THERMALLY-ACTIVATED LABEL AND METHOD FOR PRODUCING LABEL STOCK FILM FOR SAME

Abstract: The film and method of producing same of the present invention comprises a film capable of serving as self-adhering label stock and not requiring a secondary coating process or a release liner. The film comprises a smooth side, a rough side and, optionally, one or more core layers interposed between the smooth side and the rough side. A heat-activated adhering material comprised of certain polymers and co-polymers associated with the smooth side of the film prevent the need for traditional adhesive coating and/or release liner.

Description: THERMALLY-ACTIVATED LABEL AND METHOD FOR PRODUCING LABEL STOCK FILM FOR SAME RELATED APPLICATION INFORMATION: This Application claims the benefit of prior filed and co-pending U.S. Provisional Application No. 60/064,524, entitled "Thermally-Activated label and Method for Producing Label Stock Film for Same", filed November 5, 1997 (Docket No. 31358-35L, Inventors: Farid F. Ghiam, Stephen G. Junker and Paul E. Thomas), which is assigned to the same assignee as this application, and the totality of the disclosure of which is hereby incorporated by reference for all purposes. FIELD OF INVENTION: The present invention relates to label stock films and, more specifically, to a film capable of use as self-adhering label stock not requiring a secondary coating process or a release liner, and a method for producing same. BACKGROUND OF INVENTION: As the name suggests, pressure sensitive labels ("PSL") adhere to a substrate, such as a bottle or other surface, upon the application of pressure to them. Such labels are widely utilized in various industries due to their superior endurance and performance characteristics. However, several disadvantages are associated with their use. For example, PSLs require that a pressure sensitive adhesive be coated or otherwise applied to the surface of the film in a secondary process. Additionally, a release liner is required to cover the adhesive layer until such time as the label is actually used. Without the presence of a release liner, the film will adhere to itself and to other surfaces prior to its use. Thus there remains a need for a label stock film capable of use as a self- adhering label and not requiring a secondary coating step or the use of a release liner. SUMMARY OF THE INVENTION The present invention comprises a label stock film capable of serving as a self-adhering label without the need for a second adhesive coating or a release liner. The improved label stock film is preferably of the one side smooth, one side rough type (e.g. , "OSM") so that blocking and wrinkling of the film are substantially minimized, if not completely eliminated. DESCRIPTION OF THE INVENTION In accordance with the present invention there is provided a label stock film capable of serving as a self-adhering label without the need for a second adhesive coating or a release liner. The improved label stock film is preferably of the one side smooth, one side rough type (e.g., "OSM") so that blocking and wrinkling of the film are substantially minimized, if not completely eliminated. The improved label stock film of the present invention comprises a film preferentially having a smooth side, a rough side and, optionally, one or more core layers interposed between the smooth side and the rough side. The multiple layers are preferably coextruded. The smooth side comprises at least one layer of a thermoplastic film. In use, the smooth side is applied to the surface of the substrate to be labeled. The rough side is also comprised of at least one layer of a thermoplastic film. The rough side is preferably matte embossed, but can be roughened via any suitable means. The rough side prevents the film from contacting as much surface area of itself, or any other undesired surface, preventing blocking and wrinkling of the film and thus eliminating the need for a release liner. The rough side also serves to provide ink or pencil writeability and paper-like aesthetics. At least one core layer may be interposed between the smooth side and the rough side of the improved label stock film and, if present, is also comprised of a thermoplastic film, or a combination of thermoplastic films. The adhesion produced between the smooth side of the improved label stock film of the present invention and the surface to be labeled is provided via a heat-activated adhering material. Thus, in contrast to a pressure-applied label (PSL), the improved label stock film of the present invention is permanently affixed to a substrate using a predetermined thermal load. The adhering material does exhibit a small amount of tackiness without a thermal load, allowing the label to be preliminarily placed or set (and reset or repositioned, if necessary) before the thermal load is applied, permanently affixing the label into desired position. This feature of the heat-activated label stock film of the present invention represents a significant advantage over PSL films, which must be placed correctly the first time (.. e. , repositioning of a PSL is not possible since its adherence is pressure-based and subsequent attempts to remove the label result in its destruction). Although the description of a heat-activated material is described fully herein, it is noted that the adherence material of the improved label stock film of the present invention is energy-activated and can be activated through the application of energy sources other than thermal energy, including without limitation, ultraviolet light and other wave-based energy sources. Returning to the current example, the heat-activated adhering material is comprised of certain polymers and co-polymers associated with the smooth side of the film. The identity and quantities of these polymers are dictated by the conditions (e.g. , temperature) under which the improved label stock film will be applied and ultimately used. In the case of labels directed at use with bottles or the like, a preferred polymer associated with the smooth side of the first layer is a styrene-ethylene-butylene-styrene block copolymer ("SEBS"), a styrene-ethylene- propylene block copolymer ("SEP"), or blends thereof, such as Kraton®-G polymers available from Shell Chemical Company. Copolymers suitable for use in the present invention include, without limitation: relatively soft and low melt temperature copolymers, such as ethylene vinylacetates (EVA), ethylene acrylic acid ("EAA"), ethylmethyl acrylates ("EMA"), ethymethyl methacrylate ("EMMA") and metallocene catalyzed polymers (e.g., the Affinity® polymer groups available