JP2006348074A - Method for producing amine-modified epoxy resin and cationic electrodeposition coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic electrodeposition coating composition scarcely causing defect of coated film appearance, excellent in throwing power and having a few content of an organic solvent and to provide a method for producing an amine-modified epoxy resin used therefor. <P>SOLUTION: The method for producing the amine-modified epoxy resin contained in the cationic electrodeposition coating composition comprises a block step for obtaining a half-blocked isocyanate by reacting a diisocyanate compound with a blocking agent, a block prepolymer-preparing step for obtaining a block prepolymer by reacting the resultant half-blocked isocyanate with a polyol, an oxazolidone ring-producing step for obtaining an oxazolidone ring-containing epoxy resin by reacting the resultant block prepolymer with a diglycidyl ether-type epoxy resin, a chain-extending step for extending a chain of the resultant epoxy resin by using at least saturated or unsaturated hydrocarbon group-containing dicarboxylic acid and an amine-modified step for modifying the resin obtained by the chain-extending step with an amine. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating composition that hardly causes poor coating film appearance, has excellent throwing power, and has a low organic solvent content, and a method for producing an amine-modified epoxy resin used therefor.

  Electrodeposition coating using a cationic electrodeposition coating composition can be applied to the details even if the object has a complicated shape, and can be applied automatically and continuously. It has been widely put into practical use as a method for undercoating an article having a large and complicated shape such as a car body. Cationic electrodeposition coating is performed by immersing an object to be coated in a cationic electrodeposition paint as a cathode and applying a voltage.

  The deposition of the coating film in the process of cationic electrodeposition coating is due to an electrochemical reaction, and the coating film is deposited on the surface of the object to be coated by applying a voltage. Since the deposited coating film has insulating properties, the electrical resistance of the coating film increases as the deposition of the coating film progresses and the deposited film increases in the coating process. As a result, the deposition of the paint at the site where the coating film is deposited decreases, and instead, the deposition of the coating film on the undeposited site begins. In this way, paint solids are sequentially deposited on the object to be coated to complete the coating. In this specification, the property that a coating film is sequentially formed on an unattached portion of an object to be coated is called throwing power.

  In electrodeposition coating, designing an electrodeposition coating composition so that the electrical resistance value of the electrodeposition coating film is simply increased in order to ensure the throwing power increases the applied voltage during electrodeposition coating. This is not preferable because a “gas pin hole” (sometimes abbreviated as “gas pin”), which is considered to be caused by hydrogen gas generated during electrodeposition, is generated and the appearance of the coating film is likely to deteriorate. In the cationic electrodeposition coating composition, it is desired to develop a technique capable of improving throwing power without causing a decrease in the appearance of the coating film due to the occurrence of gas pinholes.

  The cationic electrodeposition coating composition is a water-based coating. However, this electrodeposition coating composition contains an organic solvent. This organic solvent has a role of improving the fluidity of the electrodeposition coating film and improving the smoothness of the resulting cured coating film. On the other hand, reduction of the content of organic solvent in the coating composition is required due to the recent improvement in awareness of environmental problems, the odor problem around the factory, and the safety problem of the coating line. Accordingly, development of a technique for reducing the content of the organic solvent without deteriorating the appearance of the resulting coating film is also desired.

  On the other hand, an anticorrosion imparting agent containing lead has been added to the electrodeposition coating composition so far in order to impart corrosion resistance. In recent years, since lead has an adverse effect on the environment, reduction of the amount of use has been demanded. Therefore, so-called lead-free cationic electrodeposition coatings that do not contain lead-containing corrosion resistance imparting agents are mainly being used. However, by not using lead in the electrodeposition coating composition, the corrosion resistance imparting performance of the electrodeposition coating film is often lowered. In preparing a lead-free cationic electrodeposition coating composition, a technique for further improving various coating performances is required.

  JP 2002-356647 (Patent Document 1) describes a lead-free cationic electrodeposition coating composition proposed by the present applicants. This proposal makes it possible to obtain a high throwing power electrodeposition coating composition, but due to the further demand for high throwing power, etc., there is room for further study of the constituent components of the binder resin.

  Japanese Patent Laid-Open No. 6-329755 (Patent Document 2) discloses a diglycidyl ether type epoxy having a prepolymer obtained by blocking a terminal isocyanate group of a prepolymer obtained by a reaction between a bifunctional active hydrogen compound serving as a soft segment and a diisocyanate compound. A modification characterized by comprising a step of chain extension by reacting with a resin and a step of introducing a cationic group by opening at least a part of the terminal epoxy ring of the chain extended epoxy resin with a cationic active hydrogen compound A method for producing an epoxy resin is described. In this method, a prepolymer is prepared using a diisocyanate compound and a bifunctional active hydrogen compound, and then reacted with a diglycidyl ether type epoxy resin. On the other hand, the present invention is described in JP-A-6-329755 in that a half-blocked isocyanate is prepared using a polyol or the like, and then further chain extension is performed using a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid. Different from the invention. The method of the present invention makes it possible to achieve both high throwing power and low organic solvent content.

  In JP-A-5-306327 (Patent Document 3), (a) a resin having an epoxy group at a terminal and containing a plurality of oxazolidone rings in a molecular chain is added to (b) monool, diol, monocarboxylic acid. A second active hydrogen compound capable of reacting at least one first active hydrogen compound selected from acids and dicarboxylic acids to open a part of the epoxy ring, and then introducing (b) an ionic group To open the remaining epoxy ring to introduce an ionic group. Hydrophilic resins for water-based paints, especially electrodeposition paints, are described. In this method, as described above, a resin containing an oxazolidone ring is reacted with at least one selected from monool, diol, monocarboxylic acid and dicarboxylic acid. On the other hand, the present invention is described in JP-A-5-306327 in that a half-blocked isocyanate is prepared using a polyol or the like, and then further chain extension is performed using a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid. Different from the invention. The method of the present invention makes it possible to achieve both high throwing power and low organic solvent content.

