Conductive paste, conductor, contact sensor, and electronic component

Abstract

To provide a conductive paste for forming electrodes which, even in the case of elongation and contraction of the electrode, can reduce the change rate of electrical resistance before and after the elongation and contraction.SOLUTION: A conductive paste comprises (A) carbon black, (B) a binder, and (C) a solvent. The (A) carbon black has a specific surface area (BET value) of 700 m2 / g or less. The (A) carbon black has a structure. The (A) carbon black has a DBP absorption of 110 cm3 / 100 g or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive paste that can be used to form electrodes on a stretchable and / or bendable substrate. [Background technology]

[0002] In recent years, conductive pastes have been developed for forming electrodes on stretchable and / or bendable substrates.

[0003] As a conductive paste for forming electrodes on a stretchable and bendable substrate, for example, Patent Document 1 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 1 also describes that the resin composition contains (A) conductive particles in a ratio of 90% by weight or more to less than 100% by weight of the total of (A) conductive particles and (B) thermoplastic polyurethane resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-104581 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, attempts have been made to form stretchable and / or bendable electrodes and / or wiring on the surface of a stretchable and / or bendable substrate. In order to form stretchable and / or bendable electrodes and / or wiring, conductive pastes such as the resin composition described in Patent Document 1 above have been developed.

[0006] Furthermore, conductive pastes for forming electrodes and / or wiring that can expand and contract and / or bend are sometimes used as electrode materials for contact sensors such as pressure-sensitive sensors and displacement sensors. For example, in the case of a pressure-sensitive sensor, the electrodes of the pressure-sensitive sensor expand when pressure is applied to the sensor. Furthermore, when pressure is removed from the pressure-sensitive sensor, the electrodes of the pressure-sensitive sensor contract and must return to their original shape before the pressure was applied. Similar to pressure-sensitive sensors, the electrodes of displacement sensors must expand and contract due to displacement, and then return to their original shape before the expansion.

[0007] However, when contact sensor electrodes are formed using conventional conductive paste, variations in electrical resistance occur when the electrodes expand and contract and then return to their original shape, which can result in poor detection accuracy. Therefore, in a contact sensor, when the electrodes expand and contract (expand and contract) and then return to their original shape, it is necessary that there be little change in their electrical characteristics (e.g., electrical resistance) from before the expansion and contraction. In this specification, one expansion and contraction (expansion and contraction) of the electrodes is sometimes referred to as "one cycle."

[0008] Therefore, an object of the present invention is to provide a conductive paste for forming an electrode that can reduce the rate of change in electrical resistance before and after expansion and contraction, even when the electrode expands and contracts.

[0009] Another object of the present invention is to provide a conductor, a contact sensor, and an electronic component manufactured using the conductive paste described above. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following configuration.

[0011] (Configuration 1) Configuration 1 is a conductive paste containing (A) carbon black, (B) a binder, and (C) a solvent, The specific surface area (BET value) of the (A) carbon black is 700 m2 / g or less, The (A) carbon black has a structure, The DBP absorption of the (A) carbon black is 110 cm 3 / 100g or more.

[0012] (Configuration 2) Configuration 2 is the conductive paste of configuration 1, wherein the primary particle size of the structure of the (A) carbon black is 10 to 70 nm.

[0013] (Configuration 3) Configuration 3 is the conductive paste of configuration 1 or 2, in which the content of (A) carbon black is 3 to 30% by weight relative to 100% by weight of the conductive paste.

[0014] (Configuration 4) Configuration 4 is the conductive paste of any one of configurations 1 to 3, wherein the content of the (A) carbon black is 20 to 70 wt % relative to 100 wt % of the solid content contained in the conductive paste.

[0015] (Configuration 5) Configuration 5 is the conductive paste of any one of configurations 1 to 4, wherein the pH of the surface of the (A) carbon black is 5.0 to 9.0.

[0016] (Configuration 6) Configuration 6 is the conductive paste of any one of configurations 1 to 5, wherein the binder (B) is a thermoplastic resin.

[0017] (Configuration 7) Configuration 7 is the conductive paste of configuration 6, wherein the ratio of hard segments to soft segments (hard segments:soft segments) of the thermoplastic resin is 1:99 to 50:50.

[0018] (Configuration 8) Configuration 8 is the conductive paste of any one of configurations 1 to 7, wherein the conductor solidified from the conductive paste has an initial length of L0, an initial electrical resistance of R0, an electrical resistance of R1 when the conductor is stretched to a length of 1.5×L0, and a rate of change in electrical resistance of the conductor, R1 / R0, is 900% or less.

