JPH08325489A - Powder coating material and coating method using the same - Google Patents

Abstract

PURPOSE: To obtain a powder coating material which enables thin coating and can be applied with a spray gun of a tribocharge type with a sufficient transfer efficiency by incorporating a specific oil into a powder coating material at least comprising a binder resin and a curative and having a specified particle size. CONSTITUTION: A silicone oil having N atoms in its structural units (e.g. an aminomodified silicone oil) is incorporated into a powder coating material at least comprising a binder resin (e.g. a polyester resin) and a curative (e.g. a blocked isocyanate) and having an average particle size of 5-20μm, pref. by causing the oil to exist on the surface of the material. Pref. the amt. of the oil contained in the material is 0.01-1.00wt.%. The material is positively charged by friction with a fluorine-contg. member (e.g. polytetrafluoroethylene) formed in a coating-material delivery section inside a spray gun and then sprayed to an object to be coated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a powder coating suitable for thin film coating.

[0002]

2. Description of the Related Art It is well known that powder coating materials have less volatile components and odors than solvent coating materials and are very useful in terms of pollution control and environmental regulations. The powder coatings that have hitherto been put on the market for general use have an average particle diameter of about 30 μm and have not been strictly classified, so that the particle diameter distribution is very broad. In order to obtain a good leveling property, it is essential to form a uniform powder adhesion layer, but for that purpose, an adhesion layer having a particle diameter of 2 to 3 times is required. Therefore, the conventional powder coating has a coating thickness of 6
If it is not more than 0 μm, a good coated surface cannot be obtained.
On the other hand, as market needs, there is a demand for improvement in leveling property, improvement in working efficiency by thinning a coating film, reduction in total cost, and the like, and a film thickness of about 30 to 60 μm, which is similar to that of solvent coating, is desired.

A corona charging type spray gun has been conventionally used as a powder coating method. In this method, the powder coating material charged by corona ions generated from the corona electrode provided at the tip of the spray gun is applied to the electric field and air flow formed between the object to be coated which is a conductor and the electrode. It flies along and adheres to the object to be coated. There are two problems with such a corona charging method. One is called the Faraday cage effect. Since the electric field (lines of electric force) is not formed in the concave part of the object to be coated, the powder coating adheres only a small amount to the concave part, and conversely the edge where electric lines of force concentrate. It is a phenomenon that a large amount adheres to the part. The other is the phenomenon called reverse ionization, which is a phenomenon in which the accumulated charge of the powder coating material and free corona ions deposited on the object becomes too large and spark discharge occurs, causing crater-like defects on the coated surface. Is.

In order to solve these problems, a tribo-charging type spray gun has been used in recent years. In this method, the powder coating material carried by the air flow is charged by friction with the inner wall of the spray gun, and fly and adhere to the object to be coated only by the air flow. In this method, since no electric field is formed, the powder coating material adheres well to the recesses, and free ions are not generated, so that the reverse ionization phenomenon is unlikely to occur. However, since the powder paint is charged only by friction, the absolute charge amount becomes lower than that of the corona charging method, and if the discharge speed of the powder paint from the spray gun is increased, a sufficient charge amount cannot be obtained. However, when continuously used, the triboelectric charge is accumulated on the inner wall of the spray gun, and the triboelectric charge amount of the powder coating is reduced, resulting in insufficient coating efficiency on the object to be coated. There is. Further, the triboelectrification phenomenon is easily influenced by environmental conditions such as temperature and humidity, and there is a problem that it is difficult to obtain a sufficient triboelectrification amount especially in a high humidity environment.

[0005]

It is an object of the present invention to use a powder coating material having a small particle diameter, which improves the above-mentioned problems and enables the coating film to be thin, and to use the powder coating material in a tribo method. It is an object of the present invention to provide a powder coating material which can maintain a sufficient coating efficiency when applied to a charging type spray gun and can be used under a wide range of environmental conditions, and a coating method thereof.

[0006]

The present invention comprises at least a binder resin and a curing agent and has an average particle size of 5 to 20 .mu.m.
m is a powder coating material containing silicone oil having a nitrogen atom as a constituent unit.

