JP3874386B2 - Cationic electrodeposition coating composition - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cationic electrodeposition coating composition, and more particularly, to a lead-free cationic electrodeposition coating composition that can form an electrodeposition coating film excellent in anticorrosion properties, finish properties and the like without containing a lead compound.
[0002]
[Prior art and its problems]
Electrodeposition paints are excellent in throwing power and can form a coating film with excellent performance such as durability and anticorrosion. Therefore, conventionally, the electrodeposition paints are used in application fields where such performances are required, such as automobile bodies. Widely used for painting, painting electrical appliances, etc.
[0003]
In order to further improve the anticorrosion properties of the electrodeposition paint, a rust preventive pigment, for example, a lead compound such as lead chromate, basic lead silicate, strontium chromate or a chromium compound is blended. The compound is a very harmful substance, and there is a problem in its use as a countermeasure against pollution. Therefore, as a non-toxic or low-toxic rust preventive pigment that replaces the lead compound, conventionally, zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc molybdate, calcium molybdate, zinc oxide, iron oxide, phosphomolybdenum The use of aluminum oxide, zinc phosphomolybdate, and the like has been studied, but these compounds do not have the rust preventive ability as the above-mentioned lead compounds and chromium compounds, and are not satisfactory in practical use.
[0004]
Bismuth is effective as a metal species that exhibits an excellent rust-preventing ability equivalent to or higher than that of lead compounds and chromium compounds in electrodeposition coatings, and it is already known that bismuth lactate is particularly effective among them.
[0005]
For example, JP-A-7-506870 discloses a positive ion which can be diluted with water after protonation and crosslinked by transesterification and / or amide exchange and / or urethane exchange and / or terminal double bond reactions. Disclosed is a method for producing a catalyst-containing cationic coating binder comprising an ionic coating binder and an aliphatic hydroxycarboxylic acid, preferably a bismuth salt of lactic acid or dimethylolpropionic acid. According to this proposal, bismuth salts are obtained by reacting 1 mol of bismuth oxide with 7 mol of each aliphatic hydroxycarboxylic acid. However, in this process, the isolated and dried bismuth salt tends to agglomerate during storage, and the amount of acid used in the reaction is then higher than that required to neutralize the entire coating binder. As a result, an excess of acid is introduced into the electrodeposition paint, thereby significantly increasing the amount of current required during operation of the electrodeposition tank.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors can stably and uniformly disperse the bismuth salt in the electrodeposition bath by using a bismuth salt excellent in water solubility. As lactic acid used in bismuth, L-form of optical isomers is found useful, and storage stability is obtained by adding bismuth lactate using the L-lactic acid in a specific ratio or more to the electrodeposition coating composition. As a result, an electrodeposition coating film that has good properties, can be uniformly dispersed in the electrodeposition bath, and has excellent finish and anticorrosion properties has been obtained.
[0007]
Thus, according to the present invention, there is provided a cationic electrodeposition coating composition characterized by containing bismuth lactate using lactic acid containing 80% or more of L isomers among optical isomers.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, bismuth lactate is formed by using lactic acid containing L of the optical isomers in an amount of 80% or more (that is, the D isomer is less than 20%), preferably 85% or more, more preferably 90% or more. If the L-form content of lactic acid used for producing the bismuth lactate is less than 80%, the water solubility of bismuth lactate cannot be obtained, which is not preferable. L-lactic acid is usually produced by a fermentation method.
[0009]
Examples of the bismuth compound used in the production of the bismuth lactate include bismuth oxide, bismuth hydroxide, basic bismuth carbonate, and bismuth oxide is particularly preferable.
