JP2001049191A - Production of water-dispersed powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing with an easy operation a water- dispersed powder coating material capable of forming a coating film having a low content of a hydrophilic compound therein, long-term durability and high water resistance and moisture resistance. SOLUTION: This method for producing a water-dispersed powder coating material comprises such processes that (1) a coating composition comprising (A) a resin as the main element for film formation and (B) an organic solvent capable of dissolving the resin A is dispersed and mixed while stirring in (C) a hydrophilic organic solvent being a nonsolvent or poor solvent for the resin A but compatible with the organic solvent B to form a minute particle dispersion through phase conversion, (2) the minute particles are separated from the minute particle dispersion obtained in the process 1 and (3) the imperfectly dried minute particles obtained from the process 2 is dispersed in water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-dispersed powder coating, and more particularly, to a coating film formed using the water-dispersed powder coating, in which the content of a hydrophilic compound is small and the water resistance is low. The present invention relates to a method for producing a water-dispersed powder coating material which can form a coating film having good long-term durability and a water-dispersed powder coating material by a simple operation.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a powder coating, a solid raw material is used for compounding a coating, and a resin which is a main component for forming a coating film and a sub-element for forming a coating film which is compounded as necessary (plasticization). Agents, curing accelerators, crosslinking accelerating catalysts, surface conditioners, ultraviolet absorbers, light stabilizers, antioxidants, fluidity regulators, anti-dripping agents, defoamers, etc.) and / or pigments such as Henschel mixers Mix uniformly with a mixer, melt-knead with a kneader such as an extruder or a hot roll, cool, and then pulverize into pellets, and finely pulverize the pellets with a pulverizer such as a hammer mill or a jet mill. After doing
A method of producing a powder coating by classification was common.

In the above-mentioned method for producing a powder coating by a combination of the melt-kneading method and the pulverizing method, in order to meet a demand for a large number of colors, color matching must be examined for each kind or for each color. After determining the type and amount of the pigment to be combined in the formulation, it was necessary to carry out from the formulation to the coating in one lot. As described above, it takes a lot of time and labor to produce one product and one product, and it is necessary to clean the apparatus such as the kneading and dispersing machine every time the color or the resin system is different. Therefore, this is an effective method for producing one kind of large-capacity powder coating material, but it is difficult to adapt it to the production of many kinds of powder coating material with a small amount.

As a method for producing a powder coating capable of solving the above-mentioned problems, a solvent-type paint having a desired color is prepared by toning from a solvent-type primary color paint, and then a phase change is carried out from the solvent-type paint. The solvent content is removed by the method to form resin particles,
It is conceivable to recover the resin particles, and the applicant has previously prepared a coating composition containing a resin and an organic solvent that dissolves the resin, by using a non-solvent or poor solvent for the resin. However, the organic solvent is dispersed and mixed with stirring in another organic solvent having compatibility to form a fine particle dispersion by phase inversion, separating fine particles from the obtained fine particle dispersion,
It was found that a powder coating composed of fine spherical particles and capable of forming a coating film having excellent smoothness and sharpness can be obtained by drying, and a patent application was filed.

[0005]

In the above-mentioned production method, in the separation and drying steps, the organic solvent constituting the coating composition adhering to the surface of the resin particles was also used in the phase inversion method. It was essential to completely remove the organic solvent. The reason is that if the organic solvent used in the phase conversion method is left attached or left on the resin particles in a state where the organic solvent used in the coating composition and the organic solvent used in the phase conversion method are mixed, the organic solvent used in the phase conversion method The solvent tends to evaporate first, and consequently, with evaporation, the concentration of the organic solvent constituting the coating composition, i.e., the solvent having a dissolving power for the resin, increases, and as a result, the surface of the resin particles Is dissolved over time, and the resin particles adhere to each other and lose fluidity as a powder coating.

[0006] This separation and drying step is a step of collecting resin particles from a large amount of mixed organic solvent and removing the solvent, and in order to prevent the above-mentioned problems from occurring, it is necessary to remove the resin particles from the surface. It is necessary to remove the residual organic solvent attached from the resin particle surface as quickly and completely as possible, and after filtering with a filter or wire mesh, further processing with a centrifuge or a flash dryer, or vacuum drying. Have gone.

