JP7487482B2 - Color Shifting Device - Google Patents

Description

The present invention relates to a color shifting device, which is a type of optically variable device.

Optical variable devices (OVDs) have been used in many products in recent years, not only to enhance the design of products and provide excellent decorative effects, but also to prevent counterfeiting. OVDs are a general term for devices that exhibit special optical effects, such as changing colors or images depending on the viewing angle.

OVDs use a relief-type diffraction grating with a fine uneven pattern, a diffraction structure such as a striped pattern with different refractive indexes, and a multilayer film made up of thin films with different optical properties. The resulting diffraction and interference of light creates a unique image and color change (color shift) depending on the viewing angle.

Relief type diffraction gratings include those whose cross section perpendicular to the longitudinal direction of the grooves is rectangular wave-shaped (see Patent Document 1 and Non-Patent Document 1), sinusoidal wave-shaped, or sawtooth-shaped.

A typical diffraction grating with a rectangular wave-like cross section is illuminated with white light from the normal direction, rotated 180 degrees around the normal, and then observed from an oblique direction at the same angle. Although the image is inverted before and after the rotation, it still displays an image of the same color.

When observed under the above conditions, a diffraction grating with a sine wave cross section also displays an image of the same color before and after rotation, just like a diffraction grating with a rectangular wave cross section, although the image is inverted before and after rotation.

On the other hand, a diffraction grating with a sawtooth cross section, i.e. a blazed diffraction grating, can display an image that is inverted and has a different brightness before and after the rotation when illuminated with white light from the normal direction and then rotated 180 degrees around the normal and observed from an oblique direction. However, the saturation and hue of the image do not change.

US Patent Application Publication No. 2004/0021945

Michael W. Farn (1992) "Binary gratings with increased efficiency", Appl. Opt. , Vol. 31, No. 22, pp. 4453-4458

The present invention has been made in consideration of the above problems, and aims to provide a color shifting device that produces a special optical effect, more specifically, a color shifting device that can change not only the color but also the number of colors and the shape when rotated 180 degrees around the normal (hereinafter sometimes simply referred to as inversion).

As a means for solving the above problems, a first aspect of the present invention is a color shifting device comprising a plurality of relief structures,
each of the plurality of relief structures extends in a first direction parallel to a display surface of the color shifting device and has a concave-convex structure arranged in a second direction perpendicular to the first direction;
the concave-convex structure has a wave-shaped reflecting surface consisting of a first inclined surface and a second inclined surface,
the first inclined surfaces and the second inclined surfaces are alternately arranged in the second direction,
the first inclined surface is inclined at a positive angle with respect to a reference plane that is perpendicular to the display surface and parallel to the first direction;
the second inclined surface is inclined at a negative angle with respect to the reference surface,
The plurality of relief structures include two or more relief structures in which a first lattice constant d1, which is an arrangement interval of the first inclined surfaces, is 700 nm or more and 1100 nm or less, and a second lattice constant d2, which is an arrangement interval of the second inclined surfaces, is 800 nm or more and 1200 nm or less and is larger than the first lattice constant d1, so that the maximum dimension in the second direction of a convex structure formed by a pair of adjacent first inclined surfaces and second inclined surfaces within the relief structure gradually increases as it proceeds in one direction of the second direction , and two of the relief structures include a color shifting device in which at least one of the values of the first lattice constant d1 and the second lattice constant d2 is not identical .

The plurality of relief structures may include a relief structure in which the first lattice constant d1 and the second lattice constant d2 are the same.

The plurality of relief structures have the first lattice constant d1 and the second lattice constant d2,
Equation: d1 x (n + 1) = d2 x n
wherein n is an integer equal to or greater than 2.
It is characterized by:

The ratio d1/d2 of the first lattice constant d1 to the second lattice constant d2 is in the range of 0.833 to 0.917.

Furthermore, the cross sections of the first inclined surface and the second inclined surface perpendicular to the first direction are both curved.

The ratio S1/S0 of the area S1 of the region of the corrugated reflecting surface that is parallel to the display surface and the area S0 of the orthogonal projection of the corrugated reflecting surface onto the display surface is 0.5 or less.

The multiple relief structures are also characterized in that they are in the form of a film or sheet.