  In JP-A-6-136301 (Patent Document 4), an equivalent ratio of an epoxy group in a polyepoxide and an amine group in a polyoxyalkylene polyamine in a reaction product of (A) a polyepoxide and a polyoxyalkylene polyamine is 1: A cationic non-gelling resin obtained by reacting within the range of 1.15 to 1.60 and neutralizing the resulting reaction product with an acid, 20 to 70% by weight, (B) of the polyepoxide and polyoxyalkylene polyamine Cationic electrodeposition coating composition containing 10 to 65% by weight of another cationic resin different from reaction product (A) and (C) 10 to 50% by weight of blocked polyisocyanate having a dissociation temperature of 100 to 140 ° C. Is described. An embodiment in which the polyepoxide in (A) is a dimer acid-modified polyepoxide is also described. However, the dimer acid used here is different from the present invention in that it is used not for preparing an amine-modified epoxy resin but for preparing a paint additive.

  Japanese Patent Laid-Open No. 2001-213938 (Patent Document 5) describes an amino polyether-modified epoxy obtained by reacting an amino polyether with a polyglycidyl ether having a molecular weight of 1000 to 7000 and an epoxy equivalent of 500 to 3500. The reaction is performed by setting the primary amino group of the amino polyether to an epoxy group of the polyglycidyl ether in an equivalent ratio within a range of 0.52 to 1.0. An amino polyether-modified epoxy is described. An embodiment in which dimer acid is used for the preparation of this amino polyether-modified epoxy is also described. However, this invention also differs from the present invention in that dimer acid is not used in preparing an amine-modified epoxy resin, but is used in preparing a paint additive.

JP 2002-356647 A JP-A-6-329755 JP-A-5-306327 JP-A-6-136301 JP 2001-213938 A

  The present invention solves the above-mentioned conventional problems, and the object of the present invention is to provide a lead-free cationic electrodeposition coating that hardly causes poor coating appearance, has excellent throwing power, and has a low organic solvent content. An object of the present invention is to provide a composition and a method for producing an amine-modified epoxy resin used in the lead-free cationic electrodeposition coating composition.

The present invention
A method for producing an amine-modified epoxy resin contained in a cationic electrodeposition coating composition comprising the following steps:
A block process in which a diisocyanate compound and a blocking agent are reacted to obtain a half-blocked isocyanate;
A block prepolymer preparation step of obtaining a block prepolymer by reacting the obtained half-blocked isocyanate with a polyol;
An oxazolidone ring production step of obtaining an oxazolidone ring-containing epoxy resin by reacting the obtained block prepolymer with a diglycidyl ether type epoxy resin;
Chain-extending the obtained epoxy resin with at least a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid, a chain-extending step, and an amine-modifying step in which the resin obtained by the chain-extending step is amine-modified,
And the above-mentioned object is achieved.

  The epoxy equivalent of the diglycidyl ether type epoxy resin used in the oxazolidone ring production step is preferably 150 to 1000.

  Moreover, it is preferable that the epoxy equivalent of the oxazolidone ring containing epoxy resin obtained by the said oxazolidone ring production | generation process is 800-3000.

  Furthermore, it is preferable that Tg of the said amine modified epoxy resin is 18-35 degreeC.

  Moreover, it is preferable that content of the oxazolidone ring containing glycidyl ether part in the said amine modified epoxy resin is 30 to 70 weight%.

  Further, the content of the saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety in the amine-modified epoxy resin is preferably 3 to 17% by weight.

  The present invention also provides a lead-free cationic electrodeposition coating composition containing an amine-modified epoxy resin obtained by the above production method.

  The amount of the organic solvent contained in the lead-free cationic electrodeposition coating composition is preferably 0.5% or less.

The present invention also provides a lead-free cationic electrodeposition coating composition in which the film resistance of a 15 μm-thick electrodeposition coating film obtained from a lead-free cationic electrodeposition coating composition is 1000 to 1500 kΩ · cm ² .

  As used herein, “lead-free” means that it contains substantially no lead, and means that it does not contain lead in an amount that adversely affects the environment. Specifically, it means that the lead compound concentration in the electrodeposition bath does not contain lead in an amount exceeding 50 ppm, preferably 20 ppm.

  The cationic electrodeposition coating composition of the present invention is lead-free and has an advantage that the load on the environment is small because the organic solvent content is small. Furthermore, it has the advantage that it is excellent in throwing power, is less likely to cause unevenness in drying, and poor in appearance of the coating film.

Electrodeposition Coating Composition The cationic electrodeposition coating composition of the present invention contains an aqueous medium, a binder resin emulsion dispersed or dissolved in the aqueous medium, a neutralizing acid, and an organic solvent. The cationic electrodeposition coating composition of the present invention may further contain a pigment. The binder resin contained in the binder resin emulsion is a resin component composed of an amine-modified epoxy resin and a blocked isocyanate curing agent.

Amine-modified epoxy resin The amine-modified epoxy resin used in the present invention is an epoxy resin modified with an amine. The amine-modified epoxy resin is typically prepared using a diglycidyl ether type epoxy resin.

  A typical example of the diglycidyl ether 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). In this invention, it is preferable to use what has an epoxy equivalent in the range of 150-1000 as a diglycidyl ether type epoxy resin.

