Electroconductive paste and stretchable conductor base material

Abstract

This electroconductive paste contains electroconductive particles in which the tap density measured in accordance with ISO 3953:2011 is 2.5 g／mL or greater and the BET specific surface area is 2.5 m2 / g or greater, (B) a thermoplastic resin, and (C) a solvent. Provided are: an electroconductive paste, an electroconductive film or an electroconductive pattern having exceptional low-resistance properties even when continuously caused to expand and contract; a cured article of said electroconductive paste, electroconductive film or electroconductive pattern; and a wearable device containing said electroconductive film or electroconductive pattern.

Description

Conductive paste and conductive stretchable substrate

[0001] The present invention relates to a conductive paste that can be used to form electrodes on a stretchable and / or bendable substrate, and to a device having a conductive film or conductive pattern using the conductive paste, particularly a conductive stretchable substrate and a wearable device using the same.

[0002] In recent years, conductive pastes have been developed for forming electrodes on stretchable and / or bendable substrates. The flexibility of conductive pastes contributes to the mitigation of forces applied to the electrode, making them a key feature in the development of electrodes that are resistant to external forces. Highly flexible conductive pastes impart bending and stretchability to the conductor itself, resulting in sheets or films with freely curved conductive wiring. Highly flexible conductive pastes can form electrodes or conductive patterns that can adapt to the movement of stretchable and / or bendable substrates, such as cloth. While conductive pastes capable of bending and curving, such as those used in PC keyboard wiring, are already known, stretchable conductive wiring is expected to be useful in applications such as manipulators that require more precise movement and wearable devices equipped with contact sensors that detect fine movements, such as those of human joints. Development is particularly progressing for wearable device applications.

[0003] As an example of the application of flexible conductive paste to wearable devices, in the case of a pressure sensor, a type of contact sensor, the electrodes of the pressure sensor expand when pressure is applied to the sensor. Furthermore, when pressure is removed from the pressure sensor, the electrodes contract and must return to their original shape before the pressure was applied. In an example where conductive paste is used to form wiring on a wearable device, the wiring is subjected to deformation forces as the wearable device bends and stretches. To prevent breakage due to this deformation, the change in electrical resistance with bending and stretching must be small.

[0004] As a conductive paste for forming electrodes on a stretchable and / or bendable substrate, resin compositions capable of forming wiring with a low probability of disconnection have been developed. 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 wt % or more to less than 100 wt % of the total of (A) the conductive particles and (B) the thermoplastic polyurethane resin.

[0005] JP 2018-104581 A

[0006] In sensing technologies such as virtual reality (VR) and motion capture, forming stretchable and / or bendable electrodes and / or wiring on the surface of a stretchable and / or bendable substrate is an important technique for tracing smooth movements. Furthermore, conductive films and conductive patterns formed on the surface of a substrate are required to be not only flexible but also durable in terms of small fluctuations in electrical resistance with continuous stretching. Conductive pastes such as the resin composition described in Patent Document 1 have been developed, but there is always a demand for realizing higher-precision sensors, and conductive pastes made from the resin composition of Patent Document 1 do not necessarily meet the demand for durability with continuous stretching.

[0007] Therefore, an object of the present invention is to provide a conductive paste, a conductive film or a conductive pattern that has excellent low resistance even when continuously stretched and contracted, and a wearable device that includes a cured product thereof, a conductive film or a conductive pattern.

[0008] In order to solve the above problems, the present invention has the following configuration.

[0009] (Configuration 1) Configuration 1 is a composition comprising: (A) a tap density measured in accordance with ISO 3953:2011 of 2.5 g / ml or less and a specific surface area measured by the BET method of 2.5 m ２ / g or more, (B) a thermoplastic resin, and (C) a solvent.

[0010] (Configuration 2) Configuration 2 is the conductive paste of configuration 1, in which component (A) contains amorphous particles.

[0011] (Configuration 3) Configuration 3 is the conductive paste of Configuration 1 or 2, in which component (A) contains 40% by weight or more of amorphous particles relative to the total amount of conductive particles.

[0012] (Configuration 4) Configuration 4 is the conductive paste of any one of Configurations 1 to 3, which has an initial resistance of 10 Ω / cm or less, and a resistance of 100 Ω / cm or less after being molded into a length of 60 mm and a width of 0.4 mm and continuously stretched 100 times at a 20% amplitude and 12 stretches per minute.

[0013] (Configuration 5) Configuration 5 is the conductive paste of any one of Configurations 1 to 4, in which, when molded into a length of 60 mm and a width of 0.4 mm and continuously stretched and contracted at an amplitude of 20% and 12 times per minute, the rate of change in resistance value after 2000 stretches relative to the initial resistance value is 400 times or less.

