JPS6333792B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive coating material for shielding electromagnetic waves that exhibits stable performance and whose initial conductivity value does not decrease even after long-term use. In daily life, we often experience that reception of television or radio is obstructed by radio noise. This is because almost all electrical equipment, including many electrical appliances used in homes, such as vacuum cleaners, hair dryers, and power tools, generate interference waves while in use. In particular, control of the radiation of radio waves (electromagnetic waves) generated from sensitive electronic devices using a large number of ICs and LSIs, such as computers, medical equipment, aviation instruments, etc., which are rapidly developing in recent years, and at the same time from various devices. Shielding radio interference has become a major problem. Moreover, there is a growing trend of switching from metal materials to plastics for various parts due to design, weight reduction, and economic efficiency, but plastics are transparent to radio waves.
For this reason, when plastics are used as housings for electronic devices, electromagnetic waves are shielded by imparting electrical conductivity to the surfaces of these plastics. This radio wave shielding effect largely depends on the frequency, so in order to expect a sufficient effect in sensitive electronic equipment that uses a large number of ICs and LSIs, it is necessary to
The volume resistivity of the material is required to be approximately 10 ^-3 Ω・cm. Specific methods for this include (A) the so-called metal spraying method, in which molten metal is made into fine particles using compressed air, etc., and sprayed onto the plastic surface to form a film;
(B) A method of applying conductive paint is mentioned. However, the metal spraying method is undesirable because it requires complicated operations and has poor adhesion to the plastic surface. Conductive paints that use silver powder as a conductive filler have a volume resistivity smaller than 10 ^-3 Ω・cm and have sufficient performance as conductive paints, but they are expensive and cannot be used in large quantities as industrial materials. It is inappropriate to do so. Furthermore, coating films made from conductive paints using commercially available nickel powder or copper powder as a conductive filler generally have a volume resistivity of about 10 ^-1 Ω・cm, and can be used as resistors, but cannot be used as conductors. is inappropriate. In particular, its effectiveness could not be expected to be sufficient as a conductive paint for shielding electromagnetic waves used in industrial machines (eg, computers, medical instruments, aviation instruments, etc.). Moreover, the electrical conductivity of the coated film increases with the passage of time, which is undesirable. This tendency is particularly strong at high temperatures and high humidity. As a result of intensive efforts by the present inventors to solve the above-mentioned drawbacks, the present inventors have succeeded in creating a conductive paint for shielding electromagnetic waves that exhibits long-lasting and excellent conductivity even when used at high temperatures for long periods of time. The present invention was completed based on this discovery. That is, the present invention provides a conductive paint for shielding electromagnetic waves using nickel powder as a conductive filler, in which 0.1 to 10 parts by weight of a primary alkanolamine having 4 or less carbon atoms and 15 parts by weight of a binder are added to 100 parts by weight of the above-mentioned conductive filler. This is a conductive paint for electromagnetic wave shielding characterized by adding ~33 parts by weight. The primary alkanolamine used in the present invention is a compound having an amino group and a hydroxyl group on different carbon atoms, such as monooxyamine, monoamino polyhydric alcohol, oxypolyhydric amine, etc., and has 4 or less carbon atoms. It is. In the present invention, particularly preferred primary alkanolamines include ethanolamine, propanolamine, butanolamine, N-(aminoethyl)-ethanolamine, and the like. The nickel powder used as the conductive filler has a particle size of 100 microns or less. If it is larger than 100 microns, the coating properties will be poor, the smoothness of the coating film will be poor, and the conductivity will be reduced. The shape of the conductive filler may be any of spherical powder, plate-shaped powder, resin-like powder, angular powder, needle-shaped powder, irregularly shaped powder, etc. In particular, nickel powder absorbs magnetic field components better and exhibits a high shielding effect from low to high frequencies. The mixing ratio of the conductive filler and primary alkanolamine in the present invention is suitably 0.1 to 10 parts by weight, particularly preferably 0.5 to 3 parts by weight, per 100 parts by weight of nickel powder.
When the amount of primary alkanolamine used is less than 0.1 part by weight, when the conductive paint is applied to the plastic surface, the volume resistivity of the paint film will be
