Photocurable conductive paste

Abstract

To provide a photocurable conductive paste, a conductive cured film, and uses thereof, having conductivity as a principal feature, and achieving both conductivity and cured film properties such as solvent resistance and adhesion to a substrate, and storage stability in the uncured paste.SOLUTION: A photocurable conductive paste comprises (A) a conductive filler, (B) a photopolymerizable resin precursor, and (C) a photopolymerization initiator, wherein the conductive filler (A) is copper having a silver-coated surface, and the photopolymerizable resin precursor (B) comprises a trifunctional (meth)acrylate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a photocurable conductive paste used for forming an electric circuit, forming an external electrode of a ceramic capacitor, and the like.

Background Art

[0002] A conductive paste is a fluid composition in which a conductive filler is dispersed in a vehicle composed of a resin binder and a solvent, and is widely used for forming an electric circuit, forming an external electrode of a ceramic capacitor, and the like.

[0003] As the conductive filler, which is a main component of the conductive paste, silver powder has been widely used in the past due to its high conductivity. However, recently, due mainly to cost reasons, the use of copper powder is becoming widespread. However, copper powder is easily oxidized in air, and the oxide film on the surface of the copper powder has a problem of increasing the connection resistance. Therefore, various methods for preventing the oxidation of the copper powder surface have been proposed (Patent Documents 1 and 2).

[0004] Among them, silver-coated copper powder in which the particle surface is coated with oxidation-resistant silver has been disclosed as a composite conductive filler that prevents oxidation of the copper powder surface and is excellent in high conductivity, migration resistance, and the like (Patent Document 3).

[0005] On the other hand, conductive pastes include a resin-curing type in which the conductive filler is crimped by curing of the resin to ensure conduction, and a firing type in which the organic components are volatilized by firing and the conductive filler is sintered to ensure conduction. However, when applying a fired conductive paste, a heating process of about several tens to several hundreds of degrees Celsius is essential to volatilize the organic components. Also, even in the case of a resin-curing type conductive paste, a heating process of about the same several tens to several hundreds of degrees Celsius is almost always essential to volatilize the organic components such as the solvent contained in the paste or to cure the resin. Therefore, it has not been possible to use a conductive paste for a substrate made of a heat-sensitive material such as polyethylene terephthalate (PET), and its application range has been limited.

[0006] Under such circumstances, since it can be cured only by irradiating ultraviolet rays or the like at room temperature without heating, it can also be applied to substrates such as heat-sensitive plastics. In addition, it has been proposed to apply it to conductive fillers such as copper powder and silver-coated copper powder that have good printability, printing accuracy, and adhesion to various substrates and exhibit stable conductivity (Patent Documents 4 and 5).

[0007] However, Patent Documents 4 and 5 did not examine the stability over time (storage) of the conductive paste in a fluid state. On the other hand, even when the inventors of the present application examined a photocurable conductive filler composed of silver-coated copper powder and several acrylate compounds, although a conductive cured film could be obtained using the paste immediately after preparation, gelation was observed in the paste within several days after preparation, and it was difficult to say that it had storage stability sufficient for practical use in terms of transportation, storage, etc.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above circumstances, and has good storage stability in a paste state. A cured film obtained from the photocurable conductive paste of the present invention has cured film properties such as good conductivity, high solvent resistance, and good adhesion to a substrate. An object of the present invention is to provide a photocurable conductive paste.

Means for Solving the Problems

[0010] As a result of intensive studies, the present inventors have found that a photocurable conductive paste containing a conductive filler made of silver-coated copper powder, a trifunctional photopolymerizable resin precursor, and a photoinitiator can achieve both good storage stability in a paste state and high conductivity after photocuring, and have completed the present invention.

[0011] That is, the embodiments of the present invention include the following configurations. [1] A conductive filler (A), A photopolymerizable resin precursor (B), and A photoinitiator (C) are included, the conductive filler (A) is copper having a surface coated with silver, the photopolymerizable resin precursor (B) is characterized by containing a trifunctional (meth)acrylate, A photocurable conductive paste. [2] The photocurable conductive paste according to [1], wherein the photopolymerizable resin precursor (B) further contains one or more (meth)acrylates selected from the group consisting of monofunctional, difunctional, and tetrafunctional or higher (meth)acrylates. [3] The photocurable conductive paste according to [1] or [2], wherein the trifunctional (meth)acrylate which is the photopolymerizable resin precursor (B) has an acrylic equivalent of 90 or more and 220 or less. [4] The photocurable conductive paste according to any one of [1] to [3], wherein the photopolymerizable resin precursor (B) contains ethoxylated glycerin triacrylate. [5] The photocurable conductive paste according to any one of [1] to [4], wherein the shape of the conductive filler (A) is dendritic. [6] The photocurable conductive paste according to [5], wherein the blending amount of the conductive filler (A) is 55 to 80% by mass based on the total mass of the photocurable conductive paste. [7] The photocurable conductive paste according to any one of [1] to [4], wherein the conductive filler (A) has one or more shapes selected from spherical or plate-like shapes, and the average particle diameter of the conductive filler (A) is 2 to 8 μm. [8] The photocurable conductive paste according to [7], wherein the blending amount of the conductive filler (A) is 85 to 90% by mass based on the total mass of the photocurable conductive paste. [9] A conductive cured film obtained by photocuring the photocurable conductive paste according to any one of [1] to [8].

