conductive paste

Abstract

The object of this invention is to provide a conductive paste that can form a wiring pattern that can suppress the decrease in conductivity during the process of forming an insulating layer. [Solution] A conductive paste comprising a curable resin composition and conductive particles, wherein the curable resin composition comprises an epoxy resin, a polyol, and an isocyanate-based curing agent, and the epoxy resin is a solid epoxy resin.

Description

Technical Field

[0001] The present invention relates to a conductive paste.

Background Art

[0002] Conductive pastes are used for forming wiring patterns in the manufacture of electronic components such as printed wiring boards. Conductive pastes usually contain a curable resin composition and conductive particles. In forming a wiring pattern, a coating film of the conductive paste is formed on a substrate by a printing method such as screen printing, and the wiring pattern is formed by curing the coating film.

[0003] Conventionally, proposals have been made to improve the performance of wiring patterns. For example, in Patent Document 1, a conductive composition (conductive paste) containing a polyol, an aromatic polyamine, and a conductive filler having a specific aspect ratio has been proposed in order to ensure the flexibility of the wiring pattern. Further, in Patent Document 2, a conductive paste containing specific inorganic flaky particles in addition to a binder resin and conductive particles has been proposed in order to suppress a decrease in the adhesion between the wiring pattern and the base material in a high-temperature and high-humidity atmosphere.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, the wiring patterns formed on the substrate are protected by an insulating layer. In forming these insulating layers, for example, an ink containing a curable resin and a diluent such as a solvent is applied to the wiring pattern to form a coating film, and this coating film is cured by ultraviolet light or the like. However, during the process of forming such an insulating layer, there is a risk that the conductivity of the wiring pattern may decrease.

[0006] In view of the above circumstances, the object of the present invention is to provide a conductive paste that can form a wiring pattern that can suppress the decrease in conductivity during the process of forming an insulating layer. [Means for solving the problem]

[0007] The conductive paste according to the present invention is as follows: (1) A curable resin composition and conductive particles are included. The curable resin composition comprises an epoxy resin, a polyol, and an isocyanate-based curing agent. The epoxy resin is a solid epoxy resin, a conductive paste.

[0008] (2) The conductive paste according to (1) above, wherein the mass-average molecular weight of the solid epoxy resin is 5000 or more.

[0009] (3) The conductive paste according to (1) or (2) above, wherein the hydroxyl value of the polyol is 80 mg KOH / g or more and 160 mg KOH / g or less.

[0010] (4) The conductive paste according to any one of (1) to (3) above, wherein the equivalent ratio (NCO / OH) of the isocyanate groups of the isocyanate-based curing agent to the hydroxyl groups of the polyol is 0.8 or more and 2 or less.

[0011] (5) The conductive paste according to any one of (1) to (4) above, wherein the content of the solid epoxy resin is 3 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the curable resin composition.

[0012] (6) The conductive paste according to any one of (1) to (5) above, wherein the polyol is at least one of polycarbonate polyol and polyester polyol.

[0013] (7) The isocyanate-based curing agent is a blocked polyisocyanate. The conductive paste according to any one of (1) to (6) above, wherein the polyisocyanate constituting the blocked polyisocyanate is of the isocyanurate type. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a conductive paste that can form a wiring pattern that can suppress the decrease in conductivity during the process of forming an insulating layer. [Modes for carrying out the invention]

[0015] An embodiment of the conductive paste according to the present invention will be described with an example of its use in the process of forming wiring patterns in the manufacturing of printed circuit boards.

[0016] The conductive paste comprises a curable resin composition and conductive particles. The curable resin composition comprises a solid epoxy resin, a polyol, and an isocyanate-based curing agent. The conductive paste may contain a solvent as a diluent. The conductive paste is liquid before the curable resin composition is cured. Note that "liquid" does not mean only low viscosity substances that exhibit fluidity solely due to gravity at room temperature (25°C), but also includes semi-solid substances referred to as pastes.

[0017] The curable resin composition of this embodiment is specifically a thermosetting resin composition.

