JP2008229406A - Coating film formation method and coating film obtained by the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of almost completely eliminating un-coated parts to be objects of touch-up by basically employing cationic electrodeposition coating. <P>SOLUTION: The coating film formation method involves an electrodeposition coating step of forming an electrodeposition film by carrying out electrodeposition coating of an object to be coated and a self-precipitation coating formation step of forming a self-precipitation coating on un-formed parts of the electrodeposition film on the object to be coated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating film forming method, particularly a coating film forming process comprising a cationic electrodeposition process and an autodeposition film forming process, and a coating film obtained therefrom.

  Electrodeposition coating can be applied to the details even if the object has a complicated shape, and it can be applied automatically and continuously. It is widely used as an undercoating method for objects to be coated that requires high rust prevention. Moreover, it is economical because the use efficiency of the paint is extremely high compared with other coating methods, and is widely used as an industrial coating method. Cationic electrodeposition coating is performed by immersing an object to be coated as a cathode in a cationic electrodeposition coating and applying a voltage.

  Electrodeposition coating is applied to the details as described above, but there are actually portions that are not painted. For example, the inside of a pipe-shaped part or the vicinity of a sharp pointed tip is known as a part where an electrodeposition coating film is hard to be formed. As a result, a portion where no electrodeposition coating film is formed is formed, and the portion where the electrodeposition coating film is not formed naturally lacks rust prevention. Cationic electrodeposition paints with improved throwing power (characteristics for electrodeposition coating to every corner) have been developed in order to reduce the portion where no coating film is formed, but none are completely satisfactory.

  For example, JP 2006-348067 (Patent Document 1) and JP 2006-002003 (Patent Document 2) and many other improvements have been made to improve the throwing power of the cationic electrodeposition paint. However, as described above, it is very difficult to completely eliminate the portion where the electrodeposition coating film is not formed. In an actual painting line, touch-up paint, etc. is manually repaired on the part where the electrodeposition coating film is not formed in order to improve the anticorrosion quality, but an increase in the number of processes and labor is inevitable. . Also, inside the pipe-shaped article, etc., it is a part that is difficult to paint by hand, and there is a limit to rust prevention.

  On the other hand, there is known a self-depositing coating composition that forms a highly rust-proof coating film on a metal steel sheet without using an electrophoretic phenomenon called electrodeposition. This method is a method of forming a coating film on a metal surface using a chemical reaction called redox without using an external factor such as voltage, and a coating film is formed wherever a chemical reaction occurs. The electrodeposition coating method has an advantage that a rust-proof coating film can be formed even in a portion where a coating film is not formed.

  Japanese Patent Application Laid-Open No. 8-173901 (Patent Document 3), Japanese Patent Application Laid-Open No. 7-233341 (Patent Document 4) or Japanese Patent Application Laid-Open No. 2001-172560 (Cited Document 5). R & D continues today.

However, both electrodeposition and auto-deposition technologies were developed individually, and if one was used as the undercoat for the metal surface, the other was not used. That is, there has been no combined use of electrodeposition coating and autodeposition coating on a single object.
JP 2006-348067 A JP 2006-002003 A JP-A-8-173901 JP-A-7-233341 JP 2001-172560 A

  The present invention provides a technique for making the unpainted portion to be touched up close to zero on the basis of cationic electrodeposition coating.

  The present invention is characterized in that after the cationic electrodeposition is applied, the unpainted portion is coated by an autodeposition technique.

That is, the present invention is an electrodeposition coating process for forming an electrodeposition coating film by electrodeposition coating of an object to be coated,
Then, a self-deposited coating composition is applied, and a self-deposited coating film forming step for forming a self-deposited coating film on the part where the electrodeposition coating film is not formed on the object is coated
A method for forming a coating film.

  In the present invention, the self-depositing coating composition contains a carboxyl group-containing resin, hydrogen fluoride and hydrogen peroxide, and the electrodeposition coating composition used in the electrodeposition coating is an amine-modified epoxy resin, It is also provided to include a blocked isocyanate curing agent and a pigment.

  The carboxyl group-containing resin is preferably a carboxyl group-containing styrene butadiene latex.

