JP2005194389A - Lead-free cationic electrodeposition coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free cationic electrodeposition coating composition having a low VOC and metal ion concentration, hardly giving effects on the environment because of a small amount of the used electrodeposition coating material itself, and having high throwing power. <P>SOLUTION: The lead-free cationic electrodeposition coating composition has 0.1-1.0 wt.% content of volatile organic components in the cationic electrodeposition coating composition, 50-500 ppm metal ion concentration, and 10-30 mg-eq. amount of neutralizing acid based on 100 g solid in a binder resin, and provides a film coated by the electrodeposition on a material to be coated so as to have 10-20 μm thickness, and having 1,000-1,500 kΩ/cm<SP>2</SP>membrane resistance. The blocked polyisocyanate curing agent is obtained by blocking a polyisocyanate containing diphenylmethanediisocyanate, and has (-5)-20°C glass transition temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lead-free cationic electrodeposition coating composition, and more particularly to a lead-free cationic electrodeposition coating composition having a high throwing power and a low volatile organic content (VOC) and metal ion concentration.

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

  Until now, in order to improve the corrosion resistance of the coating film, a metal catalyst containing lead (such as a corrosion resistance imparting agent) has been added to the electrodeposition paint. In recent years, since metal ions, particularly lead ions, have an adverse effect on the environment, it has been required to reduce the amount of metal catalyst used in electrodeposition paints.

  Furthermore, as environmental awareness has increased recently, advanced countries and the like are moving toward regulating the amount of harmful air pollutants (HAPs). The electrodeposition paint contains a volatile organic solvent as a solvent for synthesizing the resin, and as a flow aid for the electrodeposition coating film and a regulator for coating workability. Therefore, there is a fear that the use becomes difficult when the environmental regulation standard is strengthened.

  On the other hand, in recent years, it has been required to reduce the coating cost, and a reduction in the amount of paint used is also desired.

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

  Cationic electrodeposition coating is usually used for undercoating and is mainly used for rust prevention, etc. It is necessary to make it a predetermined value or more. Therefore, if the film thickness is uneven, the thick part is overcoated, and the paint is used excessively. Therefore, in order to reduce the amount of paint used, it is necessary to improve the throwing power of the electrodeposition paint and make the film thickness uniform.

  As a factor of decrease in throwing power, ionic groups, hydrated functional groups, etc. contained in the coating remain in the coating film to be formed, and these become a charge transfer medium, thereby causing an electrical resistance value of the coating film It may be possible to lower the value. Therefore, in order to achieve high throwing power in cationic electrodeposition coating, it is necessary to remove such factors and increase the electrical resistance value of the coating film.

  Another cause of the decrease in throwing power is considered to be low precipitation of the binder resin. The voltage applied to the non-deposited part of the article to be coated is weak, and the solid content of the paint hardly deposits on the article to be coated at the part. In this case, if the precipitation property of the binder resin from the coating emulsion to the coating object can be enhanced, the coating solid content is deposited even by a weak voltage applied to the non-attached portion of the coating object, and all of the coating object is deposited. A coating film is uniformly formed on the portion.

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

JP 2002-356647 A

  The present invention provides a lead-free cationic electrodeposition coating composition with high throwing power and low impact on the environment because the concentration of VOC and metal ions is low and the amount of the electrodeposition coating itself is small. There is.

The present invention relates to an aqueous medium, a binder resin containing a cationic oxazolidone ring-containing epoxy resin and a block polyisocyanate curing agent dispersed or dissolved in the aqueous medium, a neutralizing acid for neutralizing the cationic epoxy resin, A lead-free cationic electrodeposition coating composition containing an organic solvent and a metal catalyst, wherein the volatile organic content is 0.1 to 1.0% by weight, the metal ion concentration is 50 to 500 ppm, The amount of the sum acid is 10 to 30 mg equivalent to 100 g of binder resin solid content, and the film resistance of the coating electrodeposited to a thickness of 10 to 20 μm with respect to the coating is 1000 to 1500 kΩ / cm ² . Block polyisocyanate obtained by blocking polyisocyanate containing diphenylmethane diisocyanate A curing agent, the glass transition temperature of the blocked polyisocyanate curing agent is a-5-20 ° C., there is provided a lead-free cationic electrodeposition coating composition, the object is achieved.

