JPS60251973A - Formation of dual-layer film - Google Patents

Abstract

PURPOSE:To attain to enhance appearance, by forming a formula TIc-TIb>=0 between the curing start time TIc of a top coat alone and the curing time TIb of a base coat alone. CONSTITUTION:A base coat such as an acrylic/melamine paint or an acrylic/cellulose acetate butyrate/melamine paint is applied to the surface of a substrate. Subsequently, the coated one is allowed to stand at ambient temp. or heated if necessary and, thereafter, a top clear color is applied to the substrate and the whole is set or preheated if necessary and baked to simultaneously cure both base and top coats. As the curing agent for adjusting a curing start time, polyisocyanate and aminoplast are used and additives such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid or dinonylnaphthalenedisulfonic acid are used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a multilayer coating film using a two-coat one-bake method, which is used, for example, for painting the surface of an automobile body.

Conventionally, for example, in the top coating of an automobile body, a base coat containing a metallic pigment and/or a colored pigment is applied, followed by a clear top coat using a wet-on-wet method, and then the entire coating film is coated using a wet-on-wet method. hardened at the same time 2
A method of forming a multilayer coating film of one coat is widely used. This method provides a high-quality coating film with excellent finished appearance, high durability, high solvent resistance, high chemical resistance, and high durability.

Conventionally, in this two-coat, one-hake coating system, various proposals have been made to improve the finished appearance, and these have been implemented on the line. These are methods for preventing mixing of the base coat and top clear coat when applied wet-on-wet. Specifically, in order to reduce the compatibility or mutual solubility between the two, cellulose acetate butyrate is added to the base coat. These methods include methods such as mixing the base coat with chlorine, preheating the base coat to a non-volatile content above a certain level, and then applying a clear knob coat, and increasing the solubility parameters of the base coat and top coat above a certain range.

However, until now, there has been no study on the basic characteristics that the multilayer coating film should have in order to obtain an excellent finished appearance. In other words, if two types of coatings exist as a multilayer coating, unless they melt together and become uniform,
It is easy to understand that they have different curing reactions during baking. Therefore, there are natural differences between the two, such as curing start time, curing reaction rate, viscosity increase rate during baking, solvent evaporation rate, strain state due to curing shrinkage, etc., and as a result, the finished appearance of the entire multilayer coating film is affected. That is clear.

In particular, efforts have recently been made to improve the finished appearance by thickening the clear top coat, but a system that does not take into account the differences in the curing process between the base coat and top clear coat cannot expect to significantly improve the finished appearance. Will.

This invention involves applying a thermosetting resin paint containing metallic pigments and/or colored pigments as a base coat to the surface of the object to be coated, and then thermosetting the base coat using a wet-on-wet method. The present invention relates to a method for forming a composite coating film using a two-coat one-hake method, which comprises applying a transparent resin paint as a top coat and then heating and curing the entire coating film. A feature of the present invention is that under actual heat curing temperature conditions, a relationship such as Tlc-Tlb≧0 is established between the curing start time TIb of the base coat alone and the curing start time Tlc of the top coat alone. The purpose is to adjust the curing start times of the base coat and the top coat in advance so as to achieve the desired results. As a result, when formed into a multilayer coating, a high-finish appearance with smooth skin can be obtained.

On the other hand, when Tlc - Tlb < 0, the curing reaction of the top coat starts before the curing of the base coat starts, and shrinkage strain occurs. At this time, the base coat has not yet reacted sufficiently and is dragged by the shrinkage strain of the top coat, resulting in poor smoothness of the multilayer coating as a whole.

The curing start time can be adjusted by using curing agents and additives. Curing agents include polyvalent isocyanates, aminoplasts, and the like.

Amino blasts include urea, thiourea, melamine,
Condensates of henzoguanamine etc. and formaldehyde,
It includes lower alkyl (C1-C4) etherified products of these condensations. Particularly preferred is a melamine/formaldehyde condensate in which part or all of the methylol groups are etherified with butanol.

Adjustment of the curing start time using additives is performed by adding a curing accelerating catalyst or a curing retarder.

For example, polyol and lower alkyl etherified melamine/
In the case of formaldehyde condensates, sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, and mixtures thereof, and alkyl acid bosphates can be used to accelerate curing. If these curing accelerators are used in too large a quantity, they will impair the water resistance of the paint film, so if the solid content of the paint is 10
It should be less than 5 parts by weight per 0 parts by weight. Further, as the retarder used in this system, amines that do not volatilize during coating but volatilize during baking hardening are preferable. Examples include diethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, isobutylamine, diisobutylamine, cyclohexylamine, monoethanolamine, diethylethanolamine, and the like. If the amount added is too large, the necessary curing will not be obtained, so the amount should generally be 5 parts by weight or less per 100 parts by weight of the solid content of the paint.

