Causes And Preventive Measures Of Discoloration Of Gold Color Offset Printing
Oct 08, 2021In today's packaging and other printed materials, in addition to the use of bronzing process, offset printing gold printing process is still used by many manufacturers. Ink has the advantages of fine and solid imprint, good metal texture, strong hiding power, high floating force, strong metallic luster and low cost. Offset printing enterprises can directly choose gold color offset ink products or use copper gold powder and offset gold oil to self-adjust salty gold ink printing.
First, the basic composition of offset gold ink:
Bronze powder 30~50%
Gold color Offset printing oil 70~50% mix the bronze powder with gold Oil homogeneously
can become gold ink.
Second, the cause of the discoloration of the printing gold and preventive
measures:
1. Fountain solution pH value and ink balance. In offset printing based on
the principle of hydrophobic part of printing plate and hydrophilic principle
of non graphic part, the acid substance in the fountain solution can cleaning
and remove the dirt. However, if the acid is too strong, the gold printing
will be changed color and lose its metallic luster, resulting in printing
plate pattern, slow drying of imprint and sticking on the back. If the acidity
is too weak, the picture and text on the printing plate will be dirty and
paste. Therefore, the general fountain solution pH value control in 5 ~ 6 is
appropriate. Water ink balance is to use as little water as possible on the
premise that the printing plate is not dirty and paste, so that the
emulsification of the ink is controlled within the minimum range of 25%.
Because the water is too much, it is easy to cause the printing gold ink color
is too light, the gold ink is dull, the color is not bright, the gold ink is
emulsified, the paper stretch deformation causes the overprint inaccuracy and
other quality defects; too little of water, easy to make the page dirty,
greasy and the emergence of parallel paste, so it is very important to master
the balance of ink and water. In addition, the intermediate roller must be
separated from the ink path and waterway system, which is also an essential
method to avoid.
2. Printing speed. If the printing
speed is too fast, it is easy to produce intense rubbing between the rollers,
and then the heat generated will change the color of the ink. The general
experience is that it should be controlled at 5000 sheets per hour.
3. Oxidation of bronze powder. Bronze
powder has the disadvantage of easy oxidation and discoloration, so the
bronze powder must be kept in closed air as far as possible, and the storage
time should not be too long.
4. PH value of gold blending oil. Bronze
powder is easy to oxidize, so the gold adjusting oil used must be fast drying
and fast solidifying resin oil with low oxidation property and neutral pH
value. In order to avoid oxidation due to long-term storage, it is better to
use the self-adjusting method to further improve the oxidization issue.