[0019] (Configuration 9) Aspect 9 is the conductive paste of any one of aspects 1 to 8, wherein the conductor solidified from the conductive paste has an initial length of L0 and an initial electrical resistance of R0, and the conductor is stretched to a length of 1.5×L0 and then contracted to the length of L0 and has an electrical resistance of R2, and the rate of change in electrical resistance of the conductor, R2 / R0, is 500% or less.

[0020] (Configuration 10) A tenth aspect is the conductive paste of any one of the first to ninth aspects, wherein the conductive paste is a conductive paste for a stretchable material.

[0021] (Configuration 11) Aspect 11 is a conductor obtained by solidifying the conductive paste of any one of aspects 1 to 10.

[0022] (Configuration 12) Configuration 12 is a contact sensor characterized by comprising the conductor of configuration 11.

[0023] (Configuration 13) A thirteenth aspect is an electronic component comprising the conductor of the eleventh aspect. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a conductive paste for forming an electrode that can reduce the rate of change in electrical resistance before and after expansion and contraction, even when the electrode expands and contracts.

[0025] The present invention also provides a conductor, a contact sensor, and an electronic component manufactured using the conductive paste described above. DETAILED DESCRIPTION OF THE INVENTION

[0026] An embodiment of the present invention is a conductive paste comprising (A) carbon black, (B) a binder, and (C) a solvent.

[0027] When electrodes and / or wiring of an electric circuit and / or electronic circuit are formed using the conductive paste of this embodiment, even when the electrodes and / or wiring are stretched and contracted, it is possible to form electrodes and / or wiring that can reduce the rate of change in electrical resistance before and after expansion and contraction. In particular, when electrodes and / or wiring of an electric circuit and / or electronic circuit are formed using the conductive paste of this embodiment, it is possible to form electrodes and / or wiring that can reduce the rate of change in electrical resistance before and after one cycle of expansion and contraction.

[0028] In the following description, an example will be described in which the conductive paste of this embodiment is used to form electrodes of an electric circuit and / or an electronic circuit on a stretchable and / or bendable substrate. By using the conductive paste of this embodiment, not only electrodes but also wiring can be formed.

[0029] First, the conductive paste of this embodiment will be specifically described.

[0030] <(A) Carbon black> The conductive paste of this embodiment contains carbon black as component (A).

[0031] Carbon black is an aggregate of ultrafine spherical carbon particles obtained by incomplete combustion of hydrocarbons or carbon-containing compounds. Carbon black has high electrical conductivity and easily follows expansion and contraction when used as an electrode. Therefore, the conductive paste of this embodiment contains carbon black as a conductive component.

[0032] Carbon black has a structure in which many primary particles are connected together. The primary particles of carbon black are usually about 10 to 100 nm. The primary particle size of carbon black can be observed and measured using a transmission electron microscope (TEM).

[0033] The primary particle diameter of the carbon black contained in the conductive paste of this embodiment is preferably 10 to 70 nm, more preferably 20 to 60 nm. When the primary particle diameter constituting the carbon black structure is within a predetermined range, the carbon black can have a structure that easily follows expansion and contraction when used as an electrode. Therefore, by using a conductive paste containing carbon black with a primary particle diameter within the predetermined range, it is possible to form an electrode that can reduce the rate of change in electrical resistance before and after expansion and contraction, even when the electrode expands and contracts.

[0034] The carbon black contained in the conductive paste of this embodiment has a structure. The structure is a chain-like aggregate formed by connecting a large number of primary particles (e.g., several to several tens of primary particles). In order to form an electrode that can reduce the rate of change in electrical resistance before and after extension and contraction, the structure of the carbon black contained in the conductive paste of this embodiment must have a predetermined degree of development (size).

[0035] The degree of development (size) of carbon black structure can be measured using the DBP (dibutyl phthalate) absorption amount measured in accordance with JIS K6217-4 as an indicator. In carbon black, the more the structure develops, the more voids between aggregates increase, resulting in an increased DBP (dibutyl phthalate) absorption amount. Therefore, a high DBP absorption amount indicates a well-developed structure. On the other hand, a low DBP absorption amount indicates a poorly developed structure. The degree of development (size) of carbon black structure is believed to affect the dispersibility and viscosity of a conductive paste prepared by blending carbon black with a resin, as well as the conductivity of the conductor obtained by solidifying the conductive paste. Therefore, by using carbon black with an appropriate DBP absorption amount, conductors such as electrodes with appropriate conductivity can be obtained. In the present invention, by using carbon black with a well-developed structure in a conductive paste for stretchable materials, the conductivity of the coating film during stretching can be improved by allowing the carbon black particles to come into contact with each other, even when the coating film is stretched.

