KR100215144B1 - Polymeric sheet having oriented multilayer interference thin flakes therein - Google Patents

Abstract

The present invention relates to a polymeric sheet consisting of a polymer material having first and second parallel planes (12) and (13) and a plurality of multi-layer interfering thin film flakes disposed in a first layer of polymer material, wherein the flakes comprise Said flakes having one and two parallel planes (17) and (18) and width and thickness, having an aspect ratio of at least 2: 1 with respect to the width to thickness, and parallel to the first and second parallel planes of the first layer of polymeric material The flakes are oriented such that the flakes are in a plane having the first and second parallel planes of.

Description

Polymeric sheet comprising oriented multilayer interference thin flakes

U. S. Patent No. 5,135, 812 describes various types of optically variable multilayer coherent thin film flakes and describes how to incorporate such flakes into inks and paints. Efforts are needed to broaden the application of such flakes, for example, by encapsulating the flakes in plastics, in particular in extruded, coextruded and cast plastics.

The present invention relates to a polymer sheet multilayer interference thin film comprising flakes oriented therein, a product using the same, and a method of making the same.

1 is a partial cross-sectional view of a polymer sheet of the present invention comprising oriented multilayer interference thin film flakes.

2 is a cross-sectional view of the coextruded polymer sheet of the present invention bonded by a plastic substrate.

3 is a cross-sectional view of the coextruded polymer sheet of the present invention with flakes on several layers on both sides of a plastic substrate.

4 is a cross-sectional view of the polymer sheet of the present invention having a substrate comprising the flake of the present invention and each planar plastic layer that may be transparent or colored.

FIG. 5 is a cross-sectional view of a polymer sheet having a thick, transparent polymer base on a thin polymeric material containing optically variable flakes and other materials such as dyes, pigments, aluminum flakes, etc., with a transparent overlacquer.

6 is a cross-sectional view of a banknote having an embedded thin line made from the polymer sheet of the present invention that may appear on one side of the banknote.

7 is a cross-sectional view taken along the line 6-6 of FIG.

FIG. 8 is similar to FIG. 6 but illustrates a method in which a thin line is pushed into the banknote so that it appears on both sides of the banknote.

9 is a partial cross-sectional view of a safety document embodying the polymer sheet of the present invention.

It is generally an object of the present invention to provide a plastic sheet that is extruded or cast and comprises an oriented multilayer interference thin film flake, a product using the same, and a method of making the same.

Another object of the present invention is to provide a plastic sheet of the above characteristics that can be extruded or cast.

Another object of the present invention is to provide a plastic sheet of the above characteristics in which the flakes are biaxially oriented.

Another object of the present invention is to provide a plastic sheet of the above characteristics wherein the flakes are optically variable.

Another object of the present invention is to provide a plastic sheet of the above characteristics which can be produced in a conventional co-extruder line.

Another object of the present invention is to provide a plastic sheet of the above characteristics which can be coated on a plastic web that functions as a substrate web with a weak bond between the plastic sheet and the plastic web.

A further object of the present invention is to provide a plastic sheet of the above characteristics having a plastic substrate which may be white or any other color.

It is a further object of the present invention to provide a plastic sheet of the above characteristics in which the flakes can be provided in one or more layers.

Another object of the present invention is to provide a plastic sheet of the above characteristics in which flakes of different layers can have different colors.

It is a further object of the present invention to provide a plastic sheet of the above characteristics in which the flakes can be optically varied with different color shifts for each layer.

It is a further object of the present invention to provide a plastic sheet of the above characteristics in which colorants can additionally be added to the optically variable flakes in order to change the color provided or to change the optical change.

Another object of the present invention is to provide a plastic sheet of the above characteristics which can be easily incorporated into other products.

Another object of the present invention is to provide a plastic sheet of the above characteristics which can be broken into narrow strips or incorporated as a thread and used in security papers such as banknotes.

It is a further object of the present invention to provide a plastic sheet of the above characteristics which can achieve a desired optical effect and at the same time provide a relatively small amount of flakes.

Another object of the present invention is to provide a plastic sheet having the above characteristics with a smooth outer surface.

Another object of the present invention is to provide a method for producing a plastic sheet of the above characteristics wherein mechanical flow is used to induce laminar flow orientation of pigment flakes in a film optical article.

