JP7714932B2 - Diffraction Grating Pattern - Google Patents

Description

The present invention relates to a diffraction grating pattern that combines diffraction gratings, and in particular to a diffraction grating pattern formed by unit pixels that combine multiple diffraction gratings with stepwise different diffraction angles.

Display elements made up of diffraction gratings have a directional gloss that cannot be achieved with conventional printing techniques. As such, they are widely used in displays and security products designed to prevent the counterfeiting of credit cards, securities, vouchers, etc., and there is a demand for the creation of more diverse and highly original patterns.

To meet these demands, displays with diffraction grating patterns composed of a collection of cell (dot)-shaped diffraction gratings are known.

Known methods for creating displays using diffraction gratings as pixels include, for example, a method in which tiny interference fringes (diffraction gratings) created by the interference of two beams of laser light are successively exposed onto a photosensitive film by changing the pitch, direction, and light intensity, and a method in which an electron beam exposure device is used to create a diffraction grating pattern by moving an X-Y stage on which a flat substrate is placed under computer control, thereby placing multiple tiny dots made of a diffraction grating on the surface of the substrate.

Forming the produced diffraction grating pattern on security products can provide benefits such as preventing counterfeiting, but in recent years, counterfeiting techniques have become more sophisticated, resulting in a demand for even more effective counterfeit prevention. Therefore, proposals have been made to form diffraction grating patterns that combine multiple types of diffraction gratings, so that the appearance of the diffraction grating pattern changes depending on the observation conditions, such as by changing hue or switching between latent and visible image states.

For example, Patent Document 1 proposes a diffraction grating in which the pixel pattern structure formed from tiny cells made of a diffraction grating is composed of a first pixel pattern made of a diffraction grating with different grating angles and grating pitches, and a second pixel pattern with different grating angles and grating pitches. It claims that changing the pattern illumination or the angle of the device changes the hue, and that this change in hue expresses a specific pattern, resulting in a diffraction grating pattern that has a novel visual image and can further enhance counterfeit prevention.

The diffraction grating pattern proposed in Patent Document 1 only changes the hue of specific pattern portions depending on the viewing angle, and does not appear significantly different from conventional diffraction grating patterns. Furthermore, the specific pattern is always visible as a visible image and cannot be switched to a latent image, so the change in appearance and anti-counterfeiting effect are limited.

For example, Patent Document 2 discloses a diffraction grating pattern having an optical diffraction structure characterized by the diffraction grating fringes of the latent image portion and the background portion forming a 90-degree angle. However, this latent image is indistinguishable under normal visual conditions and requires a distinguishing tool, posing a problem in terms of ease of distinction.

Furthermore, Patent Document 3 discloses an encrypted recording medium in which a first encrypted pattern and a second encrypted pattern, which are generated from an encrypted image by a visual decryption secret sharing method as an original latent image, are superimposed on a substrate, so that the latent image can be seen only when a light source is irradiated from two directions, a specific angle and an angle perpendicular to that. However, this medium shines randomly under normal observation conditions, making it impossible to distinguish between the latent image portion and the background portion, and since light sources from two directions are required for observation, there is still a problem in terms of ease of discrimination.

As mentioned above, while conventional diffraction grating patterns and diffraction grating recording media offer a certain degree of protection against copying, etc., when the entire image is observed, the visual changes are limited, making it difficult to create diverse patterns that are highly effective at preventing counterfeiting. Furthermore, special equipment is required to visually recognize and distinguish the patterns, posing a problem in terms of ease of discrimination.

Patent No. 5205946 Patent No. 4334855 JP 2011-158817 A

The objective of the present invention is to provide a diffraction grating pattern that can be switched between a latent image and a visible image, does not require special equipment for visually identifying or distinguishing the pattern, and makes it easy to distinguish between authentic and counterfeit.

In order to solve the above problem, one aspect of the present invention is to
A diffraction grating pattern in which at least two types of unit pixels each made of a diffraction grating are combined and arranged in a plurality of locations such that a predetermined shape is formed by unit pixels of one type among unit pixels of another type,
At least one of the unit pixels is formed by arranging a plurality of types of diffraction gratings having different diffraction angles so that the diffraction angle gradually changes along a direction from the periphery toward the center of the unit pixel ,
At least one of the unit pixels is formed by arranging a plurality of types of diffraction gratings having different diffraction angles so that the diffraction angle gradually changes along a direction from the center of the unit pixel to the periphery thereof,
In addition, the diffraction grating pattern has an equal diffraction angle in at least one arrangement portion that is in a corresponding positional relationship in the arrangement.

