser Etchability>
A 2.5 × 10 cm rectangle of the conductive paste is applied by screen printing on the ITO of the polyester base material on which the ITO thin film is formed by the screen printing method. A conductive thin film was obtained by drying at 120° C. for 30 minutes. The surface roughness R on ITO was 0.3 μm. Printing conditions and the like were adjusted so that the film thickness was 4 to 6 μm. Next, the conductive thin film prepared by the above method is subjected to laser etching processing, the line width/line spacing shown below is drawn, and the presence or absence of fine wiring formation at each set line width/line spacing is observed with a microscope. , Conductivity, and whether or not there is a short circuit between lines. It was decided that
Line width/width between lines = 40 μm/40 μm Processable in a wider area ×, Line width/width between lines = 40 μm/40 μm to Line width/width between lines = 20 μm/20 μm Those that could be processed with line width/line spacing = 20 µm/20 µm or less were rated with ◯, and those with line width/line spacing = 15 µm/line spacing = 15 µm/15 µm were rated with ⊚.
A YAG laser was used as the laser beam, and the minimum diameter of the beam was adjusted to be less than half the width of each line. A tester with an applied voltage of 1.5 V was used to check the continuity of wiring and the presence or absence of a short circuit between lines.

<Compatibility with microcontact printing>
A fine pattern of 5 μm was formed by applying a diluted conductive paste to a PDMS plate and applying a printing pressure. When the pattern was broken, it was evaluated as x; A tester with an applied voltage of 1.5 V was used to check the continuity of wiring and the presence or absence of a short circuit between lines.

<Synthesis example>
<Polyurethane resin 1>
(Synthesis of polyester resin)
In an autoclave equipped with a thermometer and stirrer,
Dimethyl terephthalate 97 parts by weight,
Dimethyl isophthalate 97 parts by weight,
Ethylene glycol 61 parts by weight,
Propylene glycol 75 parts by weight,
1,4-cyclohexanediol 25 parts by weight,
0.1 part by weight of tetrabutoxy titanate was charged and heated at 180 to 230° C. for 120 minutes to effect transesterification. Then, the temperature of the reaction system was raised to 250° C., and the reaction was continued for 60 minutes at a system pressure of 1 to 10 mmHg to obtain a copolymer polyester resin (A1). The composition of the obtained copolymerized polyester resin (A1) was as a result of NMR analysis,
As an acid component,
Terephthalic acid 50 mol %
Isophthalic acid 50 mol %
Ethylene glycol 45 mol % as alcohol component
Propylene glycol 45 mol %
1,4-cyclohexanediol 10 mol %
It had a weight average molecular weight of 3,500.
100 parts by mass of the copolymerized polyester (A1) obtained in a reaction vessel equipped with a stirrer, a condenser, and a thermometer, DMBA: 5.3 parts by mass, and EDGAC: 174 parts were charged and dissolved, followed by HDI: 31.6 parts. , MDI: 36.8 parts, and dibutyltin dilaurate: 0.03 part as a catalyst were added and reacted at 95° C. for 6 hours. Then, the solution was diluted with 152 parts of EDGAC and 81 parts of BDGAC to obtain a polyurethane resin 1 solution.
<Polyurethane resins 2 to 4>
Ethylene oxide adduct of bisphenol A: 100 parts by mass, DMBA: 5.3 parts by mass were dissolved in EDGAC: 174 parts, HDI: 31.6 parts, MDI: 36 in a reaction vessel equipped with a stirrer, condenser, and thermometer. 0.03 part of dibutyltin dilaurate was added as a catalyst and reacted at 95° C. for 6 hours. Then, the solution was diluted with 152 parts of EDGAC and 81 parts of BDGAC to obtain a polyurethane resin 2 solution.
The solid content concentration of the obtained polyurethane resin solution was 35% by mass. The resin solution obtained in this way is dropped onto a polypropylene film, applied using a stainless steel applicator, and left to stand for 3 hours in a hot air dryer adjusted to 120 ° C. to evaporate and dry the solvent, Next, the dried resin thin film was peeled off from the polypropylene film to obtain a film-like dry resin thin film, which was used for acid value measurement and the like.
Thereafter, the raw materials were changed in the same manner, and the modification operation was performed to obtain a solution of the binder resin shown in Table 1.
[Example 1]
2857 parts of a solution of polyurethane resin 2 shown in Table 1 (1000 parts in terms of solid part),
8700 parts of flaky silver powder 1,
65 parts of curing agent,
Curing catalyst 5 parts Ion catcher 400 parts Carbon black 25 parts,
15 parts of dispersant,
As solvents, 2100 parts of EDGAC and 900 parts of BDGAC were blended and dispersed by passing through a chilled three-roll kneader twice. Next, a filter of 635 mesh (stainless mesh filter (opening 20 μm) was attached to the paste filter, and the paste was filtered. After that, the obtained conductive paste was printed in a predetermined pattern, and then heated at 130 ° C. After drying for 30 minutes, a conductive film was obtained.Using this conductive film, the basic physical properties were measured, and then the surface smoothness was examined.Furthermore, a moisture and heat resistance test, fine wiring formation by laser etching, and microcontact were performed. The printability in printing was evaluated, and the evaluation results are shown in Table 2.

