Flexographic printing originated in the United States in the 1920s. Because the aniline dye ink used is toxic, flexographic printing, originally called flexographic printing, has not been developed. In the 1970s, due to industrial progress, the development of polymer resin plates, ceramic anilox rollers, UV inks, and ultraviolet drying technology in recent years prompted a qualitative leap in the development of modern flexographic technology.

At present, the flexographic process is the fastest growing printing process in the world. As far as the label industry is concerned, the US flexographic printing accounts for about 85% of the label field; European flexographic printing started later than the United States and currently has a market share of about 45%, and the upward momentum is rapid. Flexo printing is currently in its infancy in Asia, and many manufacturers are launching new flexo printing machines. The development of flexographic printing technology is in the ascendant, and this point was fully reflected in the United States and above in Chicago in 2000. All exhibitors soon launched the latest flexographic or UV flexographic technology and equipment. Even some well-known equipment suppliers, who used to focus on the resin printing method of the sticker industry, quietly turned to flexographic printing at the 2000 Chicago Exhibition, especially UV flexographic printing. With the continuous advancement of technology, flexo printing has gradually entered a new era. Flexographic printing has been greatly developed, thanks to its economical and high-quality characteristics.

The Avery Dennison people have been involved in flexographic printing for a long time, and started manufacturing their own UV flexographic printing machines as early as fifteen years ago. At the same time, we also have a strong technical support team, and have gained a lot of experience in these years of practical accumulation. The following are some of the main factors that we believe will affect the quality of sticker printing processing for readers' reference.

1. Color separation film

The color separation film directly affects the quality and printing effect of the plate. Because flexo printing uses an anilox roller, the anilox roll cells are arranged at a certain angle (currently mostly 60 degrees or 45 degrees). In order to avoid electric grains, the screen angle of the flexographic film is 7.5 degrees compared to the offset printing Difference. If the film is made with a flat exposure mechanism, the graphic should be compressed according to the diameter of the plate cylinder, the thickness of the double-sided adhesive tape and the thickness of the plate before making the film. It should also be noted that the performance of the film and the graphic performance of the plate is matched. The use of matte film will be more conducive to the production of printing plates.

2. Plate material and production

First of all, you should select the corresponding plate material according to the type of ink used. Not all plate materials are suitable for using UV ink. Wrong selection will cause the printing plate to swell and deform during the printing process. The plate making process is also very important. The time control of each step should be just right. Insufficient exposure, excessive detackification, insufficient drying, and improper storage will reduce the life of the printing plate.

3. Anilox roll characteristics

First of all, the selection of anilox rolls should follow the following principles: the number of screen lines (line / inch or line / meter) of the color separation film should be at least 1: 3.5 with the anilox roll, and the dot printing should reach a ratio of 1: 5 . The cleanliness of the anilox roller is also very important. The anilox should be cleaned regularly and thoroughly to ensure ink delivery, ink color matching, and repeatability.

4. Ink types and compatibility, ink system

Corresponding ink systems should be used for different substrate surfaces, such as paper ink, PE, PP, PET and other plastic film ink, PVC ink, aluminum foil material ink, etc. Incorrect selection of the ink system, or poor compatibility of the ink, will lead to a drop in the performance and strength of the ink on the surface of the substrate, and may even trigger a reaction.

5. Corona treatment, surface coating, UV lamp

These factors also affect the adhesion of the ink. The printability of the plastic film can be improved by corona treatment of the printing surface and the application of a surface coating layer. The surface is coated with a variety of chemicals: acrylic, vinyl, etc., solvent-based or water-based. The advantages of using gravure wheel or flexo printing are: no time limit for printing, better wettability and ink binding force, suitable for most inks on the market, no online equipment and processing, chemical resistance And good scraping, suitable for printing at the same speed. The disadvantage is that the cost of corona treated materials is more expensive than finished products, and corona treatment is currently the most common method used to improve the coating, wettability, and binding power of PE / PP surfaces. The corona discharge is completed between the electrodes at close range, one end of the two electrodes is connected with high frequency and high voltage electricity, and the array end is grounded. For example: the corona processing frequency range of general narrow-width printing machines is between 9-30KHz, and the output is about 15,000 volts. In the case of large printing format and high speed, higher voltage is required. In the corona discharge treatment, the discharge process releases the contained electrons, ions, and protons, some of which hit the polymer surface and are added to the reaction sequence of free protons, which can introduce functional groups on the surface. Most of these functional groups contain carbon and oxygen. Normally, the surface and force of the film after corona should reach more than 40 dynes to not cause the ink to fall off. [next]

6. Ink color matching

The color of the ink directly affects the color quality of the printed product. Especially for spot color ink, it is usually first modulated in the ink chamber and detected using a colorimeter. Judgment is no longer visible to the naked eye, and the more demanding factories sometimes use the requirements. The color density meter of professional suppliers is now more complete. The instrument can give recommended ink color formulas while measuring samples according to the ink database provided by the ink manufacturer, which greatly improves work efficiency.

