JPH0798914B2 - Conductive paste and conductive coating using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive paste used as, for example, a conductive paint for electronics, a conductive adhesive, and the like, and a conductive coated body using the same.

[Prior Art] In recent years, there has been a remarkable progress in electronics technology centering on semiconductor ICs, and the applied equipment has been utilized in various industrial fields. Along with that, research on conductive pastes has become popular.

As is well known, a large number of ICs and LSIs are used not only in computer devices but also in automobiles, televisions, VTRs, and copying machines, and these devices generate various high frequency pulses.

On the other hand, a plastic material that is mainly used as a housing of an electronic device is a good insulator, but transmits radio waves and easily accumulates static electricity. Therefore, when a plastic housing is used in an electronic device with a built-in microcomputer, it is necessary to fully consider electromagnetic interference [EMI (Electromagnetic Interference)] and electrostatic discharge [ESD (Electrostatic Discharge)]. Instead, it is necessary to shield the entire housing.

The conductive paste is extremely useful for such a purpose. That is, EMI and ESD can be effectively prevented by applying a conductive paste to the substrate and forming a housing with the conductive coating body coated with the dried coating film.

The conductive paste is also used for printed wiring boards, thick film hybrid ICs and the like. Screen printing with a conductive paste directly on the substrate to draw a circuit will not waste resources and processes compared to the etching method that removes most of the copper foil by etching, and it will be possible to greatly rationalize. .

Further, the conductive paste is also used as an adhesive for taking out a lead wire for a crystal oscillator, for adhering a liquid crystal terminal of an auto choke, or for adhering a metal film resistor and a metal cap.

The above-mentioned conductive paste is at least a conductive filler,
It is composed of a resin binder and additives, and the role of the resin binder is extremely important. The resin binder is required to bring the conductive filler into close contact with the base material and at the same time to connect the conductive filler in a chain form to provide conductivity. In addition, it is necessary to provide physical and chemical stability as a coating film.

Conventionally, as a resin binder, acrylic, vinyl, epoxy, phenol, urethane, rubber and the like are known. Especially rubber-based resin binder,
For example, those using SBR, NBR and the like have excellent flexibility and are therefore used in various applications such as flexible substrates.

[Problems to be Solved by the Invention] However, the rubber-based resin binder has the following drawbacks.

Many rubber-based resin binders have a double bond in their main chains, and therefore lack chemical stability (weather resistance).

The heat resistance of rubber-based resin binders is generally low,
It is difficult to use in high temperature range.

 Adhesive strength is weak compared to other resin binders.

Therefore, although it is a rubber-based resin binder that has versatility due to its flexibility, there is a problem that it is difficult to obtain sufficient durability.

On the other hand, even if a resin binder other than a rubber type is used, its weather resistance cannot be said to be sufficient, and even a conductive coating having a dry coating film of a conductive paste using such a resin binder has sufficient durability. There is a problem that it is difficult to obtain sex.

The present invention solves the above-mentioned problems, a conductive paste having excellent durability and performance, a conductive paste used as a conductive adhesive, etc., and a conductive coating excellent in durability using the same. Is provided.

[Means and Actions for Solving Problems] To explain means taken in the present invention for solving the above problems, the first invention is a conductive material including at least a resin binder, a conductive filler and a solvent. A block copolymer in which the resin binder comprises at least one polymer block I containing a vinyl aromatic compound as a main component and at least one polymer block II containing a conjugated diene compound as a main component. A hydrogenated block copolymer, a modified block copolymer, or a modified hydrogenated block copolymer, which is obtained by bonding a molecule simple substance containing a hydrogenated and / or carboxylic acid group or its derivative group to The means of making it into a paste is taken. In addition, the second aspect of the present invention takes a means of forming a conductive coating body in which a base material is coated with the dry coating film of the conductive paste.