[0014] (Configuration 6) Configuration 6 is the conductive paste of any one of Configurations 1 to 5, in which the ratio of component (A) to the total of component (A) and component (B) is 80 to 99 wt %.

[0015] (Configuration 7) Configuration 7 is the conductive paste of any one of Configurations 1 to 6, in which (B) is a resin having oxygen atoms in the structure of the polymer main chain.

[0016] (Configuration 8) Configuration 8 is a conductive stretchable substrate comprising the conductive paste of any one of configurations 1 to 7 and a coating substrate.

[0017] (Configuration 9) Configuration 9 is the conductive stretchable substrate of configuration 8, wherein the coating substrate is a polyester elastomer sheet.

[0018] The present invention can provide a conductive paste, a conductive film or a conductive pattern that has excellent low resistance even when continuously stretched and contracted, and a wearable device that includes a cured product thereof, a conductive film or a conductive pattern.

[0019] An embodiment of the present invention is a conductive paste that includes (A) conductive particles, (B) a thermoplastic resin, and (C) a solvent.

[0020] 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 value before and after expansion and contraction, even when the electrodes and / or wiring are continuously expanded and contracted.

[0021] 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.

[0022] First, the conductive paste of this embodiment will be specifically described.

[0023] <(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 a tap density of 2.5 g / ml or less as measured in accordance with ISO 3953:2011 and a specific surface area of ​​2.5 m2 as measured by the BET method. ２ / g or more. In conventional polymer-type conductive pastes prepared into a paste by blending a polymer, strong contact between conductive particles is desirable to reduce resistance. Therefore, conductive particles with a high tap density, which allows the particles to be densely packed with few voids, have been used. Furthermore, since resistance tends to decrease as the specific surface area decreases, conductive particles with a shape that reduces the specific surface area compared to particles of the same element, such as scaly particles or a mixture of scaly particles and spherical particles, have been used. In contrast, the present inventors unexpectedly discovered that by using conductive particles with a low tap density and a large specific surface area, it is possible to suppress changes in resistance during continuous stretching while maintaining a resistance value that is sufficient for practical use, and have arrived at the present invention.

[0024] The conductive paste of this embodiment preferably contains irregular particles as conductive particles. The small proportion of spherical or nearly spherical particles in the irregular particles increases the specific surface area of ​​the conductive particles. Furthermore, when the irregular particles are mixed with a resin to form a coating, the conductive particles disperse within the polymer matrix, forming a network structure that allows for the formation of flexible, stretchable, random conductive paths, ensuring contact points between particles with a wide surface area. Furthermore, the network structure is believed to facilitate expansion and contraction due to the porous structure. This tendency is further enhanced in particles with a low tap density, in which the resin easily fills the gaps between the particles while maintaining contact, and a high specific surface area, in which the particle shape is far from spherical. Therefore, the degree of loss of contact between particles due to expansion and contraction is thought to be reduced, thereby suppressing changes in resistance value even during expansion and contraction. Herein, "irregular" refers to particles other than spherical powder and scaly powder with an aspect ratio of 100 or more.

[0025] The content of the irregular particles is preferably 40% by weight or more, more preferably 55% by weight or more, and even more preferably 70% by weight or more, of the total conductive particles.

[0026] The conductive particles contained in the conductive paste of this embodiment can be made of any electrically conductive material. Examples of conductive particles contained in the conductive paste of this embodiment include conductive metal particles such as copper (Cu), silver (Ag), gold (Au), nickel (Ni), and titanium (Ti); metal-coated material particles such as silver-coated copper and silver-coated resin; fibrous materials coated with metal such as silver-coated fibers; and mixtures thereof. By using these materials as the conductive particle material, a conductive paste capable of forming electrodes with appropriate electrical conductivity can be obtained. It is preferable to use conductive particles made of silver as the conductive particles. Note that, in this specification, "conductive particles made of A" means that elements other than A may be contained as unavoidable impurities. The same applies to components other than the conductive particles.

[0027] When the conductive paste contains silver (Ag) as the conductive particles (A), 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.

[0028] The particle shape of the conductive particles (A) may include spherical, scaly, or foil-like particles, but from the viewpoint of improving durability, it is preferable that the conductive particles (A) include amorphous conductive particles as described above.

