JP6001265B2 - Conductive paste - Google Patents

Description

  The present invention relates to a conductive paste and a method for producing a conductive pattern using the conductive paste.

  In general, photolithography using a photosensitive resin composition containing conductive powder is used to form a high-definition wiring pattern in an electronic device. However, since photolithography is a subtractive process of forming a pattern by removing material, the use efficiency of the photosensitive resin composition is low, the process is complicated, and a large facility is required for a wet process or the like. There is a problem.

  On the other hand, printing methods such as gravure printing and gravure offset printing have attracted attention as additive processes for adding materials to desired locations. For example, according to gravure offset printing, a paste resin composition is supplied to a gravure plate, which is transferred to a blanket made of silicone, for example, and further transferred to a substrate on a stage to form a pattern. Can do.

  In such a printing method, since the ink is transferred to the substrate through the plate, good transferability is required. In particular, since gravure offset printing transfers ink from a gravure plate to a substrate via a blanket, it is necessary to transfer the ink reliably in each step. In continuous printing, transfer from the blanket to the substrate is necessary. There is a demand for a paste having excellent printing suitability such as a rate of 100% and suppressing a shape defect of a pattern transferred to a substrate.

Incidentally, in recent years, formation of electrodes by low-temperature firing has been required for application to flexible devices such as electronic paper using a flexible substrate such as PET as a base material and devices with low heat resistance such as touch panels. Although various proposals have been made on thermosetting conductive pastes that can be fired at a low temperature (see, for example, Patent Document 1), it is difficult to develop a low resistance on the order of 10 ⁻⁵ Ω · cm. is there.

  As described above, when forming a wiring pattern in a device having low heat resistance by a printing method, it is required that not only good printability of a paste but also good electrical characteristics can be obtained in a wiring pattern formed by low-temperature firing. Is done. However, there is a problem that it is difficult to obtain a paste satisfying these simultaneously.

JP 2004-355933 A

  The present invention has been developed to solve these problems, and provides a conductive paste having excellent printability and capable of obtaining good conductivity in a conductive pattern formed by low-temperature firing. The purpose is to do.

The conductive paste of this embodiment contains a urethane resin, conductive powder, and an organic solvent containing 30 to 90% by mass of a high boiling point solvent having a boiling point of 250 to 330 ° C. at 760 mmHg.
With such a configuration, it is possible to obtain excellent conductivity in a conductive pattern formed by low-temperature firing, as well as excellent printability such as transferability to a substrate, straightness of a pattern, and line width reproducibility. Become.

Moreover, the conductive paste of the present embodiment is characterized in that the urethane resin includes a carboxyl group-containing urethane resin having a weight average molecular weight of 500 to 100,000.
With such a configuration, sufficient flexibility and hardness can be imparted to the obtained conductive pattern.
In addition, the conductive paste of the present embodiment further includes an epoxy resin containing at least two glycidyl groups in one molecule as a crosslinking agent.
With such a configuration, a three-dimensional network chain is formed in the formation of the conductive pattern, and the solvent resistance and adhesion of the resulting conductive pattern are improved.

Further, the conductive pattern forming method of the present embodiment forms the above-described conductive paste pattern on a plate, primarily transfers the formed pattern onto the surface of the blanket cylinder, and based on the primary transferred pattern. A secondary transfer is performed on the surface of the material, and the secondary transferred pattern is dried or cured at 80 to 200 ° C.
With such a configuration, the conductive pattern has good conductivity, and also has good straightness and line width reproducibility, so that an electronic device having high reliability and conductive characteristics can be obtained.

  According to the present invention, there is provided a conductive paste that has excellent printability such as pattern straightness and line width reproducibility, and can obtain good conductivity in a conductive pattern formed by low-temperature firing. it can.

The figure which shows the process of the gravure offset printing concerning 1 aspect of this invention. 4 is an optical micrograph of the printed material pattern of Example 4. FIG. 3 is an optical micrograph of a printed pattern of Comparative Example 1.

  As a result of intensive studies in view of the above problems, the inventors of the present invention have found that an organic solvent containing 30 to 90% by mass of a urethane resin, a conductive powder, and a high boiling point solvent having a boiling point of 250 to 330 ° C. at 760 mmHg as the conductive paste. It has been found that the above-mentioned problems can be achieved by containing the present invention, and the present invention has been completed. In particular, by using together a urethane resin and an organic solvent containing 30 to 90% by mass of a high boiling point solvent having a boiling point of 250 to 330 ° C. at 760 mmHg, transfer to a transfer medium such as a substrate in gravure offset printing in particular. And excellent printability such as straightness of the pattern after transfer and line width reproducibility, and good conductivity can be obtained in the cured product pattern.

