Patent Application
20070065662
The present invention relates to thermal bonding of substrates and more particularly to a process and apparatus for laminating a polymeric film to a substrate and activation of a mineral filled thermoplastic adhesive.
Coated embossed polymeric film materials are used in a wide variety of applications. For example, paper based products may be coated with a polymeric film and used to simulate leather panels, photographic paper, door panels, etc. These types of products are produced by extrusion coating a polymeric film onto a paper substrate and embossing a pattern onto the exposed surface of the film. Polymeric films may also be exposed to heat to activate adhesive properties thereby being used as a bonding agent. In a conductive type lamination process, the film and paper substrate are run over heated rollers. The heat employed in this lamination process is sufficient to melt the thermoplastic material (usually in the range of approximately 110° C.-120° C.) and drives the heat through the paper substrate. A drawback with using heated rollers in this manner is that the heated roller comes in contact with the film and destroys any embossed pattern on the film. In addition, the rollers must be hotter than the melting point of the thermoplastic material in order for the melting point of the material to be reached. These very hot rollers inadvertently heat the opposite surface of laminate. This creates a temperature gradient through the material which is cooler as you approach the outer surface. This temperature gradient causes bubbling because the inherent moisture content of the paper substrate escapes. This results in blistering and bubbling of the paper substrate leading to composition breakdown.
Features and advantages of the present invention are set forth herein by description of embodiments consistent with the present invention, which description should be considered in conjunction with the accompanying drawings, wherein:
The present application relates to a laminated substrate using an infrared activated thermoplastic adhesive and process for making the same. In one embodiment, a surface of a linerboard substrate is coated with a thermoplastic resin. The coating is activated by infrared emitters and the substrate may be bonded to various materials, for example polystyrene foams, wood based products, paper products, wovens, non-wovens, cloth, etc., without compromising the integrity of the linerboard substrate such as blistering and/or bubbling.
Plastic based material 130 may be, for example, polypropylene configured to prevent the escape of moisture thereby acting as a moisture barrier and maintained typically at room temperature of approximately 30° C. However, plastic based material 130 may be an extrudable plastic configured to act as a moisture barrier. Propylene is preferable because it has a higher melting point than LDPE layer 120 on the opposite side. The differential between the layers 130 and 120 assists, but is not essential to, the temperature gradient as explained in more detail below. Various types of polymers may also be used as material 130, as well as extruded polyesters, nylons and various types of polyurethanes.
Layer 130, for example polypropylene, is extruded to linerboard substrate 110 and embossed with a desired pattern. Unfortunately, a typical cardboard based linerboard has an inherent level of moisture content which will boil and outgas around 100° C. (H2O). In order to activate the thermoplastic adhesive 120 the temperature must reach at least 110° C. In this heating process, heat transfers to the cardboard linerboard and may cause bubbling and blistering of the linerboard 110 thereby compromising the integrity of the material. Linerboard 110 may be perforated or coated to further prevent blistering and bubbling from the escape of inherent moisture.
The black LDPE layer 120 is configured to absorb infrared radiation sufficient to reduce the temperature gradient through substrate 100 while allowing the thermoplastic resin to melt to activate its adhesive properties. Layer 120 acts as a heat sink by the use of mineral additives in the amounts of 3%-5% total loading in the LDPE. Examples of such mineral additives include calcium carbonate, talc, fumed silica, mica, clay, DE, and other materials configured to provide the necessary heat sink properties to layer 120. While the amount of mineral additive, such as calcium carbonate, included with black LDPE layer 120 must be sufficient to absorb the heat to melt the thermoplastic at a rate sufficient for adhesion, it must be low enough to also prevent rapid heating of layer 120 such that if layer 120 absorbs heat too quickly, undesirable heat will be transferred to layer 110 thereby causing blistering and bubbling.
Once layer 120 is heated to 110° C.-120° C. to initiate the adhesive properties, substrate 100 may be adhered to various materials. For example, substrate 100 may be used as a substrate for a polystyrene foam material used for door face surfaces or a wood based OSB product. This adhesion may be performed through the use of nipped rollers with sufficient pressure for 2-3 second duration. Obviously, pressure and duration values may be modified to provide sufficient adhesion depending on the type of material being used.
The foregoing description is provided to illustrate and explain the present invention. However, the description hereinabove should not be considered to limit the scope of the invention set forth in the claims appended here to.
