Patent Description:
Optical devices exhibiting a viewing angle-dependent visual appearance are used as efficient anti-copy means on bank notes and security documents. Optically variable inks are often used that include thin film optical interference structures having a layered structure of a reflective layer, a dielectric layer, and an absorber layer. However, thin film optical interference structures are applied as an opaque coating directing on top of a substrate. In this manner and with this opaque coating, it is not possible to hide and reveal an image on a substrate at certain angles of view. All that is seen is the color-shift.

Magnetic flakes have been used to create hide and reveal effects by using alignment of the flakes to create a "Venetian Blind Effect. " The Venetian Blind layer of magnetic flakes, at a transparent angle, absorbs a lot of light. Additionally, only light that has the exact right angle passes in and out through the Venetian Blind layer thereby contributing to the underlying image and color. However, this reduces the lightness and the chromaticity of the image.

<CIT>, <CIT>, <CIT>, <CIT> and <CIT> disclose optical devices which may be useful to understand the present invention.

What is needed is a way to brighten the image, e.g., a higher contrast, to the underlying image.

In an aspect, there is disclosed optical device according to claim <NUM>.

In another aspect, there is disclosed a method of making an optical device according to claim <NUM>.

In another aspect, there is disclosed a method of using an optical device according to claim <NUM>.

In a further aspect, there is disclosed, a method of using an optical device according to claim <NUM>.

Additional features and advantages of various embodiments will be set forth, in part, in the description that follows, and will, in part, be apparent from the description, or can be learned by the practice of various embodiments. The objectives and other advantages of various embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the description herein.

For simplicity and illustrative purposes, the present disclosure is described by referring mainly to an example thereof.

Additionally, the elements depicted in the accompanying figures may include additional components and some of the components described in those figures may be removed and/or modified without departing from scopes of the present disclosure. Further, the elements depicted in the figures may not be drawn to scale and thus, the elements may have sizes and/or configurations that differ from those shown in the figures.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are intended to provide an explanation of various embodiments of the present teachings. In its broad and varied embodiments, disclosed herein are optical devices; and a method of making and using optical devices.

The present invention is directed to an optical device <NUM> comprising a structured substrate <NUM>; a reflective layer <NUM>; and a coating <NUM> with magnetic flakes, as shown in <FIG>. The coating <NUM> with magnetic flakes <NUM> can create angle-dependent transparency variations.

The structured substrate <NUM> includes a surface, such as a plurality of surfaces, arranged to form an image. The structured substrate <NUM> includes horizontal surfaces (i.e., planar with an absence of structure) and structured surfaces (i.e. angled surfaces relative to the horizontal surface). For example, as shown in <FIG>, the left and right ends and the bottom edge illustrate horizontal surfaces <NUM> and the center illustrates a structured surface <NUM>. It should be noted that the structured surfaces <NUM> can be present on a top edge (<FIG> and <FIG>) or a bottom edge (<FIG> and <FIG>) of the structured substrate. The structured substrate <NUM> can include a surface forming an image that is defined by an area shape and configuration. The image can be present on one or more of the surfaces of the substrate <NUM>. The image can include, but is not limited to, words, symbols, numbers, patterns, and shapes.

Any substrate <NUM> commonly used for producing optical devices <NUM> can be employed for use as the structured substrate <NUM>. Suitable substrate <NUM> materials include, but are not limited to, paper, cardboard, textiles, glass, polymers, plastics or combinations thereof. The substrate <NUM> material can be a transparent material. For example, the substrate <NUM> can be an embossed UV-curable material, coated on polyethylene terephthalate, applied to a paper on the non-observing side. In an aspect, the structured substrate <NUM> can be a transparent material in which the image can be directly produced on or in a surface of the substrate to form the structured substrate <NUM>.

