JPH0770471A - Additive composition for high solid paint and coating method - Google Patents

Abstract

(57) [Abstract] [Purpose] A high solid coating composition having a high non-volatile content and a low viscosity immediately after being sprayed at the time of application, but having a high viscosity at the time of application to prevent sagging and a coating method thereof. I will provide a. [Constitution] One end has an ethylenic double bond and Mw is 50.
0-5000 macromonomers and macromonomers 10
A high solid paint containing an additive composition consisting of 1 to 10 parts by weight of a photopolymerization initiator with respect to 0 parts by weight is sprayed onto an object to be coated, and the coating particles in flight are irradiated with ultraviolet rays. Is characterized by. Since the macromonomer is polymerized and increased in viscosity by ultraviolet rays, the viscosity becomes high at the time of coating, and the sagging is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an additive composition used for a high solid paint having a high non-volatile content and a low viscosity, and a method for coating a high solid paint containing the additive composition.

[0002]

2. Description of the Related Art Thermosetting acrylic resin paints are generally used for coating automobiles and home electric appliances because of their excellent physical properties such as weather resistance. This thermosetting acrylic resin paint is mainly composed of an acrylic resin, a crosslinking agent such as a melamine resin or an isocyanate resin, and an organic solvent. Among them, the acrylic resin and the crosslinking agent react with each other by heat or the like to form a three-dimensional network structure and form a tough coating film. On the other hand, the organic solvent adjusts the viscosity of the paint to an appropriate value to facilitate the painting work such as spraying.

By the way, in recent years, from the viewpoint of protecting the global environment, reduction of the amount of organic solvent emission in the painting work has become an important issue, and water-based paints and high-solid paints have been actively developed. Above all, development of high-solid paints is regarded as important because water-based paints require wastewater treatment and drying is slow.

[0004]

The high solid coating material is a coating material having a low viscosity and a high non-volatile content, but in a solution coating material, the concentration of the dissolved resin component is proportional to the viscosity. It is quite difficult to satisfy the trade-off phenomenon of low viscosity and high non-volatile content. That is, when the amount of the organic solvent is reduced and the concentration of the resin is increased, the viscosity of the paint becomes high and it becomes difficult to carry out painting work such as spraying. Therefore, it is conceivable to use a resin having a low molecular weight to reduce the viscosity of the resin itself. However, if the viscosity of the resin itself is reduced, the increase in viscosity is slight even if the organic solvent volatilizes. There is a problem that the effect is small and sagging occurs.

For example, JP-A-59-103793 discloses an ultraviolet-curable coating composition comprising a monomer having an unsaturated double bond, a thermoplastic resin soluble in the monomer, and a photopolymerization initiator. Has been done. This coating composition has a nonvolatile content of 100% and is the most preferable as a high solid coating, but it has a problem that it has a low viscosity and drips when coated on a vertical surface. In addition, the shape of the article to be coated is restricted because the coating film is irradiated with ultraviolet rays to be cured.

The present invention has been made in view of the above circumstances and has a high non-volatile content and a low viscosity immediately after spraying at the time of application, but has a high viscosity at the time of application to prevent sagging. An object of the present invention is to provide a high solid coating composition and a coating method thereof.

[0007]

The additive composition for a high solid coating material of the present invention which solves the above problems has an ethylenic double bond at one end and has a weight average molecular weight (hereinafter referred to as Mw) of 500 to 5000. And 1 to 10 parts by weight of a photopolymerization initiator with respect to 100 parts by weight of the macromonomer.

As the macromonomer, those having an ethylenic double bond at one end and having Mw of 500 to 5000 are used. If the Mw is less than 500, it is difficult to have a high viscosity at the time of application and dripping will occur. If the Mw is greater than 5000, the viscosity of the coating material will increase and it will be difficult to achieve high solidification. Particularly preferred Mw
Is 1000 to 3000. Further, in the case of having a plurality of double bonds, the surface of the coating film is impaired because the coating particles gel during flight.

The macromonomer is added to the high solid coating material in an amount of 30 to 80% by weight. If the addition amount of the macromonomer is less than 30% by weight, the increase in the viscosity at the time of coating is small and the sagging occurs. On the other hand, when it is more than 80% by weight, the amount of the resin component in the coating material becomes relatively small, which causes a problem in coating film physical properties. A particularly preferred range is 30 to 50% by weight.

The macromonomer is, for example, a polymer prepared by polymerizing at least one ethylenically unsaturated monomer in the presence of a mercaptan compound having a thiol group and a reactive group in the molecule, and is bonded to one end of the polymer. The reactive group can be produced by reacting a bondable group capable of reacting with the reactive group and a monomer having an ethylenically unsaturated bond.

