Conductive paste, conductor, contact sensor, and electronic component

Abstract

Provided is a conductive paste for forming an electrode capable of reducing the rate of change of an electric resistance value before and after extension or contraction even if the electrode is extended or contracted.　The conductive paste contains (A) conductive particles having an average particle diameter of less than 1.5 μm, (B) a thermoplastic resin, and (C) a solvent. The restoration rate (RR1) of a shape when an electrode formed using the conductive paste is extended or contracted in one cycle with a length of 115% with respect to the length before the extension of the electrode is 8.0% or less.

Description

Conductive paste, conductor, contact sensor and electronic component

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

[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 an electrode on a stretchable and flexible 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 the (A) conductive particles in a ratio of 90% by weight or more but less than 100% by weight to the total of the (A) conductive particles and the (B) thermoplastic polyurethane resin.

[0004] JP 2018-104581 A

[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 / or contract 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 and then return to their original shape, it is necessary that the change in electrical characteristics (e.g., electrical resistance) from before the expansion and contraction is small. In this specification, one expansion and contraction (expansion and contraction) of the electrode is sometimes referred to as "one cycle."

[0008] Furthermore, since contact sensors are used repeatedly, it is necessary that the electrical resistance of the electrodes of the contact sensor after multiple extensions and contractions (expansion and contraction) (e.g., 100 cycles) does not change significantly from the electrical resistance before extension and contraction.

[0009] 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.

[0010] Another object of the present invention is to provide a conductor, a contact sensor, and an electronic component manufactured using the above-mentioned conductive paste.

[0011] In order to solve the above problems, the present invention has the following configuration.

[0012] (Configuration 1) Configuration 1 is a conductive paste comprising: (A) conductive particles having an average particle size of less than 1.5 μm; (B) a thermoplastic resin; and (C) a solvent, wherein an electrode formed using the conductive paste is stretched to a length that is 115% of the length of the electrode before stretching by applying a tensile force, and then the tensile force is removed to shrink the length of the electrode, whereby a shape recovery rate (RR) of the electrode after one cycle of stretching and shrinking is 115% of the length of the electrode before stretching. １ ) is 8.0% or less.

[0013] (Configuration 2) Configuration 2 is a method for measuring the shape recovery rate (RR) of an electrode formed using the conductive paste when the electrode is stretched and contracted for 100 cycles. １００2. The conductive paste of claim 1, wherein the content of ZnO in the conductive paste is 10.0% or less.

[0014] (Configuration 3) Configuration 3 is the conductive paste of Configuration 1 or 2, in which the (A) conductive particles are at least one selected from silver, nickel, copper, silver-coated copper, silver-coated fiber, silver-coated resin, carbon fiber, graphite, graphene, carbon black, graphite, and mixtures thereof.

[0015] (Configuration 4) Configuration 4 is the conductive paste of any one of configurations 1 to 3, wherein the conductive paste is substantially free of conductive particles having an average particle size of 1.5 μm or more.

[0016] (Configuration 5) Configuration 5 is the conductive paste of any one of Configurations 1 to 4, wherein the (B) thermoplastic resin is 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, and hydrogenated modified copolymers obtained by modifying the hydrogenated resins.

[0017] (Configuration 6) Configuration 6 is the conductive paste of any one of Configurations 1 to 5, wherein the ratio of hard segments to soft segments (hard segments:soft segments) of the thermoplastic resin (B) is 1:99 to 50:50.

[0018] (Configuration 7) Configuration 7 is the conductive paste of any one of configurations 1 to 6, wherein the number average molecular weight of the thermoplastic resin (B) is 100,000 or more.

[0019] (Configuration 8) Configuration 8 is the conductive paste of any one of configurations 1 to 7, in which the thermoplastic resin (B) is a styrene-based elastomer.

[0020] (Configuration 9) Configuration 9 is the conductive paste of any one of Configurations 1 to 8, wherein the (A) conductive particles comprise conductive carbon-based particles (A1), and the content of the (B) thermoplastic resin is 20 to 80 wt % based on the total weight of solids contained in the conductive paste.

[0021] (Configuration 10) Configuration 10 is the conductive paste of any one of Configurations 1 to 9, wherein the (A) conductive particles include conductive metal particles (A2), and the content of the (B) thermoplastic resin is 1 to 30 wt % based on the total weight of solids contained in the conductive paste.

[0022] (Configuration 11) Configuration 11 is the conductive paste of any one of configurations 1 to 10, wherein the conductive paste is a conductive paste for stretchable materials.

[0023] (Configuration 12) Configuration 12 is a method for manufacturing an electrode formed using the conductive paste, the initial resistance value (ER ０ ) and the electrical resistance value (ER) after one cycle of extension and contraction. １ ) and the resistance change rate (ER １ / ER ０ 12. The conductive paste of any one of configurations 1 to 11, wherein the ratio of the total surface area to the total surface area (wt %) ... is 200% or less.

