Conductive ink composition and conductive film

Abstract

To provide a conductive ink composition having good thin line printability and surface smoothness after printing, and capable of forming a conductive film which is stretchable and excellent in conductivity after stretching.SOLUTION: A (meth) acrylic polymer (A) and silver particles (B), wherein the (meth) acrylic polymer (A) includes a first (meth) acrylic polymer (a- 1) and a second (meth) acrylic polymer (a- 2), the first (meth) acrylic polymer (a- 1) has a glass transition temperature of 0 °C or lower and a weight average molecular weight of 500,000 or more, the second (meth) acrylic polymer (a- 2) has a glass transition temperature of 0 °C or lower and a weight average molecular weight of less than 500,000, and the surface of the silver particles (B) is coated with a fatty acid containing oleic acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive ink composition and a conductive film using the conductive ink composition. [Background technology]

[0002] In recent years, printed electronics (PE), in which electronic circuits are formed using conductive inks by printing methods such as screen printing, has been attracting attention in the field of electronic device manufacturing. By using PE, for example, it is possible to manufacture flexible devices by forming electronic circuits on thin substrates.

[0003] Patent Document 1 proposes a conductive ink for screen printing. Screen printing is a type of stencil printing in which ink is piled up on a screen and then pressed with a squeegee or the like so that the ink passes through the open mesh of the screen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-246498 Summary of the Invention [Problem to be solved by the invention]

[0005] Ink compositions used in printing fine wiring patterns by methods such as screen printing are required to have the fine line printability to form fine lines known as lines and spaces (L / S) as designed, and surface smoothness to ensure that the surface of the coating film after printing is smooth. Good surface smoothness makes it difficult for mesh marks from the screen to appear on the printed coating film. In recent years, there has also been a demand for materials that are stretchable so as to conform to stretchable substrates and that remain highly conductive even after stretching. An object of the present invention is to provide a conductive ink composition that has good fine line printability and surface smoothness after printing, and is capable of forming a conductive film that is stretchable and has excellent conductivity after stretching. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A conductive ink composition comprising a (meth)acrylic polymer (A) and silver particles (B), wherein the (meth)acrylic polymer (A) comprises a first (meth)acrylic polymer (A-1) and a second (meth)acrylic polymer (A-2), wherein the first (meth)acrylic polymer (A-1) has a glass transition temperature of 0°C or lower and a weight-average molecular weight of 500,000 or higher, and the second (meth)acrylic polymer (A-2) has a glass transition temperature of 0°C or lower and a weight-average molecular weight of less than 500,000, and the surfaces of the silver particles (B) are coated with a fatty acid including oleic acid. [2] The conductive ink composition according to [1], wherein the first (meth)acrylic polymer (A-1) has a glass transition temperature of more than -60°C and less than -30°C, a weight-average molecular weight of 500,000 or more and 990,000 or less, and a hydroxyl value of 50 mgKOH / g or more. [3] The conductive ink composition according to [1], wherein the first (meth)acrylic polymer (A-1) has a glass transition temperature of more than −60° C. and less than −40° C., a weight-average molecular weight of 750,000 or more and 990,000 or less, and a hydroxyl value of 50 mgKOH / g or more. [4] The conductive ink composition according to any one of [1] to [3], wherein the second (meth)acrylic polymer (A-2) has a glass transition temperature of more than −65° C. and less than 0° C. and a weight-average molecular weight of 150,000 or more and less than 500,000. [5] The conductive ink composition according to any one of [1] to [4], wherein the content of the oleic acid is 85 mass % or more relative to the total mass of the fatty acids. [6] The conductive ink composition according to any one of [1] to [5], wherein the loss factor tan δ measured at a temperature of 25°C, a frequency of 1 Hz, and by varying the strain amount from 0.001% to 100% is 4.0 or less. [7] A conductive film obtained by drying a coating of the conductive ink composition according to any one of [1] to [6]. [8] The conductive film according to [7], which is used for electrodes or wiring that require stretchability in electronic devices. [9] The conductive film according to [7], which is used for a detection part, an electrode, or wiring of a resistance change sensor. [Effects of the Invention]

[0007] According to the present disclosure, a conductive ink composition can be obtained that has good fine line printability and surface smoothness after printing, and can form a conductive film that is stretchable and has excellent conductivity after stretching. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following definitions of terms apply throughout the specification and claims. A numerical range indicated by "to" means that the numerical values ​​before and after "to" are the lower and upper limits of the numerical range. The (meth)acrylic polymer is a polymer containing units based on (meth)acrylate. The content of units based on (meth)acrylate relative to all units constituting the (meth)acrylic polymer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It may be 100% by mass. "(Meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acrylic" is a general term for "acrylic" and "methacrylic." The term "unit" of a polymer refers to an atomic group (monomer unit) formed from one monomer molecule.

[0009] The weight-average molecular weight (Mw) of the polymer is the polystyrene-equivalent molecular weight obtained by measurement with gel permeation chromatography using a calibration curve prepared with standard polystyrene samples of known molecular weight. More specifically, for example, as a GPC measuring device, using the product name "Alliance E2695 Separation Module" manufactured by Waters Japan K.K., it can be determined by measurement under the following GPC measurement conditions based on polystyrene-equivalent values. <GPC Measurement Conditions> · Sample concentration: 0.5 wt% (tetrahydrofuran solution) · Sample injection volume: 20 μL · Eluent: Tetrahydrofuran (THF) · Flow rate (flow velocity): 0.3 mL / min · Column temperature (measurement temperature): 40 °C · Column: Product name "TSKguard column HSPgel RT-MB-H+ HSPgel RT-2.0" (manufactured by Tosoh Corporation) · Detector: Differential refractometer (RI), product name "Alliance2414" (manufactured by Waters Japan K.K.)

[0010] The hydroxyl value of the polymer (unit: mgKOH / g) is a value calculated based on the theoretical value. It is calculated from the following formula (1). In the following formula (1), "the copolymerization amount of the monomer having a hydroxyl group" means the ratio (unit: mass%) of the monomer having a hydroxyl group to all the monomers constituting the polymer.

