JPH0730284B2 - Baking coating composition having room temperature drying property - Google Patents

Description

TECHNICAL FIELD The present invention relates to a baking coating composition mainly used for metals, and more particularly to a baking coating composition which is dried at room temperature and hardens by heating for a short time. is there.

[Prior Art] Conventionally known resin compositions such as acrylic resin-melamine resin, alkyd resin, and-melamine resin have been known as baking coating compositions. These baking paints are generally 120 ° C.
A coating film is formed by drying and curing by heating at a temperature of ~ 140 ° C for 20 minutes to 30 minutes. Also, a urethane coating composition is known as a coating composition which is similarly dried by heating. This urethane coating composition mixes a main component such as an acrylic resin or a polyester resin with a curing agent component composed of an active isocyanate compound and heats the mixture to accelerate a crosslinking reaction between an isocyanate group and a hydroxyl group.

On the other hand, a lacquer is known as a paint having a room temperature drying property. This lacquer has nitrocellulose lacquer, CA
B (cellulose acetate butyrate) lacquer, acrylic lacquer, and the like are known. High-molecular-weight resins dissolved or dispersed in a solvent form a film by volatilization of the solvent to form a coating film.

[Problems to be Solved by the Invention] Conventionally, the above-mentioned baking coating requires a high heating temperature of 120 ° C. to 140 ° C., and requires a long heating time of 20 minutes to 30 minutes. For that purpose, a special drying furnace was required, and a large amount of heat energy was required. Further, in the urethane coating composition, the main ingredient component and the active isocyanate compound are allowed to react at room temperature, so that they are generally supplied as a two-pack type coating composition to be mixed immediately before use. Therefore, it took a lot of man-hours to mix and the workability was poor. In order to solve this problem, it is also known to use a blocked isocyanate obtained by blocking active isocyanate with various blocking agents. However, even a urethane coating composition generally requires a long heating time before being cured, and has the same problems as the above-mentioned baking coating.

On the other hand, lacquer is used in various fields because it is dry at room temperature and has very good workability. However, oil, ink, etc. may adhere to the coated surface during the manufacturing process. In this case, it is a simple method to wipe off with a cloth soaked with an organic solvent, but since the lacquer coating has poor solvent resistance, this method has a problem that the coating is affected.

The present invention has been made in view of such circumstances,
It is intended to provide a baking coating composition which has the same room-temperature drying property as a lacquer, and is crosslinked by heating for a short time to exhibit solvent resistance.

[Means for Solving Problems] The baking coating composition having room temperature drying properties of the present invention contains a solvent and a hydroxyl group of at least one of a primary hydroxyl group and a secondary hydroxyl group which is dissolved or dispersed in the solvent. A high-molecular-weight resin having a weight-average molecular weight of 10,000 to 200,000 and a glass transition temperature of 40 ° C. or higher, and dissolved or dispersed in the solvent to dissociate by heat to form an active isocyanate compound, which is an isocyanate group equivalent of the active isocyanate compound. And a blocked isocyanate compound blended in such a manner that the ratio of the hydroxyl group equivalent of the high molecular weight resin is NCO / OH = 0.05 to 1.0.

The high molecular weight resin used in the present invention has at least one hydroxyl group of primary hydroxyl group and secondary hydroxyl group. That is, the hydroxyl group and the isocyanate group to be described later are crosslinked to allow the solvent resistance to appear. The hydroxyl value of this hydroxyl group is preferably 10 to 300.
When the hydroxyl value is less than 10, the cross-linking density becomes low and the solvent resistance becomes insufficient, and when the hydroxyl value is more than 300, the amount of the blocked isocyanate compound described later increases, so that the coating film becomes too hard. And leads to higher costs.

