HK1010859B - Paired optically variable device and method therefore - Google Patents

Description

Light-matching optically variable material and method for generating a coloured reflection

The present invention relates to paired optically variable material bodies with optically variable pigments, as well as inks, paints and metal foils using the same, and a method.

The color produced by the interference film can be found in natural fish-phosphor, nacre layers, and the like. Naturally occurring mica, oil film and soap lather all exhibit to some extent a rainbow scale. This iridescence or color change is a direct result of light reflection from the parallel interfaces of the single or multilayer film as the viewing angle is changed. Generally, the greater the difference in refractive index across the interface, the stronger the color effect. The interference of light produces color. Maximum destructive interference of reflected light occurs when the thickness of the layer is an odd multiple of a quarter wavelength, and maximum constructive interference of light occurs when the thickness of the layer is an even multiple of a quarter wavelength. The breaking of iridescent coatings, known as pearlescent pigments, into small pieces is described in U.S. Pat. Nos. 3,087,828 and 3,123,490. These pearlescent pigments are composed of a single layer or multiple layers having an optical thickness of 10 to 100 nm, and are typically prepared by vacuum deposition. These pearlescent pigments are white or silver in color and have very low color saturation, regardless of viewing orientation. The color is mainly generated by pure fresnel light reflection, scattering and/or absorption. In many applications, greater color saturation, i.e., chroma, is desired than pearlescent pigments. In addition to the color shades, different colors and different shades of color produced with optically variable pigments are also required. A large number of such colors are particularly desirable for countless security and other applications.

In general, it is an object of the present invention to provide a paired optically variable material body and method utilizing paired optically variable pigments to achieve different color matching useful in inks, paints and foils.

It is another object of the present invention to provide a paired body of optically variable material and method in which the paired pigments have the same color at one angle and a different color at all other angles.

It is a further object of the present invention to provide a paired optically variable device and method of the above character in which the pigment has a high degree of chroma.

It is a further object of the present invention to provide a body of paired materials and a method of the above character in which additives are provided to achieve substantially the same hue for the paired pigments when viewed at an angle.

It is yet another object of the present invention to provide a paired optically variable device and method of the above character which can be readily incorporated into printing inks.

It is still another object of the present invention to provide a paired optically variable device and method of the above character which can be easily incorporated into paint.

It is still another object of the present invention to provide a paired optically variable device and method of the above character which readily enables the incorporation of the device into a metal foil.

It is still another object of the present invention to provide a mating body of optical material having the above characteristics that can be incorporated into polymeric films, casting films, and molded parts.

It is a further object of the present invention to provide paired optically variable devices having the above characteristics which are not bleached by ultraviolet light.

It is still another object of the present invention to provide paired optically variable devices that can be paired with other paired optically variable devices.

It is yet another object of the present invention to provide a light-matching variable material body that can be used with non-fading interference pigments.

It is yet another object of the present invention to provide paired optically variable pigments that can incorporate therein certain symbols that are visible only at predetermined angles.

The present invention provides a paired optically variable device comprising a substrate having a first surface, wherein first and second bodies of optical material are carried by said first surface, at least one of the first and second bodies of optical material being optically variable, forming pairs of first and second bodies of optical material carried by the first surface of the substrate in spaced apart, non-overlapping positions on the first surface of the substrate to allow simultaneous observation by the human eye, said first and second bodies of optical material having the same matching colour for an angle of incidence between 0 ° and 90 ° without colour matching at all other angles of incidence, said first and second bodies of optical material being pigments, specularly reflective foils or multilayer thin film interference laminates.

The invention also provides a method of producing coloured reflections on a substrate having a first surface and first and second volumes of optical material formed from layers carried by the first surface, at least one of the first and second volumes of optical material being optically variable, forming pairs of the first and second volumes of optical material carried by the first surface of the substrate in spaced apart but non-overlapping positions on the first surface of the substrate to allow simultaneous viewing by the human eye, the method being characterised by comprising the steps of: forming the at least one volume of optical material having a color for an angle of incidence that is the same as a color of a second volume of optical material at the same angle of incidence; illuminating paired bodies of optical material with a light source such that the paired bodies reflect the same color for an angle of incidence between 0 ° and 90 ° and do not match color at all other angles of incidence, said first and second bodies of optical material being pigments, specularly reflective foils, or multilayer thin film interference stacks.

Additional objects and features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. In the drawings:

FIG. 1 is a plan view of a paired optically variable device of the present invention comprising paired optically variable pigments.

Fig. 2 is a sectional view taken along line 2-2 of fig. 1.

FIG. 3 is a graphical representation of the examples shown in tables I, II and III and shows the color matching of the mated design when light source A is illuminated at a 10 angle.

Fig. 4 is a graphical representation similar to that shown in fig. 3, but showing the color divergence when illuminated with light source a at a 45 ° angle.

FIG. 5 is a graphical representation of the examples shown in tables IV, V and VI showing the color divergence of the mated design when illuminated at 10 with light source A.

FIG. 6 is a graphical representation of the examples in tables IV, V and VI showing the color matching of the mated design under illuminant A when illuminated at 45.

FIG. 7 is a graphical representation of the examples shown in tables VII, VIII and IX showing the color matching of the mated design when illuminated with light source C at an angle of 10.

Fig. 8 is a graphical representation of the example shown in fig. VII to IX, showing the color divergence of the mated design when illuminated with light source C at a 45 ° angle.

FIG. 9 is a graphical representation of the example shown in tables X, XI and XII, showing the color divergence of the mated design when illuminated with light source C at an angle of 10.

FIG. 10 is a graphical representation of the examples shown in tables X, XI and XII showing the color matching of the mated design when illuminated with light source C at a 45 angle.

FIG. 11 is a graphical representation of an example shown in tables XIII, XIV and XV showing the color matching of the mated design when illuminated at an angle of 10 with light source F.

FIG. 12 is a graphical representation of an example shown in tables XIII through XV showing the color dispersion of the mated design when illuminated at a 45 angle with light source F.

Fig. 13 is a graphical representation of the examples shown in tables XVI through XVIII, showing the color divergence of the mated design when illuminated with light source F at an angle of 10 °.

Fig. 14 is a graphical representation of the examples shown in tables XVI through XVIII, showing the color matching of the mated design when illuminated with light source V at a 45 ° angle.

Fig. 15 is a cross-sectional view of a paired optically variable device incorporating the present invention utilizing a symmetric metal-dielectric interference stack.

Figure 16 is a cross-sectional view of a paired optically variable device body with fully dielectric symmetric interference laminations.

FIG. 17 is a plan view of a pair of paired optically variable material bodies incorporating the present invention and employing paired optically variable pigments.

FIG. 18 is a plan view of a paired optically variable device incorporating the present invention, incorporating a symbol within the device and which is not visible to the human eye at a predetermined angle of incidence.

Fig. 19 is a plan view similar to fig. 18, but viewed at a different angle of incidence at which the "SICPA" symbol incorporated in the paired optically variable devices is visible.

Fig. 20 is a cross-sectional view taken along line 20-20 in fig. 19.

FIG. 21 is a plan view of a paired optically variable device incorporating a dot matrix metal foil incorporating a symbol and which is not visible at an angle of incidence.

Fig. 22 is a view similar to fig. 21 with different angles of incidence, such that the symbols incorporated therein are visible.

Fig. 23 is a cross-sectional view taken along line 23-22 of fig. 22.

Generally, the bodies of optically variable material of the present invention are viewed or used under incident light and include a substrate having first and second surfaces. The first and second bodies of optical material are loaded into first and second spaced apart portions on the first surface of the substrate so as to simultaneously allow viewing by the human eye. The first optically variable pigment is arranged in a first body of optical material and the second optical pigment is arranged in a second body of material. The first and second bodies of optical material have substantially the same color at one angle of incidence and the colors differ from each other at all other angles of incidence.

More particularly, as shown in FIG. 1, the body of optically variable material 11 is comprised of a substrate 12 having first and upper surfaces 13 and a second or lower surface 14, as shown in FIG. 2. Substrate 12 may be flexible or rigid and may be constructed of any suitable material such as paper, plastic, cardboard, metal, and the like. Substrate 12 may be opaque or transparent. The paired optically variable pigments 16 in a polymeric binder are arranged on one of the two surfaces, such as on the first or upper surface 13, as shown in fig. 2, so that they do not overlap each other, but lie in spaces that are physically separated from each other in the plane of the surface 13. When the optically variable material body is observed, the paired optically variable pigments 16 can be observed at the same time.

Thus, as shown in fig. 1, the bodies 11 have a pair of optically variable pigments 16 provided in a first optically variable body or structure 17 and in a second optically variable body or structure 18. The first and second structures 17 and 18 do not overlap each other and are spaced apart from each other but are deposited adjacent each other in an abutting relationship as shown in fig. 2. The first structure 17 is rectangular or square and is arranged in a channel 19 formed by a second, also rectangular or square, structure 18 to form a border or frame around the first structure 17.

