JPH051243A - Production of powder coating material - Google Patents

Abstract

PURPOSE:To obtain at good efficiency a powder coating material having a mean particle diameter and a particle size distribution width smaller than those in prior art. CONSTITUTION:A solid mixture as a starting material for a coating material is led into a gap between a rotor 62 supported in a manner rotatable about a shaft center 61 and having a plurality of parallelly arranged axially extended protrudent streaks on the periphery and a rotor 63 having a cylindrical face opposed to the rotor, spaced from the periphery of the rotor and being openable for the purpose of exposing the periphery of the rotor and having a plurality of parallelly arranged and axially extended protrudent streaks 630 on the face, and the mixture is pulverized into a powder coating material by rotating the rotor 62.

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, a step of melting and kneading, a step of pulverizing, and a step of classifying in this order.

[0003]

The performance of the coating film formed by using the powder coating material, in particular, the presence or absence of unevenness of the coating film and the luster are influenced by the average particle diameter and the particle size distribution width of the particles of the powder coating material. receive. That is, the smaller the average particle size and / or the smaller the particle size distribution width, the better the surface smoothness, and as a result, the unevenness of the coating film disappears and the gloss also improves.

To reduce the average particle size of powder coatings,
It may be finely crushed, but at most 30 to 2 by the conventional method such as crushing with a hammer mill.
Only about 0 μm. Classification can be performed in order to reduce the particle size distribution width of the powder coating, but the classification causes a problem that the production efficiency of the powder coating is reduced.

Therefore, it is an object of the present invention to provide a method for producing a powder coating material, which can efficiently obtain a powder coating material having a smaller average particle diameter and a smaller particle size distribution width than those of the conventional methods. .

[0006]

In order to solve the above-mentioned problems, according to the present invention, a large number of ridges extending in the axial direction are provided side by side in the circumferential direction and are rotatably supported about an axis. The rotor and the peripheral surface of the rotor have a cylindrical rotor facing surface arranged at a constant interval, and a ridge extending in the axial direction extends in the circumferential direction on the facing surface. A large number of side-by-side facing stators, which are openable to expose the rotor peripheral surface, guide a solid mixture of coating materials between the stators, and the rotation of the rotor causes Provided is a method for producing a powder coating material, which comprises pulverizing the mixture to obtain a powder coating material.

According to the present invention, a crusher having a rotor and a stator as described above (hereinafter referred to as "crusher A") is used to crush the mixture between the rotor and the stator. Do it. According to this invention, for example, when the mixture is pulverized, the rotor is rotated, and an air flow of (Tg-5) ° C. or less is generated between the rotor and the stator (Tg is the glass transition temperature of the mixture). May be supplied between the rotor and the stator.

The temperature of the air flow is also (Tg-5) to (Tg).
It may be g-10) ° C.

[0009]

[Operation] When a solid mixture of coating materials is introduced between the rotor and the stator as described above and the rotor is rotated, a vortex flow is generated between the rotor and the stator. The particles of the mixture collide with each other due to the vortex and are ground. As a result, a powder coating having a small average particle size and a small particle size distribution width can be obtained. Therefore, classification is not required and efficiency is improved. Moreover, since the facing surface of the stator can be opened so as to expose the rotor peripheral surface, cleaning and inspection are easy.

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.

[0011]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings showing the examples thereof. FIG. 1 shows one embodiment of the method for producing a powder coating material of the present invention. The raw material 1 for paint is put into the pre-mixing means 30 and mixed without using a solvent, and then kneaded by the melt-kneading means 31. This mixture is introduced into the pulverizing means 6 and pulverized to obtain the powder coating material 8 without classification.