The block copolymer in the present invention means at least one polymer block I containing a vinyl aromatic compound as a main component.
And at least one polymer block II mainly composed of a conjugated diene compound, such as I-II, I-II-I,
It is a vinyl aromatic compound-conjugated diene compound block copolymer having a structure of II-I-II-I, (I-II ₄ Si, I-II-I-II-I, etc. This block copolymer is Preferably, the vinyl aromatic compound is contained in an amount of 5 to 60% by weight, more preferably 10 to 40% by weight.

Further referring to the block structure, the polymer block I containing a vinyl aromatic compound as the main component is a vinyl aromatic compound polymer block or a vinyl aromatic compound.
It has a structure of a copolymer block of a vinyl aromatic compound and a conjugated diene compound in an amount of more than 70% by weight, preferably 70% by weight or more, and further, a polymer block II mainly composed of a conjugated diene compound is , A conjugated diene compound polymer block, or a copolymer block structure of a conjugated diene compound and a vinyl aromatic compound containing the conjugated diene compound in an amount of more than 50% by weight, preferably 70% by weight or more. Further, the polymer block I containing a vinyl aromatic compound as a main component and the polymer block II containing a conjugated diene compound as a main component are the distribution of the conjugated diene compound or the vinyl aromatic compound in the molecular chain of each polymer block. May be random, tapered (in which the monomer component increases or decreases along the molecular chain), partially block-shaped, or any combination thereof. A polymer block I containing a vinyl aromatic compound as a main component
Blocks Consisting mainly of and Diene Compounds II
When there are two or more of each, each block may have the same structure or different structures.

As the vinyl aromatic compound constituting the block copolymer, for example, one kind or two or more kinds are selected from styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene and the like, and styrene is preferable. Also,
Examples of the conjugated diene compound constituting the polymer block II mainly composed of the conjugated diene compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-
One or more selected from butadiene,
Of these, butadiene, isoprene and combinations thereof are preferable. Then, the polymer block II mainly composed of the conjugated diene compound, the microstructure in the block can be arbitrarily selected, for example, in the polybutadiene block, preferably 1,2-microstructure is 10 to 80%,
More preferably, it is 10 to 65%.

The number average molecular weight of the block copolymer is preferably 5,000.
˜1,000,000, more preferably 10,000 to 800,000, most preferably 30,000 to 300,000, and the molecular weight distribution (ratio of weight average molecular weight to number average molecular weight) is preferably 10 or less.

The molecular structure of the block copolymer provided in the present invention may be linear, branched, radial or any combination thereof, and any production method may be used as long as it has the above-mentioned structure. It does not matter if it is obtained.

For example, according to the method described in JP-B-40-23708, a vinyl aromatic compound-conjugated diene compound block copolymer was synthesized in an inert solvent using a lithium catalyst or the like, and the block copolymer of the present invention was synthesized. Can be used as

This block copolymer is hydrogenated in the presence of a hydrogenation catalyst in an inert solvent by the method described in, for example, JP-B-42-8704 or JP-A-59-133203 to give the block copolymer of the present invention. The hydrogenated block copolymer of

At that time, at least 50% or more, preferably 80% or more, of the aliphatic double bond based on the conjugated diene compound of the vinyl aromatic compound-conjugated diene compound block copolymer is hydrogenated, and a heavy compound mainly composed of the conjugated diene compound is added. The combined block can be morphologically converted into the olefinic compound polymer block II. Further, regarding the hydrogenation rate of the aromatic double bond based on the vinyl aromatic compound copolymerized with the block I mainly containing the vinyl aromatic compound and the polymer block II mainly containing the conjugated diene compound, if necessary. Is not particularly limited, but the hydrogenation rate is preferably 20% or less. The amount of unhydrogenated aliphatic double bonds contained in the hydrogenated block copolymer can be easily known by, for example, an infrared spectrophotometer or a nuclear magnetic resonance apparatus.

Since the hydrogenated block copolymer as described above has a small amount or almost no double bond contained in its main chain, it can be obtained by applying a conductive paste containing the polymer as a resin binder. The dried coating film thus obtained has very excellent properties in weather resistance. Further, since this block copolymer is also excellent in heat resistance, a dry coating film made of a conductive paste using the block copolymer is
It is possible to maintain stable surface resistance from low temperature of 40 ℃ to high temperature of 80 ℃.

