Use of spacers in flexographic printing

With the continuous development of flexo printing, people have increasingly stringent requirements on the quality of flexographic products. How to improve the quality of printed products has become the most important issue plaguing the industry.

In flexo printing, liners play a very important role, but different liners (double-sided adhesives) have different effects on the prints, which are briefly explained.

The main features and classification of liners

Liner is adhesive tape, its basic role is: firmly adhere the flexographic plate on the plate cylinder, so that they do not slide.

According to the hardness of the liner, it can be roughly divided into three types: soft liner, neutral liner and rigid liner.

The thickness of the liner should be consistent. The stable and uniform thickness facilitates the control of dot gain and guarantees a good printing effect. Generally, the thickness of the pad used for narrow-width flexo printing is 0.3 mm. In plate making, the thickness of the liner is a key factor to consider.

The basic composition of the pad

The liner is generally composed of an intermediate substrate layer, a double-sided adhesive layer, a single-sided or double-sided protective paper, and the like. As shown in Figure 1.

1. Substrate Substrate is the main component that determines the thickness of the liner and its properties. According to its material, it can be divided into film base and foam base. The film-like substrate is generally a vinyl resin or a polyester and a paper, and has a good elasticity and a uniform texture and is used for a thinner flexible plate liner. Foam base materials are generally polyethylene, polyurethane foam. The base material determines the elasticity of the double-sided tape, the elasticity of the base material is too large, and the field printing is not ideal; the base material is too hard and the dot reproduction is not ideal.

2. Adhesive layer There are two points in the function of the adhesive layer, that is, the plate is firmly attached to the plate cylinder and the protective paper is adhered to the surface of the substrate. The adhesive used for the adhesive layer is divided into two types, rubber and acrylic. The viscosity of the gluing layer has a great influence on the service life of the double-sided adhesive. The viscosity of the gluing layer is low. When it is used for the second time, the plate material is not easy to stick; the viscosity is too high. It is easy to damage the double-sided adhesive surface when changing the version.

3. Protective paper The role of protective paper is to prevent the substrate layer from being scratched, to prevent dust, and to prevent blocking, which facilitates unwinding.

Selection of liners

From the analysis of compressibility, the soft liner has the highest compressibility, followed by the neutral liner, and the hard liner has the least compressibility.

When choosing a liner, first consider the following two basic elements.

1. Printing materials

Flexographic printing materials have a wide range of properties, from soft Plastic Film to rigid glass products, from the metal film to corrugated cardboard, etc., nothing less than the choice of liner must take into account the breadth of the printing materials.

2. Printing pattern features

Different layouts should be used for different liners, and the field version is best for rigid liners. Cable version is best to use soft pads. If there are both solid and small lines or small dots in the printed pattern, use a neutral liner.

Therefore, a reasonable choice of liners should be used in actual production according to different printing conditions and process requirements.

Experiment 1 Relationship between Liner Hardness and Solid Density Value

We used a 1GT-F1 flexographic fitness instrument to perform experiments and obtained the results shown in Table 1. According to the experimental data, draw the curve as shown in Figure 2.

As can be seen from Figure 2, as the liner hardness increases, the value of the field density gradually increases. This phenomenon occurs, our analysis is mainly due to the flexibility of the liner: In the printing process, the printing plate is given normal printing pressure. Under this pressure, the liner and the printing plate are deformed at the same time, but due to the good elasticity of the soft liner, the pressure on the printing plate is relatively small, so the ink on the printing plate does not completely transfer to the printing material, resulting in The printing density is small: while the hardness of the rigid liner is large, under the same other conditions, the pressure applied to the printing plate adhered with the rigid liner is greater than that of the printing plate pasted with the soft liner, so the ink The transfer is better; while the elasticity of the neutral liner is between the hard liner and the soft liner, so the density value of the printed field is also somewhere in between.

Experiment 2 Relationship between Liner Hardness and Dot Spread

Table 2 shows the test data of the effect of different liners on the dot expansion under the same conditions. The curve plotted according to Table 2 is shown in FIG. 3 .

As can be seen from FIG. 3, dot gain values ​​increase as the liner hardness increases. This is mainly due to the elasticity of the cushion. The elasticity of the soft liner is higher than that of the rigid liner. Under the same pressure, the amount of deformation of the soft liner is much larger than that of the rigid liner. Therefore, the amount of deformation of the printing plate adhered by the soft liner is smaller than that of the rigid liner. Because of the amount of deformation of the sticky plate, when the soft pad is used, the dot distortion is small, resulting in a relatively small dot gain value.

To sum up, we can draw the conclusion that it is better to use hard liners when printing in the field. When printing small lines and dots, it is more appropriate to choose a soft liner, while a neutral liner can compensate for the lack of soft liners and rigid liners. All graphics and texts can be taken into consideration. In general, neutral liners are used more widely.

In practical production, the liner utilization must also be considered when selecting the liner. The hard pad has a lower surface viscosity than the neutral pad, and the soft pad has the highest viscosity. When changing the plate, the hard pad has lower viscosity when it is reused, and the adhesiveness of the pad is poor. The soft pad has a very high viscosity. When the plate is unloaded, the middle layer of the pad is easily separated and cannot be used again; the neutral liner The pad can be reused several times. Therefore, from a savings point of view, the use of neutral liners is generally more affordable.



Author: Ding Honglei