JPS6150662B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a baking method for obtaining a good coating film having a thickness of 50 to 1000 microns in an epoxy/phenolic resin powder coating. Epoxy-phenolic resin baked finish coatings have the highest chemical resistance, adhesion, hardness, and flexibility possible for epoxy coatings and are used in can paints, high-performance primers, and wire enamels. has been done. In recent years, due to the problem of air pollution caused by solvents, there has been a growing movement to turn solution-type paints into powder and make them pollution-free. Since epoxy/phenol resin paints form a film by crosslinking through condensation and addition reactions, gases such as water and formalin are generated during baking and are emitted from the paint film. For this reason, epoxy/phenolic resin powder coatings are baked under the baking conditions used for general epoxy powder coatings (180 to 200℃/10 minutes to 30 minutes).
When cured in one step, thin films with a dry film thickness of 50 microns or less can produce smooth, bubble-free coatings, but thick films of 100 microns or more may develop blisters or pinholes due to the effect of the generated gas. , a good coating film cannot be obtained. The present invention is based on the discovery that by using at least two or more temperature coats in combination, it is possible to obtain a smooth, bubble-free coating film without leaving any blisters or pinholes on the coating film due to the generated gas. It is. To explain in more detail, in epoxy/phenolic resin powder coatings, in the low temperature range of 100 to 160°C, a condensation reaction between the methylol groups in the phenolic resin takes place, and the gas generated by this reaction causes a coating film. It was found that the smoothness of the film and the presence or absence of residual bubbles were greatly affected. Therefore, if sufficient time is allowed for the produced gas to scatter from the coating film in this temperature range, a smooth, bubble-free coating film can be obtained even in a thick film of 50 to 1000 microns. However, in this temperature range, the reactivity of epoxy groups is low, so if you want to obtain sufficient strength,
Requires post-baking at 160℃ or higher. In post-baking at 160° C. or higher, baking conditions are preferably as high as possible and for a short time from the viewpoint of manufacturing costs. For the above reasons, for epoxy/phenolic resin powder paints, baking temperature and time after applying the paint to the object to be coated can be increased to 50% by satisfying the conditions (A) and (B) below. A good coating film of ~1000 microns can be formed. (A) One or more baking conditions are selected from the following (a) to (f), and the total baking time is 30 minutes or more. (B) 100 to 110℃/1 minute to 240 minutes (B) 110 to 120℃/1 minute to 240 minutes (C) 120 to 130℃/1 minute to 240 minutes (D) 130 to 140℃/1 minute to 240 minutes (E) 140 to 150℃/1 minute to 240 minutes (F) 150 to 160℃/1 minute to 240 minutes (B) Select one or more baking conditions from the following (G) to (L). do. (g) 160-170℃/1 minute to 120 minutes (ch) 170-180℃/1 minute to 120 minutes (li) 180-200℃/1 minute to 120 minutes (nu) 200-300℃/5 seconds to 120 minutes (Le) 300~400℃/2 seconds~10 minutes The order of baking conditions must be set so that the above condition (A) is satisfied, and then the above condition (B) is satisfied. When selecting two or more conditions of (A), it is preferable to shift from a lower temperature condition to a higher temperature condition. When selecting two or more conditions of (B), it is preferable to shift from a lower temperature condition to a higher temperature condition. In the present invention, the time between the selected temperature conditions is not limited, but is preferably a temperature gradient of 1° C. and 1 minute. In the present invention, the baking temperature and time are the temperature of the paint or coating film on the object to be coated, and the time during which the temperature of the paint or coating film is maintained at a specified temperature. The printing apparatus that satisfies the conditions of the present invention is not particularly limited, and examples thereof include a circulating hot air dryer and a far-infrared heater heating dryer. The epoxy/phenolic resin powder coating used in the present invention is a solid epoxy resin and a solid resol type phenolic resin in a weight ratio of 5/95 to 95/5.
It is obtained by mixing or melt-mixing. Solid epoxy resin is a compound that has two or more epoxy groups in one molecule and has a softening temperature of 65 to 140°C, and a typical example is a condensate of epichlorohydrin and a bisphenol compound. Can be mentioned. Examples of bisphenol compounds in this case include 2,2'-bis(4,4'-hydroxydiphenyl)propane (commonly known as bisphenol A), halogenated bisphenol A, and 2,2'-bis(4,4'-hydroxydiphenyl)propane (commonly known as bisphenol A). Examples thereof include 4'-hydroxyphenyl)methane (commonly known as bisphenol F), resorcinol, tetrahydroxyphenylethane, novolak type polyfunctional phenol condensed with phenol or cresol and formalin. Solid resol type phenolic resin can be obtained by condensing 0.8 to 4 moles of aldehyde per mole of phenol in the presence of a basic catalyst, and by any means such as continuous concentration using a monotube method, solidification by salting out in water, etc. I can do it. The phenols used in this case include phenol, phenols substituted with an alkyl group having 1 to 6 carbon atoms, such as cresol, propylphenol, butylphenol, tert-butylphenol, bisphenol A, bisphenol S,
Examples include divalent phenols such as bisphenol F and resorcinol. Examples of aldehydes include formaldehyde, paraformaldehyde, furfural, and acetaldehyde. In the epoxy/phenolic resin paint used in the present invention, it is also possible to use curing agents for commonly used epoxy resins, such as novolak type phenolic resins, dicyandiamide, imidazoles, and aromatic amines. ,
Acid anhydrides can be mentioned. In the epoxy/phenolic resin paint used in the present invention, fillers, flow control agents, reinforcing agents,
Addition of fillers and pigments is possible. These may be added after grinding, but it is advantageous to add them before melt-mixing. Examples of these additives include glass fibers, asbestos fibers, carbon fibers,
Examples include polyethylene powder, quartz powder, kaolin, aluminum oxide, kaolin, silica, titanium dioxide, carbon black, and oxide color pigments. Examples will be given below to explain the present invention in more detail. Reference example 1 Weigh 100 g of phenol and 1019 g of 37% formalin into a reaction can with a cooling jacket, and add while cooling.
200 g of 25% ammonia was added in three portions, and the temperature was gradually raised to 70° C. for 3 hours. The viscosity of the reactant was 1200 cps (60°C). Transfer this to a concentrating pot with a vacuum device, and reduce the temperature to 80 mmHg under reduced pressure.
After concentrating to a temperature of .degree. C., the mixture was centrifugally filtered to obtain a solid resin. By applying this to an extruder, a solid resol resin having a water content of 1% or less was obtained. 100g of the solid resol resin obtained in this way
and bisphenol A with an epoxy equivalent of 920
150 g of a solid epoxy resin (trade name: AER-644 manufactured by Asahi Kasei Corporation) was uniformly melted and mixed at a temperature of 100 to 110° C. using a kneader, and then powdered to obtain powder coating 1. Reference Example 2 Solid resol resin 100 obtained in Reference Example 1
g, bisphenol A with an epoxy equivalent of 1950
400 g of type epoxy resin (trade name: AER-677, manufactured by Asahi Kasei Corporation) and 100 g of titanium dioxide were powdered in the same manner as in Reference Example 1 to obtain powder coating 2. Example 1 Powder 1 was applied to a degreased 0.2 mm mild steel plate using an electrostatic coating machine so that the dry film thickness was 150 to 200 microns. A thermocouple was installed on the surface to be coated, and the temperature of the surface to be coated could be measured at 125℃.
The sample was placed in a circulating hot air dryer that could be heated at a rate of 1°C/20 seconds, and left for 30 minutes. The temperature of the coated surface during the standing time was 123±2°C. After this 4℃/
Raise the temperature at a rate of 1 minute and adjust the dryer to 155℃.
It was left for 30 minutes. The temperature of the surface to be coated during the standing time is 152
The temperature was ±2℃. The temperature was further increased at a rate of 4°C/1 minute, the dryer was adjusted to 200°C, and the mixture was left for 15 minutes.
The temperature of the coated surface during the standing time was 190±5°C. The coating film thus obtained has a good surface condition and is free of bubbles. Further, the physical properties of the obtained coating film were as follows. Erichsen 7.0mm Bending resistance 6mm Pass Goban adhesion Pass Pencil hardness 4H NEK resistance Good Examples 2 to 6 Powder 2 was applied in the same manner as in Example 1, and under the conditions shown in Table 1. hardened. Table 1 also lists the physical property values of the coating films obtained.

