JPH1112498A - Production of powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a powder coating material whereby a fibrous composition having a small particle diameter close to the aimed particle size of the product and having a narrow particle size distribution can be obtained, therefore the formation of fine powders or coarse particles in a grinding step can be reduced, and the improvement in productivity as a result of reduction in a classification step and in labor and the working environment can be accomplished. SOLUTION: In an apparatus used for producing a powder coating material and having a rotor 1 provided with a punched wire gaze 2 through the openings of which a molten and kneaded powder coating material resin composition can be passed from a cylinder 4 situated on the top of the rotor 1 and which is made of a magnetic material and has a uniform pore diameter on its external periphery and a heating means for heating the punched wire gaze, the molten and kneaded powder coating resin composition is fed into the rotor 1, whereupon it can be converted into a fibrous composition having a diameter of 1.0α to 20.0α and a length of 1.0α to 40.0α (wherein αis the mean particle diameter of the obtained powder coating material), and this is subjected to an arbitrary grinding step to obtain a powder coating material having a mean particle diameter of α.

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, and more particularly to a method for producing a powder coating in which the amount of fine powder generated in a pulverizing step is small.

[0002]

2. Description of the Related Art As a method for producing a powder coating, there are a dry method and a wet method. Since the wet method is a method of dissolving or dispersing the powder coating composition in a solvent and removing the solvent after coating,
Solvent handling requires many steps and additional facilities, and its use has recently been shunned from the viewpoint of the working environment. On the other hand, the dry method is a method in which each raw material of the powder coating is melt-kneaded, cooled and pulverized.

[0003] Cooling belts are mainly used for cooling. When the cooling of the melt-kneading composition is insufficient, the cooling efficiency is lowered, and in some cases, a target particle size cannot be obtained. For pulverization, a pulperizer, a Victory mill, a ball mill, a jet mill, or the like is used, and the pulverizer is used depending on the properties of the powder and the target particle size. Usually, in order to increase the pulverization efficiency, the treatment is divided into a coarse pulverization step of forming a block of about 5 to 15 mm and a fine pulverization step of pulverizing to a target particle size.

[0004] In the case of a powder for a fluid immersion method, the average particle size is 40 to
80 μm, it is necessary to control to 30 to 60 μm for electrostatic coating, but when using a crusher such as a hammer mill, the average particle size is as large as 2 to 5 mm, and the particle size distribution is from several μm. It is as wide as 10 and several mm. Typically,
The closer the particle size of the coarsely pulverized product is to the target particle size after the fine pulverization, the shorter the time required for the fine pulverization, and the narrower the particle size distribution, the more fine powder can be generated. When the crushed material is crushed, the crushing time becomes long and many fine powders and coarse particles are generated. If the amount of fine powder in the product is too large, the coating workability deteriorates. On the other hand, if the amount of coarse powder is too large, problems such as poor coating film appearance and deterioration over time due to poor powder fluidity occur.

[0005] Although the optimum particle size distribution varies depending on the use, in any case, in the pulverization step in the conventional production method, a classification step is required because the particle size distribution of the obtained powder is wider than necessary. Discarding the classified fine powder or coarse particles leads to a decrease in yield and an increase in production cost. In addition, collecting fine powder and coarse particles, processing them and processing them into products increases processing costs. That is, when there are many fine powders and coarse particles with respect to the target particle size distribution, the production efficiency is reduced and the cost is high. In particular, the generation of fine powder causes the working environment to deteriorate.

A method for producing a powder coating material with improved pulverization efficiency is disclosed in Japanese Patent Application Laid-Open No. 8-218643 and Japanese Patent Application Laid-Open No. 8-2949.
No. 16 discloses this. By using this method, it is possible to reduce the amount of fine powder generated in comparison with a conventional fine pulverizing step that uses a hammer mill or the like.
However, when the rotor for supplying the melt-kneaded resin is a pin type disk or a vane type disk and the molten resin is made into a fibrous form using only centrifugal force as in this method,
The size of the product obtained is non-uniform and larger than the target particle size. For example, in the case of a pin-type disk, when the melt viscosity of the supplied resin is low and the resin is continuously supplied to the rotor in the form of a thread, the resin is stretched by centrifugal force between two adjacent pins and becomes a fibrous form. The fiber length is longer than the distance between the pins.

