JP2006265689A - Cation electrodeposition painting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cation electrodeposition painting method in which a solid component content of a cation electrodeposition paint is reduced, a turnover speed is lowered and a throwing power characteristic is high. <P>SOLUTION: In the cation electrodeposition painting method of subjecting an article to be painted to electrodeposition painting by using the cation electrodeposition paint, the cation electrodeposition paint has a solid component content lower than the usual content and has the high throwing power characteristic. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating method, and more particularly to a cationic electrodeposition coating method using a paint having a low solid content and a high throwing power.

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

  Cationic electrodeposition coating is performed by immersing an object to be coated, such as an automobile body, in a large paint bath called an electrodeposition bath filled with the cationic electrodeposition paint. It is pulled from the bath and cured by heat through a process such as washing with water. The electrodeposition bath is filled with a cationic vehicle called a cationic electrodeposition paint, a curing agent or the like dispersed or dissolved in water or an aqueous solvent. In this electrodeposition coating material, there is a coating component (referred to as solid content), which is deposited and deposited on the object to be coated and taken out of the system as a coating.

  The electrodeposition bath has an index representing the time until all the solid content in the electrodeposition bath is taken out as a coating film, called the turnover speed. That is, “turnover speed is 6 months” means that all of the solid content in the cationic electrodeposition paint initially charged in the electrodeposition bath has 6 months to be applied (consumed). During this time, since the paint is constantly being replenished, the turnover speed apparently means the time it takes for the paint to completely replace the new paint. The longer the turnover speed, the less the amount of paint consumed per unit time, and the longer the paint stays in the bath, so solvent detachment from the emulsion particles and particle aggregation are likely to occur. It becomes difficult to maintain the quality of the stable.

Therefore, it is advantageous that the turnover is basically low. Speaking of the cationic electrodeposition paint, the use of a low solid content cationic electrodeposition paint is preferable because the turnover speed is lowered. On the other hand, when a cation electrodeposition coating material having a low solid content is used, the performance of coating a coating material called throwing power to a deep part of a complicated shape far from the electrode tends to be deteriorated. Accordingly, when the solid content is low, the throwing power deteriorates and cannot be used for the cationic electrodeposition coating.
JP-A-9-78290 JP 2004-231989

  The present invention provides an electrodeposition coating method having high throwing power and excellent coating film performance even when the solid content is lower than usual.

  Japanese Patent Application Laid-Open No. 9-78290 (Patent Document 1) discloses a battery having a solid content of 5 to 10% by weight, which is lower than that of the prior art, and does not cause deterioration of the paint even when the turnover speed is 6 months or more. A method of coating is disclosed. However, this method is applied when the turnover speed is long, and is not a technique for shortening the turnover speed.

    Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-231989) discloses a cationic electrocoating paint having a solid content concentration of 5 to 12% by weight, which facilitates circulation and stirring of the paint and has no problems in finishing and corrosion resistance. Describe the paint. However, since the cationic electrodeposition coating used here has a low solid content, improvement in throwing power is required.

  That is, the present invention is a cationic electrodeposition coating method in which an electrodeposition coating is applied to an object using a cationic electrodeposition coating,

  Provided is a cationic electrodeposition coating method characterized in that the cationic electrodeposition paint has a solid content lower than usual and has high throwing power.

  The cationic electrodeposition paint of the present invention has a solid content of 7 to 15% by weight, preferably 10 to 12% by weight, and the pigment ash content in the paint is 10 to 25% by weight, preferably 15 to 23% by weight. .

The cationic electrodeposition coating material used in the cationic electrodeposition coating method of the present invention has a resistance value of 700 to 1800 kΩ · cm ² of an electrodeposition coating film electrodeposited on an object to be coated.

  The cationic electrodeposition paint of the present invention contains a sulfonium-modified epoxy resin, an amine-modified epoxy resin and a blocked polyisocyanate curing agent as a binder resin.

  According to the present invention, even with a low solid content, by using a paint having a high throwing power, the turnover speed can be lowered, and the coating performance, particularly the throwing power, does not change. An electrodeposition coating method can be provided. A low solid content means that energy such as circulation and stirring is less than that of a high solid content, so that the deterioration of the paint can be prevented and the stock of the paint can be reduced.

