JPH01204971A - Production of carbon paste - Google Patents

Abstract

PURPOSE:To make it possible to obtain a carbon paste markedly improved in properties and to increase the range of use of a printed resistor obtained by using this carbon paste, by specifying conditions of kneading with a roll in the production of said carbon paste. CONSTITUTION:In the production of a carbon paste by kneading a resin binder with a solvent and carbon particles, said kneading is performed with a roll of a clearance of 100-400mum.

Description

[Detailed description of the invention] (a) Object of the invention [Field of industrial application] The present invention relates to a resistance paste for printed resistors for electronic components,
In particular, it relates to a resin-based resistance paste made by dispersing carbon particles in an organic resin.

[Conventional technology]

Currently, with the demand for lighter, thinner, and smaller electronic devices, the demand for lead-based chip components such as resistors, capacitors, and inductors is rapidly increasing.

Recently, a printed resistor, in which a resistor is printed on a copper foil surface, has been developed as a surface mount alternative to chip resistors.
As a result, electronic devices are becoming lighter, thinner, shorter, and more dense.

Since a printed resistor is formed on a substrate surface by screen printing, the resistor is constructed in a planar shape with almost no thickness.

This technology not only eliminates the need for automatic mounting of chip resistors (but also makes it easier to insert other components by flattening the resistor with the largest number of components, making it easier to operate the automatic mounting machine). It has the advantage of being effective.

[Problem to be solved by the invention]

Printed resistors have traditionally been made using high-temperature firing type cermet thick film (C
There are two types: one uses a low-temperature baking polymer thick film (PTF) paste.

Printed resistors made of PTF paste are baked at low temperatures and can be applied to a wide range of applications, including not only ceramic substrates but also organic substrates and metal core substrates. It has drawbacks and its range of use is limited. PTF paste is formed by dispersing conductive fibers in a resin, and carbon particles, which have excellent resistance, dispersibility, and stability, are often used as conductive fillers. PTF paste made by dispersing carbon particles (hereinafter referred to as "carbon paste")
It is called. ) Printed resistors differ from CTP paste printed resistors and many chip resistors in that the conductive path is formed only by contact between conductive fibres. Be open to change. Therefore, at present, this resistor is only widely used as a resistor (for example, a protective resistor) for some consumer wiring boards that do not require much reliability or precision.

(B) Structure of the Invention [Means for Solving the Problems] As a result of intensive studies aimed at solving the above problems, the present inventors have found that the characteristics of carbon paste are largely due to the crosstalk process. This discovery led to the completion of the present invention, which led to the discovery that cross-talk operation under specific conditions greatly improves the characteristics of carbon paste. That is, the present invention provides a method for producing carbon paste by kneading a resin binder, a solvent, and carbon particles, which is characterized in that the kneading is carried out by roll kneading with a roll spacing of 100 to 400 μm. It is.

The carbon paste in the present invention is prepared by mixing and mixing a resin binder, a solvent, carbon particles, and optionally a non-conductive inorganic filler.

The resin binder used in the present invention includes sodium hydroxide,
This phenolic resin is obtained by polycondensing phenols such as phenol, cresol, and alkylphenol with formaldehyde using an alkali catalyst such as barium hydroxide, calcium hydroxide, ammonia, and hexamethylenetetramine. Modified phenolic resin obtained by mixing polymers such as butadiene-acrylonitrile copolymer, or by co-condensing a mixture of phenols with aniline, urea, melamine, etc. that cause a formaldehyde condensation reaction. Examples include xylene resins obtained by polycondensation in the presence of a catalyst, and modified xylene resins synthesized from a mixture of xylene, phenol, aromatic carboxylic acid, aromatic amine, etc., and formaldehyde. These can be used alone or in combination.

Industrially available products include Showa Union Synthetic BRM-421 and BLS-356, Dainippon Ink &Chemicals' Plyophen 5050-40K (all phenolic resins), and Showa Union Synthetic's BLS-51.
55, Dainippon Ink Chemical Industry ■ Priority 7 En LA
-1137 and Pryophen 5592 (modified phenolic resin), Mitsubishi Gas Chemical's Nikanol H, etc. (xylene resin), Mitsubishi Gas Chemical's Nika-/L
/NP-140, PR-1440, PR-1540 (the above modified xylene resins), and any of them can be used. Further, curing agents and curing accelerators may be added to these as necessary.

