JPH05311096A - Production of powder coating material - Google Patents

Abstract

PURPOSE:To provide the production process of powder coating material whereby the color matching can be performed within a short time, the drying can be performed efficiently, and the grinding can be performed easily. CONSTITUTION:A dispersion paste of a solid concentration of 60-80wt.% is brought to a state having a thickness of 10cm or below and being open to air on one side and dried by heating in a vacuum of 10Torr or below to obtain a bulky dry product of a solid concentration of 95wt.% or above and a density of 0.4-0.6g/cm<3>. This product is ground and classified to produce a powder coating material.

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 powder coating material.

[0002]

2. Description of the Related Art A powder coating material is usually manufactured through a step of premixing raw materials for coating material in a dry state without using a solvent, a step of melt-kneading, a step of pulverizing, and a step of classifying in this order. Has been done.

[0003]

The task of toning is important in the production of paints, but in the conventional method for producing powder coatings, from the addition of the pigment to the confirmation of the color of the coating film, We make powder paint one by one, apply this, and bake. For this reason, there is a problem that it takes time to adjust the color and wastes raw materials.

In order to shorten the toning time, the raw materials may be wet mixed. That is, when wet-mixing, the mixture is applied and dried to form a coating film, so that the color can be confirmed. Therefore, there is almost no waste of raw materials. However, when wet mixing is adopted, a new problem occurs. That is, the drying process is inefficient and crushing is not easy.

Therefore, it is an object of the present invention to provide a method for producing a powder coating material, which can adjust the color in a short time, improve the efficiency of drying, and facilitate pulverization.

[0006]

In order to solve the above problems, the present invention provides a method for producing a powder coating material, which comprises drying and pulverizing a dispersion paste obtained by mixing coating materials in the presence of a solvent. In the step of drying the dispersion paste, a dispersion paste having a solid content concentration (hereinafter referred to as “NV”) of 60 to 80% by weight is used, and the paste is opened on one side.
Provided is a method for producing a powder coating material, which comprises a step of heating and drying under a reduced pressure of Torr or less to obtain a dried product having a bulkiness of NV 95% by weight or more and a density of 0.4 to 0.6 g / cm ^3. ..

According to the present invention, after the drying, the rotor is rotatably supported about the shaft center, and a large number of projections extending in the axial direction are provided side by side on the circumferential surface.
The rotor has a cylindrical rotor facing surface that is arranged at a constant distance from the rotor circumferential surface, and a large number of axially extending ridges are arranged in the circumferential direction on the facing surface. And the opposite surface guides the dried material between the stator, which is openable to expose the rotor circumferential surface, and the dried material is finely pulverized by the rotation of the rotor, and powder coating is applied. You may get it.

In the present invention, when the dried product is finely pulverized by the rotation of the rotor, for example, an air stream having a temperature of (Tg−5) ° C. or lower is provided between the rotor and the stator (Tg is a glass of the dried product). An airflow having a transition temperature) may be supplied. The temperature of the airflow may also be (Tg-5) to (Tg-10) ° C.

[0009]

[Operation] A bulky dried product can be easily obtained by heating and drying under a reduced pressure with the dispersion paste opened on one side. The bulky dried material can be easily ground in the subsequent grinding step. When the NV of the dispersion paste is lower than the above range, the drying time becomes long and heat deterioration occurs. On the other hand,
If the NV is higher than the above range, a bulky dried product cannot be obtained.

The thickness of the dispersion paste when dried is preferably 10 cm or less. If the thickness exceeds 10 cm, the inside will be NV
It may not be possible to exceed 95%. If the depressurized state during drying is higher than 10 Torr, a large amount of solvent remains, causing pinholes in the coating film, or it becomes necessary to set the drying temperature high, which causes the curing reaction to proceed. It becomes difficult to put it into practical use.

The dried product obtained must have an NV of 95% or higher. This is because a large amount of residual solvent causes pinholes in the coating film. The dried product should have a density of 0.4 to 0.6 g / cm ³ . This is a problem that if the amount is out of this range, the pulverizing ability in the pulverizing step of the next step may be lowered, for example, the pulverizing efficiency may be poor, or un-milled substances or coarse particles may be frequently generated to widen the particle size distribution. Because.

