JPH11302567A - Production of thermosetting coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously produce the subject thermosetting type coating composition for forming the coating film having a high grade of finish appearance by adjusting the amount of organic solvents in a specific range and performing the evacuation, heating, melting and kneading in the one-pot process. SOLUTION: A solution of the raw materials for a thermosetting type powdered coating of 10-90 wt.% of solid components dispersed or dissolved in an organic solvent is heated, molten and mixed under a reduced pressure so that the organic solvent in the solution is removed until its content decreases to 1.6-5 wt.%. In an embodiment, a thermosetting type resin for powdered paint, for example, a glycidyl group-bearing acrylic resin is prepared in an organic solvent, then a curing agent, for example, an aliphatic polycarboxylic acid or the like is formulated to the resin solution to obtain the solution having predetermined specifications. Then, the solution S is thermally molten and kneaded under a reduced pressure to remove a prescribed amount of the organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel method for producing a thermosetting coating composition.

[0002]

2. Description of the Related Art Conventional powder coating compositions have been produced by dry-blending a curable resin, a curing agent, and additives, mixing and dispersing them by a melt kneader, and then pulverizing and classifying.

However, in this method, the curable resin and the curing agent are melted by heat and kneaded, so that the reaction between the curable resin and the curing agent proceeds to increase the molecular weight. For this reason, there is a problem that the melt viscosity of the powder coating material is increased and the finish is reduced.

[0004] As a method of improving such a problem,
A method in which a raw material solution for a powder coating obtained by dissolving a raw material for a powder such as a curable resin, a curing agent, and an additive in an organic solvent is melt-kneaded under reduced pressure while removing the compounded organic solvent (Japanese Patent Application Laid-Open JP-A-53-50232, JP-A-53-50233, JP-A-53-50234 and JP-A-5-31
No. 1096) is known. However, the powder coatings obtained by these known methods contain no organic solvent or have been adjusted to an amount of 1.5% by weight or less. It was found that a coating film having an excellent finished appearance could not be obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to establish a method for producing a thermosetting powder coating composition capable of forming a coating film having a higher finished appearance in the conventional method.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in the conventional production method, in particular, by adjusting the amount of the organic solvent to a specific range, the conventional method was used. It turns out that the problem can be solved,
The present invention has been completed.

That is, the present invention relates to: 1. A solid content of 10 to 10 dissolved or dispersed in an organic solvent.
A raw material solution for a thermosetting powder coating material in a range of 90% by weight is removed while heating and melting under reduced pressure so that the amount of the organic solvent is in a range of 1.6 to 5% by weight. 2. A method for producing a thermosetting coating composition, 2. The following steps (1) a step of producing a thermosetting powder resin with an organic solvent solution to obtain an organic solvent resin solution, and (2) the organic solvent resin solution A step of mixing a curing agent therein to obtain a raw material solution for a thermosetting powder coating material having a solid content of 10 to 90% by weight, and (3) the amount of the organic solvent is in a range of 1.6 to 5% by weight. And a step of obtaining a thermosetting powder coating composition by removing while heating and mixing under reduced pressure to obtain a thermosetting powder coating composition.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The raw material solution for a thermosetting powder coating material used in the present invention is obtained by dissolving or dispersing a curable resin, a curing agent and, if necessary, an additive in an organic solvent. As the curable resin, an acrylic resin, a polyester resin, an epoxy resin, a silicone resin, a fluorine resin, and two or more modified resins having functional groups such as an epoxy group, a hydroxyl group, and a carboxyl group which are solid at room temperature. Alternatively, a mixed resin or the like is used. The curable resin preferably has a glass transition temperature of 40 to 100 ° C, preferably 50 to 80 ° C, and a number average molecular weight of 1,000 to 30,000, preferably 2000 to 10,000. If the glass transition temperature is lower than 40 ° C., the resulting powder coating is not preferred because the particles fuse together and the blocking resistance deteriorates. On the other hand, when the temperature is higher than 100 ° C., not only the viscosity at the time of heat flow increases but the finish property decreases, but also the solubility decreases. When the number average molecular weight is less than 1,000, the blocking resistance of the powder coating material is poor. When the number average molecular weight exceeds 30,000, the finished appearance of the coating film is inferior, so that it is not preferable. The glass transition temperature can be determined by, for example, DSC (Differential Scanning Calorimeter).

