JPS60177080A - Electrically conductive paint - Google Patents

Abstract

PURPOSE:To obtain the titled paint for the coating of plastic case, etc., and effective to prevent the electromagnetic radiation noise, by mixing powder of Ni, etc. to a resin obtained by blending a specific chlorinated polyolefin resin with an acrylic resin prepared by polymerizing an acrylic acid ester monomer. CONSTITUTION:The objective paint can be produced by compounding (A) a resin obtained by blending (i) a chlorinated polyolefin resin having a chlorine content of 25-50wt% and an average molecular weight of 5,000-70,000 with (ii) one or more acrylic resins or oil-modified acrylic resins prepared by polymerizing an acrylic monomer in the presence of an acrylic monomer wherein the carbon number of the ester group is >=8, with (B) powder of metals such as nickel, copper, chromium, aluminum, etc. or powder of carbon black, or zinc oxide. The amount of the component B is for example, 5-20pts.wt. per 100pts.wt. of the solid content of the produced paint.

Description

[Detailed description of the invention] This invention relates to conductive paint.

The purpose is that if it is used as a paint for the plastic casing that houses electronic devices such as digital devices, the electromagnetic noise emitted from the digital device will be shielded by the casing.
An object of the present invention is to provide a conductive paint for a plastic casing that can provide electromagnetic shielding without acting as interference radio waves to V, radios, communication devices, etc.

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, but conventional conductive paints are made by combining the synthetic resin and paint vehicle that make up the plastic casing. There are no conductive paints that can be used on any kind of plastic casing because they have poor compatibility with synthetic resins (because the uniformity of the coating film is a problem and the environment in which digital devices are used is deteriorating). The disadvantage is that the coating film is damaged during use and is prone to peeling.

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. However, when used for a long period of 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, making storage difficult. mutual separation, cloudiness, gelation,
Even if you try to improve this compatibility by evenly mixing the two by mechanical force before painting, the gloss, appearance, surface roughness, adhesion to the object, and weather resistance of the paint film will be affected. There was a flaw in my sexuality.

This invention aims to solve the above-mentioned drawbacks of conventional conductive paints by providing a coating material that has good long-term stability and workability, as well as strong adhesion to various plastics and excellent weather resistance and gloss. This was achieved by developing a conductive paint with excellent electromagnetic shielding properties.

That is, this invention is a method of polymerizing a chlorinated polyolefin resin having a chlorine content of 25 to 50% by weight and an average molecular weight of 5.000 to 70,000, and an acrylic acid ester monomer having an ester group having 8 or more carbon atoms. A conductive paint made by mixing metal powder such as nickel, copper, chromium, aluminum, carbon blank, or zinc oxide powder with a resin made by mixing at least one type of acrylic resin or oil-modified acrylic resin. This is related to.

In this invention, examples of 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 (the ester group has 8 carbon atoms), and nonyl acrylate. (Ester group has 9 carbon atoms), decyl acrylate (ester group has 10 carbon atoms), 5-ethyl-1-nonyl acrylate (ester group has 11 carbon atoms), lauryl acrylate (ester group has 12 carbon atoms), I- Lysosyl acrylate (ester group has 13 carbon atoms), tetradecyl acrylate (ester group has 14 carbon atoms), hexadecyl acrylate (ester group has 16 carbon atoms),
Stearyl acrylate (ester group has 18 carbon atoms)
etc. can be used.

In the present invention, examples of acrylic acid ester monomers having an ester group having 8 or more carbon atoms include octyl methacrylate (ester group having 8 carbon atoms), capryl methacrylate (ester group having 8 carbon atoms), and belargolyl methacrylate (ester group having 8 carbon atoms). (9 carbon atoms in the group), cabrinyl methacrylate (10 carbon atoms in the ester group), lauryl methacrylate (12 carbon atoms in the ester group), etc. can be used.

