The present invention relates to a privacy film. In particular, the present invention relates to a polymeric based privacy film having a plurality of light directing elements each element being disposed substantially parallel to the next adjacent light directing element, the film being well suited for use with documents.
Products capable of providing privacy for the consumer have increased. For example, it is very common today for most personal computers and automatic teller machines to include a privacy screen allowing the user to view the image on the monitor while simultaneously limiting the view for bystanders, or at least those not in the viewing angle of the screen. Some have used light control films to provide privacy to a user who has documents containing sensitive material. The idea is similar in that the user can view the image on the document but bystanders are limited in viewing the document's content.
The art discloses various light control films that also serve the purpose of providing privacy to the user. However, as document privacy is becoming more and more of a desire for consumers, those skilled in the art seek different solutions to provide this desired feature. Thus, there is a continuing need for new privacy film constructions.
The present invention provides for a privacy film that can be used with documents to limit the angle at which a viewer can read the information on the document. In particular, when the privacy film is placed in the use orientation such that the viewing angle is coincident with the user's line of sight, the user will be able to see the contents of the documents while others will only have a limited view of the document's content.
In one aspect, the present invention pertains to a privacy film comprising a light transmissive, polymeric base sheet comprising (i) a first polymeric material, the base sheet having opposing first and second surfaces; and (ii) a plurality of light directing elements comprising a second polymeric material, wherein each element has a base, a height h, and a minor axis disposed along the height, wherein the elements protrude from the first surface of the base sheet, and wherein each element is disposed such that the minor axis of one element is substantially parallel to the minor axis of the next adjacent element and the base of one element is not joined with the base of the next adjacent element. In another aspect, the privacy film comprises elongated light directing elements.
In another aspect, the present invention pertains to a method of making a privacy film comprising the steps of (i) providing a polymeric material; (ii) depositing the polymeric material onto a microstructured mold comprising a plurality of substantially parallel, elongated channels, wherein each channel is slanted and is separated from the next channel by a land region, wherein each channel has a base disposed adjacent to and a tip distal from the land region, wherein each channel has a minor axis that runs from the base to the tip; (iii) inducing the polymeric material to flow into the channels of the microstructured mold; (iv) solidifying the polymeric material inside the channels to yield a plurality of light directing elements that are connected with one another via a polymeric base sheet having a first surface from which the light directing elements protrude and an opposing second substantially planar surface; and (iv) separating the privacy film from the microstructured mold.
As used herein, the term “light transmissive” means the ability to transmit visible light. In one embodiment, the light transmissive base sheet has an opacity of 90 or less, as measured using a Lab Scan 6000 Tester with a HuterLab Master Color Data Program, commercially available from Hunter Associates Laboratory, Inc., Reston, Va. With reference to the light directing element, the term “elongated” generally means that the element has a rail-like appearance. The rails can be continuous along the entire length of the privacy film or they can be discontinuous. In one embodiment, the discontinuous light directing elements are discrete bodies having an appearance of a stem, such as, e.g., a stem of a mushroom.
One advantage of the present invention is that it provides the privacy feature with flexible construction that is relatively easy to manufacture. The privacy film can be quickly attached to the document in a non-permanent manner. Furthermore, the privacy film is durable so that it can be used repeatedly.
In this document, the term “about” is presumed to modify all numerical values.
The invention can be better understood with reference to the following drawings, wherein:
a to 8c are schematic views of an exemplary process that can be used to make the privacy film.
These drawings are not drawn to scale and are intended only for illustrative purposes.
In use the privacy film of the present invention is disposed on the document so that the major axis L lies substantially parallel to the image or lines of text on the document. For example, on 8½ by 11 inch paper in portrait orientation where the text lies substantially parallel to the 8½ inch side of the paper, the privacy film would be oriented so that the major axis also lies along the same direction. The privacy film can be disposed on the document temporarily, meaning that the film can be removed from the substrate without damage thereto, or permanently, meaning that removal of the privacy film will most likely cause damage to the document. There exists a variety of means for attaching or disposing the privacy film to the document. For example, an adhesive can be used. The adhesive can be pressure sensitive or hot melt. The adhesive can be a repositionable adhesive, meaning that it can be applied and removed from the substrate multiple times without damage to the substrate and without significant loss in adhesion of the repositionable adhesive. In another application, the privacy film is formed as a pocket, where the privacy film forms a front, a polymeric backing or the privacy film forms a back, and the privacy film and the back are attached on three sides, leaving the fourth, typically top side, open for insertion and removal of a document. Other configurations can be used.