Another object of the present invention is to provide a method of the above characteristics for stabilizing color characteristics of flakes in a plastic sheet.

Other objects and features of the present invention will become apparent from the preferred embodiments described in detail in the following description and the accompanying drawings.

In general, the polymer sheet of the present invention consists of a layer of polymeric material having first and second parallel planes. Multiple multilayer interfering thin film flakes are disposed within a layer of polymeric material. The flakes have first and second parallel planes spaced at regular intervals and have an aspect ratio of 2: 1 for width to thickness. The flakes are in a plane whose first and second faces are substantially parallel to the first and second faces of the layer of polymeric material.

More specifically, as shown in FIG. 1 of the figure, the plastic or polymer sheet 11 has upper and lower parallel planes 12 and 13 spaced apart at regular intervals. The polymer sheet 11 can be produced by casting or extrusion. Also, as described below, it can be produced by co-extrusion of the film, where the sheet 11 forms a layer in the co-extruded film.

The thickness of the film forming the sheet 11 is generally approximately 1 micron such that the thickness of the sheet 11 is approximately twice the thickness of the flake, i.e. the thickness of the sheet is 2 microns when the flake thickness is 1 micron. The thickness of the multilayer interference thin film having a thickness of not less than twice.

In the present invention, for example, an aqueous polymer, polyvinyl alcohol, polyvinyl acetate polyvinylpyrrolidone, poly (ethoxyethylene), poly (methoxyethylene), poly (acrylic) acid, poly (acrylamide) , Poly (oxyethylene), poly (maleic anhydride), hydroxyethyl cellulose, cellulose acetate and poly (saccharides) such as gum arabic and such polymer systems may include the polymers described in the aqueous examples above. Also, poly (acetal) such as polyvinylbutyral, poly (vinyl halide) such as polyvinyl chloride and polyvinylene chloride, poly (diene) such as polybutadiene, poly (alkene) such as polyethylene, polymethyl acrylic Poly (acrylate) such as rate, poly (methacrylate) such as polymethylmethacrylate, polyoxycarbonyl oxy hexamethylene such as Poly (ester), poly (ester), poly (siloxane), poly (supide), poly (sulfone), poly (vinylnitrile), poly (acrylic) such as li (carbonate), polyethylene terephthalate Ronitrile), poly (styrene), poly (phenylene) such as poly (2,5 dihydroxy-1,4-phenyleneethylene), poly (amide), natural rubber, formaldehyde resins and the following references Other polymers that may be used (see: Polyner Handbook (Second Edition), J. Brandrup, EHEmmerton {ut, eds., John Wiley and Sons, NY, 1975 (pages IV-242)).

A plurality of multilayer interfering thin film flakes or platelets 16 are disposed on the sheet 11 between the top and base surfaces 12 and 13. The flakes 16 have upper and lower parallel surfaces 17 and 18 and have a thickness measured in a direction perpendicular to the surfaces 17 and 18 such that they have an aspect ratio of 2: 1 or more relative to the width to the thickness of the flakes and It has the highest area or area along surfaces 17 and 18. The flakes may be single color or may vary optically. Flakes can be prepared according to the methods set forth in patent 5,135,812. Optically variable pigments may be prepared by any dielectric thin film layer or metal dielectric layer as described in patent 5,135,812.

Metal dielectric to make optically variable flakes. The multilayer interference thin film coating may be in the form of an opaque metal layer having first and second sides, wherein the thin absorber layer and the low refractive index dielectric layer of each of the first and second sides are nearly consistent in the n / k ratio (n is the refractive index). K is an absorption constant). The low index material may be magnesium fluoride and the absorber layer may be chromium. The thick, substantially opaque metal layer can be made of aluminum.

Pigment flakes 16 produced by introduction into the polymer sheet may be introduced into the dry polymer and mixed just before being fed to the extruder hopper feed system. The amount of pigment flakes that may be added in a preferred ratio may be at least 30% and less than 0.1% by weight relative to the polymer. Pigment flakes are mixed inside and the polymer is heated to melt completely. The molten polymer with pigment flakes is passed through a dye, extruded onto a cold casting drum, and quickly quenched into an amorphous film. Typically, the molten polymer is cooled to 120 ° C. or less from a melting temperature of about 275 ° C. in 20 seconds.