The first body of optically variable material 17, or first structure 17, has a first pigment formed from optically variable flakes 21 structured in the manner described herein before to provide an angularly variable first color shift. The second body of optically variable material, or second structure, has a second pigment also comprised of optically variable flakes 22, constructed in a manner described hereinafter, and provides a second angularly-varying color shift. As shown in fig. 2, the pigments 21 and 22 are arranged in a conventional manner in a solidified liquid carrier 23 and 24, respectively, so that the bodies of optically variable material 17 and 18 can have the desired characteristics. For example, assuming an ink is the product produced, a conventional ink vehicle is used, whereas assuming a paint is the desired product, an appropriate type of paint vehicle is used.

In using the first or second pigments or flakes 21 and 22, it is important that the two pigments have the same color when light is at one angle of incidence and a different color when light is at all other angles of incidence. Thus, as an example, the pigments 21 and 22 may be configured such that at an angle of 10 ° of light, the two pigments have the same color, but at any other higher angle of incidence, the two optically variable pigments will have different colors, such as at an angle of 45 ° the colors are significantly different. Conversely, the pigments 21 and 22 may be configured such that they have the same color at a different angle, such as a 45 angle, and a different color at all other angles of incidence. However, it is believed that from 0 ° to 90 °, other color matches can be found. Thus, for example, with the body of material 11 shown in FIG. 1, the pigments 21 and 22 will have the same color or shade at an angle of incidence of about 10. For example green and another colour, at another angle of approximately 45 deg., magenta for the first body 17 and blue for the second body 18. Thus, it can be seen that when the incident angle of the paired optically variable devices 11 shifts from 10 ° to 45 °, a significant color shift difference occurs.

In one embodiment of the invention, as shown in figure 1, the inner first volume of optically variable material (OVD)17 has the following characteristics relative to the outer or second volume of optically variable material (OVD) 18.

External OVD18 internal OVD17

L^* 54.91 L^* 42.69

a^* -32.45 a^* 19.29

b^* -11.48 b^* -51.25

A used above^*And b^*And a recognized standard color space system. In the color space system, colors are drawn in one plane of the International Commission on illumination laboratory (CIELAB) system, where a^*Represent red and green, and b^*Indicating yellow and blue. The brightness of the colours lying on an axis at right angles to a plane from black, or L^*0, to white, to L^*At 100. Thus, at the center of the plane with chromaticity increasing from the center to the periphery of the plane, the color will be gray. The extreme edges of the plane define the highest chromaticity. For example, a laser emitting red light will have a high chromaticity. Between the center and the edge, there are various levels of red, for example, a pink color. Thus, there is a color edge L^*The axis, or the plane in which the axes of color vision luminance values move up and down. For each illuminant-observer combination of tristimulus values, the color coordinates are easily calculated and measured. It is well known to those familiar with color technology that any pigment or any color may have a different appearance depending on the light source. For example, under a fluorescent lamp, one color may be quite different from the color of the color under sunlight or a tungsten lamp. For the present invention, it is important to compare the color match at a certain angle of pigments 21 and 22 under the same light source. Thus, a pigment may be irradiated with energy across a predetermined value of wavelength to provide a pattern of power as a function of wavelength. Light or energy illuminating or striking the pigment at a given wavelength will affect the reflectance profile. The tristimulus values X, Y and Z are generated by integrating the spectral power distribution of the light source with the eye-sensitivity function, typically designated as X, Y and Z and the reflectance spectrum.

By L^*，a^*，b^*(CIELAB) color spaceThe invention is described because the system is the most uniform (color linear) system that has been recognized worldwide to date in practical applications. Thus, in the CIELAB color space, the color of any optically variable material volume can be characterized by three tristimulus values, X, Y, and Z. These tristimulus values account for the spectral distribution of the light source, the reflectance of the optically variable pigments, and the spectral sensitivity of the human eye. L is^*，a^*，b^*Coordinates, and L^*(brightness, C)^*The correlation value of (chroma), h (hue) and the associated color difference, i.e. delta L^*，delta C^*And delta h, are calculated from these X, Y, Z values. The color formula that applies is as follows.

L^*＝116(Y/Y_n)^1/3-16 formula 1

a^*＝500[(X/X_n)^1/3-(Y/Y_n)^1/3]Equation 2

b^*＝200[(Y/Y_n)^1/3-(Z/Z_n)^1/3]Equation 3

c^*＝(a^*+b^*)^1/2Equation 4

h＝arctan(b^*/a^*) Formula 5 wherein X_n，Y_nOr Z_nIs a tristimulus value for an ideal white-light diffuse illuminator and source-viewer combination.

Selecting a design for pairing optically variable pigments such that a is at the design^*b^*There are cross-over points in the figure where the optically variable pigments have the same hue and chroma. The way in which the color of the optically variable pigment varies with angle depends on the ambient lighting conditions. Thus, for the present invention, three different types of illumination are considered. Light source a represents illumination produced at 2856 ° (degrees kelvin) from incandescent (tungsten) light. Illuminant C represents average sunlight with a correlated color temperature of 6770 deg., and illuminant F represents light emitted from a cold white fluorescent light source at a correlated color temperature of 4200 deg.. These three light sources were chosen because they represent the most common form of illumination under both internal and external lighting conditions.

Representative samples of possible designs under illuminant A are shown in tables I through VI below, and in FIGS. 3-6. Thus, as in the example in table I, there are ten examples of paired optically variable pigments shown. In option 1 of table I, design 1 has two quarter-wave thin film interference stacks at 620nm, and design 2 has four quarter-wave interference stacks at 587 nm. For design 1 and design 2 in this example, the colors were nearly identical when the orientation was viewed at 10 °.

TABLE I

Light-matching variable pigments

Light source A is at 10 °

Example design 1 design 2

1) 2qw @620nm and 4 qw @587nm

2) 2qw @691nm and 4 qw @593nm

3) 3 qw @697nm and 5qw @649nm

4) 2qw @510nm and 5qw @671nm

5) 2qw @478nm and 6 qw @674nm

6) 3 qw @498nm and 6 qw @589nm

7) 3 qw @653nm and 5qw @595nm

8) 3 qw @506nm and 6 qw @642nm

9) 2qw @420nm and 5qw @577nm

10) 3 qw @534nm and 4 qw @688nm

Table II set forth below shows L for each pair in examples 1-10 consisting of design 1 and design 2^*，a^*，b^*H and c^*The calculated color value of (2). Example 1 at 10 ° to optically variable pigment, design 1 has an L^*Value 77.85, design 2 has L^*The value was 79.76. Design 1 has L when the angle is shifted to 45^*Value 91.89, and design 2 has L^*The value is 76.77. In addition, Table II shows the calculated color parameters for the design shown in Table I.

TABLE II

Color value (deg representative) example L for the examples in Table I^* a^* b^* h C^* Delta h1) a， 10 deg. 77.85 29.7 62.92 64.73 69.58

a， 45 deg 91.89 -1.91 39.76 92.75 39.81

b， 10 deg. 79.76 29.84 63.08 64.68 69.78 0.05

b， 45 deg. 76.77 -62.02 18.75 163.18 64.792) a， 10 deg. 58.53 36.17 53.01 55.69 64.17

a， 45 deg. 83.1 23.44 55.06 66.94 59.84

b， 10 deg. 78.03 35.82 53.9 56.39 64.72 -0.7

b， 45 deg. 78.58 -58.41 26.6 155.51 64.183) a， 10 deg. 81.33 -52.1 43.3 140.27 67.74

a， 45 deg. 49.72 -30.43 -66.53 245.42 73.16

b， 10 deg. 75.85 -52.49 44.06 139.99 68.53 0.28

b， 45 deg. 48.94 9.95 -53.89 280.46 54.84) a， 10 deg. 92.04 -15.83 27.36 120.05 31.61

a， 45 deg. 78.01 -30.76 -24.94 219.04 39.6

b， 10 deg. 77.84 -15.65 27.6 119.56 31.72 0.49

b， 45 deg. 53.19 -35.35 -33.02 223.05 48.375) a， 10 deg. 87.69 -28.3 4 171.96 28.58

a， 45 deg. 68.76 -25.8 -43.28 239.2 50.39

b， 10 deg. 58.53 -29.83 4.4 171.61 30.15 0.35

b， 45 deg. 75.5 27.99 -0.05 359.91 27.996) a， 10 deg. 44.24 37.16 -4.47 353.15 37.43

a， 45 deg. 71.36 31.84 56.4 60.55 64.77

b， 10 deg. 73.84 37.62 -5.69 351.39 38.05 1.76

b， 45 deg. 65.35 -78.45 15.06 169.13 79.887) a， 10 deg. 68.32 -71.62 -11.06 188.78 72.46

a， 45 deg. 39.55 13.83 -79.77 279.84 80.96

b， 10 deg. 57.19 -71.73 -11.56 189.16 72.66 0.38

b， 45 deg. 60.07 57.93 -31.07 331.79 65.738) a， 10 deg. 41.61 37.4 -19.15 332.89 42.02

a， 45 deg. 68.68 32.58 55.37 59.53 64.24

b， 10 deg. 57.74 38.71 -18.47 334.49 42.89 1.6

b， 45 deg. 77.91 -21.93 29.77 126.39 36.979) a， 10 deg. 70.53 -28.52 -41.34 235.4 50.22

a， 45 deg. 51.31 -12.96 -53.61 256.41 55.15

b， 10 deg. 49.98 -30.65 -40.7 233.02 50.95 2.38

b， 45 deg. 67.43 54.11 -2.19 357.68 54.1510) a， 10 deg. 35.03 35.58 -63.93 299.1 73.16

a， 45 deg. 59.41 33 45 43.83 52.65 55.13

b， 10 deg. 46.5 34.99 -63.1 299.01 72.15 0-09

b， 45 deg. 77.49 36.42 46.37 51.85 58.96

The color difference at a viewing angle of 10, and for each example at a viewing angle of 45, are shown in table III below. Panchromatic difference delta E (Δ E) between the color of the paired optically variable pigments, L, from equation 6^*，a^*And b^*And (3) calculating:

