JPH04198271A - Conductive paste composition - Google Patents

Abstract

PURPOSE:To obtain the title composition which has good adhesiveness to various substrate and high conductivity without the necessity for the addition of any metallic filter by using specified fine flaky graphite particles or their mixture with carbon black as conductive carbon as a principal component. CONSTITUTION:A carbonaceous conductive paste for forming a conductive circuit and resistance, made by using conductive carbon and a binder resin as principal components, adding a conductive filler thereto if necessary, and mixing them with a solvent, wherein fine flaky graphite particles having a particle diameter of 1-100mum, a thickness of 1mum or less, and an aspect ratio of 10 to 5,000 or their mixture with carbon black is used as the conductive carbon. This composition has such a high conductivity as compared with conventional carbonaceous paste that it does not need the addition of any metallic filler, such as silver, good adhesiveness to various substrate, and resistance with no frequency dependence; therefore, it is useful as the material of conductor, resistor, contact, etc., on a printed wiring board (flexible wiring board), a hybrid substrate (ceramic substrate), etc.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a conductive paste used for forming conductive circuits and resistors used in printed wiring boards and hybrid boards, or for preventing static electricity on cathode ray tubes and accelerating electron beams. Regarding the composition.

<Prior Art> Conventionally, carbon-based conductive pastes have been used for forming conductive circuits and contacts in printed wiring boards, hybrid boards, etc., and for forming resistive elements. These carbon-based conductive pastes combine carbon black, which is amorphous fine powder carbon obtained by incomplete combustion or thermal decomposition of hydrocarbon oils obtained from natural gas, coal, and petroleum, with polyester, acrylic resin, etc. It is manufactured by mixing a thermoplastic resin or a thermosetting resin such as a phenol resin or a melamine resin as a binder with a solvent.

Among these conductive pastes, those for forming conductive circuits and contacts are required to have high conductivity, and those for forming resistive elements are required to have resistivity depending on the purpose of use. The conductivity of carbon-based paste can be adjusted by changing the type of carbon black added and the mixing ratio of carbon black and binder, but in order to further increase the conductivity, it is necessary to use silver powder, etc., which has higher conductivity than carbon black. A method of mixing is also known.

For forming resistance elements, it is possible to reduce the amount of carbon black added, but if the amount of conductive filler added is too small, the range of conductivity variation will increase, making it difficult to accurately control the resistance value. becomes difficult, so
A method of adding non-conductive inorganic fillers such as kaolinite, defkite, magnesium hydroxide, vermiculite, etc. without reducing the amount of conductive filler (Japanese Patent Application Laid-open No. 61-93506, Japanese Patent Application Laid-Open No. 61-93505, etc.)
Alternatively, a method of blending organic fillers such as cross-linked polystyrene beads or benzoguanamine resin powder (vF Kaisho 6
1-163601, etc.) to control conductivity.

<Problems to be Solved by the Invention> When using the carbon-based conductive paste for forming a conductive circuit, the amount of carbon black is increased in order to improve the conductivity. The adhesion to the paste and substrate may deteriorate, and the thixotropic properties of the paste may increase, making coating and printing difficult. To a certain extent. Further, if silver powder is used in combination with carbon black, it is possible to obtain a paste having a low resistance value of several Ω/mouth, but there are major problems in that the cost increases and the silver used tends to migrate. In addition, when using carbon black to form a resistance element, reducing the amount of carbon black used will cause variation and instability in the resistance value, and if the conductivity is adjusted by filling with a non-conductive filler, the There were problems such as poor adhesion.

An object of the present invention is to solve the problems of the prior art, and to provide a conductive material that has excellent adhesion to a substrate or base material and has high conductivity without using a metal filler such as silver. An object of the present invention is to provide a conductive paste composition that has excellent adhesion to a paste composition and a substrate or base material, and exhibits a stable resistance value.

<Means for Solving the Problems> The present invention provides a carbon-based conductive paste for forming conductive circuits and resistances, which contains conductive carbon and a binder resin as main components, and optionally contains a non-conductive filler and is mixed with a solvent. , the conductive carbon has a particle size of 1 to 10
0 μm 1 thickness is 1 μm or less, aspect ratio is lO~s,
oooO A conductive paste composition characterized by using leafy graphite fine particles or a mixture of the leafy graphite fine particles and carbon black.