[0024] (Configuration 13) Configuration 13 is a method for manufacturing an electrode formed using the conductive paste, the method comprising: ０ ) and the electrical resistance (ER) after 100 cycles of elongation and contraction. １００ ) and the resistance change rate (ER １００ / ER ０ 13. The conductive paste of any one of configurations 1 to 12, wherein the rate of change in resistance with respect to the measured value (x100) is 220% or less.

[0025] (Configuration 14) Configuration 14 is a conductor obtained by solidifying the conductive paste of any one of configurations 1 to 13.

[0026] (Configuration 15) Configuration 15 is a contact sensor characterized by comprising the conductor of configuration 14.

[0027] (Configuration 16) Configuration 16 is an electronic component comprising the conductor of configuration 14.

[0028] 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.

[0029] The present invention also provides a conductor, a contact sensor, and an electronic component manufactured using the conductive paste described above.

[0030] An embodiment of the present invention is a conductive paste that includes (A) conductive particles, (B) a thermoplastic resin, and (C) a solvent.

[0031] When electrodes and / or wiring of an electric circuit and / or electronic circuit are formed using a conductive paste containing the conductive paste of this embodiment, even when the electrodes and / or wiring expand and contract, it is possible to form electrodes and / or wiring that can reduce the rate of change in electrical resistance value before and after expansion and contraction.

[0032] 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.

[0033] First, the conductive paste of this embodiment will be specifically described.

[0034] <(A) Conductive Particles> The conductive paste of this embodiment contains conductive particles as component (A). The conductive particles contained in the conductive paste of this embodiment have an average particle diameter of less than 1.5 μm. By using conductive particles with an average particle diameter of less than 1.5 μm, the electrical conductivity is high, and when used as an electrode, they easily follow expansion and contraction, thereby improving the recovery rate described below. As the material for the conductive particles contained in the conductive paste of this embodiment, an electrically conductive material can be used.

[0035] The conductive particles contained in the conductive paste of this embodiment can be broadly divided into conductive carbon-based particles (A1) using graphite, carbon black, etc., and conductive metal particles (A2) using metals such as silver and copper. Examples of conductive metal particles include metal particles such as silver (Ag), nickel (Ni), and copper (Cu), silver-coated copper, silver-coated fiber, silver-coated resin, and mixtures thereof. Examples of conductive carbon-based particles include carbon fiber, graphite, graphene, carbon black, graphite, and mixtures thereof. By using these materials as the conductive particle material, a conductive paste capable of forming an electrode with appropriate electrical conductivity can be obtained.

[0036] As the material for the conductive carbon-based particles (A1) contained in the conductive paste of this embodiment, a material containing carbon (C) can be preferably used. When the conductive paste of this embodiment contains the conductive carbon-based particles (A1), it is preferable to use at least one selected from carbon fiber, graphite, graphene, carbon black, graphite, and mixtures thereof. When forming an electrode using the conductive paste, metal particles such as silver may not be used in applications requiring reliability such as corrosion resistance. Therefore, in applications requiring reliability, conductive carbon-based particles may be used as the conductive particles.

[0037] Carbon black has high electrical conductivity and easily follows expansion and contraction when used as an electrode. Therefore, the conductive carbon-based particles (A1) contained in the conductive paste of this embodiment preferably contain carbon black, and more preferably are carbon black particles made of carbon black.

[0038] When the conductive paste of this embodiment contains conductive carbon-based particles (A1), the specific gravity of the conductive carbon-based particles (A1) is lighter than that of metals, and therefore, high loading of the conductive carbon-based particles results in poor printability. For this reason, when the conductive paste contains conductive carbon-based particles (A1), the conductive carbon-based particles (A1) are preferably present in an amount of 5 to 30 wt %, more preferably 10 to 25 wt %, and even more preferably 10 to 20 wt %, relative to 100 wt % of the conductive paste. Furthermore, the conductive carbon-based particles (A1) are preferably present in an amount of 10 to 60 wt %, more preferably 20 to 50 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 the solvent (C). When the conductive paste consists of three components: (A) conductive particles, (B) thermoplastic resin, and (C) solvent, the "total solid content" is the total content of the (A) conductive particles and the (B) thermoplastic resin.

[0039] When the conductive paste contains silver (Ag) as the conductive metal particles (A2), the conductive particles can be silver particles, silver-coated copper, silver-coated fibers, and / or silver-coated resin, etc. From the viewpoint of electrical conductivity, it is preferable that the silver particles contain 90 parts by weight or more of silver, and it is preferable that the silver particles contain 95 parts by weight or more of silver, per 100 parts by weight of the conductive particles.

[0040] When the conductive paste contains conductive metal particles (A2), the content of the conductive metal particles (A2) is preferably 30 to 90 wt %, more preferably 40 to 80 wt %, and even more preferably 50 to 70 wt %, relative to 100 wt % of the conductive paste, from the viewpoint of electrical conductivity. The content of the conductive metal particles (A2) is preferably 50 to 98 wt %, more preferably 70 to 95 wt %, and even more preferably 80 to 90 wt %, relative to the total solid content of the conductive paste.