  The metal catalyst is preferably at least one selected from the group consisting of cerium ions, bismuth ions, copper ions, zinc ions, molybdenum ions, and aluminum ions. The neutralizing acid is preferably at least one selected from the group consisting of acetic acid, lactic acid, formic acid, and sulfamic acid.

  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 lead-free cationic electrodeposition coating composition of the present invention has a low VOC and metal ion concentration, a high throwing power, and a small amount of the coating itself, and therefore has little influence on the environment.

  The cationic electrodeposition coating composition contains various additives such as an aqueous medium, a binder resin, a neutralizing acid, an organic solvent, and a metal catalyst that are dispersed or dissolved in the aqueous medium. The binder resin contains a cationic resin having a functional group and a block polyisocyanate curing agent that cures the cationic resin. As the aqueous medium, ion exchange water or the like is generally used.

  In the lead-free cationic electrodeposition coating composition of the present invention, a cationic epoxy resin in which an active hydrogen compound such as an amine is reacted with an epoxy ring of an epoxy resin as a cationic resin and the epoxy group is opened to introduce a cationic group It is preferable to use a blocked polyisocyanate curing agent obtained by blocking the isocyanate group of diphenylmethane diisocyanate.

Cationic Epoxy Resin As the cationic epoxy resin used in the present invention, a cationic oxazolidone ring-containing epoxy resin is used. As the cationic oxazolidone ring-containing epoxy resin, an amine-modified oxazolidone ring-containing epoxy resin is preferable. As the cationic epoxy resin, known resins described in JP-A Nos. 54-4978 and 56-34186 can be used together with the cationic oxazolidone ring-containing 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 bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  In the present invention, the following formula described in JP-A-5-306327 is disclosed.

[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. ] Is used for the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

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

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of this oxazolidone ring-containing epoxy resin are described in, for example, JP-A No. 2000-128959, and are 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 the primary, secondary or / and tertiary amino group-containing epoxy resin of the present invention, 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. Use.

  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.

Block polyisocyanate curing agent The block polyisocyanate curing agent of the present invention is obtained by blocking diphenylmethane diisocyanate, which is a polyisocyanate. The block polyisocyanate curing agent of the present invention has a glass transition temperature (Tg) of a lower limit of −5 ° C. and an upper limit of 20 ° C. The lower limit is more preferably 0 ° C, and the upper limit is more preferably 15 ° C. If the Tg is less than -5 ° C, the viscosity of the coating film is low and the coating resistance value cannot be obtained sufficiently, and the throwing power is inferior. If it exceeds 20 ° C, the heat flow during electrodeposition coating cannot be obtained sufficiently. There is a risk of poor appearance.

  It is sufficient to adjust the Tg of the block polyisocyanate curing agent by a method well known to those skilled in the art. Tg here is a glass transition temperature of the resin, and is a value measured by detecting a thermal change accompanying a glass transition of the resin with a differential scanning calorimeter. Examples of the differential scanning calorimeter that can be used include DSC220C manufactured by Seiko Denshi Kogyo.

  In the present invention, a polyisocyanate containing diphenylmethane diisocyanate (MDI) is used as the polyisocyanate. This is because high throwing power can be obtained by using a polyisocyanate containing diphenylmethane diisocyanate (MDI).

  As diphenylmethane diisocyanate (MDI) used in the present invention, any of diphenylmethane-4,4′-diisocyanate, diphenylmethane-2,4′-diisocyanate, or a mixture thereof, or a mixture with a polynuclear substance generally referred to as crude MDI Can also be used.