Next, the modified block copolymer of the present invention includes the block copolymer before hydrogenation having the above-mentioned structure and α, β-unsaturated carboxylic acid or its anhydride or ester (hereinafter, α, β-unsaturated). (Abbreviated as carboxylic acids) in a molten state or a solution state, with or without a radical initiator, to undergo a graft reaction. The production method is not particularly limited in the present invention, but the resulting modified block copolymer contains an undesirable component such as a gel, or a method in which the fluidity is lowered and the processability is deteriorated. It is not preferable, for example, a method of adding an additive such as an antioxidant in an extruder and performing a modification reaction under melt mixing conditions in which radicals are not substantially generated is preferable.

The modified block copolymer that can be used in the present invention is preferably one in which 0.05 to 10 parts by weight of α, β-unsaturated carboxylic acid is added to 100 parts by weight of the block copolymer. The addition amount of α, β-unsaturated carboxylic acids is 10
If the amount is more than the weight part, the electric characteristics of the conductive dry coating film are likely to be adversely affected. On the other hand, the added amount is 0.05
If the amount is less than the weight part, the adhesiveness is likely to decrease.

Here, α, β that can be used in the graft reaction
-As the unsaturated carboxylic acids, for example, maleic acid, maleic anhydride, fumaric acid, itaconic acid, acrylic acid, acrylic acid ester, crotonic acid, cis-4-cyclohexane-1,2-dicarboxylic acid and its anhydride, endo −
Examples thereof include cis-bicyclo- [2,2,1] -5-heptene-2,3-dicarboxylic acid and anhydrides thereof, maleimide, and the like. Among these, maleic anhydride is preferable. Examples of usable organic peroxides include dicumyl peroxide, di-tert-butyl peroxide, and tert.
-Butyl cumyl peroxide, 2,5-dimethyl-2,5-
Di (tert-butylperoxy) hexane and 2,5-dimethyl-2,5-di (tert-butylperoxy) hexyne-3, n-butyl-4,4-bis (tert-butylperoxy) valerate, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane and the like can be mentioned, which can be suitably selected.

The resulting modified block copolymer may be ionomerized with a metal ion having a valence of 1 or more. Further, unmodified α, β-unsaturated carboxylic acids remain unreacted in the modified block copolymer. Alternatively, it may be completely removed.

As described above, a dry coating film obtained by applying a conductive paste containing a modified block copolymer as a resin binder, the binder is a plastic such as ABS, PS, PPO, or a metal such as aluminum or copper. Also, since it has good adhesiveness to ceramics typified by alumina, a conductive layer having excellent peeling characteristics can be formed.

The modified hydrogenated block copolymer of the present invention includes a hydrogenated block copolymer having the above-described structure, an α, β-unsaturated carboxylic acid or an anhydride thereof, an ester, etc. (hereinafter, α, β-unsaturated carboxylic acid). Acid) is abbreviated) in the presence or absence of an organic peroxide. The reaction may be in a molten state or a solution state. Further, the modified hydrogenated block copolymer has 10 parts by weight or less of α, per 100 parts by weight of the hydrogenated block copolymer.
Those to which β-unsaturated carboxylic acids are added are preferable. When the addition amount of the α, β-unsaturated carboxylic acid is more than 10 parts by weight, the electrical characteristics of the conductive dry coating film are likely to be adversely affected.

The method for producing a modified hydrogenated block copolymer is not particularly limited in the present invention, but the obtained modified hydrogenated block copolymer has a structure deviating from the above-mentioned characteristics, or a gel or the like. A manufacturing method that contains an unfavorable component or has a significantly increased melt viscosity to deteriorate the processability is not preferable. As an example of a preferable production method, for example, in the extruder at a temperature of 150 ~ 350 ℃, the hydrogenated block copolymer described above, α, β-unsaturated carboxylic acids, if necessary melt-kneading an organic peroxide, There is a method of radical modification. The modified hydrogenated block copolymer obtained may be ionomerized with a monovalent or higher valent metal ion.

