Patent Abstract:
A method for preparing laminating materials and a composite prepared therefrom, the method including providing at least one layer of interleaf, extruding a thermoplastic adhesive with a die, forming a composite by applying the at least one layer of interleaf to the adhesive before cooling the adhesive, and pressing the composite with rolls to adhere the at least one layer of interleaf to the adhesive.

Full Description:
FIELD OF THE INVENTION 
     The invention relates generally to extruding plastics, and more specifically, to preparation of a thermoplastics adhesive for lamination of a composite. 
     BACKGROUND OF THE INVENTION 
     To extrude plastics, one may use an extruder, sheet die, and an embossing-stack. In one example, a thermoplastic adhesive is extruded through the die into cylinders of the embossing-stack, where the adhesive is formed into a film. The surface of the film is embossed with a finish and then the film is cooled. The cylinders of the embossing-stack have an embossed surface, which they impart onto a thermoplastic sheet. The cooled thermoplastic sheet may be collected on a roll or cut using a single layer of interleaf material to separate consecutive wraps or layers. 
     In another example, film is extruded from an extruder through sheet die onto one interleaf while the film is still thermoplastic. From a position that is near to the sheet die, the film and the interleaf layer are simultaneously pulled by a set of nip rolls that press the film and interleaf layer together while the film is still relatively warm. During this process, the texture of the interleaf layer is impressed in the film. The film and interleaf layer are lightly bonded together so that the interleaf layer can later be peeled. 
     It is believed that in the above method of preparing a thermoplastic sheet, stress is added to the sheet when the film is pulled off of the collection roll and this stress adversely affects the performance of the sheet in the preparation of a laminate. Consequently, the adverse effects from the stress may show up in the final laminated product. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods for preparing laminating materials and composites produced from the methods. In one embodiment, the method includes providing at least one layer of interleaf, extruding a thermoplastic adhesive with a die, forming a composite by applying the at least one layer of interleaf to the adhesive before cooling the adhesive, and pressing the composite with rolls to adhere the at least one layer of interleaf to the adhesive. 
     In a second embodiment, the method includes providing a pair of polyethylene layers of interleaf with a textured surface and a thickness of about 0.5–15 mils, extruding a polyurethane film, having a thickness of about 0.5–250 mils, with a die, forming a composite by applying the layers of interleaf to the polyurethane film, pressing the composite between rolls of an embossing stack, having an embossing surface, adhering the layers of interleaf to the film, impressing the textured surface of the layers of interleaf and the embossing surface into the film, passing the composite into pressure contact with a cooling surface to cool the film on the composite, and collecting the composite. 
     In a third embodiment, the composite includes at least two layers of interleaf with a surface and an adhesive adhered between the at least two layers. The adhesive is conformed thermoplastically to the surface of each layer. 
     In a fourth embodiment, the composite includes a pair of layers of polyethylene interleaf, where each layer has a textured surface, and a polyurethane film adhered between the layers of polyethylene interleaf. The film is thermoplastically adhered to the textured surface of each layer. 
     In a fifth embodiment, the composite includes at least one layer of interleaf with a surface and an adhesive adhered to the at least one layer. The adhesive is conformed thermoplastically to the surface of the at least one layer of interleaf. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate the presently preferred embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
       In the drawings: 
         FIG. 1  is a schematic diagram illustrating one embodiment of a method of the invention; 
         FIG. 2  is a side view of one embodiment of a composite prepared from the method of  FIG. 1 ; 
         FIG. 3  is a side view of another embodiment of a composite; and 
         FIG. 4  is a schematic diagram illustrating another embodiment of a method of the invention for preparing the embodiment of a composite of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It is to be understood that the Figures and description of the invention included herein illustrate and describe elements that are of particular relevance to the present invention, while eliminating, for purposes of clarity, other elements found in typical extruders. 