  As the polyisocyanate, diphenylmethane diisocyanate (MDI) is used as an essential component. In addition, aromatic diisocyanates such as tolylene diisocyanate (TDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), C3-C12 aliphatic diisocyanates such as 2,2,4-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 , 3-Diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also called norbornane diisocyanate) Aliphatic diisocyanates having 5 to 18 carbon atoms such as xylylene diisocyanate (XDI) and aliphatic diisocyanates having aromatic rings such as tetramethylxylylene diisocyanate (TMXDI); modification of these diisocyanates (Urethane product, carbodiimide, uretdione, uretoimine, burette and / or isocyanurate modified product); One of these may be contained in addition to diphenylmethane diisocyanate (MDI), or two or more thereof may be contained. However, it is more preferable to use diphenylmethane diisocyanate (MDI) alone as the polyisocyanate.

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

  A blocking agent for blocking polyisocyanate is added to a polyisocyanate group and is stable at room temperature, but can regenerate free isocyanate groups when heated to a dissociation temperature or higher.

  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 lead-free cationic electrodeposition coating composition of the present invention may contain a pigment as required. Examples of pigments that can be included include color pigments, rust preventive pigments, and extender pigments, but these pigments are used in amounts that do not significantly reduce the throwing power of the paint. Specifically, it is preferably used in such an amount that the weight ratio (P / V) between the pigment and the resin solid content contained in the coating composition is 1 / 2.5 or less.

  Specific examples of pigments that may be included in the lead-free cationic electrodeposition coating composition of the present invention include color pigments such as carbon black, kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica. Extender pigment, zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, Examples thereof include rust preventive pigments such as aluminum zinc phosphomolybdate.

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

  The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous medium. As the pigment dispersion resin, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used. Generally, the pigment dispersion resin is used at a solid content ratio of 5 to 40 parts by weight, and the pigment is used at a solid content ratio of 20 to 50 parts by weight.

Metal Catalyst The lead-free cationic electrodeposition coating composition of the present invention contains a metal catalyst as a metal ion as a catalyst for improving the corrosion resistance of the coating film. The metal ions are preferably cerium ions, bismuth ions, copper ions, and zinc ions. These are blended in the electrodeposition coating composition as an eluate from a pigment containing a salt or metal ion combined with an appropriate acid. The acid may be any of an inorganic acid or an organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and lactic acid, which will be described later as a neutralizing acid for neutralizing the cationic epoxy resin. A preferred acid is acetic acid.

  The metal catalyst is blended in such an amount that the upper limit of the metal ion concentration in the electrodeposition coating is 500 ppm. This is to reduce the environmental impact. The lower limit of the metal ion concentration in the electrodeposition coating is preferably 50 ppm, more preferably 100 ppm. The upper limit is more preferably 450 ppm. However, when a pigment is included in the coating composition, it is necessary to control within the above range in consideration of the amount of metal ions eluted from the pigment. Examples of metal ions eluted from the pigment include zinc ions, molybdenum ions, and aluminum ions.

  If the metal ion concentration in the electrodeposition coating exceeds 500 ppm, the impact on the environment will increase, and if the metal ion concentration increases, the deposition of the coating will also decrease. Also decreases. The metal ion concentration in the electrodeposition paint is measured by atomic absorption analysis of the supernatant obtained by the centrifugal separation treatment.

Electrodeposition Coating Composition The lead-free cationic electrodeposition coating composition of the present invention is prepared by dispersing the above-described metal catalyst, cationic epoxy resin, blocked polyisocyanate curing agent, and pigment dispersion paste in an aqueous medium. Is done. 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.

  When the amount of the neutralizing acid contained in the coating composition is increased, the neutralization rate of the cationic epoxy resin is increased, the affinity of the binder resin particles to the aqueous medium is increased, and the dispersion stability is increased. This means that the binder resin hardly deposits on the object to be coated during electrodeposition coating, and the depositability of the solid content of the paint is lowered.

  Conversely, if the amount of the neutralizing acid contained in the coating composition is small, the neutralization rate of the cationic epoxy resin is lowered, the affinity of the binder resin particles to the aqueous medium is lowered, and the dispersion stability is reduced. This means that the binder resin is likely to be deposited on the object to be coated at the time of coating, and the depositability of the solid content of the paint is increased.

