Latent image printed matter

Abstract

To provide a latent image printed matter which is a printed matter in which an image to be visually recognized changes depending on an observation angle, and in which a change effect of the image is clear, in a printed image formed of a raised image line having gloss.SOLUTION: In a printed image having first significant information formed using a difference in image line area ratio and second significant information formed using a difference in image line angle by a set of image lines which are glossy and raised, image lines which form a visible image and image lines which form latent image lines are separated from each other, and the image lines which form the latent image lines are formed high, and the image lines which form the visible image lines are formed low.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a latent image print that has the effect of changing the visible image into a different image by changing the observation angle, in the field of security prints that require the function of authenticating banknotes, passports, identification cards, cards, etc. [Background technology]

[0002] Recent advances in digital devices such as scanners, printers, and color copiers have made it easy to create elaborate copies of valuable printed materials. As one of the anti-counterfeiting technologies to prevent such copying and counterfeiting, there are now many products that use optical security elements, such as holograms, which change their image depending on the viewing angle.

[0003] However, unlike conventional anti-counterfeiting technologies that are formed by printing with ink, holograms are formed using complex manufacturing processes and special materials, and therefore are more time-consuming to manufacture and are extremely expensive than conventional anti-counterfeiting printed materials.For this reason, anti-counterfeiting printed materials have emerged that can be formed using ordinary printing methods by blending special light-reflecting powders such as metallic ink, interference mica, oxidized flake mica, pigment-coated aluminum flakes, and optically variable flakes into ink or paint, and by using overlapping special materials or complex halftone dot configurations, and that achieve image changes similar to those of holograms.

[0004] Among the cost-effective printed materials that achieve image changes similar to those of holograms, there are anti-counterfeit printed materials that form printed images using raised lines, which have the effect of changing the observed image when observed under specular light that strongly reflects light. These anti-counterfeit printed materials are used to determine authenticity based on whether the observed image changes or not.

[0005] The applicant has already filed an invention relating to an information carrier capable of discriminating between authentic and counterfeit, which comprises a first image formed by varying image line angles using raised image lines with specular gloss, and a second image formed by varying image line area ratios, so that when observed in an angle range where diffuse reflected light and specular reflected light are mixed, only the first image is visible, and when observed in an angle range where diffuse reflected light is dominant, only the second image is visible (see, for example, Patent Document 1). In this technology, the difference in image line area ratio in the second image is characterized by the thickness or thinness of the image line width.

[0006] The applicant has also filed an invention relating to an information carrier capable of authenticity discrimination, which has a specular gloss and is provided with a first image formed by varying the image line angle using raised image lines similar to the technology described in Patent Document 1, and a second image formed by varying the image line area ratio, so that only the first image or the second image is visible in an observation angle range where specular reflection light or diffuse reflection light is dominant (see, for example, Patent Document 2).Unlike the technology described in Patent Document 1, this technology is characterized in that the difference in image line area ratio in the second image is configured using pixels rather than by the thickness of the image line width. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4972809 [Patent Document 2] Patent No. 5900820 Summary of the Invention [Problem to be solved by the invention]

[0008] The printed matter described in Patent Documents 1 and 2 is such that at observation angles where no strong reflected light is produced from the printed matter, i.e., where diffuse reflected light is dominant, a second image constructed by differences in area ratio is visible; however, at observation angles where strong reflected light is produced from the printed matter, i.e., where diffuse reflected light and specular reflected light are mixed, the incident light is strongly reflected, increasing the brightness of the image and causing the contrast of the second image to be lost, resulting in the appearance of a first image constructed by differences in image angle; this is a technology that is also cost-effective because it can be formed in a single printing.

[0009] However, since the printed matter described in Patent Document 1 uses lines to form the entire image, the differences in image area ratio required to express the shading of the second image must be determined by the thickness of the lines. The light reflection effect of raised lines is strongly dependent on the angle of the incident light, and the amount of reflected light is particularly low for light incident from the same direction as the image direction, reducing the effect of disappearing the second image. Therefore, when the contrast of the second image viewed at an observation angle where diffuse reflection is dominant is high, the second image does not completely disappear at an observation angle where diffuse reflection and specular reflection are mixed, resulting in the problem of being perceived as an unclear image overlapping with the first image. This was an unavoidable problem with the technology described in Patent Document 1, which requires the differences in image area ratio to be determined by the thickness of the lines.

[0010] Furthermore, the printed matter described in Patent Document 2 requires that at least a portion of the difference in image area ratio be accounted for by pixels. Unlike image lines, pixels have low directional dependency on incident light and have surfaces that strongly reflect light regardless of the direction from which light is incident. Therefore, this configuration achieves a higher effect of eliminating the second image than the technology described in Patent Document 1. However, even with pixels that have low dependency on the direction of incident light, if the protrusion height exceeds a certain level, the surface opposite the surface that strongly reflects light may become a shadow, and the visible image may not completely disappear. For these reasons, although the image change effect is improved compared to the technology described in Patent Document 1, the technology described in Patent Document 2 also has a problem in that, as long as the pixels have a certain height, the second image does not completely disappear under observation angles where diffuse reflection light and specular reflection light are mixed, and the image is perceived as an unclear image overlapping the first image.

