CN102341468B - 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

technical field

The present invention relates to an electrodeposition coating composition and an electrodeposition coating method having excellent spreadability with respect to metal materials, particularly metal structures having complex shapes.

Background technique

Conventionally, as a method for imparting excellent corrosion resistance to various metal materials, especially complex-shaped metal structures, electrodeposition coating capable of uniformly depositing a coating film on every corner of a complex shape has been widely used.

Electrodeposition coating is roughly divided into anionic electrodeposition coating and cationic electrodeposition coating. Among them, anion electrodeposition coating is to make the coating film Precipitation, cationic electrodeposition coating The coating film is deposited by cathodic electrolysis of the object to be coated in a water-based paint containing a cationic resin emulsion.

The anionic resin emulsion has dispersion stability on the alkaline side and loses dispersion stability on the acidic side. On the contrary, the cationic resin emulsion has dispersion stability on the acidic side and loses dispersion stability on the basic side. Precipitation of resin by anodic electrolysis or cathodic electrolysis takes advantage of this property. In this way, in terms of the reaction mechanism, it is impossible for the nonionic resin emulsion to precipitate.

For improving the corrosion resistance of iron-based metal materials, it is very beneficial to use cationic electrodeposition coating without worrying about the dissolution of blank metal into the paint during electrolytic treatment. Cationic electrodeposition coating can be widely used as iron-based materials. The main metal structure of the car body, car parts, home appliances, building materials, etc.

As mentioned above, the biggest feature of electrodeposition coating is the spreading ability of the coating. In recent years, higher spreading ability has been demanded for the purpose of reducing the amount of paint used and improving corrosion resistance. For this reason, various studies have been conducted in order to improve the dispersibility.

For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-294143), the following lead-free cationic electrodeposition paint composition is disclosed, which is to contain an aqueous medium, and to be dispersed or dissolved in the aqueous medium, and to contain a cationic epoxy resin and A lead-free cationic electrodeposition coating composition comprising a binder resin of a blocked isocyanate curing agent, a neutralizing acid for neutralizing a cationic epoxy resin, an organic solvent, and a metal catalyst, wherein the volatile organic component content is 1 % by weight or less, the concentration of metal ions is less than 500ppm, the amount of neutralizing acid is 10-30mg equivalent relative to 100g of binder resin solid content, preferably the metal catalyst is selected from cerium ions, bismuth ions, copper ions, zinc ions, molybdenum ions ions and aluminum ions, and the neutralizing acid is at least one selected from acetic acid, lactic acid, formic acid, and sulfamic acid.

In addition, many techniques for improving spreading ability using a composition similar to the electrodeposition coating composition have also been disclosed.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-285391) is characterized in that the temperature of the electrodeposition bath is controlled, and Patent Document 3 (Japanese Patent Application Laid-Open No. 2002-285392) is characterized in that there are two types of electrodes having different glass transition temperatures of the coating film. The deposition process is characterized in that Patent Document 4 (Japanese Patent Laid-Open No. 2002-294144) is characterized in that the non-volatile solid content is specified. , the glass transition temperature and the molecular weight of specified cationic epoxy resin, the feature of patent document 7 (Japanese Patent Application Laid-Open 2002-294147) is, the minimum film-forming temperature of specified coating film, the patent document 8 (Japanese Patent Application Laid-Open 2005-194389) It is characterized in that the matrix resin skeleton of the cationic epoxy resin, the film resistance, the curing agent, and the glass transition temperature of the curing agent are specified. Patent Document 9 (Japanese Patent Laid-Open No. 2008-156655) is also characterized by a specific film resistance.

Patent Document 1 Japanese Patent Application Laid-Open No. 2002-294143

Patent Document 2 Japanese Patent Application Laid-Open No. 2002-285391

Patent Document 3 Japanese Patent Application Laid-Open No. 2002-285392

Patent Document 4 Japanese Patent Application Laid-Open No. 2002-294144

Patent Document 5 Japanese Patent Application Laid-Open No. 2002-294145

Patent Document 6 Japanese Patent Application Laid-Open No. 2002-294146

Patent Document 7 Japanese Patent Laid-Open No. 2002-294147

Patent Document 8 Japanese Patent Application Laid-Open No. 2005-194389

Patent Document 9 Japanese Patent Application Laid-Open No. 2008-156655

Patent Document 10 Japanese Patent Application Laid-Open No. 2007-314690

Patent Document 11 Japanese Patent Application Laid-Open No. 2008-538383

Non-Patent Document 1: Maeda Shigeyoshi, Asai Tsunetoshi, Okada Hideya Anticorrosion Technology: 31, 268 (1982)

Although the above-mentioned conventional technologies are indeed effective for the dispersion capability, the market demand does require further improvement of the dispersion capability. Therefore, the inventors of the present invention reconsidered the deposition mechanism itself of the cationic electrodeposition coating.

