Avoid paper defects in the on-demand printing process

Even for those who have rich experience in printing and binding, they may feel very tricky when they first start digital printing. For example, digital printing and offset printing are two completely different processes, but the paper they use is indeed the same. Therefore, people also expect that the paper can be processed in the same way, resulting in unsatisfactory results. Sometimes, it is not until the post-printing stage that the paper problem is found. The loss is very large.

The digital printing process consists of various complicated technologies, and the paper issue mentioned in this paper is just one of the common problems. The best way to avoid the problem is to learn as much as possible about the relevant knowledge, communicate with other users of similar products, and reserve the amount of information so that they are not needed.

Communicating with equipment manufacturers is also very important, and many suppliers will provide a list of paper samples labeled “approved” or “certified” to identify which papers can be used for their equipment. Ideally, these lists can accurately reflect the communication and test results between paper mills and equipment manufacturers.

Digital printing companies, though not capable of confessing these lists, are a good start. Any traditional printing company involved in digital printing should not take it for granted that the paper they used in the past can be successfully processed by a digital printer. Similarly, for every new digital device installed, a lot of experimentation should be done on the corresponding paper to make sure it works properly.

Lack of regulation

If you are operating a digital press, you will find that there are few parameters that can be adjusted on the digital press. Most of them have been set by the manufacturer. Those who have experience in the operation of traditional presses may not be accustomed to this point. . Running a problematic paper requires more attention to external factors. Once the operation has started, it is very difficult to correct the problem, so it is very important to avoid the problem in the preparation of printing.

At present, in the high-speed digital printing process, the three paper factors are mainly emphasized. This is different from the offset printing process. These three factors have a great influence on the subsequent binding process.

Winding journey

In fact, all digital presses have undergone a tortuous process in paper applications. Most of them do not use grippers or other mechanical equipment to complete the paper feed. This makes the direction of silk paper become Important. Most digital presses pick up paper in 11- or 12-inch directions, or print only 1- or 2-page prints. The proper orientation of the web is perpendicular to the direction of paper feed, which means that for 8 × 11 in. paper, it is a filament. For 11 × 17 inch paper, it is a short silk direction, otherwise it will cause unnecessary losses, such as paper jams and overprinting problems.

But this has a great conflict with the binding process. For example, if you want to process an 8×11 inch paper, it is best to print along the direction of the filament, and for the folding process. , I hope the short-term direction. If thicker paper is used, the problem between the two departments will further deteriorate.

Here's a more complicated example: A 5 x 8 paper size is printed on an 8 or 4 open machine and then glued. Appropriate silk orientation is used for printing, and when the book is bound, the page ripples occur. This is because the silk of the paper does not coincide with the direction of the spine. Therefore, the direction of the paper strands should be carefully determined before production to minimize the quality loss during the post-processing.

high temperature

Toner type digital printers are widely used in the on-demand printing process. When the fusion image is exposed on paper, due to the high temperature, the paper is prone to curling, drying, and sometimes blistering. If it is double-sided printing, such a process will be repeated twice, and the damage to the paper will be even greater. Therefore, it is extremely important to control the humidity of paper and the environment.

In addition, it is also possible to use a substance called fused oil, which is a high-viscosity silicone resin solution. Using it on paper ensures that the toner is combined with the paper material, and its effect is much better than that of a roller. Usually, these colorless liquids cause flicking on the coated material or in areas with thicker ink layers. When the liquid oil volatilizes, the tail flicker disappears, eliminating the need for ink drying time, which is also digitally printed. One major advantage.

Fused oil is different from ink, it will not scratch or rub when binding, but it is too smooth, it will bring some trouble to the paper, especially for some small printing machines in the field of fast printing. in this way.

Electrostatic charging

Since electrostatic charging is the core of laser/toner printing technology, common electrostatic control technologies, such as jetting and gold foil technology, are not well suited for digital printing applications. Similarly, electrostatic charging technology is also related to the temperature and humidity of the printing shop, and it is also the key to successful printing. Many companies set up an independent digital printing area to make environmental control easier and avoid excessive use of dusting. Unfortunately, the handling of paper is harder. If the outdoor temperature is zero while the paper is being transported, it should be moved to a workshop where the temperature has been controlled. The temperature is 25 degrees above zero, and the paper undergoes a temperature change. Temperature and humidity have a great influence on the electrostatic effect. If printing on paper that is prone to static electricity will produce deinking or white spots, the image will not transfer well and paper jams will also occur.

The ability of different thicknesses of paper to adapt to the surrounding environment is also very different. For example, a paper may need to adapt to the surrounding humidity and temperature overnight, and a forklift's paper may take a month to adapt to the environment. Therefore, when performing on-demand printing, special attention should be paid to the analysis of storage conditions. If paper is removed from the warehouse, consider drying the paper before entering the digital printing shop.

Binding

Common paper failures have the following four main characteristics:

1. Wrinkles, wave patterns

If the product produced has wave patterns, it is a poor quality product that is not acceptable to customers. Therefore, during the production process, it is necessary to pay close attention to the occurrence of wave or curling of the paper, which will cause great troubles for the post-processing process, especially for the equipment with a roller, such as a folder.

2. Paper breaks

Paper breakage is not a unique phenomenon in the digital printing process, but the phenomenon of paper breakage is even more pronounced in digital printing. This is because the image is floating on the surface of the paper instead of being absorbed by the paper during digital printing.

3. Paper peeling

Improper paper handling can cause paper peeling when printing on a toner type printer. In general, the paper peeling occurs when the image fusion is not sufficiently tight. Sometimes the peeling of paper is very obvious and sometimes it is very subtle. You only need to use your fingernail to gently cross the area of ​​the solid image to determine if this malfunction has occurred.

This problem is difficult to solve. Compared with four-color printers, monochrome machines are more prone to such problems. Printing with coated paper on black-and-white digital printers can easily explain this problem.

4. Scratches

When the paper passes through the device, it is prone to rubbing or scratches. If scratches appear on the cover, it will affect the quality of the entire book. Some printing machines are more likely to cause such problems due to the structure of the machine, so it is more necessary to carry out special processing on the paper in order to obtain high-quality prints. During offset printing, this problem can be avoided by coating or laminating. The cost of laminating digital printing products is relatively high.

Experiments have shown that if the color digital printer is matched with the appropriate paper, effective anti-friction effect can be obtained. This can not only effectively avoid failures, but also improve the competitiveness of production.

In the field of on-demand digital printing, on-line post-press processing is widely used, and some jobs do not require post-press processing at all, so that the rapidity of digital printing can be fully utilized. Otherwise, the above mentioned defects cannot be avoided. Sometimes the quality of printing is good, but friction or scratches can also occur during transport or mailing.

Brave New World

Some excellent digital printing machines have created new application areas and market scopes. Under such circumstances, consumers can have more flexible choices in paper parameters and prices, which is the basis for them to produce high-quality products.