ΔE^*＝[(ΔL^*)2+(Δa^*)2+(Δb^*)2]1/2 equation 6

TABLE III

Total color Difference (DELTAE) of the examples in Table I

Pair-wise total chromatic aberration (Delta E) design pair

Example 10 degree 45 degree

1 1.92 65.45

2 19.52 86.77

3 5.55 42.32

4 14.20 26.50

5 29.20 69.34

6 29.63 117.94

7 11.14 68.83

8 16.20 60.93

9 20.67 86.04

10 11.52 18.50

Design pairs were taken from 10 degrees.

Note: the 45 ° data shows the 10 degree color versus the color difference at 45 °.

Thus the lower the Δ E value, the more the color matching is. Δ E includes not only hue and saturation, but also lightness of the light-variable pigment.

Fig. 3 and 4 are graphical representations presented in tables I, II and III. FIG. 3 is shown at a^*b^*The degree to which the colors of the paired design examples of paired optically variable pigments in color space match in hue and chroma. As can be seen in fig. 3, the colors of each pair are almost identical when oriented at 10 °. However, both designs and each example of each color pair have widely different color characteristics when the color pairs are tilted to 45 °, which is desirable according to the present invention. Thus, ten examples of paired optically variable pigments are provided herein. At 10 °, each example had essentially no hue and chroma differences, but at 45 °, had greatly divergent hue and chroma differences. In the graphs of fig. 3 and 4, the pair designs are identified according to tables I, II and III. Thus, example 1 with design 1 is labeled "1-1" and example 1 with design 2 is labeled "1-2".

In the following tables IV, V and VI eight examples of pairing designs for pairing photo-variable pigments according to the invention are shown, wherein the ten examples given in tables I, II and III achieve the opposite result, wherein the color difference is minimized at 45 ° and the color change occurs at an angular displacement, as shown in the example at 10 °.

TABLE IV

Light-matching variable pigments

Example design 1 design 21) 3 qw with light source "A" at 45 °480nm and 4 qw679nm2) 3 qw 520nm and 4 qw684nm3) 4 qw 604nm and 6 qw625nm4) 2 qw 589nm and 6 qw646nm5) 3 qw 576nm and 6 qw678nm6) 4 qw 568nm and 5qw690nm7) 2 qw 491nm and 5 qw 668nm8) 3 qw 618nm and 5qw637nm

TABLE V

Color value examples for the examples in Table IV

L^* a^* b^* h C^* Delta h11) a， 10 deg. 50.82 36.66 27.48 36.85 45.82

a， 45 deg. 77.26 28.97 56.77 62.96 63.73

b， 10 deg. 47.7 46.3 -62.59 306.49 77.85

b， 45 deg. 79.69 29.26 57.38 62.98 64.41 -0.022) a， 10 deg. 37.69 37.4 -43.45 310.72 57.33

a， 45 deg. 64 33.27 51.52 57.14 61.33

b， 10 deg. 46.92 40.45 -63.25 302.6 75.07

b， 45 deg. 78.5 33.36 51.52 57.08 61.37 0.063) a， 10 deg. 74.39 45.24 34.56 37.38 56.93

a， 45 deg. 81.34 -49.76 40.03 141.19 63.86

b， 10 deg. 62.14 55.64 -23.07 337.48 60.24

b， 45 deg. 76.13 -49.57 40.76 140.57 64.17 0.624) a， 10 deg. 85.13 21.38 58.48 69.91 62.27

a， 45 deg. 91.67 -15.3 25.98 120.49 30.15

b， 10 deg. 57.13 32.12 -16.24 333.18 35.99

b， 45 deg. 78.01 -15.16 26.14 120.11 30.22 0.385) a， 10 deg. 38.07 2.39 -86.75 271.58 86.78

a， 45 deg. 46.99 33.03 -4.13 352.87 33.29

b， 10 deg. 59.37 -38.13 6.59 170.2 38.7

b， 45 deg. 74.75 32.92 -3.34 354.2 33.09 -1.336) a， 10 deg. 83.74 7.45 79.7 84.66 80.04

a， 45 deg. 69.8 -66.9 -7.77 186.62 67.35

b， 10 deg. 76.72 15.34 8.92 30.18 17.74

b， 45 deg. 59.47 -66.82 -7.71 186.59 67.26 0.037) a， 10 deg. 89.99 -24.07 14.12 149.61 27.9

a， 45 deg. 72.65 -28.4 -36.59 232.19 46.31

b， 10 deg. 77.78 -20.8 30.47 124.32 36.89

b， 45 deg. 52.36 -29.21 -36.58 231.39 46.81 0.88) a， 10 deg. 53.77 -52.94 -55.48 226.34 76.69

a， 45 deg. 39.14 30.35 -58.22 297.53 65.65

b， 10 deg. 73.21 -69.53 44.19 147.56 82.38

b， 45 deg. 48.88 30.35 -58.63 297.37 66.02 0.16¹Delta h is at an incident angle of 45 DEG at a^*And b^*Calculated between pairs.

TABLE VI

Total color difference (Delta E)

Examples used in Table IV

Design for Δ E Δ F

10 degrees and 45 degrees

1 90.64 2.52

2 22.06 14.50

3 59.83 5.26

4 80.51 13.66

5 103.96 27.77

6 71.56 10.33

7 20.67 20.31

8 102.89 9.75

The design pair was taken from the 45 design.

Note: the 10 ° data shows a 45 degree to 10 ° color difference.

Graphical representations of the data shown in tables IV, V and VI are shown in fig. 5 and 6 of the accompanying drawings, where fig. 5 shows color divergence at 10 ° with light source a, and fig. 6 shows no color divergence at 45 ° with light source a.

Tables VIII, VIII and IX below, with the same data as tables I, II and III except for light source C, show color matching at 10 ° and color divergence at 45 ° in fig. 7 and 8.

TABLE VII

Light-matching variable pigments

Example design 1 design 21) 2qw with light source "C" at 10 °625nm and 4 qw582nm2) 2 qw 683nm and 4 qw586nm3) 3 qw 692nm and 5qw641nm4) 2 qw 509nm and 5qw662nm5) 2 qw 475nm and 6 qw663nm6) 3 qw 644nm and 5qw586nm7) 3 qw 495nm and 5qw698nm8) 3 qw 501nm and 6 qw630nm9) 2 qw 410nm and 5qw567nm10) 3 qw 528nm and 4 qw674nm