[0029] As the conductive particles (A), multilayer particles in which the surface of metal particles is coated with other metal atoms or metal compounds can also be used, as long as the tap density and BET specific surface area satisfy the above conditions. By disposing expensive metals such as Ag, Pd, Au, and Pt on the surface of relatively inexpensive metal particles such as Cu, the overall cost of the conductive particles can be reduced while utilizing the physical properties of these metals, such as high conductivity, migration resistance, and corrosion resistance. Multilayer particles can be produced by known manufacturing methods tailored to the particle shape. For example, core-shell particles with an outer layer having a certain thickness ratio relative to the entire particle can be produced by means of a metal precipitation reaction due to a reduction reaction of a compound containing the metal in the outer layer to precipitate a metal on the surface of the metal particles in the inner layer. Alternatively, particles can be produced in which a thin coating film is formed on the surface of the metal particles in the inner layer by immersing the metal particles in the inner layer in a solution of a metal compound and then drying, for example. The outer layer does not necessarily cover the entire surface of the metal in the inner layer; in particular, coated particles may have a structure in which the metal in the outer layer coats only a portion of the metal particles in the inner layer. The thickness and weight ratio of the outer layer and the inner layer of the multi-layered particles are not particularly limited, and can be controlled by the method for producing the particles.

[0030] The tap density of the conductive particles (A) is 2.5 g / ml or less, preferably 2.4 g / ml or less, and more preferably 2.3 g / ml or less. A tap density within this range provides the conductive paste with good conductivity while also providing flexibility to bending, making it easy to achieve the effects of the present invention. There is no particular lower limit for the tap density, but it is preferably 0.1 g / ml or more, more preferably 0.15 g / ml or more, and even more preferably 0.2 g / ml or more. From the same perspective, the tap density of the conductive particles (A) is preferably 0.1 to 2.5 g / ml, more preferably 0.15 to 2.4 g / ml, and even more preferably 0.2 to 2.3 g / ml. The above tap density range is particularly preferred when the conductive particles (A) are silver particles, but this range is also acceptable for metal particles other than silver.

[0031] The tap density is a density measured based on the volume of a powder in a state where a container containing a certain weight of powder is tapped a certain number of times to apply up-and-down vibrations and fill the voids between the powder particles. In this specification, the tap density value is a value measured in accordance with ISO 3953:2011.

[0032] The specific surface area (BET value) of the conductive particles (A) is 2.5 m ２ / g or more, preferably 2.7m ２ / g or more, more preferably 2.8m ２ There is no particular upper limit to the specific surface area, but ２ / g or less, and ２ / g or less. By being in the above range, a stable resistance value can be maintained against repeated expansion and contraction. From the same viewpoint, the specific surface area (BET value) of the conductive particles (A) is preferably 2.5 to 10 m ２ / g is preferred, and 2.7 to 10m ２ / g is more preferable, and 2.8 to 8m ２ / g is more preferred.

[0033] The BET method is a method for determining the surface area of ​​particles by measuring the amount of inert gas physically adsorbed on the powder surface under low-temperature, low-humidity conditions. Measurement devices, calculation methods, etc. are known to those skilled in the art, and published values ​​can be used for commercially available particles.

[0034] It is not clear why setting the tap density and BET specific surface area of ​​the conductive particles within the above ranges results in excellent low resistance even when continuously stretched and contracted, but it is thought that the use of conductive particles with a low tap density and a large BET specific surface area gives the coating film a microscopic mesh structure, which does not significantly affect the wiring resistance even when stretched and contracted.

[0035] The conductive particles (A) may be a mixture of two or more types of conductive particles that differ in element type, particle shape, tap density, or BET specific surface area. Furthermore, as long as the tap density and BET specific surface area of ​​the overall conductive particles after mixing satisfy the above conditions, the tap density may be greater than 2.5 g / ml and / or the BET specific surface area may be greater than 2.5 cm. ２ / g. Therefore, in the present specification, when a mixture of two or more different types of conductive particles is used as the conductive particles, the values ​​of the tap density and BET specific surface area of ​​the conductive particles (A) are the values ​​for the conductive particles after mixing. From the viewpoint of suppressing an increase in resistance due to continuous stretching, the tap density is more than 2.5 g / ml and / or the BET specific surface area is less than 2.5 cm ２ The content of conductive particles that is less than 1 / g is preferably less than 50% by weight, more preferably less than 40% by weight, and even more preferably less than 25% by weight, of the total conductive particles, provided that the tap density and BET specific surface area of ​​the entire conductive particles after mixing satisfy the above conditions.

[0036] The tap density and BET specific surface area values ​​of the conductive particles (A) are measured under the above conditions, but prior to preparing the conductive particles (A), the tap density and BET specific surface area values ​​can be predicted from the particles before mixing. In the case of tap density, the tap density of the mixed particles can be roughly estimated by adding 0.1 to the weighted average of the tap densities of the mixed particles. Therefore, as long as only conductive particles with a tap density of 2.4 g / ml or less are blended, the actually measured tap density of the mixed conductive particles can be considered to be 2.5 g / ml or less. The weighted average of the values ​​of the mixed particles can be used as the approximate BET specific surface area of ​​the mixed particles.

