JPH0233069B2 - NISOTOMAKUGATASEIKEIATSUMAKUDENCHAKUTORYOSOSEIBUTSUOYOBIDENCHAKUTOSOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to obtain a thicker film in a shorter time than conventional electrodeposition coating, and the formed coating film has an epoxy underlayer with good corrosion resistance and good weather resistance. The present invention relates to an electrodeposition coating composition having a two-layer structure including an acrylic upper layer, and a method for electrodeposition coating thereof. In general, electrodeposition coating involves immersing a conductive object and a counter electrode in an electrolyte (electrodeposition bath liquid) containing charged resin particles with electrophoretic properties, and when a DC voltage is applied, a current flows through the electrodeposition bath liquid to the object. At the same time as the electric current flows, the charged resin particles migrate to the object to be coated, and are deposited as a coating film on the object in approximately proportion to the amount of current flowing, and is characterized by the uniformity of the film thickness. On the other hand, it has the disadvantage that it is difficult to form a coating film having both corrosion resistance and weather resistance, since it is difficult to obtain a thick film of 40 μm or more. Particularly in the electro-deposition coating of automobile bodies, etc., the outer panel forms a thick film with good corrosion and weather resistance, while the inner panel, which does not require much protection against UV rays, forms a thin film with corrosion resistance. Although forming a good coating film is ideal from a performance and economical point of view, it has been difficult to form such a coating film due to the drawbacks mentioned above. An object of the present invention is to provide an electrodeposition coating composition and an electrodeposition coating method that are capable of forming an ideal coating film in the electrodeposition coating of automobile bodies and the like as described above. In order to achieve the above object, the present inventors first conducted research on the drawback that a thick film cannot be obtained in electrodeposition coating, and found that the coating film deposited on the object to be coated by electrodeposition is generally an organic insulator. Since the electrical resistance is high, the paint film is deposited on all parts of the object to be coated, but conversely, the electrical resistance increases in the parts where the paint film is deposited, and the paint film is deposited one after another. This is because it prevents the film from becoming thicker. In addition, the reason why the deposited coating film has electrical resistance is that the charged resin particles dispersed in the electrodeposition bath liquid migrate to the object to be coated, and as they are deposited on the object, each resin particle is If the resin particles are simply accumulated or laminated in the form of particles, it is difficult to achieve the high electrical resistance described above, but the resin particles deposited on the object to be coated are softened by the Joule heat generated by energization, and the particles are separated. It turns out that this is to fill in the gaps. Therefore, if resin particles with a high softening point that do not soften and fill the voids are precipitated by the Joule heat generated by energization, it is difficult for the deposited coating film to create electrical resistance, and therefore a large amount of current cannot be obtained. It was found that a thick coating film could be obtained as a result. Based on these results, we examined the practical range and found that the normal electrodeposition bath temperature (15°C to 35°C)
℃), if a resin with a softening point of 80℃ or higher is used,
It has been found that a high film thickness can be obtained. Next, the present inventors conducted research on forming a coating film that has both corrosion resistance and weather resistance, and found that a specific cationic acrylic resin and a specific cationic phenolic epoxy resin were used as coating film-forming resins. It has been found that when used together under certain conditions, a coating film with both corrosion resistance and weather resistance can be obtained. That is, when limiting the compatibility, weight ratio, softening point, etc. of both resins, specifically, a cationic acrylic resin whose composition contains a monomer having a benzene nucleus at 50% by weight or less and a cationic resin whose softening point is lower than that of the acrylic resin. phenolic type epoxy resin at a weight ratio of 1
Surprisingly, when combined at a ratio of ~30:1,
The formed cured coating film consists of a lower layer (on the object side) consisting of a phenolic epoxy resin layer with good corrosion resistance and an upper layer (on the air side) consisting of an acrylic resin layer with good weather resistance.
