JPH107942A - Production of powder coating material from fine by-product powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a powder coating material capable of forming a coating film without defects in its properties from a fine by-produce powder obtd. as a by-product in the grinding step after kneading a powder coating material compsn. and to thereby recycle the by-product powder by molding the powder into granules with specified sizes and using the granules as a raw material compsn. SOLUTION: A fine by-produce powder is compression molded, e.g. with a two-roll mill pref. at 60 deg.C or lower, still pref. 40 deg.C or lower, into granules with granular sizes of 1mm or higher, pref. 1-50mm, still pref. 5-30mm, and is used as a powder coating raw material compsn. A granular size lower than 1mm degrades the mixing properties as a powder coating material while one higher than 50mm reduces the amt. per unit time of the powder flowing into a kneader, increasing the dwell time in the kneader, and deteriorating the properties of the resultant coating material. The compression molding temp. is pref. low to avoid the problems due to heat hysteresis.

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 reusing 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 the method for producing a dry powder coating that employs a melt-kneading step and a pulverizing step, the fine secondary 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. Alternatively, even if kneading is performed, the amount of inflow into the kneading machine is small, the productivity is extremely low, and the residence time in the kneading machine is increased, and the heat history of the coating composition is significantly increased. The 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. In addition, 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 Accordingly, 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 the coating film.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, compression-molded a fine by-product powder produced in a pulverizing step after a kneading step to a size of 1 mm or more. After that, when used as a raw material composition for powder coating,
The kneadability of the fine secondary powder itself, or the kneadability of the fine secondary 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 present invention has been made based on such new findings. That is, the present invention is used as a powder coating material composition after compression-molding a fine by-product powder produced in a pulverizing step after kneading the powder coating material composition to a size of 1 mm or more. And a method for producing a powder coating.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The raw material composition for a powder coating used in the present invention comprises a resin, a curing agent, a pigment, and additives that are added as needed, which are used in the production of the 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. As such a resin, for example, polyester-urethane curable resin, epoxy-polyester curable resin, epoxy resin, acrylic resin, acrylic-polyester resin fluororesin, acrylic-urethane curable resin, acrylic- Melamine-curable resins, polyester-melamine-curable resins and the like can be mentioned, and these resins can be used alone or in combination of two or more. If necessary, novolak resin, phenoxy resin, butyral resin, ketone resin,
Modified resins such as polyester resin and rosin, epoxidized oil, and plasticizers such as 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 an amide compound, an acid anhydride, a dibasic acid, a glycidyl compound, an aminoplast resin, and a blocked isocyanate. Representative examples thereof include dicyandiamide, acid hydrazide, and the like.
Triglycidyl isocyanurate, isophorone diisocyanate block, and the like. 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, cyclohexene 1,2-dicarboxylic acid and the like. As the pigment used in the present invention, for example, titanium dioxide, red iron oxide, iron oxide, zinc dust, carbon black,
There are coloring pigments such as phthalocyanine blue, phthalocyanine green, quinacridone pigments, azo pigments, isoindolinone pigments and various calcined pigments, and extender pigments such as silica, talc, barium sulfate, calcium carbonate, and glass flakes.

[0007] Examples of additives that can be optionally added include anti-sagging agents, surface conditioners, crosslinking accelerators, ultraviolet absorbers, light stabilizers, and antioxidants. The fine secondary powder used in the present invention is a fine powder which is secondary produced when the raw material composition for a powder coating is ground to a predetermined particle size. Such fine by-product powders include not only those having a small crushed particle size but also those having been exhausted without being collected in the crushing step and retained in the dust collector. These fine by-product powders have been conventionally disposed of, and none have been used effectively. Such fine secondary powders include fine powder coating compositions having a particle size of 0.1 to 60 μm, usually 0.3 to 50 μm. Such a fine secondary powder is compression-molded and has a particle size of 1 to 50 mm, preferably 5 to 50 mm.
It is also assumed that the size is up to 30 mm. If the particle size is less than 1 mm, the kneading properties as a powder coating will be poor. On the other hand, the particle size is 50mm
If it exceeds, the amount per unit time flowing into the kneading machine decreases, and the residence time in the kneading machine increases, and the paint properties deteriorate. Compression molding can be performed by various methods, the scope of which is obvious to those skilled in the art. For example, compression molding can be performed using two rolls or the like.
The pressure at the time of compression molding can be arbitrarily adopted by those skilled in the art as long as the fine secondary powder falls within the above-mentioned range of the particle diameter. The temperature during compression is preferably low to avoid problems due to thermal history. Usually 60
It is appropriate to carry out at a temperature of not more than 40 ° C, preferably not more than 40 ° C.