This high molecular weight resin has a weight average molecular weight of 10,000 to 200,000 and a glass transition temperature above room temperature. When the weight average molecular weight is less than 10,000, the dryness at room temperature becomes poor,
If it is more than 200,000, it will be difficult to dissolve it in the solvent described below, and if it is dissolved in a large amount, the viscosity of the coating material will increase and problems will occur during use, so the amount of dissolution will be limited. As a result, the non-volatile content of the blended paint is reduced, and the film thickness of the resulting coating film is extremely thin. Further, when the glass transition temperature is lower than room temperature, the drying property at room temperature becomes poor. Generally, it is desirable to use one having a glass transition temperature of about 40 ° C or higher.

As the above-mentioned high molecular weight resin, for example, epoxy resin, acrylic resin, cellulose acetate butyrate or the like can be used.

Blocked isocyanate compound used in the present invention, the isocyanate group of the active isocyanate compound conventionally used in urethane resin coatings, phenol, cresol,
It is blocked with a blocking agent such as an aromatic secondary amine, a tertiary alcohol, a lactam, or an oxime, and these blocking agents can be dissociated by heat to form an active isocyanate compound. As the active isocyanate compound to be blocked, various active isocyanate compounds such as tolylene diisocyanate (TDI), methylene diisocyanate (MDI), xylylene diisocyanate (XDI) and hexamethylene diisocyanate (HMDI) can be used.

This blocked isocyanate compound, the ratio of the isocyanate group equivalent of the active isocyanate compound generated by dissociation by heat and the hydroxyl group equivalent of the high molecular weight resin is 0.05 to
Blended to be between 1.0. Where the ratio is 0.05
When it is less than 1.0, the crosslink density is low and the solvent resistance is poor, and when it is more than 1.0, the coating film becomes hard and lacks flexibility.

The dissociation temperature of the blocking agent of blocked isocyanate is not particularly limited, but a temperature as low as possible at room temperature (40 ° C) or higher is desirable.

The high molecular weight resin and the blocked isocyanate compound are used in a state of being dissolved or dispersed in a solvent. As the solvent, a mixture of plural kinds of organic solvents is generally used. When an organic solvent mixture is used, its blending is determined in consideration of the solubility of the high molecular weight resin and the blocked isocyanate compound and the evaporation rate of each solvent. In addition, a NAD containing a high molecular weight resin and a blocked isocyanate compound dispersed in it is used with a solvent with a weak solubility.
It is also possible to

The above-mentioned solution or dispersion may be used as it is, or similarly to conventional paints, it is also possible to use conventionally known paint formulations such as color pigments, extender pigments, dispersants, and various additives. Absent.

[Operation and Effect of the Invention] In the baking coating composition of the present invention, a high molecular weight resin having a molecular weight of 10,000 to 200,000 and a glass transition temperature of room temperature or higher is blended. Therefore, the film is formed only by evaporating the solvent and has the same room-temperature drying property as the lacquer. In addition, the blocked isocyanate is dissociated by heating, and the generated active isocyanate acts as a crosslinking agent to crosslink the high molecular weight resins, but the high molecular weight resin itself is a polymer, and thus only slightly crosslinks. Then, it becomes a super macromolecule and solvent resistance appears. That is, the solvent resistance can be imparted by heating for a short time only by adding the amount of heat necessary for the blocked isocyanate to dissociate.

Further, when the coating composition of the present invention is used as a baking paint, even if the temperature in the baking oven falls to room temperature due to, for example, a failure, since the coating film is in a dry state, it can be touched with a coated product before baking. Further, the coated products can be stacked and stored until the temperature of the drying oven becomes normal. Therefore, it is not necessary to stop the painting line, and the hindrance to production can be minimized.

[Examples] Specific examples will be described below. All parts and% s mentioned below mean parts by weight and% by weight.

(Example) Bisphenol A type epoxy resin as a high molecular weight resin (weight average molecular weight 92000, hydroxyl value 120, glass transition point 12
100 parts and TDI isocyanate compound blocked by alcohol (manufactured by Nippon Polyurethane Co., Ltd.) 10
Parts were dissolved in 100 parts of an organic solvent mixture consisting of 60% methyl ethyl ketone and 40% xylene. 5 parts of carbon black and 50 parts of calcium carbonate were mixed with this resin liquid and dispersed in a ball mill to prepare a baking coating composition according to an example of the present invention. In this composition, the blocked isocyanate compound dissociates at 120 ° C. to become an active isocyanate compound, and the ratio of the isocyanate group equivalent to the hydroxyl group equivalent of the epoxy resin is 0.3.