Resin emulsions used in cationic electrodeposition coating are often endowed with cationic properties by introducing amino groups. The cationic resin emulsion should have dispersion stability on the acidic side and lose dispersion stability on the basic side. However, Document 1 discloses that the pH of the emulsion to form a coating film is about 12 by actual cathodic electrolysis.

Of course, the pH of the precipitated coating film varies with the properties of the resin emulsion, such as the molecular weight of the emulsion, the type of introduced amino group, or the rate of introduction, but the precipitation does not start at least until the pH exceeds the region of 10. In this way, it can be said that when the pH rises due to cathodic electrolysis, it is advantageous for the deposition properties of the coating film that the pH of the coating composition as the initial pH is as high as possible within the range where the resin emulsion is stabilized. pH.

Although Patent Document 10 (Japanese Patent Laid-Open No. 2007-314690) and Patent Document 11 (Japanese Patent Laid-Open No. 2008-538383) as prior art are still related to electrodeposition coating compositions, the pH of the aqueous coating composition is preferably 5-7, More preferably, it is 5.5-6.5. Disadvantages when the pH is less than 5 include reduction in electrodeposition coating efficiency and film appearance.

Although there is no specific description of pH in Patent Documents 1 to 9, in order to improve the spreading ability of electrodeposition coatings, it is preferable to reduce the amount of neutralizing acid contained in the coating composition and lower the neutralization rate of the cationic epoxy resin to Inhibit at low levels, that is, keep the pH as high as possible. In fact, since the amount of the neutralizing acid is 10 to 30 mg equivalent to 100 g of the binder resin solid content, it is obvious that the pH must be within the same range as in Patent Documents 10 and 11.

In other words, either increasing the pH of the electrodeposition coating composition itself or lowering the precipitation pH by modifying the resin emulsion has reached its limit, and improvement in spreading ability cannot be expected if other methods are used.

Therefore, the inventors of the present invention studied the reduction of the coating film precipitation pH using a coagulant as a new method. From this, it was found that Al is the most effective among various coagulants.

However, even if an Al compound is added to a conventional electrodeposition coating composition, it is instantly hydrolyzed to become a hydroxide, and the hydroxide aggregates over time, thereby losing its effect as an aggregating agent.

In Patent Documents 1 to 9, it is considered that it is preferable to contain aluminum ions as the metal catalyst. However, it is presumed from the above reasons that in actual electrodeposition coating compositions, hydrolysis occurs instantaneously to form hydroxides. Although the verification of the examples was not carried out, it is considered that the effect of the hydroxide as a coagulant can no longer be expected although the function of the hydroxide is maintained as a catalyst.

Contents of the invention

Therefore, the inventors of the present invention intentionally lowered the pH around neutral, which is common knowledge in electrodeposition coating compositions, to a range in which Al can continue to exist in an ionized state, and evaluated the effect of Al ions on the spreading ability. The pH of the composition is lowered, however very good spreadability can still be obtained.

In addition, the effect of this Al ion is also effective for a nonionic resin emulsion that cannot be electrolytically separated, and it can be deposited by cathodic electrolysis in the same way, thus completing the present invention.

That is, the present invention is (1) and (2) shown below.

(1) An electrodeposition coating composition characterized in that it contains a nonionic and/or cationic water-based resin and 20 to 500 ppm of Al ions, and when the Al ion concentration is A [ppm], the pH satisfies The following calculation formula:

3.5≤pH≤-Log ((A×1.93×10 ^-15 ) ^1/3 )

(2) An electrodeposition coating method characterized by depositing a coating film on a metal material by cathodic electrolysis using the composition of the above (1).

Description of drawings

FIG. 1 is a graph showing suitable ranges of Al ion concentration and pH.

Fig. 2 is a model diagram of a "jig for a dispersive ability test with four box plates" used in a dispersive ability test.

Fig. 3 shows the state of electrodeposition coating in the spreading ability test.

