WO2010100840A1 - Electrocoating composition and method for electrocoating - Google Patents

Abstract

Provided is an electrocoating composition with a further improved throwing power. Specifically provided is an electrocoating composition which comprises a water-borne nonionic and/or cationic resin and 20 to 500 ppm of Al ions, characterized in that the pH satisfies the relationship: 3.5 ≤ pH ≤ -Log((A × 1.93 × 10^-15)^1/3) [wherein A represents the Al ion concentration [ppm]].

Description

Electrodeposition coating composition and electrodeposition coating method

The present invention relates to an electrodeposition coating composition and an electrodeposition coating method having excellent throwing power for metal materials, particularly metal structures having complicated shapes.

Conventionally, as a method for imparting excellent corrosion resistance to various metal materials, especially metal structures with complicated shapes, electrodeposition coating that can deposit a coating film uniformly on the corners of complicated shapes Has been commonly used.

Electrodeposition coating consists of an anionic electrodeposition coating in which a coating is deposited by anodic electrolysis in an aqueous paint containing an anionic resin emulsion, and an aqueous coating containing a cationic resin emulsion. It can be roughly classified into cationic electrodeposition coating in which a coating film is deposited by cathodic electrolysis.

Anionic resin emulsion has dispersion stability on the alkali side and loses dispersion stability on the acid side. On the contrary, the cationic resin emulsion has dispersion stability on the acid side and loses dispersion stability on the alkali side. The resin is deposited by anodic electrolysis or cathodic electrolysis because of these properties. Therefore, the nonionic resin emulsion cannot be precipitated due to the reaction mechanism.

In order to improve the corrosion resistance of ferrous metal materials, cationic electrodeposition coating that does not cause the base metal to elute into the paint during electrolytic treatment is advantageous, and the automobile body is a metal component mainly composed of ferrous materials. Cationic electrodeposition coating is widely applied to automobile parts, home appliances, building materials and the like.

As mentioned above, the greatest feature of electrodeposition coating is the coating throwing power, but in recent years, more advanced throwing power has been required for the purpose of reducing the amount of paint used and improving the corrosion resistance. Various studies have been made to improve the throwing power.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-294143) neutralizes an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent, or a cationic epoxy resin dispersed or dissolved in the aqueous medium. In the lead-free cationic electrodeposition coating composition containing a neutralizing acid, an organic solvent, and a metal catalyst, the volatile organic content is 1% by weight or less, the metal ion concentration is 500 ppm or less, and the neutralizing acid Is a lead-free cationic electrodeposition coating composition having an amount of 10 to 30 mg equivalent to 100 g of binder resin solid content, and the metal catalyst is cerium ion, bismuth ion, copper ion, zinc ion, molybdenum ion, One or more selected from the group consisting of aluminum ions, the neutralizing acid is acetic acid, lactic acid, formic acid, sulfamic acid It is that it is preferably at least one selected from that group.

In addition, many techniques for improving the throwing power using a composition similar to this electrodeposition coating composition have been disclosed.
Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-285391) is characterized by temperature control of the electrodeposition bath, and Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-285392) has two types of electrodeposition processes having different glass transition temperatures of the coating film. Patent Document 4 (Japanese Patent Laid-Open No. 2002-294144) is characterized by specifying a non-volatile solid content, and Patent Document 5 (Japanese Patent Laid-Open No. 2002-294145) and Patent Document 6 (Japanese Patent Laid-Open No. 2002-294146) are characterized. It is characterized by specifying the glass transition temperature and molecular weight of the cationic epoxy resin, and Patent Document 7 (Japanese Patent Laid-Open No. 2002-294147) is characterized by specifying the minimum film-forming temperature of the coating film. JP 2005-194389) specifies the base resin skeleton of the cationic epoxy resin, the film resistance, the curing agent and the glass transition temperature of the curing agent. DOO is characterized by, Patent Document 9 (JP-2008-156655) is characterized in that also identifies the film resistance.

