The adhesive material for composite materials is a sandwich structure, and theoretically requires the tension of the base paper and the surface material to be consistent during composite, so that the overall tension is stable. If the tension of the two is inconsistent, the material will gradually elongate and deform during printing and processing, causing inaccurate printing or die-cutting, resulting in waste products. Moreover, the faster the speed of the printing machine, the greater the driving tension of the material, and the greater the elongation deformation of the material.
Let's first look at a sample of a transparent PE surface material and a Glassin base paper: when the material is composite, the surface material is tight (high tension) and the base paper is loose (low tension). During printing, the base paper and the surface material are printed as a whole under the driving tension of the equipment. However, during the printing process, PE surface material is constantly deformed under the action of the machine tension, while the base paper has a small force until there is a large tension in the base paper. When the tension of the surface material and the base paper are balanced, the overall tension of the material is balanced.
In this process, thePE surface material is constantly stretched and deformed, which causes inaccurate printing, and the faster the speed of the printing machine, the larger the tension and the more serious the inaccurate printing.
After analyzing the sample, it was found that the material was relaxed after printing and had no tension. ThePE surface material shrank and shortened, and the base paper relatively elongated, causing creases. After checking the printed patterns, it was found that there was inaccurate printing. After die-cutting, it was found that the dimensions of the label in the vertical direction became smaller, and the spacing between the cut waste increased. This phenomenon was caused by the inconsistent tension between the surface material and the base paper, resulting in a large amount of waste products.
To prove this theory and phenomenon, two case studies are used below:
A printing plant in southern China using an internationally renowned brand of woven flexo printing press, by two material suppliers to provide four different materials, each providing two, a supplier of a material with overprint inaccuracy problem. Repeated adjustments to the equipment confirmed that the overprint is not allowed with the equipment.
The material under complaint is printed at a speed of 20 m / min, the printing and die-cutting register is normal. The speed increased to 80 m / min when the register is not allowed, after equipment adjustment still can not solve the register problem. The other three materials were printed with normal overprinting, and the printing machine could reach 100 m/min without adjusting the speed.
The supplier reflected that the material complained about did not have overprint problems when printed on the intermittent machine, which is commonly used in China. In fact, this is because the intermittent machine delivery paper force is low and slow, with a speed of no more than 40 m / min, so there will be no overprinting inaccuracy problems, and thus no complaints.
The material under complaint, the quality of the surface material itself has defects, the tension between the two in the composite does not match, resulting in high-speed printing, tension enhancement, the material stretching deformation, and ultimately cause printing, die-cutting overprint inadmissible.
Material supplier coating equipment through the method of testing, select the most suitable combination of raw materials and tension matching control, the production of sample rolls, after testing by the printing plant, the final determination of technical parameters, and then formal production, to ensure the quality of the material coating and the tension of the base paper surface material match.
A printer in Tianjin, China, used a local supplier of coated paper material to print a batch of food labels with a large order volume, using two letterpress rotary printing presses of the same type. When the printing speed was 20 m/min, the label graphics were overprinted accurately, and when the speed rose to 50 m/min the phenomenon of inaccurate vertical overprinting occurred.
The machine manager rotated the problematic material on two letterpress rotary presses of the same brand, and the same overprint inaccuracy occurred after printing, but the printing was immediately restored to normal by replacing the material with that of another supplier.
When the problematic material was replaced on another brand of intermittent letterpress, the printing overprint was very accurate with no quality problems at a printing speed of 30 m/min, which is also fine at low speed but not at high speed.
The above two cases again illustrate the impact of the stability of raw material tension on the overprint accuracy, qualified material base paper and surface tension consistent, whether in high-speed or low-speed label printing presses can print a qualified product, there will be no overprint problems. And the substrate and surface tension inconsistent material can only be used in low-speed label printing presses, not for high-speed printing, the use of limitations, does not meet the requirements of the majority of label printing companies.
Printers want to get the final excellent finished product, from the material off to strictly control, material tension problems caused by poor overprinting is relatively hidden, in the actual production process of the printer, easy to be ignored, recorded for your reference.