Conductive paste and method for producing conductive paste

Abstract

A conductive paste according to the present invention comprises an elastomer composition, a conductive filler, and a nonaqueous solvent. The value of the particle gauge of the conductive paste, measured in accordance with JIS K 5600-2-5:1999, satisfies 40 µm or less.

Description

Conductive paste and method for producing the same

[0001] The present invention relates to a conductive paste and a method for producing the conductive paste.

[0002] Various developments have been made on conductive pastes. For example, a technique described in Patent Document 1 is known as a technique of this type. Paragraph 0015 of Patent Document 1 describes that the conductive paste is produced by adding a predetermined amount of flaky silver powder to a silicone resin, and optionally adding an organic solvent and kneading the resulting mixture.

[0003] Japanese Patent Application Laid-Open No. 2002-150837

[0004] However, as a result of investigations by the present inventors, it has been found that the conductive paste described in Patent Document 1 has room for improvement in terms of suppressing fluctuations in conductivity before and after expansion and contraction.

[0005] As a result of further investigation, the inventors discovered that by appropriately controlling the initial mixing conditions of the conductive filler and the elastomer composition, it is possible to suppress fluctuations in the conductivity of the produced conductive paste before and after expansion and contraction, and thus completed the present invention.

[0006] According to one aspect of the present invention, there are provided the following conductive paste and method for manufacturing the conductive paste.

[0007] 1. A conductive paste comprising an elastomer composition, a conductive filler, and a non-aqueous solvent, wherein the particle gauge value of the conductive paste measured in accordance with JIS K5600-2-5:1999 is 40 μm or less. 2. A conductive paste according to 1., wherein the particle gauge value of the conductive paste is 5 μm or more. 3. A conductive paste according to 1. or 2., wherein the viscosity of the conductive paste when measured at 25°C and a shear rate of 20 [1 / s] is 1 Pa·s or more and 100 Pa·s or less. 4. 1. to 3. 5. The conductive paste according to any one of items 1. to 4., wherein the thixotropy index calculated from η1 / η5, where η1 is the viscosity when measured at 25°C at a shear rate of 1 [1 / s] and η5 is the viscosity when measured at a shear rate of 5 [1 / s], is 1.0 or more and 3.0 or less. 5. The conductive paste according to any one of items 1. to 4., comprising a non-conductive filler. 6. The conductive paste according to any one of items 1. to 5., wherein the elastomer composition comprises a thermosetting elastomer composition for forming one or more elastomers selected from the group consisting of silicone rubber, urethane rubber, and fluororubber. 7. The conductive paste according to any one of items 1. to 6., wherein the non-aqueous solvent comprises a high-boiling-point non-aqueous solvent having a boiling point of 100°C or more and 250°C or less. 8. The conductive paste according to any one of items 1. to 7., wherein the non-aqueous solvent comprises a high-boiling-point non-aqueous solvent having a boiling point of 100°C or more and 250°C or less. 9. The conductive paste according to any one of 1. to 8., wherein the content of the conductive filler is 30% by mass or more and 85% by mass or less, based on 100% by mass of the conductive paste. 9. The conductive paste according to any one of 1. to 8., wherein the BET specific surface area of ​​the conductive filler is 0.1 m or less. ２ / g or more 5m ２ / g or less. 10. A method for producing a conductive paste, comprising a mixing step of stirring raw material components including an elastomer composition, a conductive filler, and a non-aqueous solvent in a stirring tank using stirring blades, and then kneading them using a planetary-revolution mixer to obtain a conductive paste. 11. A method for producing a conductive paste according to 10., wherein the conductive paste obtained in the mixing step has a particle gauge value of 40 μm or less, as measured in accordance with JIS K5600-2-5:1999. 12. A method for producing a conductive paste according to 10. or 11., wherein in the mixing step, the mixture of the elastomer composition and the non-aqueous solvent has a viscosity of 1 Pa·s or more and 100 Pa·s or less, as measured at 25°C and at a shear rate of 20 [1 / s]. 13. A method for producing a conductive paste according to 10. to 12. 14. The method for producing a conductive paste according to any one of 10. to 13., wherein the non-aqueous solvent contains a high-boiling-point non-aqueous solvent having a boiling point of 100°C or higher and 250°C or lower. 15. The method for producing a conductive paste according to any one of 10. to 13., wherein the BET specific surface area of ​​the conductive filler is 0.1 m ２ / g or more 5m ２ / g or less.

[0008] According to the present invention, a conductive paste that is excellent in suppressing fluctuations in conductivity before and after expansion and contraction, and a method for producing the same are provided.

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all drawings, similar components are designated by similar reference numerals, and descriptions thereof will be omitted where appropriate. Furthermore, the drawings are schematic diagrams and do not correspond to actual dimensional proportions.

[0010] An outline of the conductive paste of this embodiment will be described.

[0011] The conductive paste of this embodiment contains an elastomer composition, a conductive filler, and a non-aqueous solvent. This conductive paste satisfies the requirement that the particle gauge value measured in accordance with JIS K5600-2-5:1999 is 40 μm or less.

[0012] The inventors have discovered that the dispersibility of the conductive filler can be improved by performing appropriate stirring during the initial mixing of raw material components including an elastomer composition, a conductive filler, and a non-aqueous solvent. In other words, even when the specific gravity of the conductive filler is higher than that of the elastomer composition and the viscosity of the raw material components is relatively high, a decrease in the dispersibility of the conductive filler can be suppressed by appropriate stirring. The particle gauge value is an appropriate indicator of such dispersibility. While the detailed mechanism is unclear, it is believed that the conductive paste obtained by such stirring can suppress the occurrence of conductive filler separating from the elastomer composition and floating in the solvent, and therefore, the conductive member formed using the conductive paste exhibits characteristics that suppress fluctuations in conductivity before and after expansion and contraction.

[0013] The upper limit of the particle gauge value of the conductive paste is 40 μm or less, preferably 35 μm or less, and more preferably 30 μm or less. This makes it possible to minimize fluctuations in conductivity before and after expansion and contraction. On the other hand, the lower limit of the particle gauge value of the conductive paste is not particularly limited, but is, for example, 5 μm or more, preferably 10 μm or more, and more preferably 15 μm or more. This improves handleability. Also, it makes it possible to suppress an increase in resistance value after expansion and contraction.

[0014] The lower limit of the viscosity of the conductive paste when measured at a shear rate of 20 [1 / s] at room temperature 25°C is, for example, 1 Pa·s or more, preferably 5 Pa·s or more, and more preferably 10 Pa·s or more. This can improve film-forming properties. Also, shape retention can be improved even when forming a thick film. On the other hand, the upper limit of the viscosity of the conductive paste at room temperature 25°C is, for example, 100 Pa·s or less, preferably 90 Pa·s or less, and more preferably 80 Pa·s or less. This can improve the printability of the conductive paste.

[0015] In the conductive paste of this embodiment, the viscosity measured at room temperature 25°C at a shear rate of 1 [1 / s] is defined as η1, and the viscosity measured at a shear rate of 5 [1 / s] is defined as η5. The thixotropy index is calculated from the viscosity ratio (η1 / η5). The lower limit of the thixotropy index is, for example, 1.0 or more, preferably 1.1 or more, and more preferably 1.2 or more. This allows the shape of the wiring obtained by the printing method to be stably maintained. On the other hand, the upper limit of the thixotropy index is, for example, 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less. This allows the conductive paste to be easily printed.

[0016] The conductive paste of this embodiment has excellent applicability and film-forming properties on a substrate, and / or excellent printability such as screen printing.

