JPH11100534A - Powder coating for electrostatic coating and coating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating material excellent in coating efficiency by incorporating a specified amount of a fine conductive metal oxide powder having a volume resistivity in a specified range in a powder coating material particles by melt kneading. SOLUTION: A fine conductive metal oxide powder having a volume resistivity of 1-100 Ω.cm is used. This powder is used in an amount of 0.1-10.0 wt.% based on the powder coating composition. It is desirable that its volume-mean particle diameter is 0.01-1.0 μm. It is exemplified by a fine. conductive titanium oxide powder, a fine conductive zinc oxide powder or a fine conductive tin oxide powder. Especially, conductive titanium oxide is desirable, and a fine acicular conductive titanium oxide powder is more desirable. The fine acicular conductive titanium oxide powder is desirably one having a length/breadth ratio of 10-150 and a breadth of 0.03-0.5 μm. It is desirable that the volume-mean particle diameter of the powder coating material is 3-50 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating for electrostatic coating having excellent coating efficiency and a coating method therefor.

[0002]

2. Description of the Related Art In recent years, powder coatings have attracted attention as environmentally friendly coatings that do not contain organic solvents and are resource-saving and resource-saving, and are used for various applications and coating methods. As a method of applying these various powder coating materials, a preheating fluidized immersion method in which powder coating particles are suspended in a fluidized bed and applied to a preheated object to be coated, or a charged powder coating particle is air-flowed An electrostatic coating method such as an electrostatic spray coating method of spraying an object to be coated by spraying on the substrate is known. Among these coating methods, the electrostatic coating method is easy to control the coating film thickness,
In particular, it is widespread in fields where thin film coating is performed on electric machines, metal products, automobile parts, etc., which require aesthetics and appearance.

[0003]

In the process of the ordinary electrostatic spray spray coating method, an object to be coated is loaded on a hanger or the like in a coating booth and is applied by a corona charging type or friction charging type coating gun. Spray painted. By this spray coating, the charged powder coating particles are applied to the object to be coated,
Some of the powder coating particles are collected from a suction duct or the like in the coating booth without being applied and reused.

However, the recovered powder coating often has an average particle diameter different from that of the original powder coating, and often contains dust and the like. Usually, processing such as adjustment is necessary. When the amount of the powder paint collected in the above step is large, it is necessary to secure a wide place for storing the collected paint, and the number of processes such as dust removal increases, so that such powder Use of a paint is not preferred because workability is reduced. That is, a powder coating material in which the amount of the recovered powder particles is small and the powder coating particles are efficiently applied to the object to be coated is desired.

As a technique for solving such a problem, Japanese Patent Application Laid-Open No. 08-209033 proposes narrowing the particle size distribution width and subjecting the particles to spheroidizing treatment.

However, in order to narrow the width of the particle size distribution, it is essential to use a specific classifier or to perform sieving for a long period of time. It is necessary to perform a long-time impact or the like by using the above-described apparatus or a particle crusher, so that the working efficiency is reduced.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a powder coating material having excellent coating efficiency and a method for coating the same, with the object of improving work efficiency.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies and as a result, have found that a volume resistivity value of 1 to 100 is contained in powder coating particles.
A powder coating obtained by mixing a conductive metal oxide fine powder of Ω · cm by a melt-kneading method, wherein the conductive metal oxide fine powder is 0.1 to 10.0% by weight in the powder coating. %, And it has been found that the coating efficiency is improved by the powder coating for electrostatic coating and the coating method thereof, which led to the present invention.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The content of the conductive metal oxide fine powder in the present invention is 0.1 to 10% by weight, and 0.3 to 10% by weight.
7% by weight is more preferred. When the content of the conductive metal oxide fine powder is 0.1% by weight or less, the coating efficiency cannot be improved, and when the content is 10% by weight or more, the charge amount of the powder coating decreases. It is not preferable because the coating efficiency is reduced and the appearance is also reduced.

The volume average particle diameter of the conductive metal oxide fine powder is preferably 0.01 to 1.0 μm. When the volume average particle size is less than 0.01 μm, handling during coating production is inconvenient, and when the volume average particle size is more than 1.0 μm, the appearance is undesirably reduced.