As the curing agent, aliphatic polycarboxylic acids and their (poly) acid anhydrides, aromatic polycarboxylic acids and their (poly) acid anhydrides, aliphatic, alicyclic or aromatic polyisocyanates, and phenols Block isocyanate compounds such as those blocked with a blocking agent such as caprolactams and alcohols, polyepoxy compounds, aminoplast resins, amide compounds, acid hydrazides and the like.

[0010] Among the above, it is preferable to apply a powder coating composition obtained by blending an aliphatic polycarboxylic acid (particularly dodecane diacid) to a glycidyl group-containing acrylic resin in the method of the present invention.

In addition to the above, if necessary, for example,
Anti-armpit agent, surface conditioner, antioxidant, ultraviolet absorber,
Additives such as an ultraviolet stabilizer, an anti-blocking agent, a flow regulator, a charge control agent, a filler, and a curing accelerator can be blended.

As the organic solvent, a solvent which can dissolve or disperse a curable resin and remove it by heating and reduced pressure is preferable. As the organic solvent, those having a boiling point of 50 to 300 ° C. are preferable, and in particular, toluene, xylene, ethyl acetate, butyl acetate, cellosolve, methyl cellosolve, methyl cellosolve acetate, cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether , And propylene glycol monomethyl ether are preferably used as the main organic solvent. These main organic solvents can be used alone or in combination of two or more. Further, in addition to the main organic solvent described above, other organic solvents other than those described above may be used in combination.

In the present invention, in particular, in a powder coating material using a glycidyl group-containing acrylic resin as a base resin and dodecanediacid as a curing agent, an organic solvent that dissolves the base resin and does not dissolve dodecanediacid, for example, xylene , Toluene and the like, and as the organic solvent for dissolving the base resin and dodecanediacid, for example, an organic solvent such as a cellosolve type or an ether type is preferably used. These organic solvents can be used as a mixture of two or more kinds.

The content of the organic solvent contained in the raw material solution for the thermosetting powder coating is 10 to 90% by weight, preferably about 2% by weight.
It is in the range of 0 to 80% by weight. When the amount of the organic solvent is less than 10% by weight, the viscosity of the raw material solution becomes high and handling becomes difficult. On the other hand, when the amount exceeds 90% by weight, it takes too much time to remove the solvent, resulting in poor productivity.

In the thus obtained raw material solution for thermosetting powder coating composition, the amount of the organic solvent contained in the finally obtained thermosetting powder coating composition is 1.6 to 5% by weight, preferably 1.
It is removed so as to be in the range of 8 to 4% by weight. When the amount of the organic solvent is less than 1.6% by weight, the smoothness of the coating film becomes poor, while when it exceeds 5% by weight, the blocking resistance of the powder coating material becomes poor. Adjustment of the content of the organic solvent is performed, for example, by setting pressure reduction conditions in advance so that the amount of the organic solvent falls within the above-described range, and heating and mixing under the set pressure reduction. Alternatively, it can be produced by blending a specific amount of an organic solvent that can be removed under reduced pressure and an organic solvent having a high boiling point (for example, 140 to 300 ° C.) that cannot be removed under reduced pressure. Further, it is preferable to use, as the high boiling point organic solvent, one that volatilizes by baking a coating film.

As a device capable of heating and melting and mixing the above-mentioned raw material solution under reduced pressure, a conventional device can be used without any particular limitation. There are many such devices that have been conventionally used.
No. 3253, screw type heating / cooling apparatus, 2-25
No. 8043, a heating type stirring heat treatment machine and the like.

The powder coating obtained by heating and melting and mixing the raw material solution under reduced pressure is finally manufactured by cooling, coarse pulverization, fine pulverization and classification.

In the method of the present invention, particularly in the above-mentioned step, the organic solvent resin solution is prepared by, for example, using a raw material such as an acrylate ester monomer or other unsaturated monomer which becomes an acrylic resin in an organic solvent as a catalyst for a radical initiator. Can be used as it is as an organic solvent resin solution obtained by performing a solution radical polymerization reaction in the presence of. That is, the steps of synthesizing the resin and mixing the curing agent can be performed simultaneously in the reaction vessel, and the next step of depressurization, heating and melting and mixing can be performed by one apparatus, and these steps are continuously performed. High productivity because it can be combined.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments. Unless otherwise specified, “parts” or “%” represents a weight basis.

