Conductive paste for heated roll press, conductive laminate, wiring board, electronic device, and method for producing conductive laminate

Abstract

To provide a conductive paste capable of forming a cost-effective conductor pattern that exhibits high conductivity close to bulk metal, with volume resistivity of 10 μΩcm or less, and to provide a cost-effective conductor pattern with high conductivity.SOLUTION: A method for producing a conductive laminate includes a step (coating formation step) for patterning a conductive paste for heating roll press onto a substrate by screen printing and then drying the conductive paste, wherein the conductive paste comprises: silver-coated copper powder, wherein copper powder with an average particle size D50 of 1-30 μm and an aspect ratio of 1.5-20 is coated with silver in an amount of 5-30 wt.% relative to the copper by plating; a resin with a melting range of 150°C or higher; and a solvent with a boiling point of 150°C to 260°C, and wherein a ratio of the resin to silver-coated copper powder is 0.5-10.0%. After the step, the patterned conductive paste is subjected to heating roll press at a line pressure of 400-4000 N while heated to 100°C-200°C. Consequently, the silver-coated copper powder is spread, leading to formation of circuits with a metallic luster exhibiting volume resistivity of 10 μΩcm or less, comparable to that of bulk metal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive paste for hot roll pressing, which has excellent conductivity, a conductive laminate, a wiring board, an electronic device, and a method for producing a conductive laminate. [Background technology]

[0002] Etching and printing are commonly used methods for forming thin films or conductive circuits for electronic components, electromagnetic shielding, and RFID antennas. Etching is a broad processing technique that includes surface treatment, in which copper or aluminum is bonded to a substrate such as a polyimide film or epoxy with an adhesive, and the metal surface or shape is then dissolved or removed chemically or electrochemically. Etching is a type of chemical processing, primarily used to obtain desired patterns on metal films. However, the process is generally complex and requires wastewater treatment after processing, which can be costly and problematic. When creating electronic circuits, electromagnetic shielding materials, and RFID antennas, a method of printing a conductive paste to form a conductor circuit with a predetermined pattern is known. Conductive paste is generally produced by mixing metal powder with binder components such as resin and solvent. Base metals such as copper, aluminum, and nickel are inexpensive, but they oxidize when powdered and do not provide good conductivity. Therefore, silver, palladium, platinum, and gold are generally used, as they are less likely to oxidize in the atmosphere. Of these, silver is often used due to its low cost.

[0003] However, silver powder is also about 100 times more expensive than base metals, and there is a demand for cost reduction. To overcome these problems, Patent Document 1 proposes a conductor molding method that uses silver-coated copper powder, in which at least a portion of the copper powder surface is covered with silver, and a binder resin made of a cellulose derivative with a glass transition temperature (Tg) of 35 to 170°C, which is printed and then pressed to form. However, even after press processing, the resistivity (volume resistivity) of the resulting conductor is only 50 μΩcm, which does not reach the resistivity of circuits formed by patterning aluminum or copper by etching.

[0004] In view of the above, an object of the present invention is to provide a conductive paste for heated roll pressing and a conductor pattern that are low cost, have a volume resistivity of 10 μΩcm or less, conductivity close to that of bulk metal, and further have good fluidity and excellent printability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-123457 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above-mentioned points, and aims to provide a conductive paste that can form a conductive pattern with high conductivity close to that of bulk metal and a volume resistivity of 10 μΩcm or less at low cost, and also aims to provide a conductive pattern with high conductivity at low cost. [Means for solving the problem]

[0007] As a result of extensive research to solve the above problems, it was discovered that a conductive paste containing specific silver-coated copper powder, resin, and solvent exhibits excellent conductivity.

[0008] That is, the present invention relates to a conductive paste for heated roll pressing containing silver-coated copper powder, a resin, and a solvent, wherein the silver-coated copper powder has an average particle size D50 of 1 to 30 μm, an aspect ratio of 1.5 to 20, and a silver content of 5 to 30 mass %, the resin has a melting point of 150°C or higher, and the solvent has a boiling point of 150°C to 260°C.