As the polyol/polyvalent isocyanate-based curing accelerator, the above acids and/or amines can be used. Amine salts and ammonium salts are also good additives.

Measurement of hardening start time is as per Naganuma et al., 29.
゜519 (1972) and Izumo et al. Carp, 54 (1
0), 593-598 (1981) DSA method (D
dynamic Spring Ana-Iysis)
This was done by dynamic viscoelasticity measurements.

That is, a copper wire with a head diameter of 0.35 and an inner diameter of 2. A Q-Ryu spring with 20 turns was prepared and used as a sample support.

Approximately 0.01 g of the paint was uniformly applied to the support, dried under reduced pressure, and then subjected to measurement. The actual curing process of a paint film involves the presence of a solvent, but in that case, it is sufficient to use a sample of paint whose non-volatile content is the same as that of the paint film immediately before it is placed in a baking oven after painting. In this case, a sample with a nonvolatile content of approximately 100% was prepared, and the curing start time was used as a representative sample.

For dynamic viscoelasticity measurement, a forced stretching vibration type dynamic viscoelasticity measuring device (Hybron DDv-II type; Toyo Baldwin 0
1), and the frequency was set at -1111z and the temperature was kept constant. The time point when the sample was quickly mounted is To, the relative elastic modulus is measured over time, and the relative elastic modulus is plotted on the vertical axis and time on the horizontal axis, and the relative elastic modulus rises rapidly and increases linearly. The intersection point between the extension line of the straight part during the process and the horizontal axis was determined as the curing start time TI.

The accompanying drawing is a graphical model representing the relative modulus change over time for a coat and a topcoat with the relationship Tlc - Tlb > 0.

The present invention includes a method of forming a multilayer coating using a metallic coat and a solid color coat as base coats.

The paint for the base coat may be any commonly used paint, such as acrylic/melamine paint.

Preferred are acrylic/cellulose acetate butyrate/melamine paints, polyester/cellulose acetate butyrate/melamine paints, and acrylic/polyvalent isocyanate paints. In addition to regular inorganic and organic pigments, the pigments contained in base coat paints include kaolin,
It may contain fillers and spreading agents such as talc. Metal flake pigments are also used for metallic finishes.

The base coat paint may contain other commonly used additives, if desired. Examples include cross-linked polymer particles (microgels) that are insoluble in and stably dispersed in the paint system, viscosity modifiers such as organic montmorillonite polyamides and polyethylene, and surfaces such as silicone and organic polymers. Conditioners, ultraviolet absorbers, hindered amines, hindered phenols, etc.

As the clear top coat paint, any commonly used paint may be used, and acrylic/melamine-based and acrylic/polyvalent isocyanate-based curable paints are preferred. Further, the clear top coat paint may contain additives for the same purpose as the base coat paint, if desired, except that it does not contain pigments.

1- Set the curing start time Tic of the knob coat alone to 0.8 minutes to 10 minutes, and set the curing start time TI of the base coat alone
It is preferable that b be 0.5 minutes to 5 minutes and the time difference between them be 0.3 minutes to 5 minutes.

In the process of the present invention, a basecoat composition is applied to the surface of a previously primed or conventionally treated substrate. As for the painting method, conventional air spray painting or electrostatic painting is preferable. For substrates, metals such as iron, aluminum, and copper commonly used in automobile manufacturing, but also materials such as ceramics and plasti-nox, can withstand the temperatures that final cure these multilayer coatings. may be used as long as possible. After applying the base coat, you can leave it at room temperature or heat it if necessary (then apply the top clear coat wet-on-wet, set it or preheat as necessary, and then cure it at room temperature or heat it as needed). By performing baking at a high temperature and simultaneously curing the base coat and clear top coat, a multilayer film with a high finished appearance can be formed.

In addition, the thickness of the Heathcoat film is 10 to 30μ,
The thickness of the top clear coat film is 20~70μ (
(dry film thickness) is preferable in both cases.

Examples of the present invention are shown below, and "parts" and "%" in the examples are based on weight unless otherwise specified.

