JPS5916571A - Curing method of powder paint - Google Patents

Abstract

PURPOSE:To enable the baking and curing of a paint coated film in a short time and to improve the productivity in a continuous production stage for a precoated metallic plate, by applying a powder paint on a substrate then irradiating near IR light thereto. CONSTITUTION:Various kinds of powder paints of polyester resins, acrylic resins and epoxy resins are used as a powder paint, and a metallic plate applied thereon with said paint is baked and cured for about 10-60sec in a near UV furnace. Since the substrate is heated and cured up to the prescribed temp. uniformly in a short time by the above-mentioned stoving, the length of a baking furnace can be made shorter, hence an equipment area is required to be smaller. The near IR furnace attains 100% output in about 3sec after switching on of a power source; therefore, the selection of a set temp. during continuous operation is easy, and it is possible to stop the operation of the furnace in the event of a temporary interruption of the continuous line. A high effect of energy economization is obtained therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for curing powder coatings, and more specifically,
The present invention relates to a method for curing powder coatings that can form a powder coating film in a short period of time without reducing coating performance.

Recently, the application of painted metal sheets as a paint finishing system in the home appliance industry, steel furniture industry, etc. has begun to expand. Painted metal sheets are typified by pre-coated metal sheets such as colored galvanized iron sheets, which are coated with paint beforehand and then molded into a desired shape for final use. In addition to being widely used as construction-related materials such as siding, storm doors, and shutters, it is also used in metal products such as home appliances. This kind of pre-coated metal sheet has the advantage of streamlining the painting process1 and making the quality uniform, compared to the method where the metal sheet is first formed into a complex shape and then applied with force. It is thought that its uses will continue to expand in the future as we wait for the first point, such as saving paint consumption.

The paint applied to such pre-coated metal plates is molded into a shape according to the above application after the coating film is formed.
The membrane is required to have sufficient extensibility and adhesion to metal surfaces to withstand forming processes such as bending, roll forming, embossing press, and drawing. -For products after molding, performance suitable for each end use is required, such as a high degree of weather resistance for building exterior materials and strong corrosion resistance including processed parts; Scratch resistance and stain resistance are required.

The application of painted metal sheets has begun to expand in the home appliance industry, steel furniture industry, etc. The aim is to reduce the amount of organic solvent paint used at manufacturing sites and to eliminate health, safety, and work environment problems caused by exhaust bath agents. The aim is to alleviate the pollution and take measures to prevent pollution. As such an improvement method, flat plate coating using powder coating and pre-coating system (pre-coat method) (PcM
) is being considered. The features of such a system are:
(υ The finished appearance is similar to a wave film and has a thick film feel. (2) The cut surface can be painted, which has a corrosion-preventing effect. t3J The film thickness distribution is uniform and the coating efficiency is high. (4) ) The storage and transportation of flat painted plates does not take up much space, and the post-forming process improves the productivity of laying on the site surface. (5) Painting can be easily automated and maintenance around the painting booth is reduced. At the point.

However, from fx, when manufacturing Brecoat metal plates on a continuous line, the object to be coated is a flat plate compared to when assembling refrigerators etc. If you try to keep the line length of the baking line the same, the line length of the baking line (ff1J, the furnace length of the baking oven) will inevitably become several times larger, and conversely, the line length of the baking process will be kept the same as the line length of the baking process. If it continues, production capacity will drop significantly. In particular, when manufacturing pre-coated gold-topped plates using powder coatings, it is necessary to bake at a higher temperature (1) compared to other paints such as solvent-based paints due to storage stability and painting workability. Therefore, the above problem is -
It becomes serious.

In view of the current state of the prior art, the present inventors have conducted studies to improve the productivity of the continuous manufacturing process for Brecoat metal plates, and as a result, after applying powder coating to the object to be coated, irradiating it with near-infrared rays. By doing so, they discovered that it was possible to bake and harden the coating film in a short amount of time, and succeeded in increasing production capacity and reducing the scale of the equipment. Furthermore, it has been found that energy consumption can be further reduced by forming a coating film using far infrared rays and/or hot air after near infrared irradiation. In this specification, the term "near infrared rays" refers to an electromagnetic wave with a wavelength of 0.72 to 1.5 μm, and the near-infrared rays used in this invention include the above-mentioned magnetic wave as a living body, and may also contain electromagnetic waves exceeding 1.5 μm. . In addition, the term "far infrared rays" has a wavelength of 5.6 to 8 μm.
Conventional methods for baking and curing paint using electromagnetic waves are
Methods using a hot air stove, methods using a far-infrared furnace, and methods using a high-frequency baking furnace are known, but when using a hot air furnace, a method using a convection heat transfer method that uses gas, heavy oil, electricity, etc. as a heat source is known. Baking time is 180°C due to heating.
It takes approximately 20 minutes to 230°C. When using a far-infrared furnace, the radiator is heated using gas, heavy oil, kerosene, electricity, etc. as a heat source, and the generated far-infrared rays are absorbed by the coating film to generate heat, so it is less expensive than hot air. Although the baking time can be shortened, it takes about 3 to 5 minutes, so there is no hope for a significant time reduction. Furthermore, when using a high-quality FL baking furnace, it is possible to bake for a short time of 1 minute or less, but due to the edge effect of the dielectric current, burning spots may occur at the notches and edges of the object to be coated (flat plate). There is a big problem in terms of quality control.The above problem becomes especially noticeable in the case of wartime burn-in.