[0009] The present invention also relates to the conductive paste for hot roll pressing, wherein the content of the resin relative to the silver-coated copper powder is 0.5 to 10.0% by mass.

[0010] The present invention also relates to a conductive laminate comprising a substrate and a conductive film formed on the substrate using the conductive paste for hot roll pressing.

[0011] The present invention also relates to the conductive laminate, wherein the substrate comprises at least one substrate selected from the group consisting of a paper substrate, a polyethylene terephthalate substrate, a polyimide substrate, a polyethylene naphtholate substrate, and a polyamide substrate.

[0012] The present invention also relates to a wiring board characterized by further having an insulating layer and / or a protective layer on the conductive film side of the conductive laminate.

[0013] The present invention also relates to an electronic device comprising the above wiring board.

[0014] The present invention also relates to a method for producing a conductive laminate, which includes a step of forming a patterned conductive film on a substrate using the conductive paste for hot roll press by at least one printing method selected from the group consisting of screen printing, gravure printing, flexographic printing, gravure offset printing, and inkjet printing.

[0015] The present invention also relates to the method for producing the conductive laminate, further comprising the step of subjecting the conductive film to a heated roll press at 100°C to 200°C while applying a linear pressure of 400 to 4000 N. [Effects of the Invention]

[0016] According to the present invention, a wiring pattern having the same level of conductivity as bulk metal can be efficiently provided at low cost by a printing method without performing a complicated etching process. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross section showing an example of a wiring board of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the contactless ID of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes in detail an embodiment of the present invention. However, the following description of the requirements and other aspects is a representative example of an embodiment of the present invention, and the present invention is not limited to these details as long as it does not exceed the spirit of the invention.

[0019] <Conductive paste> The conductive paste of the present invention can be used for hot roll pressing and is characterized by containing a conductive substance, a resin, and a solvent.

[0020] (conductive material) The conductive material of the present invention is characterized by containing silver-coated copper powder, and further characterized by the silver-coated copper powder having an average particle size D50 of 1.0 to 30 μm, an aspect ratio of 1.5 to 20, and a silver content of 5 to 30 mass %. The average particle size D50 of the silver-coated copper powder is 1.0 to 30 μm, preferably 1.5 to 15 μm, and more preferably 2 to 10 μm. If the average particle size is less than 1 μm, the powder will become a nano-substance, which is expensive and difficult to handle. If the average particle size D50 is greater than 30 μm, the particle size D90 to D95 will be 50 to 100 μm, which will cause the silver-coated copper to clog the screen mesh, making good patterning impossible and the poor fluidity making printing difficult.

[0021] The aspect ratio of the silver-coated copper powder is 1.5 to 20, more preferably 2 to 10, and a mixture of spherical and flat particles is preferred. Spherical and flat particles allow for a high particle packing density, enabling low resistance when heated and pressed with a roll. Particles with an aspect ratio of less than 1.5 have a low packing density and poor conductivity, while particles with an aspect ratio of more than 20 have poor fluidity as a paste when dispersed in a binder made of resin and solvent, impairing printability.

[0022] The average particle size D50 was measured by adding 0.1% by mass of silver-coated copper powder to isopropyl alcohol (IPA), dispersing it using an ultrasonic agitator, and then measuring it using a Microtrack Bell MT3000II laser scattering diffraction particle size distribution analyzer.

[0023] The aspect ratio is calculated by [average long diameter (μm)] / [average thickness (μm)]. The average long diameter (μm) was determined by obtaining an image at an appropriate magnification (approximately 2000x) using a scanning electron microscope, directly observing the long diameters and thicknesses of approximately 30 particles in the image, and averaging these values. The average thickness of the silver-coated copper powder was determined by first preparing a sample by solidifying the silver-coated copper powder with epoxy resin, then directly observing the cross-section of the sample using a scanning electron microscope (magnification 2000x), and dividing the sum of the thicknesses of approximately 30 particles of silver-coated copper powder within the field of view by the number of particles.