TABLE VIII

Color values of the examples in Table VII

L^* a^* b^* h C^* Delta E1) a， 10 deg. 72.64 20.06 61.26 71.87 64.46

a， 45 deg. 90.38 -7.77 42.78 100.29 43.48

b， 10 deg. 76.96 20.89 60.38 70.91 63.9 0.96

b， 45 deg. 78.94 -67.69 24.79 159.88 72.082) a， 10 deg. 56.51 27.2 52.22 62.49 58.88

a， 45 deg. 81.46 11.68 52.49 77.45 53.78

b， 10 deg. 75.65 26.22 53.5 63.89 59.58 -1.4

b， 45 deg. 79.98 -66.71 29.87 155.88 73.093) a， 10 deg. 82.81 -62.64 49.66 141.59 79.94

a， 45 deg. 54.05 2.14 -59.72 272.05 59.76

b， 10 deg. 76.65 -63.43 50.66 141.39 81.18 0.2

b， 45 deg. 50.87 28.79 -52.27 298.85 59.674) a， 10 deg. 92.3 -22.4 30.75 126.07 38.05

a， 45 deg. 80.93 -22.21 -19.14 220.75 29.32

b， 10 deg. 77.62 -21.83 30.05 126 37.14 0.07

b， 45 deg. 55.54 -22.03 -30.15 233.85 37.345) a， 10 deg. 89.1 29.92 7.74 165.49 30.9

a， 45 deg. 71.49 -6.53 -39.38 260.58 39.92

b， 10 deg. 59.27 30.64 8.59 164.34 31.82 1.15

b， 45 deg. 74.52 27.69 1.75 356.39 27.756) a， 10 deg. 70.39 -64.05 -8.22 187.31 64.58

a， 45 deg. 41.49 56.46 -77.43 306.1 95.83

b， 10 deg. 59.12 -62.93 -9.48 188.57 63.64 1.26

b， 45 deg. 58.86 71.26 -33.23 335 78.637) a， 10 deg. 41.84 41.97 -10.45 346.02 43.25

a， 45 deg. 68.52 21.46 53.63 68.2 57.77

b， 10 deg. 72.02 43.2 -11.02 345.69 44.59 0.33

b， 45 deg. 67.3 -83.81 20.31 166.38 86.248) a， 10 deg. 40.08 46.15 -21.57 334.95 50.95

a， 45 deg. 66.48 22.23 52.91 67.21 57.39

b， 10 deg. 58.15 46.02 -22.39 334.05 51.17 0.9

b， 45 deg. 77.88 -35.97 36.76 134.38 51.439) a， 10 deg. 70.7 -5.86 -41.68 261.99 42.09

a， 45 deg. 51.51 16.22 -50.64 287.76 53.18

b， 10 deg. 51.82 -6.18 -41.04 261.44 41.51 0 55

b， 45 deg. 66.24 55.65 -0.31 359.68 55.6510) a， 10 deg. 35.28 65.89 -64.15 315.77 91.96

a， 45 deg. 57.52 25.14 42.43 59.35 49.32

b， 10 deg. 47.88 66.02 -64.13 315.83 92.04 0.06

b， 45 deg. 76.79 21.61 53.51 68.01 57.71

TABLE IX

Full color difference of pair (Delta E)

Examples used in Table VII

Design for Δ E

10 degrees and 45 degrees

1 4.49 63.60

2 19.21 81.60

3 6.29 27.85

4 14.71 27.67

5 29.85 50.95

6 11 40 49.74

7 30.21 110.42

8 18.09 61.47

9 18.89 65.61

10 12.60 22.51

The design is for a design taken from 10 °.

Note: the 45 ° data shows the color difference at 45 ° for a color pair of 10 °.

The designs corresponding to the designs shown in tables IV, V and VI are shown in tables X, XI and XII under source C instead of source a. Fig. 9 and 10 graphically represent the information shown in tables X to XII and show the color divergence at 10 ° and color match at 45 °.

Table X

Light-matching variable pigments

Light source "c" at 45 ° 1) 3 qw490nm and 4 qw673nm2) 4 qw 600nm and 6 qw617nm3) 2 qw 587nm and 6 qw637nm4) 4 qw 560nm and 5qw680nm5) 3 qw 571nm and 6 qw668nm6) 2 qw 482nm and 5qw657nm7) 2 qw 395nm and 5qw646nm8) 3 qw 612nm and 5qw625nm

TABLE XI

Color values of the examples in Table X

L^* a^* b^* h C^* Delta h1) a， 10 deg. 43.43 38.9 -1.07 358.4 38.91

a， 45 deg. 70.12 20.71 53.98 69.01 57.82

b， 10 deg. 47.94 67.28 -64.17 316.4 92.98

b， 45 deg. 77.06 20.51 54.79 69.48 58.5 -0.472) a， 10 deg. 70.59 43.92 26.21 30.82 51.15

a， 45 deg. 82.82 59.26 46.22 142.1 75.15

b， 10 deg. 60.93 61.29 -27.55 335.8 67.19

b， 45 deg. 76.86 -60.25 46.8 142.2 76.29 -0.113) a， 10 deg. 82.42 10.57 56.87 79.47 57.85

a， 45 deg. 91.91 -21.75 28.77 127.1 36.06

b， 10 deg. 57.36 32.99 -17.27 332.4 37.23

b， 45 deg. 77.83 -21.76 28.84 127 36.13 0.054) a， 10 deg. 82.62 10.03 81.72 97 82.34

a， 45 deg. 71.62 61.4 -5.38 185 61.64

b， 10 deg. 75.75 14.17 7.59 28.19 16.07

b， 45 deg. 61.33 61.68 5.15 184.8 61.9 0.245) a， 10 deg. 41.84 48.94 -82.46 300.7 95.89

a， 45 deg. 45.27 36.34 -7.16 348.9 37.04

b， 10 deg. 60.34 -41.51 12.6 163.1 43.38

b， 45 deg. 73.45 35.39 -6.69 349.3 36.02 -0.456) a， 10 deg. 90.18 -29.4 13.02 156.1 32.15

a， 45 deg. 73.57 -10.13 -35.74 254.2 37.15

b， 10 deg. 77.72 -32.2 36.15 131.7 48.42

b， 45 deg. 54.15 -9.56 -36.36 255.3 37.6 -1.17) a， 10 deg. 65.11 3.21 -49.13 273.7 49.24

a， 45 deg. 47.28 16.19 -47.11 289 49.82

b， 10 deg. 77.22 -54.22 47.36 138.9 71.99

b， 45 deg. 51.67 17.42 -48.07 289.9 51.13 -0.958) a， 10 deg. 57.8 -21.96 -48.94 245.8 53.64

a， 45 deg. 39.33 57.93 -59.39 314.3 82.97

b， 10 deg. 73.45 -86.61 49.34 150.3 99.68

b， 45 deg. 50.08 57.92 -59.69 314.1 83.17 0.15

TABLE XII

Full color difference of pair (Delta E)

Examples used in Table X

Design for Δ E

10° 45°

1 69.34 6.99

2 57.32 6.07

3 81.41 14.08

4 78.28 10.30

5 132.51 28.20

6 26.42 19.44

7 112.94 4.66

8 118.67 10.75

The design is for a design taken at 45 °.

Note: the 10 ° data shows the color difference for the 45 ° color pair.

In tables XIII, XIV and XV shown below, the designs shown correspond to those in tables I to III, with the difference that they are for light source F, instead of light source a, and graphical representations of the data presented there are shown in fig. 11 and 12, where fig. 11 shows the color match at 10 ° and fig. 12 shows the color divergence at 45 °.

TABLE XIII

Light-matching variable pigments

Light source "F" at 10 ° 1) 2qw640nm and 4 qw582nm2) 3 qw 689nm and 5qw644nm3) 2 qw 499nm and 5qw663nm4) 3 qw 656nm and 6 qw684nm5) 2 qw 466nm and 6 qw664nm6) 3 qw 490nm and 5qw694nm7) 3 qw 647nm and 6 qw704nm8) 3 qw 497nm and 6 qw637nm9) 4 qw 620nm and 6 qw605nm10) 3 qw 637nm and 5qw583nm11) 2 qw 405nm and 4 qw 708nm12) 3 qw 525nm and 4 qw677nm

TABLE XIV

Color values of the examples in Table XIII

L^* a^* b^* h C^* Delta h1) a， 10 deg. 70.42 17.33 68.25 75.75 70.42

a， 45 deg. 91.01 -0.06 52.65 90.03 52.35

b， 10 deg. 81.78 18.02 66.68 74 88 69.07 0.87

b， 45 deg. 76.56 -50.36 24.67 153.9 56.082) a， 10 deg. 82.02 -47.88 50.35 133.56 69.48

a， 45 deg. 47.02 3.11 -70.45 272.53 70.52

b， 10 deg. 78.72 -48.35 50.78 133.59 70.12 -0.03

b， 45 deg. 44.8 17.49 -56.3 287.26 58.963) a， 10 deg. 92.38 -18.21 27.65 123.37 33.11

a， 45 deg. 75.84 -14.15 -29 243.98 32.26

b， 10 deg. 82.31 -17.81 27.35 123.08 32.64 0.29

b， 45 deg. 47.84 -18.63 -36.81 243.15 41.254) a， 10 deg. 70.22 -52.74 4.55 175.07 52.93

a， 45 deg. 39.29 36.13 -87.28 292.48 94.46*

b， 10 deg. 56.94 -53.73 5.39 174.27 54 0.8

b， 45 deg. 74.02 41.47 -11.9 343.98 43.145) a， 10 deg. 86.1 -21.62 0.36 179.06 21.62

a， 45 deg. 65.94 -2.79 -48.83 266.73 48.91

b， 10 deg. 50.31 -24.08 1.4 176.68 24.12 2.38

b， 45 deg. 80.28 22.17 -1.29 366.67 22.216) a， 10 deg. 44.03 27.44 -3.71 352.3 27.69

a， 45 deg. 72.06 16.14 59.42 74.8 61.57

b， 10 deg. 79.12 28.38 -4.28 351.43 28.7 0.87

b， 45 deg. 59.34 -62.69 9.29 171.57 63.377) a， 10 deg. 66.41 -49.94 -8.6 189.77 50.67

