JPH0733476B2 - Silver paste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silver paste for a flexible substrate, which has excellent resistance stability and reliability against an insulating coating agent such as an undercoat and an overcoat.

[Conventional technology]

Conventionally, a conductive silver paste in which silver powder is dispersed in a binder and a solvent is known.

These pastes are often screen-printed on a hard substrate such as a glass cloth-based epoxy resin substrate or a paper-based phenol resin substrate or a so-called flexible substrate such as a polyester film or a polyimide film and used as conductor wiring or electrodes.

In recent years, the trend toward lighter, thinner, shorter, and smaller electronic devices and electronic parts is increasing, and the amount of conductive silver paste used for flexible substrates such as membrane switches is increasing.

In conventional silver pastes for flexible substrates, resins having a low softening point such as polyurethane resins, vinyl chloride, vinyl acetate resins, and polybutyral resins are generally used as a binder resin to impart flexibility.

The performance required for the silver paste used for flexible substrates is, of course, low electric resistance, excellent printability, high adhesion strength to the substrate, and excellent bending properties. However, in recent years, as its applications have expanded, higher reliability has been required, and in particular resistance stability to insulating coating agents such as undercoat and overcoat (hereinafter referred to as insulation coating resistance), heat and humidity. The demand for reliability such as stability against heat (hereinafter, stability against heat is referred to as heat resistance, stability against humidity is referred to as moisture resistance) is becoming severe.

Conventionally, silver pastes used for flexible substrates usually use a resin with a low softening point in order to improve the bending properties, and the crosslink density of the resin is usually low, and the adhesion to a polyester film is good. In order to do so, a method of introducing active groups such as -OH and -NCO groups into the binder resin is adopted.

[Problems to be solved by the invention]

However, since these resins are easily immersed in the solvent or low molecular weight compound contained in the insulation coating agent, the solvent or low molecular weight compound permeates into the cured film of the paste before the insulation coating agent hardens. As a result, the electric resistance value changes and becomes unstable with respect to heat and humidity, and since the electric resistance value easily changes over time, it has excellent insulation coating resistance and reliability, and also has good adhesion and adhesion. At present, a well-balanced silver paste excellent in bendability has not been obtained.

The present invention has been made in view of such circumstances, and an object thereof is to provide a silver paste having excellent insulation coat resistance, heat resistance, and moisture resistance. As a result of intensive studies, the present inventors have arrived at the present invention as described below.

[Means for solving problems]

That is, the present invention relates to (1) (a) silver powder, (b) polytetramethylene glycol, and a compound having two hydroxyphenyl groups or a polyoxyalkylene diol obtained by addition-polymerizing an alkylene oxide to a divalent phenol. A polyurethane which is a reaction product of a polyether ester polyol obtained by co-condensing an aromatic polybasic acid and a reactive derivative thereof with a polyfunctional isocyanate, (c) a silver paste containing a solvent as a component, and (2) (a) silver powder, (b) polytetramethylene glycol, a compound having two hydroxyphenyl groups or a polyoxyalkylene diol obtained by addition-polymerizing an alkylene oxide to a divalent phenol, and an aromatic polybase. A poly (ethylene) obtained by co-condensing an acid and its reactive derivative. Polyurethane is the reaction product of chromatography ether ester polyols and polyfunctional Isoshianeto,
A silver paste containing (c) a polyfunctional blocked isocyanate compound and (d) a solvent as components.

The silver powder used in the present invention may be any of flake-like powder, spherical powder and dendritic particles, and they may be used alone, but it is usually preferable to use them in combination.

The polyurethane used in the present invention is a reaction product of a polyether ester polyol, which is an active hydrogen-containing compound, and a polyfunctional isocyanate compound, and functions as a so-called binder.

If a polyfunctional blocked isocyanate compound is used, it also serves as a curing agent. The silver paste of the present invention is sufficiently cured to the extent required as a product even without using a polyfunctional blocked isocyanate compound as a curing agent, but when used in combination, the performance is further improved.

The polyether ester polyol, which is the raw material of the polyurethane of the present invention, is polytetramethylene ether glycol and a compound having two hydroxyphenyl groups or 2
It can be obtained by co-condensing a polyoxyalkylene diol obtained by addition-polymerizing an alkylene oxide to a hydric phenol, an aromatic polybasic acid and a reactive derivative thereof, and a polyol if necessary.