The amine-modified epoxy resin contained in the cationic electrodeposition coating composition of the present invention is an amine-modified epoxy resin obtained by amine-modifying an epoxy resin having an oxazolidone ring-containing glycidyl ether portion and a saturated or unsaturated hydrocarbon group-containing dicarbonyl portion. It is. And this amine modified epoxy resin is, for example, the following process:
A block process in which a diisocyanate compound and a blocking agent are reacted to obtain a half-blocked isocyanate;
A block prepolymer preparation step of obtaining a block prepolymer by reacting the obtained half-blocked isocyanate with monool or polyol,
An oxazolidone ring production step of obtaining an oxazolidone ring-containing epoxy resin by reacting the obtained block prepolymer with a diglycidyl ether type epoxy resin;
Chain-extending the obtained epoxy resin with at least a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid, a chain-extending step, and an amine-modifying step in which the resin obtained by the chain-extending step is amine-modified,
Can be produced by a method including:

  The process of the manufacturing method of the said amine modified epoxy resin is shown schematically using a chemical reaction formula. In the following chemical reaction formula, (1) indicates a block step, (2) indicates a block prepolymer preparation step, (3) indicates an oxazolidone ring formation step, and (4) indicates a chain extension step.

In the chemical reaction formulas (1) to (4), R ¹ —OH represents an alcohol which is an example of a blocking agent, R ² represents a residue excluding the isocyanate group of the diisocyanate compound, and R ³ represents a polyol. R ⁴ represents a residue excluding a hydroxyl group, R ⁴ represents a residue excluding a glycidyloxy group of a glycidyl ether type epoxy resin, and R ⁵ represents a carboxylic acid group of a saturated or unsaturated hydrocarbon group-containing dicarbonyl acid. Residues. An amine-modified epoxy resin is obtained by amine-modifying the acid-introduced epoxy resin obtained by the reaction formula (4). Hereinafter, each reaction will be described sequentially.

  Examples of the diisocyanate compound used in the blocking step include aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), and xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), Examples thereof include aliphatic and alicyclic diisocyanates such as isophorone diisocyanate (IPDI), 4,4′-methylenebis (cyclohexyl isocyanate), and trimethylhexamethylene diisocyanate.

  As the blocking agent used for blocking the diisocyanate compound, a blocking agent usually used in this field can be used. Examples of blocking agents that can be used include aliphatic alcohols such as methanol, ethanol, isopropanol, n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, and cyclohexanol; phenols such as phenol, nitrophenol, and ethylphenol; methyl ethyl ketoxime, and the like Oximes: lactams such as ε-caprolactam. Methanol or ethanol is preferably used. By reacting the diisocyanate compound with the blocking agent, half-blocked isocyanate in which one of the isocyanate groups of the diisocyanate compound is blocked can be obtained. The amount of the diisocyanate compound and the blocking agent used in the blocking step is such that the molar ratio of NCO group: active hydrogen contained in each is in the range of 1: 0.3 to 1: 0.7. preferable.

  The half-blocked isocyanate thus obtained is then reacted with a hydroxyl group-containing compound such as polyol to obtain a block prepolymer (block prepolymer preparation step). Here, monool may be used in combination with the polyol. Preferred polyols include, for example, aliphatic diols such as tylene glycol or propylene glycol, or bisphenol. Preferred monools include, for example, 2-ethylhexanol, nonylphenol, aliphatic monoalcohols such as mono-2-ethylhexyl ether of ethylene glycol or propylene glycol, and alkylphenols or glycol monoethers. By reacting them, the molecular weight and / or the amine equivalent can be adjusted, whereby the heat flow property and the like can be improved.

  The amount of the half-blocked isocyanate and polyol used in this block prepolymer preparation step is such that the molar ratio of NCO group: hydroxyl group contained in each block is in the range of 1: 0.3 to 1: 0.7. Is preferred. Through this step, the isocyanate group of the isocyanate compound and the hydroxyl group of the polyol react to obtain a block prepolymer linked by an amide bond.

  Next, an oxazolidone ring-containing epoxy resin is obtained by reacting the obtained block prepolymer with the diglycidyl ether type epoxy resin (an oxazolidone ring generation step). In this step, the block isocyanate group of the block prepolymer and the epoxy group of the diglycidyl ether type epoxy resin react to form an oxazolidone ring. The amount of the block prepolymer and diglycidyl ether type epoxy resin used in this oxazolidone ring production step is such that the molar ratio of blocked isocyanate group: epoxy group contained in each is in the range of 1: 2 to 1:10. It is preferred that The reaction temperature is preferably 60 ° C to 200 ° C. At the time of this reaction, it is preferable to remove the removed blocking agent (for example, methanol, ethanol, etc.) out of the system using a decanter or the like.

  Next, the oxazolidone ring-containing epoxy resin thus obtained is reacted with a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid to extend the chain (chain extension step). Examples of the saturated or unsaturated hydrocarbon group-containing dicarboxylic acid used individually include dicarboxylic acids having 20 to 50 carbon atoms having a saturated or unsaturated hydrocarbon group. Examples of the saturated hydrocarbon group include an alkyl group having 5 to 20 carbon atoms. Examples of the unsaturated hydrocarbon group include an alkynyl group having 5 to 20 carbon atoms, an alkadiynyl group, an alkatriynyl group, an alkenyl group, an alkadienyl group, and an alkatrienyl group.

The saturated or unsaturated hydrocarbon group-containing dicarboxylic acid may be a polymerized fatty acid such as dimer acid. Dimer acid is a polymerized fatty acid produced by a polymerization reaction of an unsaturated fatty acid generally obtained from a dry oil or a semi-dry oil, and has a fatty acid dimer as a main component. The main examples of dimer acid, as a main component such as C ₃₆ dibasic acids obtained by polymerization of C ₁₈ unsaturated fatty acids. However, since this dimer acid is a polymerized fatty acid, its structure is not single, but a mixture of acyclic, monocyclic and polycyclic. In addition, commercially available dimer acid may contain a small amount of monomeric acid, trimer acid and the like. Examples of fatty acids used as raw materials for dimer acids include vegetable oil fatty acids such as tall oil, soybean oil, coconut oil, castor oil, palm oil or rice bran oil, and animal oil fatty acids such as beef tallow fatty acid or tallow fatty acid. .