[0018] The wiring pattern forming process according to this embodiment includes a printing process of forming a coating film on a substrate by a printing method using the conductive paste as ink, and a curing process of curing the coating film to form a wiring pattern. Next, the wiring pattern formed on the substrate will be protected by an insulating layer. Examples of the insulating layer include an interlayer insulating film in a multilayer printed wiring board and a solder resist of various printed wiring boards. The insulating layer lamination process includes, for example, a process of applying a resin composition containing a thermosetting resin or a photocurable resin and a diluent such as a solvent on the wiring pattern to form a coating film, and curing the coating film to form the insulating layer. At this time, it is considered that a diluent such as a solvent contained in the resin composition for forming the insulating layer contacts the wiring pattern and erodes the cured product of the curable resin composition, reducing the conductivity of the wiring pattern. In contrast, the conductive paste of this embodiment is considered to be able to suppress the reduction in the conductivity of the wiring pattern as described above by containing a solid epoxy resin. Note that the performance of such a wiring pattern may be referred to as resist resistance hereinafter.

[0019] The mass average molecular weight of the solid epoxy resin is preferably 1500 or more, more preferably 2500 or more, and even more preferably 5000 or more. Also, the mass average molecular weight of the solid epoxy resin may be 10000 or more, 20000 or more, 30000 or more, or 40000 or more. The mass average molecular weight of the solid epoxy resin is, for example, 100000 or less, and may be 60000 or less. The mass average molecular weight is measured by gel permeation chromatography (GPC). The specific measurement conditions are as follows. (GPC measurement conditions) Measuring device: HLC-8120GPC (product name, manufactured by Tosoh Corporation) Column: TSKgel GMH-H(S)×2 (product number, manufactured by Tosoh Corporation) Flow rate: 0.5 ml / min Injection volume: 100 μL Column temperature: 40℃ Eluent: Tetrahydrofuran (THF) Injection sample concentration: 0.1% by mass Detector: Differential refractometer Standard material for creating calibration curves: Polystyrene

[0020] The epoxy equivalent of the solid epoxy resin is preferably 800 g / eq or more and 10,000 g / eq or less.

[0021] Examples of the solid epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, naphthalene type epoxy resin (specifically naphthol type epoxy resin), biphenyl type epoxy resin (specifically biphenol type epoxy resin), terpene type epoxy resin (specifically terpenol type epoxy resin), brominated bisphenol A type epoxy resin, tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, and other glycidyl ether type epoxy resins; 5,12-dioxahexacyclo[7.6. Examples of alicyclic epoxy resins include 1.0(2,8).0(4,6).0(10,15).0(11,13)]hexadecane and 5,12-dioxaheptacyclo[7.6.1.1(3,7).0(2,8).0(4,6).0(10,15).0(11,13)]heptadecane; and novolac-type epoxy resins such as cresol novolac-type epoxy resin, phenol novolac-type epoxy resin, bisphenol A novolac-type epoxy resin, bisphenol F novolac-type epoxy resin, brominated bisphenol A novolac-type epoxy resin, and brominated bisphenol F novolac-type epoxy resin. Furthermore, the solid epoxy resin may be a rubber-modified epoxy resin, which is a reaction product of the epoxy resin and rubber. Examples of the rubber-modified epoxy resins include NBR-modified epoxy resin, which is a reaction product of epoxy resin and acrylonitrile butadiene rubber (NBR); CTBN-modified epoxy resin, which is a reaction product of epoxy resin and carboxyl-terminated acrylonitrile butadiene rubber; and ATBN-modified epoxy resin, which is a reaction product of epoxy resin and amino-terminated acrylonitrile butadiene rubber.

[0022] The content of the solid epoxy resin is preferably 3 parts by mass or more and 15 parts by mass or less, and more preferably 3 parts by mass or more and 10 parts by mass or less, relative to the curable resin composition. This makes it possible to improve the resistance of the wiring pattern without hindering the imparting of flexibility to the wiring pattern by the polyol.

[0023] The polyol of this embodiment comprises a first polyol and a second polyol having a higher hydroxyl value than the first polyol. The hydroxyl value of the first polyol is, for example, 20 mg KOH / g or more and less than 200 mg KOH / g, preferably 30 mg KOH / g or more and 180 mg KOH / g or less. The hydroxyl value of the first polyol may be 100 mg KOH / g or more and 180 mg KOH / g or less. The hydroxyl value of the second polyol is preferably 200 mg KOH / g or more. The hydroxyl value of the second polyol is, for example, 250 mg KOH / g or less. The first polyol can increase the flexibility of the wiring pattern, and the second polyol can increase the crosslinking density of the cured product and improve the resist resistance.