Hereinafter, the conductive paste of this embodiment will be described in detail.
The urethane resin in the conductive paste of the present embodiment imparts good printability to the paste and remains in the cured product (conductive pattern) to impart physical properties such as adhesion, flex resistance, and hardness. Used as The urethane resin is not particularly limited as long as it can impart printability to the conductive paste. For example, a carboxyl group-containing urethane resin, a phenolic hydroxyl group-containing urethane resin, an amino group-containing urethane resin, etc. Is mentioned. Among these, it is particularly preferable to include a carboxyl group-containing urethane resin.

  Specific examples of the carboxyl group-containing urethane resin include a reaction of polyisocyanate (a) with bisphenol A-type alkylene oxide adduct diol (b), polycarbonate polyol (c), and dimethylolalkanoic acid (d). And those having a carboxyl group introduced by dimethylolalkanoic acid (d) and a urethane bond formed in (1) are used.

Such urethane resins are used as polyisocyanate (a), bisphenol A type alkylene oxide adduct diol (b), polycarbonate polyol (c), dimethylol alkanoic acid (d), and reaction terminator (end-capping agent). A functional monohydroxyl compound (e) is mixed and reacted, or a polyisocyanate (a), a bisphenol A type alkylene oxide adduct diol (b), a polycarbonate polyol (c), and a dimethylolalkanoic acid (d). It can be obtained by reacting and subsequently reacting the monohydroxyl compound (e).
The above reaction proceeds without a catalyst by stirring and mixing at room temperature to 100 ° C, but it is preferably heated to 70 to 100 ° C in order to increase the reaction rate.

  Examples of the polyisocyanate (a) include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, (o, m, or p) -xylene diisocyanate, (o, m, Or p) -diisocyanates such as hydrogenated xylene diisocyanate, methylene bis (cyclohexyl isocyanate), trimethylhexamethylene diisocyanate, cyclohexane-1,3-dimethylene diisocyanate, cyclohexane-1,4-dimethylene diisocyanate, 1,5-naphthalene diisocyanate Can be mentioned. These polyisocyanates can be used alone or in combination of two or more.

  Among these, toluene diisocyanate and trimethylhexamethylene diisocyanate are preferable. When these diisocyanates are used, a cured product having excellent solder heat resistance can be obtained.

  Examples of the bisphenol A-type alkylene oxide adduct diol (b) include ethylene oxide adducts, propylene oxide adducts, butylene oxide adducts of bisphenol A, and among these, propylene oxide adducts of bisphenol A are preferred. .

  As the polycarbonate polyol (c), polycarbonate diol is preferable. The polycarbonate diol includes a polycarbonate diol containing one or more linear aliphatic diol-derived repeating units as a constituent unit, and a repeating unit derived from one or more alicyclic diols as a constituent unit. Examples of the polycarbonate diol include polycarbonate diol or a repeating unit derived from both diols as a constituent unit. These polycarbonate diols can be produced by transesterification of a linear aliphatic or alicyclic diol with, for example, a carbonate ester, reaction with phosgene, or the like.

  Specific examples of the polycarbonate diol containing a repeating unit derived from a linear aliphatic diol as a constituent unit include polycarbonate diol derived from 1,6-hexanediol, 1,5-pentanediol, and 1,6- Polycarbonate diol derived from hexanediol, polycarbonate diol derived from 1,4-butanediol and 1,6-hexanediol, and derived from 3-methyl-1,5-pentanediol and 1,6-hexanediol And polycarbonate diol.

  Specific examples of the polycarbonate diol containing a repeating unit derived from an alicyclic diol as a constituent unit include, for example, a polycarbonate diol derived from 1,4-cyclohexanedimethanol.

  Specific examples of polycarbonate diols containing repeating units derived from both linear aliphatic diols and alicyclic diols as constituent units include, for example, 1,6-hexanediol and 1,4-cyclohexanedimethanol. And polycarbonate diol derived from the above.

  A polycarbonate diol containing a repeating unit derived from a linear aliphatic diol as a constituent unit tends to be excellent in low warpage and flexibility. Moreover, the polycarbonate diol which contains the repeating unit derived from alicyclic diol as a structural unit becomes high in crystallinity, and tends to be excellent in tin plating resistance and solder heat resistance. From these viewpoints, the polycarbonate diol can be used in combination of two or more kinds, or a polycarbonate diol containing a repeating unit derived from both a linear aliphatic diol and an alicyclic diol as a constituent unit can be used. . In order to achieve a good balance between low warpage and flexibility, solder heat resistance and tin plating resistance, the copolymerization ratio of the linear aliphatic diol and the alicyclic diol is 3: 7 to 7 by mass ratio. : 3 polycarbonate diol is preferably used.