from Dow Chemical Company or the Exact® polymer group available from Exxon); anhydride modified polymers, acid modified and acid/acrylate modified copolymers (e.g., the Bynel® polymer group available from duPont) and CXA resins are also useful. The above-identified polymers and copolymers can function either separately or in various combinations. The preferred polymers for use in connection with the rough side of the improved label stock film include polyolefins, such as polyethylenes (e.g. , HDPE), polypropylenes, nylons, polyesters, EVOH, polystyrene, and the like, or blends thereof. The level of adhesion can be adjusted (via controlled addition and quantity of polymers and copolymers) to provide adequate levels of adhesion to substrates at various temperatures and environmental conditions under which the label will perform. The improved label stock film of the present invention can be constructed using coextrusion technology known in the art, including, without limitation, blown, cast or calendar extrusion techniques. Extrusion dies used in connection therewith may incorporate combining adapters or can be multicavity hardware. Importantly, in contrast to PSL films, only a single coextrusion is needed since a secondary coating process is not required with the improved label stock film of the present invention. Additionally, the layer including the smooth side of the improved label stock film of the present invention may be laminated to the layer including the rough side, if desired. As previously mentioned, the blending of polymer and copolymer additives of the smooth side of the improved label stock film may be controlled to produce desired tackiness of the resulting label. The relatively rough surface of the rough side of the improved label stock film of the present invention may be produced by any number of techniques, including without limitation, embossment (using steel rollers and/or an abraded rubber roller in a nip mode and/or from a compression rolling nip including one matted roller), addition of particulate fillers which embed in and roughen the surface, or any other suitable means known in the art. The relative smoothness of the smooth side may be produced via: use of a polished or semi-polished chill roll in a nipless cast extrusion method; use of a polished or semi-polished chill roll in a nip cast extrusion method; naturally smoothing during a blown film extrusion method, or any other suitable means known in the art. The polymers and/or copolymers of the smooth side of the improved label stock film of the present invention are coextrudable and therefore generally rigid to semi-rigid at room temperature, forming ideal label stock and eliminating the need for a carrier web or the like. The lack of relative tackiness at room temperature coupled with the roughened side prevent blocking and wrinkling of the film until its use is desired. While not wishing to be bound by the following theory, it is believed that the adherence material is heat-activated to increase tackiness in one or several ways: some heat activated polymers merely soften and"wet out" in response to the application of heat. Upon cooling, a relatively strong bond is formed and enhanced by the filling up of microspaces and the like with softened polymer during the heat application phase. Other polymers undergo a chemical transformation in response to heat, increasing the affinity of the transformed material for the substrate and creating a bond. Still other polymers transform a portion of the heat applied to the substrate itself, melting a small amount of the substrate material as well as the polymer material and, upon cooling, creating a fusion of the two materials. Accordingly, it is believed that a combination of such polymers (and their varying bonding mechanisms) increases the character and strength of the bond formed between substrate and polymer material. According to the method of the present invention, the improved label stock film is produced by preselecting the one or more primary components comprising the smooth side of the improved label stock film of the present invention. It is the surface of this smooth side which will ultimately intimately contact and adhere with the surface of the substrate to be labeled. Once selected, the one or more components of the rough side are also predetermined so as to produce a functional and controlled level of adhesion force produced under a given set of the label's production conditions, environment and ultimate substrate. The remaining skin and core layers, if present, are formed of a thermoplastic. The skin and core layers are preferably coextruded to form the improved label stock film of the present invention. The resulting improved label stock film can be wound onto itself without concern of blocking or wrinkling due to its roughened side and its relative lack of tack until a thermal load is applied. Although preferred embodiments of the invention have been described in the foregoing Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements and modifications of parts and elements without departing from the spirit of the invention.

Claims: WHAT IS CLAIMED IS: 1. A thermally-activated label stock film, comprising: a first side having a smooth surface; a second side having a rough surface; said smooth surface of the first side capable of permanently adhering to a surface of a substrate upon intimate contact therewith and application of a thermal load; said first side further comprising one or more components preselected to remain relatively tackless until such time as said thermal load is applied and upon application of said thermal load form a permanent bond with the surface of the substrate. 2. A method for producing a label stock film adapted to exhibit a relatively small amount of tackiness until a thermal load is applied thereto, comprising the steps of: preselecting at least one material for use as a first layer; preselecting relative quantities of the at least one material; preselecting at least one component for use as a second layer; preselecting relative quantities of the at least one component; coextruding the at least one material and the at least one component to form a film which, upon application of said thermal load exhibits an increased level of tackiness capable of forming a permanent bond with a substrate; and roughening a surface of the second layer.

Inventors: GHIAM FARID F, JUNKER STEPHEN G, THOMAS PAUL E, GHIAM, FARID, F., JUNKER, STEPHEN, G., THOMAS, PAUL, E.
Applicants: TREDEGAR IND INC, TREDEGAR INDUSTRIES, INC.
Application year: 1998
Main classification: G09F3
IPC codes: G09F3