PROBING BELOW THE SURFACE OF PROFILE WRAPPING
Manufacturers of all types of mouldings, and furniture, windows, and doors can now enhance their product lines with a wood-grain look or any fashionable color a customer may choose. This can be done using profile lamination machines, which laminate aluminum, steel, wood and vinyl substrates with a paper/vinyl foil or wood veneer.
For moulding and furniture manufacturers, profile lamination success depends on three factors: correct choice of machine, correct choice of adhesive, and correct choice of lamination material. If one of these factors fails, everything fails. Therefore, manufacturers need to have an understanding of the equipment, the glues and the laminating materials. This article is designed to provide an introduction to profile laminating. Most suppliers offer a more thorough training program to accommodate their customers.
Trends in profile wrapping
Presently, the trend is to feature a woodgrain finish on mouldings and furniture parts. Profile lamination is most commonly used in two major areas: upgrading low cost lumber with a quality veneer wrap and wrapping vinyl/PVC extrusions with a vinyl foil as used by window manufacturers. Applying veneer onto MDF or particleboard moulding is one of the many other possibilities a profile laminator offers. The same basic machine may be used for laminating all different substrates.
The configuration of a typical profile lamination depends mainly on the type of substrate used. Aluminum and PVC extrusions require precleaning prior to the laminating process. Most users prefer a multi-purpose machine for wood and aluminum/PVC substrates. The basic machines are modular in design to enable a manufacturer to have a tailor-made lamination line or add options at a later stage.
How the process works
The substrate enters a brushing station with natural bristles to avoid any electrostatic build-up in synthetic materials. This operation is very important in preparing the substrate for the further laminating process. The substrate temperature should not be below 65F. An infrared heater station may raise the temperature of the substrate to approximately 80F. The moisture content of the wood-based substrates may not be higher than 10 to 12 percent.
The paper/veneer/vinyl laminating material roll is mounted on an unwinder shaft above the glue applicator. A precise tension control system monitors the changing roll diameter and an electrical system fine-tunes the brake to maintain preset tension at any diameter, which is an important factor for the roll material used for lamination. Depending on the profile laminated, an edge web control system may be required for the accurate guiding of the lamination material onto the substrate.
Hotmelt glue is applied onto the roll material seconds before it is laminated onto the substrate. A multi-purpose hot-melt glue system provides the user with maximum flexibility, while a control system provides the accurate glue line. As the substrate passes through the lamination area, many silicon rubber-coated pressure rollers shape the paper/foil/veneer onto the substrate.
After the workpiece leaves the laminating area, a trimming station may be considered to remove any veneer or laminate overhang. Frequency-controlled motors are adjustable at any angle to suit the application. Sound and dust enclosures with interlocked safety doors are also required for operator safety.
Since all lineals are laminated on a continuous basis, butt-to-butt, they need to be separated back to their original length after the veneer or laminate is applied. This is achieved with a flying cut-off saw, which operates at production speed.
Once the laminated or veneered sub-strates reach this point, a handling glue bond is already achieved which allows further processing immediately. Depending on the complexity of the profiles, expected production speeds range from 80 to 200 feet per minute for hotmelt glue applications.
Polyurethane (PUR) hotmelt adhesives combine the speed and convenience of conventional hotmelts with the durability of liquid urethanes. Their benefits include immediate handling bonds, no solvents, water resistance and low application temperature that prevents distortion of heat sensitive substrates. They are also used in laminating window and door components because they require no curing or drying ovens, exhibit excellent heat and cold resistance, and are flexible to withstand the expansion and contraction requirements of weathering.
To understand the benefits of PUR hotmelt adhesives, they need to be compared to conventional hotmelt and polyurethane adhesive technology. Conventional hotmelts, such as ethylene vinyl acetate or polyamide-based products, are simple to use. They are one part, solvent-free systems and allow immediate handling. Conventional hotmelts are thermoplastics, however, and don’t cure or cross-link. They have a limited heat resistance, much less than 225F, and poor solvent resistance.Standard polyurethane liquid adhesives sometimes contain solvents and are applied at room temperature. They provide little bond strength during assembly and therefore do not provide immediate handling.
Containing no solvents and requiring mixing, PUR hotmelts are stable solids at room temperature and are applied at temperatures near 225F. A self-contained pre-melter unit which accepts glue cartridges simply placed inside, is installed above the profile laminating line’s glue applicator. Large freestanding units capable of tapping into, accepting 55-gallon drums, are available for greater glue capacity. These are connected to the glue applicators via a heated hose.After the adhesive is applied, heat dissipates from the reactive hotmelt and green strength, or handling bonds, are achieved. This allows downstream operations such as trimming or routing to be performed quickly after the laminate and profile are mated. PUR strengthens as moisture is absorbed within the bond line. When this happens, irreversible crosslinking occurs within the polyurethane network.