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 coating, it is preferable that the two types of resin, the composition of the pigment, the composition of the additive 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 color mixing, when the raw material composition for powder coating is a deep color, the color of the fine secondary 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. Also,
Third- or fourth-order by-products in the process of producing powder coatings by using fine by-product powders alone or in the process of producing powder coatings by using as a part of the raw material composition for powder coatings When using the fine by-product powder of the above, in order to prevent the 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 third order and fourth
The fine by-product powder that is produced by the following process receives heat history repeatedly in the production process, so that the compatibility between the finely-produced powder and the raw material composition for powder coating is deteriorated, or the obtained coating material is used. The smoothness of the film is easily impaired.

The powder coating obtained by the method of the present invention is coated with an electrostatic spray gun, a fluid immersion, a triboelectric gun, an in-mold, etc., in the same manner as in the case of the 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.

[0010]

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. Production Example 1 A polyisocyanate resin (Hul) composed of isophorone diisocyanate blocked with ε-caprolactam was added to 50 parts of a thermosetting polyester resin having a hydroxyl value of 46 mgKOH / g (Yupika Coat GV110 manufactured by Nippon Yupika Co., Ltd.).
s Co., Ltd., B-1530) 10 parts, acrylic oligomer (Monsanto Co., Modaflow Powder III) as an additive
1), 0.2 part of benzoin as a defoaming agent and 35 parts of titanium oxide as a color pigment were mixed to prepare a raw material composition A for powder coating (white). Production Example 2 80 parts of a thermosetting acrylic resin having an epoxy equivalent of 460 g (Almatex PD7690, manufactured by Mitsui Toatsu Chemicals, Inc.)
5 parts of 1,10-decanedicarboxylic acid, acrylic oligomer (Acronal 4F, manufactured by BASF) as an additive
5 parts and 0.2 parts of benzoin as a defoaming agent were mixed to prepare a powder coating material composition B (colorless). Production Example 3 60 parts of an epoxy resin having an epoxy equivalent of 915 g (Epicoat 1004F, manufactured by Yuka Shell Epoxy Co., Ltd.), 4 parts of adipic dihydrazide as a curing agent, and an acrylic oligomer (Modaflow powder, manufactured by Monsanto) as an additive
III) One part, 0.2 parts of benzoin as a defoaming agent, 25 parts of barium sulfate as a pigment, and 1 part of carbon black were mixed to prepare a raw material composition C for powder coating (black). Production Example 4 40 parts of a polyester resin having an acid value of 53 mgKOH / g (Yupika Coat GV230, manufactured by Nippon Yupika Co., Ltd.) and 40 parts of an epoxy resin (Epicoat 1004F, manufactured by Yuka Shell Epoxy)
30 parts, 0.4 part of 2-phenylimidazole as a catalyst,
1 part of acrylic oligomer (Modaflow Powder III, manufactured by Monsanto) as an additive, benzoin as a defoamer
0.2 parts, 25 parts of barium sulfate as a pigment, and 1 part of phthalocyanine blue were mixed to prepare a raw material composition D for powder coating (blue). Production Example 5 60 parts of an epoxy resin having an epoxy equivalent of 915 g (Epicoat 1004F, manufactured by Yuka Shell Epoxy Co., Ltd.), 4 parts of adipic dihydrazide (ADH) as a curing agent, and an acrylic oligomer (Modaflow Powder, manufactured by Monsanto Co.) as an additive III) 1 part, 0.2 part of benzoin as a defoaming agent, 15 parts of barium sulfate, 10 parts of titanium oxide and 1 part of carbon black as a pigment are mixed, and the raw material composition E for powder coating is mixed.
(Grey) was prepared.

The above-prepared raw material compositions for powder coatings A to A
E was kneaded with an extruder at 120 ° C. for 0.5 minutes,
The obtained pellets were pulverized with a pin mill and classified to obtain powder coatings A to E having an average particle size of 35 μm. The powder coatings A to E were applied to a cold-rolled steel sheet so as to have a film thickness of about 60 μm using an electrostatic powder coating gun (PG-1 manufactured by Matsuo Sangyo Co., Ltd.), and baked at 180 ° C. went. The following tests were performed on the obtained coating films, and their properties were evaluated. Appearance of the coating film Obtained coating film is visually observed, according to the following criteria,
evaluated. ：: No abnormality ×: Abnormality Impact resistance of coating film DuPont φ1 / 2 '× 500 g × cm The following Table 1 shows the compositions of the raw material compositions A to E for powder coatings and the coating films obtained. The characteristic of was shown.

