JPH06165966A - Coating method - Google Patents

Abstract

PURPOSE:To improve the electrostatic coating characteristic of a finish coating material and to improve the adhesiveness to a finish coating film by using a specific conductive primer, thereby improving the org. solvent resistance of a conductive primer coating film. CONSTITUTION:A polypropylene(PP) material to be coated is coated with the conductive primer I and is then electrostatically coated with the org. solvent type finish coating material II. In addition, the specific surface resistance value of the conductive primer coating film after finish coating is confined toe <=1X10<8>OMEGA. The PP material to be coated is a material to be coated, such as bumper or side mold of an automobile, which is coated with an independent polymer of PP or a copolymer with other polymers and is subjected to a chemical conversion treatment on the surface. The conductive primer I consists essentially of urethane modified chlorinate polypropylene, melamine resin, polyester resin and conductive materials such as carbon black, silver, nickel and copper. The org. solvent type finish coating material II is selected from an acrylic resin/amino resin or polyisocyanate system, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a polypropylene article having good electrostatic coating suitability and adhesion.

[0002]

2. Description of the Related Art Polypropylene is used in automobile bumpers, door side moldings, etc., and a coating is applied to this polypropylene to improve its cosmetic appearance and durability. An electrostatic coating method is also used as a coating method.

Since polypropylene has poor suitability for electrostatic coating, it is common to coat a conductive primer in advance prior to top coating. Heretofore, as the conductive primer, one substantially composed of urethane-modified chlorinated polypropylene and a conductive substance has been used. However, when the organic solvent type top coating composition is electrostatically coated on the conductive primer coating surface, the conductive primer coating film is rapidly eroded by the organic solvent in the initial stage of coating,
Since the surface specific resistance value remarkably rises, there is a defect that the suitability for electrostatic coating of the organic solvent type top coating composition to be subsequently coated is deteriorated. In addition, it also has defects such as insufficient adhesion to the top coating film. Therefore, improvement of these defects is strongly desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the organic solvent resistance of a conductive primer coating film to improve the suitability for electrostatic coating of a top coating composition, and to improve the adhesion to the top coating film. To improve.

The above objects have been achieved by using a specific conductive primer, and the present invention has been completed here.

That is, according to the present invention, a polypropylene primer is coated with a conductive primer (I), then an organic solvent type top coat (II) is electrostatically coated, and the conductivity after the top coat is applied. The coating method is characterized in that the surface resistivity of the primer coating film is 1 × 10 ⁸ Ω or less.

The coating method of the present invention will be described in more detail.

(1) Polypropylene coated article: a coated article to which the coating method of the present invention is applied, and examples thereof include a propylene homopolymer or a copolymer with other monomers.
It is often used for automobile bumpers and side moldings. The polypropylene is molded into a desired shape,
The surface is preferably subjected to chemical conversion treatment by a known method.

(2) Conductive primer (I): (A) a urethane-modified chlorinated polypropylene, (B) a melamine resin, (C) a polyester resin and (D) a conductive primer containing a conductive substance as a main component. Is preferred. The primer (I) is an organic solvent type top coating (II) that is applied directly to a polypropylene object to impart conductivity to it.
If possible, electrostatic coating will be completed. At this time, the surface specific resistance value of the conductive primer coating film is kept at 1 × 10 ⁸ Ω or less from the initial coating of the organic solvent type top coating composition (II) to the completion of coating.

The urethane-modified chlorinated polypropylene (A) is a mixture of a chlorinated polypropylene and a polyurethane resin or an addition reaction product. Chlorinated polypropylene is obtained by chlorinating a propylene homopolymer or a copolymer thereof with other olefinic monomers, for example, and has a chlorine content of 1 to 60% by weight, particularly 10 to
40% by weight is preferred. The chlorinated polypropylene has a number average molecular weight of 5,000 to 200,000, particularly 100.
00-100,000 is suitable. Stereotactically, either isotactic or atactic may be used.

