Plate dirt
The non-graphic part of the plate drum is left with ink that is not scraped clean by the scraper, which is transferred to the film during printing to form a sheet of ink stains. Plate dirt is atomized, surface occurrence. Black ink is more prone to this phenomenon
The reason:
(1) Abrasion or poor grinding of the scraper reduces the scraping efficiency
(2) Plate cylinders have the most poor chrome plating or surface damage caused by wear
(3) The impurities and coarse particles in the ink lift the scraper
(4) The adhesion of the ink to the plate drum is too strong or the adaptability of the ink scraper is poor (poor lubrication).
Solution:
(1) Increase the pressure of the scraper, adjust the position and angle of the scraper, etc
(2) Replace or regrind the scraper
(3) Plate stains caused by the rough surface of the plate drum should be polished
(4) Reduce the viscosity or concentration of printing ink
(5) Reduce the printing speed or blow on the non-graphic part of the plate cylinder so that the unscratched ink dries quickly and cannot be transferred to the film
(6) Replace with a more suitable ink
Electrostatic stress and electrostatic streaks:
Static electricity refers to the irregular filamentary ink strips that protrude outward from the edge of the print pattern, like a beard. Electrostatic markings refer to some irregular markings formed in the large-area pattern part, mainly in the printed polyolefin film type
The reason:
(1) Plastic film is a poor conductor of electricity. It will produce more static electricity due to friction, contact, peel in the printing process. It will also produce static electricity after a long time of work if the ink itself lacks antistatic agents,
(2) Ink viscosity too low
(3) Static elimination device failure (e.g. adhesive ink, etc.)
(4) Plate roller mesh hole too deep or roller pressure too large
Solution:
(1) Generally, antistatic agents or polar solvents are added to the ink in advance. Prevent electrostatic ink spots or ink failure
(2) Control the ambient humidity, sprinkling water or putting water vapor in the printing site to reduce the temperature of the printing site and increase the humidity
(3) Check the electrostatic eliminator is well to ensure that the static electricity generated by the plastic film in the printing process is eliminated in time. The guide roller on the machine is also grounded to prevent it from being insulated due to contact with the lubricating oil in the bearing part.
(4) The ink should maintain a high viscosity when using a plate cylinder with a deep mesh hole to print. Meanwhile, the pressure of the roller should be appropriate to prevent the ink from being squeezed out of the mesh hole
Filling up
In gravure printing, the transfer rate of ink from the plate drum mesh is usually 50%-70%, and about 1/2-1/3 of the ink always remains in the plate drum mesh. If the residue rate maintained to a certain extent is accepted. However, the ink residue rate in the mesh hole gradually increases due to various reasons in the printing process. This results that the ink transfer rate also decreases resulting in blocked plate failure. After filling up, the printing pattern and text will be blurred, the printing color will change, and the serious time base will not be able to continue printing. Especially, the shallow layer of the network is easy to block.
The reason:
(1) The ink dries and settles on the page
The transfer rate of ink in the plate drum mesh hole is usually determined by the type of ink, viscosity, printing speed and other factors, and there is always 1/2-1/3 of the ink remaining in the mesh hole. When these residual inks are dry solidified (increased viscosity) under the influence of some factors, it is difficult to completely dissolve when the plate drum enters the ink tank again, and the ink transfer rate is reduced. Over time, the net hole is getting shallower and shallower, the transfer rate is getting lower and lower, and finally the blocked version is formed. Such filling up faults are of course related to ink type, solvent ratio, drying speed and other factors, and the structure of the printing press also has a great impact
(2) The ink was mixed with impurities
The printed film often generates static electricity due to high-speed operation, absorbs impurities such as surrounding dust and substrate debris and takes it into the ink when printing.
(3) Poor plate making quality
In the process of corrosion or engraving, the inner wall of the mesh hole generates small burrs, and the surface is not smooth after chromium plating. The burrs and Ω-type mesh holes produced during grinding also have a certain impact on the transfer rate of the ink, and the transfer rate is often low when the situation is serious and becomes the reason for blocking the plate.