Subsequently, forward drawing is performed for uniaxial orientation of the polymer by heating the film to a drawing temperature above 90 ° C. and stretching between two sets of nip rollers, in which the second set is operated faster than the first set. The film is stretched in one direction to align in the drawing direction, which in turn aligns the molecular chains in the film in the uniaxial orientation of the film. The film is then uniaxially oriented and passed through the side draw, resulting in a vertical or biaxial orientation of the uniaxial orientation. Side drawers are conventional stentors (not shown) which preheat the film to 80-90 ° C. and draw it at a temperature of 100-120 ° C. by pressing the edges of the film, as if drawing in the forward direction on the stenter. Is not performed). After the side draw is completed, the biaxially oriented film is passed through a conventional crystallization oven (not shown) having a temperature of 200 to 230 ° C., thereby primarily with molecular chains in which the film is packed in a regular arrangement. In order to achieve larger crystals, an increase in density is caused, and secondly, the amorphous regions are loosened, acting as pressure-relieving regions, and thirdly, the crystal regions are disoriented from the plane of the film. This change increases film intrinsic properties. Relaxation and crystallization of these chains provide a numerically very stable film.

In the present invention, it has been found that the biaxial orientation of the film has additional advantages in the orientation of the pigment flakes 16 in the film. When the film is drawn in the forward direction, the pigment flakes having the first and second faces 17 and 18 disposed perpendicularly to the draw direction are overturned so that the first and second faces 17 and 18 become It is in a plane parallel to the first and second faces. Similarly, when the film is drawn sideways, the pigment flakes 16 having a surface present perpendicular to the side draw direction are overturned so that the first and second faces 17 and 18 are the first of the film 11. And in a plane parallel to the two faces.

The result of this biaxial orientation of the film 11 is shown in FIG. 1, and as shown in the cross section of the film 11 in FIG. 1, the pigment flakes 16 are applied to the surfaces 12 and 13 of the film. Exist in parallel planes. Similarly, as also shown in FIG. 1, in the longitudinal cross section of the film, the flakes 16 are in a plane parallel to the surfaces 12 and 13 of the film.

This mechanical change during the biaxial orientation of the film results in proper alignment of the pigment flakes of the film previously described herein, which causes the flakes to be placed below the surface of the film and the smooth first and second faces 12 and 13 of It has been found to be critical to providing a film. In addition, this mechanical change during biaxial orientation is desirable, because the molten polymer is still viscous and the flakes are difficult to settle into the viscous mass during molding of the film without the use of the mechanical stretching already described herein. It has also been found that the thinner the resulting film, the greater the tendency for all or substantially all of the flakes 16 to be properly oriented. By way of example, the thickness of the film 11 may be 2 to 5 microns and the thickness of the pigment flakes may be 1 to 2 microns.

The film 11 can be cooled after passing through the crystallization oven and then cut to the desired width by trimming to a suitable size, for example 1 to 3 millimeters, and trimming the edges. The use of the film set forth in FIG. 1 will be described in further embodiments described herein.

If it is desired to provide additional support to the polymer sheet 11, the substrate or substrate layer 21 is provided to form the composite structure shown in FIG. 2. This substrate or substrate layer 21 has upper and lower planes 26 and 27 spaced apart at regular intervals. This substrate or first layer 21 may be made of a synthetic, film-forming polymeric material. Suitable polymeric materials include thermoplastic materials.

These substrate layers or the first layer 21 can be biaxially oriented in the same way that the film 11 causes biaxial stretching by stretching in the forward direction and then laterally.

In the present invention, the simultaneous biaxial orientation can be influenced by extruding the thermoplastic polymer tube and then quenched, reheated and then expanded by internal gas pressure to induce transverse orientation in one direction and axial in the opposite direction. It will be appreciated that this results in an orientation. This can be accomplished by subtracting the polymer tube in a ratio that induces longitudinal orientation at the right angle in the first direction of orientation caused by gas expansion.