  The amount of the oxazolidone ring-containing epoxy resin and saturated or unsaturated hydrocarbon group-containing dicarboxylic acid used in this chain extension step is such that the molar ratio of epoxy group: carboxylic acid group contained in each is 1: 0.03-1: It is preferably used in an amount that is in the range of 0.3. By this step, the epoxy group of the oxazolidone ring-containing epoxy resin reacts with the carboxylic acid group of the saturated or unsaturated hydrocarbon group-containing dicarboxylic acid to obtain an epoxy resin having an extended chain.

In this chain extension step, a diol can be used in combination with the saturated or unsaturated hydrocarbon group-containing dicarboxylic acid. Examples of diols that can be used in this chain extension step include:
Aliphatic diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol or 1,6-hexanediol;
Alicyclic diols such as 1,2-cyclohexanediol or 1,4-cyclohexanediol;
Aromatic diols such as bisphenol A, bisphenol F, resorcinol or hydroquinone;
Bifunctional polyether polyols such as polyoxyethylene glycol, polyoxypropylene glycol or polyoxytetramethylene glycol, and their random or block copolymers;
Bifunctional polyester polyols such as bifunctional polyester polyols obtained by esterification reaction of the above diols or polyols with polycarboxylic acids or anhydrides, or bifunctional polycaprolactone polyols obtained by polymerization reaction of the above polyols and caprolactone ;
Etc. In addition, it is preferable that the said bifunctional polyether polyol and bifunctional polyester polyol are the ranges of molecular weight 300-3000.

In this chain extension step, an aliphatic monoalcohol such as n-butanol, butyl cellosolve, octanol or stearyl alcohol,
Aromatic monoalcohols such as xylenol, pt-butylphenol or p-nonylphenol,
Acetic acid, lactic acid, butyric acid, octanoic acid, cyclohexanecarboxylic acid, lauric acid, stearic acid or aliphatic monocarboxylic acid such as 1,2-hydroxystearic acid, or aromatic monocarboxylic acid such as benzoic acid or 1-naphthoic acid, etc. Can also be used. By using these compounds, the epoxy ring of the epoxy resin can be partially opened without extending a part of the epoxy resin.

  An amine-modified epoxy resin is obtained by reacting an amine with the epoxy resin obtained in the chain extension step (amine modification step). Through this amine modification step, the epoxy group in the epoxy resin reacts with amines. Examples of amines that can be used include primary amines and secondary amines. When a bisphenol type epoxy resin is reacted with a secondary amine, an amine-modified bisphenol type epoxy resin having a tertiary amino group is obtained. Further, when a bisphenol type epoxy resin is reacted with a primary amine, an amine-modified bisphenol type epoxy resin having a secondary amino group is obtained. Furthermore, an amine-modified bisphenol type epoxy resin having a primary amino group can be prepared by using a resin having a primary amino group and a secondary amino group. Here, preparation of an amine-modified bisphenol type epoxy resin having a primary amino group and a secondary amino group is carried out by blocking the primary amino group with a ketone to form a ketimine before reacting with the epoxy resin. It can be prepared by deblocking after introduction into the epoxy resin.

  Specific examples of the primary amine, secondary amine and ketimine include, for example, butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine and the like. In addition, there are secondary amines with blocked primary amines such as aminoethylethanolamine ketimine, diethylenetriamine diketimine. Two or more of these amines may be used in combination.

  The amine-modified epoxy resin may be ring-opened with amines so that the amine equivalent is 0.3 to 4.0 meq / g, more preferably 5 to 50% of which is occupied by primary amino groups. desirable.

  The amine-modified epoxy resin thus obtained has an oxazolidone ring-containing glycidyl ether moiety and a saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety. The content of the oxazolidone ring-containing glycidyl ether moiety in the amine-modified epoxy resin is preferably 30 to 70% by weight, and more preferably 40 to 60% by weight. The content of the saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety in the amine-modified epoxy resin is preferably 3 to 17% by weight, more preferably 6 to 14% by weight.

  The amine-modified epoxy resin having this oxazolidone ring-containing glycidyl ether moiety and a saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety can be outlined as follows.

  In the above formula, (a) is an oxazolidone ring-containing glycidyl ether moiety. Here, “A ′” is an oxazolidone ring-containing glycidyl ether moiety in which the epoxy ring contained in “A” of the above reaction formula (4) is amine-modified. (B) is a saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety.

Blocked isocyanate curing agent The polyisocyanate used in the blocked isocyanate curing agent of the present invention refers to a compound having two or more isocyanate groups in one molecule. The polyisocyanate may be any of aliphatic, alicyclic, aromatic and aromatic-aliphatic, for example.

  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, uretonimine, burette and / or isocyanurate modified product); 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 the block isocyanate curing agent.

  The blocking agent is added to the isocyanate group of the polyisocyanate to block the isocyanate. This isocyanate block is stable at room temperature, but when it is heated above the dissociation temperature, it is deblocked to regenerate free isocyanate groups.

  As a blocking agent, normally used epsilon caprolactam, butyl cellosolve, etc. can be used.

Pigment The electrodeposition coating composition of the present invention may contain a commonly used pigment. Examples of pigments that can be used include commonly used 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.

