Abstract:
A pressure sensitive adhesive composition comprised of a substantially tacky polymer containing a number of prismatic or holographic platelets. When the composition is applied to a substrate, the platelets align themselves in a planar fashion parallel to the broad face of the surface on which the coating is applied. The resulting composition layer is transparent except for the platelets that refract and reflect the light striking the platelets back towards an observer. The color of the reflected light changes as the angle at which the platelets are viewed is changed. In this manner, the platelets in the coating provide an overall aesthetically pleasing appearance for the coated material that adds distinctiveness to decorative labeling, as well as to the objects on which the labeling is placed and other suitable types of laminations in which the adhesive coating may be used. Furthermore, the labeling may be used as an indication of counterfeit objects or of tampering with the object on which the labeling is placed because the platelets will either not be in an aligned position, or will shift from their aligned position within the adhesive composition when the labeling is disturbed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on provisional patent application Ser. No. 60/127,639, filed Apr. 2, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to adhesives generally, and more specifically to an adhesive composition containing small particles of prismatic or holographic film and the method of manufacturing that adhesive for the purpose of creating new and unique adhesive products used in decorative and tamper-indicating applications. 
     BACKGROUND OF THE INVENTION 
     Self-adhering labels have become very popular for use in the decoration, general-purpose marking and identification of manufactured objects. Also referred to as “stickers” or “decals”, the use of these labels continues to grow with more demand being placed upon the design and manufacture of the label material to provide increasingly unique and complex structures. As a result, labels are now printed with one or more types of eye-catching graphics in order to capture consumer attention and create a unique product image. 
     Holographic or prismatic materials are extensively used as label stock to attract attention with dazzling reflections of refracted light bouncing off the embossed patterns in the material surface. One industry in which these labels are heavily used is the beverage industry wherein the labels may be placed over the exterior of glass or polyester (PET) bottles. Furthermore, the cosmetic food and pharmaceutical industries also place a high value on eye-catching and attractive labeling of their goods. 
     The visual complexity of these materials has also been exploited to create labels and other marking media that provide evidence of counterfeiting or tampering with the objects on which labels are placed. The tamper-evident nature of prismatic or holographic media rising from the inherent difficulty in copying them also favors their inclusion in these types of labeling materials. 
     However, one problem with the typical prismatic materials used to form the above-mentioned labels is that the materials tend to be opaque since they are metallic in appearance. The opaqueness of the material detracts from the ability of a consumer to see the contents of the object through the label when placed on the object. Therefore, it is desirable to use a prismatic material to decorate an object that retains some clarity so that one may see through the label and into the contents of the object. 
     Furthermore, a second problem with prior art material labels arises with respect to the way that the labels are made. Prior art prismatic labels are normally formed entirely of a prismatic film or may include only a section of prismatic material placed on the label by way of stamping a predetermined area of the label with a prismatic or holographic foil. The prismatic materials used to form these labels tend to be expensive due to the multiple-step processes used in producing the embossed and metallized film that will eventually be converted into individual labels. 
     Therefore, it is desirable to develop an alternative label construction or adhesive composition for use in creating labels for various objects that incorporates some prismatic features to provide a striking, distinctive appearance to the object at a reduced cost, which is also substantially transparent or clear to enable a consumer to view the contents of the object through the label. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an adhesive composition and a laminate construction employing the composition that includes an amount of platelets or particles of prismatic or holographic material to give the composition a prismatic appearance. 
     It is further object of the present invention to provide an adhesive composition in which the platelets or particles have a configuration that enables the platelets to position themselves parallel to a surface on which the composition is applied in order to maximize the prismatic effect of the platelets while allowing the composition to remain substantially clear. 
     It is still a further object of the invention to provide an adhesive composition capable having a highly prismatic or holographic appearance that is inexpensive to manufacture and use in forming various types of laminate compositions, such as labels. 