The above polytetramethylene ether glycol has a molecular weight of
It is preferably 300 or more and 3000 or less. When the molecular weight is less than 300, the co-condensate is likely to solidify, and when the molecular weight exceeds 3000, it becomes an extremely high-viscosity liquid, which often causes various obstacles to the subsequent work.

Examples of the compound having two hydroxyphenyl groups include bisphenol A, dihydroxydiphenylmethane, dihydroxydiphenyl ether, and dihydroxydiphenyl sulfone, and examples of the dihydric phenol include hydroquinone, resorcinol and its derivatives. Examples of alkylene oxides that undergo addition polymerization with them include ethylene oxide, propylene oxide and butylene oxide. Specific examples of polyoxyalkylene diols obtained from these materials are, for example, propylene oxide addition polymers of bisphenol A, ethylene oxide and butylene oxide addition polymers of dihydroxydiphenyl sulfone, ethylene oxide addition polymers of dihydroxydiphenyl ether. , Ethylene oxide addition polymers of hydroquinone, ethylene oxide and propylene oxide addition polymers of resorcinol, and the like. The molecular weight of these diols is preferably 1000 or less, and when the molecular weight exceeds 1000, heat resistance and moisture resistance are reduced.

The aromatic polybasic acid is a divalent to tetravalent acid, and examples thereof include normal, iso, and terephthalic acid, trimellitic acid, and pyromellitic acid. Also, anhydrides or lower alkyl esters of these acids can be used. These aromatic polybasic acids are used alone or in combination of two or more.

The molecular weight of the polyol used as needed is 500.
The following is preferable, and if the molecular weight exceeds 500, the viscosity becomes too high, which is not preferable. Examples of the polyol include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6- Hexanediol, diethylene glycol, dipropylene glycol, hydroxypivalic acid ester of neopentyl glycol, 2,3,5-trimethylpentanediol, AOGX24 (trade name, C ₁₂ and C ₁₄ α-olefin manufactured by Daicel Chemical Industries, Ltd.) A mixture of glycols), bisphenol A, glycerin, 1,3,6-hexanetriol, trimethylolpropane, 3-methyl-1,3,5-pentanetriol, pentaerythritol, sorbitol, sucrose and the like.
Further, a polyether polyol having a molecular weight of 500 or less, which is obtained by addition-polymerizing ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran or the like to these compounds, can also be used. These components are used alone or in combination of two or more.

The co-condensed polyetherester polyol of the present invention is produced by reacting the above-mentioned mixture of glycol, diol, and optionally a polyol, with an aromatic polybasic acid. Is usually performed in a nitrogen stream in the presence of a catalyst at 100 to 250 ° C. for 10 to 30 hours under reduced pressure dehydration or dealcoholization under reduced pressure. At this time, it is preferable to use 10% by weight or more of glycol. The hydroxyl value of the obtained polyetherester polyol is preferably 10 to 160 mgKOH / g, and particularly preferably 35 to 140 mgKOH / g.

The above active hydrogen-containing compounds are used alone or in combination of two or more, and the amount thereof is 70% by weight or less, preferably 50% by weight or less in the total active hydrogen containing compounds including the polyether ester polyol. , And most preferably 5% by weight or less.

Examples of the polyfunctional isocyanate compound used in the present invention include tolylene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), naphthylene-1,5-diisocyanate (NDI), and 3,3'-dimethyl. -4,4'-biphenylene diisocyanate (TODI),
Xylene diisocyanate (XDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), crude
TDI, polymethylene polyphenyl isocyanate (crude MDI), isophorone diisocyanate (IPDI),
In addition to hexamethylene diisocyanate (HDI), hydrogenated xylylene diisocyanate (HXDI) and the like, isocyanurate modified products, carbodiimidized modified products and burette modified products of these isocyanates can be mentioned. These various polyfunctional isocyanate compounds may be used alone or in admixture of two or more.

The amount of the polyfunctional isocyanate compound used is such that the NCO group contained in the polyfunctional isocyanate compound is 0.5 or more and 1.5 or less in an equivalent ratio with respect to the total amount of active hydrogen contained in all the active hydrogen-containing compounds, preferably It is 0.8 or more and 1.0 or less. If the equivalent ratio of NCO groups to active hydrogen is more than 1.5, unreacted NCO groups tend to remain at the ends of polyurethane compounds, making them unstable to water and curing with blocked isocyanate compounds as curing agents. It causes inconvenience such as no reaction. If the equivalent ratio is less than 0.5, the bending strength of the cured product will decrease.