1.11 fat 1" 1 1d [Example 1-1 80 parts of xylene and 10 parts of methyl isobutyl ketone were charged into a container equipped with a stirrer, a temperature control device, and a reflux condenser. Next, a solution of the following composition: methacrylic acid 1.8 parts Methyl methacrylate 39.4 Ethyl acrylate 43.6 Isobutyl methacrylate 3.2 2-Hydroxyethyl acrylate 12.0 Azobisisobutyronitrile 1. Add 20 parts of 5.
Heat with stirring to increase temperature. While refluxing, the remaining 81.5 parts of the above mixed solution was added dropwise over a period of 3 hours, and then a solution consisting of 0.3 parts of azobisisobutyronitrile and 10 parts of quidylol was added dropwise over a period of 30 minutes. After the reaction solution was further stirred and refluxed for 2 hours to increase the conversion rate to resin, the reaction was terminated and the non-volatile content was 50% and the number average molecular weight was 1.
8.000 acrylic resin varnish was obtained.

Using the same equipment as Production Example 1-1, 55 parts of xylene,
Charge 7 parts of methyl isobutyl ketone, then make a solution of styrene with the following composition: 5.0 parts Ethyl acrylate 8.1 Isobutyl methacrylate 61.0 Ethylhexyl acrylate 8.4 2-Hydroxyethyl methacrylate 15.0 Methacrylic 2.5 parts of acid and 4.0 parts of azobisisobutyronitrile were added to the container, and heated while stirring to raise the temperature. While refluxing, the remaining 84 parts of the above mixed solution were added dropwise over 2 hours, and then a solution consisting of 0.3 parts of azobisisobutyronitrile, 35 parts of xylene, and 3 parts of methyl isobutyl ketone was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the conversion rate to resin, and then the reaction was terminated to obtain an acrylic resin varnish with a nonvolatile content of 50% and a number average molecular weight of 3,500.

70 parts of xylene, n using the same equipment as Production Example 1-1.
- Charge 20 parts of butanol, then prepare a solution with the following composition: methacrylic acid 1.2 parts styrene 26.4 methyl methacrylate 26.4 n-butyl acrylate 36.0 2-hydroxyethyl acrylate 10. 20 parts of 1.0 O thiazosisobutyronitrile was added and heated while stirring to raise the temperature. While refluxing, the remaining 81.0 parts of the above mixed solution was added dropwise over 2 hours, and then 0.3 parts of azobisisobutyronitrile and 10 parts of xylene were added.
of the solution was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to complete the reaction, and the nonvolatile content was reduced to 50%.
An acrylic resin varnish having a number average molecular weight of 8.000 was obtained.

57 parts of xylene, n
- Charge 6 parts of butanol, then add a solution of the following composition: styrene 30.0 parts ethylhexyl methacrylate 1.4s, 2g ethylhexyl acrylate 1-5, s part 2-hydroxyethyl methacrylate 16.2 parts methacrylic acid 3.
20 parts out of 1 part and 4.0 parts of azobisisobutyronitrile were added and heated while stirring to raise the temperature. The remaining 84 parts of the above mixed solution were added dropwise over 2 hours while refluxing, and then 0.5 parts of abbisisobutyronitrile and 2 parts of xylene were added.
A solution consisting of 3 parts and 14 parts of n-butanol was added dropwise over 20 minutes.

The reaction solution was further stirred and refluxed for 2 hours to complete the reaction,
An acrylic resin varnish with a nonvolatile content of 50% and a number average molecular weight of 3,400 was obtained.

``Manufacturing Overview'' The following raw materials were charged into a container equipped with a stirrer, a temperature control device, and a decanter, and heated while stirring.

Ethylene glycol 39 parts Neopentyl glycol 130/l Azelaic acid 2361t Phthalic anhydride 186 parts . Thereafter, the temperature was cooled to 140° C., 314 parts of Cardura E-10 (epoxy resin, manufactured by Shell Co., Ltd.) was added, and stirring was continued for 2 hours to complete the reaction.

The resulting resin had an acid value of 9, a hydroxyl value of 90, and a number average molecular weight of 1,050. This resin was diluted with xylene to a non-volatile content of 60% to obtain a polyester resin varnish having a Gardner viscosity of Y.

Using the same equipment as in Manufacturing Example 1-1, 80 parts of xylene and 10 parts of methyl isobutyl ketone were charged, and then a solution having the following composition: 2.0 parts of 2-sulfoethyl methacrylate, 0.0 parts of meccrylic acid. 8 parts Methyl methacrylate 39.0 parts Ethyl acrylate 43.0 parts Isobutyl methacrylate 3.2 parts 2-Hydroxyethyl acrylate 12.0 parts Azobisisobutyronitrile 30 parts of 1.5 parts were added and stirred. While heating, the temperature was increased. While refluxing, the remaining 71.5 parts of the above mixed solution was added dropwise over 3 hours.
Next, a solution consisting of 0.8 parts of azobisisobutyronitrile and 10 parts of quidylole was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the conversion rate to resin, and then the reaction was terminated to obtain an acrylic resin varnish with a nonvolatile content of 50% and a number average molecular weight of 16,000.