JP 2002-294143 A JP 2002-285391 A JP 2002-285392 A JP 2002-294144 A JP 2002-294145 A JP 2002-294146 A JP 2002-294147 A JP 2005-194389 A JP 2008-156655 A JP 2007-314690 A JP 2008-538383 A

The above prior art certainly has an effect on circulation, but it is certain that the market needs further improvement of circulation. Therefore, the present inventors have reconsidered the deposition mechanism itself of the cationic electrodeposition coating.

Resin emulsions used for cationic electrodeposition coating are often rendered cationic by the introduction of amine groups. The cationic resin emulsion has dispersion stability on the acidic side and loses dispersion stability on the alkali side. However, the pH at which the emulsion loses electric charge and forms a coating film due to actual cathode electrolysis reaches around 12. Is published in Document 1.

Of course, the pH at which the coating film is deposited varies depending on the properties of the resin emulsion, such as the molecular weight of the emulsion, the type of amine group to be introduced, and the introduction rate, but the deposition does not start unless the pH exceeds 10. Therefore, when the pH is increased by cathodic electrolysis, the pH of the coating composition, which is the starting pH, is advantageously as high as possible within the range where the resin emulsion is stabilized, which is advantageous for the deposition properties of the coating film. I can say that.

Patent Document 10 (Japanese Patent Laid-Open No. 2007-314690) and Patent Document 11 (Japanese Patent Laid-Open No. 2008-538383), which are prior arts, also relate to electrodeposition coating compositions, but the pH of aqueous coating compositions is 5-7. It is preferable that it is preferably 5.5 to 6.5. An adverse effect when the pH is less than 5 is that electrodeposition coating efficiency and film appearance are reduced.

In Patent Documents 1 to 9, although there is no specific description of pH, in order to improve the throwing power of the electrodeposition paint, the amount of the neutralizing acid contained in the paint composition is reduced and the cationic epoxy resin is used. It is said that it is preferable to keep the neutralization rate of the resin at a low level, that is, to maintain the pH as high as possible. In fact, since the amount of neutralizing acid is 10 to 30 mg equivalent to 100 g of binder resin solid content, it is clear that the pH is necessarily in the same range as in Patent Documents 10 and 11.

In other words, increasing the pH of the electrodeposition coating composition itself and lowering the precipitation pH by modifying the resin emulsion are already at the limits. Cannot be expected.

Therefore, the present inventors examined reducing the coating film deposition pH with a flocculant as a new technique. And it discovered that Al was the most effective among various flocculants.

However, even when an Al compound is added to a conventional electrodeposition coating composition, it is instantly changed into a hydroxide by hydrolysis, and the hydroxide aggregates over time. Will lose its effect.

Patent Documents 1 to 9 indicate that it is preferable to contain aluminum ions as a metal catalyst, but in the actual electrodeposition coating composition for the above reason, a hydroxide is formed by instantaneous hydrolysis. Estimated. Although it has not been verified in the examples, it is considered that although the hydroxide maintains its action as a catalyst, the effect as a flocculant can no longer be expected.

Therefore, the present inventors have lowered the pH near neutrality, which was common knowledge of electrodeposition coating compositions, to a range where Al can be continuously present in an ionic state, and evaluated the effect on the circulation property of Al ions. As a result, it has been found that very good throwing power can be obtained even though the pH of the composition is lowered.

And the effect of this Al ion was found to be effective even for nonionic resin emulsions that could not be electrolytically deposited, and could be deposited by cathodic electrolysis, leading to the completion of the present invention.

That is, the present invention includes the following (1) and (2).
(1) Electrodeposition containing a nonionic and / or cationic water-based resin and Al ions of 20 to 500 ppm, and the pH satisfies the following formula when the Al ion concentration is A [ppm] Paint composition.
3.5 ≦ pH ≦ −Log (A × 1.93 × 10 ⁻¹⁵ ) ^1/3
(2) An electrodeposition coating method comprising depositing a coating film of a metal material by a cathode electrolysis method using the composition of (1).

