The first point: ink in the drying process of penetration and
oxidation of conjunctiva formation of discoloration.
Printing ink in the drying process will also have a certain
color change. In the printing process of book printing China, the newly
printed ink is darker than the ink after drying, and the ink color will be
relatively shallow after drying. In this case, the discoloration is not caused
by the poor light fastness of the ink, but mainly due to the penetration and
oxidation of the conjunctiva during the drying process. The ink of relief
printing is mainly based on penetration drying. In the drying process, the
binder in the ink will penetrate into the paper fiber to a great extent. After
oxidation conjunctiva drying, it will become light, which is an inevitable
phenomenon. Therefore, when we print, we usually make the ink tone darker than
the original proofing ink, so that it can meet the requirements of sample ink
color after drying.
The second point: the ink itself caused by light fastness
fading.
All inks will have varying degrees of fading in book printing China, discoloration,
just compared to the strong and weak. This requires us in the actual inking
work, should try to choose better light fastness ink, dark ink fade slowly,
light ink fade fast. Therefore, we should not only consider the light fastness of
the diluted ink, but also consider the consistency of the light fastness of
several inks used for blending.
The
third point: the pH of the paper itself caused by the discoloration.
Our
ideal pH value of paper is 7, which is neutral. In this case of perfect paper,
the above two points on the discoloration of printed matter belong to our
controllable situation, we can according to the depth of color matching, pay
attention to the relative proportion of ink and so on to try to make the
printed matter appear perfect. The acidity and alkalinity of the paper will
determine whether the printed matter can be used in the end. The pH of raw
material paper is less than 7, it is acidic and more than 7, it is alkaline.
Acidic paper, will affect the printing ink drying speed, will also affect the
color of the ink itself. Because acid substances can inhibit the drying of
imprinted oxidation conjunctiva, the ink drying on this kind of paper will be
particularly slow. The same paper with strong acid will cause the ink to change
color due to the weak acid of the bucket solution. Therefore, under the
influence of these two factors, the final state of the printed matter after
complete drying can be imagined in book
printing China. The alkaline paper has a greater impact, in short, the ink
acid resistance is poor, alkali resistance is worse. Basically all ink will
fade or change color when it comes to alkali.