(A) The polyurethane resin used for preparing the urethane-modified chlorinated polypropylene is a urethane reaction product of a polyisocyanate compound and a polyol component, and has a free hydroxyl group and / or isocyanate group in its molecule. It is preferable to have. The polyisocyanate compound is a compound having two or more isocyanate groups in one molecule, and known aliphatic, aromatic and alicyclic polyisocyanates can be used. The polyol component has two or more hydroxyl groups in one molecule. For example, polyester polyol,
Examples thereof include polyether polyols and low molecular weight polyhydric alcohols.

The urethane-modified chlorinated polypropylene (A) used in the present invention is obtained by simply mixing the above chlorinated polypropylene and polyurethane resin at room temperature, or
It is obtained by heating to a temperature of 0 ° C. or higher and hot blending. Both components may react and be chemically bonded by hot blending. The ratio of the both components can be arbitrarily selected according to the purpose, but the chlorinated polypropylene has a ratio of 5 to 5 based on the total solid weight of the both components.
95 wt% and polyurethane resin 95 to 5 wt% are suitable.

As the melamine resin (B), known ones as a cross-linking agent for coating resins can be applied. For example, a melamine methylol compound or a part or all of the methylol group is formed from a monohydric alcohol having 1 to 6 carbon atoms. An etherified melamine resin obtained by etherifying with one or more selected is suitable. These (B) melamine resins may be simply mixed with the (A) urethane-modified chlorinated polypropylene, or both components may be hot blended in the same manner as described above.

The polyester resin (C) is an esterified product of a polybasic acid component and a polyhydric alcohol component. The polybasic acid component is a compound having two or more carboxyl groups in one molecule, and one or more kinds selected from polybasic acids such as aliphatic, alicyclic and aromatic can be used. Among these, it is particularly preferable to contain an alicyclic polybasic acid. Known polybasic acid components can be used. As the alicyclic polybasic acid, those having a 1,4-cyclohexylene structure are particularly preferable, and examples thereof include hexahydroterephthalic acid having the structure and C _1-5 lower alkyl such as methyl ester thereof. It is preferable to use an ester or the like because it is possible to easily obtain a coating film excellent in finished appearance, solvent resistance and coating film flexibility.
These anhydrides can also be applied.

The polyhydric alcohol component (C) for preparing the polyester resin is a compound having two or more hydroxyl groups in one molecule and is selected from aliphatic, alicyclic and aromatic polyhydric alcohols. One type or two or more types selected can be used, and among them, it is particularly preferable that the alicyclic polyhydric alcohol is contained. As the alicyclic polyhydric alcohol, those having a 1,4-cyclohexylene structure are preferable, and when 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F or the like having such a structure is used, a finished appearance is obtained. It is preferable because a coating film excellent in solvent resistance and coating flexibility can be easily obtained.

In the polyester resin (C), the content of the alicyclic polybasic acid and / or polyhydric alcohol component can be arbitrarily selected according to the purpose, but is 10 to 65% by weight in the polyester resin solid content, 20 to 55% by weight is particularly preferable. The polyester resin (C) can be obtained by a known esterification reaction by using the above-mentioned polybasic acid component and polyhydric alcohol component together with a monobasic acid or a hydroxycarboxylic acid, if necessary.

The polyester resin (C) also includes a urethane-modified polyester resin obtained by reacting the esterification reaction product of the above polybasic acid component and polyhydric alcohol component with a polyisocyanate compound. Examples of the polyisocyanate compound used here include aliphatic, alicyclic and aromatic polyisocyanate compounds having two or more isocyanate groups in one molecule. Furthermore, addition reaction products of these polyisocyanate compounds and polyhydric alcohols, buret type addition reaction products, isocyanuric ring type addition reaction products and the like can also be applied as the above polyisocyanate compounds. Particularly, as the polyisocyanate compound, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, 1,3- (or 1,4-) (isocyanatomethyl) cyclohexane and addition reaction products containing these are preferable. The ratio of the polyester resin and the polyisocyanate compound for preparing the urethane-modified polyester resin is preferably 0.5 to 20 parts by weight per 100 parts by weight of the polyester resin, and the hydroxyl group in the polyester resin is in the polyisocyanate compound. It is preferably in excess of the isocyanate groups.