FIG. 5 shows another 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 into the drying means 5 and dried by heating. The dried material is introduced into the pulverizing means 6 and pulverized to obtain the powder coating material 8 without classification. The raw material for 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 solvent used when the above-mentioned raw materials for coating materials are mixed in the presence of a solvent is not particularly limited, but specific examples thereof include xylene (XL), toluene,
Such as methyl ethyl ketone (MEK). The amount of the solvent is, for example, 20 to 40% by weight based on the whole dispersed paste. For mixing, for example, premix with a Henschel mixer in a dry state without adding a solvent,
Then, the mixture is melt-kneaded with an extruder or the like. The conditions of the premixing and the melt kneading may be the same as the usual method. The mixing is also carried out, for example, by solution dispersion to obtain a dispersion paste. Examples of the mixing means used at this time include an SG mill, a roll and an attritor. The mixing conditions may be the same as in the case of producing a usual paste type paint. When they are mixed by a wet method, they are dried.

In the present invention, the solid mixture of the raw materials for paint is pulverized by the air flow / mechanical pulverization method. This pulverizing method is a method in which a mixture 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 there. As shown in FIGS. 2-4, the rotor 62
Is provided rotatably around the axis and a large number of convex strips 620 extending in the axial direction are arranged side by side on the circumferential surface. 61 is a rotating shaft. The stator 63 has a cylindrical rotor facing surface which is arranged with a constant space S between the stator 63 and the rotor circumferential surface, and a convex ridge 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 a chain double-dashed line in FIG.
Reference numeral 3 indicates a portion 63a having a circumferential surface for half a circumference obtained by vertically dividing the cylindrical container into two parts and a portion 63b having a circumferential surface for the remaining half circumference.
So as to open and close in the lateral direction (indicated by arrow C). Distance S between rotor 62 and stator 63
Is set to, for example, 1 mm or less, and the rotor 62 is rotated at a speed of, for example, 6000 to 15000 rpm. At this time, in order to prevent deterioration and / or melting of the resin or the like due to temperature rise due to friction or the like, a cooling means may be provided so that the air flow for feeding the mixture can be maintained at a temperature below a certain level. Here, the term "less than or equal to a certain temperature" means, for example, a temperature lower by 5 ° C or more than the glass transition temperature (Tg) of the mixture. If the temperature of the airflow is higher than (Tg-5) ° C, the pulverized heat may cause re-fusion of the pulverized products or adhere to the rotor and the stator. The temperature of the air flow is (Tg-5) to (Tg-1
At 0) ° C., rounded particles are obtained. As shown by the arrow A, the rotor 62 and the stator 6 of the crushing means 6 for crushing the mixture.
Lead between 3 and. The crushed material is guided to the outside of the crushing means 6 as shown by arrow B. In addition, in FIG. 2 and FIG.
20, 630 are shown in a simplified manner. In Figure 2,
A part of the rotor is cut away to show the stator behind it. In FIG. 4, the portion of the circle P in FIG. 3 is shown enlarged.

As a known example of such a crushing device, for example, the one described in JP-B-61-36463 can be cited. However, the invention is not limited to those described in the publication. In the present invention, when the wet mixing is performed as described above, the dispersion paste obtained by the mixing is preferably set as follows, for example. The solid content concentration (hereinafter referred to as "NV") of the dispersed paste is set to 60 to 80% by weight.
When the NV value is in such a range, for example, the amount of solvent to be evaporated is reduced to improve the drying efficiency, or
There is an advantage that it can be prevented from being attached to a belt or the like.

In the case of wet mixing, 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. For example,
The dispersion paste is heated to dryness under a reduced pressure of 10 Torr or less with a thickness of 10 cm or less and one side open. In order to perform 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 a vacuum chamber.

In FIG. 5, 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 that the heating plate 52 has a predetermined heating temperature.

The one-side open state is achieved 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, etc. may be used. The heat for drying may be selected as appropriate, such as heat transfer, warm air, or radiation, but from the viewpoint of preventing deterioration of the material and adhesion of the material surface to the belt due to heating and melting. Is preferred. The heating temperature is not particularly limited, but is set to, for example, 70 to 110 ° C., and the heating time is also not particularly limited, but is, for example, 20 to 30 minutes. When a belt dryer is used, continuous heat drying can be performed, which is advantageous in terms of mass productivity. In addition, the belt dryer can be provided with a plurality of zones for heating and drying, which is preferable in terms of mass production. To give an example of installation of a plurality of heat drying zones, for example, 90 to 110
C. first zone (passing time is, for example, 6 to 8 minutes), 70 to 80 ° C. second zone (passing time is, for example, 5 to 25 minutes), 25 to 30 ℃
Of the third zone (passage time is, for example, 8 to 10 minutes).

