JPH11263925A - Anti-corrosive, powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition, causing no exfoliation or swelling at the edge, defect or damaged portion of the coating film, excellent in safety, and applicable also to overcoating by including a specific quantity of calcined gypsum and powder coating resin. SOLUTION: This composition is composed of (A) calcined gypsum shown by the formula CaSO4 .1/2H2 O and (B) a powder coating resin preferably having a glass transition point of 30 to 80 deg.C [epoxy resin (e.g. bisphenol A type epoxy resin), polyester resin (e.g. a product obtained by the normal method for reacting a polyhydric alcohol, e.g. ethylene glycol, with carboxylic acid, e.g. phthalic acid), fluororesin or acrylic resin]. The composition contains the component A at 2 to 30 wt.%. It is preferable that this composition has an average particle size of 30 to 40 μm. This composition may be incorporated, as required, with wax, a pigment, surface modifier or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powder coating composition for anticorrosion.

[0002]

2. Description of the Related Art Steel sheets used for durable building materials, vending machines, fences, steel furniture, and the like are usually coated to improve aesthetic appearance and corrosion resistance. Water enters the coated steel sheet (painted steel sheet) when a defect such as a pinhole or a scratch is present in the coating film. In particular, the end face of the object to be coated has a thin coating film and is likely to cause a defect. At such a defective part, rust is generated on the steel sheet by the action of an electrolyte such as sea salt particles contained in the air or rainwater. At this time, a part of the steel surface at the coating film defect becomes a minute anode, and a cathode site is formed near the defect such as a pinhole or a scratch.

At the formed cathode site, hydroxide ions are generated, and the action of the hydroxide ions reduces the adhesion between the steel sheet surface and the coating film, thereby causing peeling and blistering. In the present specification, such peeling or blistering is referred to as “cathode peeling” or “cathode blister”. These phenomena are magnified, and the water-soluble electrolyte easily penetrates into the peeling portion and blister portion, resulting in a problem that the peeling portion and blister portion are further enlarged.

[0004] In particular, in the case of a coating film coated on a steel plate subjected to the cathodic protection method such as a galvanized steel plate, a cathode portion is formed near a defect portion of the coating film, and peeling or blistering occurs as described above. Occur.

[0005] In order to suppress the peeling of the coating film and the occurrence of blisters, chromium-based pigments such as strontium chromate have been conventionally added to paints.
Chromium-based compounds adversely affect the human body and environment, and in recent years, their use has tended to be avoided. In addition, generally effective rust preventive pigments are colored and cannot be applied to the top coat, and in the field of powder coatings in which one coat finish is the mainstream, countermeasures against corrosion have been a problem.

Japanese Patent Application Laid-Open No. 6-228466 discloses a paint that uses a solid superacid carrying sulfuric acid or a metal oxide to consume hydroxide ions generated at the cathode site and prevent blistering. ing. However, this technique makes it difficult to handle solid superacids during production,
It is also disadvantageous in terms of cost. In addition, since sulfuric acid is carried, there is a possibility that the paint may deteriorate.

[0007]

SUMMARY OF THE INVENTION In view of the above, the present invention does not cause peeling or blistering at the end face, defect, or damaged portion of a coating film, has excellent safety, and can be applied to a top coat. It is an object of the present invention to provide an anticorrosion powder coating composition which can be produced at low cost and easily.

[0008]

The present invention relates to an anticorrosion powder coating composition comprising calcined gypsum and a powder coating resin, wherein the calcined gypsum is used in an amount of 2 parts with respect to the anticorrosion powder coating composition. It is a powder coating composition for anticorrosion, which is blended so as to be 30% by weight. Hereinafter, the present invention will be described in detail.

The calcined gypsum used in the present invention is a hydrate of calcium sulfate (CaSO ₄ ) of the chemical formula CaS
It is a compound represented by O ₄ .1 / 2H ₂ O. By using the calcined gypsum, it is possible to prevent cathode peeling and cathode blistering caused by the hydroxide ions. Such an effect is found only in the calcined gypsum among the above-mentioned calcium sulfate hydrates.

The calcined gypsum is blended in an amount of 2 to 30% by weight based on the powder coating composition for anticorrosion. When the amount is less than 2% by weight, the ability to prevent peeling and blistering of the obtained coating film is not sufficient, and when the amount exceeds 30% by weight, it becomes difficult to form a continuous coating film and the appearance of the coating film deteriorates. Limited to range. Preferably, it is 5 to 20% by weight.

The resin for powder coating used in the present invention is not particularly limited as long as it is usually used for powder coating, and examples thereof include epoxy resins, polyester resins, epoxy / polyester composite resins, Fluororesin, acrylic resin and the like can be mentioned. The paint resin can be appropriately selected according to the properties required for the obtained coating film. For example, when weather resistance is required, it is preferable to use an acrylic resin, Is required, a polyester resin is preferably used, and when more excellent corrosion resistance is required, an epoxy resin is preferably used.

