JPH1053729A - Production of powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a powder coating material which can form a coating film improved in smoothness, finish appearance and blocking resistance by mixing materials for forming a powder coating material with a solvent in which the binder resin is soluble and heating the resulting mixture in a vacuum to evaporate the solvent from the solution. SOLUTION: A mixture for forming a powder coating material, containing a resin binder, a curing agent insoluble in the solvent and a pigment insoluble in the solvent and a solvent in which the binder resin is soluble are fed into a resin solution preparation tank 1 and mixed with each other under heating to obtain a resin solution having a nonvolatile matter concentration of 20-90wt.%. This solution is fed through feed conduits 10a and 10b into the inlet 5a of a continuous vacuum desolventation apparatus 5 by a feed pump 4 and desolvented by heating in a vacuum under agitation to obtain a powder coating material having a nonvolatile matter concentration of 98.5wt.% or above. Next, this material is ground to a means particle size of 5-30μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a powder coating.

[0002]

2. Description of the Related Art Powder coatings are preferred from the standpoint of preventing air pollution, since no solvent is used at all. For this reason, research and development have been actively promoted in recent years, and some of them have been put to practical use. As the binder resin for the powder coating, a thermosetting resin that is solid at room temperature is used, and specifically, a polyester resin, an epoxy resin, an acrylic resin, or the like is used.

[0003] A general method of producing a powder coating is to mix such a binder resin with a curing agent and, if necessary, a pigment or other additives, melt and knead, then cool, pulverize and classify the mixture. How to The melting and kneading temperature is
It is performed at such a low temperature that the curing reaction of the binder resin does not occur, and is usually about 100 to 120 ° C.

[0004] In such a conventional powder coating, there is a problem that the smoothness and finished appearance of the coating film are not good. The smoothness and finished appearance of such a coating film are slightly improved by finely pulverizing and adding a curing agent and additives, but the smoothness and finished appearance are not sufficiently satisfactory, and Since a fine pulverization step is required, there is a problem that the production cost increases.

On the other hand, in Japanese Patent Application Laid-Open No. Hei 5-311096, for the purpose of, for example, performing color adjustment in a short time, a dispersion paste obtained by mixing paint materials in the presence of a solvent is used, and the dispersion paste is dried. Discloses a method for producing a powder coating. However, when a powder coating is produced by such a method, a powder coating having poor blocking properties may be obtained. Powder coatings obtained by such a method are superior in powder smoothness and finished appearance to powder coatings produced by conventional melt-kneading, but are even better in the market. There is a demand for properties and finished appearance.

An object of the present invention is to provide a method for producing a powder coating material which has good smoothness and finished appearance of a coating film and excellent blocking properties.

[0007]

The production method of the present invention is a method for producing a powder coating from a powder coating raw material containing a resin binder, wherein at least the resin binder is substantially added to the powder coating raw material. A step of adding and mixing a solvent to be dissolved, and a step of adding the solvent to the powder coating material into a continuous vacuum desolvation apparatus and heating while stirring under reduced pressure to obtain a non-volatile content of 98.5% by weight. The method includes a step of removing the solvent by evaporating the solvent until the above, and a step of pulverizing the powder coating material from which the solvent has been removed.

[0008] In a preferred embodiment according to the present invention, the method further comprises a step of wet-dispersing a raw material for a powder coating material to which a solvent has been added before introducing the raw material into a continuous vacuum desolvation apparatus. Such a wet dispersion step is preferable when the raw material for the powder coating contains a curing agent and / or a pigment which is not substantially dissolved in a solvent. By such a wet dispersion, the curing agent and / or the pigment and the like can be more uniformly dispersed in a better state than in the conventional melt kneading. As such wet dispersion, wet dispersion using a mill is preferable.

In the present invention, the raw material for a powder coating to which a solvent has been added is put into a continuous vacuum desolvation apparatus and heated under stirring under reduced pressure so that the nonvolatile content is 98.5.
The solvent is removed by evaporation until it is at least 9% by weight, more preferably at least 99.0% by weight. If the non-volatile component concentration is lower than these values, the effect of the present invention, that is, the improvement in the blocking property, tends to be not obtained.

