Analysis and elimination of fading and discolorati

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Analysis on the fading (discoloration) of printed matter and elimination

during the printing process or the use of printed products after printing, whether the ink color on the surface of printed matter can remain bright or not discoloration and discoloration is also an important indicator of the printing quality of printed matter

the fading and discoloration of various printing products are mainly caused by the performance of the ink, but also the improper arrangement of the printing ink process. Below we will talk about some factors that affect ink discoloration from six aspects. 1. The ink fades due to lightfastness

lightfastness is an important index to evaluate the properties of inks. Many inks will change color under sunlight. The Lightfastness of printing ink mainly depends on the pigment used by the ink, but it also meets the standard. If the pigment used has chemical reaction or crystal transformation under the action of light, the ink will change color or fade. The general experience in production is as follows

a) light color inks fade and change color seriously (y, m, g) after long-term exposure to light, and dark color inks (C, B, K) are slow

b) try to use ink with good light resistance when adjusting ink

c) when adjusting light color ink, attention should be paid to the lightfastness after dilution

d) when advertising outdoors, we should pay attention to the light resistance of the ink

e) phthalocyanine blue is more light resistant than light lake blue and Malachite blue

f) gray can be obtained by adding black ink and phthalocyanine blue to white ink

g) monochromatic phthalocyanine green can be used for emerald green (the color can be brighter by adding white ink). If it is not yellow enough, bright resin yellow can be added. (if Malachite blue and chrome yellow are used, they will fade and turn yellow over time)

when making products for outdoor use (outdoor advertising, etc.), we should consider the color sequence arrangement of printing. Try to print y and m first and then C and BK, because C and BK have better light resistance, which will prevent the fading of ink with poor light resistance at the sight of light, so as to reduce the corrosion of corrosive gas to components on the circuit board

2. Discoloration during ink drying:

in the printing process, the newly printed ink is darker. After a period of time, the ink will fade after the imprint is dry. It is mainly due to the penetration and oxidation drying of the ink during the drying process, especially for the ink based on penetration drying (such as the rotary ink for printing), the thickness of the ink layer changes significantly after drying, the ink layer becomes thinner and the color becomes lighter, so the ink color should be controlled deeper in printing. The main reason for this result is that when the ink layer is thick, the number of light refraction is more, so the reflected light is more saturated. On the contrary, when the ink layer is thin, the number of light refraction will be reduced, of course, the saturation of the emitted light will be reduced

experienced masters in the printing process will slightly adjust the color of the newly printed print to be darker than the color of the sample when checking the color during the printing process. It is for this reason that the case of intercepting the epidemic in the wood packaging materials that have been disinfected is also frequently considered

3. PH value of paper

paper is weakly alkaline. The ideal pH value of the paper should be 7, which is neutral. Due to the need to add caustic soda in the papermaking process (NaOH, sulfide, chlorine pulping process is improper, it is possible that the pH value of the paper is either acidic or alkaline). These acid-base properties mainly come from the residue of papermaking pulp

a) the acid-base property of paper has a great influence on the printing process and the color durability of printed matter

b) the alkali resistance of ink is relatively poor. Chrome yellow ink fades when it meets alkaline paper, and medium blue fades when it meets alkaline paper

c) in particular, gold and silver ink electrochemical aluminum stamping will lose its original luster when encountering alkaline substances, and the golden color will gradually change to bronze, silver ink will turn black, and the adhesion will decrease at the same time

d) the alkalinity of the paper comes from the papermaking process itself and the subsequent binding production. If the binder used in the binding process contains alkaline substances, the alkaline substances will seep into the paper

e) when selecting raw materials, first analyze the pH value and its influence on inks (including gold, silver and aluminum)

4. Heat resistance of ink

the heat resistance of the ink is 120 degrees. When the ink is rubbed on the machine, the temperature will rise (especially when dry oil is added to the ink, the oxidation polymerization reaction will also release a lot of heat), which requires the ink to have good heat resistance. When printing gold and silver ink, pay attention not to stack the printed matter too high

when printing, some printing materials need forced drying (such as iron printing ink, hose ink, thermosetting ink), or when the printed products need to be heated for special purposes, the pigment must be able to withstand high temperature without discoloration

5. Dosage of drying oil

a) the addition of red and white drying oil cannot exceed 5%, which is generally better controlled at 5%. The color of golden red ink will darken when encountering red drying oil

b) the color of red drying oil itself is red, and the addition of ink will have a certain impact on the hue of the ink, especially when printing light colored ink

also out of consideration of the impact on the ink color, the use of dry oil in the printing process should be cautious, and remember not to blindly add more

6. Discoloration in the polishing process of printed matter

there are many kinds of tensile machines on the market at present. A) UV glazing. When the ink is dry, UV glazing does not have a great impact on the ink color, but when the ink in the contact part of the glazing oil is not completely dry, the ink will change color or even fall off due to the dissolution of benzene, phenol, alcohol, ether and other components in the UV ink

b) solvent based polish. As the solvent content of solvent based varnish is 50%, the drying time needs about 2 ~ 3 minutes, which has a great impact on the ink color during the drying process

c) aqueous glazing. Generally speaking, water-based glazing does not have a great impact on the ink, but when the ink is not dry, it will also cause the ink to float

before applying UV varnish or solvent varnish, apply a layer of water-based varnish on the surface of the ink to make a base layer, and the effect is ideal. There are two functions: first, water-based varnish can protect ink from contact with UV varnish and solvent varnish; First, the floating liquid in water and oil fills the micropores of the paper and has adhesion, so that the UV glazing layer is flat and firmly attached

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