[0010]
The reaction ratio of the bismuth compound and lactic acid can be variously selected. The bismuth lactate is, for example, 2 to 10 mol, preferably 3 to 8 mol, of lactic acid containing 80% or more of L-form with respect to 1 mol of bismuth oxide. It is obtained by reacting at a ratio of
[0011]
The bismuth lactate can be introduced into the electrodeposition coating composition, for example, as an aqueous solution. Specifically, as the aqueous solution, in the presence of water, 2 to 10 mol, preferably 3 to 8 mol, of lactic acid containing 1% of bismuth oxide in an amount of 80% or more of L-form is contained at 1 to 30 at room temperature to 90 ° C. By reacting for about an hour, a uniform aqueous bismuth lactate solution can be obtained with good reproducibility, and this can be added to the electrodeposition paint. If the lactic acid is less than 2 mol, it is difficult to make the bismuth salt water-soluble. If the lactic acid exceeds 10 mol, excess acid enters the electrodeposition bath and the amount of current required during operation of the electrodeposition tank increases. This is not desirable because the coatability is reduced. Similarly, when bismuth hydroxide is used, 1 to 5 mol of lactic acid, preferably 1.5 to 4 mol, containing 80% or more of the L form in 1 mol of bismuth hydroxide is reacted. The reaction solid content concentration is usually within the range of 0.1 to 80% by weight, preferably within the range of 0.5 to 70% by weight, and more preferably within the range of 1 to 60% by weight.
[0012]
When the bismuth lactate aqueous solution is added to the electrodeposition coating composition, it may be added before the electrodeposition coating composition is dispersed in water, or may be added after the electrodeposition coating composition is dispersed in water. When added before water dispersion of the electrodeposition coating composition, there is no particular limitation on the solid content concentration of the aqueous bismuth salt solution, but when added after water dispersion of the electrodeposition coating composition, the solid content of the aqueous bismuth lactate solution is not limited. The concentration is desirably 60% by weight or less. Such an operation is necessary for uniformly dispersing the aqueous bismuth lactate solution in the electrodeposition coating composition. In view of ease of coating and storage stability, the bismuth lactate aqueous solution is preferably added after the electrodeposition coating composition is dispersed in water.
[0013]
In the present invention, the content of bismuth lactate in the electrodeposition paint is not strictly defined and can be varied over a wide range depending on the performance required for the electrodeposition paint. It is preferable that the bismuth content is 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight per 100 parts by weight of the resin solid content. If the bismuth content is less than 0.1 parts by weight, the rust prevention property of the formed coating film is not sufficient, while if it exceeds 10 parts by weight, the stability of the electrodeposition coating composition tends to be lowered. .
[0014]
The electrodeposition coating composition containing bismuth lactate is a cationic type, and as the base resin, any resin such as epoxy, acrylic, polybutadiene, alkyd, and polyester can be used. Of these, polyamine resins represented by amine-added epoxy resins are preferred.
[0015]
Examples of the amine-added epoxy resin include (i) an adduct of a polyepoxide compound and a primary mono- and polyamine, a secondary mono- and polyamine, or a 1,2 mixed polyamine (for example, U.S. Pat. No. 3,984,843). (Ii) an adduct of a polyepoxide compound and a secondary mono- and polyamine having a ketiminated primary amino group (see, for example, US Pat. No. 4,017,438); (Iii) A reaction product obtained by etherification of a polyepoxide compound and a ketiminated hydroxy compound having a primary amino group (for example, see JP-A-59-43013).
[0016]
The polyepoxide compound used in the production of the amine-added epoxy resin is a compound having two or more epoxy groups in one molecule, and is generally at least 200, preferably 400 to 4000, more preferably 800 to 2000. Those having a number average molecular weight are suitable, and those obtained by reaction of a polyphenol compound and epichlorohydrin are particularly preferred. Examples of the polyphenol compound that can be used for forming the polyepoxide compound include bis (4-hydroxyphenyl) -2,2-propane, 4,4-dihydroxybenzophenone, and bis (4-hydroxyphenyl) -1, 1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, tetra (4- Hydroxyphenyl) -1,1,2,2-ethane, 4,4-dihydroxydiphenylsulfone, phenol novolak, cresol novolak and the like.
[0017]
The polyepoxide compound may be partly reacted with polyol, polyether polyol, polyester polyol, polyamidoamine, polycarboxylic acid, polyisocyanate compound, etc. It may be obtained by graft polymerization of caprolactone, acrylic monomer or the like.
[0018]
The base resin may be of any type of external cross-linking type and internal (or self) cross-linking type. Examples of the curing agent used in the case of the external cross-linking type resin include (block) polyisocyanate. It can be a conventionally known crosslinking agent such as a thio compound or an amino resin, and a block polyisocyanate compound is particularly preferred. Further, as the internal cross-linking resin, a resin into which a block polyisocyanate type is introduced is preferable.