  The polycarbonate diol preferably has a number average molecular weight of 200 to 5,000, but the polycarbonate diol includes a repeating unit derived from a linear aliphatic diol and an alicyclic diol as structural units, When the copolymerization ratio of the alicyclic diol is 3: 7 to 7: 3 in terms of mass ratio, the number average molecular weight is preferably 400 to 2000.

  Dimethylol alkanoic acid (d) is a dihydroxy aliphatic carboxylic acid, and specific examples include dimethylolpropionic acid and dimethylolbutanoic acid. By using dimethylolalkanoic acid (d), a carboxyl group can be easily introduced into the urethane resin.

  The monohydroxyl compound (e) is a polyurethane end-capping agent and may be any compound having one hydroxyl group in the molecule, and examples thereof include aliphatic alcohols and monohydroxymono (meth) acrylate compounds. It is done.

  Specific examples of the aliphatic alcohol include methanol, ethanol, propanol, n-butanol, and isobutanol. Specific examples of the monohydroxy mono (meth) acrylate compound include 2-hydroxyethyl. An acrylate etc. are mentioned.

  The weight average molecular weight of the carboxyl group-containing urethane resin is preferably 500 to 100,000. When the weight average molecular weight of the carboxyl group-containing urethane resin is less than 500, the elongation, flexibility and strength of the cured film may be impaired. On the other hand, when the weight average molecular weight exceeds 100,000, it becomes hard and flexible. May decrease. More preferably, it is 4000-50000, More preferably, it is 6000-30000. The weight average molecular weight of the resin is a value in terms of polystyrene measured by gel permeation chromatography (GPC).

  The acid value of the carboxyl group-containing urethane resin is preferably in the range of 5 to 150 mgKOH / g. When the acid value is less than 5 mg KOH / g, the cohesive strength of the paste is lowered, and transfer defects are likely to occur during printing. On the other hand, when the acid value exceeds 150 mgKOH / g, the viscosity of the paste becomes too high, and it is necessary to add a large amount of a crosslinking agent, and it becomes difficult to impart printability. More preferably, it is 10-100 mgKOH / g. The acid value of the resin is a value measured according to JIS K5407.

  Moreover, you may contain binder resins other than the said urethane resin in order to supplement printability. Specifically, for example, various modified polyester resins such as polyester resin, urethane-modified polyester resin, epoxy-modified polyester resin, acrylic-modified polyester resin, vinyl chloride / vinyl acetate copolymer, epoxy resin, phenol resin, acrylic resin, polyvinyl butyral Examples thereof include modified celluloses such as resin, polyamideimide, polyimide, polyamide, nitrocellulose, cellulose acetate butyrate (CAB), and cellulose acetate propionate (CAP).

Among these, it is preferable to include a carboxyl group-containing resin containing two or more carboxyl groups in at least one molecule. Specific examples of such carboxyl group-containing resins include, but are not limited to, the resins listed below.
(1) A carboxyl group-containing resin obtained by copolymerizing an unsaturated carboxylic acid such as (meth) acrylic acid and one or more other compounds having an unsaturated double bond.
(2) Monofunctional epoxy such as butyl glycidyl ether or phenyl glycidyl ether in a copolymer of unsaturated carboxylic acid such as (meth) acrylic acid and one or more other compounds having unsaturated double bonds A carboxyl group-containing resin obtained by adding a compound.
(3) Copolymerization of a compound having an unsaturated double bond with an epoxy group such as glycidyl (meth) acrylate or 3,4-epoxycyclohexylmethyl (meth) acrylate, and a compound having an unsaturated double bond other than that A carboxyl group-containing resin obtained by reacting a saturated carboxylic acid such as propionic acid with a coalescence and reacting a polybasic acid anhydride with the generated secondary hydroxyl group.
(4) Obtained by reacting a copolymer of an acid anhydride having an unsaturated double bond such as maleic anhydride and a compound having an unsaturated double bond other than that with a compound having a hydroxyl group such as butanol. Carboxyl group-containing resin.
(5) A carboxyl group-containing resin obtained by reacting a polyfunctional epoxy compound with a saturated monocarboxylic acid and reacting the resulting hydroxyl group with a saturated or unsaturated polybasic acid anhydride.
(6) A hydroxyl group- and carboxyl group-containing resin obtained by reacting a hydroxyl group-containing polymer such as a polyvinyl alcohol derivative with a saturated or unsaturated polybasic acid anhydride.
(7) Reaction of a polyfunctional epoxy compound, a saturated monocarboxylic acid, a compound having at least one alcoholic hydroxyl group in one molecule and one reactive group other than an alcoholic hydroxyl group that reacts with an epoxy group A carboxyl group-containing resin obtained by reacting a product with a saturated or unsaturated polybasic acid anhydride.
(8) Saturated or unsaturated polybasic acid with respect to the primary hydroxyl group in the modified oxetane resin obtained by reacting a saturated monocarboxylic acid with a polyfunctional oxetane compound having at least two oxetane rings in one molecule. A carboxyl group-containing resin obtained by reacting an anhydride.
(9) After reacting a polyfunctional epoxy resin with a saturated monocarboxylic acid and then reacting with a polybasic acid anhydride, further react with a compound having one oxirane ring in the molecule. Carboxyl group-containing resin obtained by making it.

