JPH0280471A - Two-coat one-bake coating process - Google Patents

Abstract

PURPOSE:To make it possible to form a coating film of excellent finish by using specified acrylic resin-containing coating materials as the first and second coating materials in performing two-coat one-bake coating with an acryl/ melamine resin coating material. CONSTITUTION:This two-coat one-bake coating process comprises a first coating step of forming a first coating film by applying a first coating material of an acryl/melamine resin to the surface of a substrate, a second coating step of forming a second coating film by applying a second coating material comprising an acryl/melamine resin coating material of the same type as the first coating material to the surface of the first coating film by the wet-on-wet process and a baking step of integrally curing the first and second coating films by baking. In this process the first coating material is one containing an acrylic resin copolymerized with 10-50wt.% epsilon-carprolactone-modified vinyl monomer of formula I (wherein R is H or a methyl; and n is an integer <=5), and the second coating material is one containing an acrylic resin copolymerized with 5-30wt.% said modified monomer, and the value of n in formula I in the first coating material is larger than that in formula I in the second coating material by at least one.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention applies a paint to the surface of a workpiece in a wet-on-wet manner, and then bakes it to form a hardened paint film to improve the appearance of the finished product.
! Excellent FI (especially suppresses the appearance of armpits)!
The present invention relates to a coating method for forming a film. The coating method of the present invention includes:
It can be applied to objects to be painted for the purpose of imparting beauty and durability, such as automobiles, vehicles, industrial equipment, household electrical appliances, etc.

[Prior Art] In recent years, various two-coat, one-bake coating methods have been studied and implemented from the viewpoint of speeding up the rIi mounting line, saving resources, and saving energy. However, the two-coat, one-bake coating method has the problem that wrinkles tend to occur in the coating film due to fluctuations in temperature elevation conditions during setting and baking, and environmental conditions during coating.

It is believed that this oxidation is based on the use of low boiling point solvents, or that the scorching is due to the volatile products that sometimes form.

Therefore, in order to solve this problem,
Publication No. 028 discloses that an undercoat It (first paint) is used which contains volatile products that sometimes occur during baking and which is 17% by weight or less based on the solid weight of the paint. In other words,
In this method, in order to reduce the R1m of volatile products and suppress the formation of wrinkles, the amount of melamine resin that easily generates volatile products is reduced (or the amount of melamine resin that does not generate volatile products is reduced). Although isocyanate is used, it is still insufficient to increase the critical underarm thickness.

JP-A-55-129462 discloses undercoat FI (
There is a disclosure that the first coat of rice (IIIJ#) is formulated with an acrylic resin having a hydroxyl group and a blocked isocyanate to suppress the occurrence of wrinkles. However, in this case, the blocked part of the dissociated isocyanate does not necessarily evaporate. This blocked isocyanate has the problem of adversely affecting the coating film because it remains in the coating film without any properties, and this blocked isocyanate is more expensive than melamine resin.

JP-A No. 55-115465 discloses a compound having a glycidyl group and a carboxyl group in its side chain, and a glass transition temperature of 20 to 20.
-40℃ undercoat tan whose main component is acrylic resin
There is a disclosure that the occurrence of armpits is prevented using <first coating Fl). However, the reaction between an epoxy group and a carboxyl group is relatively slow and has the problem II'1, which requires high-temperature baking or long-time baking.

JP-A-56-24074 discloses that in a metallic coating method, the SP value (solubility parameter) of the resin of the undercoat colored metallic liquid paint (first paint) is the same as that of the resin of the topcoat transparent powder paint (second paint). There is a disclosure that uses a paint with a higher SP value to prevent the occurrence of armpits. However, although this method sufficiently improves the metallic feel of the coating film, it is not sufficient to prevent the occurrence of wrinkles.

[Problem to be Solved by the Invention 1] The present invention provides two coats of acrylic-melamine resin paint.
In order to suppress the occurrence of wrinkles in the bake coating method, an ε-caprolactone-modified vinyl monomer is used as the acrylic-melamine resin copolymerization monomer used in the first coating film and the second coating film. Therefore, one technical issue is to suppress the wrinkles that occur when baking the paint film.