[0041] The particle shape of the conductive metal particles (A2) may be spherical or scale-like. From the viewpoint of improving the extensibility of the conductor produced using the conductive paste of this embodiment, it is preferable to use conductive metal particles having an irregular shape or a spherical shape.

[0042] In this specification, the term "conductive particles consisting of A" means that elements other than A may be contained as unavoidable impurities. The same applies to components other than the conductive particles.

[0043] The average particle diameter of the conductive particles can be measured, for example, by observation using a scanning electron microscope (SEM). For example, an SEM photograph or SEM image of the (A) conductive particles is obtained at a magnification of 10,000 to 20,000 times. The outline of the (A) conductive particles present in this SEM photograph or SEM image is approximated to a perfect circle, and the diameter of the perfect circle is measured to obtain the diameter of the (A) conductive particles. The arithmetic mean value of the diameters of any 100 (A) conductive particles present in the SEM photograph or SEM image can be used as the average particle diameter of the (A) conductive particles.

[0044] The average particle diameter of the (A) conductive particles contained in the conductive paste is preferably less than 1.5 μm, more preferably less than 1.0 μm, and even more preferably less than 0.8 μm. When the average particle diameter of the (A) conductive particles is within the above range, the shape restoration rate of an electrode formed using the conductive paste can be improved. Furthermore, the lower limit of the average particle diameter of the (A) conductive particles is not particularly limited. The lower limit of the average particle diameter can be, for example, 0.02 μm or more.

[0045] The specific surface area (BET value) of the conductive metal particles (A2) is preferably 0.5 to 3.0 m ２ / g, more preferably 0.7 to 2.8 m ２ / g, more preferably 1.0 to 2.6 m ２ When the molecular weight is in the above range, the repeated elongation property and recovery rate can be improved.

[0046] Carbon black has a structure in which many primary particles are connected. In this specification, the average particle size of carbon black refers to the average particle size of the primary particles. The average particle size of carbon black is usually about 10 to 100 nm. Therefore, it can be said that the upper limit of the average particle size of carbon black is 100 nm or less. The average particle size of carbon black can be observed and measured using a transmission electron microscope (TEM). The specific surface area (BET value) of carbon black is preferably 10 to 700 m ２ / g, more preferably 20 to 250 m ２ / g, more preferably 25 to 150 m ２ When the molecular weight is in the above range, the elongation and recovery rate can be improved.

[0047] The conductive particles contained in the conductive paste of this embodiment may have a particle diameter of 1.5 μm or more, as long as the particle diameter does not adversely affect the recovery rate. Even in this case, the average particle diameter of the conductive particles must be less than 1.5 μm.

[0048] When the conductive particles contained in the conductive paste of this embodiment contain two types of conductive particles with different average particle diameters, they may contain conductive particles X having an average particle diameter of less than 1.5 μm and conductive particles Y having an average particle diameter of 1.0 μm or more. In this case, the content of conductive particles X in the conductive paste is preferably greater than the content of conductive particles Y in the conductive paste. By using such conductive particles, it is possible to more reliably improve the shape recovery rate of an electrode formed using the conductive paste. The shape recovery rate of an electrode will be described later.

[0049] The conductive paste of this embodiment preferably does not substantially contain conductive particles having an average particle diameter of 1.5 μm or more. Furthermore, the conductive particles contained in the conductive paste of this embodiment more preferably consist solely of conductive particles having an average particle diameter of less than 1.5 μm. By using such conductive particles, the shape restoration rate of the electrode formed using the conductive paste can be more reliably achieved. The shape restoration rate of the electrode will be described later.

[0050] <(B) Thermoplastic Resin> The conductive paste of this embodiment contains a thermoplastic resin as the component (B).

[0051] The thermoplastic resin that can be contained in the conductive paste of this embodiment is not particularly limited, as long as the rate of recovery of the shape of the electrode, described below, is within a predetermined range when an electrode is formed using a conductive paste containing that thermoplastic resin.

[0052] The thermoplastic resin 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 improve the shape recovery rate of the electrode, as described below. 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 a hard segment and a soft segment is preferred from the viewpoint of improving recovery.

[0053] In the conductive paste of this embodiment, the ratio of hard segments to soft segments of the thermoplastic resin (hard segments:soft segments) is preferably 1:99 to 50:50.

[0054] By using a thermoplastic resin in the above range, when the conductive paste is used as an electrode, the resin can easily follow expansion and contraction, and the rate of recovery of the electrode shape can be improved. From this viewpoint, the ratio of hard segment to soft segment is more preferably 10:90 to 50:50, and even more preferably 20:80 to 50:50.

[0055] The mechanism by which the recovery rate is improved by setting the ratio of hard segments to soft segments in a thermoplastic resin within a specific range is unclear. The mechanism is speculated to be as follows: It is believed that extensibility is obtained by deformation of the flexible soft segments contained in the thermoplastic resin, and recovery is achieved by physical crosslinking due to the cohesive force between the hard segments contained in the thermoplastic resin. However, the present invention is not limited to this speculation.

