Cationic electrodeposition coating composition

Abstract

Provided is a cationic electrodeposition coating material which does not require high-temperature sintering and drying in which CO2 is not required to be discharged in an electrodeposition coating step, and which hardly generates volatile components when a coating film is dried, and which has extremely excellent anti-rust properties. The cationic electrodeposition coating composition contains at least two different emulsions in a mixed state, and is characterized in that: one of these emulsions is an emulsion (A) of an amine-modified epoxy resin containing a primary amino group or a secondary amino group; and the other is an emulsion (B) of an epoxy compound that does not contain a primary amino group and a secondary amino group and contains two or more epoxy groups in one molecule. Also provided are a method for producing the coating composition and a coating method using the coating composition.

Description

Technical Field

[0001] The present invention relates to a cationic electrodeposition coating composition which does not require high-temperature sintering and drying to discharge CO2 in the electrodeposition coating process, generates almost no volatile matter when the coating film is dried, and has extremely excellent rust resistance. Background Art

[0002] As for cationic electrodeposition coating, since it has excellent coating workability and can obtain high-performance antirust coating, it has been widely used in automobile parts, industrial products, etc. using metal raw materials such as iron and aluminum. The reason why cationic electrodeposition coating is an excellent antirust coating is that, in its main components, an amino-containing epoxy resin (base) with a high Tg, a blocked isocyanate resin (curing agent) and a curing catalyst for forming a firm three-dimensional cross-linked coating are used, and then a rust-proof metal (rust-proof pigment) is matched. The coated article is sintered in a high-temperature drying furnace above about 140°C, and the antirust coating is completed. As for high-temperature drying furnaces, gas furnaces are the mainstream. As for CO2 produced by gas combustion, it is considered a problem as a greenhouse gas and is expected to be reduced. In addition, the blocking agent in the curing agent is detached and volatilized during sintering, so in the factory equipment, a large load is imposed on the purification treatment for discharge into the atmosphere, which can also be raised as an environmental issue.

[0003] As a technology that does not require high-temperature sintering and drying, for example, a method of using a low-temperature curable blocked isocyanate resin as a curing agent can be cited. As an example of this method, in Patent Document 1, a method of using a blocked isocyanate curing agent in which isocyanates are blocked with oxime compounds and pyrazole compounds is disclosed, but depending on the type of isocyanate combined, sometimes low-temperature curing and long-term stability of the coating cannot be taken into account. For these blocking agents, they are practically limited to combinations with aliphatic isocyanates, so the sintering and drying conditions are 110 to 120°C, staying at relatively high temperature conditions. In addition, most of these blocking agents become volatiles and are discharged outside the coating film.

[0004] Furthermore, as a technology that does not require high-temperature sintering and drying, a technology that utilizes an oxidative polymerization reaction of a room-temperature curing type can also be cited. For example, as in Patent Document 2, an anionic electrodeposition coating based on a fatty acid-modified acrylic resin is well known, and in its examples, forced drying at 80° C. for 30 minutes is shown, but the reaction rate is very slow, and the degree of crosslinking is not too high.

[0005] For room temperature drying type electrodeposition coatings, for example, as in Patent Document 3, a technology has been proposed in which a component with excellent rust prevention properties is dried at room temperature to fix it. However, this technology does not have a three-dimensional cross-linking type curing mechanism, so it is difficult to exert rust prevention performance at a level comparable to that of the current high-temperature sintering curing coating film.

[0006] In addition, for the purpose of lowering the temperature of the sintering conditions and improving the rust resistance, Patent Document 4 discloses a method of spraying a resin solution containing α,β-unsaturated carbonyl groups on a cationic electrodeposition coating (undried coating) by using Michael addition reaction for crosslinking reaction to improve the function of the coating. In this method, the electrodeposition coating contains primary or secondary amino groups, and the coating hardness is increased by utilizing the crosslinking reaction of Michael addition reaction with α,β-unsaturated carbonyl groups on the resin solution side to improve the coating performance. However, this reaction occurs only on the surface portion of the electrodeposition coating in contact with the resin solution, so the effect of improving the hardness of the coating is small. As shown in the example of the coating performance under the sintering condition of 150°C, sintering and drying at high temperature is required, and active lowering of the temperature cannot be achieved.

[0007] As a technique that also uses the Michael addition reaction for a crosslinking reaction, Patent Document 5 discloses a technique that separately produces an emulsified product of an amine-modified epoxy resin having a primary or secondary amino group and an emulsified product of a compound having an α,β-unsaturated carbonyl group, and mixes them to form an electrodeposition coating composition, thereby improving the hardness of the entire coating film compared to the method of Patent Document 4, and eliminating the need for sintering and drying at a high temperature. In the technique of Patent Document 5, an amine-modified epoxy resin having a high Tg is used as a main component, and the main component is firmly three-dimensionally crosslinked by a crosslinking reaction using the Michael addition reaction, so that a coating film with excellent rust resistance can be obtained. However, in recent years, with the improvement of the performance level in the industry, further improvement of rust resistance is required.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Re-Publication No. 2017 / 138445

[0011] Patent Document 2: Japanese Patent Application Publication No. 2003-277679

[0012] Patent Document 3: Japanese Patent No. 6398025

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 63-137777

[0014] Patent Document 5: Japanese Patent Application Publication No. 2021-138842 Summary of the invention

[0015] Problems to be solved by the invention

[0016] The present invention was conceived in view of the current status of the above-mentioned prior art, and its purpose is to provide a cationic electrodeposition coating that is a high-temperature sintering and drying cationic electrodeposition coating that does not require CO2 to be discharged during the electrodeposition coating process, produces almost no volatile matter when the coating film is dried, and has extremely excellent rust resistance.

