Conductive composition and composite using the same

Abstract

To provide a conductive composition which comprises an addition-curable silicone rubber and silver powder, and can form a conductive film having improved elasticity.SOLUTION: Disclosed is a conductive composition comprising electrolytic silver powder and an addition-curable silicone rubber. Here, when a fill factor of the electrolytic silver powder, obtained by dividing a tap density (g / cm3) of the electrolytic silver powder by a real density of the electrolytic silver powder (g / cm3) and by multiplying the quotient by 100, is denoted by X (volume %) and a ratio of a volume of the electrolytic silver powder relative to a total volume of the volume of the electrolytic silver powder and a volume of the silicone rubber is denoted by Y (volume %), the following formula is satisfied: 1.5≤(Y / X)≤4.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrically conductive composition and a composite using the same. [Background technology]

[0002] In recent years, efficiency improvements have been made in fields such as manufacturing and nursing care through the automation and mechanization of work. Accordingly, research into robots and wearable power assist devices has accelerated. Biomimetic driving materials, such as artificial muscles and actuators, used in these applications require the formation of wiring or conductive circuits (conductive films) on a stretchable substrate using conductive compositions to transmit electrical signals for driving. The conductive film must be stretchable enough to maintain its conductivity even when the biomimetic driving material is repeatedly stretched and contracted.

[0003] Prior art documents related to stretchable conductive films include Patent Documents 1 to 3. For example, Patent Document 1 discloses a conductive paste containing an elastomer, a conductive filler, and a solvent, which is used to form wiring that constitutes a stretchable wiring board. Patent Document 1 describes that the conductivity of the wiring can be maintained even after the stretchable wiring board is repeatedly stretched and contracted by 20% in the length direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-110093 [Patent Document 2] International Publication No. 2017 / 217509 [Patent Document 3] International Publication No. 2017 / 026420 Summary of the Invention [Problem to be solved by the invention]

[0005] However, biomimetic actuation materials may require even higher levels of stretchability, such as a conductive film that can maintain conductivity even when stretched to twice its original length (200%) and then returned to its original length (100%), and preferably with only a small increase in resistance after stretching.

[0006] Furthermore, for example, when the conductive paste used to form the conductive film contains an elastomer, silicone rubber or the like is used as the elastomer. Among silicone rubbers, addition-curing silicone rubbers, which cure by heat treatment at relatively low temperatures (e.g., below 100°C), are preferred from the perspective of suppressing damage to biomimetic actuator materials due to heat. However, a platinum-based catalyst is required to cure addition-curing silicone rubber, and such platinum-based catalysts can inhibit the curing of various materials, which presents a challenge. In particular, when silver powder synthesized by a liquid-phase method is used as the conductive filler, it is known that the platinum-based catalyst significantly inhibits curing, making film curing difficult.

[0007] The present invention has been made in view of the above circumstances, and its main object is to provide a conductive composition that contains addition-curing silicone rubber and silver powder and that can form a conductive film with improved elasticity. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a conductive composition containing electrolytic silver powder and an addition-curing silicone rubber. The conductive composition disclosed herein has a tap density (g / cm) of the electrolytic silver powder. 3 ) to the true density (g / cm 3 ) and multiplying by 100, the filling rate of the electrolytic silver powder is defined as X (vol %), and the ratio of the volume of the electrolytic silver powder to the total volume of the electrolytic silver powder and the silicone rubber is defined as Y (vol %), and the following formula is used: 1.5≦(Y / X)≦4.0 The present invention is characterized in that:

[0009] As described above, the conductive composition disclosed herein is characterized by containing electrolytic silver powder as the silver powder. Generally, silver powder synthesized by a liquid-phase method or the like is used, but such silver powder may contain amine components derived from the synthesis reagent. Furthermore, when such silver powder is used in combination with addition-curing silicone rubber, there is a problem that the added platinum-based catalyst is poisoned by the amine components, resulting in insufficient progress in film curing. In contrast, using electrolytic silver powder obtained by electrolytically refining crude silver metal in an electrolyte solution is preferable because it can suppress curing inhibition by the platinum-based catalyst. Furthermore, when the ratio (Y / X) satisfies the above-mentioned range, a conductive film having both electrical conductivity and excellent elasticity can be formed.

[0010] In a preferred embodiment disclosed herein, the volume ratio (Y) of the electrolytic silver powder is 10% by volume or more and 40% by volume or less, which allows the conductive film to have a good balance between electrical conductivity and elasticity.

[0011] In a preferred embodiment disclosed herein, the tap density of the electrolytic silver powder is 1.5 g / cm 3 This allows the silicone rubber to easily enter the gaps in the electrolytic silver powder, making it possible to more suitably improve the stretchability of the conductive film.

[0012] In a preferred embodiment disclosed herein, the packing ratio (X) of the electrolytic silver powder is 5% by volume or more and 15% by volume or less. When the packing ratio is a predetermined value or more, the electrolytic silver particles in the conductive film are more likely to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved. When the packing ratio is a predetermined value or less, the silicone rubber can easily enter the pores of the electrolytic silver powder, and the stretchability of the conductive film can be more suitably improved.