Among them, 1 hole with a diameter of 8 mm, 2 the outer plate (side A) in the jig for dispersing ability test with 4 box plates, and 3 the inner plate (side A) in the jig for dispersing ability test with 4 box plates ( G side), 4 electrodeposition coating baths

Detailed ways

The electrodeposition coating composition of the present invention contains nonionic and/or cationic water-based resins. Here, neither the nonionic resin nor the cationic resin is particularly limited. The effect of the present invention is not impaired regardless of the type of base resin used, however, epoxy resin, urethane resin, and acrylic resin are preferable. Here, one of the characteristics of the present invention lies in the following point, that is, based on a new mechanism of action (a mechanism in which Al ions aggregate into hydroxide colloids as the pH rises, and the surrounding resin is involved at this time), electrolysis has not been possible in the past. The nonionic resins listed above can also be used. Since nonionic resins can also be used in this way, the range of selection is widened, and various properties that cannot be imparted to the film can be imparted heretofore. In addition, in the case of using a cationic resin, in addition to the well-known mechanism that the resin itself loses dispersion stability as the pH increases, electrolysis can be achieved at a pH lower than conventional ones based on the above-mentioned novel mechanism of action.

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

For the nonionic resin emulsion, either the self-emulsification method, which is a method of introducing a nonionic functional group such as ethylene oxide into the base resin, or the forced emulsification method, which is a method of emulsifying it with a nonionic surfactant, can be used. One or both approaches to crafting. For the cationic resin emulsion, either or both of the self-emulsification method, which is a method of introducing a cationic functional group such as an amino group into the base resin, and the forced emulsification method, which is a method of emulsifying it with a cationic surfactant, can be used. to make. In addition, after introducing a cationic functional group, a nonionic surfactant can also be used as an emulsification aid. In addition, when the molecular weight of the self-emulsifying emulsion is small, it becomes a water-soluble resin instead of a particulate emulsion, but the effect of the present invention is not impaired even if it is a water-soluble resin. The water-based resin in the present invention is a generic term for water-dispersible emulsions and water-soluble resins.

In addition, a curing agent including a blocked polyisocyanate may be arbitrarily blended in the water-based resin.

The electrodeposition coating composition of the present invention preferably contains 20 to 500 ppm of Al ions. More preferably, it is 50-400 ppm, Most preferably, it is 100-300 ppm. If it is lower than the lower limit, the effect of improving the deposition of Al ions on the coating film will be insufficient, and if it is higher than the upper limit, the electrical conductivity of the composition will be too large, conversely reducing the spreading ability.

For the concentration of Al ions in the composition, the composition can be separated into solid and liquid using an ultracentrifuge, and the liquid phase can be quantified using high-frequency inductively coupled plasma emission spectrometry (ICP) or atomic absorption spectrometry (AA).

The liquid medium of the electrodeposition composition in the present invention is preferably an aqueous medium, more preferably water. Furthermore, when the liquid medium is water, other aqueous solvents (for example, water-soluble alcohols) other than water may be contained as the liquid medium.

The pH of the electrodeposition coating composition of the present invention preferably satisfies the following calculation formula when the Al ion concentration is A [ppm].

3.5≤p H≤-Log((A×1.93×10 ^-15 ) ^1/3 )

More preferably, it is the following formula.

3.6≤p H≤-Log((A×1.93×10 ^-15 ) ^1/3 )

Most preferably, it is the following formula.

3.7≤p H≤-Log((A×1.93×10 ^-15 ) ^1/3 )

If the pH is lower than the lower limit, the deposition efficiency will decrease and the spreading ability will also decrease. If the pH is higher than the upper limit, Al ions will be hydrolyzed, which is not preferable.

The term -Log((A×1.93×10 ^-15 ) ^1/3 ) was obtained from the solubility product of aluminum hydroxide at 25°C: 1.92×10 ^-32 . That is, when the pH is higher than this, Al ions are precipitated as hydroxides and are no longer ions. Here, 25° C. is a typical temperature during storage and use of the composition.

The effects of the Al ions of the present invention are as follows. That is to say, it can be inferred that ionic Al becomes a fine hydroxide colloid due to the increase in the pH of the metal surface caused by cathodic electrolysis, and when it completely loses the Z charge (ゼタ charge) at around pH 9, it starts to sharply When agglomerated, the surrounding resin emulsion is also involved and precipitated.

A series of reactions from Al ion to the disappearance of the charge of the hydroxide colloid by cathodic electrolysis need to be completed in an instant. If it becomes a hydroxide beforehand, it will start to aggregate with the lapse of time, and the aggregation ability will decrease extremely at pH9 or so. Therefore, the Al component of the present invention must always be Al ions in the composition.