The polyester resin (C) has a hydroxyl value of 5
0-150 mg KOH / g resin, especially 80-120 mg
KOH / g resin, acid value 1-40 mg KOH / g resin,
Especially 3 to 20 mg KOH / g resin, and number average molecular weight measured by GPC of 1300 to 8000, especially 15
It is preferably from 00 to 5000.

The conductive substance (D) is a substance for imparting conductivity to the conductive primer coating film, and specifically,
One or more selected from conductive carbon black, silver, nickel, copper, graphite and the like can be mentioned. These are preferably in the form of powder or particles, and the particle size is 0.1 to 500 μm. Are suitable.

The conductive primer (I) of the present invention contains the above-mentioned components (A), (B), (C) and (D) as essential components, and their compounding ratio can be arbitrarily selected according to the purpose. , For example, per 100 parts by weight of component (A),
Component (B) is 5 to 30, especially 10 to 20 parts by weight, (C)
5 to 30, especially 10 to 20 parts by weight, and (D)
The component is a total of 10 of the above-mentioned components (A), (B) and (C).
1 to 100 parts by weight, particularly 10 to 50 parts by weight, are each preferable per 0 parts by weight.

In the conductive primer (I) of the present invention, in addition to the components (A), (B), (C) and (D),
If necessary, (E) epoxy resin, (F) cellulose acetate butyrate, (G) polyether resin and the like can be appropriately blended.

As the epoxy resin (E), a bisphenol type glycidyl ether is preferable, but any epoxy resin that does not deteriorate the performance can be used. The number average molecular weight of the epoxy resin (E) is preferably 500 to 8,000, and the epoxy equivalent is 100 to 3,000.

(F) Cellulose acetate butyrate (hereinafter referred to as CAB) is a cellulose derivative obtained by further butyrylating a partially acetylated product of cellulose, preferably having an acetylation degree of generally 1 to 34% by weight,
Preferably 1 to 7% by weight: butyrylization degree is generally 16 to
60% by weight, preferably 40-60% by weight: ASTM-
The viscosity according to the measuring method described in D-1343154 is generally 0.005 to 5 seconds, preferably 0.005 to 1 second:
What is included in the range of is preferable. Specifically, the product name of Eastman Kodak Company in the United States, CAB
-171-2, CAB-381-0.2, CAB-53
1-1, CAB-551-0.2 and CAB-551
-0.01 and the like. Among them, CAB-381-0.2, CAB-551-0.2, and CAB-551-0.01, which have a high degree of butyrylization and a low viscosity, are preferable from the viewpoints of solubility, compatibility, viscosity, and the like.

The (G) polyether resin is preferably a polyether polyol obtained by using one or more alkylene oxides selected from ethylene oxide, propylene oxide, butylene oxide, tetramethylene oxide and the like. It is preferable that the polyether polyol has a number average molecular weight of about 1,000 to 200,000 and a hydroxyl value of 20 to 200 mgKOH / g resin.

In the conductive primer (I) of the present invention, the blending amounts of the components (E), (F) and (G) are as follows.
Although it can be arbitrarily selected according to the purpose, (A), (B),
Per 100 parts by weight of the total of the components (C) and (D),
The component (E) is 0 to 20 parts by weight, particularly 3 to 10 parts by weight,
The component (F) is preferably 0 to 20 parts by weight, particularly 3 to 15 parts by weight, and the component (G) is preferably 0 to 20 parts by weight, particularly 3 to 10 parts by weight.

The conductive primer (I) of the present invention is prepared by mixing and dispersing the components (A) to (G) in an ordinary organic solvent for paints and adjusting the solid content to 10 to 60% by weight. can get.