The solvent used in the present invention should have a boiling point of 170°C or higher and 25°C or higher, considering the screen printing characteristics and the evaporability of the solvent after printing.
Those below 0°C are preferred, especially butyl cellosolve acetate, butyl carpitol acetate, isophorone,
Those containing 5Qvo 1% or more of tilcineol and mixtures of two or more of these are suitable.

Carbon particles used in the present invention include carbon black and graphite powder.

Carbon black is obtained by incomplete combustion of various organic substances, and is commonly referred to as C1, such as furnace black, channel black, thermal black, acetylene black, lamp black, and Ketchen black, which are collectively called by raw materials, manufacturing methods, and characteristics. Both can be used. These are added as a conductive component in the paste to obtain the required resistance value, either alone or in combination, or in combination with graphite particles, etc., which will be described later.

Carbon black has a chemically and physically multi-order structure. It is based on a layer unit formed by bonds of six-membered ring carbon atoms, and is composed of crystallites, fine particles, and several-order chemical and physical aggregates of fine particles. Several to several tens of amperes for fine particles, several hundred amperes for fine particles,
They are high-order aggregates with sizes ranging from submicrons to several hundred μm.

The graphite particles used in the present invention are naturally produced carbon compounds with a highly crystalline layered structure, or are artificially synthesized to have a so-called graphite structure. Graphite's shape, structure 1 surface condition, purity, etc. vary depending on the production area or synthesis method, but the conductivity in the powder state is high at 10 to 10" S/as.
Available for use. These include, for example, Nippon Graphite Industries (natural graphite) C8SP, and Showa Denko (Showa Denko) UFO-82.
, UFO-85, GP-100 manufactured by Kyowa Carbon ■, ■
5GP-5 manufactured by SEC. These graphite particles are blended as a conductive component in the paste to obtain the required resistance value, either alone or in combination, or in combination with carbon black or the like.

These carbon particles differ in particle shape, structure, surface condition, and trace amounts of components depending on their raw materials and manufacturing methods, especially surface treatment methods. It was found that the fundamental factor that most influences the properties of the paste is the method of kneading.

A plurality of carbon particles gather together to form a high-order aggregate (hereinafter referred to as "strafture").As will be explained later, the amount and dispersion state of these stractures are related to the characteristics of the carbon paste, and this amount and dispersion state There seems to be a correlation between this and the kneading method.

The preferred particle size of carbon particles is 0.1 to 50 μm.

If it is less than 0.1 μm, struttles are difficult to form, and conductive paths in the paste are likely to be formed only by contact between carbon particles, resulting in a change in resistance value due to minute impact and poor reproducibility.

If it exceeds 50 μm, the carbon particles will not be uniformly dispersed, and the number of electrically conductive paths will be small, resulting in a large amount of current noise.

In addition to these, additives such as a non-conductive inorganic filler powder, an antifoaming agent, a leveling agent, a dispersion stabilizer, and the like can be blended as necessary in the production of the carbon paste. For example, as the non-conductive inorganic filler powder, colloidal silica, fused silica, alumina, Merck, mica, iron oxide, calcium carbonate, magnesium carbonate, bentonite, dolomite, kaolin, etc. can be used.

A carbon paste can be obtained by blending and kneading the above components, but the inventors of the present invention have investigated this cross-wire condition and have discovered this method to obtain a carbon paste with good characteristics. I was able to do that.

Conventionally, ink products containing such carbon pastes are used by printing to a thickness of several micrometers or less, so kneading has been carried out for the purpose of crushing and dispersing the solid components to a thickness less than the printing thickness. In addition, there are many methods for kneading, and for high viscosity materials such as carbon paste, there are three roll kneaders, mixers with stirring blades or stirring rods, kneaders with screws or blades, and beads. Various types of sand mills, sieves, mixers and kneaders using beads or balls have been used singly or in combination.

The method of the present invention is characterized in that the cross-mixing method is limited to roll kneading, and the distance between the rolls is within the range of 100 to 400 μm. This improves the reproducibility of the resistance value and provides a carbon paste with excellent properties.

Originally, roll kneading machines such as three rolls were used to crush solid materials,
The main purpose is dispersion.

