JP2006036921A - Method for producing powdery coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an acrylic-base powdery coating material which allows homogeneous dispersion of a curable acrylic resin and a curing agent by a simple means, and low-priced formation of a coating film that is excellent in smoothness and gloss. <P>SOLUTION: The method for producing a powdery coating material uses (1) a specific curable acrylic resin (A) obtained by polymerization of an unsaturated compound containing a glycidyl group and/or a methyl glycidyl group with a raw material monomer containing methyl methacrylate at a determined content, (2) 1, 3, 6-hexane tricarboxylic acid (B), and (3) one or more solvents (C) having boiling points of a specific temperature or lower and selected from a specific range; and comprises a process for mixing (A), (B) and (C) at a specific temperature or lower at least to dissolve (B) in (C), followed by a process for evaporating/removing (C) at a specific temperature or lower. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a powder coating material comprising a curable acrylic resin and a curing agent.

Powder paints are used in a wide range of fields in place of solution paints because they do not generate volatile organic substances during baking and do not cause environmental problems such as air pollution.
As such a powder coating, for example, an acrylic powder coating containing a curable acrylic resin having a glycidyl group and a curing agent represented by dodecanedioic acid is known.

  In general, the powder coating is produced by dry mixing a curable resin, a curing agent, a coating additive and a pigment, followed by kneading and dispersing with a melt kneader, followed by pulverization and classification. However, in this method, when the curable resin and the curing agent are melted by heat and kneaded, it is necessary to suppress the progress of the crosslinking reaction between the curable resin and the curing agent. For this reason, it is difficult to uniformly disperse the resin and the curing agent due to restrictions such as kneading at a temperature lower than the melting point of the curing agent. The coating film formed by the powder coating thus produced has a problem that it lacks the appearance, particularly the surface smoothness.

Therefore, as a method for improving such problems, a method of mixing a curable resin and a curing agent in a wet manner, that is, in a solvent (see Patent Documents 1, 2, 3, and 4) has been proposed. Yes.
Even with these methods, the uniform dispersion of the curable resin and the curing agent is not always sufficient, and a large-scale devolatilization / recovery device for devolatilization / removal of high boiling point solvents such as xylene is still required. Many problems remain.

In order to make the mixing with the resin uniform, a powder coating using an aliphatic tricarboxylic acid as a curing agent has also been proposed (see Patent Document 5), but the coating film smoothness has not been sufficiently improved. .
JP 54-25531 A Japanese Patent Laid-Open No. 10-53729 Japanese Patent Laid-Open No. 11-302567 JP 2000-103866 A JP 2004-75875 A

  An object of the present invention is an acrylic powder coating that can uniformly disperse a curable acrylic resin and a curing agent by a simple means, and can form a coating film having excellent smoothness and glossiness at low cost. It is in providing the method of manufacturing.

As a result of intensive studies, the present inventors have used a specific curable acrylic resin, a curing agent 1,3,6-hexanetricarboxylic acid, and a specific solvent, and 1,3,6-hexanetricarboxylic acid is the solvent. 1,3,6-hexanetricarboxylic acid can be uniformly dispersed in the curable acrylic resin, and a coating film excellent in smoothness and gloss can be formed at low cost. The manufacturing method of the acrylic type powder coating material obtained was discovered.
That is, the present invention was obtained by polymerizing (1) a raw material monomer containing at least 15 to 60 mol% of a glycidyl group and / or methylglycidyl group-containing unsaturated compound and 10 to 50 mol% of methyl methacrylate. A curable acrylic resin (A) having a number average molecular weight of 1000 to 20000 and a glass transition temperature of 30 to 90 ° C., (2) 1,3,6-hexanetricarboxylic acid (B), and (3) normal pressure A boiling point of 120 ° C. or less, and a method for producing a powder coating using a solvent (C) that is at least one selected from alcohols, ketones, ethers, and water,
The curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B), and solvent (C) are mixed with at least 1,3,6-hexanetricarboxylic acid (B) at a temperature of 130 ° C. or lower. C), a mixing step of mixing so as to dissolve, and then a devolatilization / removal step of devolatilizing the solvent (C) at a temperature of 130 ° C. or less. is there.

  A curable acrylic resin (A) obtained by polymerizing a raw material monomer containing a glycidyl group and / or methyl glycidyl group-containing unsaturated compound and methyl methacrylate, and 1,3,6-hexanetricarboxylic acid (B). In the presence of a solvent (C) having a boiling point of 120 ° C. or less at normal pressure and one or more selected from alcohols, ketones, ethers, and water, the solvent (C) is then removed. The powder coating material which gives the coating film which was excellent in smoothness, glossiness, and sharpness from the mixture of curable acrylic resin (A) and 1,3,6-hexane tricarboxylic acid (B) obtained by Can be manufactured.

  As the solvent used in the present invention, a solvent (C) having a boiling point of 120 ° C. or less at normal pressure and at least one selected from alcohols, ketones, ethers, and water is used. As the solvent (C), one or more selected from alcohols, ketones, ethers, and water are preferable because of good solubility in 1,3,6-hexanetricarboxylic acid (B). Specific examples of alcohols, ketones and ethers include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, 2-pentanol, 3-pentanol, 3 -Methyl-2-butanol, neopentyl alcohol, dipropyl ether, diisopropyl ether, butyl vinyl ether, dioxane, trioxane, 2-methylfuran, tetrahydrofuran, tetrahydropyran, 1,2-dimethoxyethane, acetal, acetone, methyl ethyl ketone, 2- Examples include pentanone, 3-pentanone, methyl isobutyl ketone, and 1-methoxy-2-propanol. In the present invention, among the above solvents, methanol, isopropanol, and acetone are preferably used. Said solvent can also be used individually by 1 type, and 2 or more types can also be mixed and used for it.

