JPH08281643A - Preparation of powder paint - Google Patents

Abstract

PURPOSE: To improve the efficiency of the dry process for making powder paint and to narrow particle size distribution by a method in which a melt- kneaded powder paint resin composition is discharged from the opening of a rotating rotor to make a fibrous composition with a specified diameter, which is converted into powder with a specified average particle size through an optional pulverization process. CONSTITUTION: In the production method of powder paint, for example, a powder paint composition melt-kneaded by an extruder 1 is discharged from the opening of a rotating rotor 2 to make a fibrous composition 1.0α-20.0α in diameter. (α is the average particle size of powder paint obtained.) Next, the fibrous composition is pulverized by an optional grinder such as a ball mill, and then fine powder is removed by cyclone 4, etc., to make an average particle size α. In this way, by making the average particle size of the obtained powder paint α, the diameter of the discharged fibrous composition is adjusted to be 1.0α-20.0α.

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 powder coating material by a dry method.

[0002]

2. Description of the Related Art A high molecular weight resin can be used for powder coating,
Since it can be easily applied thickly, it is widely used as an electrical insulating material for motors and as a sealing material for electronic components. Recently, powder coating materials have been evaluated for their merits because they do not contain any solvent, and therefore pollution problems such as air pollution, disaster problems such as fire, hygiene problems, and resource saving have been evaluated, and their applications are expanding. There are a dry method and a wet method as a method for producing the powder coating material.

The wet method, that is, the method of dissolving or dispersing the powder coating material composition in a solvent and using various methods such as spray drying to make the powder into powder while removing the solvent requires a step for handling the solvent. In addition, the production cost is high, and if the removal of the solvent is incomplete, the obtained powder tends to cause blocking, and there is a problem in the stability of the quality, so it is not a general production method. The dry method is a method in which various raw materials for powder coating are melt-kneaded, and then cooled, pulverized and classified. Since no solvent is practically used, steps such as solvent recovery are unnecessary, and it is currently the mainstream manufacturing method. An endless belt is mainly used for cooling. If the kneaded composition is not sufficiently cooled before pulverization, the pulverization efficiency is poor and in some cases, it adheres to the pulverization device. Pulperizer for crushing,
A roller mill, a Victory mill, a ball mill, a jet mill or the like is used, which is selected according to the properties of the powder and the target particle size. For example, regarding the particle size, if the particle size is 1 or more, the jaw crusher or roll mill, on the contrary,
When targeting fine particles of m or less, a vibrating ball mill or a jet mill is selected. Normally, to improve crushing efficiency,
The process is divided into a coarse crushing process for making chips of about 5 to 15 mm and a fine crushing process for crushing to a final particle size.

For classification, a centrifugal classifier, a blower type sieving machine, a vibrating sieving machine and the like are used. The particle size of the powder coating must be adjusted according to the usage form. For example, the average particle size is controlled to 40 to 80 μm in the case of powder for the fluidized-bed method, and 30 to 60 μm in the case of electrostatic coating. If the amount of fine powder is too much, the fluidity of powder, workability of thick coating, etc. are deteriorated, and if the amount of coarse powder is too much, problems such as poor appearance of the coating film, residual powder in the paint tank, and deterioration over time occur.

Although it is desirable that the particle size distribution is narrow, the powder obtained by using any of the above pulverization methods has a wide particle size distribution and requires a classification step. At present, it has a gentle distribution in the range of 5 to 150 μm in view of the balance between manufacturing cost and performance. As described above, in the conventional manufacturing technology, cooling, crushing, and classification are all interrelated, which is an essential step. The individual processes have been highly improved, and it is difficult to rationalize larger manufacturing methods.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a powder coating material having a narrow particle size distribution at a lower cost, which greatly improves the efficiency of the conventional dry coating material production method centering on pulverization. It is intended to be provided.

[0007]

According to the present invention, a melt-kneaded powder coating resin composition is first discharged from an opening of a rotating rotor and has a diameter of 1.0α to 20.0α (where α is The average particle size of the obtained powder coating material is set to.), And the average particle size is α
A method for producing a powder coating material, characterized in that a powder having a particle size distribution of

The melt-kneaded powder coating resin composition referred to in the present invention means that immediately before the cooling step in the conventional dry process. That is, various raw materials such as resins, curing agents, pigments, and other additives are dry-blended and melted by a heating kneader such as an extruder to form a uniform dispersion. The type of resin is not limited, and thermosetting resins such as epoxy resin, epoxy polyester resin, polyester resin, acrylic resin, acrylic polyester resin, and polyimide, and polyvinyl chloride, polyethylene, polyamide, fluorine resin, etc. Any of the above thermoplastic resins or modified systems or mixed systems thereof are applicable.

The curing agent is selected according to the resin. The pigment is also not particularly limited, titanium oxide, yellow iron oxide,
Inorganic colorants such as red iron oxide, carbon black, organic colorants such as phthalocyanine green, phthalocyanine blue, diazo yellow, quinacridone red pigment, and other barium sulfate, silica, calcium carbonate used for improving thermal expansion coefficient and flowability. , Talc, etc. are used.
As an additive, improve edge coverage, improve coating smoothness,
There are metal oxides and oligomers that are usually used in a proportion of several percent or less for the purpose of preventing foaming, antistatic, imparting fluidity, etc.
Both are not restricted and can be used.

The rotor used in the present invention is usually a disk type atomizer rotating disk in which a molten powder coating resin composition that has been moved is dispersed into fine particles or fibers by centrifugal force. To be done. Any of vane type, bowl type, Kessner type, pin type, etc. can be used.In general, the Kessner type and pin type have narrow diameter distribution, and the vane type has characteristics such as treatment of highly viscous materials. It can be used properly according to the composition and particle size distribution. FIG. 1 shows the shapes of a pin type disk () and a vane type disk () which are typical rotors.