  Therefore, in order to improve the throwing power of the electrodeposition coating, it is preferable to reduce the neutralization rate of the cationic epoxy resin by reducing the amount of neutralizing acid contained in the coating composition.

  Specifically, the amount of the neutralizing acid is preferably in the range of a lower limit of 10 mg equivalent and an upper limit of 30 mg equivalent with respect to 100 g of binder resin solid content including the cationic epoxy resin and the block polyisocyanate curing agent. The lower limit is more preferably 15 mg equivalent, and the upper limit is more preferably 29 mg equivalent. If the amount of the neutralizing acid is less than 10 mg equivalent, the affinity for water is not sufficient and the dispersion in water cannot be performed or the stability is extremely poor. If the amount exceeds 30 mg equivalent, the amount of electricity required for precipitation increases. , The precipitation of the solid content of the paint is lowered and the throwing power is inferior.

  In the present specification, the amount of neutralizing acid is expressed in terms of mg equivalents with respect to 100 g of binder resin solid content contained in the coating composition, and expressed as MEQ (A).

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

  The coating composition may contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a normal urethane cleavage catalyst. Since lead is not substantially contained, the amount is preferably 0.1 to 5% by weight of the resin solid content.

  An organic solvent is indispensable as a solvent when synthesizing resin components such as a cationic epoxy resin, a block polyisocyanate 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 mono-2-ethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Can be mentioned.

  Therefore, conventionally, these organic solvents are not completely removed from the resin component, and by adding an additional organic solvent, the VOC of the electrodeposition paint is increased to some extent and adjusted to about 1 to 5% on a weight basis. Yes. Here, the volatile organic content expressed by VOC (volatile organic content) means an organic solvent having a boiling point of 250 ° C. or lower, and specifically listed above.

  On the other hand, in the lead-free cationic electrodeposition coating composition of the present invention, it is preferable to lower the content of the organic solvent as compared with the conventional one. This is to prevent adverse effects on the environment. Specifically, the VOC of the coating composition is set to a lower limit of 0.1% by weight and an upper limit of 1.0% by weight. The lower limit is more preferably 0.2% by weight. The upper limit is more preferably 0.8% by weight, even more preferably 0.5% by weight. When the VOC of the coating composition is out of the above range, the influence on the environment is increased, and the coating resistance value is reduced by improving the fluidity of the deposited coating, so that the throwing power of the coating is also reduced. .

  As a method of making VOC 1.0% by weight or less, the organic solvent used for viscosity adjustment at the time of reaction is reduced by raising the reaction temperature and reacting with a low solvent or no solvent. As for the organic solvent that is absolutely necessary during the reaction, the volatile organic content in the final product can be reduced by using a low boiling point solvent so that it can be recovered in a process such as desolvation. About the organic solvent used for viscosity adjustment at the time of coating, the content can be reduced by reducing the viscosity of the resin, such as modification by a soft segment.

  VOC can be measured by performing gas chromatography measurement by an internal standard method and measuring the amount of VOC component blended as an organic solvent.

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

  Electrodeposition coating 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 (i) a process of immersing the object to be coated in the cationic electrodeposition coating composition, and (ii) a process in which a voltage is applied between the object to be coated and the anode to deposit a film. Is composed of. 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 10 to 20 μm. When the film thickness is less than 10 μm, the antirust property is insufficient, and when it exceeds 20 μm, the paint is wasted. The film resistance of the electrodeposition coating film is preferably in the range of a lower limit of 1000 kΩ / cm ^{2 and an} upper limit of 1500 kΩ / cm ^{2 at} a film thickness of 10 to 20 μm. The upper limit is more preferably 1300 kΩ / cm ² . When the film resistance of the coating film is less than 1000 kΩ / cm ² , sufficient electrical resistance is not obtained, and the throwing power is inferior, and when it exceeds 1500 kΩ / cm ² , the coating film appearance is extremely inferior. Become.

  The film resistance of the electrodeposition coating film can be adjusted by controlling the charge transfer medium amount and viscosity of the deposited film.