Various physical properties of the coating film can be adjusted by selecting various macromonomers. It is also desirable that the macromonomer has a functional group that reacts with the crosslinking agent in the high solid paint. By doing so, the macromonomer reacts with the cross-linking agent during the baking of the coating film to be integrated, so that the physical properties of the coating film are further improved. The photopolymerization initiator is one which generates radicals by irradiation of ultraviolet rays to attack the ethylenic double bond at one end of the macromonomer to initiate polymerization, and a commercially available photopolymerization initiator can be used.

The amount of the photopolymerization initiator used is 1 to 10 parts by weight based on 100 parts by weight of the macromonomer. When the amount of the photopolymerization initiator used is less than 1 part by weight, it is difficult to obtain a high viscosity at the time of application and sagging occurs because the reaction starting point is small. On the other hand, even if it is added in an amount of more than 10 parts by weight, the reaction start point is too large and it becomes difficult to obtain a high viscosity at the time of coating.

A high solid paint containing the additive composition of the present invention comprising the above macromonomer and a photopolymerization initiator is
The base resin is not particularly limited, but a common acrylic resin or the like is used. As the cross-linking agent, a melamine resin, an isocyanate resin or the like that reacts with the base resin to cross-link can be used. Then, in order to make them have a predetermined viscosity, an organic solvent is used as in the conventional case.

The coating method of the second invention for coating the high-solid coating material produced in this manner is a coating method in which the above-mentioned high-solid coating material is sprayed onto an object to be coated, and ultraviolet rays are applied to the coating particles during flight. It is characterized by irradiation. The irradiation amount of ultraviolet rays is preferably in the range of 50 to 200 mJ / cm ² . When the irradiation dose is less than 50 mJ / cm ² , the reaction between macromonomers is not sufficient, and it becomes difficult to have a high viscosity at the time of coating, resulting in dripping. ^{On the other hand} , if it exceeds 200 mJ / cm ² , the viscosity at the time of coating becomes too high, and the smoothness of the coating film is impaired. Incidentally, if least such macromonomer amount such as 10 wt%, but 200 mJ / cm ² or more suitable thickening irradiation amount is obtained, by irradiating 200 mJ / cm ² or more ultraviolet during spraying practical It's difficult.

[0015]

The additive composition of the present invention comprises a macromonomer having an ethylenic double bond at one end and a photopolymerization initiator. Of these, the macromonomer, which is the main component, has a smaller molecular weight than the acrylic resin or melamine resin in the paint and has a low viscosity itself.

Therefore, by adding a predetermined amount of this additive composition to the coating composition, the acrylic resin and the cross-linking agent are reduced, so that the viscosity becomes low, and the amount of the organic solvent is reduced. It becomes a solid paint.
The obtained high solid paint has a low viscosity and thus has excellent spray coatability, and finely divided paint particles can be obtained. When the coating particles in flight are irradiated with ultraviolet rays, the photopolymerization initiator in the coating particles is activated and the double bonds at one end of the macromonomer react with each other.

The polymerization of the macromonomer by the polymerization reaction and the volatilization of the organic solvent from the coating particles during flight increase the viscosity of the coating particles, and when the coating material is applied to the coating material, the viscosity is such that dripping is unlikely to occur. Has become. Moreover, since the particle size of the coating particles does not increase during flight, the coating particles are fine particles even when they are applied, and the coating film surface is excellent in smoothness. The wet coating film thus formed is heated to the crosslinking temperature of the crosslinking agent contained therein and baked to complete the coating.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1) Mw = 2600, a macromonomer having a methacroyl group at one end (monomer composition MMA / HEM
A = 80/20 (weight ratio)) 80 parts by weight and 4 parts by weight of "Darocur 1173" (manufactured by Ciba-Geigy Co., Ltd.) as a photopolymerization initiator were dissolved in 20 parts by weight of xylene to prepare a solution of the present example. It was an additive composition.

The viscosity of this additive composition is 25 at 25 ° C.
It was 0 cp. Next, this additive composition was placed in an aluminum dish and irradiated with ultraviolet rays using an 80 W / cm ultraviolet lamp. Then, the viscosity was measured while changing the irradiation time, and the ultraviolet irradiation dose and the viscosity up to the time of viscosity measurement are shown in Table 1. (Example 2) 50 parts by weight of the same macromonomer as in Example 1 and 2 parts by weight of the same photopolymerization initiator as in Example 1 were mixed with 20 parts by weight of xylene to obtain an additive composition of this example. . Then, 72 parts by weight of this additive composition was mixed with 30 parts by weight of an acrylic resin having Mw = 2600 (monomer composition MMA / HEMA = 80/20 (weight ratio)) to obtain a high solid coating.