In the present invention, the solvent added to the raw material for the powder coating is a solvent that substantially dissolves at least the resin binder, and generally an organic solvent is used. The raw material for powder coating generally contains a resin binder and a curing agent for curing the resin binder, and contains a pigment and other additives as necessary. The solvent used in the present invention may substantially dissolve such a curing agent or other additives, or may not substantially dissolve such a curing agent or other additives. In the present invention, “substantially soluble” refers to a state of being dissolved in a solvent without generating a precipitate in a general amount used in the present invention. Therefore, it is not necessary to dissolve in a transparent state.

The powder coating produced by the production method of the present invention may be a powder coating containing a pigment or a powder coating for a clear coating containing no pigment. The resin binder as a raw material for powder coating used in the present invention is generally a thermosetting resin that is solid at room temperature, and typical examples thereof include polyester resins, epoxy resins, acrylic resins, and combinations thereof. Acrylic resin is preferred for applications requiring weather resistance.

Polyester resins include polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane, and pentaerythritol, and terephthalic acid, isophthalic acid, phthalic acid, succinic acid, and glutaric acid. , Adipic acid, sebacic acid, and carboxylic acid of β-oxypropionic acid.

An epoxy resin is a high molecular compound having two or more oxirane groups in a molecule, and is a glycidyl ester resin, a glycidyl ether type resin represented by a condensation reaction product of bisphenol A and epichlorohydrin, an alicyclic resin, and the like. Examples include a formula epoxy resin and a linear aliphatic epoxy resin.

The acrylic resin is styrene, acrylic acid,
Methacrylic acid, methyl acrylate, ethyl acrylate,
N-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, glycidyl acrylate,
Examples thereof include those obtained by polymerizing monomers such as glycidyl methacrylate, 2-methylglycidyl methacrylate, and 2-hydroxyethyl methacrylate by an ordinary method.

The thermosetting resin as a coating film forming component preferably has a glass transition point (Tg) of 40 to 70 ° C. If the Tg is lower than this, resin particles may be fused to the pulverizer due to heat generated during pulverization, making production difficult. If the Tg is high, it may be difficult to obtain good surface smoothness.

The curing agent is appropriately selected according to the type of the functional group of the binder resin. For example, in the case of a polyester resin, a polybasic acid, an aminoplast resin such as a melamine resin, a blocked isocyanate, or the like is used.In the case of an epoxy resin, a polycarboxylic anhydride, dicyandiamide, an acrylic resin, or the like is used.In the case of an acrylic resin, Are polyvalent carboxylic acids, epoxy resins, aminoplast resins and the like.

Examples of the pigments include coloring pigments such as titanium dioxide, red iron oxide, iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacone pigments, azo pigments, and the like, such as talc, calcium carbonate, and precipitated barium sulfate. Pigments.

Other additives that may be added as required include surface modifiers such as polysiloxane and acrylic resin, plasticizers, ultraviolet absorbers, antioxidants, anti-peeling agents, pigment dispersants, and curing accelerators ( Or a curing catalyst), benzoins and the like.

In the present invention, when a hardening agent which substantially dissolves the hardening agent is used as a solvent to be added to the raw material for powder coating, the hardening agent is removed by removing the solvent in the solvent removing step. Precipitates in the resin binder. The curing agent thus precipitated is very fine and uniformly dispersed, so that when a coating film is formed, non-uniform curing shrinkage is reduced, and further excellent smoothness and finished appearance are obtained. Can be obtained.

In the present invention, the amount of the solvent to be added to the raw material for powder coating is not particularly limited.
It can be selected in a wide range such as 90% by weight. When the raw material for powder coating contains a hardening agent or a pigment which is not substantially dissolved in a solvent, from the viewpoints of handleability and dispersibility in wet dispersion, it is preferable to use 3
It is preferable to add a solvent so as to have a non-volatile concentration of about 0 to 80% by weight, and more preferably 30 to 59% by weight.

In the present invention, the powder coating material to which the solvent has been added may be preheated before the powder coating material to which the solvent has been added to the continuous vacuum desolvation apparatus. preferable. The lower limit of the preheating temperature is at least room temperature, preferably at least 30 ° C. or at least 40 ° C., and the upper limit is at most the boiling point of the organic solvent at atmospheric pressure.