  In addition, as long as the function of uniformly dispersing 1,3,6-hexanetricarboxylic acid (B) and devolatilization are not impaired, a small amount of other solvent (for example, 10 parts by weight or less per 100 parts by weight of solvent (C)) It can also be used together. Examples of other solvents include hexane, methylpentane, and benzene.

In the present invention, the curable acrylic resin (A) used as the resin component of the powder coating is solid at room temperature (20 ° C.) and contains 15 to 60 mol% of a glycidyl group and / or methyl glycidyl group-containing unsaturated compound. And a curable acrylic resin having a number average molecular weight of 1000 to 20000 and a glass transition temperature of 30 to 90 ° C., obtained by polymerizing a raw material monomer containing 10 to 50 mol% of methyl methacrylate.
As raw material monomers for the curable acrylic resin (A), 15 to 60 mol% of a glycidyl group and / or methylglycidyl group-containing unsaturated compound, and 10 to 50 mol% of methyl methacrylate, preferably glycidyl group and / or methyl It contains 25 to 55 mol% of a glycidyl group-containing unsaturated compound and 15 to 45 mol% of methyl methacrylate.
If the use ratio of the glycidyl group and / or methyl glycidyl group-containing unsaturated compound monomer as the raw material is less than 15 mol%, the corrosion resistance and hardness of the resulting coating film are reduced. The storage stability of the powder coating material and the smoothness of the coating film are lowered, and the appearance is inferior.
When the proportion of the methyl methacrylate monomer used as the raw material is less than 10 mol%, the weather resistance and high-quality feeling (deep transparency) of the resulting coating film are lowered, and when it exceeds 50 mol%, the coating obtained is obtained. The smoothness of the film is lowered and the appearance is poor.
On the other hand, the curable acrylic resin (A) has 15 to 60 mol%, preferably 25 to 55 mol% of a structural unit derived from a glycidyl group and / or methylglycidyl group-containing unsaturated compound as a structural unit derived from a monomer. And 10 to 50 mol%, preferably 15 to 45 mol% of a structural unit derived from methyl methacrylate, and may further include a structural unit derived from another unsaturated compound if necessary. . When these structural units are contained in the curable acrylic resin (A), the same effects as described above can be obtained.
For example, it can be obtained by copolymerizing a glycidyl group and / or methyl glycidyl group-containing unsaturated compound (hereinafter sometimes simply referred to as a glycidyl acrylic compound), methyl methacrylate and, if necessary, other unsaturated compounds.

  Examples of the glycidyl acrylic compound include glycidyl methacrylate, glycidyl acrylate, β-methyl glycidyl methacrylate, β-methyl glycidyl acrylate and the like, and glycidyl methacrylate is particularly preferable.

  Examples of other unsaturated compounds used as necessary when copolymerizing a glycidyl acrylic compound and methyl methacrylate include, for example, methyl acrylate, ethyl methacrylate, ethyl acrylate, n-butyl methacrylate, n-butyl acrylate, I-butyl methacrylate, i-butyl acrylate, t-butyl methacrylate, t-butyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, lauryl methacrylate, lauryl acrylate, cyclohexyl methacrylate, acrylic acid Cyclohexyl, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, caprolactone-modified 2-hydroxyethyl methacrylate, caprolactone-modified 2-hydroxyethyl acrylate, styrene, α-methylstyrene , Acrylonitrile, acrylamide, and methacrylamide, and the like, but is not limited thereto.

The amount of the other unsaturated compound is not particularly limited as long as the amount of the structural unit derived from the glycidyl-based acrylic compound and methyl methacrylate is within the above-described range. It is good to be in the range of ˜60 mol%.
Copolymerization using a glycidyl acrylic compound and methyl methacrylate is carried out by dispersing or dissolving these compounds in a polymerization solvent together with a polymerization initiator such as azobisisobutyronitrile. The polymerization is carried out under a polymerization condition of 20 MPa, and after the completion of the polymerization, the polymerization solvent is devolatilized and removed to obtain the curable acrylic resin (A) that is solid at the target normal temperature.

  As the polymerization solvent, aromatic hydrocarbon solvents such as toluene and xylene and the above-mentioned wet mixing solvents can be used, but in the present invention, in particular, the boiling point at normal pressure is 120 ° C. or less, One or more solvents (C) selected from alcohols, ketones, ethers, and water can be suitably used. Since these wet mixed solvents have a low boiling point, solvent removal can be easily performed.

Further, such a polymerization solvent is usually used in such an amount that the concentration in all the polymerization reaction components (including the polymerization solvent) is 10 to 90% by weight.
The above copolymerization is carried out to such an extent that the polymerization rate is 98 mol% or more, preferably 99 mol% or more, and most preferably 99.5 mol% or more. This is because if the polymerization rate is low, a great deal of labor is required for devolatilization of the unreacted monomer.