Further, in the modified hydrogenated block copolymer thus obtained, unreacted α, β-unsaturated carboxylic acids or derivatives thereof generally remain as unreacted products. The substance may be completely removed or may be left as it is.

A dry coating film obtained by applying a conductive paste containing a modified hydrogenated block copolymer as a resin binder as described above has excellent properties that have both weather resistance, adhesiveness, and heat resistance. It is possible to form a conductive layer having the same.

The hydrogenated, modified or modified hydrogenated block copolymers described above may each be used alone as a resin binder, or a mixture thereof, and further other resin binders such as nitrile rubber, polyvinyl acetate, and poly (vinyl acetate). You may use it, mixing with a methyl methacrylate etc. However, the amount of hydrogenated, modified or modified hydrogenated block copolymer or a mixture thereof is preferably at least 20% by weight or more based on the conductive filler.

Examples of the conductive filler include gold powder, silver powder, copper powder, nickel powder, aluminum powder, carbon black, graphite, carbon fiber, silver-plated fine particles, or a combination thereof. Silver powder, carbon black, graphite and the like are preferable in terms of cost and stability such as oxidation resistance. The particle size of the conductive filler is preferably 1 to 10 μ in the case of metal powder or graphite and 0.01 to 0.5 μ in the case of carbon black.

Examples of the solvent include aromatic solvents such as toluene, halogenated hydrocarbon solvents such as carbon tetrachloride, ether solvents such as THF, hydrocarbon solvents such as cyclohexane, amide solvents, sulfoxo solvents and the like. Examples of the mixed system include, but are not limited to.

The preparation of the conductive paste is not particularly limited, for example, the above-mentioned hydrogenation, a resin binder such as modified or modified hydrogenated block copolymer is dissolved in the solvent, the silver powder, nickel powder or carbon It can be easily carried out by adding a conductive filler such as black and thoroughly dispersing it with a ball mill, a sand mill or the like.

According to the present invention, there is provided a conductive coating body comprising a base material coated with a dry coating film of a conductive paste, which contains a hydrogenated, modified or modified hydrogenated block copolymer.
The substrate as referred to in the present invention, for example, ABS, resin such as PPO, film such as polyester, copper foil, further Al ₂ O ₃
And the like. For example, a conductive coating obtained by spray-coating a conductive paste of Nilekkel powder prepared by the above method on ABS resin or PPO can be used as a plastic housing for electromagnetic shielding. Similarly, a conductive coating of screen-printed conductive paste of carbon powder on a polyester film or copper foil is used for contact points of switches,
It is extremely useful for membrane switches, which are important for making electronic devices thinner. Furthermore, the conductive coating obtained by screen-printing a conductive paste of silver powder on a polyimide film can be used as a flexible printed wiring board.

[Effects of the Invention] As described above, a conductive paste containing the hydrogenated, modified or modified hydrogenated block copolymer of the present invention is a conductive coating material for electronics or a conductive adhesive. It is extremely useful as Furthermore, the conductive coating body obtained by coating the conductive paste on the base material can be used very effectively as an electromagnetic shield casing, a switch, and a printed wiring board.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Among the properties in the following description, breaking strength, breaking elongation, 30
The 0% modulus was measured according to JIS K 6301 under the conditions of No. 3 dumbbell and pulling speed of 500 mm / min. Further, the peeling property test was carried out in accordance with JIS G 0202, and the weather resistance test was carried out in accordance with JIS A 1415 using a weatherometer. Further, the surface resistivity was measured by connecting to the measuring circuit shown in FIG. 1 using a gold vapor deposition electrode. In FIG. 1, E, V, and A respectively represent a DC power supply, a voltmeter, and an ammeter. In addition, B, C and D are electrodes, and C and D are concentric circles. X is a measurement sample.

First, the resin binders used in Examples and Comparative Examples will be described.