【table】

[Table] Comparative Example 1 Powder 1 was applied in the same manner as in Example 1,
It was left in a dryer set at 180°C for 30 minutes. The temperature of the object to be coated at this time was 178±2°C. The resulting coating film had significant bubbles and was not smooth at all. Comparative Example 2 Powder 1 was applied in the same manner as in Example 1,
It was left in a dryer set at 210°C for 10 minutes. The temperature of the object to be coated at this time was 206±3°C. The resulting coating film had significant bubbles and was not smooth at all. Comparative Example 3 Powder 1 was applied in the same manner as in Example 1,
It was left in a dryer set at 150°C for 2 hours. The temperature of the object to be coated at this time was 147±2°C. The resulting coating film was smooth and no remaining bubbles were observed. However, the physical properties of the coating film were as follows. Erichsen value 0.2mm Bending resistance 10mm Rejected Goban adhesion Rejected Pencil hardness H

Claims (1)

[Claims] 1. In the epoxy/phenolic resin powder paint, the baking temperature and time after applying the paint to the object to be coated satisfy the following conditions (A) and (B). A method of curing paint that forms a coating film with a thickness of 50 to 1000 microns. (A) Select one or more baking conditions from the following (a) to (f), and the total baking time is 30 minutes or more. (a) 100 to 110℃/1 minute to 240 minutes ( B) 110 to 120℃/1 minute to 240 minutes (C) 120 to 130℃/1 minute to 240 minutes (D) 130 to 140℃/1 minute to 240 minutes (E) 140 to 150℃/1 minute to 240 Minutes (F) 150-160℃/1 minute-240 minutes (B) Select one or more baking conditions from the following (G)-(L) (G) 160-170℃/1 minute-120 Minutes (ch) 170-180℃/1 minute to 120 minutes (li) 180-200℃/30 seconds to 120 minutes (nu) 200-300℃/5 seconds to 120 minutes (ru) 300-400℃/2 seconds ~10 minutes 2 In claim 1, the curing of the paint satisfies the baking conditions (A) and (B) and the baking conditions are combined from low temperature conditions to high temperature conditions. Method.