JP2006137866A - Lead-free cationic electrocoating material composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free cationic electrocoating material composition capable of providing a coated film having excellent rust preventative properties and formed on the surface of a base material. <P>SOLUTION: The lead-free cationic electrocoating material composition contains a zinc polyphosphate, a cationic epoxy resin and a blocked isocyanate curing agent. The content of the zinc polyphosphate is 7-50 pts.wt. based on 100 pts.wt. solid component of the coating material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lead-free cationic electrodeposition coating composition that can form a coating film excellent in rust prevention on the surface of a substrate.

  Steel sheets such as hot-rolled steel sheets and cold-rolled steel sheets are widely used as industrial materials because of their excellent workability. These steel plates are iron and cause rust. Therefore, in applications requiring corrosion resistance such as automobile applications, galvanized steel sheets subjected to galvanizing treatment, zinc-nickel plated steel sheets subjected to zinc-nickel plating treatment, and the like are used. However, due to the recent economic situation, reduction of raw material costs is becoming an important issue, and therefore, the use of untreated steel sheets, which are cheaper in terms of cost, has been considered.

  By the way, a plurality of coating films having various roles are formed on the surface of a substrate such as an automobile to protect the substrate and at the same time give a beautiful appearance. Such a plurality of coating films include electrodeposition coating films. An electrodeposition coating film is a coating film coated on a conductive substrate, and is mainly provided to improve the corrosion resistance and rust prevention properties of the substrate.

  Until now, an electrodeposition coating composition has been added with a corrosion resistance imparting agent containing lead 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, and in particular, the surface of an untreated steel sheet is electrodeposited with a lead-free electrodeposition coating composition. The material is inferior in corrosion resistance.

  Japanese Unexamined Patent Publication No. 2001-2997 (Patent Document 1) discloses a cationic electrodeposition resin containing a resin for cationic electrodeposition coating (A), a hydrotalcite-based solid solution (B), and a bismuth-containing compound (C). The paint is described. This cationic electrodeposition paint is excellent in rust prevention even when applied to an untreated steel sheet, and can form a good coating film such as edge rust prevention, throwing power, chemical resistance and smoothness. Are listed. However, this does not necessarily have a satisfactory level of performance.

  JP 2001-329221 A (Patent Document 2) discloses a resin for cationic electrodeposition coating (A), a condensed aluminum phosphate and / or a zinc compound (B), and aluminum oxide and / or aluminum hydroxide (C). A cationic electrodeposition paint characterized in that it contains is described. According to the examples in this document, zinc oxide is used as the zinc compound. Here, aluminum hydroxide treatment is further performed on a material obtained by subjecting aluminum tripolyphosphate particles to silica and zinc oxide treatment. This is because the amount of zinc contained in zinc oxide is small compared to the present invention, and the rust prevention effect is insufficient.

JP 2001-2997 A JP 2001-329221 A

  An object of the present invention is to solve the above-described problems of the prior art. More specifically, the present invention provides a lead-free cationic electrodeposition coating composition capable of forming a coating film excellent in rust prevention on the surface of a substrate (particularly, an untreated steel sheet). Is an issue.

The present invention
Zinc polyphosphate,
A cationic epoxy resin, and a blocked isocyanate curing agent,
A lead-free cationic electrodeposition coating composition comprising:
This zinc polyphosphate provides a lead-free cationic electrodeposition coating composition containing 7 to 50 parts by weight with respect to 100 parts by weight of the solid content of the coating, thereby achieving the above object.

  The zinc polyphosphate is a cationic electrodeposition in such an amount that the concentration of zinc ions becomes 100 to 400 ppm when 0.3 g of a cured electrodeposition coating film obtained by the cationic electrodeposition coating composition is immersed in 100 ml of an aqueous solution having a pH of 4 or less. It is preferably contained in the coating composition.

  Furthermore, the lead-free cationic electrodeposition coating composition of the present invention can be used for electrodeposition coating of untreated steel sheets.

  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 electrodeposition coating composition of the present invention has excellent rust prevention performance. The electrodeposition coating composition of the present invention can impart high antirust properties despite the absence of lead-containing corrosion resistance imparting agents. In particular, the electrodeposition coating composition of the present invention can impart high rust resistance to an untreated steel sheet that has not been subjected to galvanization. By electrodeposition-coating the electrodeposition coating composition of the present invention on an untreated steel plate, it is possible to impart rust prevention equivalent to that obtained when electrodepositing a galvanized steel plate. The electrodeposition coating composition of the present invention offers the possibility of replacing galvanized steel sheets with untreated steel sheets.