FIG. 1 is a diagram showing appropriate ranges of Al ion concentration and pH. FIG. 2 is a model diagram of a “four-box with-around test jig” used in the in-around test. FIG. 3 shows the electrodeposition coating state in the throwing power test.

1. Outer plate (surface A) in a jig for testing the throwing power of a 2.4-sheet box method with an 8 mm diameter hole
3. Inner plate for G
4). Electrodeposition paint bath

The electrodeposition coating composition of the present invention contains a nonionic and / or cationic aqueous resin. Here, neither a nonionic resin nor a cationic resin is particularly limited. Whichever type of base resin is used, the effect of the present invention is not impaired, but epoxy, urethane, and acrylic are more preferable. Here, one feature of the present invention is based on a novel action mechanism (an action mechanism in which Al ions become a hydroxide colloid and aggregate as the pH rises, but the surrounding resin is involved at this time). Nonionic resins that could not be analyzed can now be used. Since nonionic resins can be used in this way, the range of selection is widened, and various properties that could not be obtained can be imparted to the film. Furthermore, in the case of using a cationic resin, in addition to the known action mechanism in which the resin itself loses dispersion stability as the pH increases, electrodeposition at a lower pH than the conventional one is based on the above-mentioned novel action mechanism. Is possible.

The concentration of the resin emulsion is not particularly specified, but it is preferably 5 to 30% by weight based on the total weight of the electrodeposition coating composition. It is more preferably 7 to 25% by weight, and most preferably 10 to 20% by weight. If the resin content is too low, the amount of film deposition is insufficient, and if the content is too high, it is economically disadvantageous.

For the nonionic resin emulsion, either or both of a method of introducing a nonionic functional group such as ethylene oxide into the base resin, that is, a self-emulsification method and a method of emulsification using a nonionic surfactant, that is, a forced emulsification method. It can be produced using a technique. For the cationic resin emulsion, either or both of a method of introducing a cationic functional group such as an amine group into the base resin, that is, a self-emulsification method and a method of emulsification using a cationic surfactant, that is, a forced emulsification method, are used. They can be used at the same time. Furthermore, after introducing a cationic functional group, a nonionic surfactant can also be used as an emulsification aid. Moreover, when the molecular weight of the self-emulsifying emulsion is small, the emulsion is no longer a particulate emulsion but a water-soluble resin, but even the water-soluble resin does not impair the effects of the present invention. The water-based resin in the present invention is a general term for water-dispersed emulsions and water-soluble resins.

In addition, a curing agent such as a blocked polyisocyanate can be arbitrarily added to the water-based resin.

The electrodeposition coating composition of the present invention preferably contains 20 to 500 ppm of Al ions. More preferred is 50 to 400 ppm, and most preferred is 100 to 300 ppm. If the lower limit is not reached, the effect of improving the coating deposition of Al ions becomes insufficient, and if the upper limit is exceeded, the electrical conductivity of the composition becomes excessive, and the throwing power is reduced.

The Al ion concentration in the composition can be determined by solid-liquid separation of the composition using an ultracentrifuge and quantifying the liquid phase using high frequency inductively coupled plasma emission spectrometry (ICP) or atomic absorption spectrometry (AA). .

As the liquid medium of the electrodeposition composition according to the present invention, an aqueous medium is preferable, and water is more preferable. When the liquid medium is water, the liquid medium may contain an aqueous solvent other than water (for example, water-soluble alcohols).

The pH of the electrodeposition coating composition of the present invention preferably satisfies the following formula when the Al ion concentration is A [ppm].
3.5 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
The following formula is more preferable.
3.6 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
The following formula is most preferable.
3.7 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
When the pH is lower than the lower limit, the deposition efficiency is lowered and the throwing power is also lowered. When the pH exceeds the upper limit, Al ions cause hydrolysis, which is not preferable.