The viscosity of this high-solid paint was 230 cp at 25 ° C. Next, this high-solid coating material was irradiated with ultraviolet rays in the same manner as in Example 1, and the change in viscosity over time was measured. (Example 3) 30 parts by weight of the same macromonomer as in Example 1 and 1.5 parts by weight of the same photopolymerization initiator as in Example 1 were mixed with 20 parts by weight of xylene to prepare an additive composition of this example. And Then, 103 parts by weight of this additive composition was mixed with 100 parts by weight of the same acrylic resin as in Example 2 to obtain a high solid paint.

The viscosity of this high-solid paint was 220 cp at 25 ° C. Next, this high-solid coating material was irradiated with ultraviolet rays in the same manner as in Example 1, and the change in viscosity over time was measured. (Comparative Example 1) 20 parts by weight of the same macromonomer as in Example 1 and 1 part by weight of the same photopolymerization initiator as in Example 1 were mixed with 20 parts by weight of xylene to obtain an additive composition of Comparative Example 1. . Then, 41 parts by weight of this additive composition was mixed with 60 parts by weight of the same acrylic resin as in Example 2 to obtain a high solid paint.

The viscosity of this high-solid paint was 200 cp at 25 ° C. Next, this high-solid coating material was irradiated with ultraviolet rays in the same manner as in Example 1, and the change in viscosity over time was measured. (Comparative Example 2) 40 parts by weight of n-dodecyl methacrylate monomer instead of the macromonomer and 2 parts by weight of the same photopolymerization initiator as in Example 1 were mixed with 20 parts by weight of xylene to prepare an additive composition of Comparative Example 2. And Then, 6 parts of this additive composition was added to 40 parts by weight of the same acrylic resin as in Example 2.
2 parts by weight were mixed to obtain a high solid paint.

The viscosity of this high-solid paint was 100 cp at 25 ° C. Next, this high-solid coating material was irradiated with ultraviolet rays in the same manner as in Example 1, and the change in viscosity over time was measured. (Comparative Example 3) 20 parts by weight of n-dodecyl methacrylate monomer instead of the macromonomer and 1 part by weight of the same photopolymerization initiator as in Example 1 were mixed with 20 parts by weight of xylene to prepare an additive composition of Comparative Example 3. And Then, this additive composition was added to 4 parts by weight of the same acrylic resin as in Example 2.
1 part by weight was mixed to obtain a high solid paint.

The viscosity of this high-solid paint was 150 cp at 25 ° C. Next, this high-solid coating material was irradiated with ultraviolet rays in the same manner as in Example 1, and the change in viscosity over time was measured.

[0025]

[Table 1]

From Table 1, the maximum value of the embodiment is 200.
While viscosity ultraviolet irradiation amount of mJ / cm ² is equal to or greater than 1000 cp, in the comparative example 520mJ / cm ²
It can be seen that the irradiation does not reach 1000 cp. The irradiation time required to reach an ultraviolet irradiation amount of 200 mJ / cm ² was 0.3 seconds, which is shorter than the time required for discharging from a spray gun in spray coating and coating the object.

Therefore, when a high solid paint containing a prescribed amount of the additive composition of this embodiment is spray-painted, since the paint has a low viscosity of about 200 cp, fine paint particles are ejected from the spray gun. Then, if the coating particles are irradiated with ultraviolet rays during a short time after the spray gun is ejected until they are applied to the object to be coated, the viscosity of the coating particles during flight is about 10 at a stroke.
Since it rises to 00 cp or more, it is possible to prevent the coating film formed by coating the object to be drooped.

The coated particles applied to the article to be coated are macromonomers that linearly polymerize to increase the viscosity, and three-dimensional crosslinking does not occur. Therefore, adjacent fine coating particles are fused together to form a coating film having an extremely smooth surface.

[0029]

[Effects of the Invention] That is, according to the additive composition of the present invention, a high solid paint can be obtained by simply adding it to an existing paint. And by applying the obtained high-solid paint by the coating method of the present invention, since the viscosity is low at the time of coating and the coating particles thicken during flight to have a high viscosity at the time of coating, the conventional high-solid paint is used. The sagging problems that are seen are prevented. Therefore, it becomes possible to coat a thicker film than in the past, and the coating quality is improved.

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Claims (2)

[Claims] 1. A macromonomer having an ethylenic double bond at one end and having a weight average molecular weight of 500 to 5000; and 1 to 10 parts by weight of a photopolymerization initiator per 100 parts by weight of the macromonomer. An additive composition for high solid coatings, characterized in that 2. A macromonomer 30-having an ethylenic double bond at one end and a weight average molecular weight of 500-5000.
A coating method for spraying a high solid paint containing 80% by weight and 1 to 10 parts by weight of a photopolymerization initiator with respect to 100 parts by weight of the macromonomer onto an object to be coated. A coating method characterized by irradiating ultraviolet rays to the surface.