The conductive metal oxide fine powder according to the present invention has a volume resistivity of 1 to 100 Ω · cm. When the volume specific resistance is less than 1 Ω · cm, the coating efficiency is reduced due to a decrease in the charge amount, and when it is larger than 100 Ω · cm, the coating efficiency is undesirably reduced.

Here, the volume resistance value is a value measured as follows. First, 1.0 g of the conductive metal oxide fine powder is pressed at a pressure of 300 kg / cm ² for 1 minute to form a pellet having a diameter of 2.0 cm. Next, the obtained pellets are left in a room at a temperature of 25 ° C. and a humidity of 50% for 24 hours, and the volume resistance is measured by an ordinary method using a resistance meter. The voltage applied when measuring the volume resistance value is not particularly limited, but is usually 100 V. Although it does not specifically limit as a resistance measuring device, TR-8652 by Takedariken is mentioned typically.

The kind of the conductive metal oxide fine powder in the present invention is not particularly limited, and may be any one that can be mixed and dispersed in the powder coating particles by a melt-kneading method. From the viewpoint of coating efficiency, it is preferable that the type is selected from at least one kind selected from the group consisting of conductive titanium oxide fine powder, conductive zinc oxide fine powder, and conductive tin oxide fine powder. As the type of the conductive metal oxide fine powder, conductive titanium oxide fine powder is preferably selected because of good concealing property and easy coloring and toning.

As the conductive titanium oxide fine powder,
Although not particularly limited, titanium oxide with antimony doped in the surface of tin dioxide, for example, ET-300W, ET-500W, ET-7 manufactured by Ishihara Sangyo Co., Ltd.
00W or EC-100, EC-20 manufactured by Titanium Industry Co., Ltd.
0, ECT-300 and the like. As the acicular conductive titanium oxide, FT-1000, F
Representative examples include T-2000, FT-2000W, and FT-3000.

The above-mentioned conductive zinc oxide fine powder is not particularly limited.
-K and the like are typical examples.

The conductive tin oxide fine powder is not particularly limited, but may be SN-10 manufactured by Ishihara Sangyo Co., Ltd.
0P and the like are representative.

The shape of the conductive metal oxide in the present invention is not particularly limited, and may be a known shape such as an irregular shape, a spherical shape, or a needle shape, but from the viewpoint of coating efficiency. More preferably, a needle-shaped fine needle-shaped conductive titanium oxide powder is selected.

The acicular conductive titanium oxide fine powder is not particularly limited as long as the particle shape is acicular, and is not particularly limited. From the viewpoint of coating efficiency, the ratio of the major axis diameter to the minor axis diameter is small. The ratio is 10 to 150 and the short axis diameter is 0.03 to
It is preferably 0.5 μm.

The powder coating for electrostatic coating according to the present invention contains a thermosetting resin and a curing agent as main components of the powder coating particles as coating film forming components. Further, a surface conditioner, a usual pigment, or other additives may be added as necessary.
Other additives include a curing accelerator (or curing catalyst), a plasticizer, an ultraviolet absorber, an antioxidant, a pigment dispersant, and benzoins.

As the thermosetting resin as a coating film forming component, a resin which is solid at room temperature is used, and typical examples thereof include polyester resin, epoxy resin, epoxy-polyester resin, fluororesin and acrylic resin. .
When it is necessary to form a coating film having good weather resistance with the powder coating of the present invention, an acrylic resin is used.When it is necessary to form a coating film having good coating properties such as impact resistance, polyester is used. When it is necessary for the resin to further form a coating film having good corrosion resistance, it is preferable to use an epoxy resin.

Polyester resins include polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane, and pentaerythritol, and terephthalic acid, isophthalic acid, phthalic acid, succinic acid, and glutanic acid. What reacted with carboxylic acid, such as adipic acid, sebacic acid, and (beta) -oxypropionic acid, by a conventional method is used.

The epoxy resin is a compound having two or more oxirane groups in a molecule, and is a glycidyl ester resin, a glycidyl ether type resin represented by a condensation reaction product of bisphenol A and epichlorohydrin, an alicyclic epoxy resin. Typical examples include a resin, a flocculent aliphatic epoxy resin, and a novolak type epoxy resin.

The acrylic resin is styrene, acrylic acid,
Methyl acrylate, ethyl acrylate, acrylic acid n-
Butyl, iso-butyl acrylate. Acrylic acid ter
Typical examples include those obtained by polymerizing monomers such as t-butyl, glycidyl acrylate, glycidyl methacrylate, and 2-methyl glycidyl methacrylate by an ordinary method.