The thus obtained curable acrylic resin (A) that is solid at room temperature has a number average molecular weight of 1000 to 20000, preferably 1300 to 10000, more preferably 1500 to 7000, and its glass transition. The temperature should be in the range of 30-90 ° C, preferably 35-80 ° C, more preferably 40 ° C-70 ° C. When the number average molecular weight or glass transition temperature is lower than the above range, the storage stability of the obtained powder coating material is lowered, and the coating film obtained by such coating material may be inflexible. Further, if the number average molecular weight or glass transition temperature is higher than the above range, the miscibility with the solvent for wet mixing described above is lowered, and it becomes difficult to obtain a powder coating material having a uniform composition, and the smoothness is excellent. It may be difficult to form a coated film.
In the present invention, the number average molecular weight is measured by gel permeation chromatography (GPC).
The glass transition temperature (° C.) is measured by the DSC method, and the midpoint glass transition temperature (Tmg) is defined as the glass transition temperature (Tg).

  Such a curable acrylic resin (A) that is solid at room temperature is subjected to a mixing step described later. When the above-described solvent for wet mixing is used as the polymerization solvent, the polymerization solvent is devolatilized. Without removal, the solution of the curable acrylic resin (A) that is the polymerization product can be directly used in the mixing step.

  The 1,3,6-hexanetricarboxylic acid (B) used in the present invention is usually 0.7 to 1.3 times equivalent per glycidyl group and / or methyl glycidyl group in the curable acrylic resin (A), It is preferably used in the range of 0.8 to 1.2 times equivalent, more preferably 0.8 to 1.1 times equivalent.

  As the curing agent that can be used in combination with 1,3,6-hexanetricarboxylic acid (B) used in the present invention, those having reactivity with the glycidyl group in the curable acrylic resin (A) described above are used. For example, dibasic acids such as azelaic acid, nonanedioic acid, sebacic acid, dodecanedioic acid, adipic acid, maleic acid, isophthalic acid, naphthalenedicarboxylic acid, succinic anhydride, phthalic anhydride, itaconic anhydride, or anhydrides thereof; Polybasic acids such as trimellitic acid, pyromellitic acid, trimellitic anhydride, pyromellitic anhydride or their anhydrides; amines or diamines such as metaphenylenediamine, metaxylenediamine, dicyandiamide, aliphatic amine, alicyclic amine A compound, an amide compound, a melamine compound, a hydrazine compound, a maleimide compound, a cyanate compound and the like can be used alone or in combination of two or more, but are not limited thereto. Of these, dibasic acids, particularly dodecanedioic acid, are preferably used in the present invention.

In the present invention, in addition to the above-mentioned curable acrylic resin (A) and 1,3,6-hexanetricarboxylic acid (B), known additives for coatings such as a melt flow regulator, pinhole prevention An agent, an ultraviolet absorber, an antioxidant, a curing catalyst, a plasticizer, a blocking resistance improver, a powder flow imparting agent, a defoaming agent, and the like can be used as necessary.
Such a coating additive is used in such an amount that a predetermined function is exhibited without impairing properties such as the film-forming ability of the powder coating. For example, it is used in the range of 0.1 to 10 parts by weight per 100 parts by weight of the curable acrylic resin (A).

  In the present invention, a pigment is further used depending on the use of the powder coating material. Examples of the pigment include, but are not limited to, titanium oxide, ben pattern, phthalocyanine blue, phthalocyanine green, carbon black, and iron oxide. Such a pigment is usually used in an amount of 200 parts by weight or less per 100 parts by weight of the curable acrylic resin (A).

The above-described curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B), and coating additives and pigments used as necessary are continuously wetted in the presence of the above-mentioned solvent (C). Then, the solvent is continuously devolatilized and removed under reduced pressure. These continuous mixing and solvent devolatilization / removal may be performed at room temperature or under heating at 130 ° C. or lower. When continuous mixing and solvent devolatilization / removal are performed under heating, the heating temperature is set to be equal to or lower than the crosslinking reaction temperature of the curable acrylic resin (A) and 1,3,6-hexanetricarboxylic acid (B). Further, as will be described later, when the solvent is side-feeded alone or as a solution of 1,3,6-hexanetricarboxylic acid (B), it is heated in the range of 50 to 130 ° C. in order to enhance the uniform kneading effect. It is preferable to perform kneading.
For the above-mentioned continuous mixing, an extruder, a kneader, an in-line mixer, etc., which will be described later, are used. Depending on the relationship between the boiling point of the solvent (C) to be used and the heating temperature, there may be pressure conditions.

In this invention, the usage-amount of a solvent is the solvent in the mixed composition which is a mixture with a curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B), and a solvent (C) normally. The amount of C) is in the range of 10 to 1000 parts by weight per 100 parts by weight of 1,3,6-hexanetricarboxylic acid (B).
However, when a mixture of the curable acrylic resin (A) obtained by the polymerization reaction and the solvent (C) is mixed with 1,3,6-hexanetricarboxylic acid (B) to produce a powder coating material The amount of the solvent (C) in the mixed composition is preferably in the range of 50 to 1000 parts by weight per 100 parts by weight of 1,3,6-hexanetricarboxylic acid (B).
Moreover, when side-feeding the solution of solvent (C) or 1,3,6-hexanetricarboxylic acid (B), 10 to 200 parts by weight per 100 parts by weight of 1,3,6-hexanetricarboxylic acid (B) In this range, there is an advantage that the effect of wet dispersion is sufficient and solvent devolatilization and removal can be simplified.
If the solvent supply amount is less than the above range, the uniform kneading effect by the solvent is small, and if it is supplied in a larger amount than the above range, a large-scale kneading-devolatilization / removal device is required, which is economically disadvantageous. Therefore, when the above solvent is used as a polymerization solvent and the obtained curable acrylic resin (A) solution is used as it is, the use amount of the polymerization solvent is set so as to satisfy the above conditions. It is good.

