Aqueous electrocoating baths containing synthetic resins capable

Details Aqueous electrocoating baths containing synthetic resins capable Aqueous electrocoating baths containing synthetic resins capable

1993-12-16

1995-06-27

Niebling, John

Chemistry: electrical and wave energy

Processes and products

Electrostatic field or electrical discharge

2041814, 524502, 524543, 525107, 526332, C25D 1310

Patent

active

054276616

DESCRIPTION:

BRIEF SUMMARY
The invention relates to aqueous electrocoating baths containing synthetic resins capable of deposition on the cathode.
Cationic electrocoating (CEC) is a surface coating process which is frequently used, above all, for priming, particularly in the field of automobile priming, in which water-dilutable synthetic resins carrying cationic groups are applied by means of direct current to electrically conducting articles.
Electrocoating baths of the type described above are disclosed, for example, in the following patent documents: German Patent Specifications 3,108,073 and 2,701,002, EP 4,090, 12,463 and 59,895, and German Offenlegungsschriften 3,103,642 and 3,215,891.
Surface coatings of excellent quality can be achieved by means of surface coating systems of this type. However, surface defects (in particular craters) which are well known to those skilled in the art often occur in the stored paint film. The causes of these surface defects can lie in the nature of the components used for the electrodeposition paints (so-called causes inherent in the system). In most cases, however, impurities carried over into the electrocoating bath are the cause of the occurrence of the abovementioned surface defects. Examples of such impurities which may be mentioned are deep-drawing greases, anti-corrosion greases, joint-sealing materials, lubricating greases and the like.
When the surface coating material is deposited, these impurities are also introduced into the film. The abovementioned surface defects can then be formed when the paint film is stoved, because of incompatibility between the surface coating binder and the impurity.
A number of attempts to suppress the occurrence of surface defects by the addition of additives are known. Thus silicone oils, for example, can be added to the electrodeposition paints. Although the surface defects can be removed in this manner, problems then occur in overpainted paint films (such as, for example, filler and finishing paint) which are, as a rule, due to defective adhesion.
Attempts have also been made to improve, by means of suitable organic resins the resistance of electrocoating baths to contamination. Japanese Patent Application J 6 1,115,974 describes a reaction product formed from a polyepoxide resin modified with dimeric fatty acids and from a polyoxyalkylenepolyamine. This product stated to suppress the tendency to crater formation of CEC materials. EP-A 70,550 describes a reaction product of a polyepoxide resin with a polyoxyalkylene-polyamine containing primary amino groups. This material is also stated to improve paint films deposited by electrical means by eliminating or at least minimizing the tendency to crater formation. However, these products also result in persistent intercoat adhesion problems for fillers and finishing paints.
The objective on which the present invention is based consists in the provision of new aqueous electrocoating baths according to the preamble of patent claim 1. In particular, the problems of the state of the art described above are to be overcome or reduced.
This object is achieved, surprisingly, by the provision of aqueous electrocoating baths containing synthetic resins capable of deposition on the cathode, which baths are characterized in that they contain a homopolymer or copolymer of an alkyl vinyl ether of the general formula CH.sub.2 =CH--O--R, wherein R represents an alkyl radical having 2 to 4 C atoms.
The advantages achieved by means of the invention are to be seen essentially in the fact that the electrocoating baths according to the invention afford paint films which exhibit only slight surface defects or none at all, without the occurrence of adhesion problems in overpainted paint films. Surprisingly, the electrocoating baths according to the invention exhibit excellent resistance to contamination, that is to say the good surface properties of the stoved films are retained even if substances causing surface defects are carried over into the electrocoating baths according to the invention.
In principle, the electrocoating ba

REFERENCES:
patent: 4192929 (1980-03-01), Wingfield
patent: 4692267 (1987-09-01), Fock et al.
patent: 4871591 (1989-10-01), Sugimura et al.

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