Furthermore, before the electrodeposition coating film forming process,
It is also possible to carry out the chemical conversion treatment of the article to be coated using a chemical conversion treatment agent containing at least one kind (A) selected from the group consisting of zirconium, titanium and hafnium and fluorine (B).

  As the chemical conversion treatment agent, a zinc phosphate chemical conversion treatment agent may be used.

  In the present invention, the object to be coated is preferably a cold-rolled steel sheet, a galvanized steel sheet, or an alloyed galvanized steel sheet.

  This invention also provides the coating film obtained by said coating-film formation method.

  In the present invention, two coating methods that have been originally developed as a single coating method have been integrated mainly by electrodeposition coating technology, and an autodeposition coating film is formed on a portion where no electrodeposition coating film is formed. Rust prevention is ensured, and the touch-up paint that has been done so far is no longer necessary, reducing the number of processes and labor. In addition, with electrodeposition coating technology and subsequent touch-up paint painting by human work, it is possible to paint the inside of pipe-shaped parts and the inside of complex shaped parts that could not be rust-proofed. Thus, the rust prevention property is greatly improved. In particular, since an autodeposition coating can be formed on the inside of a pipe-shaped part, an electrodeposition coating film is not formed, rust prevention is imparted only by the autodeposition coating, and the inside of the pipe-shaped part is Since the film is not directly physically affected from the outside, the object to be coated can be sufficiently protected only by the self-deposited film.

  In the present invention, as described above, after coating the object to be coated with the cationic electrodeposition coating, the self-deposition coating film is formed using the self-deposition coating composition. The self-deposited coating film is a film that chemically reacts with a portion where a cationic electrodeposition coating film is not formed. It is experimentally known that the self-deposited coating film is formed by changing the film thickness of the coating film to be formed by surface treatment of an object to be coated, particularly chemical conversion treatment. The following explanation will be given in the order corresponding to the treatment procedure of the object to be coated (chemical conversion treatment → electrodeposition coating → self-deposition coating).

Chemical conversion treatment step In the coating film forming method of the present invention, first, a chemical conversion treatment is performed on the article to be coated using a chemical conversion treatment agent (chemical conversion treatment step). Generally, the steel material to be coated is coated with a primary rust preventive material that adversely affects the coating, such as rust preventive oil and processing oil. These rust preventive oil and processing oil are removed by performing alkaline degreasing before coating. However, when these rust preventive oil and processing oil are removed, rust is likely to be generated. Therefore, it is necessary to first subject the coating object to chemical conversion treatment using a chemical conversion treatment agent after immersing the coating object in an alkaline degreasing solution to remove rust preventive oil and the like. And by performing a chemical conversion treatment, generation | occurrence | production of the rust which arises in a short period can be prevented, and also the adhesiveness of a to-be-coated article and a coating film can be improved.

  As the chemical conversion treatment agent used in the chemical conversion treatment step, a zinc phosphate chemical conversion treatment agent is generally used. The zinc phosphate-based chemical conversion treatment agent is mainly composed of zinc ions and phosphate ions, the oxidizing agent is at least one selected from nitrate ions, nitrite ions, chlorate ions, etc., and sodium ions as neutralization ions And the like. Further, in the zinc phosphate chemical conversion treatment liquid, for the purpose of improving the coating performance, additional metal ions such as nickel ions and manganese ions and fluorides and the like may be added as an etching agent. As such a zinc phosphate chemical conversion treatment agent, a commercially available product may be used, and examples thereof include SD-5350 manufactured by Nippon Paint Co., Ltd.

  In the present invention, a chemical conversion treatment agent that does not contain phosphate ions can also be used. Examples of such a chemical conversion treatment agent include a zirconium-based chemical conversion treatment agent.

Zirconium-based chemical conversion treatment agent The zirconium-based chemical conversion treatment agent is a chemical conversion treatment agent containing at least one (A) selected from the group consisting of zirconium, titanium and hafnium and at least fluorine (B). The zirconium-based chemical conversion treatment agent may further contain an adhesiveness and corrosion resistance imparting agent such as a silane coupling agent.