[0007] However, when the powder coating is stored as a water-dispersed powder coating and used for coating, if the solvent is compatible with water and does not adversely affect the coating, such a solvent is dispersed in water. It has been found that it does not matter if it remains in the powder coating. Of course, from the viewpoint of the properties of the paint and environmental protection, it is preferable that the content of the solvent and the like be small.

The present invention provides a method for producing the above-mentioned water-dispersed powder coating material having few disadvantages, and particularly, the content of a hydrophilic compound in a coating film formed using the water-dispersed powder coating material is reduced. It is an object of the present invention to provide a method capable of producing a water-dispersed powder coating material which can form a coating film having little water resistance and moisture resistance and having long-term durability by a simple operation.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, as a non-solvent or a poor solvent used when a solvent is removed from a solvent-type paint by a phase inversion method. If a hydrophilic non-solvent or poor solvent is used,
When the resin particles are dispersed in water in the next step, it has been found that even if some non-solvent or poor solvent remains with the resin particles, there is no problem in forming the aqueous dispersion powder coating. Also,
When the hydrophilic non-solvent or poor solvent is attached to the resin particle surface, the resin is filtered with a filter or a wire net, and after collecting the resin particles, the surfactant for wetting used when wet and dispersed in water. It has also been found that the amount of addition may be smaller than when the resin particles are completely dried and then dispersed in water.

That is, the method for producing a water-dispersed powder coating material of the present invention comprises: (1) a coating material containing a resin (A) as a main component for forming a coating film and an organic solvent (B) that dissolves the resin (A). The composition is dispersed and mixed in a hydrophilic organic solvent (C), which is a non-solvent or poor solvent for the resin (A) but is compatible with the organic solvent (B), with stirring. Forming a fine particle dispersion by phase inversion, (2) separating fine particles from the fine particle dispersion obtained in the step (1),
And (3) a step of dispersing the incompletely dried fine particles obtained in the step (2) in water.

Further, the method for producing a water-dispersed powder coating material of the present invention comprises: (1) a coating material containing a resin (A) as a main component for forming a coating film and an organic solvent (B) for dissolving the resin (A). In the composition, a hydrophilic organic solvent (C) which is a non-solvent or a poor solvent for the resin (A) but is compatible with the organic solvent (B) is added to the resin (A). (2) dispersing and mixing the coating composition obtained in the above step (1) in the hydrophilic organic solvent (C) while stirring, (3) separating fine particles from the fine particle dispersion obtained in the step (2), and (4) completely removing the fine particles obtained in the step (3). The method includes a step of dispersing fine particles that have not been dried in water.

Furthermore, in the method for producing a water-dispersed powder coating material of the present invention, in the step of separating the fine particles from the fine particle dispersion, the fine particles are recovered in a state where the dispersion medium is adhered, and in the next step, the fine particles with the dispersed medium are collected Can also be dispersed in water, which is preferred.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a water-dispersed powder coating material of the present invention will be described in detail. In the production method of the present invention, the resin (A), which is a main component of forming a coating film, includes:
Resins conventionally used in the production of powder coatings can be used without particular limitation. Specific examples of such a resin include an alkyd resin, a polyester-urethane curable resin, a polyester-epoxy curable resin, an epoxy resin, an acrylic resin, an acrylic-polyester resin, a polyester resin, a melamine resin, and a block isocyanate resin. , A fluorine resin, a silicone resin, an amide resin, an ABS resin, a novolak resin, a phenoxy resin, a butyral resin, and a ketone resin.

When the resin (A), which is the main component of the coating film, is a thermosetting resin, a curing agent for the resin (base) exemplified above can be used as the resin (A). Examples of such a curing agent include di (poly) basic acids, acid anhydrides, amino compounds, glycidyl group-containing compounds, aminoplast resins, and blocked isocyanates. Examples include dicyandiamide, acid hydrazide, triglycidyl isocyanurate, and isophorone diisocyanate block. The dibasic acids include adipic acid, pimelic acid, suberic acid, sebacic acid, 1,10-
Decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,20-eicosandicarboxylic acid, hexahydrophthalic acid, maleic acid, phthalic acid, cyclohexene 1,
Examples thereof include 2-dicarboxylic acid.