The device is also characterized by comprising a reflective layer having the reflective surface, and a relief structure forming layer that supports the reflective layer and has a relief structure having a shape corresponding to the reflective surface on a surface that is in contact with the reflective layer.

The present invention provides a color shifting device that can change not only the color but also the number of colors and the shape when rotated (flipped) 180 degrees around the normal, allowing instantaneous capture of changes in the image.

FIG. 2 is a schematic cross-sectional view illustrating a part of a relief structure which is a component of the color shifting device of the present invention. FIG. 2 is a schematic perspective view of a reflecting surface included in the relief structure shown in FIG. 1 . 2 is a schematic cross-sectional view for explaining the shape of a reflecting surface included in the relief structure shown in FIG. 1 . A schematic cross-sectional view showing the manner in which the uneven structure surface of the relief structure shown in Figure 1 is illuminated with white light from its normal direction and viewed from the first observation position (OP1) direction (forward direction) and the second observation position (OP2) direction (reverse direction). (a) A schematic plan view illustrating a portion of a relief structure constituting a color shifting device of the present invention; (b) A schematic cross-sectional view showing the manner in which the uneven structure surface of the relief structure shown in (a) is illuminated with white light from its normal direction and observed from the forward direction; (c) A schematic cross-sectional view showing the manner in which the uneven structure surface of the relief structure shown in (a) is illuminated with white light from its normal direction and observed from the reverse direction. FIG. 1 is a schematic plan view (upper part) illustrating a part of the relief structures (1) to (3) constituting one embodiment of the color shifting device of the present invention; and FIG. 2 is a schematic cross-sectional view (lower part) for explaining how colors appear when observed from the forward and reverse directions. FIG. 1 is a schematic plan view (upper part) illustrating a portion of the relief structures (4) and (5) constituting one embodiment of the color shifting device of the present invention; and FIG. 2 is a schematic cross-sectional view (lower part) for explaining how colors appear when observed from the forward and reverse directions. FIG. 8 is a plan view showing how colors appear when a color shifting device is constructed using the relief structures (1) to (5) of FIGS. 6 and 7 according to Application Example 1 of the color shifting device of the present invention. FIG. 11 is a plan view showing a second application example of the color shifting device of the present invention.

Below, an embodiment of the present invention will be described with reference to the drawings. Elements having the same or similar functions will be given the same reference numerals, and duplicate descriptions will be omitted.

Figure 1 is a schematic cross-sectional view illustrating a portion of a relief structure that is a component of the color shifting device of the present invention. Figure 2 is a schematic perspective view of a reflective surface included in the relief structure shown in Figure 1. Figure 3 is a schematic cross-sectional view for explaining the shape of the reflective surface included in the relief structure shown in Figure 1.

In the figure, the X direction is a direction parallel to the display surface of the relief structure 1. Here, the "display surface" is a surface perpendicular to the thickness direction of the relief structure 1. The Y direction is a direction parallel to the display surface of the relief structure 1 and perpendicular to the X direction. The Z direction is a direction perpendicular to the X and Y directions.

The relief structure 1 shown in FIG. 1 is in the form of a film or sheet. As shown in FIG. 1, the relief structure 1 has a relief structure forming layer 11 and a reflective layer 12 on the surface of the relief structure forming layer 11. Although not shown, a protective layer, an intermediate layer, an adhesive layer, or the like may be further provided on the reflective layer.

The relief structure 1 may have a front surface facing the viewer on the reflective layer 12 side and a rear surface on the relief structure forming layer 11 side. Alternatively, the relief structure forming layer 11 side may be a front surface facing the viewer and the reflective layer 12 side may be a rear surface. Here, as an example, the relief structure 1 has a front surface facing the viewer on the relief structure forming layer 11 side and a rear surface on the reflective layer 12 side.

The relief structure forming layer 11 is a layer having visible light transparency. According to one example, the relief structure forming layer 11 is a colorless and transparent film or sheet. The relief structure forming layer 11 may be provided on a substrate (not shown), but the substrate is not necessarily provided, and the relief structure forming layer 11 may be composed of only the relief structure forming layer and the reflective layer.

The interface between the relief structure forming layer 11 and the reflective layer 12 and the surface of the reflective layer 12 form a corrugated reflective surface RSa, as shown in FIG. 1.

