Laminations and Coatings

Laminations and Coatings

Examples of laminations with carton board include, aluminium foil, metallic polyester and greaseproof paper.

Lamination is the bonding of two different materials so they become one, usually with heat and pressure.

Aseptic packaging is a beverage and liquid food system which allows products once considered perishable to be distributed and stored without refrigeration for up to six months or more. Foods such as milk, soy beverages, juice, and nectars. The aseptic packaging system achieves this room-temperature shelf stability by filling a sterilized package with a sterile food product within the confines of a hygienic environment.

Other package types and systems use preservatives and/or refrigeration to achieve a long shelf life. The aseptic process is a major advance over traditional canning techniques, such as retort and hot-fill canning. Retort canning typically requires products to be heated in the container for 20 to 50 minutes. Hot-fill canning uses the heat of the product to sterilize both the product and the package, a process which takes 1-3 minutes for heating and another 7-15 minutes for cooling. In contrast, aseptically processed liquid foods and beverages are sterilized outside the package using an ultra-high temperature process that rapidly heats, then cools, the product before filling. The processing equipment allows the time (generally 3 to 15 seconds) and temperature (195° to 285° F) to be tailored to place the least amount of thermal stress on the product, while ensuring safety. This flash-heating-and-cooling aseptic process substantially reduces the energy use and nutrient loss associated with conventional sterilization. As a result, aseptically packaged products retain more nutritional value and exhibit more natural texture, colour, and taste.

Aseptically packaged products include milks, juices, tomatoes, soups, broths, tofu, soy and rice beverages, wines, liquid eggs, whipping cream, teas and coffee drinks.

Paper (70 percent) provides stiffness, strength and the efficient brick shape to the package. Polyethylene (24 percent) on the innermost layer forms the seals that make the package liquid-tight. A protective coating on the exterior keeps the package dry. Aluminum (6 percent) forms a barrier against light and oxygen. This ultra-thin layer of foil eliminates the need for refrigeration and prevents spoilage without using preservatives.

The aseptic package contains a total of six layers in this order: polyethylene, paper, polyethylene, aluminum foil, polyethylene, and polyethylene.

Source reduction through minimal use of materials. Because they are made with less packaging material than virtually any other comparable container, aseptic cartons create less waste from the start. By using fewer materials in manufacturing, there is less to dispose of after use.

Energy efficiency. This package also uses far less energy to manufacture, fill, ship, and store products than virtually any comparable package. The aseptic package is a lightweight, efficient brick design, and its ability to preserve beverages without refrigeration or preservatives are key factors in saving energy.

Recycling. Aseptic packages along with milk and juice cartons are recycled through a simple, well-established process called hydra pulping. The high-quality fiber is used in the production of paper products such as tissue and paper towels.

Aseptic packages and paperboard containers such as milk cartons are collected and baled through curbside and drop-off programs and then sold to an end market. At the mill, the aseptic packages and paperboard cartons are recycled together through a simple paper recycling process known as hydrapulping. In a hydrapulper, which works like a household blender, aseptic packages and milk cartons are agitated for 30 to 40 minutes until the plastic and foil layers separate from the pulp. Repeated rinsings and the use of screens further separate the fiber from the thin layers of aluminum and plastic. The high-quality paper fiber is then recycled into paper products such as paper towels and tissue products.

The benefits of aseptic packaging to the consumer are that the special aseptic process yields a shelf-stable product, which can be kept in a cupboard for extended periods of time without preservatives or refrigeration. Other benefits are safety, nutrition, and ease of handling of the aseptic package. Others prefer the aseptic carton because it is shatter-proof and tamper-evident.

Tetra Pak cartons are made up of three materials that together result in a very efficient, safe and light weight package. Each material provides a specific function.

77% Paper – to provide strength and stiffness

18% Polyethylene – to make packages liquid tight and provide a barrier to micro organisms

5% aluminium foil – to keep out air, light, and prevent changes to the flavour. Anything that can cause the food to deteriorate.

Biodegradable coated papers.

Most of the paper used for packaging in quick-service restaurants is treated with materials that provide moisture and grease resistance.

Petroleum wax-based or low-density polyethylene (LDPE) coatings are typically used for moisture resistance,

while fluorocarbon-derived treatment are sued for grease resistance, either alone or in combination with other coatings.

Waxes

The wax is stored and transported in solid blocks and has to be pre-heated similar to hot melt adhesives to obtain the correct viscosity to flow. The wax cools and adheres to the substrate.

The gravure coating process relies on an engraved roller running in a wax coating bath. The engraved dots or lines in the roller are filled with wax coating. The excess coating is wiped off by the Doctor Blade and the coating is deposited onto the substrate as it passes between the engraved roller and pressure roller.

Offset Gravure is common, where the coating is deposited on an intermediate roller before transfer to the substrate.

Immersion Coating

In this simple process, the substrate is dipped into a bath of the coating, which is normally of a low viscosity to enable the coating to run back into the bath as the substrate emerges.

This process is frequently used on porous (absorbing) substrates.

Metering Rod (Meyer Bar) Coating

In this coating process, an excess of the coating is deposited onto the substrate as it passes over the bath roller. The wire-wound metering rod, sometimes known as a Meyer Bar, allows the desired quantity of the coating to remain on the substrate. The quantity is determined by the diameter of the wire used on the rod.

This process is remarkably tolerant of non-precision engineering of the other components of the coating machine.

Curtain Coating In the Curtain Coating process, a bath with a slot in the base allows a continuous curtain of the coating to fall into the gap between two conveyors. The object to be coated, such as a door, is passed along the conveyor at a controlled speed and so receives the coating on its upper face.

Slot Die (Slot, Extrusion) Coating In the Slot Die process, the coating is squeezed out by gravity or under pressure through a slot and onto the substrate. If the coating is 100% solids, the process is termed ‘Extrusion’ and in this case, the line speed is frequently much faster than the speed of the extrusion. This enables coatings to be considerably thinner than the width of the slot.

Gap Coating (Knife Over Roll, etc.) This process relies on a coating being applied to the substrate which then passes through a ‘gap’ between a ‘knife’ and a support roller. As the coating and substrate pass through, the excess is scraped off.

This process can be used for high viscosity coatings and very high coat weights, such as plastisols and rubber coatings. There are innumerable variants of the relatively simple process which is rugged, hard-working and somewhat inaccurate.

Air Knife Coating A simple process where the coating is applied to the substrate and the excess is ‘blown off’ by a powerful jet from the air knife. This procedure is typically used for aqueous coatings and is particularly noisy.

When petroleum wax based coatings are used with hot foods, they are typically modified with high melting temperature synthetic waxes to provide the required high temperature properties to prevent the wax melting into the food.

Wax and polyethylene are also used as laminates in packaging constructions containing more than one paper layer.