     The invention provides a method for preparing laminating materials, or a film, tape, or sheet of plastic, to improve the lamination of a composite product. These laminating materials may be made by extrusion, both vertically and horizontally. As shown in  FIG. 1 , extruder  10  melts adhesive resin and forms a thermoplastic adhesive layer, or polyurethane film,  20  by passing the molten adhesive through sheet die  25 . The extrudate melt temperature may range from about 200° F. to about 500° F., but the preferred temperature is material dependent. The adhesive resin in adhesive  20  may be made of any material that is melt processible or solvent casted and can be formed into a sheet. For example, the adhesive resin may be made of polyurethane, polyvinylbutyrate, polyvinylacetate, polyester, or combinations thereof. The thickness of the adhesive  20 , preferably, is controlled by adjusting the speed of production or varying the die opening. In one embodiment, the thickness of the adhesive  20 , preferably, is about 0.5 to 250 mils, or more preferably, about 2 to 100 mils. 
     In one embodiment, rolls  30  and  31  of interleaf layers  32  and  33 , respectively, are simultaneously pulled by a roll stack  40 . Roll stack  40  includes rolls  41  and  42 . In one embodiment, interleaf layers  32  and  33 , preferably, have a textured surface  32   a  or  33   a,  however, the interleaf layers  32  and  33  may have any desired surface, including no texture or a smooth, or glossy, surface. The desired surface may be chosen to obtain an appearance of the final laminate product. Textured surface  32   a  or  33   a,  preferably, has a depth of about 5% to 100% of the thickness of the interleaf layer and, more preferably, has a depth of about 20% to 80% of the thickness of the interleaf layer. Textured surface  32   a  or  33   a  may have a random pattern, a diamond pattern, or any other desirable pattern. A pattern allows the adhesive  20  to de-air, which squeezes the air out of the space between interleaf layers  32  and  33  and adhesive  20 , as the interleaf layers  32  and  33  come in contact with the adhesive  20 . This de-airing will eliminate air bubble defects in the final laminate product. One textured surface  32   a  may have a different pattern from the other textured surface  33   a.  Interleaf layers  32  and  33  are preferably polyethylene; however, polypropylene, polyethylene terepthalate (“PET”), and other similar materials that allow interleaf layers  32  and  33  to maintain intimate contact with adhesive  20 , maintain its physical properties during pressing, maintain an embossed pattern, and/or have the flexibility to be rolled may be used. 
     In a preferred embodiment, interleaf layers  32  and  33  each have a thickness of about 0.5 to 15 mils. In a more preferred embodiment, interleaf layers  32  and  33  each have a thickness of about 2 to 6 mils. 
     Rolls  41  and  42  include metal, silicone and/or rubber outer portions for contacting a laminated product. Rolls  41  and  42  press interleaf layers  32  and  33  to adhesive  20 , while adhesive  20  is still heated from the extrusion, to adhere interleaf layers  32  and  33  to adhesive  20  and form a composite  50 . While interleaf layers  32  and  33  are pressed against adhesive  20 , preferably, textured surfaces  32   a  and  33   a  of interleaf layers  32  and  33  are impressed into adhesive  20 . This impression of texture decreases the shininess, or glossiness, of adhesive  20 . This allows the surface of adhesive  20  to de-air when it is laminated into a composite, provides a surface with a greater roughness, allows adhesive  20  to be more easily positioned during use, and allows for easier de-airation when bonding adhesive  20  to another surface. During de-airation, the texture allows the air to channel out of adhesive  20  as pressure is applied to the surface of adhesive  20 . This must be accomplished before adhesive  20  becomes tacky and traps the air. 
     During pressing, interleaf layers  32  and  33  will not transfer any material to the adhesive  20  that could affect the performance of adhesive  20 . In a preferred embodiment, the pressing prevents air from being trapped between adhesive  20  and interleaf layers  32  and  33 , which allows for an intimate contact between adhesive  20  and interleaf layers  32  and  33 . 
     Composite  50  then comes into pressure contact with a cooling surface  58  of roll  60  to cool adhesive  20  in composite  50 . The temperature of cooling surface  58  effects the surface characteristics of adhesive  20 , so the temperature must allow for cooling of interleaf layers  32  and  33  and texturing of adhesive  20 . Accordingly, the temperature is selected depending upon the physical and chemical attributes of the interleaf layer(s) and the adhesive. In a preferred embodiment, cooling surface  58  has a temperature between 40° F. and 200° F., and in a more preferred embodiment, cooling surface  58  has a temperature between about 60° F. and 150° F. After composite  50  moves along roll  60 , composite  50  is collected as a unit onto roll  65 . Alternatively, composite  50  may be cut to size and stacked as flat sheets without sticking together. In one embodiment, composite  50 , as shown in  FIG. 2 , has interleaf layers  32  and  33  and adhesive  20  therebetween. 