When the above-mentioned chlorinated polyolefin resin and acrylic resin or oil-modified acrylic resin are mixed, it is preferable to mix the former at a ratio of 10 parts by weight to 5 to 80 parts by weight of the latter. The higher the blending ratio of acrylic resin or oil-modified acrylic resin, the better the gloss and weather resistance of the coating film, but on the other hand, the adhesion to plastic gradually decreases, but the blending ratio of chlorinated polyolefin resin increases. If the amount increases, the opposite result will occur, so the mixing ratio of both should be appropriately selected depending on the purpose of use.

When producing an acrylic resin by polymerizing an acrylic acid ester monomer having 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. The acrylic resin may be produced by solution polymerization at 60 to 130° C. in a solution such as the above.

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 the present invention, a chlorinated polyolefin resin with a chlorine content of 25 to 50% by weight is used. However, once it becomes a solution, it has poor stability.
There are problems with long-term stability, such as dechlorination at high temperatures and thickening at low temperatures.On the other hand, in the case of highly chlorinated polyolefin resins with a chlorine content of more than 50% by weight, injection The so-called stringing phenomenon, in which strings are drawn from the nozzle, is likely to occur, which poses problems in terms of painting workability.Furthermore, when used for a long period of time, the coating film tends to change over time, causing problems in terms of weather resistance. On the other hand, when the chlorine content is 25 to 50
This is because when a chlorinated polyolefin resin of % by weight is used, all problems other than the above-mentioned weather resistance can be solved.

Or, the average molecular weight of the above chlorinated polyolefin resin is 5.
,000 to 70,000 is because 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, or the paint film will not harden even after hardening. However, there is a problem in that it causes blocking etc., making it impossible to obtain a coating film that can be used practically in terms of gloss and other physical properties of the coating film.On the other hand, the average molecular weight of 70
In the case of chlorinated polyolefin resins with a high molecular weight exceeding 0.000%, the problem is that they have poor coating workability, and also have extremely poor compatibility with other resins, making it difficult to modify them by mixing with other resins. However, the average molecular weight is 5,
This is because when a chlorinated polyolefin resin having a molecular weight of 000 to 70,000 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. There were problems in terms of the gloss and weather resistance of the film, for example, discoloration occurred after about 100 hours in a weatherometer test, and there were also problems in compatibility with other resins.

Therefore, as a result of various studies on resins to be mixed with chlorinated polyolefin resins having the above-mentioned specific chlorine content and average molecular weight, we found that polymerization was achieved by incorporating an acrylic acid ester monomer with an ester group having 8 or more carbon atoms. The acrylic 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.

The particle size of the metal powder such as nickel, copper, chromium, aluminum, etc. or carbon blank zinc oxide powder used as the conductive member in this invention is 5 to 50 microns, preferably about 15 to 30 microns, and an average of 15 microns. The amount to be blended 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 film 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 a mixture of chlorinated polyolefin resin having a specific chlorine content and average molecular weight, and a specific acrylic resin, so it is generally used as a paint. In terms of physical properties, it not only has good long-term stability and coating workability, but also forms a coating that adheres strongly to plastics and has excellent coating properties such as weather resistance and gloss. Therefore, the synthetic resin that makes up the plastic casing has good compatibility with the paint vehicle, and can be used on any plastic casing.It also provides a uniform coating and prevents deterioration of the environment in which digital equipment is used. Regardless, 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 will be shown below to make the effects of the present invention clearer.

(Left below) Example 1 (Manufacture 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 weight of benzoyl peroxide. A catalyst solution prepared by dissolving 0.1 parts by weight of dodecyl mercaptan in 50 parts by weight of toluene, and the remaining half of the above formulation were added dropwise over a period of 3 hours to react, and after the completion of the dropwise addition, the reaction was continued for an additional 5 hours. An acrylic resin was obtained.

