Electroconductive resin composition and conductor

Abstract

This electroconductive resin composition comprises a thermoplastic resin, a silver powder, and an organic solvent. The thermoplastic resin contains at least one selected from the group consisting of phenoxy resins, acrylic resins, polycarbonates, and polymer compounds that contain at least one of a vinyl chloride-derived constituent unit and a vinyl acetate-derived constituent unit. The silver powder contains flake-shaped silver powder at 50 mass% or more with respect to the total amount of the silver powder. The organic solvent contains a carbonyl group-bearing cyclic compound at 70 mass% or more with respect to the total amount of the organic solvent. The viscosity at 25°C and a shear rate of 10 s-1 is at least 100 dPa·s and not more than 1200 dPa·s, and the thixotropic index, which is the ratio between the viscosity at 25°C and a shear rate of 10 s-1 and the viscosity at 25°C and a shear rate of 100 s-1, is at least 1.2 and not more than 4.0.

Description

Conductive resin compositions and conductors

[0001] This invention relates to conductive resin compositions and conductors.

[0002] A commonly used method for forming wiring on a substrate involves coating the substrate with a conductive resin composition. This type of conductive resin composition, when combined with printing technology, makes it possible to form conductive circuits of a desired pattern on the substrate.

[0003] As such a conductive resin composition, for example, Patent Document 1 describes a thermosetting resin that is liquid at room temperature and has a tap density of 4.2 g / cm³. ３ A conductive paste containing silver powder, which includes the above-mentioned flake-like silver powder, is disclosed. The conductive paste contains 30% by weight or more of the above-mentioned flake-like silver powder, and 80-94% by weight of silver powder. The invention described in Patent Document 1 provides a conductive resin paste with excellent conductivity and heat dissipation properties.

[0004] Japanese Patent Publication No. 2002-50227

[0005] When the required resistance value of the wiring to be formed is small, it is desirable to apply a conductive resin composition in a relatively thick film thickness (for example, 100 μm or more). However, when applying a thick film using conventional conductive resin compositions such as the invention described in Patent Document 1, the applied conductive resin composition may sag, making it impossible to form wiring of the desired shape. In addition, shrinkage of the wiring may occur when the thickly applied conductive resin composition is solidified, which may cause disconnection of the wires.

[0006] Therefore, the present invention aims to provide a conductive resin composition that can suppress sagging and shrinkage of wiring even when a thick film coating is applied, and a conductor obtained by solidifying this composition.

[0007] The conductive resin composition according to the present invention is a conductive resin composition containing a thermoplastic resin, silver powder, and an organic solvent, wherein the thermoplastic resin comprises at least one selected from the group consisting of a polymer compound containing at least one of constituent units derived from vinyl chloride and constituent units derived from vinyl acetate, a phenoxy resin, an acrylic resin, and a polycarbonate, the silver powder comprises flake-shaped silver powder in an amount of 50% by mass or more relative to the total amount of silver powder, and the organic solvent comprises a cyclic compound having a carbonyl group in an amount of 70% by mass or more relative to the total amount of the organic solvent, at 25°C and a shear rate of 10 s. －１ The viscosity is between 100 dPa·s and 1200 dPa·s, and the temperature is 25°C and the shear rate is 10s. －１ Viscosity at 25°C and shear rate of 100 s －１ The thixotropic index, which is the ratio of viscosity to , is characterized by being between 1.2 and 4.0.

[0008] The conductor according to the present invention is characterized by being obtained by solidifying the above-mentioned conductive resin composition.

[0009] The inventors of the present invention have found that a conductive resin composition having the above configuration is less likely to sag when applied as a thick film to a substrate or the like, and is less likely to shrink during solidification, thus completing the present invention.

[0010] According to the present invention, even when a thick film coating is applied, sagging and shrinkage can be suppressed, making it easier to form wiring.