  The electrodeposition coating film obtained as described above is cured by baking at 120 to 260 ° C., preferably 160 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water.

  The following examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Production Example 1 Production of Modified Epoxy Resin Having Cationic Group In a flask equipped with a stirrer, a condenser tube, a nitrogen introduction tube, a thermometer and a dropping funnel, 940 parts of liquid epoxy, methyl isobutyl ketone (hereinafter abbreviated as MIBK) 61 4 parts and 24.4 parts of methanol were charged. The reaction mixture was heated from room temperature to 40 ° C. with stirring, and then 0.01 part of dibutyltin laurate and 21.75 parts of tolylene diisocyanate (hereinafter abbreviated as TDI) were added. The reaction was continued for 30 minutes at 40-45 ° C. The reaction was continued until the absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

  To the reaction product, 82.0 parts of polyoxyethylene bisphenol A ether and 125.0 parts of diphenylmethane-4,4'-diisocyanate were added. The reaction was performed at 55 ° C. to 60 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum. Subsequently, the temperature was raised, 2.0 parts of N, N-dimethylbenzylamine was added at 100 ° C., held at 130 ° C., methanol was fractionated using a fractionation tube and reacted, and the epoxy equivalent was 284. .

  Thereafter, the reaction mixture was diluted with MIBK until the nonvolatile content was 95%, and 268.1 parts of bisphenol A and 93.6 parts of 2-ethylhexanoic acid were added. The reaction was performed at 120 ° C. to 125 ° C., and when the epoxy equivalent reached 1320, the reaction mixture was diluted with MIBK until the nonvolatile content was 85%, and the reaction mixture was cooled. 93.6 parts of MIBK-blocked primary amine of diethylenetriamine and 65.2 parts of N-methylethanolamine were added and reacted at 120 ° C. for 1 hour. Thereafter, an oxazolidone ring-containing modified epoxy resin having a cationic group (resin solid content: 85%) was obtained.

Production Example 2 Production of Block Polyisocyanate Curing Agent A After charging 1330 parts of crude MDI and 276.1 parts of MIBK and 2 parts of dibutyltin laurate into a reaction vessel and heating it to 85-95 ° C., an ethylene glycol monobutyl ether solution of caprolactam (Equivalent ratio 20/80) 1170 parts were added dropwise over 2 hours. After completion of dropping, the temperature was raised to 100 ° C. and kept for 1 hour. In the measurement of IR spectrum, it was confirmed that the absorption based on the isocyanate group had disappeared, and thereafter, 347.6 parts of MIBK was added, and a block polyisocyanate curing agent A having a glass transition temperature of 0 ° C. was obtained.

Production Example 3 Production of Block Polyisocyanate Curing Agent B After charging 1330 parts of crude MDI and 585.6 parts of MIBK into a reaction vessel and heating it to 85-95 ° C., 456.6 parts of butyl diglycol ether was added for 2.5 hours. It was dripped over. After completion of dropping, the mixture was kept warm for 1 hour. Thereafter, 194.8 parts of MIBK was added and cooled to 50 ° C., and 532 parts of propylene glycol was added dropwise. After completion of dropping, the mixture was heated to 60 ° C. and kept for 1 hour. After adding 0.4 parts of dibutyltin laurate, the temperature was raised and the temperature was kept at 70 ° C. for 1 hour, and in the IR spectrum measurement, it was confirmed that absorption based on the isocyanate group disappeared, and the glass transition temperature was 8 ° C. The block polyisocyanate curing agent B was obtained.

Production Example 4 Production of Block Polyisocyanate Curing Agent C 1250 parts of diphenylmethane-4,4′-diisocyanate and 206 parts of MIBK were charged into a reaction vessel and heated to 45 to 50 ° C., and then 531 parts of butyl glycol ether was added over 4 hours. And dripped. After completion of dropping, the mixture was kept warm for 1 hour. Thereafter, 0.3 part of dibutyltin laurate was added. Further, 201 parts of trimethylolpropane was added in 5 parts. The temperature was raised to 120 ° C. with the heat of reaction, and the temperature was kept for 1 hour. After the incubation, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group disappeared, and diluted with 794 parts of MIBK to obtain a block polyisocyanate curing agent C having a glass transition temperature of 16 ° C.