  When the pigment is contained in the electrodeposition coating composition, the content is preferably within a range of 30% by weight or less with respect to the solid content of the coating of the electrodeposition coating composition. The pigment is more preferably contained in an amount of 1 to 25% by weight based on the solid content of the electrodeposition coating composition. When the pigment concentration exceeds 30% by weight, the horizontal appearance of the obtained electrodeposition coating film may be deteriorated.

  When using a pigment as a component of an electrodeposition paint, generally the pigment is previously dispersed in an aqueous medium at a high concentration to form a paste (pigment dispersion 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 dispersion resin, 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.

  In general, the pigment dispersion resin is used in an amount of 20 to 100 parts by weight based on 100 parts by weight of the pigment. After the pigment dispersion resin varnish and the pigment are mixed, the pigment is dispersed using a normal dispersing device such as a ball mill or a sand grind mill until the particle size of the pigment in the mixture reaches a predetermined uniform particle size. Obtain a dispersion paste.

  In addition to the above components, the electrodeposition coating composition of the present invention comprises organic tin compounds such as dibutyltin laurate, dibutyltin oxide and dioctyltin oxide, amines such as N-methylmorpholine, metals such as strontium, cobalt and copper A salt may be included as a catalyst. These can act as a catalyst for the dissociation of the blocking agent of the curing agent. The concentration of the catalyst is preferably 0.1 to 6 parts by weight with respect to 100 solid parts by weight of the binder resin in the electrodeposition coating composition.

Preparation of lead-free cationic electrodeposition coating composition The lead-free cationic electrodeposition coating composition of the present invention comprises the above-described amine-modified epoxy resin, blocked isocyanate curing agent, pigment dispersion paste and catalyst dispersed in an aqueous medium. Can be prepared. Usually, the aqueous medium contains a neutralizing acid in order to neutralize the cationic epoxy resin and improve the dispersibility. The neutralizing acid is inorganic acid or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid, sulfamic acid, acetylglycine. The aqueous medium in this specification is water or a mixture of water and an organic solvent. It is preferable to use ion exchange water as water. Examples of organic solvents that can be used include hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers (For example, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (for example, Methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoester) Ether acetate, ethylene glycol monobutyl ether acetate) or mixtures thereof.

  The amount of blocked isocyanate curing agent must be sufficient to react with active hydrogen-containing functional groups such as primary, secondary amino groups, hydroxyl groups, etc. in the cationic epoxy resin during curing to give a good cured coating In general, it is generally 90/10 to 50/50, preferably in the range of 80/20 to 65/35 in terms of solid content weight ratio (epoxy resin / curing agent) of the cationic epoxy resin and the blocked isocyanate curing agent. is there. The amount of neutralizing acid is that which is sufficient to neutralize at least 20%, preferably 30-60%, of the cationic groups of the cationic epoxy resin.

  The organic solvent is necessary as a solvent when preparing each resin component such as a cationic epoxy resin and a blocked isocyanate curing agent, and complicated operation is required for complete removal. Moreover, when the organic solvent is contained in binder resin, the fluidity | liquidity of the coating film at the time of film forming will be improved, and the smoothness of a coating film will improve. As an organic solvent normally contained in a coating composition, said organic solvent is mentioned, for example.

  The lead-free cationic electrodeposition coating composition of the present invention preferably has an organic solvent content of 0.5% or less. The content of the organic solvent is more preferably 0.1 to 0.5%, and further preferably 0.1 to 0.4%. The lead-free cationic electrodeposition coating composition of the present invention has various advantages in that poor appearance of the coating film hardly occurs, the throwing power is excellent, and the content of the organic solvent is small.

  In addition to the above components, the lead-free cationic electrodeposition coating composition can contain commonly used coating additives such as a plasticizer, a surfactant, an antioxidant, and an ultraviolet absorber.

When an electrodeposition coating film having a thickness of 15 μm is formed using the lead-free cationic electrodeposition coating composition thus obtained, the film resistance of the electrodeposition coating film obtained is preferably 1000 to 1500 kΩ · cm ² . When the film resistance of the electrodeposition coating film is in the above range, the throwing power of the electrodeposition coating composition is more excellent.

Method for coating cationic electrodeposition composition The lead-free cationic electrodeposition coating composition is electrodeposited on an object to form an electrodeposition coating film. The material to be coated is not particularly limited as long as it is electrically conductive, and examples thereof include iron plates, steel plates, aluminum plates, those obtained by surface treatment thereof, and molded products thereof.

  Electrodeposition coating of the lead-free cationic electrodeposition coating composition is usually performed by applying a voltage of 50 to 450 V between the object to be coated as a cathode and the anode. When the applied voltage is less than 50V, electrodeposition is insufficient, and when it exceeds 450V, the coating film is destroyed and an abnormal appearance is obtained. At the time of electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

  The electrodeposition process consists of a process of immersing an object to be coated in a lead-free cationic electrodeposition coating composition, and a process of depositing a film by applying a voltage between the object to be coated as a cathode and an anode. The Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 4 minutes. After completion of the electrodeposition process, the cured coating film is obtained by baking as it is or after washing with water at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes. The obtained film thickness is preferably 5 to 80 μm, particularly preferably 15 to 25 μm as a cured coating film.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. Unless otherwise specified, “parts” represents parts by weight.

Production Example 1 Production of Blocked Isocyanate Curing Agent 1250 parts of diphenylmethane diisocyanate and 266.4 parts of methyl isobutyl ketone (hereinafter referred to as “MIBK”) were charged into a reaction vessel, heated to 80 ° C., and then 2.5 parts of dibutyltin dilaurate. Was added. A solution prepared by dissolving 226 parts of ε-caprolactam in 944 parts of butyl cellosolve was added dropwise at 80 ° C. over 2 hours. Furthermore, after heating at 100 degreeC for 4 hours, in the measurement of IR spectrum, it confirmed that the absorption based on an isocyanate group disappeared, and after standing to cool, MIBK 336.1 parts was added and the block isocyanate hardening | curing agent was obtained. The obtained blocked isocyanate curing agent had a Tg of 8 ° C.