In the production method of the present invention, the resin (A)
As the organic solvent (B) for dissolving the compound (A), a usual organic solvent for dissolving a resin, a curing agent, an additive and the like can be used. For example, aromatic hydrocarbon organic solvents such as xylene and toluene, esters such as butyl acetate and ethyl acetate, ketones such as methyl ethyl ketone and methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether Ethers and the like can be suitably used.

As the organic solvent (B) actually used in the production method of the present invention, the organic solvent (B) which is a non-solvent or a poor solvent from the coating composition (resin solution) in the subsequent phase inversion method is used. The organic solvent (B) which is easily transferred into the organic solvent (C), and which facilitates the evaporative separation operation for purifying, separating, recovering and reusing the organic solvent (B) and the hydrophilic organic solvent (C). And a combination of a hydrophilic organic solvent (C). Usually, a combination of solvents having a difference in boiling point of 1 ° C. or more is used. However, if the purity of purification and separation may be poor or if it is safe to recover as a mixed solvent, the organic solvent (B) is used. There is no particular limitation on the combination of and the hydrophilic organic solvent (C). Note that N
AD (non-aqueous disperson:
As in the case of a resin coating, even a coating in which the resin is not dissolved in the organic solvent but is dispersed in the form of fine particles can be used without any problem as long as it forms resin particles after phase inversion.

In the production method of the present invention, at least one kind of the resin (A) which is a main component for forming a coating film, which is prepared by the same method as the production method conventionally used in the production method of the solvent type paint. And a coating composition (resin solution) containing an organic solvent (B) that dissolves the resin (A), or a coating composition obtained by mixing a plurality of those coating compositions at an arbitrary ratio. it can.

In the production method of the present invention, the above-mentioned coating composition can contain a coating-forming sub-element and / or a pigment. Plasticizers, curing accelerators, crosslinking accelerators, surface conditioners, ultraviolet absorbers, light stabilizers, antioxidants, fluidity regulators, anti-sagging agents, which are ordinary paint additives, as coating film forming sub-elements And an antifoaming agent.

As the pigment, a coloring pigment, a rust-preventive pigment,
Pigments to provide other functions can be used. As coloring pigments, yellow iron oxide, titanium yellow, red iron oxide, titanium oxide, zinc white, lithopone, lead white, zinc sulfide,
Inorganic pigments such as antimony oxide, Hansa Yellow 5
G, Permanent Yellow FGL, Phthalocyanine Blue, Indanthrene Blue RS, Permanent Red F
Organic pigments such as 5RK, Brilliant First Scarlet G, and Paliogen Red 3910 can be used.

The amount of the color pigment to be added is usually about 0.5% to 60% in PWC, but may not be added at all like a clear paint. Here, PWC is Pigment
Weight Concentration (pigment weight concentration), calculated by the following formula. PWC = [(weight of contained pigment) / (weight of total solid content of paint)] × 100 When a large amount of these pigments is added, particularly when a pigment having a high oil absorption is used, such a paint is used. When used to form a coating, the smoothness of the coating tends to be impaired.

In addition, barium sulfate, barium carbonate, calcium carbonate, clay, and the like are used as extenders for the purpose of adjusting the gloss value of the coating film and the hardness of the coating film.
Silica powder, finely divided silica, diatomaceous earth, talc, basic magnesium carbonate, alumina white, and the like can also be added. It is also possible to add a matting pigment as a method for adjusting the gloss, and colloidal silica, alumina, talc, etc., which are usually used for paints, can be used. In addition, two or more types of resin particles can be used, and gloss can be adjusted by a difference in compatibility or reaction rate between the resin particles. Also, acrylic resin,
Fine particles of fluororesin and the like can be added for the purpose of adjusting the gloss and providing another function of lowering the frictional resistance in the same manner as the matting pigment.