When cutting the metal plate and irradiating it with near infrared rays according to the present invention, the metal plate coated with the powder coating 'Ik is used for a short period of time (approximately 10 to 6
It was possible to bake and harden in 0 seconds), and no deterioration in coating film performance such as workability, stain resistance, impact resistance, corrosion resistance, chemical resistance, etc. was observed compared to the conventional method. Furthermore, if near-infrared irradiation is applied when producing a pre-coat metal plate using solvent-type m#+ gold, the phenomenon of wrinkling due to the protrusions of the solvent will be noticeable, except in the case of thin films, and it is difficult to obtain a practical coating film. I couldn't.

Baking by near-infrared irradiation can be achieved, for example, by heating a filament in the air and generating near-infrared gold-based electromagnetic light with a wavelength of 0.72 to 1.5 μm to heat the coating film by radiation. It can be easily carried out and, for example, a PYRO3 PAN near-infrared furnace commercially available from Research Inc. (USA) can be suitably used.

In this way, when the coating film 'ff:#i is hardened by near-infrared M irradiation, the object to be coated can be cured uniformly at a predetermined temperature l in a short time, so the length of the baking furnace can be shortened. Therefore, the equipment area can be reduced.

In addition, due to its characteristics, near-infrared furnaces reach 100% output in a short period of about 3 seconds after power is turned on, so it is easy to change the set temperature during continuous operation. Please note that the furnace continues to heat up.
1 can be stopped, resulting in a high energy saving effect.

According to the present invention, furthermore, by first heating with near-infrared irradiation and then heating with far-infrared irradiation and/or hot air, energy consumption is significantly reduced compared to bake hardening using near-infrared irradiation alone. Moreover, it is advantageous in terms of equipment costs.

In the case of this method, for example, heating by near-infrared irradiation is performed for about 5 to 20 seconds, and then heating is performed by far-infrared irradiation and/or hot air 8 degrees for 30 seconds to 2 minutes. In some cases, no deterioration in coating performance was observed compared to conventional methods.

There is no particular limitation on the type of powder coating that can be conveniently used in the method of the present invention, and for example, polyester resin-based, acrylic resin-based, and evogishi resin-based powder coatings can be used. According to the invention, by combining a near-infrared furnace with a powder coating, which could not be applied to conventional paints, it is possible to create a pre-coated metal plate using a powder coating without deteriorating the coating performance. Productivity of continuous manufacturing process all times J-, -+! You can grin.

Hereinafter, the present invention will be explained in more detail according to Examples, but the scope of the present invention is not limited to these Examples.
n) is degreased, then subjected to υnoate film chemical conversion treatment, and (
:nK=ppepreco) 300 (Nippon Paint Heat-curable polyester resin powder paint) 30-40/1m
The thus coated galvanized steel sheets were subjected to near-infrared irradiation (Example 1), a near-infrared source furnace, and a far-infrared furnace (Example 2) under the baking conditions shown in Table 1. 3), near-infrared furnace and hot-air furnace (Example 4), and hot-air furnace alone (Comparative Example 1),
Bake harden and cool. In addition, research on near-infrared furnace ° Incobore Tesodo's PYRO8PAN
A model 54775 was used as the far-infrared furnace, a BD34 (i7) manufactured by Kokusai't was used as the far-infrared furnace, and a hot-air circulation furnace of the Tabai Seisakusho Kashi laboratory type was used as the hot-air furnace.

For the coating film thus obtained, impact resistance, workability and stain resistance were added by 6 (6 (11)) and the results are shown in Table 1.

Margin below

Claims (1)

[Claims] (1) A method for curing a powder coating, which comprises applying the powder coating to an object to be coated, and then forming a coating film by irradiating it with near-infrared rays. 2. The curing method according to claim 1, wherein after near-infrared irradiation, a coating film is formed by far-infrared irradiation and/or hot air.