Production Example 5 Production of Block Polyisocyanate Curing Agent D After charging 1330 parts of crude MDI into a reaction vessel and heating it to 45 to 50 ° C., 1620 parts of dibutyl glycol ether was added dropwise over 4 hours. After completion of dropping, 2 parts of dibutyltin laurate was added. The temperature was kept at 120 ° C. for 1 hour. After the incubation, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group had disappeared, and diluted with 440 parts of MIBK to obtain a block polyisocyanate curing agent D having a glass transition temperature of −20 ° C.

Production Example 6 Production of Blocked Isocyanate Curing Agent E 199 parts of hexamethylene diisocyanate nurate and 71 parts of MIBK were charged into a reaction vessel and heated to 45-50 ° C., and then 87 parts of methyl ethyl ketoxime was added dropwise over 3 hours. After completion of dropping, 0.1 part of dibutyltin laurate was added and kept at 80 ° C. for 1 hour. After the incubation, in the measurement of IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and a blocked isocyanate curing agent E having a glass transition temperature of −5 ° C. was obtained.

Production Example 7 Production of Pigment Dispersing Resin Into a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube and a thermometer, 2220 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) and 342.1 parts of MIBK were charged and heated to dibutyl at 50 ° C. Then, 2.2 parts of tin laurate was added, and 878.7 parts of methyl ethyl ketone oxime (hereinafter abbreviated as MEK oxime) was charged at 60 ° C. Thereafter, the mixture was kept at 60 ° C. for 1 hour, and it was confirmed that the NCO equivalent was 348, and 890 parts of dimethylethanolamine was added. Incubate at 60 ° C. for 1 hour, and after confirming that the NCO peak has disappeared by IR, add 1872.6 parts of 50% lactic acid and 495 parts of deionized water while cooling so as not to exceed 60 ° C. Got. Then, 870 parts of TDI and 49.5 parts of MIBK were charged in different reaction vessels, and 667.2 parts of 2-ethylhexanol was added dropwise over 2.5 hours so as not to be 50 ° C. or higher. After the completion of dropping, 35.5 parts of MIBK was added and kept warm for 30 minutes. Thereafter, it was confirmed that the NCO equivalent was 330 to 370, and half-block polyisocyanate was obtained.

  In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube and a thermometer, 940.0 parts of liquid epoxy and 38.5 parts of methanol were diluted, and 0.1 part of dibutyltin dilaurate was added thereto. After raising the temperature to 50 ° C., 87.1 parts of TDI was added and the temperature was further raised. At 100 ° C., 1.4 parts of N, N-dimethylbenzylamine was added, and the mixture was kept at 130 ° C. for 2 hours. At this time, methanol was fractionated by a fractionation tube. This was cooled to 115 ° C., and MIBK was charged to a solid content concentration of 90%. Then, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added and heated and stirred at 125 ° C. for 2 hours. Half block polyisocyanate 516.4 parts was added dropwise over 30 minutes, and then heated and stirred for 30 minutes. 1506 parts of polyoxyethylene bisphenol A ether was gradually added and dissolved. After cooling to 90 ° C., the above-described quaternizing agent was added, and the acid value of 2 or less was confirmed while maintaining the temperature at 70 to 80 ° C. to obtain a pigment dispersion resin. (Resin solid content 30%)

Production Example 8 Production of Pigment Dispersion Paste 106.9 parts of pigment dispersion resin obtained in Production Example 7 in a sand grind mill, 1.6 parts of carbon black, 40 parts of kaolin, 55.4 parts of titanium dioxide, aluminum phosphomolybdate 3 parts and 13 parts of deionized water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content 60%).

