JP3767631B2 - Method for adjusting resistance value of conductive film - Google Patents

Description

  The present invention relates to a potentiometer type variable resistor used in various electronic devices, a resistive resin film on which a contactor such as a sensor slides, or a dispersed resin system used for forming a printed circuit board wiring circuit. The present invention relates to a method for adjusting a resistance value of a conductive film obtained from a conductive paste.

  Conventional conductive pastes are often dispersed resin-based pastes made of conductive materials. Carbon black, natural or artificial graphite, or mixed powder of graphite and carbon black (hereinafter collectively referred to as “conductive”). Material ”) is kneaded and dispersed in a synthetic resin binder such as phenol resin, epoxy resin, polyester resin, or polyimide resin dissolved in a suitable solvent, and diluted with a solvent to obtain a suitable viscosity for printing. I was making it.

  And after printing the conductive paste on a substrate such as a paper phenol laminate, a glass epoxy laminate, a ceramic substrate, a resin film or a resin molded body by a film thickness forming method such as screen printing, it is heated and cured. A resistive film such as a potentiometer type variable resistor or a sensor was formed. At this time, the resistance value of the conductive paste was adjusted by arbitrarily changing the filling ratio of the conductive material.

  If the filling ratio of the conductive material is decreased too much in order to adjust the resistance value of the conductive paste, the surface tension of the coating film is lowered. Protrusions and pinholes due to the foaming phenomenon occur and the surface properties deteriorate. For this reason, there is a problem that contact failure is likely to occur when a potentiometer-type variable resistor or a contact such as a sensor slides after being heated and cured.

  On the other hand, if the filling ratio of the conductive material is increased too much, it cannot be made into a paste, and there is a problem that there is a limit in adjusting the resistance value by increasing or decreasing the filling ratio of the conductive material.

  This invention solves the said conventional subject, and adjusts easily the resistance value of the conductive film obtained by the dispersion resin-type paste made into the same compounding filling ratio as the conductive material and synthetic resin binder which are used for a conductive paste. It is an object of the present invention to provide a method for adjusting the resistance value of a conductive coating film that can be made to have a good coating surface after printing.

  In order to achieve the above object, the present invention provides a method for adjusting a resistance value of a conductive coating obtained by a dispersed resin-based conductive paste comprising a synthetic resin binder, a conductive material, and an organic diluent solvent, wherein the conductive material Without changing the filling ratio, the organic dilution solvent is selected and mixed according to the physical properties of the solubility and the degree of association with the synthetic resin binder, and the resistance value is adjusted in correlation with the physical properties. The resistance value adjusting method is used.

  According to the present invention, the surface state of the film after printing and baking is good and can be easily adjusted to a desired resistance value without changing the filling ratio of the conductive material.

  As described above, the present invention can change the filling ratio of the conductive material by selecting and mixing the organic dilution solvent mixed with the conductive paste according to the solubility and the physical property of the association degree with the synthetic resin binder. There is an effect that it is possible to provide a method for adjusting the resistance value of a conductive coating, which can easily adjust the resistance value.

  Hereinafter, the conductive paste in one embodiment of the present invention will be described.

  The dispersion resin-based conductive paste in the present embodiment is a mixture of a thermosetting resin made of phenol resin or the like as a synthetic resin binder with a conductive material made of acetylene black, furnace black, graphite or the like alone or mixed powder. Then, after being dispersed by a roll mill, a dispersion resin-based paste adjusted to have an appropriate printing viscosity using a solvent is prepared. Thereafter, the conductive coating film heated and cured after coating is prepared by mixing and containing organic solvent having different solubility and association degree physical properties capable of adjusting the resistance value.

  The conductive paste produced by this method is heated and cured on a substrate such as a paper phenol laminate, a glass epoxy laminate, a ceramic substrate, a resin film or a resin molded body, and a potentiometer type variable resistor, sensor, etc. When the resistive coating is formed, it is possible to easily change the conductive path flowing between particles of conductive particles such as carbon particles of the conductive material dispersed in the resistive coating on the substrate.

  Hereinafter, the mechanism of the conductive paste in one embodiment of the present invention will be described with reference to the drawings.