In an aspect, the substrate <NUM> can be a material that is structured, i.e., provided with a plurality of surfaces that form the image and a background. In an aspect, the image can be formed with embossing or a micro-mirror array having co-planar surfaces. In another aspect, the image can be formed with a grating, such as a blazed grating, or variants thereof. For example, the image can be formed with a grating at a first angle and the background can be formed with a grating at a second angle that is offset from the first angle, such as <NUM>° from the first angle. A blazed grating includes a plurality of grating lines that possess a triangular, sawtooth-shaped cross-section, forming a step structure. The steps can be tilted at the so-called blaze angle with respect to the surface of the substrate <NUM>. The blaze angle can be optimized to maximize efficiency for the angle of the incident light and taking in consideration the intended uses of the optical device <NUM>. The plurality of surfaces of the structured substrate <NUM> formed by the blazed grating can reflect light at <NUM>° of the surface angle. For example, if the surface angle is <NUM>°, then the reflected light angle would be <NUM>°. The plurality of surfaces of the structured substrate <NUM> that form the image are reflective at the transparent angle of the coating <NUM> of magnetic flakes <NUM>. In this manner, the brightness of the image can be enhanced. Additionally, the image reflects far less at other angles which makes it easier to achieve an angle-dependent disappearance i.e., hiding, effect. Some areas of the substrate <NUM> are not structured, i.e. a horizontal planar surface, and the image formed by the structured surfaces can rely on different reflection angles of the structured surfaces and/or the absence of structure in some areas.

A reflective layer <NUM> can be applied on the structured substrate <NUM>. The reflective layer <NUM> can be applied in any manner so long as the reflective layer <NUM> mimics a topography of the structured substrate <NUM>, such as each surface, shape, and/or angle of the plurality of surfaces. In particular, the reflective layer <NUM> can be a metalized surface on the structured substrate <NUM>. The reflective layer <NUM> can be microstructured or can include a grating that is the same as the structured substrate <NUM>.

The reflective layer <NUM> can include a metal, non-metal, or metal alloy. In one example, the materials for the reflective layer <NUM> can include any materials that have reflective characteristics in the desired spectral range. For example, any material with a reflectance ranging from <NUM>% to <NUM>% in the desired spectral range. An example of a reflective material can be aluminum, which has good reflectance characteristics, is inexpensive, and is easy to form into or deposit as a thin layer. Non-limiting examples of reflective opaque material for use in the reflective layer <NUM> include aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, niobium, chromium, tin, iron, and combinations or alloys of these or other metals can be used as the reflective layer <NUM>. In an aspect, the material for the reflective layer <NUM> can be a white or light colored metal. In other examples, the reflective layer <NUM> can include, but is not limited to, the transition and lanthanide metals and combinations thereof; as well as metal carbides, metal oxides, metal nitrides, metal sulfides, a combination thereof, or mixtures of metals and one or more of these materials. In an aspect, the reflective layer <NUM> may include a transparent or semi-transparent material chosen from glass, silica, titania, alumina, natural mica, synthetic mica, and bismuth oxychloride. In another aspect, the reflective layer <NUM> can include a metalloid material chosen from silicon, germanium, and molybdenum.

The thickness of the reflective layer <NUM> can range from about <NUM> to about <NUM> microns, for example from about <NUM> to about <NUM> micron, and as a further example from about <NUM> to about <NUM>.

A coating <NUM> of magnetic flakes <NUM> can be applied to the reflective layer <NUM>. In an aspect, the coating <NUM> of magnetic flakes <NUM> can be an external layer of the optical device <NUM>. The coating <NUM> can include a curable binder <NUM>. Non-limiting examples of curable, binders <NUM> include vinylic resins, acrylic resins, urethane-alkyd resins, mixtures thereof, and mixtures with other polymers. The binder <NUM> can be typically transparent, such as clear and/or colorless, but can be tinted, and the magnetic flakes <NUM> can be reflective.

In one example, the coating <NUM> comprising magnetic flakes <NUM> can be applied onto the reflective layer <NUM> and/or the structured substrate <NUM> in any manner, including but not limited to, a liquid coating process. The coating <NUM> can be applied in a thickness that allows for orientation of the magnetic flakes <NUM> in all directions.

Many configurations of coating <NUM> are possible. In one configuration, the magnetic flakes <NUM> can be distributed evenly throughout the coating <NUM>. In another configuration, the magnetic flakes <NUM> can have a higher concentration in some areas of coating <NUM> than in other areas. And in yet another configuration, some portions of the volume of coating <NUM> can be essentially free of the magnetic flakes <NUM>.

The magnetic flakes <NUM> can be any size or shape and can include a material that can be magnetized in a magnetic field. Upon application of a magnetic field, the magnetic flakes <NUM> can be oriented in a predetermined direction. Once the orientation of the magnetic flakes <NUM> is obtained, the coating <NUM> with the magnetic flakes <NUM> can be cured.