  The above-mentioned continuous mixing and solvent devolatilization / removal can be performed, for example, by using a mixing-devolatilization / removal apparatus that performs continuous mixing and devolatilization / removal of the solvent volatilized by decompression. Moreover, the apparatus used at a mixing process and the apparatus used at the devolatilization and removal process of a solvent (C) can be connected in series, and mixing, devolatilization, and removal can also be performed continuously.

  The curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B) to be used for continuous mixing, and the paint additives and pigments used as necessary are each separately mixed and devolatilized. -It can also throw in in a removal apparatus and the apparatus used by a mixing process, and can also throw in after mixing these beforehand. The mixing before charging is not limited to this, but can be performed using a Henschel mixer, a tumbler or the like.

When kneading the curable acrylic resin (A) and 1,3,6-hexanetricarboxylic acid (B), all of the solvent (C) can be supplied from the first supply port and mixed by side feed. -You may supply to the apparatus used by a devolatilization / removal apparatus and a mixing process.
In the case of side feed, a solution in which the curable acrylic resin (A) and / or 1,3,6-hexanetricarboxylic acid (B) is dissolved in the above solvent is prepared and kneaded by side feed using such a solution. Can also be done. That is, a solution of the curable acrylic resin (A) and 1,3,6-hexanetricarboxylic acid (B), a solution of the curable acrylic resin (A) and a solution of 1,3,6-hexanetricarboxylic acid (B), Alternatively, wet mixing may be performed by adding a solution of the curable acrylic resin (A) and 1,3,6-hexanetricarboxylic acid (B) to a mixing-devolatilization / removal apparatus or an apparatus used in a mixing process. .
The solution of the curable acrylic resin (A) may be prepared by dissolving the curable acrylic resin (A) obtained in advance in a solvent, or may be prepared by polymerizing using the solvent as a polymerization solvent. it can.
In the present invention, the side feed is a line located on the downstream side of the main supply line that is separate from the main supply line (first supply port) in the mixing / devolatilization / removal apparatus and the apparatus used in the mixing process. It means that the substance to be kneaded is supplied from the (second supply port) through a separate input port.

  The paint additives and pigments used as necessary in the present invention can be mixed with the curable acrylic resin (A) or the curable acrylic resin (A) solution and used for continuous mixing. It can also be dissolved or dispersed in a solution of 1,3,6-hexanetricarboxylic acid (B) or 1,3,6-hexanetricarboxylic acid (B) and subjected to continuous mixing.

  The above-described mixing-devolatilization / removal apparatus includes a hopper capable of stably supplying each component (raw material for powder coating), a quantitative feeder, a quantitative pump for supplying a solvent and a solution, and the like under reduced pressure. The structure is not particularly limited as long as the solvent can be devolatilized / removed, but generally, a single or twin screw extruder or a single or twin screw kneader is used.

  The single-screw extruder has a rotary shaft having a high shearing shape such as a screw shape or a trester type suitable for kneading, a Maddock type, a topped type, etc. What you have is used. Moreover, as a twin-screw extruder, what was equipped with a pair of screw shaft which rotates in a mutually different direction or the same direction, and has a kneading function is suitable. Each of the extruders is provided with at least one devolatilization port for removing volatile components, and is preferably one that can devolatilize and remove the solvent from the devolatilization port under reduced pressure. Especially for those with multiple devolatilization ports, the degree of vacuum can be set separately in each devolatilization / removal zone. -Has removal performance. In addition, the solvent or solution is supplied to the kneading zone upstream of the vent port, but if it has a plurality of vent ports, it can be supplied to any kneading zone, and can be supplied from one location or divided into two or more locations. good. Examples of the extruder having such a structure include “TEM-37BS” manufactured by Toshiba Machine Co., Ltd. and “TP-25-T” manufactured by Thermo Plastics Industry Co., Ltd.

In addition, the kneader that can be used as a mixing-devolatilization / removal device is provided with at least one devolatilization port, with two stirring shafts arranged in a row in the barrel of the main body, and a screw and paddle on each shaft. Assembling, rotating at the same speed in the same direction, the raw material supplied from the upper part of one end of the barrel is fed into the kneading zone with a screw, kneaded by the paddle here, and continuously from the lower part of the other end, side or front of the barrel It is preferable to have a structure capable of discharging the kneaded material. Examples of such a kneader include “SC processor” and “KRC kneader” manufactured by Kurimoto Iron Works.
In any type of mixing-devolatilization / removal device, the powder coating material can be uniformly kneaded by supplying the solvent described above to the mixing zone.

In addition, when connecting the device used in the mixing process and the device used in the devolatilization / removal process in series, as an apparatus used in such a mixing process or an apparatus used in the devolatilization / removal process, In any case, the above-described single-screw or twin-screw extruder or single-screw or twin-screw kneader can be used. In the case of mixing the curable acrylic resin solution and the 1,3,6-hexanetricarboxylic acid solution, an in-line mixer can be used. Of course, when using the above-described extruder, kneader or in-line mixer as an apparatus used in the mixing process, a devolatilization port is not necessary for these. Furthermore, in this case, since the apparatus used in the devolatilization / removal step also has a mixing function, at least a part of the solvent (C) described above can be put into the devolatilization / removal apparatus. .
In the present invention, the solvent is evaporated and devolatilized by heating under reduced pressure with an apparatus used in the devolatilization / removal step until the nonvolatile content concentration is 98.5% by weight or more, preferably 99.0% by weight or more. To remove. If the nonvolatile content concentration is lower than these values, the blocking resistance may not be improved.