As shown in Figs. 1 to 3, the corrugated reflective surface RSa includes a plurality of first inclined surfaces IS1 and a plurality of second inclined surfaces IS2. Each of the first inclined surfaces IS1 and the second inclined surfaces IS2 has a shape that extends in a first direction parallel to the display surface. Here, the first direction is the X direction.

The first inclined surface IS1 is perpendicular to the display surface and inclined at a positive angle (clockwise angle) with respect to a reference plane that is parallel to the first direction. The second inclined surface IS2 is inclined at a negative angle (counterclockwise angle) with respect to the reference plane. The first inclined surface IS1 and the second inclined surface IS2 are arranged alternately in a second direction (=Y direction) that is parallel to the display surface and perpendicular to the first direction.

As shown in FIG. 3, the first inclined surfaces IS1 are regularly arranged with a period T1. The arrangement of the first inclined surfaces IS1 constitutes a first diffraction grating having a first lattice constant d1 (=T1) corresponding to the period. The first lattice constant d1 is in the range of 700 nm to 1100 nm.

On the other hand, the second inclined surfaces IS2 are regularly arranged with a period T2 that is longer than the period T1. The arrangement of the second inclined surfaces IS2 forms a second diffraction grating having a second lattice constant d2 (=T2) that is larger than the first lattice constant d1. The second lattice constant d2 is in the range of 800 nm to 1200 nm.

In the following description, including FIG. 1, the second lattice constant d2 that determines the period T2 of the arrangement of the second inclined surface IS2 is often greater than the first lattice constant d1 that determines the period T1 of the arrangement of the first inclined surface IS1. However, in the color shifting device of the present invention, in two or more relief structures, the arrangement of the first inclined surface or the arrangement of the second inclined surface is composed of either a first diffraction grating having the first lattice constant d1 or a second diffraction grating having a second lattice constant d2 larger than the first lattice constant d1, and at least one of the first lattice constant d1 or the second lattice constant d2 of at least two relief structures of the two or more relief structures is different. The fact that at least one of the first lattice constant d1 or the second lattice constant d2 is different means that the colors perceived when viewed in the forward direction or the reverse direction are different when comparing two or more relief structures.

The relief structure, which is a component of the color shifting device of the present invention, may include a relief structure in which the first lattice constant d1 is equal to the second lattice constant d2. The fact that the first lattice constant d1 is equal to the second lattice constant d2 means that the color seen when viewed in the forward direction or the reverse direction is the same.

It is preferable that the first lattice constant d1 and the second lattice constant d2 satisfy the relationship shown in the following equation.

T12 = d1 x (n + 1) = d2 x n
Here, T12 is the period of the array obtained by combining the array of period T1 and the array of period T2, and n is an integer of 2 or more. It is preferable that n is an integer of 5 or more. Also, it is preferable that n is an integer of 12 or less, and more preferably 9 or less. When n is made smaller, the period T12 becomes shorter.

When T12 becomes short, down to the wavelength level, the diffracted light with a period of T12 dominates the whole, and blazing progresses, so that the arrangement with period T12 has a greater effect on the color shift effect brought about by the arrangement with periods T1 and T2. Conversely, if n is made excessively large, it also becomes difficult to perceive the color shift effect described below.

More specifically, T12 is made significantly larger than the wavelength of visible light (≧4000 nm), and the T1 and T2 periods are set to the wavelength level of visible light. By making the T1 and T2 periods the size of the wavelength level of visible light, it is possible to visually confirm the observed colors according to the respective diffraction angles of the diffracted light of the T1 period and the diffracted light of the T2 period, and to confirm the difference between the observed colors of the T1 period and the T2 period. If the period sizes of T1 and T2 are too large or too small, the color shift effect is weakened, so optimization is required.

The ratio d1/d2 of the first lattice constant d1 to the second lattice constant d2 is preferably in the range of 0.833 to 0.917, and more preferably in the range of 0.875 to 0.9. When the ratio d1/d2 is close to 1, it becomes difficult to perceive the color shift effect described below. Conversely, when the ratio d1/d2 is excessively large, there is a possibility that the wavelength of one of the diffracted light emitted by the array with period T1 and the diffracted light emitted by the array with period T2 falls outside the visible light range.

In addition, if the convex and concave portions of the uneven structure are too thin, it becomes difficult to reproduce, so a third periodic component may be mixed in as long as it does not interfere with the color shift effect due to the difference between T1 and T2 and does not make the difference between T1 and T2 too small.