Also in the present invention, the second layer 11 and the first layer 21 coextrude each film-forming layer through each hole of the multi-orifice die, and then are still molten. By combining the layers, or preferably, the melt streams of the respective polymers are first combined in a channel, leading to a die manifold, and then extruded together from the die orifice under streamline flow conditions without mixing to create a composite sheet. It should be understood that they can be formed substantially simultaneously by co-extrusion of the channels. The co-extruded sheet may then be stretched, simultaneously molecularly oriented in both directions in the forward direction of both layers, and then laterally stretched to create biaxial orientation of both layers, and then induce partial crystallization of the second layer 11. In such a case, it may be desirable to heat the set under dimensional correction at a temperature higher than the crystal melting temperature of the second polymer layer and to cool the film so that the second layer polymer remains essentially amorphous. The thermal setting of the polymer film consisting of the first polyester layer and the second cooling polyester layer is generally at 200 to 250 ° C. By providing the second amorphous layer 11, the vacuuming around the pigment flakes during orientation is substantially eliminated or significantly reduced, providing improved optical properties of the film. Thus, as shown in FIG. 2, the second layer 11 containing the multilayer interfering thin film flakes is provided on one side, for example on top of the substrate 21 or on the first side 26. Since the flake is a high cost component, by using such a two layer arrangement, the relatively thick layer 21 and the very thin layer 11 are provided as a thin layer or a second layer containing a multilayer interfering thin film flake, so that the flake is good. It is possible to use. Thus, by (consequently) having two or three layers of optionally dispersed flakes to provide a continuous coating to a very thin thin layer using a small amount of material while providing the desired color saturation, thereby substantially the entire color It is possible to obtain saturation.

In providing the polymer sheet 11 as shown in FIG. 1, in addition to the molding by extrusion described above, the sheet can be molded, for example, by casting through a conventional slot applicator. In casting, like extrusion, multilayer interfering thin film flakes can be introduced, mixed with the solvent dissolved polymer, and then passed through a slot applicator. This casting process also results in the orientation of the flakes 16 such that the flakes are in parallel or parallel planes with respect to the top and bottom surfaces 12 and 13 of the sheet 11.

Movement of the flakes or platelets 16 to be on the wider side is achieved by three results. In the solvent cast film, gravity has a great influence on gravity to cause the flakes 16 to be present on the broad side. This movement is enhanced by the surface tension created during drying of the cast film, similar to the biaxial stretch described above. Under the influence of surface tension, when the polymer dries and the solvent evaporates, the polymer shrinks and attracts flakes. In the flow direction during the casting process, the flow orients the flakes along the direction of the flow while allowing the flakes to remain fixed and horizontal under gravity. If the polymer is a high melting material, the shear force present in the coated slot die also causes the flakes to be in plane. Thus, it can be suggested that the flakes are oriented in the same way as during biaxial stretching of the extruded film.

In the embodiment of the invention shown in FIG. 3, also one of the layers 11 is provided on the second side 27 so that the same or different color effects can be achieved on the other side of the substrate 21. . Such multilayer interference thin film flakes 16 of the present invention can be used to provide monochromatic pigments or pigments of optically variable color. Thus, the other two layers 11 on either side of the substrate may have different colors or the same color or different properties of optical variability. In order to enhance color perception, the substrate 21 can be provided in black coloration or colored to achieve other color effects in other ways. The substrate may also be white.

In FIG. 4, a composite structure in which the middle layer 11 is a layer comprising flakes and the outer layer 21 is colored or not colored to provide different or the same color effect on both sides of the layer 11. (32) is presented.

The composite structures shown in FIGS. 3 and 4 can be isotropically extruded in the manner described above. If desired, it should be understood that additional layers may also be coextruded and biaxially stretched in the manner described above.

The thickness of the polymer sheet composite embodying the present invention may be 12 to 500 microns, 3 to 175 microns, preferably 3 to 30 microns. By way of example, the second layer 11 may be 1-50%, generally 1-20% of the total composite thickness. The thickness of the second layer 11 is preferably 20 microns or less, more preferably 0.5 to 10 microns.

The multilayer coherent thin film flakes suitable for use as the pigment of layer 11 consist of a multilayer optical coating, typically 3 to 5 layers, so that a strong dichroic optical effect is produced. By way of example, the five layers of optically variable flakes are preferably symmetrical, as described in patent 5,135,812 and include a first thin translucent metal layer, a first dielectric layer, a thick metal reflective layer, a second layer of dielectric material and a second The sheet is made in the order of a translucent metal layer. The first translucent metal layer and the dielectric layer are under the optical coating of the second translucent metal and the dielectric layer. The structure is formed from an inverted optically coated undercarriage. Each translucent sheet metal layer preferably consists of a layer of chromium about 5 nanometers thick.

