The fountain solution is also called the water bucket solution, which is commonly known as the offset printing potion. It is an aqueous solution used to wet the printing plate surface during the offset printing process.
The quality of offset printing is largely related to fountain solution; therefore, the correct use of fountain solution and mastering the properties of fountain solution are the key to printing. For Heidelberg CD102-4 offset presses, how can we correctly grasp the nature and use of fountain solution?
The main components of the fountain solution used in Heidelberg CD102-4 offset presses are composed of water, alcohol and wetting powder.
Water—Neutral water is generally used for printing, and 2% —5% of wetting powder is generally added to the water. The PH value of water is generally controlled between 5.2 and 5.5. Gloss; acidity is too small, the printed product is easy to paste, dirty.
Alcohol-the role of alcohol is volatile and can take away heat. After adding alcohol to the water, it can reduce the surface tension of the water and make the water evenly distributed on the printing plate; when printing, the amount of alcohol is generally set to 12% Between -15%, the maximum should not be higher than 18%, otherwise, it will automatically stop after 15 minutes, too low will bring dirty; the standard temperature of alcohol is generally controlled between 10 ℃ -12 ℃, in summer, the minimum temperature cannot be lower than 8 ℃, the temperature is too high, the heat of the printing plate is not easy to take away, the temperature is too low, and the alcohol tank is overloaded.
Wetting powder—The main component is a surfactant, which can increase the activity of the entire water bucket. The main role of the Arabic resin glue is to protect the printing plate. In addition, there are certain additives for suppressing foaming agents. When wetting powders are used, they should be operated in strict accordance with the instructions.
Note that in the actual operation process, when adding water to the water tank, you need to add fountain solution; when the control cabinet is adding fountain solution, you also need water, and the water and fountain solution must be added at the same time.
How to use and maintain the blanket correctly
Blankets play a very important role in the printing process. Proper use and maintenance of blankets can extend their service life. The following introduces the use and maintenance methods of several blankets for readers' reference.
Blanket cutting
When cutting the blanket, pay attention to identify the direction of its strands (warp and weft), and the shape should be rectangular. The direction of warp and weft of the blanket can be judged from the direction (warp direction) of the dark color thread on the back of the blanket. The warp direction should wrap the rubber roller to withstand greater tensile strength, so that the elongation rate is small and the footprint deformation is small. Whether the shape is rectangular or not can be measured with a right triangle or diagonally equal. Non-rectangular blankets will twist and deform during printing.
Blanket installation
When the blanket is loaded into the board clamp, a 2cm long mark line can be drawn with a pen on the gripper and trailing part of the blanket to check whether the blanket is inserted into the board clamp at the same depth. The amount of the opposite sides of the two clips beyond the blanket should be the same. When tightening the plate clamp screws, tighten them one by one from the middle to both sides, paying attention to the same degree of screw tightness.
The author once encountered a case of partial ghosting failure, because the apprentice was not tightening the screws one by one from the middle to both sides when screwing the blanket clamp, so that the two sides of the blanket expanded and contracted, causing ghosting.
After the board clamp is installed, the parallelism of the board clamp should be re-measured. Then install the rubber cloth into the groove of the tensioning shaft of the rubber roller, and pay attention to the movement of the clamp screw in the mortise of the tension shaft groove, so the rubber gripper and the trailing plate clamp screw are in the mortise Move to the operation side or the transmission side at the same time to prevent twisting and deformation, and then tighten the blanket. Note that the new blanket needs to be re-tensioned after rotating for a while. The tightness of the blanket can be identified by the sound of the fingers tapping the blanket.
Blanket cleaning
The surface of the blanket is mainly composed of non-polar synthetic rubber. Observed under a magnifying glass, the smooth surface of the blanket is fluffy. Therefore, it can absorb and transfer moisture to the maximum during the printing process.
However, in the printing process, due to physical adsorption, paint particles, plant fibers and pigment particles in ink tend to stay in the villi pores of the rubber layer on the surface of the blanket to form a covering layer. Since the material of the covering layer is mostly polar material, the lipophilicity of the blanket is reduced and the hydrophilicity is enhanced, so that the small dots on the printing plate cannot be transferred to the paper through the blanket. Powdery fine spots appear on the solid part, which seriously affects the printing quality. On the other hand, the hydrophilicity of the blanket is enhanced, and the fountain solution absorbed by the non-graphic part of the printing plate is transferred to the paper through the blanket, causing the paper to elongate, the overprint is not accurate, and printing failures such as lapping and powdering . If the cover layer gradually thickens and hardens, and even produces the phenomenon of "aurora", the plastic layout of the rubber will be plastically deformed, destroying the uniformity of the thickness of the rubber cloth, and the local pressure will be insufficient when changing other products.
Therefore, it is necessary to scrub the blanket frequently and thoroughly so that its surface always remains fluffy. Because the blanket cover layer contains polar substances (paper powder, paper wool, etc.) and non-polar binders, according to the similar miscibility principle, when cleaning the blanket, first wash it with water, and then use a fast volatile organic solvent ( Such as gasoline, etc.) for cleaning.
The internal friction of the blanket
The blanket has good elasticity, which is different from ordinary materials. The blanket has a low modulus of elasticity, a large deformation rate, and will release heat during stretching and compression. Because the blanket is deformed by periodic alternating stress during the printing process, and always lags behind the stress change, part of the elastic potential energy inside the rubber is too late to be released and converted into heat energy. This phenomenon is called internal friction. The internal friction of the blanket cannot be avoided, so the temperature and humidity of the offset printing workshop and the temperature of the fountain solution should be controlled to reduce the temperature of the blanket and reduce the thermal aging of the blanket. cloth.
Blanket maintenance
Correct use and maintenance of the blanket can improve its printability, extend its service life, and improve printing quality. To prevent the aging of blankets, you can start from the following aspects.
(1) Clean the blanket frequently, remove paper powder, paper wool and other dirt on it, and pay attention to the appropriate cleaning agent.
(2) If the downtime is long, loosen the blanket to make it in a loose state, and apply talcum powder to the surface, which is conducive to its recovery of internal stress.
(3) The padding of the blanket should be smooth.
(4) Store the blanket to avoid strong light, it is best to cover it with black paper.
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