  1 and 2 are diagrams for explaining the conductive mechanism of the conductive paste in one embodiment of the present invention.

  In FIG. 1, 1 is a synthetic resin binder. This synthetic resin binder contains the conductive material 2. Reference numeral 3 denotes a main conductive path between particles of the conductive material 2. As shown in FIG. 2, the resistance value of the resistance film by the main conductive path 3 is “the resistance value 4 of the conductive material 2 (not shown in this figure)” and “the conductive material 2 (in this figure). , Not shown)) and the sum of the resistance value between the particles 5 ”. However, since the conductive material 2 is a good conductor, the “resistance value 4 of the conductive material 2” is much smaller than the “resistance value 5 between the particles of the conductive material 2”. It is determined by “resistance value 5 between particles of the conductive material 2”, and the resistance value can be adjusted by changing the resistance value 5 between the particles of the conductive material 2.

  FIG. 3 is a view for explaining the resistance between conductive material particles, which is a main part of the conductive paste in one embodiment of the present invention. The resistance between the particles of the conductive material 2 is closely related to the change in the state of enveloping the particles of the conductive material 2 by the synthetic resin binder 1, and acts on the gap between the particles of the conductive material 2. is there. In order to increase the resistance between the particles of the conductive material 2, it is necessary to widen the "gap 6 between the particles of the conductive material" as shown in FIG. In order to do this, as shown in FIG. 3B, it is necessary to narrow the “gap 7 between the particles of the conductive material”. Therefore, changing the solubility of the diluting solvent in the synthetic resin binder 1 acts to extend the polymer chain of the resin in the solvent. Therefore, if the solubility in the synthetic resin binder 1 is high, the polymer of the resin in the solvent is high. When the chain is stretched and the particles of the conductive material 2 are easily encapsulated, this state is maintained during heating, the solvent is volatilized, and the resin is cured, the resistance between the particles of the conductive material 2 is easily inhibited by the resin. The resistance value is inevitably high.

  In general, the printed coating film undergoes convection during heating until a considerable amount of solvent evaporates. At this time, the particles of the conductive material 2 which are fine particles also move, so that secondary aggregation tends to occur. When secondary agglomeration occurs, the gap between the particles of the conductive material 2 becomes narrow, and the resistance value decreases. That is, even if the molecular weight of the solvent is approximate, the viscosity of the solvent alone varies greatly depending on the state of association between the solvents. In a solvent having a high degree of association, the above-described convection in the coating film is inhibited during heating. As a result, secondary aggregation of the conductive particles of the conductive material 2 is unlikely to occur, and the solvent is evaporated and the resin is cured while the dispersed state of the conductive material 2 and the dissolved state of the resin are maintained. The resistance between the two particles increases.

  Therefore, when an organic solvent having a high solubility in the synthetic resin binder 1 and a high degree of association is applied as a dilution solvent, a high resistance value can be obtained without changing the filling ratio of the conductive material 2. .

  On the other hand, when an organic solvent having low solubility and low degree of association is applied as a dilution solvent, the lowest resistance value can be obtained without changing the filling ratio of the conductive material 2. The solubility of the resin binder in the diluting solvent can be estimated by an SP (Solubility Parameter) value, and the solubility is good when the SP value is close, and the degree of association can be estimated by the organic solvent viscosity of the diluting solvent with respect to the molecular weight. The SP value means a solubility parameter, which indicates the cohesive energy density of molecules of each substance, and is obtained by subtracting the work due to expansion accompanying evaporation from the heat of evaporation at a specific temperature. The degree of association refers to a relatively regular assembly in which two or more molecules are bonded by a relatively weak binding force such as a hydrogen bond, a charge transfer bond, or a hydrophobic bond between the same molecules. It means the degree of body formation.

(Example)
As an example of the present invention, first, a thermosetting resin such as a phenol resin is used as a synthetic resin binder, and acetylene black, furnace black, graphite, or the like is used as a conductive material to produce a dispersed resin paste of a conductive material. Thereafter, an organic dilution solvent is mixed and contained, and the viscosity is adjusted so as to obtain an appropriate printing viscosity. By changing the organic solvent such as cyclohexanol and butyl carbitol acetate, which are dilution solvents used here, the physical properties of the solubility and the degree of association are changed, and the content of the conductive resin material is changed (Table 1). The conductive paste shown in Examples 1 to 6 shown in FIG.

