Patent Application
20060222842
The present invention relates to a multilayer composite material that has a graphic image visible on a surface thereof and to a method for making such a composite material. More particularly, the invention relates to a composite material that includes a foam base layer and a printed layer adhered to the foam base layer to provide the desired graphic image. The composite material may additionally include a transparent protective top layer or skin overlying the printed layer, with the graphic image being visible through this top layer. Composite materials of this type are useful in a variety of applications. For example, they may be used in various outdoor recreational articles such as snowboards, snow sleds, bodyboards, surfboards, cushions, personal flotation devices, etc.
Recreational articles of this type have typically been produced from closed-cell polyethylene foam. Polyethylene is an inert polymer and requires special surface treatment, such as corona treatment, to obtain good adherence of printing ink. For this reason, it is impractical to apply a graphic image to the foam by printing directly onto the foam. Instead, it is more convenient to surface-treat a polyethylene film for ink application, print the graphic pattern onto the surface-treated film, and in turn, laminate the printed film to the polyethylene foam. Another practice is to laminate the printed polyethylene film to another film layer that forms a protective top layer or skin, and then to laminate this composite to the foam. These approaches have required multiple lamination steps to bond the printed film to the foam base layer and to provide a protective top layer or skin.
Schneider et al. U.S. Pat. No. 5,211,593 describes a system for applying a graphics imprinted skin to a foam base layer wherein the graphic image is reverse printed onto a transparent polyethylene film. The printed surface of this film is adhesively laminated to an opaque backing layer to produce a multilayer film structure. The backing layer of this multilayer film structure is then laminated to the foam substrate so that the transparent polyethylene film layer serves as a protective top layer for the printing. This approach is limited by the fact that it requires several lamination steps and results in a structure with adhesive interfaces that may negatively affect the aesthetics of the printing and provide opportunities for delamination.
The present invention provides a composite material and method wherein a printed layer and protective top layer or skin can be applied to foam base layer quickly and efficiently in a single operation, without requiring adhesive or multiple lamination steps. The composite material includes a polyolefin foam base layer, a printed layer overlying the foam base layer, and a top layer overlying the printed layer, and wherein the layers are bonded together in the absence of adhesives. By eliminating the requirement for an adhesive to bond the printed layer to the other layers, a simpler and more efficient process is achieved and the aesthetics of the printing or graphics are enhanced.
More particularly, according to the present invention, the layers are fusion bonded together. By the term “fusion bonded” it is meant that the layers are bonded directly to one another without an adhesive by fusing the polymer materials of the layers to one another. This is achieved by causing surface portions of the layers to soften or at least partially melt and subsequently to harden or resolidify while in contact so that they become fused. The softening is typically achieved by heating, but could be achieved in other ways, such as by application of ultrasonic energy.
The composite material is produced by positioning a printed layer over a surface of a polyolefin foam base layer and extruding a top layer onto the printed layer with sufficient heat energy that the layers are fusion bonded together in the absence of adhesives to form a composite material.
The printed layer comprises a thermoplastic polymeric film having outer and inner surfaces and a layer of printing on at least one of these surfaces. This film is fusion bonded to the foam base layer. The top layer comprises an extrusion coating of a transparent thermoplastic polymer that is fusion bonded to the printed layer.
Preferably, the thickness of the top layer is such that the ratio of the top layer thickness to the printed layer thickness is at least 6:1. This assures heat energy from the extrusion coated molten thermoplastic polymer top layer can transfer through the thermoplastic polymer film of the printed layer and produce fusion bonding between the printed film layer and the foam base layer.
According to one embodiment of the invention the composite material comprises a polyolefin foam base layer and a printed layer overlying the base layer and comprising a polyolefin film with printing on at least one surface thereof. This film is fusion bonded to the polyolefin foam base layer. Overlying the printed layer is a top layer comprising an extrusion coating of a transparent thermoplastic polymer fusion bonded to the printed layer with the printing being visible therethrough.
In accordance with a further embodiment of the invention, the composite material may additionally include a scrim stiffening layer between the base layer and the printed layer, with the printed layer being bonded to the base layer through interstices in the scrim stiffening layer.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Referring to
The printed layer 16 comprises a thermoplastic polymeric film having outer and inner surfaces and a layer of printing on at least one of these surfaces. Preferably, the polymeric film is transparent and the layer of printing is applied to the inner surface facing the base layer 15. The film is preferably a polyolefin polymer or copolymer, and most preferably polyethylene. The film suitably has a thickness in the range of from 1 to 5 mils, preferably about 2 mils. Graphic images are printed on the film using printing processes of the type commonly used for printing on polyethylene films, such as flexographic or gravure printing for example.
The protective top layer or skin 17, sometimes referred to as a “slick skin”, provides the composite material 10 a shiny surface with cushioning characteristics, while also serving to protectively cover the underlying printed layer 16. The top layer 17 is formed of a transparent thermoplastic material so that the underlying printed layer can be seen through the top layer. The top layer 17 is preferably a thermoplastic polyolefin, and more preferably an ethylene polymer, copolymer or blend. Examples of suitable such materials include linear low density polyethylene, high density polyethylene, ethylene vinyl acetate copolymer, acrylic acetate copolymer, and ionic copolymers (or ionomers) such as Surlyn®. The top layer or skin 17 can comprise a single polymer stratum or multiple strata, e.g. a coextrusion of two or more strata of differing composition. For example the top layer 17 may be formed entirely of polyethylene, or it may be a coextrusion including polyethylene on one surface (e.g. the outside surface) and an ethylene acid copolymer or ionomer such as Surlyn®, a product of DuPont, on the opposite surface to provide for enhances bonding. For certain aesthetic effects, the top layer 17 may be colored or tinted. The top layer 17 is thicker than the underlying printed layer 16, and preferably has a thickness at least several times that of the printed layer. The overall thickness of the top layer 17 is preferably from about 15 to 25 mils, and more preferably about 20 mils.
In producing the composite material 10, a printed layer 16 is first produced by imprinting a film with the desired graphics pattern using conventional film printing processes as described earlier. This printed layer is then positioned over a surface of the polyolefin foam base layer 15. Preferably, when the film layer is a transparent film, the layer of printing is oriented facing toward the base layer 15. As shown schematically in
The heat energy of the extruded molten resin transfers through the printed layer, heating the printed layer 16 and upper surface portions of the underlying foam base layer 15 sufficiently that the polymer materials soften and fuse together, creating a thermal fusion bond between the printed layer 16 and the foam base layer 15. The thus produced thermal fusion bond does not smear or otherwise adversely affect the aesthetics of the printing.
The thickness of the extrusion coated top layer 17 is controlled by the size of the opening of the slot shaped extrusion die. Preferably, the thickness of the top layer 17 is controlled so that the ratio of the top layer thickness to the thickness of the film of the printed layer 16 is at least 6:1 and more preferably at least 8:1. This assures that sufficient heat energy is present to produce a strong fusion bond at the interface between the printed layer 16 and the foam base layer 15.
As the extrusion coated top layer 17 cools, the molten polymer solidifies on the upper surface of the printed layer 16 and forms a strong fusion bond between the top layer and the printed layer. The top layer 17 may be contacted by an optional chill roll 22 (
The composite material 10 may also include layers in addition to the printed layer 16 and the top layer 17. In the embodiment shown in
Although not illustrated, it will be understood that additional layers of various materials may also be provided on the bottom side 12 of the foam base layer 10 to control the stiffness, durability or surface characteristics of the composite material 10.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