[0037] The (A) conductive particles contained in the conductive paste preferably have an average particle diameter of 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. The lower limit of the average particle diameter of the (A) conductive particles is not particularly limited, but is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. By having the average particle diameter of the (A) conductive particles within the above range, a conductive paste with excellent resistance to stretching and / or bending and workability can be obtained. If the average particle diameter is larger than the above range, problems such as clogging may occur during screen printing. If the average particle diameter is smaller than the above range, excessive fusion between particles may occur during heating and drying the paste, making it difficult to form wiring that is sufficiently resistant to stretching and / or bending. From the same perspective, the average particle diameter of the (A) conductive particles is preferably 0.5 to 30 μm, more preferably 0.8 to 20 μm, and even more preferably 1 to 10 μm. In this specification, the average particle size is expressed as a median size (D50).

[0038] 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 outlines of the (A) conductive particles present in the SEM photograph or SEM image are approximated to perfect circles, the diameters of the perfect circles are measured, and the arithmetic mean value of the diameters of 100 arbitrary (A) conductive particles can be used as the average particle diameter of the (A) conductive particles.

[0039] The conductive particles contained in the conductive paste of this embodiment may have a particle diameter of more than 30 μm, provided that the effect of the present invention is not adversely affected. Even in this case, the average particle diameter of the conductive particles must be 30 μm or less.

[0040] 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 with an average particle diameter of 30 μm or less and conductive particles Y with an average particle diameter of more than 30 μm. 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, a stable resistance value can be maintained against repeated expansion and contraction.

[0041] The conductive paste of this embodiment preferably does not substantially contain conductive particles having an average particle diameter of more than 30 μm. 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 30 μm or less. By using such conductive particles, a stable resistance value can be maintained against repeated expansion and contraction.

[0042] From the viewpoint of achieving both a high resistance value and continuous stretch resistance, the content of the (A) conductive particles is preferably 60 to 95 wt %, more preferably 70 to 95 wt %, even more preferably 75 to 90 wt %, and particularly preferably 80 to 85 wt %, relative to 100 wt % of the conductive paste. From the viewpoint of achieving both a high resistance value and continuous stretch resistance, the content of the (A) conductive particles is preferably 80 to 99 wt %, more preferably 83 to 97 wt %, and even more preferably 85 to 95 wt %, relative to the total solid content of the conductive paste. By having the conductive particle content within the above range, flexibility can be imparted to the conductive paste without impairing the conductivity provided by the thermoplastic resin. In this specification, the "total solid content" refers to the total content of the components contained in the conductive paste, excluding the (C) solvent. When the conductive paste is composed of three components, namely, (A) conductive particles, (B) thermoplastic resin, and (C) solvent, the "total solid content" refers to the total content of the (A) conductive particles and the (B) thermoplastic resin.

[0043] In addition to the above-mentioned metal particles, conductive carbon-based particles, which are materials containing carbon, can also be used as the conductive paste of the present invention. When forming an electrode using a conductive paste, metal particles such as silver may not be usable in applications requiring reliability such as corrosion resistance, so conductive carbon-based particles may be used. Examples of conductive carbon-based particles include carbon fiber, graphite, graphene, carbon black, graphite, and mixtures thereof. When using conductive carbon-based particles, it is preferable to include carbon black, which has high electrical conductivity and easily follows expansion and contraction when used as an electrode, and particles made of carbon black are more preferable.

[0044] Carbon black has a structure in which many primary particles are connected together. 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, the upper limit of the average particle size of carbon black can be said to be 100 nm or less. The average particle size of carbon black can be observed and measured using a transmission electron microscope (TEM).

[0045] The true density of conductive carbon particles is generally 1.7 to 2.3 g / ml. Since the tap density is, in principle, smaller than the true density, the tap density of conductive carbon particles is in the range of 2.5 g / ml or less. The specific surface area (BET value) of the conductive carbon particles is preferably 10 to 700 m ２ / g, more preferably 20 to 250 m ２ / g, more preferably 25 to 150 m ２ / g.

[0046] When the conductive paste of this embodiment contains conductive carbon-based particles, the amount of the conductive carbon-based particles is preferably 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 amount of the conductive carbon-based particles is preferably 10 to 60 wt %, more preferably 20 to 50 wt %, and even more preferably 30 to 50 wt %, relative to the total amount of solids contained in the conductive paste. Within this range, a conductive paste with excellent handleability can be obtained without impairing printability.