(3) The organic solvent type top coating composition (II) is a coating composition applied to the coated surface of the above-mentioned conductive primer (I), and forms a coating film excellent in weather resistance, smoothness and chemical resistance. Any paint will do. Specifically, acrylic resin /
Examples thereof include topcoat paints known per se such as amino resin or polyisocyanate system, alkyd resin or polyester resin / amino resin or polyisocyanate system. These topcoat paints (II) can be used as clear paints containing no or almost no colorants such as coloring pigments and metallic pigments, solid color paints containing coloring pigments, and metallic paints containing metallic pigments. These topcoat paints (II) are organic solvent type paints in which an organic solvent is used as a solvent or dispersion medium, and the solid content is 10 to 10.
60% by weight is preferred.

The coating method of the present invention is characterized in that the polypropylene primer is first coated with the conductive primer (I), and then the organic solvent type top coat (II) is coated on the coated surface.

The conductive primer (I) is preferably applied mainly by air spray or airless spray. The coating film thickness is 5 to 3 based on the cured coating film.
The range of 0 μm is preferable, and the coating film can be cured by heating at 80 to 150 ° C.

Then, an organic solvent type top coating composition (II) is applied to the surface of the heat-cured conductive primer (I) coated by an electrostatic coating method and heated to 110 to 150 ° C. to cure the top coating film. . The coating film thickness of the top coating film is preferably in the range of 10 to 60 μm based on the cured coating film. In that case, the top coat paint (II) is applied while the coating film of the conductive primer (I) remains uncured, and then heated as described above to simultaneously cure the primer coat film and the top coat paint film. It doesn't matter. Top coating (II)
As the coating method, there are a one-coat method using a solid color paint, a two-coat method using a solid color paint or a metallic paint, and a clear paint.

According to the coating method of the present invention, the following effects can be obtained.

(1) In the coating method of the present invention, the coating film of the conductive primer (I) has excellent adhesion to the polypropylene coating object and the top coating film, and even when immersed in warm water for a long time. No defects such as deterioration of adhesion or blister formation are observed.

(2) Since the coating film of the conductive primer (I) has excellent solvent resistance, even if the organic solvent type top coating composition (II) is applied to the surface of the coating film, the coating composition (II) does not The primer (I) coating film hardly dissolves or swells by the contained organic solvent. Therefore, the surface specific resistance value of the conductive primer (I) is maintained at 1 × 10 ⁸ Ω or less from the initial coating of the organic solvent type top coating composition (II) to the end of the coating, so that high voltage (for example, −90 KV or more) Electrostatic coating is now possible, and the coating efficiency of the top coating on the object is significantly improved.

The surface resistivity of the conductive primer (I) coating film of the present invention after coating was measured as follows. First, an organic solvent type top coating composition (II) is applied to the cured coating film of the conductive primer (I). In that case, in order to form the uncoated portion of the topcoat paint (II) at two locations (the distance between these two points is 35 mm) on a part of the coating surface of the conductive primer (I), a peelable tape is used. Attach in advance. Topcoat paint (II) is applied, the peelable tape is peeled off, and the topcoat paint (II) is removed to expose two places on the coated surface of the conductive primer (I). When 1 minute has passed at room temperature after applying the topcoat paint (II), the surface specific resistance value between the exposed coating surfaces of the conductive primer (I) is specific to the surface of the above-mentioned conductive primer (I). It is the resistance value. In the present invention, since the resistance value is maintained at 1 × 10 ⁸ Ω or less from the start to the end of the coating of the top coat, the above technical effect is exhibited.

Production examples, examples and comparative examples relating to the present invention will be described. All parts and percentages are in principle based on weight.

Production Example 1 Preparation of Samples 1) Urethane-Modified Chlorinated Polypropylene Using the chlorinated polypropylenes shown in Table 1, urethane-modified chlorinated polypropylenes A-1 to 3 having the composition ratios shown in Table 1 were prepared.

[0037]

[Table 1]

(* 1) Composition ratio: Solid content weight ratio.