When the distance between the pins is reduced to shorten the fiber length, the centrifugal force acting due to the decrease in the amount of resin between the pins is reduced, so that the resin is less likely to separate from the pins, and the resin stays inside the rotor. Will be. In order to prevent stagnation and increase the centrifugal force, it is necessary to increase the rotation speed, which requires large power and reduces the safety of work.
On the other hand, the fiber thickness depends on the resin supply amount, and therefore becomes thin when the supply amount is sufficiently small, but becomes large when the supply amount is increased in order to increase the production capacity.

Further, when the melt viscosity of the resin to be supplied is high or when the resin is intermittently supplied to the rotating disk without being able to be continuously supplied in a thread form, the supply of the resin to the local pins must be reduced. Become. Therefore, the resin is excessively supplied to the local pin, and the resin is extruded from the entire void portion of the pin, so that the pin is nonuniform and extremely large. The same can be said for the vane type disc. That is, in this method, it is insufficient to obtain the target particle size efficiently in the pulverizing step. Conventional manufacturing methods using a rotor include Japanese Patent Application Laid-Open Nos. 50-121529, 50-121530, and 59-121.
Although disclosed in JP-A-203448 and the like, all of them are aimed at producing a cotton-like product, which is different from the present invention.

[0009]

DISCLOSURE OF THE INVENTION The present invention significantly reduces the production efficiency of conventional powder coatings by reducing the fine powder and coarse particles generated during the pulverizing step, and reduces the cost and the working environment. It is an object of the present invention to provide a manufacturing method for producing a body paint.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of research on a method of producing a powder coating material which significantly improves the production efficiency of the powder coating material, is lower in cost, and has an excellent working environment. That is, a powder coating resin composition melt-kneaded can be supplied from an opening through a cylindrical body provided on an upper portion of a rotating rotor, and a rotary machine provided with a punched wire mesh formed of a magnetic material having holes on its outer periphery. In a powder coating manufacturing apparatus having a heating means for heating a core and a punched wire mesh, a diameter of 1.0α is supplied by supplying a powder coating resin composition melt-kneaded to a rotating rotor.
~ 20.0α, length 1.0α ~ 40.0α (however, α
Is the average particle size of the powder coating to be obtained), and then, using any pulverization process, and then forming a powder having an average particle size of α, the fine powder generated during the pulverization process This is a production method for producing a powder coating which can reduce coarse particles, greatly improve the production efficiency of conventional powder coatings, and is lower in cost and excellent in working environment.

BEST MODE FOR CARRYING OUT THE INVENTION

The melt-kneaded powder coating resin composition of the present invention means a resin composition immediately before a cooling step in a conventional dry process. That is, various raw materials such as resin, curing agent, filler, pigment, and other additives are dry-blended,
It was melted by a heating kneader such as a twin screw extruder to form a uniform dispersion. The type of resin is not limited, epoxy resin, epoxy-polyester resin,
Thermosetting resins such as polyester resin, acrylic resin, acryl-polyester resin, and polyimide, and thermoplastic resins such as polyvinyl chloride, polyethylene, polyamide, and fluorine-based resin, or modified or mixed systems thereof are all applicable. . The curing agent is selected according to the resin. Add fillers such as silica powder, calcium carbonate powder, talc powder, magnesia powder, wood powder, etc., and add additives such as pigments, coupling agents, leveling agents, etc. as necessary to reduce the coefficient of thermal expansion and improve impact resistance. be able to.