[0017] Means for solving problems

[0018] The present inventors have conducted intensive research to achieve the above-mentioned purpose, and as a result, found that in a cationic electrodeposition coating composition that uses a Michael addition reaction for a crosslinking reaction as in Patent Document 5, it is also important to control the speed of the Michael addition reaction that constitutes the crosslinking reaction. If the speed of the Michael addition reaction that constitutes the crosslinking reaction is too high, the coating film is cured in a short time, and the rust resistance of the obtained coating film may become insufficient. Further, it was found that the speed of the crosslinking reaction can be controlled by changing the type of the group that reacts with the amino group. It was also found that by selecting an "epoxy group" instead of an "α, β-unsaturated carbonyl group" as in Patent Document 5 as the group that reacts with the amino group, the speed of the crosslinking reaction can be reduced to a suitable range, and the curing time of the coating film can be extended to a suitable range, compared with the case where an "α, β-unsaturated carbonyl group" as in Patent Document 5 is selected, and as a result, the rust resistance of the obtained coating film can be further improved.

[0019] The present invention has been accomplished based on the above-mentioned findings and has the following structures (1) to (10).

[0020] (1) A cationic electrodeposition coating composition comprising at least two different emulsions in a mixed state, wherein one of the emulsions is an emulsion (A) of an amine-modified epoxy resin containing a primary amino group or a secondary amino group, and the other is an emulsion (B) of an epoxy compound containing no primary amino group or a secondary amino group and containing two or more epoxy groups in one molecule.

[0021] (2) A cationic electrodeposition coating composition according to (1), characterized in that the emulsion (A) contains 1.40 to 3.35 milliequivalents of NH groups of primary or secondary amino groups per 1 g of its solid content, and the emulsion (B) contains 1.60 to 9.20 milliequivalents of epoxy groups per 1 g of its solid content, and further, the emulsion (A) and the emulsion (B) are mixed so that the reaction sites between these functional groups are in the range of 0.95 to 2.25 milliequivalents per 1 g of the total solid content of the emulsion (A) and the emulsion (B).

[0022] (3) The cationic electrodeposition coating composition according to (1), further comprising a basic catalyst and / or an organic metal compound catalyst as a curing catalyst.

[0023] (4) The cationic electrodeposition coating composition according to (1), further comprising a pigment dispersion paste.

[0024] (5) A coating method characterized by comprising the steps of: immersing a metal substrate in the cationic electrodeposition coating composition according to any one of (1) to (4) to perform electrodeposition coating, followed by low temperature drying at 80°C or less.

[0025] (6) A method for producing a cationic electrodeposition coating composition, which is a method for producing a cationic electrodeposition coating composition, characterized in that the method comprises: a step of preparing at least two different emulsions, and a step of mixing these emulsions, one of these emulsions is an emulsion (A) of an amine-modified epoxy resin containing a primary amino group or a secondary amino group, and the other is an emulsion (B) of an epoxy compound that does not contain a primary amino group or a secondary amino group and contains two or more epoxy groups in one molecule.

[0026] (7) A method for producing a cationic electrodeposition coating composition according to (6), characterized in that the emulsion (A) contains 1.40 to 3.35 milliequivalents of NH groups of primary or secondary amino groups per 1 g of its solid content, and the emulsion (B) contains 1.60 to 9.20 milliequivalents of epoxy groups per 1 g of its solid content, and further, the emulsion (A) and the emulsion (B) are mixed so that the reaction sites between these functional groups are in the range of 0.95 to 2.25 milliequivalents per 1 g of the total solid content of the emulsion (A) and the emulsion (B).

[0027] (8) The method for producing a cationic electrodeposition coating composition according to (6), further comprising the step of adding a basic catalyst and / or an organic metal compound catalyst as a curing catalyst to the mixed emulsion and mixing the mixture.

[0028] (9) The method for producing a cationic electrodeposition coating composition according to (6), further comprising: a step of preparing a pigment dispersion paste; and a step of adding the pigment dispersion paste to the mixed emulsion and mixing the mixture.

[0029] (10) A coating method characterized in that a metal substrate is immersed in a cationic electrodeposition coating composition produced by any one of the methods (6) to (9) to perform electrodeposition coating, followed by low-temperature drying at 80°C or less.

[0030] Effects of the Invention

[0031] As for the cationic electrodeposition coating composition of the present invention, the speed of the crosslinking reaction is controlled within a suitable range by the appropriate selection of the type of the reactive group, and the curing time of the coating film is extended to a suitable range, so that a coating film with extremely excellent rust resistance can be obtained. In addition, since a coating film with sufficiently high hardness can be obtained even if high-temperature sintering and drying is not required, the combustion amount of the coal gas in the drying furnace can be suppressed, and the CO2 discharge amount can be reduced. In addition, since a sealing agent is not used, no by-product (detached component) accompanying the curing reaction is produced, and the load of the exhaust gas treatment equipment can also be reduced. DETAILED DESCRIPTION

[0032] The cationic electrodeposition coating composition of the present invention comprises an emulsion (A) of an amine-modified epoxy resin containing a primary amino group or a secondary amino group, and an emulsion (B) of an epoxy compound containing no primary amino group or a secondary amino group and containing two or more epoxy groups in one molecule as main components, and contains these components in a mixed state. In the present invention, its essential feature is that by selecting an "epoxy group" as a counterpart group in the emulsion (B) that reacts with the amino group in the emulsion (A), the speed of the crosslinking reaction is reduced to a suitable range, the curing time of the coating film is extended to a suitable range, and as a result, the rust resistance of the obtained coating film is further improved.