(1) (having a structure of polystyrene-polybutadiene ₄ Si, bound styrene content 18% by weight,
A block copolymer having a 2-vinyl bond content of 33%, a number average molecular weight of 105,000 and a molecular weight distribution of 1.33 was synthesized and designated as A.

Next, a block copolymer having a structure of polybutadiene-polystyrene-polybutadiene-polystyrene, the amount of bound styrene is 22% by weight, the amount of 1,2-vinyl bonds in the polybutadiene part is 29%, the number average molecular weight is 111,000, and the molecular weight distribution is 1.12. Was synthesized and designated as B.

Further, having a structure of polystyrene-polybutadiene-polystyrene, the amount of bound styrene is 40% by weight, the amount of 1,2-vinyl bonds in the polybutadiene portion is 51%, and the number average molecular weight is 123,00.
A block copolymer having a molecular weight distribution of 0 and a molecular weight distribution of 1.26 was synthesized and designated as C.

The breaking strength, breaking elongation, and 300% modulus of the obtained block copolymer C are 150 kgf / cm ² , 1000%, and 30 kgf, respectively.
It was / cm ² .

The block copolymers A, B, and C obtained above are each subjected to a modification reaction with maleic anhydride without using peroxide, and maleic anhydride is 0.16 parts by weight, respectively.
Modified block copolymers D, E, F added with 1.32 parts by weight
Got

The breaking strength, breaking elongation and 300% modulus of the obtained modified block copolymer F were 130 kgf / cm ² , 1000% and 40 kgf, respectively.
It was / cm ² .

(2) Hydrogenated polybutadiene-polystyrene-
Having a structure of hydrogenated polybutadiene-polystyrene, the amount of bound styrene is 30% by weight, the amount of 1,2-vinyl bonds in the polybutadiene portion before hydrogenation is 44%, and the number average molecular weight is 79,
A hydrogenated block copolymer having a molecular weight distribution of 000, a molecular weight distribution of 1.05 and a hydrogenation rate of 99% was synthesized with a Ti-based hydrogenation catalyst described in JP-A-59-133203, and this was designated as hydrogenated block copolymer G. .

(3) Polystyrene-hydrogenated polybutadiene-
Having a structure of polystyrene, the amount of bound styrene is 43% by weight,
The amount of 1,2-vinyl bonds in the polybutadiene part before hydrogenation is 5
2%, number average molecular weight 91,000, molecular weight distribution 1.04, hydrogenation rate 96
% Of the hydrogenated block copolymer was synthesized using the above Ti-based hydrogenated catalyst, and this was designated as hydrogenated block copolymer H.

Breaking strength, breaking elongation, 300% modulus is 270kgf / cm ² ,
It was 600% and 50 kgf / cm ² .

(4) Polystyrene-hydrogenated polybutadiene
₄ Si structure, 18% by weight of bound styrene, 29% 1,2-vinyl bond of polybutadiene before hydrogenation, number average molecular weight 42,000, molecular weight distribution 1.41, hydrogenation rate 97% A block copolymer was synthesized with the above-mentioned Ti-based hydrogenation catalyst, and this was designated as hydrogenated block copolymer I.

(5) The hydrogenated block copolymers G, H and I obtained above are subjected to a modification reaction using maleic anhydride and ridicumyl peroxide, and 0.51 parts by weight and 1.9 parts by weight of maleic anhydride, respectively. Modified hydrogenated block copolymers J, K, and L with 0.12 parts by weight added were obtained.

Breaking strength of the modified hydrogenated block copolymer K, elongation at break, 300% ^{modulus, 220kgf / cm 2, 600%} , 60kgf / cm 2
Met.

Example 1 1 part by weight of a nickel powder having an average particle size of 1 × 5 μ was mixed with 5 parts by weight of a toluene solution of the modified hydrogenated block copolymer J (20 wt% concentration) to prepare a conductive paste. Apply this conductive paste to one side of an ABS plate with a thickness of 3 mm and a size of 10 cm × 10 cm.
It was coated with a thickness of 20 μm. Table 1 shows the peeling test of the dried coating film, the measurement of the surface resistivity, and the weather resistance test result.