In the production method of the present invention, the resin (A), the organic solvent (B), the coating film forming sub-element, the mixing of the pigment and the like, and the restrictions of the dispersed coating composition (resin solution) are as follows. And solidification when the resin particles are formed, and melting or softening under baking hardening conditions for forming a coating film to form a coating film. For this reason, the softening temperature of the coating resin particles is usually about 5 ° C. to 300 ° C., preferably 5 ° C.
It is in the range of about 0 ° C to about 200 ° C.

The "hydrophilic organic solvent (C) which is a non-solvent or poor solvent for the resin (A) but is compatible with the organic solvent (B)" used in the production method of the present invention is as follows. ,
When water is added to the hydrophilic organic solvent (C), the hydrophilic organic solvent (C) and water are uniformly mixed and not separated.
It can be maintained until 5 parts by weight or more of water is added to 1 part by weight of the hydrophilic organic solvent (C), and has no dissolving power for the resin (A), or 1 part of the resin (A) has the hydrophilicity. It refers to a hydrophilic organic solvent (C) which becomes turbid at room temperature when diluted by adding 5 parts of the organic solvent (C), or separates into two layers. In addition, in terms of the production of paint resin particles, a small dilution
More preferably, the layers are separated (being a non-solvent).

In order to increase the strength and hardness of the coating resin particles to be formed, the hydrophilic organic solvent (C) preferably has a small molecular weight. The reason is as follows. When the organic solvent (B) in the resin solution is extracted into a non-solvent or a poor solvent having a large molecular weight to form paint resin particles, the non-solvent or the poor solvent adheres or adsorbs on the surface of the paint resin particles,
This non-solvent or poor solvent tends to swell the coating resin particles, and as a result, the strength and hardness of the surface of the coating resin particles tend to be insufficient, and the tackiness is completely removed. May not be possible. Therefore, even when the coating resin particles are formed using a solvent having a high molecular weight as a non-solvent or a poor solvent, it is particularly preferable to perform extraction with a non-solvent or a poor solvent having a small molecular weight in the final extraction operation. .

As the hydrophilic organic solvent (C) used in the production method of the present invention, methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol and the like are preferable. Or a mixed solvent of a plurality of combinations. Alcohols having a small number of carbon atoms, such as methyl alcohol and ethyl alcohol, are more preferable because they have a low dissolving power for resins and a large desolvating effect at the time of phase change.

In the production method of the present invention, esters such as methyl acetate and ethyl acetate, ketones such as acetone and methyl ethyl ketone, ethylene glycol, propylene glycol, and glycol ethers thereof are unsuitable. Esters, ketones and glycol ethers
When it is used as a solvent for phase change, it has a high solubility in a resin for coating and has a large effect of diluting a solvent-type coating, so that resin particles cannot be formed. Further, as a method of reducing the dissolving power of these solvents with respect to the resin, there is a method of mixing with water. However, when a solvent type paint is added to the mixed solvent to form resin particles, the mixed solvent with water is used. Only the solvent migrates into the solvent-type paint and cannot form resin particles.

The “coating composition containing the resin (A) which is the main component of the coating film and the organic solvent (B) that dissolves the resin (A)” used in the production method of the present invention has been conventionally used. Raw material resin solution (coating composition) prepared by the same preparation method as the solvent type paint, primary color coating composition containing color pigment, or required color and coating performance by combining this raw resin solution or primary color coating composition Is a coating composition prepared so as to obtain These coating compositions may be used in the same manner as in the prior art, if necessary, such as a curing agent, a plasticizer, a curing accelerator, a crosslinking accelerating catalyst, a surface modifier, an ultraviolet absorber, a light stabilizer, an antioxidant, a fluidity modifier, Components such as an anti-dripping agent and an antifoaming agent can be contained.

In the production method of the present invention, the above-mentioned coating composition is blown into a large amount of the hydrophilic organic solvent (C) or blown at a high pressure, or the hydrophilic organic solvent (C) is vigorously stirred. The organic solvent (B) is extracted from the coating composition into the hydrophilic organic solvent (C) to cause phase transition, and the dispersion of the coating resin particles in the hydrophilic organic solvent (C). Generate a liquid.