[0011] In view of the above circumstances, the present invention aims to provide a latent image print that has the effect of changing two different images between an angular region where diffuse reflected light is dominant and an angular region where diffuse reflected light and specular reflected light are mixed, and that can achieve excellent image changes without being heavily dependent on the direction of light incidence by setting a certain limit on the height of the image lines that make up the visible image, and that is easy to produce and has excellent cost performance. [Means for solving the problem]

[0012] The present invention provides a printed image having a color different from that of the substrate, on at least a portion of the substrate, the printed image comprising at least a first latent image element, a second latent image element, a first visible element, and a second visible element, each element having at least a light-dark flip-flop property and formed by a collection of a plurality of images having raised portions, constituting first significant information and second significant information, the first latent image element being formed by a plurality of first latent image images arranged in a first direction at a first area ratio, the second latent image element being formed by a plurality of second latent image images arranged in a second direction different from the first direction at the first area ratio, the first visible element being formed by a plurality of first visible images arranged in the first direction at a second area ratio smaller than the first area ratio, the second visible element being formed by a plurality of second visible images arranged in the second direction at a second area ratio, and the first latent image images and the first visible image images the second latent image print and the second visible image print are arranged with a fixed interval between each other without overlapping, the first visible image print and the second visible image print are formed to have a lower image height than the first latent image print and the second latent image print, the second significant information is formed by the difference in the arrangement direction of the first latent image elements and the second latent image elements, the first significant information is formed by the presence or absence of the first visible elements and the second visible elements, when observed at an angle where diffuse reflected light is dominant, the first significant information is visible from the difference in shade caused by the presence or absence of the first visible elements and the second visible elements and the difference in area ratio between the first area ratio and the second area ratio, and when observed at an angle where diffuse reflected light and specular reflected light are mixed, the second significant information is visible from the strength of reflected light caused by the difference in the arrangement direction of the images and the height of the images.

[0013] The present invention also provides a latent image print capable of being authenticated, characterized in that the height of the first visible image line and the second visible image line is less than half the height of the first latent image line and the second latent image line, or is less than 5 μm. [Effects of the Invention]

[0014] In the latent image print of the present invention, the image with raised features constituting the first significant information is constructed as lines or pixels independent of the lines constituting the latent image, and is constructed with a low height. Even if the image is a line, when the raised feature height is low, the angular dependency on the incident direction of incident light is significantly reduced. Therefore, compared to the conventional technology described in Patent Document 1, the effect of disappearing the first significant information when light is incident is less affected by the direction of the incident light. This makes the change effect of the image independent of the angle of incidence of light in the viewing environment, enabling stable authenticity determination.

[0015] The latent image print of the present invention has the effect of changing two different images depending on the viewing angle. Depending on the formation method, this technology can be formed in one printing, and it is easy to manufacture, so it has excellent cost performance. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is an explanatory diagram showing a latent image print in the first embodiment. [Figure 2] FIG. 2 is a diagram showing an outline of components of a print image according to the first embodiment. [Figure 3] FIG. 2 is a diagram showing a configuration of a print image in the first embodiment. [Figure 4] FIG. 2 is a diagram showing a configuration of a latent image in the first embodiment. [Figure 5] FIG. 2 is a diagram showing a configuration of a visible image element in the first embodiment. [Figure 6] FIG. 2 is a diagram showing the configuration of a first latent image element and a second latent image element in the first embodiment. [Figure 7] FIG. 2 is a diagram showing the configuration of a first visible element and a second visible element in the first embodiment. [Figure 8] 10A and 10B are diagrams illustrating the effect of a latent image print in the first embodiment. [Figure 9] 1 shows the difference in the light reflecting surface caused by different incident light in a raised image of the prior art. [Figure 10]1 shows the difference in the light reflecting surface caused by different incident light in a raised image of the prior art. [Figure 11] 10 shows the problem of the visibility of the second significant information when using the conventional technology. [Figure 12] This shows the difference in the light reflection surface caused by different incident light in the raised image lines of the present invention. [Figure 13] Examples of images used as visible images in the present invention are shown below. [Figure 14] An example in which the visible image of the present invention is constructed using pixels will be shown. DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments of the present invention will be described with reference to Figures 1 to 14. However, the present invention is not limited to the embodiments described below, and various other embodiments are included within the scope of the technical ideas set forth in the claims.

[0018] Figure 1 shows a latent image print (1) of the present invention. The latent image print (1) has a printed image (3) formed on a substrate (2). The substrate (2) may be made of any material, including fine paper, coated paper, plastic, metal, etc. There are also no particular limitations on the color or size of the substrate (2).