It is undesirable because it cannot achieve a conductivity of 10 ^-3 Ω·cm and cannot provide a satisfactory effect as an electromagnetic shielding paint for plastic housings for industrial machinery such as computers, medical instruments, and aviation instruments. If the amount exceeds 10 parts by weight, the adhesion of the conductive paint to the plastic surface and the physical properties of the paint film will deteriorate, and the vehicle used in the paint will deteriorate, which is undesirable. The conductive paint of the present invention may be manufactured by any known manufacturing method, including ABS, styrene, Noryl, FRP,
According to the present invention, a binder with good adhesion to the plastic housing used is selected from various binders such as polyethylene, polypropylene, etc., depending on the material used and the purpose, such as acrylic resin, urethane resin, polyolefin resin, vinyl chloride resin, rubber, etc. Blend the conductive filler and primary alkanolamine used in . The appropriate amount of binder used in this case is 15 to 33 parts by weight per 100 parts by weight of the conductive filler; if it is less than 15 parts by weight, the viscosity of the conductive paint for electromagnetic shielding will be insufficient. This is undesirable because it increases the coating and reduces workability, and also makes the film surface very brittle after coating and drying, resulting in a decrease in adhesion. Further, if the amount is more than 33 parts by weight, the conductivity decreases, which is not preferable. The solvent used in this case is one that has excellent compatibility with the binder and primary alkanolamine, such as alcohols,
One or more types may be selected and used from ketones and esters. As the apparatus used during production, a three-roll mill, a laika machine, a ball mill, etc. may be used. The electromagnetic wave shielding electroconductive paint of the present invention may be applied by a conventional method such as brush coating, dip spraying, or roller coating. The coating film obtained in this manner using the conductive paint for shielding electromagnetic waves of the present invention has a thickness of 10 to 50 microns and a volume resistivity value of
10 ^-3 Ω・cm, this value does not change even under the harsh conditions of 80℃ and 1000 hours, and it has sufficient electromagnetic shielding effect even when applied to the plastic housing of industrial machinery such as computers, medical instruments, and aviation instruments. It is intended to serve the purpose. The conductive paint for shielding electromagnetic waves of the present invention has a volume resistivity smaller than 10 ^-3 Ω・cm, so it can be used on the electrodes and conductors of various electronic equipment parts in place of conventional conductive paints that use silver powder as the main conductive material. There is no problem in using it as a conductive paint. Next, examples and reference examples will be shown. Note that all parts by weight are parts. Example 1 Nickel powder with a particle size of 5 microns or less 100 parts Thermoplastic acrylic resin 25 parts Ethanolamine 1 part Isopropyl alcohol 10 parts Methyl isobutyl ketone 50 parts Each of the above ingredients was kneaded uniformly on a triple roll,
A conductive paint for shielding electromagnetic waves of the present invention is obtained. The conductive paint was placed on a cleaned glass plate with a width of 15 mm.
The length was 60 mm, and the coated film was coated to a thickness of 50 microns after drying, and dried by heating at 80°C for 30 minutes. After this, a heat resistance test (80
℃ for 1000 hours) and the change in volume resistivity was measured, and the results are shown in Table 1. Furthermore, regarding the adhesion of the coating film, after spray painting on test pieces using ABS resin and Noryl resin to a film thickness of 30 microns after drying at room temperature for 3 hours, the adhesion ( The results are shown in Table 2. (A) Heat cycle test A: 85℃, 1 hour → B: 23℃, 50% humidity for 1 hour →
C) 1 hour at 29℃→D 1 hour at 23℃ and 50% humidity Example 2 The ethanolamine used in Example 1 was
Example 1 is the same except that ethanolamine (aminoethyl)-ethanolamine is used. Reference Example 1 Everything is the same as in Example 1 except for ethanolamine. Reference example 2 The amount of ethanolamine used in Example 1
It is the same as Example 1 except that the amount is 0.05 part. Reference example 3 The amount of ethanolamine used in Example 1
The procedure is the same as in Example 1 except that the volume is 15 parts.

【table】

[Table] As explained above, the volume resistivity of the coated film using the conductive paint of the present invention is 10 ^-3 Ω・ even after the heat resistance test at 80°C for 1000 hours.
cm is shown. Furthermore, as for the state of application, excellent adhesion is shown as understood from the results of the side-by-side test.

Claims (1)

[Claims] 1 In a conductive paint for electromagnetic wave shielding that uses nickel powder as a conductive filler, the conductive filler described above
0.1 to 10 parts by weight of primary alkanolamine having 4 or less carbon atoms and 15 parts by weight of binder per 100 parts by weight
A conductive paint for electromagnetic wave shielding characterized by adding ~33 parts by weight.