Laser printing and laser holographic printing and their processes

When it comes to printing, it is natural to think of our country’s rise. As early as the Song Dynasty more than 950 years ago, Bi Sheng invented the movable type printing technique, and became the four major inventions in ancient China together with gunpowder, compass, and papermaking techniques.

Bi Sheng first engraved on the clay film, a word is like a seal, and then burned hard, it became a mud character activities. Have you played the Qiqi Qiao game? With the blueprint, you can use tangrams to spell out a variety of flat patterns. At that time, Bi Sheng also had this process called typesetting. It is based on the manuscript to detect a corresponding type of movable type, and they are literally faced upwards on the iron plate. The iron plate is framed so as to fix the movable type. Then, the iron plate is slightly heated to melt the wax layer deposited on the surface of the movable type, and at the same time, the surface of the movable type is again flattened by the flat plate. In this way, when the wax layer is condensed, the bottom of one type of movable character is stuck on the iron plate, forming a huge “seal”. This large seal is literally composed of many movable characters. As long as you literally ink, you can print books on paper.

Today's printing basically follows Bi Sheng's old method. Of course, there have been major improvements in the process. The first is to replace the mud character with a typeface. In addition, there are a few more processes. After a big seal is formed by a typeface, it is usually not printed directly. Instead, a large seal is used to engrave the words on hard paper to form a paper type. The molten lead is then poured onto a paper pattern. After cooling, it becomes a lead plate with the words on it. The lead plate is then affixed to the printing press and printed with ink.

Obviously, the process is very tedious, from carving type, typesetting, making paper type, pouring lead plate, and finally printing on the machine. Therefore, this time-consuming and labor-intensive printing industry is in urgent need of improvement. So photo-composition came into being.

Photographic typesetting actually introduces the principles of optical photography. With typesetting in movable type, according to the manuscript, according to the type of painting, it is necessary to check type letters and symbols of different sizes and fonts for typesetting. Photographic typesetting is much easier. It uses the lens on the typewriter to change the size and shape of the typeface. As for the use of lenses, why can we change the size and shape of the words? This is actually equivalent to taking a "haha mirror." Shanghai's famous playground - "Big World" - a mirror of uneven mirrors, is a magic mirror, people will stop in front of the mirror will appear a variety of twisted comics, so they could not bear to live, ha ha big laugh.

With phototypesetting, only the light source is passed through the lens to image the desired text and symbols on photosensitive paper, and then developed and fixed to form a photographic film. Then just print it like a printed photo.

There are two kinds of light sources that can be used for phototypesetting. The ones just mentioned are actually ordinary light sources.

Due to the high brightness and pure color of the laser, the clarity of the image can be greatly improved, and the quality of printed books is of course high.

In addition, laser phototypesetting is much faster and easier than ordinary phototypesetting.

First of all, laser photo typesetting uses computers to turn text into dots and then uses dots to control laser scanning of negatives. That is, the laser hits the photosensitive coating on the negative film, leaving behind numerous corresponding dots, which are then converted into text or images after being developed and fixed. Here, the laser beam corresponds to the electron beam, and the photosensitive film corresponds to the television screen. Next, you can print newspapers and magazines with negatives carrying text and images.

The reason why a color TV can display red, green, and blue colors is because the screen is coated with three-color phosphors, and they will show three colors under electron impact. The laser typesetting can also use similar principles to print beautiful color images.

Laser mark printing is achieved by laser marking machine graphics, the basic principle is that the laser generator generates a high-energy continuous laser beam, when the laser acts on the substrate material, the atoms in the ground state transition to a higher energy state The atom in a higher energy state is unstable and will quickly return to the ground state. When the atoms return to the ground state, they will release additional energy in the form of photons or quantum, and convert light energy into heat energy, making the surface material. Instantly melts, even vaporizes, forming graphic symbols.

