Production Gluing of High Density Plastic Laminates
By Kent Pitcher
This article describes the gluing of high density plastic laminates (i.e. Formica, Debar, Nevamar, Micarta, Pionite and the like) to plywood, lumber core, and particleboard core panels. Such laminations are widely used for table, chest, sink, cabinet and counter tops.
Elimination of telegraphing generally requires either better surface preparations, as with particleboard, or crossbanding with at least one ply of a defect free, close-grained species of veneer, such as poplar or basswood, between the core and plastic. This veneer may be bonded to the core in a separate operation, the assembly sanded and then the plastic face and backing sheets applied.
Sometimes bonding plastic directly to lumber core, particleboard core or rough cross banding will highlight any voids, knots or glue lines present. When bonding the plastic and the veneer to the underlayment in one operation, the pressure required must be carefully controlled for it can cause any open defects, glue lines and/or rough grain in the veneer to telegraph.
Foreign matter in the glue line will also show through the plastic. Straining the glue mix to remove any sawdust, dirt or dried glue before putting it into the spreader is recommended. Also, brushing the plastic with a soft-bristle cleaning brush to remove sanding dust or clinging wood and dirt particles is suggested.
Improved wetting of the dense plastic surface by urea resins can be accomplished by addition of Craze-Proofing Liquids. Where a craze-resistant bond is required, an internally plasticized urea resin can be used. Phenol-resorcinol resins are rarely used for hot pressing, but if employed in this manner, they will provide a waterproof bond.
It is often desirable to utilize an adhesive with a high wet tack or quick set. In such instances, a polyvinyl acetate emulsion adhesive is recommended. Where both the tack and setting speed of a polyvinyl and the water resistance and economics of a urea are desired, a blend mixture of the two adhesives can be used.
Casein adhesives can be used where plant temperatures are below 65F, but utilization is somewhat limited because high moisture introduced into the glue line that may cause telegraphing through the plastic surface.
Note: Best results are obtained when the gluing surface of the laminate has been sanded. Both adhesive and stock should have a temperature of at least 70F when bonding high pressure laminates.
Telegraphing - Improper underlayment or too low a grade. Laminating pressure too high. Unsanded or rough sanded underlayment or plastic. Foreign matter in glue line or on face of plastic. Laminating directly to core stock (lumber or particle- board) without x-banding.
Loose corners or edges - Core material not sanded evenly. Non-uniform pressure due to poorly aligned platens or nip rolls. Plastic not thoroughly sanded. Too low a laminating pressure Improper loading in press.
Blisters under plastic face - Core material not sanded evenly. Plastic not thoroughly sanded. Air entrapped (contact adhesive). Too low a laminating pressure. Excessive assembly time. Insufficient glue spread.
Warping - Improper backing sheet. Core material not balanced. Too high a gluing temperature (hot pressing).
Adhesive on plastic faces - Too thin an adhesive mix. Too heavy an adhesive spread. Improper stacking in press.
Slippage - Improper stacking in press. Too heavy an adhesive spread. Too thin an adhesive mix. Improper and uneven pressure.Carelessness - spots on decorative surface must be washed off with water while soft. Wax decorative surface to prevent sticking.
This article was provided by Kent Pitcher of Custom-Pak Adhesives, Inc.
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