JPS62252472A - Baking paint composition having room temperature dryability - Google Patents

Abstract

PURPOSE:To obtain a baking paint compsn. which can be dried at room temp. and can be cured in a short time by heating, consisting mainly of a solvent, a specified high-molecular resin and a specified compd. capable of being converted into an active isocyanate compd. CONSTITUTION:A paint compsn. consists mainly of a solvent (A), a high- molecular resin (B) having primary hydroxyl groups and/or secondary hydroxyl groups, a weight-average MW of 10,000-200,000 and a glass transition temp. of not lower than room temp. which is dissolved or dispersed in said solvent, and a blocked isocyanate compd. (C) which is dissolved or dispersed in said solvent, can be dissociated by heat to form an active isocyanate compd. and is used in such an amount as to give a ratio (NCO/OH) of the isocyanate group of the active isocyanate compd. to the hydroxyl group of the resin of 0.05-1.0. Examples of the resin are epoxy resins, acrylic resins, cellulose acetate butyrate, etc.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a baking paint composition mainly used for metals, and more specifically to a baking paint composition that dries even at room temperature and hardens with short heating. be.

[Prior Art] As conventional baking paint compositions, resin-based compositions such as acrylic resin-melamine resin and alkyd resin-melamine resin are known. These baking paints are generally heated at 120°C.
By heating at a temperature of ~140°C for 20 to 30 minutes, it is dried and cured to form a coating film. Also, urethane paint compositions are known as one-component compositions that are similarly heat-dried. This urethane coating composition consists of acrylic resin, poly 1
A main component such as a stell resin and a curing agent component consisting of an active isocyanate compound are mixed and heated to promote the crosslinking reaction between the isocyanate and water MM.

On the other hand, lacquer is known as a paint that dries at room temperature. This lacquer includes nitrocellulose lacquer, C
AB (cellulose acetate butyrate) lacquer,
Acrylic lacquers and the like are known, and a high molecular weight resin dissolved or dispersed in a solvent forms a film by volatilization of the solvent.

[Problems to be solved by the invention] Conventionally, the above-mentioned baking paint has a heating temperature of 120°C to 140°C.
A high temperature is required, and the heating time is also 20 minutes to 30 minutes.
It took a long time, about minutes.

For this purpose, a dedicated drying oven was required, and a large amount of thermal energy was also required. Furthermore, in urethane coating compositions, since the reaction between the main component and the active isocyanate compound proceeds even at room temperature, they are generally supplied as a two-component coating that is mixed immediately before use. Therefore, it took a lot of man-hours to mix, resulting in poor workability. In order to solve this problem, it is also known to use blocked isocyanates obtained by blocking active isocyanates with various blocking agents. However, urethane coating compositions generally require a long heating time to cure, and have the same problems as the baking coatings described above.

On the other hand, lacquer dries at room temperature and has very good workability, so it is used in various fields. However, during the manufacturing process, oil, ink, etc. may adhere to the surface. In this case, a simple method is to wipe it off with a cloth soaked in organic solvent, but lacquering! l! Because of its poor solvent resistance, this method had the problem that the coating film would become airborne.

The present invention was made in view of these circumstances, and
The present invention provides a baking paint composition that has room temperature drying properties comparable to lacquers, and that can be crosslinked by short-term heating to develop solvent resistance.

[Means for Solving the Problems 1] The baking paint composition of the present invention, which is dryable at room temperature, comprises a solvent, a primary hydroxyl group, and at least one of the primary hydroxyl groups dissolved or dispersed in the solvent. A high molecular weight resin having an average molecular weight of 10,000 to 200,000 and a glass transition temperature above room temperature, and a high molecular weight resin that is dissolved or dispersed in the solvent and dissociated by heat to become an active isocyanate compound and the isocyanate group of the active isocyanate compound. The ratio between the equivalent weight and the molecular weight 14 fat water Fl is NCO/OH=0.0
It is characterized in that the main component is a blocked isocyanate compound blended so as to have a concentration of 5 to 1.0.