a， 45 deg. 38.08 41.75 -87.76 295.44 97.18

b， 10 deg. 66.48 -49.32 -7.89 189.09 49.95 0.68

b， 45 deg. 65.69 48.61 -19.05 338.6 52.218) a， 10 deg. 41.58 30.62 -17.96 329.62 35.5

a， 45 deg. 69.56 16.73 58.62 74.07 60.96

b， 10 deg. 52.11 32.22 -18.3 330.4 37.06 -0.78

b， 45 deg. 82.18 -19.46 27.98 124.82 34.089) a， 10 deg. 65.12 50.15 -18.32 339.93 53.4

a， 45 deg. 87.08 -29.95 72.63 112.41 78.57

b， 10 deg. 67.08 50.75 -18.6 339.88 54.05 0.05

b， 45 deg. 73.08 -62.1 47.61 -142.52 78.2510) a， 10 deg. 62.04 -44.38 -23.12 207.52 50.04

a， 45 deg. 37.3 45.43 -85.71 297.93 97

b， 10 deg. 49.09 -44.37 -23.42 207.83 50 17 -0.31

b， 45 deg. 61.23 52.61 -34.86 326 47 63.1111) a， 10 deg. 65.91 -3.46 -49.97 266.03 50.09

a， 45 deg. 48.12 10.55 -55.9 280.68 56.89

b， 10 deg. 43.12 -3.06 -50.61 266.54 50.7 -0.51

b， 45 deg. 68.5 43.66 -6.27 351.83 44.1112) a， 10 deg. 34.16 48.14 -69 304.9 84.13

a， 45 deg. 59.75 18.29 47.59 68.98 50.98

b， 10 deg. 42.9 47.78 -69.2 304.62 84.09 0.28

b， 45 deg. 80.42 20.93 54.69 69 06 58.55

TABLE XV

Total color Difference (DELTAE)

Examples used in Table XIII

Total chromatic aberration (Delta E) design of pairs III.F Delta E

10 degrees and 45 degrees

1 11.49 59.34

2 3.36 20.30

3 37.40 29.41

4 13.34 83.17

5 35.89 55.58

6 35.11 94.28

7 0.95 74.37

8 10.66 49.07

9 2.07 43.08

10 12.95 56.66

11 22.80 63.05

12 8.75 22.01

The design is for a design taken from 10 °.

Note: the 45 ° data shows the color difference at 45 ° for the 10 ° color pair.

In tables XVI, XVII and XVIII below, the data shown correspond to the designs of tables IV and VI, except that light source F is used instead of light source A. Graphical representations of these designs are shown in fig. 13 and 14, where fig. 13 shows the color divergence at 10 ° and fig. 14 shows the color match at 45 °.

TABLE XVI

Light-matching variable pigments

Light source F at 45 deg. 1) 4 qw597nm and 6 qw621nm2) 2 qw 576nm and 6 qw638nm3) 3 qw 566nm and 6 qw666nm4) 5 qw 573nm and 6 qw698nm5) 4 qw 555nm and 5qw677nm6) 2 qw 475nm and 5qw656nm7) 2 qw 394nm and 5qw648nm8) 3 qw 608nm and 5qw627nm

TABLE XVII

Color values of the examples in Table XVI

L^* a^* b^* h C^* Delta h1) a， 10 deg. 75.86 31.97 33.73 46.54 46.47

a， 45 deg. 82 -45.7 46.24 134.66 65.02

b， 10 deg. 58.73 48.61 -21.89 335.75 53.31

b， 45 deg. 79.13 -44.8 46.61 133.86 64.65 0.82) a， 10 deg. 87.43 6.52 61.63 83.96 61.98

a， 45 deg. 91.97 -17.59 26.08 124 31.46

b， 10 deg. 51.8 30.69 -17.82 329.85 35.49

b， 45 deg. 82.27 -17.75 26.59 123.73 31.97 0.273) a， 10 deg. 35.02 43.33 -95.12 294.49 104.53

a， 45 deg. 47.02 24.04 -2.29 354.55 24.15

b， 10 deg. 50.72 -28.44 2.8 174.39 28.58

b， 45 deg. 79.81 24.6 -2.59 353.99 24.74 0.564) a， 10 deg. 45.06 -20.31 -40.84 243.56 45.61

a. 45 deg. 66.06 47.12 -16.88 340.29 50.05

b， 10 deg. 63.59 -52.86 -4.05 184.38 53.01

b， 45 deg. 68.27 47.87 -17.36 340.07 50.92 0.225) a， 10 deg. 87.84 -11.09 92.92 96.81 93.58

a. 45 deg. 64.39 -43.16 -17.6 202.18 46.61

b， 10 deg. 82.22 5.43 9.35 59.86 10.81

b， 45 deg. 52.37 -43.48 -17.16 201.54 46.75 0.646) a， 10 deg. 88.27 -21.64 8.33 158.96 23.19

a， 45 deg. 68.69 -6.07 -44.24 262.19 44.66

b， 10 deg. 81.49 -29.72 37.27 128.57 47.67

b， 45 deg. 46.21 -4.92 -45.15 263.78 45.42 -1.597) a， 10 deg. 61.81 1.24 -55.67 271.27 55.68

a， 45 deg. 45.3 10.27 -52.64 281.04 53.64

b， 10 deg. 79.83 -42.51 47.11 132.06 63.46

b， 45 deg. 45.01 10.35 -53.08 281.04 54.08 08) a， 10 deg. 49.35 -13.76 -62.1.2 257.51 63.62

a， 45 deg. 38.39 41.5 -63.37 303.22 75.75

b， 10 deg. 72.05 -67.21 51.64 142.46 84.75

b， 45 deg. 45.64 41.56 -63.88 303.04 76.21 0.18

TABLE XVIII

Total color difference (DELTA E)

Examples used in Table XVI

Full color difference of pair (Delta E)

Design for Δ E

10 degrees and 45 degrees

1 60.53 3.303

2 90.37 9.71

3 122.42 32.80

4 52.50 2.38

5 85.37 12.03

6 30.80 22.53

7 113.15 0.53

8127.727.27 design vs. the design taken at 45 deg.. Note: the 10 ° data shows the color difference at 10 ° for the 45 ° color pair.

In viewing the data shown in the above table, it can be seen that there is a color difference with different types of illumination. In other words, under one light source there may be an exact color match and under another light source there may no longer be an exact color match. Thus, there is a color change, conventionally referred to as metamerism. In looking at table III, example 1 gives the lowest color difference of 1.92 and example 6 gives the highest color difference of 29.63 for a 10 ° color matched design. Table VI shows the color match at 45 °, with example 1 having a minimum color difference of 2.52 and example 5 having a maximum color difference of 27.77. Similar analysis can be performed for tables IX, XII, XV and XVIII, Table IX giving a minimum of 4.49 and a maximum of 30.21, Table XII a minimum of 4.66 and a maximum of 28.2, Table XV a minimum of 0.95 and a maximum of 37.4 and Table XVIII a minimum of 0.53 and a maximum of 32.8.

Similarly, the data in tables I through XVIII can be analyzed to determine the pairing designs under light sources A, C, and F, as shown in Table XIX below.

TABLE XIX

Panchromatic difference for matching light variable pigments

Dielectric thickness traces taken under light sources "A", "C", and "F

Delta E designs 1 and 2 for light source angle

1A 101.922 qw @620 and 4 qw @587

3A 105.553 qw @697 and 5qw @649

1A 452.523 qw @480 and 4 qw @679

3A 455.264 qw @604 and 6 qw @625

1C 104.492 qw @625 and 4 qw @582

3C 106.293 qw @692 and 5qw @641

7C 454.662 qw @395 and 5qw @646

2C 456.994 qw @600 and 6 qw @617

7F 100.953 qw @647 and 6 qw @704

9F 102.074 qw @620 and 6 qw @605

7F 450.532 qw @394 and 5qw @648

4F 452.385 qw @573 and 6 qw @698

As can be seen in Table XIX above, two best design pairs have been selected for each light source and at each angle. For example, below light source a, at a 10 ° viewing angle, the color mismatch of the two design pairs is shown to be the lowest. Similarly, under light source A, the two different pair designs have the best color match at a 45 viewing angle. Those pairs having the smallest color difference for the selected viewing angle have been selected. Similarly, two optimal color pairs have been selected below light source C, and similarly, pairs for two different orientations below light source F. Using this criterion, all optimal design pairs are found at a 45 viewing angle below the light source F. The color difference Δ E for the pair was 0.53 at 2qw at 394nm and 5qw at 648 nm by looking up table XIX.

In Table XX shown below, two design pairs are selected in Table XIX and analyzed to determine if there is still a color match under different light sources. When those designs are forced to be made under light source a, the color difference, denoted as Δ E, is 36.44, while when it is placed under light source C, its value is only 6.15. It can thus be seen that when the optimal pair of optically variable pigments under the light source F is placed under different lighting conditions, the color match is no longer an exact color match. Other mating designs were also observed under different light sources to observe the effect in their delta E color difference, which data is listed in table XX.

