Analysis of several processes for special printing

The so-called special printing refers to the general term for printing methods that are different from ordinary plate-making, printing, post-press processing methods and materials for special purposes. Specifically, the main difference between special printing and general printing is not based on the format, but is measured from five aspects of plate making, printing, post-press processing methods and material production and use. Every aspect is different from general printing. Is the scope of special printing. With the continuous development and progress of commodity economy and printing science and technology, special printing shows strong vitality and broad development prospects.

1. Flexible printing process
Flexographic printing refers to a relief method made of flexible materials such as rubber or resin, and a method of printing on the machine through an anilox roller to transfer ink. In the early stage of flexographic printing, because of the use of flexographic printing ink, it is also known as flexographic printing. Because the flexographic process has the common characteristics of embossing, offset printing and gravure printing processes, it has a wide range of adaptation to the characteristics of the substrate, simple structure and high precision. The machine is mainly composed of four parts: ink receiving roller, anilox roller, plate cylinder and impression cylinder. The flexographic printing structure is arranged in three cylinders, stacked (ie, roll-to-roll), arranged, and satellite. The three-cylinder type is composed of multi-color single groups. Each single-group structure has only three rollers. A doctor blade is installed on the metal anilox roller to adjust the amount of ink. Because the doctor blade is in contact with the metal anilox roller, it is easy to damage the anilox. Roller, this is a structural defect. The laminated flexographic printing machine is to stack the monochrome units on both sides of the host machine for printing, and each monochrome unit is driven by the gear chain of the host machine. When the roll paper of this machine passes through the printing part, the front and back printing can be performed, and the drying of the ink is completed before the back printing.

Another advantage of this machine is that when adjusting or repairing the components of the monochrome unit and color washing, the other units are not affected, and the production can be continued without downtime, and the equipment utilization rate is high. However, the accuracy of this machine's overprint is worse than that of the satellite type, and it is not suitable for printing substrates with large elasticity and thin material. The flexographic printing machine is composed of multi-color single groups. The paper operation between each color group is in a flat state, which can keep the tension more balanced, so it is suitable for printing thin paper and thick paper products. The structure of the satellite-type flexographic printing machine is that there is an impression cylinder on the main frame, and various color plate cylinders are installed around it. The advantage of this machine is that it is accurate for overprinting, and is more suitable for printing substrates with large elasticity.

2. Pearlescent printing process
Pearlescent printing refers to the special printing technology using pearlescent ink. The pearlescent ink has the natural luster of mussel pearls, which makes the package prints display colorful colors like pearlescent treasures, which is noble and elegant. The pearlescent printing process can adopt lithographic printing, letterpress printing, gravure printing or flexographic printing, and can also use screen printing. Due to different printing methods, pearlescent inks with different pigment particle size ranges should be used reasonably. For example, in the letterpress process, pearlescent pigment inks with coarse particle diameters can be used. For the lithography process, pearlescent ink with fine particles should be used. In the wire mesh process, the mesh size should be larger than that of the pearlescent pigment. In pearl printing, pearl powder can be added directly to the ink, but it should be used immediately to prevent the pearl powder from sticking to each other due to precipitation and affecting the use effect. The blending usage of pearl powder and printing ink is about 10 ~ 20%. When printing pearlescent ink with a flexographic process, an anilox roller of 30 lines / cm should be used to ensure that the pearlescent pigment is fully and evenly transferred to the printing plate surface. Printing pearlescent ink with gravure printing process. It is better to use 30 ~ 40 lines / cm net cable, and the corrosion depth is controlled to 35 ~ 40rfl, so that the ink pigment can get a good transmission effect.

The pearlescent printing substrate has good surface gloss performance, high smoothness, and the best printing effect, such as glass cardboard, coated paper, calendered whiteboard paper and plastic film.

