JPH0724808B2 - Leak prevention method in electrostatic coating - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of improving workability when electrostatic coating is performed using a coating material containing metal powder.

(Prior Art) Electrostatic atomization coating is used for coating metal products such as refrigerators and automobiles from the viewpoint of effective use of resources by automating the coating and improving the coating efficiency.

In this electrostatic atomization coating method, a spray gun is used, a grounded object is used, and a voltage of 30 KV or more is applied between them, so it is essential that the paint is not a conductor. However, there are cases where electrostatic coating is performed using a metallic paint in which a metal component such as aluminum is mixed in the paint. In such a case, a leak phenomenon in which electricity flows through the paint often occurs.

Here, the leak phenomenon means that flaky metal powder mixed in the paint continuously (bridges) to form a circuit and conduct electricity.

If a leak phenomenon occurs, the voltage between the spray gun and the object to be coated will suddenly drop, the effective charge will not be applied to the paint, and the coating efficiency will drop significantly, or in extreme cases it may cause a fire. You will not be able to satisfactorily paint. High solid type paints, which have recently begun to be used frequently for the purpose of pollution prevention and resource saving, have a low molecular weight and low viscosity in the vehicle resin. It is a point. So far, the methods for improving the leak property are to adjust the electrical conductivity of the paint by changing the solvent composition in the paint, to prevent the sedimentation of metal powder by using a thickening agent, or to prevent the metal powder from settling or to absorb the organic compound into the metal powder. Various means have been used, such as reducing conductivity. However, none of them have sufficient effects, or change the viscous behavior of the coating material or the orientation of the metal powder, which undesirably affects the line suitability and the finished appearance.

As a result of earnest research on an effective coating method for preventing leakage, the present inventors have added a crosslinkable resin particle having a particle diameter of 10 to 200 mμ (hereinafter sometimes referred to as a microgel) to a coating material and applied it to a coating surface. Therefore, they have found that leakage can be prevented, and have completed the present invention.

(Object of the Invention) An object of the present invention is to prevent leakage that occurs when electrostatic coating is performed using a coating material containing metal powder, to secure coating workability, and to form a desired coating film. is there.

(Structure of the Invention) The gist of the present invention is that when a coating material containing 0.1 to 50% by weight of metal powder is electrostatically coated under an applied voltage of 30 KV or more, the coating material is incompatible with the vehicle. Solubility and particle size
0.1 to 30% by weight of 10 to 200 mμ crosslinkable resin particles in the paint
The method for preventing leakage in electrostatic coating is characterized in that it is a coating material in which the blending amount is increased in the range of 1) as the applied voltage is increased.

That is, 0.1 to 30% by weight of microgel is added to a paint containing 0.1 to 50% by weight of metal powder.The amount of microgel depends on the content of metal powder in the paint and the length of paint hose (from the gun It depends on the distance to the ground) and the voltage.

The higher the content of the metal powder, the shorter the paint hose length, and the higher the voltage, the more the leakage is likely to occur. Therefore, it is necessary to increase the addition amount of the microgel. For example, if a high solid paint with aluminum content of 5% by weight, which is a severe condition, is applied with a paint hose length of 10 cm and a voltage of 60 KV, add a few% of microgel, and if it is applied with a voltage of 120 KV, Addition of several tens% by weight of microgel improves the leak property to a level without problems. Usually, when painting under conditions of a hose length of 20 to 40 cm which is used for painting automobiles, it is sufficient to add several% by weight of macrogel.

Therefore, in the present invention, the addition amount of the microgel is in the range of 0.1 to 30% by weight, and the compounding amount is increased as the applied voltage is increased. That is, the blending amount of the microgel has a "positive" correlation with the applied voltage.

In addition, the method of coating with the addition of microgel has less effect on the viscous behavior and the orientation of aluminum as compared with the conventional method using a thickener, etc. There are no problems with the above.

The reason why this method can improve the leak property is considered to be that the microgel physically blocks the bridge of the metal powder, or the insulating effect due to adsorption to the metal powder.

The microgel that is incompatible with the vehicle used in the present invention is a known method in which two or more radically polymerizable ethylenically unsaturated groups in the molecule are used in an amount of 0.1% or more in all monomers and emulsified by a known method. It is obtained by polymerization or polymerization in a non-aqueous organic medium. 0.1% of the above monomers
When the amount is less than the above value, sufficient crosslinking cannot be obtained, and the compound becomes soluble in a vehicle or a solvent and the effect is reduced.