[Means for Solving the Problems] The two-coat, one-bake coating method of the present invention comprises applying a first acrylic-melamine resin-based paint onto the surface of the object to be coated.
A second paint film is formed by using a first painter rod to form a paint film and applying a second paint made of an acrylic-melamine resin paint similar to the first paint film on the surface of the first paint film in a wet-on-wet manner. In the two-coat one-base painting method, the first paint includes a second coating step to form a coating film, and a baking step to integrally cure the first coating film and the second coating film. The second paint contains an acrylic resin containing 10 to 50% of ε-caprolactone modified vinyl U4ω substance represented by the following general formula, and the second paint contains 5 to 30% of ε-caprolactone modified vinyl monomer represented by the following general formula.
ffi ffi, the first paint contains an acrylic resin containing 5%, and the difference in n in the general formula is 1 or more larger in the first paint than in the second paint.

- Deceased % Formula % (However, in the formula, R represents hydrogen or a methyl group, and n does not represent an integer of 5 or less.

The acrylic resin used in this acrylic-melamine resin paint is a resin whose main component is acrylic ester or methacrylic ester.
l-n-butyl, ε-caprolactone modified vinyl LJt
It is a combination of t-form, styrene, etc. The most important feature of the present invention is that the first paint contains an ε-caprolactone-modified pinyl t11131 substance having a higher n than that used in the second paint.

By making n of the ε-caprolactone-modified vinyl single substance represented by the general formula in the first paint higher than that in the second paint, the amount of water l in the side chain of the acrylic resin is increased! The reactivity of the first coating increases, and the first coating cures faster than the second coating, and the volatile substances that cause wrinkles are quickly dispersed, and baking occurs only in the latter half of the process. The appearance of armpits due to the exudation of volatile substances is greatly suppressed. Difference between the above n △n
The larger is preferable because the first coating film is cured more quickly, but it is sufficient if the difference in n is Δn≧1.

ε-notuprolactone-modified vinyl content When the difference in n in the acrylic resin copolymerized with ε-notuprolactone is 1 or more, the methylene chain having a hydroxyl group at the end can extend well outward from the main chain and be flexible. This is thought to be due to increased stability and increased reactivity with melamine resin.

Further, it is preferable that n of the single ε-caprolactone modified vinyl is 5 or less in terms of handling of the monomer.

In this coating method, first, in a first coating step, a first coating film is formed from a first paint on the surface of the object by air spraying, airless spraying, or electrostatic coating. The object to be coated is not particularly limited, such as a steel plate directly or a steel plate coated with an undercoat film such as a mW coating film.

In the second coating step, the second to fourth films are formed on the surface of the first coating film by wet-on-wet, for example, air spray, airless spray, or electrostatic coating.

The baking process involves combining the first coating film and the second coating film formed by wet-A-wet coating into an integral cured coating film.
This is a process of heating and drying in order to In addition, the first
It is preferable to apply the paint to a film thickness of 15 to 25 μm, and the second paint has a film thickness of 20 to 40 μm.
It is preferable to apply the coating to the range of 1 to suppress the occurrence of wrinkles.

[Operations and Effects of the Invention] In the two-coat, one-bake coating method of the present invention, n of the ε-caprolactone-modified vinyl single substance represented by -deceased used in the first paint and the second paint is The curing reactivity of the first coating film is made larger than that of the second coating material. Since there is a water M group extending outward from the main part of the acrylic resin in the overall structure, the reactivity with the melamine resin increases.On the other hand, in the second paint, the caprolactone part extending outward is the first paint. Because it is shorter, the curing of the coating due to the reaction with the melamine resin is delayed.Therefore, it is necessary to release volatile substances formed during the curing of the first coating to the outside of the coating before the second coating is cured. It is possible to improve the underarm thickness of the coating film.

[Example 1 Hereinafter, this will be explained in detail using examples.

[Test Example 1] Production of acrylic resin varnish.
1 part by weight of n-butyl alcohol, 20 parts by weight of n-butyl alcohol, and 30 parts by weight of isobutyl alcohol were charged into reaction 1f'l, and the temperature was raised to 105° C. with stirring under a nitrogen gas atmosphere.

