Discoloration during ink drying process
During the printing process, the newly printed ink color is darker compared to the dried ink color. After a period of time, the ink color will become lighter after the print dries; This is not a problem with the ink being resistant to light fading or discoloration, but mainly due to the discoloration caused by the penetration and oxidation of the film during the drying process. Relief ink mainly penetrates and dries, and the ink layer of the product just printed from the printing machine is relatively thick. At this time, it takes some time for the penetration and oxidation film to dry the blank.
Ink itself is not resistant to light and fades
Ink fading and discoloration are inevitable when exposed to light, and all inks will experience varying degrees of fading and discoloration after exposure to light. Light colored ink fades and discolors severely after prolonged exposure to light. Yellow, crystal red, and green fade faster, while cyan, blue, and black fade more slowly. In practical work, when mixing ink, it is best to choose ink with good light resistance. When adjusting light colors, attention should be paid to the light resistance of the ink after dilution. When mixing ink, the consistency of light resistance between several colors of ink should also be considered.
The influence of the acidity and alkalinity of paper on ink fading and discoloration
In general, paper is weakly alkaline. The ideal pH value of paper is 7, which is neutral. Due to the need to add chemicals such as caustic soda (NaOH), sulfides, and chlorine gas during the papermaking process, improper treatment during pulp and paper making may cause the paper to become acidic or alkaline.
The alkalinity of paper comes from the papermaking process itself, and some are caused by adhesives containing alkaline substances used in post binding production. If foam alkali and other alkaline adhesives are used, the alkaline substances will penetrate into the paper fibers and react chemically with the ink particles on the paper surface, causing them to fade and discolor. When selecting raw materials and adhesives, it is necessary to first analyze the physical and chemical properties of the adhesive, paper, and the impact of acidity and alkalinity on ink, paper, electrochemical aluminum foil, gold powder, silver powder, and lamination.
Temperature induced discoloration and discoloration
Some packaging and decoration trademarks are affixed to electric rice cookers, pressure cookers, electronic stoves, and kitchen utensils, and the ink quickly fades and discolors under high temperatures. The heat resistance of the ink is around 120 degrees Celsius. Offset printing machines and other printing machinery do not operate at high speed during operation, and the ink and ink rollers, as well as the ink and printing plate plate plate generate heat due to high-speed friction. At this time, the ink also generates heat.
Discoloration caused by improper color sequence in printing
The commonly used color sequences for a four color monochrome machine are: Y, M, C, BK. The four color machine has a reverse color sequence of: BK, C, M, Y, which determines what ink to print first and then, which can affect the fading and discoloration of the printing ink.
When arranging the printing color sequence, light colors and inks that are prone to fading and discoloration should be printed first, and dark colors should be printed later to prevent fading and discoloration.
Discoloration and discoloration caused by improper use of dry oil
The amount of red drying oil and white drying oil added to the ink should not exceed 5% of the ink amount, approximately 3%. Drying oil has a strong catalytic effect in the ink layer and generates heat. If the amount of drying oil is too large, it will cause the ink to fade and discolor.
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Post time: Oct-14-2023