At least one selected from the group consisting of zirconium, titanium and hafnium (A)
At least one (A) selected from the group consisting of zirconium, titanium and hafnium contained in the chemical conversion treatment agent is a chemical conversion treatment film forming component. A chemical conversion treatment film containing at least one (A) selected from the group consisting of zirconium, titanium, and hafnium is formed on the article to be coated, thereby improving the corrosion resistance and wear resistance of the article to be coated. Adhesiveness with the coating film formed can be improved.

The zirconium source is not particularly limited, and examples thereof include alkali metal fluorozirconates such as K ₂ ZrF ₆ ; fluorozirconates such as (NH ₄ ) ₂ ZrF ₆ ; fluorozirconate acids such as H ₂ ZrF _6, etc. And soluble fluorozirconate, etc .; zirconium fluoride; zirconium oxide and the like.

The titanium source is not particularly limited. For example, alkali metal fluorotitanate, fluorotitanate such as (NH ₄ ) ₂ TiF ₆ ; soluble fluorotitanate such as fluorotitanate such as H ₂ TiF _6, etc .; titanium fluoride A titanium oxide can be mentioned.

The source of hafnium is not particularly limited, and examples thereof include fluorohafnate acids such as H ₂ HfF ₆ ; hafnium fluoride. The supply source of at least one (A) selected from the group consisting of zirconium, titanium, and hafnium is selected from the group consisting of ZrF ₆ ²⁻ , TiF ₆ ²⁻ , and HfF ₆ ²⁻ due to high film forming ability. Preferred is a compound having at least one of the following.

  The content of at least one (A) selected from the group consisting of zirconium, titanium and hafnium contained in the chemical conversion treatment agent is preferably in the range of a lower limit of 20 ppm and an upper limit of 10,000 ppm in terms of metal. If it is less than the lower limit, the resulting chemical conversion film has insufficient performance, and if it exceeds the upper limit, no further effect can be expected, which is economically disadvantageous. The lower limit is more preferably 50 ppm, and the upper limit is more preferably 2000 ppm.

Fluorine (B)
Fluorine (B) contained in the chemical conversion treatment agent plays a role as an etching agent for the object to be coated. The fluorine supply source is not particularly limited, and examples thereof include fluorides such as hydrofluoric acid, ammonium fluoride, fluorinated boronic acid, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. . Examples of the complex fluoride include hexafluorosilicate, and specific examples thereof include hydrofluoric acid, zinc silicofluoride, manganese silicofluoride, magnesium silicofluoride, and hydrosilicofluoride. Examples thereof include nickel, iron silicohydrofluorate, and calcium silicohydrofluoride.

Preparation of a zirconium-based chemical conversion treatment agent This zirconium-based chemical conversion treatment agent comprises the above-mentioned components (A) and (B), and an adhesive and corrosion resistance imparting agent such as a silane coupling agent in an aqueous solvent. Can be prepared by mixing. As the aqueous solvent, tap water, ion exchange water, pure water and the like can be used without particular limitation. The aqueous solvent may contain a small amount of alcohols as required.

Cationic electrodeposition coating process The next step is cationic electrodeposition coating. Cationic electrodeposition coating is carried out by immersing the above-mentioned chemical conversion-treated article in a cationic electrodeposition coating and applying a voltage. Examples of the electrodeposition coating composition include a cationic epoxy resin, a curing agent, and, if necessary, a pigment or an additive. Hereinafter, each component will be described.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. Cationic epoxy resins typically open all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  The following formula described in JP-A-5-306327

[Wherein R represents a residue excluding the glycidyloxy group of the diglycidyl epoxy compound, R ′ represents a residue excluding the isocyanate group of the diisocyanate compound, and n represents a positive integer. An oxazolidone ring-containing epoxy resin represented by the above formula may be used as the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a block polyisocyanate blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and a by-product lower alcohol is introduced from the system. Obtained by distilling off.

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of the oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known.

  These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. In addition, the epoxy resin can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds that can introduce a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare a primary, secondary or / and tertiary amino group-containing epoxy resin, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of amines may be used in combination.