By supplying an air stream having a temperature of (Tg-5) ° C. or less during the pulverization, the pulverization can be performed with higher efficiency. When the temperature of the air flow is (Tg-5) to (Tg-10) ° C, rounded particles can be obtained.

[0013]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings showing the examples. FIG. 1 shows an embodiment of the method for producing a powder coating material according to the present invention. The raw material 1 for paint and the solvent 2 are put into the mixing means 3 and mixed. This mixture, that is, the dispersed paste, is introduced to the drying means 5,
Heat dry. The dried material is guided to the crushing means 6, crushed, and classified by the classifying means 7 to obtain the powder coating material 8.

The coating material used in the present invention is used for producing an ordinary powder coating material and is not particularly limited. For example, resins, curing agents, pigments (not required for clear type paints), and other additives. The raw materials for the paint are mixed in the presence of a solvent. The solvent used here is not particularly limited, but specific examples thereof include xylene (XL), toluene, and methyl ethyl ketone (MEK), and the amount of the solvent is, for example, based on the entire dispersion paste. It is set to 20 to 40% by weight.

The mixing is carried out, for example, by solution dispersion to obtain a dispersion paste. Examples of the mixing means used include SG mills, rolls and attritors. The mixing conditions may be the same as in the case of producing a usual paste type paint. In the present invention, the NV of the dispersion paste needs to be 60 to 80% by weight.

After mixing, color adjustment is carried out if necessary. At this time, since the raw material for paint is a paste, a coating film can be formed immediately after applying the paste, and toning is performed in a very short time. When making a clear type powder coating, toning can be omitted. Next, the solvent is evaporated from the dispersed paste and drying is performed. In this invention, the dispersion paste is opened on one side and heated and dried under a reduced pressure of 10 Torr or less. In order to carry out the drying in such a manner, it is convenient to use, for example, what is generally called a vacuum belt dryer or a drying tray installed in the vacuum chamber.

In FIG. 1, the drying means 5 is a vacuum belt dryer. An endless belt 51 is installed in the decompression chamber 54, and is moved by a roll. The decompression chamber 54 is decompressed to a desired pressure by the decompression means 53. The dispersed paste 4 is guided onto the belt 51, and the dispersed paste 4 is dried by heat transfer and radiation from the heating plate 52. The obtained dried product is peeled from the belt 51 with a scraper (not shown) or the like, and sent to the crushing means 6. The heating plate 52 is, for example, a double pipe type, and a heating medium such as hot water or steam is introduced into the inner pipe so as to reach a predetermined heating temperature.

One side is opened by, for example, pouring or coating the dispersion paste on a substrate made of a material that allows the dispersion paste to be peeled off after drying. Examples of the substrate include, but are not limited to, a belt formed by impregnating a fluorocarbon resin such as polytetrafluoroethylene resin (PTFE) into a substrate such as glass cloth.

In order to obtain a reduced pressure atmosphere of 10 Torr or less, a normal pressure reducing means and a pressure reducing chamber, a pressure reducing means attached to a pressure reducing belt dryer and the like may be used. The heating for drying may be appropriately selected from heat transfer, warm air, radiation, etc., but radiation is preferred from the viewpoint of preventing material deterioration and increasing drying efficiency. The heating temperature is not particularly limited, but is set to, for example, 80 to 110 ° C., and the heating time is not particularly limited, but is, for example, 5 to 15 minutes. When a belt dryer is used, continuous heat drying can be performed, which is advantageous in terms of mass productivity.
The belt dryer can be provided with a plurality of zones for heating and drying, which is preferable in terms of productivity. To give an example of installation of a plurality of heat drying zones, for example, the first zone of 90 to 110 ° C. (passing time is set to 6 to 8 minutes), 70 to 80 ° C.
The second zone (passage time is, for example, 5 to 25 minutes), and the third zone at 25 to 30 ° C. (passage time is, for example, 8 to 10 minutes). ..