[0036] The DBP absorption amount of the carbon black contained in the conductive paste of this embodiment is 110 cm 3 / 100g or more, 120cm 3 / 100g or more is preferable, 125cm 3 / 100g or more is preferable. Since the lower limit of the DBP absorption amount of carbon black is the above-mentioned value, it can be said that the carbon black contained in the conductive paste of this embodiment has a sufficiently developed structure. As a result, by using the conductive paste of this embodiment, it is possible to form an electrode that can reduce the rate of change in electrical resistance before and after extension and contraction. The upper limit of the DBP absorption amount of carbon black is not particularly limited. However, the upper limit of the DBP absorption amount of carbon black is 1000 cm 3 / 100g or less is preferable, and 350cm 3 / 100g or less is more preferable, and 250cm 3 / 100g or less is more preferable, and 200cm 3 It is particularly preferable that the amount is 100g or less.

[0037] The specific surface area (BET value) of the carbon black contained in the conductive paste of this embodiment is 700 m 2 / g or less, preferably 10 to 700m 2 / g, more preferably 20 to 500m 2 / g, and more preferably 25 to 300m 2 / g. By satisfying the above range, it is possible to improve the extensibility and reduce the rate of change in electrical resistance before and after extension and contraction. Furthermore, by using carbon black with a relatively small specific surface area (BET value) in the conductive paste for stretchable materials, it is possible to improve the extensibility of the coating film when the conductive paste is used to form the coating film.

[0038] The specific surface area (BET value) of carbon black can be measured by adsorbing nitrogen onto the surface of the carbon black. The specific surface area (BET value) of carbon black after adsorbing nitrogen can be measured in accordance with JIS K6217-2.

[0039] The nitrogen adsorption amount is correlated with the surface area of ​​carbon black and is an index that represents the specific surface area of ​​carbon black. The larger this value, the larger the specific surface area of ​​carbon black, and the smaller the value, the smaller the specific surface area. Generally, the smaller the particle size, the larger the specific surface area, so the larger this index, the smaller the particle size, and vice versa.

[0040] In the conductive paste of this embodiment, the pH of the carbon black surface is preferably 5.0 to 9.0, and more preferably 6.0 to 8.0. When the pH of the carbon black surface is within the above-mentioned range, oxidation of the surface can be suppressed and conductivity can be improved.

[0041] The pH of the carbon black surface can be obtained by measuring a mixture of carbon black and distilled water with a pH meter. Generally, various compounds may adhere to the carbon black surface during the carbon black manufacturing process. To use the conductive paste of this embodiment to form a specific electrode, the surface condition of the carbon black must be appropriate. If the pH of the carbon black surface is within the above-mentioned range, the surface condition of the carbon black can be considered appropriate for use as a raw material for the conductive paste of this embodiment.

[0042] Since carbon black has a lower specific gravity than metals, a high loading of carbon black in a conductive paste will deteriorate printability. Therefore, the carbon black content is preferably 3 to 30% by weight, more preferably 5 to 30% by weight, even more preferably 8 to 20% by weight, and particularly preferably 10 to 15% by weight, relative to 100% by weight of the conductive paste.

[0043] The carbon black content is preferably 20 to 70 wt %, more preferably 25 to 60 wt %, and even more preferably 30 to 50 wt %, relative to the total solid content of the conductive paste. In this specification, the term "total solid content" refers to the total content of the components contained in the conductive paste, excluding (C) the solvent. When the conductive paste is composed of three components, namely (A) carbon black, (B) a binder, and (C) a solvent, the "total solid content" refers to the total content of (A) carbon black and (B) the binder. By ensuring that the carbon black content relative to the total solid content of the conductive paste is within a predetermined range, the conductive paste can be solidified to obtain an appropriate conductor (electrode).

[0044] <(B) Binder> The conductive paste of this embodiment contains a binder as component (B).

[0045] The binder contained in the conductive paste of this embodiment is preferably a thermoplastic resin, which makes it possible to reduce the rate of change in electrical resistance before and after expansion and contraction of the resulting electrode, even when the electrode is expanded and contracted.

