JPS58167655A - Carbon paste - Google Patents

Abstract

PURPOSE:A carbon paste, prepared by dispersing carbon powder in a binder consisting of a butyral resin and a phenolic resin and a solvent in a specific proportion, having improved adhesive property to a base material, a low curing shrinkage, and suitable for printed resistors, contacts or conductors. CONSTITUTION:A carbon paste obtained by mixing and dispersing (A) carbon powder, e.g. an electrically conductive carbon black, in (B) a binder prepared by incorporating (i) a butyral resin, preferably 50-500 average polymerization degree, with (ii) a phenolic resin at (30:70)-(90:10) weight ratio and (C) a solvent, preferably containing one or more kinds having >=120 deg.C boiling point at (5:95)-(70:30) weight ratio between the components (A) and (B). EFFECT:Good adhesive property to polyester films, a low curing shrinkage and small change in electrical resistance values with time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carbon paste. For more details,
This invention relates to a carbon paste that has excellent adhesion to a base material and has low curing shrinkage.

Conventionally, carbon pastes in which carbon powder is dispersed in a binder and a solvent are known. These carbon pastes are screen-printed onto a base material, cured by heating, and used as printed resistors, contacts, or conductors. As the substrate, a hard substrate such as a glass fiber reinforced epoxy resin substrate (hereinafter referred to as an epoxy substrate), a paper reinforced phenol resin substrate (hereinafter referred to as a phenol substrate), or a ceramic substrate, or a flexible substrate such as a polyester film or a polyimide film is used. Conventional binders used for carbon paste include epoxy resin, phenolic resin,
Butylated methylolmelamine resins or mixtures thereof have been used. However, carbon pastes using these binders adhere well to epoxy substrates, phenol substrates, and ceramic substrates, but have poor adhesion to polyester films. Therefore, its use has been limited in applications using polyester film as a base material. Furthermore, these pastes have the disadvantage of large shrinkage upon curing. Therefore, when printed on a substrate with good adhesion such as an epoxy substrate, a phenol substrate, or a ceramic substrate and cured, internal distortion occurs in the cured film, causing the electrical resistance value to change over time. In addition, when curing shrinkage was severe, cracks occurred in the cured film, making it completely unusable. The present inventor has conducted extensive research in order to obtain a carbon paste free of such drawbacks, and as a result has arrived at the present invention. That is, the present invention comprises at least carbon powder and a binder, and the weight ratio of the carbon powder and the binder is 5:
The binder is mainly composed of a butyral resin and a phenolic resin, and the weight ratio of the butyral resin and the phenolic resin is in the range of 95 to 7 o:3 o.
It is a carbon paste characterized by being within the range of 0:1 ('l).

As the carbon powder in the present invention, either carbon black or graphite powder may be used, but a mixture of the two may also be used. As the carbon black, so-called conductive carbon black is preferable. Examples of conductive carbon black include Ketjenblack EC (manufactured by Lion Corporation) and Palkan XC-72 (manufactured by Capot Corporation).
, Denkabu artificial graphite, and natural graphite can be used, and those with a particle size of 0.1 to several tens of microns are preferable, and examples such as HyoACP, C3PE (,
1 (manufactured by Hando Nippon Graphite Co., Ltd.), G5l-5 (manufactured by Nippon Carbon Co., Ltd.), and CPB-5000 (manufactured by Shinetsu Graphite Industries Co., Ltd.).

The binder composition and the ratio of carbon powder to binder are very important in achieving the objectives of the present invention. The binder used in the present invention mainly consists of butyral resin and phenol resin. Butyral resin usually has vinyl alcohol groups, vinyl alcohol groups, and vinyl acetate groups in the molecular chain, and the average degree of polymerization is 50 to 5000.
are often used. Phenol resin can be used in either resol type or novolak type. The ratio of butyral resin and phenolic resin is 3n near 0 to 90 by weight.
:10, preferably within the range of 50:50 to 811:20. If the ratio is less than 30:70, the adhesion of the carbon paste to the polyester film is insufficient, and if the ratio exceeds 9Q:10, it will take a long time to heat for sufficient curing, which is not practical. The ratio of the carbon powder to the binder used is within the range of 5:95 to 70:30, preferably 10:90 to 60:40 by weight. 5:9
If it is less than 5, the electrical resistance value of the print curing 3 will become too large to be practical. 70:30
If it exceeds this amount, the adhesion to the polyester film may decrease or cracks may occur in the cured film.

The solvent used in the present invention may be used alone or as a mixed solvent, but preferably contains one or more solvents having a boiling point of 120° C. or higher. If the carbon paste does not contain a solvent with a boiling point of 120° C. or higher, the solvent will evaporate during screen printing and the viscosity of the carbon paste will change, which is not preferable. The amount of solvent used may be appropriately selected so that the carbon paste has a viscosity suitable for screen printing.