[0011] Preferred embodiments of the present invention will be described below. However, the scope of the present invention is not limited by the examples of preferred embodiments described below.

[0012] In one embodiment, the conductive resin composition according to the present invention preferably contains a copolymer in which the thermoplastic resin has constituent units derived from vinyl chloride and constituent units derived from vinyl acetate.

[0013] This configuration has the advantage of being less prone to changes in resistance even when placed in a high-temperature, high-humidity environment.

[0014] In one embodiment, the conductive resin composition according to the present invention preferably contains 65% by mass or more and 75% by mass or less of the silver powder relative to the total amount of the conductive resin composition.

[0015] This configuration provides wiring with good conductivity. Furthermore, it is particularly effective at suppressing sagging and shrinkage.

[0016] Further features and advantages of the present invention will become clearer through the following description of exemplary and non-limiting embodiments.

[0017] Embodiments of the conductive resin composition, wiring formation method, and conductive circuit according to the present invention will be described.

[0018] [Composition of the Conductive Resin Composition] The conductive resin composition according to this embodiment contains a thermoplastic resin, silver powder, and an organic solvent. The characteristics of each component and the conductive resin composition itself will be described in order below.

[0019] Thermoplastic resins include at least one selected from the group consisting of polymer compounds containing at least one of constituent units derived from vinyl chloride and constituent units derived from vinyl acetate, phenoxy resins, acrylic resins, and polycarbonates (hereinafter referred to as the "designated polymer compound group"). Polymer compounds containing at least one of constituent units derived from vinyl chloride and constituent units derived from vinyl acetate are polymer compounds selected from the group consisting of polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, modified polyvinyl chloride (a copolymer of vinyl chloride and monomers other than vinyl acetate), modified polyvinyl acetate (a copolymer of vinyl acetate and monomers other than vinyl chloride), and modified vinyl chloride-vinyl acetate copolymers (tertiary or more copolymers of vinyl chloride and vinyl acetate and other monomers).

[0020] The thermoplastic resin preferably contains copolymers that include constituent units derived from vinyl chloride and constituent units derived from vinyl acetate. That is, the thermoplastic resin preferably contains a polymer compound selected from the group consisting of vinyl chloride-vinyl acetate copolymers and modified vinyl chloride-vinyl acetate copolymers. In the following, vinyl chloride-vinyl acetate copolymers and modified vinyl chloride-vinyl acetate copolymers may be collectively referred to as "vinyl chloride-vinyl acetate resins."

[0021] Commercially available vinyl acetate resins may be used. Examples of such commercially available products include, but are not limited to, the Solvine® series (manufactured by Nisshin Chemical Industry Co., Ltd.), the Kanevinyl® series (manufactured by Kaneka Corporation), and the VINNOL® series (manufactured by Wacker Chemie AG).

[0022] The thermoplastic resin may be a single compound or a mixture of multiple compounds. If the thermoplastic resin is a mixture, it is sufficient that at least one compound constituting the mixture is selected from the designated polymer compound group, and the other compounds are arbitrary. However, it is preferable that 70% by mass or more of the total amount of thermoplastic resin, on a solid content basis, be selected from the designated polymer compound group, and it is more preferable that the entire thermoplastic resin is selected from the designated polymer compound group. If the thermoplastic resin contains multiple compounds selected from the designated polymer compound group, the above preferred range applies to the total content of those compounds.

[0023] Preferably, the thermoplastic resin has a hydroxyl value, and specifically, the hydroxyl value is preferably 30 mgKOH / g or more. More preferably, it is 50 mgKOH / g or more. When the hydroxyl value is 30 mgKOH / g or more, the electrical resistance of a wiring formed using the conductive resin composition is less likely to change. The hydroxyl value as referred to herein is a value for the entire thermoplastic resin, that is, it reflects the amount of hydroxyl groups contained in both the vinyl chloride-vinyl acetate-based resin and other resins. The hydroxyl value of the thermoplastic resin can be specified by methods such as neutralization titration, potentiometric titration, and the pyridine-acetyl chloride method (Japanese Industrial Standard JIS K0070-1992), and it is more preferable that the hydroxyl value measured by neutralization titration is 30 mgKOH / g or more. The upper limit of the hydroxyl value of the thermoplastic resin is not particularly limited, and may be, for example, 150 mgKOH / g or less.

