JP3274311B2 - Powder coating manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a powder coating by a dry method.

[0002]

2. Description of the Related Art High-molecular-weight resins can be used for powder coatings.
Since it is easy to apply thickly, it is widely used as an electrical insulating material for motors and a sealing material for electronic components. Recently, powder paints have been evaluated for their advantages in terms of pollution, such as air pollution, fires and other disasters, as well as sanitary problems and resource savings because they contain no solvent, and their use is expanding. As a method for producing a powder coating, there are a dry method and a wet method.

[0003] The wet method, that is, a method of dissolving or dispersing a powder coating material composition in a solvent and using various methods such as spray drying and powdering while removing the solvent, requires steps for handling the solvent. In addition, if the production cost is high and the solvent is not completely removed, the obtained powder is liable to cause blocking and has a problem in quality stability, so that it is not a general production method. The dry method is a method in which various raw materials for powder coating are melted and kneaded, and the resulting mixture is cooled, pulverized, and classified. Since a solvent is not substantially used, a step of recovering the solvent or the like is not required, and is currently the mainstream production method. An endless belt is mainly used for cooling. If the kneaded composition is not sufficiently cooled before the pulverization, the pulverization efficiency is poor, and in some cases, it adheres to the pulverizer. Pulverizer for pulverization,
A roller mill, a Victor mill, a ball mill, a jet mill, or the like is used, and is properly used depending on the properties of the powder and the target particle size. For example, regarding the particle size, when the particle size is 1 or more, a jaw crusher or a roll mill is used.
In the case of targeting fine particles of m or less, a vibration ball mill or a jet mill is selected. Usually, in order to increase the grinding efficiency,
The process is divided into a crushing step for making chips of about 5 to 15 mm and a fine crushing step for crushing to the final particle size.

[0004] A centrifugal classifier, a blower-type sieve, a vibration sieve or the like is used for classification. The particle size of the powder coating must be adjusted according to the form of use. For example, the average particle diameter is controlled to 40 to 80 μm in the case of a powder for a fluid immersion method, and to 30 to 60 μm in the case of an electrostatic coating. If the amount of the fine powder is too large, the fluidity of the powder and the workability of thick coating deteriorate, whereas if the amount of the coarse powder is too large, problems such as poor appearance of the coating film, residual powder in the coating tank, and deterioration with time occur.

Although it is desired that the particle size distribution is narrow, the powder obtained by using any of the above-mentioned 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 from the balance between manufacturing cost and performance. As described above, in the conventional manufacturing technology, cooling, pulverization, and classification are all interconnected and are essential steps. The individual processes have been highly improved, and it has been difficult to rationalize even larger manufacturing methods.

[0006]

SUMMARY OF THE INVENTION The present invention greatly improves the efficiency of a conventional method for producing a powder coating by a dry method mainly based on pulverization, and provides a method for producing a powder coating having a narrow particle size distribution at lower cost. It is intended to provide.

[0007]

According to the present invention, a powder coating resin composition which has been melt-kneaded 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 diameter of the obtained powder coating material) is used as a fibrous composition.
A powder having a particle size distribution of:

[0008] The melt-kneaded powder coating resin composition according to the present invention means a resin composition immediately before a cooling step in a conventional dry process. That is, various raw materials such as a resin, a curing agent, a pigment, and other additives are dry-blended and melted by a heating kneader such as an extruder to form a uniform dispersion. The type of the resin is not limited, and a thermosetting resin such as an epoxy resin, an epoxy-polyester resin, a polyester resin, an acrylic resin, an acryl-polyester resin, a polyimide, and a polyvinyl chloride, a polyethylene, a polyamide, a fluororesin, etc. And any of modified resins and mixed resins thereof.

[0009] The curing agent is selected according to the resin. Pigment is not particularly limited, too, titanium oxide, yellow iron oxide,
Inorganic colorants such as red iron and carbon black, organic colorants such as phthalocyanine green, phthalocyanine blue, diazo yellow and quinacridone red pigments, and other barium sulfate, silica and calcium carbonate used for improving the coefficient of thermal expansion and flowability , Talc or the like is used.
Additives include edge coverage improvement, coating smoothness improvement,
There are metal oxides and oligomers usually used at several percent or less for the purpose of foaming prevention, antistatic, fluidity imparting, etc.
Both are not restricted and can be used.

