Heat sealable

Almost aU ceUophane is coated with either a moisture barrier or heat-sealable coating. This is generaUy done in tower coaters after film production. 

Some heavier gauge flexible materials, usually containing nylon, are thermoformed, ie, heated and formed into three-dimensional shapes. Such stmctures are used to provide high gas-barrier, heat-sealable containment for processed meat or cheese. 

Cast films provide a high clarity, heat sealable film and are primarily used as an overwrap for boxes and other packaging. These films have a lower density than cellophane and provide a longer product shelf life. Properties of polypropylene films are given in Table 12. 

Polymers. In combination with various metal salts, sorbitol is used as a stabilizer against heat and light in poly(vinyl chloride) (qv) resins and, with a phenohc antioxidant, as a stabilizer in uncured styrene—butadiene mbber (qv) compositions and in polyolefins (see Heat stabilizers Olefin POLYMERS Rubbercompounding). Heat-sealable films are prepared from a dispersion of sorbitol and starch in water (255). Incorporation of sorbitol in coUagen films gready restricts their permeabiUty to carbon dioxide (256). 

Clear, water-soluble, oU-and grease-resistant films of moderate strength can be cast from hydroxyethylceUulose solutions. Elexible, nontacky, heat-sealable packaging films and sheets can be produced from hydroxypropylceUulose by conventional extmsion techniques. Both gums can be used in the formulation of coatings, and both can be used to form edible films and coatings. 

The commercial grades available in the 1970s used either zinc or sodium as the cross-linking ion and ranged in melt flow index from 0.4 to 14. The main application of the ionomer resins has been for packaging film. The polymer is particularly useful in composite structures to provide an outer layer with good heat sealability. The puncture resistance of film based on ionomer film has the puncture resistance of a LDPE film of twice the gauge. 

Table I shows the chemical composition limits of various aluminum alloys presently used for packaging applications (3). In general, these alloys have good corrosion resistance with most foods. However, almost without exception, processed foods require inside enameled containers to maintain an acceptable shelf life (4, 5). Moreover, when flexible foil packages are used for thermally processed foods, the foil is laminated to plastic materials that protect it from direct contact with the food and also provide heat sealability as well as other physical characteristics (6,7).

Multilayered materials owe their properties and behavior to the properties of and the interactions between the components (5). Each of the two or more components contributes its particular property to the total performance of the multilayered material. For example, in Pouch 1, Table II, the aluminum foil provides high oxygen and water vapor permeability resistance, poly (ethylene terephthalate) provides structural strength and stiffness, and the ethylene-butene copolymer provides a heat sealable layer. If the components of the multilayered materials interact then the whole would be something different than the sum of its parts. In other words, the properties of the components of the multilayered materials are not independent of one another but rather are interdependent. 

There are two broad classes of separators employed in nickel—zinc batteries a main separator, which exhibits resistance to dendrite penetration, and an interseparator, which principally acts as an electrolyte reservoir and wicking layer. Both main and interseparator should be resistant to chemical attack by the alkaline electrolyte and resistant to oxidative attack by nascent oxygen, permanently wettable by the electrolyte, flexible, heat sealable, tear resistant, and inexpensive. 

The importance of adhesives lies in the fact that they allow for a combination of the properties of dissimilar materials. For example, a laminate of polyethylene, with its heat sealability and water resistance, is ideally combined with cellophane, a grease resistant material that accepts ink printing, for packaging applications. 

Heat shrink sheets are used for many of fhe same applications as heavy wall shrink tubing. The advantage of the sheet over a tube is that it can be conveniently slipped over the area to be protected, for example, over continuously installed cable. There are many methods to close the heat-shrinkable sheets, such as zippers, rail and channel, heat-sealable bonds, etc., some of them patented. ... 

Many methods are used to close the heat-shrinkable sheets, such as zippers, rail and channel, heat-sealable bonds, etc., some of them patented.93-96... 

The drum provides protection from light and mechanical strength to protect the liner during shipment and handling. The majority of the protection from air and moisture is provided by the liner. Because LDPE is not a particularly good moisture barrier, a drug substance that is moisture sensitive may need additional protection. An alternative to a LDPE bag is a heat-sealable laminate bag with a comparatively low rate of water vapor transmission. 

Polymer-coated heat sealable packaging materials are composed of several layers (64). The material includes a fiber base of packaging paper or packaging board, an outer polymeric heat sealing layer, such as low density poly(ethylene) (LDPE), and an inner polymeric... 

T. Penttinen, K. Nevalainen, and J. Jarvinen, Method for manufacturing heat-sealable packaging material having barrier layer containing cycloolefin copolymer, US Patent 7 344 759, assigned to Stora Enso Oyj (Helsinki, FI), March 18, 2008. 

R.D. Jester, Cycloolefin copolymer heat sealable films, US Patent 7288316, assigned to Topas Advanced Polymers, Inc. (Florence, KY), October 30, 2007. 

Films made from TPX exhibit an insufficient heat sealability. A widely adopted solution for improving such insufficient heat sealability is addition of a low density poly(ethylene) (LDPE) homopolymer or an ethylene propylene copolymer. However, the addition of these polymers only result in little improvement in their heat sealability. Instead, the addition results in poor dispersion and deteriorated impact resistance (23). 

It has been proposed to improve the heat sealability of TPX by the addition of a propylene-a-olefin copolymer. Satisfactory results have been achieved by melt mixing a TPX polymer with an 1-butene polymer and a propylene polymer (23). 

Properties of selected compositions are shown in Table 4.6. The compositions thus obtained have excellent mechanical properties including heat resistance, heat sealability, and impact resistance as well as satisfactory gas permeability. Therefore, the compositions are an appropriate material for producing various structural materials by injection molding. 

The compositions may also be extruded into films and laminate papers. The films have excellent mechanical properties, including impact resistance and tensile strength as well as satisfactory releasability and gas permeability. The films are also heat sealable and the heat sealed film has sufficient strength. Therefore, such films are quite appropriate for the use as vegetable wrapping films, industrial films, and bags for storing platelets and cells. 

Commercial Stabilizers. There is a great variety of commercial formulations utilizing the mixture of the alkali and alkaline-earth metal salts and soaps. In many cases, products are custom formulated to meet the needs of a particular application or customer. The acidic ligands used in these products vary widely and have dramatic effects on the physical properties of the PVC formulations. The choice of ligands can affect the heat stability, rheology, lubricity, plate-out tendency, clarity, heat sealability, and electrical and mechanical properties of the final products. No single representative formulation can cover the variety of PVC applications where these stabilizers are used. 

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