JPH032284A - Electrically conductive paste and electrically conductive coating film therefrom - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a conductive paste that has good electrical conductivity over a long period of time, and more specifically, to a conductive paste that can be used for circuit boards such as paper/phenol resin boards and glass/epoxy resin boards. By applying heat and curing by screen printing etc., a conductive coating film with excellent adhesion to metals and insulating layers and good conductivity over a long period of time is formed, making it suitable for electromagnetic noise countermeasures on circuit boards. Alternatively, the present invention relates to a conductive paste suitable for use as a conductor for wiring on a circuit board.

[Conventional technology]

In general, a conductive paste is basically composed of an organic binder (hereinafter abbreviated as binder) such as an epoxy resin, a polyester resin, an acrylic resin, or a phenol resin, a conductive powder, and a solvent.

This conductive paste has been conventionally used as a conductor for circuit boards.

Recently, attempts have also begun to use conductive paste as an electromagnetic shielding material for printed circuit boards.

In other words, this application applies to a printed wiring board in which a conductive layer having a circuit pattern including a ground pattern is formed on the board, and a conductive layer is formed on the board except for the part of the ground pattern on the surface of the board where the conductive layer is provided. An insulating layer is printed to cover the layer, and a conductive paste is printed to cover the insulating layer of the board and connect it to the ground pattern to form an electromagnetic shielding layer, which is used as a conductor for a circuit board for electromagnetic noise countermeasures. (Japanese Unexamined Patent Publication No. 63-154
97 and Utility Model Application Publication No. 55-29276).

[Problem to be solved by the invention]

Conventional conductive pastes such as those mentioned above require a curing time of 30 minutes or more even at a curing temperature of 150 to 200°C in order to obtain reliable coatings in terms of their conductivity, durability, heat resistance, etc. did. Especially for conductive steel pastes, which can be manufactured at low cost among conductive pastes, the lower the curing temperature is, the better to ensure its oxidation stability. To ensure this, a curing time of 30 minutes or more was required. Therefore,
For example, when manufacturing electromagnetic shielding electronic circuit boards,
If the beta time of the resist is also included, the productivity of the substrate will be greatly reduced.

In view of the current situation, the present invention reduces the curing time to 30 minutes or less while maintaining the high conductivity and durability of the conductive paste, as well as its adhesion to the substrate, and produces a high performance electromagnetic shielding substrate. The purpose is to enhance sexuality.

[Means to solve the problem]

The present inventors have made extensive studies to solve the above problems, and have found that the above objects can be achieved by devising the composition of an organic binder in the presence of conductive powder, and have completed the present invention.

That is, the present invention uses an organic binder containing a thermosetting resin in a conductive paste containing a conductive powder, an organic binder, and a solvent as essential components. Conductive paste capable of forming a highly conductive coating film with a resistivity of 10''''2Ω・Cm or less in terms of resistance value, and a conductor or conductive coating film obtained by curing the same. It is.

The conductive powder used in the present invention includes copper powder, silver powder,
Examples include metal powders such as nickel powder and aluminum powder, and powders having a coating layer of the above-mentioned metal on the surface. The shape may be dendritic, flake-like, spherical, or amorphous, but the average particle diameter is preferably 100 μm or less, more preferably about 1 to 30 μm.

This is because if the thickness exceeds 30 μm, it becomes difficult to pack the conductive powder at a high density, resulting in decreased conductivity and poor printability. The above-mentioned conductive powder can be used alone or in a mixed system.

The higher the purity of the metal powder, the better. In particular, the copper powder most preferably has a purity that matches the purity of the copper foil or plated copper layer used for the conductor of the circuit board. The blending amount of the conductive powder is 50% in the mixture with the binder.
It is preferable to use it within a range of 95% by weight.

The organic binder used in the present invention may be a thermosetting resin alone or a thermosetting resin and a weight average molecular weight of 1.00.
A mixture of 0 to 2 million polyhydroxystyrene derivatives or hydroxystyrene copolymers and/or derivatives thereof can be used. Further, as additives, saturated/unsaturated fatty acids or metal salts thereof, higher aliphatic amines, etc. can be used to prevent oxidation or improve dispersibility of the conductive powder.

As the thermosetting resin used in the present invention, known thermosetting resins such as melamine resin, phenolic resin, urea resin, polyester resin, epoxy resin, and urethane resin can be used, but trifunctional or more For example, melamine resins and combinations of melamine resins and other resins are particularly preferred. The melamine resin, which is a particularly preferred thermosetting resin used in the present invention, is an alkyl etherified melamine resin, such as Super Beckamine-105- manufactured by Dainippon Ink Chemical Co., Ltd.
60 methyl melamine resin, Super Beckamine J-8
20-60, J-840゜shi-117-60, L-12
7-60, L-1 (n-butylated melamine resin of 19-50, Super Beckamine G-821-60゜L-11
8-60, L-121-60, TO-139-60, L
-110-60゜L-125-60, 47-508-6
Examples include 1so-butylated melamine resins of 0, L-145-60, and L-116-70 (all trade names).