The paint resin particles are collected by filtration or the like, and if necessary, are again subjected to an extraction treatment with a hydrophilic organic solvent (C) to extract the residual solvent from the paint resin particles. Collect by. From the viewpoint of environmental protection and resource saving, the amount of the hydrophilic organic solvent (C) adhering or adsorbing to the surface of the coating resin particles is preferably small or non-existent. Is a hydrophilic organic solvent (C) attached or adsorbed on the surface of paint resin particles by centrifuging or suctioning under reduced pressure.
However, the amount of the hydrophilic organic solvent (C) adhering to or adsorbing to the resin particles remains in an amount that does not adversely affect the coating properties and coating performance of the water-dispersed powder coating to be manufactured next. It is preferable that the residual amount be determined from the processing cost and man-hour for reducing the residual amount.

If the hydrophilic organic solvent (C) attached or adsorbed on the surface of the coating resin particles is completely removed by a method of vacuum drying or a method of flash drying in a fluidized bed,
The surface of the coating resin particles is covered with an air layer, and the hydrophobicity becomes strong, so that a large amount of a wetting agent is required when wetted with water in the next step, and as a result, the coating film performance and the like are undesirably reduced. Generally, it is preferable to disperse the resin in water in a state where 1% by weight or more based on the weight of the coating resin particles remains.

The coating resin particles of the water-dispersed powder coating prepared through the phase inversion method are fine and have a narrow particle size distribution width.
These are paint resin particles having a shape close to a sphere. If the particle size distribution of the coating resin particles is within a predetermined range, it can be applied as it is as a water-dispersed powder coating to form a coating film. If necessary, it can be further passed through a bead mill or the like to adjust to a finer particle size distribution or a sharper particle size distribution.

In the production method of the present invention, the resin (A) is added to a coating composition containing a resin (A) which is a main component for forming a coating film and an organic solvent (B) for dissolving the resin (A). On the other hand, a hydrophilic organic solvent (C), which is a non-solvent or a poor solvent but is compatible with the organic solvent (B), is used in an amount (precipitation) that is less than or equal to the amount that causes the resin (A) to undergo phase transformation. Within limits)
The coating composition, the viscosity of which has been reduced by the addition in step (a), is dispersed and mixed in the hydrophilic organic solvent (C) with stirring to form a fine particle dispersion by phase inversion, or a large amount of the hydrophilic organic solvent. While using (C) and stirring vigorously,
By adding the coating composition in a finely dispersed state to form resin particles from a solvent-type coating, coating resin particles having a finer shape, a narrower particle size distribution width, and a shape close to a sphere are formed.

The water-dispersed powder coating obtained by the production method of the present invention has a low viscosity of the coating, a high concentration of non-volatile components, and uniform chargeability of the coating resin particles. A coating film having high efficiency and good smoothness can be formed.

A mixed solvent of the organic solvent (B) and the hydrophilic organic solvent (C) remaining after the coating resin particles are collected,
The mixed solvent recovered at the time of drying the coating resin particles is converted into a simple substance for each component by a usual distillation separation device, or a solvent in an evaporating fraction range, that is, into an organic solvent (B) and a hydrophilic organic solvent (C). Play separately.

After the separation, the organic solvent (B) and the hydrophilic organic solvent (C) are used repeatedly in the following operations. When this repetition operation is continued, as debris of the distillation separation device,
The low molecular weight resin component and various additives added for forming the coating remain as the main components. Since this distillation residue is effective as a paint component, it is effective to reuse it at the time of compounding the starting paint composition and make up for the shortage with a new raw material.

[0036]

The present invention will be described below in more detail with reference to examples and comparative examples. In the Examples and Comparative Examples, “parts” and “%” are values shown on a weight basis. <Preparation of polyester resin white primary color coating composition> Polyester resin solution (softening temperature of solid resin: 120 ° C., acid value = 4)
5. Nonvolatile content 50%, solvent content: butyl acetate / xylol = 50/50) 64 parts and epoxy resin solution (bisphenol A type epoxy resin, epoxy equivalent of solid epoxy resin = 910, nonvolatile content 60%, solvent content xylol)
46 parts, 25 parts of titanium white pigment, 6 parts of surface conditioner, 2 parts of ultraviolet absorber, 1 part of antioxidant and 1 part of curing accelerator, and the maximum particle diameter of the pigment particle size distribution is 5 μm by a kneading dispersing machine. It was dispersed uniformly as follows. This polyester resin white primary color coating composition is a solution coating composition having a nonvolatile content of 60%.

