Transient Image Technology

In today's diversified security and anti-counterfeiting measures, various new types of anti-counterfeiting technologies emerge in an endless stream, presenting a flourishing situation. The key to an anti-counterfeit technology is to extend the timeliness and uniqueness of anti-counterfeiting technology, which is also the goal of anti-counterfeiting technology. The uniqueness and the difficulty in replicating are the core contents of the anti-counterfeiting technology. The anti-counterfeit technologies mainly include: anti-counterfeiting of printing design, anti-counterfeiting of printed paper, anti-counterfeiting of printing ink, and anti-counterfeiting of printing processes. Among them, the printing process anti-counterfeiting technology is the most prominent in the reproduction, the high printing cost makes many imitation products extremely poor, and the printed matter also has a very good printing effect. At present, the anti-counterfeiting technology of the printing process is in good condition and the application range is becoming more and more extensive.

The transient image is an anti-counterfeiting technique in which the relief pattern is applied to a printed substrate. In general, there are two kinds of printing methods, gravure relief or prime embossed relief pattern. The difference between the transient image and the general image is mainly judged by the change of the light source and the observer. Transient images and light-transformed images have many similar effects, but because the light-transforming images are caused by the interference of light and diffraction effects, the transient image itself is not a luminous light-changing image technique, but is generally divided into two. Species: latent images and transient images. The latent image is observable under normal conditions and can only be observed when it is tilted; transient images can only be observed under normal conditions, and the image will disappear when the image is tilted.

Transient images cannot be reproduced by photoengraving or digital copying techniques. Duplicated counterfeits do not have corresponding optical effects. Therefore, the transient image has a strong anti-counterfeiting feature. However, transient images also have certain flaws. The wrinkling phenomenon of files using transient images during circulation will affect the anti-counterfeiting effect under certain conditions. The transient image is a kind of hidden image. Due to the unique anti-counterfeit effect under different observation conditions, the application scope is very wide.

1. Latent image

The latent image is composed of a foreground gravure grating line and a background gravure grating line, and the position angle of the background raster line is determined accordingly. Raster lines are generally printed in dark colors, and under normal observation conditions, the spatial frequency of the raster lines is such that it is difficult for the human eye to feel the existence of the raster lines. If the foreground raster raster line is tilted to a suitable angle, a shadow that darkens the base of the paper will be formed between the line and the line, which will result in a darkening of the area around the background. From a certain angle of view, the optical effect will be more pronounced because the backside raster lines will bend inward to obstruct the observation of the intermediate paper base. If the image is rotated 90° or the direction of the viewing light is rotated 90°, the foreground and background colors form the transition:

Obviously, the latent image under the counterfeit embossed relief pattern, the optical effect will completely disappear. Latent image anti-counterfeiting has been applied to many aspects, such as passports, cheques, travel checks, and so on. However, because the latent image pattern can only be observed when it is tilted, it is not easy for the public to be noticed, and only a few experts can recognize it. Therefore, for a large number of documents, the latent image pattern is not the most popular mass anti-counterfeiting.

Especially under the observation of the point light source, the gloss of the gravure ink will affect the observation effect of the latent shadow pattern. Because shadows projected onto gravure raster lines increase the color rejection, specular reflections reduce the contrast between foreground and background colors.

On paper with high gloss, if there is no relief, the effect can be easily distinguished. No embossing or embossing can be printed without ink. This printing can be embossed directly on the substrate without ink engraving. However, under normal circumstances, this pattern is difficult to observe. However, observing at an oblique angle, the specular reflection of the imprinting line will be easily observed, and the foreground or background will be very obvious. In this case, the optical effect is exactly the opposite of the above-mentioned latent image effect. As shown in Figure 3.

The application of high-gloss ink and embossed printing can be extended to the mutual use of low-frequency relief and high-frequency embossing. Since the pattern will reduce the gloss of the ink, the low-frequency pattern is difficult to show at an oblique angle. However, In the case of specular reflection, it is very obvious, as shown in Figure 4.

2. Transient image

Another very interesting application of embossing printing is the combination with the background printing. Illumination shines obliquely from the blank part, and the ink part can be hidden in the shadow of the blank part. Then, the printed text part will be in 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 shadow, the density of the shadow and the 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 viewed at a different angle, the relative areas of light and darkness will change, or alternate light and dark changes will occur. If this method is used to print a certain textual content, then these texts will alternate with light and darkness relative to the paper background, as shown in Figure 6. Take the currency of Japan as an example. In the upper right corner of the currency, if there is no normal display, there is no pattern display; when the light source is tilted from above, the “nippon” pattern is displayed, “nipp” is 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 just opposite to the above, which is determined by the characteristics of the embossed pattern changing at any time, and this kind of latent image may disappear at a specific illumination angle and viewing angle. Therefore, we refer to this type of embossed pattern as a transient image. At the same time, since this type of image is easily observed under normal observation conditions, it conforms to the easy-to-identify feature in security printing, so its security value is Higher than the latent image, can be used as the first line of defense.

In a word, because counterfeiters increasingly raise the level of counterfeit and counterfeiting, the number of counterfeit counterfeiters has promoted the emergence of new anti-counterfeiting technologies, and it is required to quickly, cheaply, and accurately reveal the authenticity of the object to be protected. Among them, 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 to life, due to the high cost and immature technology, the current use still has certain limitations. However, with the continuous progress 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.

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