Window adhesives, envelope

Fig. 62 shows how typography system works for the glueing of an envelope window. This technique may be very fast, up to 800 windows per minute on the Winkler-Dunnebier German machines with ethylene-vinyl acetate adhesives, viscosity 3000 mPas. 

Window adhesives attach the elear window film to the rest of the envelope. The window film is usually polyester, orientated polypropylene or polystyrene. Formulated homopolymers or eopolymers are used as adhesives. 

This technique comes from the printing shops. It is very convenient to apply adhesives in a given pattern, for instance the periphery of the plastic windows of postal envelopes (Fig. 62), or the tip toe of a shoe upper. Any of the four classical printing systems may be used. 

Figure 62 (a) Bonding a transparent plastic window onto an envelop with typographic stencil, (b) Stencil wheel apphcator working with Hot melt adhesive (RA 80 wheel applicator from Nordson) width upto 800 mm (by courtesy of Nordson). 

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