[0019] The printed image (3) is formed by a plurality of raised, glossy lines in a color different from that of the substrate. The color of these lines may be any color as long as they are different from that of the substrate and visible under diffuse reflected light, and are not completely transparent.

[0020] In this embodiment, the print image (3) contains first significant information representing a "shippo" image and second significant information representing the alphabet "JPN." For the sake of convenience, the character area of ​​the alphabet "JPN" will be referred to as the "information area," and the other area will be referred to as the "background area."

[0021] Figure 2 shows an overview of the configuration of the printed image (3). The printed image (3) comprises a latent image (4) representing the second significant information and a visible image (5) representing the first significant information. The latent image (4) also comprises a first latent image element (4A) representing the information portion of the alphabet "JPN" and a second latent image element (4B) representing the background portion. On the other hand, the visible image (5) comprises a first visible element (5A) and a second visible element (5B).

[0022] The printed image (3) is composed of a first latent image element (4A), a second latent image element (4B), a first visible element (5A), and a second visible element (5B). There is no overlapping area between the elements, and the printed image (3) is formed when all the image elements are fitted together. The first latent image element (4A) and the second latent image element (4B) must have the same area ratio, and are formed with a first area ratio. On the other hand, the first visible element (5A) and the second visible element (5B) are formed with a second area ratio. In the present invention, the second area ratio is smaller than the first area ratio.

[0023] In this embodiment, the "Shippo" pattern, which is the first significant information, is a binary image representing a simple mark, so the second area ratio is only one numerical value, but if the first significant information were a multi-tone image with complex shading such as a human face, there would be not just one type of second area ratio, but area ratios corresponding to the number of gradations to be expressed. In the present invention, the multiple area ratios corresponding to these gradations are collectively referred to as the second area ratio.

[0024] Next, Fig. 3 shows an enlarged view of the printed image (3). The printed image (3) is composed of four types of images: a first latent image image (4A-1) constituting the first latent image element (4A), a second latent image image (4B-1) constituting the second latent image element (4B), a first visible image image (5A-1) constituting the first visible element (5A), and a second visible image image (5B-1) constituting the second visible element (5B). It is important to note that all of the images are arranged without overlapping. Specifically, the first latent image image (4A-1) and the first visible image image (5A-1), which are images arranged in a first direction (direction S1 in the figure), are arranged at a fixed interval from each other without overlapping. In addition, the second latent image image (4B-1) and the second visible image image (5B-1), which are images arranged in a second direction (direction S2 in the figure), are also arranged at a fixed interval from each other without overlapping. The fact that the images constituting the latent image and the images constituting the visible image are arranged without overlapping is one of the features that distinguish this technology from conventional technologies. Below, we will specifically explain each image and element that constitutes the printed image (3).

[0025] An enlarged view of the latent image (4) is shown in Figure 4. The latent image consists of two types of images: a first latent image line (4A-1) having a first image line width (W1) and a second latent image line (4B-1) having a second image line width (W2).

[0026] An enlarged view of the visible image (5) is shown in Figure 5. The visible image consists of two types of images: a first visible image (5A-1) having a third image width (W3) and a second visible image (5B-1) having a fourth image width (W4).

[0027] Figure 6 shows an enlarged view of the first latent image element (4A) and the second latent image element (4B), which are two images that make up the latent image (4A). The first latent image element (4A) has a first image width (W1), and is composed of a plurality of first latent image lines (4A-1) arranged at a first pitch (P1) in a first direction (S1) to form the information portion of the second significant information, "JPN." The second latent image element (4B) has a second image width (W2), and is composed of a plurality of second latent image lines (4B-1) arranged at a second pitch (P2) in a second direction (S2), to form the background portion of the first significant information, "JPN." The information portion of the second significant information, "JPN," and the background portion are adjacent to each other without overlapping.

[0028] In addition, since the second significant information, the characters "JPN," must be concealed in an observation environment dominated by diffuse reflected light, the first latent image element (4A) and the second latent image element (4B) must be visually identical in color. Therefore, the first latent image element (4A) and the second latent image element (4B) must have the same image area ratio. Therefore, the first image width (W1) and the second image width (W2) may be the same or different, but if the first image width (W1) and the second image width (W2) are the same, the first pitch (P1) and the second pitch (P2) must also be the same. Essentially, it is desirable that the first image width (W1) and the second image width (W2) be the same value, and that the first pitch (P1) and the second pitch (P2) be the same value.

