Newspaper printing ink failure analysis - dirty, not inked and crust

Dirty

In the printing process, dirtiness and stickiness are two different concepts. Dirty generally refers to dirtiness in non-graphic areas, including blurred imprints, and even dot joints. Dirty can be divided into floating and dirty oils.

1. Dirty

Dirty refers to the appearance of light-colored stains in the non-graphical area or the graphic and text blurring in the graphic area, and it is easier to wipe off dirt.

1) Cause

1Because the ink is soft and the water resistance is not strong, some of the ink will be emulsified after being affected by the fountain solution, and enter the fountain solution through the circulation system to form an oil-in-water emulsion; 2 Chemicals and wetting agents in the paper Encourage the ink emulsification; 3 some fountain solution contains soaps, detergents and other substances, but also cause ink emulsification.

2) Solution

1 Replace with a slightly higher viscosity, good water resistance, difficult to emulsify the ink; or in the original ink to add high viscosity varnish; 2 replace the paper used; 3 adjust the amount of fountain solution to ensure the appropriate conductivity and pH value.

2. Dirty oil

Dirty oil means that the non-graphic area of ​​the printing plate has a fat-sensitive property, which causes the blank area of ​​the printing plate to become inked and stains the printed matter.

1) Cause

1The ink is too thin and soft; 2The ink is supplied for a long time during printing, and the amount of ink is too large; 3The free fatty acids and surfactants with higher concentration exist in the ink; 4The influence of the treatment agent in the pigment; And the pressure of the blanket is too large or the ageing of the printing roller and the blanket deteriorates the surface structure of the printing plate; 6 Dissolve the fat-sensitive substance from the paper coating.

2) Solution

1 Replace the ink or add high viscosity resin oil to the original ink to make the ink have better viscoelasticity; 2 control the amount of ink to be printed; 3 control the amount of fountain solution; 4 adjust the pressure of the rubber roller and rubber blanket, Or replace the rubber roller, blanket; 5 replace the paper.

Not ink

1. Cause

In the printing process, the phenomenon that the printing plate is not inked sometimes occurs. The reasons for this phenomenon are the following five aspects.

1Insufficient ink viscosity, low flowability, too high yield value; 2 Insufficient solid content in the ink, which causes the ink to lack leveling properties, the ink “stays”, and the ink becomes shorter; 3 The pigment in the ink re-aggregates And cause gelation; 4 ink into the water or ink sensitive to water, poor water resistance, so that the ink emulsification accelerated; 5 ink roll rubber surface or blanket hardened, wear plate.

2. Solution

1 For inks with short ink, add alkyd resin or other good fluidity materials to re-adjust the ink property through a three-roller; 2 Wet the pigment with a resin-based chain material with good dissolving properties to make the pigment evenly dispersed. To prevent its re-aggregation; 3 using good fluidity, strong water resistance ink. Black ink does not use rubber as much as possible to adjust the darkness, because the rubber content is more difficult to make the ink show better fluidity; 4 adjust the pressure of the rubber roller or replace the new rubber roller and blanket.

Surface crust

In the printing process, when adding a new ink, sometimes the surface of the ink around the ink drum is found to have different degree of conjunctiva phenomenon. If these ink films are added to the ink fountain, the ink supply performance of the machine will be seriously affected.

1. Cause

The binders in offset printing inks consist of synthetic resins, vegetable oils, and high-boiling point mineral oils. The linseed oils commonly used in offset printing rotary inks are dry oils because they contain more unsaturated fatty acids. Base, can evenly absorb the oxygen in the air, oxidize and polymerize into a tough solid film, so the offset printing rotary ink has better drying in the air. At the same time, due to the use of certain inorganic pigments (such as iron blue, etc.) in the ink formulation, the surface of the ink is prone to surface crusting during storage.

2. Solution

Some anti-drying agents (anti-skinning agents) can be added in an appropriate amount during the ink production process, since most of them are strong reducing agents and can be preferentially oxidized, so it is possible to retard the oxidative polymerization of drying oils. In addition, try to avoid exposing the ink to the air for a long time.

The above is a common fault in the production of ink for printing. In the printing process, no matter what faults are encountered, we must carefully observe the system analysis in combination with the appearance, and then find out the solution to the problem. We can eliminate the problems that cannot be solved at the moment and eventually solve the problems completely.

Source: "Printing Technology"