[0013] In a preferred embodiment disclosed herein, the conductive composition contains an organic solvent and is prepared in a paste form, which can improve the handleability of the conductive composition and the workability during the formation of a conductive film.

[0014] In a preferred embodiment disclosed herein, the organic solvent has a solubility parameter (SP value) of 6 (cal / cm 3 ) 0.5 More than 8(cal / cm 3 ) 0.5 The following compounds are included: This enhances compatibility with silicone rubber, making it possible to stably prepare a homogeneous paste.

[0015] The present invention also provides a composite comprising a substrate and a conductive film formed on the substrate and comprising a dried body of the conductive composition according to any one of claims 1 to 6.

[0016] In a preferred embodiment disclosed herein, the conductive film has a volume resistivity of 1 Ω·cm or less, thereby achieving a conductive film with excellent electrical conductivity.

[0017] In a preferred embodiment disclosed herein, when the composite is stretched to twice its original length and then returned to its original length, the increase in volume resistivity of the conductive film is 10% or less, thereby realizing a conductive film with excellent stretchability. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view schematically illustrating a wiring substrate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the technology disclosed herein are described below. It should be noted that matters other than those specifically mentioned in this specification (e.g., the configuration of the conductive composition) that are necessary for carrying out the present invention (e.g., the method for preparing the conductive composition and the method for using the conductive composition) can be carried out based on the technical content taught in this specification and the general technical common sense of a person skilled in the art. The present invention can be carried out based on the content disclosed in this specification and the general technical common sense of a person skilled in the art. In this specification, the expression "A to B (A and B are arbitrary values)" indicating a numerical range means not only A or more but also B or less, and also includes the meanings "preferably greater than A" and "preferably smaller than B."

[0020] <Conductive composition> The conductive composition disclosed herein contains, as its main components, (A) electrolytic silver powder and (B) addition-cure silicone rubber. The conductive composition typically contains (C) an organic solvent and can be prepared in a paste form (including a slurry form and an ink form; the same applies below). The conductive composition may further contain (D) other optional components. The conductive composition can be prepared, for example, by dispersing or dissolving (A) electrolytic silver powder, (B) addition-cure silicone rubber, and (D) other optional components in (C) the organic solvent.

[0021] The conductive composition disclosed herein can be used to form a conductive film. In this specification, the term "conductive film" refers to a film-like body (dried product) obtained by drying the conductive composition at a temperature lower than the heat resistance temperature (i.e., the maximum temperature at which it can be used) of the addition-curing silicone rubber (B), typically 200°C or lower, for example 150°C or lower, or even 120°C or lower, and preferably 100°C or lower. Each of the constituent components will be explained below in order.

[0022] <(A) Electrolytic silver powder> The conductive composition disclosed herein contains electrolytic silver powder. In this specification, "electrolytic silver powder" refers to silver powder obtained, for example, by electrolytically refining crude silver metal in an electrolyte solution (i.e., an electrolytic method). Unlike silver powder obtained by a liquid-phase method, silver powder obtained by an electrolytic method is less likely to contain substances that poison platinum catalysts, such as amine components, and is therefore preferably used in the technology disclosed herein.

[0023] The properties of the particles constituting the electrolytic silver powder (hereinafter also referred to as "electrolytic silver particles"), such as size and shape, are not particularly limited as long as they satisfy the ratio (Y / X) described below. The size of the electrolytic silver particles can be appropriately selected depending on, for example, the application of the conductive composition and the dimensions of the conductive film to be formed. The size of the electrolytic silver particles may be selected so as to fit within the minimum dimensions of the conductive film, such as its thickness and / or width. Although not particularly limited, the average particle size (D50) of the electrolytic silver particles may be approximately 0.1 μm or more, preferably 0.5 μm or more, for example, 1 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more. When the average particle size is a predetermined value or more, the addition-cure silicone rubber (B) can easily penetrate into the gaps in the electrolytic silver powder. This enhances the adhesion between the electrolytic silver powder and the addition-cure silicone rubber, thereby more suitably improving the elasticity of the conductive film. The average particle size (D50) of the electrolytic silver particles may be approximately 50 μm or less, for example, 30 μm or less, 20 μm or less, or 10 μm or less. When the average particle size is a predetermined value or less, the electrolytic silver particles tend to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved.

[0024] In this specification, the term "average particle size (D50)" refers to the particle size corresponding to the cumulative 50% from the fine particle side (50% volume average particle size) in the volume-based particle size distribution measured by laser diffraction / light scattering.

[0025] The shape of the electrolytic silver particles may be, for example, dendritic (dendrite-like), acicular (including spindle-like and cylindrical), scaly (flake-like), approximately spherical, irregular, etc. Although not particularly limited, the electrolytic silver particles may have a shape with an average aspect ratio (major axis / minor axis ratio) of 2 or more, or even 3 or more, such as dendritic or acicular. This allows for the formation of a conductive network in the direction of expansion and contraction of the conductive film, thereby improving electrical conductivity. Among these, dendritic shapes are preferred.