[0017] The conductive paste of this embodiment can be used to form various conductive members such as electrodes, wiring, sensors, heating elements, and adhesives. That is, the cured product of the conductive paste can be used as an elastic conductive member for at least one of the various applications described above. Examples of electrodes include bioelectrodes and flexible sheet electrodes. Examples of wiring include elastic wiring. Examples of sensors include displacement sensors, pressure sensors, and flow rate sensors used as inner layer materials for tubes. Examples of heating elements include heaters used in devices, vehicles, medical instruments, and the like. Examples of adhesives include conductive adhesives used in electronic devices, etc. Note that this embodiment can provide a structure including such a conductive member.

[0018] The conductive paste of the present embodiment may contain silica particles in addition to the conductive filler, which can improve the mechanical strength and durability of the conductive member formed using the conductive paste.

[0019] Here, an example of a method for producing the conductive paste of this embodiment will be described.

[0020] The method for producing a conductive paste may include, for example, a mixing step in which raw material components including an elastomer composition, a conductive filler, and a non-aqueous solvent are stirred in a stirring tank using a stirring blade (stirring process), and then kneaded using a planetary mixer (kneading process) to obtain a conductive paste (mixture). The stirring process using a stirring blade can further improve the dispersibility of the conductive filler in the conductive paste. Furthermore, for stirring using a stirring blade, it is preferable to use a raw material component (mixture) including an elastomer composition and a non-aqueous solvent that has a viscosity of 1 Pa·s to 100 Pa·s. This allows for stable stirring operation even when stirring using a stirring blade that applies high shear force. Here, the viscosity is measured at 25°C and a shear rate of 20 [1 / s]. The raw material component (mixture) to be measured for viscosity does not necessarily contain a conductive filler.

[0021] The capacity of the stirring tank and the shape of the bottom of the stirring tank can be appropriately selected depending on the viscosity and volume of the raw material components, etc. The rotation speed and rotation time of the stirring blades can also be appropriately selected depending on the viscosity and volume of the raw material components, etc.

[0022] The stirring blade may be a stirring blade for low viscosity such as a propeller blade, a turbine blade, a paddle blade, or a three-bladed swept-back blade, or may be a stirring blade for high viscosity such as an anchor blade, a helical ribbon blade, etc. Among these, from the viewpoint of suppressing sedimentation of the conductive filler during stirring, a stirring blade that can stir the entire conductive paste evenly and efficiently is preferred.

[0023] In this embodiment, the particle gauge value can be controlled by appropriately selecting, for example, the type and amount of each component contained in the conductive paste, the method for preparing the conductive paste, etc. Among these, factors for setting the particle gauge value within a desired range include, for example, performing an appropriate stirring process using a stirring blade or the like, appropriately controlling the viscosity of the raw material components to be stirred, and the BET specific surface area of ​​the metal powder.

[0024] In the manufacturing method of this embodiment, it is preferable not to use a three-roll mill during the mixing step, as the evaporation of the solvent during the three-roll mill may cause an increase in the viscosity of the paste after rolling, and the drying on the three-roll mill may reduce the recovery rate, which may result in a decrease in manufacturing stability.

[0025] The manufacturing method of this embodiment may also include a filtration step in which the mixture obtained in the mixing step is subjected to a filtration process. The manufacturing method of this embodiment may also include a degassing step in which the mixture obtained in the kneading step is subjected to a degassing process. At least one or both of the filtration step and the degassing step may be performed. The order of performing these steps is not particularly limited, and the degassing step may be performed after the filtration step. Other known processes may also be performed.

[0026] The manufacturing method of this embodiment may also include an evaluation step of determining whether the mixture obtained in the mixing step satisfies predetermined conditions for one or more properties selected from the group consisting of viscosity, solid content, and gel time. This improves the manufacturing stability of the conductive paste. The evaluation step may be performed between the above steps, or after the final step.

[0027] Each component of the conductive paste will be described in detail below.

[0028] The conductive paste of this embodiment contains an elastomer composition, a conductive filler, and a non-aqueous solvent.

[0029] (Elastomer Composition) The elastomer composition may be silicone rubber, urethane rubber, fluororubber, nitrile rubber, acrylic rubber, styrene rubber, chloroprene rubber, ethylene propylene rubber, or the like. Among these, the elastomer is a composition for forming at least one elastomer selected from the group consisting of silicone rubber, urethane rubber, and fluororubber. Among these, the elastomer composition may be a thermosetting elastomer composition or a composition containing a thermoplastic elastomer, preferably a thermosetting elastomer composition, and more preferably a silicone rubber composition.

[0030] The silicone rubber composition is preferably, for example, a silicone rubber-based curable composition containing a silicone compound, a crosslinking agent, and a catalyst. Here, an example of the silicone rubber-based curable composition will be described. In this example of the silicone rubber-based curable composition, the silicone compound contains a vinyl group-containing organopolysiloxane (A), silica particles (C), and a silane coupling agent (D) as described below, the crosslinking agent contains an organohydrogenpolysiloxane (B), and the catalyst may contain platinum or a platinum compound (E).

[0031] The lower limit of the content of the elastomer composition or silicone rubber-based curable composition in the conductive paste is, for example, preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the conductive paste. Meanwhile, the upper limit of the content of the elastomer composition or silicone rubber-based curable composition in the conductive paste is, for example, preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on 100% by mass of the conductive paste. By ensuring that the content of the elastomer composition or silicone rubber-based curable composition is equal to or greater than the above lower limit, the elastomer in the conductive paste can have appropriate flexibility. Furthermore, by ensuring that the content of the elastomer composition or silicone rubber-based curable composition is equal to or less than the above upper limit, the mechanical strength of the elastomer can be improved.

[0032] The lower limit of the content of the conductive filler or metal powder (G) in the conductive paste is, for example, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on 100% by mass of the conductive paste. Meanwhile, the upper limit of the content of the conductive filler or metal powder (G) in the conductive paste is, for example, preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 65% ​​by mass or less, based on 100% by mass of the conductive paste. By setting the content of the conductive filler or metal powder (G) to the above lower limit or more, the elastomer of the conductive paste can have appropriate conductivity. Furthermore, by setting the content of the conductive filler or metal powder (G) to the above upper limit or less, the elastomer can have appropriate flexibility.

[0033] The conductive paste may contain a non-conductive filler such as silica particles (C) as needed. In this case, the lower limit of the content of silica particles (C) in the conductive paste is, for example, preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the conductive paste. On the other hand, the upper limit of the content of silica particles (C) in the conductive paste is, for example, preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the conductive paste. By setting the content of silica particles (C) or the non-conductive filler to the above-mentioned lower limit or more, the elastomer of the conductive paste can have appropriate mechanical strength. Furthermore, by setting the content of silica particles (C) or the non-conductive filler to the above-mentioned upper limit or less, the elastomer can have appropriate conductivity.

[0034] The lower limit of the content of the silica particles (C) in the conductive paste can be, for example, 1% by mass or more, preferably 3% by mass or more, and more preferably 5% by mass or more, based on 100% by mass of the total amount of the silica particles (C) and the conductive filler. This can improve the mechanical strength of the elastomer in the conductive paste. On the other hand, the upper limit of the content of the silica particles (C) in the conductive paste can be, for example, 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the total amount of the silica particles (C) and the conductive filler. This can achieve a balance between the elastic electrical properties and the mechanical strength of the elastomer in the conductive paste.

[0035] In the conductive paste, the lower limit of the content of the silane coupling agent (D) is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the total amount of the vinyl group-containing organopolysiloxane (A). On the other hand, the upper limit of the content of the silane coupling agent (D) is preferably 100% by mass or less, more preferably 80% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of the total amount of the vinyl group-containing organopolysiloxane (A). By setting the content of the silane coupling agent (D) in the conductive paste to the above-mentioned lower limit or more, the elastomer of the conductive paste has appropriate adhesion to the substrate, and when silica particles (C) are used, this can contribute to improving the mechanical strength of the elastomer as a whole. Furthermore, by setting the content of the silane coupling agent (D) to the above-mentioned upper limit or less, the elastomer can have appropriate mechanical properties.

