JP2811948B2 - Photocurable conductive paste - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photocurable conductive paste characterized in that it is cured with light only using a photocurable resin composition as a binder.

(Conventional technology and problems) Conventionally, as a conductive paste for forming a conductor, gold,
Noble metal fine powders such as silver, platinum, palladium, etc. and thermosetting resin composition as binder (Polymer Thick Film, hereinafter referred to as PTF), base or baked with glass powder as binder (Cermet Thick Film, hereinafter referred to as CTF) Since both require heat for curing, at present, there are major problems such as warpage, deformation and shrinkage of the printed circuit board due to heat history such as heating and cooling. Therefore, the appearance of a photocurable conductive paste that cures the conductive paste at a temperature near room temperature is desired,
It has not yet reached industrial use. A method using a composition in which a photocurable resin composition is used as a binder and a conductive powder such as silver powder is mixed has been studied, but the composition is applied to an adherend as a coating film by an appropriate method and irradiated with light. Even though the resin layer on the extremely thin surface of the coating film hardens, the inside of the coating film hardly hardens. Further, when the amount of silver powder is reduced or the thickness of the coating film is extremely thinned, curing is performed but sufficient conductivity cannot be obtained.

The reason that the inside of the coating film is hard to cure is that the silver powder blocks or reflects light, so no or almost no light reaches the inside of the coating film. It is presumed that the inside hardly hardens.

(Problem to be Solved by the Invention) A conductive paste using a photocurable resin as a binder is:
For example, JP-A-61-109203, JP-A-63-154773,
JP 63-265979, JP 63-268773, etc., but these are only to temporarily cure the paste by light irradiation to facilitate the handling, as a post-processing, heating or baking. It was necessary and did not form a conductor purely by light irradiation alone. Japanese Patent Laid-Open No. Hei 2
JP-A-1113075 proposes to use a photopolymerization initiator and a thermal polymerization initiator in combination with a photocurable resin composition as a binder. However, there is a disadvantage that the storage stability of the paste is poor because the thermal polymerization initiator used is decomposed at a relatively low temperature.

Further, even when a paste is prepared using a conventionally known photocurable resin composition as a binder and irradiated with light, the paste does not seem to be cured at all or only the extremely thin surface of the coating film is cured.

However, the present invention has been made in view of such a current situation, and provides a conductive paste which is hardened only by light.

(Means for Solving the Invention) As a result of intensive studies, the present inventors have found that a photocurable resin containing, as an essential component, a photopolymerizable compound (B1) having at least one or more (meth) acrylamide groups in the molecule. When the composition (B) is used as a binder, the conductive fine powder (A)
It has been found that a light-curable conductive paste is obtained which has good dispersibility and can be uniformly cured to the inside by light irradiation, and based on this finding, the present invention has been accomplished.

 Hereinafter, the present invention will be described in detail.

The conductive fine powder (A) used in the present invention includes gold, silver,
In addition to metal powders such as copper, platinum, palladium, and nickel, those obtained by covering the surface of an inorganic substance, plastic, ceramics, or the like with the above metal can be used.

Its content is preferably from 40 to 95% by weight of the photocurable conductive paste in the present invention, more preferably
50 to 90% by weight. If the content is less than 40% by weight,
When the conductivity of the cured product decreases, on the other hand, when it exceeds 95% by weight, the viscosity of the photocurable conductive paste becomes extremely high, and printing becomes difficult.

In the present invention, at least one or more (meth)
There is no particular limitation on the photopolymerizable compound (B1) having an acrylamide group. For example, it can be easily obtained by converting the amino group of an amine compound having at least one primary or secondary amino group into (meth) acryloyl in the molecule. Examples of these amine compounds include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, ethyleneamines such as pentaethylenehexamine, piperidine,
2-methylpiperidine, 4-aminomethylpiperidine,
Piperidine derivatives such as N-aminopropyl-4-pipecholine, piperazine derivatives such as piperazine and 2-methylpiperazine, morpholine derivatives such as morpholine and N-aminopropylmorpholine, ammonia, monomethylamine, dimethylamine, diethylamine, 3 −
Ethoxypropylamine, pyrrolidine, cyclohexylamine, propylenediamine, hexamethylenediamine, 1,4-cyclohexanediamine, o-phenylenediamine, p-phenylenediamine, toluene-2,4-diamine, 4,4'-diphenylmethanediamine, poly Oxypropylenediamine, N, N-dimethylethylenediamine, N, N-dimethyl-1,3-propanediamine, isophoronediamine, iminobispropylamine, 1,2-cyclohexanediamine, poly with primary or secondary amino group Examples include amine compounds such as siloxane and polybutadiene compounds, and prepolymers such as amines at both ends. Furthermore, a photopolymerizable compound (B1) can also be obtained using a reactive monomer having a (meth) acrylamide group. For example, a reaction condensate obtained by a dehydration reaction from N-methylol acrylamide and polyethylene glycol, a reaction adduct obtained by an addition reaction of N-methitol acrylamide and hexamethylene diisocyanate, and the like are included. These photopolymerizable compounds (B1) are used alone or in combination of two or more.