On the other hand, each of the raw material compositions A to D for powder coating is kneaded by an extruder in the same manner as described above, and the obtained pellets are pulverized by a pin mill, collected by a cyclone, and discharged from the upper part of the cyclone. Secondary powder (average particle size 5
μm) was collected by a bag filter to obtain fine secondary powders A ′, B ′, C ′ and D ′, respectively. A ',
B ′, C ′ and D ′ were mixed at a weight ratio of 3: 2: 4: 1 to prepare a fine secondary powder F ′ (gray). Example 1 To 100 parts of the powder coating material composition A, 233 parts of a fine auxiliary powder A 'compression-molded to 5 mm by a two-roll mill was mixed with 100 parts, and kneaded and pulverized with an extruder in the same manner as described above, and classified. Thus, a powder coating APA ′ having an average particle size of 35 μm was prepared. Fine secondary powder generated at that time (particle diameter: 0.1 to 50 μm)
m) was designated as A ". Example 2 100 parts of the raw material composition A for powder coating was mixed with 10 parts of fine auxiliary powder A", which was compression-molded to 5 mm in the same manner as in Example 1, and mixed with the above. Example 3 A powder coating APA ″ having an average particle size of 35 μm was prepared by kneading and pulverizing. Example 3 A fine auxiliary powder A ′ compression-molded to 35 mm in the same manner as in Example 1 was kneaded and pulverized to obtain a powder coating APA having an average particle size of 35 μm. Powder coating material a was prepared Example 4 Powder raw material composition E (gray), 100 parts, fine auxiliary powder F ′ (grey), compression-molded to 6 mm in the same manner as in Example 1, 10 parts Is kneaded and pulverized in the same manner as described above to obtain an average particle size of 35.
A μm powder coating EPF ′ was prepared. The fine powder powder coating composition generated at this time was designated as F "(gray). Example 5 Powder coating raw material composition E (gray) was compression-molded into 100 parts of 6 mm in the same manner as in Example 1. 10 parts of fine secondary powder F ″ (gray) were kneaded and pulverized as described above, and the average particle diameter was 35%.
A powder coating material EPF ″ (gray) having a thickness of μm was prepared. Comparative Example 1 30 parts of the raw material composition A for powder coating material were kneaded with 70 parts of a fine auxiliary powder A ′ that had not been compression-molded as described above. Pulverized to prepare a powder coating material AA ′ having an average particle size of 35 μm Comparative Example 2 30 parts of a powder coating material composition A were prepared in the same manner as in Example 1.
70 parts of the fine secondary powder A 'compression-molded to 0.5 mm was kneaded and pulverized as described above to obtain a powder coating AP having an average particle diameter of 35 μm.
A'2 was prepared.

The raw material composition for powder coating prepared above is
Using an electrostatic powder coating gun (PG-1 manufactured by Matsuo Sangyo Co., Ltd.), coating was performed on a cold-rolled steel sheet so as to have a film thickness of about 60 μm, and baking was performed at 180 ° C. The following tests were performed on the obtained coating films and evaluated. Appearance of the coating film Obtained coating film is visually observed, according to the following criteria,
evaluated. ：: No abnormalities X: Abnormalities Impact resistance of the coating film DuPont φ1 / 2 '× 500 g × cm The coating film was visually observed.

[0014]

Table 1 Production Example 1 2 3 4 5 Raw material composition for powder coating ABCDE resin composition Thermosetting polyester resin 50 (Yupika coat GV110) Thermosetting acrylic resin 80 (Almatex PD7690) Epoxy resin 60 30 60 (Epicoat 1004F) Thermosetting polyester resin 40 (Yupikacoat GV230) Acrylic oligomer 111 (Modaflow Powder III) Acrylic oligomer 0.5 (Acronal 4F) Curing agent Polyisocyanate resin 10 (B-1530) 1,10- Decanedicarbon Acid 5 Adipic acid dehydrazide 4 4 Defoamer Benzoin 0.2 0.2 0.2 0.2 0.2 Catalyst 2-phenylimidazole 0.4 Pigment titanium oxide 35 10 Barium sulfate 25 25 15 Carbon black 1 1 Phthalocyanine blue 1 Coating properties Coating appearance ○ ○ ○ ○ ○ Impact resistance 50 50 50 50 50

[0015]

Table 2 Example Comparative Example 1 2 3 4 5 1 2 Powder coating APA 'APA "a EPF'EPF" AA 'APA' Coating appearance ○ ○ ○ ○ ○ × × Impact resistance 50 50 50 50 50 20 30 Paint color Change Change Change Change Change Change No change None None None None None None

[0016]

According to the present invention, there is provided an economical method for producing a powder coating which can effectively utilize resources without deteriorating the coating film performance as compared with the conventional powder coating.

Claims (2)

[Claims] 1. A method for producing a powder coating from a fine powder by-product produced in a pulverizing step after kneading a raw material composition for a powder coating, wherein the fine secondary powder has a particle size of 1 mm or more. A method characterized in that after compression-molding to a size, it is used as the raw material composition for powder coatings. 2. The method according to claim 1, wherein the fine secondary powder is used alone as the raw material composition for the powder coating.