Laminated Materials applied to Aluminum Foil
Materials are chosen for lamination with aluminum foil to produce constructions which will perform satisfactorily under a wide variety of conditions. Various types and weights of paper and/or plastic films are used extensively for combining with foil to satisfy both functional and decorative requirements of specific applications.
Most of the plastic films now laminated with foil alone or with other materials, are extruded from hot plastic resins and other materials. Glass, wool and other mineral fibers, as well as foamed or solid materials, also are laminated in webs or sheets to foil.
Properties of some representative aluminum foil laminations are given in Table 4. Materials frequently laminated with aluminum foil are briefly described in the sections that follow.
Paper and Paperboard
The krafts, or sulphate papers, are used where high strength is required. Bleached krafts and sulphites are used where whiteness is needed. The sulphate papers provide moderate mechanical properties and good surface smoothness in foil laminations. Ground wood papers are used to back foil for some labels, and where low strength and slight color and texture are not objectionable. Glassine, greaseproof and parchment paper are used where greater oil and moisture resistance are required.
Paperboards range in quality from bleached sulphite types to chip board. Bleached board and manila stocks produce the smoothest foil laminations; Kraft boards result in maximum structural strength and chip boards provide maximum bulk at minimum cost. The latter contains a high percentage of reclaimed fiber, resulting in less smooth foil laminations and are frequently used in insulation, poster and other industrial and commercial applications.
Many plastic films are laminated to foil, including polyethylene, polypropylene, cellophane, cellulose acetate, rubber hydrochloride, vinylí»s, polyvinylidene chloride, polyesters. All of the foregoing is used in packaging, but any of the modern plastic films can be laminated to aluminum foil for a variety of present and potential applications.
The choice of these laminates is governed by the following product requirements:
- water vapor and gas permeability
- strength, flexibility and toughness
- resistance to grease, oils, chemicals, etc.
- heat sealability
- end-use temperature range
Properties of Aluminum Foil Laminations
In many laminations, light gauge foil is the primary barrier against water vapor transfer, and creasing can create pinholes or breaks in this barrier. The effects of creasing of the foil can be minimized in lamination by proper choice of paper or film, lamination adhesives, and laminating conditions. The data in Table 5 illustrates relative barrier properties of typical foil laminates.
Additional barrier properties against water vapor transmission are built into laminated structures by the use of waxes, polyethylene, asphalt, and other appropriate compounds as the laminating adhesive, and/or through the use of heavier foils or films.
The water vapor transmission rate of the film employed in a foil/film structure may or may not be of prime importance, but the film is often relied upon for toughness. In proper gauge, the foil remains impermeable under many end use conditions. Application requirements will dictate whether the laminate must have high resistance to moisture and to folding. Laminated foil materials offer a number of options.
Laminating Related Converting Operations
Principal foil converting operations utilize high speed, web-fed rotary processing equipment. Much of which is also used for producing paper and film products in high volume. Such in-line manufacture reduces costs by making it possible to perform several, sometimes all, operations required to make a converter end product in just one roll-to-roll pass through the machine or line.
Modern foil converting equipment is remarkably versatile. Laminators, for example, not only apply adhesives and combine the webs, but also may include other integral units to do quite sophisticated coating and printing in one pass. Some combination equipment is built with several stations attached to a single frame. Other units are individual stations mounted on separate frames, but arranged in-line.
All unites and devices employed in single-ass foil web converting machines, have interlocked and synchronous regulating systems to insure a high degree of control.
In other instances, especially where a single type of product is produced more or less continuously, single-purpose equipment such as laminators, coating machines, printing presses, slitters, cut-off shears, and other equipment are employed.
Roll embossers and seal presses are almost always operated separately, and have their individual unwind and rewind units. But even in these instances, slitting and cut-off units may be included in tandem, along with stacking or conveyor delivery devices.