In the above diffraction grating pattern,
The diffraction angle of the diffraction grating may vary over approximately 180° within the unit pixel.

In the above diffraction grating pattern,
It may include areas where no diffraction grating is present.

Another aspect of the present invention is
An article having any of the above diffraction grating patterns formed on its surface.

With the diffraction grating pattern of the present invention, the pattern of diffracted light from unit pixels changes depending on the angle at which the diffraction grating pattern is viewed or the angle of illumination, eliminating the need for special determination devices. Furthermore, at certain angles, the direction of diffracted light from multiple types of unit pixels is the same, resulting in the pattern formed by the unit pixels becoming a latent image, while from other angles the direction of diffracted light differs and the pattern becomes visible, resulting in a highly distinctive pattern with significant visual variation.

FIG. 2 is an explanatory diagram of a first unit pixel that forms a diffraction grating pattern of the present invention. FIG. 2 is a conceptual diagram of a first unit pixel that forms a diffraction grating pattern of the present invention. 1 is an explanatory diagram of how a first unit pixel forming a diffraction grating pattern of the present invention appears when light is irradiated from a 0° direction. FIG. FIG. 10 is an explanatory diagram of a second unit pixel that forms a diffraction grating pattern of the present invention. FIG. 1 is an explanatory diagram of a first embodiment of a diffraction grating pattern of the present invention. FIG. 1 is an explanatory diagram of the appearance of a first embodiment of the diffraction grating pattern of the present invention when light is irradiated from a 0° direction. FIG. 10 is an explanatory view showing the appearance of the first embodiment of the diffraction grating pattern of the present invention when light is irradiated from another angle direction. 10A and 10B are explanatory diagrams of third and fourth unit pixels that form a diffraction grating pattern of the present invention. FIG. 10 is an explanatory diagram of the appearance of a second embodiment of the diffraction grating pattern of the present invention when light is irradiated from a 0° direction. 10A and 10B are explanatory views of the appearance of the second embodiment of the diffraction grating pattern of the present invention when light is irradiated from another angle direction. 10A and 10B are explanatory diagrams of fifth and sixth unit pixels that form a diffraction grating pattern of the present invention. FIG. 10 is an explanatory diagram of the appearance of a third embodiment of the diffraction grating pattern of the present invention when light is irradiated from a 0° direction. 10A and 10B are explanatory views of the appearance of the third embodiment of the diffraction grating pattern of the present invention when light is irradiated from another angle direction. 10A and 10B are explanatory diagrams of seventh and eighth unit pixels that form the diffraction grating pattern of the present invention. FIG. 10 is an explanatory diagram of the appearance of a fourth embodiment of the diffraction grating pattern of the present invention when light is irradiated from a 0° direction. 10A and 10B are explanatory views of the appearance of the fourth embodiment of the diffraction grating pattern of the present invention when light is irradiated from another angle direction. 10A and 10B are explanatory diagrams of ninth and tenth unit pixels forming a diffraction grating pattern of the present invention. FIG. 10 is an explanatory diagram of the appearance of a fifth embodiment of the diffraction grating pattern of the present invention when light is irradiated from a 0° direction. FIG. 10 is an explanatory diagram of the appearance of the fifth embodiment of the diffraction grating pattern of the present invention when light is irradiated from another angle direction.

Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, while the embodiments described below have technically preferable limitations for implementing the invention, these limitations are not essential requirements for the present invention.

Figure 1 is an explanatory diagram of a first unit pixel forming a diffraction grating pattern of the present invention. The first unit pixel 10 has a substantially circular outer shape, and the diffraction grating constituting the first unit pixel 10 emits diffracted light at an angle that gradually changes depending on the angle of rotation around the center of the first unit pixel 10. Referring to Figure 1(a), in region a1, a diffraction grating is formed in the center in the rotation direction that emits diffracted light for light incident from a 0° direction. As the diffraction grating rotates counterclockwise as indicated by the arrows in the figure, a diffraction grating is formed that emits diffracted light for light incident from gradually increasing angles. For example, a diffraction grating is formed in the similar center of region b1 that emits diffracted light for light incident from an approximately 45° direction. In other words, the numerical values of the angles listed for each region are shown as representative values for each region.

