The concept of holographic technology was first proposed by Gabor in 1948. With the advent of lasers in 1962, Leith and Upatnieks invented off-axis holography based on Gabriel holography. . In 1969, Benton invented rainbow holography to pick up a new climax of holographic three-dimensional display featuring white light. The combination of rainbow holography and the increasingly mature hologram molding replication technology at that time formed the holographic printing industry that is now popular in the world.
After decades of development, laser holographic anti-counterfeiting products have gradually evolved from the original holographic anti-counterfeiting mark to the second, third or even fourth-generation laser anti-counterfeiting technology.
First, the first generation of laser anti-counterfeiting technology
The first generation of laser anti-counterfeiting technology is mainly used to make laser-embossed holographic image anti-counterfeit labels.
The hologram was discovered by the American scientist M.J. Buerger when he took photos of the atomic structure of the crystal using X-rays. Together with Gabor, he created the holographic theory, which uses the principle of two-beam interference. The holographic image can be obtained by making the interference between the object light and another beam (reference beam) that is coherent with the object light to "merge" the phase, thereby simultaneously recording the lower phase and amplitude with the photographic film. Due to the poor monochromaticity of the ordinary light source and the poor coherence, the holographic technology is slow to develop, and it is difficult to obtain a satisfactory hologram. Until the early 1960s, the laser appeared, with its high brightness, high monochromaticity and high coherence characteristics, rapidly promoted the development of holographic technology, many kinds of holograms were produced, and holographic theory was well verified. . However, due to the special requirements of shooting and reproduction, holographic technology has been almost confined to the laboratory since its birth.
In the late 1970s, holograms were found to have surface structures that include three-dimensional information (ie, criss-cross interference fringes that can be transferred to materials such as high-density photoreceptors). In 1980, American scientists used embossed holography to transfer the holographic surface structure to the polyester film, successfully printing the world's first molded hologram. This kind of laser hologram is also called rainbow hologram. It is made by laser plate making the image onto the plastic film to produce a diffractive effect of five colors and ten colors, so that the picture has a two-dimensional and three-dimensional sense of space. Under normal light, the hidden images and information in the picture will reappear, and when the light is illuminated from a certain angle, a new image will appear on the picture. This molded hologram can be quickly copied in large quantities like printing, at a lower cost, and can be combined with various types of printed matter. At this point, holographic photography has taken a decisive step toward social applications.
At that time, the production technology of this molded hologram was very advanced, and only a few people mastered it, so it was used to make anti-counterfeiting labels. The principle of its anti-counterfeiting is:
1. In the whole process of laser hologram shooting, if there is a different condition (such as the condition of shooting rainbow hologram), the effect of holographic logo will be different;
2. The holographic information of such a holographic image cannot be photographed by ordinary photography, and thus the hologram pattern is difficult to copy.
The first product to use holograms as anti-counterfeiting labels was JohnnyWalkeWhishy, ​​a whisky that sold about 45% more than before.
Laser embossed holographic anti-counterfeiting technology was introduced to China in the late 1980s and early 1990s. From 1990 to 1994, hundreds of production lines were introduced across the country, accounting for more than half of the world's manufacturers. In the early stage of introduction, this anti-counterfeiting technology did play a certain role in anti-counterfeiting. However, with the rapid spread of laser holographic image production technology, it was quickly attacked by various counterfeiters. The laser holographic anti-counterfeiting label almost completely lost its anti-counterfeiting ability. The laser molding equipment has also dropped from the initial tens of millions of dollars to a few tens of thousands of yuan.
Second, the second generation of improved laser holographic image anti-counterfeiting technology
The proliferation of the first generation of laser holographic anti-counterfeiting technology prompted people to start looking to improve the existing technology. There are three main improvements: one is the application of computer image processing technology to improve holographic images; the second is transparent laser holographic image anti-counterfeiting technology; the third is reflective laser holographic image anti-counterfeiting technology.
Application of computer image processing technology to improve holographic images
Computer image processing technology improved laser holographic image has experienced two developments. The first form is computer synthetic holography. This technology is to optically image a series of ordinary two-dimensional images, and then process them according to the imaging principle of holographic images. A holographic recording material forms a computer pixel holographic image. When observing such a pixel holographic image, different three-dimensional images can be seen at different viewing angles, and both the graphics and the color have an extremely flexible dynamic effect and are not limited by the direction of the reproduced light. The second form is a computer-controlled direct exposure technique. Unlike ordinary holographic imaging, this technique does not require a subject to be photographed. The required graphics are completely generated by a computer. The two coherent beams are controlled by a computer to generate all the patterns point by point in units of pixels. Different points can change the angle between the two beams to create a three-dimensional hologram with special effects.
