Dry-Heat Lamination Offers Options

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
For more information on dry-heat lamination technology, contact Ian Field, sales manager,
Bandwise Reliant Ltd., United Kingdom, at 44 01494 792299.

January 2001