[0029] FIG. 7 shows an enlarged view of the first visible element (5A) and the second visible element (5B), which are two images that make up the visible image (5). In the image of "Shippo," which is the first significant information represented by the visible image (5), the area that overlaps the information portion of "JPN" is the first visible element (5A), and the area that overlaps the background portion of "JPN" is the second visible element (5B). The first visible element (5A) has a third image width (W3) and is composed of a plurality of first visible images (5A-1) arranged at a first pitch (P1) in a first direction (direction S1 in the figure). The second visible element (5B) has a fourth image width (W4) and is composed of a plurality of second visible images (5B-1) arranged at a second pitch (P2) in a second direction (direction S2 in the figure). The first visible element (5A) and the second visible element (5B) must be visually identical in color. The third image line width (W3) and the fourth image line width (W4) may be the same or different, but if the third image line width (W3) and the fourth image line width (W4) are the same, their arrangement pitches, the first pitch (P1) and the second pitch (P2), must be the same.

[0030] In an observation environment dominated by diffuse reflected light, the first significant information, cloisonné, must be visible, requiring a certain degree of shading in the visible image (5). In the present invention, this is achieved by the presence or absence of visible image lines (5A-1, 5B-1). If the first significant information is a binary image, the first visible element (5A) and the second visible element (5B) must have the same image area ratio. Therefore, the third image width (W3) and the fourth image width (W4) may be the same or different, but if the third image width (W3) and the fourth image width (W4) are the same, the first pitch (P1) and the second pitch (P2) must also be the same. Essentially, it is desirable to make the third image width (W3) and the fourth image width (W4) the same value, and to make the first pitch (P1) and the second pitch (P2) the same as well.

[0031] The printed image (3) composed of the image elements described above is formed into a raised structure using high-gloss ink, paint, coloring material, etc. The formation method may be printing, output using a digital printing machine, painting, foil stamping, embossing, etc. When forming by printing, it can be formed by printing methods other than offset that cannot obtain raised height, such as flexographic printing, gravure printing, letterpress printing, intaglio printing, and screen printing.

[0032] Here, we will explain the conditions for the height of the raised image lines in the four printing elements that make up the printed image (3). The image line heights of the first latent image line (4A-1) and the second latent image line (4B-1), which are the two image lines that make up the latent image (4), are approximately the same. If the image line heights of the first latent image line (4A-1) and the second latent image line (4B-1) are high, differences in the shading of the second significant information are more likely to occur due to differences in the angle of incidence of light in the observation angle range where diffusely reflected light and specularly reflected light coexist, thereby increasing the visibility of the second significant information. While there is no fundamental limit to the image line height, considering practicality during distribution and mass production by screen printing or intaglio printing, assuming that each image line pitch (P1, P2) is 0.5 mm, it is appropriate to form the image line height at a value between 30 μm and 5 μm, with a height of approximately 15 μm to 10 μm being more preferable.

[0033] The image heights of the first visible image (5A-1) and the second visible image (5B-1), which are the two images constituting one visible image (5A), must be approximately the same and must be at least lower than the image heights of the first latent image (4A-1) and the second latent image (4B-1). By making the image heights of the first visible image (5A-1) and the second visible image (5B-1) as low as possible, dependency on the incident light direction can be eliminated, and the effect of eliminating the first significant information in the observation angle range where diffusely reflected light and specularly reflected light coexist can be enhanced. The image heights of the first visible image (5A-1) and the second visible image (5B-1) are preferably two-thirds or less, more preferably one-half, of the heights of the first latent image (4A-1) and the second latent image (4B-1). Specifically, the image heights should be 10 μm or less, and more preferably 5 μm or less. When the height of the raised image is 5 μm or less, the angle of the raised slope approaches zero, and the directional dependency of the incident light is almost the same as that of a flat image without raised image. The effect of reducing the directional dependency by reducing the image height will be discussed later.

[0034] As described above, in order to improve the visibility of the second significant information, it is desirable to form the image height of the first latent image line (4A-1) and the second latent image line (4B-1) high, and in order to improve the disappearance effect of the first significant information, it is desirable to form the image height of the first visible image line (5A-1) and the second visible image line (5B-1) low.

[0035] In printing, it is not easy to create different image heights within a single image formed by a single printing run in one color, but it is possible with some printing methods. For example, in intaglio printing, by creating differences in image depth in parts of the plate surface, it is possible to create a difference of more than two times in image height in the finished intaglio print. There is also a correlation between image height and image width in UV screen printing, and there is a certain proportional relationship between image width and image height, especially for image widths of 0.5 mm or less. Therefore, in order to make the image height of the first visible image (5A-1) and the second visible image (5B-1) lower than that of the first latent image (4A-1) and the second latent image (4B-1), the image widths (W3, W4) of the first visible image (5A-1) and the second visible image (5B-1) must not only be narrower than the image widths (W1, W2) of the first latent image (4A-1) and the second latent image (4B-1), but must also be limited to at most half the width. In addition, by selecting ink with appropriate viscosity, the height of the visible images (5A-1, 5B-1) can be reduced to approximately half. Furthermore, among the latest printers known as digital printing presses, some models of UV-curing printers (UV-IJP) allow for flexible control of image height within the same printed material by controlling the amount of ink droplets deposited on the paper. These printers are more preferable because they can easily impart the difference in image height required in the present invention.

