JP3157095B2 - Powder paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating suitable for a triboelectric spray gun.

[0002]

2. Description of the Related Art It is well known that powder coatings have less volatile components and odors than solvent coatings and are very useful in terms of pollution control and environmental regulations. By the way, conventionally, a corona charging type spray gun has been generally used as a powder coating method. In this method, the powder coating charged by corona ions generated from the corona electrode provided at the tip of the spray gun converts the powder coating into the electric field and air flow formed between the electrode and the object to be coated. Fly along,
Attaches to substrate.

It has been found that this corona charging method has two major technical problems. One is called the Faraday cage effect, in which an electric field (line of electric force) is not formed in a concave portion of an object to be coated, so that only a small amount of powder paint adheres to the concave portion, and conversely, an edge portion where the electric line of electric force is concentrated. Is a phenomenon that a large amount adheres. The other is a phenomenon called reverse ionization, in which the accumulated charge of the powder paint and free corona ions deposited on the object to be coated becomes too large, causing spark discharge, resulting in a crater-like defective portion on the painted surface. It is.

In order to solve these technical problems, in recent years, a triboelectric charging system using a triboelectric charging spray gun has been adopted. In this method, the powder paint conveyed by the air flow is charged by friction with the powder paint conveying section inside the spray gun, and flies to and adheres to the object only by the air flow.

[0005] The powder coating material conveying section inside the tribo-charging type spray gun is generally formed or surface-treated with a member containing fluorine atoms. A member containing a fluorine atom has an advantage that physical deterioration is small after long-term continuous use. In addition, the ionization potential is large,
Since it has a strong negative charge, the paint side can be charged to a positive polarity by friction between the member and the powder paint.

As the above-mentioned member containing a fluorine atom,
Polytetrafluoroethylene, polytrifluorochloroethylene, polyvinyl fluoride, polyvinylidene fluoride,
For example, polydichlorodifluoroethylene is used.

In the tribocharging method, an electric field is not formed unlike the corona charging method, so that the powder coating adheres well to the concave portions. Further, since no free ions are generated, the reverse ionization phenomenon is less likely to occur.

[0008]

However, since the charging of the powder coating is due to friction alone, the absolute charge amount is lower than that of the corona charging system, and it is sufficient to increase the discharge speed of the powder coating from the spray gun. And that when used continuously, triboelectric charges accumulate on the inner wall of the spray gun, so that the triboelectric charge of the powder coating decreases and the adhesion to the substrate (coating efficiency) becomes poor. Problems, such as becoming sufficient, are clarified.

The present invention solves the above-mentioned problems, and when applied to a tribo-charging type spray gun, it is possible to obtain a sufficient amount of triboelectric charging, and there is practically no problem in accumulating charge on the inner wall of the spray gun. It is an object of the present invention to provide a powder coating that can be kept in a range.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a powder coating composition comprising at least a binder resin and a curing agent and used for a tribo-charging type spray gun using a fluorine-based resin in a coating material transport section, The following relationship 2P-30 ≦ Q ≦ 2P and + 10 ≦ Q ≦ + 30 is established between the charge amount Q (μC / g) by the magnet blow-off method and the number average particle diameter P (μm) by the Coulter counter method. The above object has been achieved by a powder coating characterized by the above.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the powder coating of the present invention will be described in detail. The powder coating of the present invention is a powder coating composed of powder particles containing at least a binder resin and a curing agent. As the binder resin, a polyester resin, an acrylic resin, an epoxy resin, a phenol resin, a silicon resin, a fluororesin, or the like can be used. Examples of the curing agent include isocyanate, amine, polyamide, acid anhydride, polysulfide, boron trifluoride, acid dihydrazide, imidazole and the like.

Further, other additives can be added to the powder particles as needed. For example, fillers such as barium sulfate, calcium carbonate, aluminum oxide, and calcium silicate, spreading agents such as acrylic oligomers and silicones, coloring agents such as titanium oxide, chromium oxide, iron oxide, and carbon black, and foaming An inhibitor or the like may be appropriately added.

The powder particles used in the powder coating material of the present invention can be obtained by dry-mixing the composition comprising the above-mentioned binder and the like, kneading with hot melt, pulverizing and classifying. Also,
The composition can be directly obtained by a spray drying method or various polymerization methods.

The number average particle diameter P (μm) of the powder coating material of the present invention and the charge amount Q by the magnet blow-off method
(ΜC / g) must satisfy the above relationship. The above P
FIG. 1 is a graph of the relationship between Q and Q.