  The cationic electrodeposition coating method of the present invention is characterized in that the cationic electrodeposition paint has a low solid content and a high throwing power. The low solid content means that the solid content of the cationic electrodeposition coating is usually around 20% by weight. If it is a solid content lower than this, it is not particularly limited, but it is 7 to 15% by weight, more preferably 10 to 12% by weight in order to fully exert the effects of the present invention. It is preferable. When the solid content is lower than 7% by weight, throwing power is greatly reduced.

  The cationic electrodeposition paint of the present invention needs to have high throwing power. The throwing power can be achieved by adding a sulfonium-modified epoxy resin to a combination of a commonly used amine-modified epoxy resin and a blocked polyisocyanate curing agent to the binder resin.

  The cationic electrodeposition coating composition used in the present invention contains additives such as an aqueous medium, a binder resin, a neutralizing acid, an organic solvent, a pigment, and a metal catalyst dispersed or dissolved in the aqueous medium. The binder resin contains a sulfonium-modified epoxy resin, an amine-modified epoxy resin, and a block polyisocyanate curing agent. As the aqueous medium, ion exchange water or the like is generally used.

Sulfonium-modified epoxy resin The cationic electrodeposition coating composition used in the present invention includes a sulfonium-modified epoxy resin. The sulfonium-modified epoxy resin is a resin in which a sulfonium base is introduced at the same time as the epoxy group is opened by reacting an epoxy resin with a sulfide compound and a neutralizing acid. The sulfonium-modified epoxy resin may be a conventionally known one as described in, for example, JP-A-6-128351 and JP-A-7-206968. The sulfonium-modified epoxy resin is typically produced by opening the epoxy ring of a bisphenol type epoxy resin with a sulfide compound and a neutralizing acid.

  The sulfide compound to be reacted with the epoxy resin includes all sulfide compounds that react with the epoxy group and do not contain an interfering group. The reaction between the epoxy resin and the sulfide compound needs to be performed in the presence of a neutralizing acid, and as a result, a sulfonium group is introduced into the epoxy resin.

  Specific examples of the sulfide compound may be aliphatic sulfide, mixed aliphatic-aromatic sulfide, aralkyl sulfide, or cyclic sulfide. Examples of sulfide compounds that can be used include diethyl sulfide, dipropyl sulfide, ethylphenyl sulfide, tetramethylene sulfide, pentamethylene sulfide and the like.

  Particularly preferred sulfide compounds are of the formula

[Wherein, R and R ′ each independently represents a linear or branched alkylene group having 2 to 8 carbon atoms. ]
It is a thiodialcohol represented by Such a sulfonium-modified epoxy resin has a function of delaying the formation of coating film resistance for a short time (about 10 seconds) immediately after the start of electrodeposition, and imparts water dispersion stability to the binder resin.

  Examples of thiodialcohols include thiodiethanol, thiodipropanol, thiodibutanol, 1- (2-hydroxyethylthio) -2-propanol, 1- (2-hydroxyethylthio) -2,3-propanediol, 1- (2-hydroxyethylthio) -2-butanol and 1- (2-hydroxyethylthio) -3-butoxy-1-propanol. Most preferably, the sulfide compound is 1- (2-hydroxyethylthio) -2-propanol.

Amine-modified epoxy resin The cationic electrodeposition coating composition used in the present invention includes an amine-modified bisphenol-type epoxy resin. The amine-modified epoxy resin may be a conventionally known one as described in, for example, JP-A Nos. 54-4978 and 56-34186. The amine-modified epoxy resin is typically produced by opening the epoxy ring of a bisphenol type epoxy resin with an amine.

  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).

  An oxazolidone ring-containing epoxy resin as described in the formula in the paragraph 0004 of JP-A No. 5-306327 and Chemical Formula 3 may be used as the amine-modified 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.

  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 this oxazolidone ring-containing epoxy resin are described, for example, in paragraphs 0012 to 0047 of JP-A No. 2000-128959.

  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.

  Examples of the active hydrogen compound into which a cationic group can be introduced include primary amine, secondary amine, and tertiary amine acid salts. Of these amines, secondary amines are particularly preferred. When an epoxy resin and a secondary amine are reacted, an amine-modified epoxy resin having a tertiary amino group is obtained.

  Specific examples of amines include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, aminoethylethanolamine There are secondary amines that are blocked from primary amines such as diketimine of diethylenetriamine. 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 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; zinc phosphate, iron phosphate, Like aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, zinc aluminum phosphomolybdate, silicate compounds Rust preventive pigments and the like.