[0024] The silver content in the silver-coated copper powder is 5 to 30% by mass, preferably 5 to 20% by mass. The silver content in the silver-coated copper powder indicates the amount of silver coated. If the silver content is less than 5% by mass, the copper powder cannot be completely coated with silver, resulting in oxidation and loss of conductivity. If the silver content exceeds 30% by mass, the cost will be high.

[0025] Examples of conductive materials that can be used in combination with the silver-coated copper powder include gold powder, silver powder, platinum powder, silver-coated nickel powder, silver-coated copper-nickel alloy powder, silver-coated copper-nickel-zinc alloy powder, and silver-coated aluminum powder, and two or more of these may be used in combination.

[0026] (resin) The resin used in the conductive paste of the present invention will be described. The resin used in the conductive paste of the present invention is characterized by containing a resin having a melting point of 150° C. or higher. Examples of resins having a melting point of 150° C. or higher include cellulose acetate propionate resin, polyvinylpyrrolidone, polycarbonate resin, polyethylene terephthalate, polyvinyl alcohol, polyvinylidene chloride, polyvinylidene fluoride, polyamide resin, polyacetal resin, polybutylene terephthalate, polyetherimide, polysulfone resin, polyamideimide, acetyl cellulose, nitrocellulose, cellulose propionate, ethyl cellulose, and cellulose acetate butyrate resin. However, from the viewpoints of solubility in solvents having a boiling point of 150° C. to 260° C. and printability when made into a paste, cellulose acetate propionate resin, polyvinylpyrrolidone, and polycarbonate resin are preferred. The melting point of the resin is preferably 150°C to 300°C, and more preferably 200°C to 280°C. Resins with a melting temperature of less than 150°C melt on the heat roll during heat pressing, making it impossible to form a conductive film. Resins with a melting temperature of more than 300°C do not dissolve in solvents with a boiling point of 150°C to 260°C, making it impossible to obtain good fluidity as a paste. The melting point was measured using a melting point measuring device manufactured by Sanshosha.

[0027] The resin content relative to the silver-coated copper powder is preferably 0.5 to 10.0% by mass, more preferably 2.0 to 8.0% by mass. If the resin content relative to the silver-coated copper is 10.0% by mass or less, good volume resistivity is obtained, and if it is 0.5% by mass or more, the silver-coated copper powder does not stick to each other, and a good coating is obtained.

[0028] (solvent) The solvent used in the conductive paste of the present invention is characterized by containing a solvent having a boiling point of 150 to 260°C. The boiling point of the solvent is more preferably 180 to 250°C. If the boiling point is 150°C or higher, the solvent will not volatilize during the three-roll mill dispersion process described below, resulting in good dispersion. Furthermore, the solvent will not volatilize during screen printing, resulting in stable printed products.

[0029] Furthermore, if the solvent has a boiling point of 260°C or less, there is no need to dry it at high temperatures, so the substrate will not be damaged and the conductivity will not become unstable due to residual solvent.

[0030] Commercially available hydrocarbon solvents with a boiling point of 150 to 260°C include, for example, ENEOS's T-SOL100, 150, 3040, AN45, Cactus Solvent P100, P150, P180, Cactus Fine SF-01, SF-02, Hisol 100, SS-100, SS-150, Naphthesol 160, 200, 220, decane, undecane, dodecane, tridecane, tetradecane, YHNP, SHNP, NS Clean 100, 110, 200, 220, 230, Dry Solvent Hi Soft, and Tericlean N. Examples include No. 16, N20, N22, Cleansol HS, Mineral Split, A Solvent, Base Solvent 21, Fog Solvent, LS Solvent, AF Solvent, No. 0 Solvent, Isozol 300, 400, ExxonMobil's Exozol D40, D60, D80, D95, D110, Isopar G, H, L, M, and Aqua Chemical's Aquasolvent GF, G71, AQ#300, AQ#500, D200, D400, SP20, Z-G3, Z-71, and Aquafrelax AQ#100.