The charge amount Q (μC / g) by the magnet blow-off method will be described below. Originally, in order to measure the charge amount of the powder paint, the charge amount may be measured by putting the powder paint charged by friction with the fluororesin installed in the paint transport unit into a Faraday cage. However, the amount of charge of the powder coating in actual use varies depending on the structure of the spray gun of the tribo-charging system, the feed amount of the coating, and the like. In addition, when measuring, there is a problem that it is very difficult to effectively collect the fine powder paint that is charged and floated in the air.

Therefore, in order to solve the above problem, in the present invention, the charge amount Q was measured by a magnet blow-off method.
Hereinafter, the magnet blow-off method will be described with reference to FIG. In the magnet blow-off method, a ferrite powder coated with a silicone resin used for electrophotography is used instead of a frictional charging member of a spray gun. Specifically, a ferrite powder coated with a silicon resin (trade name: FL921-1530, manufactured by Powder Tech), which is generally used for a toner charged to a positive polarity, is used. The apparatus shown in FIG. 2 is used for the measurement.
This device is a device in which a non-conductive magnet 1 in which a conductive sheet 3 such as an aluminum sheet is adhered to a crown 4 is sandwiched between holding devices 2. The capacitor 7 is connected via 6. This capacitor 7 has a voltmeter 8 for measuring its charge amount C.
There mounting only is the charge amount detection path is formed.

In order to measure the charge amount Q of the powder coating, first, a mixture of the above ferrite powder and the powder coating is stirred, and the powder coating is charged with the ferrite powder. Next, the obtained mixture is adsorbed to the top portion 4 of the magnet 1. The mixture adsorbed on the magnet 1 is such that the ferrite powder is
Due to the magnetic force of the ferrite powder, ears are firmly formed in a brush shape , and a powder coating charged with static electricity adheres to the surface of the ferrite powder with a weak force. In this state, the sum of the charges is zero. Then, a high-pressure gas, such as air or nitrogen, is blown from above through the nozzle 5 while repeating rotation or translation of the magnet so that the high-pressure gas is applied to the mixture well. Specifically, after the powder paint above the ears is blown off and separated from the ferrite powder, the nozzle 5
By appropriately narrowing the distance between the magnet and the magnet 1, the ferrite powder after the powder coating has been blown away remains , and the powder coating from the conductive sheet 3 is also blown off. When the powder coating material is separated from the ferrite powder by the high-pressure gas, the ferrite powder becomes negative, and the negative charge charges the conductive sheet 3 negatively. The negative charge Q ′ of this conductive sheet 3
Is calculated from the capacitance C of the capacitor 7 and the voltage V applied to the capacitor 7 according to the formula Q ′ = C · V. Then, the charge amount Q of the calculated conductive sheet 3 'to be divided by the weight M of the powder coating, the unit weight of the powder coating charge amount Q (Q' /
M) is calculated.

The charge amount Q thus obtained is +10
Powder coatings lower than μC / g are not preferred because, even when friction with the inner wall of the spray gun is sufficient, sufficient electrification for coating is not ensured, resulting in low coating efficiency. Further, in the case of powder paint higher than +30 μC / g, triboelectric charges easily accumulate on the inner wall of the spray gun, and in some cases, the powder paint itself adheres to the inner wall. And, as a result, the coating efficiency is lowered, which is not preferable. The charge amount Q is +1.
Even if it is 0 μC / g or more and +30 μC / g or less, in the case of Q> 2p, the paint particles are easily affected by the flow of the conveying air in the relationship between the number average particle diameter P and the charge amount Q. As a result, the amount of paint sprayed from the nozzle without being rubbed on the inner wall of the spray gun increases, and as a result, the coating efficiency decreases.
Further, in the relationship between the number average particle diameter P and the charge amount Q, when Q <2p−30, the friction inside the spray gun is sufficient, but the specific surface area of the paint particles is small. The charge amount Q tends to be low, and above all, there is a problem that the coated surface is rough or uneven due to coarse particles.

