Coating agents based on hydroxyl-containing polycondensation and

Details Coating agents based on hydroxyl-containing polycondensation and Coating agents based on hydroxyl-containing polycondensation and

1993-03-15

1994-07-05

Welsh, Maurice J.

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

524849, 524875, 525131, C08L 7504

Patent

active

053268202

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to coating agents based on hydroxyl-containing polycondensation and polyaddition products, comprising (A) and (B) are present in such amounts that the ratio of the number of free OH groups of component (A) to the number of isocyanate groups of component (B) is in the range from 1:3 to 3:1.
The invention furthermore relates to processes for the preparation of these coating agents and to the use of the coating agents in automotive refinishing, in particular as clearcoat.
Coating agents based on a combination of a polycondensation resin and a polyaddition resin are known.
Thus, in German Patent 2,806,497, clearcoats for multilayer coatings are described comprising a mixture of a hydroxyl-containing polyester and a hydroxyl-containing acrylate resin as the binder. The clearcoats contain an amino resin as the crosslinking agent. The use of aliphatic and/or cycloaliphatic polycarboxylic acids and aliphatic and/or cycloaliphatic polyols in the preparation of the polyesters gives clearcoats which, compared with clearcoats based on binders containing aromatic building blocks, have improved weathering resistance. However, these clearcoats described in German Patent 2,806,497 are in need of improvement with respect to drying capacity and processibility.
Furthermore, many product information sheets from Eastman Kodak on cyclohexanedicarboxylic acid have disclosed that the use of cyclohexanedicarboxylic acid as the acid component in polyesters which are used as binders in paints, results in good stability of gloss and crack resistance of the resulting coatings. However, coating agents based on polyesters containing cyclo-hexanedicarboxylic acid have the disadvantage that while having good drying capacity, they nevertheless have at the same time only a very limited pot life, i.e. processing time.
Furthermore, the product information sheet from Bayer AG on Desmophen.RTM.A 365 has disclosed air-drying automotive repair coatings which contain a hydroxyl-containing binder (Desmophen.RTM. A 365) as the binder and polyisocyanates, such as, for example, Desmodur.RTM. N 3390 and Desmodur.RTM. N 75, as the crosslinking agent. The coatings obtained are distinguished by a good stability of gloss and by high light stability and chalking resistance. However, their disadvantage is the extremely short pot life of the coating compositions.
Furthermore, German Offenlegungsschrift 3,806,641 has disclosed coating compositions which contain a mixture of a carboxyl-containing polyester and a carboxyl-containing acrylate resin as the binder. Epoxy resins are used in these coating compositions as the crosslinking agent.
Finally, it is known to improve the compatibility of the individual components of binder mixtures by carrying out the synthesis of one component in the presence of the other component.
Accordingly, the present invention is based on the object of providing coating compositions based on polycondensate resins and polyaddition resins which show rapid drying and simultaneously have a long pot life, i.e. can be processed in the ready-to-use state over a long period of time. Furthermore, it is desired that the coating compositions are cured at room temperature or slightly elevated temperature, thus enabling them to be used in automotive refinishing. Furthermore, they should at least fulfil the demands usually made on a clearcoat and possibly have improved mechanical properties compared with conventional clearcoats. Thus, the coating compositions should exhibit, for example, good stability of gloss, crack resistance, filling power and good flow properties.
Surprisingly, this object is achieved by coating agents based on hydroxyl-containing polycondensation and polyaddition products, comprising and (B) are present in such amounts that the ratio of the number of free OH groups of component (A) to the number of isocyanate groups of component (B) is in the range from 1:3 to 3:1.
In the coating agents, (A1) having an OH number from 0 to 200 mg of KOH/g and an acid number from 0 to 200 mg of KOH/g and number fr

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