WO2008091082A1

WO2008091082A1 - A method for preparing cationic microgel for electrodepositable coating and an electrodepositable coating composition comprising cationic microgel prepared from the same

Info

Publication number: WO2008091082A1
Application number: PCT/KR2008/000354
Authority: WO
Inventors: Seok Chan Hong; Sang Hun Kim; Duck Soo Sohn; Han Ju Yang; Man Yong Jung; Nam Ju Lee; Tae Ho Kim
Original assignee: Kcc Corporation
Priority date: 2007-01-23
Filing date: 2008-01-21
Publication date: 2008-07-31
Also published as: CN101583681A; RU2009131731A; TR201104839T1; TR200905554T1; RU2428446C2; CN101583681B; KR20080069419A; KR100929040B1

Abstract

The present invention relates to a method for preparing a cationic microgel for electrodepositable coating and an electrodepositable coating composition comprising cationic microgel prepared by the same method. More specifically, the present invention relates to the method for preparing a cationic microgel for electrodepositable coating and the electrodepositable coating composition comprising cationic microgel prepared from by same method, wherein the method for preparing cationic microgel for electrodepositable coating comprises the steps of (1) preparing tertiary amine salt by reacting a tertiary amine having a hydroxy group with diisocyanate followed by neutralizing the resulting mixture with acid; and (2) dispersing the tertiary amine salt resin and polyepoxy resin polymer in a dispersion media, and then reacting the tertiary amine salt resin and polyepoxy resin polymer in the presence of diamine. The cationic microgel for electrodepositable coating exhibits excellent mechanical properties when applied to electrodepositable coating. The electrodepositable coating with the cationic microgel is excellent for edge coating and provides a good smooth coating film by inhibiting the formation of craters by adequately controlling the flowability during the hardening of the coating film.

Description

A METHOD FOR PREPARING CATIONIC MICROGEL FOR

ELECTRODEPOSITABLE COATING AND AN ELECTRODEPOSITABLE

COATING COMPOSITION COMPRISING CATIONIC MICROGEL PREPARED

FROM THE SAME

FILED OFTHE INVENTION

The present invention relates to a method for preparing cationic microgel for electrodepositable coating and an electrodepositable coating composition comprising cationic microgel prepared from the same. More specifically, the present invention relates to the method for preparing cationic microgel for electrodepositable coating and the electrodepositable coating composition comprising cationic microgel prepared by the same method of this invention, wherein the method for preparing cationic microgel for electrodepositable coating comprises the steps of (1) preparing a tertiary amine salt by reacting a tertiary amine having a hydroxy group with diisocyanate followed by neutralizing the resulting mixture with acid; and (2) dispersing the tertiary amine salt resin and polyepoxy resin polymer in a dispersion media, and then reacting the tertiary amine salt resin and polyepoxy resin polymer in the presence of diamine. The electrodepositable coating comprised of the cationic microgel exhibits excellent mechanical properties, is excellent for edge coating and provides a good smooth coating film by effectively inhibiting the formation of craters by adequately controlling the flowability during the curing of the coating film.

BACKGROUND ART

Generally, cationic electrodepositable coating refers to a coating method in which amine salt or onium salt such as ammonium salt or sulfonium salt charged with cation is introduced into a resin, and then moved to cathode in a solution under electrical field, while simultaneously, the positively-charged resin is reduced with hydroxy anion generated from the hydrolysis of water and educed to coat the cathode, i.e., the substrate. The resin coated on the substrate is cured at a certain temperature. At this time, the coated resin becomes thinned or peeled off at the edges due to the decrease of viscosity as a result of the increase of temperature. When the coating film of the edges is thinned or peeled off, the edges are easily corroded from being exposed to the external environment. Corrosion progresses at the edges at a faster rate compared with other parts, which results in serious problems with the durability of the substrate.

Increasing the molecular weight of the resin or the amount of the inorganic pigment in the coating bath has been used to prevent the peeling of the edges due to the decrease in viscosity. However, the above method is not effective, and results in a less smoothness of the coating film. U.S. Patent No. 5,096,556 and Korean Patent Publication No. 94-9035 disclose a method comprising: mixing a cationic polyepoxide-amine reaction product and a polyepoxide cross-linking agent, and cross-linking the mixture to form a cationic microgel, and then using the obtained cationic microgel in cationic electrodepositable coating in order to prepare the electrodepositable coating with good edge coverage while maintaining a smoothness of the coating film. In these patents, an aqueous dispersion suitable for use in electrodeposition is prepared by dispersing cationic polyepoxide- amine reaction product and polyepoxide cross-linking agent in a reaction media such as water, cross-linking the mixture by heat to form a cationic microgel dispersion, and then combining the resultant dispersions with ungellated cationic resins which are

p _ electrodepositable.

