JPS5933032B2 - Metallic finishing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a metallic finishing method.

More specifically, the present invention relates to a two-coat one-bake metallic finishing method using a clear paint using a relatively low molecular weight hydroxyl group-containing acrylic resin and a high concentration, low viscosity non-aqueous dispersion type resin as a top coat. In the field of paints as well, there is an urgent need to reduce pollution and save resources by taking measures to regulate the use of solvents due to worsening air pollution, and by reflecting on the waste of resources.

One way to simultaneously solve these problems is to reduce the solvent content in the paint and increase the solid content. On the other hand, in recent years, the so-called one-coat metallic finish, in which a thermosetting paint containing metallic powder is applied and then baked as is, has been mainly used as a top coat for automobiles, and instead a thermosetting paint (base coat) containing metallic powder is being applied. However, a so-called two-coat, one-bake metallic finishing method in which a thermosetting clear paint containing no color pigments is then applied and a base coat and top coat are baked at the same time is becoming more common.

The advantage of this 2-coat, 1-bake method is that it has an excellent finished appearance, and it is less likely to cause stains, which were easily caused by the metallic powder being attacked by acid in the conventional 1-coat, 1-bake method. be. However, 2
In metallic finishes using the one-coat bake method, the resin properties of the base coat and top coat are usually quite different from each other in terms of ease of application, and the base coat contains metallic powder and the top coat is a clear coat. Because of its major feature of being a membrane, it
Problems with weather resistance that were not seen with the coat-and-bake metallic finish have been occurring. That is,
Outdoor exposure can cause cracks in the top coat or peeling of the top coat and base coat. When trying to increase the concentration of the top coat paint in a two-coat one-bake metallic finish,
It is important to achieve both extremely high weather resistance and high concentration, but this is not easy.

This is because in order to achieve a high concentration in the top coat, the resin used (especially the acrylic resin in aminoacrylic paints) must be made lower in molecular weight and softer, but this also affects the weather resistance of the top coat. This is because it leads to a decrease in We have been conducting extensive research on a two-coat, one-bake metallic finishing method that achieves both high top coat concentration and high weather resistance. Non-aqueous dispersion type thermosetting resin dispersions can have high molecular weight, high solid content concentration, and low viscosity. There is a problem with film forming properties. In addition, although there is no problem with the relationship between lower viscosity and film forming properties of amino-curing thermosetting acrylic resin solutions, there is a limit to lowering the molecular weight (lower viscosity) from the viewpoint of weather resistance. When used alone, there is a limit to the high concentration of the top coat in a two-coat, one-bake metallic finish. In our two-coat, one-bake metallic finish, we use a hydroxyl group-containing acrylic resin with a relatively low molecular weight and limited composition in the top coat in combination with a high concentration, low viscosity, non-aqueous dispersion type thermosetting resin. We have discovered that it is possible to achieve a two-coat, one-bake metallic finish using a top coat that has a high degree of weather resistance and a high solid content concentration.

That is, in the present invention, a paint (base coat) mainly composed of a thermosetting resin mixed with metallic powder and a colored pigment as necessary is applied, and then a coating mainly composed of a thermosetting resin is applied to the painted surface. In a metallic finishing method in which a clear paint (top coat) is applied and then heated and cured, the clear paint for the top coat has a number average molecular weight of about 2000 to 100 as a resin component.
00 solution-type thermosetting acrylic copolymer (B) aminoaldehyde resin and (0) high concentration and low viscosity non-aqueous dispersion-type thermosetting resin dispersion; The curable resin accounts for 20 to 45% by weight of the total resin,
The present invention also relates to a metallic finishing method, characterized in that the clear paint for top coat has a solid content concentration of 50% (wt%) or more at the time of coating.

Here, the high concentration and low viscosity non-aqueous dispersion type thermosetting resin dispersion of component (C) is defined as a low varnish viscosity D (cardner bubble viscosity, 25°C) or less at a solid content concentration of 60%. Refers to viscosity dispersion. Further, the main component in the resin component here is the solution type thermosetting acrylic copolymer, and the non-aqueous dispersion type thermosetting resin should be considered as an auxiliary component.