  In the present invention, the devolatilization / removal step of the solvent (C) may be performed using a spray drying apparatus. Spray drying equipment includes spray drying equipment for combustible organic solvents (eg, Sakamoto Giken Co., Ltd. Turning Spray Dryer, Nonflammable Gas Closed System Type, Okawahara Chemicals Corporation CL Series, etc.), and the nozzle atomizing system Although it is preferably used, a spray drying apparatus can also be used. The average particle size of the powder coating obtained by the nozzle atomizing spray drying apparatus can be arbitrarily adjusted between 1 and 100 μm, and the particle size distribution can be made very small.

  As understood from the above description, continuous mixing and solvent devolatilization / removal can be performed in various patterns depending on the apparatus used. Some typical patterns are shown below.

  For example, when the solution of the curable acrylic resin (A) obtained by polymerization in the presence of a solvent is used as it is, continuous mixing and solvent devolatilization / removal can be performed in the following pattern.

Hereinafter, embodiments of the present invention will be described.
(1) As shown in FIG. 1, the mixing-devolatilization / removal device 13 described above is used, and the curable acrylic resin (A) solution 4 and 1, 3, 3, 6-hexanetricarboxylic acid (B) 2 is supplied to continuously knead and devolatilize / remove the solvent from the devolatilization port 14, and take out the kneaded composition 6 from the mixing-devolatilization / removal device 13. . In this case, as shown in FIG. 2, a curing agent solution 5 in which 1,3,6-hexanetricarboxylic acid (B) is dissolved in a solvent is prepared, and this curing agent solution 5 and the curable acrylic resin (A) are prepared. The solution 4 can be supplied to the mixing-devolatilization / removal device 13, but at this time, the total weight of the solvent is preferably adjusted to be within the above-described range.

(2) As shown in FIG. 3, the device 11 used in the mixing step and the device 20 used in the devolatilization / removal step are connected in series, and the device 11 used in the mixing step is connected to a curable acrylic. The 1,3,6-hexanetricarboxylic acid (B) indicated by the solutions 4 and 2 of the resin (A) is supplied to perform continuous mixing, and the resulting mixture is transferred from the continuous mixer 11 to the devolatilization / removal device 20. Then, the solvent (C) is devolatilized and removed from the devolatilization port 14, and the kneaded composition 6 is taken out from the apparatus 20 used in the devolatilization and removal process. Also in this case, the curing agent solution 5 in which 1,3,6-hexanetricarboxylic acid (B) was dissolved in the solvent (C) was prepared, as shown in FIG. 1, and this curing was performed as shown in FIG. The agent solution 5 and the solution 4 of the curable acrylic resin (A) can be supplied to an apparatus used in a mixing process such as an in-line mixer.

  In addition, when using a pre-manufactured curable acrylic resin (A) (where the polymerization solvent is solvent devolatilized / removed), perform continuous mixing and solvent devolatilization / removal in the following process. Can do.

(3) As shown in FIG. 5, a mixing-devolatilization / removal device 13 similar to that used in FIG. 1 is used, and curable acrylic resins (A) 1 and 1 are used in the mixing-devolatilization / removal device 13. , 3,6-hexanetricarboxylic acid (B) 2 is supplied and continuously mixed, and the solvent (C) 3 is directly supplied to the mixing-devolatilization / removal device 13 by side feed to perform mixing and degassing. The agent is devolatilized and removed from the vapor outlet 14, and the kneaded composition 6 is taken out from the mixing-devolatilizing / removing device 13. In this case, a curing agent solution 5 in which 1,3,6-hexanetricarboxylic acid (B) was dissolved in the solvent (C) was prepared, and as shown in FIG. The mixing-devolatilization / removal device 13 can also be supplied.

(4) As shown in FIG. 7, similarly to FIG. 2, the apparatus 11 used in the mixing process connected in series and the apparatus 20 used in the devolatilization / removal process are used. The curable acrylic resin (A) 1 and 1,3,6-hexanetricarboxylic acid (B) 2 are supplied and continuously kneaded, and the solvent (C) 3 is used directly in the mixing step by side feed. It supplies to the apparatus 11, kneading | mixing and the devolatilization and removal of the solvent (C) from the devolatilization port 14 are performed, and the kneading composition 6 is taken out from the apparatus 20 used in the devolatilization / removal process. In this case, a curing agent solution 5 in which 1,3,6-hexanetricarboxylic acid (B) was dissolved in the solvent (C) was prepared, and as shown in FIG. It can also supply to the apparatus 11 used at a mixing process.
In any of the above-described FIGS. 1 to 8, pigments and coating additives used as necessary are usually mixed in advance with a curable acrylic resin (A) or a curable acrylic resin (A) solution. Although it is supplied, it can also be dissolved or dispersed in a solution of 1,3,6-hexanetricarboxylic acid (B).

  In the present invention, the acrylic powder coating thus obtained is composed of 1,3,6-hexanetricarboxylic acid (B), or additives and pigments for coatings used as required. The curable acrylic resin (A) In particular, the curing agent is present as fine particles. From this powder coating, it is possible to obtain an unprecedented smooth and beautiful coating film.