[0056] The soft segment is a portion of the thermoplastic resin that exhibits elasticity and is a segment with a low glass transition temperature (Tg). The hard segment is a portion that serves as a crosslinking point and is a segment with a high glass transition temperature (Tg). 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 preferred. The glass transition temperature Tg can be measured by differential scanning calorimetry (DSC).

[0057] 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.

[0058] 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 improve the shape recovery rate of the electrode, as described below. 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.

[0059] In the conductive paste of this embodiment, the thermoplastic resin is preferably a styrene-based elastomer. By forming an electrode using a conductive paste containing a styrene-based elastomer as the thermoplastic resin, it is possible to more reliably improve the shape recovery rate of the electrode, which will be described later. Specific examples of styrene-based elastomers include SBS (styrene-butadiene-styrene), in which the hard segment is polystyrene and the soft segment is polybutadiene; SEBS (styrene-ethylene-butylene-styrene), in which the hard segment is polystyrene and the soft segment is poly(ethylene / butylene); SBBS (styrene-butadiene-butylene-styrene), in which the hard segment is polystyrene and the soft segment is poly(butadiene / butylene); and SEPS (styrene-isoprene-styrene), in which the hard segment is polystyrene and the soft segment is polyisoprene.

[0060] Among styrene-based elastomers, it is particularly preferable to use SEBS (styrene-ethylene-butylene-styrene) from the viewpoint of improving recovery. The mechanism by which the recovery rate is improved by using SEBS can be assumed as follows. That is, since the soft segments of SEBS are poly(ethylene / butylene) copolymerized in a block form, it is assumed that they easily follow expansion and contraction when used as an electrode. Furthermore, the polystyrene hard segments of SEBS form a structure in which they are cohesive with each other. Therefore, it is assumed that recovery is achieved by physical crosslinking due to the cohesive force between the hard segments of SEBS. However, the present invention is not limited to this assumption.

[0061] When the conductive paste contains conductive carbon-based particles (A1), the content of the thermoplastic resin (B) is preferably 5 to 30 wt %, more preferably 10 to 25 wt %, and even more preferably 15 to 20 wt %, relative to 100 wt % of the conductive paste, from the viewpoint of achieving both a high recovery rate and a high resistance value. Furthermore, when the conductive paste contains conductive carbon-based particles (A1), the content of the thermoplastic resin (B) is preferably 20 to 80 wt %, more preferably 30 to 70 wt %, and even more preferably 40 to 60 wt %, relative to the total solid content of the conductive paste.

[0062] When the conductive paste contains conductive metal particles (A2), the content of the thermoplastic resin (B) is preferably 3 to 20 wt%, more preferably 5 to 15 wt%, and even more preferably 8 to 12 wt%, relative to 100 wt% of the conductive paste, from the viewpoint of achieving both a high recovery rate and a high resistance value. Furthermore, when the conductive paste contains conductive metal particles (A2), the content of the thermoplastic resin (B) is preferably 1 to 30 wt%, more preferably 3 to 20 wt%, and even more preferably 5 to 15 wt%, relative to the total solid content of the conductive paste.

[0063] 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 resin contained in the conductive paste is preferably a resin made of the above-mentioned thermoplastic resin. Furthermore, the above-mentioned thermoplastic resins may be used alone or in combination of two or more.

[0064] <(C) Solvent> The conductive paste of this embodiment contains a solvent as component (C).

[0065] The solvent contained in the conductive paste of this embodiment is not particularly limited as long as it can dissolve the specified thermoplastic resin. 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 solvents can be used alone or in combination of two or more. By using a specified solvent, the specified thermoplastic resin can be reliably dissolved. As a result, screen printing of the conductive paste for wiring formation can be facilitated.

[0066] 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 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.

[0067] The solvent can be added to the conductive paste as needed to adjust the viscosity of the conductive paste.

[0068] <Other Components> The conductive paste of this embodiment may be a conductive paste consisting only of 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 paste, as long as they do not impair the effects of this embodiment 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.

[0069] <Conductive Paste> The conductive paste of this embodiment can be produced by charging the essential components contained in the conductive paste described above ((A) conductive particles, (B) thermoplastic resin, and (C) solvent) and, if necessary, other components into a mixer such as a meteoric mixer, a dissolver, a bead mill, a Raikai mixer, a three-roll mill, a rotary mixer, or a twin-screw mixer, and mixing them. In this way, a conductive paste suitable for screen printing, dipping, or other desired coating or wiring formation methods can be prepared.

[0070] The viscosity of the conductive paste of this embodiment can be adjusted to a viscosity that can be appropriately used in a predetermined coating or wiring formation method such as screen printing, etc. The viscosity can be adjusted by appropriately controlling the amount of solvent.

