Laminate Aluminium foil

Laminate, aluminium foil, polymer, crack, fracture toughness INTRODUCTION... 

Current usage is almost entirely associated with the good adhesion to aluminium. Specific applications include the bonding of aluminium foil to plastics films, as the adhesive layer between aluminium foil and polyethylene in multilayer extrusion-laminated non-lead toothpaste tubes and in coated aluminium foil pouches. Grades have more recently become available for manufacture by blown film processes designed for use in skin packaging applications. Such materials are said to comply with FDA regulations. 

The packaging material is a laminate made from layers of paper, plastic (polyethylene) and aluminium foil. The particular composition for a given product is chosen according to its specific requirements. This affords the best protection to each product and keeps it in peak condition until consumed. Polyethylene is laminated to the board to make it impermeable, and an aluminium foil (of 10 p.m or less) is added to increase the barrier properties against external hazards such as sunlight and atmospheric oxygen, which would cause deterioration of product quality. 

So far, emphasis has been placed on the treatment of polyolefins to improve printability, but the same treatments affect also other processes. As an example, while an untreated polyethylene surface will not retain an adhesive the treated and modified surfaces are receptive to adhesives. A field of increasing importance for packaging is the production of laminates of film with other materials and, as examples, suitably pre-treated polyethylene film can be bonded securely to substrates such as cellulose or polyester films and aluminium foil, using standard adhesives, whereas this cannot be achieved without pre-treatment. 

Substrate is the material on which the print is applied. Substrates are, for example, glass, tin plate, aluminium foil, paper and board, plastics or multilayer laminates. 

Curing times with high barrier laminates containing aluminium foil may also be prolonged. 

Semi-solid products have been traditionally packed in collapsible tin tubes. Metal tubes are a potential source of metal particles in ophthalmic products, and so the tubes have to be cleaned carefully prior to sterilisation. Also, the final product must meet limits for the number of metal particles found. Plastic tubes are not suitable because of their non-collapsible nature, which causes air to enter the tube after withdrawal of each dose. However, collapsible tubes made from laminates of plastic, aluminium foil and paper are a good alternative to tin tubes. Laminated tubes fitted with polypropylene caps can be sterilised by autoclaving, whereas tubes fitted with polyethylene caps are sterilised by gamma irradiation. The tubes are usually filled aseptically, sealed with an adhesive and then crimped. 

A strip pack using an aluminium foil/low density polyethylene laminate was used for a tablet containing volatile oil constituents. Delamination between foil and film subsequently occurred as the volatile constituents passed through the polyethylene and softened the adhesive bond. It was not known that the bond was an adhesive at the time, and subsequently an extrusion-coated laminate provided a satisfactory answer. 

Soft aluminium foil has a fairly low tensile and tear strength, so it is essential that very thin gauges are supported by paper or film. In general, foil of 0.025 mm and below has to be supported. For example, 0.025 mm foil laminated to 30 g/m2 LDPE is a widely used strip packaging laminate. In theory, 0.015 mm foil laminated to 30 g/m2 LDPE would be a more economical proposition. However, at this caliper any undue stretch would be likely to perforate and tear the foil. Hence it is possible to reduce the foil caliper only if support is increased, i.e. by the addition of a paper ply. Thus if cost savings are to be made the final laminate would probably be either... 

Aluminium foil, usually as laminations for blister, strip, and sachet packaging. 

The properties of metal and plastic have been combined in the form of a laminated tube, which consists of a polyethylene/ aluminium foil/polyethylene or similar laminated body fitted with a polyethylene nozzle and is less permeable than a conventional polyethylene tube with less tendency to draw air back. To date the main usage of laminated tubes has been for toothpastes, but wider pharmaceutical applications are now found. 

Pond, W., Aluminium foil/polymer laminates as hermetic seals on treated glass, Packaging Technol., April 1982. 

One of the most widely used materials with excellent moisture protection is paper, 40-45 g, extrusion coated LDPE, 12 g/m2, 7-9 m hsoft aluminium foil, 25 g/m2 LDPE. The presence of two layers of plastic more than amply fills in any pinholes in the foil layer. The same laminate is also widely used for sachets and is technically preferred to a similar laminate with the foil on the outside. 

Usually two laminates of paper, soft temper aluminium foil and various plastics. Again the filling and sealing details are considered with the materials descriptions. 

These are usually a laminate with aluminium foil as the centre core and a heat sealable plastic as the product contact material. They can be made from either a single feed reel or twin reel feed. Firstly the carrying pouch is formed, then dosed with product, then hermetically heat sealed so that contamination is reduced to a minimum. 

Cone sleeves are made from a laminate of aluminium foil and paper. The top of the sleeve is crimped down over a cardboard disc to form a lid after product assembly is completed. Tubes are made from cardboard coated on both sides with polyethylene. The base is heat-sealed to make it leak-proof and the top is rolled to make a rim, onto which the lid is heat-sealed. Plastic tubs and containers are used for ice cream and... 

Table 4.3 provides a comparison between the helium permeation rates in two films, a laminate incorporating a 6 pm aluminium foil, PET 12 pm/Aluminium 6 pm/HDPE 50 pm (Film B) and a multi-layered barrier composed of four aluminium-sputtered PET sheets laminated onto a 50 pm PE (Film A). Tests were run at 24 °C. From the measurement of... 

A preliminary investigation of these effects has been carried out by Sugiyama and coauthors [21] for some laminated plastic films incorporating a 6 pm aluminium foil. 

All these aspects have to be optimised to get full benefits from VIP technology. As previously discussed, laminates incorporating a continuous aluminium foil provide, at present, the best gas barrier properties for VIP. Their main drawback is the loss of insulation properties at the panel flanges due to the relatively high thermal conductivity of the aluminium foil which reduces the overall insulating performance, this effect being directly related to the panel size and the aluminium foil thickness. 

The ECR values for encapsulated panels of different sizes prepared with a laminate incorporating a 6 pm aluminium foil (Table 4.3, Film B) are given in Table 4.10. The calculation has been made assuming a foam thermal conductivity of 6 mW/m K and a thickness of 0.5 cm of additional PU foam (thermal conductivity of 20 mW/m K) for a total thickness of 0.025 m. 

The ECR values achievable with the aluminium foil-based laminates are very interesting for large size panels, where the edge effect is not severe. For small panels, which are also important, since they can be easily adopted in a variety of applications, from household appliances to shipping containers, the improvement in the insulation efficiency is not as remarkable. 

As an example. Figure 4.26 shows the effect of a thermal treatment carried out at 50, 70 and 90 °C on a VIP prepared with an open cell foam and an aluminium foil-containing laminate. The foam was pre-baked at 150 °C for 20 minutes and no absorbent was used. 

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