<Preparation of polyester resin black primary color paint composition> Polyester resin white was used except that 25 parts of the titanium white pigment used in the preparation of the above polyester resin white primary color paint composition were changed to 3 parts of carbon black black pigment. In the same manner as in the preparation of the primary color paint composition, a polyester resin black primary color paint composition having a nonvolatile content of 51% was prepared.

<Preparation of Acrylic Resin Clear Coating Composition> A reaction vessel was charged with 80 parts of xylol and 20 parts of butyl acetate, and the temperature was raised to 100 ° C. 36 parts of methyl methacrylate, 13 parts of 2-ethylhexyl acrylate, 31 parts of styrene monomer, 11 parts of isobutyl methacrylate, 7 parts of hydroxyethyl methacrylate and 2 parts of acrylic acid were charged into a dropping tank, and after mixing, polymerization was started immediately before the start of dropping. 3 parts of the agent were added and dissolved. This mixture was added dropwise over 30 minutes to start the reaction. After further reacting for 2 hours, the temperature of the reaction solution was raised to 120 ° C.
A solution in which 0.5 part of the polymerization catalyst was dissolved in 4.5 parts of xylol was added dropwise over 3 minutes, the reaction was maintained for 30 minutes, and the nonvolatile content was 50%, the average molecular weight was Mw = 11,000, and Mn was 420.
An acrylic resin solution having 0, a hydroxyl value of 30, and an acid value of 15.5 was prepared. 76 parts of this acrylic resin solution was mixed with 16 parts of a butyl etherified melamine resin solution (nonvolatile content: 60%).
Parts, 2 parts of a surface conditioner and 3 parts of an ultraviolet absorber, and uniformly mixed and dissolved to prepare an acrylic resin clear coating composition having a nonvolatile content of 49%.

<Preparation of Acrylic Resin Blue Primary Color Paint Composition>
16 parts of butyl etherified melamine resin (nonvolatile content 60%), 4 parts of phthalocyanine blue (blue pigment), 6 parts of titanium white pigment, 76 parts of acrylic resin solution obtained in the above acrylic resin clear coating composition preparation, 2 parts of an agent and 2 parts of an antioxidant were added, uniformly mixed and dissolved, and further dispersed with a pigment to prepare an acrylic resin blue primary color paint composition having a nonvolatile content of 54%.

Example 1 The above-mentioned polyester resin white primary color paint composition and polyester resin black primary color paint composition were 100/0, 95/5, 5
White, light gray, gray, dark gray and black solution coating compositions were prepared by mixing at a ratio of 0/50, 30/70 and 0/100, respectively.

10 parts of each of these coating compositions was weighed,
Separately, 100 parts of methyl alcohol was gradually dropped into a container while being vigorously stirred to precipitate paint resin particles. The mixed solvent was removed from the vessel, and then 30
A part of methyl alcohol was added and stirred, and then allowed to stand to precipitate the coating resin particles, and the mixed solvent was removed. Finally, 15 parts of methyl alcohol was added, and the mixture was transferred to a filtration device together with the coating resin particles, and the solvent was removed until the nonvolatile content became 99%. 43 parts of the coating resin particles having a nonvolatile content of 99%
It was added to a solution consisting of 1 part of a nonionic surfactant having an HLB of 16 and 54 parts of water, and was dispersed by stirring. To this dispersion, 2 parts of polyethylene glycol having a molecular weight of 6000 and 1 part of a hydrocarbon-based antifoaming agent were added to obtain a water-dispersed powder coating.

