Flexo Printing Solutions (1)

(I. Introduction

With the rapid development of China’s economy, the deepening of the socialist market economy, the rapid growth of import and export trade, and the continuous improvement of the people’s living standards, the demands for the packaging and printing industry are increasingly high.

Flexographic printing technology is very suitable for the needs of the packaging and printing industry, and it is a printing technology that has developed rapidly in recent years. However, with the development of the packaging and printing industry, the requirements for packaging substrates and packaging materials are getting higher and higher, and the requirements for printing technologies and printing processes are increasingly diversified. People in the industry believe that currently including imported and domestic flexographic printing presses, the printing technology and process can not fully meet the needs of the Chinese market, flexographic printing equipment with a simple structure, advanced technology and diversified printing functions will be particularly suitable China's packaging and printing industry prints high-grade packaging products that require multiple printing technologies and processes.

(b) Definition of flexographic printing

Flexo printing, as a special method of embossing, was originally called "animation printing" and its initial name came from the volatile liquid color ink made using aniline dye at the time of its production. With the advancement of science and technology, aniline inks that are bright in color but easily discolored are no longer used, so the name “aniline printing” has no practical significance. By the 21st of October 1952, the American Packaging Society’s 14th The printing method was formally named "Flexography" in the symposium, which means that the printing plate can be flexed, and the term "flexographic printing" was introduced into China shortly thereafter.

The flexographic printing industry was officially defined by the American Flexo Printing Association in 1980 as follows: Flexographic printing is a direct rotary printing method that uses a flexible, convex image plate that can be adhered to a reproducible plate cylinder In the above, the printing plate is inked by a metal ink roller engraved with an ink hole, and the metal ink roller (an anilox roller) is controlled by another ink roller or a squeegee to control the amount of ink to be transferred. Transfer to virtually all kinds of materials.

The definition of China's printing technology standard term GB 9851.4-90: Flexographic printing is the use of flexible version, through the anilox roller printing ink transfer method.

(III) Main processes of flexographic printing

At present, the flexographic plates introduced in China are basically solid photopolymer plates, and the thickness of the plates is selected according to the requirements of the flexographic printing presses. Common plate thicknesses are 1.70 mm and 2.29 mm. The flexographic plate making process is the process of transferring pictures to plates by means of negative graphic film. The process mainly includes the following steps:

(1) Back exposure of the plate material with ultraviolet light, the role of which is to determine the height of relief on the plate, ie the depth of corrosion, and solidify the substrate.

(2) Expose the printing plate and the film under the influence of ultraviolet light to form a graphic printing portion on the printing plate and cure it.

(3) The plate is scrubbed in a solvent to remove the unexposed parts of the plate, so that the graphic part is embossed.

(4) The plate is dried in a dryer to promote the evaporation of the solvent absorbed in the plate, so that the thickness of the plate can be restored to its original standard value.

(5) The post-exposure and de-tack treatment of the dried plates can further solidify the shoulders and bases and improve the flexographic printing performance. The high-quality flexographic printing plate should have a printing rate of more than 500,000 prints and even as much as 1 million prints.

(4) Classification of flexographic printing methods

1. One type is a super-narrow flexographic machine (about 10 inches) with a width of about 250 millimeters. This kind of flexographic machine is specially used for the production of various adhesives, and some of them are also used for processing a small number of beer labels. The color group is 6 to 7 colors, and some machines are equipped with full UV function, including cold UV. The number of machines in this category is not much, accounting for about 15% of the total number of machine-type flexo.

2. The second type is a general narrow-width flexographic plate (approximately 16.5 inches) with a width of about 420 millimeters and a color set of 7 to 8 colors. The largest number of such machines is probably about 75% of the total number of unit type flexo, and the application is also the most extensive, including small size folding cartons (such as cigarette packs, kits, wine boxes, etc.); thin paper packaging products ( Such as beer labels, cigarette soft packs, etc.); self-adhesive products; paper products (including paper cups, lunch boxes, etc.) as well as a small number of plastic film prints.

3. The third category is a mid-width 7-8 color flexo, with a width of 500 to 650 mm, which is a small number, accounting for about 10% of the total. The main products are folding cartons (such as cigarette packs, medicine boxes, wine boxes, etc.); thin paper packaging products (mainly cigarette soft packs, wine labels, etc.); paper products (paper cups, lunch boxes, etc.).

(5) Features of flexographic printing process

There is no perfect way to print, flexo is not an exception:

(1) Compared with gravure printing and offset printing, the flexographic printing density curve is unstable, and the change in printing plate thickness has a great influence on the printing quality, and color overprinting is also difficult.

(2) The flexographic printing uses anilox roller to transmit ink, and the network cable of the printing plate must match the network cable of the anilox roller.

(3) The dot deformation is severe during the imprinting process.

(4) The pressure is small (only 2KG/CM, and the pressure of the embossing is 50KG/CM, the pressure of the embossing is 4-10KG/CM). A slight change in the pressure will have a great influence on the transfer of the graphic and text.

(5) has its own unique color separation principle, because the flexible version as a broader application in the field of packaging and printing, often use multi-color, 6 or even 8 colors, but also take into account the use of multi-color to compensate for network performance .

(6) Due to the characteristics of on-line processing, the flexographic printing should consider the printing and post-printing links in the design process.

(7) The dot gain of flexographic printing has been non-linearly changed, and the degree of dot enlargement displayed by large dots and small dots in the printing process is different.

(8) When making a printing plate, a flexographic plate must take into consideration the deformation of the flexographic plate in advance so that it can be deformed to a desired length after the plate is attached to the platen.

(6) Structural features of flexographic printing presses

The flexographic printing press consists mainly of an inking unit, a printing plate, and an impression cylinder, and is illustrated as the two most common schematics of the flexographic structure (the difference mainly lies in the flexographic ink supply system). The black-and-white picture is a three-roller inking system, and the color picture is a chamber-type squeegee-type inking system.