JP2002030256A - Method for producing powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an economical powder coating material capable of utilizing a resource effectively without degrading its film characteristics. SOLUTION: This method for producing the powder coating material from a fine powder byproduct produced in a crushing process after kneading a raw material composition for the powder coating material is provided by forming the fine powder byproduct at a temperature from 50 deg.C to a glass-transition temperature of a resin in the raw material of the above powder coating material for making pellets, weakly crushing the pellets by using a crusher and then using it as the above raw material composition for the 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, and more particularly, to a method for producing a powder coating by recycling fine by-product powder produced as a by-product during powder coating production.

[0002]

2. Description of the Related Art At present, in various industrial fields, resource saving or effective use of resources is being promoted worldwide. By the way, powder coatings with almost no volatiles have recently attracted much attention as coatings with less risk of environmental pollution. However, in a method for producing a dry powder coating that employs a melt-kneading step and a pulverizing step, the fine by-product powder generated in the pulverizing step has a very low bulk specific gravity, and is thus directly mixed with the raw material composition for powder coating. Or, even if the kneading is performed, the flow rate into the kneading machine is small, the productivity is significantly reduced, and further, the residence time in the kneading machine is increased, and the heat history of the coating composition to be formed is significantly increased. In addition, the coating film performance is apt to deteriorate, and when used alone, problems in the coating work such as generation of spits and deterioration of fluidity tend to occur. Therefore, these fine powder powder coatings cannot be used as coatings, and thus have to be discarded until now. Also,
The fine powder powder coating not only causes a decrease in the yield of the powder coating, but also the disposal cost is one factor that increases the price of the powder coating.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an economical method for producing a powder coating material which can effectively utilize resources without deteriorating the characteristics of a coating film.

[0004]

According to the present invention, there is provided a method for producing a powder coating from fine by-products produced as a by-product in a pulverizing step after kneading a raw material composition for a powder coating, wherein the fine by-product powder is prepared. Is molded and pelletized at 50 ° C. to the glass transition temperature of the resin in the powder coating material composition, and the pellets are weakly pulverized using a crusher, and then used as a powder coating material composition. A method for producing a powder coating is provided.

[0005]

Embodiments of the present invention will be described below in detail.

[0006] To achieve the above object, the present inventors have
As a result of intensive study, the fine by-product powder by-produced in the pulverizing step after the kneading step is molded at 50 ° C. to the glass transition temperature of the resin in the powder coating material composition, and pelletized. After using weakly pulverized, when used as a raw material composition for powder coating, the kneadability of the fine by-product powder itself, or the kneadability of the fine by-product powder and the raw material composition for powder coating is not impaired, and It has been found that a coating film having properties such as impact resistance equivalent to that of a coating film obtained from a conventional powder coating can be obtained.

The raw material composition for a powder coating used in the present invention comprises a resin, a curing agent, a pigment, and additives which are added as required, for use in the production of a powder coating. The method of the present invention can be widely applied to the conventional production of powder coatings. Therefore, the raw material composition for powder coatings used in the present invention can be variously used without particular limitation, which has been conventionally used for producing powder coatings. That is, as the resin used in the raw material composition for a powder coating, various resins conventionally used in the production of powder coatings can be used.

Examples of such a resin include a polyester-urethane curable resin, an epoxy-polyester curable resin, an epoxy resin, an acrylic resin, an acrylic-polyester resin, a fluorine resin, and an acrylic resin.
Examples include urethane-curable resins, acryl-melamine-curable resins, and polyester-melamine-curable resins, and these resins can be used alone or in combination of two or more. If necessary, a novolak resin, a phenoxy resin, a butyral resin, a ketone resin, a modified resin such as a polyester resin and rosin, and a plasticizer such as an epoxidized oil and dioctyl phthalate can be used as appropriate.

As the curing agent, for example, various curing agents commonly used for thermosetting resins can be used without particular limitation. Examples of such a curing agent include amide compounds, acid anhydrides, dibasic acids, glycidyl compounds, aminoplast resins, and blocked isocyanates.
Representative examples include dicyandiamide, acid hydrazide, triglycidyl isocyanurate, and isophorone diisocyanate block. For example, dibasic acids include adipic acid, pimelic acid, suberic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,20-eicosandicarboxylic acid, hexahydrophthalic acid , Maleic acid, phthalic acid and cyclohexene 1,2-dicarboxylic acid.