In order to set the charge amount of the powder coating within the above range, a binder resin and a curing agent, which are raw materials of the powder coating, may be selected or additives may be added. In general, the binder resin, which is the main raw material of the powder coating, has a low positive chargeability. Therefore, the charge amount Q is set within the range specified in the present invention by adding an appropriate amount of an additive having a strong positive chargeability. can do. Compounds such as quaternary ammonium salt compounds, nigrosine dyes, and triphenylmethane compounds, and surface treatment agents having a functional group having a nitrogen atom such as an amino group or an amide group include strong positively chargeable additives. And fine particles such as silica fine particles, alumina fine particles, and titanium oxide fine particles surface-treated with. The former compound can be used by being dispersed together with a curing agent in a binder resin. The latter fine particles can be used by being adhered to the surface of the powder particles in an appropriate amount using a stirring mixer having a rotating blade such as a Henschel mixer or a super mixer.

The above number average particle diameter P (μm) is
50 measured by Coulter Counter TAII
% Means diameter.

The coating material transporting portion of the spray gun of the triboelectric charging system using the powder coating material of the present invention may be formed of a member containing fluorine atoms, or may be made of a material containing fluorine atoms. It may have been processed.

[0022]

EXAMPLES The powder coating material of the present invention will be described in more detail with reference to Examples and Comparative Examples. <Example 1> Production of powder coating

[Table 1] The raw materials having the above mixing ratios are mixed by a super mixer, hot-melt kneaded at 120 ° C. using a pressure kneader, pulverized by a jet mill, and then dried with a dry air classifier so that the number average particle diameter P becomes 12 μm. Was classified. This powder 1
Per 100 parts by weight of a surface treatment agent containing a nitrogen atom (N
-(2-aminoethyl) -3-aminopropyltrimethoxysilane) hydrophobic silica fine powder
4 parts by weight were mixed with a Henschel mixer to obtain a powder coating material of Example 1.

Example 2 Production of Powder Coating

[Table 2] The raw materials having the above mixing ratios were mixed by a super mixer, hot-melt kneaded at 120 ° C. by a pressure kneader, pulverized by a jet mill, and then classified by a dry air classifier so that the 50% diameter became 20 μm. . To 100 parts by weight of this powder, 0.4 part by weight of hydrophobic silica fine powder surface-treated with dimethyldichlorosilane was mixed with a Henschel mixer to obtain a powder coating material of Example 2.

Example 3 Production of Powder Coating

[Table 3] The raw materials having the above mixing ratios were mixed by a super mixer, hot-melt kneaded at 120 ° C. by a pressure kneader, pulverized by a jet mill, and then classified by a dry air classifier so that the 50% diameter became 26 μm. . To 100 parts by weight of this powder, 0.2 part by weight of hydrophobic silica fine powder surface-treated with dimethyldichlorosilane was mixed with a Henschel mixer to obtain a powder coating material of Example 3 .

Comparative Example 1 In Example 1, the number average particle diameter P was 12 μm, and the amount of hydrophobic silica to be added was 0.1 μm. In contrast to 4 parts by weight, the number average particle diameter P after classification was 4.5 μm, and the amount of hydrophobic silica was 0.8 parts by weight. A powder coating was obtained. Comparative Example 2 In Example 1, the number average particle diameter P was 12 μm, and the amount of hydrophobic silica to be added was 0.1 μm. In contrast to 4 parts by weight, the number average particle diameter P after classification was 27.0 μm, and the amount of hydrophobic silica was 0.2 parts by weight. A powder coating was obtained. <Comparative Example 3> In Example 1, the surface treatment agent containing a nitrogen atom (N- (2
Example 1 except that hydrophobic silica surface-treated with dimethyldichlorosilane was used while hydrophobic silica surface-treated with -aminoethyl) -3-aminopropyltrimethoxysilane) was used. In the same manner as in Example 1, a powder coating material of Comparative Example 3 was obtained.

Comparative Example 4 Production of Powder Coating

[Table 4] The raw materials having the above mixing ratios were mixed by a super mixer, kneaded with heat in a pressure kneader at 120 ° C., pulverized by a jet mill, and then classified by a dry air classifier so that the 50% diameter became 12 μm. . 0.4 parts by weight of hydrophobic silica fine powder surface-treated with a surface treatment agent containing a nitrogen atom (N- (2-aminoethyl) -3-aminopropyltrimethoxysilane) based on 100 parts by weight of this powder Was mixed with a Henschel mixer to obtain a powder coating material of Comparative Example 4.

<Comparative Example 5> The powder coating material of Comparative Example 5 was prepared in the same manner as in Comparative Example 4 except that the particles were pulverized and classified so that the number average particle diameter became 26 μm, and the amount of hydrophobic silica was changed to 0.2 part by weight. Obtained.