Each dielectric charge is formed of a dielectric material, such as silicon dioxide or magnesium fluoride, to form the optical thickness of multiple half waves at a particular wavelength. The thick metal reflection layer consists of an aluminum layer formed to a thickness of about 40 nanometers or more, providing high opacity and high reflection. Alternatively, instead of using chromium in the translucent metal layer, materials such as nickel and stainless steel can be used. In addition, instead of silicon oxide having a refractive index of 1.46 in the dielectric layer, other inorganic materials such as magnesium fluoride (1.38) and aluminum dioxide (1.65) having a refractive index of 1.65 or less can be used. Instead of aluminum as the metal reflective layer, materials such as cobalt-nickel magnetic alloy, gold, copper and silver can be used.

Three layers of optically variable flakes similar to the five-layer structure can be used, but the optically coated substructure of the dielectric layer and the second translucent metal can be removed. Furthermore, three-layer optical devices can be used as interference flakes, as described in US Pat. No. 5,278,590.

Preferred examples of the five layers of optically variable flakes exhibit dark green and purplish light with varying angles of incident light. The dark green optically variable flake consists of a number of half waves for the silicon dioxide layer at a wavelength at approximately 515 nanometers. This produces an optically variable flake having a sixth order refractive index maximum at 515 nanometers. Narrow float spikes with a refractive index of at least 60% at 515 nanometer wavelengths result in near zero refractive index at adjacent wavelengths. Whether the fourth and eighth refraction maximums occur in the infrared region and the short wavelength blue region, the flakes still produce very saturated greens. Due to the low refractive index (1.46) of the silicon dioxide layer and its high order, a large amount of color change is caused by the change in the viewing angle of the coating. At an observation angle of about 45o, the sixth peak shifts to the blue region, the fourth peak shifts to red, and is present at low refraction within the 515 nanometer green region. Thus, as the viewing angle is increased, the appearance color of the coating changes from dark green to purple.

A second preferred example of a five layer optically variable flake consists of a plurality of half wave silicon dioxide layers at about 450 nanometers. This coating has a sixth order peak in the blue part of the spectrum and a fourth order refraction peak in the red part of the spectrum which, when observed at normal incidence, produces a dark purple color. When viewed from a larger angle, the fourth order peak is shifted to the green region with low refraction in red and blue. This causes the color of the coating to change from purple to green at larger viewing angles.

Thus, typically, the optically variable flakes contained in the layer 11 or the second layer of the polymer film and used in the present invention have two distinct colors, ie one color and flake when observed in the forward direction with respect to the surface of the flakes. Indicates another color when observed at an angle of 45o. Due to the use of one or more dielectric layers having a low index of refraction, preferably below 1.65, this apparent color change is achieved.

Flakes 16 suitable for use in the second polymer films or layers 11 according to the invention preferably have a particle size of the largest width of the flakes of 0.5 to 200 microns, preferably a particle size of 1 to 20 microns. Has The average particle size of the flakes, ie the maximum width of the flakes, is preferably 1 to 20 microns. The aspect ratio, which means the ratio of the width to the thickness of the optically variable flake, is suitably 2: 1 or more, preferably 5 to 10: 1.

In order to obtain the advantageous properties of the invention, the concentration of the optically variable flakes present in layer 11 is suitably 1 to 50% by weight, preferably 2 to 30% by weight, based on the weight of the polymer in layer 11. %to be.

In the present invention, in order to enhance the durability of the pigment flakes, it is preferable to bake the pigment flakes at a relatively high temperature, for example at 250 ° C. or more, for 2 to 4 hours. Although it is not understood exactly what is occurring, it is believed that high temperature baking in air or oxygen improves the durability of the flakes. Due to the high temperatures used, substantially the same effect is achieved by placing the pigment flakes in the polymer film during biaxial orientation of the polymer film and during extrusion.

In the present invention, it has been described that pigment flakes 16 may be added to the polymeric material prior to extrusion, but it should be understood that flakes 16 may be added in the autoclave or during monomer transfer if desired. However, it has been found desirable to incorporate the flakes as glycol dispersion during the esterification step of the polyester synthesis. Alternatively, the pigment flakes can be added directly to the polymer chip prior to extrusion. Thus, the flakes can be added as a dry powder into the extruded polymer melt.