The light directing elements interfere with light transmission thereby providing the privacy feature of the present inventive film. Optically active materials, such as light reflecting and or light absorbing materials, may be included. The light directing elements geometry, spacing, and the optically active materials are discussed below in detail.
In one exemplary embodiment, the heights of the light directing elements are substantially the same on the privacy film. There may be some variation in the elements' heights due to the manufacturing conditions. In another exemplary embodiment, the heights of the elements vary from one region of the privacy film to another region and even from one element to the next adjacent element. By variation in height, it is generally meant that one element will be from 75% to 95% in height of another element.
In one exemplary embodiment the h to P ratio (h:P) is greater than 0.5. In another embodiment, the h:P ratio is less than 5. In one embodiment, the width of the light directing element, as measured proximate to the first surface of the base sheet is greater than 25 microns. In another embodiment, the width is less than 750 microns. In the embodiment of
Suitable light reflecting materials include, e.g., titanium dioxide, zinc oxide, zinc sulfide, zinc phosphate, calcium carbonate, alumina, silica, antimony oxide, barium sulfate, lithopene (a co-precipitate of barium sulfate and zinc oxide), calcined kaolin, lead carbonate, magnesium oxide, and combinations thereof. Suitable light absorbing materials include, e.g., carbon black, spinel black, rutile black, iron black, and combinations thereof. When a light reflecting material is used, 1 to 50 parts by weight, based on 100 parts by weight total, is added to the polymer resin to form the light directing elements. In some embodiments, 1 to 15 parts by weight is used. In other embodiments, 2 to 10 parts by weight is used. When a light absorbing material is used, 0.1 to 50 parts by weight, based on 100 parts by weight total, is added to the polymer resin to form the light directing elements. In some embodiments 1 to 15 parts by weight of light absorbing material is used. In other embodiments, 1 to 5 parts by weight is used. A combination of light reflecting material and light absorbing material can be used to form an individual light directing element, as further discussed below. In other embodiments, color pigments, fluorescent colors, and glitter can be added to the light directing elements.
While the base sheet in all of the embodiments is light transmissive, it may include light reflecting materials. The quantity of light reflecting materials used in the base sheet can, but does not have to, be similar to that used in the light directing elements. The advantage of using similar amounts is that the process of making the privacy film, as further described below, can be simplified to using a single extruder instead of multiple extruders. In the case where substantially the same amount is used, care should be taken to select a sufficient amount to impart the privacy feature to the film without adversely affecting the readability of the underlying document.
Suitable materials for use in forming the privacy film include thermoplastic polymers and elastomers. Suitable thermoplastic polymers include, e.g., polyolefins such as polypropylene or polyethylene, polystyrene, polycarbonate, polymethyl methacrylate, ethylene vinyl acetate copolymers, acrylate-modified ethylene vinyl acetate polymers, ethylene acrylic acid copolymers, nylon, polyvinylchloride, and engineering polymers such as polyketones or polymethylpentanes. Suitable elastomers include, e.g., natural or synthetic rubber, styrene block copolymers containing isoprene, butadiene, or ethylene (butylene) blocks, metallocene-catalyzed polyolefins, polyurethane, and polydiorganosiloxanes. Mixtures of thermoplastic polymers and elastomers may also be used.
The inventive light directing element can be made in various ways. In a first exemplary method, the privacy film of the present invention can be formed by extruding a polymeric web through a die having an opening cut, for example, by electron discharge machining. The web would include the base sheet and the light directing elements disposed thereon.