  In the present invention, the amount of the pigment is expressed as pigment ash (pigment weight / paint solid weight × 100), and is 10 to 25% by weight, preferably 15 to 23% by weight. When the pigment ash content is less than 10% by weight, defects called repelling occur in the coating film, and when the pigment ash content exceeds 25% by weight, the pigment settles and the coating film finish decreases.

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 in an aqueous medium together with a pigment dispersion resin dispersion. The pigment dispersion resin dispersion is obtained by dispersing 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.

Metal Catalyst The cationic electrodeposition coating composition of the present invention may contain a metal catalyst as a metal ion as a catalyst for improving the corrosion resistance of the coating film. As the metal ions, cerium ions, bismuth ions, copper ions, and zinc ions are preferable. These are contained 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 inorganic acids or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid and lactic acid, which will be described later as neutralizing acids for neutralizing sulfonium-modified epoxy resins and amine-modified epoxy resins. I just need it. A preferred acid is acetic acid.

Electrodeposition Coating Composition The cationic electrodeposition coating composition of the present invention comprises the above-described metal catalyst, sulfonium-modified epoxy resin, amine-modified epoxy resin, blocked isocyanate curing agent, and pigment dispersion paste dispersed in an aqueous medium. Prepared by Also, the aqueous medium usually contains a neutralizing acid in order to neutralize the sulfonium-modified epoxy resin and the amine-modified 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.

  For the method of blending a sulfonium-modified epoxy resin, an amine-modified epoxy resin, and a blocked isocyanate as a curing agent and dispersing them in an aqueous medium, each of the sulfonium-modified epoxy resin and the amine-modified epoxy resin, or any one of them is blocked isocyanate. They may be mixed in a solution state to make each emulsion, and then each emulsion may be mixed, or a mixed solution in which a sulfonium-modified epoxy resin and an amine-modified epoxy resin are previously mixed in a solution state and a blocked isocyanate is added thereto. May be made into an emulsion.

  The amount of the block isocyanate curing agent reacts with active hydrogen-containing functional groups such as primary, secondary amino groups, and hydroxyl groups in the sulfonium-modified epoxy resin and amine-modified epoxy resin at the time of curing to give a good cured coating film. In general, it is generally expressed as 90/10 to 50/50 in terms of solid mass ratio (epoxy resin / curing agent) of the sum of the sulfonium-modified epoxy resin and the amine-modified epoxy resin and the blocked isocyanate curing agent. The range is preferably 80/20 to 65/35.

  The mixing ratio of the sulfonium-modified epoxy resin and the amine-modified epoxy resin is 1/99 to 50/50, preferably 10/90 to 50/50, in mass ratio. If the mass ratio of the sulfonium-modified epoxy resin is less than the mixing ratio 25/75, the gas pin resistance of the paint is inferior. If the mixing ratio exceeds 50/50, the appearance defect of the coating film is difficult to be solved.

  The coating composition may contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a normal urethane cleavage catalyst. However, since the cationic electrodeposition coating composition of the present invention does not substantially contain lead, the amount is preferably 0.1 to 5% by mass of the resin solid content.

  Organic solvents are indispensable as solvents when synthesizing resin components such as sulfonium-modified epoxy resins, amine-modified epoxy resins, blocked isocyanate curing agents, and pigment-dispersed resins, and complicated operations are 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 be coated to form an electrodeposition coating film (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 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. In the present specification, the “electrodeposition coating film” refers to an uncured coating film after electrodeposition coating after the above-described process of depositing the coating film and before baking hardening.

The film thickness of the electrodeposition coating film is preferably 5 to 25 μm, more preferably 15 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 film resistance of the electrodeposition coating film is preferably 700 to 1800 kΩ · cm ² at a film thickness of 15 μm. When the film resistance of the coating film is less than 700 kΩ · cm ² , sufficient electrical resistance is not obtained, and the throwing power is poor, and when it exceeds 1800 kΩ · cm ² , the appearance of the coating film is extremely inferior. Become. The film resistance of the coating film is more preferably 800 to 1300 kΩ · cm ² .

  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 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water. In this specification, the coating film after baking hardening is called "cured coating film".

  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 mass unless otherwise specified.

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

Production Example 2
Production of sulfonium-modified epoxy resin In a flask equipped with a stirrer, a cooling tube, a nitrogen introduction tube, a thermometer and a dropping funnel, 87 parts of 2,4- / 2,6-tolylene diisocyanate (mass ratio = 8/2), MIBK85 Part and 0.1 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 32 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. The reaction was mainly carried out in the range of 60 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

  Next, 550 parts of epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until an epoxy equivalent of 330 was reached.