(* 2) Polyurethane: A urethane reaction product of diisocyanate and glycol, having an isocyanate group at the terminal.

2) Urethane-modified polyester resin C. A urethane-modified polyester resin C is prepared by reacting the raw materials shown in Table 2 by a conventional method to prepare a polyester resin, and then subjecting the diisocyanate shown in the table to a urethane reaction. -1 to 3 were prepared. The unit of the blending amount of the polyester resin raw material and diisocyanate in Table 2 is part.

[0041]

[Table 2]

3) Preparation of Conductive Primer The components shown in Table 3 are mixed and dispersed in an organic solvent (a mixture of toluene and xylene in an equal weight), and the conductive primers i to ii.
i was prepared. The unit of the blending amount of each component is part.

[0043]

[Table 3]

(* 1) Melamine resin: Butyl etherified melamine resin.

(* 2) Ketjen Black EC: trade name, conductive carbon black, manufactured by Lion Corporation.

(* 3) Epon 1001: Shell Chemical,
Brand name, bisphenol type glycidyl ether, molecular weight about 950, epoxy equivalent 450-500.

(* 4) CAB-381-0.2: manufactured by Eastman Kodak Company, trade name, acetylation degree 5%, butyrylation degree 38%, viscosity (ASTM-D-134315).
4) 0.2 seconds.

(* 5) Polypropylene glycol: Number average molecular weight of about 2000, hydroxyl value 56 mg KOH / g resin.

Examples 1 to 3 and Comparative Example 1 The surface of polypropylene for automobile bumpers was treated with trichloroethane, and then the conductive primer obtained in Production Example 1 (adjusted to a solid content of 10%) was air sprayed. After coating to a film thickness of 10 to 20 μm based on the cured coating film and heating at 120 ° C. for 10 minutes to cure, an organic solvent type solid color top coating (polyester resin / melamine resin-based coating, trade name “So Flex # 1211
"Black", solid content 20%, Kansai Paint Co., Ltd. electrostatically coated with a bell-type electrostatic coating machine (voltage -90 KV) (25-35 μm based on the cured film thickness), and 20 minutes at 120 ° C. Heated to cure. The performance of the multilayer coating film thus formed was evaluated, and the results are shown in Table 4.

[0050]

[Table 4]

The conductive primer (iv) is obtained by removing the melamine resin and the urethane-modified polyester resin from the composition of the conductive primer (i).

Test method Resistance value: Surface specific resistance value (Ω) between two points (interval 35) of the conductive primer coating film prepared as described above.
mm) resistance value to TREK MODEL 150 (TR
It was measured by EK INC, trade name).

Water resistance: The above-mentioned coated plate was immersed in warm water of 40 ° C.
After soaking for 0 days, the appearance of the coating film was examined. ◯ indicates no abnormality, x indicates blister generation.

Resistance to water adhesion: After immersing in warm water of 40 ° C. for 10 days and then drying at room temperature, the coating film of size 2 × 2
Cut with a knife to reach the substrate so that 100 mm squares can be made. The number of square paint films that remained after the adhesive cellophane tape was attached to the surface and was rapidly peeled off. ◯ means no abnormality. × indicates that a large amount of peeling occurred.

Coating efficiency: The ratio (%) of the top coating applied to the article to the sprayed top coating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Tanaka 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Junichi Yamashita 1 Sanyo-cho, Nishikamo-gun, Aichi Kansai Paint Co., Ltd. (72) Inventor, Akihiro Tsuge, No. 1 flat land, Zuijoji, Miyoshi-cho, Nishikamo-gun, Aichi Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A polypropylene-made article to be coated is coated with a conductive primer (I), then an organic solvent type top coating (II) is electrostatically coated, and the coating of the conductive primer after the top coating is performed. A coating method having a surface specific resistance value of 1 × 10 ⁸ Ω or less. 2. The conductive primer (I) is (A) urethane-modified chlorinated polypropylene, (B) melamine resin,
The coating method according to claim 1, which comprises (C) a polyester resin and (D) a conductive substance as main components.