[0024] The hydroxyl value of the polyol (specifically, the sum of the hydroxyl values ​​of the first polyol and the second polyol) is, for example, 50 mg KOH / g or more and 250 mg KOH / g or less, and preferably 80 mg KOH / g or more and 160 mg KOH / g or less. The hydroxyl value of the polyol can be calculated by (M1 / 100 × OHV1) + (M2 / 100 × OHV2), where M1 is the mass ratio of the first polyol to the total mass of the polyol, M2 is the mass ratio of the second polyol to the total mass of the polyol, OHV1 is the hydroxyl value of the first polyol, and OHV2 is the hydroxyl value of the second polyol.

[0025] The mass ratio of the first polyol to the second polyol (mass of the first polyol:mass of the second polyol) is, for example, 0.1:1 to 50:1, preferably 0.5:1 to 10:1, and more preferably 0.5:1 to 5:1. This allows for a good balance of improved resist resistance and continuous printability.

[0026] The first polyol is preferably at least one of polycarbonate polyol and polyester polyol. The second polyol is preferably at least one of polycarbonate polyol and polyester polyol. This can improve the resist resistance.

[0027] The first polyol and the second polyol may be the same type of polyol or different types of polyol.

[0028] The isocyanate-based curing agent in this embodiment is a blocked polyisocyanate.

[0029] The polyisocyanate constituting the blocked polyisocyanate is preferably an aliphatic polyisocyanate such as hexamethylene diisocyanate. However, the polyisocyanate may also be an aromatic polyisocyanate such as tolylene diisocyanate or diphenylmethane diisocyanate.

[0030] The polyisocyanate is preferably an isocyanurate-type polyisocyanate. That is, the polyisocyanate is preferably a polyisocyanate having a nurate structure. This improves both resist resistance and continuous printability. The polyisocyanate may be billet-type or adduct-type, in which polyisocyanate is added to a polyhydric alcohol.

[0031] Examples of blocking agents constituting the blocked polyisocyanate include active methylene compounds, pyrazole compounds, imidazole compounds, oxime compounds, alcohol compounds, phenolic compounds, acid amide compounds, acid imide compounds, and amine compounds.

[0032] Examples of the active methylene compounds include dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone.

[0033] Examples of the aforementioned pyrazole compounds include pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole.

[0034] Examples of the imidazole compounds include imidazole and 2-methylimidazole.

[0035] Examples of the oxime compounds include formaldehyde oxime, acetaldehyde oxime, acetooxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0036] Examples of the aforementioned alcohol-based compounds include methanol, ethanol, 2-propanol, n-butanol, sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol.

[0037] Examples of the phenolic compounds include phenol, cresol, ethylphenol, butylphenol, nonylphenol, dinonylphenol, styrene-phenol, and hydroxybenzoic acid esters.

[0038] Examples of the acid amide compounds include acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, and γ-butyrolactam.

[0039] Examples of the aforementioned acid-imide compounds include succinimide and maleimide.

[0040] Examples of the amine compounds include diphenylamine, aniline, carbazole, di-n-propylamine, diisopropylamine, and isopropylethylamine.

[0041] Regarding the amount of the isocyanate-based curing agent, the equivalent ratio (NCO / OH) of the isocyanate groups of the isocyanate-based curing agent to the hydroxyl groups of the polyol is, for example, 0.5 to 4, preferably 0.7 to 3, more preferably 0.8 to 2, and even more preferably 0.9 to 2. Considering that the solid epoxy resin can react with the isocyanate-based curing agent, and in order to improve the resistance, the equivalent ratio (NCO / OH) is preferably 1 or more, more preferably 1.1 or more, and even more preferably 1.2 or more, so that a nurate structure derived from the isocyanate-based curing agent can be incorporated into the cured product of the curable resin composition. From this viewpoint, the content of the solid epoxy resin is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, relative to the curable resin composition.

[0042] Examples of the aforementioned solvents include ketone solvents such as methyl ethyl ketone, acetone, and acetophenone; ether solvents such as tetrahydrofuran, methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol, ethyl carbitol, butyl carbitol, and ethylene glycol monomethyl ether; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, and 3-methoxy-3-methyl-1-butyl acetate; and alcohol solvents such as 1-methoxy-2-propanol, diethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether. The aforementioned solvent may be one type or multiple types.