[0046] The thermoplastic resin that can be contained in the conductive paste of this embodiment is not particularly limited, as long as the rate of change in electrical resistance before and after one cycle of extension and contraction is within a predetermined range when an electrode is formed using a conductive paste containing that thermoplastic resin.

[0047] The thermoplastic resin (binder) contained in the conductive paste of this embodiment is preferably at least one selected from polystyrene-based resins, polyolefin-based resins, polyvinyl chloride-based resins, polyurethane-based resins, polyester-based resins, polyamide-based resins, polybutadiene-based resins, their hydrogenated products, and modified copolymer hydrogenated products obtained by modifying the hydrogenated products. Forming an electrode using a conductive paste containing such a thermoplastic resin can reduce the rate of change in electrical resistance before and after extension and contraction. The thermoplastic resin may also be an elastomer. Examples of elastomers include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, acrylic elastomers, and silicone-based elastomers. Among elastomers, a block copolymer having hard and soft segments is preferred from the viewpoint of reducing the rate of change in electrical resistance before and after extension and contraction.

[0048] In the conductive paste of this embodiment, the ratio of hard segments to soft segments (hard segments:soft segments) of the thermoplastic resin is preferably 1:99 to 50:50, more preferably 10:90 to 50:50, and even more preferably 20:80 to 50:50. When the ratio of hard segments to soft segments (hard segments:soft segments) of the thermoplastic resin is within the above-mentioned range, the conductive paste can easily follow expansion and contraction when used as an electrode, and the rate of change in electrical resistance before and after expansion and contraction can be reduced.

[0049] A soft segment is a portion of a thermoplastic resin that exhibits elasticity and refers to a low glass transition temperature (Tg) segment. A hard segment is a portion that acts as a crosslinking point and refers to a high glass transition temperature (Tg) segment. In particular, a block copolymer of a hard segment with a glass transition temperature (Tg) of less than 150°C and a soft segment with a glass transition temperature (Tg) of less than 0°C is more suitable. The glass transition temperature (Tg) can be measured by differential scanning calorimetry (DSC).

[0050] Examples of the soft segments include random polymer segments of α-olefins such as ethylene, propylene, and 1-butene, polymer segments of diene compounds such as butadiene and isoprene, and hydrogenated segments thereof. Examples of the hard segments include crystalline α-olefin polymer segments such as ethylene, propylene, and butylene, and crystalline hydrogenated segments of butadiene polymers.

[0051] The conductive paste of this embodiment preferably contains a thermoplastic resin having a number-average molecular weight of 100,000 or more, more preferably 120,000 or more, and even more preferably 140,000 or more. Forming an electrode using a conductive paste containing a thermoplastic resin in the above range can reduce the rate of change in electrical resistance before and after extension and contraction. The upper limit of the number-average molecular weight is not particularly limited, but can be 400,000 or less, or 250,000 or less. The number-average molecular weight (Mn) is a value determined using gel permeation chromatography (GPC) in terms of standard polystyrene.

[0052] In the conductive paste of this embodiment, the thermoplastic resin is preferably a styrene-based elastomer. Forming an electrode using a conductive paste containing a styrene-based elastomer as the thermoplastic resin can reduce the rate of change in electrical resistance before and after expansion and contraction. Specific examples of styrene-based elastomers include SBS (styrene-butadiene-styrene), which has a hard segment made of polystyrene and a soft segment made of polybutadiene; SEBS (styrene-ethylene-butylene-styrene), which has a hard segment made of polystyrene and a soft segment made of poly(ethylene / butylene); SBBS (styrene-butadiene-butylene-styrene), which has a hard segment made of polystyrene and a soft segment made of poly(butadiene / butylene); and SEPS (styrene-isoprene-styrene), which has a hard segment made of polystyrene and a soft segment made of polyisoprene.

[0053] From the viewpoint of achieving both extensibility and electrical resistance, the content of (B) binder is preferably 5 to 30% by weight, more preferably 10 to 25% by weight, and even more preferably 15 to 20% by weight, relative to 100% by weight of the conductive paste.

[0054] Furthermore, when the conductive paste contains conductive carbon-based particles (A1), the content of the binder (B) is preferably 30 to 80% by weight, more preferably 40 to 70% by weight, and even more preferably 50 to 65% by weight, based on the total amount of solids contained in the conductive paste.

[0055] The binder contained in the conductive paste of this embodiment may contain other resins, such as a thermosetting resin and / or a photocurable resin, as long as the effects of this embodiment are not impaired. However, in order to obtain suitable wiring, the binder contained in the conductive paste of this embodiment is preferably a resin made of the above-mentioned thermoplastic resin. Furthermore, the above-mentioned thermoplastic resins can be used alone or in combination of two or more.