[0031] Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, 3-pentanone, 2-heptanone, diisobutyl ketone, isophorone, cyclohexanone, and gamma-butyrolactone.

[0032] Examples of aromatic solvents include diethylbenzene, C5 to C20 alkylbenzenes, and chlorobenzene.

[0033] Examples of alcohols include hexanol, octanol, ethylene glycol, propylene glycol, benzyl alcohol, etc. Examples of cellosolves include methyl cellosolve, ethyl cellosolve, butyl cellosolve, hexyl cellosolve, etc.

[0034] Examples of ethers include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol mono-n-propyl ether.

[0035] Examples of esters include octyl acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and propylene glycol monomethyl ether acetate.

[0036] The solvent content in the conductive paste of the present invention is preferably 5% to 30%, and more preferably 10% to 20%. If the solvent content of the conductive paste for hot roll pressing is 5% or more, the viscosity is good and printability is good. Furthermore, if the solvent content is 30% or less, the solid content is low and a sufficient film thickness can be maintained when printed, which is preferable.

[0037] (Other ingredients) Next, other components will be described. If necessary, various additives such as ultraviolet absorbers, ultraviolet stabilizers, radical scavengers, fillers, thixotropy-imparting agents, antioxidants, antioxidants, antistatic agents, flame retardants, thermal conductivity improvers, plasticizers, anti-sagging agents, antifouling agents, preservatives, disinfectants, antifoaming agents, leveling agents, antiblocking agents, curing agents, thickeners, pigment dispersants, aluminum chelates, and silane coupling agents may be added to the conductive paste of the present invention, provided that the additives do not impair the effects of the present invention.

[0038] (Conductive paste manufacturing) The conductive paste is obtained by dispersing and mixing a conductive substance, a resin, an organic solvent, and, if necessary, other additives. As the apparatus used to obtain the conductive paste, a disperser or mixer that is normally used for dispersing pigments, etc., can be used.

[0039] Examples of such dispersers include mixers such as a three-roll mill, disperser, homomixer, planetary mixer, and planetary agitator; homogenizers such as M-Technique's "Clearmix" or PRIMIX's "Filmix"; media-type dispersers such as paint conditioners (Red Devil), ball mills, sand mills (Shinmaru Enterprises' "Dynomill" and the like), attritors, pearl mills (Eirich's "DCP Mill" and the like), and Coball mills; and media-less dispersers such as wet jet mills (Genus PY, Sugino Machine's "Starburst", Nanomizer's "Nanomizer", and the like), M-Technique's "Clear SS-5", and Nara Machine's "MICROS", but are not limited to these.

[0040] <Conductive laminate> The conductive laminate of the present invention has a substrate and a conductive circuit (conductive film) formed using the conductive paste of the present invention.

[0041] The substrate can be paper or plastic. As the paper substrate, coated paper, matte paper, uncoated paper, and various types of processed paper such as synthetic paper, polyethylene coated paper, impregnated paper, waterproof paper, insulating paper, and stretchable paper can be used, but coated paper and processed paper are preferred to obtain a stable resistance value. In the case of coated paper, the smoother it is, the more preferable it is.

[0042] As the plastic substrate, a substrate made of a highly heat-resistant polyethylene terephthalate substrate, a polyimide substrate, a polyethylene naphtholate substrate, a polyamide substrate, etc. The substrate may be in the form of a sheet, a roll, or a block.

[0043] Among these, paper substrates, polyethylene terephthalate substrates, polyimide substrates, polyethylene naphtholate substrates, and polyamide substrates are preferred.