[0026] In this specification, "aspect ratio" refers to the ratio (b / a) of the long side length (b) to the short side length (a) of a particle when a rectangle circumscribing the observed image of electrolytic silver particles is drawn using an electron microscope. The average aspect ratio refers to the arithmetic mean value of the aspect ratios of multiple particles (e.g., 100 particles). In addition, in this specification, "dendritic" refers to a shape in which multiple branches extend two-dimensionally or three-dimensionally from the longest main axis when electrolytic silver particles are observed using an electron microscope.

[0027] The electrolytic silver particles may be in the form of an agglomerated powder, which is a three-dimensional aggregation of multiple electrolytic silver particles (primary particles). The primary particles may be approximately spherical or irregular in shape. In the agglomerated powder, the primary particles are in physical contact with each other, which allows for the formation of a conductive network in the direction of expansion and contraction of the conductive film, thereby improving electrical conductivity. Furthermore, agglomerated or dendritic electrolytic silver particles are relatively bulky and have a lower tap density than, for example, approximately spherical electrolytic silver particles, which allows the (B) addition-cure silicone rubber to easily penetrate into the gaps between the electrolytic silver powder. This increases the adhesion between the electrolytic silver powder and the addition-cure silicone rubber, thereby more effectively improving the expansion and contraction of the conductive film.

[0028] Although not particularly limited, the tap density of the electrolytic silver powder is preferably 1.5 g / cm 3 or less, more preferably 1.4 g / cm 3 or less, more preferably 1.35 g / cm 3 For example, 1.0 g / cm 3 ~1.35g / cm3 When the tap density is equal to or less than a predetermined value, the (B) addition-cure silicone rubber can easily penetrate into the gaps in the electrolytic silver powder. This increases the adhesion between the electrolytic silver powder and the addition-cure silicone rubber, and the elasticity of the conductive film can be more suitably improved. The tap density of the electrolytic silver powder is approximately 0.1 g / cm. 3 or more, preferably 0.2 g / cm 3 More preferably, 0.5 g / cm 3 or more, for example, 0.5 g / cm 3 ~1.0g / cm 3 , 0.6g / cm 3 ~0.7g / cm 3 When the tap density is equal to or greater than a predetermined value, the electrolytic silver powder particles are more likely to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved. The tap density of the electrolytic silver powder can be adjusted, for example, by pulverizing or classifying the electrolytic silver powder.

[0029] In this specification, "tap density" refers to the apparent density (bulk density) after electrolytic silver powder is placed in a specified container and tapped 1000 times to apply a compressive force due to inertia. The tap density can be measured in accordance with "Metal powder - Tap density measurement method" specified in JIS Z2512:2012.

[0030] Although not particularly limited, the packing ratio X of the electrolytic silver powder, expressed by the following formula: (tap density / true density) × 100, can be generally 3 vol% or more, preferably 4 vol% or more, 5 vol% or more, or 5.5 vol% or more. The true density means the value obtained by dividing the mass of the electrolytic silver powder by the volume of the electrolytic silver powder itself, excluding the interior of the electrolytic silver particles and the voids between the electrolytic silver particles. The true density of silver is 10.5 g / cm. 3As mentioned above, tap density refers to the bulk density after application of a compressive force due to inertia. Therefore, the larger the value of the filling rate X, the fewer voids there are. When the filling rate X is a predetermined value or higher, the electrolytic silver particles in the conductive film are more likely to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved. The filling rate X can be set to approximately 30% by volume or less, preferably 20% by volume or less, 15% by volume or less, or 13% by volume or less. When the filling rate X is a predetermined value or less, the addition-cure silicone rubber (B) can easily penetrate into the voids in the electrolytic silver powder. This increases the adhesion between the electrolytic silver powder and the addition-cure silicone rubber, and more suitably improves the stretchability of the conductive film.

[0031] Although not particularly limited, when the total volume of the (A) electrolytic silver powder and the (B) addition-cure silicone rubber is taken as 100% by volume, the volume ratio Y of the electrolytic silver powder can be approximately 5% by volume or more, preferably 10% by volume or more, or 12% by volume or more. When the volume ratio is a predetermined value or more, electrolytic silver particles in the conductive film tend to come into contact with each other, thereby more suitably improving the electrical conductivity of the conductive film. The volume ratio Y is typically smaller than that of the (B) addition-cure silicone rubber, and can be approximately less than 50% by volume, preferably 45% by volume or less, 40% by volume or less, or 36% by volume or less. When the volume ratio is a predetermined value or less, the (B) addition-cure silicone rubber tends to penetrate into the gaps between the electrolytic silver powder. This enhances adhesion between the electrolytic silver powder and the addition-cure silicone rubber, more suitably improving the elasticity of the conductive film. The volume of the electrolytic silver powder can be determined by dividing the mass of the electrolytic silver powder by its true density, and the volume of the addition-curing silicone rubber can be determined by dividing the mass of the addition-curing silicone rubber by its density.