TABLE XX optimal two pairs of codes under light sources A, C and F: (^*) L^* a^* b^*Color tone c^*Delta E10 degrees, design of light source A (known) at C

1 4C1 74 19.13 60.87 72.55 63.8 12.52

4C2 75.31 27.54 51.69 61.95 58.56

2 4C1 83.46 -59.1 54.67 137.23 80.51 15.77

4C 277.45-48.4144.75137.2565.9245 degrees, design of illuminant A (known) at C

1 4C1 73.58 18.87 54.16 70.79 57.35 11.19

4C2 75.42 27.01 46.7 59.96 53.94

2 4C1 83.39 -56.17 50.41 138.09 75.48 14.80

4C2 77.66 -45.77 41.57 137.76 61.83

To code (^*) L^* a^* b^*Color tone c^*Delta E10 degrees, design of light source A (known) at F

1 7F1 76.2 15.29 67.44 77.22 69.15 13.84

7F2 79.96 22.85 56.47 67.97 60.92

2 7F1 84.08 -43.8 60.17 126.05 74.43 14.95

7F 280.08-40.9946.04131.6861.6445 degrees, design of illuminant A (known) at F

1 7F1 75.6 15 59.87 75.93 61.72 12.08

7F2 79.79 22.48 51.36 66.37 56.06

2 7F1 84.01 -41.84 55.32 127.1 69.37 13.13

7F2 80.19 -39 43.08 132.16 58.11

To code (^*) L^* a^* b^*Color tone c^*DeltaE10 degrees, C design of light source (known) at A

1 5A1 76.56 30.65 63.38 64.19 70.4 9.83

5A2 81.04 24.43 69.53 70.64 73.7

2 5A1 80.3 -56.04 37.75 146.03 67.57 12.63

5A 274.21-64.2745.14144.9278.5445 degrees, C design of light source (known) at A

1 5A1 44.65 -9.94 -47.69 258.22 48.72 26.98

5A2 48.76 15.53 -55.58 285.61 57.71

2 5A1 80.42 -53.18 35.31 146.42 63.83 11.42

5a 274.5-60.7841.44145.7173.5710 degrees, design of light source C (known) at F

1 7F1 74.77 15.89 67.78 76.8 69.62 7.41

7F2 81.78 18.02 66.68 74.88 69.07

2 7F1 82.84 -46.46 54.11 130.65 71.32 7.93

7F 277.77-52.4152.79134.874.3945 degrees, C design of light source (known) at F

1 7F1 45.55 10.33 -52.99 281.03 53.98 4.12

7F2 44.83 13.98 -54.75 284.32 56.51

2 7F1 82.9 -44.16 50.23 131.32 66.86 7.86

7F 277.88-50.0748.97135.6470.03 pairs of codes (^*) L^* a^* b^*Color tone c^*Delta E10 degree, design of light source F (known) at A

1 5A1 65.98 -70.89 -18.99 195 73.39 28.11

5A2 65.84 -63.36 8.09 172.72 63.88

2 5A1 68.31 55.32 4.94 5.11 55.54 22.70

5 A268.9953.67-17.69341.7656.5245 degrees, design of light source F (known) at A

1 5A1 35.45 -7.52 -26.69 254.27 27.73 36.44

5A2 48.87 11.84 -54.49 282.26 55.76

2 5A1 76.53 -45.75 39.82 138.96 60.66 111.57

5 A269.9250.45-16.31342.0953.0210 degrees, design of light source F (known) at C

1 4C1 71.45 -66.19 -4.28 183.7 66.33 18.17

4C2 69.19 -54.17 9.16 170.41 54.94

2 4C1 62.73 65.58 -12.97 348.82 66.85 14.03

4 C264.5164.5-26.84337.4169.8645 degrees, design of light source F (known) at C

1 4C1 47 16.12 -46.81 289 49.51 6.15

4C2 52.05 12.67 -46.18 285.34 47.88

2 4C1 77.8 -40.92 39.28 136.17 56.72 121.10

4C2 65.7 60.89 -25.17 337.54 65.89

If the present invention is used to prepare optically variable pigments for use in currency security, it will be appreciated that the exchange of banknotes is likely to be carried out under cold fluorescent lighting, as is typical in banks and retail stores. It is therefore believed that design pairs having matching colors under such illumination should be employed, such as light source F set forth above. Using this principle, the best all design pairs would be to contain two quarter waves at 394 nanometers and five quarter waves at 648 nanometers.

While a design pair containing two quarters at 394nm and five quarters at 648 nm is the best of all design pairs, the design at 394nm does not have a large amount of light shift, as can be seen with reference to fig. 13 and 14. The design pair, labeled "7-1" and "7-2", has a color divergence at 10 °, but the color change is small for the two quarter-wave design. Thus, a better design pair is the 4 th pair, which has a design of five quarter waves at 573 nanometers and six quarter waves at 698 nanometers. Both designs have significant color shift with angle. They are clearly chromatically different at 10 ° and have a reasonably good colour match at 45 °.

Referring to tables II, V, VIII, XI, XIV and XVII, it can be seen that the color match, expressed in hue, is an exact match for all practical purposes. The difference Δ E, i.e., the luminance, L, for the various design pairs as shown in tables III, VI, IX, XII, XV and XVIII^*And chroma C^*Slightly varying results. By adding a black or neutral transparent pigment or opaque pigment for the design of the pair with the highest chroma and lightness values, the change in color can be minimized. This addition is done until the luminance and chrominance match the lower chrominance and luminance design of the pair. Thus, all design pairs for color matching can be optimized by the rational addition of other color-improving materials.

All of the above principles can be used with the bodies of optically variable material shown in figure 1, in which paired optically variable pigments utilising these principles can be incorporated into two different bodies of optically variable material 17 and 18 and can be applied in the form of an ink or paint with a suitable carrier for the pigments.

To achieve the high color saturation required in connection with the present invention, and to have a large color shift as a function of viewing angle, interference pigments are used. In these pigments, either metal dielectric or full dielectric interference stacks are employed. A typical metal dielectric asymmetric interference stack 31 can be constructed by arranging a soluble release layer 32 on a flexible web 33 that serves as a substrate, as shown in fig. 15. The multilayer interference film laminate 31 can be removed by passing the web or substrate through a bath. When the soluble release layer dissolves, the thin sheet of interference film 31 breaks into a large number of fragments. Since the chip has two planar surfaces, it is necessary to provide the multilayer interference film or stack with an optical design that is symmetrical and provides the same design on each side. After the chips are collected and washed free of release material, a pigment is produced by grinding the chips to a size of 2 to 200 microns, preferably 2 to 20 microns, without destroying the color characteristics of the chips. The aspect ratio of the chips to the surface and thickness of the chips should be at least 2 to 1 and preferably 10 to 1 to maintain the correct particle orientation when they are placed in the desired carrier for an ink or paint to maximize brightness and color purity of the ink-based paint.

Thus, in accordance with the present invention, a symmetric metal dielectric laminate 31 as shown in fig. 15, which may comprise only three materials and five layers, may be used to produce a strong dichroic variable opaque pigment. It comprises a translucent metal layer 36 formed on a release coating 32 carried by a flexible web 33. Layer 36 is followed by a dielectric layer 37, a thick metal reflective layer 38, another dielectric layer 39 and finally a thin semi-transparent metal layer 41. To produce a hot-pressed dichroic metal foil (i.e., an optically variable metal foil) requires only three layers. These three layers consist of 36, 37 and 38 shown in figure 15. In this form, layers 36 and 38 are inverted. Layer 36 faces the viewer when the multilayer film is separated from release coating 32 and flexible web 33 and adhered to a reverse surface with an adhesive. As an example, each of the thin metal layers 36 and 41 may be comprised of chromium having a nominal thickness of five nanometers, while the dielectric layers 37 and 39 may each be comprised of a suitable dielectric material, such as silicon dioxide having an optical thickness of a number of half-waves at a particular design wavelength. The metallic reflective layer 38 may be comprised of an aluminum layer having a thickness of about 80 nanometers to provide opacity and high reflectivity. Although thicker reflective metal layers may be used, it is believed to be desirable to minimize stress by providing a thin layer in this layer, and to maintain the correct aspect ratio of the pigmented product.

It should be understood that the above-mentioned materials are only an example, and other grey metals, such as nickel and inconel, may be used instead of chromium when n and k (n ═ the real part of the refractive index and k ═ the imaginary part of the refractive index) have a high nk product. Also in place of silicon dioxide, which is a dielectric with a refractive index of 1.46, other low index materials can be used, such as magnesium fluoride with a refractive index of 1.65 or less, such as a refractive index of 1.38, and aluminum oxide with a refractive index of 1.65, or even lower reflective metals, such as chromium, nickel and palladium, can be used for the lower reflective pigments. Instead of aluminum, an optical metal such as gold, copper, and silver may be used as the metal reflective layer.