7. Printing machine and its operation and adjustment

This factor obviously determines the quality of printing. For example, the gear bar in flexo printing (a periodic bar formed by a gear in the transmission system of the printing unit trapped on the printed product) is affected by the defects of the printing machine itself. Quality. The tension control capability and manufacturing accuracy of the printing machine will also affect the registration and printing accuracy.

8. Die cutting

As a feature of the printing and processing of self-adhesive labels, label die cutting has always occupied a large part. The quality of the die cutting process directly affects the labeling and use of the label. At present, there are two common die-cutting methods: round-rounding and flattening. Flat-pressing and die-cutting speeds are slow and the accuracy is slightly worse, while round-pressing and circular die-cutting are not only fast and high-precision, but also have very small adjustment losses. . At present, the labeling of the Cultural Revolution has increasingly adopted automatic labeling methods, and the labeling speed is becoming more and more memorable. For small and medium labels, the speed of 250-300 Label / Min is not uncommon now. Therefore, the high-quality die-cutting process of the self-adhesive country has become the development demand of the market. At present, more and more circular die cutters that you have seen are also products that have emerged at the historic moment. The solid round die-cutting die cutter in the base has a long service life, high die-cutting accuracy, and fast operation, which is suitable for medium-length and long-term work; while working with the magnetic roller makes the thin-plate round die-cutting die cutter of h, the service life is slightly shorter than one Type die cutter, but the die cutting accuracy and running speed are also excellent, suitable for short and medium version. Moreover, the round die-cutting die cutters have been steadily declining in prices in the European and American markets in the past decade, and the drop has so far reached 30-50%. The development of die-cutting knives is a great impetus for the rotary printing methods of adhesive labels, including flexographic printing.

9. Static electricity

Static electricity is often easily overlooked, but static electricity is often a very important factor in actual production. Static electricity is formed by friction and induction, and is more obvious on the film. Therefore, the entire sticker manufacturing and printing process will generate electrostatic charge on the material and the machine. If it is not removed in time, it will cause a lot of trouble and quality problems to the adhesive tape. Problems that may be caused by static electricity in label processing :

1) Printing quality (all printing methods): the label appears as a pinhole or mesh loss, and each defect is caused by a partial discharge of a certain amount of charge (which can be regarded as a small explosion);
2) Ink aggregation or repulsion: The static electricity on the material or machine will cause the ink to be unevenly distributed on the material, which looks deeper and shallower;
3) Quality of die cutting / discharging; manifested as the labels are taken away together with the waste, so operators often mistakenly believe that the pressure of the die cutting knife is insufficient, and apply more pressure to the die cutting knife, so that the hair knife is easily worn. Or destroyed, thereby reducing the service life.
4) Tension quality: when slitting and rewinding materials, excessive static electricity may cause uneven rewinding and cause glue leakage.
5) Laminating quality: The laminating layer is not smooth due to electrostatic attraction and premature bonding.
6) Labeling quality: The label is not printed normally when labeling, but runs with the backing paper, which affects the labeling speed and quality.
7) Punching quality: After punching the label, the waste remains on the paper.
8) Thermal transfer / laser printing quality: some can be printed and some cannot be printed, and the printing quality is different (dark or light).
9) Absorb dust onto the substrate or printing plate, forming fisheye or white spot defects on the printed product;
10) Electric shock operators or other employees: This experience has been experienced by many rotary press operators, not only reducing the output and quality of products, but also deteriorating the working conditions of operators, and even causing fires and other accidents;
11) Solve the problem of static electricity:

(1) Induction: Set a metal wire on the printing path to remove or neutralize static electricity. Simple and low-cost, but requires pre-selected installation. The static-removing wire and the machine must be well grounded. Some printers connect the static-removing metal wire to the machine cabinet, which often cannot achieve the best static-removing effect, and the electric charge will accumulate on the machine, which will also cause quality problems. The distance between the metal wire and the material is also very important. Generally, the metal wire should not directly contact the surface of the substrate. It is better to leave it slightly away. If the material is thicker, the double-sided removal effect is better. If the material is thicker, the double-sided removal Better results. However, it should be noted that when the two sides are removed, the wires should not be distributed in pairs and symmetry, and staggered installation will have an increasing effect.

(2) Ionization: Use a material that can emit a large amount of positive and negative ions. The charged material absorbs the required number of positive and negative ions according to the need for neutralization. This method requires special equipment, but the effect is very satisfactory.

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