     In one example using the above method, a composite  50  of AG-5050 0.050×39″, an optical urethane provided by Thermedics Polymer Products, Woburn, Mass., was made using two outside interleaf layers  32  and  33  of polyethylene film. The interleaf layers  32  and  33  were 0.004 inches thick and had a random texture on the surface. The AG-5050 extrudate left the sheet die  25  at 340° F. and was joined with the interleaf layers  32  and  33  at rolls  41  and  42 . The temperature of roll  41  was 100° F. and roll  42  was 120° F. Composite  50  was then rolled up as finished rolls and packaged for use in security glazing. 
     In another example using the above method, a composite  50  of AG-5050 0.050×50″ was made using two outside interleaf layers  32  and  33  of film. One interleaf layer was 0.004 inch thick polyethylene film that had a random texture. The other interleaf layer was 0.002 inch thick polypropylene film that had a random texture. The AG-5050 extrudate left the sheet die  25  at 335° F. and was joined with the interleaf layers  32  and  33  at rolls  41  and  42 . The temperature of roll  41  was 105° F. and roll  42  was 120° F. The composite  50  was then rolled up as finished rolls and packaged for use in security glazing. 
     In another embodiment, as shown in  FIG. 3 , the composite  150  has one interleaf layer  132  adhered to the adhesive  120 , where interleaf layer  132  may be located on either the top or the bottom of adhesive  120 . Similar to the method of making a composite with two interleaf layers described above, extruder  110  melts adhesive resin and forms adhesive layer  120 , as shown in  FIG. 4 . Roll  130  of single interleaf layer  132  is pulled by roll stack  140 , which includes rolls  141  and  142 . As described above, interleaf layer  132  may have any desired surface and be made of any material that allows interleaf layer  132  to maintain intimate contact with adhesive  120 , maintain its physical properties during pressing, maintain an embossed pattern, and/or have the flexibility to be rolled. 
     Rolls  141  and  142  press interleaf layer  132  to adhesive  120 , while adhesive  120  is still heated from the extrusion to adhere interleaf layer  132  to adhesive  120  and form composite  150 . While interleaf layer  132  is pressed against adhesive  120 , preferably, any textured surface of interleaf layer  132  is impressed into adhesive  120 . Interleaf layer  132  will not transfer any material to adhesive  120  that could affect the performance of adhesive  120 . 
     Composite  150  then comes into pressure contact with cooling surface  158  of roll  160  to cool adhesive  120  in composite  150 . The temperature of cooling surface  158  must allow for cooling of interleaf layer  132  and texturing of adhesive  120 . After composite  150  moves along roll  160 , composite  150  is collected as a unit onto roll  165  or cut to size and stacked as flat sheets without sticking together. 
     During the lamination process, interleaf layers  32  and  33  or  132  are removed so that adhesive  20  or  120  may bond to other materials. When interleaf layers  32  and  33  or  132  are removed, adhesive  20  or  120  may be used in many manufactured products. For example, adhesive  20  or  120  may be used in touch screens, EMI screens, windows, car side windows, computer screens, monitors, television screens, bullet resistant laminates, and many other applications. Composite  50  or  150  is stiffer than adhesive  20  or  120  alone and thus allows for easier handling of adhesive  20  or  120 . Interleaf layers  32  and  33  or  132  maintain adhesive  20  or  120  in a clean, uncontaminated state and provide less internal stress on adhesive  20  or  120  by allowing adhesive  20  or  120  to lay flat, or be stacked, during the construction of the final laminate product. By maintaining a low internal stress on adhesive  20  or  120 , wrinkles and other defects are prevented, which results in a less stressed final laminate product. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Thus, it is intended that the invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Classification (CPC): 8