Offset dirty prints often occur during offset printing. We will now briefly introduce and analyze the symptoms of the dirty version, the cause of the failure, and the solutions.
The dirty version can be divided into dirty and dirty. Dirty oil is a phenomenon in which the printing plate is susceptible to ink, which is caused by the poor ink resistance of the printing plate. The buoyancy is mainly caused by the ink, and is generally more evenly appear on the entire layout, but the hydrophilic part of the printing plate still has good ink resistance.
Dirty oil can be divided into oil and dirt. Oiling refers to the irregular enlargement of the graphic, resulting in distortion of the printed text and resulting in elongated or feathered print outlets. Dirty means that the ink spots spread over a large area and often appear in relatively large non-text (blank) areas.
From the oil phenomenon 1, the phenomenon of the phenomenon of failure to expand the printed lines, the picture is not clear and complete, in the non-graphic area there are dirty phenomenon, the blanket was also glued to a block of ink-like material.
2. Causes of failure (1) The ink absorption area on the plate forms an ink-absorbing center.
(2) The surfactant in the ink or paper layer migrates to the suction area.
(3) The acid value of the side border material in the ink is too high. (4) The acidity of the fountain solution is too weak to hinder the exertion of the protective function of the peach gum film.
(5) The fountain solution is too acidic. During the printing process, the metal of the plate must be decomposed by the acid in the fountain solution to keep the plate clean. However, this effect must be carried out very slowly in order to prevent the printed film from being destroyed or disappeared.
When the fountain solution is too acidic, the chemical reaction of the layout is accelerated, so that the film cannot support it. In addition, when using lead-containing slurry drying, particularly in the case of excessive amounts, a very acidic dampening solution can damage the dried oil and form a smooth film on the printing plate. Since this layer usually contains lead phosphate or lead chromate (yellow material), the whole plate tends to be yellowish, because this layer will hinder the control of wetting, and as a result, the plateau can easily get oily. .
(6) The ink is too thin and the oiliness is too high (7) The amount of water on the plate is not enough (8) The pressure on the plate roller (such as the ink roller) is too high (9) The quality of the plate is too bad.
(10) Inadequate induction processing in non-graphic area (11) Inappropriate use of desiccant (12) Poor quality of roll, improper installation 3. Solution (1) The ink layer thickness of printed matter should be appropriate and not too thick (2) The ink should be thick and oily.
(3) The pH of the binder used in the manufacture of the ink should be lower (4) The acidity of the fountain solution should be appropriately increased (5) Some lanolin, beeswax, sodium silicate and other materials can be tried in the ink (6) Check The quality and printing speed of the edition. $Page break $
Dirty Phenomenon 1. Symptoms Many ink stains appear in the non-graphic area of ​​the printed matter.
2. Causes of failure (1) The printing press force and operation of the printing press will destroy the induction film on the printing plate that acts as an insulating barrier. These exposed metal parts are immediately acted upon by trace amounts of surfactants, polar substances, and free fatty acids. , And absorb ink, resulting in non-image area stains, destroy the quality of the entire print.
(2) Excess of residual coating left on the plate during development.
(3) Inadequate sensor processing in non-graphic areas.
(4) Bad gluing (5) The connecting material is too thin, the oiliness of the ink is too large, too soft, and the stickiness is insufficient, resulting in slippage of the plate roller and the dirtying of the water roller.
(6) The yield value of the ink is too high.
(7) The fountain solution is too low in acidity.
(8) There is not enough water on the plate.
(9) The non-graphic area of ​​the original ink sticking ink (10) is dirty.
3. Solution (1) Add some viscous binder to the ink.
(2) Increase the acidity of the fountain solution (3) Increase the amount of water supply (4) Reduce the oil and fat content in the ink formulation.
(5) Use a high concentration of ink to make the print thinner.
(6) Use a fountain solution with a relatively high surface viscosity. Otherwise, when the surface tension is too low, due to the influence of the water-soluble surfactant in the paper, polar components in the ink, and washable soap in the fountain solution, the ink and the water film on the printing plate are It is impossible to obtain proper interfacial tension, which may cause dirt.
(7) Reduce the amount of desiccant.
(8) Adjust the printing pressure between the plate cylinder and the blanket cylinder.
(9) Change to fast-drying resin type ink. $Page break $
Dirty phenomenon 1, the phenomenon of failure Symptoms of the printing plate covered with a slight ink, and transferred to the blanket, and passed to the print, so that the non-graphic area of ​​the print is also covered with a slight color. Although the ink on the plate can be wiped off, it will soon appear again. The color of the fountain solution caused by the ink or its components floating on the fountain solution or dissolved in the fountain solution. Therefore, floating dirty sometimes called ink bleeding or water.
2, the cause of the fault (1) printing paint paper is more likely to appear dirty. This is because the surfactant in the paper precipitates and forms an emulsion with the ink and adheres to the non-image area.
(2) The viscosity of the binder in the ink is too low, and some form a fine emulsion of oil in water, forming a buoyancy.
(3) Hydrophilic pigments are used in the ink.
(4) The ink is immature, the pigment used in the ink is poor in lipophilicity, and the pigment is not fully wetted by the binder.
(5) When the resin-based ink uses a low-temperature-dispersible linking material and the content of the ink oil is relatively high, emulsification easily occurs.
3. Solution (1) There should be a storage time long enough for the ink to be produced.
(2) Pigments with good lipophilicity or surface treated with hydrophilic materials should be used in the ink.
(3) The binder in the ink should have good wettability to the pigment.
(4) reduce the acidity of the fountain solution, the amount of water can also be less.
(5) Add viscous binders.
Guilin City, Guangxi printing plant Ye Jingjie
From "Printing Technology" magazine.