The cross sections perpendicular to the first direction of each of the first inclined surface IS1 and the second inclined surface IS2, here the cross sections perpendicular to the X direction, are curved. These cross sections do not have to be curved, but when they are curved, the color shift effect is more easily perceived compared to when they are not curved, as described below.

The ratio S1/S0 of the area S1 of the region of the corrugated reflective surface RSa that is parallel to the display surface (= the flat region at the top of the corrugation) to the area S0 of the orthogonal projection of the entire corrugated reflective surface RSa onto the display surface is preferably 0.5 or less, and more preferably 0.15 or less. If the ratio S1/S0 is made smaller, the uneven structure becomes more acute, and as described below, the color shift effect becomes easier to perceive. The ratio S1/S0 preferably includes a value equal to or close to zero.

The reflective layer 12 shown in FIG. 1 covers the surface of the relief structure forming layer 11 on which the relief structure is provided. The reflective layer 12 has visible light reflectivity.

The reflective layer 12 may be a metal layer made of a metal material such as aluminum, silver, gold, or an alloy thereof. Alternatively, the reflective layer 12 may be a dielectric layer having a refractive index different from that of the relief structure forming layer 11. Alternatively, the reflective layer 12 may be a laminate of dielectric layers having different refractive indices between adjacent layers, i.e., a dielectric multilayer film. In this case, it is desirable that the refractive index of the dielectric layer in contact with the relief structure forming layer 11 among the dielectric layers contained in the dielectric multilayer film is different from that of the relief structure forming layer 11.

Figure 4 is a schematic cross-sectional view showing the relief structure surface of the relief structure 1 shown in Figure 1 illuminated with white light from its normal direction and viewed from the first observation position (OP1) direction (forward direction) and the second observation position (OP2) direction (reverse direction).

In FIG. 4, reference symbol LS is a light source that emits white light. Reference symbol OP1 denotes a first observation position, and reference symbol OP2 denotes a second observation position. The first observation position OP1 and the second observation position OP2 are symmetrical with respect to a plane that passes through the center of the relief structure 1 and is perpendicular to the Y direction. In this application, the case where the relief structure 1 is viewed from the first observation position OP1 is referred to as "forward viewing," and the case where the relief structure 1 is viewed from the second observation position OP2 is referred to as "reverse viewing."

Naturally, when viewed backwards, the top, bottom, left and right of the patterns and letters are reversed compared to when viewed forward.

Figure 5(a) is a schematic plan view illustrating a portion of the relief structure 1 constituting the color shifting device of the present invention. Figure 5(b) is a schematic cross-sectional view showing the state in which the relief structure surface of the relief structure shown in Figure 5(a) is illuminated with white light from the normal direction and observed from the forward direction (forward viewing), and Figure 5(c) is a schematic cross-sectional view showing the state in which the same structure is observed from the reverse direction (reverse viewing).

As mentioned above, when a typical diffraction grating with a rectangular or sinusoidal cross section is illuminated with white light from the normal direction and then inverted and observed from an oblique direction at the same angle (i.e., the forward and reverse views are performed at the same angle θ), the image is inverted before and after the rotation, but the angle θ of the diffracted light with respect to the normal direction (diffraction angle) is the same in the forward and reverse directions, so the image displayed is the same color.

Under the same conditions, a diffraction grating with a sawtooth cross section, i.e. a blazed diffraction grating, can display images with different brightness levels when viewed from the forward and reverse directions. However, as mentioned above, if the diffraction angle is the same, the saturation and hue of the images do not change.

In contrast, in the relief structure 1 constituting the color shifting device of the present invention, as shown in Figures 1 to 3, one of the opposing side surfaces of the relief structure is a first inclined surface IS1, and the other is a second inclined surface IS2. Furthermore, the period T1 of the first inclined surface IS1 and the period T2 of the second inclined surface IS2 are different (T1<T2 in this example).

Therefore, when the relief structure constituting the color shifting device of the present invention is viewed in the forward direction (FIG. 5(b)) and the backward direction (FIG. 5(c)), the diffraction angle is larger in the former case by an amount that depends on the shorter period T1. Therefore, when the relief structure is viewed in the forward direction and the backward direction from the same angle θ, the former case appears green, for example, and the latter case appears red, for example.