[0047] <(B) Thermoplastic Resin> The conductive paste of the present embodiment contains a thermoplastic resin as component (B). There are no particular limitations on the thermoplastic resin, as long as it can be mixed with the conductive particles (A) to obtain a conductive paste with a viscosity that is easy to handle.

[0048] 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, polyether-based resins, polyurethane-based resins, polyester-based resins, polyamide-based resins, polybutadiene-based resins, silicone-based resins, their hydrogenated derivatives, and modified copolymer hydrogenated derivatives obtained by modifying the hydrogenated derivatives. Among these, resins having oxygen atoms in the polymer main chain structure are more preferred. The oxygen atoms contained in the polymer main chain structure are contained in structures such as ether bonds (-O-), ester bonds (-O-CO-), and urethane bonds (-NH-CO-O-). The groups bonded to both sides of these bonds are preferably hydrocarbon groups. When an electrode is formed using a conductive paste containing such a thermoplastic resin, the electrode's shape is easily restored when subjected to external force, making it easier to achieve the effects of the present invention.

[0049] As the resin having oxygen atoms in the polymer main chain structure, a polyether-based resin, a polyurethane-based resin, a polyester-based resin, or a silicone-based resin can be used, and it is preferable to use a polyether-based resin, a polyurethane-based resin, or a polyester-based resin, and it is more preferable to use a polyurethane-based resin.

[0050] The thermoplastic resin may be an elastomer. Examples of the elastomer include styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, acrylic-based elastomers, and silicone-based elastomers. Urethane-based elastomers are preferred. Among the elastomers, elastomers having hard and soft segments are preferred.

[0051] When an elastomer having hard segments and soft segments is used to form a conductive paste into an electrode, it easily conforms to expansion and contraction, improving the electrode's shape recovery, resulting in a conductive paste with excellent resistance to continuous stretching. From this perspective, the ratio of hard segments to soft segments (hard segments:soft segments) in the thermoplastic resin is preferably 1:99 to 50:50. The hard segment:soft segment ratio is more preferably 10:90 to 50:50, and even more preferably 20:80 to 50:50. The mechanism by which recovery is improved by maintaining the ratio of hard segments to soft segments in a specified range is unclear. The mechanism is speculated to be that extensibility is achieved by deformation of the flexible soft segments, and recovery is achieved by physical crosslinking due to the cohesive force between the hard segments. However, the present invention is not limited to this speculation.

[0052] Polyurethane is generally obtained by reacting polyol and polyisocyanate, with the polyol-derived portions making up the soft segments and the urethane and urea bond portions making up the hard segments. The hard segments act as crosslinking points within the resin, while the soft segments are the elastic portions. This allows urethane-based elastomers using polyurethane to provide conductive paste with the ability to conform to substrates and restore their shape.

[0053] Polyurethane can be endowed with various properties in addition to its elastomer properties by designing the polyol used as the raw material. Therefore, urethane-based elastomers with different properties can be appropriately selected and used in the conductive paste of the present invention depending on the application. Polyols that can be used include polyether polyols, polyester polyols, and polycarbonate polyols. Among these, polyether polyols, which can provide polyurethanes with excellent water resistance, cold resistance, and mildew resistance, are preferred because they are compatible with wearable devices.

[0054] Polyether polyols are obtained as addition polymerization products of polyhydric alcohols or alkylene oxides. Non-limiting examples of raw materials for polyether polyols include ethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylene oxide, and propylene oxide. Polyether polyols may be synthesized from these raw materials, or commercially available polyether polyols may be used for urethane synthesis.

[0055] Polyester polyols are condensation products of dicarboxylic acids and polyhydric alcohols. Non-limiting examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, sebacic acid, and cyclohexanedicarboxylic acid, and aromatic dicarboxylic acids such as phthalic acid. Non-limiting examples of polyhydric alcohols include aliphatic diols such as ethylene glycol, propylene glycol, 1,4-butanediol, and 1,6-hexanediol, and alicyclic diols such as cyclohexanedimethanol. For urethane-based elastomers, aliphatic diols are preferably used. Polyester polyols may be synthesized from these raw materials, or commercially available products may be used for urethane synthesis.

[0056] Polycarbonate polyol is a polycondensation reaction product of a polyhydric alcohol and a carbonate compound. The polyhydric alcohol may be any of the alcohols exemplified above. The carbonate compound may be dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, or the like. Polycarbonate polyol may be synthesized from these raw materials, or a commercially available product may be used for urethane synthesis.

[0057] The polyisocyanate used as a raw material for the urethane elastomer is not particularly limited, and linear, branched, or cyclic aliphatic polyisocyanates and aromatic polyisocyanates can be used without any particular limitation. Examples of polyisocyanates used in the synthesis of polyurethane include tetramethylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate (IPDI).

