JPS592712B2 - Painting method - Google Patents

Description

[Detailed description of the invention] The present invention involves coating two types of paint in layers and curing them by heating.
The present invention relates to a so-called 2-coat, 1-bake coating method, and specifically relates to a 2-coat, 1-bake coating method in which urethane is cured using an isocyanate prepolymer as a curing agent component.

Currently, the number of paints used in two-coat, one-bake painting methods, such as metallic finishing methods, is zero.Both the base coat and top coat are mainly solution-type acrylic resins, and melamine resin is used as the curing agent component. .

However, after 2 to 3 years have passed, products painted using this method will inevitably lose their luster, and may also suffer from yoking, cracking, and peeling of the paint film. In the case of
Requires high temperature baking conditions such as ~35 minutes. In addition, high non-volatile resins are desired from the viewpoint of resource conservation and pollution control, finish quality, texture, paint workability, and glossy appearance, but high solid paints However, those cured with melamine resin have the disadvantage that their durability is significantly reduced. The inventors of the present invention have conducted extensive research in order to improve these drawbacks, and have found that by using a non-yellowing isocyanate prepolymer as the curing agent component of the coating film and curing it with urethane, durability, gloss, finish feel, and It took 30 years to complete a two-coat, one-bake coating method that provides excellent appearance and texture and can be cured at low temperatures. That is, the present invention has a number average molecular weight of 2000 to 1200.
0 polyacrylic polyol or polyester polyol and a non-yellowing isocyanate prepolymer are applied as main components, and the coated surface is coated with a polyacrylic polyol having a number average molecular weight of 2000 to 8000 and a polyacrylic polyol having a number average molecular weight of 800 to 5000. After applying a coating material whose main components are a resin consisting of a polyester polyol in a weight ratio of 99/1 to 1qq-1/99 and a non-yellowing isocyanate prepolymer, when heating and curing it, the above-mentioned Isocyanate prepolymer is 0 for hydroxyl group-containing resin
The present invention provides a coating method characterized in that H/NCO is contained in an amount such that H/NCO=1/0.5 to 1/1.5 (equivalent ratio).

In the polyacrylic polyol used in the present invention, the lower layer (base coat) has a number average molecular weight of 2,000 to 12,000, preferably 6,000 to 12,000, and the upper layer (top coat) has a number average molecular weight of 2,000 to 80,001.
Preferably it is 4000-6000.

Further, such polyacrylic polyol usually has a glass transition temperature of 0 to 80°C. In addition, polyacrylic polyols include, for example, β-hydroxyethyl (meth)acrylate, β-hydroxypropyl (meth)acrylate,
Hydroxyl group-containing vinyl monomers such as β-hydroxybutyl (meth)acrylate, or adducts of monoepoxy compounds such as Cardiula E, and carboxy group-containing vinyl compounds such as acrylic acid and methacrylic acid, and acrylic acid and methacrylic acid. It is obtained by a conventional method using an acid, an unsaturated acid such as fumaric acid or itaconic acid, an alkyl ester thereof, styrene, or the like. In addition, the polyester polyol used in the base coat has a number average molecular weight of 2.
000 to 12,000, preferably 2,000 to 8,000, and those used in the top coat have a number average molecular weight of 800 to 5,000, preferably 1,000 to 30.
00.

Such polyester polyols contain polybasic acids such as isophthalic acid, phthalic anhydride, succinic anhydride, adipic acid, and trimellitic anhydride as acid components, monobasic acids such as benzoic acid and para-t-butylbenzoic acid, and neocontaining acids as alcohol components. Pentyl alcohol, trimethylolethane, trimethylolpropane, 1,6-hexanediol, 1,5-
It is appropriately synthesized using pentanediol, pentaerythritol, glycerin, ethylene glycol, etc. or,
The polyester polyol may be oil-modified, and usually has an oil length of 30% or less, and in terms of compatibility with the resin and weather resistance, it is suitable for use with non-drying oils, especially apricot oil and its fatty acids, synthetic fatty acids such as octylic acid, or cardinal oils. It can be obtained by using a monoglycidyl ester of a synthetic fatty acid such as E in combination. In the present invention, a non-yellowing isocyanate prepolymer is added as a curing agent component to the topcoat and basecoat.