By heat-drying, a bulky dried product having an NV of 95% or more and a density of 0.4 to 0.6 g / cm ³ is obtained. This dried product has a porous plate shape and is easily crushed. In the present invention, the pulverization of the dried product is a pulverization method usually used in the production of ordinary powder coatings, for example,
The hammer mill method is used. After crushing, if necessary, classify with a vibration sieve and package.

In the present invention, the crushing may be carried out by the above-mentioned hammer mill method or the like, but an air flow and mechanical crushing method may be adopted. This pulverizing method is a method in which a dried product that has been coarsely pulverized or coarsely pulverized and finely pulverized in advance as needed is introduced between a rotor and a stator having a specific shape, and finely pulverized by rotation of the rotor. Is. As shown in FIGS. 2 to 4, the rotor 62 includes a ridge 6 that is rotatably supported about an axis and extends axially in the circumferential surface.
A large number of 20 are provided side by side in the circumferential direction. 61 is a rotating shaft. The stator 63 has a cylindrical rotor facing surface which is arranged with a constant space S between the rotor 63 and the rotor circumferential surface, and a convex strip 630 extending in the axial direction extends in the circumferential direction on the facing surface. Are arranged side by side, and the facing surfaces can be opened to expose the rotor peripheral surface. For example,
As shown by the chain double-dashed line in FIG. 3, the stator 63 has a portion 63a in which a cylindrical container is vertically divided into two and has a peripheral surface for half a circumference.
And a portion 63b having a peripheral surface for the remaining half circumference is opened and closed in the lateral direction (indicated by arrow C). The distance S between the rotor 62 and the stator 63 is, for example,
The rotor 62 is set to 1 mm or less, for example, 600
Rotate at a speed of 0 to 15000 rpm. At this time, in order to prevent the deterioration and / or the melting of the resin and the like due to the temperature rise due to friction or the like, a cooling means may be provided so that the temperature can be maintained below a certain temperature. For example, you may make it cool by supplying the airflow of 5 degreeC or less lower than the glass transition temperature (Tg) of dried material. If the temperature of the air flow is higher than (Tg-5) ° C,
The pulverization heat may cause re-fusion of the pulverized products or adhere to the rotor and the stator. The temperature of the air flow is (T
In the range of g-5) to (Tg-10) ° C, rounded particles are obtained. When an air flow is used to supply the dried product, the air flow may also be used for cooling. As shown by the arrow A, the dried material is guided to the crushing means 60, and is guided between the rotor 62 and the stator 63. The crushed material is guided to the outside of the crushing means 60 as shown by arrow B. 2 and 3, the ridges 620 and 630 are shown in a simplified manner. In FIG. 2, a part of the rotor is broken to show the stator behind it. In FIG. 4, the portion of the circle P in FIG. 3 is shown enlarged.
By using such a pulverizer, a powder coating material can be obtained without performing classification.

The crusher provided with the rotor and the stator as described above is, for example, the one described in JP-B-61-36463. However, it is not limited to this. Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples. In the following, "%" means "% by weight" unless otherwise specified.