The present invention will be specifically described with reference to the following reference examples, examples and comparative examples, but it is needless to say that the present invention is not limited to these examples. Moreover, in these examples, all compounding quantities were shown on the basis of weight.
The physical properties of the curable acrylic resin and the powder coating were evaluated as follows.
1) Number average molecular weight: A tetrahydrofuran solution in which 0.3 part by weight of a curable acrylic resin was dissolved in 100 parts by weight of tetrahydrofuran was measured by 8020 GPC manufactured by Tosoh Corporation, and the number average molecular weight was calculated in terms of polystyrene. .
2) Glass transition temperature (Tg): Measured by DSC method (differential scanning calorimetry, heating rate 10 ° C./min), and the midpoint glass transition temperature (Tmg) was defined as the glass transition temperature (Tg).
3) Nonvolatile content concentration (wt%): 2 g of the powder coating material was dried at 140 ° C. for 30 minutes, and the weight retention (wt%) before and after drying was calculated.
4) Particle size (μm): The volume average particle size of the powder coating was measured using a laser diffraction type scattering particle size distribution measuring device (manufactured by Horiba, Ltd., model: LA-910).
5) Blocking resistance: 30 g of the powder coating material was put in a cylindrical container having a diameter of 2 cm, and the lump of the powder coating material after being stored at 40 ° C. for 7 days was evaluated according to the following criteria.
○: There is no lump of powder paint and no aggregates are observed.
Δ: Some lump of powder coating is observed, but cannot be picked up with a finger because the cohesive force of the lump is weak.
X: A lump of powder coating is observed, and the lump can be picked up with a finger.
6) Coating film appearance (smoothness): The surface smoothness of a coating film obtained by electrostatically coating a powder coating on a zinc phosphate-treated steel sheet and curing it in an oven at 150 ° C. for 20 minutes was visually evaluated and determined.
○: There are no dents or irregularities, and the smoothness is good.
Δ: Slight dent, irregularities are observed, and the smoothness is slightly inferior.
×: Remarkably dented, irregularities are observed, and smoothness is inferior

7) Film thickness: The film thickness of the coating film after coating and curing was measured using a film thickness measuring instrument (model: LZ-300C) manufactured by Kett Science Laboratory.
8) Centerline average roughness (Ra): The surface of the paint film after painting and curing was quantified using a surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. and SURFCOM stylus type surface roughness meter. . The cut-off is 0.8 mm, and the smaller the value, the smoother the coating film.
9) Gloss (60 °): 60 ° specular reflectance (%) of the coating film surface after coating and curing was measured. JIS K5600 4.7 was followed.

<Example 1> (Use of resin solution)
A reactor equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen pressure regulator and a bottom extraction tube was charged with 120 parts of isopropanol and heated to 110 ° C., 40 parts of methyl methacrylate, 30 parts of glycidyl methacrylate, Add 15 parts of styrene, 15 parts of n-butyl methacrylate and 6 parts of t-amylperoxyisononanoate over 2 hours and hold at the same temperature for 3 hours to obtain a curable acrylic resin solution (hereinafter referred to as resin solution). Obtained.
Separately, 11 parts of 1,3,6-hexanetricarboxylic acid (Asahi Kasei Chemicals Co., Ltd.), 0.5 part of benzoin (defoaming agent), PL-540 (flow control agent manufactured by Enomoto Kasei Co., Ltd.) 0.5 part was added to 40 parts of isopropanol to prepare a solution (hereinafter referred to as a curing agent solution), and wet mixed with the resin solution with an in-line mixer kept at 70 ° C. Subsequently, the mixed solution of the resin solution and the curing agent solution is continuously supplied to an extruder equipped with a solvent removal vent (TP-25-T manufactured by Thermo Plastics Co., Ltd.), and the cylinder temperature is 85 ° C. and the screw rotates. The solvent was devolatilized and removed at several 170 rpm and a solvent removal vent pressure of 3 kPa to obtain a kneaded composition.
This kneaded composition was pulverized using an impact pulverizer and further classified to obtain a powder coating material having an average particle diameter of 25 μm. The obtained powder coating was electrostatically coated on a zinc phosphate-treated steel sheet and cured in an oven at 150 ° C. for 20 minutes to obtain a coating film. The physical properties of the obtained coating film were evaluated, and the results are shown in Table 1 together with the physical properties of the obtained curable acrylic resin.

<Example 2>
A powder coating material was produced in the same manner as in Example 1 except that isopropanol was changed to acetone, and the physical properties of the powder coating material and the coating film were evaluated. The results are shown in Table 1 together with the physical properties of the obtained curable acrylic resin.

<Reference Example 1>
In a reactor equipped with a thermometer, a stirrer, a reflux condenser, a pressure regulator using nitrogen, and a bottom extraction tube, 100 parts of xylene (parts by weight, hereinafter the same) was charged and heated to 115 ° C., and 40 parts of methyl methacrylate. Then, 30 parts of glycidyl methacrylate, 15 parts of styrene, 15 parts of n-butyl acrylate, and 8 parts of azobisisobutyronitrile were added over 3 hours and kept at the same temperature for 6 hours to obtain a resin solution.
The obtained resin solution was distilled under reduced pressure at 170 ° C. and 1 kPa until no solvent was distilled off. After cooling, a room temperature solid curable acrylic resin was obtained.
The number average molecular weight of this resin was 3000, and the glass transition temperature (Tg) was 48 ° C.
After roughly pulverizing 50 parts of the obtained curable acrylic resin with a pulverizer, 12 parts of 1,3,6-hexanetricarboxylic acid, 0.3 part of a surface conditioner, and 0.3 part of benzoin (defoaming agent) were added. And dry blended to obtain a raw material mixture for acrylic powder coating.