The first inclined surface IS1 is inclined at a positive angle with respect to the reference plane. Therefore, when the first diffraction grating formed by the first inclined surface IS1 is illuminated with white light from the normal direction, it reflects light within the negative angle range and emits stronger diffracted light than light within the positive angle range.

On the other hand, the second inclined surface IS2 is inclined at a negative angle with respect to the reference plane. Therefore, when the second diffraction grating formed by the second inclined surface IS2 is illuminated with white light from the normal direction, it reflects light within the positive angle range and emits stronger diffracted light than light within the negative angle range.

(Method of Making Relief Structure and Color Shifting Device)
An example of a method for producing a color shifting device of the present invention having a relief structure as a constituent element will be described based on the relief structure data.

First, a metal stamper is created using photolithography as shown below to form the concave-convex structure.

First, a photosensitive resist material is applied to a smooth substrate (a glass substrate is typically used) to form a resist material layer with a uniform thickness. As the photosensitive resist material, a publicly known positive or negative material can be used. Next, a desired pattern based on the uneven structure data for the display device is written onto the resist material layer using a charged particle beam.

The resist material layer is then developed to obtain a resist structure with the desired unevenness.

When a low-sensitivity material is used as the photosensitive resist material, the degree of solubility or insolubility can be made different between certain regions by varying the intensity of the charged particle beam or the number of times of irradiation between those regions. Therefore, by utilizing this, it is possible to obtain a resist pattern in which the surfaces of the convex and concave portions are curved like the reflective surface RSa shown in Figures 1 to 3.

Next, this resist structure is used as a master plate, and a metal stamper is produced from this master plate by a method such as electroforming. Electroforming is a type of surface treatment technology in which the object to be electroformed is immersed in a specific aqueous solution and an electric current is passed through it, causing the reducing power of electrons to form a metal film on the object.

By using the above method, it is possible to accurately replicate the fine uneven structure on the surface of the original plate. The surface of the object to be electroformed must be electrically conductive. However, photosensitive resists generally do not conduct electricity, so before electroforming, a thin metal film is formed on the surface of the resist structure by sputtering or a vapor phase deposition method such as vacuum deposition.

Next, the above stamper is used to replicate the relief structure on the surface of the relief structure forming layer. First, a thermoplastic resin, a thermosetting resin, a radiation curing resin, or the like is applied to a light-transmitting substrate made of, for example, polycarbonate or polyester. Next, the stamper is attached to this coating, and in this state, heat and pressure are applied or light or electron beams are irradiated. After that, the stamper is peeled off from the resin layer to obtain a relief structure forming layer with a relief structure.

In the above, photolithography was used as the method for producing the master plate, but other methods such as machining the surface of a metal or the like by cutting or etching can also be used. Using such methods, it is possible to directly machine the surface of a metal plate, and in this case, a metal stamper can be produced directly without having to produce a metal stamper by a method such as electroforming.

Next, a metal such as aluminum or a dielectric is deposited in a single layer or multiple layers on the prepared relief structure forming layer by, for example, a vapor phase deposition method such as vacuum deposition or sputtering to form a reflective layer. Note that when only a portion of the relief structure forming layer is to be covered with a reflective layer, this can be achieved, for example, by forming the reflective layer as a continuous film by a vapor phase deposition method, and then removing a portion of it with a chemical or the like.

By the above-mentioned method, a relief structure (reference number 1 in FIG. 1) can be produced. The relief structure may be provided with various known functional layers, such as an intermediate layer, a printing layer, a protective layer, an adhesive layer, or an adhesive layer, as appropriate.

A single relief structure may be used as a color shifting device, or multiple relief structures may be combined to be used as a color shifting device.

The color shifting device may be used as a labeled display device by adhering it to an article via an adhesive or the like, or the color shifting device may be produced as a transfer foil and transferred to an article.

(Application Example 1)
6 and 7, schematic plan views illustrating parts of the relief structures (1) to (5) constituting an embodiment of the color shifting device of the present invention are shown in the upper part, and the appearance of colors when observed from the forward direction and the reverse direction are shown in the lower part. Note that the observation angle is the same with respect to the display surface in both the forward direction and the reverse direction.

