Essentials of flexographic printing process technology
The flexographic printing materials include printing plate, water-based ink, ceramic anilox roller and its related auxiliary materials.
â‘´ Flexible printing plate
The flexible printing plate uses a photosensitive polymer plate, which is made of rubber-like photopolymer. The basic composition is the main polymer, photoinitiator, acrylic hexene monomer, thermal polymerization inhibitor, additives, etc., under the action of ultraviolet light to achieve a certain rubber hardness.
The brands of flexographic printing plates currently in use are mainly: DuPont Sally version of the United States, BASF version of Germany and GS version of Shanghai.
Printing plate production is generally completed by a flexo plate-making company, and their professional expertise can provide qualified flexo plates for printing manufacturers. According to product requirements, printing companies can make plate-making companies provide corresponding types of plate materials to meet production needs.
Of course, it is not excluded that printing companies make their own plates, but there is a pros and cons relationship. Because printing companies start to engage in flexographic printing, in addition to equipment investment, such as printing plate production, due to the higher technical content of the flexographic printing plate before printing, the investment is greater. For printing companies, if they are willing to spend a large amount of money on flexo pre-press production, it is better to invest funds in the selection of printing materials, concentrate on ensuring the integrity of the printing process, and let flexo play an early economic benefit.
In recent years, the laser CTP direct plate-making technology introduced is worth recommending. The minimum dot of the screen version is 1%, which solves the problem of making high-quality screen printing plates. Now it has more sophisticated packaging and printing products are produced by the CTP technology flexographic plates for printing. These fine products are generally difficult to distinguish between lithographic, intaglio and flexographic printing under visual inspection. It has played a very important role in improving the quality of flexographic printing in China.
⑵ Double-sided tape
The flexible printing plate needs to rely on a special double-sided tape to stick on the surface of the printing plate cylinder to form a complete printing cylinder. The double-sided tape commonly used at present is an elastic pressure-sensitive adhesive material, which is composed of a polyethylene foam substrate, coated with acrylic adhesives of different viscosity on both sides, and protected by single-sided or double-sided release paper. In the flexographic printing process, the selected double-sided adhesive tape will directly affect the print quality of the printed matter.
Flexo double-sided tape has strict performance requirements:
â‘ Ensure that the plate and the plate roller are firmly bonded, and can be easily removed.
②At the printing speed of 150 ～ 250 m / min, ensure the fastness and overprinting precision of the printing plate.
â‘¢The thickness is consistent, the elasticity is uniform, and it is not easy to deform after being compressed to ensure the quality of the imprint.
The thickness of double-sided tape commonly used in flexo plates is 0.38 mm and 0.50 mm; three types of substrate density are divided into three types (taking 3M double-sided tape as an example).
Low density 1115 type, suitable for screen printing and thin line printing;
Medium density 1015 type, suitable for text, line and solid printing;
High-density 411DL type, suitable for field printing;
The new product 1815M type, which is between 1015 and 411DL, can replace 411DL.
Printing companies generally have to prepare three types of double-sided tapes with different densities to suit the printing needs of different plates and graphics.
To select the type of double-sided tape for flexible products, first analyze the network lines and text lines in the product graphics and text, which is the main type in the field; then you must know what the printing material is and choose according to daily experience. Only one type of double-sided tape can be used in the printing of the same product, regardless of the difference between the network line, the text line, and the ground in the set of printing plate graphics. This is because different types of double-sided adhesives have different densities and obvious differences in elasticity. Although the thickness is the same, it is pasted on the plate cylinder of the same diameter. After being compressed as an elastic body, the track length imprinted on the printing material is different. As a result, the length of the prints between the printing plates will change, which makes it impossible to achieve accurate registration between the colors.
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