[0032] In this embodiment, the filling rate X of the electrolytic silver powder and the volume ratio Y satisfy the following formula: 1.5≦(Y / X)≦4.0. By setting the ratio (Y / X) to a predetermined value or less, excellent elasticity can be imparted to the conductive film. Furthermore, by setting the ratio (Y / X) to a predetermined value or more, electrical conductivity can be imparted to the conductive film. From the viewpoint of improving the electrical conductivity of the conductive film, the ratio (Y / X) can be preferably 1.7 or more, 2.0 or more, or 2.1 or more. Furthermore, the ratio (Y / X) can be preferably 3.8 or less, 3.0 or less, or 2.8 or less. The ratio (Y / X) can be, for example, 1.7 to 3.8.

[0033] <(B) Addition-curing silicone rubber> The conductive composition disclosed herein includes an addition-curing silicone rubber. Silicone rubber is a component that imparts flexibility and stretchability to the conductive film and is an organic compound containing silicon (Si). The addition-curing silicone rubber may be a heat-addition-curing silicone rubber in which the curing reaction proceeds by heating, or a room-temperature addition-curing silicone rubber in which the curing reaction proceeds at room temperature (e.g., 20±5°C). The addition-curing silicone rubber may be a liquid silicone rubber that is fluid at room temperature (e.g., 20±5°C) and under normal pressure.

[0034] The addition-curing silicone rubber is not particularly limited, and one type alone or two or more types in appropriate combination can be used from among conventionally known types depending on, for example, the application of the conductive composition. The addition-curing silicone rubber can be, for example, an organopolysiloxane having at least one alkenyl group bonded to a silicon atom in the molecule represented by the following average composition formula (I): R a SiO (4-a) / 2 (I) Here, R in the above formula (I) represents the same or different unsubstituted or substituted monovalent hydrocarbon groups, and can be, for example, hydrocarbon groups having 1 to 20 carbon atoms, or even 1 to 10 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; alkenyl groups such as vinyl, allyl, and propenyl; aryl groups such as cycloalkenyl, phenyl, and tolyl; and aralkyl groups such as benzyl and 2-phenylethyl. Alternatively, examples include groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as fluorine, chlorine, and bromine atoms, or cyano groups. Among these, methyl, vinyl, phenyl, and trifluoropropyl groups are preferred, with methyl and vinyl being particularly preferred. Furthermore, a in the above formula (I) can be a positive number of 1.95 to 2.05.

[0035] As an addition-curing type silicone rubber, for example, a diorganosiloxane unit (RSiO) constituting the main chain of an organopolysiloxane is used. 2 / 2 Preferably, the repeating structure of the formula (R is the same as above, hereinafter) is composed solely of repeating dimethylsiloxane units. Also preferably, diorganosiloxane units such as methylvinylsiloxane units, methylphenylsiloxane units, diphenylsiloxane units, and methyl-3,3,3-trifluoropropylsiloxane units are introduced into a dimethylpolysiloxane structure composed of repeating dimethylsiloxane units that constitute the main chain.

[0036] Both ends of the molecular chain may be triorganosiloxy groups (RSiO) such as trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy groups, divinylmethylsiloxy groups, and trivinylsiloxy groups. 1 / 2 ) and the like. In addition, hydroxydiorganosiloxy groups such as hydroxydimethylsiloxy groups (R(HO)SiO 1 / 2 ) or the like.

[0037] The density of addition-curing silicone rubber is generally 0.5 to 2 g / cm 3 , preferably 1.0±0.3 g / cm 3 , e.g., 1.0±0.2g / cm 3 This allows the effects of the technology disclosed herein to be achieved at a higher level. The density of addition-curing silicone rubber is a value specific to the substance, and values ​​listed in various publicly known documents, dictionaries, manufacturer product catalogs, etc., can be used. Alternatively, the density can be measured by, for example, the liquid-phase displacement method (pycnometer method) in accordance with JIS K0061:2001, "Method for measuring density and specific gravity of chemical products."

[0038] Although not particularly limited, the hardness of addition-curing silicone rubber is generally 35 degrees or less, preferably 30 degrees or less. By setting the hardness to a predetermined value or less, the flexibility of the conductive film can be increased, and the stretchability of the conductive film can be more suitably improved. In this specification, the "hardness of addition-curing silicone rubber" refers to the hardness measured using a Type A durometer (rubber hardness tester). The hardness of addition-curing silicone rubber can be measured in accordance with JIS K6253-3:2012, "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness."

[0039] Although not particularly limited, the elongation at break of addition-curable silicone rubber is generally 200% or more, preferably 250% or more, for example, 300% or more. By increasing the elongation at break to a predetermined value or more, the flexibility of the conductive film can be increased, thereby more suitably improving the stretchability of the conductive film. In this specification, the term "elongation at break of addition-curable silicone rubber" refers to the elongation at break of a specific test specimen prepared and pulled using a tensile tester. The elongation at break is expressed as a percentage (%) of the initial length of the test specimen. Specifically, it is expressed by the following formula: {(test specimen length at break L1 - initial test specimen length L0) / initial test specimen length L0} × 100 (%). The elongation at break of addition-curable silicone rubber can be measured in accordance with JIS K6251:2010, "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties."