[0024] Preferably, the thermoplastic resin has a hydroxyl value, and specifically, the hydroxyl value is preferably 30 mgKOH / g or more. More preferably, it is 50 mgKOH / g or more. When the hydroxyl value is 30 mgKOH / g or more, the electrical resistance of a wiring formed using the conductive resin composition is less likely to change. The hydroxyl value as referred to herein is a value for the entire thermoplastic resin, that is, it reflects the amount of hydroxyl groups contained in both the vinyl chloride-vinyl acetate-based resin and other resins. The hydroxyl value of the thermoplastic resin can be specified by methods such as neutralization titration, potentiometric titration, and the pyridine-acetyl chloride method (Japanese Industrial Standard JIS K0070-1992), and it is more preferable that the hydroxyl value measured by neutralization titration is 30 mgKOH / g or more. The upper limit of the hydroxyl value of the thermoplastic resin is not particularly limited, and may be, for example, 150 mgKOH / g or less.

[0025] The thermoplastic resin has a weight average molecular weight of 4.0×10 ４Preferably, it is at or above the above value. When the weight average molecular weight falls within this range, the electrical resistance of a wiring formed using the conductive resin composition is less likely to change. The weight average molecular weight referred to herein is a value for the entire thermoplastic resin, that is, it reflects the molecular weight of both the vinyl chloride-vinyl acetate-based resin and other resins. The weight average molecular weight of the thermoplastic resin can be specified by, for example, a method such as gel permeation chromatography (GPC) or a light scattering method, and the weight average molecular weight measured by gel permeation chromatography (GPC) is 4.0 × 10 ４ It is more preferable that it is at or above the above value. Although the upper limit of the weight average molecular weight of the thermoplastic resin is not particularly limited, it may be, for example, 12.0 × 10 ４ or less.

[0026] The lower limit of the content of the thermoplastic resin in the conductive resin composition is not particularly limited, but may be, for example, 5% by mass or more based on the total amount of the conductive resin composition. The upper limit is also not particularly limited similarly, but may be, for example, 30% by mass or less. When the thermoplastic resin is a mixture, the total amount thereof may fall within the above range.

[0027] Silver powder is powdered silver particles. In the present embodiment, the silver powder contains flaky silver powder in an amount of 50% by mass or more based on the total amount of the silver powder. It is preferable that the silver powder contains flaky silver powder in an amount of 75% by mass or more based on the total amount of the silver powder, and it is further preferable that the entire silver powder is flaky silver powder.

[0028] Flake-like silver powder refers to silver powder with shapes such as flat plates, thin rectangular parallelepipeds, and flaks, where the thickness is small compared to the dimensions in the planar direction. For example, it may have an aspect ratio (the value obtained by dividing the average major axis by the average thickness) greater than 2. The aspect ratio here is calculated from the average major axis and average thickness, which are determined by observing a scanning electron microscope image of the flake-like silver powder before mixing in the composition. The average values ​​for each are determined as the average values ​​of the major axis and thickness of 30 flake-like silver powder particles. The aspect ratio of flake-like silver powder is preferably 3 to 100, more preferably 5 to 50, and even more preferably 10 to 40. When observing the silver powder, the measurement conditions for the scanning electron microscope may, for example, be a magnification of 1000 to 20000x, an acceleration voltage of 5 to 10kV, and a working distance of 5 to 10mm, and the aspect ratio may be determined based on the shape of the particles in the secondary electron image.

