JPS6043602B2 - Thermosetting conductive sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermosetting conductive sheet that is easy to handle during use and has excellent storage stability.

The cured product of the thermosetting conductive sheet has stable conductive properties,
Furthermore, it forms a highly elastic conductive layer with excellent heat resistance, weather resistance, moisture resistance, and mechanical properties.

Conventionally, conductive materials have been used in various industrial fields, and many of them utilize the electrical and thermal conductivity and radio wave absorption properties of conductive fillers to create conductive paints, adhesives, and electrodes. It is widely used in surface heating elements, radio wave absorbers, and various switches and sensors. Most of these conductive materials have a conductive filler held in a suitable matrix, and the matrix may be natural or synthetic solid rubber, liquid rubber such as silicone or urethane, or synthetic resin such as epoxy or polyester. types are often used. In addition, the form in which the conductive material is supplied is a sheet, tape, or sheet coated with an adhesive layer.
Tapes, paint-type products diluted with organic solvents, etc., and two-component products that are solvent-free but require a hardening agent are common. However, when using the above matrix commonly used in conductive materials, for example, in the case of solid rubber, a large amount of energy is required because shearing force is used when mixing the conductive filler and rubber, and fibrous filler etc. is easily broken.

Also, because it is molded under high pressure, unnatural distortions may occur. However, it has drawbacks such as the microscopic filler arrangement being easily disordered and the conductive properties being unstable and not reproducible.

In addition, although liquid rubber and liquid resins do not have the above-mentioned drawbacks, conventional liquid rubbers such as silicone resins have inferior mechanical strength and adhesive strength, so such strength is not required. It cannot be used for any purpose.

Further, liquid rubber such as urethane, including liquid synthetic resins such as epoxy and polyester, has poor heat resistance, weather resistance, and moisture resistance, and changes in conductive properties 4 occur due to deterioration and moisture absorption.
Furthermore, although polybutadiene liquid rubber has excellent moisture resistance, it has the disadvantage of being easily degraded by heat, ultraviolet rays, etc. due to the presence of double bonds in its molecular structure, and impairing its rubber elasticity. Further, the form in which the conductive material is generally supplied is as described above, and it is not easy to manufacture and handle during use. For example, if the adhesive is supplied in the form of a sheet or tape, or a sheet or tape coated with an adhesive, it is necessary to select an adhesive that takes into account the compatibility between the surface to be adhered and the matrix, and the process of applying the adhesive. will increase by one. In addition, if it is diluted with an organic solvent, etc.
It is also unfavorable in terms of the working environment during manufacturing and use. )Also, even when supplied as a liquid solvent-free type, most are two-part types that require a hardening agent, and the storage stability of the mixed liquid is extremely short, resulting in poor workability. There is. In view of the above-mentioned circumstances regarding conductive materials, the inventors of the present invention believe that they can be easily produced and have reproducible conductive properties during manufacturing, and that they do not require the use of adhesives or solvents during use. It exhibits self-bonding properties when heated to an appropriate level, fuses to the surface to be bonded, and completely cures to exhibit strong adhesion to any surface to be bonded, and is also heat resistant. As a result of various researches to obtain a thermosetting conductive sheet with excellent weather resistance, moisture resistance, mechanical properties, and excellent storage stability that forms a stable conductive layer,
By using urethane prepolymer A having hydroxyl groups at both ends of the molecule consisting of a hydrogenated product of a polyhydroxybutadiene polymer and a diisocyanate compound, polyisocyanate B masked with a long-chain aliphatic phenol derivative, and conductive filler C, the above-mentioned It was discovered that a thermosetting conductive sheet with improved drawbacks could be obtained, and the present invention was completed.

That is, the present invention provides a base material such as paper or plastic film with excellent releasability, which is coated with hydroxyl at both ends of a molecule having an average molecular weight in the range of 2,000 to 20,000, and is made of a hydrogenated polyhydroxybutadiene polymer and a diisocyanate compound. It is characterized in that a mixture consisting of a urethane prepolymer A having groups, a polyisocyanate B masked with a long-chain aliphatic substituted phenol derivative, and a conductive filler C is provided in a uniform thickness.