It should also be appreciated that an asymmetric metal-dielectric interference stack may be provided, if desired. If this is the case, the metallic reflective layer 37 may be formed directly on the release layer, followed by the dielectric layer 39 and the thin metallic semitransparent layer 41. It must be understood that such a three layer design, when removed from the web, will produce a five layer symmetrical laminate relatively low chroma optically variable pigment, but in any event will have a dichroic character, i.e., the color shifts with viewing angle, and can be used to produce a relatively low chroma pair of pigments having a color match at one angle and no color match at any other angle. These pigments will be equivalent to those already described, except that they have a lower overall chroma, so that the designs listed in tables I, IV, VII, X, XIII and XVI surround a^*b^*The origin of the graph yields chroma compression but nonetheless has substantially the same hue match.

If desired, a fully dielectric interference stack may be provided where deemed appropriate, typically where the required additional layers can be provided without undue expense. As shown in fig. 16, a fully dielectric interference stack 51 may be provided on a release coating 52 carried by a flexible web or substrate 53. The dielectric stack includes alternating layers 54 and 56, where 54 and 56 have the designation L₁And L₅A refractive index of 1.35 to 1.65, and expressed as H₁To H₄The high refractive index layer of (2) has a refractive index of 1.7 to 2.4, and a total of nine layers. A wide variety of low and high index materials may be employed in such a multilayer stack. For example, zinc sulfide may be used in combination with magnesium fluoride, and titanium dioxide may be used in combination with silica. Other dielectric materials such as cast, silicon, indium tin oxide, indium oxide, and silicon monoxide may also be used.

A design for a full dielectric stack can be expressed as follows:

(L/2 HL/2)ⁿwhere L and H denote the quarter-wave optical thicknesses of the low and high refractive index layers, respectively, so that L/2 denotes the eighth-wave optical thickness of the low refractive index layer where n.gtoreq.2. Such a multi-layer laminate may be separated from the web 53 in the same manner as previously described herein and reduced to the dimensions previously described herein to provide flakes having a length to width ratio wherein the major planar dimension of the surface is at least two to one, and preferably ten to one, relative to the thickness to maximize the brightness or color purity of the ink or paint employing the pigment flakes, or chips or particles. It will also be appreciated that the first four layers L are simply combined, if desired₁And L₂And H₁And H₂An asymmetric full dielectric stack can be created.

For example, in connection with the above, paired optically variable foils and/or pigments having the same matching colors as found at 0 ° and 45 ° can be used to complete an all dielectric design in which the chromaticity and hue are matchedAnd (4) preparing. Designed from (1 QW ZrO)₂/31 QW SiO₂)³/1 QW ZrO₂And an additional design (1 QW ZrO)₂/3QW SiO₂)³/1 QW ZrO₂A composition wherein the quarter wavelength thickness is 400 nm to 2500 nm. There are three possible matching pairs at 0 deg. and two at 45 deg. for a single quarter wavelength design. In contrast, the 0 ℃ design was analyzed for changes in chroma and hue (1 QQWZrO)₂/3 QWSiO₂O₂)³/1 QW ZrO₂There are two color matching pairs at 45 °, and there are four achievable color matches. Table XXI shows a dielectric pair having a color match at 0 or 45.

With respect to the above, it should be appreciated that simply increasing the logarithm of the dielectric design does not achieve a color matched registration. However, by increasing the thickness of the individual layers, color matched registration can be achieved.

TABLE XXI

Dielectric pair for angularly matching hue and chroma

Design angle design pair a^* b^* L^*(ZrO₂/SiO₂)³ZrO₂0 degree 1 qw @495 nm-43.8-6.4183.61

1 qw@1480nm -45.25 -5.56 57.96

1 qw@540nm -33.6 50.83 90.95

1 qw@1680nm 33.75 54.24 75.20(ZrO₂/SiO₂)³ZrO₂45 degree 1 qw @610 nm-26.6357.3288.97

1 qw@1860nm -26.7 55.05 73.70

1 qw@550nm -37.45 -1.47 83.25

1 qw@1630nm -39.42 -1.2 59.28(ZrO₂/SiO₂)³ZrO₂0 degree 1 qw @590nm 16.1844.1978.33

1 qw@870nm 18.2 42.68 61.57

1 qw@615nm 43.49 17.89 70.62

1 qw@940nm 44.46 16.09 46.57(ZrO₂/SiO₂)³ZrO₂45 degree 1 qw @700nm 45.139.8267.18

1 qw@1030nm 45.68 7.98 48.90

1 qw@760nm 30.4 -20.84 55.39

1 qw@2220nm 31.32 -19.38 51.52

Thus, it can be seen that metal-dielectric and all dielectric interference films can be used in the optically variable pigments employed herein to provide the paired optically variable pigments described heretofore.

The optically variable pigments of the present invention are inherently light fast. This intrinsic property stems from the fact that the color emitted from the pigment is due to interference effects and not based on any chromophore that can be bleached by uv light. All materials employed in the construction of optically variable pigments do not have any color or chromophore and are virtually colorless themselves. For example, metallic aluminum and chromium are silver and gray, while dielectric magnesium fluoride is colorless and transparent.

In fig. 17, a pair of paired optically variable materials of the invention is shown. On the left side of fig. 17, a first or one paired optically variable device 71 is shown, and on the right side, a second or other paired optically variable device 72 is shown, the two devices 71 and 72 having the same color at a certain viewing angle. The body 71 then has a circular, centrally disposed first or inner body 76 of optically variable material received within a circular aperture 77 provided in a second or outer body 78 of square or rectangular shape. Similarly, the second mating optically variable device 72 is formed of a circular inner or first body of optically variable material 81 disposed in a hole 82 of a rectangular or square second or outer body of variable material 83. The two bodies 71 and 72 lie generally in the same plane and are arranged side by side adjacent to each other. The circular body 76 and the square body 83 in the body 71 carry the same optically variable pigment, and similarly, the bodies 81 and 72 of the bodies 78 and 71, respectively, carry the same optically variable pigment.

Thus, as an example shown below, the pigment carried by bodies 76 and 83 may carry a pigment that shifts from green to magenta, while bodies 78 and 81 may carry a pigment that shifts from green to blue. When the bodies 71 and 72 are angled, both bodies 71 and 72 may have the same green colour, whereas when the bodies 71 and 72 are offset at an angle, both bodies will have two colours, the magenta and blue colours of body 71 having a centre of magenta and a boundary of blue, whereas body 72 will have a centre of blue and a boundary of magenta.

For the bodies of optically variable material, batches of optically variable pigments may be taken, which may vary slightly in hue and blend the hue to achieve the same color specification in the same batch throughput. Also, color additive theory may provide a large amount of additional color, if desired.

Furthermore, according to the present invention, there is a metamerism of colors in a certain color under a desired light source, and if it is required to achieve accurate color matching, this can be achieved by using subtractive or additive color addition, thereby achieving an exact color.

Another embodiment of a paired optically variable device 91 is disclosed in fig. 18, 19 and 20, which employs paired optically variable pigments in connection with the present invention. The body 91 of optically variable material is mounted on a substrate 92 having a surface 93 as herein before described. A body of optically variable material 94 having an optically variable pigment in the form of fragments 96 is disposed in a cured transparent carrier 97 on a surface 93. Another body of optically variable material 98 employing an optically variable pigment 99 is disposed in a transparent cured toner carrier 101 on a surface 102 and provides a symbol or message, which may be in the form of a logo 106, for example. At one angle of incidence, the symbol or logo 106, along with the optically variable pigments 96 and 99, has the same color, e.g., green, and the symbol disappears, causing the symbol to be obscured at normal incidence, but to shift in color when the body is tilted to a different angle, e.g., from green to blue with one pigment color and from green to magenta, the symbol or logo appears with the other pigment. Thus, as an example, at normal incidence a green square may appear, while at an angle, the symbol 106 appears blue on a magenta background, as depicted in fig. 19.

The optically variable material body 91 may be manufactured in some way. The optically variable pigment 96 in this example may be a green to magenta optically variable pigment 96 disposed in a solidified liquid carrier 97 on the surface 93. A symbol or logo 106 is then formed on the surface of the solidified liquid carrier 97 by various means. It can be either printed on surface 102 or electrophotographically imaged with a toner. If electrophotographic imaging is used, a toner, which may be transparent or black, may be provided in the form of an image or symbol. Once the toner image is formed on surface 102, the image is then dusted with a counterpart further optically variable pigment 99. This dusting is known as a "bronzing". In light of the above description, optically variable pigment 99 may be a green to blue shifting pigment. To fuse the optically variable pigment 99 to the toner carrier image, the body is covered with a film and passed through a heated laminator. This will melt the toner and allow the embedded pigment 99 to embed in the toner carrier 101. During the melting process, the planar pieces self-align parallel to the surface of the body of material, surface 93. After passing through the laminator, the film is removed from the cured toner image. Since the pigment is sandwiched between the toner and the film, the toner does not stick to the film. Additionally, the logo 106 may be printed using gravure, silk screen, intaglio, or other printing methods.

