A. Field of the Invention
This invention relates to poly-oxazoline-containing composition suitable for use as coatings. More particularly, it relates to a hydrocured, thermoset composition of the reaction product of a first poly-oxazoline compound, a second compound which is a polymer containing units derived from carboxylic acid cyclic anhydrides, and water; and to the use thereof as a coating on a substrate. The hydrocured, thermoset polymers are obtained by blending a poly-oxazoline compound with a polymer containing in the backbone thereof a plurality of units derived from addition polymerizable ethylenically unsaturated dicarboxylic acid cyclic anhydrides, heating the blend so as to obtain a fused blend, and crosslinking the fused blend to obtain the thermoset polymer by exposing the fused blend to moisture. The hydrocured, thermoset polymer is obtained as a ripple-free, smooth coating by applying the blended materials, preferably as a powder, to a suitable substrate prior to fusing the blend and then exposing the fused blend to moisture.
B. Description of the Prior Art
Durable and inexpensive thermoset polymers, useful as coatings, are in continual commerical demand. Of these thermoset polymers, especially those which are suitable for use in powder form are of particular interest today in light of their ability to be applied by electrostatic spary processes thereby obviating the use of noxious solvents.
Bis-oxazolines and the preparation thereof are well known in the art. (See U.S. Pat. Nos. 2,569,428; 3,208,981; 3,419,520.)
Poly-oxazolines and the preparation thereof by polymerizing 2-alkenyl oxazolines are also well known in the art. (See U.S. Pat. Nos. 2,831,858; 2,897,182; 3,535,291.)
The reaction of blends bis-oxazolines with dicarboxylic acid cyclic anhydrides and polymeric dicarboxylic acid cyclic anhydrides, in the absence of water, to form imido-ester compounds, some of which are useful as coatings, is known. (See U.S. Pat. Nos. 2,547,495; 2,547,496; 2,547,498; 2,543,602.)
Also, the reaction of blends of copolymers containing units from ethylenically unsaturated mono- and dicarboxylic acids with bis-oxazolines, in the absense of water, to provide coating materials is known. (U.S. Pat. No. 3,752,793.)
However, the known powdered polymers yet have undesirable problems associated with their use, chief among which is the problem known in the art as "orange peel." This defect occurs as a result of the competition during "stoving" (or "baking") between the flow of the polymer coating material on its substrate and the concurrent cure of the polymer which causes a surface rippling effect, or "orange peel." It has been conceived and demonstrated herein that this problem is overcome when the polymers of the invention are first heated at a temperature sufficient to provide desirable flow and then subsequently cured by further heating the resulting flowed material in the presence of moisture.