[0056] <(C) Solvent> The conductive paste of this embodiment contains a solvent as component (C).

[0057] The solvent contained in the conductive paste of this embodiment is not particularly limited as long as it can dissolve the predetermined binder. Examples of the solvent in the conductive paste of this embodiment include aromatic solvents (e.g., toluene and xylene), ketone solvents (e.g., methyl ethyl ketone and methyl isobutyl ketone), and diethylene glycol dibutyl ether. The organic solvent may be used alone or in combination of two or more. The use of a predetermined solvent ensures that the predetermined binder is dissolved. As a result, screen printing of the conductive paste for wiring formation can be facilitated.

[0058] The amount of solvent added is 100 to 1000 parts by weight, preferably 200 to 600 parts by weight, per 100 parts by weight of binder. Usually, the thermoplastic resin can be properly dissolved by using a solvent in an amount about four times the weight of the binder.

[0059] The solvent can be added to the conductive paste as needed to adjust the viscosity of the conductive paste.

[0060] <Other ingredients> The conductive paste of this embodiment may be a conductive paste consisting only of the above-described (A) carbon black, (B) binder, and (C) solvent. However, the conductive paste of this embodiment may contain components other than the above-described conductive paste, provided that the effects of this embodiment are not impaired or to improve the effects of this embodiment. 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.

[0061] In this specification, the phrase "a conductive paste consisting only of (A) carbon black, (B) binder, and (C) solvent" means that the conductive paste may contain components other than the components (A), (B), and (C) as unavoidable impurities. The same applies to other components.

[0062] <Conductive paste> The conductive paste of this embodiment can be produced by mixing the essential components ((A) carbon black, (B) binder, and (C) solvent) contained in the above-mentioned conductive paste, and optionally other components, 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 wiring formation methods can be prepared.

[0063] 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 wiring formation method, such as screen printing. The viscosity can be adjusted by appropriately controlling the amount of solvent. The viscosity of the conductive paste of this embodiment is preferably 30 to 90 Pa·s, more preferably 35 to 85 Pa·s. By adjusting the viscosity of the conductive paste within this range, the coating and / or handling properties of the conductive paste onto a substrate (base material) are improved, making it possible to apply the conductive paste to the substrate with a uniform thickness. The viscosity of the conductive paste can be measured using an HB-type viscometer (manufactured by Brookfield) (SC4-14 spindle) at 10 rpm and a temperature of 25°C.

[0064] The conductive paste of this embodiment can be formed into the shape of electrodes and / or wiring of an electric circuit and / or electronic circuit by means of screen printing or the like, followed by drying and solidification, thereby forming electrodes and / or wiring of an electric circuit and / or electronic circuit with a low probability of breakage on the surface of a stretchable and / or flexible substrate. The temperature and time for drying and solidifying the conductive paste can be appropriately selected depending on the type of binder contained in the conductive paste. The temperature and time for solidifying 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 solidifying the conductive paste can be set to 60°C to 180°C for 5 to 60 minutes, preferably 80 to 140°C for 5 to 60 minutes, and more preferably 110 to 130°C for 20 to 40 minutes.

[0065] <Rate of change in electrical resistance> A conductor such as an electrode formed using the conductive paste of this embodiment changes its electrical resistance when its shape changes due to expansion and contraction (stretching and shrinking). In this specification, the electrical resistance in the longitudinal direction (initial electrical resistance) of a conductor having a length L0 (initial length L0) formed using the conductive paste of this embodiment is defined as R0. Furthermore, the electrical resistance at a length of 1.5×L0 when a conductor of length L0 is stretched in the longitudinal direction to a length of 1.5×L0 is defined as R1. Furthermore, the electrical resistance of the conductor stretched to a length of 1.5×L0 and then shrunk in the longitudinal direction to the initial length L0 is defined as R2. In this specification, electrical resistance may also be referred to simply as "resistance."

[0066] In a conductor such as an electrode formed using the conductive paste of this embodiment, the rate of change in electrical resistance R1 / R0, calculated from the initial electrical resistance R0 at the conductor's initial length L0 and the electrical resistance R1 when the conductor is stretched to a length of 1.5 × L0, is preferably 900% or less, and more preferably 880% or less. The rate of change in electrical resistance R1 / R0 is the rate of change in electrical resistance in the longitudinal direction when the conductor is stretched to a length of 1.5 × L0. In a conductor such as an electrode formed using the conductive paste of this embodiment, even when the conductor is stretched, the rate of change in electrical resistance before and after stretching can be made relatively small.