The continuous vacuum desolvation apparatus used in the present invention may be any apparatus capable of volatilizing and removing an organic solvent by heating while stirring under reduced pressure to dry the organic solvent. It is preferable that a plurality of screw paddles are arranged so as to mesh with each other, the object to be processed is held in a gap between the screw paddles, and each screw paddle is rotated to extrude the object to be processed while stirring and heating. As such an apparatus, for example, a screw-type heating / cooling apparatus disclosed in JP-A-6-23253 can be used. This screw-type heating / cooling device is arranged so that the screw paddles of a pair of screw shafts rotating in different directions are engaged with each other, and each screw paddle is formed with a cut-out portion serving as a stagnant portion of an object to be processed. It is a type of stirring and heating device. The cutouts are formed as tangential chordal cutouts at the outer peripheral edge of the screw paddle. Further, a projection for a scraper is provided on the outer peripheral surface of the screw paddle behind the notch in the rotation direction. This continuous vacuum desolvation apparatus can heat an object to be processed from the surfaces of the screw shaft and the screw paddle and the surface of the inner wall of the apparatus. For this reason, the heating medium is designed to flow through the inside of the screw shaft and the screw paddle and the inside of the inner wall of the device. Such a continuous vacuum desolvation apparatus can be obtained, for example, as “SC processor” (screw paddle) manufactured by Kurimoto Iron Works, Ltd.

Further, as a continuous vacuum desolvation apparatus used in the present invention, a heating-type stirring heat treatment apparatus as disclosed in Japanese Patent Application Laid-Open No. 2-258043 may be used. This stirring heat treatment machine can be obtained, for example, as “SC processor” (fan-shaped paddle) manufactured by Kurimoto Iron Works Co., Ltd.

Further, the continuous vacuum desolvation apparatus used in the present invention may be constituted by a plurality of desolvation apparatuses arranged in tandem. For example, the first continuous vacuum desolvation apparatus and the second continuous vacuum desolvation apparatus may be arranged in tandem, that is, arranged in series. In this case, as the first continuous vacuum desolvation apparatus,
For example, as in the above-mentioned "SC processor", a closed-type stirring and heating device capable of reducing the pressure in which a pair of screw shafts and a screw paddle are arranged so as to mesh with each other can be used. As the second continuous type vacuum desolvation apparatus,
For example, a twin-screw extruder having a pair of screw shafts rotating in different directions or in the same direction can be used. As such a twin-screw extruder, one having a vent hole is preferable, and one capable of volatilizing and removing an organic solvent by reducing the pressure through the vent hole is preferable. As such a twin-screw extruder, there can be used a twin-screw extruder conventionally used for kneading and extrusion of plastics.

In the present invention, the powder coating material from which the solvent has been removed as described above is pulverized. This pulverization step is a step for pulverizing to an optimum particle size distribution according to the use of the powder coating. In this process, a super mixer,
Henschel mixers, jet mills and the like are typically used. The average particle size of the powder coating obtained by such a pulverizing step is preferably 5 to 30 μm, more preferably 8 to 25 μm. When the average particle diameter is less than 5 μm, the production process is often complicated, and the efficiency of applying the powder coating to the object to be coated may be reduced. Conversely, when the average particle size exceeds 30 μm, the ease of entry of the powder coating into the non-planar part of the object to be coated, for example, the concave part, is reduced, and the coating with a uniform film thickness is applied to the entire object to be coated. In some cases, it may be difficult to apply a film, or the appearance of the coating film may be deteriorated.

[0026]

According to the present invention, it is possible to obtain a powder coating excellent in smoothness and finished appearance and also excellent in blocking properties.

[0027]

FIG. 1 is a block diagram showing an example of a powder coating material manufacturing apparatus according to the present invention. As shown in FIG. 1, the resin solution preparation tank 1 is provided with a stirrer 2 for stirring the resin solution in the tank. Further, a heater 3 for heating the resin solution in the resin solution preparation tank 1 is provided. In the resin solution preparation tank 1, a binder resin as a raw material of the powder coating material, a curing agent, and, if necessary, a pigment and other additives are added to the organic solvent.