Production Example 2 Production of amine-modified epoxy resin emulsion 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2) 35 in a flask equipped with a stirrer, cooling tube, nitrogen introduction tube, thermometer and dropping funnel Part, methyl isobutyl ketone (hereinafter abbreviated as MIBK) 94 parts and dibuciltin dilaurate 0.5 parts. While stirring the reaction mixture, 7 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 12 parts of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel. Further, 33 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60 ° C. to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Next, 383 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 266.

  Subsequently, when 90 parts of bisphenol A, 47 parts of octylic acid and 71 parts of dimer acid were added and reacted at 120 ° C., an epoxy equivalent of 1460 was obtained.

  The reaction product thus obtained was then cooled, and then 31 parts of diethanolamine and 39 parts of a 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Thereafter, it was diluted with MIBK to a non-volatile content of 88%. Thus, an amine-modified epoxy resin was obtained. The number average molecular weight (GPC method) of the obtained resin was 1750, and Tg was 25.1. The amine equivalent was 82 meq / 100 g. The content of the oxazolidone ring contained in the obtained amine-modified epoxy resin was 54% by weight, and the content of the saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety was 8% by weight.

  In addition, Tg of the amine-modified epoxy resin and the blocked isocyanate curing agent in the present specification was measured using DSC (Differential Scanning Calorimeter) Seiko Electronics Industry.

Production Example 3 Production of amine-modified epoxy resin emulsion 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2) 35 in a flask equipped with a stirrer, a condenser tube, a nitrogen introduction tube, a thermometer and a dropping funnel Part, methyl isobutyl ketone (hereinafter abbreviated as MIBK) 94 parts and dibuciltin dilaurate 0.5 parts. While stirring the reaction mixture, 7 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 12 parts of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel. Further, 33 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60 ° C. to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Next, 383 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 266.

  Subsequently, 74 parts of bisphenol A, 46 parts of octylic acid and 102 parts of dimer acid were added and reacted at 120 ° C., resulting in an epoxy equivalent of 1500.

  The obtained reaction product was then cooled, and then 30 parts of diethanolamine and 38 parts of a 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Thereafter, it was diluted with MIBK to a non-volatile content of 88%. Thus, an amine-modified epoxy resin was obtained. The number average molecular weight (GPC method) of the obtained resin was 1800, and Tg was 21.9. The amine equivalent was 80 meq / 100 g. The content of the oxazolidone ring contained in the obtained amine-modified epoxy resin was 52% by weight, and the content of the saturated or unsaturated hydrocarbon group-containing dicarbonyl moiety was 12% by weight.

Production Example 4 Production of Pigment Dispersion Resin Varnish To a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel, 382.20 parts of bisphenol A type epoxy resin (trade name DER-331J) having an epoxy equivalent of 188 Then, 111.98 parts of bisphenol A was weighed, heated to 80 ° C. and dissolved uniformly, and then 1.53 parts of a 1% solution of 2-ethyl-4-methylimidazole was added and reacted at 170 ° C. for 2 hours. . After cooling to 140 ° C., 196.50 parts of 2-ethylhexanol half-blocked isophorone diisocyanate (non-volatile content: 90%) was added thereto and reacted until the NCO group disappeared. To this was added 205.00 parts of dipropylene glycol monobutyl ether, followed by 408.00 parts of 1- (2-hydroxyethylthio) -2-propanol and 134.00 parts of dimethylolpropionic acid. 0.000 part was added and it was made to react at 70 degreeC. The reaction was continued until the acid value was 5 or less. The resulting resin varnish was diluted to 350.5% non-volatile content with 1150.50 parts of ion exchange.

Production Example 5 Production of Pigment Dispersion Paste 120 parts of pigment dispersion resin varnish obtained in Production Example 4 in a sand grind mill, 2.0 parts of carbon black, 100.0 parts of kaolin, 72.0 parts of titanium dioxide, dibutyltin oxide 8. 0 part, 18.0 parts of aluminum phosphomolybdate and 184 parts of ion-exchanged water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content 48%).

Production Example 6 Production of Blocked Isocyanate Curing Agent 168 parts of 1,6-hexamethylene diisocyanate and 73 parts of MIBK were charged into a reaction vessel and heated to 60 ° C., and then 0.2 part of dibutyltin laurate was added. A solution obtained by dissolving 34.6 parts of trimethylolpropane in 50 parts of MIBK was added dropwise at 60 ° C. for 2 hours. Subsequently, the temperature was raised to 70 ° C., and 106.7 parts of methyl ethyl ketoxime was added dropwise for 2 hours. In the measurement of IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 59.4 parts of MIBK was added to obtain a blocked isocyanate curing agent. The Tg of this blocked isocyanate curing agent was −20 ° C.

Production Example 7 Production of amine-modified epoxy resin emulsion having no dicarbonyl moiety 2,4- / 2,6-tolylene diisocyanate (weight ratio) was placed in a flask equipped with a stirrer, a condenser, a nitrogen inlet, a thermometer, and a dropping funnel. = 8/2) 38 parts, 93 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibuciltin dilaurate were charged. While stirring the reaction mixture, 7 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 13 parts of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel. Furthermore, 35 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60 ° C. to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Next, 406 parts of epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 266.

