Conductive composition, conductive paste, electric circuit, flexible electric circuit body, and method for manufacturing molded body

Abstract

Provided is an electroconductive composition capable of forming electric wiring lines in an electric circuit that are less apt to break even when the electric circuit and / or the electric wiring lines are elongated and / or flexed.　The electroconductive composition comprises (A) electroconductive particles, (B) a thermoplastic resin, and (C) a solvent, wherein the thermoplastic resin (B) has a glass transition point of 140-200°C.

Description

[Technical Field]

[0001] The present invention relates to a conductive composition for forming electrodes, wiring, etc. of electric circuits and electronic circuits, etc. [Background technology]

[0002] In recent years, conductive pastes have been developed for forming electrodes and wiring on flexible and expandable substrates. Furthermore, attempts have been made to use the conductive pastes to form electrodes and wiring for thermoformable electric and electronic circuits.

[0003] For example, Patent Document 1 describes a polymer thick-film conductive composition containing (a) 30 to 70 wt% silver, (b) a first organic medium, and (c) a second organic medium. Patent Document 1 also describes that the (b) first organic medium is 10 to 40 wt% of a first organic medium containing 10 to 50 wt% of a thermoplastic urethane resin dissolved in a first organic solvent, where the weight percentage of the thermoplastic urethane resin is based on the total weight of the first organic medium. Patent Document 1 also describes that the (c) second organic medium is 10 to 40 wt% of a second organic medium containing 10 to 50 wt% of a thermoplastic polyhydroxyether resin dissolved in an organic solvent, where the weight percentage of the thermoplastic polyhydroxyether resin is based on the total weight of the second organic medium. In the polymer thick-film conductive composition described in Patent Document 1, the weight percentages of the silver, the first organic medium, and the second organic medium are based on the total weight of the polymer thick-film conductive composition.

[0004] Patent Document 2 describes a resin composition containing (A) conductive particles, (B) a thermoplastic polyurethane resin having a 100% modulus of 7 MPa or more, and (C) a solvent. Patent Document 2 also describes that the ratio of the (A) conductive particles to the total of the (A) conductive particles and the (B) thermoplastic polyurethane resin is 90% by weight or more but less than 100% by weight. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-531490 [Patent Document 2] Japanese Patent Application Publication No. 2018-104581 DISCLOSURE OF THE INVENTION

[0006] In recent years, attempts have been made to form electrodes and wiring, etc. of electric circuits and / or electronic circuits (simply referred to as "electrical wiring") on the surface of a stretchable and / or bendable substrate. Also, attempts have been made to form electrical wiring by molding using a conductive paste. The technology of forming electrical wiring by molding using a conductive paste is called "in-mold electronics (IME)." During molding such as thermoforming, the electrical wiring is deformed by the stretching and / or bending of the substrate (e.g., a flat sheet or film), which may result in disconnection of the electrical wiring, such as the electrical circuits, used in IME.

[0007] A conductive paste containing a thermoplastic polyurethane resin can be used as a conductive paste for forming electronic circuit wiring on the surface of a stretchable and / or bendable substrate. However, it has been found that when an electrical wiring pattern formed using a conductive paste containing a thermoplastic polyurethane resin is heat-molded, cracks occur in the fine line pattern (e.g., fine lines with a width of 1 mm), resulting in disconnection of the electrical wiring.

[0008] Therefore, an object of the present invention is to provide a conductive composition and a conductive paste that can form electrical wiring that is less likely to break even when the electrical wiring of an electric circuit and / or electronic circuit is stretched and / or bent. Another object of the present invention is to provide a conductive composition and a conductive paste that can form electrical wiring that is less likely to break even when the electrical wiring of an electric circuit and / or electronic circuit is formed using molding.

[0009] In order to solve the above problems, an embodiment of the present invention has the following configuration.

[0010] (Configuration 1) Configuration 1 of this embodiment is a conductive composition containing (A) conductive particles, (B) a thermoplastic resin, and (C) a solvent, wherein the glass transition point of the thermoplastic resin (B) is 140 to 200°C.

[0011] (Configuration 2) Configuration 2 of this embodiment is the conductive composition of configuration 1, in which the thermoplastic resin (B) contains a polycarbonate resin.