The thermosetting conductive sheet of the present invention exhibits self-bonding properties when heated to 60 to 70°C, and
By heating at any temperature up to 1700C, a highly elastic and conductive layer with excellent adhesiveness, heat resistance, weather resistance, and moisture resistance is formed.

The hydrogenated polyhydroxybutadiene polymer in the present invention has 1.5 or more hydroxyl groups per molecule,
Preferably 1.7 to 5. C @ has something. As the hydrogenated product of this polyhydroxybutadiene polymer,
For example, 1.4-butadiene, 1.3-butadiene, 1.
Homopolymers such as 2-butadiene, 1.3-pentadiene, and 1.4-pentadiene, or copolymers in which the content of vinyl monomers is usually 5% or less, particularly preferably 4% or less, based on butadiene, are hydrogenated. There are things that are added. If the content of the vinyl monomer is more than 5% by weight, the cured product will have poor elasticity, which is not preferable. Examples of the above-mentioned vinyl monomers include styrene, acrylotoniryl, methacrylic acid, and acrylic acid.

A specific example of polyhydroxybutadiene is Arco (
ARCO) POlyBD, R-45M, R-45H
T, CS-15, CN-11 and Nippon Soda NISSO
PBG-1000, PBG-2000, PBG-30
There are products obtained by hydrogenating polyhydroxybutadiene, such as 0, using a Raney catalyst, a stabilized nickel catalyst, etc., and the hydrogenation rate is preferably 50% or more, and one or more of these are mixed. Can be used. If the hydrogenation rate is less than 50%, oxidative deterioration of the cured product occurs and heat resistance decreases, which is not preferable.

The urethane prepolymer A having an average molecular weight of about 2,000 to 20,000 and having hydroxyl groups at both ends of the molecule, which is composed of a hydrogenated product of the polyhydroxybutadiene polymer and a diisocyanate compound and used in the present invention, is the polyhydroxybutadiene polymer. It can be easily produced by always reacting a hydrogenated product of butadiene polymer with diisocyanate in an excess amount. The molecular weight of the urethane prepolymer is such that the molar ratio of the diisocyanate to the hydrogenated product of the polyhydroxybutadiene polymer is 0.5 or more.
．． The average molecular weight is preferably in the range of 2,000 to 20,000 since it can be adjusted by reacting within a molar ratio of 9 or less.

When the average molecular weight is 2,000 or less, the sheet has low strength and is brittle, so that cracks may occur if it is bonded to an extremely bent portion. Furthermore, if the average molecular weight is 20,000 or more, the self-bonding property is reduced, requiring heating at high temperatures or using an adhesive, resulting in a reduction in workability. Further, when mixing the conductive filler, a large shearing force is required, and it is not preferable to use a fibrous filler because the fibers may break. Examples of the diisocyanate compound used in the present invention include toluene-2,6-diisocyanate, toluene-2,4-diisocyanate, diphenylmethane-4,4''-diisocyanate, diphenyl ether-4,4''-diisocyanate, hexamethylene-1,6-diisocyanate, Naphthylene-1.5-diisocyanate, m-xylylene diisocyanate, p
-xylylene diisocyanate, etc., and these diisocyanates can be used alone or in combination of two or more.

Polyisocyanate B masked with a phenolic compound, which is another component of the present invention, has the general formula ^. ．． (However, R represents an aliphatic hydrocarbon residue having 8 to 15 carbon atoms.

) is used as an addition compound. . This addition compound is compatible with the urethane prepolymer to ensure stable conductivity of the cured product.
It is necessary to obtain good mechanical properties, and for this reason,
It is preferable that the carbon number of R in the phenol compound is in the range of 8 to 15. If the number of carbon atoms in R is 8 or less, the addition compound with isocyanate will have no compatibility with the urethane prepolymer and will not be in a uniform and completely cured state, and if the number of carbon atoms is 15 or more, curing will not occur. The plasticizing effect of the liberated phenol derivative makes the conductivity unstable and the mechanical properties are significantly reduced.