The term −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 ) is obtained from the solubility product of Al hydroxide at 25 ° C .: 1.92 × 10 ⁻³² . That is, when the pH is exceeded, Al ions precipitate as hydroxides and can no longer be ions. Here, 25 ° C. is a typical temperature during storage and use of the composition.

The effects of Al ions in the present invention are as follows. In other words, when ionic Al becomes a fine hydroxide colloid due to the increase in pH of the metal surface due to cathodic electrolysis, when it completely loses the zeta charge at around pH 9 and begins to agglomerate rapidly, the surrounding resin emulsion is also involved. Presumed to be deposited.

It is necessary to complete a series of reactions from the cathode ion to the disappearance of the charge of the hydroxide colloid instantaneously. If it has become a hydroxide in advance, aggregation starts over time, and the aggregation ability around pH 9 is extremely reduced. Therefore, the Al component of the present invention must be only ions in the composition.

Moreover, Al ions can be stabilized by a specific chelating agent, but if stabilized, formation of hydroxide due to an increase in pH is also inhibited, which is not preferable. Note that organic acids such as acetic acid, formic acid, sulfamic acid, and lactic acid, which are usually blended in electrodeposition coating compositions, do not have a chelating ability to stabilize Al ions.

Al ions can be added using an Al compound. The Al compound is not particularly limited, but can be added in the form of an inorganic acid salt such as nitrate or sulfate, or an organic acid salt such as lactate or acetate.
For reference, the appropriate ranges of Al ion concentration and pH are shown in FIG.

As a method of forming a coating film on the surface of a metal material using the electrodeposition coating composition of the present invention, a cathode electrolysis method is preferable. Coating deposition cannot be expected with electroless or anodic electrolysis.
Cathodic electrolysis conditions are not particularly defined, but it is preferable to apply a voltage of 50 to 400V. More preferably, it is 100 to 300V, and most preferably 150 to 250V. It is not always necessary to use a constant voltage, and a method of gradually increasing the voltage or a method such as two-stage energization is also applicable.

In the composition of the present invention, additives usually used in the paint field such as a pigment, a catalyst, an organic solvent, a pigment dispersant, and a surfactant can be further applied as necessary. Examples of pigments include colored pigments such as titanium white and carbon black, extender pigments such as clay, talc, and barita, antirust pigments such as aluminum tripolyphosphate and zinc phosphate, and organic tin compounds such as dibutyltin oxide and dioctyltin oxide, Examples thereof include dialkyltin fatty acids such as dibutyltin laurate and dibutyltin dibenzoate, and tin compounds such as aromatic carboxylates.

The electrodeposition coating composition of the present invention is applied to various metal materials. The metal material is not particularly limited, but steel materials such as cold-rolled steel plates, hot-rolled steel plates, casting materials, steel pipes, etc., and zinc-based plating treatment and / or aluminum-based plating are applied on those steel materials. Materials, aluminum alloy plates, aluminum castings, magnesium alloy plates, magnesium castings, and the like. Moreover, even if the zinc phosphate-based chemical conversion treatment or the zirconium-based chemical conversion treatment is performed in advance as a coating ground treatment, the effect of the present invention is not impaired. It is particularly suitable for use in metal structures having complicated shapes, for example, automobile bodies, automobile parts, home appliances, building materials, etc., which are metal structures mainly composed of iron-based materials.

The contents of the present invention will be specifically described below with reference to examples and comparative examples.
In the examples, “parts” and “%” are based on weight unless otherwise specified.

Synthesis of cationic epoxy resin, flask equipped with stirrer, condenser, nitrogen inlet, thermometer and dropping funnel, 92 parts of 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2), methyl 95 parts of isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation.

Thereafter, the reaction was continued for 30 minutes, and then 57 parts of ethylene glycol mono-2-ethylhexyl ether was dropped from the dropping funnel. Further, 42 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

Next, 365 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 410.