[0067] In a conductor such as an electrode formed using the conductive paste of this embodiment, the rate of change in electrical resistance R2 / R0, calculated from the initial electrical resistance R0 at the conductor's initial length L0 and the electrical resistance R2 when the conductor is stretched to a length of 1.5×L0 and then contracted to the length L0, is preferably 500% or less, more preferably 400% or less. The rate of change in electrical resistance R2 / R0 is the rate of change in electrical resistance in the longitudinal direction when the conductor is stretched to a length of 1.5×L0 and then contracted. In this specification, one stretching and contraction (expansion and contraction) of the electrode may be referred to as "one cycle." The electrical resistance R2 is the electrical resistance after one predetermined cycle of expansion and contraction.

[0068] In a contact sensor, when the electrodes of the contact sensor expand and contract and then return to their original shape, it is necessary that there be little change in the electrical characteristics (initial electrical resistance value) before the expansion and contraction (expansion and contraction).A conductor such as an electrode formed using the conductive paste of this embodiment can make the rate of change in electrical resistance value before and after the expansion and contraction of the conductor relatively small, even when the conductor expands and contracts.

[0069] As described above, electrodes formed using the conductive paste of this embodiment show little change in electrical properties after stretching and shrinking. The conductive paste of this embodiment can be preferably used as a conductive paste for stretchable devices. In this specification, "conductive paste for stretchable devices" means a conductive paste that can be used to form a conductive film or conductive pattern on the surface of a stretchable and / or bendable substrate to form electrodes and / or wiring for electric circuits and / or electronic circuits. Furthermore, since electrodes formed using the conductive paste of this embodiment show little change in electrical properties after stretching and shrinking, they can be preferably used as a conductive paste for stretchable devices to be used as an electrode material for contact sensors.

[0070] <Conductors> In this specification, electrodes and / or wiring formed by solidifying the conductive paste of this embodiment may be referred to as a "conductor." Therefore, the conductor of this embodiment is a conductor formed by solidifying the conductive paste of this embodiment. By using the conductive paste of this embodiment, a conductor can be obtained whose electrical properties change little after expansion and contraction.

[0071] This embodiment is a contact sensor including the conductor of the embodiment described above. The electrodes of the contact sensor must be able to expand and contract. Therefore, by using the conductive paste of this embodiment, it is possible to obtain electrodes for the contact sensor that exhibit minimal change in electrical properties after expansion and contraction.

[0072] This embodiment is an electronic component including the conductor of this embodiment described above. The electronic component includes an electric circuit and / or an electronic circuit. Therefore, by using the conductive paste of this embodiment, an electronic component can be obtained that includes electrodes and / or wiring of an electric circuit and / or an electronic circuit with little change in electrical properties on the surface of a stretchable and / or bendable substrate. [Example]

[0073] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0074] <Conductive paste materials and preparation ratio> Table 1 shows the compositions of the conductive pastes of Examples 1 to 7. Table 2 shows the compositions of the conductive pastes of Comparative Examples 1 and 2. The carbon black used in the examples and comparative examples is as follows.

[0075] [(A) Carbon black] Carbon black CB1 to CB7 shown in Table 3 were used. 2 / g)" is the specific surface area (BET value) of carbon black measured based on JIS K6217-2. Also, "DBP absorption (cm 3 / 100g) is the DBP (Dibutyl Phthalate) absorption amount of the carbon black measured in accordance with JIS K6217-4. Tables 1 and 2 show the blending amounts of carbon black CB1 to CB7 for the examples and comparative examples.

[0076] [(B) Binder] The binders used in the examples and comparative examples were the following thermoplastic resins (resins 1 and 2). In the following description, "H / S" refers to the ratio of hard segments to soft segments (hard segments / soft segments). Resin 1: Part number T-8195N, thermoplastic polyurethane resin (thermoplastic urethane elastomer) (manufactured by DIC Covestro Polymer Co., Ltd.) Resin 2: Hydrogenated styrene-based thermoplastic elastomer (SEBS), product number S1605, H / S=70 / 30, number average molecular weight (Mn) 250,000 (manufactured by Asahi Kasei Corporation)

[0077] [(C) Solvent] The solvents used in the examples and comparative examples are as follows. Solvent 1:3-Methoxy-N,N-dimethylpropanamide Solvent 2: Diethylene glycol dibutyl ether

[0078] The resin used in the examples and comparative examples was dissolved in a solvent to prepare a resin solution, and carbon black was mixed into the resin solution.