[0011]

Equation

[0012] The glass transition temperature of the copolymer obtained by polymerizing the monomer mixture is the Tg (theoretical value) calculated from the Fox equation of the following formula (2) using the glass transition temperatures of the homopolymers of each known monomer. For the glass transition temperature of the homopolymer of the monomer, for example, the values described in Polymer Handbook Fourth edition (Wiley-Interscience 2003) can be used. In the following formula (2), Tg is the glass transition temperature of the copolymer (unit: K), Tg1 is the glass transition temperature of the homopolymer of monomer 1 (unit: K), Tg2 is the glass transition temperature of the monomer 2 homopolymer (unit: K), Tg n is the glass transition temperature of the homopolymer of monomer n (unit: K), W1 is the weight fraction of monomer 1 in the monomer mixture, W2 is the weight fraction of monomer 2 in the monomer mixture, W n represents the weight fraction of monomer n in the monomer mixture.

[0013]

number

[0014] The 50% average particle size of silver particles is the median diameter at 50% cumulative volume on the particle size distribution curve measured by laser diffraction particle size measurement. The content of fatty acid relative to the total mass of silver particles (amount of fatty acid coating) can be measured by TG-DTA and determined from the mass of the residue after sintering the silver particles at 800°C for 30 minutes. The composition of the fatty acids that coat the surfaces of the silver particles can be measured by GC (gas chromatography).

[0015] <Conductive ink composition> The conductive ink composition of this embodiment contains a (meth)acrylic polymer (A) and silver particles (B).

[0016] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) comprises two or more kinds of (meth)acrylic polymers. The (meth)acrylic polymer (A) includes a first (meth)acrylic polymer (A-1) (hereinafter also referred to as "polymer (A-1)") and a second (meth)acrylic polymer (A-2) (hereinafter also referred to as "polymer (A-2)"). Both polymer (A-1) and polymer (A-2) have a glass transition temperature of 0° C. or lower. The weight average molecular weight of polymer (A-1) is 500,000 or more, and the weight average molecular weight of polymer (A-2) is less than 500,000. Both polymer (A-1) and polymer (A-2) are polymers containing units based on (meth)acrylate. In each of polymer (A-1) and polymer (A-2), the content of units based on (meth)acrylate relative to all units constituting the polymer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It may even be 100% by mass. In each of the polymer (A-1) and the polymer (A-2), the units based on (meth)acrylate constituting the polymer include the following units (a1) to (a5).

[0017] [Unit (a1)] The unit (a1) is derived from a hydroxyl group-containing monomer and increases the hydroxyl value of the polymer. The unit (a1) is preferably a unit based on a (meth)acrylate having a hydroxyl group. Specific examples of the hydroxyl group-containing monomer (a1) corresponding to the unit (a1) include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxyethyl methacrylate.

[0018] [Unit (a2)] The unit (a2) is a unit based on a (meth)acrylate having an alkyl group having a carbon number of 4 to 12. The unit (a2) does not include the unit (a1). The alkyl group having 4 to 12 carbon atoms in the unit (a2) may be linear or branched. Specific examples of the (meth)acrylate (a2) corresponding to the unit (a2) include n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0019] [Unit (a3)] The unit (a3) ​​is a unit based on a (meth)acrylate having an alkyl group having 1 to 3 carbon atoms. The unit (a3) ​​does not include the unit (a1) or the unit (a2). The alkyl group having 3 carbon atoms in the unit (a3) ​​may be linear or branched. Specific examples of the (meth)acrylate (a3) ​​corresponding to the unit (a3) ​​include methyl (meth)acrylate and ethyl (meth)acrylate.

[0020] [Unit (a4)] The unit (a4) is a unit (a4) based on a carboxy group-containing monomer, and does not include the unit (a1), the unit (a2), or the unit (a3). Specific examples of the carboxy group-containing monomer (a4) corresponding to the unit (a4) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and acid anhydride group-containing monomers (maleic anhydride, itaconic anhydride, etc.).

[0021] [Unit (a5)] The unit (a5) is a unit based on a monomer other than the above units (a1) to (a4) that is copolymerizable with the units (a1) to (a4). Examples of other monomers (a5) corresponding to the unit (a5) include (meth)acrylates having a linear or branched alkyl group having 13 to 20 carbon atoms, (meth)acrylates having an aromatic ring, (meth)acrylates having a non-aromatic cyclic hydrocarbon group, epoxy group-containing (meth)acrylates, vinyl ester-based monomers, styrene-based monomers, olefin-based monomers, vinyl ether-based monomers, and polyfunctional monomers. For example, vinyl ester monomers such as vinyl acetate and vinyl propionate are preferred.

[0022] <First (meth)acrylic polymer (A-1)> The polymer (A-1) preferably contains one or more types of units (a1). The content of units (a1) relative to all units in polymer (A-1) is preferably 20 to 40% by mass, more preferably 22 to 38% by mass, and even more preferably 24 to 36% by mass. When the content of units (a1) is at least the lower limit of the above range, the hydroxyl value of polymer (A-1) becomes high, and affinity with silver particles increases, resulting in excellent elasticity. When the content is at most the upper limit, the self-cohesion force of the meth(acrylic) polymer is not too strong, and good dispersibility and good elasticity during ink production are likely to be obtained.

[0023] The polymer (A-1) preferably contains one or more types of units (a2). The content of units (a2) relative to all units of polymer (A-1) is preferably 30 to 75 mass%, more preferably 40 to 72 mass%, and even more preferably 50 to 70 mass%. When the content of units (a2) is equal to or greater than the lower limit of the above range, good surface smoothness is likely to be obtained during printing. When it is equal to or less than the upper limit, the polymer is less likely to become rigid and good stretchability is likely to be obtained.