The role of the non-aqueous dispersion type thermosetting resin dispersion is to increase the solid content concentration of the top coat and improve its weather resistance.
The increase in solid content concentration can be easily inferred from the high concentration and low viscosity properties of nonaqueous dispersion type thermosetting resin dispersions, but the improvement in weather resistance is considered as follows.
In other words, it was confirmed by electron microscopy that a non-aqueous dispersion liquid with high concentration and low viscosity has a high particulate nature, and that it maintains its particulate nature even after it becomes a dry coating film. It is believed that the particles remaining in the paint film absorb the internal stress generated within the paint film due to exposure of the paint film, thereby exerting the effect of suppressing the occurrence of cracks. In the composition of the acrylic copolymer as component (4) used in the top coat of the present invention, components (A) and (b) include 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. .

Components (A) and (c) include 2-hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate. Additionally, adducts of monoepoxy compounds such as Cardiura E (Ciel Chemical Co., Ltd. product), AOEX24 (Daicel Co., Ltd. product), and butylene oxide with αβ monoethylenically unsaturated carboxylic acids are also used as components (A) and (c). Can be used. (A) (d) As a component (meta)
These include acrylic acid and itaconic acid. CA) (e) component is methyl (meth)acrylate, ethyl (meth)
Acrylate, n-butyl (meth)acrylate, i-
Examples include butyl (meth)acrylate, t-butyl (meth)acrylate, and cyclohexyl (meth)acrylate. In addition, this acrylic copolymer contains (A)(a)-{
In addition to component e), it is also possible to copolymerize a small amount (approximately 10% by weight or less) of 3 copolymerizable monomers in order to obtain a special effect. Such monomers include, for example, N-
Examples include methylol (meth)acrylamide, (meth)acrylamide, N-n-butoxymethylol (meth)acrylamide, (meth)acrylonitrile, N-N-dimethylacrylamide, vinyl acetate, vinyltoluene, and α-methylstyrene. As the aminoaldehyde resin used in the top coat of the present invention, all amino resins commonly used for paints can be used, but melamine formaldehyde resin is most preferred from the viewpoint of weather resistance.

As the film-forming polymer component of the zero-component non-aqueous dispersion type thermosetting resin used in the top coat of the present invention, acrylic polymers are preferred, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-
Butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, 2- Hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, N-n-butoxymethylol (meth)acrylamide, meth (acryl)amide, N-methylol (meth)acrylamide, N-N-dimethyl (meth)acrylamide, ( Copolymers of meth)acrylic acid, itaconic acid, glycidyl (meth)acrylate, etc. are used.

Furthermore, styrene, vinyltoluene, α-methylstyrene, vinyl acetate, (meth)acrylonitrile, and the like can also be used. Specific examples of dispersion stabilizers used in the production of these non-aqueous dispersions are as follows.

(1) Acrylic ester or methacrylate used to obtain a film-forming polymer from an addition reaction product of a self-condensed polyester of a fatty acid containing a hydroxyl group such as 12-hydroxystearic acid and glycidyl acrylate or glycidyl methacrylate. A graft polymer obtained by copolymerizing with an acid ester. (2) Thermosetting acrylic copolymer containing monomers with long chains such as octyl acrylate, lauryl acrylate, stearyl acrylate, octyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, and stearyl methacrylate. .

(To) After copolymerizing acrylic acid or methacrylic acid with a long chain alkyl ester of acrylic acid or methacrylic acid such as octyl acrylate, lauryl acrylate, stearyl acrylate, octyl methacrylate, lauryl methacrylate or stearyl methacrylate, The above acrylic monomer used to obtain the film-forming polymer is added to a polymer having a side chain double bond obtained by reacting the carboxyl group of the copolymer with glycidyl acrylate or glycidyl methacrylate. A graft polymer obtained by polymerization.

(4) Alkylated melamine polymer with high mineral split tolerance.

When synthesizing a non-aqueous dispersion, the dispersed particles may be polymerized in the presence of a dispersion stabilizer synthesized in advance in an organic liquid, or the dispersion stabilizer may be polymerized simultaneously with the polymerization of the dispersed particles. It's okay.

Generally, after dissolving a dispersion stabilizer in an organic liquid, polymerization is carried out by dropping the monomer solution and polymerization initiator used in obtaining the film-forming polymer into this solution.