In the case of raw materials for printing applications, it is necessary to refine the particle size into a fine powder of several micrometers or less and to stably disperse it in a medium to high viscosity binder. Roll kneading machines are excellent for this purpose. In this case, it is common to keep the roll spacing to several tens of micrometers or less and to increase the number of roll passes.

On the other hand, when such strong dispersion is not required or when strong dispersion is desired to be avoided, the kneading operation is usually carried out using the above-mentioned mixer, kneader, etc.

The present invention deviates from such conventional common sense and is a unique manufacturing method for obtaining carbon paste with good characteristics.

Roll kneading is selected as the wire mixing method of the present invention.

Other methods have inferior properties and are difficult to control quality.

Further, the roll interval is selected to be 100 to 400 μm. 100
If it is less than μm, crosstalk dispersion is too strong and conductive properties are poor. Moreover, if it exceeds 400 μm, spots due to poor dispersion will be visible in appearance, and the reproducibility of the resistance value will deteriorate. Although the number of passes is not specified, it is preferable to keep it to a necessary and sufficient number; unnecessary passes degrade the characteristics. For example, in the case of a triple roll of α75 and W, it is better to limit the number of passes to 5 or less, preferably 6 or less.

When using three rolls, the rotation speed of the rolls is 50 to 20
Orpm is preferable, and the rotation ratio of the rolls is 1st roll = 2nd roll: 3rd roll = 1:2 to 4:4
~16 is preferred.

The carbon paste produced in this way is printed on a printed circuit board using an ordinary screen printer, dried and cured, and then trimmed if necessary to provide a printed resistor for practical use. In the case of ordinary printed resistors, terminal electrodes made of conductive paste such as silver paste or plated terminal electrodes made of gold, silver, nickel, etc. are used to ensure connection reliability with the circuit. In addition, in order to protect the printed resistor itself from various environments, a protective coat (overlay coat) mainly made of insulating resin is usually applied, and if necessary, it is necessary to apply a protective coat (overlay coat) between the printed resistor and the board. A similar protective coat (underlay coat) can also be applied in between. In the case of the carbon paste of the present invention, it is put into practical use through such normal steps and exhibits its performance.

[Effect]

In the kneading process, the roll spacing is 100 to 400 μm.
The reason why the properties of the dough are improved by selecting a roll kneading method with a certain temperature is considered to be as follows.

In other words, in this method, the aforementioned struf- tures are not destroyed and are appropriately dispersed, so that many stable conductive paths are formed in the carbon paste.

On the other hand, if the roll interval is narrowed, the stracture is destroyed, and the conductive path is mainly made up of contacts between unstable carbon particles. In this case, the resistance value changes with the slightest impact.

In addition, in the case of roll kneading, the aggregates are dispersed while being kneaded, whereas in the case of a mixer, the aggregates are dispersed while being broken, so that the stractures are more likely to be divided.

〔Example〕

Hereinafter, the present invention will be explained using Examples and Comparative Examples.
"Parts by weight" and "% by weight" are shown.

Example 1 As a binder, phenol resin BLS-3135 (manufactured by Showa Kobunshi ■) was solvent-substituted with butyl carbitol acetate (solid content 59.3%), and 50 parts in terms of solid content were used. Ketchen Black EC was used as carbon particles. −
A mixture of 10 parts of DJ600 (manufactured by Mitsubishi Yuka), 40 parts of Micro Ace-1 (manufactured by Nippon Talc) as a filler, and 100 parts of butyl carpitol acetate as a solvent (hereinafter referred to as "carbon paste formulation B"). ) was prepared using three rolls (manufactured by Nagase Screen ■) with a rotation ratio of 1:2.8 near and 8, and an output of 0.75. The front roll rotation speed was 120 rpm, and the roll spacing was 200 μm and 200 μm.
A carbon paste was obtained by passing the carbon paste twice. 65μm
Steel-clad glass epoxy laminate R-1701 (Matsushita Electric Works ■
A test piece was prepared by etching a copper foil within the 50 square area using a copper foil (manufactured by J.D. Co., Ltd.), followed by gold plating based on nickel plating, and patterning 10 terminals on the copper foil. On this test piece, the carbon paste was screen printed to a width of 2 mm, 2 layers between the terminals (1 layer each on both sides of the wrap with the terminal), and a solid content of 20 parts and 2 μm in thickness, and heated in a sealed oven at 150°C. The film was dried for 5 minutes at 180° C. and cured for 80 minutes at 180°C. Furthermore, that M-100
(coating material made by Nitoa Gosei Kagaku Kogyo ■, whose main components are a modified Tsunor resin binder and an inorganic filler) was coated with a coating material of 150 μm in the same way as overcoat y so that the solid content was 20 μm.
It was dried at 180°C for 5 minutes and cured at 180°C for 30 minutes. In this way, 10 test pieces were made, totaling 100 pieces.
The printing resistance was measured.