  First, the process leading to the present invention will be described. Zinc plating is known as a means for preventing iron rust. This is because zinc has a higher ionization tendency than iron, and therefore, when iron and zinc are brought into contact with each other, zinc starts to melt in the presence of water, and iron corrosion is prevented. Based on this knowledge, the present inventors obtained the same effect as when using a galvanized steel sheet by electrodeposition coating an electrodeposition coating composition containing zinc oxide powder on an untreated steel sheet. I thought it would be possible. However, when an attempt was made to add the amount of zinc oxide required to obtain these effects into the electrodeposition coating composition, problems occurred in the stage of preparing the pigment dispersion paste. Specifically, since zinc oxide is highly eluted by a neutralizing acid, zinc was eluted at the stage of preparing the pigment dispersion paste, resulting in thickening of the pigment dispersion paste, and the properties of the paint were no longer achieved.

  As a result of repeated researches, the present inventors have been able to eliminate the above-mentioned defective events related to paint preparation by using zinc polyphosphate, and further to obtain a cured electrodeposition coating film obtained by a cationic electrodeposition coating composition. By containing this zinc polyphosphate in the cationic electrodeposition coating composition in such an amount that the concentration of zinc ions is 100 to 400 ppm when immersed in 100 ml of an aqueous solution having a pH of 4 or less, 3 g of rust prevention of the electrodeposition coating is achieved. It was found that the property can be further improved.

  The present invention has found that by including zinc polyphosphate in an electrodeposition coating composition, high antirust property can be imparted even when electrodeposited on an untreated steel sheet. This has found the possibility of replacing the galvanized steel sheet with an untreated steel sheet. Hereinafter, the present invention will be described.

  The lead-free cationic electrodeposition coating composition of the present invention is an electrodeposition coating composition in which a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent is dispersed and dissolved in an aqueous medium. The electrodeposition coating composition generally contains a neutralizing acid, an organic solvent, a pigment, a curing catalyst and the like in addition to the binder resin. The lead-free cationic electrodeposition coating composition of the present invention is characterized by containing zinc polyphosphate.

Zinc polyphosphate Zinc polyphosphate is a compound mainly composed of a condensed phosphate metal salt. Among them, the condensed phosphoric acid constituting the condensed phosphoric acid metal salt is a general term for linear polymer phosphoric acid (pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, etc.) generated by dehydration condensation of orthophosphoric acid. And general formula P _n O _{3n + 1} (wherein n is an integer of 2 or more). Zinc polyphosphate can be prepared from a condensed metal phosphate metal salt and zinc oxide. Commercial products may also be used. Examples of commercially available products that can be used include ZP-SB, ZP-50S, and ZP-HS (manufactured by Kikuchi Color Co., Ltd.).

  By the way, generally the pigment mix | blended with a coating material also contains a zinc compound. In the present invention, zinc compounds such as zinc oxide are classified as pigments.

  The zinc polyphosphate is preferably contained in the cationic electrodeposition coating composition of the present invention in such an amount that the lower limit is 7 parts by weight and the upper limit is 50 parts by weight with respect to 100 parts by weight of the coating solid content. The lower limit is more preferably 10 parts by weight, and even more preferably 20 parts by weight. When the content of this zinc polyphosphate is less than 7 parts by weight, the effect (corrosion resistance) due to the addition of zinc polyphosphate is insufficient. Moreover, when content of zinc polyphosphate exceeds 50 weight part, there exists a possibility that the malfunction of the performance fall by the deterioration of a coating-film external appearance may arise.

  Furthermore, the zinc polyphosphate used in the present invention has a zinc ion concentration of 100 to 400 ppm when 0.3 g of a cured electrodeposition coating film obtained by the cationic electrodeposition coating composition is immersed in 100 ml of an aqueous solution having a pH of 4 or less. Is preferably included in the cationic electrodeposition coating composition. As a result, zinc ions eluted in a corrosive environment effectively exhibit a corrosion inhibiting action. If the concentration of zinc ions is less than 100 ppm, the corrosion inhibition effect may be insufficient. In addition, the immersion conditions in this specification are defined as the case where it immerses in 55 degreeC water for 72 hours.