[0036] The lower limit of the content of platinum or platinum compound (E) in the conductive paste is, for example, preferably 0.0001 mass% or more, more preferably 0.0002 mass% or more, and even more preferably 0.0003 mass% or more, based on 100 mass% of the conductive paste. On the other hand, the upper limit of the content of platinum or platinum compound (E) in the conductive paste is preferably 1 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less, based on the entire conductive paste. By setting the content of platinum or platinum compound (E) to the above lower limit or more, the conductive paste can be cured at an appropriate rate. Furthermore, setting the content of platinum or platinum compound (E) to the above upper limit or less can contribute to reducing the cost of producing the conductive paste.

[0037] <<Vinyl Group-Containing Organopolysiloxane (A)>> The silicone rubber-based curable composition may contain a vinyl group-containing organopolysiloxane (A). The vinyl group-containing organopolysiloxane (A) may be the main component of the silicone rubber-based curable composition.

[0038] The vinyl group-containing organopolysiloxane (A) can include a vinyl group-containing linear organopolysiloxane (A1) having a linear structure.

[0039] The vinyl group-containing linear organopolysiloxane (A1) has a linear structure and contains vinyl groups, and these vinyl groups become crosslinking points during curing.

[0040] The vinyl group content of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but preferably has two or more vinyl groups in the molecule and is 15 mol% or less, and more preferably 0.01 to 12 mol%. This optimizes the amount of vinyl groups in the vinyl group-containing linear organopolysiloxane (A1) and ensures the formation of networks with the components described below.

[0041] In this specification, the vinyl group content refers to the mol % of vinyl group-containing siloxane units when all units constituting the vinyl group-containing linear organopolysiloxane (A1) are taken as 100 mol %, where it is considered that there is one vinyl group per vinyl group-containing siloxane unit.

[0042] The degree of polymerization of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but is preferably within a range of, for example, about 1,000 to 10,000, and more preferably about 2,000 to 5,000. The degree of polymerization can be determined, for example, as the polystyrene-equivalent number average degree of polymerization (or number average molecular weight) measured by GPC (gel permeation chromatography) using chloroform as a developing solvent.

[0043] In this specification, unless otherwise specified, the range "to" indicates that the upper and lower limits are included.

[0044] Furthermore, the specific gravity of the vinyl group-containing linear organopolysiloxane (A1) is not particularly limited, but is preferably in the range of about 0.9 to 1.1.

[0045] By using a vinyl group-containing linear organopolysiloxane (A1) having a degree of polymerization and specific gravity within the above ranges, the heat resistance, flame retardancy, chemical stability, and other properties of the resulting silicone rubber can be improved.

[0046] As the vinyl group-containing linear organopolysiloxane (A1), those having a structure represented by the following formula (1) are particularly preferred.

[0047]

[0048] In formula (1), R １is a hydrocarbon group that is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or a combination thereof having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl groups, allyl groups, and butenyl groups, with vinyl groups being preferred. Examples of aryl groups having 1 to 10 carbon atoms include phenyl groups.

[0049] Also, R ２ is a hydrocarbon group that is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, or a combination thereof having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl groups, allyl groups, and butenyl groups. Examples of aryl groups having 1 to 10 carbon atoms include phenyl groups.

[0050] Also, R ３ is a substituted or unsubstituted alkyl group or aryl group having 1 to 8 carbon atoms, or a hydrocarbon group combining these. Examples of alkyl groups having 1 to 8 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of aryl groups having 1 to 8 carbon atoms include phenyl groups.

[0051] Furthermore, R in formula (1) １ and R ２ Examples of the substituent of R include a methyl group and a vinyl group. ３ Examples of the substituent include a methyl group.

[0052] In addition, in formula (1), a plurality of R １ are independent of each other and may be different from each other or may be the same. ２ , and R ３ The same is true for .

[0053] Furthermore, m and n are the numbers of repeating units constituting the vinyl group-containing linear organopolysiloxane (A1) represented by formula (1), where m is an integer of 0 to 2000 and n is an integer of 1000 to 10000. m is preferably 0 to 1000, and n is preferably 2000 to 5000.

[0054] Specific examples of the vinyl group-containing linear organopolysiloxane (A1) represented by formula (1) include those represented by the following formula (1-1):

[0055]

[0056] In formula (1-1), R １ and R ２ are each independently a methyl group or a vinyl group, and at least one of them is a vinyl group.

[0057] Furthermore, the vinyl group-containing linear organopolysiloxane (A1) preferably contains a first vinyl group-containing linear organopolysiloxane (A1-1) having two or more vinyl groups in the molecule and a vinyl group content of 0.4 mol% or less, and a second vinyl group-containing linear organopolysiloxane (A1-2) having a vinyl group content of 0.5 to 15 mol%. Combining a first vinyl group-containing linear organopolysiloxane (A1-1) with a vinyl group content typical of crude rubber, which is the raw material for silicone rubber, with a second vinyl group-containing linear organopolysiloxane (A1-2) with a high vinyl group content allows for uneven distribution of vinyl groups and more effectively creates a variation in crosslink density within the crosslinked network of the silicone rubber. As a result, the tear strength of the silicone rubber can be more effectively increased.

[0058] Specifically, the vinyl group-containing linear organopolysiloxane (A1) may be, for example, a vinyl group-containing linear organopolysiloxane represented by the above formula (1-1), １ is a vinyl group and / or R ２ a first vinyl group-containing linear organopolysiloxane (A1-1) having two or more units in the molecule in which R is a vinyl group and containing 0.4 mol% or less of the unit; １is a vinyl group and / or R ２ It is preferable to use a second vinyl group-containing linear organopolysiloxane (A1-2) containing 0.5 to 15 mol % of units in which each of the units is a vinyl group.

[0059] The first vinyl group-containing linear organopolysiloxane (A1-1) preferably has a vinyl group content of 0.01 to 0.2 mol %, and the second vinyl group-containing linear organopolysiloxane (A1-2) preferably has a vinyl group content of 0.8 to 12 mol %.

[0060] Furthermore, when the first vinyl group-containing linear organopolysiloxane (A1-1) and the second vinyl group-containing linear organopolysiloxane (A1-2) are combined and blended, the ratio of (A1-1) to (A1-2) is not particularly limited, but for example, the weight ratio of (A1-1):(A1-2) is preferably 50:50 to 95:5, and more preferably 80:20 to 90:10.

[0061] The first and second vinyl group-containing linear organopolysiloxanes (A1-1) and (A1-2) may each be used alone or in combination of two or more.

[0062] The vinyl group-containing organopolysiloxane (A) may also contain a vinyl group-containing branched organopolysiloxane (A2) having a branched structure.

[0063] <<Organohydrogenpolysiloxane (B)>> The silicone rubber-based curable composition may contain an organohydrogenpolysiloxane (B). The organohydrogenpolysiloxane (B) is classified into linear organohydrogenpolysiloxanes (B1) having a linear structure and branched organohydrogenpolysiloxanes (B2) having a branched structure, and the silicone rubber-based curable composition may contain either one or both of these.

[0064] The linear organohydrogenpolysiloxane (B1) has a linear structure and a structure in which hydrogen is directly bonded to Si (≡Si—H), and is a polymer that undergoes a hydrosilylation reaction with the vinyl groups of the vinyl group-containing organopolysiloxane (A) and with vinyl groups of components blended into the silicone rubber-based curable composition, thereby crosslinking these components.

[0065] The molecular weight of the linear organohydrogenpolysiloxane (B1) is not particularly limited, but for example, the weight average molecular weight is preferably 20,000 or less, and more preferably 1,000 or more and 10,000 or less.

[0066] The weight average molecular weight of the linear organohydrogenpolysiloxane (B1) can be measured, for example, by gel permeation chromatography (GPC) using chloroform as a developing solvent, in terms of polystyrene.