  Subsequently, when 125 parts of bisphenol A and 50 parts of octylic acid were added and reacted at 120 ° C., an epoxy equivalent of 1370 was obtained. The obtained reaction product was then cooled, and then 33 parts of diethanolamine and 41 parts of a 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Thereafter, it was diluted with MIBK to a non-volatile content of 88%. Thus, an amine-modified epoxy resin was obtained. The number average molecular weight (GPC method) of the obtained resin was 1650, and Tg was 38.7. The amine equivalent was 87 meq / 100 g, and the oxazolidone ring content contained in the amine-modified epoxy resin was 57% by weight.

  The amine-modified epoxy resin obtained in Production 7 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed so as to be uniform at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

Production Example 8 Production of amine-modified epoxy resin emulsion containing 5-mol adduct of bisphenol A-ethylene oxide 2,4- / 2,6-tolylene in a flask equipped with a stirrer, condenser, nitrogen inlet, thermometer and dropping funnel 36 parts of isocyanate (weight ratio = 8/2), 94 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibuciltin dilaurate were charged. While stirring the reaction mixture, 7 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 12 parts of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel. Further, 34 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60 ° C. to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Next, 406 parts of epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 266.

  Subsequently, 87 parts of bisphenol A, 47 parts of octylic acid, and 68 parts of a 5 mol bisphenol A-ethylene oxide adduct were added and reacted at 120 ° C., resulting in an epoxy equivalent of 1450. The reaction product thus obtained was then cooled, and then 31 parts of diethanolamine and 39 parts of a 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Thereafter, it was diluted with MIBK to a non-volatile content of 88%. Thus, an amine-modified epoxy resin was obtained. The number average molecular weight (GPC method) of the obtained resin was 1740, and Tg was 36.2. The amine equivalent was 83 meq / 100 g, and the oxazolidone ring content contained in the amine-modified epoxy resin was 54% by weight.

  The amine-modified epoxy resin obtained in Production 8 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed so as to be uniform at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

Example 1
The amine-modified epoxy resin obtained in Production Example 2 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed so as to be uniform at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  2358 parts of this emulsion and 315 parts of the pigment dispersion paste obtained in Production Example 5 and 2327 parts of ion-exchanged water were mixed to obtain a cationic electrodeposition composition having a solid content of 20% by weight.

Example 2
The amine-modified epoxy resin obtained in Production Example 3 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed so as to be uniform at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  2358 parts of this emulsion and 315 parts of the pigment dispersion paste obtained in Production Example 5 and 2327 parts of ion-exchanged water were mixed to obtain a cationic electrodeposition composition having a solid content of 20% by weight.

Comparative Example 1
The amine-modified epoxy resin emulsion having no dicarbonyl moiety obtained in Production Example 7 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed uniformly at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  2358 parts of this emulsion and 315 parts of the pigment dispersion paste obtained in Production Example 5 and 2327 parts of ion-exchanged water were mixed to obtain a cationic electrodeposition composition having a solid content of 20% by weight.

Comparative Example 2
The amine-modified epoxy resin emulsion having no dicarbonyl moiety obtained in Production Example 7 and the blocked isocyanate curing agent obtained in Production Example 6 were mixed uniformly at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  2358 parts of this emulsion and 315 parts of the pigment dispersion paste obtained in Production Example 5 and 2327 parts of ion-exchanged water were mixed to obtain a cationic electrodeposition composition having a solid content of 20% by weight.

Comparative Example 3
The amino-modified epoxy emulsion containing the bisphenol A-ethylene oxide 5-mol adduct obtained in Production Example 8 and the blocked isocyanate curing agent obtained in Production Example 1 were mixed so as to be uniform at a solid content ratio of 70/30. Glacial acetic acid was added so that the milligram equivalent of acid (MEQ (A)) was 30 per 100 g of resin solid content, and ion-exchanged water was slowly added to dilute this. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  2358 parts of this emulsion and 315 parts of the pigment dispersion paste obtained in Production Example 5 and 2327 parts of ion-exchanged water were mixed to obtain a cationic electrodeposition composition having a solid content of 20% by weight.

  Using the cationic electrodeposition coating compositions obtained in Examples and Comparative Examples, evaluation was performed by the following method.

The organic solvent content was measured by adjusting the coating material using ethylene glycol monohexyl ether so that the coating voltage was 200 V at a bath temperature of 30 ° C. The amount of organic solvent contained in the adjusted coating was measured using GC (Gas Chromatography) GC-14A manufactured by Shimadzu Corporation.

Film Resistance of Electrodeposition Coating Film An electrodeposition bath containing a cationic electrodeposition coating composition obtained in each Example and Comparative Example was applied to a zinc phosphate-treated steel sheet (JIS G 3141 SPCC-SD, Surfdyne SD-2500 (Japan). Treatment (made by Paint Co., Ltd.)) (dimensions: 70 mm × 150 mm, thickness 0.7 mm) was immersed in an electrodeposition paint by 10 cm. A voltage was applied to the steel sheet, the voltage was increased to 200 V over 30 seconds, and electrodeposition was performed for 150 seconds. The coating voltage with a coating thickness of 15 μm at a bath temperature of 30 ° C. and the residual current at the end of electrodeposition were measured to calculate the coating resistance value (kΩ · cm ² ). The results are shown in Tables 1 and 2.

Throwing power The throwing power was evaluated by a so-called four-sheet box method. That is, as shown in FIG. 1, four zinc phosphate-treated steel plates (treated with JIS G3141 SPCC-SD, Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.)) 11-14 are in a standing state. A box 10 was prepared, which was arranged in parallel with an interval of 20 mm, and the bottom and bottom surfaces of both sides were sealed with an insulator such as cloth adhesive tape. In addition, the steel plates 11 to 13 other than the steel plate 14 are provided with an 8 mmφ through hole 15 at the bottom.