In addition, although Al ions can be stabilized by a specific chelating agent, if they are stabilized, the formation of hydroxides due to the increase in pH is also inhibited, which is not preferable. Furthermore, organic acids such as acetic acid, formic acid, sulfamic acid, and lactic acid generally blended in electrodeposition coating compositions do not have chelating ability to the extent that Al ions can be stabilized.

Al ions can be added using an Al compound. The Al compound is not particularly limited, but may be added in the form of inorganic acid salts such as nitrates and sulfates or organic acid salts such as lactates and acetates.

For reference, suitable ranges of Al ion concentration and pH are shown in FIG. 1 .

As a method for forming a coating film on the surface of a metal material using the electrodeposition coating composition of the present invention, cathodic electrolysis is preferred. In the case of non-electrolysis or anodic electrolysis, deposition of a coating film cannot be expected.

The cathodic electrolysis conditions are not particularly specified, but it is preferable to apply a voltage of 50 to 400V. More preferably, it is 100-300V, Most preferably, it is 150-250V. In addition, constant voltage is not necessarily required, and a method of gradually increasing the voltage, or 2-step energization may be applied.

In the composition of the present invention, additives generally used in the coatings field, such as pigments, catalysts, organic solvents, pigment dispersants, and surfactants, may also be used as needed. Examples of pigments include colored pigments such as titanium dioxide and carbon black, filler pigments such as clay, talc, and barium oxide, antirust pigments such as aluminum tripolyphosphate and zinc phosphate, and organic pigments such as dibutyltin oxide and dioctyltin oxide. Tin compounds, tin compounds such as fatty acids of dialkyltin such as dibutyltin laurate and dibutyltin dibenzoate, or aromatic carboxylates.

The electrodeposition coating composition of the present invention can be applied to various metal materials. The metal material is not particularly limited, but steel materials such as cold-rolled steel sheets, hot-rolled steel sheets, casting materials, steel pipes, etc., materials that have been subjected to zinc-based plating and/or aluminum-based plating, aluminum alloys, etc. plate, aluminum casting material, magnesium alloy plate, magnesium casting material, etc. In addition, the effects of the present invention are not impaired even if zinc phosphate-based chemical conversion treatment or silicon-based chemical conversion treatment is previously performed as a coating base treatment. It is especially suitable for complex-shaped metal structures, such as automobile bodies, automobile parts, home appliances, building materials, etc., which are metal structures mainly composed of iron-based materials.

Example

The content 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 indicated.

Synthesis of Cationic Epoxy Resin

In the flask equipped with stirrer, cooling pipe, nitrogen introduction pipe, thermometer and dropping funnel, add 92 parts of 2,4-/2,6-toluene diisocyanate (weight ratio=8/2), 95 parts of formaldehyde methyl isobutyl ketone (hereinafter referred to as MIBK) and 0.5 parts of dibutyltin dilaurate. While stirring the reaction mixture, 21 parts of methanol were added dropwise. The reaction started at room temperature and was exothermic to 60°C.

Thereafter, after continuing the reaction for 30 minutes, 57 parts of ethylene glycol mono-2-ethylhexyl ether were dropped from the dropping funnel. Next, 42 parts of bisphenol A-propylene oxide 5-mol adducts were added to the reaction mixture. The reaction proceeds mainly in the range of 60 to 65°C, and continues until the absorption due to the isocyanate group disappears in the measurement of the IR spectrum.

Then, 365 parts of epoxy resins with an epoxy group equivalent weight of 188 synthesized by known methods from bisphenol A and epichlorohydrin were added to the reaction mixture, and the temperature was raised to 125°C. Then, 1.0 parts of benzyldimethylamine was added, and it was made to react at 130 degreeC until it became epoxy group equivalent weight 410.

Next, after adding 87 parts of bisphenol A and making it react at 120 degreeC, epoxy group equivalent weight became 1190. Thereafter, the reaction mixture was cooled, and a 79% by weight MIBK solution of 11 parts of diethanolamine, 24 parts of N-ethylethanolamine, and 25 parts of a ketimide of aminoethylethanolamine was added, and reacted at 110° C. for 2 hours. . Thereafter, it was diluted with MIBK to a non-volatile content of 80% to obtain an amine-modified epoxy resin (resin solid content: 80%) having a glass transition temperature of 22°C. In addition, this manufacturing method is based on the manufacturing example 1 of the Example of the patent document 1 (Japanese Unexamined-Japanese-Patent No. 2002-294143).

