Books, albums, newspapers, posters for advertisements, New Year pictures, and other printed products can be seen in sunlight, fluorescent lamps, incandescent lamps, and other light sources, and they can be seen through the selective absorption and reflection of ink color materials in order to present colorful and colourful colors. There are many factors that cause print discoloration and discoloration. The light resistance properties of the ink, the acidity and alkalinity of the paper, the temperature, the arrangement of the printing color sequence, etc. are the causes of discoloration and discoloration of the printed product.
1. Discoloration of the ink drying process
In the printing process, the freshly printed ink ink and the dried ink ink are compared. The freshly printed ink has a darker ink. After a certain period of time, the ink will become lighter after the print is dried; this is not an ink. The problem of discoloration and discoloration is mainly due to the discoloration caused by the infiltration and oxidation of the conjunctiva during the drying of the ink. The letterpress ink is mainly permeable to dryness. The product that has just been printed out from the printing press table has a relatively thick ink layer. At this time, it takes a while to infiltrate and oxidize the dried film of the conjunctiva. Then, a large part of the binder in the oil storm penetrates into the inside of the paper fibers. The thinning of the ink layer after drying through the oxidized conjunctiva and the lightening of the color will be inevitable. This is an unavoidable phenomenon that is often seen. In the printing, the ink color should be controlled to be slightly darker than the color of the original printing sample. When the ink is dry, the color of the proof ink will be met.
The color rendering mechanism of prints is carried out by subtractive coloration. Sunlight, fluorescent lamps, incandescent lamps, and other light particles that illuminate fine particles of ink pigments. The color light reflected by the selective absorption of light by the pigment can show beautiful colors. The deeper the light passes through the ink film, The reflected color light becomes more saturated, so the ink layer is thicker and the color is deeper; the transparency of the ink is good and the color is brighter.
2. The ink itself is not resistant to light and fades
It is unavoidable that the ink will be discolored and discolored in case of light. All inks will have different degrees of discoloration and discoloration after encountering light. Light color ink fades after long-term exposure to light, and discoloration is severe. Yellow, crystal red and green fade quickly, while blue, blue and black fade slowly. The actual work in the transfer of ink, should try to use good lightfast performance, adjust the light color should pay attention to the light after the dilution of the ink, with the ink when the ink should also consider several colors of light between the performance of - Consequences. Outdoor advertising posters due to exposure to sunlight easily fade, we must consider the lightfastness of ink. The same blue ink, phthalocyanine blue than light blue, peacock blue light, not easy to change color. Gray can be a little black ink and white turnip ink in white ink; Emerald green available in a single color phthalocyanine green, not enough yellow, then you can add lighting resin yellow ink, if you add a little more white ink color more vivid. If you use peacock blue and chrome yellow ink, it will fade over time, change color and yellow.
3, the acidity of the paper on the ink fade, the impact of discoloration
In general, paper is weakly alkaline. The ideal paper has a pH value of 7 and is neutral. Due to the need to add caustic soda (NaOH), sulfides, chlorine, and other chemicals in the papermaking process, improper handling in the pulp and papermaking process may cause paper. Acidic or alkaline. There is a certain amount of residual chlorine and organic acids in the slurry. If not properly processed, the resulting paper will become acidic; if alkaline fillers and colorants are used in the papermaking process, there are Residual alkaline solution, but without the necessary treatment, so that the resulting paper is alkaline.
1 The acidity and alkalinity of paper has a great influence on the printing process and the color durability of prints. Paper acidity and alkalinity have a direct effect on the drying of the oxidized conjunctiva of the blot, and the acid blotting of the large paper blots is particularly slow, because the acidic substances can inhibit the drying of the imprinted conjunctiva.
2 The acidity and alkalinity of the paper can also cause the ink to fade or discolor. Raw paper pH value is less than 7 is acidic, is more than 7 is alkaline, acid strong paper and due to the water bucket solution is also weak acid and other factors, it will affect the ink, make it discoloration, such as peacock blue turn green after acid .
