JPS6234077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a powder coating material with improved boiling water resistance and recoatability. To make powder coatings, pigments are melted and dispersed in resin in an extruder, but in the case of thermosetting resins, there is a particular risk of gelation, and the process must be carried out in a short period of time. Sufficient dispersion cannot be expected. Therefore, a method has been adopted in which the pigment is premixed with the resin without a curing agent. (For example, the invention described in Japanese Patent Application Laid-Open No. 52-47031.) However, the powder obtained by treating the pigment with a resin in advance, adding a curing agent, etc. to it, and melting and kneading it in an extruder. Although the paint has good pigment dispersion and forms a smooth coating film, the coating film has the disadvantage of poor boiling water resistance and recoatability. To this end, the present inventors added a resin having a crosslinkable functional group together with a hardening agent to a colored resin composition obtained by premixing and dispersing a resin containing a crosslinkable functional group in a pigment without a hardening agent. He previously applied for an invention in which dry mixing was performed, then melt-kneaded using an extruder, and then mechanically pulverized (Japanese Patent Laid-Open No. 54
-50533). However, even with the powder coating obtained in this way, although a coating film with excellent gloss, sharpness, and smoothness can be obtained, the disadvantage is that the coating film still has poor secondary adhesion and recoatability. It is. In view of this, the present inventor has conducted extensive research and found that (A) a premix of a pigment and a thermosetting resin, (B) 5 to 100 parts by weight per 100 parts by weight of the pigment contained in (A).
Parts by weight of the same or different pigments, (C) at least 5 parts by weight of a thermosetting resin based on 100 parts by weight of the resin contained in (A), and (D) a curing agent are melt-kneaded and pulverized by a conventional method. We discovered that the thermosetting powder coating obtained by this method has a good pigment dispersion state, and therefore has excellent coating film smoothness and sharpness, with almost no decrease in boiling water resistance or recoatability. He came up with an invention. Accordingly, the present invention provides a method for producing such a thermosetting powder coating. The method of the present invention is particularly effective when the base resin is a vinyl polymer having a glycidyl group as a functional group. Such resins often have poor pigment dispersibility. Furthermore, the method of the present invention is particularly effective when it is necessary to incorporate a large amount of titanium oxide as a pigment in order to increase the negative power. The premix of a pigment and a thermosetting resin in the present invention is a pigment that has been treated with a resin in advance. There are no particular limitations on the processing method, but extremely advantageous methods include mixing the pigment with a molten resin and kneading it with an extruder, or dispersing the pigment in a resin solution and solidifying it by removing the solvent. Examples include. The ratio of pigment to resin in the premix varies depending on the type of pigment, and for example, in the case of an inorganic white pigment, a ratio of 70/30 to 30/70 (weight ratio) is appropriate. The pigment to be mixed later is preferably the same as or similar to the pigment used in the premix. Its usage amount depends on the amount of pigment contained in the premix
5 to 100 parts by weight, preferably 10 to 100 parts by weight
The amount is 50 parts by weight, and if it exceeds 100 parts by weight, the appearance of the coating film will deteriorate. The resin to be mixed subsequently must be the same as the resin used in the premix or contain functional groups or functional groups having the same reactivity as the resin. The amount used is at least 5 parts by weight, preferably 10 to 200 parts by weight, based on 100 parts by weight of resin contained in the premix. The effect of the present invention cannot be achieved even if only one of the pigments and the resin is mixed later, and the object of the present invention cannot be achieved if the amount is outside the scope of the present invention. In view of the effects of the present invention, titanium oxide is preferred as the pigment to be used, but other known organic or inorganic pigments may also be used. As for the resin, vinyl polymers having glycidyl groups are most preferable, but thermosetting resins such as vinyl polymer polyesters and epoxy resins having hydroxyl groups and carboxyl groups can also be used. The curing agent is selected according to the functional group of the resin used, and when the functional group is glycidyl group, sebacic acid,