Such isocyanate prepolymers include non-yellowing diisocyanates such as hexamethylene diisocyanate, isopropylidene dicyclohexyl isocyanate, isoborone diisocyanate, and trimethylhexamethylene diisocyanate, and at least 2 active hydrogen atoms such as water, polyhydric alcohols, and low molecular weight alkyds. The main component is an isocyanate group-containing adduct with an individual compound, or one or more oligomers thereof, or a mixture thereof, and these isocyanate prepolymers are further blocked with a known and commonly used blocking agent. can also be used. Known commercial products include Burnock DN-950 (product of Dainippon Ink Chemical Co., Ltd.), Dismodule N-75 (product of Bayer Co., Ltd., Haccoronate HL (product of Nippon Polyurethane Co., Ltd.), etc. In the present invention, the upper layer (top coat)
The weight ratio of the polyacrylic polyol and polyester polyol is 99/1 to 1/99, preferably 90.
It is contained at a ratio of /10 to 30/70.

If the amount of such polyester polyol is less than 1% by weight, the feeling of fleshiness etc. will be inferior, while if the amount of polyacrylic polyol is less than 1% by weight? If the amount is less than 1, the chemical resistance and stain resistance will be poor, which is not preferable. In addition, the non-yellowing isocyanate prepolymer used as a curing agent has an 0H/NCO ratio of 1/0.5 to 1/1.5 (equivalent ratio) to the hydroxyl group-containing polymer in both the top coat and the base coat. ), preferably in an amount of 1/0.8 to 1/1.2. The amount of this isocyanate prepolymer is 0.0.0.
If the amount is less than 5 equivalents, the resulting coating film will not have sufficient physical properties, and if it exceeds 1.5 equivalents, it will be unfavorable in terms of cost. The method of the present invention is based on a two-coat, one-bake method, and is particularly excellent in metallic finishing.

That is, a paint containing a colored pigment, particularly a metallic powder, and more preferably a cellulose compound such as cellulose acetate butyrate (CAB) is applied as a base coat, and a top coat is applied thereon. In addition to the above-mentioned polymer and curing agent, a coloring pigment is added in an amount such that the formed coating film becomes colored and transparent or translucent, or after coating a paint containing no coloring pigment at all, it is heated at 60 to 180°C for 10 to 10 minutes. A method of heating and curing for 30 minutes is suitable. Incidentally, it is preferable that a curing accelerator be added to the paint used for the top coat and base coat in the present invention. This curing accelerator is suitable because it greatly contributes to relaxing the baking conditions and the required physical properties can be obtained in a short time. Although known curing accelerators can be used, colorless organic acid metal salts such as dibutyltin dilaurate, zinc octylate, and tin octylate are preferred because of their low odor and coloration over time. The amount used is 0.0001 to 0.0% based on the solid content of the hydroxyl group-containing resin, from the viewpoint of shortening the pot life.
．． Selected within the range of 0.01%. Also, if the base coat paint is metallic, use CA to improve the metal adhesion.
It is preferable to add a cellulose compound such as Bl nitrocellulose (NC), and the amount used is preferably 10 to 3070% based on the solid content of the polymer. Additionally, small amounts of other resins, such as amino resins, vinyl resins, and silicone resins, may optionally be blended into both the top coat and the base coat. Examples of the metallic material include aluminum powder, copper powder, mica powder, etc., and examples of the coloring pigment include common inorganic and organic pigments such as titanium oxide, phthalocyanine blue, and silver sand.

The amount of such metallic powder to be blended is usually preferably 3 to 20 parts by weight per 100 parts by weight of the resin content, and the amount of the coloring pigment is preferably 2 to 100 parts by weight per 100 parts by weight of the resin content. In the coating method of the present invention, the base coat paint is coated with a diluent such as xylene, toluene, butyl acetate, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, etc. to a viscosity of 14 to 20 seconds (Food Cup #4/20°C).
) and apply spray coating, airless spray, electrostatic coating, etc. directly to a substrate such as a steel plate or aluminum plate, or on a substrate coated with a primer coating, to a dry film thickness of about 10 to 30μ. Apply the base coat using any suitable painting method.

Next, after setting at room temperature for 1 to 10 minutes, the top coat paint was adjusted to 20 to 40 seconds (Food Cup #4/20'C) with a diluent, and the dry film thickness was 20 to 50.
Approximately 5 coats are applied over the base coat film so that the thickness is μ.
After ~20 minutes, this is achieved by heating and curing at 60-120°C for 10-30 minutes. The invention will now be explained in more detail by way of example.

