Laminating and coextrusion

Films, Laminates, and Coextrusions. Many films are used in medical device packaging applications. Both flexible formed and nonformed pouches, as well as bags, use films for their manufacture. These materials offer a high degree of versatility and are available in a countless variety of forms in monofilms, laminations, and coextrusions. The specific material to be used for a medical device is dependent upon the performance properties required for the device application. For example ... 

An approach that can be applied to laminates and coextrusions is to selectively dissolve and remove polymer layers by careful selection of solvents. Thus, the nylon layer in a polyethylene/nylon/polyethylene coextrusion can be isolated by boiling in xylene. Alternatively, the nylon could be removed by boiling in formic acid. Solvents for the selective removal of polymers are listed in Table 2. Acids or alkalis should be avoided on some polymers where there is a risk of reaction with the polymer. An example would be the use of concentrated sodium hydroxide solution on a metallized film comprising certain acrylic/ethylene... 

However, such addition of UVAs or pigments into the bulk of the composites is not a cost effective method. A better option is to improve the surface resistance of the composites where the weathering occurs primarily. The methods used for improving surface resistance of the composites include coating, lamination and coextrusion. All of these methods entail producing a UV resistant layer on the surface of the composites. Of these, coating is the most widely used method in the wood industry [ 14]. 

One disadvantage is the ability to provide printed structures where the print layer is sandwiched as is often used with conventional adhesive lamination. A way around this is to use a combination of adhesive lamination and coextrusion coating such that the coextruded structure is assembled with a pre-printed web of film. In addition, other non-extrudable materials, such as paper and metal foils, can be combined. 

Schematic illustrations showing coextrusion process to fabricate FMs (a) initial feedrod formation, (b) coextrusion, (c) lamination, and (d) hot-pressing. 

Lamination may be achieved by adhesives, extrusion and coextrusion (Figures 9.2 and 9.3). 

Films, foils and laminates, including coextrusions and metallisation... 

Now that we have discussed the processes that can be used to create multilayer structures, coating, coextrusion, and lamination, the question arises, which process should be used, and when Liquid adhesive systems usually run faster than extrusion laminating and coating systems. If one is using a solvent-based system, there is the issue of whether or not any residual odors that might affect the product to be packaged remain. Water-based systems do not have solvent odors, but they are not necessarily odor-free. 

Adhesion promoters include the substances that create close physical and/or chemical bonds between two substrates [108]. The substrates to be cormected are fibrous reinforcing or particulate fillers on the one hand and plastics or metals on the other. The adhesion promoters always form bridges between the interfaces of the two components. For example, adhesion promoter resins based on styrene/butadiene alloys serve as adhesive layers for laminating panels and coextrusion of foils made of styrene polymers with polyolefins, PC, PMMA, and PA [30]. 

Coextrusion is the simultaneous extrusion of two or more layers of different polymers to make a film. Coextruded films have three main advantages over other types of film they have very high barrier properties, similar to laminates but produced at a lower cost they are thinner than laminates and are therefore easier to use on filling equipment and the layers do not separate. There are three main groups of polymers that are coextruded ... 

Cloeren, P. P., Feedback Coextrusion Systems, TAPPI Laminations and Coatings Conference Proceedings, pp. 501-512, 1987. 

Barex resin extruded sheet and/or calendered sheet (153) can be easily ther-moformed into lightweight, rigid containers (152,154). Packages can be printed, laminated, or metallized. Recent developments in extrusion and injection blow molding (152,155), laminated film structures (152,156), and coextrusion (153,157) have led to packaging uses for a variety of products. Barex resins are especially well-suited for bottle production. These acrylonitrile copolsmiers also provide a... 

These requirements are met with a multilayer structure containing a thicker central layer of the copolymer with thin outer layers of polypropylene (17). Such film structures are made by lamination or coextrusion, respectively using appropriate adhesive or tie layers. Other uses for these films include packaging of personal care and consumer products as in, for instance, blister bottles. 

Coextrusion is an important process for manufacturing layered plastic composites, such as film, sheet, and tubing (Middleman, 1977 Schrenk and Alfrey, 1983 Schrenketal., 1963). A costly alternative would be the fabrication of individual layers of plastics followed by conventional lamination and coating. An additional advantage of the coextrusion technique is its ability to handle extremely thin films on the order of 10 xm. One of the most colorful applications of this technique is the iridescent film, which consists of hundreds of very thin layers of alternating low and high refractive indices. A typical example of this type of film consists of 116 layers of poly(methyl methacrylate) (PMMA) with refractive index 1.49 and 115 layers of polystyrene (PS) with refractive index 1.59 and total film thickness of about 20 o.m (Radford et al., 1973). 

Strength they are of interest as a streteh film for meat packaging and for cling-wrap purposes. Some EVA is used in coextrusion processes for the manufacture of laminated film. 

In chapter 7, section 7.2.8 an example of permeation through a functional barrier is described. Three-layered coextruded PET films were produced in which the core layer (P) was contaminated with chlorobenzene and the outer barrier layers (B) were made with virgin material. During the coextrusion process a partial contamination of the virgin layer occurred. The symmetrical structure of this film leads to a simplified treatment of it as a two layer laminate with the thickness d = a + b = 160 + 40 = 200 pm. For the modeling of this problem with numerical mathematics all parameters given in Section 7.2.8 are used. 

From Fig. 8-6 one can clearly see that the very short (1 s) high coextrusion has an important impact on the migration of chlorobenzene from the core layer towards B and later into F. The subsequent migration in the laminate for 10 days at 50 °C produces only a small transfer of the contaminant into B. The time dependence of the amount migrated from the laminate into F is shown in Fig. 8-7. 

Coextrusion produces multilayer laminates in a single process step. Two or more extruders feed different molten polymers into a multi-manifold die which layers them directly, or into a modular feedblock which layers them before feeding them into the die. This is used primarily in the packaging field, to sandwich an impermeable barrier layer between two commodity outer-film layers, and often includes adhesive tie layers to bond the barrier layer to the outer layers. 

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