  Among these, it is particularly preferable to use the carboxyl group-containing resins (1), (2) and (3). These can arbitrarily adjust the molecular weight, the glass transition point, and the like, and can appropriately adjust the printing suitability of the paste and the adhesion to the substrate.

  Moreover, it is preferable that the acid value of such carboxyl group-containing resin is 40-200 mgKOH / g. If the acid value of the carboxyl group-containing resin is less than 40 mg KOH / g, the cohesive strength of the paste is reduced, and transfer defects are likely to occur during printing. On the other hand, if it exceeds 200 mgKOH / g, the viscosity of the paste becomes too high, and it becomes difficult to impart printability, such as the need to add a large amount of a crosslinking agent. More preferably, it is 45-150 mgKOH / g.

  The blending ratio of the binder resin other than the urethane resin is preferably 50% by mass or less in the total binder resin. If the blending ratio exceeds 50% by mass, the adhesiveness with the substrate is lowered or the line width of the printed pattern is disturbed and the properties of the paste are impaired. More preferably, it is 30 mass% or less.

  The conductive powder in the conductive paste of this embodiment imparts conductivity to the formed conductive pattern. Specifically, for example, Ag, Au, Pt, Pd, Ni, Cu, Al, Sn, Pb Zn, Fe, Ir, Os, Rh, W, Mo, Ru, etc. can be mentioned.

These conductive powders are not limited to those used in a single form, and may be any of these alloys or a multilayer body having any of these as a core or a coating layer. Furthermore, oxides such as tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), and ITO (Indium Tin Oxide) may be used.

  As the shape, various shapes such as a spherical shape, a flake shape, and a dentlite shape can be used, but in consideration of printability and dispersibility, it is preferable to use a spherical shape as a main component.

  Such conductive powder is preferably 85 to 95% by mass based on the nonvolatile component of the conductive paste (the component that does not volatilize from the paste in the drying step and remains in the film). If it is less than 85% by mass, it will be difficult to obtain sufficient electrical conductivity, and if it exceeds 95% by mass, it will be difficult to obtain sufficient printability and to maintain the shape of the conductive pattern. More preferably, it is 90-94 mass%.

  When the spherical conductive powder is used, the particle size of the conductive powder is an average particle size of 10 random conductive powders observed at 10,000 times using an electron microscope (SEM), and is 0.1 to 5 μm. Is preferred. When the average particle size is less than 0.1 μm, the contact between the conductive powders hardly occurs and the conductivity is lowered. On the other hand, when the average particle diameter exceeds 5 μm, it is difficult to obtain straightness of the line edge when printing. More preferably, it is 0.4-2 micrometers. In addition, it is preferable to use the thing of the magnitude | size of 0.5-3.5 micrometers in the average particle diameter measured with the micro track | truck.

  Moreover, when using flaky conductive powder, it is preferable that it is 0.1-10 micrometers by the average particle diameter of ten random conductive powders observed by 10000 time using the electron microscope (SEM). When the average particle size is less than 0.1 μm, the contact between the conductive powders hardly occurs and the conductivity is lowered. On the other hand, when the average particle diameter exceeds 10 μm, it becomes difficult to obtain straightness of the line edge when printing. More preferably, it is 0.4-5 micrometers. In addition, it is preferable to use the thing of the magnitude | size of 0.5-7 micrometers in the average particle diameter measured with the micro track | truck.

As such a conductive powder, silver powder is preferable. In that case, the silver powder preferably has a specific surface area of 0.01 to ² m ² / g. When the specific surface area is less than 0.01 m ² / g, sedimentation tends to occur during storage. On the other hand, when the specific surface area exceeds 2 m ² / g, the oil absorption is increased and the fluidity of the paste is impaired. More preferably, it is 0.5 to 1.5 m ² / g.