Note that here and hereinafter, the angle of incident light is based on the angle in the direction shown in Figure 1(b). For simplicity, the angle of incident light at which diffracted light is emitted from a diffraction grating will be referred to simply as the "angle of the diffraction grating."

The angle of the diffraction grating changes as you move counterclockwise from region a1, but there are no particular restrictions on how it changes. For example, it could be 0° for the entire region a1, 45° for the entire region b1, and so on, with region c1 at 90°, region d1 at 135°, and region a2 at 180°. Note that when the diffraction grating angle is 180°, the optical effect is the same as when it is 0°, so this is considered to be 0°, and the subsequent angles are 45° for region b2, 90° for region c2, and 135° for region d2.

The angle of the diffraction grating may change in ways other than those described above. For example, it may change in fine increments, such as 1°, 5°, or 10° increments, from region a1 to region b1. It may also change smoothly and continuously. To avoid misunderstanding, it should be noted that the angle values shown in Figure 1(a) are guideline values that indicate the manner of change. For example, if the diffraction grating is in 10° increments, the angle is 40° on the region a1 side of the center in the circumferential direction of region b1, and 50° on the region c1 side. Furthermore, the designations such as regions a1, b1, etc. and the lines dividing the regions are for illustrative purposes only and do not indicate physical divisions of the diffraction grating.

Figure 2 is a conceptual diagram of a first unit pixel that forms the diffraction grating pattern of the present invention. The diffraction grating that constitutes the first unit pixel 10a is engraved with countless diffraction grating patterns, with the angle of the diffraction grating changing depending on the angle in the rotation direction. The diffraction gratings at each angle form a continuous pattern, and as a whole, the diffraction gratings at different angles are arranged in a concentric circle 10b.

Figure 3 is an explanatory diagram of how the first unit pixel forming the diffraction grating pattern of the present invention appears when light is irradiated from the 0° direction. When light is irradiated from the 0° direction, strong diffracted light is emitted, particularly from the center, from region a1, where the diffraction grating angle is 0°, and region a2, where the angle is 180°, and the diffracted light becomes weaker towards the periphery. Since no diffracted light is emitted from other regions, regions a1 and a2 appear bright overall, while other regions appear dark.

Figure 4 is an explanatory diagram of a second unit pixel that forms the diffraction grating pattern of the present invention. The second unit pixel 11 has approximately the same diameter as the first unit pixel 10. Like the first unit pixel 10, the diffraction grating that constitutes the second unit pixel 11 has a diffraction grating angle that gradually changes in the direction around the center of the second unit pixel 11, but the direction of rotation is reversed. As the diffraction grating rotates clockwise as shown by the arrow, it emits diffracted light in response to incident light at gradually increasing angles. The diffraction grating is formed so that it is arranged in a concentric pattern as shown in Figure 2.

Of the diffraction gratings that make up the second unit pixel 11, the portions where the diffraction grating angles are 0°, 90°, and 180° are located in the arrangement portions that correspond to the first unit pixel 10. Therefore, for incident light from these angles, the first unit pixel 10 and the second unit pixel 11 emit diffracted light in the same way.

Figure 5 is an explanatory diagram of a first form of diffraction grating pattern of the present invention. Diffraction grating pattern 1 is formed by combining the aforementioned first unit pixels 10 and second unit pixels 11. The combination is not particularly limited, but Figure 5 shows an example in which the first unit pixels 10 serve as a base and the second unit pixels 11 are combined to form a square-shaped pattern. Furthermore, because both the first unit pixels 10 and the second unit pixels 11 are approximately circular, a gap region 10c is created that is not included in either pixel. A diffraction grating of any pattern may or may not be formed in this gap region 10c.

Figure 6 is an explanatory diagram of the appearance of the first form of the diffraction grating pattern of the present invention when light is irradiated from the 0° direction. When light is irradiated from the 0° direction onto the above-mentioned diffraction grating pattern 1, as described above, both the first unit pixel 10 and the second unit pixel 11 emit diffracted light in areas a1 and a2, resulting in the appearance of diffraction grating pattern 1a in which the same area is illuminated overall, and the "square" pattern formed by the second unit pixel 11 is invisible, remaining in the state of a latent image. Note that the same appearance occurs when the diffraction grating is irradiated from a direction with an angle of 180°.

