Causes and countermeasures of curling of cut thin paper sheets

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.

4. 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 transported by Feida to the paper-feeding table, then the paper is sent to the front stopper by the belt drive, and then the paper is pulled to the specified position through the side guide to the paper on the paper-feeding board. Only after two actions can the tooth be delivered to:

The first action is the longitudinal movement, which is the movement to come forward; the second movement is the lateral movement, 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 be pulled out of the pull gauge; any paper larger than 90° (on the side of the pull tab) will have its tail side Beyond the rules. 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.