[0040] The conductive composition may be primarily composed of addition-curable silicone rubber (a component accounting for 50% or more by volume) on a volume basis. While not particularly limited, when the total volume of the (A) electrolytic silver powder and the (B) addition-curable silicone rubber is taken as 100% by volume, the volume ratio of the addition-curable silicone rubber is typically greater than that of the (A) electrolytic silver powder, and may be approximately 50% or more by volume, preferably 60% or more by volume, 65% or more by volume, or for example, 70% or more by volume. When the volume ratio is greater than or equal to a predetermined value, the elasticity of the conductive film can be more suitably improved. The volume ratio of the addition-curable silicone rubber may be approximately 95% or less by volume, preferably 90% or less by volume, for example, 85% or less by volume. When the volume ratio is less than or equal to a predetermined value, electrolytic silver particles in the conductive film are more likely to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved.

[0041] Although not particularly limited, when the entire conductive composition is taken as 100% by mass, the mass ratio of the addition-curing silicone rubber may be approximately 5% by mass or more, typically 7% by mass or more, for example, 10% by mass or more, 15% by mass or more. When the mass ratio is a predetermined value or more, the elasticity of the conductive film can be more suitably improved. The mass ratio of the silicone rubber may be approximately 50% by mass or less, typically 40% by mass or less, 35% by mass or less, for example, 30% by mass or less. When the mass ratio is a predetermined value or less, electrolytic silver particles in the conductive film are more likely to come into contact with each other, and the electrical conductivity of the conductive film can be more suitably improved.

[0042] In addition, a curing agent (catalyst, crosslinking agent, etc.) may be used in the curing reaction of addition-curing silicone rubber. The catalyst may be one that is conventionally known as a catalyst for addition-reaction-curing silicone rubber compositions. Examples of such catalysts include platinum group metal catalysts (e.g., platinum group metals and their compounds). The amount of catalyst added may be within a range that contributes to accelerating the addition reaction (e.g., a catalytic amount). The crosslinking agent may be any of those conventionally known as crosslinking agents for addition reaction curing silicone rubber compositions. Examples of such crosslinking agents include organohydrogenpolysiloxanes (1,1,3,3-tetramethyldisiloxane, methylhydrogencyclopolysiloxane, methylhydrogenpolysiloxanes capped at both ends with trimethylsiloxy groups, and dimethylpolysiloxanes capped at both ends with dimethylhydrogensiloxy groups). The amount of crosslinking agent added is not limited thereto, but is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.3 to 10 parts by mass, per 100 parts by mass of the organopolysiloxane.

[0043] In addition to the above catalysts, an addition crosslinking inhibitor may be used to adjust the curing rate, such as ethynylcyclohexanol or tetramethyltetravinylcyclotetrasiloxane.

[0044] <(C) Organic Solvent> The organic solvent is an optional component that dissolves or disperses the solid components of the conductive composition, mainly (A) electrolytic silver powder and (B) addition-cure silicone rubber, to adjust the fluidity of the conductive composition. Adjusting the fluidity of the conductive composition can improve the handleability of the conductive composition and the workability when forming a conductive film.

[0045] The organic solvent is not particularly limited, and one type alone or two or more types in appropriate combination can be used from among conventionally known organic solvents, depending on, for example, the application of the conductive composition and the type of substrate on which the conductive film is formed. Examples of organic solvents include hydrocarbon solvents, ether solvents, ester solvents, glycol solvents, glycol ether solvents, glycol ester solvents, and alcohol solvents. Examples of hydrocarbon solvents include aliphatic hydrocarbons such as N-pentane, N-hexane, cyclohexane, N-heptane, N-nonane, N-octane, N-decane, N-undecane, N-dodecane, tridecane, tetradecane, kerosene, petroleum hydrocarbons, naphtha, dipentene, and turpentine oil, and aromatic hydrocarbons such as benzene, toluene, and xylene. The organic solvent may be a nonpolar solvent. Among these, from the viewpoint of improving the storage stability of the conductive composition and the handleability during conductive film formation, organic solvents that are less likely to volatilize and less flammable (e.g., having a flash point of 40°C or higher) are preferred.

[0046] Although not particularly limited, the solubility parameter (SP value) of the organic solvent is generally 4 (cal / cm 3 ) 0.5 Typically, 5 (cal / cm 3 ) 0.5 More than 6 (cal / cm 3 ) 0.5 For example, 6.5 (cal / cm 3 ) 0.5 The solubility parameter of the organic solvent may be approximately 10 (cal / cm 3 ) 0.5 Typically, 9 (cal / cm 3 ) 0.5 Preferably, 8 (cal / cm3 ) 0.5 or less. The SP value is a value that serves as a measure of the "ease of mixing" between the solid content of the conductive composition and the organic solvent. According to the inventor's studies, by setting the solubility parameter of the organic solvent within the above range, compatibility with (B) addition-curing silicone rubber can be improved, and a homogeneous paste can be stably prepared. In addition, the range (variation) of applicable substrates can be expanded.

[0047] In this specification, the term "solubility parameter (SP)" refers to the solubility parameter calculated by the so-called Fedors method, which is described in R.F. Fedors, Polymer Engineering Science, 14, p. 147 (1974). The solubility parameter is a value specific to each compound. The SI unit of the SP value is (J / cm 3 ) 0.5 or (MPa) 0.5 However, in this specification, the conventionally used term (cal / cm 3 ) 0.5 The unit of the SP value is expressed by the following formula: 1 (cal / cm 3 ) 0.5 ≒2.05(J / cm 3 ) 0.5 ≒2.05 (MPa) 0.5 ; can be converted.