[0019]
The block polyisocyanate compound that can be used in the external crosslinking type can be an addition reaction product of a theoretical amount of a polyisocyanate compound and an isocyanate blocking agent. Examples of the polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis (isocyanate methyl) cyclohexane, tetramethylene diisocyanate, and hexamethylene diester. Aromatic, cycloaliphatic or aliphatic polyisocyanate compounds such as isocyanate, methylene diisocyanate, isophorone diisocyanate, etc., and ethylene glycol in excess of these isocyanate compounds And terminal isocyanate-containing compounds obtained by reacting low-molecular active hydrogen-containing compounds such as propylene glycol, trimethylolpropane, hexanetriol and castor oil.
[0020]
On the other hand, the isocyanate blocking agent is added and blocked to the isocyanate group of the polyisocyanate compound, and the block polyisocyanate compound produced by the addition is stable at room temperature and about 100 to 200 ° C. When heated to a high temperature, it is desirable that the blocking agent can be dissociated to regenerate free isocyanate groups. Examples of the blocking agent that satisfies such requirements include lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenol, para-t-butylphenol, crezo Phenolic compounds such as n-butanol; Aliphatic alcohols such as n-butanol and 2-ethylhexanol; Aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol And ether alcohol compounds such as ethylene glycol monobutyl ether. Of these, oxime-based and lactam-based blocking agents are particularly suitable from the viewpoint of curability of the electrodeposition coating composition because they are blocking agents that dissociate at a relatively low temperature.
[0021]
As a method for introducing a block isocyanate group into a base resin in a type having a block isocyanate group in the base resin molecule and self-crosslinking, a conventionally known method can be used. It can be introduced by reacting the free isocyanate group in the polyisocyanate compound with the active hydrogen-containing part in the base resin.
[0022]
In the case of a cationic resin, the base resin is generally neutralized and made aqueous by neutralizing the resin with a water-soluble organic acid such as formic acid, acetic acid, and lactic acid to make it water-soluble and water-dispersed. At that time, part or all of the aqueous bismuth lactate solution can be used for neutralization. It is preferable to use acetic acid and / or formic acid as a neutralizing agent because it is excellent in finish, throwing power, low temperature curability and the like.
[0023]
The electrodeposition coating composition of the present invention can further contain a tin compound. Examples of the tin compound include organic tin oxides such as dibutyltin oxide and dioctyltin oxide; dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoate Examples thereof include aliphatic or aromatic carboxylates of dialkyltin such as tooxy, dioctyltin dibenzoate, dibutyltin dibenzoate, etc. Among them, dialkyltin aromatic carboxylates are preferred from the viewpoint of low-temperature curability. It is. The content of the tin compound in the electrodeposition coating composition is not strictly defined and can be varied over a wide range according to the performance required for the electrodeposition coating. It is suitable that the tin content per 100 parts by weight of the resin solid content is in the range of 0 to 8 parts by weight, preferably 0.05 to 5 parts by weight.
[0024]
The electrodeposition coating composition of the present invention can further contain a zinc compound. Examples of the zinc compound include zinc phosphate, zinc formate, zinc acetate, zinc molybdate, zinc oxide, and zinc phosphomolybdate. The content of the zinc compound in the electrodeposition coating composition is not strictly defined and can be varied over a wide range according to the performance required for the electrodeposition coating. It is suitable that the zinc content per 100 parts by weight of the resin solid content is in the range of 0 to 8 parts by weight, preferably 0.05 to 5 parts by weight.
[0025]
The electrodeposition paint composition of the present invention may further contain paint additives such as pigments, organic solvents, pigment dispersants, and coating surface conditioners as necessary.
[0026]
The electrodeposition coating composition of the present invention can be applied to a desired substrate surface by electrodeposition coating. Generally, electrodeposition coating is diluted with deionized water or the like so that the solid content concentration is about 5 to 40% by weight, and the pH is adjusted within the range of 5.0 to 9.0. An electrodeposition bath composed of a coating composition can usually be adjusted to a bath temperature of 15 to 35 ° C. and carried out under a load voltage of 100 to 400V.
[0027]
The film thickness of the electrodeposition coating film that can be formed using the electrodeposition coating composition of the present invention is not particularly limited, but is generally within the range of 10 to 40 μm based on the cured coating film. preferable. Moreover, the baking hardening temperature of the coating film is generally suitable in the range of 100 to 200 ° C.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by this. “Parts” and “%” indicate “parts by weight” and “% by weight”.