[0024] The polymer (A-1) may contain one or more types of units (a3). The content of units (a3) ​​relative to all units in polymer (A-1) is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. It may be zero. When the content of units (a3) ​​is the upper limit or less, excellent adhesion to the substrate is achieved. On the other hand, in terms of excellent flexibility and sufficient stretchability, the polymer (A-1) preferably contains one or more types of units (a3). For example, the content of units (a3) ​​relative to the total units of the polymer (A-1) may be 2% by mass or more, 5% by mass or more, or 7% by mass or more.

[0025] The polymer (A-1) may contain one or more types of units (a4). The content of units (a4) relative to all units in polymer (A-1) is preferably 0.35% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.25% by mass or less. It may even be zero. When the content of units (a4) is the upper limit or less, the cohesive strength of (meth)acrylic acid is not too high, and good stretchability is likely to be obtained. On the other hand, in terms of good affinity with silver particles, it is preferable that the polymer (A-1) contains one or more types of units (a4). For example, the content of units (a4) relative to all units in the polymer (A-1) may be 0.05% by mass or more, 0.10% by mass or more, or 0.15% by mass or more.

[0026] The polymer (A-1) may contain one or more types of units (a5). The content of units (a5) relative to the total units of polymer (A-1) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. It may even be zero. When the content of units (a5) is the upper limit or less, suitable printability can be ensured.

[0027] The glass transition temperature of the polymer (A-1) is 0° C. or lower, preferably lower than −15° C., more preferably lower than −30° C., and even more preferably lower than −40° C. When the glass transition temperature of the polymer (A-1) is the above upper limit or lower, a good elongation rate can be obtained. The lower limit of the glass transition temperature of the polymer (A-1) is preferably above −60° C. When the glass transition temperature of the polymer (A-1) is above −60° C., sufficient stretchability is likely to be obtained. The glass transition temperature of the polymer (A-1) is, for example, preferably higher than -60°C and lower than -15°C, more preferably higher than -60°C and lower than -30°C, and even more preferably higher than -60°C and lower than -40°C.

[0028] The weight average molecular weight of the polymer (A-1) is 500,000 or more, preferably 600,000 or more, more preferably 670,000 or more, and even more preferably 750,000 or more. When the weight average molecular weight is the above lower limit or more, the polymer (A-1) has excellent elasticity. The upper limit of the weight average molecular weight of the polymer (A-1) is preferably 990,000 or less from the viewpoint of ensuring flexibility and fully exhibiting electrical conductivity. The weight average molecular weight of the polymer (A-1) is, for example, preferably 500,000 or more and 990,000 or less, more preferably 600,000 or more and 990,000 or less, even more preferably 670,000 or more and 990,000 or less, and particularly preferably 750,000 or more and 990,000 or less.

[0029] The hydroxyl value of the polymer (A-1) is preferably 50 mgKOH / g or more, more preferably 75 mgKOH / g or more, and even more preferably 100 mgKOH / g or more. When the hydroxyl value of the polymer (A-1) is 50 mgKOH / g or more, the affinity between the silver particles and the polymer (A-1) is appropriately high, and the polymer (A-1) has excellent elasticity. The upper limit of the hydroxyl value of the polymer (A-1) is preferably 200 mgKOH / g or less, more preferably 175 mgKOH / g or less, and even more preferably 150 mgKOH / g or less, so as not to inhibit the conductivity of the silver particles. The hydroxyl value of the polymer (A-1) is, for example, preferably 50 mgKOH / g or more and 200 mgKOH / g or less, more preferably 75 mgKOH / g or more and 175 mgKOH / g or less, and even more preferably 100 mgKOH / g or more and 150 mgKOH / g or less.

[0030] Preferred embodiments of the polymer (A-1) include, for example, the following embodiments (A1-i), (A1-ii) and (A1-iii). [Aspect (A1-i)] The content of the unit (a1) is 20 to 40 mass %; The content of units (a2) is 30 to 75 mass %; The content of the unit (a3) ​​is 0 to 50 mass %; The content of the unit (a4) is 0 to 0.35 mass %; The content of units (a5) is 10% by mass or less, The glass transition temperature is greater than -60°C and less than 0°C. The weight average molecular weight is 500,000 to 990,000, A (meth)acrylic polymer having a hydroxyl value of 50 mgKOH / g or more and 200 mgKOH / g or less, wherein the total of the units (a1) to (a5) does not exceed 100 mass %.

[0031] [Aspect (A1-ii)] The content of the unit (a1) is 22 to 38% by mass, The content of units (a2) is 40 to 72 mass %; The content of the unit (a3) ​​is 0 to 40 mass %; The content of the unit (a4) is 0.10 to 0.30 mass %; The content of units (a5) is 5% by mass or less, The glass transition temperature is higher than -60°C and lower than -30°C, The weight average molecular weight is 670,000 to 990,000, A (meth)acrylic polymer having a hydroxyl value of 75 mgKOH / g or more and 175 mgKOH / g or less, wherein the total of the units (a1) to (a5) does not exceed 100 mass %.

[0032] [Aspect (A1-iii)] The content of the unit (a1) is 24 to 36% by mass, The content of units (a2) is 50 to 70 mass %; The content of the unit (a3) ​​is 0 to 30 mass %; The content of the unit (a4) is 0.15 to 0.25 mass %, The content of units (a5) is 2% by mass or less, The glass transition temperature is greater than -60°C and less than -45°C. The weight average molecular weight is 750,000 to 990,000, A (meth)acrylic polymer having a hydroxyl value of 100 mgKOH / g or more and 150 mgKOH / g or less, wherein the total of the units (a1) to (a5) does not exceed 100 mass %.

[0033] <Second (meth)acrylic polymer (A-2)> The polymer (A-2) may contain one or more types of units (a1). The content of units (a1) relative to all units in polymer (A-2) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. It may even be zero. When the content of units (a1) is at most the upper limit, the self-cohesion force of the meth(acrylic) polymer is not too strong, and good dispersibility and good stretchability during ink production are likely to be obtained. On the other hand, in terms of excellent stretchability, it is preferable that the polymer (A-2) contains one or more types of units (a1). For example, the content of units (a1) relative to all units of the polymer (A-2) may be 0.05% by mass or more, 0.1% by mass or more, or 0.15% by mass or more.