In contrast, Figure 7 shows the appearance when the direction of incident light is changed from 0°. The images shown here are for illumination from directions of (a) 22.5°, (b) 45°, (c) 67.5°, and (d) 90°.

When incident light is irradiated from a direction of 22.5°, diffraction grating pattern 1b emits diffracted light from near the boundary between regions a1 and b1 and near the boundary between regions a2 and b2 in the area where the first unit pixels 10 are formed, whereas diffracted light is emitted from near the boundary between regions a1 and d2 and near the boundary between regions a2 and d1 in the "R"-shaped area where the second unit pixels 11 are formed. As a result, the areas that emit light differ between the area where the first unit pixels 10 are formed and the area where the second unit pixels 11 are formed, and a "R"-shaped pattern appears against the background.

When incident light is irradiated from a 45° angle, diffraction grating pattern 1c emits diffracted light from near the centers of regions b1 and b2 in the area where the first unit pixels 10 are formed, whereas diffracted light is emitted from near the centers of regions d2 and d1 in the "R"-shaped area where the second unit pixels 11 are formed. As a result, the "R"-shaped pattern is visible from the background, and its emission pattern is different from diffraction grating pattern 1b.

When incident light is irradiated from a direction of 67.5°, diffraction grating pattern 1d emits diffracted light from near the boundary between regions b1 and c1 and near the boundary between regions b2 and c2 in the area where first unit pixels 10 are formed, whereas in the "R"-shaped area where second unit pixels 11 are formed, diffracted light is emitted from near the boundary between regions d2 and c2 and near the boundary between regions d1 and c1. As a result, the "R"-shaped pattern appears different from diffraction grating pattern 1b and diffraction grating pattern 1c.

When incident light is irradiated from a 90° direction, diffraction grating pattern 1e emits diffracted light in areas c1 and c2 of both the first unit pixel 10 and the second unit pixel 11, resulting in the appearance of diffraction grating pattern 1e in which the same areas are illuminated overall. The "square" pattern formed by the second unit pixel 11 is not visible, and appears as a latent image.

As can be seen from the above examples, when incident light is rotated counterclockwise from a 0° direction, the "R" pattern begins as a latent image and is invisible. In the first unit pixel 10, which is the underlying part, the light-emitting part rotates counterclockwise, and in the second unit pixel 11, which is shaped like the "R", the light-emitting part appears to rotate clockwise, and the "R"-shaped part appears as a visible image, before changing back to a latent image. In this way, with the diffraction grating pattern of the present invention, the unique visual effect can be obtained simply by changing the angle of the incident light, without the need for any special determination device.

The above-described unit pixels and diffraction grating patterns can be formed using known methods such as two-beam interference and electron beam (EB) imaging.

By forming such a diffraction grating pattern on the surface of an article, an article can be obtained that can prevent counterfeiting by copying. Items that require counterfeit prevention include all items that require credibility, such as cards, prepaid cards, gift certificates, traveler's checks, bankbooks, tickets, admission tickets, and business cards. The material can be paper, resin, metal, or any other material, and the surface does not have to be flat; it can also have curvatures or irregularities to the extent that they do not affect the visual appearance or the ability to read the diffraction grating pattern.

The preferred method for forming a diffraction grating pattern on the surface of an article is to form it in the form of a transfer sheet or sticker (label). A transfer sheet can be constructed, for example, by sequentially laminating a release protective layer, a diffraction grating pattern forming layer, a thin film layer, a resin layer, and an adhesive layer on a support film.

A transfer sheet having such a diffraction grating pattern is placed on a substrate via an adhesive layer, and the pattern is transferred by heat and pressure. After transfer, the support film is peeled off to obtain an article having a diffraction grating pattern.

Figure 8 is an explanatory diagram of the third and fourth unit pixels that form the diffraction grating pattern of the present invention. In the third unit pixel 12, as with the first and second unit pixels, the angle at which diffracted light is emitted gradually changes depending on the angle of rotation in the direction orbiting the center. Representative values of the diffraction grating angles in each region are 0° in region a1, 22.5° in region b1, 45° in region c1, 67.5° in region d1, 90° in region a2, 112.5° in region b2, 135° in region c2, and 157.5° in region d2. In other words, the angle rotates by 22.5° per region as the pixel rotates counterclockwise.

