JPS59199778A - Electrically conductive coating material - Google Patents

Abstract

PURPOSE:An electrically conductive coating material, consisting of electrically conductive powder, and a binder resin consisting essentially of a methacrylic acid ester or an acrylic acid ester, etc. having improved retaining property of electric conductivity under high humidity, and useful for preventing electromagnetic waves, e.g. communication equipment or computers, etc. CONSTITUTION:An electrically conductive coating material obtained by incorporating (A) electrically conductive powder, e.g. nickel carbonyl powder containing >=70wt% particles having <=30mu particle diameter, with (B) a binder resin containing 70wt% or more (meth)acrylic acid ester in the monomeric component, and having >=10,000 weight-average molecular weight and <=20 acid value at preferably at (1:0.15)-(1:0.3) weight ratio, and (C) adding 10pts.wt. or less, based on 100pts.wt. coating material, additive, e.g. an amide based wax, for preventing the settling of the electrically conductive powder in the coating material and (D) a solvent, e.g. containing >=50% water-insoluble solvent, to the resultant mixture. EFFECT:The coating material can be easily dispersed with little settling of the electrically conductive particles, and the workability is good.

Description

[Detailed Description of the Invention] This invention relates to a conductive powder composite paint that forms a film, and furthermore, the conductive powder in the paint has little sedimentation, and even if the paint is left standing for a long period of time, the conductive powder remains intact during use. The present invention relates to a coating composition that is easy to redisperse and has significantly improved workability.

With the recent development of digital devices, interference with communications due to electromagnetic waves and malfunctions of converters, etc. are increasing significantly.As a countermeasure, it is necessary to make the surface of the casing conductive so that electromagnetic waves can be reflected and absorbed by the casing. It has started to be done. To achieve such conductivity, there are methods such as plating, sputtering, etc., in which a metal layer is directly formed on the surface of the casing, and methods, such as zinc spraying, in which molten metal is sprayed onto the casing surface to form a conductive layer. However, all of these methods have many drawbacks, such as poor adhesion between the conductive layer and the casing, and high costs. Therefore, in order to improve these drawbacks, a method has been proposed in which a conductive substance is mixed with a binder JjV and coated on the housing to form a conductive layer.

Examples of conductivity-imparting agents in the form of paints are known to be used to prevent electrostatic interference in the housings of electrical and electronic equipment. There is a need for a paint that provides a coating film that is more orange and highly conductive than that used to prevent static electricity damage, and for this purpose, paints that use metal powder to increase conductivity are considered suitable. . However, metal powders are susceptible to oxidative deterioration, and oxidized metal powders do not have enough conductivity to prevent electromagnetic interference. More and more coating and adhesive compositions have been discovered that have excellent electrical conductivity retention under conditions of high temperature and high humidity, which are susceptible to corrosion.

In addition, in paints in which such conductive powder is mixed with binder resin, the affinity between the binder resin and the conductive powder is poor, so the conductive powder settles and aggregates during standing.
It becomes extremely difficult to uniformly redistribute the paint when diluted and applied, resulting in decreased workability and productivity, and a decrease in conductivity due to non-uniform dispersion of the conductive powder during painting. There were also drawbacks such as a decrease in reliability due to variations in conductivity.

The inventors of the present invention have conducted intensive studies on a composition with good conductivity that eliminates the drawbacks of conductive paints as described above, and have found that it has excellent conductivity retention performance, especially under high humidity.
In addition, the present invention has achieved a coating material with good workability that allows for easy redispersion of conductive particles with little sedimentation.

That is, the present invention comprises a conductive powder (1), a binder resin (2), and a binder resin (2).
), an additive (3) and a solvent (4) to prevent the conductive powder from settling in the paint, and a binder resin.
5. The top of the 70-weight plate of the 70mer component constituting the resin (2) is (meth)acrylic acid ester, and the N weight average molecular weight of the resin is 10,000 or more and the acid value is 20 or less. The present invention relates to a conductive paint having moisture resistance and good workability. When the paint forms a conductive coating,
It has good workability during painting, high productivity, and reliability, and the formed coating film has high conductivity, and there is little decrease in conductivity over time, especially in high humidity. Demonstrate.

The conductive powder (x)id included in the present invention is gold, silver, iron, nickel, palladium, carbine, etc. obtained by mechanical pulverization method, suspension method, chemical reduction method, etc., and the shape is spherical or plate-like. , scale-like, needle-like, etc. are used. Among these, metal powders are preferred in order to obtain high conductivity, and gold, silver, nickel, and radium are suitable if you want to obtain good moisture resistance under particularly harsh conditions. Considering industrial economy, nickel and nickel alloys,
Particularly preferred is nickel composite powder. Further, these conductive powders may be used alone or in combination of one or more kinds of conductive powders. Furthermore, these conductive powders are industrially produced (5).Although single metal powders, alloy powders, or composite powders may be used, their surfaces are already oxidized during paint production and become conductive. If the surface is degraded, it is necessary to perform a cleaning or reduction treatment by some physical or chemical means before use or at the time of coating to substantially clean the surface and increase its conductivity. be. Such treatment can be carried out by a known method, such as treating the metal powder with a reducing compound, but it must be carried out in a manner that does not affect basic properties such as coldness and moisture resistance.