[0012] (Configuration 3) Configuration 3 of this embodiment is the conductive composition of Configuration 1 or 2, in which the thermoplastic resin (B) includes at least one selected from poly(4,4'-cyclohexylidene diphenyl) carbonate and copoly[2,2-bis(4-hydroxyphenyl)propane / 2,2-bis(4-hydroxy-3-methylphenyl)propane] carbonate.

[0013] (Configuration 4) A fourth aspect of this embodiment is the conductive composition according to any one of the first to third aspects, in which the boiling point of the solvent (C) is 200° C. or higher.

[0014] (Configuration 5) A fifth aspect of the present embodiment is the conductive composition according to any one of the first to fourth aspects, wherein the solvent (C) includes at least one selected from isophorone, 3-methoxy-N,N-dimethylpropanamide, benzyl alcohol, butyl carbitol, ethyl carbitol acetate, and tetraglyme.

[0015] (Configuration 6) Configuration 6 of this embodiment is the conductive composition of any one of configurations 1 to 5, in which the weight ratio of the (A) conductive particles to the (B) thermoplastic resin (weight of the (A) conductive particles:weight of the (B) thermoplastic resin) is 99:1 to 70:30.

[0016] (Configuration 7) A seventh aspect of this embodiment is the conductive composition of any one of the first to sixth aspects, in which the (A) conductive particles are silver particles.

[0017] (Configuration 8) The eighth aspect of this embodiment is a conductive paste containing the conductive composition of any one of the first to seventh aspects.

[0018] (Configuration 9) Configuration 9 of this embodiment is the conductive paste of configuration 8, which is a conductive paste for forming a flexible electrical circuit body.

[0019] (Configuration 10) Configuration 10 of this embodiment is the conductive paste of configuration 8, and is a conductive paste for in-mold electronics.

[0020] (Configuration 11) An eleventh aspect of this embodiment is an electric circuit including a cured product of the conductive paste of any one of the eighth to tenth aspects.

[0021] (Configuration 12) Component 12 of the present invention is a flexible electrical circuit comprising a flexible substrate and the electrical circuit of component 11 disposed on the flexible substrate.

[0022] (Configuration 13) A thirteenth aspect of the present invention is a method for producing a molded body, comprising: forming an electric circuit on a surface of a flexible substrate using the conductive paste of any one of aspects eight to ten; and molding the flexible substrate on which the electric circuit has been formed and a molding resin to form a molded body.

[0023] The present invention can provide a conductive composition and a conductive paste that can form electrical wiring that is less likely to break even when the electrical wiring of an electric circuit and / or an electronic circuit is stretched and / or bent.Furthermore, the present invention can provide a conductive composition and a conductive paste that can form electrical wiring that is less likely to break even when the electrical wiring of an electric circuit and / or an electronic circuit is formed by molding. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the following embodiments are forms for embodying the present invention and are not intended to limit the scope of the present invention.

[0025] This embodiment is a conductive composition containing (A) conductive particles, (B) a thermoplastic resin, and (C) a solvent. The glass transition temperature of the thermoplastic resin (B) contained in the conductive composition of this embodiment is 140 to 200°C.

[0026] By including a predetermined component in the conductive composition (e.g., conductive paste) of this embodiment, it is possible to form electrical wiring that is less likely to break even when the electrodes and wiring (also simply referred to as "electrical wiring") of an electric circuit and / or electronic circuit (sometimes simply referred to as "electrical circuit") are stretched and / or bent. Furthermore, the conductive composition (e.g., conductive paste) of this embodiment can form electrical wiring that is less likely to break, even when the electrical wiring is formed using molding.

[0027] In this specification, the term "flexible substrate" refers to a substrate that is the target of printing when an electrical wiring pattern included in an electrical circuit is printed using a conductive paste. In this specification, the flexible substrate is also simply referred to as "substrate." In addition, since the "flexible substrate" is generally in the form of a flat sheet or film, the flexible substrate may also be referred to as a "flat sheet" or "film." Preferred examples of the flexible substrate include flat sheets (films) made of polycarbonate resin, polyethylene terephthalate (PET) resin, and / or acrylic resin. The flexible substrate is a substrate that has flexibility, such as the ability to undergo deformation, such as extension and / or bending, when heated to at least a predetermined temperature. Therefore, the flexible substrate does not need to have flexibility at room temperature (e.g., 30°C or lower). The predetermined temperature when heated is, for example, 140°C to 180°C.