Curing Agent The curing agent used in the present invention is preferably a blocked polyisocyanate obtained by blocking polyisocyanate with a blocking agent, where polyisocyanate refers to a compound having two or more isocyanate groups in one molecule. . The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) , Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethylcyclo Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretoimine, burette and / or isocyanurate modified product); and the like. These may be used alone or in combination of two or more.

  Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as curing agents.

  The polyisocyanate is preferably an aliphatic polyisocyanate or an alicyclic polyisocyanate. This is because the formed coating film is excellent in weather resistance.

  Preferred specific examples of the aliphatic polyisocyanate or alicyclic polyisocyanate include hexamethylene diisocyanate, hydrogenated TDI, hydrogenated MDI, hydrogenated XDI, IPDI, norbornane diisocyanate, dimer (biuret) and trimer thereof. (Isocyanurate) etc. are mentioned.

  The blocking agent is added to a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

  As a blocking agent, when low temperature curing (160 ° C. or lower) is desired, lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam and β-propiolactam, and formaldoxime, acetoald It is preferable to use an oxime blocking agent such as oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, and cyclohexane oxime.

  The binder containing the cationic epoxy resin and the curing agent is generally contained in the electrodeposition coating composition in an amount that occupies 25 to 85% by mass, preferably 40 to 70% by mass of the total solid content of the electrodeposition coating composition. The

Pigment The electrodeposition coating composition used in the present invention may contain a commonly used pigment. Examples of pigments that can be used include commonly used inorganic pigments, for example colored pigments such as titanium white, carbon black and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; Zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, phosphomolybdic acid Examples include rust preventive pigments such as aluminum zinc.

  The pigment is generally contained in the electrodeposition coating composition in an amount of 1 to 35% by mass, preferably 10 to 30% by mass, based on the total solid content of the electrodeposition coating composition.

Pigment-dispersed paste When a pigment is used as a component of an electrodeposition paint, generally the pigment is dispersed in an aqueous medium at a high concentration in advance together with a resin called a pigment-dispersed resin to form a paste. This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

  The pigment dispersion paste is prepared by dispersing a pigment in an aqueous medium together with a pigment dispersion resin varnish. As the pigment-dispersed resin varnish, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used. Generally, the pigment-dispersed resin varnish is used at a solid content ratio of 5 to 40 parts by mass, and the pigment is used at a solid content ratio of 10 to 30 parts by mass.

  After the pigment dispersion resin varnish and the pigment are mixed in an amount of 10 to 1000 parts by mass with respect to 100 parts by mass of the resin solid content, a ball mill or a sand grind is used until the pigment in the mixture has a predetermined uniform particle size. A pigment dispersion paste is obtained by dispersing using a normal dispersing device such as a mill.

Preparation of electrodeposition coating composition The electrodeposition coating composition is prepared by dispersing a cationic epoxy resin, a curing agent, and a pigment dispersion paste in an aqueous medium. Further, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the cationic epoxy resin. Neutralizing agents are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The amount is an amount that achieves a neutralization rate of at least 20%, preferably 30-60%.

  The amount of curing agent is sufficient to react with active hydrogen-containing functional groups such as primary, secondary or / and tertiary amino groups and hydroxyl groups in the cationic epoxy resin during curing to give a good cured coating film. In general, it is generally in the range of 90/10 to 50/50, preferably 80/20 to 65/35, expressed as a solid mass ratio of the cationic epoxy resin to the curing agent.

  The electrodeposition paint can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a usual urethane cleavage catalyst. Since what does not contain lead substantially is preferable, it is preferable that the quantity shall be 0.1-5 mass% of a block polyisocyanate compound.

  The electrodeposition coating composition may contain conventional coating additives such as water-miscible organic solvents, surfactants, antioxidants, ultraviolet absorbers, and pigments.

  The object to be coated when performing electrodeposition coating using the electrodeposition coating composition is a conductor that has been subjected to surface treatment such as zinc phosphate treatment or zirconium chemical conversion treatment by dipping or spraying in advance. However, the surface treatment may not be performed. Even when the surface treatment is not performed, the degreasing treatment (treatment for removing oil adhering to the surface of the object to be coated) is usually performed. The “conductor” is not particularly limited as long as it can serve as a cathode in performing electrodeposition coating, and is a metal substrate such as cold-rolled steel sheet, high-strength steel, high-strength steel, cast iron, zinc and zinc. Examples thereof include plated steel, alloyed galvanized steel sheet, aluminum and aluminum alloy. Preferably, it is a cold rolled steel sheet, a galvanized steel sheet, or an alloyed galvanized steel sheet.