  4 liters of cationic electrodeposition paint was transferred to a vinyl chloride container to form a first electrodeposition bath. As shown in FIG. 2, the box 10 was immersed in an electrodeposition paint container 20 containing an electrodeposition paint 21 as an object to be coated. In this case, the paint 21 enters the box 10 only from each through hole 15.

  The coating material 21 was stirred with a magnetic stirrer (not shown). And each steel plate 11-14 was electrically connected and the counter electrode 22 was arrange | positioned so that the distance with the nearest steel plate 11 might be set to 150 mm. A voltage was applied with each steel plate 11-14 as a cathode and the counter electrode 22 as an anode, and cationic electrodeposition was applied to the steel plate. The coating is boosted to a voltage at which the film thickness of the coating film formed on the A-side of the steel plate 11 reaches 15 μm within 5 seconds from the start of application, and then the voltage is 175 seconds for normal electrodeposition and 115 seconds for short-time electrodeposition. It was performed by maintaining.

  Each steel sheet after painting is washed with water, baked at 170 ° C. for 25 minutes, and after air cooling, the film thickness of the coating film formed on the A surface of the steel sheet 11 closest to the counter electrode 22 and the farthest from the counter electrode 22 The film thickness of the coating film formed on the G surface of the steel plate 14 was measured, and the throwing power was evaluated by the ratio (G / A value) of film thickness (G surface) / film thickness (A surface). When this value exceeds 60%, it is good, and when this value is 60% or less, it can be judged as defective. The results are shown in Tables 1 and 2.

A zinc phosphate-treated steel sheet (JIS G 3141 SPCC-SD, Surfdyne SD-2500 (manufactured by Nippon Paint Co., Ltd.)) was applied to the electrodeposition bath containing the cationic electrodeposition coating composition obtained in the dry unevenness examples and comparative examples. Treatment) (dimensions: 70 mm × 150 mm, thickness 0.7 mm) was immersed in an electrodeposition paint by 10 cm. A voltage was applied to the steel sheet, the voltage was increased to 200 V over 30 seconds, and electrodeposition was performed for 150 seconds. After electrodeposition coating, the object to be coated pulled up from the electrodeposition bath in the stainless steel container is left to dry on the liquid surface for 180 seconds, washed with water, and heated and cured at 170 ° C. for 25 minutes. It was prepared and visually evaluated according to the following criteria.
○: No dry unevenness occurred.
Δ: Some unevenness of drying occurred.
X: Drying unevenness occurred remarkably.

  From the results of the examples, it was confirmed that the cationic electrodeposition coating composition of the present invention was excellent in throwing power and hardly caused uneven drying. In particular, the cationic electrodeposition coating composition of the present invention has a smaller amount of organic solvent contained in the electrodeposition coating composition than that of the comparative example, as can be seen from the examples. The electrodeposition coating composition of the present invention has the advantages that the amount of the organic solvent is small, the throwing power is excellent, and uneven drying is unlikely to occur.

  According to the present invention, it is possible to provide a cationic electrodeposition coating composition that is lead-free and has a low organic solvent content and has a low environmental load. This cationic electrodeposition coating composition further has an advantage that it has excellent throwing power, is less likely to cause unevenness in drying, and is less likely to cause poor coating appearance.

It is a perspective view which shows an example of the box used when evaluating throwing power. It is sectional drawing which shows typically the evaluation method of throwing power.

Explanation of symbols

10: Box,
11-14: Zinc phosphate-treated steel sheet,
15: through hole,
20: Electrodeposition coating container,
21: Electrodeposition paint
22: Counter electrode.

Claims (9)

A method for producing an amine-modified epoxy resin contained in a cationic electrodeposition coating composition comprising the following steps:
A block process in which a diisocyanate compound and a blocking agent are reacted to obtain a half-blocked isocyanate;
A block prepolymer preparation step of obtaining a block prepolymer by reacting the obtained half-blocked isocyanate with a polyol;
An oxazolidone ring production step of obtaining an oxazolidone ring-containing epoxy resin by reacting the obtained block prepolymer with a diglycidyl ether type epoxy resin;
The obtained epoxy resin is chain-extended using at least a saturated or unsaturated hydrocarbon group-containing dicarboxylic acid, a chain extension step, and the amine obtained by the chain extension step is amine-modified.
Manufacturing method.   The manufacturing method of Claim 1 whose epoxy equivalent of the diglycidyl ether type epoxy resin used in the said oxazolidone ring production | generation process is 150-1000.   The manufacturing method of Claim 1 or 2 whose epoxy equivalent of the oxazolidone ring containing epoxy resin obtained by the said oxazolidone ring production | generation process is 800-3000.   The manufacturing method in any one of Claims 1-3 whose Tg of the said amine modified epoxy resin is 18-35 degreeC.   The manufacturing method in any one of Claims 1-4 whose content of the oxazolidone ring containing glycidyl ether part in the said amine modified epoxy resin is 30 to 70 weight%.   The manufacturing method in any one of Claims 1-5 whose content of the saturated or unsaturated hydrocarbon group containing dicarbonyl part in the said amine modified epoxy resin is 3 to 17 weight%.   A lead-free cationic electrodeposition coating composition comprising an amine-modified epoxy resin obtained by the production method according to claim 1.   The lead-free cationic electrodeposition coating composition according to claim 7, wherein the amount of the organic solvent contained in the lead-free cationic electrodeposition coating composition is 0.5% or less. The lead-free cationic electrodeposition coating composition according to claim 7 or 8, wherein the film resistance of an electrodeposition coating film having a thickness of 15 µm obtained from the lead-free cationic electrodeposition coating composition is 1000 to 1500 kΩ · cm ² .

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