[0079] 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.

[0080] <How to calculate resistivity> Two pieces of tape, each about 75 to 95 μm thick, were attached parallel to a glass substrate with a 2 mm gap between them, and each conductive paste, measuring 2 mm wide x 50 mm long x about 80 μm thick, was printed between the two pieces of tape, and then heated and solidified in a constant temperature dryer at 120°C for 30 minutes. After measuring the film thickness of each conductive paste after heating, the resistance was measured using the four-terminal method to determine the specific resistance.

[0081] <Method for measuring the rate of change in electrical resistance> Rectangular samples were prepared using the conductive pastes of the examples and comparative examples, and the electrical resistance R0 before stretching to a predetermined length, the electrical resistance R1 after stretching to a predetermined length, and the electrical resistance R2 after one cycle of stretching were measured.

[0082] The conductive pastes (resin compositions) of the examples and comparative examples were printed on a urethane sheet using a screen printer to form a wiring pattern with a width of 10 mm and a length of 100 mm, and the pattern was then heated and solidified in a constant temperature dryer at 120°C for 30 minutes.

[0083] Next, both ends of the wiring pattern in the longitudinal direction were fixed to a testing machine at room temperature (specifically, 25°C) so that the initial length of the wiring pattern in the longitudinal direction was 40 mm (= L0). In this state, the initial electrical resistance value (resistance value of the conductor wire before stretching) R0 of the wiring pattern in the longitudinal direction of the length L0 (= 40 mm) was measured. The electrical resistance value of the wiring pattern was also measured using a digital multimeter (model number: 2001) manufactured by TFF Keithley Instruments, Inc.

[0084] Next, a load was applied to one of the fixed ends, and the wiring pattern was stretched at a pulling rate of 72 m / min until the length in the longitudinal direction reached 60 mm (50% elongation). In this state, the electrical resistance value R1 (electrical resistance value after 50% elongation) of the 60 mm long wiring pattern (conductor) after elongation in the longitudinal direction was measured using the digital multimeter described above.

[0085] Next, the load applied to the sample was removed at a rate of 72 mm / min to shrink the wiring pattern, returning it to its initial length (L0 = 40 mm). In this state, the electrical resistance R2 (electrical resistance after 50% stretching) of the 40 mm long wiring pattern (conductor) after stretching was measured using the digital multimeter described above.

[0086] From the above measurement results, the rate of change in electrical resistance in the length direction R1 / R0 when the wiring pattern (conductor) was stretched to a length of 1.5 x L0, and the rate of change in electrical resistance in the length direction R2 / R0 when the wiring pattern (conductor) was stretched to a length of 1.5 x L0 and then shrunk were calculated. Tables 1 and 2 show the electrical resistance value (initial electrical resistance value) R0 before stretching, the electrical resistance value R1 after 50% stretching, the electrical resistance value R2 after 50% stretching, the percentage of the rate of change in electrical resistance after 50% stretching R1 / R0, and the percentage of the rate of change in electrical resistance after 50% stretching R2 / R0 for the examples and comparative examples.

[0087] When the conductive paste of Comparative Example 1 was used, problems arose during printing of the conductive paste, and it was not possible to print the conductive paste, solidify it, and form the wiring pattern (conductor) of Comparative Example 1. Specifically, it is presumed that the conductive paste of Comparative Example 1 has a large specific surface area (BET value) of carbon black, so that the resin components and solvent components in the paste adhere to the surface of the carbon black, increasing the viscosity of the paste and making it impossible to print the conductive paste. For this reason, it was not possible to measure the electrical resistance value of the wiring pattern of Comparative Example 1. On the other hand, when the conductive paste of Comparative Example 2 was used, it was possible to stretch the wiring pattern, but the electrical resistance value was large. The cause of this is presumed to be as follows. That is, the DBP absorption amount of the carbon black contained in the conductive paste of Comparative Example 2 was 103 cm 3 The value was relatively small, at 1 / 100g. This indicates that the structure was not well developed. Therefore, when the conductive paste of Comparative Example 2 was used, there were few contact points between the carbon black particles even when the wiring pattern was stretched, and it is presumed that this resulted in a large rate of change in electrical resistance before and after stretching and shrinking.