Next, the charge amount Q and the coating efficiency of the powder coatings obtained in <Example 1> to <Example 3> and <Comparative Example 1> to <Comparative Example 5> were measured by the following methods. did. (1) Charge amount Q of powder coating material 4 parts by weight of powder coating materials obtained in Examples and Comparative Examples, and ferrite powder (manufactured by Powder Tech Co., trade name: FL921)
-1530) and 96 parts by weight were mixed in a V-type blender for 10 minutes, and the charge amount Q of the powder coating was measured by the magnet blow-off method described above. The results are shown in Table 5 below. (2) Coating Efficiency The powder coatings obtained in the Examples and Comparative Examples were applied to a tribo-charging type spray gun (manufactured by Matsuo), and the discharge amounts were 80, 100, 120, and 150 g under the following coating conditions. /
min. And the powder coating was applied to the steel sheet. In addition, the discharge rate was 100 g / min. And sprayed continuously for 10 minutes to apply the powder coating to the steel plate. The steel plate used was a 300-mm square zinc-phosphated steel plate (SPCC-SB plate) that had been subjected to a bright finish and a 300-mm square steel plate was temporarily attached to the center of the steel plate so as to be positioned perpendicular to the surface of the steel plate. It is made. Conveyor speed 2.0 m / min. Reciprocator Stroke 1000 mm Speed 20 m / min. Gun distance 200 mm Next, the 300 mm square steel plate which was temporarily attached was peeled off, and from the adhesion amount (X) of the powder paint on the steel plate and the theoretical total adhesion amount (Y) obtained from the discharge amount, The coating efficiency was derived according to the following equation. Coating efficiency (%) = (X / Y) × 100

[0029]

[Table 5] In Table 5 , * 1 indicates that the discharge amount of the powder coating from the spray gun of the tribo-charging method was 100 g / min. Means continuous spraying for 10 minutes.

FIG. 3 is a graph showing the results of Table 5 above. As is clear from Table 5 and FIG. 3, the number average particle diameter P and the charge amount Q of the powder coating material were calculated as follows: 2P−30 ≦ Q
By setting so as to satisfy ≦ 2P and + 10 ≦ Q ≦ + 30, the powder coating material has a small change in the coating efficiency with respect to the spray amount of the powder coating material and does not decrease the coating efficiency even during continuous spraying. Can be obtained.

[0031]

The powder coating composition of the present invention is a powder coating composition comprising at least a binder resin and a curing agent and used for a spray gun of a tribo-charging system using a fluorine-based resin in a coating material conveying section, Charge amount Q by magnet blow-off method
(μC / g) and the number average particle diameter P (μm) by the Coulter counter method, 2P−30 ≦ Q ≦ 2P, and +
A powder coating material characterized by satisfying 10 ≦ Q ≦ + 30. By limiting the charge amount Q and the number average particle diameter P of the powder coating by the magnet blow-off method to the above ranges, good chargeability can be obtained when applied to a tribo-charge type spray gun, and at the same time, the spray gun inner wall can be obtained. Since the accumulation of charge on the substrate can be kept within a practically acceptable range, it is possible to obtain a powder coating material in which there is little change in the efficiency of application to the object with respect to the spray amount of the powder coating material.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a charge amount Q and a number average particle diameter P in the present invention.

FIG. 2 is a view schematically showing a magnet blow-off method.

FIG. 3 shows Examples 1 to 3 and Comparative Examples 1 to 5.
FIG. 5 is a view showing the relationship between the charge amount Q and the number average particle diameter P of the powder coating obtained in the step (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet 6 Code 2 Holding device 7 Capacitor 3 Conductive sheet 8 Voltmeter 4 Head 5 Nozzle

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-7-207197 (JP, A) JP-A-5-271584 (JP, A) JP-A-3-775 (JP, A) JP-A-4-207 249585 (JP, A) JP-A-1-153773 (JP, A) JP-A-8-20735 (JP, A) JP-A-8-24786 (JP, A) JP-A-3-120570 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C09D 5/03 C09D 201/00-201/10 WPIDS (STN)

Claims (1)

(57) [Claims] 1. A powder paint comprising at least a binder resin and a curing agent and used for a spray gun of a tribo-charging method using a fluorine-based resin in a paint conveying section, wherein a charge amount Q ( powder coating, wherein the following relationship 2P-30 ≦ Q ≦ 2P and + 10 ≦ Q ≦ + 30 is established between μC / g) and the number average particle diameter P (μm) determined by the Coulter counter method. .