<Example 3> (Solvent side feed)
As the mixing-devolatilization / removal device, the same extruder as in Example 1 was used. The raw material mixture for acrylic powder coating obtained in Reference Example 1 was supplied to the mixing-devolatilization / removal device and extruded at a cylinder temperature of 85 ° C. and a screw rotation speed of 170 rpm at a rate of 3 kg / h.
At this time, methanol is supplied at 1 kg / h to the first kneading zone downstream of the raw material supply port of the mixing-devolatilization / removal device, and the acrylic powder coating material is continuously kneaded and adjusted to 53 kPa downstream. The volatile matter was partially devolatilized by the first vent. Furthermore, kneading and devolatilization / removal were performed through the second kneading zone, the second vent (5 kPa), the third kneading zone, and the third vent (3 kPa) to obtain a kneaded composition.
From this kneaded composition, a powder coating material was produced in the same manner as in Example 1. The physical properties of the powder coating material and the coating film were evaluated, and the results are shown in Table 1.

<Example 4>
As a device used in the mixing process, a continuous twin-screw kneader S1 type KRC kneader (manufactured by Kurimoto Iron Works, screw diameter 25 mm) is used, and as a device used in the devolatilization / removal process, a single-screw extruder TP20 (manufactured by Thermo Plastic Industry Co., Ltd., screw diameter: 20 mm) was connected in series to an apparatus used in the mixing step by a discharge pipe.
The raw material mixture for powder coating obtained in Reference Example 1 is supplied to the hopper of the apparatus used in the mixing process at a rate of 2 kg / h using a quantitative feeder, and methanol is added to the body of the apparatus used in the mixing process. The mixture was fed at a rate of 0.5 kg / h and kneaded continuously at a cylinder temperature of 85 ° C. and a screw rotation speed of 100 rpm.
This kneaded composition was directly supplied to the apparatus used in the devolatilization / removal step adjusted to a cylinder temperature of 85 ° C. and a screw rotation speed of 100 rpm, and the solvent was devolatilized under a vent pressure of 3 kPa. A powder coating material was produced from the kneaded composition from which the solvent had been devolatilized and removed in the same manner as in Example 1. The physical properties of the powder coating material and the coating film were evaluated, and the results are shown in Table 1.

<Comparative Example 1>
An acrylic resin solution was prepared in the same manner as in Example 1 except that 120 parts of isopropanol was changed to 100 parts of xylene and the heating temperature 110 ° C. was changed to 125 ° C., and a powder coating was produced in the same manner. Table 2 shows the evaluation results of the physical properties of the powder coating material and the coating film.
In this example, xylene could not be completely devolatilized / removed in the extruder, and the curing agent was not uniformly dispersed, resulting in poor blocking properties and coating film properties.

<Comparative example 2>
A powder coating material was produced in the same manner as in Example 3 except that the acrylic powder coating material was kneaded without supplying methanol, and the physical properties of the powder coating material and the coating film were evaluated. there were. The results are shown in Table 2.

<Comparative Example 3>
A powder coating material was produced in the same manner as in Example 3 except that toluene was supplied instead of methanol, and the physical properties of the powder coating material and the coating film were evaluated. The results are shown in Table 2.

Table 1
Example 1 Example 2 Example 3 Example 4
Curable acrylic resin Number average molecular weight 4500 4500 3000 3000
Tg (° C) 51 51 48 48
Powder paint
Nonvolatile content concentration (wt%) 99.4 99.5 99.5 99.6
Particle size (μm) 25 27 26 27
Blocking resistance ○ ○ ○ ○
Film thickness (μm) 48 47 45 44
Paint film appearance (smoothness) ○ ○ ○ ○
Gloss (60 °) 94 95 95 94
Ra (μm) 0.12 0.11 0.10 0.10

Table 2
Comparative Example 1 Comparative Example 2 Comparative Example 3
Curable acrylic resin Number average molecular weight 4500 3000 3000
Tg (° C) 51 48 48
Powder coating material Non-volatile content (wt%) 97.7 99.8 98.3
Particle size (μm) 26 24 24
Blocking resistance × ○ ×
Film thickness (μm) 51 50 49
Paint film appearance (smoothness) × × ×
Gloss (60 °) 87 86 87
Ra (μm) 0.20 0.18 0.18