1. Laser generator

The following will take the xenon lamp laser marking system as an example to illustrate the principle of the laser generator. After the xenon lamp is energized, the xenon lamp in the xenon lamp is turned off with a high voltage of 20 kV, and the power supply automatically converts the output voltage to 100 V (5 A), maintaining the continuous arc discharge of the xenon lamp. In the laser generator, the xenon lamp is located at a focal point of an elliptical condenser cavity. After the arc generated by the xenon lamp is reflected by the condenser cavity, the xenon lamp is focused on another focus, YAG crystal. After YAG absorbs the pumping light, it forms a continuous laser with a wavelength of 1060 nm. The continuous laser oscillates back and forth between the front mirror and the rear mirror perpendicular to the optical axis in the resonant cavity, and outputs it from the front mirror.

2. Marking principle

The RF driver controls the on/off state of the Q-switch. The continuous laser becomes a pulsed light with a peak power of 110 kW under the action of a Q-switch. After the pulsed light reaches the threshold, the output from the resonator reaches the expanded beam. Mirror and beam are amplified by the beam expander and transmitted to the scanning mirror. The servo motor drives the scanning lens in the X-axis and Y-axis directions to scan the light. Finally, the power of the laser is further amplified by the plane-focusing field to focus on the work plane. Marking. The whole process is controlled by the computer according to the program.

Because the laser has good monochromaticity and coherence, the holography applied to printing can reproduce a large number of white light reproduction holograms, producing a third generation product of holograms, calling it "holographic printing."

Holographic printing belongs to the category of special printing and is an important supplement to traditional printing. Now all countries in the world attach great importance to holographic printing and actively carry out applied research and development work. According to the data, the market for holographic image printing products grew at an average annual rate of 36.2% from 1985 to 1995. It has been widely used in fields such as publishing and printing, packaging and decoration, and anti-counterfeit encryption of commodity documents. It has become a development project with economic benefits and social benefits, which has aroused great interest in the printing and packaging industries.

Holographic printing is also referred to as a large number of molded copies of holograms. It is an important application field of holographic technology and has broad application prospects. The hologram's embossed copying technology was first proposed by the American Radio Corporation (RCA) in 1969, and the first embossed hologram exhibition was held in Japan in 1981. In 1984, the United States National Geographic magazine first applied the embossed hologram to the cover of the magazine. To expand the application field, the development has been extremely rapid in the past 10 years.

Holographic printing process

The molding hologram production process can be divided into three stages: laser holographic mastering, electroforming metal stencils and molding.

The so-called embossed holography is to use a holographic technique that can realize white light reproduction, and an embossed hologram (called an original plate) is made on a holographic recording medium such as a photoresist. The original hologram is then converted into a metal relief hologram (called a casting plate) by electroforming, and the relief information on the metal hologram is pressed into a PVC or PET plastic film by hot pressing, preferably by vacuum aluminum plating. The hologram becomes a hologram for reflection observation.

1. Laser hologram mastering. The original hologram used for holographic printing must be an embossed ā-type phase hologram capable of achieving white light reproduction. Producing a high-quality hologram is one of the most critical steps in determining the quality of a holographic print.

There are many methods for producing white light reproducing holograms, and rainbow holograms, image plane holograms, and reflection holograms are commonly used in the embossed holographic replication technology. The following focuses on the rainbow hologram production method.

(1) Rainbow hologram production. First, a Fresnel type hologram H1 of an object was recorded with a silver salt dry plate (Tianjin holographic type I), which was bleached and used as a master hologram. The He-Ne laser beam reaches the beam splitter S after being reflected by the M1, and the transmitted light is reflected by the M2. After being expanded by the beam filter L1, the beam is collimated by the concave mirror M and irradiated on the recording plate H1 as a reference light. The beam reflected by the other beam splitter S is taken as object light, reflected by M3 and M4, and then expanded by the beam expander L2 to irradiate the object so that the object light and the reference light interfere on the hologram plate H1. Darkroom processing yields an H1 hologram, a master hologram.