[10] A substrate having the conductive cured film according to [9].

[11] An electronic component having the conductive cured film according to [9] or the substrate according to

[10] . [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide a photocurable conductive paste that does not gel even after being stored for one week in an environment of 45°C in a paste state and has good storage stability, and can be cured by irradiating light such as ultraviolet rays without heating. Further, the cured film obtained from the photocurable conductive paste of the present invention has good solvent resistance and adhesion to the substrate, and can obtain high conductivity. [Embodiments for Carrying Out the Invention]

[0013] As described above, the basic composition of the photocurable conductive paste of the present invention comprises a conductive filler (A), a photopolymerizable resin precursor (B), and a photoinitiator (C). Hereinafter, each component will be described in detail.

[0014] 1. Conductive filler (A) The conductive filler (A) used in the present invention is composed of copper particles coated (covered) with silver on the surface and is in the form of a powder having a spherical, dendritic, plate-like or flaky shape. In this specification, the powdered copper coated with silver will be referred to as "silver-coated copper powder". By using silver-coated copper powder in the photocurable conductive paste of the present invention, sufficient conductivity of the cured film can be obtained.

[0015] Examples of the shape of the conductive filler (A) include spherical, dendritic, plate-like, or flaky. In the photocurable conductive paste of the present invention, a single-shaped conductive filler may be used, or these may be used in combination. From the viewpoint of reducing entanglement between the fillers and improving dispersibility in the conductive paste, it is preferable to use spherical or plate-like fillers. Also, since conduction in the cured film is easily ensured and good conductivity can be obtained even when the amount of the conductive filler used is small, it is more preferable to use dendritic fillers. Note that the term "dendritic" refers to a fibrous shape that may or may not have branches.

[0016] The average particle size of the conductive filler is preferably 1 to 10 μm from the viewpoint of easily preventing aggregation and viscosity increase of the conductive filler in the photocurable conductive paste and ensuring adhesion between the cured film and the substrate. Note that the average particle size means the particle size D50 of the particle size distribution 50%, and can be measured by well-known methods such as the dynamic light scattering method (DLS), laser diffraction method, precipitation method, etc.

[0017] Examples of the silver-coated copper powder as the conductive filler (A) used in the present invention include ACAX-225, ACAX-225M, ACBY-225, 10%Ag / 1100Y, 10%Ag / 02K, ACPZ-2, 10%Ag / 03K, ACRZ-2, 10%Ag / 05K-2, ACFZ-2, 10%Ag / 1100YP, 10%Ag / 1200YP, 10%Ag / 05KP (all are product names of Mitsui Mining & Smelting Co., Ltd.), 10%Ag-coated Cu-HWF-6, 10%Ag-coated Cu-HWQ, 10%Ag-coated Cu-FCC-TBX, 10%Ag-coated Cu-FCC-2000, 10%Ag-coated Cu-FCC-115, 10%Ag-coated CE-1110, 10%Ag-coated 2L3 (all are product names of Fukuda Metal Foil & Powder Co., Ltd.).

[0018] In the photocurable conductive paste of the present invention, from the viewpoint of achieving both the conductivity of the cured film and the low viscosity of the photocurable conductive paste, the blending amount of the conductive filler (A) is preferably 55 to 90% by mass based on the total mass of the photocurable conductive paste. The photocurable conductive paste of the present invention can have a relatively large blending amount of the conductive filler (A) compared to conventional conductive pastes, and can exhibit good printability despite the large amount of the conductive filler. In addition, since the radical polymerization reaction during curing by ultraviolet rays or the like proceeds rapidly, the cured film exhibits good conductivity without losing conductivity.

[0019] In the photocurable conductive paste of the present invention, when a dendritic filler is used as the conductive filler (A), from the viewpoint of achieving both the conductivity of the cured film and the low viscosity of the photocurable conductive paste, the blending amount of the conductive filler (A) is preferably 55 to 80% by mass based on the total mass of the photocurable conductive paste.

[0020] In the photocurable conductive paste of the present invention, when spherical or plate-shaped fillers are used as the conductive filler (A), from the viewpoint of achieving both the conductivity of the cured film and the low viscosity of the photocurable conductive paste, the blending amount of the conductive filler is preferably 80 to 90% by mass, more preferably 85 to 90% by mass, based on the total mass of the photocurable conductive paste.

[0021] From the perspective of achieving both the prevention of filler aggregation and viscosity increase in the conductive paste and ensuring high conductivity and substrate adhesion after curing due to insufficient polymerization reaction during photocuring, the size of the spherical or plate-shaped conductive filler preferably has an average particle size of 2 to 8 μm. The average particle size means the particle size D50 of the particle size distribution, and can be measured by well-known methods such as the dynamic light scattering method (DLS), laser diffraction method, precipitation method, etc.