[0036] Furthermore, the "high gloss" required for each raised image line is an essential requirement for producing a strong reflected light when incident light is reflected. In this specification, "having a high gloss" refers to at least the property of strongly reflecting light when incident light is applied to a material, thereby increasing the material's brightness, a so-called light-dark flip-flop property. A specific numerical value for "high gloss" refers to a property in which the difference between the brightness of the material measured under diffuse reflected light and the brightness of the material measured under specular reflected light exceeds 20. Failure to meet this requirement is undesirable, as it reduces the effect of eliminating the first significant information when observed at an angle where diffuse reflected light and specular reflected light coexist, thereby relatively reducing the image change effect of the present invention. Furthermore, in addition to the light-dark flip-flop property of increasing brightness by reflecting light, the material may also have a color flip-flop property of changing hue by reflecting light. In this case, in addition to the image disappearance effect, the image hue also changes, resulting in the formation of a latent image print (1) with excellent color change.

[0037] Possible methods for forming lines and pixels that satisfy the above-mentioned characteristics by printing include printing with a functional ink in which a functional pigment such as a metal pigment, glass material, or liquid crystal material with excellent light reflectivity is mixed into the ink, or using a high-gloss resin selected for the resin component of the varnish or medium that makes up the majority of the ink, thereby utilizing the gloss of the resin in the ink, etc. Also usable are methods in which raised lines or pixels that do not have gloss are formed, and then a high-gloss varnish is printed on top of them, or a glossy resin or pigment is sprayed on to give a final gloss.

[0038] When printing with functional inks, the functional pigments that can be used include metal powders such as aluminum, brass, and copper, as well as scaly mica pigments, scaly metal pigments, glass flakes, and cholesteric liquid crystal pigments, typified by pearlescent pigments that can achieve special hue changes. In particular, when raised lines are formed using pearlescent inks or liquid crystal inks, they can be given a so-called color flip-flop effect, in which not only the brightness but also the hue changes when light is incident, which is more difficult to imitate than printed images that use simple light-dark flip-flops (3), making them more resistant to counterfeiting and also enhancing designability, making them more desirable.

[0039] The effect of the latent image print (1) of the present invention formed using the above configuration will be described below with reference to FIG. 8. As shown in FIG. 8(a), when the latent image print (1) of the present invention is observed in an angular region where diffuse reflected light is dominant, the first significant information, a "shippo" image, is visible in the printed image (3). The angular region where diffuse reflected light is dominant refers to an angular region where the angle between the line connecting the light source (6) and the printed material and a vertical (90-degree) line (the incident angle of the incident light) is significantly different from the angle between the line connecting the latent image print (1) and the observer's viewpoint (7a) and a vertical (90-degree) line (the receiving angle of the reflected light). If the incident angle is approximately 45°, this region corresponds to a light receiving angle range of approximately -90 to 10° (0° in FIG. 8(a)).

[0040] When the latent image print (1) of the present invention is observed in the angular region where diffuse reflected light and specular reflected light coexist, as shown in Figure 8(b), the alphabet characters "JPN," which are the second significant information, are visible in the printed image (3) in either a positive (dark image area and light background area) or negative (light image area and dark background area). The angular region where diffuse reflected light and specular reflected light coexist refers to an angular region where the angle between the line connecting the light source (6) and the print and a vertical (90-degree) line (the incident angle of the incident light) is relatively close to the angle between the line connecting the latent image print (1) and the observer's viewpoint (7b) and a vertical (90-degree) line (the receiving angle of the reflected light). In Figure 8(b), the incident angle is approximately 45°, and the receiving angle is in the range of approximately 10° to 80° (50° in Figure 8(b)).

[0041] The principle behind the above-described effect will now be explained. In the angle range where diffusely reflected light is dominant, the observer perceives differences in the color of the materials as more emphasized than subtle differences in the three-dimensional structure of the materials. That is, in the present invention, the influence on the perceived image of differences in the image line angle of raised image lines and the three-dimensional shape of pixels is extremely small, while the influence on the perceived image of differences in shading caused by differences in the image line or pixel area ratio is significant. Therefore, the observer perceives the first significant information constituted by differences in area ratio.

