Three major shortcomings
1. Dyes control is difficult
The difficulty in controlling the color difference of embossed labels is a problem that people know. The current countermeasures mainly rely on the captain's ability to respond and the level of on-site adjustment. The captain's usual practice is to observe the amount of ink consumed by the printed image to adjust the amount of ink discharged from the ink fountain roller. In addition, since the embossing speed increase will affect the amount of ink, there must be a step, that is, to increase the speed and adjust the amount of ink. Few embossing captains dare to speed up in a short time. Even so, it is difficult to avoid chromatic aberration at the beginning and end of each roll.
2. The expansion of outlets is difficult to control
The graphic printing has a hard mouth, the dot has a border, and the dot level cannot be attenuated to zero.
The same as the round dot, the flexo dot can be printed solid and full, rarely deformed, and not even out of shape. However, the embossed circular dots are different. The center is an ink dot, and the periphery is a deep circle. In the middle of the dots and circles, the ink color is relatively light. The embossed solid edge is also very interesting, and there must be a thin border, like a shadow. The reason is that the printing pressure is too large, and the dots or the edges of the ground are deformed.
In the traditional printing machine structure, the two rolls are tangent, due to the relationship between machining precision, there must be an error, that is, the radial runout data of the roller, also known as TIR in the industry. The method of flexo printing to handle this error is to use a double-sided tape with a thickness of 0.38 mm or 0.50 mm as a buffer, so that the elasticity of the double-sided tape has a high, medium, and low score. However, the embossing basically uses only a double-sided adhesive of 0.1 mm thickness, which means that the double-sided adhesive used for the embossing has only a bonding effect and has no buffering effect. The buffer of the embossing mechanism is a layer of 8 to 12 mm thick rubber layer wrapped on the embossing roller, but unfortunately, the rubber layer of the embossing machine has a relatively high hardness, and generally has a Shore hardness of 90° to 92°. The hardness of the plate is far less than this, even if some of the hard-coded plates have a Shore hardness of only about 90°. This configuration makes the printing plate a buffer layer, that is, the mechanical error of the embossing transfer mechanism, which is not buffered by the rubber layer of the embossing roller and the double-sided tape, but is buffered by the printing plate which must be controlled to be deformed. Therefore, as long as the embossing machine has precision errors, the offset error must be based on the printing plate.
In order to control the deformation of the printing plate, the current practice in the industry is to increase the hardness of the printing plate. Since the circumference of the embossing plate is generally small, that is, the diameter of the plate roller is not very large, the plate having a large hardness is pasted on the plate roller having a smaller diameter, and in order to prevent the plate from sticking to the plate, the predetermined type processing is often required. Before the plate is placed, the plate is shaped into a cylindrical shape. Thin, hard, and pre-set, these factors cause the plate to crack easily during the low-temperature drying season, especially in the winter, which has become a "bottleneck" for improving plate utilization.
3. The product can not prevent the dirty spots
These dirty spots often appear as small white spots exposed in the printed area, and there are hidden defects in the color of the field or color block.
The embossing also has such a feature that within 4 to 5 hours, the temperature of the ink roller of the embossing machine rises from 25 ° C to 60 ° C to 70 ° C at the time of starting, which is an inevitable result of the ink roller cutting ink. When the temperature of the ink roller rises, the viscosity of the ink decreases, and the original ink level characteristics of the ink path also change. Therefore, the dirty spot of the ink inherent in the embossed product is inevitable.
How to improve?
According to the specific treatment of specific problems, the three major flaws still have a way to deal with it.
(1) The chromatic aberration control mainly relies on human control. It cannot use the process documents to regulate people like flexo printing, so that the products reach consistency. But it can be like the offset printing , through the captain's control, to achieve the basic consistency of the product. Under the conditions that are difficult to control people at present, how to do offset printing, embossing should also do so.
(2) Since you don't want the letterpress to become the buffer layer for the mechanical operation accuracy error, you must consciously look for the "dead ghost" and establish the required buffer layer. It is a good choice to reduce the hardness of the embossing roller or to create a buffer layer on the plate roll using foam double-sided tape.
(3) The embossing often chooses offset ink as its own ink, but we already know that the embossed ink path is much different from the offset ink path, and the same viscous ink is used under the condition that the ink path is very different, on the ink color.焉 Can not produce quality failure? Take offset printing as an example: sheetfed offset presses and web offset presses are offset, the difference in ink path is not very large, the industry is not very familiar with the characteristics of the equipment is generally not easy to distinguish. However, how many printing companies use the same offset ink on two different types of offset presses? And where are the biggest differences between the two different types of inks? This is what we deserve to think about. Therefore, adjusting the viscosity of the offset printing ink used on the current embossing machine should be an idea that can be implemented.
The above content is selected from the 4th issue of 2015, Label Printing Technology , and more journal content please pay attention to the journal channel .
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