  This zinc polyphosphate may be added in the form of a paste in the same manner as the pigment when producing a pigment paste used for the preparation of the electrodeposition coating composition. Alternatively, the zinc polyphosphate paste may be prepared individually in the same manner as the pigment paste and added to the electrodeposition coating composition.

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

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

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

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

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

  Particularly preferred epoxy resins are oxazolidone ring-containing epoxy resins. This is because a coating film having excellent heat resistance and corrosion resistance and further excellent impact resistance can be obtained.

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

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

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

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

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

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, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) , Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethylcyclo Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretoimine, burette and / or isocyanurate modified product); 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 a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

  As the blocking agent, those usually used such as ε-caprolactam and butyl cellosolve can be used. However, among these, many volatile blocking agents are regulated as targets of HAPs, and it is preferable that the amount used is minimized.

Pigment The cationic electrodeposition coating composition of the present invention may contain a commonly used pigment. Examples of pigments that can be used include colored pigments such as titanium white, carbon black and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; iron phosphate, calcium phosphate, molybdic acid Examples include rust preventive pigments such as aluminum, calcium molybdate and aluminum phosphomolybdate.

  When these pigments are used, they are generally contained in the electrodeposition coating composition in an amount of 1 to 35 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the solid content of the electrodeposition coating composition. . However, since the zinc polyphosphate used in the present invention is a solid component and can be considered as a pigment replacement, the amount of the pigment contained in the electrodeposition coating composition of the present invention is reduced.

  In the cationic electrodeposition coating composition of the present invention, the total pigment concentration including the above-mentioned zinc polyphosphate and the pigment is generally 7 to 50 parts by weight with respect to 100 parts by weight of the solid content of the electrodeposition coating composition. Preferably, it is 10-45 weight part, More preferably, it is 20-45 weight part. If the total pigment concentration is less than 7 parts by weight, sufficient performance may not be obtained. Moreover, when the total pigment concentration exceeds 50 parts by weight, the appearance of the coating film may be deteriorated.

  However, when the electrodeposition paint of the present invention is a lead-free cationic electrodeposition paint, corrosion resistance imparting agents containing lead, for example, lead such as basic lead silicate, basic lead sulfate, red lead, and cyanamide lead The anticorrosive pigment should not be used or should be used in such an amount that the lead ion concentration of the diluted paint (added to the electrodeposition bath) is 100 ppm or less. This is because when the lead ion concentration is high, the load on the environment is large.

Pigment-dispersed paste It is desirable that the above-mentioned zinc polyphosphate and, if necessary, the pigment are dispersed in an aqueous solvent at a high concentration in advance to prepare a paste. This is because zinc polyphosphate and the pigment are 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 zinc polyphosphate and an optional pigment together with a pigment dispersion resin varnish in an aqueous solvent. 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 solvent, ion-exchanged water or water containing a small amount of alcohol is used. In general, the pigment-dispersed resin is used in an amount of 20 to 100 parts by weight based on 100 parts by weight of the total pigment including zinc polyphosphate and an optional 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. A dispersion paste can be obtained.

Curing catalyst Examples of the curing catalyst used in the present invention include dibutyltin oxide, dioctyltin oxide, monobutyltin oxide, and mixtures thereof. Dibutyltin oxide is preferable. These curing catalysts act as catalysts for the blocking agent dissociation of the blocked isocyanate curing agent.

  The curing catalyst is blended in an amount of 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the resin solid content in the electrodeposition paint.

Preparation of lead-free cationic electrodeposition coating composition The lead-free cationic electrodeposition coating composition of the present invention comprises a pigment dispersion paste containing the above-described curing catalyst, cationic epoxy resin, blocked isocyanate curing agent, and zinc polyphosphate. It can be prepared by dispersing in an aqueous medium. Further, the aqueous medium usually contains a neutralizing acid in order to neutralize the cationic epoxy resin and improve the dispersibility of the binder resin emulsion. The neutralizing acid is an inorganic or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The amount is an amount that achieves a neutralization rate of at least 20%, preferably 30-60%.

  As a method of blending a cationic epoxy resin and a blocked isocyanate as a curing agent and dispersing them in an aqueous medium, there is a method of mixing a cationic isocyanate with a cationic epoxy resin in a solution state to form an emulsion.