It was found that a two-layer structure was formed. In addition, in the electrodeposition coating method using resin as described above, a complex-shaped object having an outer panel and an inner panel, such as an automobile body, is immersed as a conductive object to be coated, and a voltage is applied between it and a counter electrode. When applying electrodeposition coating, first apply a normal voltage, then change the voltage,
When applying a voltage 1.5 to 15 times the initial voltage,
By applying the initial voltage, an electrodeposited coating consisting of two layers with a thickness of about 50μ or more is formed mainly on the outer panel, and by applying a voltage of 1.5 to 15 times the thickness after that, an electrodeposited coating film of about 5 to 50μ thick is formed on the inner panel as well. It was found that an electrodeposition coating film of about 30μ was formed. Based on the above results, the present inventors continued their research and found that a cationic acrylic resin with a softening point of 80°C or higher and a cationic phenolic epoxy resin with a softening point of 75°C or lower were used under the above conditions. It has been found that the object of the present invention can be achieved by using the present invention. That is, the present invention contains 50% by weight or less of a monomer having a benzene nucleus in the composition, and has a softening point.
Contains a cationic acrylic resin (A) with a temperature of 80°C or higher and a cationic phenolic epoxy resin (B) with a softening point of 75°C or lower, and the weight ratio of (A) to (B) is 1 to 30.
A two-layer coating-forming thick-film electrodeposition coating composition characterized in that the composition is 1 to 1; When electrocoating an article with a complex shape by dipping it and applying a voltage between it and a counter electrode, a normal voltage is first applied to form a thick electrocoated film consisting of two layers mainly on the outer panel. and then the initial voltage of
The present invention provides an electrodeposition coating method characterized in that a thin electrodeposition coating film is formed on an inner plate portion by applying a voltage of 1.5 to 15 times. The cationic acrylic resin used in the present invention is a monomer having αβ-unsaturated double bonds, specifically styrene, vinyltoluene and their derivatives, acrylic acid derivatives such as acrylic acid and n-butyl acrylate, methacrylic acid, and copolymers of methacrylic acid derivatives such as methyl methacrylate, dimethylaminoethyl methacrylate, glycidyl methacrylate, and 2-hydroxyethyl methacrylate, and when an amino group-containing monomer such as dimethylaminoethyl methacrylate is included in the copolymer composition. , made cationic by neutralizing it with acids such as formic acid, acetic acid, lactic acid, phosphoric acid, etc., and when containing an epoxy group-containing monomer such as glycidyl methacrylate in the copolymer composition, amine, A cationic compound can be used by adding sulfonium or the like and neutralizing it with the acid mentioned above. However, the content of the monomer having a benzene nucleus in the cationic acrylic resin used in the present invention is 50% by weight or less, preferably 20% by weight in the total acrylic composition.
The following must be selected, with a softening point of 80°C or higher. If the content of monomers with benzene nuclei exceeds 50% by weight, the compatibility with the phenolic epoxy resin improves, so the electrodeposited coating will not form a good two layer and will also exhibit better weather resistance. It becomes impossible. Further, if the softening point is less than 80°C, a thick electrodeposition coating film, which is one of the objects of the present invention as described above, will not be formed. The cationic phenolic epoxy resin used in the present invention includes phenolic epoxy resins such as bisphenol A-epichlorohydrin and bisphenol F-epichlorohydrin; phenols; and novolac phenols such as glycidyl ether of nuclear-substituted phenol formaldehyde novolak. Epoxy resins made cationic by adding amines, sulfonium, etc. and neutralizing them with acids such as formic acid, acetic acid, lactic acid, phosphoric acid, etc. can be used, but choose ones with a softening point of 75°C or lower. Must. If the softening point exceeds 75°C, a large amount of cationic phenolic epoxy resin will precipitate during electrodeposition as described above, and the viscosity difference with the cationic acrylic resin will become smaller when the coating film is baked, causing the epoxy resin to form in the lower layer. , a two-layer coating of acrylic resin will no longer be formed on the upper layer. In addition, the softening point of the resin in the present invention is determined by the solid content.