Further, the reaction of the polyether ester polyol of the present invention and the polyfunctional isocyanate compound is carried out by a conventional method, but the thermoplastic polyurethane solution obtained has a solid content of 15 to
60% and a viscosity of 200-70,000 centipoise (25 ° C) are common.

The polyfunctional blocked isocyanate compound used as a curing agent is "urethanes: Chemistry and Technology I. Chemistry" (Polyurethanes: Chemistry).
and Technology I. Chemistry) (John Willie and Sons Incorporated, published 1962)
As described in detail on pages 118-121, a polyfunctional isocyanate compound is reacted with a compound having some kind of active hydrogen. For example, when the polyfunctional isocyanate compound is treated at a temperature of 100 ° C or higher, the original polyfunctional Regenerate the isocyanate compound.

Typical examples of the polyfunctional isocyanate compound used to obtain the polyfunctional blocked isocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, metaxylene diisocyanate, naphthalene diisocyanate or these diisocyanate compounds. Ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, glycerin, 1,2,6-hexanetriol, trimethylolpropane, trimethylolethane , Pentaerythritol and the like.

Examples of the compound having active hydrogen that reacts with the polyfunctional isocyanate compound include ethyl malonate, acetylacetone, hydroxylamine, pyrocatechol, acetone oxime, methyl ethyl ketone oxime, phenol, alkylphenol, allyl mercaptan, and aliphatic mercaptans. Is typical.

Specific examples of the blocked isocyanate compound include HD-1, HD-2 shown in Examples 1, 3 and 4 below.
In addition to HD-3, the following are listed.

The solvent used in the present invention preferably has a boiling point of 100 ° C. or higher. If the boiling point is less than 100 ° C., the solvent is liable to volatilize, the viscosity of the silver paste changes during printing, and skinning occurs, which is not preferable. Further, a solvent having no active group that reacts with isocyanate in the molecule is preferable.

Commonly used solvents are xylene, cyclohexanone, methylcyclohexanone, diisobutyl ketone, isophorone, dimethyl carbitol, diethyl carbitol, dibutyl carbitol, butyl cellosolve, ethylene glycol dibutyl ether, dipropylene glycol dimethyl ether, butyl cellosolve acetate, carbitol acetate, butyl. Examples thereof include carbitol acetate, butyl acetate, amyl acetate, cyclohexyl acetate, methyl acetoacetate, ethyl acetoacetate, methyl adipate, dimethyl dalutate and dimethyl succinate. These solvents may be used alone or in combination of two or more.

The amount of each component in the silver paste is not particularly limited, but the following ratios are preferably used. That is, the solvent in the silver paste is 10 to 50% by weight (hereinafter, all parts are by weight), the ratio of the silver powder and the binder polyurethane is 50 to 90 parts to 50 to 10 parts, and the curing agent is usually The functional blocked isocyanate compound is 0 to 50 parts per 100 parts of polyurethane.

To produce the silver paste of the present invention, for example, the silver powder,
Polyurethane as binder, polyfunctional blocked isocyanate compound as curing agent and three rolls of solvent,
A kneader such as a kneader or a crusher is used, or a spatula is used to knead by hand to form a paste. At this time, a filler such as silica powder or talc and other additives may be added and kneaded. The polyurethane and the polyfunctional blocked isocyanate compound are conveniently prepared in advance as a solution in a solvent. Further, the polyfunctional blocked isocyanate compound may be mixed with the silver paste immediately before use such as printing on a substrate without kneading.

The silver paste produced in this manner is usually screen-printed at the time of printing into a desired shape on a flexible substrate such as a polyester film or a polyimide film,
A conductor circuit such as a conductor wiring or a conductor contact can be formed by printing on the thickness and heat treatment. Heat treatment is usually 80
Do above ℃ until the paste is fully cured. When a curing agent is used, the temperature is preferably 100 ° C or higher. Depending on the case, it can be applied to a hard substrate such as a glass fiber reinforced epoxy resin substrate, a paper reinforced phenol resin substrate, a ceramic substrate, an aluminum substrate, and an enamel substrate.