[0067] Furthermore, it is generally preferred that the linear organohydrogenpolysiloxane (B1) does not contain a vinyl group, which can reliably prevent the crosslinking reaction from proceeding within the molecule of the linear organohydrogenpolysiloxane (B1).

[0068] As the linear organohydrogenpolysiloxane (B1) described above, for example, one having a structure represented by the following formula (2) is preferably used.

[0069]

[0070] In formula (2), R ４ is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, a hydrocarbon group combining these, or a hydride group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl groups, allyl groups, and butenyl groups. Examples of aryl groups having 1 to 10 carbon atoms include phenyl groups.

[0071] Also, R ５is a substituted or unsubstituted alkyl group, alkenyl group, aryl group, a hydrocarbon group combining these, or a hydride group having 1 to 10 carbon atoms. Examples of alkyl groups having 1 to 10 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of alkenyl groups having 1 to 10 carbon atoms include vinyl groups, allyl groups, and butenyl groups. Examples of aryl groups having 1 to 10 carbon atoms include phenyl groups.

[0072] In addition, in formula (2), a plurality of R ４ are independent of each other and may be different from each other or may be the same. ５ The same applies to multiple R ４ and R ５ At least two of these are hydride groups.

[0073] Also, R ６ is a substituted or unsubstituted alkyl group or aryl group having 1 to 8 carbon atoms, or a hydrocarbon group combining these. Examples of alkyl groups having 1 to 8 carbon atoms include methyl groups, ethyl groups, and propyl groups, and among these, methyl groups are preferred. Examples of aryl groups having 1 to 8 carbon atoms include phenyl groups. ６ are independent of each other and may be different from each other or may be the same.

[0074] In addition, R in formula (2) ４ , R ５ , R ６ Examples of the substituent include a methyl group and a vinyl group, and a methyl group is preferred from the viewpoint of preventing intramolecular crosslinking reactions.

[0075] Furthermore, m and n are the numbers of repeating units constituting the linear organohydrogenpolysiloxane (B1) represented by formula (2), where m is an integer of 2 to 150 and n is an integer of 2 to 150. Preferably, m is an integer of 2 to 100 and n is an integer of 2 to 100.

[0076] The linear organohydrogenpolysiloxane (B1) may be used alone or in combination of two or more.

[0077] Because the branched organohydrogenpolysiloxane (B2) has a branched structure, it forms regions with high crosslink density and is a component that significantly contributes to the formation of a sparsely crosslinked structure in the silicone rubber system. Similarly to the linear organohydrogenpolysiloxane (B1), it has a structure in which hydrogen is directly bonded to Si (≡Si—H), and undergoes a hydrosilylation reaction with the vinyl groups of the vinyl group-containing organopolysiloxane (A) and with the vinyl groups of other components incorporated into the silicone rubber-based curable composition, forming a polymer that crosslinks these components.

[0078] The specific gravity of the branched organohydrogenpolysiloxane (B2) is in the range of 0.9 to 0.95.

[0079] Furthermore, it is generally preferred that the branched organohydrogenpolysiloxane (B2) does not contain a vinyl group, which can reliably prevent the crosslinking reaction from proceeding within the molecule of the branched organohydrogenpolysiloxane (B2).

[0080] The branched organohydrogenpolysiloxane (B2) is preferably one represented by the following average composition formula (c):

[0081] Average compositional formula (c) (H ａ (R ７ ) ３－ａ SiO １／２ ) ｍ (SiO ４／２ ) ｎ (In formula (c), R ７ is a monovalent organic group, a is an integer ranging from 1 to 3, and m is H ａ (R ７ ) ３－ａ SiO １／２ The number of units, n, is SiO ４／２ (number of units)

[0082] In formula (c), R ７is a monovalent organic group, preferably a substituted or unsubstituted alkyl group or aryl group having 1 to 10 carbon atoms, or a hydrocarbon group consisting of a combination thereof. Examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, and propyl groups, with methyl being preferred. Examples of aryl groups having 1 to 10 carbon atoms include phenyl groups.

[0083] In formula (c), a is the number of hydride groups (hydrogen atoms directly bonded to Si), and is an integer ranging from 1 to 3, preferably 1.

[0084] In addition, in formula (c), m is H ａ (R ７ ) ３－ａ SiO １／２ The number of units, n, is SiO ４／２ The number of units.

[0085] The branched organohydrogenpolysiloxane (B2) has a branched structure. The linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) differ in their structures, that is, whether they are linear or branched, and the number of alkyl groups R bonded to Si (R / Si), where the number of Si is 1, is in the range of 1.8 to 2.1 for the linear organohydrogenpolysiloxane (B1) and 0.8 to 1.7 for the branched organohydrogenpolysiloxane (B2).

[0086] Because the branched organohydrogenpolysiloxane (B2) has a branched structure, it leaves a residue amount of 5% or more when heated, for example, in a nitrogen atmosphere to 1,000° C. at a heating rate of 10° C. / min. In contrast, because the linear organohydrogenpolysiloxane (B1) is linear, it leaves a residue amount of almost zero after heating under the above conditions.

[0087] Specific examples of the branched organohydrogenpolysiloxane (B2) include those having a structure represented by the following formula (3).

[0088]

[0089] In formula (3), R ７is a substituted or unsubstituted alkyl group or aryl group having 1 to 8 carbon atoms, or a hydrocarbon group combining these, or a hydrogen atom. Examples of alkyl groups having 1 to 8 carbon atoms include methyl groups, ethyl groups, and propyl groups, with methyl groups being preferred. Examples of aryl groups having 1 to 8 carbon atoms include phenyl groups. R ７ Examples of the substituent include a methyl group.

[0090] In addition, in formula (3), a plurality of R ７ are independent of each other and may be different from each other or may be the same.

[0091] In addition, in formula (3), "-O-Si≡" indicates that Si has a branched structure that spreads three-dimensionally.

[0092] The branched organohydrogenpolysiloxane (B2) may be used alone or in combination of two or more.

[0093] Furthermore, the amount of hydrogen atoms (hydride groups) directly bonded to Si in the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) is not particularly limited. However, in the silicone rubber-based curable composition, the total amount of hydride groups in the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) is preferably 0.5 to 5 moles, more preferably 1 to 3.5 moles, per mole of vinyl groups in the vinyl group-containing linear organopolysiloxane (A1). This ensures the reliable formation of a crosslinked network between the linear organohydrogenpolysiloxane (B1) and the branched organohydrogenpolysiloxane (B2) and the vinyl group-containing linear organopolysiloxane (A1).

[0094] <<Silica Particles (C)>> The silicone rubber-based curable composition may contain silica particles (C) as a non-conductive filler, if necessary. The non-conductive filler is not limited to silica particles (C), and may contain other non-conductive fillers. This can improve the hardness and mechanical strength of the elastomer formed from the conductive paste. Known materials can be used as the non-conductive filler, but for example, silica particles, silicone rubber particles, talc, etc. may also be used. These may be used alone or in combination of two or more.

[0095] The silica particles (C) are not particularly limited, but examples thereof include fumed silica, calcined silica, precipitated silica, etc. These may be used alone or in combination of two or more.

[0096] The silica particles (C) have a specific surface area measured by the BET method of, for example, 50 to 400 m ２ / g, and 100 to 400m ２ / g, and more preferably 200 to 400m ２ The average primary particle size of the silica particles (C) is preferably, for example, 1 to 100 nm, and more preferably about 5 to 20 nm.

[0097] By using silica particles (C) having a specific surface area and average particle size within the above ranges, it is possible to improve the hardness and mechanical strength, particularly the tensile strength, of the silicone rubber formed.

