Thin paper printing curl causes and solutions

In the process of cutting thin paper sheets (such as dictionary sheets, etc.), curling and warping of printed sheets frequently occur, which affects the progress and quality of the cutting process. The main reason for the analysis is that the water content of the printed sheets is caused by the unbalanced temperature and humidity of the environment. The following methods can be adopted to solve the problems.

Dehumidification

Because the inside of the printed sheet is lower than the moisture content in the air, the radial section after cutting must absorb moisture quickly to achieve a corresponding balance. Therefore, the moisture in the indoor air should be properly reduced to avoid curling in the radial section after cutting. Solution: Use the dehumidification function of the air conditioner to remove excess moisture from the indoor air and effectively achieve dehumidification. The relative humidity is 50% RH, the temperature is 20 ~ 29 °C, the temperature and humidity meet the standard requirements, and the printed sheets are not easily curled and deformed.

2 page method

If curling occurs after the paper is printed, it can be solved by using the stencil method. The printed sheets were turned over first, and the curled printed sheets were punched on many fold lines by hand by means of a manual “crepe paper” method. The support force generated between the fold line and the fold line was used to forcibly change the curved printed sheets to make them relatively flat.

3. Paper method

The paper-drying method uses a paper-hanging machine to blow or dry the cut or uncut white paper, so that the internal humidity and air humidity of the paper are relatively balanced, and it is not easy to be deformed during printing and post-press processing. This can improve the printing quality. , also to the binding process to reduce a lot of trouble.

In addition, in order to ensure a reasonable amount of moisture inside the paper (about 5%), should also pay attention to the stacking position of the paper, not against the wall, by the window, by the heating (winter), but not on the open air, so as not to be too dry, damage the paper a reasonable moisture , causing paper warpage inequality.

Dot-line cutting method

In the traditional collision table, the tail of the printed sheet is usually a vertical line, but sometimes the printed sheet is irregularly jagged. It is also very accurate to observe the front and the back of the sheet. How can we cut the rules? Through careful observation and research on the cutting process, equipment used, and printing presses, we have found a rule that any printed matter that deviates from the vertical line (the vertical line formed by the combination of the tail lines after a collision) is skewed. Misplaced printed sheets, to be exact, printed sheets that are not at right angles are offset from the vertical line. How to solve and respond? We have reached the following conclusions from various aspects of the discussion and analysis:

(1) If you want to fundamentally solve the problem, you need to make the cut paper 90°.

(2) The solution to the cutting of finished printed sheets is the “dotted line cutting method”.

To explore this method, we must first understand the printer's paper feeding mechanism. The paper feeding mechanism of the printing press is fed to the paper transporting table by feeder, and then the paper is sent to the front gear through the belt drive, and the paper is pulled to the specified position through the side guide (as shown in Figure 1). . The paper sent to the paperboard must pass through two actions before it can be handed to the tusks. The first motion is longitudinal motion, which is the motion to come forward. The second motion is lateral motion, which is the movement of the pull gauge. Observed that if the paper sent to the front gauge is closer to the pull gauge, if it is less than 90°, the tip of the paper will go out of the pull gauge (as shown in Figure 1); any paper larger than 90° (on the side of the tab ), the tail side will exceed the pull gauge. When the crux of the problem is found, there is a solution. The position of the printed paper is composed of dots and lines. The point is the point determined by the pull gauge bearing, and the line is the line formed by the front baffle. Through the understanding of the printing press, in order to cut out a more accurate finished product, we decided to reconstruct the collision table. Change the collision table into a dotted line structure. Specific approach: Add a piece of width 100mm, thickness about 20mm on the original collision table, and the length of the board is higher than the height of the original side of the original collision board, and put it to the position of the pull gauge. Using this type of page-flipping method, the printed sheets are in place, and the printed sheets are also particularly suitable for cutting. However, the method of cutting did not change, or it did not meet the ideal requirements, so it added a cutting device. Specific approach: use the same specifications of the board fixed it on the pusher, through the measurement and practice, in the pusher from the side to help the 110 ~ 120mm (press the machine's pull gauge position) with double strands of 8 wire nest into horseshoe In the form of a card stuck to the board and one card stuck to the paper feeder, the thickness of each stack should be 70mm. This method is easy to handle, flexible, and does not affect the structure of the knife. As long as the overprinting is accurate, it can be beautifully cut, improving the reliability of high-quality products, reducing the loss rate caused by cutting and “bleeding”, as well as the cost loss caused by the offset printing and improving work efficiency. Through more than 10 years of application, the effect is very good.

Effect of blade structure and style on cutting quality

The style of the blade depends mainly on the edge angle. There are usually two types of edge angles: the arc-type edge angles milled by a vertical grinding machine; the edge angles ground using a horizontal grinding machine are linear, and such edge angles can be adapted to replace various soft and hard materials at any time. The cut object. The method of machining such a blade is to grind an angle of 26[deg.] on its edge at 24[deg.]. It is suitable for arc-shaped edge angles for slower initial speeds. Because of the lower resistance when the edge angle is initially cut, this is mainly due to the arc's arc shape. It is worth noting that the knife cut speed is slow and should choose a smaller edge angle within the allowable range. If the knife cuts faster, the larger edge angle should be selected within the range. The relationship between the cutting speed and the edge angle of the cutter is also inseparable and should be adjusted correctly and flexibly. The choice of edge angle can refer to Table 1.

In addition, the impact of blunt knives on cutting quality is also very large. Since the blades form a round head, when the blade is cut, the blades cannot cut the paper at a time, but press down until the paper basket is in a groove shape (as shown in FIG. 3 ). At this time, the paper basket almost became a whole, and the blade edged through the paper basket to complete the cutting. However, the corner formed on the paper basket formed was not entirely square, but an arc of the paper basket was probed at about 60°. Corner. Therefore, the probing part must be larger than the paper under the paper basket and form the so-called upper and lower blades. Therefore, it is necessary to change the knife immediately after finding out that the paper is cut, so as not to affect the cutting quality. Under normal circumstances, the blade can be changed by 1000 to 1500 times.

Source: Printing Technology