The resin solution prepared in the resin solution preparation tank 1 is supplied by the supply pump 4 through the supply conduits 10a and 10b to the continuous vacuum desolvation apparatus 5 from the input port 5a. In the present embodiment, as a continuous type vacuum desolvation apparatus 5,
“SC Processor” manufactured by Kurimoto Iron Works Co., Ltd. (SCP-
100, screw paddle, screw diameter 100m
m, screw length 900 mm, heat transfer area 1.0 m ² )
Is used. The continuous vacuum desolvation apparatus 5 is provided with a pair of screw shafts rotating in mutually different directions, and the screw shafts of the screw shafts are arranged so as to mesh with each other. Specifically, it has the structure of a screw heating / cooling device disclosed in JP-A-6-23253. The heating medium heated by the heating medium heater 6 is supplied to the continuous vacuum desolvation apparatus 5, and the heating medium flows through the inside of the screw shaft and the screw paddle and the inside of the apparatus inner wall, The supplied resin solution is heated on the surfaces of the screw shaft and the screw paddle and the surface of the inner wall of the device. A steam discharge conduit 10c is connected to the steam discharge port 5b.
c is connected to the condenser 7. Cooling water 8 is passed through the condenser 7 to condense the organic solvent. A vacuum pump 9 is connected to the condenser 7. The vacuum pump 9 reduces the pressure inside the continuous vacuum desolvation apparatus 5 to a predetermined pressure.

As described above, in the continuous vacuum desolvation apparatus 5, the organic solvent is removed from the resin solution by heating the resin solution under reduced pressure, and the resin solution has a predetermined non-volatile content. Dried until The dried product is discharged from the dried product discharge port 5c and taken out.

The resin discharged from the continuous vacuum desolvation apparatus 5 is formed into a predetermined shape as required, cooled and solidified, and then pulverized and classified. In the present embodiment, the supply conduits 10a and 10a are provided so that the temperature of the resin solution supplied from the resin solution preparation tank 1 to the continuous vacuum desolvation apparatus 5 does not decrease.
A heat insulating material is provided around the pipe b.

Example 1 A powder coating was manufactured using the powder coating manufacturing apparatus shown in FIG. The binder resin of the powder coating is styrene 17.
1 part by weight, 20.2 parts by weight of methyl methacrylate, 20.5 parts by weight of glycidyl methacrylate, 10.6 parts by weight of n-butyl methacrylate, 1.4 parts by weight of azobisisobutyronitrile as an initiator A solution-polymerized solution using 47.2 parts by weight of xylene as a solvent was used. Using this resin raw material solution, a resin solution was prepared in the resin solution preparation tank 1 shown in FIG.

Binder resin solution 117 parts by weight Dodecanedicarboxylic acid 19 parts by weight Benzoin 0.5 parts by weight Surface conditioner 0.5 parts by weight Methanol 67 parts by weight

With the above composition, the resin solution was heated in the resin solution preparation tank 1 so as to have a liquid temperature of 40 to 60 ° C., and mixed with stirring by the stirrer 2 to obtain a transparent resin solution 1. The obtained transparent resin solution is supplied to the supply conduit 1 by the supply pump 4.
Through 0a and 10b, it was supplied to the continuous vacuum desolvation apparatus 5 from the inlet 5a. Supply pump 4 and supply conduit 1
0a and 10b were kept warm at 40-60 ° C.

In the continuous type vacuum solvent removal apparatus 5, the resin solution was heated to remove the organic solvent under the conditions of a throughput of 9 kg / hour, a screw rotation speed of 10 rpm, a heating medium temperature of 100 ° C. and a degree of vacuum of 70 Torr. From the dry matter discharge port 5c,
The nonvolatile content of the discharged dried product was as shown in Table 1. The dried product is made into flakes having a diameter of 1 to 3 mm or less using a coarse crusher, and then crushed into an average diameter 10
It was pulverized to a powder of μm and classified.

The powder coating obtained as described above contains no pigment and can be used as an acrylic clear powder coating. The powder coating was applied to a steel plate by an electrostatic spraying method and baked at 150 ° C. for 20 minutes to obtain a cured coating film. The resulting coating film was evaluated for smoothness and appearance.

As for the smoothness (Rmax), a film thickness of 50
The point of μm was measured with a stylus type roughness meter. The finished appearance of the coating film was evaluated with the naked eye, and a good one was marked with a circle, a slightly poor one was marked with a triangle, and a poor one was marked with a cross.