[0058] As the urethane-based elastomer, polyurethanes synthesized from these raw materials can be used, but commercially available urethane-based elastomers may also be used.

[0059] The conductive paste of this embodiment preferably contains a thermoplastic resin with a number-average molecular weight of 100,000 or more, more preferably 120,000 or more, and even more preferably 140,000 or more. By using a conductive paste containing a thermoplastic resin within the above range, the shape restoration of the electrode can be improved. 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.

[0060] The conductive paste of this embodiment may use a resin that does not contain oxygen atoms in the molecular structure of the polymer main chain. Examples of such resins include polystyrene-based resins, polyolefin-based resins, polyvinyl chloride-based resins, polyamide-based resins, and polybutadiene-based resins. These resins may also be elastomers, such as styrene-based elastomers, olefin-based elastomers, polyamide-based elastomers, and acrylic-based elastomers.

[0061] From the viewpoint of improving the ability to follow expansion and contraction and the ability to recover from physical deformation, the thermoplastic resin may particularly contain a styrene-based elastomer. 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. Among styrene-based elastomers, it is particularly preferable to use SEBS (styrene-ethylene-butylene-styrene), in which the soft segment is a block copolymer of poly(ethylene / butylene).

[0062] 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.

[0063] <(C) Solvent> The conductive paste of this embodiment contains a solvent as component (C).

[0064] The solvent contained in the conductive paste of this embodiment is not particularly limited as long as it can dissolve the specified thermoplastic resin. In the conductive paste of this embodiment, examples of the solvent include aromatic solvents (e.g., toluene, xylene, benzyl alcohol, etc.), ketone solvents (e.g., cyclohexanone, isophorone, methyl ethyl ketone, methyl isobutyl ketone, etc.), ether solvents (e.g., diethylene glycol dibutyl ether, etc.), and amide solvents (e.g., 3-methoxy-N,N-dimethylpropanamide, dimethylformamide, dimethylacetamide, etc.). In the conductive paste of the present invention, the solvent preferably contains at least one selected from isophorone, diethylene glycol diethyl ether, 3-methoxy-N,N-dimethylpropanamide, cyclohexanone, dimethylformamide, dimethylacetamide, and benzyl alcohol, and more preferably contains isophorone. The solvent may be used alone or in combination of two or more. An example of a mixture of two or more solvents is a solvent obtained by mixing diethylene glycol diethyl ether, isophorone, and 3-methoxy-N,N-dimethylpropanamide in a ratio of 1:1:1. By using a predetermined solvent, the predetermined thermoplastic resin can be dissolved reliably, which makes it easier to perform screen printing of a conductive paste for forming wiring.

[0065] 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.

[0066] The solvent can be added to the conductive paste as needed to adjust the viscosity of the conductive paste.

[0067] <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 curing agent, a curing catalyst, a curing accelerator, a silane coupling agent, a leveling agent, a thixotropic agent, and an antifoaming agent. The preferred types and amounts of each additive are known to those skilled in the art.

[0068] <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.

[0069] 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. The viscosity can be adjusted by appropriately controlling the amount of solvent. Methods for measuring viscosity are known to those skilled in the art, and the viscosity of the conductive paste of the present invention is preferably 50 to 400 Pa·sec, and more preferably 150 to 350 Pa·sec, under measurement conditions of a rotation speed of 10 rpm.

[0070] The conductive paste of this embodiment can be formed into the shape of electrodes and / or wiring for electric and / or electronic circuits by means of screen printing or the like, followed by drying and solidification, thereby forming electrodes and / or wiring for electric and / or electronic circuits with a low likelihood 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 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 set to 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.

[0071] <Characteristics of the Conductive Paste> An electrode formed using the conductive paste of the present invention exhibits little change in electrical properties after extension and contraction. Therefore, the conductive paste of the present invention can be effectively used in contact sensors and the like, which are used repeatedly and require 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. The change in electrical properties is evaluated mainly by the fluctuation of the electrical resistance. In this specification, the ratio of the electrical resistance before extension and contraction (stretching and contraction) (initial resistance) to the electrical resistance after extension and contraction (stretching and contraction) and return to the original shape may be referred to as the "rate of change in electrical resistance after extension and contraction" or the "rate of change in electrical resistance after stretching and contraction." In this specification, the electrical resistance may also be simply referred to as the "resistance." In this specification, one extension and contraction (stretching and contraction) of a sample is defined as "one cycle," and the electrical resistance after n cycles of extension and contraction is represented by the symbol ER. ｎ The initial resistance value (ER) of the conductive paste of the present invention is shown as ０ ) is preferably 10 Ω / cm or less, more preferably 5 Ω / cm or less.