[0042] On the other hand, in angular regions where diffuse reflected light and specular reflected light coexist, the observer perceives reflected light generated by the material's reflection. Therefore, compared to observation environments dominated by diffuse reflected light, the three-dimensional structure of the material is relatively emphasized. This tendency is particularly pronounced when the material has strong light-reflecting properties. The information portion of the second significant information visible in angular regions where diffuse reflected light and specular reflected light coexist always comprises multiple lines arranged in a first direction. On the other hand, the background portion of the second significant information comprises multiple lines arranged in a direction different from the first direction. Therefore, due to differences in the three-dimensional structure characteristics, including the line orientations of the lines constituting the second significant information, the amount of reflected light generated from the information portion of the second significant information differs from the amount of reflected light generated from the background portion of the second significant information. This phenomenon makes the previously invisible second significant information visible depending on the amount of reflected light. In this case, the difference in shading due to the difference in area ratio representing the first significant information becomes lighter as the image lines reflect light, the shading difference is visually compressed, and the contrast of the first significant information is lost and therefore visually disappears. As described above, in angular regions where diffuse reflected light and specular reflected light are mixed, the first significant information disappears as the printed image (3) reflects light, and the second significant information becomes visible, resulting in an image change effect. Based on the above principle, the first significant information is visible in angular regions where diffuse reflected light is dominant, and the second significant information is visible in angular regions where diffuse reflected light and specular reflected light are mixed.

[0043] One of the features of this technology is the high image change effect, which is derived from the high effect of eliminating the first significant information in the angle region where diffuse reflected light and specular reflected light are mixed. The high effect of eliminating the first significant information is due to the fact that the first visible image (5A-1) and second visible image (5B-1) constituting the first significant information of the latent image print (1) are formed with a lower protuberance height compared to the first latent image (4A-1) and second latent image (4B-1) constituting the second significant information. The reason for this will be explained below.

[0044] FIG. 9 shows an image structure formed by the prior art configuration described in Patent Document 1. As shown in FIG. 9(a), the visible image is composed of thick and thin image lines, and is therefore composed of a basic latent image line (4B-1) combined with visible image lines (5B-1) on both sides. As shown in FIG. 9(b), when light is incident on this image line from a first direction (S1) perpendicular to the image line direction, only the lower half of the image line from the center strongly reflects light. Also, as shown in FIG. 9(c), when light is incident on this image line from the first direction (S1) parallel to the image line direction, the center of the image strongly reflects light. To achieve an image change effect, comparing the areas of the light reflecting surfaces in FIG. 9(b) and FIG. 9(c), it is desirable for the difference in the areas of the reflecting surfaces of the latent image line (4B-1) to be large, while it is desirable for the reflecting surface of the visible image line (5B-1) to be large in both cases.

[0045] In the case of the image shown in FIG. 9, the light reflection area of ​​the visible image (5B-1) in FIG. 9(b) is half the total area of ​​the visible image (5B-1), and the light reflection area of ​​the visible image (5B-1) in FIG. 9(c) is zero. Therefore, while a certain elimination effect can be achieved for incident light from the first direction (S1) shown in FIG. 9(b), no elimination effect can be achieved for incident light from the second direction (S2) shown in FIG. 9(c). Therefore, in the case of a conventional configuration using image thickness and thinness, the elimination effect of the first significant information is low in the angle range where diffuse reflected light and specular reflected light coexist. Furthermore, in this configuration, if the latent image (4B-1) becomes taller, the height of the visible image (5B-1) also inevitably becomes taller.

[0046] Next, FIG. 10 shows a configuration in which the visible image (5B-1) is separated from the latent image (4B-1), similar to the image configuration in the technology of the present invention. However, the configuration shown in FIG. 10 differs from the configuration of the present invention in that there is no significant difference in image height between the latent image (4B-1) and the visible image (5B-1). In this configuration, a certain disappearance effect can be achieved for incident light from the first direction (S1) shown in FIG. 10(b), as the lower half of the image reflects light. However, for incident light from the second direction (S2) shown in FIG. 10(c), unlike the example in FIG. 9(c), the center of the visible image (5B-1) reflects light, resulting in a disappearance effect, albeit to a lesser extent. Therefore, in the configuration in which the visible image (5B-1) is separated from the latent image (4B-1), the disappearance effect of the first significant information in the angular region where diffuse reflection light and specular reflection light coexist is not sufficient, but is relatively high compared to the configuration of FIG. 9.

[0047] Figure 11 shows an image that is visible in the printed image (3) in an angle region where diffusely reflected light and specularly reflected light coexist when the latent image print (1) of the present invention is constructed using the image configurations of Figures 9 and 10. Figure 11(a) shows the case where light is incident from the first direction (S1), in which the first significant information in the background portion is completely lost due to the latent image image that is perpendicular to the light and strongly reflects the light, but the shading of the first significant information contained in the information portion is not lost, and as a result, the information portion of the second significant information is visualized as an unclear image in which the shading of the first significant information is reflected.

[0048] On the other hand, Figure 11(b) shows the case where light is incident from the second direction (S2). While the first significant information in the information area is completely erased due to the strong reflection of the latent image lines perpendicular to the light, the shading of the first significant information contained in the background area is not lost. As a result, the first significant information is visualized as an unclear image in which the shading of the first significant information is reflected in the background area of ​​the second significant information. From the above, when the raised image lines constituting the visible image (5) are formed with a constant height, it is difficult to eliminate the dependency on the direction of light incidence, making it difficult to completely erase the first significant information. To solve this problem, the present invention aims to enhance the effect of completely erasing the first significant information by setting a condition for the height of the raised image lines constituting the visible image (5). The effect is specifically described below.

