JPS6272750A - Electrically conductive paste - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive paste having excellent adhesivity and flexibility, high curing rate and long pot-life and suitable for the bonding of a quartz plate, etc., by compounding a urethane prepolymer, a hydroxypolyester and electrically conductive powder. CONSTITUTION:The objective composition can be produced by compounding and uniformly kneading (A) a binder consisting of (a) a urethane prepolymer (preferably a prepolymer produced by blocking a polyester, polyolefin, hydrogenated polybutadiene, etc., having isocyanate group at the terminal with an active hydrogen compound (e.g., acetoacetic acid ester) and (b) a polyester having hydroxyl group at the terminal and derived from epsilon-caprolactone and a polyhydric alcohol [the equivalent ratio of the dissociated NCO of the component (a) to the OH of the component (b) (NCO/OH) is 0.5-3] with (B) electrically conductive powder having an average particle diameter of <=30mum. The weight ratio of A/B is preferably 30/70-10/90 and the kneading of the components is carried out with a three-roll mill, etc.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to adhesiveness used in cases where flexibility is required, such as circuit formation on a flexible print r3 base or adhesion of crystal pieces in a crystal resonator. , relates to a conductive paste with excellent flexibility and long pot life.

[Technical Background of the Invention and Problems Therewith] In general, a conductive paste is mainly composed of a binder such as an epoxy resin or a phenol resin, and a conductive powder mainly composed of silver powder or the like. In the case of conductive pastes that use epoxy resin as a binder, polyamide resins, amines,
Various hardening agents such as imidazoles, melamines, acid anhydrides, boron trifluoride, and amine mirrors are used.

However, epoxy resin-based one-component conductive paste is
Those with a fast curing speed lack stability, while those with good stability have a problem of slow curing and poor adhesion.

On the other hand, those using phenolic resin as a binder have moderate adhesion and stability, but are inferior in flexibility, and if the adherend on which the conductive paste is printed is flexible, it may be difficult to bend or bend the adhesive. There was a problem in that printed circuits would crack or peel off due to such methods.

In particular, when used as a conductive adhesive for the lead conductor of a crystal resonator, which requires a high degree of flexibility, whether it is an epoxy resin-based adhesive or a phenolic resin-based adhesive, cracks may occur in the crystal piece or property fluctuations may occur. There was a problem. In addition, even in urethane resin systems, those using dihydric alcohols or blocked isocyanates have poor reactivity, while those using simple difunctional or higher polyhydric alcohols have high reactivity but poor flexibility. there were.

[Object of the Invention] The object of the present invention was to solve the above-mentioned drawbacks, and it has excellent adhesion, flexibility, and flexibility stability, and has good conductivity stability despite its fast curing speed. The present invention aims to provide a conductive paste that has a long pot life and good stability.

[Summary of the Invention] In order to achieve the above object, the inventors of the present invention, as a result of repeated tax research, have discovered that a hydroxy polyester consisting of ε-caprolactone and a polyhydric alcohol is used as a binder for a conductive paste. The present inventors have discovered that results satisfying the above objectives can be obtained by the above methods, and have completed the present invention.

That is, the present invention comprises (A) a urethane prepolymer, (B)
This is a conductive paste characterized by containing a hydroxy polyester made of ε-caprolactone and a polyhydric alcohol, and (C) conductive powder. The urethane prepolymer is obtained by blocking the terminal active isocyanate groups of the polymer with an active hydrogen compound, and
The isocyanate 1 group (NC○-) that dissociates from the urethane prepolymer and the hydroxyl group (-
The equivalence ratio (NC○/O)-1) with 0 and 1) is 0.5
Conductive paste 1-, which is within the range of ~3.0.

The (A) urethane prepolymer used in the present invention is as follows:
Although all kinds of prepolymers that form urethane can be used, block isocyanate prepolymers in which terminal active isocyanate groups are blocked with active hydrogen compounds are preferably used. . Typical of these are polyesters, polyolefins, or hydrogenated polybutadienes having terminal active isocyanate groups, which are blocked with blocking agents such as acetoacetate, cyclohexanone oxime, phenol, and imidazole. Specifically, Desmodule AP Stable (manufactured by Bayer, trade name)
These can be used alone or in combination of two or more. These blocked urethane prepolymers are stable at room temperature, but have the property of dissociating isocyanate groups when heated to 100° C. or higher.

