How much is the packaging offset? (111-116)

111. What is the static protection of the printing plate?

The static protection of a printing plate refers to the protection measures that the printing plate should take when it is in the state of printing. The static protection of the printing plate should pay attention to the following points.

1 Non-graphical part of the plate wetting properties protection. The surface of the blank part of the printing plate is a high-energy surface. If it is exposed to air or comes into contact with other oily substances, it can easily absorb excessive non-polar molecules, oil and other impurities, resulting in decreased hydrophilicity and easy adsorption in the printing process. Dirty ink. Therefore, the surface of the blank part of the printing plate needs to be covered with a water film, or the surface of the printing plate is coated with a layer of gum arabic.

2 plates to be protected from light. The graphic part of the plate should not be exposed to light for a long time, especially to avoid direct sunlight.

3 to prevent rigid damage to the plate. To prevent scratching and scratching of the surface of the plate, be careful not to cause "horseshoe-print" irregularities on the plate when taking the plate.

112. Why can gum arabica have good protection for printing plates?

Gum arabic is a high molecular compound that is a mixture of arabic and potassium arabinates and calcium salts. Their molecular structure contains multiple hydroxyl groups (-OH) and has good hydrophilicity and oleophobicity. The gum arabic is rubbed on the surface of the PS plate, and the low energy surface of the polymer compound replaces the high energy surface of the blank part of the alumina. This can prevent the adsorption of non-polar molecules such as air and impurities on the alumina film of the blank part of the printing plate. At the same time, it can also prevent oxidation of the aluminum substrate to protect its wetting properties. At the beginning of printing, since the gum arabic has good hydrophilicity, is easily soluble in water, and is washed with water to remove the adhesive layer, the high-energy surface wettability of the non-graphic part can be restored.

113. to pay attention to the issue of printing plate eraser?

1 The concentration of gum arabic solution should be moderate. If the concentration is too high, the acidity is too large and the printing plate is corroded. If the concentration is too low, a good protective film cannot be formed. The surface of the printing plate, the wiping cloth or the sponge can not contain too much water, and the printing plate after wiping off can no longer adhere to the water droplets. Otherwise, the concentration of the glue liquid will be partially or completely reduced, and there will not be enough glue layer covering the plate surface to cause dirt.

2 The non-graphic part of the plate must ensure that there is no missing area. At the same time, the glue should be rubbed evenly to avoid the condensation of the glue droplets. Therefore, it must be repeated at least twice. The graphic part can be erased in the field.

(3) The rags or sponges of the wiping solution must not be sticky with oily substances such as gasoline or ink, otherwise the surface of the blank part is not protected by the adhesive layer before it has absorbed the oily substance and it is dirty. When printing is stopped for a short time, you can wipe the glue without cleaning the ink on the plate. When you reprint, you must wash the paste and ink with the platewash paste and water before printing. If you directly put the water roll Water supply, the use of water on the roller to dissolve the film will increase the amount of glue in the wetting fluid. However, once printing is completed, plates that need to be stored for a long period of time must be thoroughly cleaned and then wiped. Otherwise, the ink on the plate surface will be difficult to wash off after the ink is dried.

4 After wiping off, dry the adhesive on the plate and collect it. If plates that have not dried are brought together, molds may form on the surface or adhere to each other. After wiping the glue on the printing press, in order to speed up the drying of the printing plate, the machine can be started to idle for a while.

114. How do you decide if you need to remove the glue when the printing stops?

In the printing production process, it is often stopped halfway for various reasons. At this time, the wiper can play a good role in protecting the printing plate. However, when printing after wiping, you need to clean the printing ink and film first, which will result in waste of materials and time. In addition, the wash paste has a slight corrosion effect on the printing plate graphic portion, which will reduce the printing plate's resistance to printing force. Therefore, in the printing production, the machine is shut down for a short period of time. Only when it is necessary, it is wiped off and protected. The length of time that the machine can keep the plate from being dirty is not related to the following factors.