[0048] When the conductive composition contains an organic solvent, the amount of the organic solvent can be adjusted appropriately to a level that allows the solid content to be uniformly dissolved or dispersed and to provide a viscosity suitable for forming a conductive film. For example, when the entire conductive composition is taken as 100% by mass, the mass ratio of the organic solvent may be approximately 5% by mass or more, typically 7% by mass or more, for example, 10% by mass or more, or 15% by mass or more. The mass ratio of the organic solvent may be approximately 50% by mass or less, typically 40% by mass or less, 35% by mass or less, for example, 30% by mass or less. Minimizing the amount of solvent allows for the formation of a dense conductive film, and at least one of the electrical conductivity and elasticity of the conductive film can be more suitably improved.

[0049] <(D) Other optional ingredients> In addition to the above-described components, the conductive composition may further contain various optional components as needed, as long as the effects of the technology disclosed herein are not significantly impaired. The optional components may be selected from conventionally known components used in general conductive compositions, and may be used singly or in appropriate combinations of two or more. Examples of optional components include dispersants, thickeners, surfactants, antifoaming agents, plasticizers, stabilizers, antioxidants, pH adjusters, preservatives, cure accelerators, cure retarders, organic binders, and (B) binder components other than addition-curing silicone rubber (e.g., various elastomers). Among these, a dispersant is preferable. The conductive composition may also contain (A) conductive powders other than electrolytic silver powder (e.g., noble metals such as platinum (Pt), gold (Au), and palladium (Pd); base metals such as nickel (Ni), aluminum (Al), and copper (Cu); carbonaceous materials such as carbon black; and mixtures or alloys thereof), either singly or in appropriate combinations of two or more.

[0050] The dispersant is a component that suppresses aggregation of (A) electrolytic silver powder and improves the dispersion stability of the conductive composition. In this specification, the term "dispersant" refers to any amphiphilic compound having a hydrophilic moiety and a lipophilic moiety, and includes surfactants, wetting dispersants, and emulsifiers. As the dispersant, one type may be used alone or two or more types may be used in appropriate combination from among conventionally known dispersants. Examples include carboxylic acid-based dispersants having carboxyl groups, phosphoric acid-based dispersants having phosphonic acid groups, sulfonic acid-based dispersants having sulfonic acid groups, and amine-based dispersants having amino groups. From the viewpoint of enhancing affinity with (B) addition-curing silicone rubber and / or (C) organic solvents, acid value dispersants having an acid value are preferred.

[0051] When the conductive composition contains optional components, the dispersant may be present in an amount of approximately 0.01 to 1 part by mass, for example, 0.1 to 0.5 parts by mass, relative to 100 parts by mass of (A) electrolytic silver powder, which satisfies the above ratio (Y / X) and effectively suppresses aggregation of the conductive powder.

[0052] When the conductive composition contains optional components, the amount of the optional components is typically less than the amounts of (A) electrolytic silver powder, (B) addition-cure silicone rubber, and (C) organic solvent. For example, when the entire conductive composition is taken as 100% by mass, the mass ratio of the optional components (e.g., dispersant) may be approximately 5% by mass or less, typically 3% by mass or less, 2% by mass or less, 1% by mass or less, for example, 0.5% by mass or less. Furthermore, when the total of (A) electrolytic silver powder, (B) addition-cure silicone rubber, and (D) other optional components is taken as 100% by mass, the total amount of (A) electrolytic silver powder and (B) addition-cure silicone rubber may be approximately 80% by mass or more, typically 90% by mass or more, 95% by mass or more, for example, 98% by mass or more, 99% by mass or more, or 99.5% by mass or more. Minimizing the amount of optional components can more effectively improve at least one of the electrical conductivity and elasticity of the conductive film.

[0053] <Method of using the conductive composition> The conductive composition can be preferably used for forming wiring or conductive circuits, joining or mounting various electronic components, connecting circuits, adhering various components together, etc. In one use example, a stretchable substrate is first prepared. However, the substrate does not necessarily have to be stretchable. Examples of stretchable substrates include substrates made of rubber or elastomers such as silicone rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber, styrene rubber, chloroprene rubber, ethylene rubber, propylene rubber, ethylene propylene rubber, and natural rubber.

[0054] Next, the conductive composition is applied to the substrate to a desired thickness (e.g., 0.01 to 10 mm, 0.1 to 1 μm). The application (typically coating) of the conductive composition can be carried out using, for example, screen printing, gravure printing, a bar coater, a doctor blade, a slit coater, a gravure coater, a dip coater, a spray coater, a dispenser, or the like.