Of the relief structures (1) to (5) in Figures 6 and 7, relief structures (1) and (5) have the same arrangement of the relief structures in the Y direction, while relief structure (3) has the arrangement of the relief structures in the Y direction reversed from that of relief structures (1) to (5). Therefore, unlike the relief structures so far, the lattice constant that determines the period T1 (shown as Y) at which the first inclined surfaces IS1 are arranged is the second lattice constant d2, and the lattice constant that determines the period T2 (shown as B) at which the second inclined surfaces IS2 are arranged is the first lattice constant d1.

The relief structure in Figure 6 (1) is fabricated to have a period T(Y) such that it appears yellow (Y) when viewed in the forward direction, where the first inclined surface IS1 (see Figures 1 to 3) dominates, and a period T(R) such that it appears red (R) when viewed in the reverse direction, where the second inclined surface IS2 dominates. Here, T(R) is greater than T(Y).

The relief structure in Figure 6 (2) has projections and recesses of a certain size arranged in the Y direction. Therefore, it is made to have a period T (Y) that appears yellow (Y) when viewed from both the forward and reverse directions.

The relief structure in FIG. 6 (3) has a reversed arrangement of the relief structure in the Y direction compared to relief structure (1). Therefore, the relief structure in FIG. 6 (1) is produced to have a period T(Y) that makes it appear yellow (Y) when viewed in the forward direction, where the first inclined surface IS1 dominates, and a period T(B) that makes it appear blue (B) when viewed in the reverse direction, where the second inclined surface IS2 dominates. Here, T(Y) is greater than T(B).

The relief structure in Figure 7 (4) has projections and recesses of a certain size arranged in the Y direction. Therefore, it is made to have a period T (B) that appears blue (B) when viewed from both the forward and reverse directions.

The relief structure in Figure 7 (5) has the same arrangement of the concave-convex structure in the Y direction as the relief structure in Figure 6 (1), but is fabricated to have a period T (V) that appears purple (V) when viewed in the normal direction, and a period T (B) that appears blue (B) when viewed in the reverse direction. Here, T (B) is larger than T (V).

In addition, in FIG. 6 and FIG. 7, the number of projections and recesses in the projection-recess structure is depicted as eight or nine, but this is for convenience. If the projections and recesses are arranged in order of periodic length, they are as follows:
T(V) < T(B) < T(Y) < T(R)
It is.

Figures 8(a) to (d) are plan views showing how colors appear when one embodiment of the color shifting device of the present invention is constructed using the relief structures (1) to (5) of Figures 6 and 7.

In each of Figures 8(a) to (d), any of the relief structures (1) to (5) in Figure 6 or Figure 7 are arranged in three rows and three columns. Specifically, the relief structure in Figure 6(3) is arranged in the center, and the eight relief structures arranged around it are the relief structure in Figure 6(2) in Figure 8(a), the relief structure in Figure 7(4) in Figure 8(b), the relief structure in Figure 6(1) in Figure 8(c), and the relief structure in Figure 7(5) in Figure 8(d).

From the color appearance explained in Figures 6 and 7, in Figures 8(a) and (c), the central square is clearly perceived as a different color from the surrounding squares and is blue only when viewed in the reverse direction, while the entire square is perceived as the same yellow color when viewed in the normal direction. Also, in Figures 8(b) and (d), the central square is clearly perceived as a different color from the surrounding squares and is blue only when viewed in the normal direction, while the entire square is perceived as the same color (blue in both (b) and (d)) when viewed in the reverse direction.

(Application Example 2)
9(a) to (d) are plan views showing a second application example of the color shifting device of the present invention.

In FIG. 9(a), the entire surface appears to be the same color when viewed from the normal direction, but the a2 portion has a relief structure that is different from the a1 portion of the background. In other words, the relief structure of the a1 portion appears to be the same color when viewed from the normal direction and the reverse direction, but the relief structure of the a2 portion has a different color when viewed from the normal direction when viewed from the reverse direction. As a result, there is a color shift effect that gives the impression that the a2 portion appears when viewed from the reverse direction.

In Figure 9(b), the entire surface appears to be the same color when viewed from the normal direction, but part b2, which depicts the contour line, has a different relief structure from part b1, the background. In other words, the relief structure of part b2 appears to be the same color when viewed from both the normal direction and the reverse direction, but the relief structure of part b1 appears to be a different color when viewed from the normal direction when viewed from the reverse direction. As a result, when viewed from the reverse direction, the figure does not change, but there is a color shift effect in which the background color of part b1 changes, giving the impression that the number of colors has changed.