The magnetic flakes <NUM> are generally small, thin flakes that are flat or reasonably flat. Typical dimensions for the magnetic flake <NUM> might be about twenty microns across and about one micron thick; however, these dimensions are merely exemplary and not limiting. Much larger or much smaller flakes could be used, as could flakes with different aspect ratios. Optically variable pigment ("OVMP"™) pigment flakes include an optical interference structure, such as a Fabry-Perot structure, made from thin film layers. The OVMP shifts color with viewing angle. Different optical interference designs can produce various hues and color travel. A thin film layer of magnetic material, such as a layer of nickel or ferrochrome about <NUM> to about <NUM> thick can provide a suitable magnetic structure for orienting or aligning pigment flakes within coating <NUM>. Other magnetic materials could be used, and suitable materials might form permanent magnets or not, but it is generally desirable to avoid permanent magnetization of the flakes prior to application to avoid clumping. Some magnetic flakes <NUM> might be simply made from magnetic material, such as nickel flakes, which could be used for a reflective, non-color-shifting effect.

The coating <NUM> comprising the magnetic flakes <NUM> can be applied to the reflective layer <NUM> and/or the structured substrate <NUM> using a deposition technique, such that the coating <NUM> is external to either the reflective layer <NUM> and/or the structured substrate <NUM>. The coating <NUM> of the magnetic flakes <NUM> can be applied to any layer of the optical device <NUM> to either completely cover a layer or cover a portion of a layer. For example, the coating <NUM> of the magnetic flakes <NUM> can cover a portion of the reflective layer <NUM>. A magnetic field can be applied to the magnetic flakes <NUM> to orient or align one or more of the flakes while the binder <NUM> in the coating <NUM> is still fluid. The binder <NUM> can then dry, cure, or set to fix the alignment of the magnetic flakes <NUM>.

The magnetic flakes <NUM> can be arranged to achieve a Venetian blind effect. In particular, the magnetic flakes <NUM> can be aligned so that along a specific direction of observation they give visibility to the reflective layer <NUM> and/or structured substrate <NUM> so that the image present on or in the structured substrate <NUM> becomes apparent to the observer while, at the same time, the magnetic flakes <NUM> impede the visibility along another direction of observation. The alignment of magnetic flakes <NUM> can be at a similar angle throughout the coating <NUM>, or the alignment of the magnetic flakes <NUM> can be at a different angle in a portion of the coating <NUM> so that the Venetian blind effect occurs at different viewing angles or orientations.

At certain alignment angles the magnetic flakes <NUM> can create a foil-like appearance by reflecting a large fraction of the incoming light so that the underlying image is not seen. At other alignment angles, much of the incoming light passes between the aligned flakes and reaches the structured substrate <NUM> which reflects the light, and the underlying image is discernable.

In an aspect, the optical device <NUM> can further include at least one layer, such as a base <NUM>, an adhesive <NUM>, a multilayer coating <NUM>, or combinations thereof. The at least one layer can be located in various positions throughout the optical device <NUM> depending upon the intended visual effect, light source, angle of observation, etc. In a further aspect, the multilayer coating <NUM> can comprise a multilayer optical interference coating. In another aspect, the multilayer coating <NUM> can comprise a color shifting coating.

<FIG> illustrates a cross-section of an optical device <NUM> including a base <NUM> having an adhesive <NUM> applied to a surface of the base <NUM>. Non-limiting examples of the base <NUM> include a document, a banknote, paper, cardboard, any material that can support an optical device, or any material that can include a security feature. The adhesive <NUM> can be any material, colored or transparent, that can affix or bond the base <NUM> to the other layers in the optical device <NUM>. For example, the structured substrate <NUM> can be adhered to the base <NUM> via adhesive <NUM>.

As shown in <FIG>, the optical device <NUM> can also include a multilayer coating <NUM>. The multilayer coating <NUM> can be positioned anywhere within the optical device <NUM>, such as between the reflective layer <NUM> and the coating <NUM> of magnetic flakes <NUM>. The multilayer coating <NUM> can be opaque or can provide transmission at one or more wavelengths. In the multilayer coating <NUM>, each layer can be the same or different, for example in terms of the materials present in each layer of the multiple layers or in terms of colors visualized by each layer. For example, the multilayer coating <NUM> can include a reflector layer, a dielectric layer and an absorber layer. The multilayer coating <NUM> can be opaque and can be positioned upon the structured substrate and/or adjacent to the reflective layer <NUM>. The multilayer coating <NUM> can be an optical interference coating.