[0071] The conductive paste of this embodiment can be used to form the shape of electrodes and / or wiring for electric and / or electronic circuits by means of screen printing or the like. By drying and solidifying this shaped conductive paste, electrodes and / or wiring for electric and / or electronic circuits with a low likelihood of breakage can be formed 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 thermoplastic resin 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 5 to 60 minutes at 60°C to 180°C, preferably 5 to 60 minutes at 80 to 140°C, and more preferably 20 to 40 minutes at 110 to 130°C.

[0072] <Restoration Rate of Electrode Shape> An electrode can be formed using the conductive paste of this embodiment. The restoration rate of the shape RR of an electrode formed using the conductive paste of this embodiment after one cycle of expansion and contraction under predetermined conditions is １ The restoration rate is sometimes referred to as the restoration ratio (RR).

[0073] In this specification, the term "restoration rate RR" refers to the ratio of the strain remaining after the load (tensile force) is removed (when the electrode has recovered to the state before the load was applied) to the strain that occurs when an electrode is formed using the conductive paste and a predetermined load (tensile force) is applied to the electrode itself for a predetermined time at a predetermined temperature.

[0074] The inventors have calculated the recovery rate RR of the electrode shape after one cycle of expansion and contraction. １ The inventors have found that by setting the value of the electrical resistance of the electrode to a predetermined range, it is possible to reduce the rate of change in the electrical resistance of the electrode after multiple extensions and contractions (expansion and contraction) of the electrode, and have arrived at the present invention. １By setting the recovery rate RR to 8.0% or less, even when the electrode is stretched and contracted, the rate of change in the electrical resistance before and after the stretching and contraction can be reduced. １ The recovery rate RR is more preferably 7.0% or less, and even more preferably 6.0% or less. １ The lower limit of the recovery rate RR is not particularly limited. １ The lower limit value of can be, for example, 1.0% or more.

[0075] Recovery rate RR １ can be measured as follows. First, a rectangular sample (length 60 mm x width 10 mm x thickness 100 μm) simulating an electrode is prepared using the conductive paste of this embodiment. Next, both ends of the rectangular sample (electrode) are spaced apart by a predetermined distance L ０ It is fixed so that L ０ is sometimes referred to as the "length in the longitudinal direction of the sample" or the "initial length." Next, a predetermined load (tensile force) is applied to one fixed end of the sample to stretch it to a predetermined length (for example, L ０ The sample is stretched to a length (×1.15) and held in the stretched state for a predetermined time. Next, the applied load is removed to shrink the sample. After shrinkage, the distance L between both ends of the sample is １ (length in the longitudinal direction of the sample). The length L of the sample in the longitudinal direction before elongation and contraction ０ and the deformation length after elongation and contraction (L １ -L ０ ) and the ratio [(L １ -L ０ ) / L ０ ] is the recovery rate RR １ (the percentage of residual strain), i.e., the percentage recovery rate RR １ can be expressed by the following formula (1): １ = (L １ -L ０ ) / L ０ × 100 (%) ... (1)

[0076] It is preferable that the change in the shape of the electrode after the expansion and contraction (expansion and contraction) of the electrode is small.１ =L ０ In formula (1), L １ =L ０ In the case of RR １ Therefore, in this specification, "improving the restoration rate" means that the restoration rate RR １ This means that σ becomes closer to zero (0).

[0077] In the electrode formed using the conductive paste of this embodiment, the above-mentioned predetermined recovery rate RR １ The length of extension when measuring the recovery rate RR is preferably 115% of the length (initial length) of the electrode before stretching (for example, 40 mm before stretching to 46 mm after stretching). Therefore, the predetermined load applied to the electrode (sample) is preferably a load that causes the electrode to be stretched 115% of the length before stretching. １ By measuring the recovery rate RR １ can be measured with good reproducibility.

[0078] The temperature when measuring the restoration rate can be room temperature (specifically, 25° C.). In addition, when measuring the restoration rate, the distance L between both ends of the sample before elongation and contraction is ０ The predetermined load (tensile force) when measuring the recovery rate is the length L of the electrode before elongation. ０ The load (tensile force) can be set to such that the length is elongated to 115% of the initial length.

[0079] In this specification, one extension and contraction (stretching and contraction) of the sample is referred to as "one cycle." In addition, in this specification, the distance between both ends of the sample after n cycles of stretching and contraction of the sample is referred to as L. ｎ The above-mentioned L １ means the distance between both ends of the sample after one cycle of stretching. In this specification, the recovery rate of the sample after n cycles of stretching is called RR. ｎ Therefore, the recovery rate RR of the sample after n cycles of stretching is ｎ (Percentage, %) can be expressed by the following formula (2): RR ｎ = (L ｎ -L０ ) / L ０ × 100 (%) ... (2)

[0080] Recovery rate RR of the sample after n cycles of stretching ｎ By setting the value of the resistance of the electrode within a predetermined range, it is possible to reduce the rate of change in the electrical resistance of the electrode after multiple extensions and contractions (expansion and contraction) of the electrode.