[0028] In this specification, the term "flexible electrical circuit" refers to a flexible substrate (flat sheet or film) on which an electrical wiring pattern (electrical circuit pattern) is printed using a conductive paste, and the printed conductive paste is then dried and solidified. Flexible electrical circuits can be used for molding. Flexible electrical circuits including a flexible substrate are flexible at least when heated to a predetermined temperature. Therefore, flexible electrical circuits do not necessarily have flexibility at room temperature (for example, 30°C or lower). As with flexible substrates, the predetermined temperature when heated is, for example, 140°C to 180°C.

[0029] In this specification, the term "molded product" refers to a product obtained by molding a flexible electrical circuit (a flat sheet or film having an electrical wiring pattern) together with another resin (molding resin). Molding refers to a processing method for forming a material into a predetermined shape using a mold, such as heat molding, pressure molding, and vacuum molding.

[0030] The conductive paste of this embodiment is preferably a conductive paste for in-mold electronics. Generally, a technique for bonding a flat sheet-like or film-like substrate simultaneously with molding is called in-mold. There is also a technique called in-mold electronics (IME) that utilizes in-mold. In-mold electronics is a technique for manufacturing a molded product with integrated electrical wiring by forming an electrical wiring pattern (flexible electrical circuit body) on a flat sheet-like or film-like substrate and molding it by in-mold. By using the conductive paste of this embodiment, electrical wiring that is less likely to break can be formed even when the substrate is stretched and / or bent. Therefore, the conductive paste of this embodiment can be preferably used as a conductive paste for in-mold electronics.

[0031] Next, the conductive composition of this embodiment will be described.

[0032] <(A) Conductive particles> The conductive composition of the present embodiment contains conductive particles as component (A).

[0033] The conductive particles contained in the conductive composition of this embodiment preferably contain at least one selected from silver (Ag), gold (Au), copper (Cu), palladium (Pd), nickel (Ni), titanium (Ti), and carbon (C). When the conductive particles contain a specific metal, electrical wiring with low electrical resistance can be formed. More preferably, the conductive particles contained in the conductive composition of this embodiment contain at least one selected from silver (Ag), gold (Au), copper (Cu), palladium (Pd), and carbon (C). Silver (Ag) has particularly high electrical conductivity. Therefore, it is preferable to use silver (Ag) particles (i.e., conductive particles made of silver) as the conductive particles. By using silver particles as the conductive particles, electrical wiring with low electrical resistance can be formed.

[0034] In this specification, for example, "conductive particles made of silver" means that no components other than silver are intentionally added, and the conductive particles are allowed to contain unavoidable impurities. The same applies to conductive particles made of metals other than silver and components other than conductive particles.

[0035] The particle shape and particle size (also referred to as particle diameter) of the conductive particles are not particularly limited. Examples of particle shapes that can be used include spherical and scale-like particles. The particle size of the conductive particles can be determined by the particle size (D50) of 50% of the total particle size. In this specification, D50 is also referred to as the average particle size. The average particle size (D50) can be determined from the results of particle size distribution measurement using a microtrack method (laser diffraction scattering method).

[0036] The average particle size (D50) of the conductive particles is preferably 0.1 to 30 μm, more preferably 0.2 to 20 μm, even more preferably 0.5 to 15 μm, and particularly preferably 0.8 to 10 μm, from the viewpoints of resistance to stretching and / or bending and workability. If the average particle size (D50) is larger than the above range, problems such as clogging may occur during screen printing. If the average particle size is smaller than the above range, the particles may be excessively sintered during firing, making it difficult to form electrical wiring that is resistant to stretching and / or bending.

[0037] The size of the conductive particles can be expressed as a BET value (BET specific surface area). The BET value of the conductive particles is preferably 0.1 to 10 m 2 / g, more preferably 0.2 to 5m 2 / g, more preferably 0.5 to 3m 2 / g.

[0038] <(B) Thermoplastic resin> The conductive composition of the present embodiment contains a thermoplastic resin as component (B).

[0039] The glass transition temperature of the thermoplastic resin contained in the conductive composition of this embodiment is 140 to 200°C, preferably 140 to 190°C. The glass transition temperature of the thermoplastic resin can be measured by differential scanning calorimetry (DSC). The typical temperature for hot molding of in-mold electronics is 140 to 180°C, the temperature for pressure molding is 140 to 160°C, and the temperature for vacuum molding is 180°C. By using a resin component of the conductive paste with a glass transition temperature that is similar to or higher than the molding temperature, the flat sheet (film) and the conductive paste can conform well to each other during molding. Therefore, even if the electrical wiring pattern is deformed during molding, the possibility of electrical wiring breakage can be reduced.

