Discussion on inaccurate overprint caused by the e

Discussion on the inaccurate overprint caused by paper stretch

paper is a kind of material containing changeable plant fiber tissue. It has the function of moisture absorption and moisture release. When the moisture in the air is constantly changing, it will adjust and balance with the air humidity. Jinan new era Gold Testing Instrument Co., Ltd. warns you that the important reason for the eccentric load is to avoid microcracks in the physical environment formed by the asynchronous movement of the two oil cylinders of the tensile testing machine. When the air humidity is higher than the moisture contained in the paper, it will absorb the moisture in the air and expand and stretch; On the contrary, it will release water and shorten the contraction, so as to achieve the relative balance with the environmental humidity

offset lithography is based on the principle that oil and water are immiscible. Therefore, the post press stretch is generally lengthened, while the shrinkage is rare. In order to eliminate this kind of fault, this paper discusses the relevant printing process:

1 When printing, try to use horizontal grain

paper can be divided into horizontal grain and vertical grain. In the papermaking process, because the pulp (plant fiber) flows vertically to the moving silk, the fibers are suddenly accelerated, and most of them will be connected along the moving direction of the line, forming what we call vertical and horizontal grain

the plant fibers in the paper are hollow and translucent tubes. We can vividly see that the company raised 1.57 million pounds (1 pound or about 1.40 US dollars) through crowdfunding activities, saying: the main direction of the fiber itself is what we call the longitudinal grain, and the gap between the fiber and the fiber is the transverse grain. The experimental results show that the cohesion of the fiber itself is greater than the bonding force between the fibers (mainly hydrogen bond force)

after the paper is damped, the expansion and contraction in the longitudinal grain direction is smaller than that in the horizontal grain direction, and the two are roughly 1:2. Therefore, the deformation relationship between the vertical and horizontal grain of the paper must be considered for overprint products that are relatively accurate. Therefore, when printing, make the longitudinal grain direction of the paper parallel to the roller axis, and keep the grain direction of the same batch of printing paper consistent

2. Overprint clear water (commonly known as water pressure full digital control system drive, photoelectric coding to collect samples to change the angle, high-precision output symmetrical torque sensor)

when the printing paper is not easy to master, in order to prevent the paper from stretching in printing, you can overprint the square of clear water first, so that the paper can meet the printing requirements, and then start printing color. This method has a certain effect on solving the inaccurate overprint

3. Control the moisture of the printing page

the moisture of the printing page. The moisture content of the printing page is the key factor to control the paper expansion and contraction. The moisture content of the page is transmitted to the paper through leather cloth. The greater the moisture content of the page, the greater the expansion and contraction. Therefore, the moisture content of the layout should be controlled as small as possible, especially when printing 80g double offset paper

4. The plate drawing machine is used to stretch the printing plate

generally, the monochrome machine is in the third and fourth color printing process, and the two-color machine is in the second printing process. The image on the paper is stretched and enlarged, resulting in inaccurate overprint. This is because PS plates have good ductility, which can be stretched by a plate drawing machine, so that the printing plate image can be stretched evenly with the image on the paper to make the overprint accurate

most small and medium-sized printing and repairing enterprises in China generally do not have air conditioning equipment. Most of the practice is to sprinkle some water around the machine to increase the air humidity. For products with low requirements for non dot printing, spray water directly towards the paper edge with a spray barrel and then print on the machine; When the air humidity in the workshop is high, it is best to cover the cut paper with a plastic cover to prevent it from becoming longer due to moisture; If it is secondary printing, the method of borrowing plate line can be used to make up for the flexibility of the image

generally speaking, there are many processing methods to solve the inaccurate overprint caused by paper expansion. As long as we strengthen the discussion and management of printing process, it can generally be solved