[0049] FIG. 12 shows an image configuration according to the present invention in which the visible image (5B-1) is separated from the latent image (4B-1), and the image height of the latent image (4B-1) is high and the image height of the visible image (5B-1) is low. When the image height of the visible image (5B-1) is low, the directional dependency of the reflected light on the incident light is relatively low or eliminated. In the configuration shown in FIG. 12, the entire visible image (5B-1) reflects light from the first direction (S1) shown in FIG. 12(b), resulting in a high fading effect. Similarly, the entire visible image (5B-1) reflects light from the second direction (S2) shown in FIG. 12(c), resulting in an extremely high fading effect. Essentially, the lower the visible image height, the higher the fading effect. The fading effect is greatest when the visible image height is completely flat. The high image change effect in the present invention is due to the image structure in which the latent image (4B-1) and the visible image (5B-1) are separated, and the image height of the latent image (4B-1) is made high and the image height of the visible image (5B-1) is made low.

[0050] As mentioned above, the angular region where diffuse reflected light and specular reflected light coexist corresponds to an incident angle of approximately 45° and a light-receiving angle ranging from approximately 10° to 80° in the diagram of Figure 8(b). However, strictly speaking, the first significant information is again visible at a light-receiving angle of approximately 45° ± 5°. This is because specular reflected light is dominant in this angular region (specular reflected light accounts for a significantly larger proportion than diffuse reflected light), again emphasizing differences in area ratio over slight differences in the three-dimensional structure of the object. However, this is a phenomenon that is recognized when light is incident on a latent image print from a single light source. In the typical environment in which we live, where there are many light sources, this angular region does not exist or is extremely narrow, making it difficult to recognize this phenomenon without careful observation. Therefore, in this specification, this angular region where specular reflected light dominates is also treated as an angular region where diffuse reflected light and specular reflected light coexist, and is treated as an angular region in which the second significant information is observed.

[0051] Here, the first area ratio and the second area ratio will be described. The first area ratio is a value closely related to the visibility of the second significant information, and a high value is generally required to ensure a certain level of image height for images with a certain degree of elevation. By configuring the first area ratio to be between 20% and 60%, the visibility of the second significant information can be improved. On the other hand, the second area ratio is a value related to the visibility of the first significant information. By configuring the second area ratio to be between 10% and 30%, the visibility of the second significant information visible under diffuse reflected light can be maintained, and a high disappearance effect can be achieved in areas where diffuse reflected light and specular reflected light are mixed. Since the appropriate first area ratio and second area ratio depend on the color and reflection characteristics of the pixel, appropriate differences must be found each time the constituent color materials or brightness flip-flop characteristics change.

[0052] Next, the first direction (S1) and the second direction (S2) will be described. The first direction (S1) and the second direction (S2) must not be at the same angle, so an angular difference is required. The angular difference that produces the greatest difference in the amount of reflected light is 90 degrees, where the image lines are perpendicular to each other. As the angular difference from 90 degrees decreases, the amount of reflected light decreases. Therefore, the visibility of the second significant information in the angle range where diffuse reflected light and specular reflected light coexist is maximized at an angular difference of 90 degrees and minimized at 0 degrees, where the two directions are parallel. Since the second significant information becomes invisible at 0 degrees, in the present invention, the angular difference between the first direction (S1) and the second direction (S2) at which the second significant information is visible is set to 5 degrees. Therefore, the angular difference between the first direction (S1) and the second direction (S2) must be within the range of 90 degrees to 5 degrees and must not deviate from this range, i.e., 0 degrees to less than 5 degrees.

[0053] There are no particular restrictions on the line pitch (P1, P2), but assuming that it is to be used for security prints of the size of banknotes, gift certificates, or passports, it is desirable to configure it in the range of approximately 0.1 mm to 5 mm.

[0054] FIG. 13 shows examples of the first visible image (5A-1) and the second visible image (5B-1) constituting the visible image (5) of the present invention. In the present invention, an image is defined as a set of pixels having a certain length, which are formed by a set of dots, the smallest unit of image components, gathered in a certain direction. Therefore, even wavy or dashed lines are considered to be images as long as they have a certain directionality (image angle). As shown in FIGS. 13(b) and 13(c), a visible image may be provided with varying thickness and thinness to impart gradation to the visible image. Furthermore, the dashed line may be a dashed line without periodicity in the non-image portion, as shown in FIG. 13(d), or a dashed line with periodicity in the non-image portion, as shown in FIG. 13(e). Gradation may also be expressed by varying thickness and thinness in the dashed line.