The epoxy resin is not particularly limited as long as it has two or more oxirane groups in the molecule. Examples thereof include bisphenol A epoxy resin, bisphenol F epoxy resin, novolak epoxy resin, and alicyclic epoxy resin. Examples include a formula epoxy resin and a flocculent aliphatic epoxy resin. In addition, these epoxy resins
For example, it can be used in any combination with a curing agent such as an amine-based curing agent, a carboxylic acid-based curing agent, and a phenol-based curing agent.

The polyester resin is not particularly restricted but includes, for example, polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane and pentaerythritol, and terephthalic acid, isophthalic acid, Examples thereof include those obtained by reacting carboxylic acids such as phthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, and β-oxypropionic acid in a conventional manner.

The curing type of the polyester resin is not particularly limited, and examples thereof include isocyanate curing types and triglycidyl isocyanurate (TGIC) curing types of general polyester resins.

The epoxy / polyester composite resin is not particularly limited as long as it utilizes a system in which a glycidyl group of an epoxy resin is reacted with a carboxylic acid of a polyester resin. And the like.

The acrylic resin is not particularly limited as long as it reacts the glycidyl group of the acrylic resin with an aliphatic dibasic acid. Examples thereof include styrene, acrylic acid, methyl acrylate, ethyl acrylate and n-acrylate. -Butyl, isobutyl acrylate, t-butyl acrylate,
Glycidyl acrylate, glycidyl methacrylate,
Examples thereof include those obtained by polymerizing a monomer such as 2-methylglycidyl methacrylate by an ordinary method.

The above resin for powder coating has a glass transition point (T
g) is preferably from 30 to 80 ° C. If the temperature is lower than 30 ° C., the resin particles are fused to the pulverizer due to heat generated during the pulverization, making it difficult to produce the resin particles. If the temperature exceeds 80 ° C., it is difficult to obtain good surface smoothness.

The anticorrosive powder coating composition of the present invention may be added with an additive such as a wax and a combined resin such as a butyral resin in order to impart flexibility and control film forming properties. Good.

The powder coating composition for anticorrosion according to the present invention has a pigment and a surface condition within a range that does not deteriorate the cathode peeling resistance and the cathodic blister resistance and that does not impair coating workability. Other paint additives such as an agent may be added.

The above-mentioned pigments are not particularly limited. For example, extenders such as precipitated barium sulfate, calcium carbonate, clay, talc, silica and mica; coloring such as titanium oxide, titanium dioxide, red iron oxide, carbon black and iron oxide Inorganic pigments; coloring organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone pigments, azo pigments, and benzidine yellow; rust preventive pigments such as zinc phosphate and aluminum phosphate; metal powders such as zinc powder and aluminum powder. be able to.

The surface conditioner is not particularly limited.
For example, silicones such as dimethyl silicone and methyl silicone; acrylic oligomers;

The method for producing the anticorrosive powder coating composition of the present invention is not particularly limited, and it can be produced by a method used in producing a conventional powder coating. For example, a resin for powder coating, a curing agent, a pigment, a surface conditioner, and the like are mixed by a high-speed mixer, the premixed product is melt-mixed by a kneader, and the mixture is cooled into pellets. Subsequently, a powder coating having a predetermined particle size is manufactured from the pellets using a crusher and a classifier.

The average particle size of the anticorrosion powder coating composition of the present invention can be arbitrarily set according to the purpose. The average particle size of a general anticorrosion powder coating composition is 30 to 4
Although it is 0 μm, the average particle diameter is preferably 5 to 30 μm in order to form a uniform coating film with few irregularities. In this case, an improvement in corrosion resistance due to the uniformity of the coating film can be expected.

The anticorrosive powder coating composition of the present invention can be applied to an object to be coated in a usual manner by negatively charged electrostatic coating (corona), triboelectrically charged electrostatic coating (tribo), fluid immersion coating, or the like. Can be.

The object to be coated is not particularly limited as long as it requires corrosion protection, and examples thereof include steel sheets such as cold-rolled steel sheets and hot-rolled steel sheets; and steel materials.

The coated steel sheet coated with the anticorrosive powder coating composition of the present invention can be suitably used for durable building materials, vending machines, fences, steel furniture and the like.

The anticorrosive powder coating composition of the present invention is prepared by blending gypsum in an amount of 2 to 30% by weight of the anticorrosive powder coating composition of the present invention. In a steel plate or a steel material coated with the powder coating composition, peeling of the coating film and blistering do not occur. This is due to the fact that hydroxide ions are generated from the cathode site formed near the damaged part such as pinholes and scratches on the coating film, which reduces the adhesion between the steel plate and the steel material and the coating film. The burning gypsum is
This is considered to be due to the function of capturing the hydroxide ions.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Examples 1-5, Comparative Examples 1-2 Epoxy resin
Production Method of Fatty Powder Coating In accordance with the composition shown in Table 1, a resin for powder coating, a curing agent, a pigment, a surface conditioner, and the like are mixed by a high-speed mixer, and the premix is melt-mixed by a kneading machine. Was cooled to a pellet. Subsequently, the pellets were pulverized with a pulverizer and a classifier, and classified into a predetermined average particle size, to obtain epoxy resin-based powder coating materials 1-1 to 1-7.