The binder resin (2), which is the second component of the present invention, has the form of a paint, maintains adhesion to the substrate when formed into a paint film, and prevents oxidative deterioration by nucleating metal powder. It is necessary to provide not only the property of preventing metal powder from settling, but also the property of maintaining conductivity. The resin obtained by copolymerizing the vinyl monomer contained on the heavy-duty plate is easily compatible with conductive powder and various coated objects, and has excellent performance such as moisture resistance and conductivity (6). It's convenient.

The resin component may be used alone or as a mixture of different resins. In addition, the higher the molecular S' of the resin component is, the better it is for maintaining moisture resistance, and the weight average molecular weight is 10.0.
00 or more is preferable. Next, if the acid value of the resin component is too high, it may react with the conductive powder and reduce its conductivity, or it may increase the affinity of the resin itself for water, making it easier to absorb moisture, which may have an unfavorable effect on moisture resistance. Therefore, the acid value of the binder resin is preferably 20 or less. The binder resin is obtained by ordinary solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization, and is used in the form of a solution.

Next, as the additive (3) to prevent the conductive powder from settling in the paint, known additives can be used.
In particular, in order to achieve the two objectives of maintaining moisture resistance and facilitating the redispersion of the conductive powder to improve workability and fully demonstrate its performance, it is necessary to It is necessary to use an additive consisting of a group and a functional group that has an affinity with the resin component. Examples of the functional group that has an affinity with the conductive powder include a hydroxyl group, a carboxylic acid group, an amino group, an amide bond, etc. organic functional groups, inorganic functional groups such as phosphoric acid groups, phosphorous acid groups, sulfonic acid groups, or salts thereof, and moieties that have affinity or compatibility with the binder resin component include alkyl groups. , functional groups consisting of aromatic derivatives are included, but there is no problem as long as the part has less polarity than the part that has affinity with the conductive powder, and within that range, if it is appropriately combined, it can be used even if it is in the same group as above. I can't help it. In particular, when used under severe conditions or when reliability is required over a long period of time, additives containing nitrogen in the fine parts are preferable. Examples of additives include amide waxes, amide polymers, amino group-containing oligomers, ethanolamine salts, etc. Of course, these may also be used in combination with one or more additives. The blending amount of the above additive is 10 parts or less per 100 parts by weight of the paint.

As the solvent (4), aromatic hydrocarbons, aliphatic hydrocarbons, ketones, esters, alcohols, etc. commonly used in paints can be used alone or in combination, but choose one with good workability. Of course.

In particular, when using metal powder, the moisture contained in the solvent or the moisture contained in the air may dissolve into the solvent and promote oxidation of the surface of the metal powder, so 50% by weight or more of the solvent may be used. It is preferable to use a water-insoluble solvent.

These conductive powders, binder resins, additives, and solvents are mixed and stirred to form a paint using known methods, but they are used to impart flexibility to the paint film without sacrificing conductivity or moisture resistance. It is okay to add plasticizers to improve the properties of the coating, leveling agents, anti-sag agents, antifoaming agents, etc. to improve the properties of the coating film.

The blending ratio of the above compound varies depending on the required conductivity and the condition of the object to be coated, but the weight ratio of the conductive powder to the binder is from 0.1 to 1:0.5, preferably 1:0.
:015 to 1:03 is suitable.

Examples are shown below. Naobu and Chi are both heavy busy sound IS
, Ding f1 Kei Chi.

(9) Example-1 A stirrer, a thermometer, and a condenser were attached to a 4-meter flask, and 45 parts of methyl methacrylate was added to a mixed solvent of 60 parts of toluene, 30 parts of inbutanol, and 10 parts of butyl acetate.
parts, n-butyl methacrylate 35 parts, styrene 19 parts, methacrylic acid 1 part, azobisisobutyronitrile 0
．． 5 parts of the mixed monomer solution was added dropwise at 85° C. for 5 hours. Thereafter, a solution of 50 parts of xylene and 20 parts of azobisin butyronitrile was added dropwise over 3 hours. After the dropwise addition was completed, the mixture was kept at 85° C. for an additional 5 hours and then cooled to obtain a transparent resin solution.

The solid content of the resin solution was 40 inches, the weight average molecular weight was 50,000, and the acid value was 3.6.

To 25 parts of this resin solution, 50 parts of Kerr's Nylnickel powder was added, and the mixture was ground in a ball mill for 24 hours, and then the amide additive Dis-Glon 6 was dispersed in 20 parts of toluene.
Add 4 parts of 900-20X (manufactured by Kusumoto Kasei Co., Ltd.), and
hrs kneading was continued. More than 90% of the particle size of the nickel powder in the paint after kneading was 30μ or less.