■, Heathcote ゛ ''' 1 base 1 11-1. Acrylic Paint I Ink Paste: Materials having the following composition were weighed into a stainless steel container and stirred using a laboratory stirrer to prepare a paint.

Varnish of Production Example I-1 100 parts Modaflow (manufactured by Mitsubishi Monsando) 0.3 parts ■-2
, 7 Rilmetal■・Kuhes.

A coating material was prepared in the same manner as in Production Example n-1.

Varnish of Production Example 1-1 ioo part aluminum aluminum paste 1109A 13 parts Modaflow 0
．． Part 3 ■-3, Mej.Kbase S A paint was prepared in the same manner as in Production Example n-1.

Varnish of Production Example 1-2 100 parts Yuhan 205E-60 (melamine resin manufactured by Mitsui Toatsu Co., Ltd.,
Non-volatile content = 60%) 21 parts aluminum paste 1109
To M 13 parts G-soap #103 (manufactured by Shiraishi Calcium Co., Ltd.) 1 part Production example 1-5 100 parts of polyester varnish 100 parts Acid Lunatan R-5N (manufactured by Sakai Kagaku Co., Ltd.) 90 parts Weigh 90 parts into a dispersion container and apply paint conditioner. Further, 32 parts of Cymel 370 (melamine resin manufactured by Mitsui Toatsu Co., Ltd., non-volatile content -80%), 32 parts of para-toluenesulfonic acid, 0
．． Adjusted by adding 1 part 0.591'.

■-5, Hesco Ac 1 Ruso 1 Sodo Blue Rhyme I [In the same way as -4 II -5-I II -
5-2 Production Example 1-2 Varnish 100 parts 100 parts Titanium oxide R-82040 parts 40 parts Dibutylsilaurylate 0.1 part■-6. Heath Coat Silver Metallic' Production Example 1
The paint was prepared in the same manner as in 1-1.

Varnish of Production Examples I to 6 100 parts Kneepan 128 (melamine resin manufactured by Mitsui Toatsu Co., Ltd.) 21 parts Aluminum paste 51-231 13 parts (manufactured by Toyo Aluminum Co., Ltd.) Modaflow 0.6 parts 1- Materials having the following composition were weighed into a stainless steel container and stirred using an experimental stirrer to prepare paints for each production example.

ff-1 Varnish of Production Example 1-3 100 parts Kneepan 125 36 parts Modaflow 0.15 part I [1-2 Varnish of Production Example 1-3 100 parts Super Beckamine 14-559 36 parts Modaflow
0.1 part 1 [1-3 Varnish of Production Example 1-4 100 parts Kneepan 205E-6036 parts Tributylamine 1 part-4 Ill -4-2III -4-2 Varnish of Production Example I-4 100 parts ioo parts Size Suru 3
70 28 parts 28 parts para-toluenesulfonic acid 1. o Part o, 1 part Torre Silico: / 5H-290, 1 part 0.1 part Tinubi: /
900 0.5 part 0.5 part (manufactured by Ciba Geigy) Su/-Ls-292' 0.5 part 0.5 part (manufactured by Ciba Geigy) ■-5 III -5-I III-5-2 Production example I-3 varnish 10 (1 part 100 parts Desmodur N-7517 parts 17 parts Dibutyltin laurylate 0.1 part - Modaflow 0.5 part 0.5 part IV, [15 议 - Materials book"" Group JI The measurement sample for the IHυ 11σ curing start time was prepared by uniformly applying the paint of each production example to the spring and drying it at room temperature under reduced pressure to remove the non-volatile content.
The one adjusted to 100% was used. The finished appearance was evaluated by creating a multilayer coating film in the following manner.

First, among the manufacturing examples of each paint, the paint for hair coat was diluted with the following mixed solvent (hereinafter referred to as hair thinner) cellosolve acetate 50, butyl acetate 30, xylene 20 in a positive 4 Ford cup for 15 seconds at 20°C. It was adjusted.

In addition, the clear paint of each manufacturing example was mixed with the following mixed solvent (hereinafter referred to as top clear thinner) xylene 50 Swasol 1000 (First Arrival Petroleum) 50, No.
Dilution was adjusted to 25 seconds/20°C using 4 food cups.