[0098] <<Silane Coupling Agent (D)>> The silicone rubber-based curable composition may contain a silane coupling agent (D). The silane coupling agent (D) may have a hydrolyzable group. The hydrolyzable group is hydrolyzed by water to form a hydroxyl group, and this hydroxyl group undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of the silica particles (C), thereby modifying the surface of the silica particles (C).

[0099] Furthermore, this silane coupling agent (D) may contain a silane coupling agent having a hydrophobic group. This provides the surface of the silica particles (C), thereby reducing the cohesive force of the silica particles (C) in the silicone rubber-based curable composition, and ultimately in the silicone rubber (reducing aggregation due to hydrogen bonding through silanol groups). This is thought to result in improved dispersibility of the silica particles in the silicone rubber-based curable composition. This increases the interface between the silica particles and the rubber matrix, enhancing the reinforcing effect of the silica particles. Furthermore, it is thought that the slipperiness of the silica particles within the matrix improves during deformation of the rubber matrix. The improved dispersibility and slipperiness of the silica particles (C) improve the mechanical strength (e.g., tensile strength, tear strength, etc.) of the silicone rubber due to the silica particles (C).

[0100] Furthermore, the silane coupling agent (D) can contain a silane coupling agent having a vinyl group. This allows the vinyl group to be introduced onto the surface of the silica particles (C). Therefore, when the silicone rubber-based curable composition is cured, that is, when the vinyl group of the vinyl group-containing organopolysiloxane (A) and the hydride group of the organohydrogenpolysiloxane (B) undergo a hydrosilylation reaction to form a network (crosslinked structure), the vinyl group of the silica particles (C) also participates in the hydrosilylation reaction with the hydride group of the organohydrogenpolysiloxane (B), and the silica particles (C) are also incorporated into the network. This allows the formed silicone rubber to have a low hardness and a high modulus.

[0101] As the silane coupling agent (D), a silane coupling agent having a hydrophobic group and a silane coupling agent having a vinyl group can be used in combination.

[0102] Examples of the silane coupling agent (D) include those represented by the following formula (4).

[0103] Y ｎ -Si-(X) ４－ｎ...(4) In the above formula (4), n represents an integer of 1 to 3. Y represents a functional group having a hydrophobic group, a hydrophilic group, or a vinyl group, and when n is 1, it is a hydrophobic group, and when n is 2 or 3, at least one of the groups is a hydrophobic group. X represents a hydrolyzable group.

[0104] The hydrophobic group is an alkyl group having 1 to 6 carbon atoms, an aryl group, or a hydrocarbon group formed by combining these groups, such as a methyl group, an ethyl group, a propyl group, or a phenyl group, with a methyl group being particularly preferred.

[0105] Examples of the hydrophilic group include a hydroxyl group, a sulfonic acid group, a carboxyl group, and a carbonyl group, and among these, a hydroxyl group is particularly preferred. Although a hydrophilic group may be contained as a functional group, it is preferable that the hydrophilic group is not contained from the viewpoint of imparting hydrophobicity to the silane coupling agent (D).

[0106] Further, examples of the hydrolyzable group include an alkoxy group such as a methoxy group or an ethoxy group, a chloro group, or a silazane group. Among these, a silazane group is preferred because of its high reactivity with the silica particles (C). Note that, in the case of a compound having a silazane group as a hydrolyzable group, the (Y ｎ The resulting structure has two —Si— structures.

[0107] Specific examples of the silane coupling agent (D) represented by the above formula (4) include those having a hydrophobic group as a functional group, such as alkoxysilanes like methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, and decyltrimethoxysilane; chlorosilanes like methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and phenyltrichlorosilane; and hexamethyldisilazane. Examples of the vinyl group-containing silane include alkoxysilanes such as methacryloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropylmethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinylmethyldimethoxysilane; chlorosilanes such as vinyltrichlorosilane and vinylmethyldichlorosilane; and divinyltetramethyldisilazane. Among these, taking into consideration the above, hexamethyldisilazane is particularly preferred as the silane having a hydrophobic group, and divinyltetramethyldisilazane is particularly preferred as the silane having a vinyl group.

[0108] <<Platinum or Platinum Compound (E)>> The silicone rubber-based curable composition of this embodiment can contain platinum or a platinum compound (E). The platinum or platinum compound (E) is a catalytic component that acts as a catalyst during curing. The amount of platinum or platinum compound (E) added is a catalytic amount.

[0109] As the platinum or platinum compound (E), known substances can be used, such as platinum black, platinum supported on silica or carbon black, chloroplatinic acid or an alcohol solution of chloroplatinic acid, a complex salt of chloroplatinic acid and an olefin, a complex salt of chloroplatinic acid and a vinylsiloxane, etc. The platinum or platinum compound (E) may be used alone or in combination of two or more.

[0110] Alternatively, a catalyst other than component (E) may be used in place of or in combination with platinum or platinum compound (E). Examples of catalysts other than component (E) include organic peroxides such as ketone peroxides, diacyl peroxides, hydroperoxides, dialkyl peroxides, peroxyketals, alkyl peresters, peroxyesters, and peroxydicarbonates.

[0111] <<Water (F)>> The silicone rubber-based hardening composition of this embodiment may contain water (F) in addition to the above components (A) to (E).

[0112] Water (F) functions as a dispersion medium for dispersing the components contained in the silicone rubber-based curable composition, and is also a component that contributes to the reaction between the silica particles (C) and the silane coupling agent (D). Therefore, the silica particles (C) and the silane coupling agent (D) can be more reliably bonded to each other in the silicone rubber, and uniform properties can be exhibited overall.

[0113] <<Other Components>> Furthermore, the silicone rubber-based curable composition of this embodiment can further contain other components in addition to the above components (A) to (F). Examples of these other components include inorganic fillers other than the silica particles (C), such as diatomaceous earth, iron oxide, zinc oxide, titanium oxide, barium oxide, magnesium oxide, cerium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, glass wool, and mica, as well as additives such as reaction inhibitors, dispersants, pigments, dyes, antistatic agents, antioxidants, flame retardants, and thermal conductivity improvers. Examples of inorganic fillers other than the silica particles (C) include diatomaceous earth, iron oxide, zinc oxide, titanium oxide, barium oxide, magnesium oxide, cerium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, glass wool, and mica.

[0114] Here, an example of a method for producing a silicone rubber-based hardening composition will be described.

[0115] First, the components of the silicone rubber-based hardening composition are mixed uniformly using any kneading device to prepare the silicone rubber-based hardening composition.

[0116] [1] For example, predetermined amounts of vinyl group-containing organopolysiloxane (A), silica particles (C), and silane coupling agent (D) are weighed, and then kneaded using any kneading device to obtain a kneaded product containing these components (A), (C), and (D).

[0117] The kneaded mixture is preferably obtained by first kneading the vinyl group-containing organopolysiloxane (A) with the silane coupling agent (D) and then kneading the silica particles (C) in the mixture, which further improves the dispersibility of the silica particles (C) in the vinyl group-containing organopolysiloxane (A).

[0118] Furthermore, when obtaining this kneaded mixture, water (F) may be added to the kneaded mixture of the components (A), (C), and (D) as needed, thereby ensuring the reaction between the silane coupling agent (D) and the silica particles (C).

[0119] When water (F) is further contained, its content can be appropriately set, but specifically, for example, it is preferably in the range of 10 to 100 parts by weight, more preferably in the range of 30 to 70 parts by weight, relative to 100 parts by weight of the silane coupling agent (D), which allows the reaction between the silane coupling agent (D) and the silica particles (C) to proceed more reliably.

[0120] Furthermore, the kneading of components (A), (C), and (D) is preferably carried out through a first step in which the components are heated at a first temperature and a second step in which the components are heated at a second temperature. This allows the surfaces of the silica particles (C) to be surface-treated with the coupling agent (D) in the first step, and allows by-products generated by the reaction between the silica particles (C) and the coupling agent (D) to be reliably removed from the kneaded mixture in the second step. Thereafter, component (A) may be added to the resulting kneaded mixture, if necessary, and further kneaded. This improves the compatibility of the components in the kneaded mixture.