Figure 9 (c) is divided into part c1 and parts c2 and c3 of the pattern, but part c1 is a part that does not have a structure with a coloring function, and parts c2 and c3 have different relief structures. In other words, parts c2 and c3 are the same color when viewed from the normal direction, but when viewed from the reverse direction, part c2 does not change color, but part c3 is made to be a different color. Therefore, the figure is partially colored, and there is a color shift effect in which the number of colors changes.

In FIG. 9(d), when viewed from the normal direction, the character "8" appears against the background of part d1, but in reality the character pattern is divided into parts d2 and d3, each of which has a different relief structure. In other words, when viewed from the reverse direction, part d2 does not change color, but parts d1 and d3 are made so that part d3 has the same color as part d1 when viewed from the normal direction, and part d1 has the same color as d2. Therefore, when switching from normal viewing to reverse viewing, the character "8" changes to the character "5," creating a color shift effect that combines the function of swapping the colors of the figure and the background and the function of deforming the figure.

As mentioned above, the color shifting device of the present invention can change not only the color but also the number of colors and shapes, making it easier to capture changes in the image even if the observation conditions change.

1...Relief structure 11...Relief structure forming layer 12...Reflective layer IS1...First inclined surface IS2...Second inclined surface RSa...Reflective surface T1, T2, T12...Period LS...Light source OP1...First observation position OP2...Second observation position a1, b1, b2, c1, c2, c3, d1, d2, d3...Viewing portions a1', b1', b2', c1', c2', c3', d1', d2', d3' when viewed in the normal direction
...Viewing part by looking in the opposite direction

Claims (8)

1. A color shifting device comprising a plurality of relief structures,
each of the plurality of relief structures extends in a first direction parallel to a display surface of the color shifting device and has a concave-convex structure arranged in a second direction perpendicular to the first direction;
the concave-convex structure has a wave-shaped reflecting surface consisting of a first inclined surface and a second inclined surface,
the first inclined surfaces and the second inclined surfaces are alternately arranged in the second direction,
the first inclined surface is inclined at a positive angle with respect to a reference plane that is perpendicular to the display surface and parallel to the first direction ;
the second inclined surface is inclined at a negative angle with respect to the reference surface,
The plurality of relief structures include
the relief structure includes two or more relief structures in which a first lattice constant d1, which is an arrangement interval of the first inclined surfaces, is 700 nm or more and 1100 nm or less, and a second lattice constant d2, which is an arrangement interval of the second inclined surfaces, is 800 nm or more and 1200 nm or less and is larger than the first lattice constant d1, such that a maximum dimension in the second direction of a convex structure formed by a pair of adjacent first inclined surfaces and second inclined surfaces in the relief structure gradually increases as it proceeds in one direction in the second direction ,
Two of them have at least one of the first lattice constant d1 and the second lattice constant d2 that is not the same value .
A color shifting device comprising: The plurality of relief structures include a relief structure in which the first lattice constant d1 and the second lattice constant d2 are the same .
2. The color shifting device of claim 1. The plurality of relief structures have the first lattice constant d1 and the second lattice constant d2,
Equation: d1 x (n + 1) = d2 x n
wherein n is an integer equal to or greater than 2.
3. A color shifting device according to claim 1 or 2. The ratio d1/d2 of the first lattice constant d1 to the second lattice constant d2 is in the range of 0.833 to 0.917.
A color shifting device according to any one of claims 1 to 3. The first inclined surface and the second inclined surface have cross sections perpendicular to the first direction, and the cross sections are both curved.
A color shifting device according to any one of claims 1 to 4. a ratio S1/S0 of an area S1 of a region of the corrugated reflective surface that is parallel to the display surface to an area S0 of an orthogonal projection of the corrugated reflective surface onto the display surface is 0.5 or less;
A color shifting device according to any one of claims 1 to 5. the plurality of relief structures are in the form of a film or sheet;
A color shifting device according to any one of claims 1 to 6. a reflective layer having the reflective surface; and a relief structure forming layer supporting the reflective layer and having a relief structure having a shape corresponding to the reflective surface on a surface in contact with the reflective layer,
A color shifting device according to any one of claims 1 to 7.