[0033] [Emulsion of amine-modified epoxy resin containing primary or secondary amino group (A)]

[0034] Among the components constituting the above-mentioned resin, the epoxy skeleton is a polycondensate of a glycidyl ether of a polyphenol having two epoxy groups per molecule and two phenolic hydroxyl groups in one molecule. Preferred polyphenols include resorcinol, hydroquinone, 2,2-bis-(4-hydroxyphenyl)-propane, 4,4'-dihydroxybenzophenone, 1,1-bis-(4-hydroxyphenyl)-methane, 1,1-bis-(4-hydroxyphenyl)-ethane, 4,4'-dihydroxybiphenyl, etc., and 2,2-bis-(4-hydroxyphenyl)-propane and so-called bisphenol A are particularly preferred. In addition, the glycidyl ether of a diol having two alcoholic hydroxyl groups in one molecule can also be used in combination with the glycidyl ether of the above-mentioned polyphenol. Preferred diols include low molecular weight diols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, and 1,4-cyclohexanediol, and oligomer diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, but are not limited thereto.

[0035] As for the epoxy terminal in the epoxy skeleton, since it is basically aminated, in order to contain a primary amino group, a ketimine compound obtained by reacting ethylaminoethylamine, N-(aminoethyl)ethanolamine, diethylenetriamine, etc., which have one secondary amino group and one or more primary amino groups in one molecule, with a ketone compound such as methyl ethyl ketone and methyl isobutyl ketone, is used, and the secondary amino group contained in the compound is added to the epoxy group. As for the ketiminated part, the primary amino group is easily hydrolyzed and regenerated by the water used when the resin is emulsified, so an amine-modified epoxy resin containing a primary amino group is completed. In addition, in order to contain a secondary amino group, a method of reacting one of the two active hydrogens of the primary amino group with, for example, monoepoxy, monoisocyanate, etc. to convert it into a secondary amino group can be cited. According to this method, the ratio of the primary amino group to the secondary amino group in the epoxy resin can be varied in various ways.

[0036] When the concentration of primary and secondary amino groups in epoxy resin is to be reduced, reducing the amount of the above-mentioned ketimine compound is also a method. However, if a large amount of epoxy groups are left, the primary amino groups regenerated due to the small amount of water in the resin may react with the epoxy groups, thereby damaging the stability of the resin. In order to prevent this, as required, an amine compound having one active hydrogen in one molecule, a compound having one carboxyl group in one molecule, a compound having one phenolic hydroxyl group in one molecule, etc. can be added to a part of the epoxy groups to block the epoxy groups. If general compounds are briefly exemplified, as amine compounds having one active hydrogen in one molecule, N-methylethanolamine, diethanolamine, etc. can be listed, as compounds having one carboxyl group in one molecule, acrylic acid, linoleic acid, etc. can be listed, as compounds having one phenolic hydroxyl group in one molecule, 4-tert-butylphenol, 4-octylphenol, etc. can be listed, but they are not limited to these.

[0037] The number average molecular weight of such amine-modified epoxy resin is preferably 1500 to 3500. If the number average molecular weight is less than the lower limit, the resin becomes soft and the rust resistance of the coating may be reduced, while if the number average molecular weight exceeds the upper limit, the resin becomes hard and the coating surface may not be smooth.

[0038] The emulsion (A) of the amine-modified epoxy resin can be prepared by adding a neutralizing acid to the amine-modified epoxy resin to form an emulsion. Examples of the neutralizing acid include acetic acid, lactic acid, formic acid, propionic acid, methanesulfonic acid, and aminosulfonic acid. Furthermore, a known solvent or plasticizer may be added to form an emulsion as required.

[0039] The concentration of the NH groups of the primary or secondary amino groups in the emulsion (A) is preferably 1.40 to 3.35 milliequivalents per 1 g of the solid content of the emulsion (A), and more preferably 1.45 to 3.30 milliequivalents. If the concentration of the NH groups of the primary or secondary amino groups in the emulsion (A) is less than the above lower limit, the curing property of the coating film is insufficient and the rust resistance of the coating film may be reduced. If it exceeds the above upper limit, the conductivity of the emulsion is excessively enhanced, it is difficult to control the electrodeposition deposition property, and the uniformity of the coating film may be reduced.

[0040] [Emulsion (B) of epoxy compound containing no primary or secondary amino group and containing two or more epoxy groups in one molecule]

[0041] The epoxy compound containing no primary and secondary amino groups and containing two or more epoxy groups in one molecule is not particularly limited. In order to fully ensure the reactivity with amines, a compound having a benzene ring structure in the main chain such as bisphenol A type epoxy resin is preferred. More preferably, the epoxy group is a multifunctional and low molecular weight compound. If such a compound is used, the functional group can be adjusted to a high concentration, and the number of reaction sites for cross-linking increases, so that the coating becomes stronger and it is easy to ensure good rust resistance.

[0042] Specifically, as an epoxy compound that does not contain a primary amino group and a secondary amino group and has two or more epoxy groups in one molecule, for example, a compound obtained by reacting a polyphenol compound with epichlorohydrin can be used. As the above-mentioned polyphenol compound, for example, bis(4-hydroxyphenyl)2,2-propane [bisphenol A], bis(4-hydroxyphenyl)methane [bisphenol F], bis(4-hydroxycyclohexyl)methane [hydrogenated bisphenol F], 2,2-bis(4-hydroxycyclohexyl)propane [hydrogenated bisphenol A], 4,4′-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-3-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetrakis(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4′-dihydroxydiphenyl sulfone, etc. can be listed.

[0043] In addition, glycidyl ether-type epoxy compounds such as ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,2-propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butylene glycol diglycidyl ether, diglycidyl ether, and neopentyl glycol diglycidyl ether may also be mentioned. Compared with the epoxy compounds obtained by the reaction of the above-mentioned polyphenol compounds and epichlorohydrin, the reactivity with amines may be lowered, so it is preferably used together with the epoxy compounds obtained by the reaction of the above-mentioned polyphenol compounds and epichlorohydrin.

[0044] Examples of epoxy compounds containing an average of more than 2 epoxy groups include 4,4′-methylenebis(N,N-diglycidylaniline)-4-(2,3-epoxypropane-1-yloxy)-N,N-bis(2,3-epoxypropane-1-yl)-2-methylaniline, 1,3-bis(oxiranylmethoxy)-2-propanol, tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, tetraglycidylphenylenediamine, triglycidylaminophenol, triglycidylaminocresol, phenol novolac-type epoxy, cresol novolac-type epoxy and the like.