[0121] The first temperature is preferably, for example, about 40 to 120° C., and more preferably, for example, about 60 to 90° C. The second temperature is preferably, for example, about 130 to 210° C., and more preferably, for example, about 160 to 180° C.

[0122] The atmosphere in the first step is preferably an inert atmosphere such as a nitrogen atmosphere, and the atmosphere in the second step is preferably a reduced pressure atmosphere.

[0123] Furthermore, the time for the first step is, for example, preferably about 0.3 to 1.5 hours, more preferably about 0.5 to 1.2 hours, and the time for the second step is, for example, preferably about 0.7 to 3.0 hours, more preferably about 1.0 to 2.0 hours.

[0124] By setting the conditions for the first and second steps as described above, the above-mentioned effects can be more significantly obtained.

[0125] [2] Next, predetermined amounts of organohydrogenpolysiloxane (B) and platinum or a platinum compound (E) are weighed out, and then, using any kneading device, the components (B) and (E) are kneaded into the kneaded product prepared in the above step [1], thereby obtaining a silicone rubber-based curable composition (elastomer composition).

[0126] When components (B) and (E) are kneaded together, it is preferable to first knead the mixture prepared in step [1] with the organohydrogenpolysiloxane (B), and then knead the mixture prepared in step [1] with platinum or a platinum compound (E), and then knead these mixtures together. This ensures that components (A) to (E) are dispersed in the silicone rubber-based curable composition without promoting the reaction between the vinyl group-containing organopolysiloxane (A) and the organohydrogenpolysiloxane (B).

[0127] The temperature at which components (B) and (E) are kneaded is, for example, preferably about 10 to 70°C, more preferably about 25 to 30°C, as the roll setting temperature.

[0128] Furthermore, the kneading time is preferably, for example, about 5 minutes to 1 hour, and more preferably about 10 to 40 minutes.

[0129] In steps [1] and [2], by maintaining the temperature within the above range, it is possible to more effectively prevent or inhibit the progress of the reaction between the vinyl group-containing organopolysiloxane (A) and the organohydrogenpolysiloxane (B). Furthermore, by maintaining the kneading time within the above range in steps [1] and [2], it is possible to more reliably disperse the components (A) to (E) in the silicone rubber-based curable composition.

[0130] The kneading device used in each of steps [1] and [2] is not particularly limited, but for example, a kneader, a two-roll mill, a Banbury mixer (continuous kneader), a pressure kneader, etc. can be used.

[0131] Furthermore, in this step [2], a reaction inhibitor such as 1-ethynylcyclohexanol may be added to the kneaded mixture. This makes it possible to more effectively prevent or inhibit the progress of the reaction between the vinyl group-containing organopolysiloxane (A) and the organohydrogenpolysiloxane (B), even if the temperature of the kneaded mixture is set at a relatively high temperature. By the above step [2], a silicone rubber-based curable composition is obtained as an elastomer composition.

[0132] (Conductive Filler) The conductive filler may be a known conductive material, but may also contain, for example, one or more selected from the group consisting of powdery or fibrous metal-based fillers, carbon-based fillers (conductive carbon materials), metal oxide fillers, and metal-plated fillers. Among these, metal-based fillers may be used, or the following metal powder (G) may be used.

[0133] The metal constituting the metal powder (G) is not particularly limited, but may include, for example, at least one of copper, silver, gold, nickel, tin, lead, zinc, bismuth, antimony, or metal powders alloyed with these, or two or more of these. Among these, the metal powder (G) preferably contains silver or copper, i.e., silver powder or copper powder, due to its high conductivity and easy availability. Note that these metal powders (G) coated with other metals may also be used.

[0134] The shape of the metal powder (G) is not particularly limited, and conventionally used shapes such as dendritic, spherical, scale-like, etc. Among these, scale-like metal powder (G) may be used.

[0135] The lower limit of the particle size of the metal powder (G) or the flaky metal powder (G) is not particularly limited, but the average particle size D ５０ The particle size of the metal powder (G) or the flaky metal powder (G) is, for example, 0.001 μm or more, preferably 0.01 μm or more, more preferably 0.1 μm or more, and further preferably 1 μm or more. ５０ and is, for example, 1,000 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less. ５０ By setting the specific surface area of ​​the conductive filler or metal powder (G) in this range, the conductive paste can exhibit appropriate conductivity as an elastomer. ２ / g or more, preferably 0.5m ２ / g or more, more preferably 1.0m ２ On the other hand, the upper limit of the BET specific surface area of ​​the conductive filler or metal powder (G) is, for example, 5 m ２ / g or less, preferably 3 μm or less, more preferably 2 m ２ / g. This makes it possible to keep the paste viscosity low. The particle size of the metal powder (G) can be defined as the average particle size of 200 arbitrarily selected metal powder particles obtained by observing the conductive paste or its elastomer with a transmission electron microscope or the like and performing image analysis.

[0136] (Non-aqueous solvent) As the non-aqueous solvent, various known non-aqueous solvents can be used, including, for example, high-boiling point non-aqueous solvents. These may be used alone or in combination of two or more.

[0137] The lower limit of the boiling point of the high-boiling-point non-aqueous solvent is, for example, 100°C or higher, preferably 130°C or higher, and more preferably 150°C or higher. This can improve printing stability in screen printing and the like. On the other hand, the upper limit of the boiling point of the high-boiling-point non-aqueous solvent is not particularly limited, but may be, for example, 300°C or lower, 290°C or lower, or 280°C or lower. This can suppress excessive thermal history during wiring formation, thereby preventing damage to the base substrate and maintaining a good shape of the wiring formed from the conductive paste. Furthermore, the upper limit of the boiling point of the high-boiling-point non-aqueous solvent may be 250°C or lower, 240°C or lower, or 200°C or lower. This can suppress residual solvent in the cured product when the conductive paste is cured.

[0138] The non-aqueous solvent can be appropriately selected from the viewpoint of the solubility and boiling point of the elastomer composition, and may include, for example, an aliphatic hydrocarbon having 5 to 20 carbon atoms, preferably an aliphatic hydrocarbon having 8 to 18 carbon atoms, and more preferably an aliphatic hydrocarbon having 10 to 15 carbon atoms.

[0139] Examples of non-aqueous solvents include aliphatic hydrocarbons such as pentane, hexane, cyclohexane, heptane, methylcyclohexane, ethylcyclohexane, octane, decane, dodecane, and tetradecane; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene, mesitylene, trifluoromethylbenzene, and benzotrifluoride; diethyl ether, diisopropyl ether, dibutyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, and diethylene glycol. Examples of suitable solvents include ethers such as glycol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl-n-propyl ether, 1,4-dioxane, 1,3-dioxane, and tetrahydrofuran; haloalkanes such as dichloromethane, chloroform, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, and 1,1,2-trichloroethane; carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and esters such as diethyl carbonate. These may be used alone or in combination of two or more. The solvent used here may be appropriately selected from solvents that can uniformly dissolve or disperse the components of the conductive paste.

[0140] In addition, the polarity term (δ ｐ ) is, for example, 10 MPa １／２ is preferably 7 MPa or less １／２ More preferably, it is 5.5 MPa or less. １／２ The conductive paste may contain a first non-aqueous solvent having the following polarity term (δ ). This makes it possible to improve the dispersibility and solubility of an elastomer composition such as a silicone rubber-based curable resin composition in the conductive paste. ｐ The lower limit of the pressure is not particularly limited, but is, for example, 0 Pa. １／２ More than that is fine.