However, when the coating film is formed from the water-dispersion containing microgel prepared by the above method, there is a possibility of a decrease in dispersability according to the difference in the content and molecular weight of the amine which reacts with the epoxide. Also, if the cross-linking agent and polyepoxide- amine reaction product reacts vigorously during the preparation of the microgel, there will be a problem that the dispersion solution is precipitated due to the high cross-linking density of the reactant. Also in such case, the smoothness of the coating will be seriously deteriorated due to the large size of the dispersion particles of the dispersion solution. On the other hand, if the cross-linking agent and polyepoxide-amine reaction product do not react sufficiently, there will be problems with weakening of the mechanical properties and insufficient control to the density decrease at the edges due to the low cross-linking density of the particles in the dispersion solution.

SUMMARY OF THE INVENTION

In the attempt to resolve the above mentioned problems of the prior art, the purpose of the present invention is to provide a method for preparing a cationic microgel for electrodepositable coating and an electrodepositable coating composition comprising the cationic microgel prepared by the method, in which the cationic microgel exhibits excellent mechanical properties when applied to electrodepositable coating. The electrodepositable coating with the cationic microgel is excellent for edge coating and provides a good smoothness to the coating film by adequately controlling of flowability and so inhibiting the formation of craters during the curing of the coating film.

According to one aspect of the present invention, a method for preparing a cationic microgel for electrodepositable coating comprising the steps of:

(1) preparing a tertiary amine salt by reacting the tertiary amine having a hydroxy group with diisocyanate followed by neutralizing the resulting mixture with acid; and (2) dispersing the tertiary amine salt resin and polyepoxy resin polymer in a dispersion media, and then reacting the tertiary amine salt resin and polyepoxy resin polymer in the presence of diamine is provided.

According to another aspect of the present invention, an electrodepositable coating composition comprising a water-dispersion of the cationic microgel prepared by the method of the present invention is provided.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail hereafter.

In the step (1) of the preparation method of cationic microgel according to the present invention, a tertiary amine salt resin is prepared by reacting a tertiary amine having a hydroxy group with diisocyanate followed by neutralizing the resulting mixture with acid.

The tertiary amine is an alkanolamine such as dimethylethanolamine, N- methylethanolamine, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, 2-

(butylamino)ethanol or a derivative thereof, and it is preferable that one or more of the alkanolamine such as those of Formula 1 below are used. [Formula 1]

(wherein, Ri is alkylene group with 1-4 carbon atoms, R₂ and R₃ are alkyl group with 1-10 carbon atoms, aryl group with 5-18 carbon atoms, ether group with 1-10 carbon atoms, or ester group with 1-10 carbon atoms or derivatives thereof) The diisocyanate is an aliphatic or aromatic diisocynate, preferably an aliphatic diisocyanate such as isophorone diisocyanate(IPDI), hexamethylene diisocyanate(HDI), isocyanurate, etc.; aromatic diisocyanate such as toluene diisocyanate(TDI), methane diphenyl diisocyanate(MDI), polymeric MDI, hydrogenated MDI, xylene diisocyanate(XDI), tetramethyl-xylene diisocyanate(TMXDI), etc.; or a mixture thereof, and more preferably MDI.

In the step (1) of the preparation method of cationic microgel according to the present invention, the reaction molar ratio of the tertiary amine having a hydroxy group and diisocyanate is not particularly limited, and preferably tertiary amine and diisocyanate are reacted in a molar ratio of 1 :0.8 to 1.2. If the reaction molar ratio of diisocyanate per 1 mole of tertiary amine is less than 0.8, side reactions due to unreactive tertiary amine and poor water-dispersion stability may occur. If the reaction molar ratio of diisocyanate per 1 mole of tertiary amine exceeds 1.2, problems such as poor water- dispersion stability, poor mechanical properties, etc., may occur.

The reaction conditions for the reaction of the tertiary amine having a hydroxy group and diisocyanate are not specifically restricted. For example, the reaction can be performed at temperatures of 60 to 90 ^°C for 8 to 9 hours in reaction media. According to an embodiment of the present invention, the reaction is performed by adding methylisobutylketone and diisocyanate as a reaction media to a reaction vessel followed by dropwise addition of the tertiary amine having a hydroxy group such as dimethylethanolamine. The reaction mixture is heated to 80 ^°C after the dropwise addition, and allowed to react for 4 hours. When the reaction is completed, butylcellosolve is incorporated. The reaction mixture is then cooled and neutralized with an acetic acid or the like.