(Comparative Example 1) 100 parts of nitrocellulose (viscosity 1/4 seconds, manufactured by Asahi Kasei Co., Ltd.) and 200 seconds of viscosity nitro in 200 parts of a mixed solvent consisting of 35% xylene, 50% methyl ethyl ketone, and 15% isopropyl alcohol. 50 parts of cellulose, 20 parts of dibutyl phthalate (DBP), and 30 parts of carbon black were mixed and 10 parts of the color chips, which had been previously dispersed, were stirred and dissolved with a despar to prepare the lacquer of Comparative Example 1.

(Comparative Example 2) 100 parts of short oil length alkyd resin (Phtalkid 133-60, manufactured by Hitachi Chemical Co., Ltd.), 20 parts of methylol melamine resin (Nicalac MX-031, manufactured by Sanwa Chemical Co., Ltd.) and 100 parts of xylene. Mix and further carbon black 5
Parts and 20 parts of calcium carbonate were mixed and dispersed in a ball mill to prepare the baking coating composition of Comparative Example 2.

(Test) Using the coating compositions of Examples, Comparative Examples 1 and 2 obtained as described above, the coating viscosity (20 seconds, Ford cup NO4, 20 ° C) was diluted with a dedicated thinner, and then air-sprayed on a steel sheet. It was coated so that the dry film thickness would be 20μ. Then, the drying conditions were 20 ° C. × 10 minutes, 120 ° C. × 2 minutes, and 120 ° C. × 20 minutes, and three points were taken and dried under these conditions.

The obtained test pieces were tested for pencil hardness and lacquer thinner resistance, and the results are shown in the table. Also, the dryness to touch of the coating film after standing for 10 minutes at 20 ° C. was tested, and the results are shown in the same table.

Here, the pencil hardness is expressed by the hardness of the pencil immediately before scratching each coating film with a pencil of various hardness. The lacquer thinner resistance was evaluated by visually observing the state of the coated surface after being immersed in the lacquer thinner for 24 hours, taken out and dried. As for the evaluation, there was no abnormality, and the one completely dissolved was marked with x.

The touch dryness was evaluated by touching the coated surface with a finger and evaluating the degree of dryness. As for the evaluation, there is no stickiness ○, and there is stickiness ×
And

(Evaluation) Clearly from the table, the coating compositions of the examples of the present invention were 20 ° C x 10
It is sufficiently dried even under a drying condition of a minute, and has the same performance as the lacquer of Comparative Example 1. Also, the lacquer thinner resistance appears only by drying at 120 ° C for 2 minutes. On the other hand, the lacquer of Comparative Example 1 is naturally inferior in lacquer thinner resistance, and the baking coating composition of Comparative Example 2 is inferior in normal temperature dryness.
That is, the coating composition of the present invention has room temperature drying properties and exhibits solvent resistance by heating for a short time.

Claims (2)

[Claims] 1. A solvent and a solvent which is dissolved or dispersed in the solvent and has at least one hydroxyl group of a primary hydroxyl group and a secondary hydroxyl group and has a weight average molecular weight of 10,000 to 200,000 and a glass transition temperature of 40 ° C. or higher. And a high molecular weight resin having a high molecular weight resin, which is dissolved or dispersed in the solvent and dissociated by heat to form an active isocyanate compound, and the ratio of the isocyanate group equivalent of the active isocyanate compound to the hydroxyl group equivalent of the high molecular weight resin is NCO / OH = 0.05 to 1.0. A baked coating composition having room temperature drying properties, which comprises a blocked isocyanate compound blended so that 2. A baking coating composition having room temperature drying properties according to claim 1, wherein the high molecular weight resin has a hydroxyl value of 10 to 300.