Discussion on related factors affecting the quality of UV printing (3)
Fig. 3 Adhesion of water droplets with or without surface treatment
6. Introduction of surface treatment methods
Because the printing method of UV ink is surface attachment rather than oxidation or penetration, the amount of surface tension is very important. Since the plastic surface is non-polar and incompatible, even solvent-based inks are difficult to attach. The principle is that we can understand the relationship between surface tension and cohesion by the water droplets on the lotus leaf. In addition, since additives in plastics often float to the surface, there may be cases where they cannot be physically connected. The surface treatment methods can be divided into three types:
1. Corona treatment
It is a kind of electric shock treatment. It uses a method of generating high voltage and high frequency to ground and induce electric shock to the electric nozzle respectively. No current passes between them until the voltage reaches 3000-5000 volts / square centimeter, and electric shock molecules are ejected from the air nozzle. With high-energy free electrons, it rushes towards the positive electrode, which is in addition to changing the polarity of the material and increasing the roughness of the surface.
The Dyne value of the printed material after corona treatment is not as high as possible. The difference between the normal Dyne value and the ink is about 10, which is more suitable. It is often asked why the Dyne value is already high, why is it still not printing smoothly? One of the reasons is that many of the printed materials contain many additives, and these additives will float out of the surface of the material due to high temperature and cause printing failure. The surface tension value of materials processed in this way will gradually decline with the increase of days, so it is recommended to test with a dyne pen to understand related information before printing. In addition, not all materials are suitable for surface treatment in this way, such as PP.
Figure 4 Dyne pen and dyne water Figure 5 Schematic diagram of corona treatment Figure 6 Schematic diagram of flame treatment
2. Primer primer processing
A layer of film is used as the medium between the ink and the printed material, which is normally used for materials that cannot be corona treated, such as PP. The processing method is divided into on-line PRIMER and offline PRIMER processing.
The thickness of this film is closely related to the smoothness of printing. Too thick is easy to cause waste, and too thin is easy to cause printing failure.
3. Flame treatment
It is carried out in flame mode. It is generally suitable for irregular shape or high-speed (1000 m / min) film treatment, and is generally used for bumpers.
6. Test methods and items related to UV printing
In the UV printing related tests, there are about 5 methods including surface tension test, adhesion test, drying test, UV energy test and ink film hardness test.
1. Surface tension test
First test with a dyne pen 38. If the condition on the right of Figure 7 appears, the dyne value on the surface of the material to be printed is below 38. , You must test with a higher number until the situation on the right occurs.
2. Adhesion test
This test mainly understands the adhesion of ink and printed materials. Take 3M 610 tape as the main test tool.
Figure 7 Surface tension test situation
3. Dryness test
The degree of drying of the ink is very much related to whether it can be post-processed. Because UV printing is not a surface penetration drying, if it is not completely dried, its scratch resistance and friction resistance performance is not ideal. In terms of ink drying, in addition to the following items, the opacity of the ink will also have a great impact. The higher the opacity, the worse the drying.
The factors affecting drying are the following
(1) Thickness of UV ink
(2) Different printed materials
(3) The speed of the machine
(4) Types of UV reflector
(5) UV lamp intensity
VII. Conclusion
This article gives an in-depth introduction to the related technologies of UV printing technology. The economic benefits that UV printing can bring, such as increased output, shortened delivery time, space saving, improved working environment, increased product accuracy, solvent resistance, and resistance Scratching, saving electricity, and the waste of ink without skin, etc., all help the industry reduce costs and improve quality, and at the same time can meet the needs of environmental protection. As the entry barrier is relatively high, the following suggestions are provided for manufacturers who want to transform.
1. Collection of relevant information:
There are many things to consider before you want to engage in UV printing, including plant, location, machine purchase, personnel technology, future positioning, etc. are all information that needs to be collected in advance. Information collection can be obtained from domestic or foreign agents , Or through the channel to obtain the situation of peer use, or through the Internet search, it is recommended that the company should have a person in charge or set up a research and development team.
2. Investment considerations in the early, mid- and long-term planning:
Each investment needs to be carefully evaluated. If you do not make investment planning in advance, you will lack a lot of things during operation. The general investment scale will vary greatly depending on the financial strength of each house, such as whether you need to have prepress equipment Or auxiliary equipment, because of the ozone generated by UV printing, in addition to the planning of its ventilation system, some basic equipment will ignore the purchase because many bosses do not know its importance, such as illuminance meter, intensity meter, concentration meter, and sink PH value. Equipped with gauges, conductivity meters, dyne pens, small UV drying equipment, and color development machines.
3. Confirm the positioning and attributes of the product:
The focus of this article is on lithographic UV printing. Lithographic UV printing can print a wide range of prints. At present, in addition to facing competition from the same industry, domestic manufacturers also need to consider the low-cost competition in the mainland. How to develop well and enhance the company's image It is very important to make good product segmentation and positioning. If the company ’s operations are still maintained at a low price, I believe this is by no means a long-term plan for the company ’s future development.
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