The conditions under which electrodeposition is performed are generally the same as those used for other types of electrodeposition coating. The applied voltage may vary greatly and may range from 1 volt to several hundred volts. The current density is usually about 10 amperes / m ^{2 to} 160 amperes / m ² and tends to decrease during electrodeposition.

Autodeposition coating process In this invention, the to-be-coated object obtained by the said electrodeposition coating process is attached | subjected to an autodeposition coating process. Self-depositing coating compositions are known, and various patent documents such as JP-B-47-17630, JP-B-48-14412, JP-B-52-21006, JP-B-52-35692, and JP-B-53. -15093, JP-B 53-16010, JP-B 53-44949, JP-A 60-58474, JP-A 61-168673, JP-A 61-246267, JP-A-8-173901 JP-A-7-233341, JP-A-2001-172560, and the like.

  The self-depositing coating composition is a water-dispersible or water-soluble organic film-forming resin, an acidic aqueous coating composition containing an acid and an oxidizing agent as essential components, and a metal surface such as iron, zinc, iron alloy and zinc. By bringing the surface of the alloy or the like into contact, an excellent resin film can be efficiently coated on the metal surface. The self-depositing coating composition may contain a pigment, particularly a rust preventive pigment, if necessary.

  The self-depositing coating composition is a composition capable of forming a resin film whose thickness or weight increases with the immersion time by immersing a metal surface in the coating composition. Furthermore, film formation by the composition is achieved by the chemical action of the coating composition on the metal surface (metal ions eluted from the metal surface by etching act on the resin particles and precipitate on the metal surface). The resin film can be effectively formed on the metal surface without using external electricity like electrodeposition.

  The water-dispersible or water-soluble film-forming resin that can be used in the present invention is not specified, and a known resin can be used. For example, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl Polymer resin comprising one or more monomers selected from methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylamide, acrylonitrile, styrene, ethylene, butadiene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylic acid, methacrylic acid, etc. And urethane resin, epoxy resin, and polyester resin. The film-forming resin preferably has a carboxyl group. A carboxyl group becomes a reaction point with a metal ion at the time of precipitation. The self-depositing coating composition does not contain a curing agent, and heat-flows to form a film.

  More specifically, a copolymer in which the copolymer is composed of vinylidene chloride, such as vinylidene chloride 50 to 70% by weight, vinyl chloride about 5 to 35% by weight, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate , Ethyl methacrylate, acrylamide, methacrylamide, acrylonitrile, at least one selected from the group consisting of about 5 to 20% by weight vinyl compound and about 0.1 to 5% by weight sulfoethyl methacrylate Copolymer, preferably a vinylidene chloride copolymer consisting of about 15-20% by weight vinyl chloride, 2-5% by weight butyl acrylate, 3-10% by weight acrylonitrile and about 1-2% by weight sulfoethyl methacrylate. Coalesced (eg Daran latex; WR Grace Co., Serfene latex; Morton Chemical, Haloflex 202; InperialChemical Industries) compositions containing dispersed is disclosed in JP-A-60-58474. Also preferred are carboxyl group-containing styrene butadiene latexes, which are commercially available as JSR0533 and JSR0693 from Nippon Synthetic Rubber Co., Ltd.

  The preferred resin content in the autodeposition-type aqueous coating composition of the present invention is in the range of 5 to 550 g / L, more preferably 50 to 100 g / L. In addition, pH of the coating composition of this invention is 1.6-5.0, and if it remove | deviates from this range, a favorable coating film will not be formed.

  In addition to the resin component, the known self-depositing water-based coating composition that can be used in the present invention requires an acid and an oxidizing agent. Moreover, a metal ion may be contained as an optional component. For example, as described in JP-A-49-108135, the dispersion resin has a solid content concentration of about 5 to 550 g / L, and the acid is an appropriate acid that can supply metal ions in the composition. Although there is no limitation, preferably hydrofluoric acid is about 0.4 to 5.0 g / L, and the type of oxidizing agent is not particularly limited, but is preferably about 3.0 g / L or less of peroxide water, metal Examples of the metal compound that can supply ions include, for example, in the case of ferric fluoride, an autodeposition-type aqueous coating composition that is about 1 to 50 g / L.