[0034] The polymer (A-2) preferably contains one or more types of units (a2). The content of units (a2) relative to all units of polymer (A-2) is preferably 70 to 98 mass%, more preferably 73 to 95 mass%, and even more preferably 76 to 92 mass%. When the content of units (a2) is equal to or greater than the lower limit of the above range, good surface smoothness is likely to be obtained during printing. When it is equal to or less than the upper limit, the polymer is less likely to become rigid and good stretchability is likely to be obtained.

[0035] The polymer (A-2) may contain one or more types of units (a3). The content of units (a3) ​​relative to the total units of polymer (A-2) is preferably 2.0 mass% or less, more preferably 1.8 mass% or less, and even more preferably 1.6 mass% or less. It may be zero. When the content of units (a3) ​​is the upper limit or less, excellent adhesion to the substrate is achieved. On the other hand, in order to obtain excellent flexibility and sufficient stretchability, it is preferable that the polymer (A-2) contains one or more types of units (a3). For example, the content of units (a3) ​​relative to the total units of the polymer (A-2) may be 0.4 mass% or more, 0.6 mass% or more, or 0.8 mass% or more.

[0036] The polymer (A-2) preferably contains one or more types of units (a4). The content of units (a4) relative to all units of polymer (A-2) is preferably 1 to 7 mass%, more preferably 1 to 5 mass%, and even more preferably 1 to 3 mass%. When the content of units (a4) is at least the lower limit of the above range, excellent affinity with silver particles is achieved, and sufficient stretchability is easily obtained. When the content is at most the upper limit, the cohesive force of (meth)acrylic acid is not too high, and good stretchability is easily obtained.

[0037] The polymer (A-2) may contain one or more types of units (a5). The content of units (a5) relative to all units in polymer (A-2) is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. It may even be zero. When the content of units (a5) is the upper limit or less, the cohesive strength of (meth)acrylic acid is not too high, and good stretchability is likely to be obtained. On the other hand, from the viewpoint of enhancing affinity with silver particles, it is preferable that the polymer (A-2) contains one or more types of units (a5). For example, the content of units (a5) relative to all units of the polymer (A-2) may be 1% by mass or more, 3% by mass or more, or 5% by mass or more.

[0038] The glass transition temperature of the polymer (A-2) is 0° C. or lower, preferably lower than 0° C., more preferably lower than −15° C., and even more preferably lower than −30° C. When the glass transition temperature of the polymer (A-2) is the above upper limit or lower, a good elongation rate can be obtained. The lower limit of the glass transition temperature of the polymer (A-2) is preferably above −70° C., more preferably above −65° C., and even more preferably above −60° C. When the glass transition temperature of the polymer (A-2) is above −70° C., sufficient stretchability is likely to be obtained. The glass transition temperature of the polymer (A-2) is, for example, preferably higher than -70°C and lower than -0°C, more preferably higher than -65°C and lower than -15°C, and even more preferably higher than -60°C and lower than -30°C.

[0039] The weight-average molecular weight of the polymer (A-2) is less than 500,000, preferably not more than 450,000, more preferably not more than 400,000, and even more preferably not more than 350,000. When the weight-average molecular weight is not more than the upper limit, the viscosity of the ink does not become too high, and the printability is excellent. The lower limit of the weight average molecular weight of the polymer (A-2) is preferably 100,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, from the viewpoint of excellent stretchability. The weight average molecular weight of the polymer (A-2) is, for example, preferably 100,000 or more and less than 500,000, more preferably 150,000 or more and less than 450,000, and even more preferably 200,000 or more and 400,000 or less.

[0040] The hydroxyl value of the polymer (A-2) is preferably 50 mgKOH / g or less, more preferably 20 mgKOH / g or less, and may be 0. When the hydroxyl value of the polymer (A-2) is the above-mentioned upper limit or less, the affinity between the silver particles and the polymer (A-2) is not too high, and the ink has an appropriate viscosity, resulting in excellent printability.

[0041] Preferred embodiments of the polymer (A-2) include, for example, the following embodiments (A2-i) and (A2-ii). [Aspect (A2-i)] The content of units (a1) is 10% by mass or less, The content of units (a2) is 70 to 98% by mass, The content of units (a3) ​​is 2.0% by mass or less; The content of the unit (a4) is 1 to 7 mass %; The content of units (a5) is 12% by mass or less, The glass transition temperature is greater than -70°C and less than 0°C. The weight average molecular weight is 100,000 or more and less than 500,000, A (meth)acrylic polymer having a hydroxyl value of 0 to 50 mgKOH / g, wherein the total of the units (a1) to (a5) does not exceed 100 mass %.

[0042] [Aspect (A2-ii)] The content of the unit (a1) is 0.05 to 1 mass %; The content of units (a2) is 73 to 95% by mass, The content of the unit (a3) ​​is 0.8 to 1.6 mass %; The content of units (a4) is 1 to 3 mass %; The content of units (a5) is 5 to 8% by mass, The glass transition temperature is greater than -65°C and less than -15°C, The weight average molecular weight is 200,000 or more and less than 400,000, A (meth)acrylic polymer having a hydroxyl value of 0 to 20 mgKOH / g, wherein the total of the units (a1) to (a5) does not exceed 100 mass %.

[0043] <(Meth)acrylic polymer composition> The (meth)acrylic polymer (A) may be produced by a known method for producing a (meth)acrylic polymer, or a commercially available product may be used. The polymers (A-1) and (A-2) may be used in the preparation of the conductive ink composition in the form of a (meth)acrylic polymer composition containing a (meth)acrylic polymer and an optional solvent. The solid content of the (meth)acrylic polymer composition is not particularly limited, but from the viewpoint of handling during blending, a viscosity that imparts appropriate fluidity is desirable. The solid content of the (meth)acrylic polymer composition is, for example, preferably 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less. The solvent contained in the (meth)acrylic polymer composition may be any solvent that is compatible with the polymer (A-1) and the polymer (A-2). For example, it may be a solvent (such as ethyl acetate) known as a polymerization solvent when synthesizing a (meth)acrylic polymer. It may also be a solvent listed as an example of the solvent (C) described below.