Example 1 Production of Cationic Electrodeposition Coating Composition The oxazolidone ring-containing modified epoxy resin having a cationic group obtained in Production Example 1 and the block polyisocyanate curing agent A obtained in Production Example 2 in a solid content ratio of 70/30 And mixed uniformly. Further, 3% of 2-ethylhexyl glycol added to the resin solid content was neutralized with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solid content was 33, and further ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1730 parts of this emulsion and 295 parts of the pigment dispersion paste obtained in Production Example 8, 1970 parts of ion-exchanged water, 20 parts of a 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The amount of the solvent in the paint of this cationic electrodeposition coating composition was 0.5%, the milligram equivalent of acid per 100 g of resin solids was 27.7, and the total amount of cerium ions and zinc ions eluted was 210 ppm. The coating voltage of 15 μm at a bath temperature of 30 ° C. was 200 V, and the coating resistance value calculated from the residual current at the end of electrodeposition was 1050 KΩ · cm ² .

Example 2
The oxazolidone ring-containing modified epoxy resin having a cationic group obtained in Production Example 1 and the block polyisocyanate curing agent B obtained in Production Example 3 were mixed so as to be uniform at a solid content ratio of 70/30. Further, 2% hexyl glycol added to 2% of resin solids was neutralized with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solids was 27, and further ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1730 parts of this emulsion and 295 parts of the pigment dispersion paste obtained in Production Example 8, 1970 parts of ion-exchanged water, 40 parts of 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The amount of solvent in the paint of this cationic electrodeposition coating composition was 0.4%, the milligram equivalent of acid per 100 g of resin solids was 25.2, and the total amount of cerium ions and zinc ions eluted was 448 ppm. The 15 μm coating voltage at a bath temperature of 30 ° C. was 220 V, and the coating film resistance calculated from the residual current at the end of electrodeposition was 1150 KΩ · cm ² .

Example 3
The oxazolidone ring-containing modified epoxy resin having a cationic group obtained in Production Example 1 and the block polyisocyanate curing agent C obtained in Production Example 4 were mixed so as to be uniform at a solid content ratio of 70/30. Further, the mixture was neutralized with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solids was 33%, and further diluted with ion-exchanged water. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1730 parts of this emulsion and 295 parts of the pigment dispersion paste obtained in Production Example 8, 1970 parts of ion-exchanged water, 20 parts of a 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The amount of solvent in the paint of this cationic electrodeposition coating composition was 0.9%, the milligram equivalent of acid per 100 g of resin solid content was 28.1, and the total amount of cerium ions and zinc ions eluted was 195 ppm. The 15 μm coating voltage at a bath temperature of 30 ° C. was 220 V, and the coating film resistance value calculated from the residual current at the end of electrodeposition was 1230 KΩ · cm ² .

Comparative Example 1
The oxazolidone ring-containing modified epoxy resin having a cationic group obtained in Production Example 1 and the block polyisocyanate curing agent D obtained in Production Example 5 were mixed so as to be uniform at a solid content ratio of 70/30. Further, 1.5% of 2-ethylhexyl glycol added to the resin solid content was neutralized with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solid content was 27, and further diluted slowly with ion-exchanged water. . By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1730 parts of this emulsion and 295 parts of the pigment dispersion paste obtained in Production Example 8, 1970 parts of ion-exchanged water, 20 parts of a 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The amount of the solvent in the paint of this cationic electrodeposition coating composition was 0.2%, the milligram equivalent of acid per 100 g of resin solids was 24.8, and the total amount of cerium ions and zinc ions eluted was 205 ppm. The 15 μm coating voltage at a bath temperature of 30 ° C. was 180 V, and the coating film resistance value calculated from the residual current at the end of electrodeposition was 800 KΩ · cm ² .

