Process Control of Quality Control of Printing Products in Offset Printing

Third, the control of printing process

With the ideal materials and good printing equipment, we may be able to print good printing products, but it is by no means necessarily able to print good prints. The next most important point is the need for reasonable control of the printing process.

(1) Shaiban. Shaiban is a very important part of the printing process. Let's take a look at the factors that need to be controlled during the printing process:

1) determine the correct exposure time; 2) determine the correct extraction time; 3) dust removal work; 4) adjustment range: 2% -98%; 5) determine the position of the printing plate rinse; 6) drying printing plate Quality control bar.

· The issues we should pay attention to in the printing work are:

Pay attention to the quality of PS version body

1. PS version background color is not good. 2. Improper development time. 3. After development, there is a "blue bottom" that causes the printing to be dirty. 4. Not easy to ink, PS printing on the machine is not easy to ink. 5. Local "flower version", paste version. 6. Interruption of the printing process. 7. Partially dropped. 8. Locally out of print. 9. PS plate surface roughness is not good 10. PS version of ink affinity, poor alkali resistance. 11. Improper proportion of photosensitive ratio. 12. Photosensitive film is too thin.

The above issues are all of our attention in the printing work. The appearance of any point will lead to a decline in the quality of the printed matter or even invalidation.

(2) Water and ink balance control in printing

1 water control. In fact, we don't need water at all in the final printed matter. Even we always complain that water has caused various defects for our products (such as the low ink gloss on the printed surface due to the presence of water). So we are always looking for a lithographic printing that does not require water at all, so waterless offset printing has emerged. Although it has various advantages that are not comparable to water offset printing, the only drawback is that the cost is too high to make it impossible. Better promotion. Therefore, we also need to start with the printing of water. Because of restrictions on printing plates and inks, we still need water for traditional water printing equipment. All we can do in printing is to keep the ink in the blank as much as possible. Under the premise of reducing the water consumption, doing so can reduce the ink emulsification, make the edge of the dot clearer (the boundary of the oil and water is clear), and secondly, the ink can be smoothly transferred to the surface of the substrate. Thirdly, the reduction of the amount of water can be avoided. The large resulting surface properties of the substrate are reduced, and the substrate absorbs water.

· To ensure that outlets are clear and blank areas are not dirty, minimizing water consumption is a basic principle of our use of water in offset printing. Some people say that there is water printing. Controlling the quality of water helps us to master the printing. It does make sense to produce better printing quality.

§ Appendix (1) How to judge the excess of water

The ink on the printed matter is light, and even if the ink volume is increased, the ink color is not deepened in time;

The amount of ink accumulated on the ink roller increases, and the ink particles become thicker;

The sheets absorb excess moisture, and the amount of water on both sides is uneven and the paper is curled;

There is too much moisture in the surface of the ink film, and the ink added to the ink fountain is not easy to stir evenly, and the roller has a slip phenomenon;

There is sticky water at the tip of the blanket, and there are drops of water at both ends of the roller;

Before and after the printing was interrupted, there was a large gap between the darkness of the printed ink.

After the shutdown, the board will not dry.

(2) Ink volume control. Our control of the amount of ink in printing is mainly based on printed samples. This process is mainly carried out through the human eye, but experienced operators can often do very well.

First, we need to determine a reasonable color sequence based on the process characteristics of the product. Different color sequences will have different degrees of influence on print quality.

Then there is the comparison between the proofs after printing and the printed samples. There are generally two methods for this comparison. One is the visual inspection method, which compares the printed sheets and proofs immediately after printing to identify the color shades of each part (if it is The monochrome machine is not sure about the yellow color of the first printing, and it can use red or blue color filter); one is the method of hand-feeling, that is, pressing the hand on the printed image on the printed sheet immediately, if the hand is lifted, it can feel a little Sticky, that is more appropriate ink. However, these two methods require very experienced operators to use them, and they are subjective and their quality is not stable.

Modern, more advanced printing systems have introduced relatively sophisticated ink control devices. For example, HEIDELBERG's CPC system, ROLAND's CCI system, and KOMORI's PQC system all provide smart ink color control functions, replacing the artificial judgment of ink with the intelligent judgment of the computer. These systems provide possibilities for the scientificization and dataization of printed ink.

(3) Pressure control during printing

The presence of printing pressure can cause many problems such as dot gain, but since printing pressure is a prerequisite for ink transfer during printing, it is impossible to avoid it completely. Therefore, as with the above-mentioned water volume control, a general principle is also proposed for pressure control. That is, under the premise that the ink can be reasonably transferred, we advocate the use of the minimum printing pressure. This has many advantages, such as: minimizing the spread of dots under pressure; minimizing the amount of deformation of the blanket under pressure, thereby reducing the line speed difference at the surface of the drum and reducing the speed due to this Distortion caused by poor printing; reduced wear on the printing plate, reduced the number of printing plates in the printing process, increased the stability of the printing quality; improved the service life of the blanket, and made the pressure during printing more stable……

(4) Overprint control of printed matter

Overprinting of printed matter is usually an important factor in determining the quality of the printed matter. If the problem of overprinting cannot be guaranteed, then there will be no more high quality problems.

The control over the accuracy of overprinting out of the precise adjustment of the printing equipment we mentioned in the “equipment” (provided that the printing equipment is available), there are the following factors:

1. Humidify the substrate so that its own humidity is equal to or slightly higher than the ambient humidity of the workshop.

2. Keep the workshop environment constant temperature and humidity.

3. Minimize the amount of water used during the printing process.

4. Ensure that the thickness of the printing plate liner in each color group is the same during the printing process. Due to the calendering problem of multi-color printing and the participation of water in the printing process, it is now recommended that the thickness of the printing plate liner after the color printing is slightly less than The color pad thickness is 0.03 mm.

In fact, there are many factors that can improve the precision of overprinting of printed materials, which are not listed here.



Source: Bison