The kind and amount of the acid which is used in neutralizing the reaction mixture of the tertiary amine having hydroxy group and diisocyanate are not restricted. For example, the reaction mixture can be neutralized with an acid, such as formic acid, lactic acid, acetic acid, sulfonic acid, etc., in suitable amounts.

In step (2) of the preparation method of cationic microgel according to the present invention, the cationic microgel is prepared by reacting tertiary amine salt resin obtained in the above step (1) and polyepoxy resin to prepare polyepoxy resin containing quaternary ammonium salt, dispersing the prepared polyepoxy resin in dispersion media, and reacting in the presence of diamine.

The polyepoxy resin is a polymerization product of polyol and polyepoxide, preferably a polymer of one or more aliphatic or aromatic polyol and bisphenol A type diglycidyl ether with epoxy equivalent weight (EEW) of 180 to 700.

Preferably, the amount of the tertiary amine salt resin which is prepared in the above step (1), used in the step (2) is 15 to 90% of the equivalent weight to 100% of the equivalent weight of the epoxide group in the polyepoxide resin. If the amount is less than 15% of the equivalent weight, dispersity may noticeably decrease. If the above amount exceeds 90% of the equivalent weight, there is apprehension of gellation of the reactant. There are no limitations as to what dispersion media is used, and preferably deionized water is used.

The diamine, used as a cross-linking agent, preferably may be ethylenediamine, hexamethylenediamine, pentamethylenediamine, tetramethylenediamine, 2- methylpentamethylenediamine, or a mixture thereof. The amount of the diamine used is preferably 10 to 99% of the equivalent weight to 100% of the equivalent weight of the residual epoxide group in the main chain, more preferably 30 to 90% of the equivalent weight. If the above amount is less than 10% of the equivalent weight, improvement of the anti-corrosive effect for the edges and the inhibition of craters may decrease. If the amount exceeds 99% of the equivalent weight, there is apprehension of deterioration of the appearance of the coating film.

After reacting the tertiary amine salt resin and polyepoxy resin in the presence of diamine, the reaction mixture is preferably neutralized with acid is preferable for improving storage stability of the microgel water-dispersion and the electrodepositable coating composition. At this time, as the acid for neutralization, formic acid, lactic acid, acetic acid, sulfonic acid, etc., are available. Amounts of the acid used for neutralization is preferably in the molar ratio of 0.2 or more per 1 mole of amine group in the diamine.

The conditions for reaction of the tertiary amine salt resin and polyepoxy resin are not specifically limited. For example, the reaction can be performed at temperatures of 40 to 60 ^°C for 1 to 3 hours in the reaction media. According to one embodiment of the present invention, the cationic microgel water-dispersion is prepared by dispersing the reactant of tertiary amine salt resin and polyepoxy resin in water, adding ethylenediamine there, and allowing the mixture to react at 45 ^°C for 5 hours, and then neutralizing the reaction product with acetic acid.

According to the present invention, an electrodepositable coating composition comprising the water-dispersion of the cationic microgel prepared according to the present invention is provided.

There is no limitation in the amount of the cationic microgel comprised in the electrodepositable coating composition of the present invention. Preferably, 0.1 to 10% by weight of the cationic microgel is comprised in 100% by weight of the coating composition. The cationic microgel of the present invention is comprised in the electrodepositable coating composition according to the present invention. The microgel bears cationic characteristics due to the quaternary ammonium salt in the main chain, which results in the improved dispersity of the microgel dispersion solution. Also, because the pH can be easily controlled by using the neutralizing acid after cross- linking with the diamine, there is the advantage that the cationic microgel can be applied without deteriorating the stability of the electrodeposition bath solution. Also, the cationic microgel prevents the generation of craters by controlling the flowability during the curing of the coating film.

The present invention is explained in more detail by the following Examples, but is not limited thereto. Preparation Example 1: Preparation of polyepoxy resin

The polymer of polyepoxide and polyol were prepared from the mixture of the ingredients shown in TABLE 1 below. TABLE 1 Preparation composition of polyepoxy resin

1. Epoxy resin (Kukdo Chemical Co.)

2. Polyol (Dow Chemical Co.)

3. Amine intermediate (KCC Co.)

The epoxy resin (YD-128), polyol (Tone0201), ethoxylated bisphenol A and xylene were placed in reaction vessel, heated to 120^°C, followed by the recovery of xylene under vacuum. After the propylene glycol methyl ether (1st) and BDMA (Benzyl dimethyl amine) were added, the reaction mixture was heated to 145 ^°C . Taking caution to heat generation, the reaction mixture was held at this temperature for 3.5 hours, then cooled to 90-100^°C . And then, the amine intermediate (R9787), ketimine (diketimine derivative prepared from methyl isobutyl ketone and diethylene triamine) and N-methylethanolamine were added. The temperature of the reaction mixture was adjusted to 100^°C and held at this temperature for 2.5 hours. The propylene glycol methyl ether (2nd) was added to dilute the reaction mixture.