[0141] The hydrogen bond term (δ ｈ ) is, for example, 20 MPa １／２ is preferably 10 MPa or less １／２ More preferably, it is 7 MPa or less. １／２ This allows the dispersibility and solubility of an elastomer composition such as a silicone rubber-based curable resin composition to be improved in the conductive paste. ｈ The lower limit of the pressure is not particularly limited, but is, for example, 0 Pa. １／２ More than that is fine.

[0142] Hansen solubility parameter (HSP) is an index that indicates the solubility of a substance, i.e., how much a substance dissolves in another substance. HSP expresses solubility as a three-dimensional vector. This three-dimensional vector is typically expressed as a dispersion term (δ ｄ ), polar term (δ ｐ ), hydrogen bond term (δ ｈ ) and those with similar vectors can be judged to have high solubility. The similarity of the vectors can be judged by the distance of the Hansen solubility parameter (HSP distance).

[0143] The Hansen solubility parameter (HSP value) used in this specification can be calculated using software called HSPiP (Hansen Solubility Parameters in Practice). The computer software HSPiP, developed by Hansen and Abbott, includes a function for calculating HSP distances and a database listing the Hansen parameters for various resins and non-aqueous solvents or non-non-aqueous solvents. The solubility of each resin in pure non-aqueous solvents and in non-aqueous solvent mixtures of good and poor non-aqueous solvents is investigated, and the results are entered into the HSPiP software to calculate D: dispersion term, P: polar term, H: hydrogen bonding term, and R: solubility sphere radius.

[0144] As the non-aqueous solvent, for example, one can be selected in which the difference in HSP distance, polarity term, or hydrogen bond term between the elastomer or the structural units constituting the elastomer and the non-aqueous solvent is small.

[0145] The above describes embodiments of the present invention, but these are merely examples of the present invention, and various other configurations can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. are included within the scope of achieving the object of the present invention. Examples of reference embodiments are listed below. 1. A conductive paste comprising an elastomer composition, a conductive filler, and a non-aqueous solvent, wherein the degree of dispersion of the conductive paste measured using a particle gauge in accordance with JIS K5600-2-5:1999 is 40 μm or less. 2. The conductive paste according to 1., wherein the viscosity of the conductive paste measured at 25°C and a shear rate of 20 [1 / s] is 1 Pa·s or more and 100 Pa·s or less. 3. 1. or 2. The conductive paste according to any one of items 1. to 5., wherein the thixotropy index calculated from η1 / η5, where η1 is the viscosity when measured at 25°C at a shear rate of 1 [1 / s] and η5 is the viscosity when measured at a shear rate of 5 [1 / s], is 1.0 or more and 3.0 or less. 4. The conductive paste according to any one of items 1. to 3., comprising a non-conductive filler. 5. The conductive paste according to any one of items 1. to 4., wherein the elastomer composition comprises a thermosetting elastomer composition for forming one or more elastomers selected from the group consisting of silicone rubber, urethane rubber, and fluororubber. 6. The conductive paste according to any one of items 1. to 5., wherein the non-aqueous solvent comprises a high-boiling-point non-aqueous solvent having a boiling point of 100°C or more and 300°C or less. 7. The conductive paste according to any one of items 1. to 6. 7. The conductive paste according to any one of the above items, wherein the content of the conductive filler is 30% by mass or more and 85% by mass or less, based on 100% by mass of the conductive paste. 8. A method for producing a conductive paste, comprising a mixing step of stirring raw material components including an elastomer composition, a conductive filler, and a non-aqueous solvent in a stirring tank using stirring blades, and then kneading them using a planetary mixer to obtain a conductive paste.

[0146] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0147] <Elastomer Composition> A vinyl group-containing organopolysiloxane (A), a silane coupling agent (D), and water (F) were mixed in a predetermined ratio, and a predetermined amount of silica particles (C) was added and further mixed to obtain a silicone rubber compound. To the silicone rubber compound, predetermined amounts of an organohydrogenpolysiloxane (B) as a crosslinking agent, platinum or a platinum compound (E) as a catalyst, and a reaction inhibitor were added and mixed to obtain an elastomer composition (silicone rubber-based curable composition).

[0148] <Production of Conductive Paste> [Example 1] A predetermined amount of decane (non-aqueous solvent, boiling point 174°C) was added to the obtained elastomer composition and mixed to obtain a mixture. The viscosity of the mixture measured at 25°C and a shear rate of 20 [1 / s] using an E-type viscometer (TPE-100H, manufactured by Toki Sangyo Co., Ltd.) was 15 Pa s. Silver powder A (conductive filler, BET specific surface area: 1.5 m) was further added to the obtained mixture. ２ / g) was mixed, and then stirred using an anchor blade mixer (Three-One Motor (registered trademark), manufactured by Shinto Scientific Co., Ltd.) at a rotation speed of 15 rpm for 10 minutes. The mixture was then thoroughly kneaded using a planetary centrifugal mixer (Awatori Rentaro (registered trademark), manufactured by Thinky Corporation) to obtain the conductive paste of Example 1. [Example 2] A predetermined amount of tetradecane (a non-aqueous solvent, boiling point 253°C) was added to the obtained elastomer composition and mixed to obtain a mixture. The viscosity of the mixture was measured using an E-type viscometer (TPE-100H, manufactured by Toki Sangyo Co., Ltd.) under conditions of 25°C and a shear rate of 20 [1 / s], and was found to be 20 Pa s. Silver powder A (conductive filler, BET specific surface area: 1.5 m) was further added to the obtained mixture. ２ / g) was mixed, and then stirred using an anchor blade mixer (Three-One Motor (registered trademark), manufactured by Shinto Scientific Co., Ltd.) at a rotation speed of 15 rpm for 10 minutes. The mixture was then thoroughly kneaded using a planetary centrifugal mixer (Awatori Rentaro (registered trademark), manufactured by Thinky Corporation). Additional kneading was performed using a three-roll mill to obtain the conductive paste of Example 2. [Example 3] A predetermined amount of decane (a non-aqueous solvent, boiling point 174°C) was added to the obtained elastomer composition and mixed to obtain a mixture. The viscosity of the mixture measured using an E-type viscometer (TPE-100H, manufactured by Toki Sangyo Co., Ltd.) at 25°C and a shear rate of 20 [1 / s] was 12 Pa s. Silver powder B (conductive filler, BET specific surface area: 0.7 m) was further added to the obtained mixture. ２ / g) were mixed, and then stirred at 15 rpm for 10 minutes using a stirrer with anchor blades (Three-One Motor (registered trademark), manufactured by Shinto Scientific Co., Ltd.). Thereafter, the mixture was thoroughly kneaded using a planetary centrifugal mixer (Awatori Rentaro (registered trademark), manufactured by Thinky Corporation) to obtain a conductive paste of Example 3.

[0149] Comparative Example 1: The conductive paste of Comparative Example 1 was obtained in the same manner as in Example 1, except that the mixing and kneading were performed by hand without using the mixer or the planetary mixer. In Comparative Example 1, lumps were observed in the resulting conductive paste. These lumps are presumed to be derived from the elastomer composition. In Examples 1 to 3, the presence of such lumps was not confirmed in the mixture after mixing. Comparative Example 2: The same conditions as in Example 1 were used, except that the amount of decane added to the mixture was reduced to obtain a mixture with a viscosity of 130 Pa·s, to which silver powder A was then added and stirred with an anchor blade mixer. In Comparative Example 2, stirring was started using the anchor blade mixer, but the mixture became unable to be stirred midway through. The production process was terminated when stirring became impossible.

[0150] [Evaluation of Conductive Paste] The obtained conductive paste was evaluated according to the following items.