(Manufacture of paints for plastics) Chlorinated polyethylene resin 50 parts by weight Chlorine content 25% by weight Average molecular weight 5,000, manufactured by Osaka Soda Akiku Co., Ltd. Product name Emullux A Above acrylic resin 50 parts by weight Titanium White 30 Toluene 5 Carbon black 30 The above formulations were uniformly mixed and dispersed to obtain a conductive paint.

Example 2 (Manufacture of acrylic resin) An acrylic resin was obtained in accordance with 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 20,000, manufactured by Osaka Soda ■ Product name Emullux A Above acrylic resin 50 parts by weight Titanium White 30 Toluene 5 Silver powder 1O The above mixture was 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 1O Butyl acrylate 20 Toluene 100 Half of the above mixture was heated to 90°C, and dicumyl was added to it. Baroxa 411 parts by weight and octyl mercaptan 0
．． A catalyst obtained by dissolving 1 part by weight in 50 parts by weight of toluene and the remaining half of the above formulation were reacted while being dropped over a period of 3 hours, and after the dropwise addition was completed, the reaction was continued for an additional 4 hours to form an acrylic resin. Obtained.

(Manufacture of paints for plastics) Chlorinated polypropylene resin 50 parts by weight Chlorine content 35% by weight Average molecular weight 50,000, manufactured by Toyo Kasei A Kiku, product name Birdren 15L Above acrylic resin 50 Titanium White 25 Luen 5 Gold powder 5 The above formulations were 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 meth-relay 1 was used instead of lauryl acrylate 1 in Example 3.

(Manufacture of paints for plastics) Chlorinated polypropylene resin 50 parts by weight Chlorine content 50% by weight Average molecular weight 70,000, manufactured by Toyo Kasei ■ Product name Bardren Acrylic resin above 50 ~ Titanium White 25 True 5 Nickel powder 10 The above formulations were uniformly mixed and dispersed to obtain a conductive paint.

Example 5 Example 2 except that a linseed oil-modified acrylic resin [manufactured by Harima Kasei@] 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 manufactured according to the method.

Comparative Example 1 In the resin composition of Example 2, no acrylic resin was used, 60 parts by weight of chlorinated polyethylene resin, and titanium white 3.
A conductive paint was produced by uniformly mixing and dispersing 0 parts by weight, 10 parts by weight of toluene, and 10 parts by weight of silver powder.

Comparative Example 2 In the resin composition of Example 2, chlorinated resin was not used, and 60 parts by weight of acrylic resin, 30 parts by weight of titanium white, 10 parts by weight of toluene, and 10 parts by weight of silver powder were uniformly mixed and dispersed. produced a synthetic 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 4.500 was used, and a paint was produced in accordance with Example 2 with the other exceptions. Curing was not carried out smoothly, and a conductive coating material 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.
It does not mix smoothly with acrylic resins, and also causes stringiness during spray painting, making it impossible to apply smoothly.
A conductive paint that could be put to practical use could not be obtained.

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 compatible with the chlorinated polyethylene resin. It did not dissolve and could not be put to practical use.

Test Examples 1 to 5 Molded objects were made from polypropylene resin at 60 cm, 30 cm,
.

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 E, P, and L companies) by the usual method, and organic phosphorus electromagnetic shielding paint with a thickness of 0.04 m was applied. was painted.

This electromagnetic shielding paint uses a paint in which nickel powder is dispersed and acrylic synthetic resin is used as the vehicle. '' Damage test These casings were tested at 60 degrees Celsius and 40% humidity, and
Each was placed in an apparatus with 4 revolutions (rotation) per minute for - days to damage the surface.

This damage test corresponds to the use between two parts.

These cases can be used as commercially available 32-bit suit minicomputers.
The electric field strength of the radiated interference radio waves (30 m, 40 MHz) was measured before and after the above damage test.

The results are shown in the table below.

(Margin below)

Claims (1)

[Claims] (11 chlorine content 25 to 50% by weight, average molecular weight 5,
000 to 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. A conductive paint made by mixing resin with metal powder such as nickel, copper, chromium, aluminum, or carbon black or zinc oxide powder.