[0022] 2. Photopolymerizable resin precursor (B) The photopolymerizable resin precursor (B) used in the present invention uses a compound having a radically polymerizable ethylenically unsaturated group, and from the viewpoints of solvent resistance, adhesion, conductivity, and storage stability, trifunctional (meth)acrylate is essentially included. When trifunctional (meth)acrylate is not included, if a (meth)acrylate having an acrylic functional group number larger than trifunctional is used, the storage stability as a conductive paste may deteriorate. Similarly, when trifunctional (meth)acrylate is not included, if a (meth)acrylic monomer having an acrylic functional group number smaller than trifunctional is used, the effect of curing shrinkage during curing of the conductive paste may not be sufficiently obtained, resulting in deterioration of the conductivity of the cured film. The trifunctional (meth)acrylate may be a single compound or a mixture of two or more compounds.

[0023] Within the range that can achieve the object of the present invention, a compound having a radically polymerizable ethylenically unsaturated group other than (meth)acrylate may be included. Further, monofunctional, difunctional, and tetrafunctional or higher (meth)acrylates can be arbitrarily used in combination with trifunctional (meth)acrylate. When monofunctional and difunctional (meth)acrylates are used in combination, the viscosity of the photocurable conductive paste can be reduced, so that the viscosity can be adjusted. On the other hand, when tetrafunctional or higher (meth)acrylates are used in combination, the curing rate by light increases, and the curing rate of the photocurable conductive paste can be increased. Note that the compound having a radically polymerizable ethylenically unsaturated group other than (meth)acrylate, monofunctional (meth)acrylate, difunctional (meth)acrylate, and tetrafunctional or higher (meth)acrylate may be selected from these compound groups as a single compound and used in combination with trifunctional (meth)acrylate, or two or more kinds may be selected and used in combination with trifunctional (meth)acrylate.

[0024] The term "(meth)acrylate" in the present specification is used to indicate both or either of acrylate and methacrylate, and the term "(meth)acryloyl" is used to indicate both or either of acryloyl and methacryloyl. Further, terms such as "trifunctional" in the form of "Chinese numeral + functional" are intended to represent the number of (meth)acryloyl groups in the compound.

[0025] The acrylic equivalent of the trifunctional (meth)acrylate used as the photopolymerizable resin precursor (B) of the present invention is preferably 80 or more and 390 or less, more preferably 90 or more and 220 or less, and most preferably 90 or more and 130 or less from the viewpoint of achieving both the storage stability of the paste and the conductivity of the cured film as photocurable conductivity. Note that the "acrylic equivalent" in the present specification is an index represented by (molecular weight of the photopolymerizable resin precursor (B)) ÷ number of functional groups, and is calculated as follows. (Molecular weight of the photopolymerizable resin precursor (B)) ÷ (number of (meth)acryloyl groups) The "(meth)acryloyl group number" refers to the total representation of the number of acryloyl groups contained in the photopolymerizable resin precursor (B) and the number of methacryloyl groups contained in the photopolymerizable resin precursor (B), respectively.

[0026] Examples of the trifunctional (meth)acrylate include trimethylolpropane triacrylate (trade name: NK Ester A-TMPT, NK Ester A-TMPT-9EO (manufactured by Shin-Nakamura Chemical Co., Ltd.)), ethoxylated trimethylolpropane triacrylate (trade name: NK Ester AT-20E (manufactured by Shin-Nakamura Chemical Co., Ltd.)), ethoxylated glycerin triacrylate (trade name: NK Ester A-GLY-3E, A-GLY-9E, A-GLY-20E (manufactured by Shin-Nakamura Chemical Co., Ltd.)), tris(2-acryloxyethyl) isocyanurate (trade name: NK Ester A-9300 (manufactured by Shin-Nakamura Chemical Co., Ltd.)), pentaerythritol triacrylate (trade name: NK Ester A-TMM-3, A-TMM-3L, A-TMM-3LM-N (manufactured by Shin-Nakamura Chemical Co., Ltd.)), Trimethylolpropane trimethacrylate (trade name: NK Ester TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.), trimethylpropane acrylate (trade name: Aronix M-309, manufactured by Toagosei Co., Ltd.), trimethylolpropane PO-modified triacrylate (trade names: Aronix M-310, 321, manufactured by Toagosei Co., Ltd.), trimethylolpropane EO-modified triacrylate (trade names: Aronix M-350, 360, manufactured by Toagosei Co., Ltd.), isocyanuric acid EO-modified triacrylate (trade names: Aronix M-313, 315, manufactured by Toagosei Co., Ltd.), pentaerythritol triacrylate (trade names: Aronix M-306, 305, manufactured by Toagosei Co., Ltd.), trimethylolpropane triacrylate (trade name: Light Acrylate TMP-A, manufactured by Kyoeisha Chemical Co., Ltd.), pentaerythritol triacrylate (trade name: Light Acrylate PE-3A, manufactured by Kyoeisha Chemical Co., Ltd.), trimethylolpropane trimethacrylate (trade name: Light Ester TMP, manufactured by Kyoeisha Chemical Co., Ltd.). However, from the viewpoints of having an acrylic equivalent that achieves both storage stability and conductivity and having good solubility, ethoxylated glycerol triacrylate, namely NK Ester A-GLY-3E (trade name of Shin-Nakamura Chemical Co., Ltd.), A-GLY-9E (trade name of Shin-Nakamura Chemical Co., Ltd.), A-GLY-20E (trade name of Shin-Nakamura Chemical Co., Ltd.), or trimethylolpropane EO-modified triacrylate (trade names: Aronix M-350, 360, manufactured by Toagosei Co., Ltd.) is preferably used. These may be used alone or in combination of two or more kinds.