[0072] The rate of change in electrical resistance after stretching can be evaluated by the number of continuous stretches and retractions until the resistance exceeds a specified value by repeatedly stretching and retracting the sample, or the percentage increase in resistance after a specified number of continuous stretching operations. Durability evaluation by stretching and retracting a sample can be performed mechanically. For example, in the case of a wire-like sample where resistance is an issue, one end of the wire in the sample is fixed, and the other end is reciprocated at a constant speed parallel to the sample (left and right if the sample is placed horizontally, or up and down if the sample is placed vertically) while measuring the resistance between the terminals. In this specification, the number of continuous stretches is evaluated as the number of stretches until the resistance reaches 100 Ω / cm when a conductive paste is applied to a substrate with a wire width of 0.4 mm and continuously stretched at an amplitude of 20% and 12 times per minute. The number of continuous stretches under the above conditions is preferably 100 or more, more preferably 110 or more, and even more preferably 120 or more.

[0073] In this specification, the rate of increase in resistance is the rate of change in resistance after 2000 stretches relative to the initial resistance (ER ２０００ / ER ０ The rate of change in resistance value under the above conditions is preferably 400 times or less, more preferably 300 times or less, even more preferably 250 times or less, and particularly preferably 200 times or less of the initial resistance value. If it is within this range, the period during which the resistance value after continuous stretching remains at a practical level is sufficiently long, and the conductive material can be said to have high resistance to continuous stretching.

[0074] As described above, electrodes formed using the conductive paste of this embodiment exhibit little change in electrical properties after expansion and contraction. The conductive paste of this embodiment has excellent stretchability and flexibility even when continuously expanded and contracted, and can be suitably used as a conductive paste capable of forming wiring that is less likely to break. Furthermore, the conductive paste of the present invention can be suitably used as a conductive expandable substrate together with a coating substrate. The coating substrate is not particularly limited, but examples include polyester elastomer sheets, polyurethane sheets, silicone sheets, and thermosetting elastomer sheets. A polyester elastomer sheet is preferred from the viewpoint of maintaining good wiring during expansion and contraction.

[0075] <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.

[0076] 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.

[0077] 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 minimal change in electrical properties on the surface of a stretchable and / or bendable substrate. Examples of articles that include such electronic components include wearable devices such as VR gloves and motion capture suits that generate electrical signals in response to the wearer's movements or contact with an object.

[0078] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0079] <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 outlines of the (A) conductive particles present in the SEM photograph or SEM image were approximated to a perfect circle, and the diameter of the perfect circle was measured. The arithmetic mean value of the diameters of 100 arbitrary (A) conductive particles was taken as the average particle diameter of the (A) conductive particles.

[0080] [Conductive particles (A)] Conductive metal particles A-1: ​​silver particles, tap density 2.22 g / ml, specific surface area (BET) 2.85 m ２ / g, average particle diameter 1.32 μm, particle shape is irregular (product number P903-2 manufactured by Metalor) Conductive metal particles A-2: silver particles, tap density 0.2 g / ml, specific surface area (BET) 4.26 m ２ / g, particle shape is foil (product number SF50S, manufactured by Ames Advanced Materials) Conductive metal particles A-3: silver particles, tap density 1.48 g / ml, specific surface area (BET) 2.95 m ２ / g, average particle diameter 3.47 μm, particle shape is irregular (product number P903-3 manufactured by Metalor) Conductive metal particles A-4: silver particles, tap density 0.73 g / ml, specific surface area (BET) 3.48 m ２ / g, average particle diameter 4.18 μm, particle shape is irregular (product number P903-1 manufactured by Metalor Co., Ltd.) Conductive metal particles A-5: silver particles, tap density 2.9 g / ml, specific surface area (BET) 1.33 m ２ / g, average particle diameter 1.96 μm, particle shape is scale-like (product number SF70A manufactured by Ames Advanced Materials) Conductive metal particles A-6: silver particles, tap density 2.4 g / ml, specific surface area (BET) 1.15 m ２ / g, average particle size 6.4 μm, particle shape is scale-like (product number AA-40719 manufactured by Metalor)

[0081] The thermoplastic resins used in the examples and comparative examples are as follows: [(B) Thermoplastic Resin] Resin B-1: Urethane resin, product number T-8195N (manufactured by DIC Covestro Polymer Co., Ltd., ether-based urethane resin)

[0082] In the examples and comparative examples, a 1:1:1 mixture of diethylene glycol diethyl ether, isophorone, and 3-methoxy-N,N-dimethylpropanamide (KJCMPA) was used as the solvent (C).

[0083] 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.