Transparent laser holographic image anti-counterfeiting technology
Ordinary laser holographic images are generally molded by aluminized polyester film (which can also be first molded and then aluminized with a polyester film). The effect of aluminizing is to increase the intensity of the reflected light to make the reproduced image brighter. Both the illumination light and the viewing direction are on the observer side, and such a laser rainbow embossed hologram is opaque. The transparent laser holographic image actually eliminates the aluminized layer and directly molds the holographic image onto the transparent polyester film. In 1996, the Ministry of Public Security of China applied the transparent laser holographic image to the resident ID card, and covered the ID card with a transparent film. When observing the front of the ID card under the light, not only can the contents of the certificate be seen, but also the transparent film can be seen. Two-dimensional, three-dimensional rainbow holographic images ("Chinese and English" in the "Great Wall" and "China").
Reflective laser holographic image anti-counterfeiting technology:
The principle of reflective laser holographic image imaging is to project incident laser light onto a transparent holographic latex medium, some of which is used as reference light, and another part illuminates the object through the medium, and then the object is scattered back to the medium as object light, and the object light and the reference light are mutually Interference, a multi-layer interference fringe surface is generated inside the medium, and the dielectric film is processed to generate a multi-layer semi-transparent reflecting surface inside the medium (for example, there may be more than 20 reflecting surfaces in a 6-micron thick latex layer), and irradiated with a white light source. The hologram, the multi-layer semi-transparent reflecting surface generated inside the medium reflects the light back, and can see the virtual image of the original against the reflected light, so it is called a reflected laser hologram.
Third, the third generation of encrypted holographic image anti-counterfeiting technology
The encrypted holographic image refers to an encrypted image that is invisible or becomes some speckle obtained by encrypting the anti-counterfeit image by using optical image encoding and encryption techniques such as random phase encoding encryption, moiré encoding encryption, and laser speckle encryption. The image encrypted by the random phase encoding is invisible, and the original image can be displayed only by using a special photoelectric decoder. Currently, it is mainly used for anti-counterfeiting of various cards. An image encrypted by Mohr-encoded encryption and laser speckle is superimposed only on the decoded raster or decoded speckle to display the original image, which can be used for anti-counterfeiting of general merchandise.
Encrypted holographic images have a certain anti-counterfeiting function because they are invisible or only show a piece of noise, such as no key is difficult to decipher.
Fourth, the fourth generation BOPP laser holographic anti-counterfeiting shrink film packaging anti-counterfeiting technology
BOPP laser holographic anti-counterfeiting shrink film packaging anti-counterfeiting technology is a new anti-counterfeiting technology developed by combining the first three laser technologies. Since this technology has special requirements for BOPP shrink film substrates, the purchase and development of BOPP production equipment is expensive, which blocks the possibility and feasibility of counterfeiting fraud at the source. The laser holographic anti-counterfeiting shrink film is the first in the production to combine the wide holographic transparent molding technology with the encryption holographic image anti-counterfeiting technology, and cleverly solves the contradiction between hot pressing and substrate heat shrinking; in the use of BOPP anti-counterfeiting shrink film two surfaces The heat seal is provided, and the packaged object is completely wrapped; the BOPP anti-counterfeit film must be torn open at the time of unpacking, and this also destroys the integrity of the original anti-counterfeit film. Due to the complicated technical level, high anti-counterfeiting force, fine craftsmanship and exquisite appearance, the anti-counterfeiting means was highly praised by the Professional Committee of Laser Holographic Technology of China National Defense Industry Association.
The anti-counterfeiting effect of BOPP laser holographic anti-counterfeiting shrink film is much stronger than that of laser holographic image anti-counterfeiting mark, and its anti-counterfeiting life is much longer than the anti-counterfeiting life of laser holographic image anti-counterfeiting mark. Because the laser holographic image anti-counterfeiting mark is printed by the printing house, it cannot ensure that the master does not flow out or illegally copy from the printing process. At the same time, for the counterfeiter, the laser holographic mark can be purchased directly, without the need for equipment investment or mastering. technology. And use BOPP laser holographic anti-counterfeiting shrink film for packaging anti-counterfeiting,
The high price of BOPP production line and the complicated processing technology of heat-sealed heat shrinkable film, together with transparent holographic anti-counterfeiting images and secret miniature passwords, make it difficult for scattered small and medium-sized factories to make fakes.
Laser holographic anti-counterfeiting technology is a modern laser application technology that has received widespread attention at home and abroad in recent years. It is favored and loved by consumers with complex holographic imaging principles and colorful flash effects. Compared with general printed trademarks, laser holographic image anti-counterfeiting labels have unique advantages and charms, and can be widely used in trademarks, securities, confidential cards and luxury handicrafts of light industry, medicine, food, cosmetics and electronics industries. Security. However, there are many domestic manufacturers and the management is extremely chaotic, which greatly affects the credibility of the laser holographic image anti-counterfeiting mark in people's minds. The BOPP laser holographic anti-counterfeiting shrink film that has been anti-counterfeiting from the substrate will be replaced and will make its due contribution to the development of transparent anti-counterfeiting technology at home and abroad.
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