FIG. 1 shows mixing and devolatilization / removal of a solvent by supplying a solution of 1,3,6-hexanetricarboxylic acid (B) and a curable acrylic resin (A) using a mixing-devolatilization / removal apparatus. Is the process of FIG. 2 shows a kneading and devolatilization of a solvent by supplying a solution of 1,3,6-hexanetricarboxylic acid (B) and a solution of a curable acrylic resin (A) using a mixing-devolatilization / removal device. -A process of removing. FIG. 3 shows the apparatus used in the mixing process and the apparatus used in the devolatilization / removal process, supplying a solution of 1,3,6-hexanetricarboxylic acid (B) and curable acrylic resin (A). This is a process of mixing and removing the solvent. FIG. 4 supplies a solution of 1,3,6-hexanetricarboxylic acid (B) and a solution of curable acrylic resin (A) using an apparatus used in the mixing process and an apparatus used in the devolatilization / removal process. In this process, mixing and devolatilization / removal of the solvent are performed. FIG. 5 shows the mixing and devolatilization / removal device, when mixing 1,3,6-hexanetricarboxylic acid (B) and curable acrylic resin (A), the solvent is directly side-feeded, This is a process for devolatilization and removal of solvent. FIG. 6 shows the mixing and devolatilization / removal device, when mixing the curable acrylic resin, the solvent of 1,3,6-hexanetricarboxylic acid (B) is directly side-fed to mix and devolatilize the solvent. -A process of removing. FIG. 7 shows the solvent used when mixing 1,3,6-hexanetricarboxylic acid (B) and curable acrylic resin (A) using the apparatus used in the mixing process and the apparatus used in the devolatilization / removal process. This is a process that performs side feed directly to mix and devolatilize and remove the solvent. FIG. 8 shows that when the curable acrylic resin (A) is mixed using the apparatus used in the mixing process and the apparatus used in the devolatilization / removal process, the solvent of the curing agent is directly side-feeded, It is a process for devolatilization and removal.

Explanation of symbols

1 ... curable acrylic resin (A)
2 .... 1,3,6-hexanetricarboxylic acid (B)
3. Solvent (C)
4 ... Solution of curable acrylic resin (A) 5 ... Solution of 1,3,6-hexanetricarboxylic acid (B) 6 ... Kneading composition 11 ... Device used in mixing step 13 ..Mixing-devolatilization / removal device 14 ... Vapor vent 20 for devolatilization

Claims (12)

The number average molecular weight obtained by polymerizing at least (1) a raw material monomer containing 15 to 60 mol% of a glycidyl group and / or methylglycidyl group-containing unsaturated compound and 10 to 50 mol% of methyl methacrylate is 1,000 to 1,000. Curable acrylic resin (A) having a glass transition temperature of 30 to 90 ° C., (2) 1,3,6-hexanetricarboxylic acid (B), and (3) a boiling point at atmospheric pressure of 120 ° C. or less. A method of producing a powder coating using a solvent (C) that is at least one selected from alcohols, ketones, ethers, and water,
The curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B), and solvent (C) are mixed with at least 1,3,6-hexanetricarboxylic acid (B) at a temperature of 130 ° C. or lower. A method for producing a powder coating material comprising a mixing step of mixing so as to dissolve in C), and then a devolatilization / removal step of devolatilizing the solvent (C) at a temperature of 130 ° C. or lower. In an amount in which 1,3,6-hexanetricarboxylic acid (B) contains 0.7 to 1.3 times equivalent functional group per glycidyl group and / or methyl glycidyl group constituting curable acrylic resin (A) The method for producing a powder coating material according to claim 1, which is used. The curable acrylic resin (A) contains 25 to 55 mol% of a structural unit derived from a glycidyl group and / or methylglycidyl group-containing unsaturated compound, and 15 to 45 mol% of a structural unit derived from methyl methacrylate. The method for producing a powder coating material according to claim 1 or 2, wherein the number average molecular weight is 1300 to 10,000 and the glass transition temperature is 35 to 80 ° C. The method for producing a powder coating material according to any one of claims 1 to 3, wherein the solvent (C) is used in an amount of 10 to 1000 parts by weight per 100 parts by weight of 1,3,6-hexanetricarboxylic acid (B). The curable acrylic resin (A) is produced by a polymerization reaction using the solvent (C) as a polymerization solvent, and the curable acrylic resin (A) obtained by the polymerization reaction and the solvent (C) The powder according to any one of claims 1 to 4, wherein the mixture is mixed with 1,3,6-hexanetricarboxylic acid (B) or 1,3,6-hexanetricarboxylic acid (B) and solvent (C). Manufacturing method of paint. The mixing process of the curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B) and the solvent (C), and the devolatilization / removal process of the solvent (C) The method for producing a powder coating material according to any one of claims 1 to 5, which is carried out continuously using a removing device. The method for producing a powder coating material according to claim 6, wherein the mixing-devolatilization / removal device is a single-screw or twin-screw extruder or kneader provided with at least one devolatilization port. A device used in the mixing step of the curable acrylic resin (A), 1,3,6-hexanetricarboxylic acid (B) and the solvent (C), and a device used in the devolatilization / removal step of the solvent (C) The method for producing a powder coating material according to claim 1, wherein mixing, devolatilization, and removal are continuously performed by connecting the components in series. The method for producing a powder coating material according to claim 8, wherein the apparatus used in the mixing step is a single or twin screw extruder, a single or twin screw kneader, or an in-line mixer. 1,3,6-hexanetricarboxylic acid (B) dissolved in solvent (C) and 1,3,6-hexanetricarboxylic acid solution and curable acrylic resin (A) dissolved in solvent (C) The method for producing a powder coating material according to claim 1, wherein the acrylic resin solution is prepared separately, and the 1,3,6-hexanetricarboxylic acid solution and the curable acrylic resin solution are mixed. The powder coating material is obtained by pulverizing a mixture of the curable acrylic resin (A) obtained by devolatilizing and removing the solvent (C) and 1,3,6-hexanetricarboxylic acid (B). Manufacturing method of powder coating. The method for producing a powder coating material according to claim 1, wherein the devolatilization / removal step of the solvent (C) is performed using a spray dryer.

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