28 ноября, 2015 
Pokraskin Many articles for daily use are packed in bags, pouches and sacks. For this, special adhesives have been developed for manifold applications (e. g. side-seam bonding, bottom pasting, partial lamination), ranging from simple paper bags that are still bonded with starch-based adhesives to elaborate pouch designs bonded with dispersion adhesives or hot melts.
Depending on the adhesion requirements, the dispersion adhesives used are based on plasticized polyvinyl acetate homopolymers, EVA copolymers or acrylates. Resin dispersions can be admixed to improve adhesion. For nonabsorbent materials such as polypropylene films, hot-melt adhesives are used that are based on thermoplastic rubbers (e. g. styrene-butadiene-styrene or styrene-isoprene-styrene block copolymers) mixed with resins and oils, depending on the application. Bags and pouches, ranging from simple cornet bags to elaborate block-bottom and cross-bottom bags, can be manufactured from a wide variety of materials and material combinations. Occasionally, these materials are imprinted, and this must be taken into consideration in the bonding process. As bags and pouches are produced on highspeed machines with a performance of 150 to 200 bags or pouches per minute, the adhesives must also provide for a clean machine run.
In the manufacture of paper bags, starch-based adhesives are still widely used for side-seam bonding and even for bottom bonding. For the gluing-in of valves and for the bonding of internal layers made from PE, dispersion adhesives with a large adhesion spectrum are used; these may be EVA copolymers, acrylates or natural rubber, mixed with resin dispersions.
In the manufacture of pouches and sacks, one special challenge is that of the handles, particularly when using recycling paper, bogus paper or soda/kraft paper. Occasionally, dispersion adhesives bleed through, and although this might not be visually discernible, it may hinder a hassle-free production process. A possible solution here is to use coarsely dispersed dispersion adhesives containing minor amounts of low-molecular-weight substances, or starch-containing dispersion adhesives (provided that they do not dry too slowly). The bonding of the handles may give rise to further problems. Very fast-curing dispersion adhesives or, alternatively, hot-melt adhesives, can be used to avoid displacement of the handles during the production process on machines running at ever-increasing speeds.
Polyethylene sacs are bonded with reactive two-part polyurethane adhesives, with the adhesive being applied by means of rollers for the bottom pasting. The valves used
to fill the sacs are also bonded with reactive, two-part polyurethane adhesives or, alternatively, with hot melts based on synthetic thermoplastic rubbers mixed with resins and oils.
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