[0045] Representative examples of the material of the epoxy compound include the compounds described above, but are not limited thereto, and two or more of these may be used in combination.

[0046] It should be noted that the epoxy compound containing no primary and secondary amino groups and containing more than two epoxy groups in one molecule does not have an amino group, unlike the amine-modified epoxy resin containing primary or secondary amino groups in the emulsion (A). Therefore, it cannot be emulsified by adding a neutralizing acid alone. Therefore, an auxiliary component for emulsification is required. As an example of the auxiliary component, a tertiary amine epoxy resin with a tertiary amino group at the epoxy end can be cited. The resin is blended with the epoxy compound containing no primary and secondary amino groups and containing more than two epoxy groups in one molecule, and a neutralizing acid is added, thereby enabling emulsification. As for the epoxy skeleton of the tertiary amine epoxy resin, it is a polycondensate of a glycidyl ether of a polyphenol having two epoxy groups per molecule and two phenolic hydroxyl groups in one molecule, and preferably a tertiary amine epoxy resin using bisphenol A. In addition, in terms of emulsification and rust resistance, it is preferred that the epoxy end is from an alkanolamine having a hydroxyl group such as N-methylethanolamine and diethanolamine. In the manufacturing process of tertiary amine epoxy resin, these amines react with epoxy groups to become tertiary amines, and active hydrogen disappears, so the obtained tertiary amine epoxy resin does not have reactivity with epoxy groups. Therefore, even if the tertiary amine epoxy resin is blended with an epoxy compound that does not contain primary and secondary amino groups and contains more than two epoxy groups in one molecule, it will not react with the epoxy groups in the epoxy compound and is stable. As neutralizing acid, acetic acid, lactic acid, formic acid, propionic acid, methanesulfonic acid, aminosulfonic acid, etc. can be listed as emulsion (A). Furthermore, as needed, known solvents and plasticizers can be added to emulsify.

[0047] An emulsifier may be used in place of the above-mentioned tertiary amine type epoxy resin to prepare an emulsion. Examples of the emulsifier include cationic emulsifiers and nonionic emulsifiers. Two or more of these may also be mixed and used. In addition, in the case of a compound having multiple epoxy groups in one molecule, an emulsion having the same function may be prepared by reacting a part of the compound with an amine so that the remaining epoxy groups are two or more per molecule.

[0048] The concentration of epoxy groups in the emulsion (B) is preferably 1.60 to 9.20 milliequivalents per 1 g of solid content of the emulsion (B). The lower limit of the concentration of epoxy groups in the emulsion (B) is more preferably 1.90 milliequivalents, further preferably 2.50 milliequivalents, and particularly preferably 3.00 milliequivalents. On the other hand, the upper limit of the concentration of epoxy groups in the emulsion (B) is more preferably 9.15 milliequivalents, further preferably 9.00 milliequivalents, and particularly preferably 8.80 milliequivalents. If the concentration of epoxy groups in the emulsion (B) is less than the above lower limit, the curing property of the coating film is insufficient and the rust resistance of the coating film may be reduced. On the other hand, when the concentration of epoxy groups in the emulsion (B) exceeds the above upper limit, it is limited to increasing the proportion of the epoxy group-containing compound (insoluble component) in the emulsion (B) and reducing the proportion of the tertiary amine type epoxy resin mixed as an auxiliary component for emulsification, but it may become difficult to ensure the stability of the emulsion (B).

[0049] [Curing catalyst]

[0050] As for the cationic electrodeposition coating composition of the present invention, in order to promote the addition reaction of the amine in the emulsion (A) of the amine-modified epoxy resin and the epoxy in the emulsion (B) of the epoxy compound, it is preferred to further contain a basic catalyst and / or an organic metal compound catalyst as a curing catalyst. As the basic catalyst, specifically, alkali metal hydroxides, alkali metal carbonates, quaternary ammonium compounds, tertiary amine compounds, guanidine compounds, amidine compounds, tertiary phosphine compounds, phosphazene compounds, tertiary sulfonium compounds, quaternary phosphonium compounds, and imidazole compounds can be listed. As the organic metal compound catalyst, cobalt octanoate, manganese octanoate, zinc octanoate, zirconium octanoate, acetylacetone complex of cobalt, acetylacetone complex of zinc, acetylacetone complex of zirconium, etc. There is no particular limitation on the type of the above-mentioned curing catalyst, and one type can be used alone or two or more types can be used in combination. Organic tin compounds such as dibutyltin dilaurate and dioctyltin oxide can also be used to function as a catalyst, but since their toxicity has been considered a problem in recent years, regulations on their use have been studied, and they are preferably not used in the cationic electrodeposition coating composition of the present invention.

[0051] [Cationic electrodeposition coating composition]

[0052] The cationic electrodeposition coating composition of the present invention is prepared by preparing an emulsion (A) and an emulsion (B) separately and mixing these emulsions. As for the mixing ratio of the emulsion (A) and the emulsion (B) constituting the cationic electrodeposition coating composition of the present invention, it is preferred that the reaction sites of the primary amino group or secondary amino group brought by the emulsion (A) and the epoxy group brought by the emulsion (B) are in the range of 0.95 to 2.25 milliequivalents per 1g of the total solid content of the emulsion (A) and the emulsion (B), and more preferably in the range of 1.00 to 2.20 milliequivalents. If the amount of the reaction sites is less than the above lower limit, the reaction sites are insufficient, the curing property cannot be fully exerted, and the rust resistance may be reduced. In addition, if the amount of the reaction sites exceeds the above upper limit, the reaction sites become excessive, the curing speed becomes excessively fast, and the fluidity of the coating film may be reduced.