     The present invention is an adhesive formulation including a clear, optically transparent adhesive layer that contains a number of thin, generally opaque prismatic or holographic particles or platelets randomly, but evenly, dispersed throughout the adhesive layer. The platelets serve to refract light striking them to give the adhesive a colorful, distinctive and consistent appearance. The adhesive layer containing the platelets is extruded in a thin and continuous layer that is laminated onto a clear film. The adhesive layer is preferably a pressure sensitive adhesive to facilitate the instantaneous bonding of the laminate to the surface of an object. The laminated construction formed by the adhesive and the film is preferably cut into individual sections to form labels that may be applied to a surface by pressing the adhesive portion of the laminate against the surface. The individual laminate sections provide a decorative effect to the objects on which they are applied whereby the platelets reflect light back towards an observer in a prismatic dispersion of color. Furthermore, should a laminate including the adhesive composition be tampered with after being placed on an object, the prismatic platelets will shift and form voids or bubbles in the configuration of the platelets in the composition, providing evidence of a counterfeit object or of tampering with the laminate. 
     The present invention may take various forms and can be made by employing different techniques to achieve similar end products. A preferred embodiment is hereinafter described to enable one of ordinary skill in the art to understand and reproduce the same. Furthermore, it may be apparent to one of ordinary skill in the art that certain improvements may be made to the present invention and its application that are not specifically stated herein. Therefore, the preferred embodiment described herein is only intended to be illustrative of the present invention and should not be construed to limit the scope of the invention as claimed. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a cross-sectional, exploded view of a laminate construction including the adhesive composition of the present invention; 
     FIG. 2 is a cross-sectional, isometric view of the laminate construction of FIG. 1 showing the arrangement of the releasable substrate, the adhesive composition and the platelets in the composition; 
     FIG. 3 is a cross-sectional, isometric view of a laminate construction similar to FIG. 1 showing a platelet located adjacent or protruding through the surface of the adhesive composition; and 
     FIG. 4 is an isometric view of a platelet removed from the laminate construction and covered with adhesive layers above and below the platelet. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Wherein like reference numerals designate like parts throughout the disclosure, in one aspect of the invention, the present invention is an adhesive composition indicated by  12  in FIG. 2 for use in a variety of adhesive applications. In another aspect of the invention, the adhesive composition  12  is a portion of a decorative laminate construction  10  shown in FIG. 1 that can be cut into individual labels which may have printed images or other indicia present on the labels. The laminate construction  10 , best shown in FIG. 1, is comprised of a generally clear film  14  that has the substantially transparent adhesive composition  12  on one side of the film  14 . The adhesive composition  12  bonds the film  14  to the surface on which the film  14  is placed. The adhesive composition  12  also contains a number of prismatic platelets  18  that provide the striking decorative appearance to the laminate construction  10 . A releasable substrate  16  is placed over the adhesive composition  12  opposite the film  14  to cover and protect the adhesive during transport. Substrate  16  prevents the adhesive composition  12  from bonding with any surface until the substrate  16  is removed and the adhesive is applied to the surface of an object (not shown) that is to be decorated or labeled with the film  14 . 
     In the present invention, any polymeric medium can be used to form the adhesive composition  12  for the laminate construction  10  as long as the medium is able to bond to the surface of an object and is also substantially clear in its final form. 
     Examples of suitable types of adhesive mediums would include rubber-based mixtures, silicone polymers, acrylics, polyesters, and polyurethanes that are sufficiently tacky to function in the desired adhesive manner. These types of adhesives can be obtained from a number of adhesive manufacturers such as Rohm &amp; Haas, Solutia, National Starch &amp; Chemical and Ashland Chemical. For the purposes of the present invention, the preferred polymeric medium is a pressure sensitive adhesive selected from this group. Both solvent-borne and water-based pressure sensitive adhesives may be used, provided the adhesive chosen displays the properties desired in a general pressure sensitive adhesive. These properties include adequate adhesion to the surface of the object and adequate cohesion to maintain the bond between the surface and the adhesive for an extended period of time. Most preferably, the polymeric medium is a pressure sensitive water borne acrylic, known as an emulsion acrylic. These adhesives tend to be half water and half polymer suspended or emulsified into the water portion. This medium is also preferred for its ability to coat easily into a smooth and continuous layer before drying. Another desirable property of the adhesive is its propensity to bond strongly with the clear film  14  that will eventually form the laminate construction  10 . 