[0055] Fig. 14 shows an embodiment in which the visible image is configured with dashed lines (pixels). The image configuration is similar to the technology described in Patent Document 2, but by forming the dashed lines of the visible image portion at a low height, the image change effect is enhanced.

[0056] Hereinafter, examples of latent image prints specifically produced in accordance with the above-described embodiment of the invention will be described in detail, but the present invention is not limited to these examples. [Example]

[0057] An embodiment of the present invention will be described with reference to Figures 1 to 8. Figure 1 shows a latent image print (1) of the present invention. The latent image print (1) has a substrate (2) made of ordinary white coated paper (manufactured by Nippon Paper Industries Co., Ltd.) on which a silver printed image (3) is formed.

[0058] In this Example 1, the printed image (3) contains first significant information representing a "shippo" image, as in the embodiment, and second significant information representing the letters "JPN" of the alphabet.

[0059] The image structure of the print image (3) in this example is the same as that described in the embodiment, and therefore a detailed description of the structure will be omitted. In this example, the first pitch (P1) and second pitch (P2) were 0.4 mm, the first image width (W1) and second image width (W2) were 0.16 mm, and the third image width (W3) and fourth image width (W4) were 0.06 mm. The first area ratio in this example was 40%, and the second area ratio was 15%. The first direction (S1) was vertical, and the second direction (S2) was horizontal, with the image directions intersecting at an angle of 90 degrees.

[0060] A printed image (3) composed of the above image elements was printed by a UV-drying screen printing method using a silver UV screen ink (Mirashene, manufactured by Wolstenholm). This ink is a glitter ink containing evaporated aluminum as a light-reflecting functional material, and has extremely excellent reflectivity, emitting extremely strong specular reflection light by reflecting light and increasing the brightness of the image by 200 or more. In this embodiment, the image height of the first latent image (4A-1) and the first latent image (4B-1) was approximately 15 μm, and the image height of the first visible image (5A-1) and the first visible image (5B-1) was approximately 4 μm.

[0061] The effect of the latent image print (1) formed using the above configuration will be explained using FIG. 8. As shown in FIG. 8(a), when the latent image print (1) of the present invention is observed in an angle region where diffuse reflected light is dominant, the "Shippo" image, which is the first significant information, is visible in silver in the printed image (3). Furthermore, when the latent image print (1) of the present invention is observed in an angle region where diffuse reflected light and specular reflected light are mixed, as shown in FIG. 8(b), the printed image (3) strongly reflects light and appears white, and the alphabet characters "JPN," which are the second significant information, are visible in the printed image (3) in either a positive (dark image area and light background area) or negative (light image area and dark background area). As described above, it was confirmed that the effect of changing the image visible in the printed image (3) can be obtained between an angle region where diffuse reflected light is dominant and an angle region where diffuse reflected light and specular reflected light are mixed. [Explanation of symbols]

[0062] 1 Latent image prints 2 Base material 3 Printed images 4 Latent Image 4A First Latent Image Element 4B Second latent image element 4A-1 First latent image 4B-1 Second latent image 5 Visible images 5A First Visible Element 5B Secondary Visible Element 5A-1 First Visible Image 5B-1 Second Visible Image 6 light source 7a, 7b viewpoints

Claims

1. a printed image on at least a portion of a substrate, the printed image having a different color than the substrate; the print image comprises at least a first latent image element, a second latent image element, a first visible element, and a second visible element, each of which has at least a light-dark flip-flop property and is formed by a collection of a plurality of raised image lines, constituting first significant information and second significant information; the first latent image element is composed of a plurality of first latent image lines arranged in a first direction at a first area ratio; the second latent image element is configured by arranging a plurality of second latent image lines in a second direction different from the first direction at the first area ratio, the first visible element is configured by arranging a plurality of first visible images in a first direction with a second area ratio smaller than the first area ratio; the second visible element is formed by arranging a plurality of second visible images in a second direction with the second area ratio; the first latent image line and the first visible image line, and the second latent image line and the second visible image line are arranged at regular intervals without overlapping with each other; the first visible image line and the second visible image line are formed to have a lower image height than the first latent image line and the second latent image line, the second significant information is formed by the difference in arrangement direction between the first latent image elements and the second latent image elements; the first significant information is formed by the presence or absence of the first visible element and the second visible element; When observed at an angle where diffuse reflected light is dominant, the first significant information is visually recognized from a difference in shading caused by the presence or absence of the first visible element and the second visible element and the difference in area ratio between the first area ratio and the second area ratio, When observed at an angle where diffuse reflected light and regular reflected light are mixed, the second significant information is visible due to the intensity of reflected light resulting from differences in the arrangement direction and height of the image lines.

2. 2. The authentic latent image print according to claim 1, wherein the height of the first visible image line and the second visible image line is less than half the height of the first latent image line and the second latent image line, or is less than 5 μm.

Images