[0027] Examples of the monofunctional (meth)acrylate include isopentyl acrylate, lauryl acrylate, stearyl acrylate, ethoxydiethylene glycol acrylate, methoxy-triethylene glycol acrylate, 2-ethylhexyl diglycol acrylate, methoxy-polyethylene glycol acrylate, methoxydipropylene glycol acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxy-polyethylene glycol acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl-succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxyethyl-phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, neopentyl glycol-acrylic acid-benzoic acid ester, 2-acryloyloxyethyl acid phosphate, Ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, ter-butyl methacrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, n-lauryl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, benzyl methacrylate, phenoxyethyl methacrylate, isobornyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, methoxypolyethylene glycol acrylate, phenoxydiethylene glycol acrylate, ethoxylated-o-phenylphenol acrylate, 2-acryloyloxyethyl succinic acid, methoxydiethylene glycol methacrylate, methoxytetraethylene glycol methacrylate, methoxypolyethylene glycol methacrylate, phenoxyethylene glycol methacrylate, methacryloyloxyethyl succinic acid. From the viewpoint of being able to reduce the viscosity, it is preferable to use isobornyl acrylate and tetrahydrofurfuryl acrylate. These may be used alone or in combination of two or more.

[0028] Examples of the bifunctional (meth)acrylate include triethylene glycol diacrylate, PEG200# diacrylate, PEG400# diacrylate, PEG600# diacrylate, polytetramethylene glycol diacrylate, polytetramethylene glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, dimethylol-tricyclodecane diacrylate, EO adduct diacrylate of bisphenol A, PO adduct diacrylate of bisphenol A, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,6-hexanediol dimethacrylate, glycerin dimethacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, and EO adduct dimethacrylate of bisphenol A. From the viewpoint of solubility, it is preferable to use 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, or dimethylol-tricyclodecane diacrylate. These may be used alone or in combination of two or more.

[0029] Examples of the tetrafunctional or higher functional (meth)acrylate include pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, and ditrimethylolpropane tetraacrylate. From the viewpoint of solubility, it is preferable to use ethoxylated pentaerythritol tetraacrylate. These may be used alone or in combination of two or more.

[0030] (B) The blending amount of the photopolymerizable resin precursor is preferably 10 to 45% by mass based on the total mass of the photocurable conductive paste from the viewpoints of curability and coatability of the photocurable conductive paste and conductivity of the cured film.

[0031] 3. Photopolymerization Initiator (C) The photoinitiator (C) absorbs the irradiated ultraviolet rays or the like, generates radicals, and initiates the photopolymerization reaction. There is no particular limitation as long as it has the function of initiating radical polymerization by photoexcitation. From the viewpoint of curability by UV-LED irradiation that is lower in cost and more environmentally friendly than a mercury lamp, a compound in which the function of the photoinitiator is exhibited by light with a wavelength of 450 to 300 nm is preferable. Examples of the photoinitiator that can be used include, as the molecular cleavage type, 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one, 2-benzyl-2-(dimethylamino)-4-morpholinobutyrophenone, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl-2,4,6-trimethylbenzoyldiphenylphosphine oxide 6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,4-trimethylpentylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone, benzoin alkyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, etc. Examples of the hydrogen abstraction type include benzyl, benzophenone, 4-phenylbenzophenone, isophthalophenone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, 4-benzoyl-4'-methyl-diphenyl sulfide, etc.

[0032] The photopolymerization initiator (C) of the present invention preferably exhibits photosensitivity capable of obtaining sufficient curability even in a conductive paste with poor light permeability. Among the above-mentioned photopolymerization initiators, 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one has good curability by UV-LED irradiation at a lower cost and with more environmental consideration than a mercury lamp, and can be suitably used for curing a relatively thick conductive paste with poor light permeability.

[0033] The blending amount of the photopolymerization initiator (C) is not particularly limited. However, from the viewpoints of suppressing uncuring of the photocurable conductive paste and suppressing deterioration caused by the uncured portion reacting with the cured film when receiving light, it is preferably 0.2 to 5.0% by mass based on the total mass of the photocurable conductive paste of the present invention.

[0034] It is also possible to use a sensitizer in combination to reduce oxygen inhibition in the photopolymerization reaction system and promote the initiation reaction of the above-mentioned photopolymerization initiator (C). Examples of the sensitizer include trimethylamine, triethylamine, methyldiethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N,N-dimethylbenzylamine, and 4,4'-bis(diethylamino)benzophenone. The blending amounts of the photopolymerization initiator and the sensitizer are within a range that does not impair the effects of the present invention.

[0035] 4. Other Components The photocurable conductive paste of the present invention may be mixed with other components such as a polymerization inhibitor, an antioxidant, and a surfactant as necessary within a range that can achieve the object of the present invention.