The thermosetting resin as a coating film forming component preferably has a glass transition point (Tg) of 30 to 80 ° C.
If the Tg is lower than this, resin particles are fused to the pulverizer due to heat generated during pulverization, making production difficult. When Tg is high, it is difficult to obtain good surface smoothness.

As the surface conditioner, silicone or acrylic oligomer is used. Typically, dimethyl silicone, methyl silicone and the like can be mentioned.

The curing agent is appropriately selected depending on the type of the functional group of the resin. For example, blocked isocyanates,
Examples thereof include aliphatic polycarboxylic acids such as sebacic acid, aminoplast resins, aliphatic acid anhydrides, triglycidyl isocyanate, amine-based curing agents, dicyandiamide, phenol resins, and epoxy resins.

Pigments include, for example, titanium dioxide, red iron oxide,
Color pigments such as iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacone pigments and azo pigments, and extenders such as calcium carbonate, talc, and precipitated barium sulfate.

Benzoins refer to benzoin and derivatives obtained by adding 1 to 3 kinds of functional groups to benzoin.

The powder coating for electrostatic coating in the present invention preferably has a volume average particle size of 3 to 50 μm. If the volume average particle diameter is 3 μm or less, it is difficult to produce a powder coating, and if it is 50 μm or more, the smoothness of the coating film is undesirably reduced. Further, the volume average particle diameter of the powder coating for electrostatic coating in the present invention, when coating a three-dimensional object such as a high appearance is required, good penetration into recesses and corners. In order to reduce the amount of recovered paint, the average particle size is preferably 5 to 30 μm.

The powder coating of the present invention is usually produced in the order of a raw material preparation step, a premixing step, a melt kneading step, a cooling step, a coarse pulverizing step, a fine pulverizing step, and a filling step.
If necessary, a dry blending step or a classification step for adjusting the particle size distribution may be performed in order to attach the silica fine particles to the surfaces of the powder coating particles.

The conductive metal oxide fine powder in the present invention is added in the raw material preparation step and / or the premixing step, and mixed in the melt kneading step.

The raw material preparation step is a step of selecting and weighing various raw materials such as a resin, a pigment, a curing agent, and an additive.

The premixing step is a step of charging various raw materials into a mixer and preliminarily mixing them. Representative examples of the mixer include a super mixer and a Henschel mixer.

The above-mentioned melt-kneading step is a step of mixing the preliminarily mixed raw materials under heating and dispersing them at the molecular level. Buscon kneaders, extruders and the like are typically used.

The cooling step is a step in which the melt-kneaded dispersion is formed into a sheet by a pressure roll and solidified by cooling.

The coarse pulverizing step is a step of coarsely pulverizing the solidified sheet into chips.

The above-mentioned pulverization step is a step of pulverization to an optimum particle size distribution according to the use of the coating material. In this step, a hammer mill, a pin mill, a jet mill, or the like is typically used.

The classifying step for adjusting the particle size distribution includes:
This is for sieving to remove powder particles having a large particle size. However, the standard deviation of the particle size distribution may be set to 20 μm or less as an automotive paint or the like that requires a high appearance.

The above-mentioned sieving means that the powder coating material passes through the screen by an essentially vertical vibration, and a metal screen of 42 to 325 mesh is used.

In the present invention, fine silica particles may be added as an external additive to adhere the fine silica particles to the surfaces of the powder coating particles. Further, the addition of the silica fine particles is not particularly limited, as it may be added as a dry blending step after the coarse pulverizing step or the fine pulverizing step. This dry blending step is carried out by an ordinary method typified by dry mixing with a super mixer, Henschel mixer or the like.

The present invention is applied by a usual method such as a corona charging method or a tribocharging method as an electrostatic coating method.
It is preferable to perform electrostatic spray coating by a corona charging method.

[0042]

EXAMPLES Examples and comparative examples will be described below.