Furthermore, the fourth unit pixel 13 has approximately the same diameter as the third unit pixel 12. The diffraction grating that constitutes the fourth unit pixel 13, like the third unit pixel 12, gradually changes the angle at which diffracted light is emitted depending on the angle of rotation in the direction orbiting the center of the fourth unit pixel 13, but the direction of rotation is reversed, and a diffraction grating is formed in which diffracted light is emitted in response to incident light at gradually increasing angles as the direction of rotation goes clockwise.

Figure 9 is an explanatory diagram of the appearance of the second form of the diffraction grating pattern of the present invention when light is irradiated from the 0° direction. Similar to the diffraction grating pattern of Figure 5, the third and fourth unit pixels are combined to form the third unit pixel 12 in the base area and the fourth unit pixel 13 in the "K"-shaped pattern area. When this diffraction grating pattern is irradiated from the 0° direction, as described above, both the third unit pixel 12 and the fourth unit pixel 13 emit diffracted light in area a1, resulting in a diffraction grating pattern 2a in which the same area is illuminated overall. The "K" pattern formed by the fourth unit pixel 13 is invisible, resulting in a latent image.

In contrast, Figure 10 shows the appearance when the direction of incident light is changed from 0 degrees. Here, the images are shown for illumination from directions of (a) 22.5 degrees, (b) 45 degrees, (c) 67.5 degrees, and (d) 90 degrees.

When incident light is irradiated from a direction of 22.5°, diffraction grating pattern 2b emits diffracted light from near the center of region b1 in the area where third unit pixels 12 are formed, while diffracted light is emitted from near the center of region d2 in the "H"-shaped area where fourth unit pixels 13 are formed. As a result, the areas that emit light differ between the area where first unit pixels 10 are formed and the area where second unit pixels 11 are formed, and the "H"-shaped pattern becomes visible from the background.

When incident light is irradiated from a 45° angle, diffraction grating pattern 2c emits diffracted light from near the center of region c1 in the area where the third unit pixel 12 is formed, while diffracted light is emitted from near the center of region c2 in the "R"-shaped area where the fourth unit pixel 13 is formed. As a result, the "R"-shaped pattern is visible from the background, and its emission pattern is different from that of diffraction grating pattern 2b.

When incident light is irradiated from a direction of 67.5°, diffraction grating pattern 2d emits diffracted light from near the center of region d1 in the portion where third unit pixel 12 is formed, whereas diffracted light is emitted from near the center of region b2 in the "H"-shaped portion where fourth unit pixel 13 is formed. As a result, the "H"-shaped pattern appears different from diffraction grating pattern 2b and diffraction grating pattern 2c.

When incident light is irradiated from a 90° direction, the diffraction grating pattern 2e is formed such that both the third unit pixel 12 and the fourth unit pixel 13 emit diffracted light near the center of region a2, resulting in the same illuminated region of diffraction grating pattern 2e as a whole. The "R" pattern formed by the fourth unit pixel 13 is not visible, and instead appears as a latent image.

Figure 11 is an explanatory diagram of the fifth and sixth unit pixels that form the diffraction grating pattern of the present invention. The fifth unit pixel 14 shown in Figure 11(a) has a roughly circular outer shape, and the diffraction grating that constitutes the fifth unit pixel 14 has a diffraction grating angle that gradually changes depending on the distance from the center in the direction from the outer periphery toward the center of the fifth unit pixel 14, i.e., in the radial direction. As shown in Figure 11(a), the diffraction grating angle is 0° in the outermost region and gradually increases toward the center. The 180° region is essentially equivalent to 0° as described above, and further increases to 45° and 90°, with the diffraction grating angle at the center being 180°. Note that the angle values shown for each region are representative values for each region.

Furthermore, the sixth unit pixel 15 shown in Figure 11(b) has approximately the same diameter as the fifth unit pixel 14, and the diffraction grating that constitutes it has a diffraction grating angle that changes in the opposite direction to that of the fifth unit pixel 14.In other words, the diffraction grating angle is 0° at the center, and gradually increases from the center to the periphery, reaching 180°, then changing again to 45° and 90°, and finally reaching 180° in the outermost region.The angle values shown for each region are representative values for each region.