  Subsequently, 100 parts of bisphenol A and 36 parts of octylic acid were added and reacted at 120 ° C., resulting in an epoxy equivalent of 1030. Thereafter, 107 parts of MIBK was added to cool the reaction mixture, 52 parts of SHP-100 (1- (2-hydroxyethylthio) -2-propanol, Sanyo Chemical Co., Ltd.), 21 parts of ion-exchanged water, and 39 parts of 88% lactic acid were added. The reaction was performed at 80 ° C. The reaction was continued until the acid value was below 5, and an epoxy resin having a tertiary sulfonium base (resin solid content: 80%) was obtained.

  The obtained resin was mixed with the blocked isocyanate curing agent obtained in Production Example 1 so as to be uniform at a solid content ratio of 60/40. Thereafter, ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, a blocked isocyanate-containing sulfonium-modified epoxy resin emulsion having a solid content of 36% was obtained. Further, the milliequivalent of the base per 100 g of resin solid content of this emulsion was 10.

Production Example 3
Production of amine-modified epoxy resin In a flask equipped with a stirrer, a condenser tube, a nitrogen inlet tube, a thermometer and a dropping funnel, 87 parts of 2,4- / 2,6-tolylene diisocyanate (mass ratio = 8/2), MIBK85 Part and 0.1 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 32 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. The reaction was mainly carried out in the range of 60 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

  Next, 650 parts of epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until an epoxy equivalent of 300 was reached.

  Subsequently, when 165 parts of bisphenol A and 29 parts of octylic acid were added and reacted at 120 ° C., the epoxy equivalent was 1160. Thereafter, 107 parts of MIBK was added to cool the reaction mixture, 85 parts of diethanolamine was added, and the mixture was reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became 80% of non volatile matters, and the epoxy resin (resin solid content 80%) which has a tertiary amino base was obtained.

  The obtained resin was mixed with the blocked isocyanate curing agent obtained in Production Example 1 so as to be uniform at a solid content ratio of 60/40. Thereafter, formic acid was added so that the number of milliequivalents of acid was 25 per 100 g of resin solids, and further ion-exchanged water was slowly added for dilution. MIBK was removed under reduced pressure to obtain a blocked isocyanate-containing amine-modified epoxy resin emulsion having a solid content of 36%.

Production Example 4
Production of amine-modified epoxy resin In a flask equipped with a stirrer, a condenser tube, a nitrogen inlet tube, a thermometer and a dropping funnel, 87 parts of 2,4- / 2,6-tolylene diisocyanate (mass ratio = 8/2), MIBK85 Part and 0.1 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 32 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. The reaction was mainly carried out in the range of 60 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

  Next, 492 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 360.

  Subsequently, when 70 parts of bisphenol A and 29 parts of octylic acid were added and reacted at 120 ° C., the epoxy equivalent was 850. Thereafter, 107 parts of MIBK was added and the reaction mixture was cooled. 48 parts of methylethanolamine and 70 parts of ketiminized diethylenetriamine were added and reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became 80% of non volatile matters, and the epoxy resin (resin solid content 80%) which has a tertiary amino base was obtained.

  The obtained resin was mixed with the blocked isocyanate curing agent obtained in Production Example 1 so as to be uniform at a solid content ratio of 60/40. Thereafter, formic acid was added so that the number of milliequivalents of acid was 25 per 100 g of resin solids, and further ion-exchanged water was slowly added for dilution. MIBK was removed under reduced pressure to obtain a blocked isocyanate-containing amine-modified epoxy resin emulsion having a solid content of 36%.

Production Example 5
Production of amine-modified epoxy resin In a flask equipped with a stirrer, a condenser tube, a nitrogen inlet tube, a thermometer and a dropping funnel, 87 parts of 2,4- / 2,6-tolylene diisocyanate (mass ratio = 8/2), MIBK85 Part and 0.1 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 32 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. The reaction was mainly carried out in the range of 60 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

  Next, 834 parts of epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 270.

  Subsequently, when 194 parts of bisphenol A and 29 parts of octylic acid were added and reacted at 120 ° C., the epoxy equivalent was 1540. Thereafter, 107 parts of MIBK was added to cool the reaction mixture, 85 parts of diethanolamine was added, and the mixture was reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became 80% of non volatile matters, and the epoxy resin (resin solid content 80%) which has a tertiary amino base was obtained.