Hereinafter, the present invention will be described in detail. The powder coating material used in the present invention comprises powder particles containing at least a binder resin and a curing agent. As the binder resin, a resin having good weather resistance such as polyester resin, acrylic resin, silicone resin or fluororesin is used. As the curing agent, isocyanate, amine, polyamide, acid anhydride,
Polysulfide, trifluoroboric acid, acid dihydrazide,
Examples include imidazole and the like. Further, the powder particles include fillers such as barium sulfate, calcium carbonate, aluminum oxide and calcium silicate, leveling agents such as acrylic oligomer and silicone, coloring agents such as titanium oxide, chromium oxide, iron oxide and carbon black, You may add a foaming inhibitor etc. suitably.

The particle diameter of the powder coating material of the present invention is 5 to 2 in volume 50% measured by Coulter Counter TAII type.
It must be in the range of 0 μm. Volume 50
Powder particles having a% diameter of less than 5 μm have a large inter-particle force due to van der Waals forces and the like, and are apt to agglomerate, which deteriorates the fluidity of the powder and is not practical as a powder coating material. Further, when it is attempted to manufacture such powder particles having a small particle diameter by a general melt-kneading and pulverizing and classifying method, a large amount of energy is required in the pulverizing and classifying step, so that the manufacturing cost becomes considerably high. If the 50% volume diameter exceeds 20 μm, a thin and uniform powder adhesion layer cannot be obtained on the surface to be coated, and a good thin film cannot be obtained.

The powder coating material of the present invention is characterized by containing silicone oil having a nitrogen atom as a constituent unit. By containing the silicone oil, the flowability at the time of baking is improved and the smoothness of the coating film surface is improved.
Further, since the silicone oil having a nitrogen atom as a constitutional unit has a good positive charging property, the powder coating material of the present invention has a short rise time of triboelectric charging, which is sufficient in the tribo-charging type spray gun. Easily charged up to the amount of charge. In addition, it is possible to obtain a practically sufficient amount of charge even in a high humidity environment where charging failure is likely to occur until now.

As the silicone oil used in the present invention, a silicone oil modified with a functional group containing a nitrogen atom such as an amino group or an amide group can be used. As the silicone oil used in the present invention,
Amino-modified silicone oil having a structure in which amino groups are introduced into both ends or side chains of dimethyl silicone skeleton, or silicone oil similarly modified with amide group or imide group having nitrogen base paper like amino group can be used Is. Commercially available products include Toray Dow Corning
BY16-853, BY16-853 from Silicone
B, BY16-828, BY16-850, SF841
7, BY16-849, KF-39 from Shin-Etsu Chemical Co., Ltd.
3, KF-857, KF-369 and the like. The silicone oil used in the present invention is 0.01 to 1.00% by weight, preferably 0.02 to 0.
It may be added so as to be 50% by weight. If it is less than 0.01% by weight, the effect of improving smoothness after baking is small.
On the other hand, if the addition amount exceeds 1.00% by weight, the fluidity of the powder coating material is deteriorated, and the coating material is not smoothly supplied to the coating portion, resulting in uneven coating.

The powder coating material used in the present invention is obtained by dry-mixing the composition, hot-melt kneading, pulverizing and classifying. Alternatively, the above composition may be directly obtained by a spray drying method or various polymerizations.

The silicone oil used in the present invention is
The composition including at least a binder resin and a curing agent may be added during dry mixing, or may be attached to the surface after pulverization, but the latter is preferable if possible. Since most of the silicone oil is included inside the powder when added during dry mixing, the contribution to the chargeability with respect to the added amount is inferior to when added to the surface. To attach the silicone oil to the surface of the powder, the powder may be held in a fluid state and the silicone oil may be dropped or sprayed.

To the powder coating material of the present invention, a fine powder of hydrophobic silica or alumina may be added for the purpose of improving fluidity. In order to adhere the fine powder to the surface of the powder particles, both may be dry mixed with a high speed mixer such as a Henschel mixer manufactured by Mitsui Miike Co., Ltd. or a super mixer manufactured by Kawata Seisakusho.

The powder coating material of the present invention is used for a tribo-charging type spray gun. That is, the coating method of the powder coating material of the present invention, after the above powder coating material is rubbed with a member containing a fluorine atom formed in the powder coating material conveying section inside the spray gun to be positively charged. The method is characterized by spraying and coating an object. A member containing a fluorine atom has an advantage that physical deterioration is small in continuous use for a long period of time, and since it has a strong negative charging property,
By friction between this member and the powder coating, the coating side can be positively charged. As the member containing a fluorine atom, polytetrafluoroethylene, polytrifluorochloroethylene, polyvinyl fluoride, polyvinylidene fluoride, polydichlorodifluoroethylene or the like is used.