Preparation Example 2: Preparation of aromatic polyisocyanate

An aromatic polyisocyanate capped with polyfunctional alcohol and mono- functional alcohol was prepared from the mixture of the ingredients shown in TABLE 2 below. TABLE 2 Preparation composition of aromatic polyisocyanate

The MDI, MIBK (1st) and DBTDL were placed in reaction vessel, and heated to 50 ^°C . Taking caution that the temperature would not exceed 50⁰C , the butyl carbitol was added slowly over 1.5 hours. The reaction mixture was held at 50 ^°C for 30 minutes, until NCO% reached 9 to 10%. The TMP was added portionwise with caution to heat generation. The reaction mixture was then heated to 80 ^°C . The reaction mixture was held at 80 ^°C for 1 hour, and when NCO% reached 0%, MIBK (2nd) was added to dilute the mixture. Preparation Example 3: Preparation of tertiary amine salt resin

A tertiary amine salt resin was prepared from the mixture of the ingredients shown in TABLE 3 below. TABLE 3 Preparation composition of tertiary amine salt resin

The M80 (polymeric MDI) and methylisobutylketone were placed in a reaction vessel, and then the dimethylethanolamine was added dropwise slowly into the reaction vessel. After dropwise addition was completed, the reaction mixture was heated to 80 ^°C and held for 4 hours. After completion of the reaction, the reaction mixture was cooled by adding butylcellosolve and then, neutralized with acetic acid.

Preparation Examples 4-6: Preparation of microgel water-dispersion

Microgel water-dispersions of Preparation Examples 4-6 were prepared from the mixtures of the ingredients shown in TABLE 4-6 below, respectively.

TABLE 4 Preparation composition of microgel water-dispersion of Preparation Example 4

TABLE 5 Preparation composition of microgel water-dispersion of Preparation Example 5

TABLE 6 Preparation composition of microgel water-dispersion of Preparation Example 6

The YD- 128, bisphenol A, ethoxylated bisphenol A and xylene were placed in a reaction vessel and heated to 120 ^"C . Xylene was recovered under vacuum. After the propylene glycol methyl ether (1st) and BDMA were added, the reaction mixture was heated to 145 ^°C . Taking caution to heat generation, the reaction mixture was held at that temperature for 3.5 hours, then cooled to 90-100 ^°C . The propylene glycol methyl ether (2nd) and deionized water (1st) were then added and the temperature of the reaction mixture was adjusted to 50 ^°C . The tertiary amine salt resin of Preparation Example 3 was added dropwise. The reaction mixture was held at 50 ^°C for 1 hour. The reaction mixture was dispersed in water by dropwise addition of deionized water (2nd). Ethylenediamine was added, and the mixture was held at 45 ^°C for 5 hours. Upon completion of the reaction, the reaction mixture was neutralized with acetic acid to prepare the microgel water-dispersion.

Preparing Example 7: Preparation of pigment paste

A pigment paste was prepared from the mixture of the ingredients shown in TABLE 7 below. TABLE 7 Preparation composition of pigment paste

The resin for pigment dispersion, carbon black, titanium dioxide and dibutyltinoxide paste were placed in a vessel and mixed by agitation. The deionized water was added to the mixture, and then the mixture was agitated. The mixture was dispersed by using dispersing device until the size of the dispersion particles became 10- 12μm for preparation of the pigment paste.

Preparation Examples 8-12: Preparation of water-dispersion resin for elecrodepositable coating

Water-dispersion resins for elecrodepositable coating of the Preparation Examples 8-12 were prepared from the mixtures of the ingredients shown in TABLE 8- 12 below, respectively.

TABLE 8 Preparation composition of water-dispersion resin for elecrodepositable coating of Preparation Example 8

TABLE 9 Preparation composition of water-dispersion resin for elecrodepositable coating of Preparation Example 9

TABLE 10 Preparation composition of water-dispersion resin for elecrodepositable coating of Preparation Example 10

TABLE 11 Preparation composition of water-dispersion resin for elecrodepositable coating of Preparation Example 11

TABLE 12 Preparation composition of water-dispersion resin for elecrodepositable coating of Preparation Example 12

The polyepoxy resin of Preparation Example 1 and capped polyisocyanate of Preparation Example 2 were placed in a vessel and heated to 90 ^°C . After the mixture was held at this temperature for 30 minutes, the vessel was sealed, and the solvent in the mixture was recovered under vacuum. The surfactant and formic acid were added, and the deionized water was added dropwise over 2 hours. Finally, the microgel water- dispersion of each Preparation Example (except Preparation Example 12) was added to prepare each water-dispersion resin for the elecrodepositable coating.