Then, the solvent-degreased tin plate was held horizontally, and each Hose paint was applied with a wider 71 (
A dry film was applied in one coat to a thickness of 15 μm using an air cup gun (manufactured by Iwata Co., Ltd.), and then left at room temperature for 3 minutes to form a heath film. Next, the combinations of the diluted 1 to knob clear paints of each example were applied in one coat using Wider 71 by wet-on-wet on the Heath film. The clear film was dried and set to 35μ. Next, the mixture was left at room temperature for 10 minutes and then baked in a dryer at 140°C or 100°C for 30 minutes to obtain a multilayer film.

Coating Production Example The curing start time of paint n-1 for hair coat and 1-1 for clear coat was measured at 140°C, and the results are shown in the table.

Furthermore, as a result of creating a multi-layer coating film, the reaction of the coating film proceeded too quickly, resulting in shrinkage distortion, poor skin quality, and poor finished appearance.

Practical Survey-V Paint Production Example The curing start time at 140°C of 1-2 for hair and In-2 for clear was measured, and the results of creating a multilayer coating film are shown in the table.

The finished appearance was good by setting the cure start time of the clear later than that of the base.

The curing start time of Paint Production Example 1l-3 (for base) and ■-3 (for clear) at 140°C was measured, and the results of creating a multilayer coating are shown in the table. In order to obtain a good finished appearance even with 2 coats and 1 hake of '1 isolid, it is possible to achieve the objective by adjusting the curing start time between the base and clear.

Table 1 shows the results of manufacturing examples n-4-2 (for base) and I [-4-1 (for clear), by measuring the curing start time at 140°C or by creating a multilayer coating film. Shown below. The skin was poor as a solid color with 2 coats and 1 bake.

Implementation side 1 Production example ■-4-2 <for base) and lll-4-2 (
The curing start time at 140° C. was measured for the clear material), and the results of creating a multilayer coating are shown in the table. 2
The finished appearance of Coat 1 Hake Solid Color can be greatly improved by adjusting the curing start time of the base and clear.

, comparative control base paint n-5-1 and clear paint lll-5
-1 was measured at 100° C. by DSA to determine the curing start time.

The results are shown in the table.

The table also shows the appearance of the multilayer coating. The clear reaction was fast and a shrinking pattern appeared.

Huji base ↓ Base paint n-5-2 and clear paint 111-5-
The curing start time at 100° C. of No. 2 was determined, and a multilayer coating film was prepared and the appearance was evaluated, and the results are shown in the table. It had a better appearance than Comparative Example 3.

The curing start time of base paint 11-6 at 140°C was determined. Then, wet-on-wet coating films of n-6 base and I[l-2 clear were prepared, and the finished appearance was evaluated.

The results are shown in the table.

The finished appearance was good.

(Margin below)

[Brief explanation of drawings]

The drawing shows the relationship between the curing start time Tlb of the base coat alone and the curing start time Tic of the top coat alone.
- A model of the graph of the relative elastic modulus over time for each time when Tlb > 0. Patent applicant Nippon Paint Co., Ltd., agent patent attorney,
Takumi Akaoka: Pa, ＼ T,, 1. ．． E' and Procedural Amendment 1, Indication of Case 1982 Patent Application No. 10 U2/? No. 2. Name of the invention: Method for forming a multi-layer coating film 3. Relationship with the case of the person making the amendment Name of the patent applicant: Nippon Paint Co., Ltd. 4. Spontaneous by the agent 6. Number of inventions to be increased by the amendment None. 7. Amendment Contents of target amendment 1: "Production example 11-4-2J" on page 23, line 13 of the specification has been replaced with "Production example 11-44J"
I am corrected.

Claims (1)

[Claims] +11 A thermosetting resin paint containing metallic pigments and/or colored pigments is applied as a base coat to the surface of the object to be coated, and then a thermosetting resin clear paint is applied as a top coat on the base coat by wet-on coating. In a two-coat, one-hake method of forming a multi-layer coating film, which comprises coating by a wet method and then heat-curing the entire coating film, the curing start time of the base coat alone under the heat-curing temperature conditions. Between Tlb and the curing start time TIc of the top coat alone, Tic - Tl
A method for forming a multilayer coating film, characterized in that curing start times of the base coat and the top coat are adjusted in advance so that the relationship b≧0 is established. (2) the Tie is between 0.8 minutes and 10 minutes;
The method of claim 1, wherein said Tlb is between 0.5 minutes and 5 minutes. (3) The method of item 1, in which the curing start time is adjusted using a curing agent, and the reactivity of the curing agent in the base coat is relatively faster than the reactivity of the curing agent in the top coat. (4) The method of item 1, in which the curing start time is adjusted using an acid catalyst and/or an amine.