  The obtained resin was mixed with the blocked isocyanate curing agent obtained in Production Example 1 so as to be uniform at a solid content ratio of 60/40. Thereafter, formic acid was added so that the number of milliequivalents of acid was 25 per 100 g of resin solids, and further ion-exchanged water was slowly added for dilution. MIBK was removed under reduced pressure to obtain a blocked isocyanate-containing amine-modified epoxy resin emulsion having a solid content of 36%.

Production Example 6
Manufacture of pigment-dispersed resin dispersion First, 222.0 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) is placed in a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe, and a thermometer, and diluted with 39.1 parts of MIBK. After that, 0.2 parts of dibutyltin dilaurate was added thereto. Then, after heating this to 50 degreeC, 131.5 parts of 2-ethylhexanol was dripped over 2 hours in dry nitrogen atmosphere, stirring. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI (resin solid content: 90.0%) was obtained.

  Next, 87.2 parts of dimethylethanol, 117.6 parts of 75% lactic acid aqueous solution and 39.2 parts of ethylene glycol monobutyl ether are added in order to a suitable reaction vessel, and the mixture is stirred at 65 ° C. for about half an hour to add the quaternizing agent. Prepared.

  Next, 710.0 parts of EPON 829 (bisphenol A type epoxy resin manufactured by Shell Chemical Company, epoxy equivalent 193 to 203) and 289.6 parts of bisphenol A were charged into a suitable reaction vessel, and the reaction was conducted under a nitrogen atmosphere. When heated to 150 to 160 ° C., an initial exothermic reaction occurred. The reaction mixture was allowed to react at 150-160 ° C. for about 1 hour, then cooled to 120 ° C., and then 498.8 parts of previously prepared 2-ethylhexanol half-blocked IPDI (MIBK solution) was added.

  The reaction mixture is kept at 110-120 ° C. for about 1 hour, then 463.4 parts of ethylene glycol monobutyl ether are added, the mixture is cooled to 85-95 ° C. and homogenized, and then the quaternizing agent 196 prepared above is used. .7 parts were added. After maintaining the reaction mixture at 85 to 95 ° C. until the acid value becomes 1, 964 parts of deionized water is added to finish quaternization in the epoxy-bisphenol A resin, and a pigment dispersion having a quaternary ammonium salt portion A resin dispersion was obtained (resin solid content 50%).

Production Example 7
Production of Pigment Dispersion Paste 120 parts of pigment dispersion resin dispersion obtained in Production Example 6 in a sand grind mill, 2.0 parts of carbon black, 50 parts by weight of calcined kaolin, 50.0 parts of silicic acid compound, 80.0 of titanium dioxide Part, 18.0 parts of aluminum phosphomolybdate and 221.7 parts of ion-exchanged water were dispersed until the particle size became 10 μm or less to obtain a pigment paste (solid content 48%).

Example 1
The sulfonium-modified epoxy resin emulsion obtained in Production Example 2 and the amine-modified epoxy resin emulsion obtained in Production Example 3 were mixed to obtain a resin solid content ratio of 10/90, and then the pigment dispersion obtained in Production Example 7 The paste was mixed. Furthermore, 1% by mass of dibutyltin oxide and ion-exchanged water are added to the resin solid content, and the cationic electrodeposition having a solid content of 15% by weight, a pigment ash content of 25% by weight, and a membrane resistance value (at 15 μ) of 1260 kΩ · cm ^2. A coating composition was obtained.

  The throwing power (four-sheet box method) and turnover (calculated value) of the thus prepared cationic electrodeposition paint were evaluated. The evaluation results are shown in Table 1.

