In
commodity book
printing, packaging and label printing , gold ink is often used to
realize the printing of gold graphics and texts, and give people a feeling of
delicacy, gorgeous and nobility. As a special printing method, gold ink
printing is slightly different from ordinary ink printing in the use of
printing raw materials and process operation.
1.
Gold ink blending
Gold
ink is made of gold powder, gold blending oil and a small amount of auxiliary
materials. Ordinary color inks are pasted and stored in cans. Usually, gold ink
is stored in two different containers with gold powder and gold blending oil,
Then proportionally (usually the ratio of gold powder to gold blending oil is
1:1) prepare gold ink. At present, there is also a ready prepared gold ink
supply in the market, which can be printed directly. However, when printing
plants use gold ink, they should consider factors such as the amount of ink
used in the layout, printing cycle and product quantity. Because the printing
performance of gold ink will change and lose the original metallic luster after
it is opened for 1 ~ 2 hours, gold ink is used Ink printing is best used with
adjustment.
2.
Gold ink printing process
Gold
ink printing generally adopts neutral or neutral hard lining, and the pressure
of inking roller on the printing plate cannot be too large, otherwise it will
cause the phenomenon of plate pasting
Gold
ink printing process in book printing. During
printing, when the gold ink layer on the printing plate is transferred to the
surface of paper or other substrate, there is often insufficient ink or even bottom
exposure. Therefore, in order to saturate the gold ink and fully show its
unique metallic luster, the secondary printing method is generally adopted. At
present, there are basically two secondary printing methods: one is to print
fake gold ink as the background color, and then overprint gold ink; Second,
direct printing of gold ink twice. The fake gold ink used in the former method
is generally mixed with transparent yellow or medium yellow ink. If the paper
is loose and the flatness of the paper surface is poor, the fake gold ink is
mainly medium yellow, and an appropriate amount of gold ink is added. If the
paper is tight and smooth, use transparent yellow and a small amount of gold
ink to prepare fake gold ink. When printing, the amount of ink in the
background color shall be as small as possible, in the principle of no bottom
exposure and no edge penetration. When the background ink is not completely
dry, overprint the gold ink, and the ink amount can be slightly larger, so as
to reach the saturation state of the gold ink. When using the latter method, it
should also be emphasized that it is appropriate to overprint the gold ink for
the second time when the gold ink printed for the first time is not completely
dry. This is because the gold powder in the gold ink is a metal pigment. If it
is printed after it is dry, its particles are not easy to stick.
3.
Precautions for gold ink printing
(1)
Properties of paper
The
properties of paper will have a great impact on the quality of gold ink
printing. The higher the smoothness and tightness of paper, the better the
metal effect of printing; On the contrary, printing on paper with porous
surface and rough texture will have a poor effect. In addition, the pH value of
the paper surface is preferably greater than 5.5
Otherwise,
when printing is stacked and stored, the sulfate contained in the paper will
cause the gold powder to change color and blacken, and even cause the gold
powder to be corroded and disappear.
(2)
Gold ink printing
The
picture and text of gold ink printing layout should not be too thin, otherwise
it is easy to cause paste, and its reflection effect will become worse.
(3)
Wear resistance
The
wear resistance of gold ink layer after printing is an important index to
measure the quality of gold ink printing. At present, there are two measures to
solve the wear resistance of gold ink: one is to mix gold ink with gold
adjustment oil with slightly higher viscosity, and the other is to polish with
bright paste after printing.
(4)
Gold ink discoloration
After
the gold ink printing products are placed for a period of time, the gold powder
will be invaded by sulfur, oxygen and moisture in the air, which will darken or
even blacken the imprinted surface, affecting the product quality. This is what
we usually call the discoloration of gold ink. We should pay attention to it in
the process of printing storage.
(5)
Gold ink and other color ink overprint
The
gold ink printing process in the printed matter should print the gold ink on
the dark field as far as possible, such as printing gold on red, blue and
black, with better effect, especially when printing gold ink on purple, black
and dark blue.
In
addition, book
printing ordinary color ink on gold ink should be avoided as far as
possible. If you must print ordinary color ink on a large area of gold ink, you
should first reduce the viscosity of ordinary ink, and you must wait until the
gold ink is completely dry before printing, otherwise it will lead to the
flower of gold ink.