In addition, the part in the example and ? is based on weight. Production Example 1 (Production of polyacrylic polyol (4)) Stirrer,
15 parts of toluene, 10 parts of butyl acetate, and 0.2 parts of benzoyl peroxide were placed in a four-sided flask equipped with a thermometer and a reflux condenser, and heated to an internal temperature of 100°C. After 1 hour, 21 parts of methyl methacrylate, 10 parts of ethyl methacrylate, 15 parts of ethyl acrylate, 5 parts of isobutyl methacrylate, 8 parts of β-hydroxyethyl acrylate, 1 part of methacrylic acid, 15 parts of toluene and 0.5 part of azobisisobutylnitrile. A solution consisting of 2
The mixture was added over a period of time, and polymerized by maintaining the temperature at 100° C. for 6 hours to produce a polyacrylic polyol (4) having a nonvolatile content of 60%, a hydroxyl value of 34.7, and a number average molecular weight of 10,000.

Production Example 2 (Production of Polyacrylic Polyol 8) 10 parts of xylene, 5 parts of butyl acetate, and 0.3 parts of t-butyl perbenzoate were put into a four-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, and the internal temperature was It was heated to 120°C.

After 1 hour, a solution consisting of 18 parts of styrene, 21 parts of isobutyl methacrylate, 16 parts of ethyl methacrylate, 9 parts of β-hydroxyethyl methacrylate, 1 part of acrylic acid, 20 parts of xylene, and 1 part of azobimeisobutyronitrile was added for 2 hours. The mixture was further maintained at 120° C. for 6 hours for polymerization to produce a polyacrylic polyol (b) having a nonvolatile content of 65%, a hydroxyl value of 390, and a number average molecular weight of 6,000.

Production Example 3 (Production of polyester polyol (1)) 200 parts of isophthalic acid, 200 parts of phthalic acid, 237 parts of adipic acid, 365.3 parts of neopentyl glycol, and trimethylol were placed in a reaction vessel equipped with a stirrer, a thermometer, and a water separator. 124 parts of propane was added, and the temperature was raised to 180'C while stirring.

The temperature was raised from 180°C to 230°C at a nearly constant rate for 5 hours, and then maintained at 230°C.

Furthermore, 720 parts of Xical was gradually added, and the azeotropic condensation method was switched to. The acid value of the resin was economically monitored while the reaction temperature was maintained at 230°C, and the reaction was terminated when the acid value reached 4.0. The obtained polyester polyol (1) had a hydroxyl value of 54, a nonvolatile content of about 60%, and a number average molecular weight of 3000.
It was oil-free. Example 1 A coating film of an automotive electrodeposition primer and an intermediate coating of surfacer was created on a mild steel plate that had been subjected to degreasing and phosphate conversion treatment, and then a polyacrylic polyol consisting of the following formulation A was applied as the main component. The base coat was applied to a viscosity of 15 seconds using a diluted thinner consisting of 70% toluene, 15% butyl acetate and 15% ethyl acetate (food cup #4, 25°C).
The coating was adjusted to have a dry film thickness of approximately 20 μm.

Next, after leaving it at room temperature for about 5 minutes and confirming dryness by touch, a top coat paint made of polyacrylic polyol of the following formulation B adjusted to a viscosity of 30 seconds (Food cup #4/20°C) with xylol was applied as a base coat. Apply in the same manner so that the dry film thickness is approximately 30μ, and
After being left for 5 minutes, it was baked and dried at 100'C for 30 minutes, and then painted with silver metallic. The physical properties of the resulting coating film are shown in Table 1. <Formulation A (base coat)> Polyacrylic polyol (4)...Manufacturing example 11
00 parts Burnock DN-95020 parts (75% nonvolatile content)
, NCO content 12.5%; manufactured by Dainippon Ink Chemical Co., Ltd.) Aluminum Paste #1109MA 12 parts (manufactured by Toyo Aluminum Co., Ltd.) NCO/0H in top formulation A = 1/1 <Formulation B (top coat)> Polyacrylic polyol 8. ...Production example 260 parts Burnock 0DE-16023 parts (polyester polyol with oil length 26%, hydroxyl value 140, number average molecular weight 20
00, non-volatile content 70%; manufactured by Dainippon Ink Chemical Co., Ltd.) Burnock DN-9504 2.3 parts ω NCO/0H2 in formulation B 1/1 Example 2 A base coat paint of the following formulation C was prepared in the same manner as in Example 1. After coating in the same manner as in Example 1 using the top coat paint of formulation B used in Example 1, it was baked to give a silver metallic coating.