The blocking property of the powder was evaluated as follows. 5 g of the blocking powder coating was placed in a sample bottle, and allowed to stand in an incubator at 30 ° C. After one week, the state of the lump of the powder coating was pinched with a finger, and evaluated according to the following criteria.

Good: Even if there is a lump, it cannot be gripped with a finger, or the lump can be gripped with a finger, but easily collapses. Poor ... has clumps, can be grasped with fingers and does not break easily. Table 1 shows the evaluation results of the blocking properties, smoothness, and finished appearance.

Example 2 A powder coating was produced in the same manner as in Example 1 except that 67 parts by weight of isopropyl alcohol was used instead of methanol, and the obtained powder coating was evaluated. Table 1 shows the results.

Example 3 A powder coating was produced in the same manner as in Example 1 except that 67 parts by weight of methyl cellosolve was used instead of methanol, and the obtained powder coating was evaluated. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 In Example 1, the processing amount of the continuous vacuum desolvation apparatus 5 and the screw rotation were adjusted so that the nonvolatile matter concentration of the dried product discharged from the dried product discharge port 5c was 98.0% by weight. A powder coating was produced in the same manner as in Example 1 except that the number, the heat medium temperature, and the degree of vacuum were adjusted, and the obtained powder coating was evaluated. Table 1 shows the results.

Comparative Example 2 As a binder resin as a raw material for a powder coating, the solvent in the binder resin solution used in Example 1 was removed using the continuous vacuum desolvation apparatus used in Example 1. This was used as a granular solid resin. This solid resin was melt-kneaded with the following composition using a Buscon kneader (manufactured by Bus).

Solid resin 70 parts by weight Dodecane dicarboxylic acid 19 parts by weight Benzoin 0.5 parts by weight Surface conditioner 0.5 parts by weight

After cooling the melt-kneaded resin as described above, it is made into flakes having a diameter of 1 to 3 mm or less using a crusher, and then crushed into powder having an average diameter of 10 μm using an air-flow crusher. Classified. The obtained powder coating was evaluated in the same manner as in Example 1. Table 1 shows the results.

[0045]

[Table 1]

As is clear from Table 1, the powder coatings of Examples 1 to 3 in which the solvent was removed so that the nonvolatile content became 98.5% by weight or more according to the present invention were different from those of Comparative Example 1. In comparison, it turns out that blocking property is favorable. Further, it can be seen that the powder coatings of Examples 1 to 3 according to the present invention show better smoothness and finished appearance than the powder coating of Comparative Example 2 of the related art.

FIG. 2 is a schematic view showing another example of a powder coating material manufacturing apparatus according to the present invention. As shown in FIG. 2, the resin solution is supplied from the resin solution supply device 11 to the continuous vacuum desolvation apparatus 5 through the supply conduit 10a. The resin solution that has been subjected to wet dispersion processing by the disperser 14 is supplied to the resin solution supply device 11.

In the present embodiment, Pure Glenmill PM-G4M (manufactured by Asada Iron Works Co., Ltd.), which is a horizontal medium disperser using glass beads, is used as the disperser 14.
As the resin solution feeder 11, a MONO pump NELS type (manufactured by Heishin Kiki Co., Ltd.), which is a pump for high viscosity and high concentration liquids, is used. Other configurations are the same as those of the powder coating material manufacturing apparatus shown in FIG.

Example 4 A binder resin solution was prepared in the same manner as in Example 1, and to this was added dodecanedicarboxylic acid as a curing agent, and other additives and organic solvents shown below in the following proportions. Then, a wet dispersion treatment was performed by the dispersion machine 14 shown in FIG.

Binder resin solution 117 parts by weight Dodecane dicarboxylic acid 19 parts by weight Benzoin 0.5 parts by weight Surface conditioner 0.5 parts by weight Xylene 20 parts by weight Dodecane dicarboxylic acid as a curing agent is added to xylene as the above solvent. On the contrary, it hardly dissolves.

The resin solution obtained as described above was charged into the resin solution feeder 11 from the disperser 14 as shown in FIG. In the continuous vacuum desolvation apparatus 5, the throughput is 8.4 kg / hour, the screw rotation speed is 18 rpm, the heating medium temperature is 100 ° C., and the degree of vacuum is 4
The solvent was removed under the condition of 0 Torr.