Examples 2 to 9 The modified hydrogenated block copolymer J used in Example 1 was used as D, E, F,
A dry coating film was prepared in the same manner as in Example 1 except that each of G, H, I, K and L was replaced, and an evaluation test was conducted. The results are shown in Table 1.

Comparative Examples 1 and 2 The modified hydrogenated block copolymer J used in Example 1 was used as A, NBR.
A dry coating film was prepared in the same manner as in Example 1 except that the acrylonitrile portion was 40% by weight and the butadiene portion was 60% by weight. The results are shown in Table 1.

Example 10 Carbon black powder having an average particle diameter of 30 mμ (RAVEN 41 manufactured by Industrial Carbon Black Colombian)
0) 1 part by weight was mixed with 5 parts by weight of a toluene solution of the modified hydrogenated block copolymer J (20 wt% concentration) to prepare a conductive paste. This conductive paste is 100 μm thick and 10 cm
A copper foil having a size of × 10 cm was coated on one surface with a thickness of 20 μm. Table 2 shows the peeling test of the dried coating film and the measurement result of the surface resistivity.

Examples 11 to 18 The modified hydrogenated block copolymer J used in Example 10 was prepared as D, E, F,
A dry coating film was prepared in the same manner as in Example 10 except that each of G, H, I, K, and L was replaced, and an evaluation test was conducted. The results are shown in Table 2.

Comparative Examples 3 and 4 The modified hydrogenated block copolymer J used in Example 10 was used as A, NBR.
A dry coating film was prepared in the same manner as in Example 10 except that the acrylonitrile portion was 40% by weight and the butadiene portion was 60% by weight. The results are shown in Table 2.

Example 19 2 parts by weight of silver powder having an average particle size of 1 × 5 μ was mixed with 5 parts by weight of a toluene solution of the modified hydrogenated block copolymer J (20 wt% concentration) to prepare a conductive paste. This conductive paste was applied to one side of a polyimide film having a thickness of 25 μm and a size of 10 cm × 10 cm to a thickness of 20 μm. Table 3 shows the results of the peeling test of the dried coating film, the measurement of the surface resistivity and the weather resistance test.

Examples 20 to 27 The modified hydrogenated block copolymer J used in Example 19 was used as D, E, F,
A dry coating film was prepared in the same manner as in Example 19 except that each of G, H, I, K, and L was replaced, and an evaluation test was conducted. The results are shown in Table 3.

Comparative Examples 5 and 6 The modified hydrogenated block copolymer J used in Example 19 was used as A, NBR.
A dry coating film was prepared in the same manner as in Example 19 except that the acrylonitrile portion was 40% by weight and the butadiene portion was 60% by weight. The results are shown in Table 3.

[Brief description of drawings]

 FIG. 1 is an explanatory diagram of a method for measuring surface resistivity.

Claims (2)

[Claims] 1. A conductive paste containing at least a resin binder, a conductive filler and a solvent, wherein the resin binder comprises at least one polymer block I mainly containing a vinyl aromatic compound and a conjugated diene compound. A hydrogenated block copolymer comprising a block copolymer composed of at least one polymer block II as a main component, and a molecular monomer containing a hydrogenated and / or carboxylic acid group or its derivative group bonded to the block copolymer, A conductive paste containing a modified block copolymer or a modified hydrogenated block copolymer. 2. A conductive paste containing at least a resin binder, a conductive filler and a solvent, wherein the resin binder comprises at least one polymer block I mainly containing a vinyl aromatic compound and a conjugated diene compound. A hydrogenated block copolymer comprising a block copolymer composed of at least one polymer block II as a main component, and a molecular monomer containing a hydrogenated and / or carboxylic acid group or its derivative group bonded to the block copolymer, A conductive coating, wherein a substrate is coated with a dry coating film of a conductive paste containing a modified block copolymer or a modified hydrogenated block copolymer.