Process for the preparation of binder dispersions capable of bei

Details Process for the preparation of binder dispersions capable of bei Process for the preparation of binder dispersions capable of bei

1990-06-13

1992-02-04

Michl, Paul R.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523415, 523416, 523417, 523420, C08G 5940, C09D 544

Patent

active

050860909

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the preparation of aqueous dispersions to be further processed to electrocoating paints with baking temperatures below 160.degree. C. and baking times .ltoreq.30 minutes, which dispersions contain modified epoxide-amine adducts as binders and polyisocyanates blocked by hydroxyl groups as cross-linking agents.
Cathodic electrocoating is a painting process frequently used particularly for priming, in which water-thinnable synthetic resins carrying cationic groups are deposited on electrically conducting objects with the aid of direct current. The binders which are suitable for the cathodic deposition, contain predominantly amino groups which are neutralized with acids in order to render the binders soluble in water.
A particularly preferred group of binders is represented by the group of binders which are based on modified epoxy resins. Binders of this type are disclosed, for example, in the following patent documents: U.S. Pat. No. 4,031,050, U.S. Pat. No. 3,799,854, U.S. Pat. No. 3,984,299, U.S. Pat. No. 4,252,703, U.S. Pat. No. 4,332,711 and DE-PS 3,108,073.
They are crosslinkable by virtue of admixed polyisocyanates blocked by hydroxyl groups. These crosslinking agents thus contain at room temperature urethane groups (=blocked isocyanate groups). These blocking components are then split off at elevated temperatures and the isocyanate groups are regenerated. Subsequently these isocyanate groups may effect the crosslinking of the binders via the hydroxyl groups and/or the primary and/or secondary amino groups contained therein. Such non-self crosslinking binder systems represent the present state of the art. Their accretion and preparation are described, for example, in DE-PS 3,108,073, particularly in Examples 1 to 5, or in EP 74,634 A2, Example A.
The crosslinking agents used therein react, because of the structure of their blocking components, only at temperatures above 160.degree. C. The method described in the examples can therefore be followed without any difficulties.
However, in recent years the demand has steadily grown for crosslinking agents which become active at considerably lower baking temperatures. This is due in the automotive industry, for example, to the joint use of plastic components in the construction of automobile bodies.
Attempts were therefore made to prepare suitable blocked polyisocyanates as crosslinking agents for reduced baking temperatures. Crosslinking agents of this type are described, for example, in EP 118,743 A1 and in EP 206,071 A2. However, if these crosslinking agents are used instead of the crosslinking agents described above, the resultant paint surface lacks any reproducible properties and exhibits breakdown phenomena and poor flow-out.
It is thus the object of the invention to make available a process which would make it possible, even when using crosslinking agents with low baking temperatures and modified epoxide-amine adducts as binders, to obtain aqueous dispersions which give rise, after being further processed to electrocoating paints, to reproducible surfaces formed by cathodic electrocoating with very good mechanical properties.
This object is achieved according to the invention by a process for the preparation of aqueous binder/crosslinking agent dispersions, wherein attached to aromatic and/or (cyclo)aliphatic molecular fragments per molecule, preferably between 100.degree. and 180.degree. C., to furnish circuit (for example cooling via cooling coils filled with heat transfer oil or water) and the resultant resin solution is boiled under reflux, if necessary in vacuo, until the temperature of the solution drops to 95.degree. C. to 20.degree. C.; free state in the epoxy resin and either crosslinking agent (F) is admixed, or mixture is dispersed in a water-acid mixture.
In the first stage of the process according to the invention epoxide-containing intermediates are first prepared from the components (A) and (B) in the presence of catalysts.
Any compound whose molecule contains on average more than 1 epoxide group, m

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