(Comparative example)
As comparative examples of the present invention, conductive pastes shown in Comparative Examples 1 to 6 shown in (Table 1) are prepared using isophorone as a diluent solvent in the same dispersion resin paste as in the examples. At this time, other conditions are produced under the same conditions as in the example.

(Comparison method)
Examples shown in Table 1 in which the conductive paste obtained in the example or the comparative example is straddled on a paper phenol substrate having an electrode on which both sides of the upper surface are pre-printed and fired with a resin-based silver paste (Table 1) 1 to 6 and Comparative Examples 1 to 6 are screen-printed, and this is heated and cured at about 200 ° C. for about 10 minutes in a hot-air circulating furnace combined with far infrared to form a resistance film, for resistance value measurement This is a resistor. And how to output the resistance value of this resistor is evaluated and shown in (Table 1). At this time, the sheet resistance value is calculated from the resistance value output in a 3 mm * 30 mm pattern.

(Pass / fail judgment)
About the surface state of the resistance film formed on the paper phenol substrate, the quality of the surface state was judged by the presence or absence of projections and pinholes after screen printing and baking.

  As is clear from Table 1, when the filling ratio of the conductive material of Comparative Example 1 exceeds 65% by weight, the amount of powder in the conductive paste is too large to make a paste. Therefore, when the filling ratio of the conductive material that can be made into paste is 65% by weight, the sheet resistance value becomes the lowest of 0.052 kΩ / □ (52Ω / □) when the dilution solvent is isophorone, and the conductivity is gradually increased. When the filling ratio of the material is decreased, the sheet resistance value is increased (Comparative Examples 2 to 5). However, when the filling ratio of the conductive material of Comparative Example 6 is less than 20% by weight, the surface tension of the coating film after screen printing decreases due to the decrease in the powder amount of the conductive material. Protrusions and pinholes have occurred.

  In Examples 1 and 2, as in Comparative Example 2, when the filling ratio of the conductive material was 65% by weight and the sheet resistance value was measured by changing the dilution solvent, the dilution solvent was less soluble than isophorone, and the association was By using butyl carbitol acetate or ethyl carbitol acetate having a low degree, the sheet resistance value can be adjusted lower than in Comparative Example 2.

  Further, as in Comparative Example 5, when the filling ratio of the conductive material was set to 20% by weight, and the sheet resistance value was confirmed by changing the dilution solvent, only the solubility in Example 3 was compared with that of isophorone as the dilution solvent of Comparative Example 5. When high benzyl alcohol is applied, the sheet resistance value can be made higher than that in Comparative Example 5. In Examples 4 to 5, even higher sheet resistance can be obtained by applying as an organic dilution solvent having high solubility and high degree of association. In particular, the sheet resistance value can be adjusted to the highest value by using cyclohexanol having the highest solubility and the degree of association in Example 6 as a diluent solvent.

  In the present embodiment, the diluting solvent is selected in terms of solubility in the phenol resin, but the same effect that the resistance value can be adjusted by the solubility and the degree of association in other resin binders can be obtained.

  The method for adjusting the resistance value of the conductive film according to the present invention has the effect that the resistance value can be easily adjusted without changing the filling ratio of the conductive material. This is useful when adjusting the resistance value of the conductive film obtained from the conductive paste.

The figure explaining the conductive mechanism of the electrically conductive paste in one embodiment of this invention Diagram explaining the conduction mechanism The figure explaining the resistance between the electroconductive material particles which are the principal parts

Explanation of symbols

1 Synthetic resin binder 2 Conductive material 3 Main conductive path

Claims (1)

A method for adjusting a resistance value of a conductive film obtained by using a dispersion resin-based conductive paste comprising a synthetic resin binder, a conductive material, and an organic diluent solvent, wherein the organic system without changing the filling ratio of the conductive material A method for adjusting a resistance value of a conductive film, wherein a dilution solvent is selected and mixed depending on the physical properties of solubility and association degree with the synthetic resin binder, and the resistance value is adjusted in correlation with the physical properties.

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