[0055] Next, the conductive composition applied to the substrate is dried. From the viewpoint of preventing damage to the substrate, it is preferable to set the drying temperature sufficiently lower than the heat resistance temperature of the substrate. Furthermore, from the viewpoint of promoting curing and improving work efficiency, drying by heating may be performed as appropriate. When a substrate with low heat resistance is used, the upper limit of the heating temperature should be approximately 200°C or less, preferably 150°C or less, and more preferably 100°C or less. Furthermore, the drying time should typically be about 1 hour to several days (for example, about 1 to 5 days). This results in the formation of a conductive film on the substrate. Furthermore, components with boiling points lower than the above heating temperature, such as (C) the organic solvent and (D) other optional components, can be vaporized and removed from the conductive film.

[0056] FIG. 1 is a cross-sectional view of a wiring board 10. The wiring board referred to here includes circuit boards, printed circuit boards, and the like. The wiring board 10 includes a substrate 12 and a conductive film 14 formed on (e.g., on) the substrate 12. The conductive film 14 is composed of a dried form of the conductive composition disclosed herein. The conductive film 14 is formed in a predetermined circuit pattern on the substrate 12 according to a predetermined design drawing. The conductive film 14 may be formed on only one side of the substrate 12 as shown in FIG. 1, or on both sides of the substrate 12. The conductive film 14 may be formed on only a portion of the substrate 12, or may be formed over the entire surface of the substrate 12.

[0057] Conductive film 14 is primarily composed of (A) electrolytic silver powder and (B) addition-cure silicone rubber. When the entire solid content of conductive film 14 is taken as 100% by volume, the total of (A) electrolytic silver powder and (B) addition-cure silicone rubber is generally 80% by volume or more, typically 90% by volume or more, 95% by volume or more, for example, 98% by volume or more, 99% by volume or more, 99.5% by volume or more, or may be substantially 100% by volume.

[0058] Considering practical levels, the initial volume resistivity of the conductive film 14 should be approximately 5 Ω·cm or less, for example, 2 Ω·cm or less, preferably 1 Ω·cm or less, 0.5 Ω·cm or less, or even 0.2 Ω·cm or less. Furthermore, when the wiring board 10 is stretched in the longitudinal direction to twice its original length (200%) and then returned to its original length (100%), the rate of increase in the volume resistivity of the conductive film 14 should be approximately 100% or less, for example, 50% or less, preferably 10% or less, or even 5% or less.

[0059] <Applications of conductive compositions> The conductive composition disclosed herein has excellent electrical conductivity and elasticity, and can therefore be suitably used in biomimetic driving materials such as artificial muscles and actuators, actuators and sensors for various electronic devices (e.g., pressure sensors, impact sensors, vibration sensors, etc.), wearable devices, robotic devices, power assist devices, power generation devices, shock absorbing materials, vibration damping materials, etc.

[0060] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those examples.

[0061] [Preparation of conductive composition] First, the silver powders shown in Tables 1 to 4, addition-curing silicone rubber, organic solvents, and dispersants were prepared.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] Next, the prepared silver powder, silicone rubber, organic solvent, and dispersant were mixed in the masses shown in Tables 5 and 6 for each example, and the mixture was uniformly stirred using a vacuum-equipped stirring and degassing device (Mazerustar KK-VT300, manufactured by Kurabo Industries, Ltd.). Thus, conductive compositions (Examples 1 to 15) were prepared. Tables 5 and 6 also show the volume ratio Y of the silver powder, the packing rate X, and the ratio (Y / X) along with the mass. The volume of the silver powder was determined by multiplying the mass by the true density (10.5 g / cm). 3 ) was calculated by dividing by

[0067] [Preparation of test specimens] Next, the conductive composition was applied to the surface of a silicon nitride substrate (size: length 35 mm x width 35 mm x thickness 0.32 mm) by screen printing using a metal mask (opening size: 10 mm x 10 mm, thickness: 0.12 mm). Next, the silicon nitride substrate with the conductive composition was heated and dried for 1 hour on a hot plate at 100°C. This cured the silicone rubber to form a conductive film on the silicon nitride substrate, and a test specimen (hereinafter also referred to as "test specimen 1") for each example was produced. In addition, in the same manner as in test piece 1, a conductive film was formed on a silicone rubber substrate (size: length 40 mm x width 40 mm x thickness 1 mm, hardness: 30 degrees), thereby producing a test piece for each example (hereinafter also referred to as "test piece 2").

[0068] [Evaluation of test specimens] The test pieces prepared above were evaluated for the following items (1) to (5). The evaluation results are shown in the corresponding columns of Tables 5 and 6. (1) Film curing "Good": A conductive film was formed, and the conductive film was not deformed or sticky when touched. "X": A conductive film could not be formed, and the conductive film was deformed or sticky when touched.

[0069] (2) Volume resistivity and conductivity The volume resistivity of the conductive film of test piece 1 was measured by a four-probe method using a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., model: Loresta GP MCP-T610). Note that "OL" indicates that the upper limit of measurement was exceeded, and "-" indicates that the measurement was not yet performed. The conductivity is represented by the following symbols. "Good": The volume resistivity was 1 Ω·cm or less. "×": Volume resistivity exceeded 1 Ω·cm.

