JP2582238B2 - Conductive color-adjusted automotive primer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to electrostatic coating of plastic substrates. More particularly, it relates to a two-layer primer system comprising a chromatic, non-conductive first coating and a relatively thin, translucent, conductive second coating. More specifically,
The present invention relates to a conductive primer that is color-adjusted to the color of the topcoat.

[0002]

BACKGROUND OF THE INVENTION Until recently, conductive black primers were the only primers useful for electrostatic coating of plastic products. This made it difficult to conceal the primer with a white or colored top coat, and also caused the scratches in the top coat to be very noticeable. The introduction of conductive white or sharp pigments in recent years has made it possible to develop chromatic conductive primers that match the topcoat, but these pigments are very expensive and therefore produced from them. The cost of the primers used is very high.

[0003]

The production of a single non-black conductive coating layer having both excellent substrate hiding power and conductivity has many problems. To conceal in a colored system, substantially more non-conductive pigment powder must be present in the coating composition, but at the same time it must be converted to a conductive coating layer. No. For this purpose, it is necessary to add an expensive conductive pigment in an amount sufficient to cancel the insulating effect of the concealing pigment. Since the effective amount of conductive pigment is very large, such a one-layer coating system is very expensive.

[0004]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to hide a substrate with a colored non-conductive first coating layer and to provide conductivity by a translucent thin coating layer containing a conductive pigment. To provide an inexpensive two-layer primer system for electrostatic coating of plastic products.

Another object related to the present invention is to provide a color-tuned primer for plastic articles to be electrostatically coated.

Another object related to the present invention is to provide a wet-on-wet method for applying two coats containing a colored primer suitable for electrostatic coating of a topcoat.

[0007] These and other objects of the present invention, which will become apparent in the following description, are to apply a non-conductive colored primer paint to conceal a substrate, followed by a wet surface of the non-conductive primer. By applying a translucent conductive primer to the substrate as well as baking the applied substrate. In the context of this specification, color and all terms derived from color are used to represent chromatic colors for white and black, ie, colorless and all color combinations of the spectrum, respectively. Although the substrate may be metal and plastic, the present invention has been found to be useful for painting plastics. The translucency of the conductive coating layer results from the weakness of the conductive pigment in hiding power and the relatively thinness of the conductive primer as compared to the first coating layer that hides the substrate.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The binder used in both the non-conductive and conductive primer coatings is a hydroxyl-functional polyester having an OH number from about 170 to about 240, preferably from about 190 to about 220. The polyester is preferably prepared from saturated fatty acids and polyols by well known methods commonly practiced by those skilled in the art. Approximately 135 to 22 while blowing a stream of an inert gas such as nitrogen to remove water released in the reaction.
The reactants may be heated in a temperature range of 0 ° C (about 275-430 ° F). Vacuum at an appropriate temperature or an azeotropic agent may be used to assist in water removal. Examples of suitable dicarboxylic acids include malonic acid, succinic acid, adipic acid,
Methyl adipic acid, sebacic acid, and suberic acid are included. Preferred polyols are ethylene glycol, 1,
There are 3-propylene glycol, diethylene glycol, neopentyl glycol, and trimethylolpropane. A mixture of the acid and the polyol may be used. If a vacuum is used to remove water, it is necessary to take into account the possibility of loss due to sublimation of the polyol. Although a catalyst may be used, satisfactory results can be obtained without using a catalyst. The weight average molecular weight (Mw) is about 500 to about 20,000, preferably about 600 to about 10
00 range. The hydroxy functionality of the preferred resin is about 3 / molecule, and the carboxy functionality is about 0.3.
1 / molecule. The Brookfield viscosity of this resin is about 3.6 to about 7.2 Pascal seconds (about 3600 to about 7200) when rotated at 20 rpm on a # 3 spindle.
Centipoise). The density of this resin is about 1.09
g / cc or about 9.06 pounds / gallon. Polyesters suitable for practicing the present invention are under the trade name Rucof.
Ruco and Lexmodes as Desmophen
Available from Miles.

The dispersion in a solvent containing one or more non-conductive pigments and from about 20 to about 40% by weight of a polyester, and optionally a suitable amount of a curing agent and / or an epoxy resin, is prepared using a sand mill to form about 6.5+. Hegman grind, or a particle size of about 20 microns or less.

[0010] Epoxy resins suitable for the present invention are prepared by generally well-known methods. The epoxy resin is a compound or a mixture of compounds containing at least one, but generally one or more 1,2-epoxys. These may be saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compounds. Examples of suitable epoxy resins include polyglycidyl ethers of polyphenols, such as bisphenol A and bisphenol F, polyglycidyl ethers of mononuclear polyhydric phenols, such as resorcinol and pyrogallol, and polyhydric acids such as ethylene glycol and pentaerythritol. Includes polyglycidyl ethers of alcohols. A minimum amount of less than about 2% by weight of the paint is an effective specific formulation.