Examples of the above-mentioned phenol compounds include 4-octylphenol, 4-nonylphenol, 4-dodecylphenol, and cardanol, and one or two of these may be used.
More than one species can be mixed and used.

On the other hand, as the polyisocyanate, it is possible to use not only the diisocyanate compound which is a component of the urethane prepolymer, but also triphenylmethane-4,
It is also possible to use trifunctional or more than trifunctional isocyanates, such as 4'',4'''' monotriisocyanate or the reaction product of 1 mole of trimethylolpropane and 3 moles of diisocyanate.

The masked polyisocyanate can be produced by adding an isocyanate group and a hydroxyl group according to a conventional method. The mixing ratio of the urethane prepolymer A having hydroxyl groups at both ends of the molecule and the polyisocyanate B masked with the above phenol compound is preferably an amount corresponding to 0.8 to 1.5 equivalents of isocyanate groups per hydroxyl group.

If it is outside the above range, the mechanical properties of the cured conductive sheet will be poor. Further, as the conductive filler C used in the present invention, all commonly used conductive substances such as carbon black, carbon fiber, metal powder, metal fiber, etc. can be used in the present invention.

The above-mentioned conductive filler is added to the urethane prepolymer A at a ratio of 1 to 9 weight percent to A to provide a thermosetting material with a predetermined conductivity in the range of 1σ to 10-3Ω. A conductive sheet can be obtained.

The thermosetting conductive sheet with the above-mentioned composition uses a urethane prepolymer with a lower molecular weight than solid rubber as a matrix, so it does not require large shearing force when mixing the conductive filler, which saves labor. This leads to a reduction in utility costs, and the fibrous conductive filler can be mixed without being broken.

Furthermore, when molding into a sheet, it can be easily molded to any desired thickness at low pressure, so it has the advantage that the microscopic arrangement of the conductive filler is less likely to be disturbed.

Therefore, the conductive properties of the obtained sheet are stable and have good reproducibility. In addition, the thermosetting conductive sheet is
Since a polyisocyanate masked with a phenolic compound is used as a curing agent, it exhibits extremely long storage stability and also solves concerns regarding the toxicity of isocyanates. Furthermore, since the thermosetting conductive sheet exhibits self-adhesive properties when heated to 60 to 70°C, it has an excellent feature that no adhesive is required. Furthermore, the thermosetting conductive tape of the present invention can be heated to 90 to 170°C to obtain highly elastic conductivity, and the curing time can be adjusted by selecting the heating temperature. can.

If necessary, a catalyst for promoting the curing reaction, such as trialkylamine, dialkylaniline, N,
Amines such as N''-dialkylpiperazine and triethylenediamine, organic tin compounds such as dibutyltin dilaurylate and tin octylate, acetylacetone metal salts, etc. can be added. Because it has stable conductive properties and excellent heat resistance, weather resistance, moisture resistance, mechanical properties, and adhesive properties, its applications are wide-ranging, and the industrial value of the present invention is extremely high. Below are reference examples, comparative examples,
The present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and are not intended to be limiting.

[Reference Example 1] Polyhydroxybutadiene polymer POlyBDR-4
5M (manufactured by ARCO, 1.4-trans 60%, 1.4
-20% cis, 20% 1.2-vinyl, 0H value 44) at 120 Da.

101 y of Raney nickel catalyst and 100 y of dioxane
Put it in an autoclave with hydrogen pressure of 10k9/Clt.
Hydrogenation was carried out at a reaction temperature of 80°C to obtain a hydrogenated product of polyhydroxybutadiene polymer (hydrogenation rate 95
%). [Reference Example 2] POlyBDC which is a polyhydroxybutadiene polymer
S-15 (manufactured by ARCO, 1.4-trans 60%, 1
．． 4-cis 20%, 1.2-vinyl 20%, butadiene to styrene ratio 75:25 copolymer 0H value 42) 10
0da was subjected to hydrogen reduction in the same manner as in Reference Example 1 to obtain a hydrogenated polyhydroxybutadiene polymer.