The high molecular weight resin used in the present invention has at least one of a primary hydroxyl group and a secondary water Mu. That is, the water IIM and the isocyanate group described below are crosslinked to exhibit solvent resistance. The hydroxyl value determined by water IIM is preferably 10 to 300. If this hydroxyl value is less than 10, the crosslinking density will be low and solvent resistance will be insufficient, and if the water WI value is more than 300, the amount of the blocked isocyanate compound described below will be increased. 1 The film may become too hard, leading to increased costs.

This polymer is a resin! It has a weight average molecular weight of 10,000 to 200,000 and a glass transition temperature above room temperature. If the weight average molecule a is less than 10,000, the room temperature drying property will be poor, and if it is larger than 20,000, it will be difficult to dissolve in the solvent described below, and if it is dissolved in many mouths, the viscosity of the paint will increase. However, problems occur during use, and the amount of dissolution is limited. As a result, the nonvolatile content of the blended paint decreases, and the thickness of the resulting paint film also becomes extremely thin. Furthermore, if the glass transition temperature is lower than room temperature, the room temperature drying properties will be poor. Generally, it is desirable to use a glass transition temperature of about 40'C or higher.

As the above-mentioned polymeric ff1sl resin, for example, epoxy resin, acrylic resin, cellulose acetate butyrate, etc. can be used.

The blocked isocyanate compound used in the present invention is a conventional urethane resin [the isocyanate group of the active isocyanate compound used in material 1] is
It is possible to use a compound blocked with a blocking agent such as an aromatic secondary amine, a tertiary alcohol, a lactam, or an oxime, which is dissociated by heat to become an active isocyanate compound. Examples of active isocyanate compounds to be blocked include tolylene diisocyanate (TOI), methylene diisocyanate (MD I), xylylene diisocyanate (XDI), and hexamethylene diisocyanate (HM).
Various active isocyanate compounds such as D I ) can be used.

This blocked isocyanate compound has a ratio of the isocyanate group equivalent of the active isocyanate compound generated by thermal dissociation to the hydroxyl group equivalent of the high molecular weight resin of 0.0.
It is blended so that it is between 5 and 1.0. If the ratio is less than 0.05, the crosslinking density will be low and solvent resistance will be poor, and if it is larger than 1.0, the coating will become hard and lack flexibility.

Solution 11 The temperature of the blocking agent for blocked isocyanate is not particularly limited, but a temperature as low as possible above room temperature (40° C.) is desirable.

The above polymeric female resin and blocked isocyanate compound are used in a state dissolved or dispersed in a solvent. Generally, a mixture of a plurality of organic solvents is used as this solvent. In addition, when using an organic solvent mixture, the blending thereof is determined by taking into account the solubility of the high molecular weight resin and the blocked isocyanate compound, as well as the evaporation rate of each solvent. In addition, using a solvent with weak dissolving power, NA in which a high molecular weight resin and a blocked isocyanate compound are dispersed is used.
It is also possible to set it as D.

The above solutions or dispersions may be used as they are, or similarly to conventional paints, conventionally known paint formulations such as coloring pigments, extender pigments, dispersants, and various additives H1 may be used. do not have.

[Operation and efficacy of the invention] The baking paint composition of the present invention has a molecular weight of 10,000 to 200,000,
A high molecular weight resin having a glass transition temperature of 1 or higher is usually blended. Therefore, it forms a film simply by volatilization of the solvent, and has room temperature drying properties equivalent to lacquer. In addition, when heated, the blocked isocyanate dissociates, and the generated active isocyanate acts as a crosslinking agent, causing the above-mentioned high molecular weight resins to crosslink, but since the high molecular weight resin itself is a polymer, it is only slightly crosslinked. It becomes a large molecule and exhibits solvent resistance. In other words, solvent resistance can be imparted by heating for a short period of time by simply absorbing the amount of heat necessary for dissociating the blocked isocyanate.

[Example] The following is a concrete explanation using Examples. Note that the parts and % mentioned below mean a total of 11 color parts and lff1%.