Figure 12 is an explanatory diagram of the appearance of the third form of the diffraction grating pattern of the present invention when light is irradiated from the 0° direction. By combining fifth and sixth unit pixels, the fifth unit pixel 14 is formed in the base area and the sixth unit pixel 15 is formed in the "K"-shaped pattern area, similar to the first form of the diffraction grating pattern in Figure 5. When this diffraction grating pattern is irradiated from the 0° direction, as described above, both the fifth unit pixel 14 and the sixth unit pixel 15 emit diffracted light in the areas marked 0° and 180° in Figure 11, resulting in the appearance of diffraction grating pattern 3a in which the same area is illuminated overall. The "K" pattern formed by the sixth unit pixel 15 is invisible, resulting in a latent image.

In contrast, Figure 13 shows what happens when the direction of incident light is changed from 0 degrees. The images shown here are for illumination from directions of (a) 22.5°, (b) 45°, (c) 67.5°, and (d) 90°.

When incident light is irradiated from a 22.5° direction, diffraction grating pattern 3b emits diffracted light from near the boundary between the 0° region and the 45° region inside it in the area where the fifth unit pixel 14 is formed, whereas diffracted light is emitted from near the boundary between the 0° region and the 45° region outside it in the "R"-shaped area where the sixth unit pixel 15 is formed. As a result, the areas that emit light differ between the area where the fifth unit pixel 14 is formed and the area where the sixth unit pixel 15 is formed, and the "R"-shaped pattern becomes visible from the background.

When incident light is irradiated from a 45° direction in diffraction grating pattern 3c, diffracted light is emitted from near the center of the 45° region in the area where the fifth unit pixel 14 and the area where the sixth unit pixel 15 are formed. However, because the positions are different, the areas that emit light are different, so a "R"-shaped pattern is visible from the background, and the emission pattern is different from that of diffraction grating pattern 3b.

When incident light is irradiated from a direction of 67.5°, diffraction grating pattern 3d emits diffracted light from near the boundary between the 45° region and the 90° region inside it in the area where the fifth unit pixels 14 are formed, whereas diffracted light is emitted from near the boundary between the 45° region and the 90° region outside it in the "R"-shaped area where the sixth unit pixels 15 are formed. Therefore, since the areas that emit light are different in the area where the fifth unit pixels 14 are formed and the area where the sixth unit pixels 15 are formed, a "R"-shaped pattern is visible and the emission pattern is different from both diffraction grating pattern 3b and diffraction grating pattern 3c.

When incident light is irradiated from a 90° direction, the fifth unit pixel 14 and the sixth unit pixel 15 both emit diffracted light in the areas marked 0° and 180° in Figure 11, resulting in the appearance of diffraction grating pattern 3e in which the same areas are illuminated overall, and the "R" pattern formed by the sixth unit pixel 15 is not visible, resulting in a latent image.

Figure 14 is an explanatory diagram of the seventh and eighth unit pixels that form the diffraction grating pattern of the present invention. The seventh unit pixel 16 shown in Figure 14(a) has a rectangular shape formed by cutting out a concentric diffraction grating. The diffraction grating that constitutes the seventh unit pixel 16 has a diffraction grating angle that gradually changes depending on the distance from the center in the direction from the outer periphery toward the center of the seventh unit pixel 16. As shown in Figure 14(a), the diffraction grating angle is 0° in the corner areas of the rectangle at the outermost periphery, and gradually increases toward the center. The 180° area is essentially 0° as described above, and further increases to 45° and 90°, with the diffraction grating angle at the center being 180°. Note that the angle values shown for each area are representative values for each area.

The eighth unit pixel 17 shown in Figure 14(b) has the same configuration as the seventh unit pixel 16, but the diffraction grating it constitutes has an angle change direction opposite to that of the seventh unit pixel 16. That is, the angle of the diffraction grating is 0° at the center, and gradually increases from the center toward the periphery, reaching 180°, then changing again to 45° and 90°, and finally reaching 180° in the region corresponding to the corner of the outermost rectangle. Note that the angle values shown for each region are representative values for each region.

Figure 15 is an explanatory diagram of the appearance of the fourth form of the diffraction grating pattern of the present invention when light is irradiated from the 0° direction. Similar to the first form of the diffraction grating pattern in Figure 5, the seventh and eighth unit pixels are combined to form the seventh unit pixel 16 in the base area and the eighth unit pixel 17 in the "K"-shaped pattern area. When this diffraction grating pattern is irradiated from the 0° direction, as described above, both the seventh unit pixel 16 and the eighth unit pixel 17 emit diffracted light in the areas marked 0° and 180° in Figure 14, resulting in the appearance of diffraction grating pattern 4a in which the same area is illuminated overall. The "K" pattern formed by the eighth unit pixel 17 is invisible, resulting in a latent image.