100% of the resin is measured based on JIS-K-5665. The electrodeposition coating composition of the present invention must contain the cationic acrylic resin (A) and the cationic phenolic epoxy resin (B) in a weight ratio of 1 to 30:1. If the content ratio of (A) is less than 1, the epoxy resin (lower layer) and the acrylic resin (upper layer) will not be well separated,
Good corrosion resistance and weather resistance cannot be exhibited. On the other hand, if it exceeds 30, it becomes difficult to uniformly and continuously cover the object to be coated with the epoxy resin in the lower layer, and good corrosion resistance cannot be exhibited. In addition, in order to further enhance the effects of the present invention, the equivalent ratio of the polar groups in the cationic acrylic resin (A) and the polar groups in the cationic phenolic epoxy resin (B) should be such that (A) < (B). Therefore, it is desirable to select (A) and (B). That is, by making the polar group of (B) larger than the polar group of (A), it becomes possible to increase the ease of precipitation of (A) per the same amount of electricity during electrodeposition, and the lower layer epoxy resin, This is because it makes it easier to form two layers of upper acrylic resin. As a method for curing the electrodeposition coating composition of the present invention, known methods such as isocyanate crosslinking, ester crosslinking, melamine crosslinking, amide crosslinking, etc. can be applied. Further, the electrodeposition coating composition of the present invention may contain, in addition to the above-mentioned components, a crosslinking agent, a pigment resin, a solvent, an additive auxiliary agent, water, etc. that are used in ordinary electrodeposition coatings. In the electrodeposition coating method of the present invention, the electrodeposition coating composition of the present invention having the composition as described above is diluted with water to give a conductive coating in an electrodeposition bath at a temperature of 15 to 35°C with a nonvolatile content of 5 to 20%. By immersing an object as a cathode and applying a voltage of about 10V to 600V between it and the counter electrode (anode) for about 5 seconds to 5 minutes, two layers of an epoxy lower layer and an acrylic upper layer are applied to the object. A thick electrodeposited coating film is formed. In addition, when electrocoating complex-shaped objects such as automobile bodies that have outer and inner panels as conductive objects, the initial voltage is approximately 50 to 150 V.
×A voltage is applied for 5 to 30 seconds to form a two-layer thick (50 to 200μ) electrodeposited coating mainly on the outer panel.
After that, 1.5 to 15 times the initial voltage, approximately 75V~
By applying a voltage of 750V, an electrodeposited coating film with a thickness of approximately 5 to 30 μm is formed on the inner plate portion. The present invention will be explained below with reference to Examples. Preparation of cationic acrylic resin (A-1) (1) Ethylene glycol monoethyl ether
35 parts by weight (2) Isopropyl alcohol 7 (3) N-n-butoxyacrylamide 4 (4) 2-hydroxyethyl methacrylate
20 (5) n-butyl methacrylate 28 (6) Styrene 15 (7) Methyl methacrylate 25 (8) Dimethylaminoethyl methacrylate
6 〃 (9) Azobisisobutyronitrile 2 〃 (10) Prosocyanate (product name B-1065 manufactured by Hueva) 17 〃 (11) Glacial acetic acid 3.5 〃 (12) Deionized water 1007.5 〃 First, (1) ) to (2) are put into a Kolben and heated,
(3) to (9) were added dropwise over 90 minutes at 100-120°C, and then maintained at 110-120°C for 3 hours. Then (10) at 110℃
and stirred until uniform. Add (11) to (12) to the resin thus obtained, stir and mix uniformly, and cationic acrylic resin (A-
1) was prepared. The resulting resin (A-1) had a softening point of 95°C, a nonvolatile content of 10%, and an MEQ of 50. MEQ: Acid required for neutralization per 100g of resin solids
mg equivalent number. Preparation of cationic acrylic resin (A-2) (1) Ethylene glycol monoethyl ether
35 parts by weight (2) Isopropyl alcohol 7 (3) N-n-butoxyacrylamide 4 (4) 2-hydroxyethyl methacrylate
20 〃 (5) n-butyl acrylate 40 〃 (6) Methyl methacrylate 28 〃 (7) Dimethylaminoethyl methacrylate
6 〃 (8) Azobisisobutyronitrile 2 〃 (9) Blocked isocyanate (product name B-1065 manufactured by Hueva) 17 〃 (10) Glacial acetic acid 3.5 〃 (11) Deionized water 1007.5 〃 (1)～( 11) was reacted and mixed in the same manner as the resin (A-1) to obtain a cationic acrylic resin (A-2).
was prepared. The resulting resin (A-2) had a softening point of 70°C, a nonvolatile content of 10%, and an MEQ of 50. Note that resin (A-1) corresponds to the cationic acrylic resin of the present invention, but resin (A-1) corresponds to the cationic acrylic resin of the present invention.