[0043] Examples of the conductive particles include copper particles, silver particles, nickel particles, silver-coated copper particles, nickel-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, and solder particles (including not only those made of an alloy mainly composed of lead and tin, but also those made of so-called lead-free solder that does not contain lead). The shape of the conductive particles is not particularly limited and can be spherical, flake-shaped, dendritic, etc. The average particle size of the conductive particles is preferably 0.5 to 30 μm. The average particle size of the conductive particles can be determined from the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method.

[0044] The content of the conductive particles is, for example, 500 parts by mass or more and 1500 parts by mass or less, and preferably 700 parts by mass or more and 1500 parts by mass or less, per 100 parts by mass of the curable resin composition.

[0045] The solvent content is, for example, 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the curable resin composition.

[0046] The diluent may be an epoxy resin, such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, or 1,6-hexanediol diglycidyl ether, which are reactive diluents that are liquid at room temperature (25°C).

[0047] The viscosity of the conductive paste is preferably 80 Pa·s or less, and more preferably 70 Pa·s or less. The viscosity is measured using a Brookfield E-type viscometer (cone plate type), with a CPA-52A spindle, at 25°C and a rotation speed of 5 rpm.

[0048] Other additives include, for example, plasticizers, flame retardants, antioxidants, defoamers, adhesion promoters, leveling agents, rheology control agents, and fillers.

[0049] The conductive paste of this embodiment can be manufactured by any suitable method. For example, it can be obtained by dissolving the solid epoxy resin (phenoxy resin) in the solvent to prepare a varnish, adding the conductive particles, the polyol, the isocyanate-based curing agent, and optionally the diluent to the varnish, and stirring. Each component can be added in any suitable order. Methods for stirring each component include using a rotary mixer, a three-roll mixer, a kneader, etc.

[0050] Although one embodiment has been shown above as an example, the conductive paste according to the present invention is not limited to the configuration of the above embodiment. Furthermore, the conductive paste according to the present invention is not limited by the above-described effects. The conductive paste according to the present invention can be modified in various ways without departing from the spirit of the present invention.

[0051] For example, the conductive paste according to the present invention can be used as a bonding material to electrically connect wiring patterns and electronic elements, or as a filler to fill through holes. [Examples]

[0052] The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

[0053] [Raw materials used] Solid epoxy resin 1: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1256, mass-average molecular weight: 50000, epoxy equivalent weight: 7500-8500 g / eq) Solid epoxy resin 2: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1010, mass-average molecular weight: 5500, epoxy equivalent weight: 3000-5000 g / eq) Solid epoxy resin 3: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1007, mass-average molecular weight: 2900, epoxy equivalent weight 1750~2200 g / eq) Solid epoxy resin 4: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1004, mass-average molecular weight: 1600, epoxy equivalent weight 875-975 g / eq) Polyol 1: Polyalkylene carbonate diol (manufactured by Asahi Kasei Corporation, hydroxyl value: 51-61 mg KOH / g, number average molecular weight 2000) Polyol 2: Polyalkylene carbonate diol (manufactured by Asahi Kasei Corporation, hydroxyl value: 200-250 mg KOH / g, number average molecular weight 500) Polyol 3: Polyester polyol (Polylite manufactured by DIC Corporation, hydroxyl value: 56 mg KOH / g) Polyol 4: Polyester polyol (Nipporan, manufactured by Tosoh Corporation; hydroxyl value: 142-160 mg KOH / g) Polyol 5: Polyester polyol (Nipporan, manufactured by Tosoh Corporation; hydroxyl value: 205-221 mg KOH / g) Polyol 6: Polyester polyol (Polylite manufactured by DIC Corporation, hydroxyl value: 25 mg KOH / g) Isocyanate-based curing agent 1: Hexamethylene diisocyanate (manufactured by Asahi Kasei Corporation, Duranate WM44-L70G, solids content: 70% by mass, effective NCO%: 5.3%) Isocyanate-based curing agent 2: Hexamethylene diisocyanate (manufactured by Asahi Kasei Corporation, Duranate SBN-70D, solids content: 70% by mass, effective NCO%: 10.1%) Conductive particles: Silver-coated copper powder (spherical, average particle size 5-6 μm)