The solid content of the dried product discharged from the continuous vacuum desolvation apparatus 5 was 99.5% by weight. Using the obtained dried product, it was pulverized and classified in the same manner as in Example 1, and the coating film was evaluated using the obtained powder coating material. Table 2 shows the blocking properties of the powder coatings and the evaluation results of the coating films.

Example 5 The conditions for desolvation in the continuous vacuum desolvation apparatus 5 were as follows:
A powder coating was produced and evaluated in the same manner as in Example 4 except that the pressure was 6 kg / hour, the screw rotation speed was 20 rpm, the heating medium temperature was 80 ° C., and the degree of vacuum was 15 Torr. Table 2 shows the evaluation results.

Comparative Example 3 The throughput of the continuous vacuum desolvation apparatus 5 was adjusted such that the nonvolatile matter concentration of the dried substance discharged from the dried substance discharge port 5c of the continuous vacuum desolvation apparatus 5 was 98.1% by weight. A powder coating was produced and evaluated in the same manner as in Example 4 except that the screw rotation speed, the heat medium temperature, and the degree of vacuum were adjusted. Table 2 shows the evaluation results.

[0055]

[Table 2]

As is evident from Table 2, the powder coatings of Examples 4 and 5 obtained by removing the solvent according to the present invention so that the non-volatile content becomes 98.5% or more are the same as those of Comparative Example 3. It can be seen that good blocking properties are exhibited as compared with the powder coating. In addition, it can be seen that the powder coatings of Examples 4 and 5 according to the present invention show good smoothness and good finished appearance.

FIG. 3 is a schematic view showing still another example of the apparatus for producing a powder coating according to the present invention. As shown in FIG. 3, in this manufacturing apparatus, a first continuous vacuum desolvation apparatus 5 and a second continuous vacuum desolvation apparatus 13 are provided as continuous vacuum desolvation apparatuses. These continuous vacuum desolvation apparatuses 5 and 13 are arranged in tandem, and the dried product discharged from the continuous vacuum desolvation apparatus 5 is:
A second continuous vacuum desolvation device 13 passing through the connection pipe 12
Supplied to Here, the organic solvent is further removed and dried. The dried product from the second continuous type vacuum desolvation apparatus 13 is discharged from a dried product discharge port 13a. In the present embodiment, the first continuous-type vacuum desolvation apparatus 5 is the one shown in FIG.
And the same “SC” as in the continuous vacuum desolvation apparatus 5 shown in FIG.
Processor "is used. As the second continuous type vacuum desolvation apparatus 13, a plastic twin screw extruder "PC
M30 "(produced by Ikegai Corporation).

Example 6 The same binder resin solution as in Example 4 was prepared, and this binder resin solution was supplied to a resin solution feeder 11. The conditions for the desolvation treatment in the continuous vacuum desolvation apparatus 5 include a treatment amount of 10.5 kg / hour and a screw rotation speed of 20.
rpm, the heating medium temperature was 90 ° C., and the degree of vacuum was 70 Torr. The first discharged from the first continuous type vacuum desolvation apparatus 5
The nonvolatile content of the dried product after the drying step is 99.0% by weight.
Met.

The conditions of the desolvation treatment in the second continuous type decompression desolvation apparatus 13 are as follows: heating medium temperature: 80 ° C., degree of vacuum: 5 To
rr. The nonvolatile content of the dried product discharged from the second continuous vacuum desolvation apparatus 13 was 99.6% by weight. This dried product was pulverized and classified in the same manner as in Example 1 to obtain a powder coating, and evaluated in the same manner as in Example 1. Table 3 shows the evaluation results.

Example 7 A powder coating was produced and evaluated in the same manner as in Example 6 except that the same binder resin solution as in Example 1 was used. Table 3 shows the evaluation results.

COMPARATIVE EXAMPLE 4 The concentration of nonvolatile matter in the dried product discharged from the first continuous vacuum desolvation apparatus 5 was set to 96.0% by weight, and the nonvolatile matter discharged from the second continuous vacuum desolvation apparatus 13 was determined. 98.0 concentration
A powder coating was produced and evaluated in the same manner as in Example 6 above, except that the conditions for the solvent removal treatment in each of the solvent removal devices were adjusted so as to obtain the weight%. Table 3 shows the evaluation results.