At this time, the solid content concentration and viscosity can be freely changed by appropriately selecting the synthesis conditions. For example, even at a high solid content concentration of 50 to 60%, a dispersion with a low viscosity can be produced Can be easily synthesized.
The composition of the acrylic copolymer as component (5) used in the top coat of the present invention must be within the above-mentioned range.

If the amount of styrene in component (A) GIL) in the monomer components exceeds 30% by weight, the weather resistance will be significantly reduced and the object of the present invention will not be met. (5% by weight of (meth)acrylic acid ester having 8 to 24 carbon atoms of side chain alcohol as component A(5)
If it is less than 40%, the dispersion stability of the coating material when mixed with a non-aqueous dispersion liquid will be low, and if it is more than 40%, the weather resistance and coating hardness will be insufficient. (A) Content of hydroxyl group-containing acrylic polymerizable monomer in component (c): 10% by weight
If it is less than 45% by weight, the curability of the coating film will be insufficient, and if it is more than 45% by weight, the viscosity of the varnish will become too high, making it impossible to ensure a solid content concentration of 50% or more during coating. (A) (d) α of component
・If β-ethylenically unsaturated carboxylic acid is contained in an amount of 8% by weight or more, the viscosity of the varnish becomes too high, making it impossible to maintain a solid content concentration of 50% or more during coating, and the hardening of the coating film is too rapid, causing the coating film to deteriorate. It becomes brittle. Also d・β
When the monoethylenically unsaturated carboxylic acid content is reduced to O or very low, a curing acid catalyst is externally added as necessary. The acrylic copolymer resin (A) used in the top coat of the present invention must have a number average molecular weight in the range of about 2,000 to 10,000.

If the number average molecular weight is less than 2000, the weather resistance is not sufficient,
If it exceeds 10,000, the varnish will have a high viscosity and the solid content concentration during coating will decrease, making it impossible to achieve the objective of the present invention. The non-aqueous dispersion type thermosetting resin dispersion of component (c) used in the top coat of the present invention must be in the range of 20 to 45% by weight, preferably 25 to 40% by weight of the total resin. There is.

If it is less than 20% by weight, the effects aimed at by the present invention of improving weather resistance and increasing the solid content concentration during coating will not be sufficient, and if it is more than 45% by weight, the film forming properties of the coating will be insufficient or dust will be generated during coating. This tends to occur, adhere to painted surfaces, and cause paint defects.

Furthermore, although coloring pigments are not blended into the top coat, surface conditioners, anti-cissing agents, extender pigments, etc. can be added as necessary. The base coat used in the present invention may be any coating material whose main component is a resin that cures and crosslinks when heated, but acrylic thermosetting resins are most preferred from the viewpoint of ease of application and weather resistance.

Furthermore, although the base coat has a thermosetting resin as its main component, a resin that does not cure and crosslink, such as cellulose acetate butyrate resin, may also be used in combination. Furthermore, as the type of paint for the base coat, either a solution type paint using an organic solvent as a medium or a non-aqueous dispersion type paint can be used. Metallic powder mixed into base coat,
The color pigments added as necessary may be those used in conventional paints, such as aluminum powder, which is the most common metallic powder, copper powder, mica powder, and mica-like powder coated with titanium oxide. etc., and ordinary paint pigments can be used as coloring pigments. The metallic finish using the two-coat, one-bake method of the present invention is exactly the same as the conventional painting method that uses a solution-type paint or a dispersion-type paint whose main component is a relatively high-viscosity non-aqueous dispersion as the top coat. It is done.

That is, first the base coat is diluted with a diluent of 10 to 30%
After adjusting the viscosity to 20°C (foed cup +4/20°C) and applying it directly to a material (such as a steel plate or aluminum plate) or forming a primer coating, the dry coating film will be approximately 10 to
Paint it to a thickness of 30μ. The painting method is spray painting or electrostatic painting. Next, after leaving it at room temperature for several minutes, add a diluting solvent for 20 to 40 seconds (Food Cup◆4
/20°C) is applied by spray coating, electrostatic coating, etc. to a dry coating thickness of 20 to 50μ. Then, after being allowed to stand at room temperature for several minutes, the base coat and top coat are simultaneously cured by heating at 120 DEG to 160 DEG C. for 10 to 30 minutes to obtain the metallic finish desired by the present invention. Hereinafter, the present invention will be explained in more detail with reference to Examples.