  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 expressed as 90/10 to 50 / in solid weight ratio (epoxy resin / curing agent) of a cationic epoxy resin (sulfonium-modified epoxy resin and / or amine-modified epoxy resin) and a blocked isocyanate curing agent. 50, preferably in the range of 80/20 to 65/35.

  The organic solvent is necessary as a solvent when synthesizing resin components such as a cationic epoxy resin, a blocked isocyanate curing agent, and a pigment dispersion resin, 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.

  Examples of the organic solvent usually contained in the coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethyl hexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monophenyl ether and the like.

  In addition to the above, the coating composition may contain conventional coating additives such as a plasticizer, a surfactant, an antioxidant, and an ultraviolet absorber.

  The cationic electrodeposition coating composition of the present invention 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.

  Especially the electrodeposition coating material composition of this invention can provide high rust prevention property with respect to an untreated steel plate. Therefore, the cationic electrodeposition coating composition of the present invention can also be used as a cationic electrodeposition coating composition for electrodeposition-coating an untreated steel sheet. Examples of the untreated steel plate include a hot rolled steel plate and a cold rolled steel plate. In addition, the term “no treatment” in the present invention refers to a steel plate that has not been subjected to a plating treatment such as a hot dip galvanizing treatment or an electrogalvanizing treatment.

  Electrodeposition coating 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 includes a process of immersing an object to be coated in a cationic electrodeposition coating composition, and a process of applying a voltage between the object to be coated as a cathode and an anode to deposit a film. Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 4 minutes.

  The film thickness of the electrodeposition coating film is preferably 5 to 25 μm, more preferably 20 μm. When the film thickness is less than 5 μm, the rust prevention property is insufficient, and when it exceeds 25 μm, the paint is wasted.

  The electrodeposition coating film obtained as described above is cured by baking at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water.

  The present invention will be described in detail by the following examples, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Production Example 1 Production of Blocked Isocyanate Curing Agent 199 parts of hexamethylene diisocyanate trimer (Coronate HX: manufactured by Nippon Polyurethane Co., Ltd.) and methyl in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel 32 parts of isobutyl ketone and 0.03 part of dibutyltin dilaurate were weighed out, and 87.0 parts of methyl ethyl ketoxime was added dropwise from the dropping funnel over 1 hour while stirring and bubbling nitrogen. The temperature was increased from 50 ° C. to 70 ° C. Thereafter, the reaction was continued for 1 hour, and the reaction was continued until the absorption of the NCO group disappeared with an infrared spectrometer. Thereafter, 0.74 parts of n-butanol and 39.93 parts of methyl isobutyl ketone were added to obtain a nonvolatile content of 80%.

Production Example 2 Production of amine-modified epoxy resin emulsion In a flask equipped with a stirrer, a cooler, a nitrogen injection tube and a dropping funnel, 71.34 parts of 2,4 / 2,6-tolylene diisocyanate (80/20 wt%), Methyl isobutyl ketone (111.98 parts) and dibutyltin dilaurate (0.02 parts) were weighed out and 14.24 parts of methanol was added dropwise from a dropping funnel over 30 minutes while stirring and nitrogen bubbling. The temperature was raised from room temperature to 60 ° C. due to heat generation. Thereafter, the reaction was continued for 30 minutes, and then 46.98 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from the dropping funnel over 30 minutes. The temperature was raised to 70 to 75 ° C. due to heat generation. After continuing the reaction for 30 minutes, 41.25 parts of bisphenol A propylene oxide (5 mol) adduct (BP-5P manufactured by Sanyo Chemical Industries, Ltd.) was added, the temperature was raised to 90 ° C., and the IR spectrum was measured. The reaction was continued until the NCO group disappeared.

  Subsequently, 475.0 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 475 (YD-7011R manufactured by Toto Kasei Co., Ltd.) was added and dissolved uniformly, and then the temperature was raised from 130 ° C. to 142 ° C. To remove water from the reaction system. After cooling to 125 ° C., 1.107 parts of benzyldimethylamine was added to carry out an oxazolidone ring formation reaction by a demethanol reaction. The reaction was continued until an epoxy equivalent of 1140.