(However, the (meth) acrylamide group represents a methacrylamide group and an acrylamide group.) The photopolymerizable compound (B2) in the present invention is not particularly limited. For example, (1) styrene compounds such as styrene and α-methylstyrene, (2) mono (meth) acrylate compounds such as methyl (meth) acrylate, ethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, (3) ) Ethylene glycol di (meth) acrylate, alkylene glycol di (meth) acrylate compounds such as 1,6-hexanediol (meth) acrylate, (4) trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, etc. (Meth) acrylate compounds and the like, and these are used alone or in combination of two or more.

(However, (meth) acrylate represents methacrylate and acrylate.) The mixing ratio of the photopolymerizable compound (B1) and the photopolymerizable compound (B2) in the photocurable resin composition (B) used in the present invention is as follows. Photopolymerizable compound (B1): Photopolymerizable compound (B2) = 100: 0-1
The ratio is preferably 5:85 (weight ratio), more preferably 75% by weight or less of the photopolymerizable compound (B2). When the content of the photopolymerizable compound (B2) exceeds 90% by weight, the polymerization rate of the photocurable resin composition (B) becomes slow, and the curing time of the photocurable conductive paste becomes long. Of course, it is most preferable to use the photopolymerizable compound (B1) alone. When the photopolymerizable compound (B1) or (B2) is solid, the photocurable resin composition (B) is mixed with another liquid photopolymerizable compound (B1) or (B2). There is no problem because it can be used as a component.

The photopolymerization initiator (B3) used in the present invention includes, for example, 1-hydroxycyclohexylphenyl ketone, 2
-Hydroxy-2-methyl-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 4-t-betyl-
Trichloroacetophenone, 2-methyl-1- [4-
(Methylthio) phenyl] -2-morpholinopropanone-1, benzyldimethyl ketal, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, methyl benzoyl benzoate, 3,
3'-dimethyl-4-methoxybenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, 2,4
-Dimethylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and the like, and these are used alone or in combination of two or more.

In the present invention, the amount of the photopolymerization initiator (B3) in the photocurable resin composition is 0.05 to 20% by weight, preferably 0.5 to 20% by weight.
~ 10% by weight. 0.05% by weight of photopolymerization initiator
When the amount is less than the above, the photocurable resin composition cannot be sufficiently polymerized, and when the amount of the photopolymerization initiator is 20% by weight or more, the chemical resistance and the physical properties after curing deteriorate.

The conditions for curing the photocurable conductive paste of the present invention are not particularly limited. Light sources used for light irradiation include sunlight, chemical lamps, low-pressure mercury lamps, metal halide lamps, xenon lamps, carbon arc lamps, and the like.

The material of the printed circuit board includes paper phenol, glass epoxy, alumina, enamel, beryllia, aluminum nitride, silicon carbide, PET, plastic, and the like, and these are not particularly limited.

(Action) The polymerization rate of the photocurable resin composition in the present invention is much higher than that of an acrylate-based resin which is considered to have a higher polymerization rate among commercially available photocurable resins. Therefore, if the photocurable resin composition according to the present invention is used, even if radical polymerization is initiated only on the surface of the coating film, the polymerization is completed before the radicals at the growth terminals are deactivated and the inside of the coating film is uniform. It is presumed to be cured.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
Of course, the invention is not limited in any way by these examples. In the examples, “parts” means “parts by weight”.

Example 1 An amino group of methyliminobispropylamine (manufactured by Koei Chemical Industry Co., Ltd.) was acryloylated to prepare a bifunctional acrylamide resin.

100 parts of the above acrylamide resin, 300 parts of Agc-B (scale silver powder, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) and 3 parts of photopolymerization initiator Irgacure 907 (manufactured by Ciba Geigy) are well kneaded with a three-roll mill and light-cured. A conductive paste (I) was obtained.

Example 2 An amino group of diethylenetriamine (manufactured by Kanto Denka Kogyo KK) was acryloylated to prepare a trifunctional acrylamide resin.

70 parts of the above acrylamide resin, 30 parts of pentaerythritol tetraacrylate, 300 parts of Agc-B (silver powder on scale, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), photopolymerization initiator Lucirin T
Three parts of PO (manufactured by BASF) were thoroughly kneaded with a three-roll mill to obtain a photocurable conductive paste (II).

Example 3 Iminobispropylamine (manufactured by Koei Chemical Industry Co., Ltd.)
Was acryloylated to prepare a trifunctional acrylamide resin.

100 parts of the above-mentioned acrylamide resin, 300 parts of Agc-B (flaky silver powder, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) and 3 parts of photopolymerization initiator lucilin TPO (manufactured by BASF) are kneaded well with a three-roll mill and are photocurable. A conductive paste (III) was obtained.

