JPH0368475A - Formation of coating film - Google Patents

Abstract

PURPOSE:To improve physical and chemical properties in the surface of a coating film by coating the surface to be coated with a thermosetting paint, heating and drying a coating film, and then hardening the coating film by irradiating the coating film with active light of 200-700nm wavelength. CONSTITUTION:A surface to be coated is coated with a thermosetting paint, and the resulting coating film is irradiated, after heating and drying, with active light of 200-700nm wavelength, by which a hardened coating film is formed. As a resin as base material in the thermosetting paint used at this time, the one consisting of linear polymer or three-dimensional polymer containing carbon atoms bonded to one hydrogen atom in a molecule by >= about 0.05 mole/kg and having functional group, such as hydroxyl group, for cross linking reaction with hardening agent is suitably used. Further, as the hardening agent for hardening the resin as base material, melamine-formaldehyde resin, urea-formaldehyde, polyisocyanate, etc., are suitably used.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a coating film forming method, and more particularly, to a coating film forming method for improving the physical and chemical properties of a forced-dried or heat-dried coating surface. The present invention relates to a film forming method.

[Conventional technology and problems to be solved by the invention] Conventional paint film formation technology involves forcing the paint to dry or heat drying it after painting, and then forming the finished paint film as it is or by applying treatments such as polishing or wax coating. . on the other hand,
BACKGROUND OF THE INVENTION As the need for improved coating film quality continues to increase, interest in the development of new coating technologies is increasing worldwide, and various new materials have been announced. Among the needs for improving the quality of paint films, in particular improvements in the acid resistance and scratch resistance of paint films must be related to paint materials, but for the development of new materials and research on imparting ease of painting. It is difficult to develop a paint that can satisfy these requirements in a short period of time, requiring a huge amount of cost and time.

[Means for Solving the Problems] The present inventors have conducted extensive research to find a means that can meet the above requirements by subjecting currently commonly used paints to further post-treatment after forced drying or heat drying. As a result of repeated efforts, it was discovered that irradiation of the coating film obtained by baking with actinic light containing a large amount of light in the ultraviolet region was effective, and the present invention was completed. Thus,
According to the present invention, in order to cure the coating film after applying the thermosetting paint, after heating and drying, a further wavelength of 200 nm to 70 nm is applied.
Provided is a coating film forming method characterized by irradiating with 0n+m actinic rays.

The base resin in the thermosetting paint used in the present invention contains 0.05 mol of carbon atoms bonded to one hydrogen atom in the molecule.
/kg or more, and the base resin contains a functional group (such as a hydroxyl group) for crosslinking with a curing agent (such as an amino resin).
have.

Examples of the base resin used in the present invention include acrylic esters, acrylic acid, polymers such as acrylonitrile and styrene, and two or three of the above monomers.
copolymers of one or more of the above monomers and one or more monomers such as methacrylic acid esters, methacrylic acid, mecrylonitrile, etc. It will be done. The acrylic resin obtained by the above method, polyester resin, alkyd resin, epoxy resin,
One kind of silicone resin or the like or two or more resins can be used in combination. As a curing agent for curing these base resins, amino resins (melamine/formaldehyde resin, urea/formaldehyde resin, etc.), polyisocyanates, etc. are used. In addition to this, a curing catalyst can be blended, and pigments and other additives can also be blended.

Conventionally known methods for polymerizing the acrylic resin, polyester resin, alkyd resin, epoxy resin, silicone resin, etc. can be used.

In the present invention, not only paints containing an acrylic resin having a specific structure as described above, but also paints containing ordinary polyester resins or alkyd resins and an amino resin as a curing agent, can be treated by applying active rays after heating and drying. It has been recognized that irradiation is effective for surface modification of paint films. In this case, an increase in ether bonds and the like is observed in the thin upper layer of the coating film due to irradiation with actinic rays, so it is thought that a condensation reaction or the like is occurring. In this respect, it is thought that a similar condensation reaction occurs in paints containing the above-mentioned acrylic resin and amine resin.

Normally, organic chemicals are eventually degraded and
It is a well-known fact that decomposition 0 For example,
Paints made of polyester or acrylic resins blended with melamine-formaldehyde resins have long been used in many applications, including automobiles. Among these, it has always been a problem that when exposed outdoors for a long time, the resin deteriorates and decomposes due to sunlight, water, oxygen, etc., and the gloss of the coating film decreases.

The present inventors have discovered that in addition to such reactions of resin deterioration and decomposition due to sunlight (mainly ultraviolet rays), there is also a crosslinking reaction, and the present invention takes advantage of this. In other words, when coatings made of a base resin with a certain chemical structure or other ordinary thermosetting coatings are exposed to ultraviolet light, the aforementioned crosslinking reaction occurs in the scratched surface layer, resulting in excellent surface modification. Quality is achieved.

The improvement of the acid resistance and scratch resistance of the coating film will be explained below.

The need to improve the acid resistance of paint films is important in automotive painting, especially when exported cars are stored in outdoor motorbikes due to acid rain or soot.

! ! ! Due to the increasing number of cases of stains on the M1 surface, improving the quality of the paint film appearance has become an important issue recently, and acid-resistant Demand for improved sexual performance is increasing.

Currently, paints made of polyester (or alkyd) resin or acrylic resin mixed with melamine/formaldehyde resin are mainly used for automobiles, but acid rain and soot fall on the paint film on new cars soon after painting. However, it has been observed in some cases that stains are less likely to occur if a car is exposed to acid rain or soot after being exposed to the outdoors for a while. That is, this is understood to be because a chemical reaction progressed on the surface of the coating film while it was exposed outdoors after the coating film was formed, resulting in improved acid resistance.