Furthermore, binder components that are particularly effective in the present invention include polyhydroxystyrene derivatives and hydroxystyrene copolymers and/or derivatives thereof having a weight average molecular weight of 1,000 to 2,000,000. By adding these binder components, a coating film with sufficiently high conductivity can be easily produced even by high-speed curing.

These polyhydroxystyrene derivatives, hydroxystyrene copolymers and/or derivatives thereof are represented by the following general formula (A).

[In the formula; m≧Q, n≧3, respectively general formula (A)
An arbitrary number until the weight average molecular weight of the organic polymer becomes 2 million; 0≦≦2°; 0≦p≦2°; 1≦U≦2°: provided that +p+m>Q.

, R1 and R3 are H or an alkyl group having 1 to 5 carbon atoms;
is a polymerizable vinyl monomer; Y and Z are the same or different, and 4-3O3,
-C-3O3M, -Y', -0CH3゜(R”
)2-r or an alkyl or aryl group having 1 to 18 carbon atoms, (wherein, M is H, an alkali metal, an alkaline earth metal, or an organic cation such as amines: Y'+ Y' is a halogen, and Y2- to Y3- are a halogen ion and an organic acid anion.

A counter ion such as an inorganic acid anion; formerly S or 0, R4-R8 are the same or different, and are linear or branched alkyl groups or alkyl group derivatives such as hydroxyalkyl groups, or aromatic groups or Hl, and R4 and R7
may form a ring with the N group.

, R9 to RI8 are the same or different, and are linear or branched alkyl groups, alkyl derivative groups such as hydroxyalkyl groups, aromatic groups, or H; q, s, and t are 0 or 1; r is 0 .1 or 2)] In the present invention, when fatty acids, higher aliphatic amines, etc. are added as additives, a favorable effect can be obtained for improving dispersibility.

Saturated fatty acids that can be used in the present invention include valmitic acid, stearic acid, arachidic acid, etc.
Preferred unsaturated fatty acids include, for example, oleic acid and linoleic acid. Metal salts thereof also have similar effects, such as sodium salts and potassium salts. It is also possible to use vegetable oils containing 60% or more of unsaturated fatty acids, such as soybean oil, sesame oil, olive oil, and safflower oil. The total amount of additives added is 0.1 to 2 parts by weight per 100 parts by weight of conductive powder.
0 parts by weight, preferably 0.5 to 10 parts by weight.

Moreover, any organic compound having an amino group can be used as the higher aliphatic amine used in the present invention, and may have other substituents. For example, it may be an amine having a hydroxyl group derived from an α-olefin. However, because of the need to use it together with conductive powder, for example, solid materials that do not dissolve in solvents cannot be used. Preferred are higher aliphatic amines having 8 to 22 carbon atoms. Such higher amines include stearylamine, palmitylamine, behenylamine, cetylamine,
Examples include saturated monoamines such as octylamine, decylamine, and laurylamine, unsaturated monoamines such as oleylamine, and diamines such as stearylpropylene diamine and oleylpropylene diamine.

In the present invention, the higher aliphatic amine is used as a conductive powder 10
It is preferable that the total amount is 0.1 to 10 parts by weight based on 0 parts by weight.

Furthermore, the effects of the polyhydroxystyrene derivative or hydroxystyrene copolymer used in the present invention are more pronounced when metallic copper powder is used.
The invention is of particular importance for the production of conductive copper pastes.

Solvents used in the present invention include, for example, benzene, toluene, hexanone, dioxane, solvent naphtha, industrial gasoline, cellosolve acetate, ethyl cellosolve, butyl cellosolve, butyl cellosolve acetate, butyl carpitol acetate, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, Known solvents include alcohol-based solvents such as isopropyl alcohol and butanol, and ketone-based solvents such as methyl ethyl ketone, and it is not necessary to choose a solvent with a particularly low boiling point.

In the present invention, low-temperature curing refers to an air oven (for example, Perfect Oven PH-30 manufactured by Tabai Spac Co., Ltd.).
0) refers to heat curing at a temperature of 100°C or higher and 250°C or lower. The conductivity of the coating film is a value obtained by measuring the volume resistivity of the heat-cured coating film using a digital multimeter (R6551 manufactured by Atopan Test Co., Ltd.) using a two-terminal method. Note that the formula for calculating the volume resistivity is shown in formula (1).

Volume resistivity (Ω・cm) = R: Resistance value between electrodes (Ω) t: Thickness of coating film (cm) W: Width of coating film (cm) L: Distance between electrodes (cm) Curing time In the measurement, the pendulum period is measured using a pendulum type (curing process) viscoelasticity meter (Model DDV-OPA manufactured by Orientic Co., Ltd.), and the time until the value becomes 0 is taken.