The shape of the die opening is designed to generate a web with a desired cross-sectional shape or profile. The web can be quenched after leaving the die opening by pulling it through a quenching material such as water. A wetting agent may be added to the quenching medium to wet the entire surface of the extruded web, including spaces between the light directing elements. The extruded web may be further processed, e.g., by applying a light absorbing coating to the tips of the elements (as shown in
When the inventive privacy film contains multiple different layers, as when the base sheet and the light directing elements are of different materials or as when the light directing elements contain multiple sections (see, e.g.,
A second exemplary method of making the privacy film is shown schematically in
Two adjacent channels are placed such that, as viewed from an imaginary line normal to the land region, the tip of one channel coincides with the base of the next channel. This feature is similar to that shown in
b shows a subsequent step in the process where the polymeric material has flowed into and filled the channels thereby replicating the shape of the channels. The replicated polymeric material solidifies in the mold. The term “solidifies” means generally that the polymeric material cools and hardens sufficiently to allow it to be separated from the mold. In one process, the polymeric material includes light reflecting material, such as the ones listed above. When used, the light reflecting material constitutes less than 20%, and in some embodiments, less than 5% of the total weight of the polymeric material.
c shows yet another step in the process where the replicated polymeric material has been separated from the mold to yield privacy film 810 having a plurality of distinct light directing elements 818, each connected to another by a polymeric base sheet 812 having first surface 812a from which the light directing elements protrude and opposing second substantially planar surface 812b. The separation step results in substantially no distortion on the light directing elements of the privacy film. That is, when the replicated polymeric material is separated from the mold, each light directing elements of the resulting privacy film is nearly an exact replica of its corresponding channel, so that there would be less than 20% and preferably less than 10% variation in the dimensions of the light directing element as compared to the dimensions of the corresponding channel.
The polymeric material can be in the form of a thermoplastic material, such as a thermoplastic film, a molten resin, or a liquid resin. When in the thermoplastic film form, a combination of heat and pressure can be used to induce the polymeric material to flow into the channels. Such a method can be generally described as compression molding and are discussed in publications such as U.S. Pat. No. 4,244,683 (Rowland) and U.S. Pat. No. 4,601,861 (Pricone et al.). In the molten resin state, the heat of the molten resin, along with heating the mold are useful steps in inducing it to flow into the channels. U.S. Pat. No. 4,097,634 (Bergh) discloses an exemplary extrusion cast and embossing method. In a liquid resin state, heat and or pressure can be used to induce the polymeric material to flow into the channels. Useful liquid resins are light curable resins, such as an ultraviolet light curable resin. In such a case, the solidifying step will involve exposing the light curable resin to a light source. U.S. Pat. No. 3,869,346 (Rowland); U.S. Pat. No. 4,576,850 (Martens); and U.S. Pat. No. 5,183,597 (Lu et al.) disclose exemplary liquid cast and light curing processes. These patents are incorporated by reference in their entirety.
The polymeric material may include at least two layers, i.e., it may be of a multilayer construction. In one embodiment, the polymeric material includes a first layer that is substantially free of light absorbing and light reflecting materials and a second layer that comprises light absorbing materials, light reflecting materials, or a combination thereof. In such cases, the channels of the microstructured mold contacts the layer containing the light absorbing and/or light reflecting materials.
A privacy film, made generally according to
A polypropylene film containing 2% by weight of TiO2 pigment was used as the thermoplastic polymeric film. The polypropylene film was 5 mil (0.13 mm) thick. The film was induced to flow into the channels using a heat press set at 170° C. under a pressure of 160 pounds per square inch (psi) for 30 seconds. The compression molded film was cooled to 100° C. under the same pressure, after which time it was separated from the mold to yield a privacy film having a plurality of light directing elements connected to one another by a base substrate. A small amount of black ink was applied to the top of the light directing elements.
The present application is a continuation-in-part of U.S. patent application Ser. No. 11/250,676 filed on Oct. 14, 2005, which is incorporated by reference in its entirety.
Number | Date | Country | |
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Parent | 11250676 | Oct 2005 | US |
Child | 11580382 | Oct 2006 | US |