2) has a low softening point and does not correspond to the cationic acrylic resin of the present invention. Cationic phenolic epoxy resin (B-1)
Preparation (1) Phenol-type epoxy resin (trade name Epicote #1001 manufactured by Ciel Corporation) 450 parts by weight (2) Diethanolamine 105 〃 (3) Isopropyl alcohol 270 〃 (4) Blocked isocyanate (trade name B-1065 manufactured by Hueva Corporation) 55 〃 (5) Glacial acetic acid 18.3 〃 (6) Deionized water 5199 〃 After reacting (1) to (3) at 80℃ to 85℃ for 3 hours, add (4) at 85℃ and mix evenly. Stir and mix until the mixture is mixed. (5) to (6) were added to the resin thus obtained and mixed by stirring uniformly to prepare a cationic phenolic epoxy resin (B-1). The resulting resin (B-1) had a softening point of 72°C, a nonvolatile content of 10%, and an MEQ of 50. Cationic phenolic epoxy resin (B-2)
Preparation (1) 1000 parts by weight of phenolic epoxy resin (trade name Epicote #1004, manufactured by Shell Co., Ltd.) (2) Diethanolamine 105 〃 (3) Isopropyl alcohol 535 〃 (4) Blocked isocyanate (trade name B, manufactured by Hueva Corporation)
-1065) 200 (5) Glacial acetic acid 39.2 (6) Deionized water 11173 (1) to (6) are reacted and mixed in the same manner as the resin (B-1) to obtain a cationic phenolic epoxy resin. (B-2) was prepared. The resulting resin (B-2) had a softening point of 125°C, a nonvolatile content of 10%, and an MEQ of 50. Note that resin (B-1) corresponds to the cationic phenolic epoxy resin of the present invention, but resin (B-2) has a high softening point and is not equivalent to the cationic phenolic epoxy resin of the present invention. It's something you don't do. The electrodeposition coating composition of each example is a mixture of resin (A-1) or (A-2) and (B-1) or (B-2) at the mixing ratio (solid content) shown in Table 1. A zinc phosphate-treated steel sheet product having the shape of an automobile body as a conductive object to be coated is immersed in an electrodeposition bath with a bath temperature of 25°C, and a voltage of 200 V is applied between the anode and the opposite electrode. Electricity was applied for 20 seconds, and then the voltage was increased to 600V for 2 minutes. The properties and performance of the resulting coating film were as shown in Table 1. 【table】

Claims (1)

[Scope of Claims] 1. A cationic acrylic resin (A) containing 50% by weight or less of a monomer having a benzene nucleus in its composition and having a softening point of 80°C or higher, and a cationic acrylic resin (A) having a softening point of 75°C or lower. 1. A thick film electrodeposition coating composition for forming a two-layer coating film, comprising a phenolic epoxy resin (B) and a weight ratio of (A) to (B) of 1 to 30:1. 2 A cationic acrylic resin (A) containing 50% by weight or less of a monomer having a benzene nucleus in its composition and a softening point of 80°C or higher, and a cationic phenolic epoxy resin (B) having a softening point of 75°C or lower. ), and the weight ratio of (A) to (B) is 1 to 30:1. When electrodepositing an object by immersing it as a cathode and applying a voltage between it and the counter electrode (anode), a normal voltage is first applied to form a thick electrocoated film consisting of two layers mainly on the outer panel. , and then applying a voltage 1.5 to 15 times the initial voltage to form a thin electrodeposition coating on the inner plate.