Method for producing a pigment paste, aqueous electrocoat material, use thereof, method for cataphoretic electrocoating, and coated article

Abstract

The invention relates to a method for producing a pigment paste and an electrocoat containing the paste, the past being made by mixing solid pigment particles with a grind resin in the presence of water and/or an organic liquid, wherein the grind resin includes a dispersion of core-shell particles in an epoxide prepolymer which is liquid at 20 C. and the core-shell particles have a silicone core and a polymer shell.

Claims

1. An aqueous electrocoat material which comprises a cataphoretically depositable resin system and a pigment paste obtained by a method comprising: mixing at least one pigment, in the form of solid particles, with a grind resin in the presence of at least one of water or an organic liquid, thereby obtaining a pigment paste wherein the grind resin comprises a dispersion of core-shell particles in an epoxide prepolymer which is liquid at 20 C., and the core-shell particles have a silicone core and a polymer shell.

2. The aqueous electrocoat material as claimed in claim 1, wherein the resin system comprises at least one epoxide-based monomer or at least one prepolymer and at least one curing agent for epoxides.

3. The aqueous electrocoat material as claimed in claim 1, which is in the form of a miniemulsion.

4. The aqueous electrocoat material as claimed in claim 1, which comprises at least 30 ppm of bismuth in dissolved form, based on the total preparation, wherein calculated amount is based on the amount of bismuth metal in the aqueous electrocoat material.

5. The aqueous electrocoat material as claimed in claim 1, which comprises at least 100 ppm of bismuth in dissolved form, based on the total preparation, wherein calculated amount is based on the amount of bismuth metal in the aqueous electrocoat material.

6. The aqueous electrocoat material as claimed in claim 1, which comprises at least 200 ppm of bismuth in dissolved form, based on the total preparation, wherein calculated amount is based on the amount of bismuth metal in the aqueous electrocoat material.

7. The aqueous electrocoat material as claimed in claim 1, which comprises at least 250 ppm of bismuth in dissolved form, based on the total preparation, wherein calculated amount is based on the amount of bismuth metal in the aqueous electrocoat material.

8. The aqueous electrocoat material as claimed in claim 1, wherein the method further comprises homogenizing a pigment paste obtained from said mixing.

9. The aqueous electrocoat material as claimed in claim 8, wherein the pigment particles, during said homogenizing, are comminuted to a preselected particle size and dispersed by introduction of mechanical energy.

10. The aqueous electrocoat material as claimed in claim 1, wherein the polymer shell of the core-shell particles comprises at least one poly(meth)acrylate.

11. The aqueous electrocoat material as claimed in claim 1, wherein the epoxide prepolymer has an epoxy equivalent weight in the range from 150 to 300 g/eq.

12. The aqueous electrocoat material as claimed in claim 1, wherein the dispersion of core-shell particles is present in an epoxide prepolymer, in an amount such that the pigment paste obtained from said mixing comprises 1 to 6 wt % of core-shell particles, based on the total amount of the grind resin.

13. A method for cataphoretic electrocoating of metal surfaces, comprising: contacting a metal surface with the aqueous electrocoat material as claimed in claim 1.

14. The method as claimed in claim 13, wherein said contacting comprises: (1) immersing the metal surface with said aqueous electrocoat material (2) applying, for at least ten seconds, a voltage in a range of from 1 to 50 V to the immersed metal surface; and (3) applying, for at least ten seconds, a voltage in a range of from 50 to 400 V to the immersed metal surface, provided the voltage applied during said (3) applying is not less than 10 V more than the voltage applied during said (2) applying.

15. The method according to claim 13, wherein the metal surface is an aluminum surface.

Description

WORKING AND COMPARATIVE EXAMPLES

Comparative Example 1

Comparative Example: Producing an Aqueous Preparation for Verifying the Coating Properties with Bismuth Complex

(1) 42.60 parts of a 40% cationic electrocoating dispersion (CathoGuard 520, commercial product from BASF Coatings GmbH) are mixed with 49.94 parts of DI water. Then 6.12 parts of an aqueous pigment preparation (CathoGuard 520 pigment paste, commercial product of BASF Coatings GmbH) are added together with 1.34 parts of an aqueous bismuth L(+)-lactate solution, with stirring.

Inventive Examples 2, 3, and 4

Examples: Modifying the Pigment Paste and Producing an Aqueous Preparation for Verifying the Coating Properties with Bismuth Complex and Core-Shell Particles Having a Silicone Core

(2) An aqueous pigment paste based on the formula of a customary composition for use in electrocoating material (CathoGuard 520 pigment paste, commercial product from BASF Coatings GmbH) is prepared. In this pigment paste formulation, 1%, 5%, or 10% of the grind resin typically employed, based on the solids content, is replaced, and a product is used that comprises core-shell particles, containing a silicone core (KANE ACE MX 960), and aqueous pigment pastes are produced as described above. The fractions of the product containing core-shell particles in the modified pigment paste formulation are 0.71% in example 2, 3.54% in example 3, and 6.97% in example 4.

(3) 42.60 parts of a 40% cationic electrocoating dispersion (CathoGuard 520, commercial product from BASF Coatings GmbH) are mixed with 49.94 parts of DI water.

(4) TABLE-US-00001 TABLE 1 Compositions of the test baths (all figures in parts by weight) Comparative Inventive Inventive Inventive example 1 example 2 example 3 example 4 DI water 49.94 49.94 49.94 49.94 Binder dispersion 42.60 42.60 42.60 42.60 CathoGuard 520 Pigment paste 6.12 (CathoGuard 520) Pigment paste (based on CathoGuard 520, containing 6.97% Kane Ace 156) Pigment paste 6.12 (based on CathoGuard 520, containing 0.71% Kane Ace 960) Pigment paste 6.12 (based on CathoGuard 520, containing 3.54% Kane Ace 960) Pigment paste 6.12 (based on CathoGuard 520, containing 6.97% Kane Ace 960) Bismuth L(+)- 1.34 1.34 1.34 1.34 lactate 11.9% Bi

(5) Then 6.12 parts of the aqueous pigment preparations described above are added together with 1.34 parts of an aqueous bismuth L(+)-lactate solution, with stirring.

(6) Results:

(7) Surface Quality/Defects

(8) The defects in the grey coating that are formed in particular on aluminum substrates are rendered visible by means of a test. In this test, a further application of a black electrocoat material is carried out on the panels coated and baked as stipulated.

(9) After rinsing and baking, the defects (pinholes) appear black, since at these locations the actual coating has holes. Evaluation takes place by counting the defects within one cm.sup.2 on each of the test panels (table 2).

(10) TABLE-US-00002 TABLE 2 Number of pinholes on a 1 cm.sup.2 area of the test panels in question Comparative Inventive Inventive Inventive example 1 example 2 example 3 example 4 Number of 56 48 12 3 defects [per cm.sup.2]

(11) Corrosion Control

(12) TABLE-US-00003 TABLE 3 Results for corrosion/delamination after 10 days CASS test on aluminum (Copper Accelerated Acetic Acid Salt Spray Test acc. to DIN EN ISO 9227 CASS) Comparative Inventive Inventive Inventive example 1 example 2 example 3 example 4 Corrosion/ 1.5 2 1 0.9 delamination [mm]

(13) TABLE-US-00004 TABLE 4 Longest thread after 42 days filiform test on aluminum (Filiform acc. to DIN EN 3665) Comparative Inventive Inventive Inventive example 1 example 2 example 3 example 4 Longest 7.8 8.3 5.5 4 thread [mm]