Talking about transient image technology
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Today, with the diversification of security and anti-counterfeiting measures, various new anti-counterfeiting technologies are emerging one after another, presenting a situation of blooming. The key to an anti-counterfeiting technology is to extend the timeliness and uniqueness of anti-counterfeiting technology, which is also the goal pursued by anti-counterfeiting technology. Uniqueness and difficulty in copying are the core contents of anti-counterfeiting technology. Anti-counterfeiting technology mainly includes: anti-counterfeiting of printing design, anti-counterfeiting of printing paper, anti-counterfeiting of printing ink and anti-counterfeiting of printing process. Among them, the printing technology anti-counterfeiting technology is the most prominent in copying, the high printing cost makes many imitation products have very poor effect, and the printed matter also has very good printing effect. At present, the printing technology anti-counterfeiting technology is in a good situation and the application range is increasingly wide.
A transient image is an anti-counterfeiting technique in which an embossed pattern is applied to a printed substrate. Generally speaking, there are two printing methods, gravure embossing or prime embossing embossing. The difference between a transient image and a general image is mainly judged by changes in the light source and the observer. Transient images and light-changing images have many similar effects, but since the photo-induced image is caused by the interference of light and the diffraction effect, the transient image itself is not a kind of illuminating photo-variable image technology, generally divided into two. Species: latent image and transient image. The latent image is not observed under normal conditions, and can only be observed under tilt; the transient image can only be observed under normal conditions, and the image disappears under certain tilt conditions.
Transient images cannot be reproduced by photolithography or digital reproduction techniques, and the copied counterfeits do not have the corresponding optical effects. Therefore, transient images have a strong anti-counterfeiting function. However, transient images also have certain defects, and wrinkles in the circulation process of files using transient images may affect the anti-counterfeiting effect under certain circumstances. Transient images are a type of hidden image that has a wide range of applications due to its unique anti-counterfeiting effect under different viewing conditions.
1. Latent image
The latent image is composed of a foreground gravure raster line and a back gravure raster line, and the position angle of the back view raster line is determined accordingly. The raster lines are typically printed in dark colors, and under normal viewing conditions, its spatial frequency is such that it is difficult for the human eye to feel the presence of raster lines. If the foreground raster line is tilted to the proper angle, a shadow portion that darkens the paper base is formed between the line and the line, which causes the portion around the back view to become dark. From a certain angle of view, the optical effect will be more obvious, because the rear view raster line will bend inside to block the observation of the middle paper base. If the image is rotated 90° or the direction of the light is rotated by 90°, the foreground and back views form a transition:
Obviously, the optical image will completely disappear under the forged gravure embossed image. Latent shadow anti-counterfeiting has been used in many ways, such as passports, checks, traveler's checks, and so on. However, since the latent image pattern can only be observed under the tilt, it is not easy for the public to be valued, and only a few experts can recognize it. Therefore, for a large number of documents, the latent image pattern is not the most important public security.
Especially under the condition of point light source, the gloss of the gravure ink will affect the observation effect of the latent image pattern. Because the shadow cast onto the gravure raster line increases the inverse color rate, specular reflection reduces the contrast between the foreground and back views.
On paper with high gloss, if there is no relief, the effect is easily distinguished. No embossing or embossing can be carried out without ink, which can be embossed directly on the substrate by inkless engraving. However, under normal circumstances, this pattern is difficult to observe. However, when viewed at an oblique angle, the specular reflection of the embossed line will be easily observed, and the foreground or background lines will be very noticeable. In this case, the optical effect is exactly the opposite of the latent image effect mentioned above. As shown in Figure 3.
The cross-application of high-gloss ink and embossed printing can be extended to the mutual use of low-frequency embossing and high-frequency embossing. Since the pattern reduces the gloss of the ink, the low-frequency pattern is difficult to appear at an oblique angle, however, In the case of specular reflection, it is very obvious, as shown in Figure 4.
2. Transient image
Another interesting application of embossed printing is the combination of undertone printing. The illumination is obliquely illuminated from the blank portion, and the ink portion can be hidden in the shadow of the blank portion. Then, the printed graphic portion is in the shadow, and the printing density will not increase the density of the entire printed image. At the same time, under normal conditions, the image still maintains a certain degree of gloss. Conversely, if the blank portion is in the shadow, the density of the shadow and printing ink will determine the brightness of the entire pattern, and the brightness of the entire pattern will decrease.
If the printed embossed pattern is changed at an angle, the relative areas of the light and dark will change, or an obvious change in brightness and darkness will occur. If a certain text content is printed by this method, then the text will alternate between light and dark with respect to the paper background, as shown in Fig. 6. Take the Japanese currency as an example. In the upper right corner of the currency, if there is no pattern display under normal observation; when the light source is obliquely illuminated from above, the “nippon” pattern is displayed, “nipp” is relatively dark relative to the background, and “on” is relatively The background brightness is relatively high; if the light source is illuminated from below, the effect is exactly opposite to the above, which is determined by the changing characteristics of the embossed pattern, which may disappear at a specific illumination angle and viewing angle. Therefore, we call this embossed pattern a transient image. At the same time, since this image is easily observed under normal observation conditions, it conforms to the easy identification characteristics in anti-counterfeiting printing, so its anti-counterfeiting value is Higher than the latent image, it can be used as the first line of defense.
In short, as the level of counterfeiting and counterfeiting of imitations is increasing and the number of counterfeiting is large, the new anti-counterfeiting technology is promoted, and the authenticity of the object to be protected can be quickly, cheaply and accurately revealed. The anti-counterfeiting technology has played an important role. effect. Transient image technology has also emerged. Although the current transient technology has been greatly developed and applied in life, due to the high cost and immature technology, the current use still has certain limitations. However, with the continuous advancement of society, many difficulties will be solved. We believe that this very easy-to-use anti-counterfeiting method will become an important part of anti-counterfeiting technology.