Ink fading, discoloration reasons
Time:2023-08-01
Views:682
Chemicals such as surface active substances can also easily cause fading and discoloration problems:
1. Ink penetration and conjunctiva process of discoloration: in the printing process, the ink color is darker when the print is just printed, however, after a period of time, the color of the ink will become lighter, which is not the reason for the ink resistance to light, mainly the reason for the ink penetration and conjunctiva during the drying process. The light shines on the pigment particles through the connecting material, and the color light is absorbed and reflected by the pigment‘s selection of sunlight. The deeper the light passes through the ink film, the more saturated the color light is reflected back.
Therefore, if the ink layer is thicker, the color is thicker, and the ink layer is more transparent, the color is more bright and dazzling. Freshly printed products have thicker ink layers. However, after drying, a large part of the connecting material in the ink will penetrate into the interior of the paper fiber, so the ink layer after drying will be shallow, so that the color will become lighter. When printing, the color should be controlled to a slightly thicker degree than the primary color sample, so the ink will meet the requirements of the original color after drying.
2. Ink due to light caused by fading: when we adjust the ink, we should try to choose good light fastness ink, any ink in the sunlight or other light source irradiation, there will be different degrees of fading phenomenon, in the deployment of light color ink should be estimated after the ink is diluted light resistance. Such as light lake blue is best to use phthalocyanine blue, do not use peacock blue, because phthalocyanine blue is more light resistant, not easy to change color. Gray ink can be slightly black ink and phthalocyanine ink in white ink; Emerald green color can be used monochrome phthalocyanine green, not yellow enough can add bright resin yellow ink, bright a little can also add white ink, if the use of peacock blue and chromium yellow ink, over time, easy to yellow.
If the products we print are posted in the outdoor advertising pictures, posters, New Year pictures, etc., because these products are posted in the outdoor by direct sunlight, under the action of ultraviolet rays in the sun, wind and rain, the bright color of a long time is easy to fade, and it is found that only black and blue ink of these two colors still exists. Light color, yellow, red ink are fading, so in order to reduce the fading after the sun‘s ultraviolet irradiation, it is best to four-color overprint the y, m two colors first printing, C, BK two colors on the back printing, so that the overprint in the last C, BK two colors have the effect of light and heat resistance, thereby reducing the fading phenomenon of printed products.
3. Paper loose, rough discoloration: if the printed paper smoothness is poor, the surface of the paper is rough, loose offset paper, letterpress paper, newsprint, kraft paper, etc., the paper absorption is large, the ink pigment particles are small, and the ink color is gradually absorbed by the paper along with the connecting material in the slow drying process, so the ink color becomes lighter. The absorption of ink on the paper and the increase of ink penetration on the paper will lead to the separation of the connecting material and the color material, causing the ink film to become thinner, discoloration, poor gloss, reducing the absorption and penetration time of the paper, it is necessary to increase the drying speed accordingly, and increase the amount of red and white drying oil in the ink.
4. Ink is not resistant to acid and alkali fading, discoloration: malachite blue ink will turn green when encountering acid, offset printing wetting liquid is often acidic, PH value is controlled between 4.5 and 6, acidic wetting liquid will affect ink discoloration, ideal wetting liquid PH =7, neutral, acidic paper, wetting liquid also has the effect of resisting ink drying.
Under normal circumstances, the ink is not alkali resistant, gold ink printing, gold stamping electrochemical aluminum foil will become ancient yellow when encountering alkaline, and dull no gloss, blue ink will fade when encountering alkali, chrome yellow ink becomes red when encountering alkali, so it can not be used to print alkaline packaging printing products. Peach, emerald green, green lotus, bluish blue, light blue and other inks are not alkali resistant, the alkaline resistance of malachite blue is better, most of the paper is weakly alkaline, if printing soap, soap, white alkali and other alkaline substances packaging products, it is necessary to consider the alkali resistance, saponification resistance of the printed product.
In the post-press processing to avoid the use of alkaline adhesives on the impact of ink discoloration of printed products, such as foam alkali adhesive is alkaline can not be used, otherwise easy to change color, should choose those natural, pollution-free, PH =7, neutral and environmentally friendly adhesive is appropriate.
5. The ink is not resistant to alcohol and discoloration: there are ethanol and isopropyl alcohol in the offset printing wetting solution.
Alcohol wetting has:
① The wettability can be good, and the layout has good spreading performance;
② Because the alcohol has a certain volatility, the layout moisture transferred to the blanket, the moisture has a certain degree of volatilization, so the paper water absorption will be reduced;
When the alcohol is volatilized, it can take away a lot of heat, reduce the plate temperature, and ensure the flow performance of the ink.
In addition to ethanol, offset printing wetting liquid will also use glycerol, polyethylene glycol and other alcohols, alcohol wetting liquid printed out of the printing, after a long time to change color, indicating that the ink alcohol resistance is poor.
6. Inks are not heat resistant and discolor and fade: Under normal circumstances, the heat resistance of the ink is about 120℃, the heat resistance of the gold red ink is worse, only about 70℃, the printing process of the ink in the ink roller and plate page 5000 / hour high-speed operation, friction will heat generally in 40~50℃, the ink will release heat during the drying process, so the ink should not be stacked too thick, to be ventilated, reduce the temperature, Prevent discoloration by heat.
If the printing in the pile drying process is too thick close to 60~70 ° C, the gold red ink will change color, fade, gold red ink + white ink + yellow ink, and other light color ink, often appear more bright printing, placed for a period of time, the light color will become yellow, which is the reason for the heat resistance of gold red ink. Pressure cookers, stoves, rice cookers and other kitchen utensils are often used when the ink color is not heat resistant and discolored and faded.
Seven. Discoloration caused by desiccant drying oil added to ink: Dark color ink should be added to red dry oil, light color ink to add white dry oil, the amount of dry oil does not exceed 5% of the amount of ink, if the amount of more than 20% to make the ink discoloration, gold red ink if added red dry oil is easy to turn brown, red dry oil itself with darker purple, the deployment of light ink will have some impact, but the amount of dry oil is small. White dry oil does not look any color, its essence is a light brown after the conjunctiva, so a lot of light ink with white dry oil, speed up the ink film oxidation conjunctiva drying, color looks bright, but after drying will be yellowish brown.
8. Discoloration caused by chemicals in paper: papermaking due to rinsing and processing process, pulp often contains sulfides or other compounds, due to different manufacturing methods, some paper is acidic, or alkaline, the ideal PH value of paper =7, neutral, acid and alkaline paper will affect the ink color, especially the impact on light ink.
The sulfides or acids in the paper react with the inorganic pigments in the ink, and change color when the ink connection material and the color material are dried when the oxide conjunctiva permeates into the paper fiber and the paper surface surface, and the color becomes dark.
The iron compounds contained in the paper can make the light ink turn brown, the gold ink of the printing gold, the electrochemical aluminum foil of the hot gold by sulfide erosion is easy to become black and poor luster. If the white coating and adhesive on the surface of the coated paper are alkaline, they react with the acidic pigment iron blue and so on, and are prone to discoloration.
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