Some Discussions on the Dirty Printing of Offset Printing Products (Part Two)

Second, in the process of paper transport, the contact between printed sheets and printed sheets, between printed sheets and the machine leads to picking up.

1. Dirty between printed sheets.

1 Because the ink layer is too thick, it causes slow drying;

2 due to the paper surface smoothness is too high or poor absorption;

3 Ink emulsification seriously causes the ink to dry slowly;

4 When the ink layer is not completely dry, the printing material is too high...

As mentioned above, after all printing is completed, the dirtiness between the printed sheets on the paper receiving table can be avoided by the following means: when the ink layer is thick in real time, proper dusting at the delivery end; About 1000-2000 sheets are added between the paper stacks. Of course, this height can also be changed according to the thickness of the paper; do not apply large impact force on the pile surface before the ink layer is dry (if the operator is sitting un-dried On the pile of paper, using heavy objects to beat on the pile of paper, etc.)

When a four-color offset printing machine prints a large-area field version of a product, the printed matter is often scratched and given dirt by the delivery roller. Since most of the used printing presses (such as manroland, Heidelberg, Komori, etc.) have their anti-adhesive papers (or anti-sticking nets) damaged and their equipments are not fully equipped, it is quite a struggle to deal with sticky problems. Let's talk about our experience in using imported four-color offset printing machines to print large-area field prints for reference.

1). In the printing sequence, try to place the full version on the ground in the fourth group to reduce the damage to the printed product.

2). The fluidity of the ink in the field version should be greater than normal. The combination of red dry oil and varnish is used in winter, and the proportion is about 8%. This kind of ink is used for printing copper plate paper and white cardboard. Ordinary paper printing inks can be blended in normal proportions.

3). When replacing the new release paper still does not solve the problem, it is recommended to install 3 to 5 springs (circumferential direction) with a diameter of about 6 mm on the delivery roller. Without a suitable spring, find a few diameters with a plastic sheath. It is possible to replace the wire with 2mm or so, but the effect is slightly worse.

4). The non-solid part of the printed product is glued to the corresponding part of the delivery roller to a small piece of foam of 5 mm thick, which raises the distance between the delivery roller and the printed product. If the field version is arranged in the first few groups, the thickness of the foam must be controlled within the range that does not affect overprinting.

5). When printing with manroland four-color machine, the ground plate is arranged in one or two groups, and the middle transfer tooth row will also touch the dirty prints due to the ink deposit. So long as it is cleaned frequently, it can solve the problem.

6). Some manroland machines only have a few delivery rollers on the delivery rollers. If printing plates are often used, it is best to retrofit them with reference to the home machine's delivery drum and it is easier to do.

2. Contact between the sheet and the machine results.

1 Some parts of the machine are leaking. The most common is Feder's mouthpiece leaking oil, and the oil leaking from the bottom of the machine when the paper passes under the machine.

Usually, the oil leakage from Feida's mouthpiece is very good to judge, so long as the wind pump is cleaned properly. In addition, it is necessary to keep the machine underneath (especially a multi-color machine with two or more colors) clean, and frequently clean the support bar on the paper drive line under the machine, and replace the bent and deformed support bar. Modern imported equipment will have air cushions on the paper path, so ensuring the air vents on the air cushion is an important part of daily maintenance.

2 Some parts of the paper are dirty on their own, or the ink on the sheets is smeared by some machine parts on the paper.

More typical is the hem of some printing presses, such as HDB CD102, when the printed sheets have not yet dried and turned over to print, it is easy to appear, the back of the paper-feeding pendulum during the back of the printed product (this time the back is already printed ) Dirty. In this case, generally there is no good way, only after the printed products are completely dry and printed.

On the printing machines produced by our country's Beiren (08,05), there is a mechanism called the cage (the hollow cylinder with many crossbars) in the delivery direction. It is mainly used to hold the printed sheets, and there are many on the crossbar. The rubber apron, and sometimes the position of the rubber apron, if it happens to be in the graphic part with a large amount of ink, can easily cause the back stain. Cleaning these rubber bands after printing a batch is necessary and often overlooked.

In multi-color printing, the proofs drawn must not only check the ink on the front side of the page, but also often look at the back side for smeared ink. If found to solve the problem in a timely manner.

3 The sideview pulls the ball at the exact position where it was dropped. When turning over, the pattern is transferred between the prints by the ball on the side scale.

When an experienced master prints some prints, he often sees whether the graphic (front, back) on the side of the rules of the paper will be picked up by the ball on the rules. If possible, then according to the operating equipment, try to adjust The position of the version is avoided.

Third, other.

In the printing unit, there are oil leaks, especially three (including printing plate, blanket, and embossing) rollers. The roller shaft head leaks oil. When the oil enters the edge of the printing plate, it will appear like a dirty surface. Dirty. This situation should also pay attention to analysis and processing during operation. The author once encountered such a device. The main problem was the oil seal of the shaft of the plate cylinder. However, because there was no time for repair, he had to find a long cloth to dip some water and wrap it around the roller shaft. Really played a big role.

In addition, the static content of paper is too large, and it can often cause back-scratch problems. In addition, due to the excessive static electricity content, and the excessive ink viscosity caused by the ink head is too long, together caused by the ink phenomenon, especially in the first color group, will cause the first color ink to splash on the surface of the paper on the paperboard , can also cause ink spots on the surface of the paper.

The water roller wadding has not been cleaned for a long time and may also leave a stain on the surface of the print.

The fountain solution has not been replaced for a long time. The pigment of the dissolved ink in the fountain solution, or the emulsified ink in the fountain solution, can also cause the surface of the printing plate to float.

The author always wanted to make a definite limitation on what was discussed here. Actually, it seems unnecessary. The printed matter we need is very simple to say. It is necessary to have ink in places where there is ink, and the amount of ink is appropriate. There is no ink. The place is not ink. This is the effect we need to achieve in offset printing. It is easy to say, and it is difficult to do it. The above mentioned issues are only part of the problems that can be encountered in actual production. In production, we must also pay attention to the different characteristics of different issues, and we must conduct specific analysis to eliminate them.



Source: Bison