Plastics surface preparation foams

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Plastic foams are generally treated by the same surface-preparation methods used for the base polymer. This is particularly true for the... 

For the preparation of the foam, a solution of 1 g technical sodium diisobutyl naphthalene sulfonate in 50 ml of 3% orthophosphoric acid is prepared. 20 ml of this solution are poured into a 11 beaker and air is stirred in with a fast running mixer until the cream-like dispersion has reached a volume of 300-400 ml.Then,20 ml of the prepared urea/formaldehyde resin are mixed in, whereby the resin must be evenly distributed. After 3-4 min the introduced resin gellifies into a molded article permeated with many water/air pores under the influence of the acidic catalyst. After 24 h,the crosslinking is completed. Drying for 12 h at 40 °C in a circulating air dryer yields a brittle thermoset foam.The foamed plastic obtained is hydrophobic and has a large internal surface. It can take up about 30 times its own weight of petroleum ether. 

The type of polymer obtained depends on factors such as the pH and temperature of reaction, the ratio of melamine to formaldehyde, and the type of catalyst employed. For decorative laminates, melamine-formaldehyde is prepared by reacting melamine in stainless steel kettles under reflux, alkaline conditions with 37% to 46% formaldehyde in aqueous solution. The reaction temperatures used vary from 80 to 100°C and are maintained until the condensation has reached the desired end point—that is, reacted sufficiently but still water-soluble. The end point is checked by measurements of viscosity, cure time, and water tolerance. Depending on the type of laminate to be produced, other constituents (surfactants, plasticizers, release and anti-foam agents) normally are added to the base resin before impregnation of the surface papers. It is common practice also at this stage to adjust the pH by adding acid catalysts. 

Thermoplastic polymer foams can be prepared from starch-polyester graft copol zmers. Water is used as the plasticizer as well as the blowing agent (3). The foams have improved processability, surface properties, and an extended range of mechanical properties. 

---