[0053] [Pigment dispersion paste]

[0054] In the cationic electrodeposition coating composition of the present invention, in addition to the emulsion (A), the emulsion (B) and the curing catalyst, a dispersion paste of pigments such as a body pigment and a rust-proof pigment can also be added as needed. The resin used to disperse the pigment can be a well-known resin, and the tertiary amine type in which the amine-modified epoxy resin is neutralized with formic acid, acetic acid, lactic acid, aminosulfonic acid, methanesulfonic acid, etc., and the quaternary ammonium salt type in which the epoxy terminal is quaternized can be used. Kaolin, talc, aluminum silicate, calcium carbonate, mica, clay, silicon dioxide, etc. can be used in the body pigment, carbon black, titanium white, red iron oxide, etc. can be used in the coloring pigment, and zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, bismuth compounds, etc. can be used in the rust-proof pigment. In addition, surfactants such as defoamers and surface tension regulators can be used without special restrictions as long as they are also well-known substances. It should be noted that when adding a pigment dispersion paste, the solid content is preferably in the range of 15 to 55 parts by mass relative to 100 parts by mass of the total solid content. A solvent can also be added, but since the cationic electrodeposition coating composition of the present invention is mainly dried at low temperatures, if used in large quantities, the solvent does not separate from the coating film, which may damage the curability of the coating film. In addition, the large-scale use of a solvent is not preferred from the environmental perspective in terms of the large-scale discharge of the solvent into the atmosphere.

[0055] In order to use the cationic electrodeposition coating composition of the present invention for coating, it is sufficient to immerse the metal coating object in the cationic electrodeposition coating composition manufactured as described above and perform electrodeposition coating. As the metal coating object, for example, automobile parts and industrial products using metal raw materials such as iron and aluminum can be used as the object. In addition, there is no particular limitation on the conditions for electrodeposition coating, and it can be carried out according to conventional methods. As for the coating film formed by the cationic electrodeposition coating composition of the present invention, since it has a sufficiently high hardness, it is not necessary to carry out sintering and drying at a high temperature of more than 140°C as in the past for further curing, and it is sufficient to use drying at a low temperature of about 80°C or less for removing moisture.

[0056] Example

[0057] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto. "Parts" in the Examples refer to parts by mass, and "%" refers to % by mass.

[0058] Preparation of raw materials

[0059] Production of amine-modified epoxy resin (R-1) containing primary or secondary amino groups

[0060] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 277 parts of bisphenol A diglycidyl ether with an epoxy equivalent of 187, 512 parts of polypropylene glycol diglycidyl ether with an epoxy equivalent of 300, 257 parts of bisphenol A, 55 parts of methyl isobutyl ketone, and 0.4 parts of tributylamine were placed, and the temperature was started to rise while stirring. After keeping the temperature at 150°C for 7 hours, 295 parts of methyl isobutyl ketone were added while cooling to 90°C. Next, 203 parts of a ketimine compound (70% concentration) synthesized in advance from ethylaminoethylamine and methyl isobutyl ketone were added, and after keeping the temperature at 100°C for 5 hours, the mixture was cooled to 70°C to obtain an amine-modified epoxy resin (R-1) containing primary or secondary amino groups with a solid content of 70%. The number average molecular weight of the resin was 2406. In addition, the content of primary or secondary amino groups (NH groups) in the resin was 1.50 milliequivalents per 1g of solid content.

[0061] Production of amine-modified epoxy resin (R-2) containing primary or secondary amino groups

[0062] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 275 parts of bisphenol A diglycidyl ether with an epoxy equivalent of 187, 509 parts of polypropylene glycol diglycidyl ether with an epoxy equivalent of 300, 256 parts of bisphenol A, 54 parts of methyl isobutyl ketone, and 0.4 parts of tributylamine were placed, and the temperature was started to rise while stirring. After keeping the temperature at 150°C for 7 hours, 236 parts of methyl isobutyl ketone were added while cooling to 90°C. Next, 107 parts of a ketimine compound (70% concentration) synthesized in advance from ethylaminoethylamine and methyl isobutyl ketone and 167 parts of a ketimine compound (70% concentration) synthesized in advance from diethylenetriamine and methyl isobutyl ketone were added in sequence, and after keeping the temperature at 100°C for 5 hours, the mixture was cooled to 70°C to obtain an amine-modified epoxy resin (R-2) containing primary or secondary amino groups and having a solid content of 70%. The number average molecular weight of the resin was 2422. The content of primary or secondary amino groups (NH groups) in the resin was 2.35 milliequivalents per 1 g of solid content.

[0063] Production of amine-modified epoxy resin (R-3) containing primary or secondary amino groups

[0064] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 274 parts of bisphenol A diglycidyl ether with an epoxy equivalent of 187, 507 parts of polypropylene glycol diglycidyl ether with an epoxy equivalent of 300, 255 parts of bisphenol A, 54 parts of methyl isobutyl ketone, and 0.4 parts of tributylamine were placed, and the temperature was started to rise while stirring. After keeping the temperature at 150°C for 7 hours, 173 parts of methyl isobutyl ketone was added while cooling to 90°C. Next, 351 parts of a ketimine compound (70% concentration) synthesized in advance from diethylenetriamine and methyl isobutyl ketone was added, and after keeping the temperature at 100°C for 5 hours, it was cooled to 70°C to obtain an amine-modified epoxy resin (R-3) containing primary or secondary amino groups with a solid content of 70%. The number average molecular weight of the resin was 2436. In addition, the content of primary or secondary amino groups (NH groups) in the resin was 3.26 milliequivalents per 1g of solid content.

[0065] Preparation of emulsion (A)

[0066] Preparation of emulsions E1 to E3

[0067] Three types of emulsions (A) E1 to E3 were prepared according to the raw material formulations described in Table 1. The specific steps are as follows.