[0029] The tap density of the flake-shaped silver powder is 2.0 g / cm³. ３ The above is preferable. The tap density may be a value measured by, for example, the method specified in JIS Z 2512:2012. Note that the tap density in question here is the value of the flake-like silver powder in the composition before kneading.

[0030] Various flake-type silver powders with different aspect ratios, particle sizes, particle size distributions, and particle shapes are available on the market, and these can be used as part or all of the silver powder according to this embodiment without any particular restrictions. The flake-type silver powder contained in the silver powder may be of one type or multiple types. If the silver powder contains multiple types of flake-type silver powder, the mass ratio of the flake-type silver powder to the silver powder is the ratio of the total mass of each type of flake-type silver powder to the total mass of the silver powder. Furthermore, "containing 50% or more by mass of flake-type silver powder relative to the total amount of silver powder" means that when preparing silver powder by mixing physically inseparable units such as manufacturing lot units or purchased packaging units, the raw material classified as flake-type silver powder accounts for 50% or more by mass. For example, when mixing one or more types of flake-type silver powder with non-flake-type silver powder, it is sufficient if the former accounts for 50% or more by mass.

[0031] When the silver powder contains silver powder components other than flake-shaped silver powder, the shape of the particles in the silver powder components is not particularly limited and may be spherical, approximately spherical, spheroidal, approximately spheroidal, dendritic, etc.

[0032] Commercially available silver powder may be used. Examples of such commercially available products include, but are not limited to, the Silcoat® series (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.), the Silbest series (manufactured by Tokuriki Honten Co., Ltd.), K-0082P, and AA-4703 (manufactured by METALOR Inc.).

[0033] The silver powder content in the conductive resin composition is preferably 65% ​​by mass or more and 75% by mass or less of the total amount of the conductive resin composition. If the silver powder is a mixture of multiple components, the total amount thereof shall be treated as the silver powder content.

[0034] The organic solvent is a liquid that functions as a dispersion medium for the thermoplastic resin and silver powder. In this embodiment, the organic solvent contains 70% by mass or more of a cyclic compound having a carbonyl group relative to the total amount of the organic solvent. Preferably, the organic solvent contains 80% by mass or more of a cyclic compound having a carbonyl group relative to the total amount of the organic solvent, and more preferably, all of it is a cyclic compound having a carbonyl group. Examples of cyclic compounds having a carbonyl group include isophorone, cyclohexanone, 2-methylcyclohexanone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and the like. By containing 70% by mass or more of a cyclic compound having a carbonyl group relative to the total amount of the organic solvent, the conductive resin composition according to this embodiment can be used for coating and wiring formation regardless of the substrate.

[0035] The organic solvent, excluding cyclic compounds having a carbonyl group, may comprise 30% by mass or less and may be compounds commonly used as dispersion media for conductive resin compositions. Examples include ketones such as methyl ethyl ketone and methyl isobutyl ketone, aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene, cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, glycol ethers such as propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether, as well as ethyl acetate and cellulose acetate. Examples of organic solvents include, but are not limited to, esters such as butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; alcohols such as ethanol, propanol, ethylene glycol, and propylene glycol; aliphatic hydrocarbons such as octane and decane; petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha; 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, and terpineol. The organic solvent may be a single compound or a mixture of multiple compounds.

[0036] The lower limit of the organic solvent content in the conductive resin composition is not particularly limited, but it may be, for example, 15% by mass or more. Similarly, the upper limit is not particularly limited, but it may be, for example, 30% by mass or less. If the organic solvent is a mixture, its total amount may fall within the above ranges.

[0037] The conductive resin composition according to this embodiment may contain components other than the thermoplastic resin, silver powder, and organic solvent described above. Examples of these main components include, but are not limited to, defoaming agents, leveling agents, coupling agents, dispersants, and inorganic fillers.

[0038] The conductive resin composition according to the present embodiment can be produced by mixing a thermoplastic resin, silver powder, an organic solvent, and optionally added other components by a known method.