The pigments used in the present invention include, for example, titanium dioxide, red iron oxide, zinc dust, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigments, azo pigments, isoindolinone pigments and various kinds of calcined pigments. There are coloring pigments such as pigments, and extenders such as silica, talc, barium sulfate, calcium carbonate, and glass flakes.

Further, examples of additives that can be optionally added include anti-sagging agents, surface conditioners, crosslinking accelerators, ultraviolet absorbers, light stabilizers, and antioxidants.

The fine by-product powder used in the present invention is a fine powder produced as a by-product when the raw material composition for powder coating is crushed to a predetermined particle size. Such fine by-product powder includes not only powder having a small crushed particle size but also powder which is exhausted without being collected in the crushing step and stays in the dust collector. These fine by-product powders have been conventionally disposed of, and have not been used effectively. Such fine by-product powder has a particle size of 0.1 to 60 μm, usually 0.3 to 5 μm.
A 0 μm fine powder coating composition is included. Such a fine by-product powder is compression-molded to have a particle size of 1 to 50 mm,
Preferably, the size is 5 to 30 mm. 1mm
If the particle size is smaller than this, the moldability as a powder coating material will be poor.
On the other hand, when the particle size exceeds 50 mm, the amount per unit time flowing into the molding machine decreases, and the residence time in the molding machine increases, and the paint properties deteriorate.

The fine by-product powder may be used alone as a raw material composition for powder coatings, or may be used as a part of the raw material composition for powder coatings. In order for the obtained powder coating to have uniform properties, or to obtain good kneading properties,
When the fine by-product powder is used as a part of the raw material composition for powder coatings, it is preferable that the two types of resin, the pigment composition, the additive composition, and the like substantially match. In addition, it is preferable that the two colors also match,
Not required. Although there is a problem of color mixing, the application may be appropriately selected according to the coloring of the obtained product. However, in order to reduce the problem due to the color mixture, when the raw material composition for a powder coating is a deep color, the color of the fine by-product powder is preferably as close to that as possible. When the raw material composition for powder coating is light-colored, it may be used in a small amount, for example, so as not to change the color tone of the raw material composition for powder coating.

A powder coating is produced by using the fine by-product powder alone, or a tertiary by-product produced in the process of producing a powder coating by using it as a part of a raw material composition for powder coating. And 4
When using a fine by-product powder such as the following, in order to prevent adverse effects due to heat history, based on 100 parts by weight of the raw material composition for powder coating, preferably 20 parts by weight or less, more preferably 15 parts by weight or less Is preferably mixed. Such 3
The fine by-product powder by-produced in the next or fourth order is subjected to heat history repeatedly in the production process, so that the compatibility between the fine by-product powder and the raw material composition for powder coating deteriorates, The smoothness of the resulting coating film is easily impaired.

If the molding temperature is less than 50 ° C., the speed of heat transfer to the molded article during molding is low, and the glass transition temperature is 50 ° C.
Even if the powder is smaller than the above, it is not preferable because an excess heat history is applied as a result, and there is an influence on leveling at the time of molding. When the temperature exceeds the glass transition temperature, there is a material that is melted and integrated by a molding object, and as a result, a pellet similar to the usual kneading is formed, and the subsequent pulverization step and classification step are performed by a normal powder coating. This requires energy equivalent to that described above, and as a result, it is not preferable because it is no different from simply producing a powder coating from raw materials.

The powder coating obtained by the method of the present invention can be coated by using an electrostatic spray gun, a fluid immersion, a triboelectric charging gun, an in-mold, etc. in the same manner as in the case of the coating of a conventional powder coating. A coating film can be formed by coating an object, for example, an object to be coated such as a steel plate, and baking it in a hot air furnace, an infrared furnace, an induction heating furnace, or the like.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples and Comparative Examples. The “parts” and “%” in Production Examples, Examples and Comparative Examples are based on weight.