According to the present invention, the punched wire mesh is formed by applying an AC power supply to a rotor having a punched wire mesh formed of a magnetic material having a hole on the outer periphery thereof and an exciting coil provided on the upper portion of the punched wire mesh. In the apparatus for manufacturing the powder coating to be heated, the powder coating resin composition melt-kneaded is supplied from the opening through the cylindrical body installed on the upper part of the rotating rotor, and is brought into contact with the heated punched wire mesh, Since the melt viscosity of the resin decreases, fine particles or fibrous materials can be easily formed by scattering the resin by centrifugal force, and a method for producing a powder coating material that can reduce fine powder and coarse particles generated during the pulverizing step can be provided.

Next, an example of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view for carrying out the method for producing a powder coating material of the present invention, FIG. 2 shows a rotor and an exciting coil, and FIG. 3 shows a cylinder installed on the rotor. The resin melt-kneaded in the twin-screw extruder 7 is supplied to the rotor 1 through the cooled cylindrical body 4 through a coolant between the inner wall and the outer wall. At this time, if the cylindrical body 4 is not cooled, the resin easily adheres to the wall of the cylindrical body, and it is difficult to supply a stable resin, which is not preferable. The rotor 1 is connected to a motor 8 and can be rotated at an arbitrary rotation speed. The punched wire mesh 2 formed of a magnetic material having a hole provided on the upper portion thereof provided on the outer periphery of the rotor is accompanied by the passage of an alternating magnetic flux generated when an AC power supply is supplied to an exciting coil 3 provided on the upper portion. , Heat is generated due to eddy current loss and hysteresis loss. The magnetic material is, for example, an iron material or silicon steel, and one or two or more magnetic materials can be used in combination. After the resin is supplied to the rotor,
It flies to the punched wire net 2 heated by the centrifugal force.

The resin that has come into contact with the heated wire mesh 2 has a reduced melt viscosity and is easily discharged through the holes of the wire mesh 2. The heating temperature can be set arbitrarily according to the characteristics of the applied resin. In the case of using a thermosetting resin, if the heating temperature is too high, the curing of the resin may proceed, and the properties may be deteriorated or the deposition may proceed in the holes of the punched wire netting 2. Since the contact time of the wire mesh 2 is extremely short, the influence on the characteristics is extremely small. The discharged fibrous composition is collected in an outer tank 6 provided around the rotor 1. If the inner diameter of the outer tub 6 is too small, the fibrous composition is not sufficiently cooled, so that there is a possibility that the fibrous composition may adhere to the inner wall or cause fusion between the resins, which is not preferable. Generally, the rotation of the rotor generates a flow of air to provide a cooling effect. However, if necessary, cool air may be introduced, or the outer tank may be cooled by a chiller or the like. For example, when the diameter of the rotor is 20 cm, the inner diameter is 60 mm.
cm can prevent adhesion and fusion.

Assuming that the average particle size of the obtained powder coating is α, the diameter of the collected fibrous composition is 1.0α to 20.0
α and the length are adjusted to 1.0α to 40.0α. The fiber diameter and fiber length are adjusted by the supply speed of the molten powder coating resin composition, the melt viscosity, the rotation speed of the rotor, the hole diameter of the punched wire mesh, and the heating temperature. When the diameter of the fibrous composition is 20.0α or more or the fiber length is 40.0α, the effect of reducing fine powder and coarse particles generated in the subsequent pulverization process is small and the productivity and work environment can be sufficiently improved. I can't.

For the pulverization of the fibrous composition, any pulverization step can be used. Any system such as a ball mill, a Victory mill, a jet mill, and a pulperizer can be applied. Then, micron separator, cyclone,
Fine powder and coarse particles are removed by a classifier such as a turbo screener or a sieve to obtain a powder coating having a target particle size distribution. The powder coating obtained by the present invention has a small amount of fine powder and coarse particles generated in the pulverizing step, or the classification step can be omitted or
Labor saving can be achieved.