[0044] In a process prior to forming the conductive circuit, the substrate may be subjected to a surface modification treatment such as corona treatment, plasma discharge treatment, or flame treatment to enhance adhesion to the substrate, and the substrate may further be coated with an anchor coating agent or various varnishes. Furthermore, after forming the conductive circuit, a foam or sponge (protective layer) may be attached to the circuit or a resin coating (insulating layer) may be applied to protect the circuit. Furthermore, the joints between the circuit and the detector etc. can be protected by overprinting a conductive carbon paste using epoxy resin, polyester resin or the like as a binder.

[0045] <Method of manufacturing conductive laminate> The conductive paste for hot pressing of the present invention is printed on a substrate to form a coating layer, and then dried to form a patterned conductive film on the substrate, thereby obtaining the conductive laminate of the present invention. Examples of printing methods include screen printing, inkjet printing, gravure printing, flexographic printing, and gravure offset printing, with screen printing being preferred. Specifically, the conductive film can be formed in a desired pattern by, for example, performing rotary screen printing using a cylindrical screen plate.

[0046] Drying is carried out using a box oven, hot air or infrared electric furnace, etc. at a temperature of 60°C to 180°C, more preferably 80°C to 150°C. If the drying temperature is below 60°C, the solvent will remain and the resistance value will increase. If the drying temperature is above 180°C, the substrate will be easily damaged.

[0047] <Heated roll press> The patterned conductive film obtained by printing is heated to 100-200°C and then subjected to a linear pressure of 400-4000N under hot roll pressing to obtain a conductive film with a volume resistivity of 10μΩcm or less, comparable to that of bulk metal. There are flat type and heated roll type heat presses, but the press used in the present invention is preferably a heated roll press that can apply a linear pressure of 400 to 4000 N between two rollers heated to 100 to 200° C. Pressurization methods include mechanical and hydraulic methods, but either method is acceptable as long as the desired temperature and pressure can be obtained.

[0048] <Wiring board with conductive film> The wiring board of the present invention comprises a substrate, a conductive film formed from a silver-coated copper paste for hot roll pressing, and an insulating layer and / or a protective layer. The conductive film functions as a signal wiring, and can conduct electricity as an electrical signal, for example, for wiring circuits, ground wiring, antenna wiring, etc. The wiring board can be used, for example, as a printed circuit board or a flexible printed circuit board.

[0049] <Electronic device having a wiring board> The electronic device of the present invention includes a wiring board, and examples of the electronic device include a solar cell, a touch panel, and a contactless ID.

[0050] An example of a basic configuration using a wiring board is shown in Figure 1. For example, the silver-coated copper paste for hot roll pressing of the present invention is screen-printed onto a substrate such as polyester film to form a signal wiring pattern, followed by heat drying and hot roll pressing, and then an insulating layer (protective layer) is printed on the required area.

[0051] Figure 2 shows an example of the configuration of a contactless ID. An IC chip is bonded to a conductive antenna that has been patterned and hot-roll pressed using the silver-coated copper paste for hot-roll pressing that has been subjected to heat drying and hot-pressing of the present invention on a substrate, and a protective film is attached using an adhesive. Here, IC chips store, accumulate, and perform calculations on data. Contactless IDs, such as RFID (Radio Frequency Identification), contactless IC cards, contactless IC tags, data carriers (recording media), and wireless cards, use radio waves to identify individuals and send and receive data between a reader or reader / writer. Applications include ID management and history management in toll collection systems, and location management in road usage management systems and cargo and parcel tracking and management systems. [Example]

[0052] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the scope of the invention in any way. In the examples and comparative examples, "parts" means "parts by mass."

[0053] <Average particle size of conductive material> The average particle size D50 was measured by adding 0.1% by weight of the conductive material to isopropyl alcohol (IPA), dispersing it using an ultrasonic agitator, and then measuring it using a Microtrack Bell laser scattering diffraction particle size distribution measuring device MT3000II.