(Hydrogenation rate?%). [Reference Example 3] Polyhydroxybutadiene polymer NISSOPBG2OOO (manufactured by Nippon Soda, 90% 1.2-vinyl, 10% 1.4 bond, 0H value 56) was subjected to elementary reduction in the same manner as in Reference Example 1. A hydrogenated product of polyhydroxybutadiene polymer was obtained (hydrogenation rate ?%).

[Example 1] A urethane prepolymer having hydroxyl groups at both ends of the molecule was synthesized as follows.

That is, four hydrogenated polyhydroxybutadiene polymers 204y obtained in Reference Example 1 were charged into a flask,
Attach a stirrer, a temperature meter, a dropping load, and a nitrogen gas inlet pipe, and add 14.5 y of diphenylmethane-4,4''-diisocyanate to the dropping load. Next, heat the four-bottle flask to about 80°C. The temperature was raised to melt the polyhydroxybutadiene polymer, and stirring was started while passing nitrogen gas.

Keeping the reaction temperature at 80'C, diphenylmethane-4.4
'-diisocyanate was gradually added dropwise, and the addition was completed after about 1 drop. After the dropwise addition was completed, the reaction temperature was raised to 130° C. and maintained at the same temperature for 1 hour to complete the reaction. The 0H value of the obtained urethane prepolymer was 10 and the average molecular weight was 11,000. Next, as a laxative for the urethane prepolymer 100y obtained by the above method,
Diphenylmethane masked with nonylphenol-4
, 4″ diisocyanate 4.9y and carbon black (trade name Vulcan XC-72) as a conductive filler.
After adding 31.5V and kneading until uniform with a hot roll at 50°C, apply the above mixture to one side of release-treated paper with a hot roll at 100'C to a thickness of 2 gourds, Then, it was passed through a cooling roll to obtain a thermosetting conductive sheet. The above tape is easy to handle as it has no stickiness at room temperature, and when attached to an iron plate heated to 80℃,
The sheet is sticky and sticks to the iron plate.

Even when the iron plate was allowed to cool to room temperature, the sheet did not fall off. Next, the above sheet was used as a No. 2 dumbbell test piece (JIS
The paper was peeled off, placed on a fluororesin sheet, and heated at 150° C. for 2 hours to cure. Table 1 shows various properties of the cured product. Further, in order to examine the heat resistance of the cured product, the volume resistivity, tensile strength, and elongation were measured after heat treatment at 120° C. for 20 days, and the results showed almost no change, indicating that the cured product had excellent heat resistance.

[Examples 2 to 7] A urethane prepolymer having hydroxyl groups at both ends of the molecule was obtained in the same manner as in Example 1 using a hydrogenated product of the polyhydroxybutadiene polymer obtained in Reference Examples 1 to 3 and a diisocyanate. Ta.

Furthermore, using the urethane prepolymer, masked polyisocyanate, and conductive filler, Example 1
A thermosetting conductive sheet was obtained in the same manner as above. Table 2 Part 1 shows the composition of the urethane prepolymer, and Table 2 Part 2 shows the composition of the thermosetting conductive sheet.

Further, Table 3 shows various properties of each thermosetting conductive sheet after curing at 150° C. for 2 hours. The conductive filler in Table 2 is Vulcan XC as a commercially available carbon black.
-72 (manufactured by CabOt), Kureha KCF-3000 (manufactured by Kureha Chemical) with a fiber length of 3 crn as carbon fiber
There are some using Yellow Composition of masked polyisocyanate a Toluene masked with nonylphenol - 2,4! -diisocyanate b Diphenylmethane-4,4-diisocyanate masked with nonylphenol C Triphenylmethane-4,4',4-triisocyanate masked with cargunol Comparative Example 1
~2 As a comparative example, EPT rubber (manufactured by Nippon Epil Rubber Co., Ltd.)
The conductive filler was kneaded using an open mill in the amount shown in Table 4 with respect to the basic formulation of product name: JSR P-33).