By heating and 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 is in the form of a porous plate and is easily crushed. A bulky dried product can be easily obtained by heating and drying the dispersion paste under reduced pressure with one surface open. The bulky dried product can be easily ground in a subsequent grinding process.

If the NV of the dispersion paste is lower than the above range, the drying time becomes long and the viscosity is low, so there is a risk of leakage from both ends of the belt. If the NV is higher than the above range, a bulky dried product cannot be formed, and stable supply is difficult due to the high viscosity, which may deteriorate the dried product. If the thickness of the dispersed paste exceeds 10 cm during drying, it may be difficult to keep the inside of NV 95% or more.

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. The reaction progresses, which makes practical application difficult. The obtained dried product 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 is 0.4 to 0.6 g / cm ^3.
Must have a density of. This is because if it is out of this range, there are problems that the pulverization efficiency is poor, or that unpulverized materials and coarse particles are often generated and the particle size distribution is widened. Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples.

-Example 1- [Blending 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 [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 Co., Ltd. was used. The above raw material for coating material (without solvent) is melt-kneaded at 90 ° C. using an extruder (manufactured by Buss Co., Ltd.), and the kneaded material is crushed into pellets of about 1 cm, and the crusher A is used.
(Kawasaki Heavy Industries Co., Ltd. air flow and mechanical crusher (trade name "Kriptron" KTM-X type) was used) was continuously guided by an air flow (2.5 Nm ³ / min) at a temperature of 12 ° C. for crushing. It carried out and obtained the powder coating material. The crushing conditions are as follows: raw material (coarse crushed material) supply rate 5 kg / hr, rotor speed 12000
It was rpm.

Example 2-The above-mentioned raw materials for coating materials were mixed in the presence of a solvent (40 parts by weight of xylene) 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% by weight. This dispersion paste was continuously supplied and heated and dried as follows. That is, the dispersion paste was continuously discharged from the raw material supply nozzle onto the PTFE-impregnated glass cloth belt so as to have a thickness of 10 cm in a decompression chamber decompressed to 10 Torr, and the belt was moved at a constant speed with one side open. Temperature 9
A 5 ° C. zone was passed for 7 minutes, a temperature 80 ° C. zone was passed for 15 minutes, and a temperature 30 ° C. zone was passed for 10 minutes to dry, and a scraper was used to obtain a dried product. The obtained dried product was bulky with an NV of 98% by weight and a density of 0.6 g / cm ³ . The dried product was pulverized in the same manner as in Example 1 to obtain a powder coating material.

-Examples 3 and 4- Powder coating materials were obtained in the same manner as in Examples 1 and 2 except that the procedure shown in Table 1 was used. —Comparative Example 1— The kneaded product obtained in Example 1 was hammermilled (trade name “Sample Mill” KII-1 manufactured by Fuji Paudal Co., Ltd.).
Type) to obtain a powder coating material. The conditions for crushing are to use six hammers, the rotation speed is 5000 rpm, and the raw material supply amount is 5 kg /
It was hr.

-Comparative Example 2-The powder coating material obtained in Comparative Example 1 was sieved through a Tyler standard sieve, and particles passing through 150 mesh were collected to obtain a powder coating material. —Comparative Example 3— The dried material obtained in Example 2 was crushed with a hammer mill in the same manner as in Comparative Example 1 to obtain a powder coating material.