Next, these dispersions are cured with a hardening agent, a matting agent, a flow control agent, and a non-conductive coating of the first coating layer and a conductive coating of the second coating layer having desired properties. As well as other additives such as dispersants, surfactants, UV absorbers, and more with a sufficient amount of polyester.

The non-conductive coatings of the present invention may be made from about 1 to about 55% by weight of the non-conductive dispersion and from about 5 to about 20% by weight of the added polyester. Titanium dioxide is the main component in the above non-conductive dispersion, and because of its hiding power, becomes the main pigment in the non-conductive primer coating. To provide a color-tuned primer for the plastic article to be electrostatically coated, the color pigment is preferably the same as that present in the topcoat,
It may also be an organic or inorganic compound and is exemplified by phthalocyanine blue, phthalocyanine green, quinacridone red, perylene red, isoindolenone yellow, and various other types of iron oxide. Very small amounts of these pigments, on the order of about 0.15% by weight, based on the total weight of the non-conductive pigment, are sufficient to give the desired color. About 0.1% by weight of a conductive pigment, such as carbon black, may be present in the non-conductive paint. The non-conductive coating may include up to about 4% by weight microgel.

The conductive primer paint is EM Indu
stories, Inc. From about 15 to about 25% by weight of a conductive white or chromatic pigment, exemplified by antimony-doped tin oxide on a mica carrier sold under the trade name MINATEC. Another example of a suitable conductive pigment is Otsuka Chemical Co. , LT
D. There is a sodium titanate fiber sold under the trade name TISMO. TISMO 200B powder is a particular example of such a pigment. Antimony / tin oxide is disclosed in U.S. Patent Nos. 4,655,966 and 5,104,
No. 583, which is incorporated herein by reference. It is preferable to add the above-mentioned coloring pigment in order to bring the color of the conductive paint closer to the color of the non-conductive primer coating layer and to maintain the color of the primer and the top coat which is the object of the present invention. Further, a small amount of a conductive black pigment may be added. The weight ratio of pigment to binder in the conductive paint is less than about 1: 1.7, expressed as a percentage, and the weight of pigment is less than about 60% of the weight of binder. The final conductive paint of the present invention comprises from about 15 to about 25
Manufactured from a dispersion of a pigment comprising about 20% to about 30% by weight of a conductive pigment and about 20% to about 30% of a polyester.

The polyesters are curable with aminoplasts through hydroxyl groups, the aminoplasts being formed by reaction of aldehydes, especially formaldehyde, with substances containing amino or amide groups exemplified by melamine, urea, dicyanodiamide and benzoguanamine. Oligomer. Particularly advantageous are aminoplasts modified with alkanols having 1 to 4 carbon atoms. Other suitable aminoplast resins include alkoxymethylglycolyl, such as tetra (methoxymethyl) glycolyl. Accordingly, various types of commercially available aminoplasts and their precursors are useful for combining with the direct polyesters of the present invention. Particularly preferred amino crosslinkers are America
n Trade names Cymel and Mo from Cyanamid
It is sold by nsanto under the trade name Resimene. In particular, Cymel 301, Cy
mel303, Cymel385, Resimene7
45 and Resimene 755 alkylated melamine formaldehyde resins are useful. Of course, it is possible to use all mixtures of the above N-methylol products. At least 1.5 of the hydroxyl groups of the polyester
A crosslinker reactive to hydroxyl groups is generally provided in an amount sufficient to react twice as much, ie, at least 1.5 times the stoichiometric amount of hydroxyl functionality. . The crosslinker is preferably in an amount sufficient to substantially completely react with all of the hydroxyl groups of the polyester, and corresponds to about 1 to about 12 of the nitrogen-containing crosslinker in an amount equivalent to the hydroxyl functionality of the polyester. The desired amount of crosslinking agent is supplied. The non-conductive paint of the first coating layer is about 10
The conductive coating contains from about 12 to about 25% by weight of the curing agent, while containing about 20% by weight of the curing agent. Production of dispersions,
Further, the solvent used to produce the coating from this dispersion is one that imparts excellent wettability and fluidity to the coating while not attacking the plastic substrate to be applied. N-methyl-2-pyrrolidone (NMP), ethylbenzene, isobutanol, xylene, ethyl-3-ethoxypropionate, aromatic naphtha, dipropylene glycol monomethyl ether acetate (DPMA), propylene glycol methyl ether acetate (PM acetate) , And mineral spirits are examples of suitable solvents. Often, mixtures of solvents selected to meet such requirements are used. The dispersion contains about 15 to about 65% by weight of solvent, and the solvent content of the coating is about 20 to 40% by weight.