[0081] The shape recovery rate RR of an electrode formed using the conductive paste of this embodiment after 100 cycles of expansion and contraction １００ The predetermined recovery rate RR of the electrode formed using the conductive paste of this embodiment is preferably 10.0% or less. １００ By making the recovery rate RR 10.0% or less, it is possible to more reliably reduce the rate of change in the electrical resistance before and after extension and contraction, even when the electrode is repeatedly extended and contracted. １００ The recovery rate RR is more preferably 9.0% or less, and even more preferably 8.0% or less. １００ The lower limit of the recovery rate RR is not particularly limited. １００ The lower limit value of can be, for example, 1.0% or more.

[0082] In this specification, the ratio of the electrical resistance value (initial resistance value) before stretching and contraction (expansion and contraction) to the electrical resistance value after stretching and contraction (expansion and contraction) and returning to the original shape may be referred to as the "rate of change in electrical resistance value after stretching and contraction" or the "rate of change in electrical resistance value after stretching and contraction." In addition, in this specification, the electrical resistance value may be simply referred to as the "resistance value." In this specification, the electrical resistance value after n cycles of stretching and contraction is represented by the symbol ER ｎ Shown as:

[0083] Since the contact sensor is used repeatedly, it is necessary that the electrical resistance of the electrode after multiple extensions and contractions (stretching and contraction) does not change significantly from the electrical resistance before multiple cycles of extension and contraction. In this specification, the electrical resistance before extension and contraction (stretching and contraction) (initial resistance) is referred to as ER. ０ , the electrical resistance value ER of the electrode after one cycle of extension and contraction (stretching and contracting) １, the electrical resistance ER of the electrode after 100 cycles of elongation １００ It is defined as:

[0084] The electrical resistance (initial resistance) of the electrode formed using the conductive paste of this embodiment before expansion and contraction (expansion and contraction) is defined as ER ０ and the electrical resistance value ER of the electrode formed using the conductive paste of this embodiment after one cycle of extension and contraction. １ The rate of change with (ER １ / ER ０ × 100) is preferably 200% or less, more preferably 150% or less, and even more preferably 140% or less.

[0085] In a contact sensor, when an electrode of the contact sensor expands and contracts and returns to its original shape, it is necessary that the change from the electrical characteristics (initial resistance value) before expansion and contraction is small. From this viewpoint, the electrical resistance value (initial resistance value) of an electrode formed using the conductive paste of the embodiment before expansion and contraction (expansion and contraction) is defined as ER ０ and the electrical resistance value ER of the electrode formed using the conductive paste of this embodiment after 100 cycles of extension and contraction. １００ Resistance change rate (ER １００ / ER ０ × 100) is preferably 230% or less, more preferably 200% or less, and even more preferably 150% or less.

[0086] 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. As used herein, "conductive paste for stretchable devices" refers to 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 stretchable conductive paste for use as an electrode material for contact sensors.

[0087] <Conductor> In this specification, electrodes and / or wiring formed by solidifying the conductive paste of the present embodiment may be referred to as a "conductor." Therefore, the conductor of the present embodiment is a conductor formed by solidifying the conductive paste of the present embodiment. By using the conductive paste of the present embodiment, a conductor can be obtained whose electrical properties change little after expansion and contraction.

[0088] 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.

[0089] 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.

[0090] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0091] <Materials and Preparation Ratios of Conductive Paste> Table 1 shows the compositions of the conductive pastes of the examples and comparative examples. The conductive particles used in the examples and comparative examples are as follows. The average particle diameter of the conductive particles was determined as follows. First, a scanning electron microscope (SEM) was used to obtain an SEM photograph or SEM image of the (A) conductive particles at a magnification of 15,000 times. Next, the outline of the (A) conductive particles present in this SEM photograph or SEM image was approximated to a perfect circle, and the diameter of this perfect circle was measured. The arithmetic mean value of the diameters of 100 arbitrary (A) conductive particles measured in this way was taken as the average particle diameter of the (A) conductive particles.

[0092] [Conductive carbon particles (A1)] Conductive carbon particles A1-1: Carbon black, primary particle diameter 50 nm (product number 3050B, manufactured by Mitsubishi Chemical Corporation) Conductive carbon particles A1-2: Carbon black, primary particle diameter 40 nm (product number Ketjenblack, manufactured by Lion Specialty Chemicals) Conductive carbon particles A1-3: Carbon black, primary particle diameter 38 nm (product number F-200GS, manufactured by Asahi Carbon Co., Ltd.) Conductive carbon particles A1-4: Graphite, scaly graphite with an average particle diameter of 5 μm (product number JB-5, manufactured by Nippon Graphite Co., Ltd.)

