JPH02290280A - Method for curing conductive coating material - Google Patents

Abstract

PURPOSE:To obtain a film excellent in properties by curing a coated material by the irradiation with electron beam when the temp. thereof is specific or higher. CONSTITUTION:300 pts.wt. or more of a conductive filler (e.g. silver powder) is compounded with 100 pts.wt. of an electron beam curable resin such as unsaturated polyesters or polyester (meth)acrylates. This composition is preheated to temp. higher than 50 deg.C and irradiated with far UV ray or electron beam to be cured. By this method, excellent conductivity is obtained and workability can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of curing a coating film formed from a conductive composition using an electron beam. In particular, the present invention provides a curing method for providing a cured coating film with excellent conductivity and high reliability.

[Prior Art] Conductive paints in which conductive metal fillers are dispersed in synthetic resins are widely used as compositions that provide coating films with high conductivity. Conventionally, such conductive paints have been applied to housing materials of electrical equipment for the purpose of shielding electromagnetic waves. Particularly in recent years, the method of forming conductive circuits on printed circuit boards has changed from the conventional method of partially etching the copper layer of a copper composite board consisting of copper and an insulating board to directly applying conductive paint to the board. A method of forming and curing a circuit by printing using a method such as screen printing is being considered. Compared to the conventional method, this method can omit the steps of applying etching resist, etching, and removing etching resist, and can also solve the problem of processing waste etching liquid. Expectations are high. In addition, recently, as computer malfunctions caused by interfering electromagnetic waves have become a social problem, countermeasures against noise have become a focus of attention. As a countermeasure to this problem, a method of coating a printed wiring board with a conductive paint and using the formed conductive layer to cut off the noise from the source is considered to be a promising method, and some of the methods have begun to be put into practical use.

[Problems to be Solved by the Invention] On the other hand, materials used for such electronic components are generally required to have a high degree of heat resistance from the viewpoint of reliability. Improvement is possible and expectations are high. Various types of thermosetting conductive paints with excellent heat resistance have been developed for the above purpose. However, since the base material to which the paint is applied is also a synthetic resin, heating the thermosetting conductive paint for a long time to cure it causes deterioration of the base material itself and deformation such as warping. Become,
Long-term reliability cannot be achieved. In this respect, a curing method using electron beam irradiation, which allows curing at room temperature, is extremely advantageous.

However, it is difficult to obtain a coating film with excellent conductivity by curing only by electron beam irradiation. In order to overcome such drawbacks that occur in the case of electron beam curing, JP-A-56-905!10 proposes a method of heating after electron beam irradiation. Although the conductivity improved by this method is remarkable, the heating after irradiation is at a temperature of 100 to 150°C, and the heating time may range from 5 minutes to 60 minutes.
Deformation and deterioration of the substrate that occurs during heating cannot be avoided, and workability is also poor. JP-A-62-200703 discloses a technique for creating resistance circuits having various resistance values by heating a carbon-based resistance paste before, during, or after irradiation with an electron beam. . However, this method was insufficient as a method for obtaining a highly conductive coating film using carbon-based fine powder as a conductive filler.

The present invention, as a result of various studies on curing methods for conductive paints using electron beams, provides a new curing method that does not have the above-mentioned drawbacks and provides a coating film with excellent performance. .

[Means for Solving the Problems] The present invention provides a method for curing a coated article formed from a composition in which 100 parts by weight of an electron beam curable resin is added in an amount of more than 300 parts by weight. temperature is 50℃
The above is a method of curing a conductive paint, which is characterized by curing by irradiating with an electron beam.

The electron beam curable resin used in the present invention refers to a resin having functionality that causes a curing reaction when irradiated with an electron beam, such as unsaturated polyesters, polyester (meth)acrylates, and epoxy resins. (meth)acrylates, polyol (meth)acrylates, polyurethane (meth)acrylates, polyether (meth)acrylates, allyl compounds, divinyl compounds,
Examples include compounds obtained by modifying silicone resin with acrylate, polybutadiene resins, spiroacetal resins, and other polymers having functionality in the molecule. These functional resins may be used alone or in combination if necessary, and may also be used in combination with other functional monomers or oligomers, such as 2-
Ethylhexyl (meth)acrylate, (meth)acrylic acid, dimethylaminomethacrylate, triallyl isocyanurate, triallyl cyanurate, triallyl trimate, etc. can also be added. The silver powder used in the present invention is metallic silver with a purity of 99% or more, and has a flake or lump shape and an average particle size of 0.1 to 25μ.
It is possible to use fine particles of the order of m in size, with or without surface treatment. There are no particular limitations on the shape or particle size of the silver powder, but considering conductivity and economic efficiency, it is better to use particles with a flaky shape and a large specific surface area.Also, when considering screen printing, etc., the particle size It is desirable to select one with a small value.

When fillers other than silver powder are used, sufficient conductivity and long-term reliability cannot be obtained.

It is essential that the amount of silver powder added to 100 parts by weight of the electron beam curable resin is more than 300 parts by weight. Addition is 30
If the weight is less than 0, sufficient conductivity cannot be obtained.

Desirably, the range is more than 300 centimeters and 700 centimeters or less.

In addition, it is also possible to add viscosity adjusting materials such as solvents, colorants, extender pigments, etc. to adjust the form of the paint. In order to create a paint by mixing electron beam curable resin, silver powder, viscosity control material, etc., the paint is usually kneaded uniformly by a method of adjusting the paint, such as mixing with three rolls, mixing with a kneader, or mixing with a ball mill. It is possible to do so.