[0151] <Measuring the Grain Gauge Value> The grain gauge value of the resulting conductive paste was measured in accordance with JIS K5600-2-5:1999 as follows. First, a clean, dry grain gauge was placed on a smooth, horizontal, non-slip surface. Next, at room temperature of 25°C, the sample was thoroughly stirred using a spatula. A sufficient amount of sample (conductive paste) was then poured into the deeper end of the groove, allowing it to slightly overflow. Next, a scraper was held between the thumbs and fingers of both hands, with the long side of the scraper parallel to the width of the gauge and the cutting edge in contact with the deep end of the groove. While holding the scraper perpendicular to the surface of the gauge, it was dragged across the surface of the gauge at a uniform speed perpendicular to the long side of the groove over 1 to 2 seconds, down to a depth of 0. Sufficient force was applied to the scraper so that the groove was filled with the sample and the excess was removed. Within 3 seconds after the end of the pulling, the sample was observed by shining a light at a viewing angle of 20° to 30° relative to the surface of the gauge perpendicular to the long side of the groove so that the pattern of the sample was easily visible. In the above observation, the gauge scale was read at the position of the first speck that appeared among multiple specks that appeared in the groove, and this was taken as the grain gauge value (μm).

[0152] (Grain gauge used in the above measurements) Material: Stainless steel Dimensions: Length approx. 165 mm, width 35 mm, thickness 13 mm Grooves: 2, length approx. 125 mm, width 12 mm Maximum groove depth: 100 μm Scale interval: 10 μm Measurement range: 0 to 100 μm

[0153] (Scraper used in the above measurements) Material: Stainless steel Cutting edge: Both sides, long side is straight, R: approx. 0.25 Dimensions: approx. length 50 mm, approx. width 38 mm, approx. thickness 5 mm

[0154] The particle gauge values ​​were measured three times and the average values ​​were calculated. As a result, the particle gauge values ​​were 21 μm for Example 1, 8 μm for Example 2, 32 μm for Example 3, and over 40 μm for Comparative Example 1.

[0155] <Viscosity> The viscosity of the obtained conductive paste was measured at 25°C and a shear rate of 20 [1 / s] immediately after preparation using a TPE-100H (E-type viscometer) manufactured by Toki Sangyo Co., Ltd. The unit of viscosity is Pa s. In Example 1, the viscosity at 25°C was 20 Pa s.

[0156] <Thixotropy Index> The obtained conductive paste was measured immediately after preparation using a TPE-100H (E-type viscometer) manufactured by Toki Sangyo Co., Ltd., with the viscosity measured at 25°C at a shear rate of 1 [1 / s] as η1 and the viscosity measured at a shear rate of 5 [1 / s] as η5. The unit of viscosity is Pa s. The thixotropy index was calculated from the η1 / η5 viscosity ratio. In Example 1, the thixotropy index was 1.7.

[0157] <Measurement of Resistance Values ​​Before and After Stretching> The resulting elastomer composition was cured at 170°C for 120 minutes and molded into a sheet. A silicone rubber substrate measuring 5 cm wide, 500 μm high, and 5 cm long was then fabricated. Subsequently, a rectangular wiring pattern was drawn on the resulting substrate using the resulting conductive paste. This was cured at 170°C for 120 minutes to form a wiring pattern measuring 30 mm wide, 30 mm long, and 70 μm thick. The rectangular wiring pattern was stretched 50% diagonally and then released from the stretched state, a stretching operation repeated 100 times. The resistance of the unstretched diagonal wiring pattern was measured before and immediately after the 100th stretching operation. In Example 1, the resistance value before the stretching operation was 0.4Ω and the resistance value after the stretching operation was 0.6Ω, in Example 2, the resistance value before the stretching operation was 0.3Ω and the resistance value after the stretching operation was 0.5Ω, in Example 3, the resistance value before the stretching operation was 0.4Ω and the resistance value after the stretching operation was 0.7Ω, and in Comparative Example 1, the resistance value before the stretching operation was 3.2Ω and the resistance value after the stretching operation was 27Ω. [Reference Example 1] A polymer having a primary particle diameter of 0.4 μm (a BET specific surface area of ​​4 m ２A conductive paste of Reference Example 1 was obtained having a particle gauge value of 3 μm, except that silver powder C (at a concentration of 1 / g) was used. It was confirmed that the resistance value of Reference Example 1 after the stretching operation, measured according to the above <Measurement of resistance value before and after stretching>, was lower than that of Comparative Example 1, but higher than that of Examples 1 to 3.

[0158] The conductive pastes of Examples 1 to 3 showed results in which the difference between the initial resistance value and the resistance value after the stretching operation was smaller than that of Comparative Example 1. It was found that the conductive pastes of such Examples were able to suppress fluctuations in conductivity before and after stretching.

[0159] The conductive pastes of Examples 1' to 3' were obtained using the same raw material components and mixing and kneading conditions as in Examples 1 to 3, except that the elastomer composition, silver powder, and non-aqueous solvent content in the non-aqueous solvent were the same. The resulting pastes of Examples 1' to 3' were cured at 170°C for 120 minutes, and the degree of residual solvent in the resulting cured products was evaluated. It was confirmed that the conductive pastes of Examples 1' and 3' had a lower degree of residual solvent in the cured product than the conductive paste of Example 2', which used a non-aqueous solvent with a boiling point above 250°C.

[0160] This application claims priority based on Japanese Patent Application No. 2023-144192, filed September 6, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A conductive paste comprising an elastomer composition, a conductive filler, and a non-aqueous solvent, wherein the conductive paste has a grain gauge value of 40 μm or less as measured in accordance with JIS K5600-2-5:1999.

2. The conductive paste according to claim 1, wherein the grain gauge value of the conductive paste is 5 μm or more.

3. A conductive paste according to claim 1 or 2, wherein the viscosity of the conductive paste when measured at 25°C and at a shear rate of 20 [1 / s] is 1 Pa·s or more and 100 Pa·s or less.

4. A conductive paste according to any one of claims 1 to 3, in which the thixotropic index calculated by η1 / η5, where η1 is the viscosity measured at 25°C at a shear rate of 1 [1 / s] and η5 is the viscosity measured at a shear rate of 5 [1 / s], is 1.0 or more and 3.0 or less.

5. The conductive paste according to any one of claims 1 to 4, which contains a non-conductive filler.

6. The conductive paste according to any one of claims 1 to 5, wherein the elastomer composition comprises a thermosetting elastomer composition for forming one or more elastomers selected from the group consisting of silicone rubber, urethane rubber, and fluororubber.

7. A conductive paste according to any one of claims 1 to 6, wherein the non-aqueous solvent contains a high-boiling-point non-aqueous solvent having a boiling point of 100°C or higher and 250°C or lower.

8. A conductive paste according to any one of claims 1 to 7, wherein the content of the conductive filler is 30% by mass or more and 85% by mass or less in 100% by mass of the conductive paste.

9. The conductive paste according to any one of claims 1 to 8, wherein the BET specific surface area of ​​the conductive filler is 0.1 m ２ / g or more 5m ２ / g or less.

10. A method for producing a conductive paste, comprising a mixing step of stirring raw material components including an elastomer composition, a conductive filler, and a non-aqueous solvent in a stirring tank using a stirring blade, and then kneading the components using a planetary centrifugal mixer to obtain a conductive paste.

11. A method for producing a conductive paste according to claim 10, wherein the conductive paste obtained in the mixing step has a grain gauge value of 40 μm or less as measured in accordance with JIS K5600-2-5:1999.

12. A method for producing a conductive paste according to claim 10 or 11, wherein in the mixing step, the mixture of the elastomer composition and the non-aqueous solvent has a viscosity of 1 Pa·s or more and 100 Pa·s or less when measured at 25°C and a shear rate of 20 [1 / s].

13. A method for producing a conductive paste according to any one of claims 10 to 12, wherein the non-aqueous solvent contains a high-boiling point non-aqueous solvent having a boiling point of 100°C or higher and 250°C or lower.

14. The method for producing a conductive paste according to any one of claims 10 to 13, wherein the BET specific surface area of ​​the conductive filler is 0.1 m ２ / g or more 5m ２ / g or less.

Images