Next, 1.2 parts of the initiator 2,2'-azobisisobutyronitrile was mixed and dissolved in a 100-layer hanging part of the mixture having the composition shown in Table 1, and 2 parts of the mixture was added at a uniform speed.
After stirring for another hour at the same temperature, 0.6 parts by weight of the initiator 2,2-azobisisobutyronitrile was added at 10 minute intervals.
It was added in 4φ portions over 4 hours. 105℃ for another hour
After stirring was continued at a constant temperature, the mixture was cooled. (The removed resin liquid A is an acrylic resin varnish with a solid content of 50%. TO<glass transition temperature) 19°C, acid value 15.6, water 1111
The base price was 35.7.

In addition, Plaxel FM-3 in Table 1 is a single ε-caprolactone modified vinyl represented by -deceased, where R is a methyl group and n is 3 (under the trade name of Daicel Chemical Industries @ J%l). be). Plaxel FM-1 is an ε-caprolactone-modified vinyl monocamellia in which R is a methyl group and n is 1 (it is a trade name manufactured by Daicel Chemical Industries t4@).

In a similar manner, acrylic resin varnishes B1C and D were prepared with the seven-layer compositions shown in Table 1. Table 1 shows the characteristic values of the obtained resin. The resin liquid was prepared without copolymerizing the ω form in ε-caprolactone modified vinyl represented by the general formula.

Coating composition 1 each of the above acrylic resin varnishes A, B, C, and D
00111 parts, 20 parts by weight of Kneepan 20SE-60 (manufactured by Mitsui Toatsu Chemical ■, melamine tree gB) and 4 parts by weight of xylene were mixed to prepare a stock solution with a non-volatile content of 50% by weight. 1-luene/xylene/S-1000 (
Maruzen Petrochemical Co., Ltd. Surface product name) / Ibusol-150 (
Idemitsu Petrochemical ■Socket product name) = 30/10/40/20)
27 seconds (Ford Cup N0.4 20
℃) to give paints ■, ■, ■, and IV.

Table 2 shows the composition of the paint.

Evaluation of paint Paint ■ is applied as the first coat onto a mild steel plate (100 x 25 x 1.6 mm) uniformly to a film thickness of 20 to 25 μm, and after a flash time of 30 seconds, paint ■ is applied as the second coat. The total film thickness is 50~9o! Five coated plates were coated at intervals of 10 μm up to in+, and after a setting time of 3 minutes, they were heated to 140℃ in a circulating drying oven for 30 minutes.
A cured coating was formed by baking for a minute.

Regarding the five coated plates on which coating films with different thicknesses were formed, the occurrence of wrinkles was visually observed.

The results are shown in Example 1 in Table 3. In addition, the first paint and the second
Examples 2 to 3 and Comparative Examples 1 to 3 in Table 3 show the results of coating and baking the same combinations of paints as shown in Table 3 in the same manner as above.

Paint (first paint) Get ε-force prolactone modified vinyl represented by the general formula n in the monomer m is 3, and the paints ■, 田, ■ are ε-force prolactone modified expressed by the general formula n in vinyl monotony is 1. Therefore, in Examples 1 to 3, there are two differences in n in the ε-Cab O lactone modified vinyl monomer represented by the general formula, and g!
No wrinkles were observed even in thick films with a thickness of 90 μ≠ or more.

Δ Slight occurrence of armpits × Occurrence of entire armpits (blank below) On the other hand, in Comparative Example 1, a paint in which n is 3 in the ε-caprolactone modified vinyl 01 fJ% body expressed by the general formula was used as the first paint and the second paint. It is layered and has a film thickness of 60mm.
Armpits up to μ width are not allowed. However, the film thickness is 60-8
At 0 μm, armpits were slightly observed, and P! Thickness is 80μm
In the above case, armpits were appearing all over the body. In Comparative Example 2, the first coating material and the second coating material (■) of Example 2 are reversed, and the second coating material has n of 3 in the ε-caprolactone modified vinyl ttlffi body represented by the general formula. In the ε-caprolactone modified vinyl element represented by the general formula of the first paint, n is 1 and t is -2, and the second paint cures faster, so no anti-scratching effect was observed. all 1i
I had armpits due to lu. Comparative Example 3 did not contain the copolymerizable polymer shown in the general formula of the present invention, but instead contained acrylic acid.
This is an example of applying an acrylic-melamine resin paint using 2-human[1-xyethyl], and no wrinkles occur up to a coating thickness of 60 μl, but slight wrinkles occur at 60 to 70 μm, and the thickness exceeds 70 μm. I developed armpits all over my body. Therefore, the difference between the ε-caprolactone-modified vinyl simple substance n expressed by the general formula of the first paint and the ε-caprolactone-modified vinyl substance n expressed by the general formula of the second paint is 1
When using the first paint having a larger thickness than the above, it was possible to increase the critical underarm film thickness.

