Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2000-09-08
2002-04-16
Schwartz, Jordon (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C427S146000, C427S148000, C428S172000
Reexamination Certificate
active
06373636
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical devices wherein the image seen by a viewer depends on the viewer's angle of regard with respect to the plane of the windowpane-shaped device. More particularly, the invention relates to an extraordinarily thin lenticular sheet with periodic optical elements formed in such a way that the viewer will perceive a series of images that change depending on the viewer's angle of regard. The invention presents an improved manufacturing technique for such sheets that overcome the unsatisfactory results achieved in dimensional tolerance and stability with current methods applied to fine dimensions.
DESCRIPTION OF RELATED ART
The concern of this patent is very thin lenticular sheets wherein the finished product is of comparable overall thickness to 10 to 24-lb bond paper. Thus, the product can be used for magazine blow-ins or pages in magazines that use perfect bindings. It can be used in many other special applications that have heretofore been unattainable due the relatively stiff nature of the lenticular product. For example, a sufficiently thin lenticular film can be used to decorate a tee-shirt, or be incorporated any imaginable place where paper-thin products might be used.
A lens array is fabricated by first designing a cutting tool with the desired lens shape, then using this tool to cut the negative of the shape of the array of lenses into a cylindrical roll. A lenticular plastic sheet is usually produced by the extrusion of a single layer from a thermoplastic resin melt into a continuous web. The extrusion equipment consists of a die, followed by a roll stack whereby the lens pattern on the cylinder is pressed into the viscous resin using an embossing roll with counter pressure being provided by a nip roll. In manufacturing plants today, the lens array is almost always produced by molding the appropriate shape into the surface. Cross-linking of the thermoplastic is enabled thermally in the extrusion process. Cooling the thermoplastic lenticular resin sets the relief pattern on the surface. In some cases, actinic radiation, usually in the form of ultraviolet light of appropriate wavelength and radiance is used to cross link said resin and thereby set the relief pattern.
To get said thermoplastic web in condition to be divided into sheets or readied for shipment on a take-spool, pull-rolls are used to draw the substantially cooled and set material. These rolls unavoidably introduce longitudinal tension into the web. Longitudinal tension is tension in the machine direction. This tensioning sometimes causes significant stretching and necking of a thin web causing the lenticular surface to distort. The distortion is not uniform. The lens pattern departs from design increasingly from the center of the web outward. The distortion is only approximately predictable. The tension can vary. Dimensions can shift when the web is divided into sheets. Temperature variability induces distortion variability. Some newly formed thermoplastics are hygroscopic and ambient humidity induces distortion variability. Attempts at introducing windage based on distortion data from a specific extrusion plant and material ameliorate the distortion somewhat. However, this solution is increasingly inadequate for increasingly thin end material. For the objectives of this patent, these effects are paramount. For thin sheets (0.012-inches to 0.002-inches thick), the aforementioned dimensional stability problems can result in an unacceptable product. The required linear registration can be problematic or impossible.
It is important to put the lenticular sheet in context of the end product. A computer-generated image is printed on the planar side of the product. The printing can be direct or a print can be prepared in a separate operation and laminated to the lenticular sheet. Either way, the print is registered and precisely aligned to the front-side lenticular array that consists of a set of parallel, longitudinal, cylindrical elements that are substantially circular in cross section. If the lenses run up and down, three-dimensional images, that is, multiple images at apparently different distances from the eyes in space, can be designed. These images are not continuous like holograms, but are convincing. For example, one image may occlude another on a “deeper” plane. The viewer can shift their angle of regard right or left and the previously occluded image will appear. If the lenses are horizontal, other interesting optical effects called flip, morph, motion, zoom and others are possible. Typically, a repertoire of two to eight images is dissected and affixed in a precisely aligned and registered fashion to said lenticular array.
If extremely thin products were not a concern, the image may be affixed in a number of ways. A registration mark is molded into the lenticular array. Since the array consists of linear parallel lenses, only one alignment mark is needed, the array itself provides the angular reference from that mark. The image can be printed on paper by almost any high-resolution printing technique. The paper can be aligned to the previously mentioned mark and laminated to lenticular away. Since our final product thickness is comparable to a sheet of paper, this technique is not available. The precision of the printing is critical. The array thickness is related to the lens spacing. A rule-of-thumb is that the overall thickness must be the lens spacing, D, times n/2n(n−1) where n is the index of refraction of the material. Since the instant invention seek sicknesses on the order of 0.002-inches, the lens spacing is unavoidably on the order of 0.005-inches. The printer image technology must be at least five times more accurate than the lens spacing, on the order of 1000 lines per inch or more. The alignment must be on the order of 0.0005-inches and the orthogonality within a small fraction of a degree. Several suitable technologies are based on photolithographic printing and thermal or piezoelectric ink jet printing which are conventional except for the alignment means. With advances in photolithographic techniques driven by the semiconductor industry's pursuit of Moore's law, it is and likely will continue to be the highest resolution printing technique. The actual implementation of photolithographic printing may involve precision printing on a transfer roll and transfer printing on the end product. Despite assertions to the contrary, intaglio printing such as gravure printing wherein Cyan, Yellow, Magenta and Black inks are placed in a series of steps and thus require four precision alignments and registrations are generally applicable to lower resolution and therefore thicker embodiments of lenticular products. Due to the resolution of the eye, there is little discernable difference between 600 and 1200 pixels per inch when viewed at 15 to 18-inches. However, each repertoire image must exist at each lens crossing. To achieve eight images at an effective resolution of 600 pixels per inch requires 4800 sub pixels per inch, since the lens selects only an eighth of the underlying print at any specific angle of regard. The print resolution is therefore determined by the thickness objectives.
We are aware of the following related art:
U.S.
Pat. No.
Year
Inventor
Name
4,420,502
1983
Conley
Apparatus and Method for Producing a
Flexible Sheet Material having a
Predetermined Surface Characteristic
4,420,527
1983
Conley
Thermoset Relief Patterned Sheet
4,414,316
1983
Conley
Composite Lenticular Screen Sheet
5,362,351
1994
Karszes
Method of Making Lenticular Plastics and
Products therefrom
4,042,569
1977
Bell et
Heat-setting process for polyester film
al.
The teachings of U.S. Pat. No. 4,420,502 ('502) differ from the currently used manufacturing technique in that a base film that is intended to be dimensionally invariant covers the nip roll while a lenticular resin is extruded between the molding roll and the nip roll. In a first embodiment, the base film is incorporated into the product, thus would either receive print
Dougherty & Clements LLP
Schwartz Jordon
Thompson Tim
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