JPH0149389B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to conductive paint. Its purpose is to use it as a coating agent for plastic casings containing electronic devices such as digital devices, so that electromagnetic noise emitted from the digital devices will be shielded by the casing, causing interference with TVs, radios, communication devices, etc. An object of the present invention is to provide a conductive paint for a plastic casing that can provide electromagnetic shielding without causing interference. In recent years, with the spread of digital devices (computers, minicomputers, microcomputers, etc.), the electromagnetic noise oscillated by the clock frequency oscillators built into these digital devices has become a source of interference to ordinary household electrical devices. There are many problems. In order to prevent this electromagnetic noise, electromagnetic shielding electromagnetic shielding paints have already been used to shield the surface of plastic casings. There are no conductive paints that can be used on any type of plastic casing because they have poor compatibility with synthetic resins, and there are problems with the uniformity of the paint film and the environment in which digital devices are used is worsening. The drawback was that the coating film was easily damaged and peeled off easily. In general, chlorinated polyolefin resins have good adhesion to polyolefin plastics such as polyethylene and polypropylene, and to other plastics, but on the other hand, they have problems in terms of long-term stability, painting workability, etc. When used for a long time, the paint film tends to yellow or change in quality due to the release of chlorine over time, and the weather resistance of the paint film is poor. In order to overcome these drawbacks, attempts have been made to improve weather resistance by mixing general-purpose acrylic resins, but this chlorinated polyolefin resin and general-purpose acrylic resins have poor compatibility; Phenomena such as mutual separation, cloudiness, and gelation may occur during storage.
Even if the two were uniformly mixed by mechanical force immediately before painting in an attempt to improve this compatibility, there were drawbacks in the gloss, appearance, adhesion to objects, and weather resistance of the paint film. This invention aims to solve the above-mentioned drawbacks of conventional conductive paints, and provides a coating material that has good long-term stability and coating workability, as well as strong adhesion to various plastics, excellent weather resistance and gloss. This was achieved by developing a conductive paint with excellent electromagnetic shielding properties. That is, this invention has a chlorine content of 25 to 50% by weight,
A chlorinated polyolefin resin with an average molecular weight of 5,000 to 70,000 is mixed with at least one type of acrylic resin or oil-modified acrylic resin polymerized by containing an acrylic acid ester monomer in which the ester group has 8 or more carbon atoms. The invention relates to a conductive paint made by mixing resin with metal powder such as nickel, copper, chromium, aluminum, or powder of carbon black or zinc oxide. In this invention, the acrylic acid ester monomers in which the ester group has 8 or more carbon atoms include octyl acrylate (the ester group has 8 carbon atoms);
2-ethylhexyl acrylate (8 carbon atoms in the ester group), nonyl acrylate (9 carbon atoms in the ester group), decyl acrylate (10 carbon atoms in the ester group), 5-ethyl-1-nonyl acrylate (11 carbon atoms in the ester group) ), lauryl acrylate (ester group has 12 carbon atoms), tridecyl acrylate (ester group has 13 carbon atoms), tetradecyl acrylate (ester group has 14 carbon atoms), hexadecyl acrylate (ester group has 16 carbon atoms),
Carbon number of stearyl acrylate ester group: 18)
etc. can be used. In this invention, the acrylic acid ester monomers in which the ester group has 8 or more carbon atoms include octyl methacrylate (the ester group has 8 carbon atoms);
Capryl methacrylate (8 carbon atoms in the ester group), belargolyl methacrylate (9 carbon atoms in the ester group), caprinyl methacrylate (10 carbon atoms in the ester group), lauryl methacrylate (12 carbon atoms in the ester group), etc. can be used. . In addition, when mixing the above chlorinated polyolefin resin with an acrylic resin or an oil-modified acrylic resin, 5 to 5 parts by weight of the latter is added to 10 parts by weight of the former.
It is preferable to mix in a proportion of 80 parts by weight, especially,
As the blending ratio of acrylic resin or oil-modified acrylic resin increases, the gloss and weather resistance of the coating film improve, but on the other hand, the adhesion to plastic gradually decreases, but as the blending ratio of chlorinated polyolefin resin increases If the amount increases, the result will be opposite to the above, so it is better to select the mixing ratio of both appropriately depending on the purpose of use. In addition, when producing an acrylic resin by polymerizing an acrylic acid ester monomer with an ester group having 8 or more carbon atoms, for example, butyl acrylate, which is commonly used as an acrylic resin-like raw material, Methyl methacrylate, butyl methacrylate, etc. are used together with an acrylic acid ester monomer having 8 or more carbon atoms in the ester group, and toluene is added in the presence of a peroxide catalyst such as benzoyl peroxide, dicumyl peroxide, dibutyl peroxide, etc. 60 to 60 in a solution such as
Acrylic resin can be produced by solution polymerization at 130°C. In addition, the acrylic resin or oil-modified acrylic resin produced as described above is mixed with a chlorinated polyolefin resin when cold or heated to form a vehicle, and in addition to the conductive material, titanium white is added as necessary. , a pigment such as carbon black, and a solvent such as toluene to produce a conductive paint. In addition, in the present invention, the reason why a chlorine content of 25 to 50% by weight is used as the chlorinated polyolefin resin is that in the case of a low chlorinated polyolefin resin with a chlorine content of less than 25% by weight, the solvent There are problems in terms of long-term stability, such as being difficult to dissolve in water, difficult to form a complete solution, and poor stability even once it becomes a solution, causing dechlorination at high temperatures and thickening at low temperatures. In the case of highly chlorinated polyolefin resin with a content of more than 50% by weight, a so-called stringing phenomenon in which strings are drawn from the injection nozzle is likely to occur during painting, which poses problems in terms of painting workability.