The hydroxy polyester (B) consisting of ε-caprolactone and a polyhydric alcohol used in the present invention is a polyester having a hydroxyl group at the end obtained by ring-opening polymerization of ε-caprolactone and a polyhydric alcohol, and is a polyester that has a hydroxyl group at the terminal. How about it,
It has a long chain alkyl group for flexibility. A specific compound is P L manufactured by Daicel Chemical Industries, Ltd.
-308.

PL-320, PI-360, PLL-320ΔL
, PLL-350AL, etc., and these may be used alone or in combination with two or more types or other polyols.

This hydroxy polyester is reacted with the isocyanate groups lidded from the urethane prepolymer described above to form a binder.

Dialkyltin dilaurate and the like can generally be used as a catalyst to promote this reaction system. The blending ratio of the urethane prepolymer and the hydroxypolyester is determined by the equivalent ratio of the dissociated isocyane 1-W (-NC○) and the water Mu (Of-1) of the hydroxypolyester (NCOloH
) is preferably within the range of 0.5 to 3.0.

If this ratio is less than 0.5 or more than 3.0, predetermined characteristics will not be achieved, which is undesirable. Therefore, it is limited within the above range.

Examples of the (C) conductive core 1) powder used in the present invention include silver powder, copper powder, nickel powder, and powder having a metallic surface on the surface. All of these conductive powders preferably have an average particle size of 30 μm or less.

This is because if the average particle size exceeds 30 μm, high-density packing becomes impossible, the paste does not form, and coating performance deteriorates.

The blending ratio of the above-mentioned binder and conductive powder is 3 by weight.
It is desirable that it is 0□'70 to 1o/90.

If the proportion of the conductive powder is less than 70 parts by weight, satisfactory conductivity will be lost by 1q, and if it exceeds 90 parts by weight, workability and adhesion will deteriorate, which is not preferable. Therefore, it is limited within the range shown.

The conductive paste used in the present invention may contain an organic solvent, if necessary, in order to adjust its viscosity. Solvents used include dioquitnan, hexanone,
Examples include cyclohexane, bempine, 1-toluene, solvent naphtha, industrial gasoline, acetic acid atrosolve, butyl cellosolve acetate, butyl carpitol acetate midridone, and the like.

In order to manufacture a conductive paste using each of the above-mentioned components, each component is uniformly kneaded using three rolls or the like. These conductive pastes are applied by screen printing or dispensing to a predetermined location, and then heated and cured before use.

This conductive paste can be cured under various curing conditions, but preferably 150°C for 30 minutes or 120°C for 60 minutes.

[Examples of the Invention] Next, the present invention will be explained by examples, but the present invention is not limited to these examples.

Examples 1 to 3 Each component shown in Table 1 was kneaded three times using three rolls to produce a -liquid conductive paste. This conductive paste was applied onto mR or polyester film and cured at 150°C for 30 minutes. The cured pastes were tested for conductivity, pot life and adhesion and flexibility on copper foil or polyester film.

As a comparative example in Table 1, a conventional phenolic-liquid conductive paste was also subjected to characteristic tests in the same manner as in the Examples. The results are shown in Table 1, and in all cases the remarkable effects of the present invention were confirmed.

[Effects of the Invention] As is clear from the above explanation and Table 1, the conductive paste of the present invention has good adhesion to flexible polyester films, etc., and shows no cracks ( No cracks) or peeling, excellent flexibility,
Moreover, despite its fast curing speed, it was found to have excellent stability and a very long pot life, and was also found to have excellent electrical conductivity and electrical conductivity stability. Therefore, it is not suitable as a conductive paste 1 for one-component screen printing on flexible circuit boards or for adhering crystal pieces, which requires a high degree of flexibility.

Claims (1)

[Scope of Claims] 1. A conductive paste characterized by containing (A) a urethane prepolymer, (B) a hydroxy polyester made of ε-caprolactone and a polyhydric alcohol, and (C) a conductive powder. 2. The conductive paste according to claim 1, wherein the urethane prepolymer is obtained by blocking terminal active isocyanate groups of the polymer with an active hydrogen compound. 3 Isocyanate groups (NCO-) dissociated from the urethane prepolymer and hydroxyl groups (NCO-) of the hydroxy polyester
-OH) (NCO/OH) is 0.5 to 3.
The conductive paste according to claim 1 or 2, which is within the range of 0.