Example 2
The sulfonium-modified epoxy resin emulsion obtained in Production Example 2 and the amine-modified epoxy resin emulsion obtained in Production Example 3 were mixed to obtain a resin solid content ratio of 50/50, and then the pigment dispersion obtained in Production Example 7 The paste was mixed. Furthermore, 1% by mass of dibutyltin oxide and ion-exchanged water are added to the resin solid content, and the cationic content of the solid content is 75% by weight, the pigment ash content is 10% by weight, and the membrane resistance (at 15 μ) is 890 kΩ · cm ^2. A coating composition was obtained. The electrodeposition coating composition thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3
The sulfonium-modified epoxy resin emulsion obtained in Production Example 2 and the amine-modified epoxy resin emulsion obtained in Production Example 3 were mixed to obtain a resin solid content ratio of 1/99, and then the pigment dispersion obtained in Production Example 7 The paste was mixed. Furthermore, 1% by mass of dibutyltin oxide and ion-exchanged water are added to the resin solid content, and the cationic electrodeposition paint has a solid content of 75% by weight, a pigment ash content of 15% by weight, and a membrane resistance value (at 15 μm) of 790 kΩ · cm ^2. A composition was obtained. The electrodeposition coating composition thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1
The pigment-dispersed paste obtained in Production Example 7 was mixed with the amine-modified epoxy resin emulsion obtained in Production Example 4. Furthermore, 1% by mass of dibutyltin oxide and ion-exchanged water are added to the resin solid content, and the cationic electrodeposition coating composition has a solid content of 20% by weight, a pigment ash content of 25% by weight, and a membrane resistance value (at 15 μm) of 650 kΩ · cm ^2. A composition was obtained. The electrodeposition coating composition thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2
The pigment-dispersed paste obtained in Production Example 7 was mixed with the amine-modified epoxy resin emulsion obtained in Production Example 5. Further, 1% by mass of dibutyltin oxide and ion exchange water are added to the resin solid content, and the cationic electrodeposition coating composition has a solid content of 20% by weight, a pigment ash content of 15% by weight, and a membrane resistance value (at 15 μm) of 510 kΩ · cm ^2. A composition was obtained. The electrodeposition coating composition thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 3.

  The electrodeposition coating film and the cured coating film obtained by electrodeposition coating the cationic electrodeposition coating compositions obtained in Examples and Comparative Examples were evaluated by the following methods.

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

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

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

  Each steel sheet after painting is washed with water, baked at 170 ° C. for 25 minutes, and after air cooling, the film thickness of the coating film formed on the A surface of the steel sheet 11 closest to the counter electrode 22 and the farthest from the counter electrode 22 The film thickness of the coating film formed on the G surface of the steel plate 14 was measured, and the throwing power was evaluated by the ratio (G / A value) of film thickness (G surface) / film thickness (A surface). Generally, when this value exceeds 50%, it is good, and when this value is 50% or less, it can be judged as defective. The results are shown in Table 1.

<Membrane resistance of electrodeposition coating>
Electrodeposition paint containing zinc phosphate-treated steel sheet (JIS G 3141 SPCC-SD surfdyne SD-2500 treatment) (dimensions: 70 mm x 150 mm, thickness 0.7 mm) in an electrodeposition bath containing a cationic electrodeposition paint composition Was immersed in 10 cm. A voltage was applied to the steel sheet, the voltage was increased to 200 V over 30 seconds, and electrodeposition was performed for 150 seconds. The coating voltage with a coating thickness of 15 μm at a bath temperature of 28 ° C. and the residual current at the end of electrodeposition were measured to calculate the coating resistance value (kΩ · cm ² ).

<turnover>
Each turnover value is defined by the following calculated value assuming that Comparative Example 1 has a turnover of 6 months.

  That is, in the case of the first embodiment, 6 × 15 ÷ 20 = 4.5 months.

  From the above results, it can be seen that even with a low solid content, a cationic electrodeposition coating method having higher throwing power than conventional ones is obtained.

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

DESCRIPTION OF SYMBOLS 10 ... Box, 11-14 ... Zinc phosphate processing steel plate, 15 ... Through-hole, 20 ... Electrodeposition coating container, 21 ... Electrodeposition paint, 22 ... Counter electrode.

Claims (4)

In the cationic electrodeposition coating method of applying an electrodeposition coating to an object using a cationic electrodeposition paint,
A cationic electrodeposition coating method, wherein the cationic electrodeposition paint has a solid content lower than usual and has high throwing power.   2. The cationic electrodeposition coating method according to claim 1, wherein the cationic electrodeposition paint has a solid content of 7 to 15% by weight and a pigment ash content of 10 to 25% by weight. The cationic electrodeposition coating method according to claim 1, wherein the resistance value of the electrodeposition coating film in which the cationic electrodeposition coating material is electrodeposited with a thickness of 15 μm on an object to be coated has 700 to 1800 kΩ · cm ² . The cationic electrodeposition coating method according to claim 1, wherein the cationic electrodeposition coating composition contains a sulfonium-modified epoxy resin, an amine-modified epoxy resin, and a blocked polyisocyanate curing agent as a binder resin.

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