[0044] <Silver particles (B)> The surfaces of the silver particles (B) are coated with fatty acids including oleic acid. The 50% average particle size of the silver particles (B) is preferably 0.5 to 14.0 μm, more preferably 1.0 to 12.0 μm. The shape of the silver particles (B) is not particularly limited. For example, they may be spherical or flat in one direction (such as flakes or scales). Preferred examples of silver particles (B) include spherical silver particles having a 50% average particle size of 0.5 μm or more and less than 5 μm, and flaky silver particles having a 50% average particle size of 5 μm or more and 15 μm or less.

[0045] The fatty acid coating the surfaces of the silver particles (B) may contain a fatty acid other than oleic acid. The content of oleic acid relative to the total mass of the fatty acids is preferably 85% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. In this specification, the fatty acid coating amount is defined as the content of fatty acid relative to the total mass of silver particles (B). The fatty acid coating amount on silver particles (B) is preferably 0.01 to 2.0 mass%, more preferably 0.05 to 1.5 mass%, and even more preferably 0.1 to 1.0 mass%.

[0046] <Solvent (C)> The conductive ink composition may contain a solvent (C) as needed. The solvent (C) is not particularly limited as long as it can uniformly disperse the (meth)acrylic polymer (A) and the silver particles (B), has low volatility to stably maintain the properties of the ink, and can be removed in the drying step during the formation of the conductive film. Examples of the solvent (C) include ester-based solvents such as diethylene glycol monoethyl ether acetate (also known as ethyl carbitol acetate), hydrocarbon-based solvents such as decane, tetradecane, and cyclohexane, and alcohol-based solvents such as 2-ethylhexanol, 2-ethylhexyl ether derivatives, and diethylene glycol monobutyl ether.

[0047] <Optional ingredients> The conductive ink composition may contain optional components other than the (meth)acrylic polymer (A), silver particles (B), and solvent (C) to the extent that the effects of the present invention are not impaired. As the optional components, components known in the field of conductive ink compositions can be used. For example, in order to improve printability, components that adjust the interfacial tension of the ink (e.g., surfactants, leveling agents, etc.), components that adjust the viscosity of the ink (e.g., thixotropic agents), etc. may be blended. In addition, in order to improve adhesion to each substrate, it is possible to blend a binder component other than the (meth)acrylic polymer (A). Examples of binder components include polyurethane polymers, epoxy polymers, ester polymers, terpene resins, and terpene resin derivatives (e.g., terpene phenol resins). The binder component can be blended in an amount that does not impair elasticity. In addition, an ion scavenger can be added to prevent migration.

[0048] <Content> The content of the (meth)acrylic polymer (A) relative to the solid content of the conductive ink composition is preferably 5 to 20 mass%, more preferably 6 to 18 mass%, and even more preferably 7 to 16 mass%. When the content of the (meth)acrylic polymer (A) is equal to or greater than the above lower limit, sufficient stretchability is likely to be obtained. When the content is equal to or less than the above upper limit, a sufficient content of silver particles (B) is likely to be secured, and good conductivity during stretching is likely to be obtained.

[0049] The polymer (A-1) and the polymer (A-2) contained in the conductive ink composition may each be one type, or two or more types may be used in combination. The total content of the polymer (A-1) and the polymer (A-2) relative to the total mass of the (meth)acrylic polymer (A) is preferably 90 mass % or more, more preferably 95 mass % or more, and may be 100 mass %. In the conductive ink composition, the mass ratio of the content of polymer (A-1) to the content of polymer (A-2) is preferably 65:35 to 95:5, more preferably 70:30 to 90:10, and even more preferably 75:25 to 85:15. When the mass ratio of (A-1):(A-2) is equal to or greater than the lower limit, sufficient elasticity is easily obtained. When the mass ratio is equal to or less than the upper limit, a viscosity suitable for printing is easily obtained.

[0050] The silver particles (B) contained in the conductive ink composition may be of one type, or two or more types may be used in combination. The content of silver particles (B) relative to the solid content of the conductive ink composition is preferably 80.0 to 97.0 mass%, more preferably 83.0 to 95.0 mass%, and even more preferably 86.0 to 93.0 mass%. When the content of silver particles (B) is equal to or greater than the above lower limit, good conductivity is likely to be obtained. When the content is equal to or less than the above upper limit, a sufficient content of components other than silver particles (B) is likely to be secured, and good properties such as stretchability are likely to be obtained.

[0051] The optional components contained in the conductive ink composition may be one type, or two or more types may be used in combination. The content of the optional components relative to the solid content of the conductive ink composition is preferably 10% by mass or less, more preferably 5% by mass or less, and may be zero.

[0052] The solid content of the conductive ink composition is preferably 55 to 87% by mass, more preferably 57 to 84% by mass, and even more preferably 60 to 82% by mass, based on the total mass of the composition. When the solid content is equal to or greater than the lower limit, sufficient extensibility and good conductivity when elongated are likely to be obtained. When the solid content is equal to or less than the upper limit, a viscosity suitable for printing is likely to be obtained. The solid content of the conductive ink composition can be adjusted by the content of the solvent (C). The conductive ink composition may contain one type of solvent (C) or two or more types of solvents (C) in combination.

[0053] <Method of manufacturing conductive ink composition> The conductive ink composition can be obtained by uniformly mixing the polymer (A-1), the polymer (A-2), the silver particles (B), the solvent (C) as needed, and any other optional components. The polymer (A-1) and the polymer (A-2) may be mixed in advance for use. As the polymer (A-1), the polymer (A-2), or a mixture thereof, a (meth)acrylic polymer composition containing a solvent compatible with both the polymer (A-1) and the polymer (A-2), and the polymer (A-1), the polymer (A-2), or a mixture thereof may be used. A known mixing method can be used. For example, the conductive ink composition can be produced by premixing all the components in a stirrer and kneading the resulting premixture multiple times using a three-roll mill.