When used for a long period of time, the coating film tends to change over time and there are problems with weather resistance, but when using a chlorinated polyolefin resin with a chlorine content of 25 to 50% by weight, This is because all problems other than the above-mentioned weather resistance can be solved. Furthermore, the reason why the average molecular weight of the above chlorinated polyolefin resin was limited to 5,000 to 70,000 was as follows.
In the case of low-molecular-weight chlorinated polyolefin resins with an average molecular weight of less than 5,000, the paint will not harden smoothly, and even after hardening, the paint film will cause blocking, resulting in poor gloss and other physical properties of the paint film. On the other hand, in the case of high molecular weight chlorinated polyolefin resins with an average molecular weight of over 70,000, the coating process is poor, and other resins are difficult to coat. There is a problem that the compatibility with the resin is extremely poor and it is difficult to modify it by mixing with other resins.
This is because when a 70,000 chlorinated polyolefin resin is used, all problems other than the gloss of the coating film and poor compatibility with other resins can be solved. As mentioned above, by using a chlorinated polyolefin resin with a specific chlorine content and average molecular weight, it is possible to improve the long-term stability and painting workability of the paint, but There were problems with the gloss and weather resistance of the coating film, for example, discoloration occurred after about 100 hours in a weatherometer test, and there were also problems with compatibility with other resins. Therefore, as a result of various studies on resins to be mixed with chlorinated polyolefin resins having the above-described specific chlorine content and average molecular weight, we found that acrylic resins that are polymerized by containing an acrylic acid ester monomer with an ester group having 8 or more carbon atoms. The resin or oil-modified acrylic resin is smoothly compatible with the chlorinated polyolefin resin having the above-described specific chlorine content and average molecular weight, and can significantly improve gloss and weather resistance. Further, metal powders such as nickel, copper, chromium, aluminum, etc. or carbon black zinc oxide powders used as conductive members in this invention include:
The particle size is about 5 to 50 microns, preferably about 15 to 30 microns, with an average of about 15 microns, and the blending amount is preferably 5 to 20 parts by weight per 100 parts by weight of the solid content of the paint. The reason for this is that if the amount is 20 parts by weight or more, the coating properties will deteriorate, and if the amount is less than 5 parts by weight, the electromagnetic shielding effect will not be sufficient. It exists because it doesn't exist. As mentioned above, the conductive paint of the present invention is made by mixing a specific acrylic resin with a chlorinated polyolefin resin having a specific chlorine content and average molecular weight. It also has the effect of improving the long-term stability and workability of the paint, as well as forming a film that adheres strongly to plastics and has excellent physical properties such as weather resistance and gloss. Therefore, the synthetic resin that makes up the plastic housing has good compatibility with the paint vehicle, so it can be used on any plastic housing and provides a uniform coating despite the deterioration of the environment in which digital equipment is used. The coating film is less likely to be damaged or peeled off during use, and the electromagnetic shielding effect can be obtained over a long period of time. Examples, comparative examples, and test examples are shown below.