In the conductive paste composition of the present invention, the leaf-shaped graphite fine particles added as a conductive filler have a particle size of 1 to 1
These are graphite fine particles having a very special shape, with a thickness of 1 μm or less and an aspect ratio of 10 to 100 μm. These flaky graphite particles are manufactured from expanded graphite and have a developed graphite crystal structure.
The electrical resistivity is approximately 5×10”Ω・1, which is an order of magnitude lower than the 3~5×10−3Ω・1 of ordinary carbon black, and the thermal conductivity is 1.5×10”Ω・1 of carbon black.
It has the characteristic that it is significantly larger than -1 at 200 w·-1·k−1. Such flaky graphite fine particles are produced by, for example, dispersing expanded graphite obtained by expanding natural graphite through acid treatment, heat treatment, etc. in an aqueous solvent, and then crushing it by applying ultrasonic waves. can do. These flaky graphite fine particles are made by powdering raw material graphite such as natural graphite in a state where the layers are separated while retaining its crystalline form, and have the special shape and high crystallinity mentioned above. For example, flaky graphite obtained from natural graphite produced in China has developed hexagonal graphite crystals, a lattice constant of 6.70, and a crystallite thickness of approximately 700 mm.
Spread of people and crystals It is flaky graphite with a high crystallinity of about 1,000 people.

The conductive paste composition of the present invention is manufactured, for example, by the following method. That is, a conductive filler that is a combination of flaky graphite fine particles having the above characteristics or a combination of these flaky graphite fine particles and carbon black known as furnace black or acetylene black is mixed with a binder, and a solvent is added if necessary. The mixture is added and kneaded using a kneader such as a three-roll mill, and if necessary, a solvent is added to adjust the viscosity. Further, in the case of making a paste for forming a resistance element, fine powder of a non-conductive filler such as kaolin, talc, silica, alumina, calcium carbonate, etc. is added.

In the paste of the present invention, as a binder, thermoplastic resins such as polyester, polyvinyl butyral, and acrylic resins, which are used as binders for ordinary carbon pastes, and thermosetting resins such as epoxy resins, melamine resins, and phenolic resins are used. can be used.

These binder components are usually preferably used in liquid or solution form.

Solvents used as liquid components of the paste include aromatic oils such as toluene and xylene, esters such as methyl acetate, ethyl acetate, and butyl acetate, methanol,
Alcohols such as ethanol, butylcarpitol, butylcarpitol acetate, α-terpineol,
Ketones such as dimethyl ketone and methyl ethyl ketone,
Examples include ethers such as diethyl ether and methylpropyl ether, and cellosolves such as methyl cellosolve and ethyl cellosolve.
They may be appropriately selected and used in combination depending on the solubility of the binder, the properties required for the paste of the product, the drying state when applied or printed on a substrate, etc.

The blending ratio of each component in the conductive paste composition of the present invention varies depending on the properties of each raw material used, the purpose of use of the resulting product, the required properties, etc., but the ratio of conductive carbon filler to 100 parts by weight of the binder component is 10
Preferably, the amount of ffi is ~250 parts.
In addition, the ratio of leafy graphite fine particles and carbon black in the conductive carbon filler is 100 times the leafy graphite fine particles and carbon black.
By blending an appropriate amount of carbon black into the flaky graphite particles, which may contain up to 900 parts by weight of carbon black, the effect of imparting electrical conductivity is synergistically improved.

The amount of the non-conductive filler added to adjust the conductivity is 80 parts by weight or less per 100 parts by weight of the binder.

In addition, the amount of solvent to be used is approximately 10 to 50% in the conductive paste composition of the final product, taking into account losses during kneading.
It is preferable to adjust the amount to % by weight.

The conductive paste composition of the present invention can be applied onto any substrate or substrate such as a glass epoxy laminate, a paper phenolic resin laminate, a ceramic substrate such as alumina, or a synthetic resin film by coating, spreading, or printing methods such as screen printing. Accordingly, a conductive circuit or a resistive element can be formed by forming an arbitrary pattern and curing it by appropriate post-treatment such as heat treatment. Further, by adding a curing agent or a curing catalyst to the paste in advance, it is possible to cure the paste at room temperature.

Conductive paste of the present invention) Only carbon-based material is used as the composite oxide conductive filler, and the surface resistance is 10Ω.
A low resistance of 10Ω/mm has been achieved, and it has high conductivity far exceeding the 10Ω/mm of conventional carbon-based pastes. In addition, by controlling the additive mixture of the binder, conductive filler, and non-conductive filler, it is possible to
The conductivity can be adjusted to any value within the range of Ω/mouth. In addition, it has good adhesion to substrates and base materials, and the formed conductive circuits and resistance elements exhibit uniform and stable resistance values, making it ideal for forming conductive circuits and resistance elements used in printed wiring boards and hybrid boards. It has extremely good properties as a conductive paste composition, and is also useful as a conductive paste composition for antistatic use in cathode ray tubes and for accelerating electron beams.