The silver paste of the present invention is used as a conductor wiring or a contact of a flexible substrate by printing and curing, and, for example, a so-called membrane switch is one of the preferable applications.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to specific examples. Various tests were conducted as follows.

<1> Substrate used Polyester film thickness 50 μm <2> Insulation coating resistance Five patterns of 2 mm width x 80 mm length are printed on the substrate with a hand-printing machine (screen mesh, 225, emulsion thickness 10 μm) and then hot air 80 ° C for 30 minutes or 150 in a circulating electric thermostat
After curing at 30 ° C. for 30 minutes, the electrical resistance value was measured using a 4-terminal resistance meter (wide range digital ohm meter, DR-1000, manufactured by Sanwa Keiki Seisakusho Co., Ltd.). Insulation coating agent (Register Coat TMD-430, manufactured by Nippon Acheson Co., Ltd.)
Was printed and cured on the silver paste cured body so that both ends of the pattern were left 5 mm each, and the electrical resistance value of each pattern was measured with a 4-terminal resistance meter. The rate of change in the electric resistance value before and after coating with the insulation coating agent was obtained and used as a measure of the insulation coating resistance.

<3> Reliability After printing and curing in the same manner as in <2> above and measuring the electric resistance value, reliability tests of the following a and b were performed to determine the rate of change of the electric resistance value over time.

B. Heat resistance Using a hot air circulation type electric thermostat, a test was conducted for 1000 hours at a temperature of 80 ° C.

For heat resistance, obtain the rate of change of electrical resistance value after 1000 hours of testing,
I used it as a guide.

(B) Humidity resistance A 1000-hour test was performed in an environment of 40 ° C and 95% RH (relative humidity) using a thermo-hygrostat.

Moisture resistance is the change rate of the electrical resistance value after 1000 hours test,
I used it as a guide.

Example 1 As a binder, 215 parts of polytetramethylene ether glycol having a molecular weight of 650 (parts by weight are shown below: the same applies below), 500 parts of a diol obtained by adding ethylene oxide to bisphenol A having a molecular weight of 345, and isophthalic acid having a molecular weight of 166. Polyether ester polyol which is a reaction product with 185 parts (OH value; 56.1 mgKOH / g, acid value 0.1 mgKOH /
g) Polyurethane solution obtained by reacting 550 parts, diphenylmethane diisocyanate 290 parts, phenyldiethanolamine 140 parts and 1,3,5-pentanetriol 20 parts (nonvolatile content 30.2% by weight, viscosity 6680 centipoise / 25 ° C,
Solvent butyl cellosolve acetate) 32.28 parts, Silver Coat AgC-A (manufactured by Fukuda Metal Foil Powder Co., Ltd.) 32.25
Part and Silcoat AgC-O (same as above) 32.25 parts, as a curing agent
HD-1 0.97 parts (lower structural formula) and butyl cellosolve acetate 2.25 parts as a solvent were kneaded with a three-roll to obtain a silver paste. The HD-1 used was a solution prepared in advance using 1.46 parts of butyl cellosolve acetate used before kneading. The above various evaluations were performed using the obtained silver paste. Curing of silver paste is 150
It was performed at 30 ° C. for 30 minutes.

HD-1 Example 2 Example 1 was repeated except that 64.5 parts of Silcoat AgC-O was used as the silver powder.

Example 3 A polyurethane solution obtained by reacting 550 parts of the polyether ester polyol of Example 1, 287 parts of diphenylmethane diisocyanate, 151 parts of phenyldiethanolamine, and 12 parts of 1,3,5-pentanetriol as a binder (nonvolatile matter 30.0 Weight%, viscosity 25000 centipoise / 25
℃, solvent butyl carbitol acetate) 30.00 parts, silver coat Silcoat AgC-A54.0 parts and AgC-O 6.0 parts, hardener HD-2 (lower structural formula) 0.9 parts, solvent butyl carbitol acetate 9.1 parts Was kneaded with 3 rolls to obtain a silver paste.

The HD-2 used was a solution prepared in advance by using 7.66 parts of butyl carbitol acetate to be used and before kneading.

Hereinafter, the evaluation was performed according to Example 1.

Example 4 Example 3 was repeated except that HD-3 having the following structural formula was used as a curing agent.