Next, the particle size of the microgel is effective within a certain range. That is, if the particle size of the microgel is too small, the physical barrier effect is deteriorated, and if it is too large, the stability in the paint, the transparency of the coating film, and the gloss are deteriorated, which is not preferable and therefore 10 to 200 mμ.

Such a microgel comprises, for example, various acrylic monomers disclosed in JP-A-58-129066 as a main component, emulsion-polymerized, and an ethylenically unsaturated monomer disclosed in JP-A-56-90819. Those having a core of a cross-linked polymer, an aqueous microgel emulsion of an acrylic resin cross-linked with a polyfunctional cross-linking agent disclosed in JP-A-56-76447, disclosed in JP-B-60-27702. ) A hydroxyalkyl ester of acrylic acid,
Copolymer containing (meth) acrylic acid, JP-A-56-5802
There are crosslinked addition polymer fine particles having a hydroxymethylamino group, an alkoxymethylamino group, and a functional group capable of copolymerizing with these, which are disclosed in Japanese Patent Laid-Open Publication No. 2003-242242.

The lower the voltage during painting, the more advantageous it is for leakiness, but 30KV
Below, the coating effect becomes poor. If it is too high, the risk of leakage increases, so the range of 30 to 120 KV is preferable.

The longer the paint hose length is, the more advantageous it is to leak, but
Problems such as paint loss and long cleaning time occur when changing colors. If the length is too short, the leak property cannot be prevented, so that the length is preferably 5 to 200 cm.

Further, in the present invention, the metal powder is a metal powder having conductivity such as aluminum powder, copper powder, copper alloy powder, tin powder, and stainless powder, but generally refers to aluminum powder in many cases. These metal powders are blended in the paint in an amount of 0.1 to 50% by weight, and if the amount is 0.1% by weight or less, there is no effect as a metallic paint,
On the other hand, if it exceeds 50% by weight, the leak property cannot be prevented and the coating film performance such as water resistance is deteriorated, which is not preferable.

As the vehicle used in the present invention, one conventionally used for electrostatic coating is selected and used. As such a vehicle, for example, acrylic resin, polyester resin, alkyd resin, epoxy resin or the like is used. These resins are used together with a cross-linking agent such as amino resin or blocked isocyanate, if necessary. As examples of the cross-linking agent, alkoxy groups such as n-butylated melamine resin and tributylated melamine resin are methoxy group, ethoxy group, and n-
Examples thereof include an alkylmethylmelamine resin having a butoxy group and an i-butoxy group, and a benzoguanamine resin. These resins are usually obtained by reacting an amino compound such as melamine or benzoguanamine with formaldehyde or paraformaldehyde by addition reaction or addition condensation reaction with a monohydric alcohol having 1 to 4 carbon atoms for etherification. It is produced by. Further, as a blocking agent for blocked isocyanate, phenol, p-nitrophenol, m-cresol, acetylacetone,
Acetone ethyl acetate, ε-caprolactam and the like are used.

When used as a thermosetting resin using a cross-linking agent, the mixing ratio of the acrylic resin or polyester resin and the melamine resin as the cross-linking agent is 9: 1 to 5: 5 as a weight ratio, preferably 85:15 to 6: Set to 4. If the blending amount of the melamine resin exceeds the above ratio, the coating film strength will be insufficient, and if it falls below the above ratio, the coating film will crack. When the isocyanate compound is used as the crosslinking agent, it is desirable to set the molar ratio of the isocyanate group to the hydroxyl group in the thermosetting resin component to be 0.3: 1 to 1.5: 1. If the compounding amount of the isocyanate compound is less than the above molar ratio, curing becomes poor,
If this ratio is exceeded, water resistance will decrease.

Further, as the solvent, those conventionally used for dilution of electrostatic coating and viscosity adjustment are selected and used.

Such solvents include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as n-hexane and heptane, and various boiling point ranges mainly containing aliphatic hydrocarbons and containing some aromatic hydrocarbons. Petroleum fractions with butyl acetate, esters such as butyl acetate, ethylene glycol diacetate, 2-ethoxyethyl acetate, ketones such as acetate and methyl isobutyl ketone, alcohols such as butyl alcohol, and water. However, when a polyisocyanate compound is applied to the cross-linking agent, a solvent having an active hydrogen group that reacts with the polyisocyanate compound cannot be used.

In addition, in carrying out the present invention, additives such as a surface conditioner, an ultraviolet absorber, a dispersant and a leveling agent may be added.

Next, a specific description will be given with reference to examples.