[0039] The conductive resin composition according to the present embodiment has a condition of 25°C and a shear rate of 10 s －１ viscosity η at １ is not less than 100 dPa·s and not more than 1200 dPa·s. When the viscosity η １ is within this range, the conductive resin composition is easily used for applications where wiring is formed using a dispenser or the like. The viscosity η １ is more preferably not less than 150 dPa·s and not more than 1000 dPa·s. The viscosity η １ is even more preferably not less than 150 dPa·s and not more than 500 dPa·s.

[0040] The viscosity of the conductive resin composition is measured, for example, in accordance with JIS Z 8803:2011, and as an example, it is measured using a cone-plate rotational viscometer specified in the JIS standard. For example, when performing measurement using an E-type viscometer (cone-plate) model TV-35 (manufactured by Toki Sangyo Co., Ltd.), which is an example of a cone-plate rotational viscometer conforming to the JIS standard, with 3°×R9.7 used as the cone rotor, the viscosity at a shear rate of 10 s －１ can be measured when the measurement is performed under the condition of a rotor rotation speed of 5 rpm.

[0041] The conductive resin composition according to the present embodiment has a condition of 25°C and a shear rate of 10 s －１ viscosity η at １ and a shear rate of 100 s at 25°C －１ viscosity η at ２ , and the thixotropic index Ti (=η １ / η ２ ) is not less than 1.2 and not more than 4.0. When the thixotropic index Ti is within this range, it is preferable in that the conductive resin composition applied in a relatively thick thickness is less likely to sag, and wiring shrinkage during heating and drying is easily suppressed. The thixotropic index Ti is more preferably not less than 1.2 and not more than 3.0. The thixotropic index Ti is even more preferably not less than 1.5 and not more than 2.5.

[0042] The thixotropic index of a conductive resin composition is defined as the ratio of its viscosity at two predetermined shear rates. The viscosity at each shear rate is measured, for example, according to JIS Z 8803:2011. In this embodiment, the conditions are 25°C and a shear rate of 10 s. －１ viscosity η １ And, 25℃, shear rate 100s －１ viscosity η ２ and the ratio η １ / η ２ This is defined as the thixotropic index Ti. The viscosity measurement method is as described above, and viscosity measurement at each shear rate can be achieved by changing the rotor rotation speed, etc. When measuring using the aforementioned E-type viscometer (cone plate) TV-35 model (manufactured by Toki Sangyo Co., Ltd.) with a cone rotor of 3° × R9.7, the viscosity η is measured under the condition of a rotor rotation speed of 5 rpm. １ The viscosity η under the condition of a rotor rotation speed of 50 rpm ２ Each of these can be measured.

[0043] [Wiring Formation Method] Next, a method for forming wiring using the conductive resin composition according to this embodiment will be described. The wiring formation method according to this embodiment includes applying the conductive resin composition to a substrate and drying the conductive resin composition. In this embodiment, the application and drying of the conductive resin composition may be carried out in separate steps, or they may be carried out in steps that overlap in part or in whole.

[0044] The substrate to which the conductive resin composition is applied can be used without particular limitations and can be appropriately selected according to the purpose. Examples of substrates include paper-phenol resin, paper-epoxy resin, glass cloth-epoxy resin, glass-polyimide, glass cloth / nonwoven fabric-epoxy resin, glass cloth / paper-epoxy resin, synthetic fiber-epoxy resin, substrates using composite materials such as fluororesin, polyethylene, polyphenylene ether, and cyanate, substrates made of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate, plastics such as polyimide, polyphenylene sulfide, polyamide, polycarbonate, and acrylic, substrates made of thermoplastic elastomers such as polyester, polyurethane, polyolefin, and styrene block copolymers, and glass and ceramics.