A preferred thixotropic is the trade name Cab.
-Fumed silica, such as those available as O-Sil and Aerosil. If present in the paint, less than 1% of the total weight is used. SCM
Amorphous silica available from the Company is useful as a matting agent in amounts of less than 2% by weight. Dispersants, surfactants, UV absorbers, and other additives are all conventionally used in coatings. A conventional curing catalyst is added to each primer composition prior to its use. The amount of active catalyst may be from about 0.2 to 1.2% by weight based on the weight of the total composition. The active catalyst is very good if it is an organic-soluble acid exemplified by p-toluenesulfonic acid and phenyl acid phosphate. A catalyst solution containing 17.5% by weight of p-toluenesulfonic acid and 13.1% by weight of phenyl acid phosphate is preferred, but the proportions of the two components can be varied to meet the requirements of the particular coating. Is also good.

The following examples illustrate the invention.
Unless otherwise stated, all amounts, parts and percentages are by weight.

[0017]

EXAMPLE 1 Model No. 1 sold by Chicago Boileer Company. Red Head L
A non-conductive pigment dispersion was prepared from the following components using a 3J water-cooled sand mill. The Hegman grind of the non-conductive dispersion was 7+.

[0018]

[Table 1]

Example 2 A non-conductive paint was prepared from the dispersion of Example 1 according to the formulation in the table below.

[0020]

[Table 2]

Example 3 A conductive paint was prepared according to the formulation in the table below.

[0022]

[Table 3]

Immediately before the application of the first primer coat, Example 2
3 parts of catalyst were dissolved in the non-conductive paint per 100 parts of the product. Similarly, 3 parts of catalyst per 100 parts of the product of Example 3 were dissolved in the conductive paint.

In the present invention, it is desirable to apply the two types of primer compositions by a wet-on-wet method using a spray gun in order to increase the throughput of the applied portion. To form a film having a dry thickness sufficient to conceal the substrate (eg, about 18 to about 20 μm (about 0.7 to about 0.8 mil))
The primary paint was sprayed from the gun onto the plastic part at an air pressure of about 4.2 kg / cm ² (60 psi) and left at ambient temperature for about one minute to volatilize a portion of the solvent.
Next, about 7.
Dried films having a thickness of 6 to about 10 μm (about 0.3 to about 0.4 mil) were formed. After air drying at ambient temperature for about 10 minutes, the coated portion was baked at a temperature of about 250 ° F. for about 30 minutes. The conductivity of the applied part is Ran
sburg spray suitability meter No. It was about 130 to about 165 Ransburg units as measured using 8333-00.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Dean Smith United States, Indiana 46301, Crown Point, Park Place 4251 (56) References JP-A-6-165966 (JP, A) JP-A-62-289268 (JP, A)

Claims (11)

(57) [Claims] 1. A method of adapting a plastic substrate for electrostatic coating of a topcoat, said method comprising applying a non-conductive colored primer paint on the substrate to conceal the substrate; , 7.6 to 10 μm (0.3 to 0.4
(Mil)). A method comprising applying an amount of conductive primer paint to the surface of the non-conductive primer sufficient to provide a dry film having a thickness of (mils), and baking said coated substrate. 2. The method according to claim 1, wherein the non-conductive paint is still wet when the conductive paint is applied. 3. The method of claim 1, wherein said non-conductive primer is color-tuned with respect to said topcoat. 4. The method according to claim 1, wherein said conductive primer comprises a color pigment. 5. The method according to claim 3, wherein the color pigment is selected from those which are close to the color of the non-conductive primer. 6. The method of claim 1, wherein the conductive paint comprises a binder and a conductive pigment in a weight ratio of 1: 4 or less. 7. A plastic article having a colored non-conductive first primer coating and a translucent conductive second primer coating having a thickness of 7.6-10 μm (0.3-0.4 mil). 8. The plastic article of claim 7, wherein said conductive coating layer comprises a pigment and a binder in a weight ratio of about 1: 1.7 or less. 9. The plastic product according to claim 7, wherein the conductive primer coating layer is colored so as to be close to the color of the non-conductive primer coating layer. 10. A colored non-conductive first primer coating, a 7.6-10 μm (0.3-0.4 mil) thick conductive second primer coating, and a non-conductive primer coating. Plastic products with an electrostatically painted topcoat that matches the color. 11. The conductive second primer coating layer,
A pigment and a binder in a weight ratio of 1: 1.7 or less.
0 plastic products.