<Example> Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Leaf-like graphite fine particles having an average particle diameter of 2θ μm, a thickness of about 0.1 μm, and an aspect ratio of about 200 were processed in a ball mill for 300 hours, and 100 parts by weight of the resultant was added with an epoxy resin (manufactured by Yuka Shell Co., Ltd.) as a binder. Product name Epicote 11001
) and 40 parts by weight of melamine resin (manufactured by Hitachi Chemical Co., Ltd., trade name Melan 27) were mixed and kneaded to obtain 133 parts by weight of a mixed solvent consisting of 85% by weight of α-terpineol and 15% by weight of butyl carpitol acetate. was further mixed and kneaded to obtain a conductive paste composition of the present invention. The ratio of (conductive filler + binder resin)/solvent in this paste was approximately 1.5, and the pastes were adjusted to this ratio in all of the following Examples and Comparative Examples. This paste was printed on a glass epoxy substrate and cured by treating it at 150℃ for 30 minutes to form a cured coating film with a thickness of 20us on the surface of 2 x 2 layers.When the resistance value was measured, the surface resistance was 175Ω. /It was a mouth.

Comparative Example 1 Example 1 except that commercially available highly conductive carbon black (furnace black) was used instead of the flaky graphite fine particles.
When mixing and kneading were carried out in the same manner as above, the filler and binder became dry at the time they were mixed, and a paste could not be obtained. Therefore, we reduced the amount of carbon black used, and when we reduced the amount of carbon black to 11 parts by weight, we were able to mix it, and by adding a solvent and kneading, we were able to obtain a printable paste (solvent amount: 74 parts by weight). The paste was printed and cured on a substrate in the same manner as in Example 1, and the surface resistance was measured to be 113 Ω/mm.

From the results of Example 1 and Comparative Example I, it can be seen that the conductivity imparting effect of flaky graphite as a carbon-based conductive filler is significantly greater than that of carbon black-based filler.

Example 2 A cured coating fi (2×2■, thickness 20 μm) obtained by the same procedure as in Example 1 except that the amount of flaky graphite fine particles used was 43 parts by weight and the amount of solvent used was 95 parts by weight. The surface resistance is 1
, 490Ω/hole, and had good adhesion to the substrate, making it useful as a resistance paste with stable resistance value.

Example 3 As a conductive filler, instead of 100 parts by weight of leafy graphite fine particles, 60 parts by weight of leafy graphite fine particles and an average particle size of 76
A cured coating film (2×
When I measured the surface resistance of 2 cabinets (20μ thick), it was 7Ω.
/It was a mouth. Moreover, this coating film adhered well to the substrate. This result shows that when an appropriate amount of carbon black is added to the flaky graphite fine particles as a conductive filler, the conductivity of the resulting paste is significantly improved.

Comparative Example 2 Highly crystalline artificial graphite fine particles (average particle size 0.5 μm) were used instead of 100 parts by weight of flaky graphite fine particles as a conductive filler.
The same procedure as in Example 1 was carried out except that 194 parts by weight was used and the amount of solvent was changed to 196 parts by weight, and the surface resistance of the cured coating film was measured and found to be 44 Ω/mouth. This value belongs to the highest class among those using conventional carbon diameter fillers, and it can be seen that the conductive filler of the present invention has extremely superior performance in comparison.

Example 4 Curing made in Examples 1 and 3! ! ! The AC impedance of the membrane (measured with a precision LCR meter manufactured by Yokogawa Hurent-Baccard) is at a frequency of 10011z.
- IMllz, there was no change and it was constant. On the other hand, the AC impedance of the cured coating film prepared in Comparative Example 1 decreased from around 10 KHz, and decreased to the initial value of 1710 at I Mllz.6 The conductive paste composition of the present invention has frequency dependence. It can be seen that it has excellent characteristics for use in circuit elements.

<Effects of the Invention> The conductive paste) & 11 composition of the present invention has higher conductivity than conventional carbon-based pastes, does not require the addition of metallic fillers such as silver, and is compatible with various coatings. It has good adhesion to the mounting substrate and has no frequency dependence of resistance, making it useful as a material for conductors, resistors, contacts, etc. of printed wiring boards (flexible wiring boards), hybrid boards (ceramic boards), etc. In addition, it is possible to achieve a shield with extremely low resistance, and it can also be used as an EMI shielding paint.

Claims (1)

[Claims] 1. Main ingredients are conductive carbon and binder resin,
In a carbon-based conductive paste for forming conductive circuits and resistances, in which a non-conductive filler is added as necessary and mixed with a solvent, the conductive carbon has a particle size of 1 to 100 μm.
, the thickness is 1 μm or less and the aspect ratio is 10 to 5,000.
A conductive paste composition characterized in that it uses leaf-like graphite fine particles or a mixture of leaf-like graphite fine particles and carbon black.