[0045] The conductive resin composition can be applied to a substrate by known methods. Examples of such methods include, but are not limited to, printing methods and dispensing methods. Examples of printing methods include gravure printing, offset printing, and screen printing. The dispensing method is a method of forming a pattern by extruding the conductive resin composition from a needle while controlling the amount applied, and is suitably used for forming thick film patterns and patterns on substrates with curved or uneven surfaces.

[0046] The conductive resin composition applied to the substrate can be dried by known methods. Examples of such methods include, but are not limited to, hot air circulating drying ovens, IR ovens, hot plates, convection ovens, etc. (methods using a heat source equipped with a steam-heated air heating system to bring hot air in a countercurrent contact with the drying oven, and methods of blowing hot air onto the support from a nozzle). Drying may also be carried out by heating. The temperature when heating is not limited as long as it is a temperature that the substrate can withstand, but for example it may be between 60°C and 200°C. The drying time may be, for example, between 15 minutes and 150 minutes.

[0047] By applying a conductive resin composition to a substrate, the shape of the wiring to be formed on the substrate is defined. Subsequently, by drying the conductive resin composition, the organic solvent is removed, and a composition in which silver powder is dispersed with the resin composition as a binder remains on the substrate. This composition contains a high concentration of silver powder and functions as a conductive circuit. In other words, wiring can be formed by the above method.

[0048] [Conductive Material] The conductive material according to this embodiment is obtained by solidifying the conductive resin composition described above. For example, a wiring-like conductive material can be formed by applying the conductive resin composition to a substrate and drying and solidifying it.

[0049] The method for solidifying the conductive resin composition is not particularly limited and can be achieved by utilizing the characteristics of the polymer compounds contained in the thermoplastic resin. Non-limited examples of processing methods used when solidifying the conductive resin composition to form a conductor include drying, heat treatment, and molding. Various processing methods, including those exemplified here, can be appropriately combined to obtain a conductor of a desired shape.

[0050] Conductors may be products in themselves or used as components. Conductors can be used, for example, in snow melting devices placed in the covers of vehicle lighting systems, electromagnetic shielding, and grounding wiring.

[0051] [Examples] The present invention will be further described below with reference to examples. However, the following examples are not limiting to the present invention.

[0052] [Preparation of Conductive Resin Composition] (1) Components (1-1) Thermoplastic Resin The following resins A1 to A4 were used as thermoplastic resins. Of these, resins A1 to A4 all belong to the designated polymer compound group. Resin A1 is a modified vinyl chloride-vinyl acetate copolymer and is an example of a vinyl chloride-vinyl acetate resin. A1: Solvine (registered trademark) TA3 A ternary copolymer of vinyl chloride, vinyl acetate, and hydroxyalkyl acrylate, manufactured by Nisshin Chemical Industry Co., Ltd. The weight-average molecular weight is 6.4 × 10 ４The hydroxyl value is 56 mg KOH / g. A2: Phenoxy PKHC, a phenoxy resin manufactured by Huntsman Corporation. The weight-average molecular weight is 4.3 × 10⁻⁶. ４ A3: Clarity (registered trademark) LA2250 is an acrylic block copolymer (an example of acrylic resin) manufactured by Kuraray Co., Ltd. A4: Panlite (registered trademark) TS2020 is a polycarbonate manufactured by Teijin Limited.

[0053] (1-2) Silver powder: Silver powders B1 to B5 were used as silver powder. Of these, silver powders B1 to B3 are flake-type silver powders. B1: Flake-type silver powder AA-4703 (manufactured by Metalor Technologies SA) (tap density 3.6 g / cm³) ３ ) B2: Flake-type silver powder Silcoat AgC-221PA (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) (Tap density 5.5-6.5 g / cm³) ３ ) B3: Flake-type silver powder Silcoat AgC-252 (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) (Tap density 2.8 g / cm³) ３ ~4.5 g / cm ３ ) B4: Spherical silver powder Silcoat AgC-H (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) (Tap density 1.9 g / cm) ３ ) B5: Spherical silver powder K-1322P (manufactured by Metalor Technologies SA) (tap density 4.5 g / cm) ３ )

