Surfacing with Paper and PVC Foil
The smooth, stable surfaces of MDF make it an ideal substrate for Surfacing with decorative paper or PVC foils. The well compacted Surface layer of fibres and the absence of voids allows the use of thin or lightweight foils without the risk of appearance defects resulting from any show through of the substrate.
PVC foil surfaced MDF panels can be used for applications where vee grooving and folding is the preferred method of construction for television cabinets and loudspeaker boxes, for instance.
For the best results the following procedures are recommended for laminating paper or PVC foils.
1. The MDF should have been finish sanded by the board manufacturer with 100 grit or better. The surfaces should be free from sanding defects which may be emphasised by the decorative treatment.
2. Boards should be substantially flat and have a thickness tolerance of not more than ±0.2mm up to 30 mm nominal thickness and ±0.3mm for thicker boards.
3. The colour of the MDF surface may have an effect on the appearance of panels surfaced with lightweight white or pale coloured foils. A lighter colour MDF should be selected for these applications.
4. Uniform porosity of the board surface is an important requirement for high speed pressing operations as variations in this property will affect the quality of bonding achieved during the short time under pressure in a short cycle flat press or roller laminator.
5. The surfaces and edges of boards should be well brushed in a vacuum unit immediately before laminating to remove all loose particles and fibres.
Bonding conditions for paper foils are dependent upon the type of laminating equipment that is available. Flat platen presses developed for wood veneering can be used for bonding the thicker foils at 80g/m2 or heavier.
When medium and lightweight foils were first introduced about fifteen years ago, short cycle, heated platen presses were used for bonding foils with mixed application urea formaldehyde (UF) or copolymer dispersion adhesives. Nowadays, most foil laminators have continuous, hot roller lamination presses for bonding foils with UF adhesive using a separate application method with the hardener applied by a secondary roller or with copolymer dispersion adhesive. Adhesive coating weights in the range 80-120 g/m2 are typical for both types of pressing.
Lightly textured surfaces can be created by the use of a textured matrix or press platen in a short cycle press or a textured roller in a continuous laminator.
PVC foils are normally bonded at room temperature in a roller laminator using copolymer dispersion or epoxide adhesives. The panels emerging from the press should be stacked on a flat base for several hours to allow the bonds to achieve full strength before further processing.
Experience has shown that panels bonded with epoxide adhesives which have higher heat resistance than copolymer dispersion adhesives require closer control of the vee grooving and folding process.