[0036] Among the above, the polymerization inhibitor can be used to improve the storage stability of the photocurable conductive paste. Specific examples of the polymerization inhibitor include 4-methoxyphenol, hydroquinone, hindered amine, and phenothiazine.

[0037] The polymerization inhibitor used in the photocurable conductive paste of the present invention may be one kind or a mixture of two or more kinds.

[0038] When the content of the polymerization inhibitor is 0.001 to 1% by weight based on the total amount of the photocurable conductive paste, it is preferable because the increase in viscosity is small even during long-term storage. Considering the balance with photocurability, it is more preferably 0.001 to 0.5% by weight, and even more preferably 0.001 to 0.1% by weight.

[0039] 5. Method for preparing the photocurable conductive paste The photocurable conductive paste of the present invention can be obtained by mixing the above components (A), (B), (C) and other components in an arbitrary order. It is preferable to perform the mixing promptly. As the dispersion method, methods such as a two-roll mill, a three-roll mill, a sand mill, a roll mill, a ball mill, a colloid mill, a jet mill, a bead mill, a kneader, a homogenizer, and a rotating and revolving mixer can be adopted.

[0040] 6. Viscosity of the photocurable conductive paste When the photocurable conductive paste of the present invention is used, it is supplied onto a substrate by coating, dropping, etc., and thus has a film-like shape or a predetermined pattern on the substrate. From the viewpoint of enhancing the ease of supplying the polymerizable composition onto such a substrate, the photocurable conductive paste of the present invention preferably has a viscosity at 25°C of 100 Pa·s or less. In particular, when the supply of the photocurable conductive paste onto the substrate is performed by flexographic printing, gravure printing, pad printing, dispenser printing, or inkjet printing, it is preferable to satisfy the above viscosity range.

[0041] 7. Storage of the photocurable conductive paste The photocurable conductive paste of the present invention has a small increase in viscosity during storage and good storage stability when stored at -20 to 50°C.

[0042] 8. Method for producing a cured film of the photocurable conductive paste 8-1. Coating Method of Photo-Curable Conductive Paste As the coating method of the photo-curable conductive paste of the present invention, it can be used in known coating methods such as screen printing, pad printing, dispenser printing, flexographic printing, gravure printing, inkjet printing, offset printing, bar coating method, applicator method, dip coating method, flow coating method, spin coating method, roller coating method, reverse coating method, air knife coating method, etc., and can be appropriately selected according to the shape of the substrate to be coated. In particular, when forming an electronic circuit on various substrates by flexographic printing, gravure printing, pad printing, dispenser printing, or inkjet printing, by using the photo-curable conductive paste of the present invention, good printing can be achieved without causing rubbing or pinholes. Also, in conventional flexographic printing, gravure printing, pad printing, dispenser printing, and inkjet printing, it was difficult to cure with only ultraviolet rays without heating the conductive paste, but by using the photo-curable conductive paste of the present invention, it can be cured at room temperature. Therefore, the photo-curable conductive paste of the present invention is suitable for flexographic printing, gravure printing, pad printing, dispenser printing, and inkjet printing.

[0043] 8-2. Curing Method of Photo-Curable Conductive Paste As the energy rays for curing the photo-curable conductive paste of the present invention, ultraviolet rays, visible light, infrared rays, electron beams, etc. are used, but ultraviolet rays and electron beams are preferred for realizing high-speed printing.

[0044] As an ultraviolet irradiation device, a light source that usually includes light in the range of 200 to 500 nm, for example, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a gallium lamp, a xenon lamp, a carbon arc lamp, or a light-emitting diode (LED) can be used. On the other hand, when curing with an electron beam, an electron beam accelerator having an energy of usually 100 to 500 eV can be used. The conductive paste of the present invention can obtain excellent curability even when an LED is used as the light source. In addition, when using an LED, curing can be performed with low energy without generating ozone. The light from the LED is preferably an active energy ray whose wavelength peak is within the range of 365 to 420 nm.

[0045] As an example of the ultraviolet irradiation device, a UV-LED (manufactured by CCS Inc., lamp wavelength: 365 nm) equipped with a UV-LED lamp "LSS-08aAUV" as the light source can be mentioned. Also, as preferable ultraviolet irradiation conditions, conveyor speed: 1.3 m / min, peak illuminance: 2800 mW / cm 2 , integrated light quantity: 5000 mJ / cm 2 are exemplified. Note that the UV illuminance and UV exposure amount were measured using a UV monitor (UV-Pad, manufactured by Opsytec), and the wavelength was in the range of UV-A (315 - 400 nm).

[0046] The film thickness of the cured film formed using the photocurable conductive paste of the present invention is usually 3 to 50 μm, preferably 5 to 30 μm. If it is within the range of 5 to 30 μm, sufficient hardness can be obtained without a decrease in adhesion to the substrate, and the risk of non-conduction is also low.

[0047] The material of the substrate to which the photocurable conductive paste of the present invention is applied is not limited as long as the paste can be applied. For example, polyvinyl alcohol, polyvinyl chloride, polyester, heat-shrinkable polyester, styrene resin, polyolefin, polyimide, polycarbonate, triacetyl cellulose, polyethersulfone, polyethylene terephthalate, and glass can be mentioned.