Production Example of Acrylic Resin 63 parts by weight of xylene was charged into a reactor equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel.
Heated to 0 ° C. Using a dropping funnel, glycidyl methacrylate 45 parts by weight, styrene 20 parts by weight,
A mixture of 27 parts by weight of methyl methacrylate and 8 parts by weight of isobutyl methacrylate, 6.5 parts by weight of t-butylperoxy-2-ethylhexanoate, and an initiator solution of 6 parts by weight of xylene were added for 3 hours. And dropped. After the completion of the dropwise addition, the mixture was kept warm for 30 minutes, and then 0.1 parts by weight of t-butylperoxy-2-ethylhexanoate and xylene 7
A part by weight was dropped using a dropping funnel. After completion of the dropwise addition, the mixture was further kept at 130 ° C. for 1 hour, and then xylene was distilled off under reduced pressure to obtain an acrylic resin having a Tg of 52 ° C. and an average molecular weight of 3,200.

Example 1 [Polyester Powder Coating] Polyester resin (Finetech M8021 manufactured by Dainippon Ink and Chemicals, Inc.) 60 parts by weight ε-caprolactam blocked isocyanate (Adduct B-1530 manufactured by Huls) 10 parts by weight Carbonic acid Calcium 5 parts by weight Titanium dioxide 15 parts by weight Conductive titanium oxide (ET-500W) 5 parts by weight Surface conditioner (CF-1056, manufactured by Toshiba Silicone Co., Ltd.) 0.5 parts by weight For about 3 minutes, and melt-kneaded at about 100 ° C. using a co-kneader (manufactured by Bus). Cooled at room temperature, after coarse pulverization, atomizer (Fujisha Paudal)
And sieved with a 150-mesh sieve to obtain powder coating particles having a volume average particle diameter of 35 μm. The volume average particle diameter was measured using a particle size analyzer Microtrac HRA X-10.
0 (manufactured by Nikkiso Co., Ltd.). In this regard, the following examples and comparative examples are also the same.

Further, the shape, volume average particle diameter, short axis diameter, and the like of the conductive metal oxide used in each of the examples and comparative examples were
Table 1 shows the major axis diameter and the volume specific resistance.

[0046]

[Table 1]

Example 2 [Polyester powder coating] Powder coating particles were obtained in the same manner as in Example 1, except that 1 part by weight of conductive titanium oxide was used instead of 5 parts by weight.

Example 3 [Polyester powder coating] The powder coating obtained in Example 1 was applied to a jet mill IDS-2.
It was pulverized with a mold (manufactured by Nippon Pneumatic Co., Ltd.) to obtain powder coating particles having a volume average particle diameter of 15 μm.

Example 4 [Polyester powder coating] In place of conductive titanium oxide, needle-shaped conductive titanium oxide (F
Except for using T-1000), the same operation as in Example 1 was performed to obtain powder coating particles.

Example 5 [Polyester powder coating] In place of conductive titanium oxide, conductive zinc oxide (23-
Except for using K), the same operation as in Example 1 was performed to obtain powder coating particles.

Example 6 [Polyester powder coating] Instead of using 5 parts by weight of conductive titanium oxide, 3 parts by weight of conductive titanium oxide (ET-500W) and 2 parts of conductive tin oxide (SN-100P) 2 were used. Except for using parts by weight, the same operation as in Example 1 was performed to obtain powder coating particles.

Example 7 [Acrylic powder coating] Acrylic resin of the above-mentioned production example 48 parts by weight Decanedicarboxylic acid 12 parts by weight Surface conditioner (CF-1056, manufactured by Toshiba Silicone) 0.1 part by weight Benzoin 0.3 part by weight Bisphenol A type epoxy resin (YD-012, manufactured by Toto Kasei Co., Ltd.) 2.2 parts by weight Conductive titanium oxide (ET-500W) 3 parts by weight Same as Example 1 except that the above components were used as raw materials. The operation was performed to obtain powder coating particles.

Example 8 [Epoxy powder coating] Epoxy resin (Epicoat 1004, manufactured by Yuka Shell Epoxy Co.) 65 parts by weight Dicyandiamide 5 parts by weight Titanium dioxide 15 parts by weight Conductive titanium oxide (ET-500W) 5 parts by weight Carbonic acid Calcium 5 parts by weight Surface conditioner (CF-1056, manufactured by Toshiba Silicone) 0.5 part by weight The same operation as in Example 1 was carried out except that the above components were used as raw materials, to obtain powder coating particles.

Comparative Example 1 [Polyester powder coating] Powder coating particles were obtained in the same manner as in Example 1 except that the conductive titanium oxide (ET-500W) as a raw material was not used.