Various methods are used to form the coating film depending on the purpose. Specific examples include printing methods such as screen printing, offset printing, gravure printing, and letterpress printing, and coating methods such as spray coating, brush coating, roll coating, casting, and spin coating. The thickness of the coating film is preferably 10 μm to 100 μm. After printing, if the electron beam curable conductive paint contains a volatile solvent, the solvent is removed by heating. It is also possible to combine heating for solvent removal and coating film heating.

The printed conductive paint is then cured by irradiation with electron beams in air or an inert gas atmosphere.

The conditions for electron beam irradiation include an acceleration voltage of 150 to 500
kV, radiation fit 3 to 30 Mrad. As the electron beam irradiation method, any of non-scanning methods such as curtain type, laminar type, broad beam type, area beam type, and pulse type, or low energy and medium energy scanning methods can be used. There is no particular limitation on the 02 concentration in the irradiation atmosphere, but it is preferably 02a degrees and 500 ppm or less.

In the present invention, the temperature of the coated material during electron beam irradiation is 50°C.
The above is necessary. The temperature of the coated material can be directly determined by embedding a thermal lightning pair in the wrapped material. When the film thickness of the coated material is between 10 μm and 100 μm, the temperature distribution in the film thickness direction can be almost ignored, and both the surface and bottom portions exhibit approximately the same temperature.

If the temperature of the coated material is lower than 50° C., sufficient conductivity cannot be obtained. A temperature range of 50°C to 150°C is particularly desirable. Temperature of the coated material: With J8, by setting the temperature of the irradiation chamber itself to 50° C. or higher, the coated material can be heated to a predetermined temperature and irradiated with electron beams. Alternatively, the method of the present invention can be carried out by placing the coated sample on a preheated tray and irradiating it with an electron beam when the sample reaches a predetermined temperature. Furthermore, it is possible to heat the coated material in advance to a temperature higher than 50°C, and to cure it by irradiating the coated material with an electron beam while the temperature of the coated product is 50°C or higher.

In this method, the effects of the present invention are achieved by preheating at a high temperature for a short time, for example, at 200°C for 30 seconds, and then curing with Ichiko ray irradiation while the temperature of the coated material is 50°C or higher. This is a method that is extremely advantageous in practice, as it allows full use of the effects. Furthermore, during the preheating at 200° C. for 30 seconds, it is also possible to extrude the solvent portion, making it possible to improve the efficiency of the work.

There are no particular limitations on the heating means;
Commonly used methods such as heating with hot air,
Heating by far infrared rays, dielectric heating, etc. can be used.

[Example] The present invention will be explained in more detail by the following example.
The present invention is not limited in any way by these Examples.

Example 1 Silver powder (AgC-A, Fukuda Metal ■
80 parts by weight of ethyl cellosolve, 1
After adding 0 parts by weight, kneading was performed using three rolls to prepare a conductive paint.

The paint is applied to a phenol substrate with a thickness of about 30 μm as shown in Figure 1.
After drying at 50°C for 2 hours, it was cured by electron beam irradiation while heating at 55°C and 115°C. Electron beam irradiation conditions: 1OMrad, 5mA. 50
At 0kV, the 02 concentration is less than 1Oppm. The volume resistivity of the cured coating film is 1.7 x -410 Ω-am at a heating temperature of 55°C, and 4.9XIO' at a heating temperature of 115°C.
It showed extremely good conductivity of Ω-cnn.

Example 2 Silver powder (AgC-A, Added 77 parts of Fukuda Kinzoku (manufactured by Fukuda Metals), and further added ethyl cellosolve,
After adding 10 parts by weight, kneading was performed using three rolls to prepare a conductive paint.

The paint was applied to a thickness of about 3C on a phenol substrate as shown in Figure 1, and after drying at 50°C for 2 hours, the coating was cured by irradiation with an electron beam while heating to 115°C. The electron beam illumination conditions are the same as in Example 1.

The volumetric U resistance of the cured coating is 2.2X10-4Ω-c
It was m.

Example 3 A conductive paint coating prepared in the same manner as in Example 1 was heated at 200° C. for 30 seconds, and then immediately cured by electron beam irradiation. The electron beam irradiation conditions are 10Mr
ad, 25mA, 250KV. Further, the coating film temperature during electron beam irradiation was 70 to 100°C. The cured coating had a vague volume resistivity of 5.2 x 10' ohm-cm.

Comparative Example 2 A conductive paint coating prepared in the same manner as in Example 2 was dried at 50°C for 2 hours, and then irradiated with an electron beam at a temperature of 25°C to cure the coating. The electron beam irradiation conditions are the same as in Example 2.

The volume solid U resistance of the cured coating film was 10 3 Ω-cm or more.

Comparative Example 2 A conductive paint coating prepared in the same manner as in Example 3 was heated at 200° C. for 30 seconds and then left at room temperature for 15 minutes. At this time, the temperature of the coated material decreased to 30°C. Thereafter, electron beam irradiation was performed under the same electron beam irradiation conditions as in Example 3 to cure the coating film.

The volume resistivity of the cured coating film is 3. OXIO'Ω-am
Met.

[Effects of the present invention] The conductive coating film obtained by the method of the present invention not only has excellent conductivity but also has extremely high long-term reliability. Also, it is very good in terms of workability.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual diagram of a substrate for measuring conductivity (volume specific resistance) of the present invention. 1... Conductive coating film 2... Copper foil 3...
phenol substrate

Claims (1)

[Claims] In a method for electron beam curing of a coating formed from a composition in which more than 300 parts by weight of silver powder is added to 100 parts by weight of an electron beam curable resin, electron beam irradiation is performed at a temperature of the coating at 50°C or higher. A method for curing conductive paint, which is characterized by curing.