[0040] The conductive composition of the present embodiment preferably contains a polycarbonate resin as (B) a thermoplastic resin having a glass transition point of 140 to 200° C. More preferably, the thermoplastic resin is made of a polycarbonate resin.

[0041] During molding, a molded product having electrical wiring can generally be produced by printing predetermined electrical wiring on a flat sheet (film) of polycarbonate resin and using the flat sheet for molding. By including polycarbonate resin in the thermoplastic resin, the electrical wiring can be made to conform well to deformation of the flat sheet during molding. This reduces the possibility of electrical wiring breaking.

[0042] The inventors have discovered that when an electrical wiring pattern formed using a conductive paste containing a thermoplastic polyurethane resin is subjected to heat molding, cracks occur in the fine line pattern (e.g., fine lines 1 mm wide), resulting in the electrical wiring being broken.

[0043] Therefore, the present inventors investigated various materials to be used in a conductive paste for forming electrical wiring by heat molding. The present inventors discovered that by using a thermoplastic resin with a glass transition temperature of 140 to 200°C as the thermoplastic resin contained in the conductive paste, electrical wiring with a low probability of disconnection can be formed by heat molding, thereby arriving at the present invention. In in-mold electronics, a substrate (flat sheet or film) on which an electrical wiring pattern is printed using a conductive paste is used for molding. The substrate material is not particularly limited as long as it is a substrate that can be heat molded. Preferred substrate materials include substrates made of polycarbonate resin, polyethylene terephthalate (PET), and acrylic resin. When the substrate material is polycarbonate resin, using the same type of material as the thermoplastic resin contained in the conductive paste of this embodiment makes it easier for the deformation of the electrical wiring pattern to follow the deformation of the flat sheet or film during heat molding. This reduces the possibility of disconnection of the electrical wiring. In particular, by making the glass transition point and softening point of the substrate (flat sheet or film) material and the resin component of the conductive paste approximately the same, the expansion of the flat sheet or film during heat molding can appropriately follow the expansion of the resin component of the conductive paste, thereby further reducing the possibility of disconnection of the electrical wiring.

[0044] The thermoplastic resin (polycarbonate resin) contained in the conductive composition of this embodiment preferably contains at least one selected from poly(4,4'-cyclohexylidene diphenyl) carbonate and copoly[2,2-bis(4-hydroxyphenyl)propane / 2,2-bis(4-hydroxy-3-methylphenyl)propane]carbonate (sometimes referred to as "predetermined polycarbonate resin"). Note that two or more different types of thermoplastic resins (polycarbonate resins) can be used as the thermoplastic resin.

[0045] The molecular weight of the polycarbonate resin contained in the thermoplastic resin is preferably 10,000 to 100,000, more preferably 10,000 to 80,000, and even more preferably 10,000 to 60,000. When the molecular weight of the polycarbonate resin is high, it is necessary to increase the amount of solvent blended to achieve the desired viscosity. When a large amount of solvent is blended, the coating film becomes too thin. By ensuring that the molecular weight of the thermoplastic resin (polycarbonate resin) is within the above range, it is possible to achieve a good balance of viscosity, elongation properties when heated, and electrical resistance of the cured product.

[0046] Some types of polycarbonate resins have high crystallinity. Highly crystalline polycarbonate resins have the problem of crystallizing when heated and dissolved in a solvent and then returned to room temperature. It is not easy to use such polycarbonate resins as resin components of conductive pastes. On the other hand, the above-mentioned specific polycarbonate resins can be dissolved in specific solvents, such as isophorone, which has a high boiling point, and the problem of crystallization after returning to room temperature can be avoided. Therefore, by using polycarbonate resins as thermoplastic resins, the possibility of electrical wiring breakage can be further reduced.

[0047] When the conductive paste contains polycarbonate resin, an electrical wiring pattern can be easily printed on the surface of a flexible substrate made of polycarbonate resin, and also on the surface of a substrate made of a material other than polycarbonate resin.

[0048] In the conductive composition of this embodiment, the weight ratio of the (A) conductive particles to the (B) thermoplastic resin (weight of the (A) conductive particles:weight of the (B) thermoplastic resin) is preferably 99:1 to 70:30, more preferably 98:2 to 75:25, and even more preferably 98:2 to 80:20. By setting the weight ratio of the conductive particles to the thermoplastic resin within an appropriate range, the shape of the printed pattern of the electrical wiring can be properly maintained and the electrical resistance of the electrical wiring can be reduced.