The conductive coating film obtained from the conductive paste of the present invention is:
Curing time is less than 30 minutes, and at the same time I×10-20・
It means a cured product or cured coating film with excellent electrical conductivity and a specific volume resistivity of cm or less.

〔Effect of the invention〕

According to the invention, by using the system of organic binders described above in the presence of conductive powder, the curing time can be increased to 15
Even at 0℃, it is possible to cure at a low temperature of less than 10 minutes, which is surprisingly short compared to conventional technology, and the conductivity is 10-2.
A coating film exhibiting high conductivity of 0 cm or less can be obtained. This effect is probably due to the synergistic effect between the catalytic ability of the conductive powder, thermosetting resin such as melamine resin, and thermoplastic component when using a hydroxystyrene binder. It is thought that a part of the thermoplastic component becomes a solution when heated and acts to promote the polymerization reaction, but the exact mechanism of the effect of the present invention has not yet been elucidated. .

The conductive paste of the present invention can be used in various fields that use conductive coatings by thermosetting, and can significantly improve productivity.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited only to these Examples. In Examples and Comparative Examples, "parts" means "parts by weight."

Paste Preparation/Printing Conductive powder shown in Table 1, thermosetting resin shown in Table 2,
A conductive paste is prepared by thoroughly and uniformly kneading the hydroxystyrene copolymer and additives shown in Table 3 using a disper or triple roll so as to have the composition shown in Table 4. Using each of the obtained conductive pastes, a screen printing machine with a 180 to 250 mesh screen was used.
Width 2mm, total length 36cm on glass epoxy resin board
pattern was printed.

Table 4 also shows the results of examining the characteristics of the conductive circuits obtained in the above process.

Measurement of conductivity Electrodes were set at both ends of the printed pattern and connected to a digital multimeter (R6551 manufactured by Atopan Test Co., Ltd.), and changes in conductivity during heat curing were converted into volume resistivity and tracked.

Measurement of the curing process The curing process of the coating film was measured at 130 to 200°C by measuring the pendulum period using a pendulum type (curing process) viscoelasticity meter (Model DDV-OPA manufactured by Orientic Co., Ltd.).
The evaluation was carried out at a constant temperature.

In this measurement, the point where the pendulum period became O was considered to be the end of curing.

Humidity Resistance Test The humidity resistance of the coating film was determined by performing a standing test for 500 hours in an environment of 60° C. and 95% relative humidity, and determining the rate of change in resistance value W before and after the test.

Resistance change rate W, (%) = I evaluated it more. The judgment criteria are as follows.

○: Good printability △ D: Printable to some extent ×: Unprintable Table 1 Ro: Resistance value (Ω) of coating film before test R6°. :50
The moisture resistance of the coating film is expressed as follows based on the resistance value (Ω) WiIO value after the 0 hour test.

AA: W is less than 10% A: W is 10% or more and less than 30% B: W is 30% or more and less than 100% C: W* is 100% or more Printability test The printability of each conductive paste was determined at 250%. Table 4 shows the results of screen printing using a mesh tetron screen] Table 4 shows various characteristics of the conductive paste according to the present invention, together with comparative products.

The conductive pastes of the products Nα1 to Nα6 of the present invention each have a 10-
It exhibits an excellent volume resistivity on the order of 3Ω・cm to 10−sΩ・cm, and both the time (Rmin time) and curing time (even when cured at 140°C) until it shows the minimum value in the resistance change over time during curing is 20 It can be seen that the moisture resistance and printability are also superior compared to the comparative products.

From the above, it can be seen that by using the conductive paste of the present invention, it is possible to greatly shorten the heat curing time and provide a conductive layer with excellent durability.

[Conclusion

Claims (1)

[Scope of Claims] 1. A conductive paste containing a conductive powder, an organic binder, and a solvent as essential components, wherein the organic binder contains a thermosetting resin, the curing time is 30 minutes or less, and the volume at the end of curing is A conductive paste characterized by forming a coating film having a resistivity of 10^-^2 Ω·cm or less in terms of specific resistivity. 2. The conductive paste according to claim 1, wherein the organic binder contains a melamine resin and a polyhydroxystyrene derivative or a hydroxystyrene copolymer and/or a derivative thereof having a weight average molecular weight of 1,000 to 2,000,000. 3 A volume-specific paste obtained by coating or printing a conductive paste containing conductive powder, an organic binder containing a thermosetting resin, and a solvent as essential components on a base material, and then curing at a low temperature in a curing time of 30 minutes or less. Resistivity converted to 10＾-＾2Ω・cm
A conductive coating exhibiting the following resistivity. 4 Applying or applying a conductive paste containing a conductive powder, a solvent, and a melamine resin and a polyhydroxystyrene derivative or a hydroxystyrene copolymer and/or its derivative with a weight average molecular weight of 1,000 to 2 million on a base material. A conductive coating film that is obtained by curing at a low temperature for a curing time of 30 minutes or less after printing and exhibits a resistivity of 10^-^2 Ω·cm or less in terms of volume resistivity.