In the second step, the principal hologram H1 is illuminated along the conjugated direction of the original reference light after alignment with the 457.9 nm of the Ar+ laser or the 441.6 nm wavelength of the He-Cd laser. By placing a slit device in front of H1, a real image (as object light) can be obtained when the light is reproduced through the master hologram. Then, a photoresist-type recording plate H2 is placed near the real image so that the object light and the reference light interfere on H2 and recorded, and after development, an embossed rainbow hologram is obtained. Since in the H2 exposure, the slit is also recorded as an object in the rainbow hologram, an image of a slit is formed at the time of reproduction. Because the recording process is performed in two steps, it is often referred to as two-step rainbow holography. It was first proposed by Benton in 1969.

If rainbow holograms are illuminated with white light at the time of reproduction, light of each wavelength forms a set of slit images and object images. In general, this series of images appears in different spatial locations. If the viewer moves his or her gaze up and down near the slit image with his eyes, objects of different colors from red to purple can be seen. This is because only one color of the object image can be seen through the position of a slit image. The reason why it is called rainbow hologram is because this series of different colors is like a rainbow.

2. Metal template production. The purpose of this procedure is to replicate the relief pattern on the photoresist original hologram onto a metal plate to make a working die for a molding press. This is an integrated technology involving chemical analysis, electrochemistry, and surface physics. People call it molding technology for the people. Electroforming is also called electroforming.

(1) Surface treatment. The purpose of the surface treatment is to remove grease and impurities from the surface of the adhesive layer to ensure the fidelity of the image and the firmness of the coating. Since photoresists are easily soluble in alkaline solutions, they must be cleaned with a neutral detergent.

(2) Sensitization. The sensitization process ionizes the surface of the photoresist to form uniformly distributed ionic particles (ie, reaction centers) to ensure that the silver plating reaction can proceed uniformly. The sensitizer is a stannous chloride solution.

(3) Electroless silver plating. This is the key to the entire electroforming process. Silver plating has two functions: 1 A thin conductive layer is formed on the surface of the photoresist, about 3-5 μm, which becomes the cathode of electrolytic nickel plating; 2 A fine silver layer of particles is plated on the surface of the relief. The relief grooves on the photoresist can be completely transferred to the metallic nickel layer. Its basic chemical process is the so-called silver mirror reaction. The reaction can be expressed as:

nAg++3/2nOH-+C6H12O6→nAg+ānH2O+1/2nRCOO-

(4) Electroforming nickel. The entire electroforming process is performed in an electroforming bath where the bath is acidic and the photoresist plate placed in the bath serves as the cathode. The main salt of the electroplating bath is nickel sulfamate. Nickel sulfate and nickel chloride can also be used. Nickel sulfate is a strong electrolyte that completely dissociates nickel ions in the bath:

Ni[(NH3SO3)→Ni2++SO2-3+NH3↑

The positively charged nickel ions in the solution move toward the cathode (ie, the photoresist plate) and receive electrons at the cathode, becoming nickel atoms and plating on the cathode, ie: Ni2 + + 2 e → Ni

In the electroforming process, the current and time should be adjusted according to the required thickness, and at the same time, attention should be paid to controlling the temperature and acidity and eliminating the plating stress.

After the nickel mold is peeled from the base, the adhesive is removed with an organic solvent such as acetone to obtain a so-called first-generation stencil (silver edition), which is customarily called "grandmother" edition.

(5) Surface passivation treatment. The stencil is passivated in a passivating solution (dichromic acid solution) to form a layer of silver oxide on the surface, which facilitates easy stripping during plating of the working stencil.

(6) Turn casting. After cleaning and passivation treatment, the first generation stencil is placed in a plating bath to rapidly electrocast nickel, which results in a second-generation stencil (called grandmother version). Then use the second generation template electroforming third generation template (called master). Finally, the master is placed in a hard plating bath (containing a hardness agent) to mold a working die for molding.

Nickel plate has high hardness, abrasion resistance and corrosion resistance