[0049] The conductive composition of the present embodiment may contain other resins such as thermoplastic resins, thermosetting resins, and / or photocurable resins, to the extent that the effect is not impaired. However, in order to obtain suitable electrical wiring, the resin contained in the conductive composition is preferably a thermoplastic resin having a glass transition point of 140 to 200°C, and more preferably a polycarbonate resin.

[0050] <(C) Solvent> The conductive composition of this embodiment contains a solvent as component (C).

[0051] The conductive composition of this embodiment preferably uses a solvent with a boiling point of 200°C or higher and 300°C or lower. The use of a high-boiling-point solvent, such as isophorone, makes it possible to dissolve polycarbonate resin. Furthermore, by using a solvent with a boiling point higher than a predetermined temperature, the drying time can be appropriately extended without shortening it after screen-printing an electrical wiring pattern using the conductive paste. Therefore, it is easier to deform the electrical wiring pattern in response to deformation of the flat sheet or film during molding. Note that if the boiling point of the solvent exceeds 300°C, the solvent may not be sufficiently removed during heating for drying and molding.

[0052] Specifically, the solvent preferably contains at least one selected from isophorone, 3-methoxy-N,N-dimethylpropanamide, benzyl alcohol, butyl carbitol, ethyl carbitol acetate, and tetraglyme. These specific solvents can reliably dissolve polycarbonate resin. Furthermore, the inclusion of a specific solvent in the conductive paste can further reduce the likelihood of breakage in the resulting electrical wiring. In particular, when poly(4,4'-cyclohexylidene diphenyl) carbonate and / or copoly[2,2-bis(4-hydroxyphenyl)propane / 2,2-bis(4-hydroxy-3-methylphenyl)propane]carbonate is dissolved in a solvent as the thermoplastic resin, the above-mentioned solvents can be preferably used. This facilitates the formation of a paste from the conductive composition, further reducing the likelihood of breakage in the resulting electrical wiring.

[0053] The solvent preferably contains isophorone. By using isophorone as the solvent, polycarbonate resin can be more easily dissolved in the solvent. Furthermore, the boiling point of isophorone is 215°C, which is considered to be a suitable boiling point for a solvent for printing conductive pastes. Conductive pastes containing isophorone solvents have the advantage of being less likely to gel or solidify even when left standing and not undergoing solid-liquid separation during printing. Therefore, the solvent preferably contains isophorone, and more preferably consists solely of isophorone. In particular, when poly(4,4'-cyclohexylidene diphenyl) carbonate and / or copoly[2,2-bis(4-hydroxyphenyl)propane / 2,2-bis(4-hydroxy-3-methylphenyl)propane] carbonate is dissolved in a solvent as the thermoplastic resin, a solvent containing isophorone can be preferably used.

[0054] The amount of solvent added is preferably 50 to 1000 parts by weight, more preferably 80 to 900 parts by weight, and even more preferably 100 to 800 parts by weight, relative to 100 parts by weight of the thermoplastic resin. Usually, the thermoplastic resin can be properly dissolved by using a solvent in an amount about four times the weight of the thermoplastic resin.

[0055] The solvent can be added to the conductive composition as needed to adjust the viscosity of the conductive composition.

[0056] <Conductive paste> This embodiment is a conductive paste containing the above-described conductive composition.

[0057] The conductive paste of this embodiment may be a conductive paste consisting solely of the conductive composition containing the above-described (A) conductive particles, (B) thermoplastic resin, and (C) solvent. However, the conductive paste of this embodiment may contain components other than the above-described conductive composition, provided that the effects of the present invention are not impaired or to improve the effects of the present invention. For example, the conductive paste of this embodiment may further contain at least one selected from the group consisting of an inorganic pigment, an organic pigment, a silane coupling agent, a leveling agent, a thixotropic agent, and an antifoaming agent.

[0058] The conductive paste of this embodiment can be produced by mixing the components contained in the conductive composition described above and other components that are added as needed in a mixer such as a meteoric mixer, dissolver, bead mill, Raikai mixer, three-roll mill, rotary mixer, or twin-screw mixer. In this way, a conductive paste suitable for screen printing, dipping, or other desired coating or electrical wiring formation methods can be prepared.