The coating resin particles in these water-dispersed powder coatings had an average particle diameter of about 5 μm and were relatively close to true spheres. These white, light gray, gray, dark gray and black water-dispersed powder coatings are each applied by air spray coating to a zinc phosphate-treated steel sheet so that the film thickness becomes 40 μm, and from normal temperature to 100 ° C. in 3 minutes. Heat, then 200 ° C
The film was further heated to 200 ° C. and baked and cured for 20 minutes to form a coating film.

Each of the formed coating films is white, light gray, gray, dark gray and black in a range that hardly differs from the color of the coating film formed by the solution coating obtained by toning and blending the solution coating. The coating film had a gloss of 90 or more, and was a smooth and good coating film. In the preparation of these water-dispersed powder coatings, when the solution coating composition is quantitatively mixed as in this example, the raw material mixing of the powder coating, particularly the mixing ratio of the pigment, is calculated backward from the mixing ratio of the coating. It may be determined, but in the case of each prepared by a normal manufacturing method, that is, in the case of making resin pellets toned to the specified color, further wet pulverized into a water-dispersed powder coating, in the case of completely unknown , Repeat the trial about three times,
It is necessary to calculate the pigment compounding ratio from the change amount, and to confirm it again when preparing the final product, and for the gray color other than white and black this time, the powder paint toned to these prescribed colors, Comparing the time man-hour when preparing by the manufacturing method of the above-mentioned embodiment of the present invention and the time man-hour when preparing by the usual manufacturing method of the powder coating, in the latter case, the time required for preparing the powder coating is reduced. It required five times as many man-hours.

Example 2 A nozzle having a large number of small holes was attached to the side wall of a container so that the nozzle could be blown into the container. This container was charged with 100 parts of ethyl alcohol, and the upper space was replaced with nitrogen gas to make it inert. 10 parts of the acrylic resin clear coating composition having a nonvolatile content of 49% was ejected from the nozzle at a pressure of 12 MPa to form coating resin particles instantaneously. The dispersion in which the coating resin particles were dispersed was separated by a wet cyclone, and further centrifuged at a low speed to obtain coating resin particles having a nonvolatile content of 98%. The paint resin particles were treated in the same manner as in Example 1 to obtain a water-dispersed powder clear paint.

This water-dispersed powder clear paint is electrostatically coated on a chrome-plated part so as to have a film thickness of 25 μm, heated at 80 ° C. for 10 minutes, and then cured by heating at 160 ° C. for 20 minutes. I got the parts. The coated part coated with this acrylic resin coating film had an extremely high gloss value and had an appearance excellent in metallic appearance. Also, if you touch it with your hand,
A hand mark was left on the painted part having only the plated surface, but no hand mark was left on the painted part coated with the acrylic resin coating film.

Example 3 20 parts of n-butyl alcohol were gradually added to 50 parts of the above acrylic resin blue primary paint composition while stirring to obtain a uniform blue paint composition. On the other hand, 50 parts of methyl alcohol was charged into the container used in Example 2, and this blue coating composition was jetted out in the same manner as in Example 2, and treated similarly to obtain an acrylic resin blue water-dispersed powder coating. . This acrylic resin blue water-dispersed powder coating was applied to an automotive part obtained by applying an electrodeposition coating to a zinc phosphate-treated steel sheet so as to have a thickness of 50 μm, and was cured by heating in the same manner as in Example 2. did. This coated part also had a gloss value of 95 and was excellent in appearance.

Comparative Example 1 In Example 1, 43 parts of paint resin particles from which the solvent was removed until the nonvolatile content became 99%, 1 part of a nonionic surfactant having an HLB = 16, 54 parts of water, polyethylene glycol having a molecular weight of 6,000 A water-dispersed powder coating material was prepared using 2 parts and 1 part of a hydrocarbon-based antifoaming agent. In this comparative example, the solvent was removed until the nonvolatile content became 99.9% or more, and the dried coating resin particles were dried. 42.6 parts (reduced by the reduced amount of solvent), 1 part of nonionic surfactant having HLB = 16, 54.4 parts of water (increased by the reduced amount of solvent in paint resin particles), molecular weight 6000 A water-dispersed powder coating material was similarly prepared using 2 parts of polyethylene glycol and 1 part of a hydrocarbon-based antifoaming agent. When a coating film was formed in the same manner as in Example 1 using this water-dispersed powder coating material, there was no difference in the color and gloss of the coating film from the coating film formed in Example 1, but The smoothness was slightly inferior.