[0068] In a stainless steel beaker equipped with a stirrer and a thermometer, a prescribed amount of the amine-modified epoxy resin (R-1), (R-2), or (R-3) produced as described above, which is an amine-modified epoxy resin containing a primary or secondary amino group, is placed, and the temperature is raised while stirring. Next, a 70% aqueous solution of methanesulfonic acid is added as a neutralizing acid, and after keeping the temperature at 70°C for 1 hour, the heating is stopped, and deionized water is slowly added to emulsify. The container is not covered, and stirring is continued at room temperature for 48 hours, and the volatilized portion is filled with deionized water to obtain emulsions E1 to E3 with a solid content of 15.0%.

[0069] [Table 1]

[0070]

[0071] ※The values ​​in the table indicate mass [g].

[0072] Preparation of emulsion (B)

[0073] Production of Emulsions E4 to E6

[0074] Three types of emulsions (E4 to E6) were prepared as emulsions (B) according to the raw material formulations described in Table 2. The specific procedures are as follows.

[0075] In a stainless steel beaker equipped with a stirrer and a thermometer, a predetermined amount of (i) bisphenol A diglycidyl ether (epoxy group content: 5.35 milliequivalents per 1 g of solid content), (ii) 4-(2,3-epoxypropane-1-yloxy)-N,N-bis(2,3-epoxypropane-1-yl)-2-methylaniline (epoxy group content: 10.31 milliequivalents per 1 g of solid content), or (iii) novolac-modified epoxy resin (epoxy group content: 5.49 milliequivalents per 1 g of solid content), which is an epoxy compound containing no primary or secondary amino groups and containing two or more epoxy groups in one molecule, was placed, and a tertiary amine type epoxy resin (T-1) produced as described below was added as an auxiliary component for emulsification, and the temperature was started to rise under stirring. Next, a 70% aqueous solution of methanesulfonic acid was added as a neutralizing acid, and the mixture was kept at 70°C for 1 hour, then the heating was stopped and deionized water was slowly added to emulsify the mixture. The container was not covered and stirring was continued at room temperature for 48 hours, and the evaporated portion was filled with deionized water to obtain emulsions E4 to E6 with a solid content of 15.0%.

[0076] Production of tertiary amine epoxy resin (T-1) (auxiliary component for emulsification)

[0077] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 493 parts of bisphenol A diglycidyl ether with an epoxy equivalent of 187, 267 parts of polypropylene glycol diglycidyl ether with an epoxy equivalent of 300, 265 parts of bisphenol A, 71 parts of methyl isobutyl ketone, and 0.3 parts of tributylamine were placed, and the temperature was started to rise while stirring. After keeping the temperature at 150°C for 3 hours, 241 parts of methyl isobutyl ketone was added while cooling to 90°C. Next, 120 parts of diethanolamine was added, and after keeping the temperature at 100°C for 2 hours, the temperature was cooled to 70°C to obtain a tertiary amine type epoxy resin (T-1) with a solid content of 70%.

[0078] Preparation of Emulsion E7

[0079] Emulsion E7 is an example in which auxiliary components for emulsification are not required by using (iv) a tertiary amine epoxy resin (S-1) based on a novolac-modified epoxy resin as an epoxy compound having no primary or secondary amino groups and having two or more epoxy groups in one molecule.

[0080] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 519 parts of a novolac-modified epoxy resin (the content of epoxy groups is 5.49 milliequivalents per 1g of solid content) and 257 parts of methyl isobutyl ketone were placed, and the temperature began to rise while stirring. 81 parts of diethanolamine were added at 90°C, and after keeping the temperature at 100°C for 2 hours, the temperature was cooled to 60°C to obtain a tertiary amine type epoxy resin (S-1) in which amine was added to a part of 70% of the solid content. Next, a 70% aqueous solution of methanesulfonic acid was added as a neutralizing acid, and after keeping the temperature at 70°C for 1 hour, the heating was stopped, and deionized water was slowly added to emulsify. The container was not covered, and stirring was continued at room temperature for 48 hours. The volatile part was filled with deionized water to obtain an emulsion E7 with a solid content of 15.0%.

[0081] [Table 2]

[0082]

[0083] ※The values ​​in the table indicate mass [g].

[0084] Preparation of All-in-One Emulsion E8 (for Comparative Example)

[0085] As a comparative example, the highly reactive amine-modified epoxy resin containing primary or secondary amino groups and the compound containing no primary or secondary amino groups and containing two or more epoxy groups in one molecule were not prepared separately as emulsion (A) and emulsion (B), but the two components were mixed from the beginning to prepare an integrated emulsion (emulsion E8) existing in the same emulsion. The specific steps are as follows.

[0086] In a stainless steel beaker equipped with a stirrer and a thermometer, a predetermined amount of the raw materials listed in Table 3 was placed and stirring was started. Next, a 70% aqueous solution of methanesulfonic acid was added as a neutralizing acid, and after keeping the temperature at 30°C for 1 hour, deionized water was slowly added to emulsify. The container was not covered, and stirring was continued at room temperature for 48 hours, and the volatilized portion was filled with deionized water to obtain an emulsion E8 with a solid content of 15.0%.

[0087] Preparation of a compound containing two or more α,β-unsaturated carbonyl groups in one molecule and emulsion E9 (compared to Manufacturing of

[0088] As a comparative example, a compound containing two or more α,β-unsaturated carbonyl groups in one molecule was prepared in place of the epoxy group in the compound contained in the emulsion (B), and emulsion E9 was prepared using the compound.

[0089] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 602 parts of polymeric MDI (trade name: Sumizu 44V-20L) and 480 parts of methyl isobutyl ketone were placed, and the temperature was raised under stirring. 518 parts of 2-hydroxyethyl acrylate was added dropwise at 60-80°C, and after the addition was completed, the temperature was kept at 85°C for 5 hours to obtain a compound containing α,β-unsaturated carbonyl groups with a solid content of 70%. The content of α,β-unsaturated carbonyl groups in the compound was 3.98 milliequivalents per 1g of solid content.