[0070] (3)Stretchability Test piece 2 was attached to a tensile tester and stretched laterally to twice its length (200%), and then returned to its original length (100%). The state of the conductive film after stretching was then visually confirmed. In addition, the volume resistivity was measured before and after stretching in the same manner as in (2) above, and the increase rate of volume resistivity was calculated using the following formula: {(volume resistivity after stretching - volume resistivity before stretching) / volume resistivity before stretching} × 100. The stretchability is represented by the following symbols. Note that "-" indicates that the measurement was not performed. "Good": No cracks were generated in the conductive film after stretching, and the increase in volume resistivity after stretching was 10% or less. "X": Cracks occurred in the conductive film after stretching, or the increase in volume resistivity after stretching exceeded 10%.

[0071] (4) Possibility of reusing the conductive composition The reusability of the conductive compositions according to Examples 1 to 15 was investigated. Specifically, in the preparation of the test pieces in (1) above, after printing was performed using the conductive composition according to each Example, it was confirmed whether or not the remaining conductive composition could be recovered and reused. The reusability is indicated by the following symbols. Note that "-" indicates that the measurement was not performed. "◯": The conductive composition was not hardened and was in a state where it could be used again for printing.

[0072] (5) Overall evaluation "Good": Conductivity and stretchability (and reusability) were both "good." "×": Conductivity and / or stretchability were "×".

[0073] [Table 5]

[0074] [Table 6]

[0075] In Example 1, where the ratio (Y / X) was greater than 4.0, and in Examples 5 and 6, where the ratio (Y / X) was less than 1.5, the overall evaluation was "x". Specifically, in Example 1, although electrical conductivity of the conductive film was obtained, it could not withstand stretching to twice its length (200%), and the conductive network was broken, failing to meet the stretchability standard. Furthermore, in Examples 5 and 6, the volume resistivity was out of range, and conductivity could not even be achieved. Furthermore, in Examples 9 and 10, which used dendritic silver, although the ratio (Y / X) was within the range of 1.5 to 4.0, the stretchability and conductivity items were both "x", and therefore the overall evaluation was "x".

[0076] In contrast to these examples (i.e., Examples 1, 5, 6, 9, and 10), Examples 2 to 4, 7, 8, and 11 to 15, which used dendritic electrolytic silver and had the ratio (Y / X) of 1.5 or more and 4.0 or less, had a volume resistivity of 1 Ω cm or less and an elasticity of 200%, satisfying the criteria for conductivity and elasticity. It was also confirmed that these materials could be reused. These results support the technical significance of the invention disclosed herein.

[0077] Although not intended to be particularly restrictive, the present inventors believe that one of the reasons why a conductive film having both conductivity and stretchability can be formed by satisfying the above ratio (Y / X) is as follows: The above filling rate X and the above volume ratio Y are both the volume fraction of electrolytic silver powder. To obtain sufficient stretchability, it is necessary to ensure a certain volume ratio of addition-curing silicone rubber in the solid components (the total of electrolytic silver powder and addition-curing silicone rubber) in the conductive film. To achieve this, it is necessary to suppress the filling rate X of the electrolytic silver powder. If the volume ratio Y is too large relative to the filling rate X, the electrolytic silver powder will be excessive in the conductive film, and although conductivity is possible, it can be assumed that the film strength is insufficient and it cannot withstand stretching. Conversely, if the volume ratio Y is too small relative to the filling rate X, the volume fraction of electrolytic silver powder will be small, making it difficult to achieve conductivity. Therefore, it can be considered that balancing the above ratio (Y / X) is necessary to form a conductive film having both conductivity and stretchability.

[0078] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0079] 10. Wiring board 12 PCB 14 Conductive film

Claims

1. A conductive composition comprising electrolytic silver powder and an addition-curing silicone rubber, The tap density (g / cm ３ ) to the true density (g / cm ３ ) and multiplying the result by 100 to obtain a packing rate of the electrolytic silver powder, where X (volume%) is the packing rate of the electrolytic silver powder. When the ratio of the volume of the electrolytic silver powder to the total volume of the electrolytic silver powder and the silicone rubber is Y (vol %), the following formula is satisfied: 1.5≦(Y / X)≦4.0 A conductive composition characterized by satisfying the above.

2. The conductive composition according to claim 1, wherein the volume ratio (Y) of the electrolytic silver powder is 10% by volume or more and 40% by volume or less.

3. The tap density of the electrolytic silver powder is 1.5 g / cm ３ 3. The conductive composition according to claim 1, wherein:

4. The conductive composition according to any one of claims 1 to 3, wherein the filling rate (X) of the electrolytic silver powder is 5% by volume or more and 15% by volume or less.

5. The conductive composition according to claim 1 , which contains an organic solvent and is prepared in the form of a paste.

6. The organic solvent has a solubility parameter (SP value) of 6 (cal / cm ３ ) ０．５ Above 8 (cal / cm ３ ) ０．５ 6. The conductive composition of claim 5, comprising the following compound:

7. A substrate; a conductive film formed on the substrate and comprising a dried body of the conductive composition according to any one of claims 1 to 6; A complex with.

8. 8. The composite according to claim 7, wherein the conductive film has a volume resistivity of 1 Ω·cm or less.

9. 9. The composite according to claim 7, wherein when the composite is stretched to twice its original length and then returned to its original length, the increase in volume resistivity of the conductive film is 10% or less.

Images