Test guidelines for gluelines
As far as testing of adhesives and standards regarding their use, there is a lot of discussion within the profile laminating industry concerning what is generally referred to as the Type 1 glue line. Most of the discussion is based on the idea that the laminated profile should be waterproof. There are several tests that are generally used in the woodworking industry to determine Type 1 glue lines.
None of the tests are specifically designed for the profile laminated materials, and none are generally appropriate for products ASTM D 3110-88 moulding and millwork. One might assume based on the title, this would be an appropriate test. However, this test is designed to establish the suitability of fingerjointed, edge-glued and face-glued construction for exterior applications. This test is for solid mouldings that have been glued up to dimensions greater than a single width, thickness or length. There are no provisions for the application of a veneer overlay.The second test is NWWDA IS-87 Flush Doors and Veneered Frames, the basis for most claims of Type 1 glue bonds within the profile lamination industry. This outlines the procedures for testing flush doors. The doors are cut into small pieces, and the procedures test the bond of veneer to a solid wood substrate.
Finally, there is ANSI/HPMA HP 1983 Hardwood Plywood, a specification covering the durability of plywood constructed of multiple layers of wood veneer or other laminates. Testing is to certify the bond of various layers.
There is a need for a standard test, which will prove to be a reliable method for determining the suitability and durability of solid wood mouldings, vinyl wood mouldings, vinyl, or aluminum when laminated with vinyl or wood veneers using adhesives rated Type 1 by the vendor of the adhesive. Such a test will also enable the producer of laminated parts to certify with confidence that its products will demonstrate performance equal to Type 1 boilable bond requirements set forth in NWWDA IS 1.6.86 Testing and Inspection for Wood Flush Doors.
One advantage offered by profile laminating is that it reduces the high inventory costs associated with storing profiles with different colors or finishes. Any substrate can be laminated to a specification, and color can simply be changed by changing the roll material. The primary choices are real and wood veneers; vinyl laminates or paper, which are available in a variety of woodgrain patterns; colors; and other patterns such as marble. An important recommendation is that whatever type of lamination is used on the product or components, whether it is going to appear on the interior or exterior side of the finished product, it should be a material designed for exterior use.
When laminating vinyl, aluminum or wood, the key is water resistance, which can only be achieved at this stage of the technology if the veneer is bonded to its backing with polyurethane adhesive to avoid delamination problems resulting from condensation and/or humidity. The choice of the veneer backing is also important, as the veneer should be flexible enough to be laminated closely around the profiles, but should still have enough stiffness to be used in modern laminating equipment.Wood veneers using various species are available in a variety of roll widths and are also available cut to specific width. Numerous options are offered with such products including indexed veneer joints (finger or butt joints at specific increments). The machine will detect the indexed joint and place it at the end or between the profile being wrapped.
PVC foils for a variety of applications are also available in various standard size rolls as well as custom widths. The products generally consist of a PVC film containing a plasticizer that keeps it from being brittle, but keeps it stiff enough to allow application without wrinkling. They also must be flexible enough to allow easy gluing. The base foil as well as printing inks used in producing these foils need to utilize highly light and stable pigments. After that, an acrylic layer is applied and sometimes embossed with a “woodgrain touch”. The acrylic, which should be free from pinholes and impermeable, provides resistance to weather attack. By using a UV absorber as well, it provides future protection to the pigments of the print and the base foil against bleaching.
Suppliers of these films have performed accelerated weather testing to the German DIN standards, including over 5,000 hours in tests that mirrors five years of exterior use in central Europe. Tests carried out on components in Europe also give results which correspond with those obtained in lab testing. There are some products, for example, which do not show change at all after five years of weathering.
Immersion and abrasion resistance testing have also been performed. The surface of the foil shows typical acrylic properties. It is not sensitive to everyday household agents such as water, alcohol, non-abrasive cleaners and building materials such as cement or gypsum. Thus it can be cleaned with normal household products.
The advancement in hotmelt glues and new machinery technology has opened new possibilities in laminating. An investment with fast return and minimum labor involvement, profile lamination offers furniture, millwork, window/door manufacturers and custom laminators a tremendous freedom and virtually unlimited choices of surface finishes and textures.