All parts and percentages in the examples are by weight. 1. Production of acrylic resin solution for top coat (1)
Preparation of Acrylic Resin Solution A 40 parts of cellosolve acetate was charged into a normal acrylic resin reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, etc., heated and stirred, and when the temperature reached 135°C, the following monomer mixture was added to 3. Time After addition of the above monomer mixture, the reaction was continued at 135°C for 1 hour, and then a mixture consisting of 10 parts of cellosolve acetate and 0.6 parts of α-1-azobisisobutyronitrile was added for 1 hour and 30 minutes. Added.

After reacting for 2 hours, cellosolve acetate was distilled off under reduced pressure to adjust the resin concentration to 65%, thereby producing acrylic resin solution A. The number average molecular weight of the resin component of the acrylic resin solution A (measured by vapor pressure osmosis method) is 6100, and the viscosity of the acrylic resin solution A is Z2 (Cardner bubble viscosity,
25°C). (2) Production of acrylic resin solution B-H Acrylic resin solution B is prepared in the same manner as acrylic resin solution A.
-H was produced.

Table 1 shows the monomer composition, number average molecular weight, and varnish viscosity of each resin.
Shown below. 2. Production of nonaqueous dispersion type thermosetting resin dispersion A (for top coat) 126 parts of melamine, 412 parts of butyl formaldehyde (40%), 190 parts of n-butanol, and 36 parts of xylene were placed in a reaction vessel and heated. After reacting for 7 hours while separating the distilled water with a water separator, the system was depressurized and 100 parts of the distillate was removed, and then the hydrocarbon solvent Ciel Sol 140 (product of Ciel Sekiyu Co., Ltd.) was added. 50 parts, add 50 parts of n-heptane, and the resin content is 6
Melamine resin solution A with a varnish viscosity of 0% and a varnish viscosity of J (cardner bubble viscosity of 25° C.) was produced.

58 parts of the above melamine resin solution A, 30 parts of n-heptane,
0.15 part of benzoyl peroxide was charged into a reaction vessel, which was heated to 95°C, and the following monomer mixture was added dropwise over a period of 3 hours.

One hour after the completion of the dropwise addition of the monomer mixture, 0.65 parts of t-butyl peroctoate and 140 parts of Cielzol were added.
3.5 parts of the mixture was added dropwise over 1 hour.

Thereafter, the temperature was maintained at 95° C. for 30 minutes and stirring was continued for 2 hours. Thereafter, 34 parts of the solvent was removed under reduced pressure to obtain a non-aqueous dispersion type thermosetting resin dispersion A having a resin content of 60% and a varnish viscosity of A (cardner bubble viscosity). 3.
Production of acrylic resin solution 1 (for base coat) 35 parts of styrene, 20 parts of methyl methacrylate, 30 parts of ethyl acrylate, 21 parts of n-butyl methacrylate, 2
- 12 parts of hydroxyethyl methacrylate and 2 parts of acrylic acid were polymerized in xylene using a polymerization initiator α-l-azobisisobutyronitrile, and the resin content was 50%.
Acrylic resin solution 1 having a varnish viscosity of Z1 was obtained.

4. Production of nonaqueous dispersion type thermosetting resin dispersion B (for base coat) Poly-12-
Hydroxystearic acid and glycidyl methacrylate adduct 30%, styrene 10%, methyl methacrylate 2
0%, 2-ethylhexyl methacrylate 17%, 2-
Hydroxyethyl methacrylate 20%, acrylic acid 3
% copolymer and vinyl monomer (styrene 3 parts
0% methyl methacrylate, 23% 2-ethylhexyl acrylate, 15% 2-hydroxyethyl acrylate, and 2% acrylic acid) were dispersion polymerized in n-heptane in a conventional manner to obtain a resin. A non-aqueous dispersion type thermosetting resin dispersion B having a content of 54% was produced.