Examples 1-4 and Comparative Example

Cationic electrodeposition solutions were prepared by mixing the ingredients below, respectively. TABLE 13 Preparation composition of Examples 1-4 and Comparative Example

The 1197 parts by weight of water-dispersion resin of each Preparation Example, 1503 parts by weight of deionized water and 3 parts by weight of acetic acid were added to a bath at room temperature, and agitated. While the bath solution was agitated, 297 parts by weight of the pigment paste of Preparation Example 7 was added to prepare each cationic electrodepositable bath solution.

The pH of the prepared bath solution was 5.8 to 6.2. The steel plate pretreated with zinc phosphate was electocoated in the electrodeposition bath at 28 ^°C under 240 voltages for 2 minutes. The coating film was cured in oven at 170^°C for 25 minutes.

Test Example

TABLE 14 Result of test

1. Erichsen Tester: Coated sample was pressurized with a sphere having 1.5cm of radius. A dent depth was measured when the coating film was peeled or broken off. (unit: mm)

3. Leveling was measured by using Surtronic 3+ of Taylor-Hobson Co.

4. The coated sample pretreated with zinc phosphate was tested in a salt-fog tester for 960 hours, and then coating film was peeled off with transparent tape. The length of peel-off was measured.

5. The sample perforated with circle and tetragon was electrocoated, and then tested in a salt-fog tester for 240 hours. After the test, the sample was peeled off with transparent tape, and then the state of the peel-off face of the perforation was compared. ( O(bad) - »^► lθ(good) )

INDUSTRIAL APPLICABILITY According to the present invention, a cationic microgel for electrodepositable coating having excellent mechanical properties when applied to the electrodepositable coating is obtained. The electrodepositable coating composition comprising this cationic microgel is excellent for edge coating and provides a good smooth coating film by effectively inhibiting the formation of craters by adequately controlling the flowability during the curing of the coating film.

Claims

1. A method for preparing a cationic microgel for electrodepositable coating, comprising the steps of:

(1) preparing tertiary amine salt resin by reacting a tertiary amine having a hydroxy group with diisocyanate followed by neutralizing the resulting mixture with acid; and

(2) dispersing the tertiary amine salt resin and polyepoxy resin polymer in a dispersion media, and then reacting the tertiary amine salt resin and polyepoxy resin polymer in the presence of diamine.

2. The method for preparing the cationic microgel for electrodepositable coating according to claim 1, wherein the tertiary amine having a hydroxy group is the alkanolamine of Formula 1 below:

Formula 1 wherein, Ri is alkylene group with 1-4 carbon atoms, R₂ and R₃ are alkyl group with 1-10 carbon atoms, aryl group with 5-18 carbon atoms, ether group with 1-10 carbon atoms, or ester group with 1-10 carbon atoms or derivatives thereof.

3. The method according to claim 1, wherein the diisocyanate is selected from isophorone diisocyanate, hexamethylene diisocyanate, isocyanurate, toluene diisocyanate, methane diphenyl diisocyanate, polymeric methane diphenyl diisocyanate, hydrogenated methane diphenyl diisocyanate, xylene diisocyanate, tetramethyl xylene diisocyanate, and mixtures thereof.

4. The method according to claim 1, wherein the polyepoxy resin polymer is a polymerization product of polyol and polyepoxide.

5. The method according to claim 1 , wherein the tertiary amine resin prepared in the step (1) is used in an amount of 15 to 90% by equivalent weight to 100% by equivalent weight of the epoxide group in the polyepoxide resin polymer.

6. The method according to claim 1, wherein the diamine is selected from ethylenediamine, hexamethylenediamine, pentamethylenediamine, tetramethylenediamine, 2-methylpentamethylenediamine, and mixtures thereof.

7. The method according to claim 1 , wherein the diamine is used in an amount of 10 to 99% by equivalent weight to 100% by equivalent weight of the residual epoxide group in main chain.

8. The method according to claim 1, wherein the tertiary amine salt resin and polyepoxy resin polymer are reacted in the presence of diamine, and then neutralized with acid.

9. An electrodepositable coating composition comprising the water-dispersion of cationic microgel prepared by the method according to any one of claims 1 to 8.