When the average particle diameter of the obtained powder coating material is α, the diameter of the fibrous composition discharged is 1.0α to 20.0.
Adjusted to α. The fiber diameter is adjusted mainly by the feed rate of the molten powder coating resin composition, the viscosity, and the rotation speed of the rotor, in addition to the disk shape. If the diameter of the fiber is 20.0α or more, labor saving effect in the subsequent pulverization step cannot be sufficiently obtained, and if the diameter of the fiber is 1.0α or less, the average particle diameter of the powder coating material after pulverization is α And can't. On the contrary, the fiber length is not limited.

Generally, when the viscosity is low and the rotation speed is low, the fibers are short, and conversely, when the viscosity is high and the rotation speed is high, the fibers tend to be long, but they do not hinder the transportation to the subsequent crushing step. It can be as long as possible. It is considered that shorter ones are easier to pulverize later, but if the viscosity is lowered to shorten the length, the gel time of the composition is shortened due to the high temperature, and problems such as easy re-fusion after forming into fibers occur. It is not preferable.

If the inner diameter of the apparatus in which the rotor is mounted is too small, the fibrous material may not be sufficiently cooled and may be remelted, which is not preferable. When the rotor rotates, a flow of air is generated, so that there appears to be a certain cooling effect. Generally, for example, when the diameter of the rotor is 10 cm, re-fusion can be sufficiently prevented if the inner diameter of the device is 50 cm. If necessary, cold air may be introduced.

Any crusher can be used to crush the fibrous material. Any of the above-mentioned methods such as a ball mill, a Victory mill, a jet mill, and a pulperizer can be applied, but it should be noted that over-milling does not occur, and it is important to stop the fiber diameter to the extent that it can be maintained. Then, the fine powder is removed by a cyclone or the like to obtain a powder coating having a desired particle size. FIG. 2 is a schematic diagram of a flow (an example) for carrying out the method for producing a powder coating material of the present invention, in which 1 is an extruder, 2 is a rotor, 3 is a crusher, and 4 is a cyclone.

The powder coating material obtained according to the present invention has a narrow particle size distribution at this stage, and thus the classification step after pulverization as in the conventional case can be omitted or labor can be saved.

[0016]

The present invention will be described below with reference to examples. Example 1 Bisphenol A type epoxy resin (Epicoat 1002) 5 kg, 2-phenylimidazole 0.
1 kg, calcium carbonate 5 kg, flow control agent 0.02 k
g was heated and kneaded by a twin-screw extruder to obtain a molten powder coating resin composition at 110 ° C. This was introduced into a rotor having a diameter of 10 cm, which had a large number of slits of 1.2 mm width in the peripheral portion, heated to 200 ° C., and rotating at 4000 rpm, and discharged to obtain a fibrous material having an average diameter of 80 μm. When this was placed in a ball mill and subjected to 50 rotations, a powder coating having an average particle size of 80 μm containing almost no fine powder of 3 μm or less was obtained. When the iron plate was coated by the fluidized-bed method, the powder fluidity was good and a smooth coated surface could be obtained.

Example 2 13 kg of bisphenol A type epoxy (Epicoat 1002), 9 kg of brominated bisphenol A type epoxy, 0.7 kg of 2-phenylimidazole, 1.6 kg of titanium oxide, 28 hydrated alumina.
kg and 0.4 kg of antimony oxide were heated and kneaded by a twin-screw extruder to obtain a 110 ° C. molten powder coating composition. This was introduced onto the same rotor as in Example 1 rotating at 195 ° C. and 1200 rpm and discharged to give a fibrous substance having an average diameter of 0.3 mm, which was directly pulverized by jet mill pulverization to obtain a powder coating. And The average particle size was 64 when the particle size distribution was measured by Microtrac with 80 mesh cut.
It was confirmed that fine particles of 10 μm or less were not substantially contained in μm. When a steel plate was coated in the same manner as in Example 1, a smooth coated surface could be obtained.

[0018]

The present invention has the following features. (1) The cooling step and coarse crushing step after heating and kneading can be omitted as compared with the conventional dry manufacturing method. (2) The quality of the resin composition for powder coating is stable because the time for being placed in a high temperature state including the cooling step is shortened. (3) The pulverization process can be saved. (4) Since fine powder is not substantially generated, the classification step can be omitted or labor can be saved. (5) Since the crushing and classifying process is simplified, the transportation pipe can be omitted or shortened. (6) This means that the line color changing process can be simplified. (7) The yield of powder coatings is improved because the production method produces less fine powder. (8) Equipment costs can be reduced, operability and safety can be improved by simplifying the process.

[Brief description of drawings]

FIG. 1 is a front view (a right half is a cross-sectional view) of a rotor (example) used in the present invention, where is a pin type disk and is a vane type disk.

FIG. 2 is a schematic diagram of a flow for carrying out the powder coating material manufacturing method of the present invention.

[Explanation of symbols]

 1 Extruder 2 Rotor 3 Crusher 4 Cyclone

Claims (2)

[Claims] 1. A melt-kneaded powder coating resin composition is first discharged from an opening of a rotating rotor to have a diameter of 1.0α.
˜20.0 α (where α is the average particle size of the resulting powder coating material), and then this is subjected to an arbitrary pulverization process to obtain a powder having an average particle size of α. A method for producing a powder coating material, comprising: 2. The method for producing a powder coating material according to claim 1, wherein the rotor is a pin type disk or a vane type disk.