Manufacture of blocked isocyanate curing agent

1250 parts of diphenylmethane diisocyanate and 266.4 parts of MIBK were put into the reaction container, and after heating it to 80 degreeC, 2.5 parts of dibutyltin dilaurate were added. A solution in which 226 parts of ε-caprolactam was dissolved in 944 parts of butyl cellosolve was dropped there over 2 hours at 80°C. Further, after heating at 100° C. for 4 hours, it was confirmed that absorption due to isocyanate groups disappeared in IR spectrum measurement, and after natural cooling, 336.1 parts of MIBK were added to obtain a blocked isocyanate curing agent. In addition, this manufacturing method is based on the manufacturing example 2 of the embodiment of the patent document 1 (Japanese Unexamined-Japanese-Patent No. 2002-294143).

Manufacture of pigment dispersion resin

First, 222.0 parts of isophorone diisocyanate (hereinafter referred to as IPDI) was added to a reaction vessel equipped with a stirring device, a cooling pipe, a nitrogen introduction pipe and a thermometer, diluted with 39.1 parts of MIBK, and 0.2 parts of Dibutyltin dilaurate. Then, after heating up this to 50 degreeC, 131.5 parts of 2-ethylhexanols were dripped over 2 hours in dry nitrogen atmosphere with stirring. The reaction temperature was maintained at 50°C with appropriate cooling. As a result, 2-ethylhexanol semi-blocked IPDI (resin solid content: 90.0%) was obtained.

Then, add 87.2 parts of dimethylethanolamine, 117.6 parts of 75% lactic acid aqueous solution and 39.2 parts of ethylene glycol monobutyl ether to an appropriate reaction vessel, and stir at 65°C for about half an hour to prepare a quaternary salt agent.

Then, 710.0 parts of EPON 829 (bisphenol A type epoxy resin manufactured by Shell Chemical Co., epoxy group equivalent 193～203) and 289.6 parts of bisphenol A are added in an appropriate reaction vessel, and heated under a nitrogen atmosphere After reaching 150-160°C, an initial exothermic reaction occurs. The reaction mixture was reacted at 150-160° C. for about 1 hour, and then, after cooling to 120° C., 498.8 parts of 2-ethylhexanol semi-blocked IPDI (MIBK solution) prepared earlier was added.

Keep the reaction mixture at 110-120°C for about 1 hour, then add 1390.2 parts of ethylene glycol monobutyl ether, cool the mixture to 85-95°C, after homogenization, add 196.7 parts of quaternary salt prepared before agent. Keep the reaction mixture at 85-95°C until the acid value reaches 1, then add 37.0 parts of deionized water to complete the quaternization in the epoxy-bisphenol A resin to obtain a pigment dispersion with a quaternary ammonium salt part Resin (resin solid content 50%). In addition, this manufacturing method follows the manufacturing example 3 of the embodiment of patent document 1 (Japanese Patent Laid-Open No. 2002-294143).

Manufacture of Pigment Dispersion Paste

Add 120 parts of resin for pigment dispersion, 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 221.7 parts of ion-exchanged water to the sand mill, and disperse until the particle size reaches 10 μm or less, a pigment dispersion paste (solid content 48%) was obtained. In addition, this manufacturing method is based on the manufacturing example 4 of the Example of the patent document 1 (Japanese Unexamined-Japanese-Patent No. 2002-294143) except having used zinc phosphate tetrahydrate instead of aluminum phosphomolybdate.

Manufacture of Cationic Epoxy Electrodeposition Coating Composition

The cationic epoxy resin and the blocked isocyanate curing agent were uniformly mixed at a solid content ratio of 70/30. Then, ethylene glycol-2-ethylhexyl ether was added so that it might become 2 weight% with respect to solid content. Glacial acetic acid was added thereto so that the milliequivalent (MEQ(A)) of the acid per 100 g of resin solid content was 24, and then ion-exchanged water was added slowly for dilution. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1960 parts of this emulsion and 197 parts of pigment dispersion paste are mixed with 14.5 parts of dibutyl tin oxide and 1843 parts of ion-exchanged water to obtain a solid content of 20% by weight electrodeposition coating composition (hereinafter abbreviated as " R1"). In addition, this manufacturing method follows the example 1 of the example of patent document 1 (Japanese Patent Laid-Open No. 2002-294143) except that 10% cerium acetate aqueous solution is not mixed.