  In the conductive paste of this embodiment, an organic solvent is used in order to impart good printability. Such an organic solvent can be dissolved without chemically reacting with the urethane resin, and is included in the conductive paste to prevent drying of the paste in the printing process such as gravure offset printing, and to maintain transferability. It is necessary for the organic solvent to contain a high boiling point solvent having a boiling point in the range of 250 to 330 ° C. at 760 mmHg.

  If the boiling point of the high boiling point solvent at 760 mmHg is lower than 250 ° C., the paste transferred to the blanket in the off-setting step at the time of printing becomes easy to dry and does not transfer to the substrate in the setting step. On the other hand, when the temperature is higher than 330 ° C., drying in the printing process can be suppressed, but in the drying process after printing, the solvent tends to remain in the printed pattern, causing problems such as an increase in resistance and a decrease in adhesion. . More preferably, it is 250 degreeC-300 degreeC. Moreover, it is preferable that the ratio of the said high boiling point solvent in the organic solvent contained in an electrically conductive paste is 30-90 mass%. When the ratio of the high boiling point solvent is less than 30% by mass, the printed pattern is printed finer than the plate size, and it becomes difficult to obtain a good print pattern. On the other hand, if it is more than 90% by mass, the printed pattern is likely to be blurred, and it is difficult to obtain a good printed pattern. More preferably, it is a ratio of 30 to 80% by mass.

  Examples of such a high-boiling solvent include diamylbenzene (boiling point: 260 to 280 ° C.), triamylbenzene (boiling point: 300 to 320 ° C.), n-dodecanol (boiling point: 255 to 259 ° C.), diethylene glycol dibutyl ether ( Boiling point: 255 ° C), diethylene glycol monoacetate (boiling point: 250 ° C), triethylene glycol (boiling point: 276 ° C), triethylene glycol monoethyl ether (boiling point: 256 ° C), triethylene glycol monobutyl ether (boiling point: 271 ° C) Tetraethylene glycol (boiling point: 327 ° C), tetraethylene glycol monobutyl ether (boiling point: 304 ° C), tripropylene glycol (boiling point: 267 ° C), 2,2,4-trimethyl-1,3-pentanediol monoisobuty Rate (boiling point: 53 ° C.), and the like. Also, as petroleum-based hydrocarbons, AF Solvent No. 5 (boiling point: 275-306 ° C.), No. 6 (boiling point: 296-317 ° C.), and No. 7 (boiling point: 259-282 ° C.) manufactured by Nippon Oil Corporation ) And the like, and two or more of them may be included as necessary. Of these, triethylene glycol derivatives or tripropylene glycol derivatives are preferably used.

  Examples of the organic solvent other than the high boiling point solvent include toluene, xylene, ethyl acetate, butyl acetate, methanol, ethanol, isopropyl alcohol, isobutyl alcohol, 1-butanol, diacetone alcohol, diethylene glycol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether. Examples include acetate, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether acetate, tripropylene glycol monomethyl ether, terpineol, methyl ethyl ketone, carbitol, carbitol acetate, and butyl carbitol. These can be used alone or in admixture of two or more.

  Such an organic solvent is appropriately contained so that the conductive paste has a viscosity suitable for printing or the like.

  The viscosity of the conductive paste of this embodiment is 50 to 1000 dPa · s as measured with a cone plate viscometer (25 ° C.) in order to obtain good printability, particularly when used for gravure offset printing. Is preferred. When the viscosity is less than 50 dPa · s, the ratio of the organic solvent in the conductive paste is too large, and transferability is lowered, making it difficult to perform good printing. On the other hand, when the viscosity exceeds 1000 dPa · s, it is difficult to fill the gravure plate, the scraping property with a doctor blade is deteriorated, and background stains (adhesion of paste to the non-image area) are likely to occur. More preferably, it is 100-650 dPa * s. In addition, it is also possible to dilute appropriately at the time of printing.

  Moreover, it is preferable that the tack value which shows the dynamic adhesiveness of such an electrically conductive paste is 5-35. If the tack value is less than 5, the transferability at the time of printing may be inferior and the print quality may be deteriorated. On the other hand, when the tack value exceeds 35, picking of the printed material (breaking of the printed material) and jamming (the printed material clogs the printing machine) easily occur during printing. More preferably, it is 10-30. The tack value is a value measured using a rotary tack meter (generic name: incometer) under the conditions of 30 ° C. and 400 revolutions.