[0054] <Thickness and aspect ratio of conductive material> The average long diameter of 30 particles was directly observed using a scanning electron microscope, and a sample was prepared by solidifying the conductive material with a commercially available epoxy resin. The cross section of the sample was directly observed using a scanning electron microscope (magnification 2000x), and the average thickness of 30 fine particles within the field of view was determined, and the average aspect ratio was calculated. The scanning electron microscope used was a TM-1000 manufactured by Hitachi High-Technologies Corporation.

[0055] <Adjustment of resin solution> (Adjustment of binder 1) Binder 1 was obtained by dissolving 40 parts of cellulose acetate propionate resin CAP-482-0.5 (melting point 188°C) manufactured by Eastman Chemical in 60 parts of ethyl diglycol acetate (boiling point 214°C) by heating at 80°C.

[0056] (Adjustment of binder 2) Binder 2 was obtained by dissolving 40 parts of Nippon Shokubai's polyvinylpyrrolidone K-30 (melting point 225°C) in 60 parts of ethylene glycol (boiling point 197°C) at 80°C under heating.

[0057] (Adjustment of binder 3) Binder 3 was obtained by dissolving 40 parts of polycarbonate resin PCZ220 (melting point 261°C) manufactured by Mitsubishi Gas Chemical Company in 60 parts of isophorone (boiling point 215°C) at 80°C under heating.

[0058] (Adjustment of binder 4) Binder 4 was obtained by dissolving 40 parts of cellulose acetate butyrate resin CAB-381-0.1 (melting point 155°C) manufactured by Eastman Chemical in 60 parts of ethyl diglycol acetate (boiling point 214°C) by heating at 80°C.

[0059] (Adjustment of binder 5) Binder 5 was obtained by dissolving 40 parts of Mitsubishi Chemical's epoxy resin JER4250 (melting point 105°C) in 60 parts of butyl diglycol acetate (boiling point 247°C) with heating at 80°C.

[0060] (Adjustment of binder 6) Binder 6 was obtained by dissolving 40 parts of cellulose acetate propionate resin CAP-482-0.5 (melting point 188°C) manufactured by Eastman Chemical in 60 parts of ethylene glycol monomethyl ether acetate (boiling point 145°C) at 80°C.

[0061] (Adjustment of binder 7) Binder 7 was obtained by dissolving 40 parts of Nippon Shokubai's polyvinylpyrrolidone K-30 (melting point 225°C) in 60 parts of tetraethylene glycol dimethyl ether (boiling point 275°C) at 80°C under heating.

[0062] <Silver-coated copper powder> (Silver-coated copper powder (1)) A mixture of spherical and flat particles (average particle size 4.5 μm, aspect ratio 2.5, silver content 10 mass%) manufactured by DOWA Electronics was used as silver-coated copper powder (1). (Silver-coated copper powder (2)) A mixture of spherical and flat particles (average particle size 4.5 μm, aspect ratio 3.4, silver content 20% by mass) manufactured by DOWA Electronics was used as silver-coated copper powder (2). (Silver-coated copper powder (3)) A mixture of spherical and flat particles (average particle size 8.5 μm, aspect ratio 7.8, silver content 10 mass%) manufactured by DOWA Electronics was used as silver-coated copper powder (3). (Silver-coated copper powder (4)) Flake-shaped silver-coated copper powder (average particle size 15.0 μm, aspect ratio 25, silver content 20% by mass) manufactured by DOWA Electronics was used as silver-coated copper powder (4). (Silver-coated copper powder (5)) Spherical silver-coated copper powder (average particle size 0.9 μm, aspect ratio 1.1, silver content 10 mass%) manufactured by Mitsui Mining & Smelting Co., Ltd. was used as silver-coated copper powder (5).