1 plate non-graphic oxide film wear. The older the plate is, the more severe the wear is, the less water is stored, and the shorter the allowable downtime is, the less time the glue is removed.

2 content of gum arabic in wetting fluid. The wetting fluid generally contains gum arabic, which can protect the printing plate on the one hand when the machine stops for a short time. On the other hand, it can also improve the wettability of the printing plate by the wetting fluid. However, excessive content of gum arabic easily leads to The ink is heavily emulsified. When the old version is printed and frequent downtime is required, the content of gum arabic in the dampening solution can be slightly increased.

3 ink type. For oily inks, such as red ink, the allowable shutdown time of the printing plate is shorter.

4 environmental factors. The higher the temperature, the lower the humidity, the better the ventilation around the printing press, the faster the printing plate dries, and the shorter the allowable downtime is.

115. What is the strength of the printing plate?

The printing plate resistance force refers to the number of printing plates that can withstand the quality condition within the allowable range, that is, the quality required by the customer's sample.

116. What are the factors that determine the printing plate resistance?

1 Intrinsic factor of printing plate. The intrinsic factors of the printing plate include the mechanical strength and chemical stability of the printing plate itself. Different manufacturers produce plates with different printing forces. After the plate processed by baking, the printing resistance will be greatly improved.

2 print quality. The runaway of the printing plate in the printing process, the insufficient density of the original graphic part, the long exposure time, and excessive development (including too long development time, high developer concentration, and high temperature) will reduce the printing plate's resistance to printing.

3 plate static protection status. If the sensitized printing plate receives more light before it is printed on the machine, its resistance to printing will decrease.

4 printing plate dynamic protection situation. The dynamic protection of printing plates refers to the measures that should be taken to avoid or reduce the damage of various factors to printing plates when printing plates are in the state of combined printing on the printing press. It includes the following aspects.

a. Select the appropriate liner. The rigid lining has a large elastic modulus and the wear of the printing plate is more severe than that of the soft lining. According to the product quality requirements, the nature of the substrate, the performance of the machine and other factors, choose the right lining.

b. The pressure between the plate cylinder and the blanket cylinder should be appropriate. The greater the pressure, the more severe the wear of the printing plate. It is required to use the minimum printing pressure to print under the premise of ensuring good ink transfer.

c. Minimize roll

2 slides between the cylinders.

The lining thickness of plate cylinder and blanket cylinder should use the data provided by the printing press manufacturer to minimize the sliding caused by the speed difference between the rollers. The blanket cannot be stretched too tightly. Experiments have shown that the data of the synchronous rolling ratio will increase with the tightening degree. Excessive tension will increase the sliding between the rollers.

d. To properly adjust the pressure between the water roller and the ink roller and the plate cylinder, try to eliminate the wear caused by the axial movement of the water roller and the ink roller.

e. Correctly understand the composition and pH of the wetting fluid. By using the phosphoric acid in the dampening solution and the non-graphical part of the aluminum oxide film, the aluminum metal exposed after abrasion reacts to form aluminum phosphate, and the hydrophilicity of the blank part can be maintained. Maintaining a properly stable pH is a necessary condition for the above reaction to occur. Excessively high or low pH will erode the blank part of the plate. If the pH is too high, the wetting solution will also dissolve the diazo compounds in the graphic part, rendering the graphic part incomplete.

f. Adjust the viscosity and fluidity of the ink to control the thickness of the ink layer on the layout. It is necessary to avoid the spreading of the ink layer, and also to satisfy the protection of the rest of ink on the layout.

g. Use high quality paper as much as possible. If the paper is severely powdered and the blanket is piled up, the blanket must be washed to prevent the deposit from abrading the plate.

h. Use well-washing paste to properly adjust the concentration of the wash paste to prevent the wash paste from attacking the graphic basis.

Source - Printing Technology