  Further, in the conductive paste of this embodiment, it is preferable to further contain a crosslinking agent in order to form a three-dimensional network chain structure and improve the solvent resistance and adhesion of the formed pattern.

  Any crosslinking agent may be used as long as it can react with the urethane resin without causing deterioration in printability and can be crosslinked. Such a crosslinking agent is not particularly limited as long as it is a resin curable by heating, and examples thereof include epoxy resins, phenol resins, melamine resins, alkyd resins, polyester resins, acrylic resins, polyimide resins, and modified resins thereof. These can be used alone or in combination of two or more. Other examples include oxetane compounds having at least two oxetanyl groups in the molecule.

  Among such crosslinking agents, it is preferable to include an epoxy resin containing at least two glycidyl groups in at least one molecule. Examples of such epoxy resins include bisphenol A type, hydrogenated bisphenol A type, bisphenol F type, bisphenol S type, phenol novolac type, cresol novolak type, bisphenol A novolak type, biphenol type, bixylenol type, and trisphenol. Known epoxy resins such as methane type, N-glycidyl type, N-glycidyl type epoxy resin, alicyclic epoxy resin, etc., are not limited to specific ones, and these may be used alone or Two or more kinds can be used in combination. Among these, it is preferable to use an epoxy resin having an epoxy equivalent (gram number of resin containing 1 gram equivalent of an epoxy group) in the range of 100 to 300 because crosslinking can be efficiently performed with a small amount of addition.

  1-100 mass parts is suitable for 100 mass parts of urethane resins, and, as for the mixture ratio of such an epoxy resin, Preferably it is 5-40 mass parts.

  In addition to these, curing agents such as amine compounds and imidazole derivatives for accelerating the reaction between the urethane resin and the crosslinking agent, and metal dispersants, thixotropic agents, and antifoaming agents as long as the printability is not impaired. , Additives such as leveling agents, plasticizers, antioxidants, metal deactivators, coupling agents and fillers may be blended.

Using such a conductive paste, a conductive pattern is formed as follows.
First, a coating pattern of a conductive paste is formed on a substrate by gravure offset printing. FIG. 1 shows a schematic diagram of gravure offset printing.
As shown in FIG. 1, a conductive paste 12 is filled in a recess 11a formed in a gravure plate 11 to have a desired pattern shape. Thereafter, the image is transferred onto a silicone blanket 13 that is an intermediate transfer member (primary transfer). The conductive paste transferred onto the silicone blanket 13 is further transferred onto the substrate 15 placed on the stage 14 (secondary transfer), thereby forming the coating film pattern 16.

  As a base material used here, flexible boards, such as a resin film other than a printed wiring board and a glass substrate, can be used. The gravure plate used is made by subjecting the surface of a cylinder or planographic plate made of copper, 42 alloy, glass or the like to photolithography or laser engraving. If necessary, chrome plating treatment or DLC (diamond-like carbon) treatment may be performed to improve the durability of the intaglio.

The coating pattern 16 formed on the substrate by the printing is dried or cured at 80 to 200 ° C. for 1 to 60 minutes to form a conductive pattern.
In addition, although the gravure offset printing method is mentioned as a conductive pattern formation method, the conductive paste of this embodiment is replaced with a conventional conductive paste, and a pattern is formed using a known printing method other than the above method. Of course, it can be formed.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this embodiment is demonstrated concretely, this invention is not limited to these Examples. In the following description, “%” is based on mass unless otherwise specified.

<Synthesis of urethane resin>
(Synthesis Example 1)
In a reaction vessel equipped with a stirrer, a thermometer and a condenser, polycarbonate diol derived from 1,5-pentanediol and 1,6-hexanediol as polyol components (Asahi Kasei Chemicals, T5650J, number average molecular weight 800) 288 g (0.36 mol), bisphenol A type propylene oxide modified adduct diol (ADEKA, BPX33, number average molecular weight 500) 45 g (0.09 mol), dimethylol butanoic acid 81.4 g (0 .55 mol), 11.8 g (0.16 mol) of n-butanol as a molecular weight modifier (end-capping agent), 250 g of carbitol acetate (manufactured by Daicel Chemical Industries) as a solvent, and all raw materials at 60 ° C. Dissolved.

While stirring this solution, 200.9 g (1.08 mol) of trimethylene diisocyanate was added dropwise as a polyisocyanate using a dropping funnel. After completion of the dropwise addition, the reaction was continued with stirring at 80 ° C., and it was confirmed that the absorption spectrum (2280 cm ⁻¹ ) of the isocyanate group had disappeared in the infrared absorption spectrum, and the reaction was terminated. After completion of the reaction, carbitol acetate was added so that the solid content was 60 wt% to obtain a urethane resin solution (varnish 1).