[0063] <Preparing conductive paste> Example 1 5.0 parts of binder (1), 81.0 parts of silver-coated copper powder (1), and 14.0 parts of ethyl diglycol acetate were blended and mixed using a planetary centrifugal mixer to obtain a conductive paste 1.

[0064] (Examples 2 to 7, Comparative Examples 1 to 5) Conductive pastes 2 to 12 were obtained in the same manner as in Example 1, except that the blending types and blending amounts were changed as shown in Table 1.

[0065] <Volume resistivity measurement> The volume resistivity of the conductive film was measured to evaluate the conductivity. The conductive paste was printed onto a Mitsubishi Paper Mills matte paper substrate (basis weight 127.9 g / m²) using a stainless steel screen plate (screen mesh 200 lines / inch, linearity 40 μm) with eight 15 x 30 mm patterns. After drying in a circulating box oven at 80°C for 30 minutes, the paste was heated and pressed in a Thank Metals heated roll press at 150°C, linear pressure 2800 N, and 0.5 m min. The surface resistivity was measured using a 4-depth resistivity meter (Loresta GP, Mitsubishi Chemical Analytech). Furthermore, cross-sectional photographs were taken using an electron microscope to determine the film thickness and calculate the volume resistivity. The results are shown in Table 1. (Evaluation criteria) A: Volume resistivity less than 6μΩcm B: Volume resistivity 6 μΩcm or more and less than 8 μΩcm C: Volume resistivity 8μΩ or more and less than 10μΩcm D: Volume resistivity 10μΩcm or more The practical level is rated A to C.

[0066] <Suitable for heated roll press> Conductive paste was printed onto a paper substrate, Mitsubishi Paper Mills matte paper (basis weight 127.9 g / m²), using a stainless steel screen plate (screen mesh 200 lines / inch, linearity 40 μm) with eight 15 x 30 mm patterns. After drying in a circulating box oven at 80°C for 30 minutes, the paste was heated and pressed in a Thank Metals heated roll press under conditions of 150°C, linear pressure 2800 N, and 0.5 m min. The percentage of the printed conductive paste that was transferred to the heated roll of the heated roll press was evaluated. The results are shown in Table 1.

[0067] (Evaluation criteria) A: No transfer of conductive paste to the heating roll B: Less than 2% of the conductive paste is transferred to the heating roll. C: 2% or more but less than 5% of the conductive paste is transferred to the heating roll D: 5% or more of the conductive paste is transferred to the heating roll The practical level is rated A to C.

[0068] <Liquidity> Using an E-type viscometer TV250H (manufactured by Toki Sangyo Co., Ltd.) with rotor No. 5, the viscosity was measured at 2, 5, and 20 rotor rotations at 25°C to evaluate fluidity. The viscosity and thixotropy index (TI) values ​​are defined below, and the viscosity value measured 2 minutes after the start of rotation was used. The results are shown in Table 1. Viscosity: measured at 5 revolutions TI value = (viscosity at 2 revolutions) / (viscosity at 20 revolutions)

[0069] (Evaluation criteria (viscosity)) A: Viscosity is 3 Pa·s or more but less than 30 Pa·s (good) B: Viscosity 30 Pa·s or more but less than 80 Pa·s (usable) C: Viscosity is 80 Pa·s or more but less than 150 Pa·s (slightly poor) D: Viscosity is 150 Pa·s or more but less than 250 Pa·s (poor) The practical level is rated A to C.

[0070] (Evaluation criteria (TI value)) A: TI value = 1 or more but less than 1.5 (good) B: TI value = 1.5 or more and less than 3 (usable) C: TI value = 3 or more but less than 5 (slightly poor) D: TI value = 5 or more (bad) The practical level is rated A to C.