  If desired, other components can optionally be added to the autodeposition coating composition. For example, a suitable pigment can be included in the coating composition. Examples of pigments that can be used include carbon black, phthalocyanine blue, phthalocyanine green, quinacridone red, benzidene yellow, and titanium dioxide. The amount of pigment added to the composition must be that which gives the film the desired color and / or the desired density or hue. The amount of pigment used is determined by the type of pigment used and the desired film color.

  Various pigments can be included in the aqueous dispersion, and this dispersion may contain a surfactant or dispersant for maintaining the pigment particles in a dispersed state.

  The colored film can be formed using a dye. Examples of dyes include rhodamine derivative dyes, methyl violet, safranine, anthraquinone derivative dyes, nigrosine, and alizarin cyanine green.

  Other additives that can be used in the autodeposition resin composition include additives generally known for use in preparing coating compositions, such as UV stabilizers and viscosity modifiers. The surfactant is preferably anionic.

  In preparing the autodeposition resin composition, the components can be added and mixed by any suitable method, such as the method described in US Pat. No. 4,191,676.

  The method for coating the surface of the object to be coated with the self-depositing coating composition of the present invention is not particularly limited, but the dipping method is more preferable, but a spray method, a curtain coating method or a combination thereof may be used. Also good. The treatment temperature and treatment time are not particularly limited, but in the case of immersion treatment, the treatment is generally performed at 15 to 30 ° C., preferably 20 to 25 ° C. for 10 seconds to 600 seconds, preferably 30 seconds to 300 seconds. preferable. If the treatment is out of the above range, the target coating film of the present invention is not formed.

  Although there is no restriction | limiting in particular about the coating amount to the to-be-coated surface of the self-deposition type coating composition of this invention, As a film thickness of the coating film after drying, it is 5-40 micrometers, Preferably it is the range of 10-25 micrometers. If the film thickness is less than 5 μm, the desired coating film performance cannot be obtained. If it exceeds 40 μm, blistering is likely to occur in the coating film, and the appearance quality is significantly impaired.

  According to the present invention, the coating material on which the coating film is formed by the above-described cationic electrodeposition coating method and autodeposition coating method is subjected to an ordinary method such as a baking oven, a baking oven or an infrared heat lamp at an elevated temperature. Bake and harden. The baking temperature may vary but is usually about 140 ° C to 180 ° C. The coated material coated by the electrodeposition coating system of the present invention is preferably dried and baked after washing with water.

  The following preparation examples and examples are given by way of illustration only and not limitation. In these, “parts” and “%” are based on weight unless otherwise specified.

Preparation of Degreasing Test Pieces Cold-rolled steel sheets (JIS G3141, SPCC-SD) were processed with a degreasing agent (EC-90: manufactured by Nippon Paint Co., Ltd.) to obtain cold-rolled steel sheets subjected only to degreasing.

Preparation of zinc phosphate-treated specimens Degreased cold-rolled steel sheets (JIS G3141, SPCC-SD) were treated with Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.) to treat zinc phosphate-treated cold-rolled steel sheets. Got.

Preparation of zirconium-treated specimens Zircon hydrofluoric acid, zinc nitrate and amino group-containing silane coupling agent KBM-603 (N-2 (aminoethyl) 3-aminopropyltrimethoxysilane: effective concentration 100%: Shin-Etsu Chemical Co., Ltd. A chemical conversion treatment agent was prepared using These were added to ion-exchanged water and mixed so that the zirconium concentration was 250 ppm, the amino group-containing silane coupling agent concentration was 100 ppm, and the zinc concentration was 500 ppm. Further, iron (III) ammonium citrate was used as a chemical conversion reaction accelerator. A zirconium chemical conversion treatment agent was obtained by adding to 200 ppm and then adjusting the pH to 4 using sodium hydroxide.