[0029]
Preparation of Cation-Electric Clear Emulsion “Epon 1004” (Note 1) 1900 parts dissolved in 1012 parts butyl cellosolve, 124 parts diethylamine was added dropwise at 80 to 100 ° C., and held at 120 ° C. for 2 hours to give an amine value of 47 Having an epoxy resin-amine adduct.
[0030]
Next, 1000 parts of a dimer acid type polyamide resin (trade name “Basamide 460”, product of Henkel Hakusui Co., Ltd.) having an amine value of 100 is dissolved in 429 parts of methyl isobutyl ketone and heated to 130 to 150 ° C. under reflux. The generated water was distilled off to change the terminal amino group of the amide resin to ketimine. This was held at 150 ° C. for about 3 hours, and cooled to 60 ° C. after the distillation of water stopped. Next, this was added to the epoxy resin-amine adduct, heated to 100 ° C., held for 1 hour, and then cooled to room temperature to obtain a varnish of epoxy resin-amino-polyamide addition resin having a solid content of 68% and an amine value of 65. Obtained.
[0031]
Mix 103 parts of varnish obtained above (70 parts by solid resin content), 30 parts of 2-ethylhexyl alcohol blocked product of tolylene diisocyanate (solid content), 15 parts of 10% acetic acid, and uniformly After stirring, 150 parts of deionized water was added dropwise over about 15 minutes with vigorous stirring to obtain a cation electrodeposition clear emulsion having a solid content of 33.6%.
[0032]
(Note 1) “Epon 1004”: manufactured by Yuka Shell Epoxy Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent of about 950
Production of aqueous bismuth lactate salt Production Example 1
A flask was charged with 300 g of 90% L-lactic acid (3 mol as L-lactic acid) and 657 g of deionized water, and heated to 60 ° C. Next, 233 g (0.5 mol) of bismuth oxide was slowly added thereto, and the mixture was stirred at 60 ° C. for 4 hours to be reacted. After confirming that the reaction solution was free of yellow solids and became transparent, 3572 g of deionized water was added to obtain an aqueous bismuth lactate salt solution (1) having a solid content of 10%.
[0033]
Production Example 2
A flask was charged with 250 g of 90% L-lactic acid (2.5 mol as L-lactic acid) and 606 g of deionized water and heated to 60 ° C. Next, 233 g (0.5 mol) of bismuth oxide was slowly added thereto, and the mixture was stirred at 60 ° C. for 4 hours to be reacted. After confirming that the reaction solution was free of yellow solids and became transparent, 3270 g of deionized water was added to obtain an aqueous bismuth lactate salt solution (2) having a solid content of 9.8%.
[0034]
Production Example 3
A flask was charged with 200 g of 90% L-lactic acid (2 mol as L-lactic acid) and 555 g of deionized water, and heated to 60 ° C. Next, 233 g (0.5 mol) of bismuth oxide was slowly added thereto, and the mixture was stirred at 60 ° C. for 4 hours to be reacted. After confirming that the reaction solution was free of yellow solids and became transparent, 2964 g of deionized water was added to obtain an aqueous bismuth lactate salt solution (3) having a solid content of 9.5%.
[0035]
Production Example 4
A flask was charged with 300 g of 90% lactic acid (racemic substance having a D / L of 1/1) (3 mol as lactic acid) and 657 g of deionized water, and heated to 60 ° C. Next, 233 g (0.5 mol) of bismuth oxide was slowly added thereto, and the mixture was stirred at 60 ° C. for 4 hours to be reacted. After confirming that the reaction solution was free of yellow solid and became transparent, 3572 g of deionized water was added, and a large amount of insoluble matter was produced. The aqueous solution (4) after this was filtered had a solid content of 1.3%.
[0036]
Production Example 5
A flask was charged with 150 g of 90% lactic acid (racemate) (1.5 mol as lactic acid), 150 g of 90% L-lactic acid (1.5 mol as L-lactic acid), and 657 g of deionized water, and heated to 60 ° C. . Next, 233 g (0.5 mol) of bismuth oxide was slowly added thereto, and the mixture was stirred at 60 ° C. for 5 hours to be reacted. After confirming that the reaction solution was free of yellow solid and became transparent, 3572 g of deionized water was added, and a large amount of insoluble matter was produced. The aqueous solution {circle around (5)} after filtration had a solid content of 2.3%.