[0017]

EXAMPLES The present invention will be described in more detail with reference to Examples. << Example 1 >> 5 kg of bisphenol A type epoxy resin (epoxy equivalent: 850), 5 kg of crystalline silica powder, 2-
Methyl imidazole 0.06 kg, leveling agent 0.0
After blending 2 kg with a Henschel mixer, the mixture was melt-kneaded with a twin-screw extruder to obtain a 120 ° C. molten powder coating resin composition. This has a hole diameter of 1.2 mm,
13 cm diameter and 3000 r.p. with punched wire mesh heated to 20 ° C. p. m, and a fibrous composition having an average fiber diameter of 500 μm and an average fiber length of 1.2 mm was obtained. This was pulverized at 4000 revolutions with a pulperizer to obtain a powder coating material having an average particle size of 70 μm containing no fine powder of 5 μm or less and coarse particles of 200 μm or more.

Example 2 The resin composition for molten powder coating at 120 ° C. obtained in Example 1 had a hole diameter of 0.6 mm and had a diameter of 13 cm provided with a punched wire mesh heated to 120 ° C. by an exciting coil. 3000r. p. m, the average fiber diameter is 270 μm, and the average fiber length is 1.0 m.
m of a fibrous composition was obtained. This is pulperizer 4
When pulverized at 000 rotations, a powder coating material having an average particle size of 65 μm containing no fine powder of 10 μm or less and coarse particles of 180 μm or more was obtained.

Comparative Example 1 5 kg of a bisphenol A type epoxy resin (epoxy equivalent: 850), 5 kg of crystalline silica powder, 0.06 kg of 2-methylimidazole and 0.02 kg of a leveling agent were blended with a Henschel mixer, and then mixed with a twin screw extruder. And melt-kneaded. After cooling with a cooling belt, coarse grinding is performed with a hammer mill and the average particle size is 800
A coarsely pulverized product having a particle size distribution of 40 μm to 10 mm was obtained.
This was pulverized at 4000 revolutions with a pulperizer. Fine powder of 10 μm or less was obtained at 11 wt% and 180 μm.
A powder coating material having an average particle size of 70 μm containing 8% of the above coarse particles was obtained.

[0020]

EFFECTS OF THE INVENTION In the method for producing a powder coating according to the present invention, a fiber composition having a small particle size close to the target particle size of the product and having a narrow particle size distribution can be stably obtained. The generation of coarse particles can be reduced. That is, it is possible to improve the productivity and the working environment due to the reduction of the classification process or labor saving.

[Brief description of the drawings]

FIG. 1 illustrates a method for producing a powder coating according to the present invention.
It is an example from melt kneading of a resin to production of a fibrous product.

FIG. 2 is an example of a sectional view of a rotor and an exciting coil used in the present invention.

FIG. 3 is an example of a cross-sectional view of a cylinder for introducing a melt-kneaded powder coating resin composition into a rotor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotor 2 Punched wire mesh 3 Excitation coil 4 Cylindrical body 5 AC power generator 6 Outer tank 7 Twin screw extruder 8 Motor

Claims (3)

[Claims] 1. A punched wire mesh formed of a magnetic material having a hole on its outer periphery, through which a powder coating resin composition melt-kneaded can be supplied from an opening through a cylindrical body provided above a rotating rotor. In a powder coating manufacturing apparatus having a rotor provided with a heating means for heating a punched wire mesh, a diameter of 1.0α to 20 is supplied by supplying a powder coating resin composition melt-kneaded to a rotating rotor. .0α,
A fibrous composition having a length of 1.0α to 40.0α (where α is the average particle diameter of the obtained powder coating material) is used, and then this is subjected to an optional pulverization step to obtain an average particle diameter of α. A method for producing a powder coating, wherein the method is to form a certain powder. 2. The method for producing a powder coating according to claim 1, wherein the cylindrical body installed on the upper part of the rotor is a double tube type, and the cylindrical body can be cooled by passing a refrigerant between the inner wall and the outer wall. 3. The powder coating according to claim 1, wherein the punched wire mesh formed of a magnetic material having a hole on the outer periphery of the rotor can be heated by supplying an AC power supply to an exciting coil provided on the upper portion thereof. Manufacturing method.