In contrast, Figure 16 shows the appearance when the direction of incident light is changed from 0 degrees. The images shown here are for illumination from directions of (a) 22.5°, (b) 45°, (c) 67.5°, and (d) 90°.

When incident light is irradiated from a 22.5° direction, diffraction grating pattern 4b emits diffracted light from near the boundary between the 0° region and the 45° region inside it in the area where the seventh unit pixel 16 is formed, whereas diffracted light is emitted from near the boundary between the 0° region and the 45° region outside it in the "R"-shaped area where the eighth unit pixel 17 is formed. As a result, the areas that emit light differ between the area where the seventh unit pixel 16 is formed and the area where the eighth unit pixel 17 is formed, and the "R"-shaped pattern becomes visible from the background.

When incident light is irradiated from a 45° direction in diffraction grating pattern 4c, diffracted light is emitted from near the center of the 45° region in the area where the seventh unit pixel 16 and the eighth unit pixel 17 are formed. However, because the positions are different, the areas that emit light are different, so a "R"-shaped pattern is visible from the background, and the emission pattern is different from that of diffraction grating pattern 4b.

When incident light is irradiated from a direction of 67.5°, diffraction grating pattern 4d emits diffracted light from near the boundary between the 45° region and the 90° region inside it in the area where the seventh unit pixel 16 is formed, whereas diffracted light is emitted from near the boundary between the 45° region and the 90° region outside it in the "R"-shaped area where the eighth unit pixel 17 is formed. Therefore, since the areas that emit light are different in the area where the seventh unit pixel 16 is formed and the area where the eighth unit pixel 17 is formed, a "R"-shaped pattern is visible and the emission pattern is different from both diffraction grating pattern 4b and diffraction grating pattern 4c.

When incident light is irradiated from a 90° direction, the seventh unit pixel 16 and the eighth unit pixel 17 both emit diffracted light in the areas marked 0° and 180° in Figure 14, resulting in the appearance of diffraction grating pattern 4e in which the same areas are illuminated overall, and the "R" pattern formed by the eighth unit pixel 17 is not visible, resulting in a latent image.

Figure 17 is an explanatory diagram of the ninth and tenth unit pixels forming the diffraction grating pattern of the present invention. The ninth unit pixel 18 shown in Figure 17(a) has a rectangular configuration formed by combining strip-shaped diffraction gratings, and the diffraction grating that constitutes the ninth unit pixel 18 has a diffraction grating angle that gradually changes in the direction from one side of the ninth unit pixel 18 to the opposite side. As shown in Figure 17(a), the diffraction grating angle is 0° in the strip-shaped region at the top edge and gradually increases toward the bottom edge. As mentioned above, the 180° region is essentially equal to 0°, and further increases to 22.5° and 45°. In the strip-shaped region at the bottom edge, the diffraction grating angle is 157.5°. The angle values shown for each region are representative values for each region.

17(b) has the same configuration as the ninth unit pixel 18, and the diffraction grating that constitutes it has a diffraction grating angle that changes in the opposite direction to that of the ninth unit pixel 18. That is, the angle of the diffraction grating is 22.5° in the band-shaped region at the bottom side, and the angle of the diffraction grating gradually increases toward the top side, and the region where it reaches 180° is essentially equivalent to 0° as described above, and further increases to 22.5° and 45°, and in the band-shaped region at the top side, the angle of the diffraction grating is 180°. Note that the numerical values of the angles written in each region are shown as representative values for each region.

Figure 18 is an explanatory diagram of the appearance of the fifth form of the diffraction grating pattern of the present invention when light is irradiated from the 0° direction. Similar to the first form of the diffraction grating pattern in Figure 5, the ninth and tenth unit pixels are combined to form the ninth unit pixel 18 in the base area and the tenth unit pixel 19 in the "square" pattern area. When this diffraction grating pattern is irradiated from the 0° direction, as described above, both the ninth unit pixel 18 and the tenth unit pixel 19 emit diffracted light in the areas marked 0° and 180° in Figure 17, resulting in the appearance of diffraction grating pattern 4a, where the same band-shaped area is illuminated overall. The "square" pattern formed by the eighth unit pixel 17 is invisible, resulting in a latent image.