  A cold-rolled steel sheet treated with zirconium was obtained by treating the degreased cold-rolled steel sheet (JIS G3141, SPCC-SD) with the zirconium treating agent.

Creation of cationic electrodeposition paint
Production Example 1
Cationic resin having amino group (A)
In a flask equipped with a stirrer, cooler, nitrogen inlet tube, thermometer and dropping funnel, 92 parts of 2,4- / 2,6-tolylene diisocyanate (mass ratio = 8/2), methyl isobutyl ketone (MIBK) 95 parts and 0.5 parts of dibutyltin dilaurate were added, and 21 parts of methanol was further added dropwise while stirring them. The reaction started from room temperature, but was heated to 60 ° C. due to exotherm. Then, after continuing reaction for 30 minutes, 57 parts of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel, and also 42 parts of bisphenol A-propion oxide 5 mol adducts were added. The reaction was mainly carried out in the range of 60 to 65 ° C., and continued until the absorption based on the isocyanate group disappeared while measuring the infrared spectrum.

  To the block polyisocyanate thus obtained, 365 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin was added, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until an epoxy equivalent of 410 was reached. Subsequently, 87 parts of bisphenol A was added to the flask and reacted at 120 ° C., resulting in an epoxy equivalent of 1190. Thereafter, the mixture was cooled, 11 parts of diethanolamine, 24 parts of N-methylethanolamine and 25 parts of a ketimine compound of aminoethylethanolamine (79% by mass MIBK solution) were added and reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became non-volatile content 80%, and the cationic resin (A) which has an amino group was obtained.

Production Example 2
Curing agent (B)
To a flask equipped with a stirrer, a cooler, a nitrogen inlet tube, a thermometer, and a dropping funnel, 723 parts of isophorone diisocyanate, 333 parts of methyl isobutyl ketone and 0.01 part of dibutyltin dilaurate were added, and the temperature was raised to 70 ° C.

  And after the content melt | dissolved uniformly, 610 parts of methyl ethyl ketone oximes were dripped over 2 hours. After completion of dropping, the reaction was continued until the absorption based on the isocyanate group disappeared while measuring the infrared spectrum while maintaining the reaction temperature of 70 ° C. to obtain a curing agent (B).

Production Example 3
Main emulsion (C)
67 parts of the cationic resin (A) having an amino group obtained in Production Example 1 (solid content conversion), 33 parts of the curing agent (B) prepared in Production Example 2 (solid content conversion) were mixed uniformly, and then 2% of ethylene glycol mono-2-ethylhexyl ether and 2% of dibutyltin dilaurate were added to the solid content. Acetic acid was added thereto so that the neutralization rate was 50.0% (neutralization rate with respect to the cationic group of the resin), and ion-exchanged water was added to dilute until the solid content became 37.0% by mass.

  Thereafter, the mixture of MIBK and water was removed under reduced pressure until the solid content was 41.9% by mass, thereby preparing a main emulsion (C).

Production Example 4
Pigment dispersion paste (D)
A bisphenol-type epoxy resin having an epoxy equivalent of 450 is reacted with a half-blocked isophorone diisocyanate of 2-ethylhexanol, and tertiary sulfonium is formed with 1- (2-hydroxyethylthio) -2-propanol and dimethylolpropionic acid to form tertiary sulfonium. A resin varnish for pigment dispersion having a conversion rate of 70.6% by mass and a resin solid content of 60% by mass was prepared.

  Disperse 50.0 parts of the pigment-dispersing resin varnish prepared above, 100.0 parts of ion-exchanged water and 100.0 parts of the granular mixture shown in Table 1 below with a sand grind mill, and further reduce the particle size to 5 μm or less. The mixture was pulverized until a pigment dispersion paste (D) (solid content 52.0 mass%) was obtained.

Examples 1-4
By mixing 979.5 parts of the main emulsion (C) obtained in Production Example 3, 284.0 parts of the pigment dispersion paste (D) obtained in Production Example 4, and 1236.5 parts of ion-exchanged water, A 20.0% cationic electrodeposition coating composition was obtained.