Example 1 A coating material was produced by a known method so that the composition at the time of making it into a coating composition was as shown in Table 1 below, and 2% of the microgel disclosed in Reference Example 1 of JP-A-58-129066 was added. After that, toluene / butanol / Solvesso 150 (shell chemistry) = 5/1/4
The viscosity was adjusted to 14 seconds with a No. 4 Ford cup using the thinner mixed with.

Table 1 Paint blending Raw material blending amount (parts by weight) DIANAL HR 584 Note 1) 45.0 Uban 20N-60 Note 2) 8.0 Cyanimble-G-314 Note 3) 0.1 Alpaste 7130N Note 4) 5.0 Toluene 35.0 Butanol 7.0 go 100.1 Note 1) Acrylic varnish manufactured by Mitsubishi Rayon Co., Ltd. Note 2) N-butyl modified melamine resin manufactured by Mitsui Toatsu Chemicals, Inc. Note 3) Phthalocyanine pigments manufactured by Sanyo Dye Co., Ltd. Note 4) Toyo Aluminum Co., Ltd. ) Aluminum paste This was set on an electrostatic coating machine REA gun manufactured by Randsburg Japan and painted with a paint hose length of 20 cm and an applied voltage of 60 KV. As a result, no leak was observed and a good coating film was continuously obtained. However, when microgel was not added, leaks occurred under these conditions and coating could not be performed. Next, the dull steel plate was degreased with Rydrin 75 (Nippon Paint Co., Ltd. weak alkaline non-silicate degreasing agent), Granodine SD5000 (Nippon Paint Co., Ltd. zinc phosphate type chemical conversion treatment agent), and then as a primer, Power Top U30 (Nippon Paint Co., Ltd.). (Cation type electrodeposition paint) was applied and baked at 180 ° C for 20 minutes. Then
Olga 100 TG75 (Nippon Paint Co., Ltd. melamine / alkyd resin based intermediate coating) dried film thickness (hereinafter simply referred to as film thickness)
After spraying so as to be 35 μm, it was baked at 140 ° C. for 20 minutes and sharpened with water. On top of this, the main paint (2% of microgel added) was electrostatically coated under the above conditions to a film thickness of 20μ,
Wet-on-wet Superlac 0-28M clear (acrylic / melamine resin paint from Nippon Paint Co., Ltd.) was applied to a film thickness of 30μ, and baked at 140 ° C for 20 minutes. The coating performance is shown in Table 2.

Example 2 The coating composition shown in Table 1 was used to increase the amount of Alpaste 7130N from 5.0 to 20.0 to produce a coating by a known method.
After adding 10% by weight of the microgel disclosed in Reference Example 2 of JP-A-6, the viscosity was adjusted in the same manner as in Example 1 and coating was performed with a paint hose length of 30 cm and an applied voltage of 60 KV. An excellent coating film was obtained. However, a leak occurred when the microgel was not added.

The coating film performance is shown in Table 2 as in Example 1.

Example 3 The amount of microgel added in Example 1 was 10% by weight and the applied voltage was 10%.
As a result of coating in the same manner as in Example 1 except that the content was changed to 0 KV, no leak was observed and a good coating film was obtained. The coating film performance is shown in Table 2 as in Example 1.

Comparative Example 1 A coating material was produced by a known method so that the composition at the time of making it into a coating material was shown in Table 1, a coating film was prepared by the same coating system as in Example 1, and the results of performance comparison are shown in Table 2. It was However, in this case, the paint hose length was set to 1 m to prevent leakage.

Comparative Example 2 Example 1 except that the applied voltage of Example 1 was changed to 100 KV.
As a result of coating in the same manner as above (amount of added microgel was 2% by weight), a leak occurred.

Evaluation method Gloss JIS-K-5400 6.7 60 ° Specular reflectance Pencil hardness JIS-K-5400 6.14 Impact resistance JIS-K-5400 6.13 Goggles eye test JIS-K-5400 6.15 Accelerated weather resistance Weather meter 800 hours (JIS- K-5400 6.17) Color difference (ΔE) JIS-Z-8730 (Effect of the invention) By adopting the method of the present invention, it has been possible to achieve defects in coating workability and homogenization of the finished coating film, which often occur due to the conventional leak phenomenon. We were able to.

Claims (1)

[Claims] 1. When a paint containing 0.1 to 50% by weight of a metal powder in the paint is electrostatically coated under an applied voltage of 30 KV or more, the paint is incompatible with the vehicle and has a particle size of 10 to 10. 20
A method for preventing leakage in electrostatic coating, characterized in that the coating composition has 0 mμ of crosslinkable resin particles in the range of 0.1 to 30% by weight and the compounding amount is increased as the applied voltage is increased.