[0088] <Evaluation of cracks after 50% expansion and contraction> When measuring the rate of change in electrical resistance, the samples were evaluated using a digital microscope (VHX-8000, manufactured by Keyence Corporation) to determine whether cracks had occurred after 50% stretching. It was confirmed that no cracks had occurred in the samples of Examples 1 to 7 and Comparative Example 2 after 50% stretching. As mentioned above, it was not possible to form a sample (conductor) for Comparative Example 2, so crack evaluation was not possible. The results are shown in the "Evaluation of cracks after 50% stretching" column in Tables 1 and 2. "Good" in Tables 1 and 2 indicates that it was confirmed that no cracks had occurred in the sample. "Poor" in Tables 1 and 2 indicates that evaluation was not possible because cracks had occurred in the sample or the sample could not be prepared.

[0089] <Measurement results of Examples and Comparative Examples> The specific surface area (BET value) of the carbon black contained in the conductive pastes of Examples 1 to 7 was 700 m 2 / g or less, and DBP (Dibutyl Phthalate) absorption is 110cm 3 / 100g or more. Therefore, the change rate of electrical resistance value R1 / R0 after 50% elongation in Examples 1 to 7 was in the range of 381% to 872%. Furthermore, the change rate of electrical resistance value R2 / R0 after 50% elongation in Examples 1 to 7 was in the range of 223% to 377%. In contrast, the specific surface area (BET value) of the carbon black contained in the conductive paste of Comparative Example 1 was in the above-mentioned range (700 m 2 / g or less). Therefore, when the conductive paste of Comparative Example 1 was used, a conductor could not be formed. In addition, the DBP absorption amount of the carbon black contained in the conductive paste of Comparative Example 2 was within the above-mentioned range (110 cm 3 / 100g or more). Therefore, in the conductor using the conductive paste of Comparative Example 2, the rate of change in electrical resistance value after 50% elongation R1 / R0 and the rate of change in electrical resistance value after 50% expansion and contraction R2 / R0 were higher than those in Examples 1 to 7. From the above, it was revealed that when the conductive pastes of Examples 1 to 7 are used, electrodes can be formed that can reduce the rate of change in electrical resistance value before and after expansion and contraction.

[0090] [Table 1]

[0091] [Table 2]

[0092] [Table 3]

Claims

1. (A) carbon black; (B) a binder; and (C) a solvent; A conductive paste comprising: The specific surface area (BET value) of the (A) carbon black is 700 m ２ / g or less, The (A) carbon black has a structure, The DBP absorption of the carbon black (A) is 110 cm ３ / 100g or more.

2. 2. The conductive paste according to claim 1, wherein the primary particle diameter of the structure of the carbon black (A) is 10 to 70 nm.

3. 3. The conductive paste according to claim 1, wherein the content of said (A) carbon black is 3 to 30% by weight relative to 100% by weight of said conductive paste.

4. 4. The conductive paste according to claim 1, wherein the content of the (A) carbon black is 20 to 70% by weight relative to 100% by weight of the solid content contained in the conductive paste.

5. The conductive paste according to any one of claims 1 to 4, wherein the pH of the surface of the (A) carbon black is 5.0 to 9.

0.

6. The conductive paste according to any one of claims 1 to 5, wherein the binder (B) is a thermoplastic resin.

7. 7. The conductive paste according to claim 6, wherein the ratio of the hard segment to the soft segment (hard segment:soft segment) of the thermoplastic resin is 1:99 to 50:

50.

8. The initial length of the conductor obtained by solidifying the conductive paste is L ０ and the initial electrical resistance is R ０ and the conductor has a length of 1.5×L ０ The electrical resistance when stretched to R １ and the rate of change in the electrical resistance of the conductor R １ / R ０ The conductive paste according to any one of claims 1 to 7, wherein the conductivity is 900% or less.

9. The initial length of the conductor obtained by solidifying the conductive paste is L ０ and the initial electrical resistance is R ０ and the conductor has a length of 1.5×L ０ After extending the conductor to a length L ０ When the electrical resistance is reduced to R ２ and the rate of change in the electrical resistance of the conductor R ２ / R ０ The conductive paste according to any one of claims 1 to 8, wherein the porosity is 500% or less.

10. The conductive paste according to any one of claims 1 to 9, wherein the conductive paste is a conductive paste for stretchable use.

11. A conductor obtained by solidifying the conductive paste according to any one of claims 1 to 10.

12. A contact sensor comprising the conductor according to claim 11.

13. An electronic component comprising the conductor according to claim 11.

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