JPS59113072A - Electrically conductive paint - Google Patents

Abstract

PURPOSE:To provide the titled paint available at a low cost, having excellent oxidation resistance, capable of keeping the electrical conductivity and the capability to shield electromagnetic radiation, and suitable for the electromagnetic shielding of electronic apparatuses, by using fine copper powder as main conductive material, and adding an organic binder, beta-keto-acid ester, and orthoboric acid thereto. CONSTITUTION:The objective composition can be prepared e.g. by compounding (A) 50-90wt% (based on the solid component of the paint) of fine copper powder (preferably finer than 200 mesh) with (B) an organic binder (e.g. polyvinyl butyral, etc.), (C) 0.3-0.5wt%, based on the component (A), of a beta-keto-acid ester [e.g. beta-(alkylcarbonyl)acetic acid, etc.] and (D) 0.03-0.5wt%, based on the component (A), of orthoboric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductive paint that uses fine copper powder as a main conductive material and has long-lasting conductivity and electromagnetic shielding properties.

With the rapid development of the electronic equipment industry, electromagnetic interference generated by electronic equipment is becoming a social problem as a new type of industrial pollution. That is, in reality, electromagnetic waves generated from electronic devices often cause other devices to malfunction or cause communication failures. In particular, plastic molded products that are transparent to electromagnetic waves are often used for the housings of electronic devices due to demands such as weight reduction, aesthetic appeal, low cost, and mass production. In other words, it has become essential to provide electromagnetic shielding. In light of this situation, moves have already begun to create legal regulations regarding electromagnetic interference. By the way, specific methods for electromagnetic shielding for electronic devices that use plastics for their housings include applying conductive paint to the housing, spraying zinc on the housing, and using conductive methods in which conductive filler is mixed in. Methods such as using plastics have already been proposed, but among these methods,
The method of applying conductive paint has low equipment costs for sea/redo processing, can be easily applied to objects with complex shapes, can be applied to all types of plastics, and is suitable for mass production. This is the most promising method because it has advantages such as excellent properties. This conductive paint is made by mixing and dispersing conductive fine powder in an organic binder. something is known.

Among these, conductive paints containing fine copper powder are the most economical and have good conductivity and electromagnetic shielding properties during preparation, but when stored for a long time or in the paint film after painting, the It has the disadvantage that copper is oxidized and its conductivity and electromagnetic seeding properties gradually decrease.

In view of the above circumstances, the inventors of the present invention conducted extensive research and found that copper fine powder was used as the main conductive material, and an organic binder,
It was discovered that a conductive paint containing β-keto acid ester/vm and orthoboric acid is relatively inexpensive, has excellent antioxidant properties, and maintains conductivity and electromagnetic shielding properties over a long period of time. , we have completed the present invention.

The copper powder used in the present invention is preferably a spherical, dendritic, or scale-like powder of 200 meters, and the amount used is usually 50 to 90%, preferably 65 to 90%, based on the solid content of the conductive paint. 85 ton 8%.

Furthermore, the organic binder that can be used in the present invention includes all organic binders used in general paints, such as vinyl chloride/vinyl acetate copolymer, polyvinyl/reptylar/acrylic acid ester/ resin, thermoplastic resin such as ethylene-vinyl acetate co-electrolyte partially hydrolyzed product, epoxy resin, polyurethane resin, thermosetting acrylic resin, phenolic resin,
Thermosetting resins such as melamine 7μ chito resin are preferably used.

These binders may be diluted with organic solvents.

The organic solvent is appropriately selected depending on the type of binder1)
, fc Toeha) Those used as ordinary paint solvents, such as μene, quinolene, acetic acid esters, ketones, etc., or mixtures thereof, are used in the New Year. However, it is necessary to take care not to erode the plastic material to be coated or to prevent the occurrence of drainage cracks.

Examples of the β-keto acid esters used in the present invention include esters of β-acyl fatty acids such as β-(alkylcaleponi/di)-acetic acid and β-(allylcica/levonyl)-JT-te. /shira, specifically acetoacetic acid, propionyl acetic acid, butyroyl acetic acid, imbutyroyl yv vinegar,
Pencey / acetic acid, etc. / acetic acid methyμ,
Eti/Reenute, PropiμEnute/Shi.

It includes isopropyl esters I, butyl enetel, inbutyl esters, and alkyfures such as tertiary butyl esters and tertiary butyl esters. These may be used alone or in combination of two or more. The amount used is 0.3 to 5.0 (weight)% of the fine copper powder, preferably 0.5 to 2.0%.
(weight)%.

In addition, the amount of orthoboric acid used in the present invention is 0% of the copper fine powder.
．． 03-0.5% (by weight), preferably 0.05-0.
It is 2 (weight)%. In addition, o/rethoboric acid is used as is! However, it may be used after being dissolved or dispersed in a suitable solvent or dispersion medium in advance. In particular, glycerin contains 5
It is convenient to use a solution dissolved at about 13% (by weight) when formulating the composition.

The above β-keto acid ester and o/rethoboric acid additives are:
It is indispensable to impart strong resistance to oxidation to the copper thread conductive paint that is the object of the present invention, and to maintain excellent conductivity and excellent electromagnetic/reading properties over a long period of time. The object of the present invention can only be achieved by using them together.

When producing the conductive paint according to the present invention, the above-mentioned additives may be added after mixing the fine copper powder and the organic binder, but they may be added and mixed in advance to the organic binder to be used. A method in which fine copper powder is added and mixed later is suitable for facilitating the dispersion of fine copper powder. In addition, in order to prevent the fine copper powder in the conductive paint composition from settling during storage and to ensure good dispersion, thixotropic additives such as colloid/resilica or coupling agents such as silane coupling agents are used. Use may also be effective in some cases.

