Whipped foam (coating agent)
Whipped foam is a liquid, aqueous textile coating agent that is applied to textiles directly or using the reverse process.
Manufacturing
Aqueous polyurethane or acrylate dispersions are used, which are initially given a paste-like consistency through intensive stirring or whipping. The process is very similar to making whipped cream. For this reason, the term mechanical whipped foam is also common. The foams are usually produced with an air content between 20 and 70 percent by volume. The density of the foams is given as the foam liter weight . Although the aqueous dispersions easily form foam on their own, additives to stabilize the foams, such as. B. ammonium stearate or SLES required. The foams may also contain other customary in the coating as needed additives such as color pigments , additives , active ingredients and fillers included. The dispersions used should have correspondingly high solids contents so that a sufficient foam liter weight can be achieved. Solids contents of 50 to 60% are customary for polyurethane dispersions.
application
To produce the foams, continuously working, industrial foam units are used, as they also occur in the food industry. The whipped foam is usually applied using a doctor blade ; the gap width set largely determines the wet film thickness. The foams have to be dried at higher temperatures in order to obtain usable coatings. In order to remove the water contained in the foam, the wet foam is dried in several stages with increasing temperatures in a circulating air flow, in such a way that the water does not boil and the foam structure is not destroyed. The final temperature in the drying process is approx. 160 ° C. The dried foams have closed-cell or open-cell structures, depending on the foam liter weight used. The dry film thickness is usually slightly less than the wet film thickness. The thicknesses of the coatings are between 0.05 and 1.0 millimeters, but several millimeters are also possible. The foams are much finer than the usual known foams, such as are known from sponges or foam pads.
The purpose of coating with foam is to give volume while at the same time using low material consumption and weight. In addition, the foam structure makes the coatings very soft and pleasant to the touch. This is why whipped foams are used in clothing, in medical and technical articles, but also in the manufacture of leather-like materials. In some cases, the foam must be provided with additional, compact layers to prevent damage and also for design reasons. The advantage of using whipped foams is that they can be processed with zero or very low emissions.
Comparable products
Similar articles are also available on the basis of soft PVC ( plastisol ), which receive a fine foam structure through the use of chemical blowing agents . These articles are widely used e.g. B. in artificial leather . The disadvantage of these products is their tendency to stiffen or material break at low temperatures and the high content of plasticizers , which, among other things, can be hazardous to health.
Another possibility of producing fine foam coatings is the use of chemical blowing agents in high solids polyurethane coatings, which are used in applications comparable to whipped foams. These coatings are of excellent quality, but their possible uses are not so variable and they often contain proportions of solvents.
literature
See literature references under textile coating