Increasing the baking temperature or lengthening the baking time during coating film formation will improve the crosslinking density of the coating film, making it difficult for acidic water to penetrate and improving acid resistance, but on the other hand, the coating film will become harder and physical Defects such as cracking and cracking are likely to occur due to impact.

Therefore, from this point of view, it is desirable to accelerate the curing reaction only on the surface portion of the coating film, and the method for modifying the coating film surface of the present invention satisfies this requirement.

In addition, the demand for improved scratch resistance of paint films has increased due to the trend toward higher quality paint exteriors, and the trend toward darker colors (black, gray, etc.) in automotive paints. The minute scratches caused by paint are considered a problem as they impair the appearance of the paint.

Scratch resistance largely depends on the hardness of the coating surface, and like the acid resistance mentioned above, modification of the coating surface is extremely effective.

In addition, in this research, we discovered that irradiating the paint film with ultraviolet rays is also effective in improving the gloss of the paint film.

Paints and inks that cure and dry through a chemical reaction caused by ultraviolet irradiation have been well known for some time, but this type of paint is a paint in which a polymerization initiator is blended with a photosensitive resin. On the other hand, the paint that is the object of the present invention is a general heat-drying paint, and is characterized in that it is further irradiated with ultraviolet light after being cured by heat.

In addition, as for ultraviolet treatment of polymeric materials, examples are known in which it is used to generate chemical functional groups in the material, but the method of the present invention, as described above, includes a set of heating drying and ultraviolet irradiation. It is characterized by the fact that it cures the coating film using ultraviolet rays, and is quite different in purpose and content from the generation of functional groups by ultraviolet rays.

An embodiment of the present invention will be described below using painting of an automobile body as an example.

Automobile painting involves applying a phosphate-based chemical conversion treatment to a steel plate (for example, a cold-rolled steel plate), then applying an IIT primer and an intermediate coat if necessary, and finally applying a top coat.
Normally, the exterior painting of the body is completed, but in the method of the present invention, equipment is then provided to irradiate the painted surface with ultraviolet rays. Generally, the conveyor speed during topcoating is 4 to 6 m/min, and it is sufficient to pass the conveyor through a tunnel equipped with an ultraviolet lamp at this speed, which seems to be easily possible in an actual coating line.

Examples of ultraviolet irradiation lamps include low-pressure mercury lamps, high-pressure mercury lamps,
An appropriate one can be selected from among ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, carbon arc lamps, and the like.

The irradiation intensity can be controlled by the number of these lamps, the irradiation distance, the type of condensing lamp house, the focal length, etc.

〔Example] Hereinafter, the method of the present invention will be specifically explained with reference to Examples.

Fujikron No. is an acrylic resin thermosetting top coating.
, l OOO-A clear (trade name, manufactured by Kansai Paint Co., Ltd.) is painted on a painted board that has been previously painted with black enamel of the same type, and after baking at 140°C for 30 minutes, a reflective mirror is installed to collect light. Using two ultraviolet irradiation lamps (high-pressure mercury pump UVH-7000, made by Ushio Electric Co., Ltd., with a power output of 160 W/cm),
Table 1 shows the results of acid resistance and scratch resistance before and after UV irradiation.

Wataru Group Magikron N is an acrylic resin top coat.

The same procedure as in Example 1 was carried out except that 1000-B Clear (trade name, manufactured by Kansai Paint Co., Ltd.) was used, and the results are shown in Table 1.

The procedure was carried out in the same manner as in Example 1, except that Neoamilac Na 300 Green (trade name, manufactured by Kansai Paint Co., Ltd.), which is a thermosetting top coat based on Jotachihandan amino alkyd resin, was applied to the undercoated iron plate. Shown in the table.

In Table 1, 6, which has 0 irradiation times, can be considered as a comparative example, compared to the UV ts irradiation rgJ number of 1 or more times (these are examples). If you look at Table 1 from a different perspective, the differences between the two become clear.

The test method and its evaluation method were carried out in accordance with the following.

(1) Acid-resistant test coated board is immersed in a 40% sulfuric acid aqueous solution and left in the liquid part at 40°C for 16 hours. After lifting, wash thoroughly with tap water and air dry.

■Adhesiveness The degree of stickiness of the painted surface was evaluated by touching it with a finger.

×: Extremely sticky (resin decomposes due to acid and becomes sticky) △: Slightly sticky ○: Almost no stickiness ■20 degree gloss ! ! ! Since the film surface is decomposed by acid and the gloss is reduced, 20 degree specular reflectance was measured as a substitute for acid resistance.

(2) Place about 0.5 g of a commercially available cleanser moistened with water on the scratch resistance test ti1 plate, and rub it under the following conditions using a character-type abrasion fastness tester. A tIA test was performed.

Load: 500g Number of frictions: 20 times Temperature = 20±2℃ Friction surface: Cover with two pieces of flannel cloth.

For evaluation, the 20 degree specular reflectance after the test was used as a substitute characteristic. (If it gets scratched, the gloss will decrease).

Claims (1)

[Claims] 1. A method for forming a coating film, which comprises applying a thermosetting paint, drying it by heating, and further irradiating active light with a wavelength of 200 nm to 700 nm in order to cure the coating film.