[0054] (1-3) Organic solvents The following solvents C1 to C3 were used as organic solvents: C1: Isophorone C2: γ-butyrolactone C3: Carbitol acetate

[0055] (2) Preparation of conductive resin compositions The formulations of the conductive resin compositions in each example and comparative example are shown in Table 1 below. For each example, thermoplastic resin, silver powder, and solvent were weighed according to the formulations shown in Table 1, stirred with a stirrer, and then kneaded into a paste using a three-roll mill to prepare the conductive resin composition.

[0056] The viscosity of the obtained conductive resin composition at 25°C was measured using an E-type viscometer (cone plate) TV-35 (manufactured by Toki Sangyo Co., Ltd.). Shear rate: 10 s －１ (Measured at rotor speed of 5 rpm) viscosity η １ And the shear rate is 100 s. －１ (Measured at rotor speed of 50 rpm) viscosity η ２ The thixotropic index Ti was defined as the ratio of viscosity measurements η. １ / η ２ It was calculated as follows.

[0057] Table 1 shows the formulations of the conductive resin compositions for each example and comparative example, as well as the viscosity and thixotropic index values.

[0058] Table 1: Examples and Comparative Examples

[0059] [Evaluation of Conductive Resin Compositions] (1) Wiring Formation The conductive resin compositions of each example in the examples and comparative examples were dispensed onto a polycarbonate substrate. An ML-5000X2 (Musashi Engineering Co., Ltd.) was used as the pressure control device, a desktop robot SHOTMASTER 200DS (Musashi Engineering Co., Ltd.) was used as the drawing device, and a TPND-22G-U (inner diameter 0.4 mm, Musashi Engineering Co., Ltd.) was used as the discharge nozzle. After coating, the substrate was placed flat on a heat-resistant rack with the coated surface facing upwards, and dried and solidified at 120°C for 1 hour using a hot air circulation drying device FineOvenDF612 (Yamato Scientific Co., Ltd.) to form the wiring. For each conductive resin composition of Examples 1 to 9 and Comparative Examples 1 to 3 and 5, coating was performed so that the wiring dimensions after drying were a film thickness of 100 μm, a wiring width of 1 mm, and a wiring length of 10 cm. In Comparative Example 4, the coating film sagged, and after drying, it was not possible to form wiring with a film thickness of 100 μm and a wiring width of 1 mm. Furthermore, for the conductive resin composition of Example 1, wiring coated to a film thickness of 200 μm after drying was separately prepared and designated as Example 1A.

[0060] (2) Evaluation of Sagging Properties (Sagging) For each example of the examples and comparative examples, the sagging properties of the conductive resin composition applied to the substrate were evaluated. Immediately after dispensing, the coating film was photographed, and the substrate was immediately stood upright with the long side of the coating film parallel to the floor. This position was maintained for 30 seconds, and then the coating film was photographed again. From the photographs of the coating film before and after standing the substrate upright, the change in line width in the short side direction of the coating film due to sagging was evaluated according to the following criteria. The criteria for evaluation A (pass) and evaluation C (fail) were as follows: A (pass): Line width change rate of the coating film before and after standing the substrate upright is less than 50% C (fail): Line width change rate of the coating film before and after standing the substrate upright is 50% or more

[0061] (3) Evaluation of Wiring Shrinkage (Shrinkage) For each example in the examples and comparative examples, the coating film was photographed immediately after dispensing, measured, and then dried and solidified immediately. After drying, the coating film was photographed again. From the photographs of the coating film before and after drying, the change in line width in the short-side direction of the coating film due to shrinkage was evaluated according to the following criteria. Note that in all of Comparative Examples 1 to 5, wire breakage occurred, and samples suitable for further evaluation could not be obtained. A (Pass): Shrinkage rate is less than 5%. B (Pass): Shrinkage rate is 5% or more and less than 10%. C (Fail): Shrinkage rate is 10% or more, or the coating film is visually confirmed to be broken.