Example 4 An amino group of triethylenetetramine (manufactured by Kanto Denka Kogyo KK) was acryloylated to prepare a tetrafunctional acrylamide resin.

70 parts of the above acrylamide resin, 30 parts of pentaerythritol tetraacrylate, 300 parts of Agc-B (flaky silver powder manufactured by Fukuda Metal Foil & Powder Co., Ltd.), photopolymerization initiator Lucirin T
Three parts of PO (manufactured by BASF) were thoroughly kneaded with a three-roll mill to obtain a photocurable conductive paste (IV).

Example 5 Tetraethylenepentamine (manufactured by Kanto Denka Kogyo Co., Ltd.)
Was acryloylated to prepare a pentafunctional acrylamide resin.

70 parts of the above acrylamide resin, 30 parts of pentaerythritol tetraacrylate, 300 parts of Agc-B (silver powder on scale, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), photopolymerization initiator Lucirin T
Three parts of PO (manufactured by BASF) were thoroughly kneaded with a three-roll mill to obtain a photocurable conductive paste (V).

Comparative Example 1 Photocurable resin NKESTER A600 with acrylates at both ends
(Shin Nakamura Chemical Co., Ltd.) 100 parts, Agc-B (Fukuda Metal Foil Powder Co., Ltd., silver powder on scale) 300 parts, photopolymerization initiator Darocur 1173 (Merck) 3 parts The mixture was kneaded well with a roll to obtain a paste (VI).

Example 6 [Production and evaluation of cured product and printed circuit board] A commercially available conductive paste [Dotite FA-3] on a PET substrate
01CA (manufactured by Fujikura Kasei Co., Ltd.)] was used to print two predetermined conductor circuits (hereinafter referred to as electrodes) using a 270 mesh polyester screen plate. The electrode on the printed PET substrate was cured at 120 ° C. for 5 minutes. Next, a photocurable conductive paste (I) was printed so as to partially overlap these two electrodes, and a digital ohmmeter was connected to the electrodes. Immediately thereafter, under a 400W air-cooled high-pressure mercury lamp,
While irradiating light at a distance of 10 cm, the change in the resistance of the paste was monitored.
Seconds was the curing time of the paste. The surface of the obtained printed matter was rubbed with a fingertip, but was not rubbed. When the volume resistivity was calculated from the resistance value and the film thickness at that time, it was 5.00 × 10 ⁻⁴ Ω · cm.

When the adhesion to the substrate was checked according to JIS K5400, it was found that 100
/ 100, indicating good adhesion.

Further, after the above-mentioned coating film was immersed in boiling water at 100 ° C. for 1 hour, the same test was carried out, and it was 100/100. As for its conductivity, the volume resistivity was 4.95 × 10 ⁻⁴ Ω · cm, and almost no deterioration in performance was observed.

270 mesh polyester to check printability
Printing was performed using a screen plate, and when the edge portion was visually judged, no bleeding was observed.

 Table 1 shows the results of these evaluations.

Examples 7 to 10 Evaluation was performed in the same manner as in Example 6 except that the photocurable conductive paste (II to V) was used instead of the photocurable conductive paste (I). It was shown to.

Comparative Example 2 The photocurable conductive pastes (I to
Evaluation was performed in the same manner as in Examples 6 to 10 except that the paste (VI) of Comparative Example 1 was used instead of V).
It is shown in the table.

(Effect of the Invention) The following points are mentioned as excellent effects of the photocurable conductive paste according to the present invention.

(1) The conductive paste can be completely cured only by light irradiation and a few seconds to a few tens of seconds. Therefore, the production line can be significantly speeded up as compared with the conventional thermosetting conductive paste.

(2) There is no problem such as warpage, deformation or shrinkage of the printed circuit board due to heat history such as heating and cooling. It can be used as an adherend.

(3) Since no solvent is contained, the solvent does not evaporate during screen printing or coating, and the screen plate is not clogged. Also, it has excellent work environment.

(4) The obtained final cured product is excellent in adhesion to an adherend and flexibility.

The photo-curable conductive paste of the present invention takes advantage of the above advantages to form a conductive circuit on a printed circuit board, bond chip components, bond between contacts, bond lead wires, and hybrid.
It can be used for a wide variety of applications such as conductors for ICs and electrode terminal parts for resistors.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C09D 5 / 24,4 / 00-4/06 H01B 1/22 H05K 1/09

Claims (3)

(57) [Claims] 1. A photopolymerizable compound (B1) having (A) a conductive fine powder and (B) (I) at least one (meth) acrylamide group in a molecule, or the compound (B1) and a molecule. Mixture with photopolymerizable compound (B2) having no (meth) acrylamide group in it and (II) photopolymerization initiator (B3)
A photocurable conductive paste comprising, as an essential component, a photocurable resin component containing: 2. A cured product obtained by curing the photocurable resin composition according to claim 1 by light irradiation. 3. A printed circuit board comprising a cured product obtained by curing the photocurable resin composition according to claim 1 by light irradiation, on a substrate surface.