[Test Example 21 Monomer composition of acrylic resin A: A skewer of 2.2”-azobisisobutyronitrile as an initiator was added to a 100-layer suspended portion of acrylic resin A.
Acrylic resin E was produced by polymerizing in the same manner as in Test Example 1 except that the amount was 5 parts by weight.

Next, 20 parts of Kneepan 208E60 was added to the acrylic resin E100 hand part, and hirulose acetate butyrate resin (CAB55 manufactured by Eastman Kodak Company) was added.
1-0.2) 10-fold opening, Alpaste 779ON (
Toyo Aluminum @ J Aluminum Powder) 10-fold opening was blended, and the viscosity was adjusted to 15 seconds using a mixed solvent of ethyl acetate/toluene/Ibusol 150 (Idemitsu Petrochemical System) = 75/15/10 (Ford Cup). No. 4 (20°C) to prepare metallic paint V.

5PC-D steel plate with coating J3 and evaluation zinc phosphate treatment (0°8 x 10
Apply the metallic paint V on the 0100x300 cationic electrodeposited film using a spray gun at 25-27°C.
The film was coated at a relative humidity of 60% to give a dry film thickness of 20 μ-.

After flashing this product at 25℃ for 2 minutes, apply the second paint! Paint work as clear paint for head coat,■,■
, IV was applied to one coated plate continuously while changing the film thickness, and after setting for 3 minutes, the plate was held in a heat-pressure circulation type drying oven at 150°C and baked for 30 minutes. (The lowest film thickness at the location where the wrinkles occurred was evaluated as the critical coat thickness for the coated plates. The results are shown in Table 4.

(Hereinafter in the margin) (Hereinafter in the margin) Since the test conditions are different from Test Example 1, the occurrence level of W4: (
However, in Comparative Example 4 where the first paint and the second paint have almost the same reaction rate, the average underarm critical film thickness is 52.
．． In Examples 4 to 6, in which the reactivity of the second paint was slowed down, the average underarm critical film thickness 1+ff was 77.
7.72.0.71.7 and Comparative Example 4, 20 to 25 μm
It's improving. Therefore, even if J5 is used as a metallic material, it has 21+ Song, which reduces the appearance of armpits by 1ftl Ll+.

Patent applicant Agent: A Ishin Kako Co., Ltd.
Patent attorney Hiroshi Okawa

Claims (1)

[Claims] (1) A first painting step of applying a first acrylic-melamine resin paint onto the surface of the object to be coated to form a first coating film, and an acrylic-melamine resin paint of the same type as the first paint. Wet-on-a second paint is applied onto the surface of the first paint film.
A two-coat, one-bake type painting method comprising: a second coating step of wet painting to form a second coating film; and a baking step of baking the first coating film and the second coating film and curing them integrally. In, the first paint contains an acrylic resin copolymerized with 10 to 50% by weight of an ε-caprolactone modified vinyl monomer represented by the following general formula, and the second paint contains an acrylic resin copolymerized with an ε-caprolactone modified vinyl monomer represented by the following general formula. The first paint contains an acrylic resin copolymerized with 5 to 30% by weight of the ε-caprolactone-modified vinyl monomer represented by A 2-coat, 1-bake type painting method characterized by using a paint. General formula CH=C(R)COOC_2H_4O(CO-(CH_
2)_5O)nH In the formula, R represents hydrogen or a methyl group, and n represents an integer of 5 or less.