5. Preparation of base coat (1) Preparation of base coat A A solution type base coat was prepared using acrylic resin solution 1 with the following formulation.

Next, this base coat was adjusted to a viscosity of 14 seconds (foed cup Φ4/20°C) with a mixed solvent consisting of 40 parts of toluene, 30 parts of Swasol◆1000 (product of Maruzen Sekiyu Co., Ltd.), 20 parts of butyl acetate, and 10 parts of n-butanol. did.

(Support) Preparation of Base Coat B Base coat B was prepared using non-aqueous dispersion type thermosetting resin dispersion B with the following formulation.

Then, this base coat was coated with a mixed solvent consisting of 30 parts of the hydrocarbon solvent naphthesol Φ150 (product of Nisseki Chemical Co., Ltd.), 60 parts of cellosolve acetate, and 10 parts of carbitol acetate to a viscosity of 14 seconds (foed cup +4).
/20°C) to prepare base coat B.

6. Preparation of Top Coat (1) Preparation of Top Coat A Top Coat A was prepared using acrylic resin solution A and the following formulation by dispersion in a disk bar.

〉 Next, I made a top coat of Φ150.
35 parts, butyl cellosolve 35 parts, n-butanol 30 parts
The viscosity is 35 seconds with a mixed solvent consisting of
/20°C) to prepare a top coat A having a solid content concentration of 53%.

2) Preparation of Top Coat B-K Top Coat B-K was prepared in the same manner as Top Coat A.

Mixing and viscosity adjustment of each top coat (Food cup Φ4
Table 2 shows the solid content concentration after 35 seconds/20°C.

Example 1 A polybutadiene electrocoating paint was electrocoated on a 0.81 m thick dull steel plate that had been subjected to zinc phosphate chemical conversion treatment to a dry film thickness of about 20μ, and baked at 170°C for 20 minutes, and then ◆4
Sand with 00 sandpaper and wipe with petroleum benzene to degrease.

Next, dry the car intermediate coating Surf Acer for about 25 minutes.
After painting with air spray to give μ, baking at 140℃ for 30 minutes, sanding with +400 sandpaper,
Drain and dry. Then, it is degreased with petroleum benzine and used as a material for testing. On top of that, apply the aforementioned base coat A using an air spray gun (manufactured by Meiji Kikai Seisakusho, trade name F-5), leave it for 3 minutes at room temperature, and then apply top coat A with an air spray gun (manufactured by Meiji Kikai Seisakusho, trade name F-5). After painting using F-5), leave it for 10 minutes. Thereafter, it was heated and cured in an electric hot air dryer at 140° C. for 30 minutes to obtain a metallic finish with a dry specular reflectance of 60 and a good appearance of 93. This is designated as test coated plate &1. Examples 2 to 4, Comparative Examples 1 to 7 Test coated plate S was prepared in the same manner as the test coated plate black 1 of Example 1.
). 2 to black 11 were created.

Claims (1)

[Scope of Claims] 1. A paint (base coat) whose main component is a thermosetting resin containing metallic powder and, if necessary, a colored pigment.
In a metallic finishing method in which a clear paint (top coat) containing a thermosetting resin as a main component is applied to the painted surface and then cured by heating, the clear paint for the top coat has as a resin component, A (
a) Styrene 0 to 30% by weight (b) Acrylic acid having 8 to 24 carbon atoms as a side chain alcohol (
or methacrylic acid) ester 5 to 40% by weight (c) Hydroxyl group-containing acrylic polymerizable monomer 1
A number consisting of 0 to 45% by weight (d) 0 to 8% by weight of α/β-ethylenically unsaturated carboxylic acid and (e) the remaining amount of acrylic acid (or methacrylic acid) ester having 1 to 7 carbon atoms in the side chain alcohol A solution-type thermosetting acrylic copolymer having an average molecular weight of about 2,000 to 10,000. B consists of an aminoaldehyde resin and C a highly concentrated and low viscosity non-aqueous dispersion type thermosetting resin dispersion, of which the non-aqueous dispersion type thermosetting resin accounts for 20 to 45% by weight of the total resin,
and a metallic finishing method characterized in that the clear paint for top coat has a solid content concentration of 50% (weight %) or more at the time of coating.