[0084] Next, the materials in the above-mentioned predetermined preparation ratios were mixed in a planetary mixer, and then dispersed in a three-roll mill to form a paste, thereby preparing a conductive paste. The components contained in the conductive paste of each Example and Comparative Example and the physical properties of the (A) conductive particles are summarized in Table 1. Note that the tap density of Examples 2 and 6 and Comparative Example 3 is a calculated value obtained by adding 0.1 to the weighted average value of the values ​​of each particle used, and the BET specific surface area is a weighted average value of the values ​​of each particle used.

[0085] (Physical property measurement method) [Viscosity] The viscosity of the conductive paste was measured using a Brookfield viscometer at a temperature of 25° C., with the spindle rotating 6 times over 10 revolutions. Unless otherwise specified, a #14 spindle was used.

[0086] [Specific Resistivity Value] The specific resistance value was measured by the following method. A wiring having a length of 60 mm and a width of 0.4 mm was formed on a PET (polyethylene terephthalate) substrate using a conductive paste, and the wiring was dried by heating at 120° C. for 30 minutes. Thereafter, the wiring length, wiring width, thickness, and wiring resistance were measured, and the paste specific resistance was calculated by dividing the wiring resistance×wire length (cm) by the wire width (cm)×thickness (cm).

[0087] [Resistance Change] A conductive paste was screen-printed onto a Toray Celanese Hytrel 3001 polyester elastomer sheet to form a 60 mm long, 0.4 mm wide wiring pattern. The pattern was then dried at 120°C for 30 minutes to obtain a sample for resistance measurement. The polyester sheet containing the wiring was stretched and flexed up to 2000 times using a Yuasa System Co., Ltd. DMLHP continuous stretch measuring instrument at 20% amplitude and 12 strokes per minute, while measuring the wiring resistance. The wiring resistance before stretching was defined as the initial wiring resistance, and the number of stretches and flexes at the time when the resistance reached 100 Ω / cm and the rate of change in the wiring resistance after 2000 stretches relative to the initial resistance were evaluated.

[0088]

[0089] <Measurement Results of Examples and Comparative Examples> The conductive paste of Comparative Example 1 uses silver particles with a high tap density. When used as wiring, the initial resistance was low and the conductivity was excellent. However, the resistance exceeded 100 Ω / cm after only 25 stretches and contractions, and the resistance reached infinity after 2,000 stretches, i.e., the wiring broke. The conductive paste of Comparative Example 2 uses silver particles with a tap density below the specified value but a small specific surface area. This paste also showed the same tendency as Comparative Example 1 when used as wiring, resulting in wiring breakage. The conductive paste of Comparative Example 3 uses conductive particles with a small specific surface area. Although no breakage occurred within the test conditions, the rate of increase in resistance was large, and practical durability against stretching could not be achieved. In contrast, in the example using particles with a low tap density and a large specific surface area, the initial resistance was slightly higher than that of the comparative example, but was still at a practically acceptable level, and maintained a resistance value of around 100 Ω / cm even after several hundred stretches and contractions. Furthermore, even after 2,000 stretches and contractions, the resistance remained low enough to be used as an electrode without breakage, demonstrating that the conductive paste is highly durable against stretching.

Claims

1. (A) The tap density measured in accordance with ISO 3953:2011 is 2.5 g / ml or less, and the specific surface area measured by the BET method is 2.5 m ２ / g or more; (B) a thermoplastic resin; and (C) a solvent.

2. The conductive paste according to claim 1, wherein component (A) contains irregular particles.

3. The conductive paste according to claim 1 or 2, wherein component (A) contains 40% by weight or more of amorphous particles relative to the total amount of conductive particles.

4. The conductive paste according to any one of claims 1 to 3, which has an initial resistance of 10 Ω / cm or less, and a resistance of 100 Ω / cm or less after being molded into a length of 60 mm and a width of 0.4 mm and subjected to 100 consecutive stretches at a 20% amplitude and 12 stretches per minute.

5. The conductive paste according to any one of claims 1 to 4, wherein when the paste is molded into a length of 60 mm and a width of 0.4 mm and continuously stretched and contracted at an amplitude of 20% and 12 times per minute, the rate of change in resistance after 2,000 stretches is 400 times or less relative to the initial resistance.

6. The conductive paste according to any one of claims 1 to 5, wherein the ratio of component (A) to the total of component (A) and component (B) is 80 to 99% by weight.

7. The conductive paste according to any one of claims 1 to 6, wherein (B) is a resin having oxygen atoms in the polymer main chain structure.

8. A conductive expandable substrate comprising the conductive paste according to any one of claims 1 to 7 and a coating substrate.

9. The conductive stretchable substrate according to claim 8, wherein the coating substrate is a polyester elastomer sheet.

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