The layer of the film produced according to the present invention may contain additives commonly used in the preparation of polymer films. Thus, agents such as dyes, pigments, lubricants, anti-oxidants, anti-blockers, surface active agents, ultraviolet stabilizers, viscosity modifiers and dispersion stabilizers may be suitably incorporated into the first and / or second layer. In particular, the dichroic optical effects of the optically variable flakes can be combined with the additive colorimetric or contrast dye colors and / or pigments added to the second polymer material layer to produce other colors with different color-burning effects. Transparent pigments and dyes can be used to block undesirable colors, for example as described in patent 5,135,812.

It should also be understood that the composite structure herein may be formed of a material that is sealed into itself, or alternatively, additional layers may be provided to achieve sealing. In addition, one or more of the polymer films produced according to the invention can form composites or laminates which exhibit improved properties such as antistatic, adhesion enhancement or release compared to the component materials, such as inks, lacquers and / or metal layers. It should be understood that additional coating may be applied to one or both sides.

Biaxial orientation can typically be performed by stretching in the forward and lateral directions in an amount suitable to achieve production of a film having the desired thickness. As an example, one film is stretched 3.6 times the original area in the forward direction and 4.2 times the original area in the lateral or reverse direction. The film composite is finally heat-set under dimensional correction in a stentor oven at about 225 ° C.

Biaxially oriented polymer film optical products made in accordance with the present invention as described above and containing multilayer interfering thin film flakes oriented therein can be used in many other products. In particular new preferred color effects can be obtained which can be used for various decorative purposes. When the flakes are in the form of optically variable pigments, they are particularly useful for providing guarantees in guaranteed certificates such as driver's licenses and in guarantee documents such as credit cards, certificates and bills. In order to eliminate the need for a large amount of film, a small proportion of polymer film can be incorporated into the safety document. They can also be incorporated into the marking or packaging of products that can be forged. The presence of only a small amount of polymer sheet in the safety document enables, for example, almost anyone to easily distinguish genuine from counterfeit by observing the presence or absence of color change.

Since the complex technology used inside makes it very difficult (not impossible) for counterfeiters to duplicate multilayer interfering thin film flakes, a guarantee is provided. In addition, high costs are required to equally incorporate into biaxially oriented polymer films in order to produce the desired optical effect. In addition, since the optically variable characteristic cannot be copied by the color copier, the guarantee document cannot be duplicated in the color copier.

In FIG. 5, another composite polymer sheet structure 34 is shown in which the polymer sheet is provided as a base or substrate 36 having an upper surface 37 and a lower surface 38. Compared to the substrates of the embodiments described above, the base substrate 36 may be relatively thick and clean, such as, for example, 5 mils to 3/8 inches. The middle layer 11 on the surface 37 may be in the form herein, and may be in the form of a thin layer of polymer material containing the optically variable flakes described above. In addition to the optically variable flakes, other materials such as dyes, pigments, aluminum flakes and the like can be incorporated into the layer 11.

Such dyes, pigments and the like can be used for various purposes known to those skilled in the art. For example, they can be used to block undesirable colors at different angles. They can also be used to subtract colors. Overlap layer 39 may be provided on layer 11 and may be in the form of a suitable relatively rigid material, such as a lacquer. Such a composite structure 34 as shown in FIG. 5 can be applied in various ways, for example, flooring materials and other decorative effects.

An example of how the polymer film of the present invention may be used in the security document 41 is shown in FIG. 6, in which the guarantee document is spaced at regular intervals and partially embedded in the bill. It is in the form of a sheet of material, such as a paper bill, having first and second faces 42 and 43 parallel to and having a thickness of 2 to 3 mils. The thin line 46 extends across the paper toward one end as shown in FIG. 6, and as shown in FIG. 7, the portion 46a spaced at regular intervals of the thin line is one side or top surface. Exposed to 42, the intermediate portion 46b is embedded in the bill holding material. Alternatively, as shown in FIG. 8, the thin line 46 has a gap portion 46a appearing as the surface 42, the middle portion 46b being embedded into the bill paper, and a further gap. The portion 46c may be embedded in the bill paper by appearing on the other side 43 of the bill.

The thin line 46 is formed from the biaxially oriented polymer sheet 11 or cast film described above, for example, by cutting the sheet 11 to a thickness of .5 mils and an area of 1.5 to 3 mils. It is possible to provide an elongated strip that functions as line 46. This thin line has a rectangular cross section. According to the invention, the thin line can be incorporated into a banknote, as shown in FIG. 6, to provide one optically variable effect or one color or to remove one color from one side of the banknote.

