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Dry-Heat Lamination Offers Options

Dry-heat lamination increases production and improves working environments.

Dry-heat laminating is best described as high-volume production bonding of two or more different substrates in a continuous reel-to-reel operation, using dry adhesive, at relatively low temperatures.Low-temperature laminating is an effective, controlled and flexible procedure, which allows for a wide range of substrates to be bonded together on the same production line with quick changeover times between production runs.The process of flat-bed, dry-heat laminating involves a combination of heat, pressure and the speed at which the substrates are transported through the laminating machine. The machine is a heating tunnel consisting of an upper and lower conveyor, which sandwich and transport the layers of materials to be laminated, and inter-layers of adhesive. The process relies on moving the upper and lower conveyors until they come into contact with the materials, and then applying heat to the upper and lower surfaces of the sandwiched materials. Heating is achieved through a series of parallel, electrically heated elements, which are sited immediately behind both conveyors. The materials are transferred through this heating section at an optimum speed, which ensures the inter-layers of adhesive medium are melted to produce a strong bond between the materials.At the end of the heating section, the materials then pass through nip rollers that run the full width across the middle of the machine. The nip rollers exert pressure on the materials and molten adhesive, which spreads the adhesive, expels any trapped air and creates a permanent bond.Immediately after the nip roll section, cooling of the laminate takes place. This is achieved using parallel aluminum cooling modules, which are found immediately behind the upper and lower belts. Refrigerated water from a central chiller system is pumped through the modules, which cool the laminate and solidify and cool the inter-layers of adhesive. Finally, the product can be rewound on a separate rewinding station after leaving the laminating machine. Dry-Heat Lamination AdvantagesBecause of increasing worldwide concerns and legislation regarding the release of toxic emissions into the atmosphere, as well as the need for clean, safer working environments, textile and lamination companies have been forced to seriously consider cleaner, safer alternatives. These concerns include the elimination of high isocyanate and chemicals emissions and heavy energy usage associated with solvent- and flame-lamination processes. Moving to dry-heat laminating technology can provide the following advantages: complete elimination of toxic emissions; clean, dry and safe production processing; lower energy use; processing temperatures as low as 80°C; controlled production with the ability to stop mid-flow without causing problems; flexible or rigid bonding possibilities for different substrates up to 150 millimeters thick on flat-bed laminating tunnels; fast or slow production speeds; heating and cooling both sides of the lamination to reduce energy consumption; continuous reel-to-reel production or piece-by-piece panel production; no shelf-life problems and no need for special storage conditions for adhesives; and quick changeover of adhesives.The technology is being used by producers of laminated materials as they come under increasing pressure to produce stronger and more durable textile laminates. Another advantage is the ability to change production rapidly and automatically to cope with just-in-time (JIT) manufacturing, while retaining quality control and process control, and eliminating batch-to-batch variations as demanded by the customer.Textile laminates can be used in a wide variety of end products. Some of the possible applications include: automotive interior components (carpeting, headliners, air bags and seat construction); defense (gas-mask filters and body armor); footwear and apparel uses (sports shoes, inner soles, interlinings and fabric coatings); and medical uses (bandages, filters and protective fabrics), just to name a few. Adhesives AvailableIn order to remain at the forefront of adhesion technology, adhesive manufacturers must develop and produce the best adhesive solutions for new lamination technology. These producers have invested a large amount of research and funding to develop the optimum adhesive medium for the industry.One example of this adhesive technology at work is an automotive interiors application, whereby the laminated substrate is subjected to temperature extremes over a continuous cycle program to ensure the adhesives used will perform as intended during a vehicles lifetime. When used in the production of an automotive interior laminate, the adhesives are expected to withstand temperatures of more than 130°C to less than minus 40°C over a 900-hour continuous cycle. At the end of this cycle, a delamination test is done to assess the adhesives performance. Only then is the adhesive approved for usage.Obviously, with an infinite number of different substrates and materials to be bonded, there needs to be a sizeable range of different adhesives available to provide the optimum bonding strengths for different structures. There is also a need to provide these adhesives in different formats to suit the applications. The most common formats in which adhesives are available are webs, films and dry powders. These are normally derived from thermoplastic compounds such as EVA, polyurethane, polyamide, polyethylene or acetyl. They can also be provided in various widths and lengths to suit the application. They are inert and completely safe. No special storage is required for these adhesive formats.These thermoplastic materials have the ability to be melted again and again if necessary, which may be useful for multi-pass laminating, whereby a user may prefer to build up the lamination layer-by-layer.There are also thermoset adhesives, which, once heat-activated, will melt into the fabrics, set permanently and give a very powerful bond.

 Benefits Of Low-Temperature BondingThere are several reasons why it is important to maintain relatively low-temperature bonding for a wide range of substrates, including: ability to process heat-sensitive materials; elimination of material shrinkage; prevention of laminating problems, such as strike back and strike through; importance of maintaining the original appearance of the materials; and possibility of lower temperatures and higher speeds in longer heating tunnels.In most dry-heat laminating applications, processing temperatures between 60°C to 150°C are the normal temperatures at which bonding between substrates will take place. The temperature will vary, however, according to the thickness, density and number of layers of material through which the heat must penetrate.It is also important that heating take place simultaneously above and below the substrates to maximize process efficiency for best results. ConclusionBecause of industry demands for faster production and shorter lead times with JIT manufacturing, as well as the necessity to reduce or eliminate harmful toxic emissions, dry-heat laminating provides an excellent alternative to and improvement upon traditional processes of flame, solvent and calendering production.  For more information on dry-heat lamination technology, contact Ian Field, sales manager, Bandwise Reliant Ltd., United Kingdom, at 44 01494 792299.

January 2001



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