[0059] The viscosity of the conductive paste of this embodiment can be adjusted to a viscosity that can be appropriately used in a predetermined coating film or electrical wiring formation method such as screen printing, etc. The viscosity can be adjusted by appropriately controlling the amount of solvent.

[0060] The viscosity of the conductive paste of this embodiment is preferably 10 to 1000 Pa·sec, more preferably 20 to 700 Pa·sec, and even more preferably 25 to 600 Pa·sec. The viscosity can be measured using a Brookfield (B-type) viscometer with an SC4-14 spindle (utility cup and spindle (UC / S)=#14) at a rotation speed of 10 rpm and a measurement temperature of 25°C.

[0061] By using the conductive paste of this embodiment, electrical wiring of an electric circuit and / or electronic circuit that is less likely to break can be formed on the surface of a stretchable and / or bendable substrate by means of screen printing or the like.

[0062] This embodiment is an electrical circuit including a cured product of a predetermined conductive paste. In this specification, the "cured product" refers to the product obtained by printing the conductive paste of this embodiment in a predetermined pattern and then drying it by heating at 120°C for 30 minutes, for example. The cured product can be used as electrical wiring for an electrical circuit or the like. Therefore, the conductive paste of this embodiment can be used to form an electrical circuit with a low possibility of breakage. Note that the heating of the conductive paste when producing the cured product does not have to be the final heating.

[0063] In this specification, a flexible electrical circuit may refer to a flexible substrate (for example, a flat sheet or film made of polycarbonate resin) on which an electrical circuit pattern is printed and the printed conductive paste is dried. A flexible electrical circuit includes a flexible substrate and an electrical circuit disposed on the flexible substrate.

[0064] The conductive paste of this embodiment can be preferably used as a conductive paste for forming a flexible electrical circuit body. By using the flexible electrical circuit body of this embodiment in molding, a molded body including a desired electrical circuit can be produced.

[0065] The temperature and time for drying the electrical wiring pattern of the conductive paste can be appropriately selected depending on the type of thermoplastic resin contained in the conductive composition. The temperature and time for drying the conductive paste can be appropriately adjusted and determined taking into account the heat resistance of the substrate. For example, the temperature and time for drying the conductive paste can be 60°C to 160°C and 3 to 60 minutes, preferably 80°C to 150°C and 3 to 60 minutes, and more preferably 100°C to 130°C and 3 to 30 minutes. A cured product of the electrical wiring pattern can be obtained by drying the electrical wiring pattern at a predetermined temperature and for a predetermined time.

[0066] <Molded body> The molded body of this embodiment can be manufactured by molding the flexible electrical circuit body together with another resin (molding resin). That is, the molded body of this embodiment includes an electrical circuit. The technology for manufacturing a molded body including an electrical circuit is called in-mold electronics. Therefore, the conductive paste of this embodiment can be preferably used as a conductive paste for in-mold electronics.

[0067] The molded body of this embodiment is preferably molded by heat molding. By heating a wiring pattern formed on a flexible electrical circuit using the conductive paste of this embodiment, it becomes possible to stretch and / or bend the wiring pattern. The flexible electrical circuit of this embodiment, including the electrical circuit, is flexible, so it can be molded into a desired shape by heat molding.

[0068] In the method for manufacturing a molded body using in-mold electronics according to this embodiment, first, an electric circuit is formed on the surface of a flexible substrate using the conductive paste according to this embodiment described above. Next, the flexible substrate on which the electric circuit has been formed (flexible electric circuit body) and a molding resin are molded to form a molded body.

[0069] Specifically, an example of a manufacturing process for a molded body using in-mold electronics is as follows.

[0070] First, the conductive paste of the present embodiment is produced.

[0071] Next, the conductive paste of this embodiment is printed on the surface of a flexible substrate (for example, a flat sheet or film made of polycarbonate resin) to form a printed pattern (electrical circuit pattern).

[0072] Next, the printed pattern (electrical circuit pattern) of the conductive paste printed on the flexible substrate is heated and dried to produce a flexible electrical circuit. Drying conditions can be, for example, a heating temperature of 120°C and a heating time of 30 minutes.

[0073] Next, the flexible electric circuit body with the electric circuit formed thereon is formed into a three-dimensional shape by molding such as heat molding, pressure molding, or vacuum molding. In molding such as heat molding, the heating temperature of the flexible electric circuit body is preferably 140°C to 180°C.