[0054] The glass transition temperatures of the polymer (A-1) and the polymer (A-2) contained in the conductive ink composition may be the same or different. The absolute value of the difference between the highest and lowest glass transition temperatures of the polymer (A-1) and the polymer (A-2) contained in the conductive ink composition is preferably 60°C or less, and more preferably 30°C or less.

[0055] The weight-average molecular weight of the polymer (A-1) is higher than that of the polymer (A-2) contained in the conductive ink composition. The absolute value of the difference between the highest and lowest weight-average molecular weights of the polymer (A-1) and polymer (A-2) contained in the conductive ink composition is preferably 200,000 to 890,000, and more preferably 300,000 to 500,000. For example, it is preferable that the weight average molecular weight of polymer (A-1) is 600,000 or more and the weight average molecular weight of polymer (A-2) is 400,000 or less.It is more preferable that the weight average molecular weight of polymer (A-1) is 800,000 or more and the weight average molecular weight of polymer (A-2) is 300,000 or less.

[0056] The hydroxyl value of the polymer (A-1) is preferably higher than that of the polymer (A-2) contained in the conductive ink composition. The absolute value of the difference between the highest and lowest hydroxyl values ​​of the polymer (A-1) and polymer (A-2) contained in the conductive ink composition is preferably 0 to 200 mgKOH / g, more preferably 50 to 150 mgKOH / g. For example, it is preferred that the hydroxyl value of polymer (A-1) is 100 mgKOH / g or more and the hydroxyl value of polymer (A-2) is 50 mgKOH / g or less, and it is more preferred that the hydroxyl value of polymer (A-1) is 120 mgKOH / g or more and the hydroxyl value of polymer (A-2) is 25 mgKOH / g or less.

[0057] <Physical properties> The conductive ink composition preferably has a loss factor tanδ of 4.0 or less, measured at a temperature of 25°C, a frequency of 1 Hz, and with the strain varied from 0.001% to 100%. When the tanδ is 4.0 or less, the conductive ink composition has excellent printability, for example, excellent fine line printability and excellent surface smoothness after printing. In view of excellent surface smoothness, the tan δ is preferably 4.0 or less, more preferably 3.0 or less. In view of excellent fine line printability, the lower limit of the tan δ is preferably 0.5 or more, more preferably 1.0 or more. The value of tan δ can be adjusted mainly by the glass transition temperature and weight-average molecular weight of each of polymer (A-1) and polymer (A-2), the combination of polymer (A-1) and polymer (A-2), the mass ratio of polymer (A-1) to polymer (A-2), or the type of fatty acid coating the surface of silver particles (B). When the fatty acid coating silver particles (B) is oleic acid, the value of tan δ tends to be small.

[0058] <Conductive film> The conductive ink composition is applied to a substrate or the like to form a coating film, and the coating film is dried to remove volatile components such as the solvent (C), thereby obtaining a conductive film. The material and shape of the substrate are not particularly limited. A stretchable substrate is preferable. Examples of stretchable materials include polyurethane, ethylene propylene rubber, silicone rubber, and various elastomers.

[0059] The conductive ink composition can be applied to a substrate by any known application method, such as printing, dipping, spraying, or bar coating. From the viewpoints of versatility and accuracy, printing is preferred. Examples of printing methods include inkjet printing, flexographic printing, gravure printing, screen printing, pad printing, lithography printing, etc. In particular, screen printing is preferred because it can easily reduce costs, is suitable for large-area printing, and can easily increase the thickness of the conductive film.

[0060] The coating film may be heated during the drying process. The heating temperature during drying is preferably a temperature that does not adversely affect the substrate and allows complete removal of the solvent in the coating material. Although this varies depending on the type of substrate, a temperature of 80 to 150°C is preferred, for example. The thickness of the conductive film after drying is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 80 μm. When the thickness is equal to or greater than the lower limit of the above range, conductivity is easily exhibited, and when the thickness is equal to or less than the upper limit, the device to be fabricated can be made smaller.

[0061] As shown in the examples below, the conductive film of this embodiment is stretchable and has good conductivity after stretching. For example, after stretching at an elongation rate of 50%, the conductive film can achieve a surface resistivity of less than 0.7 Ω / sq, preferably less than 0.6 Ω / sq, and more preferably less than 0.5 Ω / sq. That is, the conductive ink composition of this embodiment can be suitably used as a conductive material for forming wiring, electrodes, etc. on a stretchable substrate, and can provide good followability to the expansion and contraction of the substrate. In addition, the conductive ink composition of this embodiment has excellent printability, as shown in the examples described below. Specifically, when a line-and-space (L / S) pattern is printed using the conductive ink composition, the difference between the line width of the printed pattern and the designed value is small, resulting in excellent fine-line printability. Furthermore, the surface roughness of the coating film after printing is small, resulting in excellent surface smoothness of the coating film. Therefore, the conductive ink composition of this embodiment is suitable for applications in which conductive members such as wiring and electrodes are formed on a stretchable substrate by a printing method.

[0062] The conductive film of this embodiment can exhibit high conductivity even when stretched, and therefore can also be used for conductive members (wiring, electrodes, antennas, heating elements, etc.) that constitute stretchable articles. Specific examples include use in conductive members (wiring, electrodes, antennas, etc.) that constitute the wearable sensor, the pressure-sensitive sensor, moving parts of robots, artificial muscles, flexible displays, etc., wiring for in-mold molded parts, heating elements for flexible heaters, etc. For example, the conductive film of this embodiment is suitable for use in electrodes that require stretchability in electronic devices, or for use in wiring that requires stretchability in electronic devices. For example, the conductive film of this embodiment is suitable for use in the detection portion of a resistance change type sensor, the electrodes of a resistance change type sensor, or the wiring of a resistance change type sensor. Specific examples of resistance change sensors include wearable or flexible sensors that detect expansion and contraction through changes in electrical resistance, strain sensors that measure the amount of strain through changes in electrical resistance, and pressure sensors that can sense deformation and measure the amount of deformation through changes in electrical resistance. [Example]

[0063] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description. In the following, the unit of content "%" is "% by mass" unless otherwise specified.