Another embodiment of a paired optically variable device is shown in fig. 21, 22 and 23, in which a paired optical device 111 is provided on a suitable type of substrate 112. It may be flexible or rigid and may be constructed of cloth, paper, plastic, or the like. The substrate 112 has an upper surface 113 on which are deposited first and second bodies 116 and 117 of optically variable material. The bodies 116 and 117 are in the form of optically variable metal foils 118. Optically variable materials 116 and 117 are placed on surface 113 of substrate 112 by first and second stamps (not shown) aligned with each other in a matrix of dots. As described in the above embodiments of the present invention, the metal foils used in the material bodies 116 and 117 are substantially the same color at the same incident angle, while the color is different at all other incident angles. Thus, as in the above scheme, one of the foils may shift from green to blue and the other from green to magenta, so that at one angle the optically variable metallic foils have the same color, e.g., green, in bodies 116 and 117 and at another angle the optically variable thin film coatings in bodies 116 and 117 have two different colors, blue and magenta. In the dot matrix shown in fig. 21 and 22, the dots 116 employed in the body 111 may be a body of green to blue color shifting material, while the dots 117 may be a body of green to magenta color shifting material. These metal foils can be made either by casting optically variable pigment chips into a release-supported hot stamped polymer film on a flexible substrate or by casting multiple layers of optically variable film coatings as an optically variable specularly reflective metal foil supported by release on a flexible substrate. Thus, in the one-angle stamping matrix transfer shown in fig. 21, all dots have the same color, while in fig. 22, at different angles, the structure of the dots making up the number 20 is made up of a green to magenta shifting material body, so that when the angle of incidence for matching the light variable material body 111 is changed, the dots on the substrate 112 will change from all green to blue as a background, and the number 20 to magenta, providing a good contrast, rendering the number 20 readily visible to the human eye. Optically variable materials such as logos, numbers and other materials may be incorporated with the material to aid authentication and provide security.

While the embodiment shown in fig. 21, 22 and 23 has been disclosed as a body of hot stamping transfer material, it should be understood that the same principles can be used in conjunction with paints or inks associated with the optically variable pigments of the present invention.

From the above, it can be seen that the paired optically variable material bodies of the present invention all adopt the principle of two interference designs with optically variable properties, and the paired optically variable materials have the same color when designed to have one incident angle and have unmatched colors when designed to have all other angles. Thus, if pigments are used, it is difficult to repeat one pigment and its color shift, and it is much more difficult to provide a pair of pigments that have the same matching color when repeated at the same angle. The inclusion of paired optically variable pigments in a printed image would make counterfeiting extremely difficult, if not impossible. It is understood in accordance with the present invention that these paired optically variable pigments can be paired with another pair of optically variable pigments, or with a pigment that does not change color. Also, an interference light variable pigment may be paired with a non-variable pigment so that at an angle; the color of the non-color changing pigment and the color of one of the optically variable pigments match. Thus, for example, in fig. 21 and 22, the dot matrix may include a set of dots aligned with each other, the dots having a pigment thereon in the form of a constant color matching the color of a color changing pigment, such as green, so that the composite has a full green color at one angle and a magenta color number 20 against a green background at a different angle.

It should be appreciated that the highest chromaticity and the greatest color change with angle change can be achieved with a metal dielectric type design, rather than using a full dielectric design with the same number of layers. This is because, in addition to interference, the metal dielectric design includes selective color absorption. While maintaining high brightness, the pigments exhibit high chroma and hue variations as a function of viewing angle. According to the present invention, the entire range of colors suitable for forgery prevention can be significantly increased by using the light-matching variable material body.

Claims (26)

1. A paired optically variable device comprising a substrate (12) having a first surface (13), wherein first and second optical devices (17, 18) are carried by said first surface, at least one of the first and second optical devices being optically variable, forming pairs of first and second optical devices carried by the first surface of the substrate in spaced apart, non-overlapping positions on the first surface of the substrate to allow simultaneous observation by the human eye, the first and second optical devices having the same matching color for an angle of incidence that is a color matching angle between 0 ° and 90 ° and no color matching at all other angles of incidence, the first and second optical devices being pigments, specularly reflective foils or multilayer thin film interference laminates.

2. The paired optically variable devices of claim 1, wherein at least one of the first and second devices comprises a metal-dielectric interference stack (31).

3. The paired optically variable devices of claim 1, wherein at least one of the first and second devices comprises a fully dielectric interference stack (31).

4. The paired optically variable devices of claim 1, wherein said color matching angle is a low incidence angle and is between 0 ° and 10 °.

5. The paired optically variable devices of claim 1, wherein said color matching angle is an angle of incidence of 30 ° or greater.

6. The paired optically variable devices of claim 1, wherein at least one of the first and second devices is non-offset.

7. The paired optically variable devices of claim 1, wherein said first and second devices are opaque.

8. The paired optically variable devices of claim 7, wherein the first and second optical devices each comprise an opaque optically variable pigment.

9. The paired optically variable devices of claim 7, wherein each of the first and second bodies of optical material comprises an opaque optically variable foil.

10. The paired optically variable devices of claim 7, wherein said first and second devices are arranged in an ink carrier to provide ink.

11. The paired optically variable devices of claim 7, wherein said first and second devices are arranged in a paint carrier to provide paint.

12. The paired optically variable devices of claim 1, further comprising a release film disposed on the first surface of the substrate and a hot stamped polymer film disposed on the release film, the first and second optical devices being combined in the polymer film to form a hot stamped foil.

13. The paired optically variable devices of claim 1, wherein each said optically variable device comprises optically variable pigments.

14. The paired optically variable devices of claim 13, wherein each optically variable pigment is opaque.

15. The paired optically variable devices of claim 1, wherein each of the first and second optical devices comprises an opaque optically variable foil.

16. The paired optically variable devices of claim 1, wherein said first and second bodies of optical material form a pair of first pairs of bodies (71) and further comprising a second pair of bodies (72) of optical material in which at least one of the first and second bodies of optical material is optically variable, the first and second bodies of optical material of said second pair of bodies of optical material having the same matching color for an angle of incidence having a color matching angle between 0 ° and 90 ° and no color matching at all other angles of incidence.

17. The paired optically variable devices of claim 14, wherein said first and second optically variable pigments have the same color match under a light source temperature of 2856K.

18. The paired optically variable devices of claim 14, wherein the first and second optically variable pigments have the same color match under a light source at a temperature of 6770K.

19. The paired optically variable devices of claim 14, wherein said first and second optically variable pigments have the same color match under a light source temperature of 4200K.

20. The paired optically variable devices of claim 1, further comprising a symbol, said symbol being comprised of the first and second bodies of optical material.

21. The paired optically variable devices of claim 1, wherein said first and second bodies of optical material are optically variable, and wherein the first body of optical material is a symbol and the second body of optical material is the background of the symbol.

22. The paired optically variable devices of claim 1, wherein the first and second devices are optically variable specularly reflective opaque foils.

23. The paired optically variable devices of claim 1, further comprising a hot stamped polymer film, wherein the first and second optical devices are combined to form first and second foils in the polymer film.

24. A method of generating coloured reflections on a substrate (12) having a first surface (13) and first and second volumes of optical material (17, 18) formed as layers carried by the first surface, at least one of the first and second volumes of optical material being optically variable, forming pairs of the first and second volumes of optical material carried by the first surface of the substrate in spaced apart but non-overlapping positions on the first surface of the substrate to allow simultaneous viewing by the human eye, the method being characterised by comprising the steps of: forming the at least one volume of optical material having a color for an angle of incidence that is the same as a color of a second volume of optical material at the same angle of incidence; illuminating paired bodies of optical material with a light source such that the paired bodies reflect the same color for an angle of incidence between 0 ° and 90 ° and do not match color at all other angles of incidence, said first and second bodies of optical material being pigments, specularly reflective foils, or multilayer thin film interference stacks.

25. The method of claim 24, wherein the pair of bodies of optical material is a first pair of bodies of optical material (71), and further comprising a second pair of bodies of first and second optical material (72), the second pair of bodies of first and second optical material (72) being disposed at spaced locations on the first surface of the substrate without overlapping, at least one of the second pair of bodies of first and second optical material being optically variable to allow simultaneous observation of the first and second pairs of bodies of optical material with the human eye, the second pair of bodies of optical material reflecting a color for the one angle of incidence that is the same as the color reflected by the first pair of bodies of optical material at the one angle of incidence and no color matching at all other angles of incidence when the first and second pairs of bodies of optical material are illuminated with the same light source.

26. The method of claim 24, further comprising the steps of: the first and second volumes of optical material are combined to form a symbol which is not visible at said one angle of incidence and is visible at the other angles of incidence.