If a thin line is incorporated into the banknote as shown in FIG. 7 and is visible on the opposite side of the thin line branching, two different color effects or optically variable effects can be achieved on both sides of the banknote. For example, a gold to green shifter can be incorporated on one side and a green to blue shifter can be incorporated on the other. Alternatively, one side may be a metalized reflector in which aluminum flakes are incorporated therein, and the other may have an optically variable effect.

In the following, it should be understood that, in addition to the strip, a small portion of the polymer film of the present invention may be incorporated into the guarantee document to produce a complete portion thereof. Thus, this part can be used in credit cards, tolls or other important documents.

An example of a security document is shown in FIG. 9, which may be in the form of a California driver's license 51 of a suitable size, for example 2 × 3 ^1/4 , so that it can easily fit in a conventional wallet. The California driver's license is provided with a relatively rigid substrate 52 of suitable plastic of the type described above. It may be of suitable thickness, for example 2 to 10 mils. It has upper and lower parallel planes 53 and 54 spaced at regular intervals. Sheet 56 of suitable material, such as paper, may be laminated to surface 53 by the use of an adhesive and pressure and heat application. The sheet 56 applied to the security document may include printed information 58 and a picture or photo 57 as shown in FIG. 8. For example, the picture may be a color picture, and the printed information may be information printed in another color. In this case, the sheet 56 may be transparent. However, it should be understood that the sheet 56 may be a semi-transparent material, if desired.

The polymer sheet 61 embodying the present invention is attached to the sheet 56 by application of suitable heat and pressure and by lamination by the use of a transparent adhesive (not shown) to complete the safety document. . The polymer sheet contains multilayer coherent thin film flakes 62 of the type described above. By way of example, the polymer sheet 61 may be a relatively thin sheet, for example of 2-3 microns. The flakes are at relatively low concentrations, for example the low concentrations presented above, and the polymer sheet 61 is translucent so that the information on the sheet 56, such as the photograph 57 and the printed information 58, is visible to the human eye. May appear. In such a case, the flakes 62 may be optically variable by providing a relatively low color depth where the color change still appears in the human eye in order to provide an additional level of assurance to the safety guarantee document 51.

In summary of the invention, by incorporating multilayer interfering thin film flakes into a polymer film, it is possible to minimize the amount of flakes required and to maximize the optical effect from the optical flakes. This is important because pigment flakes are relatively expensive compared to the cost of polymer films. In theory, maximum optical function can be achieved by having the flakes on a single plane to be in contact with each other so that they can be monolayer with minimal use of the flakes. In practice, this optimal arrangement of flakes is difficult to achieve because the polymer sheet is three dimensional and the flakes cannot be present on a single plane. There may also be overlap between the flakes and the clay. However, by orienting the flakes in the polymer sheet, as described above, the optimum optical function of the flakes is achieved. By using a relatively high temperature of about 250 ° C. or higher in the extrusion process, the viscosity of the molten polymer is reduced.

This allows the flakes to be more easily oriented in the preferred manner described above. In addition, the polymer film is extruded and then drawn to become thin, thereby optimizing the dispersion of the flakes. By using a dark or black background, the observer perceives an optical effect that is brighter than the white background. By using dyes in the coextrusion layer, still other optical effects can be achieved. The polymer sheet produced in the present invention by casting or extrusion is very safe and durable.

Claims (34)