[0064] <Production Example of (Meth)acrylic Polymer Composition> The monomers shown in Table 1 are as follows: [Hydroxyl group-containing monomer (a1)] 2HPA: 2-hydroxypropyl acrylate. 4HBA: 4-hydroxybutyl acrylate. 2HEA: 2-hydroxyethyl acrylate. 2HEMA: 2-hydroxyethyl methacrylate. [C4-12 alkyl (meth)acrylate (a2)] BA: butyl acrylate. 2EHA: 2-ethylhexyl acrylate. [C1-3 alkyl (meth)acrylate (a3)] MA: methyl acrylate. MMA Methyl methacrylate. [Carboxy group-containing monomer (a4)] AA: acrylic acid. [Other monomers (a5)] Vac: vinyl acetate.

[0065] (Production Example 1-1: Production of (meth)acrylic polymer composition) The monomer mixture shown in Table 1 was polymerized in a polymerization solvent to synthesize a (meth)acrylic polymer, and further solvent was added to adjust the solid content concentration to obtain a (meth)acrylic polymer composition. Specifically, 29.8 parts by mass of 2HPA, 57.2 parts by mass of BA, 12.8 parts by mass of MA, and 0.2 parts by mass of AA as monomers, 0.02 parts by mass of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 43 parts by mass of ethyl acetate as a polymerization solvent were placed in a separable flask. Nitrogen gas was introduced to remove oxygen from the polymerization system, and the temperature was raised to 70 ° C. and the reaction was carried out for 8 hours to obtain a (meth)acrylic polymer A-1-1. Ethyl acetate was added to this to adjust the solids concentration to 33% by mass, and a (meth)acrylic polymer composition (1-1) was obtained. The glass transition temperature, weight average molecular weight and hydroxyl value of the (meth)acrylic polymer are shown in Table 1 (the same applies hereinafter).

[0066] (Production Examples 1-2, 1-3, 2-1, 2-2, 3-1: Production of (meth)acrylic polymer compositions) The composition of the monomer mixture was changed as shown in Table 1, and the monomer mixture was polymerized in the same manner as in Production Example 1-1 to synthesize a (meth)acrylic polymer. Ethyl acetate was added to this to adjust the solid content concentration as shown in Table 1, thereby obtaining a (meth)acrylic polymer composition. Production Examples 1-2 and 1-3 are examples in which a first (meth)acrylic polymer (A-1) was produced, and Production Examples 2-1 and 2-2 are examples in which a second (meth)acrylic polymer (A-2) was produced. Production Example 3-1 is an example in which a (meth)acrylic polymer (A-3-1) having a glass transition temperature exceeding 0°C was produced.

[0067] [Table 1]

[0068] <Silver particles (B)> Silver particles B1 to B3 coated with fatty acids were used. Table 2 shows the shape, 50% average particle size, main fatty acid component, content of main component relative to the total mass of fatty acid (referred to as "main component / fatty acid" in the table), and fatty acid coating amount for each silver particle.

[0069] [Table 2]

[0070] <Solvent (C)> The following solvents were used: Solvent (C1): Diethylene glycol monoethyl ether acetate.

[0071] (Examples 1 to 8, Comparative Examples 1 to 5) Silver particles and a solvent were blended into a (meth)acrylic polymer composition according to the formulations shown in Tables 3 and 4. All of the ingredients were premixed using a stirrer and then kneaded using a three-roll mill (Imex product name "BR-150VIII") to obtain a conductive ink composition. The kneading was carried out twice at a rotation speed of 350 rpm and a roll distance of 40 μm, after which the roll distance was reduced to 10 μm and the kneading was carried out two more times. The table shows the solid content, (meth)acrylic polymer (A) content, and silver particle (B) content relative to the total mass of the conductive ink composition for each example. The table also shows the (meth)acrylic polymer (A) content and silver particle (B) content relative to the solid content (referred to as (meth)acrylic polymer (A) / solid content and silver particle (B) / solid content, respectively). A blank space in the table means that the component is not included.

[0072] Evaluation Method <Ink evaluation> [Loss factor of conductive ink composition] The dynamic viscoelasticity of the ink was evaluated using a rheometer (Anton Paar product name "MCR301"). The storage modulus (G') and loss modulus (G") were measured at a frequency of 1 Hz, a measurement temperature of 25°C, and strain varying from 0.001% to 100%, and the loss factor (Tan δ) was calculated using the following formula. tanδ = loss modulus G” / storage modulus G' The results of storage modulus (G'), loss modulus (G"), and loss factor (G" / G') at 100% strain are shown in the table.

[0073] Evaluation Method <Printability evaluation> (Method for evaluating fine line printability) The ink composition obtained in each example was screen-printed onto a substrate using a screen printer (Microtec product name "MT-320") and then dried to form a conductive film (fine wiring pattern) with a thickness of 12 μm (design value). Specifically, a fine wiring pattern was printed using a screen plate with a fine wiring pattern on an area of ​​15 mm length by 15 mm width on a 1 mm thick substrate, and then dried at 130°C for 20 minutes. The fine wiring pattern had a line width of 500 μm and a line-to-line width of 300 μm (L / S = 500 μm / 300 μm). The printing conditions are as follows: The substrate was made of elastic polyurethane, but it is not limited to this and other rubber or elastomer materials such as EPDM rubber (ethylene propylene rubber) or silicone rubber are also possible. (Screen printing conditions) Screen: Stainless steel 325 mesh. ·Line length: 30μm Calendering thickness: 75μm Emulsion thickness: 20 μm Screen frame: 320 x 320 mm Squeegee angle: 70° Squeegee hardness: 80° ·Squeegee speed: 150mm / sec. Squeegee pressure: 0.2 MPa Clearance: 1.5mm

[0074] The conductive film (fine wiring pattern) obtained after drying was evaluated for fine line printability by the following method. The screen-printed fine wiring pattern was photographed at 500x magnification using a digital microscope (Keyence Corporation, product name "VHX-6000"), and five randomly selected wirings (design line width 500 μm) were measured for their line width in the resulting image, and the average value of the five was calculated. Based on the average line width obtained, the fine line printability was evaluated according to the following evaluation criteria. (Evaluation criteria) ◎: The average line width is 480 μm or more and less than 520 μm. Good: The average line width is 475 μm or more and less than 480 μm, or 520 μm or more and less than 535 μm. ×: The average line width is less than 475 μm or 535 μm or more.