3 poor performance of oil and alkali resistance. Basically all inks will fade or change color when they encounter alkali. The chrome yellow ink will turn red in case of alkali, and the blue paper in the case of alkali will fade. In particular, gold ink, silver ink, and electro-aluminum foil bronzing will lose their original luster when they encounter alkaline substances. The golden light color turns into pale yellow, and silver turns black and does not shine, and the adhesion is reduced, often resulting in scrapped prints.
The paper's alkalinity comes from the papermaking process itself, but also from the binder containing the alkaline substance used in the post-order bookmaking. If you use battoin and other alkaline binders, the alkaline material will penetrate into the paper fibers and react with the ink pigment particles on the surface of the paper to cause them to fade and discolor. When selecting raw materials and adhesives, first analyze the physical and chemical properties of the binder, the physical and chemical properties of the paper, and the influence of the acid and alkali on the ink, paper, electro-aluminum foil, gold powder, silver powder, and coating film.
4. Temperature-induced discoloration, discoloration
Some packaging and decoration labels are affixed to rice cookers. Pressure cookers, electronic fire pits, and kitchen utensils, the ink quickly fades and changes color at high temperatures. The heat resistance of the ink is about 120 degrees Celsius. Offset presses and other printing machines are not ready to operate at high speeds. Ink and ink rollers, ink and plate layouts are subject to high-speed friction and heat. The inks will also generate heat at this time. Especially in the ink added red, white dry oil, the ink drying process will heat, require the ink to have good heat resistance, gold. Silver printing products should pay attention to the fact that it is not possible to overbuild the delivery table. Otherwise, the print will fade or change color due to heat. The solution: Take paper with a layer of paper and put it thin. Reduce fever,
5. Discoloration and discoloration caused by improper color sequence of printing
The color sequence commonly used in the four-color monochrome machine of Yamatake is: Y, M, C, and BK. The four-color machine is the reverse color sequence: BK, c, M, Y, and the four colors of ink are printed first. What will be printed after printing will have an effect on the fade and discoloration of printing inks, especially advertisement posters. Posters, New Year pictures, couplets, and small commercial advertisements are advertised outdoors in the actual production work. Therefore, when printed, they will take into account the light and heat resistance characteristics of the printed matter. Because these products are affixed to the outdoors to be exposed to the direct sunlight of the sun's ultraviolet rays, the weather will be long and long, and the wind and rain will cause the colors of the prints to fade and discolor. Only long-term exposure to outdoor printing products
c, BK two deep-color inks are still part of the remaining, Y, M two colors have faded, which shows that c, BK two kinds of ink light, heat resistance is better. So say advertising paintings, New Year pictures. Posters, couplets, etc. are printed on outdoor prints, in order to reduce the sun's ultraviolet radiation. It is best to print Y and M colors first, and C and Bk two-color inks on the final printing, which can reduce the fading problem of prints.
When arranging printing color sequence, light color and ink that is easy to fade and change color are printed first. Dark color ink after printing, can prevent discoloration, discoloration
6. Discoloration and discoloration caused by improper use of dry oil
Red dry oil, white dry oil in the ink in the amount of not more than 5% of the amount of ink, about the amount of about 3%, dry oil in the ink layer has a strong catalytic effect, and fever, if excessive dry oil consumption , it will fade the ink discoloration.
When using desiccants should pay attention:
1 is separated from the air. Now use the current distribution to avoid conjunctiva;
(2) The content of desiccant in the ink is 3%, not excessive, otherwise it will be easy to appear crystallization and discoloration, discoloration;
3 second color more than the first color - point;
4 In winter, the climate is cold and the temperature is low. Should put more - point; put less in the summer.
Red dry oil itself has a deep purple color, when used in the deployment of light-colored ink will have a slight impact on the ink, deployment of darker colors of ink with red dry oil; white dry oil is not dry before the white, The conjunctiva is light brown after drying, and when light-colored ink is formulated, if dry oil is added too much, it will appear pale brown.