It is desirable that the colloidal silica or the coupling agent be added before the addition of the β-keto acid ester and orthoboric acid.

The conductive paint according to the present invention thus obtained is sprayed 9 on the front or back surface of the molded article to be coated.
It can be applied using a conventional coating method such as a brush wheel V.

The present invention will be specifically explained below with reference to Examples.

Example 1 75 parts by weight of to/renin and 15 parts by weight of ethyl acetate were added to commercially available acrylic resin BRi02 (product of Mitsubishi Rayon Co., Ltd.) for paints.
A mixed solvent consisting of 1 part by weight and 10 parts by weight of butylacetate was added to prepare a resin solution with a nonvolatile content of 20% by weight. To this solution, a glycerin solution containing colloidal silica, ethyl acetoacetate, and 10% by weight of orthoboric acid was added in the mixing ratio shown in Table 1 in the order shown, and the mixture was stirred and mixed using a high-speed mixer each time to ensure uniform dispersion. .

Next, a predetermined amount of dendritic copper fine powder (350 mesh pass 8
8% by weight or more) and mixed with a high speed mixer to obtain a conductive paint.

Experiments ff14, 5.6, and 7 shown are compositions according to the present invention, and experiments 1 to 3 contain neither β-keto acid esters nor orthoboric acid (+1hl),
Does not contain either of the two components (Ilh2,
3).

A dry coating film of these conductive paints on an ABS molded plate is 20 μm.
I spray painted it to look like this. Each dried coating film had a pencil hardness of rHJ, a cross-cut test value serving as an index of layer density of 100/100, and an initial surface resistivity of the order of 10 QΩ.

As shown, the change in surface resistivity after accelerated exposure of a painted ABS board to 100°C conditions was approximately 3 Ω in experiments &4, 5.6 and 7 related to the present invention. On the other hand, in the case of reference example series 1 to 3, a remarkable increase is observed in all cases.

(Leaving space below) Example 2 Amount 2.040) 334 parts by weight of a mixed solvent of equal weight of toluene, ethyl acetate/reketone, and cello/rebu acetate were added to 100 parts by weight to form a solution, and to this was added colloidal/resilica. A glycerin solution containing 2 parts by weight of methyl-7toacetate/reeste 7 and 10% by weight of orthoboric acid was added and mixed in the amount shown in Table 2. Next, spherical copper fine powder (average particle size 15μ, specific surface area 2.700ts)
/f, purity 9.9.7%) was added and mixed using a high speed mixer to obtain a conductive composition.

To this composition, add 18 parts by weight of ure equivalent (365) and a mixed solvent containing J bacteria, mix thoroughly, and immediately
Dry coating thickness is 30μ on one side of I11 ABS flat molded plate.
I spray painted it to look like this. This coated plate was mounted on the apparatus shown in FIG. 1, and the electromagnetic conductivity was measured by the method of measuring electric field strength. In this case, "after 6 months of exposure" refers to the electromagnetic/reactive properties measurement results after the coated plate was exposed to temperature and humidity at 45° C. and 95% RH for 6 months.

As shown in the description, the electromagnetic shielding properties after coating all show good sea/redo notes, but the electromagnetic shielding properties after being exposed to hot and humid conditions are limited to cases 11 to 14 according to the present invention. shows good electromagnetic shielding.
It is recognized that those of ~10 deteriorated with exposure.

For reference, Table 2 also lists the surface resistivity I11 results after painting []3: and after 6 months of exposure! I gave up. This result is also similar to the above, and Experimental No. 11 related to Kou'6 Ming.
It was confirmed that the conductivity retention properties of the coating films No. 1 to 14 were outstandingly good.

Example 3 Example 1. Experimental Examples 5 and 7) /lil: Add acid ethyl ester to the same amount of benzoyl acetate ethyl 7
A sample was prepared in the same manner as in Example 1, except that L' was replaced, and the surface resistivity of the coating film was tracked by accelerated exposure at 100°C.

The results are shown in Table 3, and it was found that the resistivity retention of the Z-conductive coating film according to the present invention was good.

Table 3

[Brief explanation of the drawing]

Figure 1 shows the tank weight of the electric field strength measuring device.
x30cx), 2. is AB with conductive paint applied to the inner surface.
S test 1 board, 3 is the transmitting antenna, 4. is the transmitter (Mo,
645A Anritsu'IFkiηhei), 5. is the receiving antenna, 6 is the receiving antenna 175 (30MH2: KNM 402 Kyoritsu', 1oo, 300MH2: 5TODDAR
T NM 37157 nonger). 'j' in the drawing! 2 (No change in content) 2゜ㅅ Go to 3 - Indication of the case of the Commissioner of the Patent Office dated April 12, 1982. Name of the invention, Patent Application No. 22224.8 of 1982. Related Permit applicant address 2-27 Doshomachi, Higashi-ku, Osaka Name (
293) Take 1]] Yakuhin Kogyo Co., Ltd. Representative Kura
Iku Hayashi Department 4 (and 1 other person) Agent Tokyo contact information (License Law Division) @ story 278-2219, 2
2186 Drawing subject to amendment 7, content of amendment as shown in attached sheet 8, list of attached documents (1) attached sheet (Figure 1) 1 or more copies

Claims (1)

[Claims] Fine copper powder is used as the main conductive material, and an organic binder is added thereto. A conductive paint containing β-keto acid NTP and orthoboric acid.