Example 1 The following raw materials for coating materials were mixed in the presence of the following solvents with an SG mill (trade name "Neo Glen Mill" manufactured by Asada Iron Works Co., Ltd.) to obtain a dispersion paste. The resulting dispersed paste was NV 60%. The dispersion paste was continuously supplied and heated and dried as follows. That is, 10
The dispersion paste was put in a decompression chamber decompressed to Torr from a raw material supply nozzle to a PTFE impregnated glass cloth belt with a thickness of
Discharge continuously to reach cm, and move the belt at a constant speed with one side open, the temperature 95 ° C zone for 7 minutes, the temperature 80 ° C zone for 15 minutes, and the temperature 30 ° C zone. Were sequentially passed for 10 minutes to be dried, and peeled with a scraper to obtain a dried product. The obtained dried product is NV
It was bulky with 98% and a density of 0.6 g / cm ³ . The dried product was roughly crushed into pellets of about 1 cm, and then the airflow and the mechanical crusher manufactured by Kawasaki Heavy Industries, Ltd. (trade name “Kriptron” KTM-X type) had a temperature of 12 ° C. (2.5 Nm). ⁽³ / min) and continuously pulverized to obtain a powder coating. The conditions for pulverization were a raw material (coarse crushed material) supply rate of 5 kg / hr and a rotation speed of the rotor of 12000 rpm. [Composition of raw materials for coating material] Resin solid content 70 parts by weight Dodecane diacid 11 parts by weight Titanium dioxide 30 parts by weight Surface modifier 0.5 parts by weight Benzoin 0.5 parts by weight [Solvent] Xylene 40 parts by weight [Resin solids content Is styrene 25 parts by weight, methyl methacrylate 29.57 parts by weight, glycidyl methacrylate 30.
It was obtained by solution polymerization using 0 parts by weight, 15.43 parts by weight of n-butyl methacrylate and 2 parts by weight of azobisisobutyronitrile, and heating under reduced pressure. As the surface conditioner, a product name of ACRONAL 4F manufactured by BASF was used. -Examples 2 to 6- A powder coating material was obtained in the same manner as in Example 1 except that the changes were made as shown in Table 1.

Example 7 The dried product obtained in Example 1 was treated with a hammer mill (trade name "Sample Mill" KII-1 manufactured by Fuji Paudal Co., Ltd.).
Type). The condition of crushing is to use 6 hammers,
The rotation speed was 5000 rpm and the raw material supply rate was 5 kg / hr. The obtained pulverized product is sieved with a Tyler standard sieve,
Particles passing through 150 mesh were collected to obtain a powder coating material.

The Tg of the dried product in the examples is 70.
It was about ℃. -Comparative Example 1-In Example 1, an attempt was made to obtain a powder coating material in the same manner as in Example 1 except that the NV of the dispersion paste was 50%, but the NV of the dried product was 82%. -Comparative Example 2-In Example 1, an attempt was made to obtain a powder coating material in the same manner as in Example 1 except that the NV of the dispersion paste was set to 90%. Could not supply.

-Comparative Example 3-A powder coating material was obtained in the same manner as in Example 1 except that the atmospheric pressure during drying was set to 15 Torr, but the atmospheric pressure during drying was too high. As a result, a dried product having an NV of 95% or more could not be obtained. -Comparative Example 4-A powder coating material was obtained in the same manner as in Example 1 except that the NV content of the dried product was changed to 90%. A hole arose.

Comparative Example 5 The above raw materials for paint were premixed in a Henschel mixer at a rotation speed of 1000 rpm for 30 minutes without using a solvent,
Then, using an extruder (manufactured by Buss), the temperature was adjusted to 9
After melt-kneading at 0 ° C., a powder coating material was obtained in the same manner as in Example 2 except for the steps after pulverization.

-Comparative Example 6- The melt-kneaded product prepared in Comparative Example 5 was pulverized in the same manner as in Example 1 to obtain a powder coating material. Table 1 shows the drying and crushing conditions. In the above Examples 1 to 7,
Toning was performed by changing the pigment. At this time, the dispersion paste was applied to a tin plate in a thickness of 0.75 mm, dried at 140 ° C. for 30 minutes and cured to form a coating film, and the color could be confirmed. On the other hand, in Comparative Examples 5 and 6, when the pigment was changed, it was necessary to once manufacture the powder coating material, apply it, and bake it to form a coating film and confirm the color.

The average particle diameter, particle size distribution width and particle shape of each powder coating material of the above-mentioned examples were investigated. The particle shape was examined by a scanning electron microscope, and shown by the following criteria. Spherical: Round with no corners (see Figure 6). Non-spherical: There are corners (see FIG. 5). The cold-rolled steel sheet (JIS-G3141) was coated with each powder coating material of the above-mentioned Examples and Comparative Examples by electrostatic coating,
It was baked at a temperature of 140 ° C. for 30 minutes to form a coating film having a film thickness of 0.06 mm. The surface smoothness of each coating film was indicated by the presence or absence of unevenness and the gloss.