[0048] 9. Substrate with a conductive cured film The substrate with the conductive cured film of the present invention is not particularly limited as long as it has the conductive cured film of the present invention. However, it is preferable that the above-mentioned cured film is provided on at least one type of substrate selected from the group consisting of the substrate, particularly polyvinyl alcohol, polyvinyl chloride, polyester, heat-shrinkable polyester, styrene resin, polyolefin, polyimide, polycarbonate, triacetyl cellulose, polyethersulfone, polyethylene terephthalate, and glass. Such a substrate with a cured film can be formed, for example, by applying the photocurable conductive paste of the present invention on a substrate such as polyethylene terephthalate in a full area or a predetermined pattern (such as a line pattern) by the above-mentioned coating method or the like, and then subjecting it to the drying treatment and the curing treatment as described above.

[0049] 10. Electronic components and other applications The electronic component of the present invention is an electronic component having the above-mentioned conductive cured film or a substrate with a conductive cured film. Examples of such electronic components include RF-ID, solar cell circuits, antennas, electromagnetic wave shields, substrate circuits, touch panel electrodes, electronic circuits, precision conductor circuits, EL circuits, LED circuits, membrane wirings, GPS antennas, flexible circuits, display wirings, IC tags, and wearable electronics. In addition, the photocurable conductive paste of the present invention can be used for various substrates, particularly for food products, beverages, drugs, cosmetics, personal care products, photographic films, etc. that cannot be heat-treated, which have been difficult to use conductive pastes with excellent conductivity in the past, for packaging bodies, thin films, electrode materials, etc.

Examples

[0050] Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. Each physical property in the examples and comparative examples was measured under the following conditions.

[0051] 1. Storage stability The prepared photocurable conductive paste was stored in a constant temperature bath at 45°C for a certain period, and its storage stability was evaluated. The number of days of storage when solidification was observed in a part of the stored composition and it could not return to the original paste state even after stirring with a spatula was recorded. In Tables 1 and 2, those that maintained the paste state even after 7 days were marked with ○, and those that did not maintain the paste state within 7 days were marked with ×.

[0052] 2. Evaluation of volume resistivity Using a resistivity meter (Loresta-GP, probe: ESP, manufactured by Nitto Seiko Analytic Co., Ltd.), the resistance value of the cured film prepared on PET from the photocurable conductive paste was measured. Also, the size and film thickness of the cured film were measured, and the volume resistivity was obtained from the measured resistance value. It can be judged that the lower the volume resistivity, the higher the conductivity. In Tables 1 and 2, when the volume resistivity was less than 11.0×10 -4 Ω·cm, it was marked with ○○, when the value was between 11.0 and 14.0×10 -4 Ω·cm, it was marked with ○, and when the value was greater than 14.0×10 -4 Ω·cm, it was evaluated as ×. For those with a measured resistance value that was too high to be evaluated, it was marked as Over.

[0053] 3. Solvent resistance A paper wipe (Kimwipe; registered trademark, manufactured by Nippon Paper Crecia Co., Ltd.) was impregnated with acetone, and the cured film prepared on PET from the photocurable conductive paste was rubbed 3 times. In Tables 1 and 2, during this rubbing, if the cured film did not peel off or dissolve and did not adhere to the wipe and there was no change on the surface of the cured film, the solvent resistance was marked as ○, if the surface of the cured film was slightly dissolved and the surface became rough, it was marked as △, and if the film was completely wiped off, it was marked as ×. For films with insufficient curing and a soft film surface where this test could not be performed, they were considered uncured.

[0054] 4. Adhesion A tape for peeling was attached to a cured film prepared on PET from a photocurable conductive paste, and the peeling state when peeled off was observed. In Tables 1 and 2, it was evaluated as ○ if the cured film was not peeled off together with the tape, and as × if peeling occurred. As the tape for peeling, Scotch #610 (product name, manufactured by 3M) was used.

[0055] In the examples and comparative examples, the following components were used. Appropriate abbreviations shown below are used to indicate each component. Hereinafter, the term "particle size" shall mean the average particle size (particle size distribution 50% particle size D50).

[0056] Conductive filler (A) · A-1: 10% Ag-coated FCC-TBX; dendritic silver-coated copper powder (particle size; 6.8 μm, product name manufactured by Fukuda Metal Foil & Powder Co., Ltd.) · A-2: ACBY-225; dendritic silver-coated copper powder (particle size; 6.4 μm, product name manufactured by Mitsui Mining & Smelting Co., Ltd.) · A-3: 10% Ag-coated Cu-HWQ; spherical silver-coated copper powder (particle size; 6.4 μm, product name manufactured by Fukuda Metal Foil & Powder Co., Ltd.) · A-4: 10% Ag-coated 05KY-2; spherical silver-coated copper powder (particle size; 5.4 μm, product name manufactured by Mitsui Mining & Smelting Co., Ltd.) · A-5: 10% Ag-coated 03K; spherical silver-coated copper powder (particle size; 3.3 μm, product name manufactured by Mitsui Mining & Smelting Co., Ltd.) · A-6: 10% Ag-coated 05KP; plate-shaped silver-coated copper powder (particle size; 6.1 μm, product name manufactured by Mitsui Mining & Smelting Co., Ltd.) · A-7: 10% Ni-P-coated 05KY-2; spherical nickel-coated copper powder (particle size; 5.8 μm, prepared by the preparation method described below) · A-8: MA-C05KY-2; spherical copper powder (particle size; 5.2 μm, product name manufactured by Mitsui Mining & Smelting Co., Ltd.)