3. Spice ink printing process
In daily life, we can see some prints that can emit fragrant odors, such as business cards, greeting cards and packaging products. This print is printed with fragrance ink. This process can be used to add spices directly to the ink, printing with relief printing, flexographic printing and offset printing machine, the method is simple, but the fragrance is difficult to preserve for a long time. At present, perfume inks enclosed in capsules are often used for printing. In this printing method, the fragrance is slowly broken by the microcapsules and emits a fragrant smell, which can be stored for a long time. Use perfume ink to print with silk screen process. Due to the large amount of printing ink, it is difficult to dry. Therefore, the drying problem of ink should be considered. The amount of ink should be properly controlled. The inked area of ​​30% screen should be used to avoid excessive concentration due to full version. Fragrant. Products printed with perfume inks should avoid heavy pressing and folding. Spice inks have various fragrance types such as flowers, fruits and cheeses. When printing, appropriate choices can be made according to product characteristics and customer requirements. Spice inks are not only suitable for printing on paper, but also for printing on plastics, fabrics and wood.

4. Color-changing printing process
The ink used in color-changing printing can change color with the change of temperature. This kind of ink is also called temperature display ink. It usually uses the change of ink color to display the temperature of an object or environment. The discoloration of ink is due to the discoloration mechanism of the pigment. The color-changing mechanism of pigments mainly includes crystal transfer type, thermal decomposition type and crystal structure change type. The crystal transfer type is to change the color due to the transfer of the crystal type of the pigment due to heat, and to restore the original crystal and color after cooling. This is a reversible color change ink. The pigment that decomposes with heat is able to release gas and change color after chemical decomposition reaction caused by heat. It will not restore its original color after cooling. This kind of pigment is called irreversible high-temperature color-changing ink. The crystal structure-changing pigment can change color due to the loss of its crystal water when heated, and it will not be reduced immediately after cooling, but it will slowly form crystals and return to its original color when it is wet. This is a reversible low-temperature color change ink. In addition to the color change mechanism of the color-changing ink, the type and performance of the fillers, binders and solvents in the ink also directly affect the color-changing properties of the color-changing ink. Color-changing inks are mainly used for over-temperature notices, color block cards for body temperature, postcards, weather forecast prints, boiler high-temperature indication prints, anti-counterfeiting trademarks, and surface temperature measurement for aviation equipment. Color-changing inks are mostly screen-printed, and can also be printed by offset and gravure printing processes.

5. Foam printing process
The so-called foam printing refers to a printing method in which microsphere foaming ink is screen printed on paper or silk object, and then heated to form a raised relief-like graphic or braille reading. Because the graphics printed by foaming can swell, it uses microsphere foaming ink. This kind of ink is made of high molecular polymer monomer through synthesis and has a diameter of 5 ~ 80m. The hollow is filled with a low boiling point solvent. Plastic spheres, when the microspheres are heated, the low boiling point solvent in the spheres is heated and vaporized, so that the diameter of the microspheres quickly increases to 5 to 30 times that of the original spheres, so the surface of the substrate forms a relief-like graphic. Microsphere foam printing is widely used in new braille printing technology systems. The braille printing system is different from the original braille production method. This method uses a computer. Print the braille with foaming ink and make the braille raised after heating. Therefore, not only can be printed in large quantities quickly, but also can be printed on both sides of the paper, can also print patterns.

6. Decal printing process
Decal printing is achieved by indirect transfer. First, the pattern is printed on the gummed paper or plastic film by a flat printing process, and then the finished product of this decal is attached to the surface of the object to be decorated. Using the water solubility of the gum, the gum is dissolved by soaking in water, and then the paper or The plastic film is torn off, and the picture and text are transferred to the surface of the object. The main processes of decal printing process are: paper mounting, plate making, printing, transfer and post-processing. The paper-laminating process is divided into manual and mechanical laminating methods. The manual laminating process is relatively simple and does not require special equipment, but the quality of the laminating is difficult to control well, so it is only suitable for small batch production. The mechanical laminating paper is carried out by special coating equipment, which is suitable for mass production. The plate-making method of decal printing adopts the lithographic plate-making method, and the printed image is forward-shaped, and the image is reversed after being printed on the "mounting paper", and it becomes positive after it is moved to the decorative object To graphic structure. Before decal printing, you must first print a layer of transparent ink on decal paper. When printing, the color with strong transparency should be printed first, and the color with strong hiding power should be printed afterwards, so that after transfer, you can get the same graphics and text as the ordinary printing color sequence.

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