[0093] [Conductive metal particles (A2)] Conductive metal particles A2-1: silver particles, average particle diameter 0.81 μm, specific surface area (BET) 2.59 m ２ / g, particle shape is irregular (product number K-79124P manufactured by Metalor)

[0094] The thermoplastic resins used in the examples and comparative examples are as follows: In the following description, "H / S" means the ratio of hard segments to soft segments (hard segments / soft segments). [(B) Thermoplastic Resins] Resin 1: Hydrogenated styrene thermoplastic elastomer (SEBS), product number S1606, H / S=50 / 50, number average molecular weight (Mn) 200,000 (manufactured by Asahi Kasei Corporation) Resin 2: Maleic anhydride-modified styrene thermoplastic elastomer, product number M1911, H / S=30 / 70, number average molecular weight (Mn) 63,000 (manufactured by Asahi Kasei Corporation) Resin 3: Hydrogenated styrene thermoplastic elastomer (SEBS), product number S1613, H / S=30 / 70, number average molecular weight (Mn) 140,000 (manufactured by Asahi Kasei Corporation) Resin 4: Hydrogenated styrene thermoplastic elastomer (SEBS), product number S1615, / S=70 / 30, number average molecular weight (Mn) 250,000 (manufactured by Asahi Kasei Corporation) Resin 5: Thermoplastic urethane elastomer, product number P-2294 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., ether-based urethane resin)

[0095] 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

[0096] The resin used in the examples and comparative examples was dissolved in a solvent to prepare a resin solution, and conductive particles were mixed into the resin solution.

[0097] 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.

[0098] <Method for measuring the recovery rate of the electrode shape> Recovery rate RR １ was measured as follows. Measurement was performed using a universal material testing machine Model 5566 manufactured by INSTRON Corporation (measurement conditions: tensile speed = 72 mm / min). First, a rectangular sample (length 60 mm x width 10 mm x thickness 50 μm) was prepared using the conductive paste of this embodiment. The conductive paste was dried in a constant temperature dryer at 120°C for 30 minutes to obtain a rectangular sample (conductor). Next, the rectangular sample was dried at room temperature (specifically 25°C) until the length in the longitudinal direction was 40 mm (= L ０ Both ends of the rectangular sample in the longitudinal direction were fixed to the testing machine so that the distance between the fixed ends was 46 mm. Next, a load was applied to one of the fixed ends, and the sample was stretched at a tensile speed of 72 mm / min until the length in the longitudinal direction reached 46 mm. After the sample reached 46 mm of stretch, the load was removed at a speed of 72 mm / min, causing the sample to shrink. This single stretch and contraction (expansion and contraction) of the electrode is called "one cycle." After that, the length in the longitudinal direction of the sample after shrinkage (the distance between the fixed ends (= L １ The length L of the sample in the longitudinal direction before elongation and contraction was measured. ０ and the deformation length after elongation and contraction (L １ -L ０ ) and the ratio [(L １ -L ０ ) / L ０ ] is the recovery rate RR １ The percentage recovery rate RR １ (%) can be expressed by the following formula (1): １ = (L １ -L ０ ) / L ０ × 100 (%) ... (1)

[0099] The above recovery rate RR １The sample was stretched and contracted for 100 cycles under the same conditions as in the measurement of ０ and the length (L １００ ) and L ０ and the deformation length (L １００ -L ０ ) and the ratio (recovery rate RR １００ The recovery rate RR after 100 cycles of expansion and contraction was measured. １００ (Percentage, %) can be expressed by the following formula (3): RR １００ = (L １００ -L ０ ) / L ０ × 100 (%) ... (3)

[0100] Table 1 shows the recovery rates RR of the examples and comparative examples measured as described above. １ and recovery rate RR １００ Shows.

[0101] <Method for measuring electrical resistance> Recovery rate RR of the above-mentioned Examples and Comparative Examples １ and recovery rate RR １００ During the measurement, the electrical resistance values ​​at both ends of the sample were continuously measured. Table 1 shows the electrical resistance values ​​(initial electrical resistance values) ER of the electrodes formed using the conductive pastes of the Examples and Comparative Examples before extension and contraction (expansion and contraction). ０ , electrical resistance value ER after one cycle of extension and contraction １ , and the electrical resistance value ER after 100 cycles of extension and contraction １００ The electrical resistance value was measured using a digital multimeter (model number: 2001) manufactured by TFF Keithley Instruments, Inc.

[0102] In addition, the rate of change of the electrical resistance value was calculated by taking the initial electrical resistance value (ER ０ ) and the electrical resistance (ER) after one cycle of extension and contraction １ ) and the resistance change rate (ER １ / ER ０ × 100) and the initial electrical resistance value ER ０ and the electrical resistance (ER) after 100 cycles of extension and contraction. １００ ) and the resistance change rate (ER １００ / ER ０× 100) was calculated as a percentage.

[0103] <Measurement Results of Examples and Comparative Examples> From the above, it was revealed that when the conductive paste of the examples was used, an electrode capable of reducing the rate of change in electrical resistance before and after extension and contraction could be formed. Specifically, the recovery rates RR of Examples 1 to 7 were １ is 8.0% or less, and the initial resistance value (ER ０ ) and the electrical resistance (ER) after one cycle of extension and contraction １ ) and the resistance change rate (ER １ / ER ０ × 100) was shown to be 200% or less. １ In Examples 1 to 7, where the resistance change rate (ER １ / ER ０ × 100) is in the range of 117.7 to 158.8%. １ The resistance change rate (ER) of Comparative Example 1 is 8.4%. １ / ER ０ × 100) was 224.4%, which is significantly larger than those of Examples 1 to 7. This indicates that the recovery rate RR of 8.0% １ This means that the tendency of the resistance change rate is significantly different across the boundary. １ It can be said that it has been found that the rate of change in resistance value can be reduced by setting the value to 8.0% or less.