[0015]

EXAMPLES Hereinafter, examples will be described. Example 1

The raw materials having the above blending ratios are mixed in a super mixer, melted and kneaded by heating in a pressure kneader at 120 ° C., pulverized by a jet mill, and then dried by a dry air stream classifier so that a volume of 50% is 13 μm. It was classified into To 100 parts by weight of this powder, an amino-modified silicone oil (trade name: BY1 manufactured by Toray Dow Corning Silicone Co., Ltd.
6-828) 0.1 part by weight was added dropwise and mixed by stirring with a Henschel mixer. Further, 0.4 part by weight of hydrophobic silica was mixed with 100 parts by weight of the treated powder in a Henschel mixer to obtain a powder coating material of Example 1.

Example 2 A powder coating material of Example 2 was obtained in the same manner as in Example 1 except that BY16-853B manufactured by Toray Dow Corning Silicone Co., Ltd. was used as the amino-modified silicone oil.

Comparative Example 1 A powder coating material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the 50% volume volume after classification was 4.5 μm. in this case,
A lot of energy was consumed in the crushing process, and the yield was low.

Comparative Example 2 A powder coating material of Comparative Example 2 was obtained in the same manner as in Example 1 except that the 50% volume diameter after classification was 26.0 μm.

Comparative Example 3 A powder coating material of Comparative Example 3 was obtained in the same manner as in Example 1 except that silicone oil was not used.

Comparative Example 4 Dimethyl silicone oil containing no nitrogen atom (Toray
Dow Corning Silicone product name: SH200
A powder coating material of Comparative Example 4 was obtained in the same manner as in Example 1 except that oil was used.

Examples 1 to 2, Comparative Examples 1 to 4
Apply the powder paint of the
Bright finish zinc phosphate treated steel plate (SPCC-
It was sprayed onto the SB plate) so that the film thickness after baking would be 30 μm, and baked at 200 ° C. Table 1 shows the coating efficiency after spraying and the state thereof and the evaluation results of the coating surface after baking. The coating efficiency in this case was measured by the following. Tribo charging type spray gun (Matsuo)
1000mm square bright finish zinc phosphate treated plate (SPCC-SB plate) under the following coating conditions
The obtained powder coating material was applied to a temporary attachment of the 300 mm square steel plate suspended vertically in the central part of the above. Conveyor speed 2.0 (m / min) Reciprocator stroke 1000 (mm) Speed 20 (m / min) Gun distance 200 (mm) Discharge rate 100 (g / m ² ) Next, coating was performed by the discharge rate. 30 mm from the adherend
Peel off the steel plates on all sides, and attach the powder coating on the steel plates (X)
Then, the deposition efficiency was derived from the theoretical total deposition amount (Y) obtained from the discharge amount. Adhesion efficiency (%) = (X / Y) × 100 In Comparative Example 2, a thin film having a smooth surface was not obtained, but when the film thickness was 60 μm, a good coated surface could be obtained.

[0023]

[Table 1]

As is clear from Table 1, in the present invention, the coating efficiency on the object to be coated with respect to the spray amount of the powder coating is good,
It is possible to obtain a coating method of a powder coating which is not affected by the environmental conditions at the time of coating and the coating surface after baking is good.

[0025]

As described above, in the present invention, since the average particle diameter of the powder coating material is 5 to 20 μm, the coating film can be made thin, and the silicone oil containing a nitrogen atom is contained as a constitutional unit. Therefore, it is possible to provide a powder coating which can obtain good charging performance even when used in a tribo-charging type spray gun and can obtain a coating film having good smoothness after baking.

Claims (4)

[Claims] 1. A powder coating material comprising at least a binder resin and a curing agent, having an average particle diameter of 5 to 20 μm, containing a silicone oil having a nitrogen atom as a constituent unit. paint. 2. The powder coating material according to claim 1, wherein the silicone oil is present on the surface of the powder coating material. 3. The powder coating material according to claim 1, wherein the amount of the silicone oil added is 0.01 to 1.00% by weight in the powder coating material. 4. A powder coating material comprising at least a binder resin and a curing agent and having an average particle diameter of 5 to 20 μm, characterized by containing silicone oil having a nitrogen atom as a constituent unit. A method for coating powder coating material, which comprises charging the coating material to a positive polarity by friction with a member containing a fluorine atom in a coating material transporting portion, and then spraying it onto an object to be coated.