[0074] Next, the three-dimensionally shaped flexible electric circuit body and molding resin are integrally molded by molding such as hot molding, pressure molding, vacuum molding, etc. The heating temperature during this integral molding is preferably 140°C to 180°C.

[0075] According to the above-described steps, a molded body using in-mold electronics can be manufactured. According to the molded body manufacturing method of this embodiment, a molded body having an electric circuit with a low possibility of breakage can be manufactured by molding. [Example]

[0076] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0077] <Conductive paste materials and preparation ratio> Tables 1 and 2 show the compositions of the conductive pastes of Examples 1 to 14 and Comparative Examples 1 and 2. The compositions are shown with the weight of the conductive particles as 100 parts by weight. The conductive pastes of the Examples and Comparative Examples are conductive compositions comprising silver particles (conductive particles), a thermoplastic resin, and a solvent.

[0078] <(A) Conductive particles> In the examples and comparative examples, silver particles were used as the conductive particles. Table 3 shows the manufacturers and model numbers, particle shapes, average particle diameters (D50), tapped (TAP) densities, and specific surface areas of the silver particles A to E (conductive particles A to E) used in the examples and comparative examples. Tapped density is the "bulk density" obtained after mechanically tapping a container containing a powder sample.

[0079] <(B) Thermoplastic resin> Table 4 shows the manufacturers and model numbers of resins A to F used as thermoplastic resins in the examples and comparative examples, as well as the types of resins, molecular weights, and glass transition points.

[0080] <(C) Solvent> The manufacturers and model numbers, solvent types and boiling points of solvents A to F used in the examples and comparative examples are shown in Table 5. The thermoplastic resin was dissolved in the solvent and mixed with the conductive particles.

[0081] <Preparation of conductive paste> Next, the materials in the predetermined preparation ratios described above were mixed in a planetary mixer, and then dispersed in a three-roll mill to form a paste, thereby preparing a conductive paste.

[0082] <Viscosity measurement method> The viscosity of the conductive pastes of the examples and comparative examples was measured at a temperature of 25° C. using a Brookfield (B-type) viscometer with an SC4-14 spindle (utility cup and spindle (UC / S)=#14) at a rotation speed of 10 rpm. The measurement results are shown in Tables 1 and 2.

[0083] <Method for measuring resistivity> The substrate used was a flexible, flat sheet (film) made of polycarbonate resin. The substrate measured 10 cm × 2 cm and was 250 μm thick. This substrate was deformable (stretchable) at a temperature of 160°C. A wiring pattern (width: 3 mm, length: 50 mm) of the conductive paste (conductive composition) of the Examples and Comparative Examples was printed on the surface of this substrate. The electrical resistance value, described below, was measured by placing electrodes on both ends of the 50 mm length. A screen printer was used for printing. After printing, the pattern was dried by heating at 120°C for 30 minutes in a constant temperature dryer. The film thickness of the resulting cured wiring pattern (simply referred to as the "wiring pattern") was 10 μm. The film thickness was measured using a surface roughness and shape measuring instrument (model number: Surfcom 1500SD-2) manufactured by Tokyo Seimitsu Co., Ltd.

[0084] First, the electrical resistance (initial resistance) of the wiring patterns of the Examples and Comparative Examples was measured by placing electrodes on both ends of a 50 mm length in the longitudinal direction without stretching the pattern and passing a current through them. The electrical resistance of the wiring pattern was measured by the four-terminal method using a 7461A digital multimeter manufactured by ADC Corporation. The specific resistance was calculated from the electrical resistance and the dimensions of the wiring pattern. Tables 1 and 2 show the initial specific resistances calculated from the initial resistances of the Examples and Comparative Examples.

[0085] Next, while measuring the electrical resistance of the wiring pattern, the wiring pattern was stretched at a temperature of 160°C in the longitudinal direction (the length direction of the 50 mm long pattern) until it was stretched 100% (the length after stretching was 100 mm). The "Rate of change in resistance at 100% stretch relative to the initial resistance (times)" column in Tables 1 and 2 shows the resistance values ​​after stretching for the Examples and Comparative Examples divided by the initial resistance. Note that Comparative Examples 1 and 2 broke during stretching. Therefore, for Comparative Examples 1 and 2, the stretch rate at the time of breakage ([stretched length - initial length 50 mm] / initial length 50 mm) is shown.