(Example) Bisphenol A type epoxy resin (
Weight average molecule ff 192000, hydroxyl value 120, glass transition point 120°C) 100i'! S oyo'rf? 10 parts of alcohol-blocked TDI isocyanate compound (Nippon Polyurethane Co., Ltd.%) and 10 parts of an organic solvent mixture consisting of 60% methyl ethyl ketone and 40% xylene.
Dissolved in 0 parts. 5 parts of carbon black and 50 parts of calcium carbonate were blended with this resin liquid and dispersed in a ball mill to prepare a baking paint composition according to an example of the present invention.

In addition, in this composition, the blocked isocyanate compound dissociates at 120°C to become an active isocyanate compound, and the isocyanate group equivalent and the water W of the epoxy resin
The ratio to the i-base layer is 0.3.

(Comparative Example 1) In 200 parts of a mixed solvent consisting of 35% xylene, 50% methyl ethyl ketone, and 15% isopropyl alcohol, 100 parts of Nido-O Cell O-S (viscosity 1/4 second, manufactured by Asahi Kasei Corporation) and a viscosity of 1. A lacquer of Comparative Example 1 was prepared by stirring with a death bar and dissolving 10 parts of color chips in which 50 parts of nitrocellulose, 20 parts of dibutyl phthalate (DBP), and 30 parts of carbon black were mixed and dispersed in advance.

(Comparative Example 2) 100 parts of short oil length alkyd rsm<7 Talkyd 133-60, manufactured by Hitachi Chemical Co., Ltd.), 20 parts of methylolmelamine resin (Nikaratsuku MX-031, manufactured by Sanwa Chemical Co., Ltd.), and 100 parts of xylene 5 parts of carbon black and 20 parts of calcium carbonate were mixed and dispersed in a Pall mill to prepare a baking paint composition of Comparative Example 2.

(Test) According to the above (9) Examples, Comparative Example 1 and Comparative Example 2
Using the following paint compositions, each was diluted with a dedicated thinner to a coating viscosity (20 seconds, Ford Cup No. 4, 20°C), and then painted onto a steel plate by air spraying to a dry film thickness of 20 μm. The drying conditions were 20℃ x 10 minutes, 120℃
It was dried under three conditions: 2 minutes at 120°C and 20 minutes at 120°C.

(The test pieces were tested for pencil hardness and lacquer thinner resistance, and the results are shown in the table. In addition, the dryness to the touch of the coating film after being left at 20°C for 10 minutes was tested, and the results are also shown in the table. .

Here, pencil hardness is expressed by scratching each coating film with pencils of various hardnesses, and the hardness of the pencil just before scratches occur. Lacquer thinner resistance was evaluated by visually evaluating the state of the table surface after immersing it in lacquer thinner for 24 hours, taking it out and drying it. As for the evaluation, ○ indicates no abnormality, and × indicates complete dissolution.

Dryness to touch was evaluated by touching the coated surface with a finger and evaluating the degree of dryness. As for the evaluation, non-adhesive is O1, and adhesive is ×
And so.

(Evaluation) It is clear from the table that the coating composition of the example of the present invention was
It dries sufficiently even under drying conditions of 10 minutes, and has the same performance as the lacquer of Comparative Example 1. In addition, lacquer thinner resistance appears just by drying at 120°C for 2 minutes. On the other hand, the lacquer of Comparative Example 1 naturally has poor lacquer thinner resistance, and the baking paint composition of Comparative Example 2 has poor room temperature drying properties.

That is, the coating composition of the present invention has room temperature drying properties and exhibits solvent resistance when heated for a short time.

Claims (2)

[Claims] (1) A polymer having a solvent, dissolved or dispersed in the solvent, having at least one of a primary hydroxyl group and a secondary hydroxyl group, a weight average molecular weight of 10,000 to 200,000, and a glass transition temperature above room temperature. The resin 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=
1. A baking paint composition having normal temperature drying properties, comprising as a main component a blocked isocyanate compound blended so as to have a concentration of 0.05 to 1.0. (2) The baking paint composition having room temperature drying properties according to claim 1, wherein the high molecular weight resin has a hydroxyl value of 10 to 300.