[0057] Preparation method of the above A-7 MA-C05KY-2; spherical copper powder (particle size: 5.2 μm, trade name of Mitsui Mining & Smelting Co., Ltd.) was plated with a nickel and phosphorus mixture so that the plating amount was 10 wt%. Spherical powder with a particle size of 5.8 μm (A-7: 10% Ni-P coated C05KY-2; spherical nickel-coated copper powder) was obtained.

[0058] Photopolymerizable resin precursor (B) The number of functional groups and acrylate equivalent of the main component are shown. Note that the number of functional groups represents the number of (meth)acrylate groups. · IBXA; isobornyl acrylate (acrylate equivalent: 208.3, number of functional groups: 1, manufactured by Osaka Organic Chemical Industry Co., Ltd.) · A-DOD-A; 1,10-decanediol diacrylate (NK Ester A-DOD-A; trade name, acrylate equivalent: 141.2, number of functional groups: 2, manufactured by Shin-Nakamura Chemical Co., Ltd.) · M-930; glycerin triacrylate (Aronix M-930; trade name, acrylate equivalent: 86.1, number of functional groups: 3, manufactured by Toagosei Co., Ltd.) · A-GLY-3E; ethoxylated glycerin triacrylate (NK Ester A-GLY-3E; trade name, acrylate equivalent: 128.8, number of functional groups: 3, manufactured by Shin-Nakamura Chemical Co., Ltd.) · A-GLY-9E; ethylene oxide-modified glycerin triacrylate (NK Ester A-GLY-9E; trade name, acrylate equivalent: 216.9, number of functional groups: 3, manufactured by Shin-Nakamura Chemical Co., Ltd.) · A-GLY-20E; ethylene oxide-modified glycerin triacrylate (NK Ester A-GLY-20E; trade name, acrylate equivalent: 378.4, number of functional groups: 3, manufactured by Shin-Nakamura Chemical Co., Ltd.) · ATM-4E; ethoxylated pentaerythritol tetraacrylate (NK Ester ATM-4E; trade name, acrylate equivalent: 132.1, number of functional groups: 4, manufactured by Shin-Nakamura Chemical Co., Ltd.) · DPEA-12; ethylene oxide-modified dipentaerythritol hexaacrylate (KAYARAD DPEA-12; trade name, acrylate equivalent: 184.5, number of functional groups: 6, manufactured by Nippon Kayaku Co., Ltd.) · DPCA-60; Caprolactone-modified dipentaerythritol hexaacrylate (KAYARAD DPCA-60; trade name, acrylic equivalent: 210.6, number of functional groups: 6, manufactured by Nippon Kayaku Co., Ltd.)

[0059] Photopolymerization initiator (C) · Irg379; 2-(Dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one (Omnirad379EG; trade name, manufactured by IGM Resins B.V.)

[0060] Other components · Phenothiazine (molecular formula: C 12 H 9 NS, manufactured by FUJIFILM Wako Pure Chemical Corporation)

[0061] [Example 1] <Preparation of photocurable conductive paste 1> After weighing A-GLY-3E (100 g), which is a photocurable resin precursor (B), (C) photocuring initiator Irg379 (10 g), and phenothiazine (0.05 g) in a container, the obtained solution was filtered through a membrane filter made of ultra-high molecular weight polyethylene (hydrophobic) with a pore size of 1.0 μm (manufactured by Nippon Integris Co., Ltd.) to obtain a photocurable binder composition. Subsequently, 29 g of the photocurable binder composition and 71 g of 10% Ag-coated FCC-TBX, which is (A) a conductive filler, were weighed and mixed in a plastic container, and then stirred at 2000 rpm for 5 minutes using a planetary mixer (Avatoki Ren-taro ARE-310, manufactured by Shin-Kee Co., Ltd.; Avatoki Ren-taro is a registered trademark) to obtain photocurable conductive paste 1. When the viscosity of the paste was measured using an E-type viscometer (TV-22 manufactured by Toki Sangyo Co., Ltd.), it was 1.5 Pa·s. In addition, the storage stability was evaluated using the prepared photocurable conductive paste 1. The above results are shown in Table 1.

[0062] <Production of cured film> On a PET film (Cosmoshine (registered trademark), one-sided easy-adhesion type A4160, thickness 188 μm, manufactured by Toyobo Co., Ltd.), a photocurable conductive paste 1 (not after storage stability evaluation) prepared using an applicator (manufactured by Tester Sangyo Co., Ltd.) was applied. Then, using a UV-LED lamp "LSS-08aAUV" light source: UV-LED (manufactured by CCS Inc., lamp wavelength: 365 nm), ultraviolet light with a wavelength of 365 nm was irradiated at a UV illuminance of 2800 mW / cm 2 and a UV exposure dose of 5000 mJ / cm 2 to obtain a conductive cured film 1 of the photocurable conductive paste. The UV illuminance and UV exposure dose were measured using a UV monitor (UV-Pad, manufactured by Opsytec) in the range of UV-A (315 - 400 nm).