In contrast, Figure 19 shows the appearance when the direction of incident light is changed from 0 degrees. The images shown here are for illumination from directions of (a) 22.5°, (b) 45°, (c) 67.5°, and (d) 90°.

When incident light is irradiated from a 22.5° direction, diffraction grating pattern 5b emits diffracted light from near the center of the 22.5° region in both the portion where ninth unit pixel 18 is formed and the "R"-shaped portion where tenth unit pixel 17 is formed. However, because the positions are different, the portions that emit light are different in the portion where ninth unit pixel 18 is formed and the portion where tenth unit pixel 19 is formed, and the "R"-shaped pattern becomes visible from the background.

When incident light is irradiated from a 45° direction in diffraction grating pattern 5c, diffracted light is emitted from near the center of the 45° region in the area where ninth unit pixel 18 and tenth unit pixel 19 are formed. However, because the positions are different, the areas that emit light are different, so a "R"-shaped pattern is visible from the background, and the emission pattern is different from that of diffraction grating pattern 5b.

When incident light is irradiated from a 67.5° direction, diffraction grating pattern 5d emits diffracted light from near the center of the 67.5° region in both the portion where ninth unit pixel 18 is formed and the "R"-shaped portion where tenth unit pixel 17 is formed. However, because the positions are different, the portions that emit light are different in the portion where ninth unit pixel 18 is formed and the portion where tenth unit pixel 19 is formed. As a result, a "R"-shaped pattern is visible, and the emission pattern is different from both diffraction grating pattern 5b and diffraction grating pattern 5c.

When incident light is irradiated from a 90° direction, the ninth unit pixel 18 and the tenth unit pixel 19 of the diffraction grating pattern 5e both emit diffracted light in the area marked 90° in Figure 17, resulting in the appearance of diffraction grating pattern 5e in which the same area is illuminated overall, and the "square" pattern formed by the tenth unit pixel 19 is not visible, resulting in a latent image.

In the above examples, we have described diffraction grating patterns constructed from a combination of two types of unit pixels, but the diffraction grating patterns of the present invention are not limited to this and can also be constructed from a combination of three or more types of unit pixels.

As described above, with the diffraction grating pattern of the present invention, as the angle of illumination from the light source is changed, the pattern from which diffracted light is emitted appears to rotate or the emitting portion appears to move, without the need for any special determination device or the like. Furthermore, any pattern can be switched between appearing as a latent image and a visible image on the background, thereby obtaining a diffraction grating pattern with unique optical effects.

1, 1a, 1b, 1c, 1d, 1e, 2a, 2b, 2c, 2d, 2e, 3a, 3b, 3c, 3d, 3e, 4a, 4b, 4c, 4d, 4e, 5a, 5b, 5c, 5d, 5e... Diffraction grating patterns 10, 10a... First unit pixel 10b... Concentric circle 10c... Gap 11... Second unit pixel 12... Third unit pixel 13... Fourth unit pixel 14... Fifth unit pixel 15... Sixth unit pixel 16... Seventh unit pixel 17... Eighth unit pixel 18... Ninth unit pixel 19... Tenth unit pixel

Claims (4)

A diffraction grating pattern in which at least two types of unit pixels each made of a diffraction grating are combined and arranged in a plurality of locations such that a predetermined shape is formed by unit pixels of one type among unit pixels of another type,
At least one of the unit pixels is formed by arranging a plurality of types of diffraction gratings having different diffraction angles so that the diffraction angle gradually changes along a direction from the periphery toward the center of the unit pixel ,
At least one of the unit pixels is formed by arranging a plurality of types of diffraction gratings having different diffraction angles so that the diffraction angle gradually changes along a direction from the center of the unit pixel to the periphery thereof,
The diffraction grating pattern has an equal diffraction angle in at least one arrangement portion that is in a corresponding positional relationship in the arrangement. The diffraction grating pattern of claim 1, characterized in that the diffraction angle of the diffraction grating varies over approximately 180° within the unit pixel. 3. The diffraction grating pattern according to claim 1, further comprising an area where no diffraction grating is present. An article having the diffraction grating pattern according to any one of claims 1 to 3 formed on its surface.