The presence or absence of irregularities was examined by NSIC (Mapping and Visualization) and visually. The larger the value of NSIC,
There are few irregularities. The visual results are as follows: ○: no unevenness, △:
There are slight irregularities, and ×: there are many irregularities. The gloss is
It was examined by the 60-degree specular gloss of JIS-K5400.
The results are shown in Table 2. Scanning electron micrographs of the powder coating materials obtained in Examples 3 and 4 are shown in FIGS.

[0031]

[Table 1]

[0032]

[Table 2] As shown in Tables 1 and 2, a coating film having no unevenness and good gloss was obtained. When the airflow temperature at the time of pulverization is lower than (Tg-10) ° C, angular paint particles are obtained as shown in Fig. 5, and when the airflow temperature is set to (Tg-5) to (Tg-10) ° C, the results are shown in Fig. 6. A rounded powder coating is obtained as shown in Fig.
The pulverizers used in Examples 1 to 6 had less adherence than those used in Example 7, and the adhered substances were easily removed.

[0033]

EFFECTS OF THE INVENTION According to the method for producing a powder coating material of the present invention, it is possible to carry out color matching in a short time, improve the efficiency of drying, and facilitate pulverization. In particular, in the present invention, if the dried product is crushed by the above-mentioned specific airflow / mechanical crushing method, a finer powder coating material can be obtained, and the crushing device can be easily washed.

In the present invention, the temperature of the air flow during pulverization is (T
When the temperature is g-5) ° C. or less, the coating material adheres little to the crushing device and the cleaning is easy. In the present invention, when the temperature of the air flow during pulverization is (Tg-5) to (Tg-10) ° C, the coating particles have a rounded shape as compared with the conventional pulverization method, so that blocking is difficult and handling is performed. An easy powder coating can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a method for producing a powder coating material of the present invention.

FIG. 2 is a schematic vertical sectional view showing an example of a crushing means used in the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of a crushing means used in the present invention.

FIG. 4 is an enlarged view of a portion of a circle P in FIG.

5 is a photograph showing a particle structure and a scanning electron microscope photograph of the powder coating material obtained in Example 3. FIG.

FIG. 6 is a photograph showing a particle structure, which is a scanning electron microscope photograph of the powder coating material obtained in Example 4.

[Explanation of symbols]

 1 Raw material for paint 2 Solvent 3 Mixing means 4 Dispersion paste 5 Drying means 6 Grinding means 7 Classification means 8 Powder coating 51 Belt 52 Heating plate 53 Pressure reducing means 54 Pressure reducing chamber 60 Grinding means 62 Rotor 63 Stator 620 Rotor Ridge 630 ridge of stator

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 24, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Claims (4)

[Claims] 1. A method for producing a powder coating material, which comprises drying and pulverizing a dispersion paste prepared by mixing coating materials in the presence of a solvent, wherein the dispersion paste drying step comprises a solid content concentration of 60 to 80% by weight. The dispersion paste of No. 1 was used, the paste was opened on one side, and dried by heating under reduced pressure of 10 Torr or less to obtain a solid content concentration of 95% by weight or more and a density of 0.4 to
A method for producing a powder coating material, which comprises a step of obtaining a dried product of 0.6 g / cm ³ . 2. A rotor, which is rotatably supported about an axis and has a plurality of projections extending in the axial direction on the circumferential surface, and the rotor is fixed between the rotor and the circumferential surface of the rotor. Has a cylindrical rotor facing surface that is arranged at intervals, and a large number of projections extending in the axial direction are arranged side by side in the facing surface, and the facing surface is the rotor peripheral surface. The powder paint according to claim 1, wherein the dried material is introduced between a stator that can be opened to expose the powder, and the dried material is pulverized by rotation of the rotor to obtain a powder coating. Production method. 3. The rotor is rotated when finely pulverizing the dried product, and an air stream having a temperature of (Tg-5) ° C. or lower (Tg is the glass transition temperature of the dried product) is applied between the rotor and the stator. The method for producing the powder coating material according to claim 2, which is supplied. 4. The temperature of the air flow is (Tg-5) to (Tg-1).
The method according to claim 3, wherein the temperature is 0) ° C.