  Thereafter, the mixture was cooled to 100 ° C., 24.56 parts of N-methylethanolamine, 11.46 parts of diethanolamine and 26.08 parts of aminoethylethanolamine ketimine (78.8% methyl isobutyl ketone solution) were added, and 110 ° C. for 2 hours. Reacted. Thereafter, 20.74 parts of ethylene glycol mono-2-ethylhexyl ether and 12.85 parts of methyl isobutyl ketone were added to dilute to adjust to 82% non-volatile matter. The number average molecular weight (GPC method) was 1380, and the amine equivalent was 94.5 meq / 100 g.

  In another container, 145.11 parts of ion-exchanged water and 5.04 parts of acetic acid were weighed, and 320.11 parts of the amine-modified epoxy resin heated to 70 ° C. (75.0 parts as a solid content) and Production Example 1 A mixture of 190.38 parts of a blocked isocyanate curing agent (25.0 parts as a solid content) was gradually added dropwise and stirred to disperse uniformly. Thereafter, ion exchange water was added to adjust the solid content to 36%.

Production Example 3 Production of Pigment Dispersion Resin Varnish To a flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer and a 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 uniformly dissolved, 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.

Example 1
In a sand grind mill, 100 parts of the pigment-dispersed resin varnish obtained in Production Example 3, 100 parts of zinc polyphosphate (ZP-SB, manufactured by Kikuchi Color Co., Ltd.), and 70 parts of ion-exchanged water are put to a particle size of 10 μm or less. Until dispersed. Thus, a pigment dispersion paste could be obtained without increasing the viscosity.

  To 100 parts of the cationic epoxy resin emulsion obtained in Production Example 2, 20 parts of the pigment dispersion paste was added and mixed. Furthermore, 0.6 parts of dibutyltin oxide and 110 parts of ion-exchanged water were added to obtain a cationic electrodeposition coating composition. The content of zinc polyphosphate with respect to 100 parts by weight of the solid content of the paint was 16 parts by weight.

Example 2
In a sand grind mill, 100 parts of the pigment-dispersed resin varnish obtained in Production Example 3, 100 parts of zinc polyphosphate (ZP-SB, manufactured by Kikuchi Color Co., Ltd.), and 70 parts of ion-exchanged water are put to a particle size of 10 μm or less. Until dispersed. Thus, a pigment dispersion paste could be obtained without increasing the viscosity.

  To 100 parts of the cationic epoxy resin emulsion obtained in Production Example 2, 40 parts of the pigment dispersion paste was added and mixed. Furthermore, 0.6 parts of dibutyltin oxide and 144 parts of ion-exchanged water were added to obtain a cationic electrodeposition coating composition. The content of zinc polyphosphate with respect to 100 parts by weight of the solid content of the paint was 26 parts by weight.

Example 3
In a sand grind mill, 100 parts of the pigment-dispersed resin varnish obtained in Production Example 3, 100 parts of zinc polyphosphate (ZP-SB, manufactured by Kikuchi Color Co., Ltd.), and 70 parts of ion-exchanged water are put to a particle size of 10 μm or less. Until dispersed. Thus, a pigment dispersion paste could be obtained without increasing the viscosity.

  To 100 parts of the cationic epoxy resin emulsion obtained in Production Example 2, 106 parts of the pigment dispersion paste was added and mixed. Furthermore, 0.6 parts of dibutyltin oxide and 239 parts of ion-exchanged water were added to obtain a cationic electrodeposition coating composition. The content of zinc polyphosphate with respect to 100 parts by weight of the solid content of the paint was 44 parts by weight.

Comparative Example 1
In a sand grind mill, 100 parts of the pigment-dispersed resin varnish obtained in Production Example 3, 100 parts of aluminum phosphomolybdate and 70 parts of ion-exchanged water are dispersed and dispersed to a particle size of 10 μm or less to obtain a pigment-dispersed paste. It was.

  To 100 parts of the cationic epoxy resin emulsion obtained in Production Example 2, 40 parts of the pigment dispersion paste was added and mixed. Furthermore, 0.6 parts of dibutyltin oxide and 144 parts of ion-exchanged water were added to obtain a cationic electrodeposition coating composition. The content of aluminum zinc phosphomolybdate relative to 100 parts by weight of the solid content of the paint was 26 parts by weight.

Comparative Example 2
In a sand grind mill, 100 parts of pigment dispersion resin varnish obtained in Production Example 3, 20 parts of zinc polyphosphate (ZP-SB, manufactured by Kikuchi Color Co., Ltd.), 39 parts of titanium dioxide, 1 part of carbon black, 40 parts of kaolin And 25 parts of ion-exchanged water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste.