[0063] [Evaluation of the cured film] The volume resistivity, solvent resistance, and adhesion of the obtained conductive cured film were evaluated. The above results are shown in Table 1.

[0064] [Examples 2 - 15] Except for using the raw materials shown in Table 1, photocurable conductive pastes 2 - 15 were prepared in the same manner as the photocurable conductive paste 1 prepared in Example 1. Also, the storage stability of the prepared photocurable conductive pastes 2 - 15 was evaluated in the same manner as in Example 1. The evaluation results of the storage stability are shown in Table 1. Using photocurable conductive pastes 2 - 15 (not after storage stability evaluation), conductive cured films 2 - 15 were produced in the same manner as in Example 1, and the volume resistivity, solvent resistance, and adhesion were evaluated. The above results are shown in Table 1.

[0065] [Comparative Examples 1 - 8] Except for using the raw materials shown in Table 2, photocurable conductive pastes 16 - 23 were prepared in the same manner as the preparation method of the photocurable conductive paste used in Example 1. Also, the storage stability of the prepared photocurable conductive pastes 16 - 23 was evaluated in the same manner as in Example 1. The evaluation results of the storage stability are shown in Table 2. Using photocurable conductive pastes 16 to 23 (not those after storage stability evaluation), conductive cured films 16 to 23 were produced in the same manner as in Example 1, and the volume resistivity, solvent resistance, and adhesion were evaluated. The above results are shown in Table 2.

[0066] Tables 1 and 2 show the evaluation results of the raw materials, viscosities, and storage stabilities of the photocurable conductive pastes 1 to 23 used in Examples 1 to 15 and Comparative Examples 1 to 8, and the physical property evaluation results of the conductive cured films 1 to 23. In these tables, the term "number + functional" means that it has the number of (meth)acrylate groups corresponding to the number. For example, if it is "bifunctional", it has two (meth)acrylate groups in one molecule.

[0067]

Table 1

[0068]

Table 2

[0069] In Tables 1 and 2 above, when comparing Examples 1 to 15 with Comparative Examples 1 to 6, it was found that when the photocurable conductive paste contains trifunctional (meth)acrylate, both conductivity (i.e., low volume resistivity) and storage stability are achieved. From Examples 11 to 15, it was found that even when using (meth)acrylate other than trifunctional (meth)acrylate in combination with trifunctional (meth)acrylate, both conductivity and storage stability can be achieved. When comparing Examples 1 to 13 with Examples 14 and 15, it was found that when the acrylic equivalent of trifunctional (meth)acrylate is 90 or more and 220 or less, higher conductivity is ensured. When comparing Examples 1 to 3 with Examples 4 to 13, it was found that when using dendritic silver-coated copper powder, the addition amount of the conductive filler can be suppressed. Comparing Examples 4 to 8 and Examples 10 to 13 with Example 9, it was found that better conductivity can be obtained when the spherical silver-coated copper powder is 85 to 90% by mass based on the total mass of the photocurable conductive paste.

Industrial Applicability

[0070] The photocurable conductive paste of the present invention can be suitably used in the formation of electric circuits and in the formation of external electrodes of ceramic capacitors. In addition, the conductive cured film obtained from the photocurable conductive paste of the present invention can be suitably used alone or as a substrate for many electronic components.

Claims

1. A conductive filler (A), a photopolymerizable resin precursor (B), and a photoinitiator (C) are included, wherein the conductive filler (A) is copper coated with silver on its surface, and the photopolymerizable resin precursor (B) contains a trifunctional (meth)acrylate, characterized in that it is a photocurable conductive paste.

2. The photocurable conductive paste according to Claim 1, wherein the photopolymerizable resin precursor (B) further contains one or more (meth)acrylates selected from the group consisting of monofunctional, difunctional, and tetrafunctional or higher (meth)acrylates.

3. The photocurable conductive paste according to Claim 1, wherein the trifunctional (meth)acrylate that is the photopolymerizable resin precursor (B) has an acrylic equivalent of 90 or more and 220 or less.

4. The photocurable conductive paste according to Claim 3, wherein the photopolymerizable resin precursor (B) contains ethoxylated glycerol triacrylate.

5. The photocurable conductive paste according to Claim 1, wherein the shape of the conductive filler (A) is dendritic.

6. The photocurable conductive paste according to Claim 5, wherein the blending amount of the conductive filler (A) is 55 to 80% by mass based on the total mass of the photocurable conductive paste.

7. The photocurable conductive paste according to Claim 1, wherein the conductive filler (A) has one or more shapes selected from spherical or plate-like, and the average particle diameter of the conductive filler (A) is 2 to 8 μm.

8. The photocurable conductive paste according to Claim 7, wherein the blending amount of the conductive filler (A) is 85 to 90% by mass based on the total mass of the photocurable conductive paste.

9. A conductive cured film obtained by photocuring the photocurable conductive paste according to Claim 1.

10. A substrate having the conductive cured film according to Claim 9.

11. An electronic component having the conductive cured film according to Claim 9 or the substrate according to Claim 10.

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