[0075] (Surface smoothness evaluation method) The ink composition obtained in each example was applied to a substrate and then dried to form a conductive film, and the average surface roughness (arithmetic mean roughness Ra) of the conductive film was measured. The arithmetic mean roughness Ra was measured using a method in accordance with JIS B0601:1994. The substrate material was polyurethane, and the coating method was screen printing. The drying conditions were 130°C and 20 minutes, and the average thickness of the conductive film after drying was 12 μm. The surface roughness of the conductive film was measured using a surface profiler (laser scanning microscope, Keyence Corporation, product name "VK-9700"). Based on the measurement results of the average roughness, the surface smoothness was evaluated according to the following evaluation criteria. (Evaluation criteria) ◎: Average roughness is less than 0.2 μm. ○: Average roughness is 0.2 μm or more and less than 0.4 μm. ×: Average roughness is 0.4 μm or more.

[0076] <Evaluation of the elasticity of conductive films> (Measurement of surface resistivity after stretching) The ink composition obtained in each example was applied to a substrate cut into a No. 3 dumbbell shape and dried to form a conductive film, thereby obtaining a laminate of the substrate and the conductive film. The resulting laminate was set as a sample in a tensile tester. The distance between the gauge lines (initial dimension) was 2 mm. The sample was pulled at a tensile speed of 10 mm / min at 23°C until it reached an elongation of 50%. After reaching 50%, the sample was returned to its initial state at a return speed of 10 mm / min. 3 minutes after returning to the initial state, the surface resistivity (unit: Ω / sq) between the gauge lines was measured using a tester. Based on the results of measuring the surface resistivity, the stretchability of the conductive film was evaluated according to the following evaluation criteria. (Evaluation criteria) ◎: Less than 0.5Ω / sq. 〇: 0.5Ω / sq or more, less than 0.7Ω / sq. ×: 0.7Ω / sq ​​or more.

[0077] [Table 3]

[0078] [Table 4]

[0079] As shown in Tables 3 and 4, the conductive ink compositions of Examples 1 to 8 were excellent in printability (surface smoothness, fine line printability) and were able to form stretchable conductive films. The conductive ink compositions of Examples 1 to 8 had a tan δ of 4.0 or less. In contrast, Comparative Example 1, which did not contain the second (meth)acrylic polymer (A-2) and instead used (3-1) with a Tg exceeding 0° C., had a tan δ exceeding 4.0 and poor printability. In Comparative Example 2, in which the fatty acid coating the surfaces of the silver particles did not contain oleic acid, the tan δ exceeded 4.0, and the printability was poor. Comparative Example 3, which did not contain the second (meth)acrylic polymer (A-2), had a tan δ of more than 4.0 and was poor in printability. Comparative Example 4, which did not contain the first (meth)acrylic polymer (A-1), had a tan δ of more than 4.0, and was poor in printability, and the conductive film also had poor stretchability. Comparative Example 5, which contained two types of first (meth)acrylic polymers (A-1) but no second (meth)acrylic polymer (A-2), had a tan δ of more than 4.0 and was poor in printability.

Claims

1. Contains a (meth)acrylic polymer (A) and silver particles (B), the (meth)acrylic polymer (A) comprises a first (meth)acrylic polymer (A-1) and a second (meth)acrylic polymer (A-2), the first (meth)acrylic polymer (A-1) has a glass transition temperature of more than −60° C. and 0° C. or less, a weight average molecular weight of 500,000 or more and 990,000 or less, and a hydroxyl value of 50 mgKOH / g or more and 200 mgKOH / g or less, the second (meth)acrylic polymer (A-2) has a glass transition temperature of more than −70° C. and not more than 0° C., a weight average molecular weight of 100,000 or more and less than 500,000, and a hydroxyl value of 20 mgKOH / g or less, (A-1):(A-2), which represents the mass ratio of the content of the first (meth)acrylic polymer (A-1) to the content of the second (meth)acrylic polymer (A-2), is 65:35 to 95:5, The conductive ink composition, wherein the surfaces of the silver particles (B) are coated with a fatty acid including oleic acid.

2. 2. The conductive ink composition according to claim 1, wherein the first (meth)acrylic polymer (A-1) has a weight average molecular weight of 600,000 or more and 990,000 or less.

3. 2. The conductive ink composition according to claim 1, wherein the first (meth)acrylic polymer (A-1) has a glass transition temperature of more than −60° C. and less than −40° C. and a weight average molecular weight of 600,000 or more and 990,000 or less.

4. 2. The conductive ink composition according to claim 1, wherein the second (meth)acrylic polymer (A-2) has a glass transition temperature of more than −65° C. and less than 0° C. and a weight average molecular weight of 100,000 or more and 400,000 or less.

5. The conductive ink composition according to claim 1 , wherein the content of the oleic acid is 85% by mass or more relative to the total mass of the fatty acids.

6. 2. The conductive ink composition according to claim 1, wherein the loss factor tan δ measured at a temperature of 25° C., a frequency of 1 Hz, and by varying the strain from 0.001% to 100% is 4.0 or less.

7. A conductive film obtained by drying a coating of the conductive ink composition according to any one of claims 1 to 6.

8. The conductive film according to claim 7, which is used for electrodes or wiring that require stretchability in electronic devices.

9. The conductive film according to claim 7 , which is used for a detection part, an electrode, or a wiring of a resistance change type sensor.

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