[0062] (4) Evaluation of Resistance (Initial Resistance) For each embodiment, the resistance of a 1 mm wide, 10 cm long wire immediately after it was formed on the substrate was measured. The measurement was performed using a milliohm high tester 3540 (manufactured by HIOKI E.E. CORPORATION), with probes placed on both ends of the wire and measured using the four-terminal measurement method. Based on the resistance value, it was classified into the following three levels. However, there were no examples that fell into level C. A (Pass): Resistance value is less than 1.0 Ω. B (Pass): Resistance value is 1.0 Ω or more and 10 Ω or less. C (Fail): Resistance value is greater than 10 Ω. -: Evaluation was not possible due to a break in the wire.

[0063] (5) Evaluation of Resistance Change After Maintaining a High Temperature and High Humidity Environment (Resistance Change) The wiring formed for each example was left standing for 1000 hours in an environment of 85°C and 85% RH using a constant temperature and humidity chamber IG-400 (manufactured by Yamato Scientific Co., Ltd.). After the wiring was returned to room temperature, the resistance value was measured in the same manner as the initial resistance evaluation. Based on the rate of decrease in resistance value relative to the value immediately after wiring formation, each example was classified into the following four levels. However, there were no examples that fell into level D. A (Pass): The rate of change in resistance value is less than 10%. B (Pass): The rate of change in resistance value is 10% or more and less than 20%. C (Pass): The rate of change in resistance value is 20% or more and less than 30%. D (Fail): The rate of change in resistance value is 30% or more. -: Evaluation was not possible due to wire breakage.

[0064] [Results] Table 2 shows the evaluation results of the conductive resin compositions for each example and comparative example. Each example from Examples 1 to 9 and Example 1A showed good performance in both sagging and wiring shrinkage, demonstrating superiority over Comparative Examples 1 to 5. Furthermore, each example from Examples 1 to 9 and Example 1A showed performance at a level sufficient for practical use in the evaluation of both initial resistance and resistance change.

[0065] Table 2: Examples and Comparative Examples

[0066] [Other Embodiments] With regard to other configurations, the embodiments disclosed herein are illustrative in all respects, and it should be understood that the scope of the present invention is not limited thereto. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the invention. Therefore, other embodiments modified without departing from the spirit of the invention are naturally included within the scope of the present invention.

[0067] This invention can be used in snow melting devices installed in the covers of vehicle lighting devices, etc.

Claims

1. A conductive resin composition containing a thermoplastic resin, silver powder, and an organic solvent, wherein the thermoplastic resin comprises at least one selected from the group consisting of a polymer compound containing at least one of constituent units derived from vinyl chloride and constituent units derived from vinyl acetate, phenoxy resin, acrylic resin, and polycarbonate; the silver powder comprises flake-shaped silver powder in an amount of 50% by mass or more relative to the total amount of silver powder; and the organic solvent comprises a cyclic compound having a carbonyl group in an amount of 70% by mass or more relative to the total amount of the organic solvent. (Tested at 25°C, shear rate 10s) －１ The viscosity is between 100 dPa·s and 1200 dPa·s, and the temperature is 25°C and the shear rate is 10s. －１ Viscosity at 25°C and shear rate of 100 s －１ A conductive resin composition having a thixotropic index, which is the ratio of viscosity to , of 1.2 or more and 4.0 or less.

2. The conductive resin composition according to claim 1, wherein the thermoplastic resin comprises a copolymer having constituent units derived from vinyl chloride and constituent units derived from vinyl acetate.

3. The conductive resin composition according to claim 1, wherein the content of the silver powder is 65% by mass or more and 75% by mass or less with respect to the total amount of the conductive resin composition.

4. A conductor obtained by solidifying the conductive resin composition according to any one of claims 1 to 3.

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