  The weight average molecular weight of the obtained urethane resin was 18300, and the acid value of the solid content was 50.3 mgKOH / g. In addition, the weight average molecular weight was calculated | required by the value converted into polystyrene using the gel carrier liquid chromatography (HLC-8120GPC Tosoh Corporation make).

(Synthesis Example 2)
In a reaction vessel equipped with a stirrer, a thermometer and a condenser, polycarbonate diol derived from 1,5-pentanediol and 1,6-hexanediol as polyol components (Asahi Kasei Chemicals, T5650J, number average molecular weight 800) 360 g (0.45 mol), 81.4 g (0.55 mol) of dimethylolbutanoic acid as dimethylolalkanoic acid, and 11.8 g (0.16 mol) of n-butanol as molecular weight regulator (terminal blocking agent), solvent As a sample, 250 g of carbitol acetate (manufactured by Daicel Chemical Industries, Ltd.) was charged, and all raw materials were dissolved at 60 ° C.

  While stirring this solution, 200.9 g (1.08 mol) of trimethylene diisocyanate as polyisocyanate was dropped with a dropping funnel. After completion of the dropwise addition, the reaction was continued with stirring at 80 ° C., and it was confirmed by the infrared absorption spectrum that the absorption spectrum (2280 cm −1) of the isocyanate group had disappeared. After completion of the reaction, carbitol acetate was added so that the solid content was 60 wt%, and a urethane resin solution (varnish 2) was obtained.

  The weight average molecular weight of the obtained polyurethane resin was 21,200, and the acid value of the solid content was 48.0 mgKOH / g. The weight average molecular weight was determined in the same manner as in Synthesis Example 1.

(Synthesis Example 3)
In a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel and a condenser, methyl methacrylate and acrylic acid are charged in a molar ratio of 0.80: 0.20, and triethylene glycol monobutyl ether (boiling point: 271 ° C.) as a solvent, Azobisisobutyronitrile was added as a catalyst and stirred at 80 ° C. for 6 hours in a nitrogen atmosphere to obtain an acrylic resin solution (varnish 3) having a nonvolatile content of 40 wt%. The obtained resin had a number average molecular weight of 15,000, a weight average molecular weight of about 40,000, and an acid value of 97 mgKOH / g. The weight average molecular weight was determined in the same manner as in Synthesis Example 1.

(Synthesis Example 4)
An acrylic resin solution (varnish 4) having a nonvolatile content of 40 wt% was obtained in the same manner as in Synthesis Example 3 except that triethylene glycol monobutyl ether was changed to diethylene glycol monoethyl ether acetate. The obtained resin had a number average molecular weight of 15000, a weight average molecular weight of about 42000, and an acid value of 98 mgKOH / g. The weight average molecular weight was determined in the same manner as in Synthesis Example 1.

(Preparation of conductive paste)
Each component was mix | blended with the mixture ratio (mass ratio) shown in Table 1, and it kneaded with the 3 roll mill, and obtained the electrically conductive paste of Examples 1-4 and Comparative Examples 1-3. The viscosity of the paste was adjusted to 150 dPa · s.
The tack value was between 10 and 25 (30 ° C., 60 seconds value).

[Remarks]
* 1: Spherical silver powder (average particle size: 0.8 μm, specific surface area: 1.0 m ² / g)
* 2: jER828 (Mitsubishi Chemical Corporation, epoxy equivalent = 190 g / eq)
* 3: jER1001 (Mitsubishi Chemical Corporation, epoxy equivalent = 500 g / eq)
* 4: Curazole 2E4MZ (manufactured by Shikoku Kasei Kogyo Co., Ltd., imidazole curing agent)

  Table 2 shows the ratio of the high boiling point solvent in the organic solvents contained in the conductive pastes of Examples 1 to 4 and Comparative Examples 1 to 3.

<Evaluation of printability by simple gravure printing>
Each of the obtained conductive pastes was filled into a concave portion of a glass intaglio plate on which a stripe pattern of line / space = 70/30 μm and plate depth: 10 μm was formed using a steel doctor.

  Next, the glass intaglio was applied to a blanket cylinder made of silicone rubber having a rubber hardness of 30 °, and the conductive paste filled in the depressions was transferred to the surface of the blanket cylinder (off process, primary transfer). 30 seconds after the conductive paste was transferred to the surface of the blanket cylinder, the pattern of the conductive paste on the surface of the blanket cylinder was transferred to the surface of soda lime glass having a thickness of 1.8 mm (setting process, secondary transfer). The following evaluation was performed about the printed matter pattern obtained in this way.