[0090] Furthermore, 686 parts of the compound containing an α,β-unsaturated carbonyl group were placed in a stainless steel beaker equipped with a stirrer and a thermometer, and 171 parts of the compound (T-1) of Preparation Example 4 were added as an auxiliary component for emulsification, and the temperature was started to rise under stirring. Next, 13 parts of a 70% aqueous solution of methanesulfonic acid were added as a neutralizing acid, and after keeping the temperature at 70°C for 1 hour, the heating was stopped, and deionized water was slowly added to emulsify. The container was not covered, and stirring was continued at room temperature for 48 hours, and the volatilized part was filled with deionized water to obtain an emulsion E9 with a solid content of 15.0%.

[0091] [Table 3]

[0092]

[0093] ※The values ​​in the table indicate mass [g].

[0094] Production of pigment dispersion paste

[0095] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 518 parts of bisphenol A diglycidyl ether with an epoxy equivalent of 187, 45 parts of polypropylene glycol diglycidyl ether with an epoxy equivalent of 300, 221 parts of bisphenol A, and 1.6 parts of dimethylbenzylamine were placed, and the temperature was raised under stirring. After keeping the temperature at 150°C for 4 hours, 550 parts of butyl cellosolve were added while cooling to 70°C. Next, 87 parts of dimethylethanolamine and 177 parts of a 50% aqueous solution of lactic acid were added, and the temperature was kept at 80°C for 2 hours to obtain a quaternary ammonium salt type pigment dispersion resin with a solid content of 60%.

[0096] Place 1952 parts of deionized water in a container, and add 1193 parts of the above-mentioned pigment dispersion resin, 711 parts of kaolin, 928 parts of titanium oxide, 36 parts of carbon black, and 108 parts of bismuth oxide in sequence under stirring. The product uniformly mixed at room temperature for 1 hour is dispersed using a bead mill until the dispersed particle size becomes less than 15 μm, thereby obtaining a pigment dispersion paste with a solid content of 53%.

[0097] (Examples 1 to 10, Comparative Examples 1 to 3)

[0098] Cationic electrodeposition coating compositions of Examples 1 to 10 and Comparative Examples 1 to 3 were prepared according to the formulations described in Tables 4 to 6. The specific procedures are as follows.

[0099] Predetermined amounts of the emulsions E1 to E9 prepared as described above were weighed in a container and uniformly mixed. Furthermore, the pigment dispersion paste prepared as described above was added to Example 10. Thus, a total of 13 cationic electrodeposition coating compositions were obtained.

[0100] The obtained cationic electrodeposition coating composition was used to coat the metal object by the following steps to prepare a test plate. The test plate was used to evaluate the coating surface smoothness, curability and rust resistance by the following steps. In addition, the obtained cationic electrodeposition coating composition was used to evaluate the bath stability by the following steps. These results are shown in Tables 4 to 6 together with the coordination and characteristics of the coating composition.

[0101] "Preparation of test panels"

[0102] A cold rolled steel sheet (70×150×0.8 mm in size) treated with zinc phosphate was immersed in a bath of a cationic electrodeposition coating composition adjusted to a liquid temperature of 28°C, and the coating was performed by adjusting the voltage so that the coating film thickness would be 15 μm. After coating, the steel sheet was washed with water and dehydrated and dried at 80°C for 20 minutes for use in the test.

[0103] "Surface smoothness"

[0104] The Ra value of the test plate was measured with a cutoff of 2.5 using a surface tester (SJ-301) manufactured by Midoyo Co., Ltd. and evaluated according to the following criteria: Evaluations A to C were considered acceptable, and D was considered unacceptable.

[0105] A: Ra value is 0.30 μm or less.

[0106] B: Ra value is greater than 0.30 μm and less than 0.40 μm.

[0107] C: The Ra value is larger than 0.40 μm, but there are no uniform uncoated portions (obvious defects).

[0108] D: Ra value is larger than 0.40 μm, and there are uneven uncoated areas (obvious defects).

[0109] "Curing (friction)"

[0110] The test plate was reciprocated 10 times with a load of 1 kg using absorbent cotton soaked in MIBK, and the state of the absorbent cotton and the coating film was evaluated according to the following criteria: Evaluations A to C were considered acceptable, and D was considered unacceptable.

[0111] A: The coating film was not dissolved at all.

[0112] B: The coating film was slightly dissolved, and a few flaws were generated.

[0113] C: The coating film was dissolved and the gloss of the rubbed portion was reduced.

[0114] D: The coating film is almost completely dissolved.

[0115] "Rust resistance"

[0116] A cutter was used to form a cross cut that reached the base of the test plate, and a salt spray tester (SST, 5% salt water, 35°C) was used for 840 hours to measure the corrosion width (rust width and expansion width) from the cross cut part and evaluate according to the following standards. Evaluations A to C were considered acceptable, and D was considered unacceptable.

[0117] A: The maximum corrosion width is less than 3 mm from the cut portion on one side.

[0118] B: The maximum corrosion width is greater than 3 mm and less than 4 mm from the cut portion on one side.

[0119] C: The maximum corrosion width is greater than 4 mm and less than 5 mm from the cut portion on one side.

[0120] D: The maximum corrosion width is greater than 5 mm from the cut portion on one side.

[0121] "Bath stability"

[0122] The cationic electrodeposition coating composition sealed in a container was stirred continuously at 30°C for 30 days, and the mass of the residue (agglomerate) when filtered through a 325-mesh metal net was measured and evaluated according to the following criteria: A to C were considered acceptable, and D was considered unacceptable.

[0123] A: The mass of the residue is less than 1.0 mg / L.

[0124] B: The mass of the residue is greater than 1.0 mg / L and less than 2.0 mg / L.

[0125] C: The mass of the residue is greater than 2.0 mg / L and less than 3.0 mg / L.

[0126] D: The mass of the residue was greater than 3.0 mg / L and the aggregates also adhered to the container and the stirring blade.