  To 100 parts of the cationic epoxy resin emulsion obtained in Production Example 2, 32 parts of the pigment dispersion paste was added and mixed. Furthermore, 0.6 parts of dibutyltin oxide and 139 parts of ion-exchanged water were added to obtain a cationic electrodeposition coating composition. The content of zinc polyphosphate with respect to 100 parts by weight of the solid content of the paint was 5 parts by weight.

Comparative Example 3
When 100 parts of the pigment-dispersed resin varnish obtained in Production Example 3, 100 parts of zinc oxide, and 70 parts of ion-exchanged water were dispersed in a sand grind mill, the dispersion paste thickened and could be dispersed. Thus, an electrodeposition coating composition could not be prepared.

  The cationic electrodeposition coating compositions obtained in the examples and comparative examples and the electrodeposition coating films obtained by electrodeposition coating thereof were evaluated by the following methods.

Evaluation
As a cyclic corrosion test substrate, a cold-rolled steel sheet treated with zinc phosphate (a steel sheet obtained by treating JIS G3141, SPCC-SD with Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.)) was used. On this base material, the cationic electrodeposition coating compositions of Examples and Comparative Examples were electrodeposited so that the film thickness of the dried coating film was 20 μm, and baked at 160 ° C. for 25 minutes to be cured. The heat-cured coating film was cross-cut with a knife so as to reach the substrate, and JASO M609-91 “Automobile Material Corrosion Test Method” was performed 100 cycles. Thereafter, the occurrence of rust and blistering from the crosscut portion was observed. The observation evaluation results are shown in Tables 1 and 2.

As an evaluation of Table 1 and Table 2,
◎ The maximum width of rust or swelling is less than 2mm from the cut part (both sides);
○ The maximum width of rust or swelling is 2mm or more and less than 3mm from the cut part (both sides);
Δ The maximum width of rust or blisters is 3 mm or more and less than 4 mm (both sides) from the cut part, and some blisters are observed in the flat part;
× The maximum width of rust or swelling is 4 mm or more from the cut part, or blisters are observed on the entire surface;
It shows that.

Measurement of the dissolved zinc ion concentration of the cured electrodeposition coating film A part of the cured electrodeposition coating film having a film thickness of 25 μm prepared as the test piece for the cycle corrosion test was peeled off to prepare a 0.3 g coating film piece. This coating film piece was placed in 100 ml of pH 4 phthalic acid standard buffer (manufactured by Wako Pure Chemical Industries, Ltd.) and immersed at 55 ° C. for 72 hours, and the concentration (ppm) of eluted zinc ions was measured. did. The zinc ion concentration was measured by quantifying zinc ions by preparing a calibration curve by fluorescent X-ray measurement using a zinc ion standard solution. The measurement results are shown in Tables 1 and 2.

  It can be seen from Tables 1 and 2 that excellent corrosion resistance is exhibited when the electrodeposition coating composition of the present invention is electrodeposited on an untreated steel sheet. On the other hand, it can confirm that the thing of a comparative example is inferior to corrosion resistance.

The lead-free cationic electrodeposition coating composition of the present invention is excellent in rust prevention performance. The electrodeposition coating composition of the present invention can impart high antirust properties despite the absence of lead-containing corrosion resistance imparting agents. In particular, the electrodeposition coating composition of the present invention can impart high rust resistance to an untreated steel sheet that has not been subjected to galvanization. The electrodeposition coating composition of the present invention provides the possibility of using an untreated steel sheet instead of a galvanized steel sheet.

Claims (2)

Zinc polyphosphate,
A cationic epoxy resin, and a blocked isocyanate curing agent,
A lead-free cationic electrodeposition coating composition comprising:
The zinc polyphosphate is contained in an amount of 7 to 50 parts by weight with respect to 100 parts by weight of the solid content of the paint.
Lead-free cationic electrodeposition coating composition. The zinc polyphosphate is prepared in such an amount that the concentration of zinc ions becomes 100 to 400 ppm when 0.3 g of a cured electrodeposition coating film obtained by the cationic electrodeposition coating composition is immersed in 100 ml of an aqueous solution having a pH of 4 or less. The lead-free cationic electrodeposition coating composition according to claim 1, which is contained in the coating composition.