     To form the adhesive coating, the platelets  18  are mixed with the adhesive while the adhesive is in a liquid state. The ratio of the amount of the adhesive to the amount of the platelets added to the adhesive may range from 100 parts adhesive to 0.25 parts platelets, up to 100 parts adhesive to 10 parts platelets. More preferably, the ratio is between 100 parts adhesive to 0.5 parts platelets and 100 parts adhesive to 2 parts platelets. Using a larger amount of platelets, i.e., above 2.0 parts platelets per 100 parts adhesive, increases the probability that the platelets  18  will stack upon each other in the composition  12  when the adhesive composition  12  is extruded to form the laminate construction  10 . Any such stacking of the platelets  18  will result in an uneven or bumpy surface for the finished adhesive composition  12  that will appear somewhat opaque and lessen the aesthetically pleasing appearance of the laminate construction  10 . Stacking also results in an inefficient use of the platelets  18  because each platelet  18  in the adhesive composition  12  is not able to add to the overall refractive effect of the adhesive composition  12 . This occurs because the platelets  18  are in close proximity with each other, interfering with the refraction from other platelets  18  and giving the appearance of a continuous prismatic film to the construction  10 . Therefore, to optimize the aesthetically pleasing qualities of the finished construction  10 , small amounts of the platelets  18  are added at specific intervals when forming the adhesive composition  12  to allow the previously added platelets to disperse in the adhesive  12 . This process gives an appearance of consistent spacing to the platelets  18  in the composition  12  while leaving the majority of the adhesive composition  12  to remain transparent. To best accomplish this, a ratio of 100 parts adhesive to 1 part platelets is most preferred. 
     The platelets  18  used in the present invention are obtained from Spectratek Technologies, Inc. of Los Angeles, Calif. The trade name of the platelet particles is Geometric Pigments. These platelets are made from embossed, aluminized polyester film that has been communed into very small pieces. The platelets come in a range of colors, sizes, and thicknesses. For the purposes of the present invention, a preferred platelet size has each side measuring approximately 100 microns and a thickness of about 9 microns. An alternate preferred platelet size measures about 200 microns on each side and has a thickness of about 12 microns. The preferred platelet has a silver appearance, but has been embossed with a diffraction grating that splits incoming white light into the colors of the visible spectrum. Platelets having a different base color, such as gold, copper or pewter, may also be utilized to generate a shift in the overall color of the defracted and reflected light. Pre-tinted particles are also available that can restrain the spectral change to a very narrow range of colors such as blue to blue-green, green to greenish-yellow, red to orange, etc. Furthermore, the size and thickness of the platelet may vary further with the thickness of the adhesive composition  12  on the film. Adjusting the platelet size in accordance with the thickness of adhesive composition  12  will allow the platelets  18  to be completely contained within the adhesive composition  12 . This will prevent the platelets  18  from creating any texture on the exterior surface of the adhesive composition, as the platelets  18  will not protrude from the exterior surface of the adhesive composition  12  when extruded onto the film  14 . 
     To mix the platelets  18  with the adhesive composition  12 , the adhesive is weighed to determine the total solids content and placed in a vessel sufficiently large to hold the amount of adhesive. The adhesive composition  12  is then stirred with a small mixing blade using just enough force to create a vortex in the adhesive. The platelets  18  are then added in generally equal portions at selected time intervals to allow the previously added portion to disperse throughout the adhesive. The number of portions added to the adhesive will depend on the amount of solids present in the adhesive and ratio of solids to platelets necessary to obtain the desired appearance for the laminate construction  10 . Mixing continues for thirty minutes after adding the last portion of the platelets  18 , and the adhesive composition  12  containing the platelets  18  is ready to be coated or extruded into a thin layer on a suitable substrate  16 . 