(Printability 1: Straightness evaluation)
The glass substrate on which the pattern of each conductive paste was transferred was observed with an optical microscope, and the straightness of the printed pattern was evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 3.
○: Straightness is good.
Δ: Slightly lacking in straightness
X: Remarkably lacking in straightness and disconnection.

(Printability 2: Evaluation of line width reproducibility)
The glass substrate to which the pattern of the conductive paste was transferred was observed with an optical microscope, and the line width of the printed pattern was evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 3.
○: The line width is the same as that of the glass intaglio, or the error is within ± 10% of the plate size.
Δ: Line width error is more than ± 10% and within ± 30% of the plate size.
X: An error in line width exceeds ± 30% with respect to the plate size.

(Printability 3: Evaluation of transferability after leaving on a blanket for 60 seconds)
After the off process (primary transfer), a setting process (secondary transfer) was performed 60 seconds later, and it was visually evaluated whether the conductive paste remained on the surface of the bracket body. The evaluation criteria are as follows. The evaluation results are shown in Table 3.
○: No conductive paste remains on the blanket surface (100% transfer).
Δ: The conductive paste remains on a part of the blanket surface.
X: The conductive paste remains on the entire blanket.

<Measurement of specific resistance value>
A test pattern having a line width of 1 mm and a length of 40 cm was printed, and heat treatment was performed at 120 ° C. for 30 minutes using a hot air circulation type drying furnace. The resistance value of the obtained pattern was measured using a tester (Miriome High Tester 3540 manufactured by HIOKI), and the specific resistance value was calculated from the film thickness of the pattern.

As shown in Table 3, in Examples 1 to 4 using the conductive paste of the present embodiment, all are excellent in the line width reproducibility and straightness of the printed pattern, and from the off process to the setting process. It can be seen that the paste maintains transferability even when the time is long. In Comparative Example 3, the paste was dried on the blanket, and printing could not be evaluated.
As an example of the printed pattern image using the conductive paste of the present embodiment, an optical micrograph of the printed pattern of Example 4 is shown in FIG. As shown in FIG. 2, the line width reproducibility is that the printed pattern has a line width of 64 to 67 μm (error: −8.6% to −4.3%) with respect to the plate size of 70 μm. It can be seen that the property is also good.

On the other hand, Comparative Example 1 which does not include the urethane resin of the present embodiment maintains the transferability even when the time from the off process to the setting process is long, but the obtained printing pattern has a line width reproducibility and straightness. I understand that it is scarce. Moreover, in the comparative example 2 which does not contain both the urethane resin of this embodiment and a high boiling point solvent, when it is left on a blanket for a long time, it turns out that a paste dries and transferability is impaired.
In FIG. 3, the optical microscope photograph of the printed matter pattern using the electrically conductive paste of the comparative example 1 is shown. As shown in FIG. 3, with respect to the line width reproducibility, the printed pattern has a line width of 58 to 62 μm (error: −17.1% to −11.4%) with respect to the plate size of 70 μm, and goes straight. As for the sex, it can be seen that the pattern is undulating and lacks straightness.

DESCRIPTION OF SYMBOLS 11 ... Gravure plate 11a ... Concave part 12 ... Conductive paste 13 ... Silicone blanket 14 ... Stage 15 ... Base material 16 ... Coating film pattern

Claims (5)

A carboxyl group-containing urethane resin, a conductive powder, and an organic solvent containing 30 to 90% by mass of a high boiling point solvent having a boiling point of 250 to 330 ° C. at 760 mmHg,
The conductive paste, wherein the carboxyl group-containing urethane resin has an acid value of 5 mgKOH / g or more and 150 mgKOH / g or less (excluding 20 mgKOH / g or less).   The conductive paste according to claim 1, wherein the urethane resin includes a carboxyl group-containing urethane resin having a weight average molecular weight of 500 to 100,000.   The conductive paste according to claim 1 or 2, further comprising an epoxy resin containing at least two glycidyl groups in one molecule as a crosslinking agent.   A pattern of the conductive paste according to any one of claims 1 to 3 is formed on a plate, the formed pattern is primarily transferred to a blanket cylinder surface, and the primary transferred pattern is a substrate. A method of forming a conductive pattern, wherein the pattern is secondarily transferred to the surface, and the secondarily transferred pattern is dried or cured at 80 to 200 ° C. The conductive pattern which consists of a dried material or hardened | cured material of the electrically conductive paste as described in any one of Claims 1-3 .