Comparative Example 2 [Polyester Powder Coating] Powder coating particles were obtained by performing the same operation as in Example 1 except that 13 parts by weight of conductive titanium oxide (ET-500W) as a raw material was used.

Coating Efficiency Test A phosphoric acid-treated steel plate having a thickness of 0.8 mm and a size of 200 × 600 mm (hereinafter referred to as “substrate”) was placed on a substrate having a plane perpendicular to the coating direction. Three sheets were arranged and suspended on a horizontally movable overhead conveyor so that the interval between the materials was 100 mm. Corona charging coating gun (GEMA
The coating gun was set so that the distance from the tip of the gun head of PG-1) to the substrate was 300 mm. The powder coating was electrostatically spray-coated on the three substrates by moving at a constant conveyor moving speed and passing the coating gun in front of the coating gun.

The powder coatings of Examples 1 to 8 and Comparative Examples 1 and 2 were applied under the following coating conditions to obtain a coated base material having an average film thickness of about 60 μm after baking of each base material.

Overhead conveyor moving speed: 1.8 m / min Coating gun application voltage: -80 kv Discharge amount: 100 g / min Discharge pressure: 1.0 kgf / cm ² Air flow rate: 4.5 m ³ / h

The weight of the powder coating applied to the three coated substrates was measured with an electronic balance to obtain the total coating amount. The coating efficiency was determined from the ratio between the total coating amount and the effective discharge amount. here,
The effective discharge amount refers to the amount of the powder paint discharged while the substrate to be coated passes through the spray pattern of the coating gun. A sample having a coating efficiency of 65% or more was evaluated as ○, and a sample with less than 65% was evaluated as ×.

Coating efficiency (%) = (total coating amount [g]) /
(Effective discharge amount of powder coating [g]) × 100

Appearance test Various powder coatings were applied to a phosphoric acid-treated steel plate having a thickness of 0.8 mm and a size of 200 × 600 mm using a corona charging coating gun (GE).
Spray painting with PG-1) manufactured by MA under the following conditions
Baking treatment was performed at 180 ° C. for 20 minutes in a hot-air drying furnace to form a coating film having an average film thickness of about 60 μm. The obtained coated plate was visually evaluated according to the following criteria.

Painting gun application voltage: -80 kv Discharge amount: 100 g / min Discharge pressure: 1.0 kgf / cm ² Air flow rate: 4.5 m ³ / h

Appearance Evaluation Criteria 凹凸: Smooth coating state with little unevenness. ：: Smooth coating state with some unevenness. ×: There are bumps and the like, and the smoothness is poor.

Table 2 shows the test results of Examples 1 to 8 and Comparative Examples 1 and 2.

[0065]

[Table 2]

The resin systems in Table 2 are: A: polyester system,
B: means acrylic and C: means epoxy.

[0067]

The present invention relates to a powder coating for electrostatic coating having excellent coating efficiency and a coating method thereof.

Claims (6)

[Claims] 1. A powder coating material having a volume resistivity of 1 to 1
A powder coating obtained by mixing a conductive metal oxide fine powder of 00 Ω · cm by a melt-kneading method, wherein the conductive metal oxide fine powder is contained in the powder coating in an amount of 0.1 to 10.0. A powder coating for electrostatic coating, characterized in that it is a weight percentage. 2. The powder coating for electrostatic coating according to claim 1, wherein the volume average particle diameter of the primary particles of the conductive metal oxide fine powder is 0.01 to 1.0 μm. . 3. The method according to claim 2, wherein the conductive metal oxide fine powder is at least one selected from the group consisting of conductive titanium oxide fine powder, conductive zinc oxide fine powder, and conductive tin oxide fine powder. The powder coating for electrostatic coating according to claim 1 or 2. 4. The powder coating for electrostatic coating according to claim 1, wherein said conductive metal oxide fine powder is acicular conductive titanium oxide fine powder. 5. The powder coating for electrostatic coating according to claim 1, wherein the volume average particle diameter is 5 to 30 μm. 6. A powder coating material having a volume resistivity value of 1 to 1
A powder coating obtained by mixing a conductive metal oxide fine powder of 00 Ω · cm by a melt-kneading method, wherein the conductive metal oxide fine powder is contained in the powder coating in an amount of 0.1 to 10.0. A coating method, which comprises electrostatically coating a powder coating for electrostatic coating, which is a percentage by weight, on an object to be coated.