-Comparative Example 4- The powder coating material obtained in Comparative Example 3 was sieved through a Tyler standard sieve, and particles passing through 150 mesh were collected to obtain a powder coating material. The Tg of the mixture in each Example and Comparative Example was about 70 ° C. The average particle diameter, particle size distribution width and particle shape of each powder coating material of the above Examples and Comparative Examples were examined. The particle shape was examined by a scanning electron microscope and shown by the following criteria.

Spherical: No corners and rounded (see FIG. 7) Non-spherical: Has corners (see FIG. 6) Cold-rolled steel plate ( Coating to JIS-G3141),
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 shown by the presence or absence of unevenness and the gloss.

The presence or absence of irregularities was examined by NSIC (Mapping and Imaging) and visually. The larger the numerical value of NSIC,
There are few irregularities. The results of visual inspection are ◯: no unevenness, Δ:
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 2 and 4 are shown in FIGS.

[0031]

[Table 1]

[0032]

[Table 2] As can be seen from Tables 1 and 2, the results of improving the physical properties of the coating film were obtained by pulverizing. When the airflow temperature at the time of pulverization is lower than (Tg-10) ° C, paint particles with corners are obtained as shown in Fig. 6, and the airflow temperature is from (Tg-5) to (Tg).
When the temperature is set to -10) ° C, a rounded powder coating is obtained as shown in Fig. 7.

In Examples 1 to 4, when the state of adhesion to the crushing device after crushing was continued for 24 hours was examined, the crushed material outlet (portion B in FIG. 2), the ridges of the rotor and the stator. There is some adhesion on (at 620 and 630 in FIGS. 3 and 4),
This deposit could be wiped off with a waste cloth and completely removed in about 10 minutes. On the other hand, in the hammer mill used in the comparative example, when the state of adhesion after crushing for 5 hours was examined, melt adhesion occurred on the entire inner surface of the hammer and the housing, and for complete removal of the adhered material It took 2 hours with an organic solvent (xylene or MEK).

[0034]

According to the method for producing a powder coating material of the present invention, it is possible to efficiently obtain a powder coating material having a smaller average particle diameter and a smaller particle size distribution width than those obtained by a conventional method such as a hammer mill. Moreover, the crushing device can be easily washed. In this invention, the temperature of the air flow during pulverization is (Tg-5)
When the temperature is at or below 0 ° C, the amount of paint adhered to the crushing device is small and cleaning is easy.

In the present invention, the temperature of the air flow during pulverization is (T
When the temperature is g-5) to (Tg-10) ° C, the coating particles have a rounded shape as compared with the conventional pulverizing method, so that a powder coating which is hard to block and easy to handle 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.

FIG. 5 is a flowchart showing another embodiment of the method for producing powder coating material of the present invention.

FIG. 6 is a photograph showing a particle structure, which is a scanning electron microscope photograph of the powder coating material obtained in Example 2.

FIG. 7 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]

Raw material for 1 paint 6 crushing means 8 powder paint 30 premixing means 31 Melt-kneading means 62 rotor 63 Stator 620 ridge of rotor 630 Stud ridge

[Procedure amendment]

[Submission date] June 25, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

Claims (3)

[Claims] 1. A rotor, which is rotatably supported about an axis and has a plurality of axially extending ridges arranged in a circumferential direction on a circumferential surface, and a rotor is circumferentially fixed. Has a cylindrical rotor facing surface that is arranged at intervals, and a plurality of axially extending ridges are arranged side by side in the circumferential direction on the facing surface, and the facing surface is the rotor peripheral surface. Of the powder paint to obtain a powder paint by introducing a solid mixture of the raw materials for paint between the stators that can be opened to expose the powder, and finely pulverizing the mixture by the rotation of the rotor. Production method. 2. The rotor is rotated when the mixture is pulverized, and an air stream having a temperature of (Tg-5) ° C. or lower (Tg is the glass transition temperature of the mixture) is supplied between the rotor and the stator. The method for producing the powder coating material according to claim 1. 3. The temperature of the air flow is (Tg-5) to (Tg-1).
The method according to claim 2, wherein the temperature is 0) ° C.