     The adhesive composition  12  containing the platelets  18  can be applied to the substrate  16  in any of a number of techniques that are known in the art. These techniques include a reverse gravure technique, a slot die, a reverse roll and a Meyer rod. The releasable substrate  16  is normally pre-coated with a releasing agent (not shown) on one side to allow the substrate  16  to be easily removed from the adhesive composition  12 . The substrate  16  may be formed of various types of materials, such as polyethylene, polyester papers, or a combination of the two and the releasing agent present on the substrate  16  can be selected from silicone, teflon, carbamate or polyethylene. 
     The substrate  16  comes as a continuous roll of material significantly longer than it is wide. The substrate  16  is placed on and unrolled through a coating machine (not shown) and the adhesive composition  12  is applied to it in a continuous, smooth and uniform layer using one of the above-mentioned methods. In a representative embodiment, adhesive composition  12  is applied at the rate of 12 to 18 pounds of adhesive composition per 3,000 square feet of substrate  16 . The coated substrate  16  then passes into a drying tunnel typically filled with blown, heated air in order to remove the carrier fluid from the adhesive composition  12  in a short period of time. As the carrier fluid is removed, the adhesive solids coalesce into a dried polymer layer. The platelets  18  are retained in the layer of adhesive composition  12  during this drying period and become aligned parallel with the substrate  16 , as shown in FIG.  2 . 
     When extruded onto the substrate, the prismatic platelets  18  will level themselves in the major plane of the adhesive composition  12  generally parallel to the substrate  16 . This action of leveling is created by the planar form of platelets  18  and the hydrodynamic resistance forced upon each platelet  18  at the moment of passing through a gap or metering opening in the extrusion process. The platelets  18  align themselves in the direction of the fluid to present the lowest amount of resistance. The small particle size of platelets  18  allow platelets  18  to pass through orifices or metering gaps commonly used in extrusion processes. The self-leveling of these particles during extrusion results in the platelets  18  being laid flat in the major plane of the finished adhesive. The effect is beneficial for thin films of adhesive since all of the platelets  18  present a reflective surface that is substantially perpendicular to most viewing angles. The unique ability of the prismatic platelets  18  to reflect light at many angles presents a constantly changing image as the line of sight for the viewer is changed. The overall effect is best described as a myriad of small, bright reflections, similar to the radiant sparkle of crystals, crushed glass or even the twinkle of starlight. As the viewer&#39;s line of sight moves across the coated and finished adhesive composition  12 , a color shift is apparent such as blue to green to yellow or red to orange to yellow. 
     The thickness of the adhesive composition  12  after drying is important in achieving a consistent and aesthetically pleasing material. The adhesive composition  12  is deposited so that its final dried thickness is greater than that of any individual platelet  18 . As shown in FIG. 3, if the adhesive composition  12  is too thin, a platelet  18  can protrude through the upper surface of the adhesive composition  12  when laminating the adhesive composition  12  to the substrate  16 . In this situation, an air bubble (not shown) is trapped around the platelet  18  and when the laminate construction  10  is made into a decorative label, this bubble is highly visible in the finished label, which is an unacceptable result. Therefore, because the minimal deposition of a typical adhesive composition  12  needed to embed the platelets  18  is 22-26 grams per square meter, which provides an average thickness of 20-22 microns, a coating weight or thickness equal or greater than these amounts is required to prevent platelets  18  from becoming embedded during the drying process and protruding through the upper surface of the adhesive composition  12 . 
