Several Ways of Grafting Paper in Gravure Machines

1. Does not slow down the transfer of paper and deceleration transfer paper

According to whether the speed of the machine is changed during the entire transfer process, the transfer of paper without stopping the machine is as follows: there are two modes of decelerating the transfer of the paper and decelerating the transfer of the paper.

Most gravure printing machines that use non-stopping transfer papers have the same machine speed, and no artificial changes occur. That is, the “non-stopping—not slowing down” transfer mode is adopted. However, there are also some gravure printing machines, which first reduce the speed of the machine to a certain range when the paper is handed over, and then restore the previous working speed after the paper is handed over. That is, the “non-stop-deceleration” method is used to transfer the paper. The latter method is adopted to simplify the system structure, reduce the impact of the paper handling process on the tension system, and maintain the stability of the registration. For example, if a high-speed machine is used to produce standard products, under the control of a computer, the machine speed can be reduced from 500 meters/minute to 250 meters or so.

2. Lapping the transfer paper and docking transfer paper

According to the connection mode between the old and new material tapes, there are two types of docking and lap-jointing papers.

Lapping refers to a certain length of overlap between the new material and the old material, with a double-sided adhesive tape between the two. Obviously there is a certain increase in the thickness of the joints. It is currently the most common material connection method, suitable for all thin films, thin paper (flexible packaging, decorative, tipping paper, etc.) and small cardboard thickness.

For paperboards with thicknesses above a certain range (approximately 250 g/m2), it is not advisable because the overlap thickness affects the secondary printing pressure, which may cause the machine to vibrate and damage the impression cylinder. In this case, docking should be used. There are actually two types of docking: high-speed docking and docking with paper storage.
(1) High speed docking paper

The start-up mechanism requirements of such systems are stronger than lap joints, and the time control is more critical and more complex, but it can achieve “head-to-head” docking at speeds of up to 200 m/min or even higher. Obviously, the front edge must be specially prepared. Zero gap docking can be achieved, but usually there is a gap of approximately 2-3 mm, which can be taped.

On some gravure machines that require printing on thick paper, there are usually two systems, lap and high-speed docking. In this way, the operator can use lap joints when printing thin paper, and high-speed docking can be used when printing paperboard.

(2) Using paper storage docking paper

A considerable length of tape is stored in the stocker.

Paper storage is commonly used in the coating process, and is often seen in the packaging gravure printing machine.

Its main drawback is that the total tape length is large and affects the continuity of the tension control, which in turn affects overprinting. Proponents believe that zero-speed splicing can reduce vibration compared to high-speed splicing paper. In either case, the regenerative motor drive can correct tension disturbances.

Frequently, the first unit needs to be back-printed. At this time, the printer is required to reversely unwind and transfer the paper. More and more flexible packaging gravure printing machines use two-way unwinding/cross-docking.

However, "bi-directional rewinding/hand-over paper" is seldom used, because generally the printing is required to face outwards, ie, one-way.

3. Synchronous transfer of paper and non-synchronous transfer paper

According to whether the unwinding and rewinding parts of the transfer paper are synchronized, the non-stop transfer paper can be divided into: synchronous transfer paper and asynchronous (asynchronous) transfer paper.
Normally, the start-up time for unwinding and rewinding the transfer paper is determined by the operator.

In this way, the start-up time difference of the take-up reel is controlled by humanism. Therefore, a certain length of scrap will inevitably appear, and sometimes the length of scrap will be very large. In order to minimize the waste generated from the transfer paper, the best way is to make the two transfer points (cutting points) of the unwinding and rewinding transfer papers the same. Calculating the lag time of the winding relative to the unwinding/contracting paper according to the timing of the squeaking of the press machine, the length of the tape between the unwinding and winding, and the machine running speed, thereby controlling the splicing paper of the winding mechanism time.
It should be said that the vast majority of gravure machines currently have no synchronous transfer function, but only use asynchronous transfer paper.

4. Visual inspection of the transfer of paper, fixed diameter transfer paper and fixed length transfer paper

According to the basis for starting the transfer of paper, there are two ways to transfer the paper without stopping the machine: visually handing over the paper, setting the diameter transfer paper, and setting the length of the transfer paper.

The most common way of visually picking up the paper is to transfer the paper. The operator can complete this critical process in a very personal way, mainly based on their experience with the press and the printing materials to determine the start time of the transfer paper. The operator's experience is a major factor in stabilizing the successful transfer of the paper when unwinding a particular material, within a certain range, at a certain speed, and with certain assistance. This is especially true for packaging gravure printers.

The process of starting the transfer paper according to the set diameter is such that the operator preliminarily sets a diameter. When the old material roll is reduced to the set diameter, the process of the transfer paper is started automatically, and no operator intervention is required for the entire completion. Ultrasonic sensors are often used for the detection of the roll diameter. For high-speed gravure presses, fixed-diameter transfer paper is a safety measure. However, due to different material thicknesses and different machine operating speeds, the cross-over diameters should also be different, and determining the proper diameter requires some experience.

The process of starting the transfer paper according to the set length is as follows: The operator presets a length of the tape, and when the print length reaches the set value, the process of the transfer paper is started automatically, and no operator intervention is required for the entire completion. By equal-width cross-linked paper, it is meant that the old and new material tapes have the same or substantially the same width. Commonly used packaging gravure machines generally use equal width cross-connection paper type.

Unequal width of cross-linked paper means that the widths of new and old tapes are different. It mainly appears in wide gravure machines (decorative gravure machines). For example, on some wide decorative gravure presses, there are four unwinding or four winding support shafts, and different widths of paper rolls can be installed to meet the requirements of different users. However, at this time, it is required that the lateral positioning of the paper roll, correction of the scanning head, and tension setting be automatically adjusted accordingly.

In unequal cross-docking, the old and new material belts also have different arrangements for "center line" and "pair line".