[0104] On the other hand, Comparative Example 1 has a recovery rate (RR １ ) exceeds 8.0%, and the rate of change in resistance (ER １ / ER ０ The reason is that the conductive paste of Comparative Example 1 contained a large number of conductive particles of 1.5 μm or more, and therefore the recovery rate (RR １) is thought to have become larger. In addition, in the conductive paste of Comparative Example 2, a thermoplastic urethane elastomer was used as the thermoplastic resin (B). In the rectangular sample of Comparative Example 2, fracture occurred in the test piece after one cycle of extension and contraction. In the conductive paste of Comparative Example 3, a maleic anhydride-modified styrene-based thermoplastic elastomer was used as the thermoplastic resin (B). In the rectangular sample of Comparative Example 3, fracture occurred in the test piece after one cycle of extension and contraction. This is presumably because the molecular weight of the thermoplastic resin was small and it was unable to follow the extension.

[0105] From the above, it is possible to improve the recovery rate (RR) of an electrode formed using a conductive paste by appropriately selecting the type and content of the conductive particles and thermoplastic resin. １ It is clear that the recovery rate (RR) of the electrode can be controlled. １ It is clear that by setting the ratio of change in electrical resistance (ER1 / ER0×100) to 8.0% or less, the rate of change in resistance (ER1 / ER0×100) can be made 200% or less. Therefore, 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 expansion and contraction, even when the electrode expands and contracts.

[0106]

Claims

1. A conductive paste comprising: (A) conductive particles having an average particle diameter of less than 1.5 μm, (B) a thermoplastic resin, and (C) a solvent, wherein an electrode formed using the conductive paste is stretched to a length of 115% with respect to the length before elongation by applying a tensile force, and then the tensile force is removed to contract the length of the electrode. One cycle is defined as one cycle of elongation and contraction, and the shape recovery rate (RR １ ) is 8.0% or less. Conductive paste.

2. The shape restoration rate (RR １００ ) of the electrode formed using the conductive paste when subjected to 100 cycles of elongation and contraction is 10.0% or less. The conductive paste according to claim 1.

3. The conductive paste according to claim 1 or 2, wherein the (A) conductive particles are at least one selected from silver, nickel, copper, silver-coated copper, silver-coated fiber, silver-coated resin, carbon fiber, graphite, graphene, carbon black, graphite, and mixtures thereof.

4. The conductive paste according to any one of claims 1 to 3, wherein the conductive paste substantially does not contain conductive particles having an average particle diameter of 1.5 μm or more.

5. The conductive paste according to any one of claims 1 to 4, wherein the (B) thermoplastic resin is at least one selected from polystyrene resins, polyolefin resins, polyvinyl chloride resins, polyurethane resins, polyester resins, polyamide resins, polybutadiene resins, and hydrides thereof, and modified copolymer hydrides obtained by modifying the hydrides.

6. The conductive paste according to any one of claims 1 to 5, wherein the ratio of the hard segment to the soft segment of the (B) thermoplastic resin (hard segment: soft segment) is 1:99 to 50:

50.

7. The conductive paste according to any one of claims 1 to 6, wherein the number average molecular weight of the (B) thermoplastic resin is 100,000 or more.

8. The conductive paste according to any one of claims 1 to 7, wherein the (B) thermoplastic resin is a styrenic elastomer.

9. The conductive paste according to any one of claims 1 to 8, wherein the (A) conductive particles contain conductive carbon-based particles (A1), and the content of the (B) thermoplastic resin is 20 to 80% by weight based on the total solid content contained in the conductive paste.

10. The conductive paste according to any one of claims 1 to 9, wherein the (A) conductive particles contain conductive metal particles (A2), and the content of the (B) thermoplastic resin is 1 to 30% by weight based on the total solid content contained in the conductive paste.

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

12. The initial resistance value (ER ０ ) of the electrode formed using the conductive paste, and the electrical resistance value (ER １ ) after one cycle of elongation and contraction, and the resistance change rate (ER １ / ER ０ ×100) is 200% or less. The conductive paste according to any one of claims 1 to 11.

13. The initial resistance value (ER ０ ) of the electrode formed using the conductive paste, and the electrical resistance value (ER １００ ) after 100 cycles of elongation and contraction, and the rate of change in resistance value (ER １００ / ER ０ ×100), wherein the rate of change in resistance value is 220% or less. The conductive paste according to any one of claims 1 to 12.

14. A conductor, characterized in that it is obtained by solidifying the conductive paste according to any one of claims 1 to 13.

15. A contact sensor, characterized in that it comprises the conductor according to claim 14.

16. An electronic component, characterized in that it comprises the conductor according to claim 14.

Images