     Upon exiting from the drying tunnel, the substrate  16  and adhesive composition  12  are then laminated to a clear film  14  such that the adhesive composition  12  contacts one side of the film  14 . Many clear polymeric films can be used including films formed of polyethylenes, polypropylenes, polyesters, polystyrenes and vinyls. The film is a preferably clear polymer film, such as Mobil Chemical 2.0 mil biaxially oriented propylene. However, the film may also be a slightly opaque polymer, such as Avery Dennison 2.5 matte/clear polyolefin sold by Avery Engineered Films Division. Furthermore, films that have been tinted in various colors may also be utilized, but the tinting on these films  14  will reduce the number of colors that are reflected back by the platelets  18  through the film  14 . The resulting laminate construction  10  is passed through compression rollers that complete the intimate bonding of the adhesive composition  12  to the film  14 . 
     After the film  14  is laminated over the adhesive composition  12  opposite the substrate  16 , the resulting laminate construction  10  is converted into individual labels by running the laminate construction  10  underneath a rotary die that cuts the laminate construction  10  into the desired shapes. After cutting the laminate construction  10  into the labels, the unused portion of the laminate construction  10  is removed, leaving behind the individual labels. The labels may be printed with logos, images, foils, or other information as desired, either before or after cutting. In this form, the labels may be applied to the surfaces of objects such as packaging containers, bottles, boxes, and the like, by removing the releasable substrate  16  from the laminate construction  10  and placing the adhesive composition  12  against the object to present a pleasing and eyecatching look for the object. 
     The phenomena of the platelets  18  lying flat in the major plane of the adhesive composition  12 , essentially suspended within the thin layer of adhesive composition  12 , can also be exploited for the purposes of creating an anti-counterfeit or tamper-indicating label. The laminate construction  10  of the present invention will become irreparably altered when it is removed from the surface of an object to which it is attached. This alteration occurs within the adhesive composition  12  during removal because some of the platelets  18  have a relatively thin layer  20  of adhesive composition  12  above them, as shown in FIG.  4 . When this arrangement occurs, the thin adhesive layer  20  above the platelet  18  will have a weaker bonding strength than the thicker layer  22  below the platelet  18 . During removal of the laminate construction  10  from the object, these platelets  18  will preferentially break away from the surrounding adhesive composition  12  and remain bonded to the object. These platelets  18  and adhesive composition  12  bonded to the object are difficult to remove from the surface of the object due to the strength of the bond between the adhesive composition  12  and the object, such that the evidence of removal of the laminate construction  10  is not readily concealed. 
     Furthermore, the laminate construction  10  will now have voids (not shown) in the adhesive composition  12  where the platelets  18  bonded to the object were previously located. If the removed laminate construction  10  were to be re-applied to another object, the voids would be obvious as flaws in the overall appearance of the laminate. These flaws manifest themselves as air bubbles or blisters that appear silvery-white and much larger than the platelets  18  themselves. 
     In another embodiment of the laminate construction  10  of the present invention, the adhesive composition  12  is extruded onto the releasable substrate  16  opposite the releasing agent and dried as previously discussed. The releasable substrate  16  including the dried adhesive composition  12  is then wound about a take-up roll. From this roll, the adhesive composition  12  and releasable substrate  16 , or overlaminate, can be unrolled as is known in the art for application to a web of printed material (not shown), such as pre-printed labels. In this arrangement, the overlaminate is applied to the web of pre-printed labels before the labels are die-cut to provide a protective layer over the graphics printed on the labels. 
     In still another embodiment of the present invention, the adhesive composition  12  may be extruded between a pair of releasable substrates to form a transfer adhesive (not shown). In this arrangement, the adhesive composition  12  contacts a side of each releasable substrate that has been coated with a releasing agent. The transfer adhesive may then be applied to a label that has printing on both sides of the label material by removing one of the substrates to allow the adhesive to be affixed to one surface of the label. The label may then be applied to a surface of a clear container, such as a glass bottle. Due to the generally transparent nature of the adhesive coating in the transfer adhesive, when the label is applied to the surface of a clear container, a person may view the printed material on the interior surface of the label through the container and through the adhesive coating between the label and container. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.