The physical properties of the resulting coating film are shown in Table 1. <Formulation C (base coat)> Polyester polyol (1)...Manufacturing example 3100 parts CAB (manufactured by Eastman Kodatsu)
Part 6 Burnock DN-95032 Part Aluminum Paste #
1109MA 15 parts NCO/0H-1/1 in formulation C Example 3 A base coat paint of formulation D below was applied in the same manner as in example 1, and then a top coat paint of formulation B used in example 1 was applied. The coating was applied in the same manner as in Example 1 and baked to give a silver metallic coating.

The physical properties of the resulting coating film are shown in Table 1〇〇Formulation D (base coat)〉Polyacrylic polyol (A) 10
0 parts CAB 6 parts Burnock DN-950 20 parts Aluminum paste #1109MA 12 parts (1) NCO/0H in formulation D = 1/1 Example 4 After applying the base coat paint according to the following formulation E in the same manner as in Example 1, A top coat paint of formulation B in Example 1 was applied in the same manner as in Example 1, and baked to give a silver metallic coating.

The physical properties of the resulting coating film are shown in Table 1. <Formulation E (base coat)> Polyacrylic polyol (A) 10
Part 0 Burnock DN-95020 Part First Genble CK Nippon Ink Kasei? feather) 15 parts titanium oxide
15 parts (1) NC at formulation E
O/0H = 1/1 Comparative Example 1 A base coat mainly composed of polyacrylic polyol of the following formulation F was coated with a diluted thinner consisting of 30% toluene, 35% xylene, 20% ethyl acetate, and 15% butyl cellosolve. and viscosity 15 seconds (Food Cup #4/20
℃), and the coating was applied so that the dry film thickness was about 20 μm.

Next, leave it at room temperature for 5 minutes and check that it is dry to the touch, then apply a top coat of the following formulation G with Swasol 1000.
(Aromatic solvent, manufactured by Etsuso Standard) with a viscosity of 30
Apply the same method as the base coat to a dry film thickness of about 30μ, leave it for about 15 minutes, and then bake it at 140'C for 30 minutes to create a silver metallic coating. I did the painting. The physical properties of the resulting coating film are shown in Table 1. <Formulation F (base coat)> Polyacrylic polyol (A) 100 parts Supervetsukamine L-117-6025 parts (butylated melamine resin; manufactured by Dainippon Ink Chemical Co., Ltd.) Aluminum paste 1109MA 13 parts <Formulation G (top coat)> Polyacrylic Polyol (B) 60 parts Betucosol EZ-3530 12.5 parts Super Betsukamine L-117-6027 parts Comparative Example 2 After applying the base coat paint of the following formulation H in the same manner as Comparative Example 1, A top coat paint was applied in the same manner as in Comparative Example 1, baked and dried to form a silver metallic coating.

The physical properties of the resulting coating film are shown in Table 1. <Formulation H (Base coat)> Polyester polyol (1) 100 parts Supervetsucomin L-117-6025 parts Aluminum paste 1109MA 13 parts Comparative example 3 After applying the base coat paint with the following formulation in the same manner as in Comparative example 1, Comparative example A top coat paint of formulation G of No. 1 was applied in the same manner as in Comparative Example 1, baked and dried to form a solid glass coating.

The physical properties of the resulting coating film are shown in Table 1. <Composition (base coat)>

Claims (1)

[Claims] 1. Apply a paint mainly composed of polyacrylic polyol or polyester polyol with a number average molecular weight of 2,000 to 12,000 and a non-yellowing isocyanate prepolymer, and then coat the coated surface with a polyacrylic polyol or a polyester polyol with a number average molecular weight of 2,000 to 8,000. Molecular weight 800-500
0 polyester polyol in a weight ratio of 99/1 to 1
After coating a paint mainly composed of a resin and a non-yellowing isocyanate prepolymer in a ratio of /99, when heating and curing, the isocyanate prepolymer has an OH/NCO ratio of OH/NCO of 1/99 to the hydroxyl group-containing resin. 0.5~1/
A coating method characterized by containing the content in an amount of 1.5 (equivalent ratio).