The effects of this invention will be made clearer. Example 1 (Production of acrylic resin) Octyl acrylate 20 parts by weight Methyl methacrylate 50 〃 Butyl acrylate 30 〃 Toluene 100 〃 Half of the above mixture was heated to 80°C, and to this was added 1 part by weight of benzoyl peroxide and dodecyl mercaptan. A catalyst solution prepared by dissolving 0.1 part by weight in 50 parts by weight of toluene and the remaining half of the above formulation were added dropwise for 3 hours or more to react, and after the addition was completed, the reaction was continued for another 5 hours to form an acrylic resin. Obtained. (Manufacture of paints for plastics) Chlorinated polyethylene resin 50 parts by weight Chlorine content 25% by weight Average molecular weight 5000, manufactured by Osaka Soda Co., Ltd. Product name Emullux A Above acrylic resin 50% by weight Titanium White 30 Torr En 5 Carbon Black 30 The above formulation was uniformly mixed and dispersed to obtain a conductive paint. Example 2 (Manufacture of acrylic resin) An acrylic resin was obtained in the same manner as in Example 1 except that tridecyl acrylate was used instead of octyl acrylate. (Manufacture of paints for plastics) Chlorinated polyethylene resin 50 parts by weight Chlorine content 40% by weight Average molecular weight 20000, manufactured by Osaka Soda Co., Ltd. Product name Emullux A Above acrylic resin 50 parts by weight Titanium White 30 Torr En 5 Silver powder 10 The above formulations were uniformly mixed and dispersed to obtain a conductive paint. Example 3 (Production of acrylic resin) Lauryl acrylate 30 parts by weight Methyl methacrylate 40 〃 Butyl methacrylate 10 〃 Butyl acrylate 20 〃 Toluene 100 〃 Half of the above mixture was heated to 90°C, and dicumyl was added to it. A catalyst solution prepared by dissolving 1 part by weight of peroxide and 0.1 part by weight of octyl mercaptan in 50 parts by weight of toluene, and the remaining half of the above formulation were added dropwise for 3 hours to react. An acrylic resin was obtained by reacting for a period of time. (Manufacture of paints for plastics) Chlorinated polypropylene resin 50 parts by weight Chlorine content 35% by weight Average molecular weight 50000, manufactured by Toyo Kasei Co., Ltd., product name Hardren 15L Above acrylic resin 50 〃 Titanium White 25 〃 True Gold powder 5 The above formulation was uniformly mixed and dispersed to obtain a conductive paint. Example 4 (Manufacture of acrylic resin) An acrylic resin was obtained in accordance with Example 3 except that lauryl metharylate was used instead of lauryl acrylate. (Manufacture of paints for plastics) Chlorinated polypropylene resin 50 parts by weight Chlorine content 50% by weight Average molecular weight 70000, manufactured by Toyo Kasei Co., Ltd. Product name Hardren Acrylic resin above 50 Titanium White 25 True 5 Nickel powder 10 The above formulation was uniformly mixed and dispersed to obtain a conductive paint. Example 5 The same procedure was carried out as in Example 2 except that a linseed oil-modified acrylic resin (manufactured by Harima Kasei Co., Ltd.) was used as the acrylic resin, and 15 parts by weight of copper powder was used instead of 10 parts by weight of silver powder. A conductive paint was produced according to Example 2. Comparative Example 1 In the resin composition of Example 2, no acrylic resin was used, and 60 parts by weight of chlorinated polyethylene resin, 30 parts by weight of titanium white, and 10 parts by weight of toluene,
A conductive paint was manufactured by uniformly mixing and dispersing 10 parts by weight of silver powder. Comparative Example 2 In the resin composition of Example 2, no chlorinated resin was used, 60 parts by weight of acrylic resin, and 30 parts by weight of titanium white.
Parts by weight, 10 parts by weight of toluene, and 10 parts by weight of silver powder were uniformly mixed and dispersed to produce a conductive paint. Comparative Example 3 In Example 2, a chlorinated polyethylene resin with a chlorine content of 23% by weight and an average molecular weight of 4500 was used, and a paint was manufactured in accordance with Example 2 with the other exceptions, but it gelled easily and hardened. The process was not carried out smoothly, and a conductive paint that could be put to practical use could not be obtained. Comparative Example 4 In Example 2, a chlorinated polyethylene resin with a chlorine content of 55% by weight and an average molecular weight of 75,000 was used, and a paint was produced in accordance with Example 2, with the other exceptions, and it mixed smoothly with the acrylic resin. Not compatible,
Furthermore, a stringy phenomenon occurred during spray coating, making it impossible to apply the coating smoothly, making it impossible to obtain a conductive coating material that could be used for practical purposes. Comparative Example 5 In Example 2, when a general-purpose acrylic resin made by polymerizing methyl acrylate and methyl methacrylate in which the number of carbon atoms in the ester group is less than 8 was used as the acrylic resin, it was found that it smoothly bonded with the chlorinated polyethylene resin. They were not compatible and could not be put to practical use. Test Examples 1 to 5 Molded objects were made from polypropylene resin by 60 cm, 30 cm,
The molded body was constructed as an open body with a length of 15 cm and a thickness of 2 mm, and the conductive paints obtained in Examples 1 to 5 were applied to the surface of this molded body to a thickness of 25 μm. Comparative Example 6 Opening bodies of 45 cm, 45 cm, and 13 cm with a thickness of 4 mm were molded from Noryl (trade name manufactured by EPL) using the usual method.
An organic phosphorus-based electromagnetic shielding paint with a thickness of 0.04 mm was applied. This electromagnetic shielding paint disperses nickel powder,
A paint with an acrylic synthetic resin vehicle was used. Damage Test Each of these casings was left for one day in an atmosphere of 60 degrees Celsius and 40% humidity in a device that rotates 4 times per minute (rotation) in order to damage the surface. This damage test corresponds to two years of use. These casings were used as casings for commercially available 32-bit super minicomputers, and the field strength of the radiated interference radio waves (30 m, 40 MHz) of this equipment was measured before and after the damage test described above. The results are shown in the table below.

[Table] As can be seen from the above results, it can be seen that the conductive paint according to the present invention is excellent.

Claims (1)

[Claims] 1 Chlorine content 25 to 50% by weight, average molecular weight 5000
- 70,000 chlorinated polyolefin resin and at least one type of acrylic resin or oil-modified acrylic resin polymerized by containing an acrylic acid ester monomer whose ester group has 8 or more carbon atoms. , nickel, copper, chrome,
A conductive paint made by mixing metal powder such as aluminum, carbon black, and zinc oxide powder.