(Preparation of Powder Coating A and By-product A ′) IPDI ε- was added to 60 parts of a saturated polyester resin having a hydroxyl value of 49 mgKOH / g (GV110 manufactured by Nippon Yupika Co., Ltd.).
16 parts of isocyanate resin of caprolactam block (Clenova: Vestagon B-1530), 1 part of silica-adsorbed acrylic acid oligomer (Monsanto: Modaflow Powder 2000) as a surface conditioner, 0.2 parts of benzoin as a defoamer, Titanium dioxide (CR-95, manufactured by Ishihara Chemical Co., Ltd.) was mixed as a white pigment, kneaded with an extruder, and ground and classified to obtain a white powder coating A having a 50% average volume particle size of 30 µm. In addition, a powder coating by-product A ′ having a 50% average volume particle size of 10 μm generated at that time was obtained. The glass transition temperature of the powder coating material A and the by-product A ′ is 58 ° C.

(Preparation of Powder Coating B and By-product B ') IPDI ε- was added to 80 parts of a saturated polyester resin having a hydroxyl value of 49 mgKOH / g (manufactured by Nippon Yupika Ltd .: GV110).
20 parts of an isocyanate resin of caprolactam block (Vestagon B-1530 manufactured by Clenova) and 1.5 parts of a silica-adsorbed acrylic acid oligomer (Modaflow Powder 2000 manufactured by Monsanto) as a surface conditioner.
Parts, benzoin 0.3 parts as a defoaming agent, 4 parts of carbon black (MA-100, manufactured by Mitsubishi Chemical Corporation) (white pigment / black pigment = 1/100) as a black pigment, and kneaded with an extruder. After pulverization and classification, a black powder coating material B having a 50% average volume particle size of 30 μm was obtained. In addition, a powder coating by-product B ′ having a 50% average volume particle size of 10 μm generated at that time was obtained. The glass transition temperature of the powder coating material B and the by-product B ′ is 50 ° C.

(Example 1) Powder coatings A and B were mixed at a ratio of 1/1, and one side was heated to 80 ° C (the other side was at room temperature), compression-molded to 5 mm by two rolls, and pulverized by a pin mill. After that, a powder coating AB having a 50% average volume particle size of 30 μm was prepared.

(Example 2) Powder coatings A 'and B' were
The mixture was mixed at a ratio of 1 and one side was heated to 80 ° C. (the other was at normal temperature), compression-molded to 5 mm by two rolls, pulverized by a pin mill, and classified, and then 50% average volume particle size 30 μm
A'B 'was prepared.

Comparative Example 1 Powder coatings A and B were mixed at a ratio of 1/1 to prepare powder coatings A / B.

(Comparative Example 2) The powder coatings A 'and B' were
The powder coatings A ′ / B ′ were prepared by mixing at a ratio of 1.

(Comparative Example 3) Powder coatings A and B produced were mixed at a ratio of 1/1, and one side was heated to 40 ° C. (the other side was at room temperature) and compression-molded to 5 mm using a two-roll mill. After pulverization and classification, 50% average volume particle size 30μ
m of powder coating AB2 was prepared.

Each paint is applied to a cold-rolled steel sheet at a load voltage of -80 KV using a powder coating machine (manufactured by Ransberg Gemma Co., Ltd .: PG-1).
For 10 minutes, and the following evaluation was performed.

<State of coating film>: It was observed from a distance of 20 cm whether each dot could be visually judged. Table 1 shows the results.

[0027]

[Table 1]

[0028]

As described above, according to the present invention, it is possible to provide an economical method for producing a powder coating material in which resources can be effectively used without deteriorating the characteristics of the coating film.

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Claims (2)

[Claims] 1. A method for producing a powder coating material from a fine by-product powder by-produced in a pulverizing step after kneading a raw material composition for a powder coating material, wherein the fine by-product powder is heated to 50 ° C. After molding and pelletizing at the glass transition temperature of the resin in the coating material composition, the pellets were weakly pulverized using a crusher,
A method for producing a powder coating, which is used as the raw material composition for a powder coating. 2. The method for producing a powder coating according to claim 1, wherein said fine powder is compression-molded to a particle size of 1 to 50 mm in said pelletization.