Printing and processing of hoses (top)

Keywords: flexographic printing hose anilox roller BCM tension pressure

In recent years, with the continuous improvement of people’s living standards and the strengthening of personal hygiene requirements and environmental protection awareness, aluminum toothpaste tubes we were familiar with more than 10 years ago have completely withdrawn from the stage of history. Instead, they replaced them with “aluminum foil”. Base, both front and back, are new materials that combine EAA (ethylene acrylic acid copolymer) and PE (polyethylene). We call it a "composite sheet," and toothpaste tubes made of this material are also called "composite tubes" or "composite hoses." Compared to the aluminum tooth manufacturers that we generally use before, we use composite hoses to pack our own toothpaste products.

As a green and environmentally friendly printing process, the flexographic printing plate is even more capable of printing on composite hoses.

1. Process of printing composite pipe flexographic printing

Before printing, first of all do a good job in the feasibility analysis of the prepress process. When we receive the sample of the toothpaste tube provided by the customer, we must carefully analyze the designer's design focus, determine the main screen (such as the product's brand identity, product background pattern, etc.) and auxiliary screen (such as the product's text description, product Components, weights, etc.), determine the color number and color sequence of the product color, and appropriately expand or contract the color of two or more fasteners and butt joints. According to the customer's requirements, add the pipe cursor, filling and closing cursor and the "sleeve point" needed in the production on the sample draft. After the preliminary preparation work, the revised draft will be handed to the plate making company. Then, we refer to the pattern of each color of the printing plate (such as solid, lines, network lines, gradients, etc.) and the color intensity of each color, etc., and perform the anilox roller configuration for each color unit and make a Final adjustments to restore the color to its best condition.

For the printing of composite hoses, our factory is equipped with dozens of different anilox rollers from 250 to 800 lines per inch and BCM from 3.0 to 12.0. The basic configuration in production is shown in Table 1.

After selecting the number of lines of the anilox roller, it is necessary to compare the BCM values ​​in the same line number of anilox rollers. Only in this way can the selection be more reasonable, and the configured anilox roller color reproduction is closer to the original color. Then we can print production.

Our factory introduced the Jarus EM410 unit flexo printing machine, with eight color group full UV

Printing unit and two sets of die-cutting, slitting units. The main program in printing production:

On the composite sheet roll → go material → adjust the bias device → install each color group anilox roll → install the plate roll → adjust the pressure between the anilox roll, plate roll, printing roller → embossing → adjust tension → cover Quasi-printing version → UV ink curing → slitting composite sheet → winding

2. Control parameters of composite hose printing

The unit type flexo press is basically the same for the process of printing and printing coated paper, offset paper and self-adhesive paper on composite hoses, but due to the thicker composite sheet, the total thickness is about 300μ, the unit weight is large, and the internal and external surfaces are again Is a PE film, so compared with the general paper or sticker paper, cardboard, etc., tension control and printing pressure is particularly critical, once the print tension control is not good or improper printing pressure adjustment of each printing group will cause overprinting error , and it is difficult to control and adjust.

Let's talk about tension control first. The tension system of the unit type flexo press is divided into three parts: unwinding part, printing part and winding part.

Unwinding Part Tension System We also call the pre-leveling tension. Its function is to pre-stretch and tighten the composite sheet to improve the elasticity of the two sides of the sheet produced during the manufacturing process of the composite sheet. , uneven and "foliage" and other phenomena.

The printing part tension system refers to the tension value during the constant printing process from the time the sheet passes through the second leveling tension system until it is printed. These two sets of tension control devices are collectively referred to as "print tension." The role of the printing tension is to balance the tension and resistance of the composite sheet subjected to the imprinting pressure of each plate roller and between the composite sheet and the rollers such as the feed roller and the UV cooling roller, and to maintain the printing process. Tension value. The value of the printing tension value should be determined by the degree of bending of the composite sheet. The higher the degree of flexion of the composite sheet, the greater the tension value; conversely, the lower the bending stiffness of the composite sheet, the smaller the tension value. In actual production, the friction coefficient of the surface of the composite sheet is relatively small, and in the middle there is an “aluminum foil” as the skeleton. We will set the tension value as large as possible to ensure that the composite sheet is not stretched after printing. Taking a composite sheet of 400mm width and 275u total thickness as an example, we usually set the printing tension to 320N in the front and 360N in the back. The suitable point for printing tension control is that all "color registration points" in multi-color printing are all registered, and "move" is not used before or after the standard. If it is found that the “color point” of each color is “moved” in front of the printing process, the value of the printing tension value can be appropriately adjusted. Another thing to note is that the speed of printing can also affect the stability of printing. We choose to first set the printing tension value within the common range of using the sheet specification, then basically register the printing plates of each color group, gradually increase the vehicle speed to the normal production speed, and then according to the “moving” trend of the “color registration point” to the printing tension. Make appropriate fine-tuning.

Winding part Tension system refers to the constant rolling force and torque at the rear end when the flexo printing machine is used for roll-to-roll production. Its role is to neatly print the good material, and make the entire roll of paper from the inside of the core to the roll core of the rolling force to maintain the same. When printing composite sheets, in order to make the two sides of the toothpaste sheet that has been cut into smaller rolls flatter, the roll force and the torsional force of each roll are more stable. We have set a relatively fixed roll force value based on the data obtained during the actual operation. And torque value. The set value is 60% of the roll force and 50% of the torque, which ensures the quality stability of the printed sheet of each roll in the tube making process.

When printing composite hoses on a flexographic printing machine, the accuracy of the tension control determines the overprint quality and the overall quality of the finished product. Of course, there are many factors that determine the magnitude of the tension value, including the production environment of each batch of composite sheet. Changes, differences in sheet manufacturers, equipment for manufacturing sheets, differences in width and thickness of composite sheets during printing, differences in printing equipment, and so on. We need to master the properties and construction of various sheets and various equipment, find out the range of tension values, and adjust the optimal tension value during normal production.