Subsequently, when 87 parts of bisphenol A was added and reacted at 120 ° C., the epoxy equivalent was 1190. Thereafter, the reaction mixture was cooled, 11 parts of diethanolamine, 24 parts of N-ethylethanolamine and 25 parts of 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became 80% of non volatile matters, and obtained the amine modified epoxy resin (resin solid content 80%) whose glass transition temperature is 22 degreeC. This manufacturing method is based on Manufacturing Example 1 in the example of Patent Document 1 (Japanese Patent Laid-Open No. 2002-294143).

Production of blocked isocyanate curing agent 1250 parts of diphenylmethane diisocyanate and 266.4 parts of MIBK were charged into a reaction vessel, which was 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. This manufacturing method is based on Manufacturing Example 2 in the embodiment of Patent Document 1 (Japanese Patent Laid-Open No. 2002-294143).

Production of pigment dispersion resin First, 222.0 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) was 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. Here, 0.2 part of hedibutyltin dilaurate was added. Thereafter, the temperature was raised to 50 ° C., and 131.5 parts of 2-ethylhexanol was added dropwise with stirring in a dry nitrogen atmosphere over 2 hours. 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 dimethylethanolamine, 117.6 parts of 75% aqueous lactic acid solution, and 39.2 parts of ethylene glycol monobutyl ether are added to a suitable reaction vessel in this order, and the mixture is stirred at 65 ° C. for about half an hour to form quaternization. An agent was 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 reacted at 150-160 ° C. for about 1 hour, then cooled to 120 ° C., and 498.8 parts of the 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 1390.2 parts of ethylene glycol monobutyl ether is 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 85-95 ° C. until the acid value is 1, 37.0 parts of deionized water is added to terminate the quaternization in the epoxy-bisphenol A resin and have a quaternary ammonium salt moiety. A pigment dispersing resin was obtained (resin solid content 50%). This manufacturing method is based on Manufacturing Example 3 in the embodiment of Patent Document 1 (Japanese Patent Laid-Open No. 2002-294143).

Manufacture of pigment dispersion paste 120 parts of resin for pigment dispersion in sand grind mill, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, 18.0 parts of zinc phosphate tetrahydrate and ions 221.7 parts of exchange water was added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content 48%). This production method is in accordance with Production Example 4 in the example of Patent Document 1 (Japanese Patent Laid-Open No. 2002-294143) except that zinc phosphate tetrahydrate is used instead of aluminum phosphomolybdate.

Production of Cationic Epoxy Electrodeposition Coating Composition A cationic epoxy resin and a blocked isocyanate curing agent were mixed so as to be uniform at a solid content ratio of 70/30. Thereafter, ethylene glycol-2-ethylhexyl ether was added to 2 wt% based on the solid content. Glacial acetic acid was added so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solids was 24, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1960 parts of this emulsion, 197 parts of pigment dispersion paste, 14.5 parts of dibutyltin oxide and 1843 parts of ion-exchanged water were mixed to obtain an electrodeposition coating composition having a solid content of 20% by weight (hereinafter abbreviated as “R1”). It was. This manufacturing method is in accordance with Example 1 in the example of Patent Document 1 (Japanese Patent Laid-Open No. 2002-294143) except that a 10% cerium acetate aqueous solution was not mixed.

Production of Cationic Acrylic Electrodeposition Coating Composition Cationic acrylic resin “Saxade # 1000” (solid content: 65%) manufactured by Shinto Paint was diluted with deionized water to adjust the solid content to 18% (hereinafter abbreviated as “Abbreviation“ R2 ").

Production of Nonionic Urethane Electrodeposition Coating Composition Nonionic Urethane Resin “VONDIC2220” (solid content: 40%) manufactured by DIC was diluted with deionized water to adjust the solid content to 18% (hereinafter abbreviated “R3”). .