<FIG> illustrates a cross-section of an optical device <NUM> according to another aspect. The optical device <NUM> can include a base <NUM> with an adhesive <NUM> affixing the multilayer coating <NUM> to the base <NUM>. The multilayer coating <NUM> can be metallic, opaque, or can provide transmission at one or more wavelengths. The multilayer coating <NUM> can be positioned between the adhesive <NUM> and the reflective layer <NUM>. The structured substrate <NUM> can be between the reflective layer <NUM> and the coating <NUM> with magnetic flakes <NUM>.

<FIG> illustrates a cross-section of an optical device <NUM> according to another aspect. The optical device <NUM> can include a base <NUM>, an adhesive <NUM>, a reflective layer <NUM>, a structured substrate <NUM>, a multilayer coating <NUM>, and a coating <NUM> of magnetic flakes <NUM>. The structured substrate <NUM> can be transparent, colorless, or can be colored. The multilayer coating <NUM> can be a transparent color shifting multilayer dichroic coating. For example, the multilayer coating <NUM> can be stack of alternating layers of high refractive index materials and low refractive index materials. As another example, the multilayer coating <NUM> can comprise a transparent, colored resin.

A method of making the optical device <NUM> includes forming an image on a structured substrate <NUM>; applying a reflective layer <NUM> on the structured substrate so that the reflective layer <NUM> mimics a topography of the structured substrate <NUM>; and applying a coating <NUM> comprising magnetic flakes <NUM>. The method can include applying a multilayer coating <NUM> between the reflective layer <NUM> and the coating <NUM> of magnetic flakes <NUM>. The method can further include providing a base <NUM> and applying an adhesive <NUM> to the base. The method can also include adhering the structured substrate <NUM> to the base <NUM> via the adhesive <NUM>. The method can also include applying a multilayer coating <NUM>, such as an optical interference colorant, to the reflective layer <NUM> so that the multilayer coating <NUM> mimics a topography of the reflective layer <NUM>. In one aspect, the multilayer coating, such as an optical interference colorant can comprise a color shifting colorant.

A method of making an optical device can include providing a base <NUM>, applying an adhesive <NUM> to the base, adhering a multilayer coating <NUM> to the adhesive <NUM>, applying a reflective layer <NUM> to the multilayer coating <NUM>, applying a structured substrate <NUM> to the multilayer coating <NUM>, and applying a coating <NUM> with magnetic flakes <NUM> to the structured substrate <NUM>. The reflective layer <NUM> and/or the multilayer coating <NUM> can mimic a topography of the structured substrate <NUM>.

A method of making an optical device can include providing a base <NUM>, applying an adhesive <NUM> to the base, applying a reflective layer <NUM> to the adhesive <NUM>, applying a structured substrate <NUM> to the reflective layer <NUM>, applying a multilayer coating <NUM> to the structured substrate <NUM>, and applying a coating <NUM> with magnetic flakes <NUM> to the multilayer coating <NUM>. The reflective layer <NUM> and/or the adhesive <NUM> can mimic a topography of the structured substrate <NUM>.

A method of using an optical device <NUM>, can include forming an optical device <NUM> including a structured substrate <NUM>, a reflective layer <NUM> on the structured substrate <NUM>, and a coating <NUM> with magnetic flakes <NUM> on the reflective layer <NUM>; and tilting the optical device <NUM> to visualize an image formed on the structured substrate <NUM> as a top layer. The coating <NUM> with magnetic flakes <NUM> can be an external layer of the optical device <NUM>. The coating <NUM> with magnetic flakes <NUM> can exhibit a Venetian blind effect. In an aspect, the image can be visualized between the magnetic flakes <NUM> that exhibit the Venetian blind effect. In another aspect, the image is not visualized between the magnetic flakes <NUM> that exhibit the Venetian blind effect. As an additional option, the area of the reflective layer <NUM> covered by the coating <NUM> can be patterned, and thereby not cover all areas of reflective layer <NUM>.

Claim 1:
An optical device (<NUM>) comprising:
a structured substrate (<NUM>);
a reflective layer (<NUM>) on the structured substrate (<NUM>); and
a coating (<NUM>) with magnetic flakes (<NUM>) on the reflective layer (<NUM>) or on another side of the structured substrate (<NUM>);
wherein the structured substrate (<NUM>) includes a planar portion (<NUM>) with an absence of structure and a structured portion (<NUM>) having a plurality of angled surfaces relative to the planar portion (<NUM>), the angled surfaces arranged to form an image on the substrate;
wherein the magnetic flakes are aligned to provide a transparent angle for viewing the image; and
wherein the plurality of angled surfaces that form the image are reflective at the transparent angle and reflect far less at other angles.