To produce the carbon paste of the present invention, inorganic and organic fillers and other additives may be added depending on the carbon powder, butyral resin, and phenolic resin.

The carbon paste produced in this way is printed on a substrate by screen printing, hardened by heating,
Can be used as printed resistors, contacts, and conductors.

Heating conditions = 4 - Normally, the heating temperature is 100 to 250°C and the heating time is 0.
It takes 2 to 5 hours. The printed cured product obtained in this way has good adhesion to a substrate such as a polyester film, has little curing shrinkage, and has little change in electrical resistance value over time.

The present invention will be explained in more detail with reference to Examples below.

Parts and ratios in the examples are based on weight unless otherwise specified. The various tests described in the Examples were conducted as follows.

(1) Polyester film with adhesion strength of 100μ, carbon paste with hand printing machine (screen mesh 225, emulsion thickness 4
0μ) to a size of 20mm x 20mm, and
It was cured for 1 hour at 0°C. In the obtained cured film, 11 vertical and horizontal cuts were made perpendicularly with a cutter knife at 1.0 mm intervals to form 100 squares.

After sufficiently pressing a cellophane tape onto the film, it was rapidly peeled off, and the proportion of the squares remaining on the polyester film among the 100 squares was expressed as a fraction and the adhesion strength was determined.

(2) Print and harden terminals in advance with silver paste on the electrical resistance value engineering 2x board (terminal spacing 10mm'), then print a 10mm line across the terminals using the same method as in (1). After hardening, the snow resistance between the terminals was measured.

Examples 1 to 3, Comparative Examples 1 to 2 Denka black (carbon black manufactured by Denki Kagaku Kogyo Co., Ltd.), 40% methyl ethyl ketone solution of Chinka Butyral Sai 3ooo+ (butyral resin manufactured by Denki Kagaku Kogyo Co., Ltd.), Hytanol 4010 ( Phenol resin manufactured by Hitachi Kago Industries, Ltd. (solid content 50%) was mixed in the proportions shown in Table 1 on a dry weight basis, an appropriate amount of calpitol was added, and mixed wire I ~, carbon It was made into a paste. Kalbi)-Luno amount is approximately 4 viscosity of carbon paste
00 to 600 poise. The obtained carbon paste was evaluated by the above method, and Examples 1 to 3, which were within the scope of the present invention, all had good adhesion to the polyester film and small electrical resistance. In Comparative Example 1, the lightning 1@ and the analysis were large. In Comparative Example 2, which is particularly outside the scope of the present invention, the adhesion strength to the polyester film was small, and the cape and air resistance at 1C could not be measured because cracks occurred in the cured film.

*Cracks occurred in the hardening value and density measurements were not possible Examples 4 to 6, l + Comparative Examples 3 to 4 CPB-5000 (graphite powder manufactured by Nakadai Graphite Co., Ltd.) was used instead of Denka Black h), and CPB-
A carbon paste was obtained in the same manner as in Example 1, except that the amounts of Denka Butyral 5000, Denka Butyral 3000, and Hytanol 40107 were increased in the proportions shown in Table 2. The evaluation results are shown in Table 2, and Examples 4 to 6, which are within the scope of the present invention, all had good adhesion to the polyester film, and the electric side folded pile was small, but it is outside the scope of the present invention. Tohi Comparative Example 3 had a high electric resistance (direction), and Comparative Example 4 had a low adhesion strength to the polyester film.

81 Examples 7-9, Scolding σII 5-6 CPB-5000, Denka Butyral 13000K,
1 carbon paste was added in the same manner as in Example 4 except that the proportion of Hytanol 4010 used was as shown in Table 3.
4. The evaluation results are shown in Table 3, and Examples 7 to 9, which fall within the scope of the present invention, all had good adhesion to the polyester film and small electrical resistance values. Comparative Example 5, which is outside the scope of the present invention, had low adhesion strength to the polyester film. Similarly, in Comparative Example 6, which is outside the scope of the present invention, the cured film remained sticky even after being treated at 150° C. for a total of 5 hours, and curing was insufficient.

**The cured film was sticky, and although it was further treated at 150°C for 4 hours, the stickiness was not completely eliminated, so the adhesion strength and electrical resistance values were not measured.

patent applicant Mitsui Toatsu Chemical Co., Ltd. −11= 374-

Claims (1)

[Claims] (consisting of carbon powder, binder and solvent,
The weight ratio of carbon powder to binder is 5:95 to 70:
:'10, the binder mainly consists of butyral resin and phenol resin, and the weight ratio of butyral resin and phenol resin is 7! I) Near 0-9n
: A carbon paste characterized by being within a range of 10.