The kneaded material was pressed under the conditions of 155 mm x 3 g and 10 k9/d to obtain a sheet with a thickness of 2 mm. Samples of appropriate sizes were cut out from three locations on the obtained sheet, and the resistance was measured. The results are shown in Table 4. Comparative Examples 1 and 2 shown in Table 4
The volume resistivity of carbon fibers varies greatly, and sheets using carbon fibers have high resistance values because the carbon fibers break when kneaded in an open mill.

In comparison, Examples 2 and 5 exhibit excellent conductivity. Comparative Example 3 As a comparative example, commercially available epoxy resin (Araldite
034) with conductive filler (Vulcan XC-7, 72)
and conductive filler 3.
A sheet with a saliva content of % was obtained.

Cut out samples of appropriate size from three locations on the sheet,
Changes in resistance were measured when drying and wetting were performed under the following conditions, and the results shown in Table 5 were obtained.

[Conditions] Dry: 100'C x 5llr, wet: 30℃,
95%RH×1511r The conductive sheet of Comparative Example 3 is as follows:
Compared to the resistance change after wetting is very large, Examples 2 to 3
For the sheet No. 8, the wet conditions were more severe than those described above (80°C, 1
00% RH x 7 days later), but the resistance value was very stable.

Example 9 In order to examine the weather resistance of the cured thermosetting conductive sheet according to the present invention, the cured sheets obtained in Examples 3 and 5 were exposed to a Sunshine Weather-Ometer for 125 Ctf (equivalent to about 5 years). When the changes in volume resistivity, tensile strength, and elongation were measured, the amount of change was very small and there was almost no difference from the initial values shown in Table 3.

Example 10 Examples 2 to 2 produced in the same manner as Example 1
After leaving the thermosetting conductive sheet No. 8 in a constant temperature room at 25°C for about 3 months, we investigated its self-adhesion and hardening properties. As a result, it had good adhesion to an iron plate heated to 80°C, the same as during manufacturing. in,
Moreover, the volume resistivity, tensile strength, and elongation of the sheet cured at 1500 x 2 hours showed no change from the properties at the time of manufacture.

As described above, the thermosetting conductive sheet of the present invention is easy to handle during use, has excellent storage stability, and
The cured product of the sheet forms a conductive layer with stable conductive properties and excellent heat resistance, moisture resistance, weather resistance, and mechanical properties, so the industrial value of the present invention is extremely large.

Claims (1)

[Claims] 1. An average molecular weight of about 2.0 obtained from a hydrogenated polyhydroxybutadiene polymer and a diisocyanate compound.
Urethane prepolymer (A) having 00 to 20,00 hydroxyl groups at both ends of the molecule, and the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R is aliphatic charcoal having 8 to 15 carbon atoms. A sheet formed by applying a mixture containing polyisocyanate B masked by a phenolic compound (representing a hydrogen residue) and conductive filler C onto a base material with excellent releasability. thermosetting conductive sheet. 2. The thermosetting conductive sheet according to claim 1, wherein the polyisocyanate is used in an amount of 0.8 to 1.5 equivalents as an isocyanate group per 1 equivalent of a hydroxyl group in the urethane prepolymer. 3 Add 1 to 10% of conductive filler to urethane prepolymer
The thermosetting conductive sheet according to claim 1 or 2, characterized in that it contains 90% by weight. 4 As a hydrogenated product of polyhydroxybutadiene polymer, there are 60 butaene residues consisting of 1.4 bonds in the polymer chain.
The thermosetting conductive sheet according to any one of claims 1 to 3, characterized in that the hydrogenated polyhydroxybutadiene polymer is present in an amount of at least % by weight. 5 60% by weight or more of butadiene residues are present in the polymer chain as a hydrogenated product of polyhydroxybutadiene polymer,
Thermosetting conductive material according to any one of claims 1 to 3, characterized in that a hydrogenated product of a polyhydroxybutadiene group polymer containing 40% by weight or less of styrene residue is used. sheet. 6. The thermosetting conductive sheet according to any one of claims 1 to 5, characterized in that a nonylphenol compound is used as the phenol compound.