[0010] The rotor referred to in the present invention is usually a disk type atomizer rotating disk in which the melted powder coating resin composition is dispersed by centrifugal force to produce fine particles or fibrous materials. Is done. Any type such as vane type, bowl type, Kessner type and pin type can be used.Kesner type and pin type generally have narrow diameter distribution, and vane type has characteristics such as advantageous treatment of high viscosity materials. It can be used properly according to the composition to be used and the particle size distribution. FIG. 1 shows the shapes of a pin type disc () and a vane type disc () which are typical rotors.

Assuming that the average particle size of the obtained powder coating is α, the diameter of the fibrous composition to be discharged is 1.0α to 20.0
Adjusted to α. Adjustment of the fiber diameter mainly depends on the supply speed and viscosity of the molten powder coating resin composition and the rotation speed of the rotor in addition to the disk shape. If the fiber diameter is 20.0α or more, a sufficient labor-saving effect in the subsequent pulverization step cannot be obtained, and if the fiber diameter is 1.0α or less, the average particle size of the pulverized powder coating material is α. Can not be. Conversely, the fiber length is not limited.

In general, when the viscosity is low and the rotation speed is low, the fiber is short. On the contrary, when the viscosity is high and the rotation speed is high, the fiber tends to be long, but there is no problem in transportation to the subsequent pulverization step. It may be as long as possible. It is considered that shorter is easier to pulverize later, but if the viscosity is lowered to shorten the length, the gel time of the composition becomes shorter due to the high temperature, and problems such as easy re-fusion after fibrillation also occur. It is not preferable.

If the inner diameter of the device on which the rotor is mounted is too small, the fibrous material is not yet sufficiently cooled and may be re-fused. When the rotor rotates, air flow is generated, which seems to have a certain cooling effect. In general, for example, when the diameter of the rotor is 10 cm, if the inner diameter of the device is 50 cm, re-fusion can be sufficiently prevented. Cold air may be introduced as needed.

An arbitrary pulverizer can be used for pulverizing the fibrous material. Any of the above-mentioned systems such as a ball mill, a Victor mill, a jet mill, a pulperizer and the like can be applied. However, it should be noted that excessive grinding does not occur, and it is important to keep the fiber diameter small enough. Next, 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 view of a flow (one example) for carrying out the method for producing a powder coating material of the present invention, wherein 1 denotes an extruder, 2 denotes a rotor, 3 denotes a crusher, and 4 denotes a cyclone.

The powder coating obtained by the present invention has a narrow particle size distribution at this stage, and the classification step after pulverization as in the prior art 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%.
1 kg, calcium carbonate 5 kg, flow regulator 0.02 k
g was heated and kneaded with a twin-screw extruder to obtain a resin composition for a molten powder coating at 110 ° C. This was introduced into a rotor having a diameter of 10 cm having a large number of slits of 1.2 mm width at the periphery, heated to 200 ° C. and rotating at 4000 rpm, and discharged to obtain a fibrous material having an average diameter of 80 μm. This was placed in a ball mill and subjected to a 50-rotation treatment to obtain a powder coating material having an average particle diameter of 80 μm and containing almost no fine powder of 3 μm or less. When the iron plate was coated by the fluid immersion method, the powder flowability 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 with 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, discharged and made into a fibrous material having an average diameter of 0.3 mm. And When the particle size distribution was measured using a microtrack with an 80 mesh cut, the average was 64
It was confirmed that the fine powder of 10 μm or less was not substantially contained. 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 the coarse pulverizing 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 stabilized because the time for which the resin composition is placed in a high temperature state including the cooling step is shortened. (3) The fine pulverizing process can be labor-saving. (4) Since fine powder is not substantially generated, the classification step can be omitted or labor can be saved. (5) Since the crushing and classification process is simplified, a transport pipe is unnecessary or can be shortened. (6) This means that the line color changing process can be simplified. (7) The yield of powder paint is improved because of the production method with less generation of fine powder. (8) The simplification of the process will reduce equipment costs, improve operability and improve safety.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 1 Extruder 2 Rotor 3 Crusher 4 Cyclone

Claims (2)

(57) [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.
~ 20.0α (where α is the average particle size of the obtained powder coating material) as a fibrous composition, which is then converted into a powder having an average particle size of α by using an arbitrary pulverization process. A method for producing a powder coating, comprising: 2. The method according to claim 1, wherein the rotor is a pin-type disk or a vane-type disk.