People who run PE extrusion often ignore “hot melt” until you say adhesive resin for extrusion coating. The class showed up in the early 1970s and was later refined. Fully compounded grades can be tailored: low-temperature heat seal, bonds between dissimilar webs, and in many cases better barrier than a straight polyolefin coat. They stay thermoplastic (no crosslink), so design for service temperature and internal stress. Cattie #8159 is an extrusion / gravure / slot-die heat-seal lidding grade (FDA 21 CFR 175.105). Call 800-249-0337.
What they do
Practical lower heat-seal is about 160 °F (71 °C) — roughly 100 °F below LDPE — so you can run heat-sensitive product or webs. The same coat can still seal near 300 °F (148 °C) with usable hot tack. Besides sealing to itself, a coated web can bond paper, PE, polyester, PP, cellophane, nylon, vinyl, PVA, PS, cellulose esters, polycarbonate, nitrile barrier resins, acrylic copolymer sheet, PVDC, PETG, fabric, foil, glass, and metallized films. Extrusion lamination with these resins often keeps the barrier of the stack.
Peel vs destruct depends on substrates, grade, coat weight, seal conditions, service temperature, melt temperature, and any tie layer. Laminating grades often build bond on age (the sheet’s example: metallized PP / adhesive / corona-treated CPP went from about 150 to 275 g/in in 24 h, metal then leaving the PP). That aging is a problem if you need a stable heat-seal peel. Heat-seal profiles can be written for kraft-to-kraft or primed polyester-to-rigid vinyl by picking the grade.
Barrier and product resistance
WVTR of these coats can approach PVDC and beat LDPE. Examples on the sheet (g/100 in²/24 h, 100 °F, 95% RH): 1 mil on MG kraft, about 1–1.5; ½ mil on MG kraft, about 0.4–0.8 (LDPE 2–3; PVDC 0.4–0.8); ½ mil on glassine, about 0.25–0.40 (PVDC 0.2–0.40). Paper / PVDC / extrudable adhesive is stronger still. Oxygen barrier exists but EVOH is better; combine structures. Grease and oil in direct contact are a weak spot; soaps are generally fine. Primers and barrier sublayers often decide whether the pack works. Test filled containers.
Physical properties and the extruder
Versus a typical LDPE: density about 0.935–0.961 g/cc (LDPE ~0.923); melt flow at 190 °C often 90+ g/10 min vs ~3.7; ring-and-ball about 72–98 °C vs 100+. Lower extrusion temperature and back pressure; high flow helps wet contamination at the seal.
Typical barrel (depends on screw and L/D; higher L/D is easier): feed 180–200 °F; transition, metering, adapter, die 300–380 °F (die ends ~10 °F hotter). Air gap as short as you can, often 4–5 in. Back pressure 500–1,200 psi. Chill 60–70 °F matte for non-barrier, 100–125 °F gloss for barrier. Screen pack 50/200/200/50 mesh. Plan 1½–2 hours to cool down from LDPE to these high-flow resins once the crew has done it.
Coextrusion with PE, EVA, or PP has been run, but the temperature and flow gap is wide. Newer dies were being tried when the paper was written; treat coex as a trial, not a given.
Lidding-style end uses
The sheet’s application table (no supplier grade numbers here) is juice lidding on primed foil, paper, HDPE, or PP into PVC, LDPE, HDPE, PS, HIPS, PP; dairy and creamer stock on paper, glassine, primed foil, or MET PET into foil, PE, PVC, PET, HIPS, with a wide coat-weight window and useful MVTR on glassine; airline creamer lids; aseptic pudding and hot-fill jams/jellies on PE for hot tack. Starting activation about 160 °F at 40 psi / 0.5 s — substrate dependent. Coat weights in the table ran about 6–32 lb/ream (10–50 g/m²). Recommend ~600 psi back pressure. Treat or prime films to beat slip, antistat, and oil. Always confirm on filled packs.
Related: heat seal adhesives, hot melt (#8159 extrusion lidding), extrusion, lidding heat seals, extrusion coating principles, co-extrusion hot melt settings.