(4) Ink dissolving badness
Ink deterioration or changes in solvent balance cause a decrease in solubility, or mixed with different types of ink, misuse of solvents and so on all can result ink dissolution and deterioration, which give rise to a low transfer rate at the same time directly cause blocking
(5) Chemical changes
Two-liquid inks or reactive inks will gradually cross-link and other chemical reactions with the printing process, the fluidity becomes worse, the viscosity increases, and the transfer rate decreases which may also become one of the reasons for blocking the plate.
Solution:
(1) Solvents or special cleaning agents should be used for cleaning when the blocking failure occurs in the production process of plastic gravure printing, and aim at the causes of filling up to solve the problems.
(2) Adjust the appropriate ambient temperature and humidity, select the solvent ratio that is suitable for the printing speed and printing environment
(3) The distance between the scraper and the embossing roll is as short as possible to prevent the hot air from leaking out of the drying box from blowing the layout directly
(4) Mixed use of slow drying solvent, properly improve the printing speed, reduce the viscosity of the working ink
(5) The ink should be replaced in time (or contact the ink supplier to solve) if it is caused by the blockage caused by the oil performance defect. Try to avoid the ink combination with a significant difference in proportion
(6) The ink in the ink tank should be stirred frequently to keep the ink in a good flow state, and the new ink should be added or replaced in time to reduce the occurrence of skin film phenomenon
(7) Plate blocking caused by the quality of the inner wall of the mesh hole should be re-plated or plate making
(8) Wipe plate roller with solvent before or just after driving. Try to avoid stopping during the printing process, and wash the plate cylinder first when stopping for a long time, or immerse the plate cylinder in the ink continuously idling
(9) In the fresh ink, due to the temperature difference and other reasons, when the additives and wax substances in the ink crystallized out, you can try to warm the ink before use (temperature control at 40-50 degrees) to dissolve it
(10) Misuse of solvents or ink deterioration, mixed with dissimilar ink will significantly affect the resolubility of ink. Therefore, a regular special dilution solvent should be used, and the ink should be replaced after fully washing the ink tank and circulating pump
Flushing
The flushing of printing ink skin film can be divided into two kinds: solvent flushing phenomenon and resin flushing phenomenon
The reason:
(1)、Solvent flushing
This flushing phenomenon is more common in alcohol-soluble ink. The ink will be cooled near the film due to the evaporation of the solvent latent heat phenomenon when the humidity is high. Thus, water droplets mixed into resulting in ink film flushing. Of course, this phenomenon is more likely to occur when using solvents with high latent heat of evaporation
(2) Resin flushing
The solvent balance in the ink is poor, the true solvent is volatilized first yet the diluent remains in the ink which will precipitate the resin in the ink causing bleaching
Solution:
(1) Solvent flushing solution
a. Minimize the ambient humidity
b. Reduce ink drying speed
c. Heat drying while printing
(2) Resin flushing solution
a. Replace the ink or add some real solvent with a slower evaporation rate
b. Change the formula of the solvent
Blade line
Linear stains are produced regularly or irregularly in non-printed pattern areas
The reason:
(1) The small soft impurities in the ink tank are instantly sandwiched between the plate roll and the scraper
For example, there are precipitates in the ink (pigment agglomeration, wax powder, resin precipitation), skin caused by excessive drying, ink tank is not cleaned, foreign bodies on the substrate, etc
(2) The precision of the plate roll, processing and polishing is poor, or does not match the hardness of the scraper
(3) The printing viscosity is too high, and the scraper is poorly lubricated
Solution:
(1) Improve the coating property of the resin to the pigment
(2) Ink tank clean thoroughly, residual ink filter before machine
(3) Use sandpaper for S-shape grinding before using
(4) Appropriate use of slow drying solvents for dilution in order to prevent dry crust,