[0127]

[0128] [Table 5]

[0129]

[0130] "Supplement to the contents of Tables 4 and 5"

[0131] ※ The units of the NH group concentration and epoxy group concentration, and the reaction sites between NH groups and epoxy groups shown in the properties are "meq / g-solid content" (milliequivalent per 1g of solid content).

[0132] * The reaction sites of NH groups and epoxy groups shown in the items of characteristics correspond to at least one of the NH group concentration and the epoxy group concentration in (A+B).

[0133] [Table 6]

[0134]

[0135] "Supplement to the contents of Table 6"

[0136] ※ The units of the NH group concentration and C=C group concentration, and the reaction sites between NH groups and C=C groups shown in the properties are "meq / g-solid content" (milliequivalent per 1 g of solid content).

[0137] * The reaction sites of NH groups and C=C groups shown in the item of characteristics correspond to at least one of the NH group concentration and the C=C group concentration in (A+B).

[0138] As shown in Table 4, in Examples 1 to 10 that meet the essential features of the present invention, the two components of the highly reactive amine-modified epoxy resin containing primary or secondary amino groups and the compound containing no primary or secondary amino groups and containing two or more epoxy groups in one molecule are divided into emulsion (A) and emulsion (B) for coordination, so even if sintering and drying at high temperature is not performed after the coating film is formed, an excellent coating film with a qualified level of coating surface smoothness, curability and rust resistance can be obtained, and the bath stability as a coating composition is also excellent. In contrast, in Comparative Example 1 of Table 5, the two components of the highly reactive amine-modified epoxy resin containing primary or secondary amino groups and the compound containing no primary or secondary amino groups and containing two or more epoxy groups in one molecule are mixed and allowed to exist in the same emulsion, so although the curability is excellent, the coating surface smoothness and rust resistance are unqualified, and the solution stability as a coating composition is also unqualified. In Comparative Examples 2 and 3 in Table 6, although a compound containing an α,β-unsaturated carbonyl group was used instead of the epoxy group of the compound containing no primary or secondary amino group and containing two or more epoxy groups in one molecule, the rust prevention properties were very poor compared with Examples 1 to 10 and were unqualified in terms of rust prevention properties.

[0139] Industrial Applicability

[0140] As for the cationic electrodeposition coating composition of the present invention, since the speed of the crosslinking reaction is controlled to a suitable range and the curing time of the coating film is extended to a suitable range by the appropriate selection of the type of the reactive group, a coating film with extremely excellent rust resistance can be obtained. In addition, since a coating film with sufficiently high hardness can be obtained without the need for high-temperature sintering and drying, the combustion amount of the coal gas in the drying furnace can be suppressed and the CO2 discharge can be reduced. In addition, since a sealing agent is not used, no by-product (detached component) accompanying the curing reaction is produced, and the load of the exhaust gas treatment equipment can also be reduced. Therefore, the present invention is extremely useful.

Claims

1. A cationic electrodeposition coating composition comprising at least two or more different emulsions in a mixed state, characterized in that: One of these emulsions is an emulsion (A) of an amine-modified epoxy resin containing a primary or secondary amino group, and the other is an emulsion (B) of an epoxy compound containing no primary or secondary amino group and containing two or more epoxy groups in one molecule.

2. The cationic electrodeposition coating composition according to claim 1, characterized in that: Emulsion (A) contains 1.40 to 3.35 milliequivalents of NH groups of primary or secondary amino groups per 1 g of its solid content, and emulsion (B) contains 1.60 to 9.20 milliequivalents of epoxy groups per 1 g of its solid content. Furthermore, emulsion (A) and emulsion (B) are mixed so that the reaction sites between these functional groups are in the range of 0.95 to 2.25 milliequivalents per 1 g of the total solid content of emulsion (A) and emulsion (B).

3. The cationic electrodeposition coating composition according to claim 1, characterized in that: A basic catalyst and / or an organic metal compound catalyst is also contained as a curing catalyst.

4. The cationic electrodeposition coating composition according to claim 1, characterized in that: Also contains pigment dispersion paste.

5. A coating method, characterized in that: The cationic electrodeposition coating composition according to any one of claims 1 to 4 is used to immerse a metal substrate for electrodeposition coating, followed by low-temperature drying at 80°C or less.

6. A method for producing a cationic electrodeposition coating composition, characterized in that: The method comprises: a step of preparing at least two different emulsions, and a step of mixing these emulsions, wherein one of the emulsions is an emulsion (A) of an amine-modified epoxy resin containing a primary amino group or a secondary amino group, and the other is an emulsion (B) of an epoxy compound containing no primary amino group or a secondary amino group and containing two or more epoxy groups in one molecule.

7. The method for producing a cationic electrodeposition coating composition according to claim 6, characterized in that: Emulsion (A) contains 1.40 to 3.35 milliequivalents of NH groups of primary or secondary amino groups per 1 g of its solid content, and emulsion (B) contains 1.60 to 9.20 milliequivalents of epoxy groups per 1 g of its solid content. Furthermore, emulsion (A) and emulsion (B) are mixed so that the reaction sites between these functional groups are in the range of 0.95 to 2.25 milliequivalents per 1 g of the total solid content of emulsion (A) and emulsion (B).

8. The method for producing a cationic electrodeposition coating composition according to claim 6, characterized in that: The method further comprises the step of adding a basic catalyst and / or an organic metal compound catalyst as a curing catalyst to the mixed emulsion and mixing the mixture.

9. The method for producing a cationic electrodeposition coating composition according to claim 6, characterized in that: The method further includes the steps of preparing a pigment dispersion paste and adding the pigment dispersion paste to the mixed emulsion and mixing the mixture.

10. A coating method, characterized in that: The method comprises: immersing a metal substrate in the cationic electrodeposition coating composition produced by the method according to any one of claims 6 to 9 to perform electrodeposition coating, followed by low temperature drying at 80°C or less.

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