The reason for this is that, since the drying of the resin particles took a long time, the surface of the resin particles in contact with the outside air was completely dried, and a water-dispersed powder coating was prepared using the resin particles in a slightly aggregated state. That's why. When 2 parts of a nonionic surfactant was further added to the water-dispersed powder coating material to increase the wettability, and the agglomerated portion was deagglomerated with a bead mill, and the smoothness of the coating film was also improved. However, as a result of increasing the amount of the surfactant, Example 1 was used.
In the moisture resistance test (50 ° C., 98% RH), there was no abnormality even after 240 hours or more. However, the coating film of this comparative example started to generate small blisters in the moisture resistance test in 120 hours. .

[0049]

According to the production method of the present invention, the coating resin particles are dispersed in water while some hydrophilic organic solvent remains on the surface of the coating resin particles, so that the surface of the resin particles is prevented from becoming hydrophobic. Can be used as a water-dispersed powder coating,
In addition to shortening the operation process, the surface of the resin particles is covered with a hydrophilic organic solvent and easily wetted with water when dispersed in water, so the amount of surfactant required for wetting should be reduced. As a result, the content of a hydrophilic compound such as a surfactant in the coating film is reduced, and a coating film having good water resistance and moisture resistance and long-term durability can be formed.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G065 AA01 BB06 CA03 CA11 DA06 FA01 4J038 CD091 CE071 CG001 CP081 CR071 DA051 DA161 DB001 DB471 DD001 DF061 DG111 DG301 DH001 DL031 EA011 KA03 LA05 MA08 PA02

Claims (5)

[Claims] (1) A coating composition containing a resin (A), which is a main component for forming a coating film, and an organic solvent (B) that dissolves the resin (A) is non-aqueous to the resin (A). Dispersing and mixing with stirring in a hydrophilic organic solvent (C) which is a solvent or a poor solvent but is compatible with the organic solvent (B) to form a fine particle dispersion by phase inversion; (2) a step of separating fine particles from the fine particle dispersion obtained in the above step (1), and (3) a dispersion of the not completely dried fine particles obtained in the above step (2) in water. A method for producing a water-dispersed powder coating, comprising the steps of: 2. A coating composition containing (1) a resin (A) as a main component for forming a coating film and an organic solvent (B) for dissolving the resin (A), wherein the resin (A) A step of adding a hydrophilic organic solvent (C), which is a non-solvent or a poor solvent but is compatible with the organic solvent (B), in an amount not more than the amount that causes the resin (A) to undergo phase transformation. (2) a step of dispersing and mixing the coating composition obtained in the step (1) in the hydrophilic organic solvent (C) with stirring to form a fine particle dispersion by phase inversion; A step of separating fine particles from the fine particle dispersion obtained in the above step (2), and (4) a step of dispersing the not completely dried fine particles obtained in the above step (3) in water. A method for producing a water-dispersed powder coating, comprising: 3. The method according to claim 1, wherein in the step of separating the fine particles from the fine particle dispersion liquid, the fine particles are recovered in a state where the dispersion medium is adhered, and the fine particles adhered to the dispersion medium are dispersed in water in the next step. 3. The method for producing the water-dispersed powder coating material according to 2. 4. The resin (A), which is a main component of the coating film, is made of an alkyd resin, an acrylic resin, a polyester resin, an epoxy resin, a melamine resin, a blocked isocyanate resin, a fluororesin, a silicone resin, an amide resin, an ABS resin, a novolak. 4. The method for producing a water-dispersed powder coating according to claim 1, comprising at least one member selected from the group consisting of a resin, a ketone resin, a butyral resin, and a phenoxy resin. 5. The method according to claim 1, wherein the hydrophilic organic solvent (C) is methyl alcohol, ethyl alcohol, n-propyl alcohol, is
5. The method for producing a water-dispersed powder coating according to claim 1, wherein o-propyl alcohol or n-butyl alcohol is used alone or in a mixture thereof.