[0030]

[Table 1]

In Table 1, the epoxy resin was Epicoat 10
04F (manufactured by Yuka Shell Epoxy), butyral resin is Eslek BLS (manufactured by Sekisui Chemical Co., Ltd.), the curing agent is dicyandiamide, and the curing accelerator is Curezole 2MZ (manufactured by Shikoku Chemicals). And
The calcined gypsum is calcined gypsum PH-200 (manufactured by Cobblestone Gypsum Co.), and the extender pigment is precipitated barium sulfate.
The coloring pigment is titanium dioxide, and the surface conditioner is Acronal 4F (manufactured by BASF). The average particle diameter was measured using a particle diameter measuring device based on a laser light scattering method.

[0032] Examples 6-9, Comparative Example 3-6 polyester
Production of Polyester Resin Powder Coating In accordance with the composition shown in Table 2, polyester resin powder coatings 2-1 to 2-8 were obtained in the same manner as in Example 1.

[0033]

[Table 2]

In Table 2, the polyester resin is Finedick M8021 (manufactured by Dainippon Ink and Chemicals, Inc.) and the curing agent is ε-caprolactam blocked isocyanate [Adduct B-1530 (manufactured by Huls)]. Gypsum is calcined gypsum PH-200 (manufactured by Cobblestone Gypsum), extender pigment is calcium carbonate, coloring pigment is titanium dioxide, and surface preparation agent is CF-
1056 (manufactured by Toshiba Silicone Co., Ltd.).

[0035] Examples 10-13 and Comparative Examples 7-8 epoxy
Preparation of Si / Polyester Composite Resin Powder Coating In accordance with the composition shown in Table 3, in the same manner as in Example 1, epoxy / polyester composite resin powder coating 3-1 to 3-6.
I got

[0036]

[Table 3]

In Table 3, the epoxy resin corresponds to Epicoat 10
04F (Yuika Shell Epoxy Co., Ltd.) and polyester resin is Yupika Coat GV230 (Nippon Yupika Co., Ltd.)
, And the curing accelerator is Curezol C ₁₇ Z (Shikoku Chemicals Corporation), baked gypsum, calcined gypsum PH-2
00 (manufactured by Cobblestone Gypsum), the extender is precipitated barium sulfate, the coloring pigment is titanium dioxide, benzoin is benzoin B (manufactured by Wako Pure Chemical Industries), and the surface preparation agent is CF-1056 (manufactured by Toshiba Silicone Co., Ltd.).

Preparation of Test Plate Each of the powder coatings obtained in Examples 1 to 13 and Comparative Examples 1 to 8 was negatively charged electrostatically coated on a 70 × 150 × 0.8 mm zinc phosphate treated cold-rolled steel plate. Is applied so that the film thickness becomes 50 μm (35 μm in Example 5).
After baking for a minute, a test plate was obtained. Using this test plate,
The salt spray test was performed for 500 hours, the blisters around the cut portion were observed, and the creep width was measured. The results are shown in Tables 4 and 5.

Salt water spray test A cross cut was made on a part of the surface of the test plate with a cutter knife, and then a saline solution adjusted to a salt concentration of 5 ± 0.5% was sprayed from a spray nozzle, and 500 hours passed. Thereafter, the surface was observed. The maximum cross-cut width on one side of the test plate surface after the blister salt spray test around the cut portion was determined according to ASTM D-714-56. Measurement of creep width A cellophane adhesive tape was stuck to the coating film after the salt spray test, and was rubbed with an eraser to completely adhere the cellophane adhesive tape to the coating film. After 2 minutes, the tape was peeled off.
At this time, the size of the peeled coating film on one side of the cross cut was measured as a creep width.

[0040]

[Table 4]

[0041]

[Table 5]

From the above results, in any of the epoxy resin-based powder coating, the polyester resin-based powder coating, and the epoxy / polyester composite resin-based powder coating, when gypsum is added, the vicinity of the cut portion of the coating film is obtained. No blisters were generated around the exposed areas. Also, the creep width and peel width
It was smaller when calcined gypsum was added, and it was found that even when the salt spray test was performed, the adhesion of the coating film did not decrease. On the other hand, the addition of CaSO ₄ · 2H ₂ O is
It was found that blisters occurred around the cut portion and the exposed portion of the coating film, and the creep width and peeling width after the salt spray test were large, and the adhesion was reduced.

[0043]

Since the anticorrosion powder coating composition of the present invention has the above-mentioned constitution, even if it is only one coat, it can cause peeling or blistering at the end face, defect or damaged portion of the coating film. , Is excellent in safety, and can be manufactured at low cost. Further, the anticorrosion powder coating composition of the present invention can be suitably used for steel plates of durable building materials, vending machines, fences, steel furniture and the like.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Koji Inada 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Inside Nippon Paint Co., Ltd.

Claims (1)

[Claims] An anticorrosion powder coating composition comprising calcined gypsum and a resin for powder coating, wherein the calcined gypsum is present in an amount of 2 to 30% by weight based on the anticorrosion powder coating composition. A powder coating composition for anticorrosion, which is to be blended.