A polymer sheet comprising a first layer of polymeric material having first and second parallel planes and disposed with a plurality of multilayer interfering thin film flakes, the flakes having first and second parallel planes, the width and thickness of the flakes being wide A polymer sheet formed with a thickness of at least an aspect ratio of 2: 1, wherein the first and second parallel planes of the flakes are parallel to the first and second parallel planes of the first polymeric material layer and are oriented such that the flakes are positioned in a plane. The method of claim 1, further comprising a second polymer material layer attached to the first polymer material layer, wherein the second polymer material layer is used as the primary layer and the first polymer material layer is used as the secondary layer. Polymer sheet made with. The polymer sheet of claim 2 wherein the flakes are optically variable. 3. The polymer sheet of claim 2 wherein said second polymer material layer is colored. 3. The polymer sheet of claim 2 wherein the first polymer material layer is amorphous. 6. The polymer sheet of claim 5 wherein said second polymer material layer is crystalline. The method of claim 6, wherein the second polymeric material layer has first and second parallel planes, the first polymeric material layer is disposed on the second first surface, and the second polymeric material layer is formed of the second polymeric material layer. Having a plurality of multi-layered interfering thin film flakes attached to the second surface and having a third polymer material layer disposed therein, the flakes in the third polymer material layer having first and second parallel planes of the first and second parallel planes of the third polymer material layer Oriented so as to be in a plane parallel to the polymer sheet. The polymer sheet of claim 1 which is extruded. The polymer sheet of claim 1 which is cast. The polymer sheet of claim 1 wherein the flakes are oriented biaxially. The polymer sheet of claim 2 wherein the primary layer and the secondary layer are coextruded. 12. The polymer sheet of claim 11 wherein said primary layer is crystalline and said secondary layer is amorphous. 13. The polymer sheet of claim 12, wherein both the primary layer and the secondary layer are oriented biaxially. 3. The polymer sheet of claim 2 wherein the primary layer is colored. The material sheet has first and second sides, the optical article consists of a layer of polymeric material having first and second parallel planes and is supported by the material sheet, and a plurality of oriented multilayer interference thin film flakes are placed in the polymeric material layer Wherein the flakes have first and second parallel planes, the width and thickness of the flakes are formed such that the width-to-thickness has an aspect ratio of at least 2: 1, and the first and second faces of the flakes are formed of a polymeric material layer. So as to lie parallel to the first and second sides, thereby ensuring a safety product as the material sheet. 16. The layer of claim 15 wherein the polymeric material layer is biaxially oriented and the flakes are planar in the biaxial orientation and the first and second surfaces of the flake are parallel to the first and second surfaces of the polymeric material layer. Product, characterized in that the safety. 16. The product of claim 15, further comprising an additional layer of polymeric material attached to the first layer of polymeric material. 18. The product of claim 17, wherein the additional polymeric material layer is colored. 16. The product of claim 15, wherein the flakes are optically variable. 16. The product of claim 15, wherein the optical product is in the form of an elongated strip, wherein the strip is at least partially sandwiched in a sheet of material. 21. The security product of claim 20, wherein the strip has one or more portions that are visible through one or more surfaces of the security document. 22. The product of claim 21, wherein the strip has an additional portion that is visible to another surface of the sheet of material. 16. The security as claimed in claim 15, wherein the security product comprises a sheet carrying an image disposed on the first face under the optical product, the optical product being translucent so that the image can appear through the optical product. product. 16. The product of claim 15, wherein at least one filler in the form of a dye or pigment is incorporated into the polymeric material. 25. The product of claim 24, wherein the dye or pigment is selected to block undesirable colors at different angles. 16. The product of claim 15, wherein the polymeric material is in the form of a biaxially oriented polymeric layer or cast layer. 27. The product of claim 26, wherein the dye or pigment is disposed in a polymeric material. 28. The product of claim 27, wherein the dye or pigment is selected to block undesirable colors at different angles. A method of making an optical product using multilayer interfering thin film flakes having first and second parallel planes, the width and thickness being formed such that the width to thickness has an aspect ratio of at least 2: 1, comprising: melting a polymer material, flakes Introducing the polymer material into a melt with the flakes therein, such that the flakes are oriented in the melt as they are molded into sheets having first and second parallel planes, thereby allowing the first and second sides of the flakes to Positioning in the first and second parallel planes of the sheet, and cooling the sheet to solidify to form the sheet. 30. The method of claim 29, wherein the cooled sheet is heated and the sheet is stretched in the first and second directions to orient the molecular chain biaxially within the sheet while at the same time orienting the flakes in a plane in the biaxial orientation. And cooling the sheet. 30. The method of claim 29, further comprising coextruding the sheet with the additional polymeric material layer such that the additional polymeric material layer is attached to the first side of the sheet. 32. The method of claim 31, further comprising introducing color to the additional coextruded material layer. 32. The method of claim 31, further comprising coextruding the sheet with another layer of polymeric material such that another layer of polymeric material is attached to the second side of the sheet. 30. The method of claim 29, further comprising forming a melt onto the detachable substrate, drawing the polymer sheet to orient the flakes in the polymer while solidifying, and removing the solidified polymer sheet from the detachable substrate. Characterized in that.