Example 1 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device was charged with 100 parts of xylene, heated to 82 ° C. while blowing nitrogen gas, and heated to 50 parts of cyclohexyl methacrylate. , A mixture of 15 parts of methyl methacrylate, 35 parts of glycidyl methacrylate, and 7 parts of azobisdimethylvaleronitrile was dropped over about 3 hours. After the completion of the dropwise addition, the mixture was left at 82 ° C. for 2 hours to terminate the reaction, thereby preparing an organic solvent resin solution A.

Next, the resin solution A20 cooled to 40 ° C.
To 0 parts, 25 parts of dodecanedioic acid and xylene were added, and the compounded dodecaneedioic acid was dispersed in a resin solution by a sand mill disperser, and then a thermosetting powder having a solid content of 74% (organic solvent content: 26%) was obtained. A coating material solution B was obtained.

Next, the obtained resin solution B is supplied through a supply conduit to a continuous vacuum desolvation apparatus (manufactured by Kurimoto Iron Works Co., Ltd.).
(Using type SCP-100)
It was manufactured at a heating medium temperature of 100 ° C., a screw rotation speed of 20 rpm, a coating amount of 9.1 kg / hour, and a degree of vacuum of 40 Torr.
The obtained product was cooled to 20 ° C., coarsely pulverized, and finely pulverized.
The powder coating of Example 1 was obtained by classification with a mesh sieve.

Examples 2 to 3 The powder coatings of Examples 2 to 3 were produced in the same manner as in Example 1 except for the conditions and compositions shown in Table 1.

Comparative Examples 1-2 The powder coatings of Comparative Examples 1-2 were produced in the same manner as in Example 1, except for the conditions and compositions shown in Table 1.

The results are shown in Table 1.

[0026]

[Table 1]

In Table 1, * 1 means propylene glycol monomethyl ether / butyl cellosolve = 1/1 weight ratio, and * 2 means xylene / swazole 1000 = 98/2 weight ratio.

In Table 1, solid content (or amount of organic solvent)
Was measured by heating and drying 1 g of a sample at 150 ° C. × 1 hour, and was determined by the formula of (weight of sample after heating / weight of initial sample) × 100.

The tests in Table 1 were performed as follows.

Blocking resistance of powder coating: The powder coating placed in a polyethylene bag was left in a storage room at 30 ° C. for one month, and the state of the powder coating was examined. ○ indicates a good one without any change compared to the initial one, △ indicates a small clump which is difficult to loosen by hand, and × indicates a large clump as a whole.

Finish appearance of coating film: An epoxy-based cationic electrodeposition coating material was electrodeposited on a 0.8 mm thick dull steel plate subjected to a zinc phosphate chemical conversion treatment so as to have a dry film thickness of 20 μm, and baked. Then, the surface of the material is electrostatically coated with a powder coating so that the film thickness becomes about 50 microns, and dried by a dryer.
The composition was cured by heating at 60 ° C. for 30 minutes. The following test was performed on the obtained coated plate and evaluated according to the following criteria.は: good, △: poor smoothness, x: very poor smoothness.

Coating resistance of coating film: A coating film was formed in the same manner as described above, and the coating resistance of the coating film was evaluated according to the following criteria. ○
Indicates that there is no armpit, △ that armpit is recognized, and x is marked.

Pellet flow property: Pellet flow property: An aluminum plate which was formed by pressing about 0.8 g of powder coating material into a cylindrical shape having a diameter of 13 mm and a height of about 4 mm at a pressure of 30 kg / mm ² and kept horizontally. And the spread length when heated at 150 ° C. for 10 minutes was measured.

[0034]

According to the present invention, since it has the above-described structure, a coating film having particularly excellent finished appearance can be formed.

Claims (2)

[Claims] 1. A raw material solution for a thermosetting powder coating material having a solid content of 10 to 90% by weight dissolved or dispersed in an organic solvent is reduced to an organic solvent amount of 1.6 to 5% by weight. A method for producing a thermosetting coating composition, wherein the composition is removed while being heated, melted and mixed under reduced pressure. 2. The following steps: (1) a step of synthesizing a resin for thermosetting powder in an organic solvent to obtain an organic solvent resin solution of the resin for thermosetting powder; Adding a curing agent to the mixture to obtain a raw material solution for a thermosetting powder coating material having a solid content of 10 to 90% by weight, (3) the amount of the organic solvent is in a range of 1.6 to 5% by weight. A step of obtaining a thermosetting powder coating composition by removing while heating and mixing under reduced pressure to obtain a thermosetting powder coating composition.