[0037]
Examples and Comparative Examples The cation electrodeposition coating compositions were obtained by adding the aqueous bismuth lactate salt solution prepared as described above with the composition shown in Table 1 to the above-described clear emulsion for cationic electrodeposition and stirring.
[0038]
(Note 2) 40% LSN105: trade name, manufactured by Sansha Kogyo Co., Ltd., butyl cellosolve / methyl isobutyl ketone 40% solution of dibutyltin dibenzoate
Coating test In each of the cationic electrodeposition coating compositions obtained in the above examples and comparative examples, 0.8 × 150 × 70 mm cold-rolled dull steel plate (untreated plate) and Palbond # 3030 without chemical conversion treatment were used. Cold-rolled dull steel plates (chemical conversion treatment plates) of the same size subjected to chemical conversion treatment (manufactured by Nihon Parkerizing Co., Ltd., zinc phosphate treatment agent) were dipped, and electrodeposition coating was performed using them as cathodes. Electrodeposition conditions were a voltage of 300 V, an electrodeposition coating film having a film thickness (based on the dry film thickness) of about 20 μm was formed, washed with water, and baked. Baking was performed using an electric hot air drier at an atmosphere temperature of two stages and a baking time of 20 minutes. Table 1 shows the performance test results of the obtained coated plate.
[0039]
The performance test was performed according to the following method.
[0040]
(* 1) Curability: The coating surface of each electrodeposition coating plate obtained at a baking temperature of 150 ° C. is about 3 to 3 at a pressure of about 4 kg / cm ² with a four-layered gauze impregnated with methyl isobutyl ketone. The appearance of the coated surface when the length of 4 cm was rubbed 20 times was visually evaluated according to the following criteria.
○: No scratches are observed on the coating surface. Δ: Scratches are observed on the coating surface, but the substrate is not visible. X: The coating film is dissolved and the substrate is visible. (* 2) Corrosion resistance: Each obtained at a baking temperature of 170.degree. The electrodeposition coating plate is cross-cut with a knife so as to reach the substrate, and this is subjected to salt-resistant spraying for 480 hours when using an untreated plate and 840 hours when using a chemical conversion treatment plate according to JIS Z-2371. The test was conducted, and evaluation was made according to the following criteria based on the rust and blister width from the knife scratch.
[0041]
A: Maximum width of rust and blisters is less than 1 mm from the cut part (one side)
○: The maximum width of rust and blisters is 1 mm or more and less than 2 mm from the cut part (one side)
Δ: The maximum width of rust and blisters is 2 mm or more and less than 3 mm (one side) from the cut part, and the blister is considerably conspicuous on the flat part. -Is observed [0042]
【The invention's effect】
In the present invention, bismuth lactate using L-lactic acid in a specific proportion or more as lactic acid can be stably produced with good reproducibility and is excellent in water solubility, so that it can be dispersed stably and uniformly in the electrodeposition bath, and the obtained electrodeposition It can be uniformly present in the coating film. Therefore, by adding bismuth lactate containing L-lactic acid as a lactic acid in a specific ratio or more to the electrodeposition coating composition, it can be used without using a rust preventive pigment such as a lead compound which has a problem in pollution control. An electrodeposition coating film having excellent anticorrosion properties and finish properties equivalent to or higher than when blended is obtained.
[0043]
[Table 1]

Claims (4)

A cationic electrodeposition coating composition comprising bismuth lactate using lactic acid containing 80% or more of L isomers among optical isomers. The cation according to claim 1, wherein bismuth lactate is added as a bismuth lactate aqueous solution obtained by reacting lactic acid containing 1% by mole of bismuth oxide in an amount of 80% or more in the presence of water at a ratio of 2 to 10 moles. Electrodeposition paint composition. The cationic electrodeposition coating composition of Claim 1 or 2 which contains bismuth lactate so that bismuth content may be 0.1-10 weight part with respect to 100 weight part of resin solid content in an electrodeposition coating material. The cationic electrodeposition coating composition according to claim 1, comprising a dialkyltin aromatic carboxylate compound.