(10) Iwatakazo NK-
II It was diluted to a viscosity of 13 seconds and spray painted on an ABS resin board. The film thickness was determined from the weight of the coating film and was 30 μm. Dispersibility of conductive powder in paint, surface resistance value of paint film,
The electromagnetic shielding properties, the conductivity after the moisture resistance test, and the adhesion to the base material were as shown in Table 1.

Example-2 Monomer network formation during resin polymerization was performed using methyl methacrylate 9
Example-1 except that 0 parts and 10 parts of ethyl acrylate
Similarly, 60 parts of fine silver powder was added to 50 parts of the resin solution obtained.
1 part, 1 part of stearic acid ethanolamine salt, and 0.5 part of titanium coupling agent (Plenac) TTS (manufactured by Ajinomoto Co., Inc.) were added to form a paint and evaluated in the same manner as Example 1f11i.

Comparative Example-1 A paint was obtained and evaluated in the same manner as in Example-1 except that no additives were used.

(11) Comparative Example-2 A coating material was obtained and evaluated in the same manner as in Example-1 except that bentonite was used as an additive.

Comparative Example-3 Resin 1 (solid content 40%, weight average molecular weight 5000, acid value 4 A resin solution of .0 was obtained, and a coating material was obtained and evaluated in the same manner as in Example-1.

Comparative Example 4 A resin solution having a solid content of 42 cm, a weight average molecular weight of 60,000, and an acid value of 40 was obtained in the same manner as in Example 1, except that the methacrylic acid in the initial charge was replaced with 11 parts of acrylic acid. −
It was made into a paint and evaluated in the same manner as in 1.

Comparative Example-5 A coating material was obtained and evaluated in the same manner as in Example-1 except that a 40% xylene solution of polystyrene resin was used as the resin component.

(12) Evaluation method Sedimentation: Put the paint in a test tube and compare the degree of sedimentation of the conductive powder after letting it stand for 7 days.Difficult to settle.Redispersibility: After letting the paint stand for 14 days, compare the degree of sedimentation of the conductive powder. Compare the ease of dispersion when dispersing.Easy to disperse.Difficult to disperse.Surface resistance:
A 1-width coating film is formed on the ABS $ fat board (film thickness 30
μm) Measure the electrical resistance value at an electrode distance of 10c1n (digital multimeter manufactured by Takeda Riken) Adhesion:
Add 1 dark square of gopan to the coating film (film thickness: 30 μm) on the ABS resin board and compare the number of squares remaining after peeling off the cellophane tape with the number of squares before peeling. Moisture resistance test: At 50°C and 198% RH. 28 days.

56 days (14) - As is clear from the table, this is an example in which the combination of the present invention, the conductive powder, the binder resin, and the additive for improving the dispersibility of the conductive powder, is well balanced. 1.2 exhibits sufficient characteristics in all respects of dispersibility, conductivity, adhesion, moisture resistance, and reliability.

In Comparative Example 1, in which no additives were added, the uneven distribution of the conductive powder led to large variations in surface resistance, resulting in a lack of reliability.

Furthermore, the adhesion is also low for the same reason.

Comparison f in which bentonite, which has little compatibility, is added to the resin
- In 11-2, the dispersion stability is somewhat good, but the moisture resistance is extremely poor, and the nickel powder peels off from the coating surface, making it unsuitable for practical use.

Ratio:]-3 using a resin with a low molecular weight has low moisture resistance and unsatisfactory adhesion.

Comparative Example 4, which uses a resin with a high acid value, has high complaints, but is not practical due to its low moisture resistance.

In Comparative Example 5, which does not contain (meth)acrylic acid ester as a resin component, the metal particles settle and cannot be redispersed, and the reliability of the performance decreases, making it unsuitable for practical use.The adhesion to the soil also decreases. Metal particles peel off from the surface and are no longer able to retain their properties.

Claims (1)

[Claims] 1. A conductive powder (1), a binder resin (2), an additive for preventing the conductive powder from settling in the paint (
3) and a solvent (4), 70% by weight or more of the monomer component constituting the binder resin (2) is (meth)acrylic acid ester, and the weight average molecular weight of the resin is 10,000 or more, r 1. A conductive paint with good moisture resistance and workability, which is characterized by having an adhesive value of 20 or less. 2. The conductive powder according to claim 1, wherein the conductive powder (1) is nickel, a nickel alloy, or a nickel composite powder. 3. The conductive paint according to item 2 of the patent, characterized in that the conductive powder (1) is carbonyl nickel powder, and the particle size of 70% by weight or more of the particles is 30μ or less. . 4. A patent characterized in that the additive for preventing the conductive powder from settling in the TF family consists of a part that has an affinity for the conductive powder and a part that has an affinity for the binder resin component. The conductive paint according to claim 1. 6. The conductive paint according to claim 1, wherein 50% by weight or more of the solvent is a water-insoluble solvent.