[0071] <Printability evaluation> The obtained conductive paste for heated roll press was attached to a semi-automatic screen printer SSA-PC250IP (Seria Corporation) equipped with a stainless steel screen plate (200 mesh, 200 lines / inch, 40 μm linearity) and printed sheet by sheet onto polyester film (Toray PET film "Lumirror T60", 100 μm thick) to form a coating layer with a 50 × 100 mm pattern. A total of 100 sheets were printed, and the 100th print was dried in a circulating heating oven heated to 80 °C, and the print condition was evaluated visually. The results are shown in Table 1. (Evaluation criteria) A: No scratches and good smoothness B: No scratches and slightly poor smoothness C: Scratched and slightly poor smoothness D: Many scratches and poor smoothness The practical level is rated A to C.

[0072] [Table 1]

[0073] Examples 1 to 3, 5 and 6 were at practical levels in all evaluations. Example 4 was slightly inferior to Examples 1 to 3, 5 and 6 in all evaluations, but was still at a practical level. In Example 7, in which the ratio of resin to silver-coated copper was high, the volume resistivity, viscosity, and TI value were high, but were at a practical level.

[0074] In Comparative Example 1, 100% transfer occurred on the heated roll press, making it impossible to measure the volume resistivity. Comparative Example 2, which used silver-coated copper powder with a large particle size and aspect ratio, had a high volume resistivity and did not reach a practical level in terms of viscosity, TI value, and printability. Comparative Example 3, which used silver-coated copper powder with a small particle size and a small aspect ratio, also had a high volume resistivity and was not suitable for practical use. In Comparative Example 4, which used ethylene glycol monomethyl ether acetate with a boiling point of 145°C, the solvent evaporated during printing, causing an increase in viscosity, making the printability unsuitable. In addition, there was a lot of blurring and the volume resistivity was also unsuitable. Comparative Example 5, in which tetraethylene glycol dimethyl ether having a boiling point of 275°C was used, had residual solvent and was unsuitable in terms of volume resistivity and suitability for hot roll pressing. [Explanation of symbols]

[0075] 1. Insulation layer (protective layer) 2. Signal wiring (silver-coated copper paste for heat pressing) (conductive film) 3, 8 Base material 4 Protective Film 5. Adhesive 6 Conductive antenna (silver-coated copper paste for heat pressing) (conductive film) 7 IC chip

Claims

1. A conductive paste for hot roll pressing containing silver-coated copper powder, a resin, and a solvent, The silver-coated copper powder has an average particle size D50 of 1.0 to 30 μm, an aspect ratio of 1.5 to 20, and a silver content of 5 to 30 mass %, The resin contains a resin having a melting point of 150°C or higher, The conductive paste for hot roll pressing is characterized in that the solvent contains a solvent having a boiling point of 150°C to 260°C.

2. 2. The conductive paste for hot roll pressing according to claim 1, wherein the content of the resin relative to the silver-coated copper powder is 0.5 to 10.0 mass %.

3. 3. A conductive laminate comprising a substrate and a conductive film formed on the substrate using the conductive paste for hot roll pressing according to claim 1.

4. 4. The conductive laminate according to claim 3, wherein the substrate comprises at least one selected from the group consisting of a paper substrate, a polyethylene terephthalate substrate, a polyimide substrate, a polyethylene naphtholate substrate, and a polyamide substrate.

5. 4. A wiring board further comprising an insulating layer and / or a protective layer on the conductive film side of the conductive laminate according to claim 3.

6. An electronic device comprising the wiring board according to claim 5.

7. 3. A method for producing a conductive laminate, comprising a step of forming a patterned conductive film on a substrate by applying the conductive paste for use in heated roll press according to claim 1 or 2 to a substrate by at least one printing method selected from the group consisting of screen printing, gravure printing, flexographic printing, gravure offset printing, and inkjet printing.

8. The method for producing a conductive laminate according to claim 7, further comprising a step of subjecting the conductive film to a heated roll press while applying a linear pressure of 400 to 4000 N in a state where the conductive film is heated to 100°C to 200°C.

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