In Table 1, Bis-A-EO: ethylene oxide adduct of bisphenol A, molecular weight 316
Bis-F-EO: ethylene oxide adduct of bisphenol F molecular weight 288
Bis-S-EO: ethylene oxide adduct of bisphenol S molecular weight 456
DMBA: dimethylolbutanoic acid
EDGAC: ethyl diglycol acetate manufactured by Daicel Corporation HDI: 1,6-diisocyanatohexane MDI: 4,4'-diphenylmethane diisocyanate.

[Examples 2 to 10] [Comparative Example 1]
Examples 2 to 10 and Comparative Example 1 were carried out by changing the resin and composition of the conductive paste. Table 2 shows the results. In the examples, good coating properties could be obtained by heating in an oven at a relatively low temperature of 130° C. for 30 minutes for a short period of time. Adhesion to the ITO film and adhesion after the wet heat environment test were also good. Furthermore, it showed good fine wiring formability by laser etching, and also had good suitability for microcontact printing.

In Table 2, silver powder 1: flaky silver powder (D50: 1.5 μm, tap density 3.7 g/cm ³ )
Silver powder 2: Spherical silver powder (D50; 0.8 μm, tap density 5.3 g/cm ³ )
Silver powder 3: Nano silver powder (D50; 600 nm)
Silica: #300 manufactured by Nippon Aerosil Co., Ltd.
Ion catcher: IXE-100 manufactured by Toagosei Co., Ltd.
Carbon black: Ketjen ECP600JD manufactured by Lion Corporation
Curing agent: BI-7960 manufactured by Baxenden
Curing catalyst: KS-1260 manufactured by Kyodo Pharmaceutical Co., Ltd.
Leveling agent: Kyoeisha Chemical Co., Ltd. MK Conch Dispersant 1: Disperbyk 2155 manufactured by BYK-Chemie Japan Co., Ltd.
Dispersant 2: Malonic acid EDGAC: Ethyl diglycol acetate manufactured by Daicel Corporation BDGAC: Butyl diglycol acetate manufactured by Daicel Corporation.

As described above, the conductive paste of the present invention has a high degree of dispersion, and the conductive film obtained from the paste of the present invention has good laser etching properties. It can be usefully utilized as a member for an input/output interface such as. Moreover, it can be suitably used for wiring layers such as printed TFTs that require fine wiring.

Claims (4)

In a conductive paste containing at least a conductive filler, an organic solvent, and a binder resin, a diol compound having a bisphenol structure as the binder resin,
A dihydroxy compound containing a carboxyl group and a carboxyl group-containing polyurethane resin that is a polyaddition reaction product of an isocyanate compound are used , and the diol compound having a bisphenol structure is an alkylene oxide adduct of bisphenol A and an alkylene oxide adduct of bisphenol F. and bisphenol S alkylene oxide adduct . The content of the organic solvent is 5 to 100 parts by mass with respect to 100 parts by mass of the conductive filler, and the content of the binder resin is 5 to 25 parts by mass with respect to 100 parts by mass of the conductive filler. The conductive paste according to claim 1, characterized by: 3. The conductive paste according to claim 1 , wherein the diol compound having a bisphenol structure has a molecular weight of 500 or less . The conductive filler according to any one of claims 1 to 3 , wherein the conductive filler is a metal powder having a center diameter D50 of 0.8 µm or more and less than 2.0 µm as measured by a laser diffraction method. paste.