[0086] <Measurement results of Examples and Comparative Examples> The conductive pastes of Examples 1 to 14 contained a thermoplastic resin (polycarbonate resins A to D) with a glass transition temperature of 140 to 200°C as the thermoplastic resin. Therefore, the wiring patterns of Examples 1 to 14 did not break when stretched 100%, and the rate of change in resistance at 100% stretch relative to the initial resistance was 54 times or less. In addition, in the case of Examples 1 to 4 and 6 to 14, which used only thermoplastic resins (polycarbonate resins A to D) with a glass transition temperature of 140 to 200°C, the rate of change in resistance at 100% stretch relative to the initial resistance was 47 times or less.

[0087] Since the wiring patterns of Examples 1 to 14 did not break when stretched 100%, it is clear that they will not break even when stretched at a temperature of, for example, 160° C. The substrates of the Examples on which the wiring patterns were formed were bent before stretching, but no significant effect on the electrical resistance was observed before and after bending, and no breaks occurred.

[0088] On the other hand, the conductive pastes of Comparative Examples 1 and 2 contain, as the (B) thermoplastic resin, thermoplastic resins (resins E and F) having a glass transition point of 98° C. or less. In Comparative Example 1, the wiring pattern broke when stretched by 13%, and in Comparative Example 2, the wiring pattern broke when stretched by 80%.

[0089] From the above, it was revealed that by using the conductive pastes of Examples 1 to 14, it is possible to form electrical wiring that is less likely to break even when the electrical wiring is stretched and / or bent. Furthermore, in Examples 1 to 14, no breakage occurred even when the wiring pattern was stretched 100% at a temperature of 160°C, and no significant effect on bending was observed. Therefore, it can be said that if the conductive pastes of Examples 1 to 14 are used, it is possible to form electrical wiring that is less likely to break, even when the electrical wiring of an electric circuit and / or electronic circuit is formed using molding.

[0090] [Table 1]

[0091] Table 2

[0092] Table 3

[0093] Table 4

[0094] Table 5

Claims

1. A conductive paste for forming a flexible electrical circuit, comprising a conductive composition, The conductive composition is (A) conductive particles; (B) a thermoplastic resin; (C) a solvent having a boiling point of 200°C or higher; Including, The glass transition temperature of the thermoplastic resin (B) is 140 to 200°C, A conductive paste in which the weight ratio of the (A) conductive particles to the (B) thermoplastic resin (weight of the (A) conductive particles:weight of the (B) thermoplastic resin) is 99:1 to 70:

30.

2. A conductive paste for in-mold electronics comprising a conductive composition, The conductive composition is (A) conductive particles; (B) a thermoplastic resin; (C) a solvent having a boiling point of 200°C or higher; Including, The glass transition temperature of the thermoplastic resin (B) is 140 to 200°C, A conductive paste in which the weight ratio of the (A) conductive particles to the (B) thermoplastic resin (weight of the (A) conductive particles:weight of the (B) thermoplastic resin) is 99:1 to 70:

30.

3. The conductive paste according to claim 1 or 2, wherein the thermoplastic resin (B) includes a polycarbonate resin.

4. A conductive paste described in any one of claims 1 to 3, wherein the (B) thermoplastic resin comprises at least one selected from poly(4,4'-cyclohexylidene diphenyl) carbonate and copoly[2,2-bis(4-hydroxyphenyl)propane / 2,2-bis(4-hydroxy-3-methylphenyl)propane] carbonate.

5. The conductive paste according to any one of claims 1 to 4, wherein the boiling point of the solvent (C) is 300°C or lower.

6. The conductive paste according to any one of claims 1 to 5, wherein the solvent (C) includes at least one selected from isophorone, 3-methoxy-N,N-dimethylpropanamide, benzyl alcohol, butyl carbitol, ethyl carbitol acetate, and tetraglyme.

7. The conductive paste according to any one of claims 1 to 6, wherein the (A) conductive particles are silver particles.

8. An electric circuit comprising a cured product of the conductive paste according to any one of claims 1 to 7.

9. a flexible substrate; The electrical circuit of claim 8 disposed on a flexible substrate; A flexible electrical circuit comprising:

10. Forming an electric circuit on the surface of a flexible substrate using the conductive paste according to any one of claims 1 to 7; forming a molded body by molding the flexible substrate on which the electric circuit is formed and a molding resin; A method for producing a molded body, comprising:

Images