Comparative Example 5 The dry matter discharged from the first continuous vacuum desolvation apparatus 5 was set to have a nonvolatile content of 95.0% by weight, and the nonvolatile matter discharged from the second continuous vacuum desolvation apparatus 13 was used. Concentration 97.9
A powder coating was produced and evaluated in the same manner as in Example 7 except that the conditions for the desolvation treatment in the respective desolvation apparatuses were adjusted so that the weight percent was obtained. Table 3 shows the evaluation results.

[0063]

[Table 3]

As is clear from the results shown in Table 3, the powder coatings of Examples 6 and 7 obtained by removing the solvent so as to have a non-volatile content of 98.5% or more according to the present invention were obtained in Comparative Example 4.
It can be seen that the blocking properties are better than those of the powder coatings Nos. 5 and 5. In addition, it can be seen that the powder coatings of Examples 6 and 7 can obtain good coating films in terms of smoothness and finished appearance.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a powder coating production apparatus according to the present invention.

FIG. 2 is a schematic view showing another example of the powder coating material manufacturing apparatus according to the present invention.

FIG. 3 is a schematic view showing still another example of the powder coating material manufacturing apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Resin solution preparation tank 2 ... Stirrer 3 ... Heater 4 ... Supply pump 5 ... Continuous vacuum desolvation apparatus 5a ... Input port 5b ... Steam discharge port 5c ... Dry matter discharge port 6 ... Heat medium heater 7 ... Condenser 8 ... Cooling water 9 ... Vacuum pump 10a, 10b ... Supply conduit 10c ... Discharge conduit 11 ... Resin solution supply device 12 ... Connection piping 13 ... Second continuous type desolvation apparatus 13a ... Dry matter outlet 14 ... Dispersion machine

Claims (12)

[Claims] 1. A method for producing a powder coating from a powder coating raw material containing a resin binder, wherein a solvent that substantially dissolves at least the resin binder is added to the powder coating raw material and mixed. And the step of feeding the powder coating material to which the solvent has been added into a continuous vacuum desolvation apparatus and heating while stirring under reduced pressure until the nonvolatile content becomes 98.5% by weight or more. A method for producing a powder coating material, comprising: a step of evaporating and removing a solvent; and a step of pulverizing the powder coating material from which the solvent has been removed. 2. Prior to charging the continuous type desolvation apparatus,
The method for producing a powder coating according to claim 1, further comprising a step of wet-dispersing the raw material for the powder coating to which the solvent has been added. 3. The powder according to claim 1, wherein the powder coating material contains a curing agent for curing the resin binder, and the curing agent is substantially dissolved in the solvent. Method of producing paint. 4. The powder according to claim 1, wherein the powder coating material contains a curing agent for curing the resin binder, and the curing agent is not substantially dissolved in the solvent. Method of producing paint. 5. The method for producing a powder coating according to claim 1, wherein the raw material for the powder coating contains a pigment that is substantially insoluble in the solvent. 6. The method for producing a powder coating according to claim 1, wherein the raw material for the powder coating is a raw material for a clear coating containing no pigment. 7. The powder coating material to which the solvent is added has a nonvolatile content of 20 to 90% by weight.
The method for producing a powder coating according to any one of the above. 8. The powder coating material to which the solvent has been added has a nonvolatile content of 30 to 80% by weight.
The method for producing a powder coating according to any one of the above. 9. The method according to claim 1, further comprising a step of preheating the raw material for the powder coating material to which the solvent has been added before charging the raw material for a powder coating into the continuous vacuum desolvation apparatus. Manufacturing method of powder coating. 10. The continuous vacuum desolvation apparatus, wherein a plurality of screw paddles are arranged so as to mesh with each other, an object to be processed is held in a gap between the screw paddles, and each of the screw paddles is rotated to rotate the object to be processed. The method for producing a powder coating according to any one of claims 1 to 9, wherein the apparatus is a device for stirring and heating while extruding. 11. The method for producing a powder coating according to claim 1, wherein said continuous vacuum desolvation apparatus comprises a plurality of desolvation apparatuses arranged in tandem. 12. The method according to claim 12, wherein the pulverizing step has an average particle diameter of 5 to 30.
The method for producing a powder coating according to claim 1, wherein the method is a step of pulverizing the powder coating to μm.