[0054] [Example 1] A varnish was prepared by mixing 5.0 parts by mass of solid epoxy resin 1 (manufactured by Mitsubishi Chemical Corporation, trade name "jER1256", bisphenol A type epoxy resin, mass average molecular weight: 50000), isocyanate-based curing agent 1 (manufactured by Asahi Kasei Corporation, trade name "Duranate WM44-L70G", solid content: 70% by mass, effective NCO%: 5.3%), and 38.2 parts by mass of butyl carbitol. To the above varnish, 35.0 parts by mass of polyol 1 (manufactured by Asahi Kasei Corporation, polyalkylene carbonate diol, hydroxyl value: 51-61 mg KOH / g, number average molecular weight 2000), 12.3 parts by mass of polyol 2 (manufactured by Asahi Kasei Corporation, polyalkylene carbonate diol, hydroxyl value: 200-250 mg KOH / g, number average molecular weight 500), and 1055.4 parts by mass of silver-coated copper powder (average particle size 5-6 μm) were added and stirred to obtain a conductive paste.

[0055] [Evaluation 1: Conductivity (Volume Resistivity)] A PET film with a thickness of 188 μm is screen printed using a stainless steel 290-mesh screen printing plate (length 100 mm, width 0.8 mm), and then heat-cured at 130°C for 30 minutes to form a wiring pattern. Next, the resistance value (R) between both ends of the wiring pattern is measured using a tester, and the cross-sectional area (S, cm) is determined. 2 The volume resistivity is calculated from the length (L, cm) using the following formula (1). The results are shown in Tables 1 to 6. Volume resistivity = (S / L) × R···(1) (Evaluation Criteria) ○: 0.7 × 10 -4 less than △: 0.7 × 10 -4 ~1.0×10 -4 ×: 1.0 × 10 -4 Ω cm or more

[0056] [Evaluation 2: Continuous printing capability] A screen printing machine (MT-320TVC) manufactured by Microtech Co., Ltd. was used to perform 80 screen prints (length 100 mm, width 0.8 mm). After screen printing, the viscosity was measured using an E-type viscometer, and the viscosity change rate was calculated from the viscosity before printing. The results are shown in Tables 1 to 6. (Evaluation Criteria) ○: Viscosity change rate is +20% or less △: Viscosity change rate is greater than +20% but less than +50% ×: Viscosity change rate is +50% or more

[0057] [Rating 3: Resistance] A 188μm thick PET film is screen printed (100mm long, 0.8mm wide) using a stainless steel 290-mesh screen printing plate, and then heat-cured at 130°C for 30 minutes to form a pattern. Next, the resistance (R) between both ends of the pattern is measured using a tester, and then UV-curable resist (UVR-150G R60, manufactured by Taiyo Ink Manufacturing Co., Ltd.) is applied to the pattern and cured with ultraviolet light (cumulative light intensity: 2000mJ / cm²). 2 After the resist has cured, the resistance between the patterns is measured using a tester, and the resistance change rate is calculated. The results are shown in Tables 1 to 6. (Evaluation Criteria) ○: Resistance change rate is +50% or less △: Resistance change rate is greater than +50% but less than +100% ×: Resistivity change rate is +100% or more

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] [Table 4]

[0062] [Table 5]

[0063] [Table 6]

Claims

1. A curable resin composition and conductive particles are included. The curable resin composition comprises an epoxy resin, a polyol, and an isocyanate-based curing agent. The epoxy resin is a solid epoxy resin, a conductive paste.

2. The conductive paste according to claim 1, wherein the mass-average molecular weight of the solid epoxy resin is 5000 or more.

3. The conductive paste according to claim 1, wherein the hydroxyl value of the polyol is 80 mg KOH / g or more and 160 mg KOH / g or less.

4. The conductive paste according to claim 3, wherein the equivalent ratio (NCO / OH) of the isocyanate groups of the isocyanate-based curing agent to the hydroxyl groups of the polyol is 0.8 or more and 2 or less.

5. The conductive paste according to claim 4, wherein the content of the solid epoxy resin is 3 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the curable resin composition.

6. The conductive paste according to any one of claims 1 to 5, wherein the polyol is at least one of polycarbonate polyol and polyester polyol.

7. The isocyanate-based curing agent is a blocked polyisocyanate. The conductive paste according to any one of claims 1 to 5, wherein the polyisocyanate constituting the blocked polyisocyanate is of the isocyanurate type.

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