In the examples and comparative examples, Al ions were added using aluminum nitrate nonahydrate, aluminum sulfate 14-18 hydrate, or aluminum lactate. Further, the pH of the composition was adjusted with nitric acid or ammonia as necessary. The composition of the composition is shown in Table 1.

Preparation of test plate A cold rolled steel plate: SPCC (JIS 3141) 70 × 150 × 0.8 mm was used as a test plate, and its surface was previously used with a strong alkaline degreasing agent “FC-E2001” manufactured by Nihon Parkerizing Co., Ltd. for 120 seconds. A degreasing treatment was performed by spraying. After the degreasing treatment, it was washed with spray water for 30 seconds, immersed in the compositions shown in Examples and Comparative Examples, and subjected to cathode electrolytic treatment. The test plate after completion of electrolysis was immediately spray-washed with deionized water for 30 seconds and baked in an electric oven at 170 ° C. for 20 minutes.

Evaluation of throwing power The throwing power was evaluated by the “four-sheet box method”. As shown in FIG. 3, a “four-box testability jig with a box method” (see FIG. 2) in which holes of 8 mm in diameter were formed in the test plate and four steel plates were installed at 2 cm intervals was wired. Of the four steel plates shown in FIG. 3, the left side facing the leftmost steel plate is referred to as “A surface”, and the right side surface toward “B surface”. Similarly, the left and right surfaces of the second steel plate from the left are “C surface” and “D surface”, respectively, and the left and right surfaces of the third steel plate from the left are “E surface” and “F surface”, respectively. The right and left surfaces of the rightmost steel sheet are the “G plane” and the “H plane”, respectively. In the apparatus shown in FIG. 2, electrodeposition was applied at a coating bath temperature of 30 ° C., a distance between the A-side and the electrode of 10 cm, and a current-carrying time of 3 minutes, at a voltage of A-side film thickness of 20 μm.

The throwing power was evaluated by the film thickness on the G surface. G-plane film thickness: less than 5 μm x, 5 μm or more and less than 10 μm ◯, 10 μm or more as ◎.
However, R3 was not a four-sheet box method, and one test plate was subjected to cathodic electrolytic treatment at 200 V for 3 minutes, and the coating thickness after baking was evaluated. The evaluation results are also shown in Table 1.

From Examples 1 to 6 in Table 1, it can be seen that by using the electrodeposition coating composition of the present invention, good throwing power is obtained for the metal material.

On the other hand, Comparative Examples 1 to 3, which do not contain Al ions, which is the greatest feature of the present invention, have not only a sufficient throwing power but also no precipitation with respect to the nonionic resin emulsion.

Further, Comparative Example 4 is under the lower limit of Al ion concentration, and Comparative Example 5 is under the excessive Al ion concentration and lower pH limit.

Further, Comparative Example 6 is a composition in which the pH of Example 4 was raised, and the throwing power was still insufficient, but this is a neutralization step for raising the pH, and most of Al ions are water. This is probably because the precipitates were deposited as oxides, and the effect of Al ions was no longer exhibited. In fact, it has been confirmed by liquid analysis after centrifugation that the Al ion concentration is 0 ppm.

As described above, the cathodic electrolysis treatment of a metal material using the composition of the present invention can provide excellent throwing power, which cannot be achieved by conventional cationic electrodeposition coating, and can be obtained by conventional electrolytic deposition. It can be seen that this is an epoch-making technique that enables electrolytic deposition of a nonionic resin emulsion that has been impossible.

Claims (2)

1. An electrodeposition coating composition comprising a nonionic and / or cationic water-based resin and Al ions of 20 to 500 ppm, wherein the pH satisfies the following formula when the Al ion concentration is A [ppm] .
   3.5 ≦ pH ≦ −Log ((A × 1.93 × 10 ⁻¹⁵ ) ^1/3 )
2. An electrodeposition coating method comprising depositing a coating film of a metal material by a cathode electrolysis method using the composition of claim 1.
   
   

Images