The measurement was carried out using a tester under the conditions of 20° C. and humidity of 65° C.

Converted to a thickness of 20 μm, these sheet resistance values are the average t
71Ω/mouth・(20μm), standard deviation 0, 20 KG
/low (20 μm), indicating good reproducibility.

In addition, when the temperature coefficient (Tel) of the resistance value was measured according to JIS-C-5202 Section 5.2, it was found to be -182 ppm/'C on average between 20°C and 125°C, indicating a small rate of change. .

Example 2 Phenol modified xylene resin PR-1 as binder
Example 1 except that 440 (manufactured by Mitsubishi Gas Chemical ■) whose solvent was replaced with butyl carpitol acetate (solid content 55.2%) and H8-500 (manufactured by Asahi Carbon ■) were used as carbon particles. Carbon paste was obtained in the same manner as above and tested.

The resistance value converted to a thickness of 20 μm is 2.47 Ω/mouth·(20 μm) on average, and the standard deviation is α65KQ/mouth·(20 μm).
The reproducibility was good, and the TCR between 20°C and 125°C was -151 ppm/°C on average, and the rate of change was small.

Comparative Example 1 Phenol-modified xylene resin PR-1 as binder
440 with butyl carpitol acetate as the solvent (solid content 55.2%), 50 parts in terms of solid content,
H8-50 ([10 parts] as a filler, 40 parts of -1 in Micro Ace as a filler, and 50 parts of butanol as a solvent (hereinafter referred to as "compound A for carbon paste")) for iooy Contains 1009 glass beads with a diameter of 1n.
The mixture was shaken and kneaded in a paint conditioner (manufactured by Red Devil ■) in a container for 1 hour and 8 hours. Evaluation was performed in the same manner as in Example 1, and the resistance value converted to 20 μm thickness was 8.62 Ω/mouth (20
μm), standard deviation! h, 21, Ω/mouth (20 μm),
Average of 197.6 KQ 1 port (20μm) for 8 hours of crosstalk
The resistance value was high, with a standard deviation of 201 KO/mouth (20 μm), and the reproducibility was also poor.

Comparative Example 2 Carbon paste formulation A200 with the same composition as Comparative Example 1
．． 9 to 1 cod diameter glass beads 200.9, sand grinder (manufactured by Igarashi Kikai Seisaku) 1100
The mixture was stirred and kneaded using a rotary blade at a rotation speed of 0 rpm for 0.5 hours and t5.6 hours.

Evaluation was carried out in the same manner as in Example 1, and the resistance value converted to a thickness of 20 μm was as shown in Table 1 (high (and the reproduction was also poor).

Table 1 Comparative Examples 6 and 4 Carbon paste formulation B having the same composition as Example 1 was kneaded using the three rolls of Example 1.

However, the roll spacing was 20 μm and 20 μm in Comparative Example 3,
In Comparative Example 4, two passes were made with V00 μm and +00 μmK. As a result of evaluation in the same manner as in Example 1, as shown in Table 2 (
It was defective.

Table 2 (C) Effects of the Invention The carbon paste produced by the method of the present invention has good reproducibility of resistance value and has a small temperature coefficient of resistance value, so printed resistors obtained using this paste can be used instead of conventional resistor parts. Since it can be used satisfactorily for many applications, it can greatly contribute to high-density packaging and cost reduction of electronic components.

Claims (1)

[Claims] 1. A method for producing carbon paste by kneading a resin binder, a solvent, and carbon particles, characterized in that the kneading is carried out by roll kneading with a roll interval of 100 to 400 μm.