Manufacture of Cationic Acrylic Electrodeposition Coating Composition

The cationic acrylic resin "SUCCED#1000" (solid content: 65%) manufactured by Shinto Paint was diluted with deionized water, and the solid content was adjusted to 18% (hereinafter abbreviated as "R2").

Manufacture of nonionic polyurethane electrodeposition coating composition

Nonionic polyurethane resin "VONDIC 2220" (solid content: 40%) manufactured by DIC Corporation was diluted with deionized water to adjust the solid content to 18% (hereinafter abbreviated as "R3").

Regarding the levels of Al ions added in Examples and Comparative Examples, Al ions were added using aluminum nitrate nonahydrate, aluminum sulfate fourteen to octadecahydrate, or aluminum lactate. In addition, nitric acid or ammonia water was used to adjust the pH of the composition as needed. The composition of the composition is shown in Table 1.

Production of test boards

As a test plate, a cold-rolled steel sheet: SPCC (JIS3141) 70×150×0.8 mm was used, and the surface thereof was degreased by spraying for 120 seconds with a strong alkaline degreasing agent “FC-E2001” manufactured by Parkerizing Co., Ltd., Japan. After the degreasing treatment, it was sprayed with water for 30 seconds, immersed in the compositions shown in Examples and Comparative Examples, and subjected to cathodic electrolytic treatment. Immediately after the electrolysis, the test plate was sprayed with deionized water for 30 seconds, and baked in an electric oven at 170° C. for 20 minutes.

Dispersion ability evaluation

The spreading ability was evaluated by the "4-box-board method". A hole with a diameter of 8 mm was opened in the test plate, and the "jig for the dispersive ability test of the 4-sheet box method" (see FIG. 2 ) in which 4 steel plates were installed at intervals of 2 cm was wired as shown in FIG. 3 . Among the four steel sheets in FIG. 3 , the leftmost surface of the steel sheet is referred to as "A surface", and the right surface is referred to as "B surface". Similarly, let the left and right surfaces of the second steel plate from the left be respectively referred to as "C surface" and "D surface", and the left and right surfaces of the third steel plate from the left be respectively referred to as "E surface" and "F surface". In addition, the left and right surfaces of the rightmost steel plate are respectively referred to as "G surface" and "H surface". In the device shown in Figure 2, under the conditions of coating bath temperature of 30°C, distance between surface A and electrode of 10cm, and energization time of 3 minutes, electrodeposition coating was carried out at a voltage with a film thickness of A to 20μm.

The spreading ability is evaluated by the film thickness of the G surface. The thickness of the G mask was less than 5 μm as ×, 5 μm or more and less than 10 μm was as ○, and 10 μm or more was as ◎.

However, R3 was not evaluated by the four-panel method, but one test panel was subjected to cathodic electrolytic treatment at 200V for 3 minutes, and the thickness of the coating film after baking was evaluated. The evaluation results are combined and recorded 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 spreadability with respect to metal materials can be obtained.

On the other hand, Comparative Examples 1 to 3, which did not contain Al ions, which is the most characteristic feature of the present invention, not only had insufficient spreading ability, but also did not precipitate in the nonionic resin emulsion.

In addition, in Comparative Example 4, the Al ion concentration was lower than the lower limit, and in Comparative Example 5, the Al ion concentration was too high and the pH was below the lower limit, and the dispersion ability was not sufficient.

In addition, Comparative Example 6 is a composition whose pH was raised in Example 4, but the spreading ability is still not sufficient. This is considered to be because most of the Al ions are used as hydroxides in the neutralization process for raising the pH. Precipitation of the substance precipitated out, and the effect of Al ions could no longer be exerted. In fact, it was confirmed by liquid analysis after centrifugation that the Al ion concentration was 0 ppm.

It can be seen that the cathodic electrolytic treatment of metal materials using the composition of the present invention can obtain excellent spreading ability that cannot be achieved by conventional cationic electrodeposition coatings, and can also realize non-ionic coatings that cannot be electrolytically deposited in the past. The electrolysis of permanent resin emulsion is an epoch-making technology.

[Table 1]

*Formula value＝-Log(A×1.93×10 ^-15 ) ^1/3

Claims (2)

1. an electrodeposition coating composition, is characterized in that, the Al ion of the aqueous resin that contains nonionic and/or cationic and 20～500ppm, being made as A[ppm by Al ionic concn] time, pH meets calculating formula below:

3.7≤pH≤-Log((A×1.93×10 ^-15) ^1/3)。

2. a method for electrocoating, is characterized in that, right to use requires the composition described in 1, utilizes katholysis to separate out film in metallic substance.

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