Heat-seal ability

In many operations, the product is made up of multiple layers of polymer combined into a single film. Each layer serves a specific purpose, such as reduced cost, low oxygen permeability, strength, printability, heat-seal ability, and so on. These products are processed using a coextrusion die that is fed by two to five (sometimes more) extruders. 

Other requirements for packaging materials include processing capacity, ability to be heat-sealed, ability to be recycled or composted, and low cost. ... 

The EVA is prepared by controlled hydrolysis of ethylene vinyl acetate copolymer. For most food applications, VA ranging from 5 to 20% is recommended. The EVA has good flexibility (better than LDPE), excellent toughness at low temperatures and heat seal-ability. As the melting temperature is low, it has to be processed at relatively lower tem-... 

Cast film, sheet and tubes can also be formed by extrusion processes. Paper and board can be extrusion coated and these products exhibit good heat seal-ability, adhesion and moisture barrier properties. 

A change in size on scale-up is not the sole determinant of the seal-ability of a unit operation or process. Scalability depends on the unit operation mechanism(s) or system properties involved. Some mechanisms or system properties relevant to dispersions are listed in Table 2 (59). In a number of instances, size has little or no influence on processing or on system behavior. Thus, scale-up will not affect chemical kinetics or thermodynamics although the thermal effects of a reaction could perturb a system, e.g., by affecting convection (59). Heat or mass transfer within or between phases is indirectly affected by changes in size while convection is directly... 

Hot tack strength is the ability of a heat-seal layer to hold together while molten, before the seal cools and sets up. This is a technically important property which is difficult to measure reproducibly in the laboratory. Owing to the reinforcing effect of ionic bonding on melt strength, ionomer sealing layers provide superior performance in a wide spectrum of applications. 

PVC films surpass polyolefine films in strength, resistance to oils and impermeability to gases and aromatic substances. Stiff PVC films display mold-ability. Their drawbacks are low thermal-, light- and frost-resistance, poor heat-sealing and propensity to agglutination. Soft PVC films are produced from a plasticized polymer. Introduction of a plasticizer into the polymer base adds elasticity, transparency and glitter, improves frost resistance and... 

Uses Adhesive for PVC and other films, and in nonblocking coating applies. Features Waterborne high performance heat-activating good tens, str., heat and water resist., flexibility in low VOC systems ability to heat seal at relatively low temps. 

The introduction of metallocene catalysts has permitted new variants of LLDPE to be produced, with much improved ability to tailor properties to end-use requirements. LLDPEs that incorporate higher a-olefins as co-monomers have much improved heat seal properties, for instance. These new polymers are likely to further displace LDPE and result in even greater ability to downgauge films in both LDPE and LLDPE applications. These same catalyst systems are likely to also permit source reduction through downgauging in HDPE, PP, and other applications. 

Ionomers are used in apphcations such as golf ball covers and bowling pin coatings, where their good abrasion resistance is important. The puncture resistance of films allows these materials to be widely used in packaging apphcations. One of the early applications was the packaging of fishhooks. They are often used in composite products as an outer heat-seal layer. Their ability to bond to aluminum foil is also utilized in packaging applications. Ionomers also find apphcation in footwear for shoe heels. ... 

It must be reiterated that an atmospheric plasma glow discharge provides a treatment with high uniformity and homogeneity, along with the ability to micro-etch and functionalize the surface of films (in this case with carbon-based functionality). In the case of OPP film, the level of heat seal strength is 20% higher than the level obtained with corona pretreatment. 

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