HD-3 Example 5 Polyether which is a reaction product of 630 parts of polytetramethylene ether glycol having a molecular weight of 1000 as a binder, 210 parts of a diol obtained by adding ethylene oxide to bisphenol A having a molecular weight of 345, and 160 parts of isophthalic acid having a molecular weight of 166. Reaction of ester polyol (OH value 55.0 mg KOH / g, acid value 0.1 mg KOH / g) 150 parts, diphenylmethane diisocyanate 110 parts, neopentyl glycol 35 parts and 3-methylpentane-1,3,5-triol 6 parts The same procedure as in Example 1 was carried out except that the polyurethane solution thus obtained (nonvolatile matter: 30.0%, 33,500 centipoise / 25 ° C.) was used.

Comparative Example 1 Instead of the polyether ester polyol of Example 1, a polyester polyol (OH value, which is a reaction product of 123 parts of ethylene glycol and 296 parts of adipic acid having a molecular weight of 146,
The same procedure as in Example 1 was carried out except that 56.3 mgKOH / g and an acid value of 0.1 mgKOH / g) were used.

Comparative Example 2 The procedure of Example 1 was repeated except that HD-4 having the following structural formula was used instead of HD-1 as the curing agent.

HD-4 Example 6 Example 1 was repeated except that the hardener HD-1 was not used. The curing of silver paste is 80
It was performed at 30 ° C. for 30 minutes.

Example 7 Except that the curing agent HD-1 was not used in Example 2,
The same procedure as in Example 2 was performed. The curing of silver paste is 80
It was performed at 30 ° C. for 30 minutes.

Example 8 The procedure of Example 3 was repeated except that the curing agent HD-2 was not used. The curing of silver paste is 80
It was performed at 30 ° C. for 30 minutes.

Example 9 The procedure of Example 5 was repeated except that the curing agent HD-1 was not used. The curing of silver paste is 80
It was performed at 30 ° C. for 30 minutes.

Comparative Example 3 In Example 6, as a binder, a resol-type phenol resin Hitanol 4010 (manufactured by Hitachi Chemical Co., Ltd., solid content)
(50.0%) 19.5 parts except that 19.5 parts was used.

Comparative Example 4 Example 1 Instead of the polyether ester polyol, a polyether ester polyol (OH value 56.4 mgKOH / g, which is a reaction product of 750 parts by weight of polypropylene glycol having a molecular weight of 1200 and 90 parts by weight of adipic acid having a molecular weight of 146) Acid value
The same procedure was performed as in the example except that 0.1 mgKOH / g) was used. The evaluation of the obtained silver paste was insulation coat resistance +22.8, heat resistance -8.2, and humidity resistance +12.5.

The above evaluation results are shown in Table-1 and Table-2, but Examples 1 to 9 which are within the scope of the present invention are all insulative coat resistance, heat resistance and moisture resistance as compared with Comparative Examples 1 to 4. Is highly reliable.

[Effects of the Invention] As described above, the silver paste according to the present invention is extremely excellent in resistance to an insulating coating agent, and further excellent in reliability such as heat resistance and moisture resistance.

 ─────────────────────────────────────────────────── --- Continuation of front page (56) References JP-A-59-157148 (JP, A) JP-A-61-47760 (JP, A) JP-A-62-72750 (JP, A) JP-A-62- 51106 (JP, A)

Claims (2)

[Claims] 1. A silver powder, (b) polytetramethylene glycol, a compound having two hydroxyphenyl groups or a polyoxyalkylene diol obtained by addition-polymerizing an alkylene oxide to a dihydric phenol, and an aromatic polyamine. A silver paste containing a polyurethane (c) solvent, which is a reaction product of a polyether ester polyol obtained by co-condensing a basic acid and a reactive derivative thereof, and a polyfunctional isocyanate compound as a component. 2. (a) Silver powder (b) Polytetramethylene glycol, a compound having two hydroxyphenyl groups or a polyoxyalkylene diol obtained by addition-polymerizing an alkylene oxide to a dihydric phenol, and an aromatic polyamine. Polyurethane (c) a polyfunctional blocked isocyanate compound (d) which is a reaction product of a polyether ester polyol obtained by co-condensing a basic acid and its reactive derivative with a polyfunctional isocyanate compound, as a component Silver paste.