The meaning of blankets and normalized operations

The task of the blanket is to accurately transfer the graphic on the printing plate to the substrate. In order to achieve a high transfer effect, it is necessary to have very high requirements on the quality of the blanket, and also to pay attention to the standardization of the blanket. operating.

High quality blankets should have the characteristics

1. Thick and even

The flatness error of the blanket should be within ±0.04mm, otherwise the printing pressure will be uneven, and the ink color of the printed product will be significantly uneven, which will seriously affect the quality of the printed product.

2. Small compression deformation

In order to prevent the thickness of the blanket from decreasing, the elasticity is reduced, and the hardness is increased during the printing process, a blanket with a small compression deformation should be selected.

3. Small elongation

The smaller the elongation of the blanket, the better, so that the printing process can ensure accurate overprinting, complete dot and clear text, thus greatly improving the printing quality.

4. Good transfer performance

As an intermediate medium for the transfer of dots, the blanket must have good ink adsorption capacity, ink transfer ability and strong hydrophobicity. At the same time, the surface rubber layer of the blanket should have a certain roughness, and the surface is smooth and free from impurities.

5. Abrasion resistance, oil resistance, heat resistance and anti-aging

The blanket cannot be swelled by contact with chemicals in the printing process, thereby damaging its performance. Therefore, high-quality blankets should be resistant to abrasion, oil and heat.

Standardized operation is important for print quality

Only when the blanket has the above characteristics can a high-definition print be printed. In addition, standardized operations have a significant impact on print quality.

1. Determine the flatness of the blanket

It is well known that standardized operations are essential in the offset process. The first is to correct the "three flats", that is, the blanket is flat, the roller is flat, and the ink roller is flat; the second is to adjust the "two small", that is, the water volume is small and the pressure is small; in addition, to do "three Qin", that is, check the proofs frequently. Stir the ink fountain and check the moisture on the plate. The blanket flat referred to here means that the surface of the blanket cylinder is to be flat.

The effect of the flatness of the blanket is mainly the underlay under the blanket. The padding must be flat to ensure that the blanket is flat. When installing the blanket, prevent the foreign matter from being caught in the gasket, causing the gasket to wrinkle.

So, how do you determine if the blanket is flat? The traditional method is to confirm with the method of "drawing a map". The specific method is as follows: the ink on the ink roller is evenly mixed (usually with yellow ink), and the inking roller is pressed against the plate to make the printing plate evenly inked and then pressed. If the blanket is evenly inked, it means that the surface of the blanket is flat; if the surface of the blanket is uneven like a map, it means that the surface of the blanket is not flat. You can use a pencil to draw the shape of the bump like a map on a liner or blanket. The fabric is then directly applied to the liner or fabric with different thicknesses of paper to flatten the surface of the blanket.

2. The operator should have a serious and responsible attitude

The following is an example of a quality accident caused by a blanket that omits the operation steps due to the trouble of the map.

When I used a MANROLAN ROLAND 707 LV+UV device to print a job with a large area of ​​red and yellow, there was a change in the rules and conditions, and the changes were more regular. Both the operating side and the drive side appeared. The rule line gradually becomes stepwise and gradually becomes larger at the tip and the mouth, and then gradually falls back step by step. Each time the sample is sampled, the rule line is straight and there is no error. Only when comparing the sample after printing thousands of sheets with the previous sample, the error can be seen. About 5,000 proofs per print, the rule line will change to the mouth and the tip position by as much as 0.3mm, which directly affects the quality of the printed product.

After inspection, the paper-feeding mechanism and the front-end mechanism of the printing equipment were all fine, which made the author confused. After careful observation, only the rule line of the red solid color group changes, while the rule lines of other color groups are normal, and the embossing process is overprinted on the red ground. Therefore, the author believes that it should be the blanket of the color set, There is a problem with the plate or the impression cylinder. After the investigation, the equipment has no problems, and the cause of the printing plate failure is gradually eliminated, leaving only one factor of the blanket. After inspection, the author found that the blanket was not fast enough to be installed, and it would make a dull sound when hit by hand. After tightening the blanket with a torque wrench, the problem is solved.

When the new blanket is attached to the machine, it should be tightened first, and then the blanket should be checked for wrinkles and bubbles. If there is no problem after inspection, let the roller press for a few turns and then tighten it. The new blanket has good elasticity and good stretchability. The stretched blanket should be gradually carried out. It is required to carry out both the tip and the mouth of the mouth at the same time. Do not tighten the one side. Each time it is stretched, it will be pressed and pressed for 3 to 5 minutes, so that it can be tightened several times. After the blanket is tightened, you should also use your fingers to hit the blanket at the mouth of the mouth. After hearing the crisp sound, you can judge that the blanket is tight. Sometimes, in order to save time, the operator saves the inspection and confirmation process, and it is too late to check after printing the waste.

In addition, the surface of the blanket should be kept clean during the printing process. After each long stop, the ink on the surface of the blanket should be washed off and dried to prevent the surface rubber from being too smooth and hardened, leading to premature aging. When there are many impurities such as paper wool, powder and filler on the surface of the blanket, it is necessary to insist on washing the blanket to keep the surface of the blanket clean, to prevent the impurities from accumulating too thick, and to harden into a solid, thereby pressing the blanket. The rubber partially loses its elasticity and the like.

In short, the quality of the blanket directly affects the quality of the printing quality. The correct use of the blanket also plays a very important role in the printing process, which needs to be highly valued by the printing enterprise.