Comparative Example 2
The oxazolidone ring-containing modified epoxy resin having a cationic group obtained in Production Example 1 and the blocked isocyanate curing agent E obtained in Production Example 6 were mixed so as to be uniform at a solid content ratio of 70/30. Further, neutralize with 1.5% of 2-ethylhexyl glycol added to the resin solid content with glacial acetic acid so that the milligram equivalent of acid per 100 g of resin solid content is 27, and then slowly add ion-exchanged water for dilution. did. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1730 parts of this emulsion and 295 parts of the pigment dispersion paste obtained in Production Example 8, 1970 parts of ion-exchanged water, 20 parts of a 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The amount of solvent in the paint of this cationic electrodeposition coating composition was 0.2%, the milligram equivalent of acid per 100 g of resin solids was 25.1, and the total amount of cerium ions and zinc ions eluted was 220 ppm. The coating voltage of 15 μm at a bath temperature of 30 ° C. was 200 V, and the coating resistance value calculated from the residual current at the end of electrodeposition was 750 KΩ · cm ² .

  The following items were evaluated for the cationic electrodeposition coating compositions obtained in Examples 1 to 3 and Comparative Examples 1 and 2. The results are shown in Table 1.

Throwing power The throwing power was evaluated by a so-called four-sheet box method. That is, as shown in FIG. 1, four zinc phosphate-treated steel plates (JIS G 3141 SPCC-SD surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.) treatment) 11 to 14 in an upright state with an interval of 20 mm. A box 10 is used, which is arranged in parallel and the lower and bottom surfaces of both sides are sealed with an insulator such as cloth adhesive tape. In addition, the steel plates 11 to 13 other than the steel plate 14 are provided with an 8 mmφ through-hole 15 at the bottom. As shown in FIG. 2, the box 10 is immersed in an electrodeposition coating container 20 containing the electrodeposition paint 21 of each example or comparative example, and the diluted paint 21 enters the box 10 only from each through hole 15. To do. And each steel plate was electrically connected and the counter electrode 22 was arrange | positioned so that the distance with the nearest steel plate 11 might be set to 150 mm. A voltage was applied to each steel plate 11 to 14 as a cathode and the counter electrode 22 as an anode to apply cation electrodeposition to the steel plate. The coating was performed by increasing the voltage up to a voltage at which the film thickness of the coating film formed on the A surface of the steel plate 11 reached 20 μm within 5 seconds from the start of application, and then maintaining the voltage for 175 seconds. The electrodeposition coating temperature at this time was adjusted to 28 ° C. Each coated steel sheet was washed with water, baked at 160 ° C. for 20 minutes, and after air cooling, the film thickness of the coating film formed on the A surface of the steel sheet 11 closest to the counter electrode 22 and the steel sheet 14 farthest from the counter electrode 22. The film thickness of the coating film formed on the G surface of the film was measured, and the film thickness (G surface) / film thickness (A surface) ratio (G / A value) when the G surface film thickness was 10 μm Circumstance was evaluated. It can be evaluated that the greater the value, the better the throwing power.

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

Explanation of symbols

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

Claims (3)

An aqueous medium, a binder resin containing a cationic oxazolidone ring-containing epoxy resin and a blocked polyisocyanate curing agent dispersed or dissolved in an aqueous medium, a neutralizing acid, an organic solvent, a metal for neutralizing the cationic epoxy resin A lead-free cationic electrodeposition coating composition containing a catalyst,
Volatile organic content is 0.1 to 1.0% by weight,
The metal ion concentration is 50-500 ppm,
The amount of neutralizing acid is 10 to 30 mg equivalent to 100 g of binder resin solid content,
The film resistance of the coating film electrodeposited to a thickness of 10 to 20 μm with respect to the object to be coated is 1000 to 1500 kΩ / cm ² ,
The block polyisocyanate curing agent is a block polyisocyanate curing agent obtained by blocking polyisocyanate containing diphenylmethane diisocyanate,
The block polyisocyanate curing agent has a glass transition temperature of -5 to 20 ° C.
Lead-free cationic electrodeposition coating composition.   The lead-free cationic electrodeposition coating composition according to claim 1, wherein the metal catalyst is at least one selected from the group consisting of cerium ions, bismuth ions, copper ions, zinc ions, molybdenum ions, and aluminum ions. The lead-free cationic electrodeposition coating composition according to claim 1, wherein the neutralizing acid is at least one selected from the group consisting of acetic acid, lactic acid, formic acid, and sulfamic acid.

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