  The cationic electrodeposition coating composition was placed in a 4 L stainless beaker. Half of the test specimens shown in Table 2 were immersed, heated to 30 volts for 30 seconds at a liquid temperature of 30 ° C., and held for 200 seconds for 150 seconds to apply a voltage. Formed. The test piece on which this electrodeposition coating film was formed was washed with water.

  Next, in another 2 L plastic container, 200 parts by weight of 21% styrene butadiene latex (resin Tg 20 ° C., non-volatile content 50%, pH 7.0, average particle size 130 nm) as JSR0693 from Nippon Synthetic Rubber Co., Ltd. 16 parts by weight of acid, 8 parts by weight of 35% hydrogen peroxide water and 50 parts by weight of Bengala were added to 730 parts by weight of deionized water and mixed to prepare an autodeposition paint (1). The test piece in which the electrodeposition coating film was formed in half was immersed in the autodeposition coating (1), and immersed at a temperature of 20 ° C. for the time shown in Table 2.

  The obtained test piece was washed with water and then baked and cured at 160 ° C. for 10 minutes. The obtained coated test piece was subjected to a salt spray test, and the results are shown in Table 2. Table 2 shows the film thickness of the uncured self-deposited coating film on the test piece (degreasing only, zinc phosphate treatment, zirconium oxide film treatment) and the results when a salt spray test was performed on each test piece. did.

Example 5
Styrene butadiene latex commercially available from Nippon Synthetic Rubber Co., Ltd. blended with the autodeposition paint (1) of Example 1 above, JSR0533 commercially available from Nippon Synthetic Rubber Co., Ltd. (Tg-20 ° C. of resin, 50% non-volatile content) , PH 8.3, average particle diameter 105 nm), except that the test was conducted in the same manner as in Example 1. The results are shown in Table 2. In this case, the prepared self-depositing paint is referred to as self-depositing paint (2).

Comparative Examples 1 and 2
Without using the self-depositing paint (1) of Example 1 above, only the electrodeposition coating film (half face) was formed on the test piece (Comparative Example 1) with only degreasing and the test piece (Comparative Example 2) with zinc phosphate treatment. The same test as in Example 1 was performed. The results are shown in Table 2.

Salt spray test A test piece having a cured coating film was scratched with a cutter knife, and after spraying 5% salt water for 24 hours, the degree of rust generation was visually observed. The evaluation was as follows.
○… No rust ×… Significant rust

  As is clear from the above results, the test piece immersed in the autodeposition coating exhibits extremely high salt spray resistance, that is, rust prevention. In that case, the film thickness of the self-deposited film changes slightly depending on the presence or absence of chemical conversion treatment or the chemical conversion treatment agent, but does not affect the rust prevention property. On the other hand, the comparative example is a test piece that was not immersed with the self-deposited paint, and the rust prevention property is very poor in the salt spray test.

Claims (7)

An electrodeposition coating process in which an electrodeposition coating is formed by electrodeposition coating of an object;
Then, an autodeposition coating composition is applied to form an autodeposition coating on the non-deposited portion of the electrodeposition coating on the substrate,
A method for forming a coating film.   The self-depositing coating composition contains a carboxyl group-containing resin, hydrogen fluoride and hydrogen peroxide, and the electrodeposition coating composition used in the electrodeposition coating comprises an amine-modified epoxy resin, a blocked isocyanate curing agent, and The coating-film formation method of Claim 1 containing a pigment.   The coating film forming method according to claim 2, wherein the carboxyl group-containing resin is a carboxyl group-containing styrene butadiene latex. Before the electrodeposition coating film formation process,
A chemical conversion treatment step of chemical conversion treatment of the object to be coated using a chemical conversion treatment agent containing at least one (A) and fluorine (B) selected from the group consisting of zirconium, titanium and hafnium;
The coating-film formation method in any one of Claims 1-3 including this. Before the electrodeposition coating film formation process,
A chemical conversion treatment step, using a zinc phosphate chemical treatment,
The coating-film formation method in any one of Claims 1-3 including this.   The coating film formation method of Claim 1 whose said to-be-coated article is a cold-rolled steel plate, a galvanized steel plate, or an alloyed galvanized steel plate.   The coating film obtained by the coating-film formation method in any one of Claims 1-6.