Examples include dibasic acids such as decanedicarboxylic acid, blocked isocyanate compounds and melamine resins in the case of hydroxyl groups, and epoxy resins in the case of carboxyl groups. Regarding the means for embodying the manufacturing method of the present invention,
Although there is no particular limitation, generally a premix, a pigment,
A method is adopted in which the thermosetting resin, curing agent, other fluidity regulators, etc. are dry mixed, then melt-kneaded using an extruder, cooled, and pulverized. Next, the present invention will be explained by examples. still,
Parts represent parts by weight. Example 1 20 parts of glycidyl methacrylate 10 parts of β-methyl glycidyl methacrylate Stirring was continued for a further 8 hours to obtain a 50% solution of the vinyl copolymer. The solvent was directly removed from this solution using a thin film evaporator to obtain a polymer. Separately, 100 parts of titanium oxide was added to 200 parts of the above copolymer solution, and after stirring and mixing, the solvent was removed in the same manner to obtain a preliminary mixture of pigment and resin. Next, 100 parts of the premix, 10 parts of polymer, 10 parts of titanium oxide, 0.5 parts of 2-ethylhexyl acrylate polymer (flow regulator), and 10 parts of decanedicarboxylic acid were dry mixed in a mixer, and then extruded in an extruder (co-kneader manufactured by Buss). Melt and knead at 100℃, cool to room temperature, crush, pass through a 200 mesh wire mesh,
The resulting PWC46% powder coating was applied to a zinc phosphate treated iron plate by electrostatic spraying and baked at 180°C for 20 minutes. Comparative Example 1 A coating film was obtained in exactly the same manner as in Example 1 except that titanium oxide was not post-added. Comparative Example 2 A coating film was obtained in exactly the same manner as in Example 1 except that the polymer was not post-added. Comparative Example 3 A coating film was obtained in the same manner as in Example 1 except that 50 parts of the polymer and 50 parts of titanium oxide were used instead of the premix. Example 2 Glycidyl methacrylate 20 parts β-methylglycidyl acrylate 5 parts Styrene 30 parts Dibutyl fumarate 15 parts β-hydroxyethyl methacrylate 5 parts Isobutyl methacrylate 25 parts 3 parts azobisisobutyronitrile and 1 part benzoyl peroxide were heated at 100°C. The mixture was added dropwise to 100 parts of xylene over 2 hours, and stirring was continued for 8 hours at the same temperature to obtain a 50% solution of the vinyl copolymer. Next, this resin solution was supplied to a thin film evaporator and subjected to solvent removal treatment to obtain a polymer. The obtained polymer (resin temperature: 170° C.) and titanium oxide were continuously supplied to a twin screw extruder at a ratio of 1:1 (weight ratio) to obtain a premix. The barrel temperature of this twin-screw extruder was 170°C. Next, 5 parts of the polymer, 5 parts of titanium oxide, 9 parts of decanedicarboxylic acid, and 0.5 parts of 2-ethylhexyl acrylate polymer (flow regulator) were added to 100 parts of this colored premix that had been cooled to room temperature, and mixed in a mixer. After dry mixing, the mixture was melted and kneaded at 100℃ using a Conida extruder, crushed, and then separated using a 200 mesh wire mesh to form PWC46.
% powder coating was obtained. After that, the powder coating of 200 mesh or less obtained in this way was applied to a mild steel plate by electrostatic spraying.
Baked at 180°C for 20 minutes. Test Example The appearance and physical properties of the coating films obtained in each Example and Comparative Example were investigated. (1) Secondary adhesion After immersing in boiling water for 30 minutes, cross-cut the paint film, apply cellophane tape, peel it off, and compare the adhesion of the paint film. (2) Recoatability After painting and baking the paint film again under the same conditions, cross-cut the paint film, stick cellophane tape on it, and then peel it off. Interlayer adhesion between the upper and lower paint films. Compare. 【table】

Claims (1)

[Claims] 1. (A) A premix of a pigment and a thermosetting resin, (B) 5 to 100 parts by weight per 100 parts by weight of the pigment contained in (A).
parts by weight of the same or different pigments; (C) at least 5 parts by weight of a thermosetting resin having the same or the same reactive functional groups per 100 parts by weight of the resin contained in (A); and (D) curing. A method for producing a thermosetting powder coating, which comprises melting, kneading, and pulverizing the agent.