Factors affecting the fading and discoloration of inks in cosmetic packaging boxes

Factors affecting the fading and discoloration of inks in cosmetic packaging boxes

Printing ink is composed of colorants (pigments), binders, fillers and auxiliary materials in accordance with the suitability requirements of the printing process and printing materials, so that the colorants (pigments) are uniformly dispersed in the binder composed of polymer compounds. And the formation of a stable suspension colloidal substance.

　　 One, the pigment of Cosmetic Boxes ink

　　 There are generally two types of ink pigments: ①inorganic pigments; ②organic pigments. The pigment itself does not emit light. It is the color exhibited by the selective absorption and reflection of light (including artificial light such as sunlight, fluorescent lamp, incandescent lamp, xenon lamp, dysprosium lamp, etc.) by the pigment object, which is the manifestation of the structure of the object.

  1. The role of pigments in ink:

　　①Color the ink, and determine the concentration of the ink according to the amount of usage;

　　② Give the ink a certain thickness and other physical properties;

　　③To maximize the durability of the ink;

　　④ It affects the drying properties of the ink to a certain extent, and the most obvious one is the oxidized conjunctival type drying.

  2. The binder of the ink is a fluid medium that has a certain viscosity and plays a role in dispersing the pigment in the ink. Its role is as follows:

　　① Give the ink a certain viscosity, viscosity, fluidity and thixotropy;

　　②Determine the drying type and drying speed of the ink;

　　③ Determine the gloss, abrasion resistance, and firmness of the ink.

　　3. The role of auxiliary materials in ink:

　　 The auxiliary materials in the ink make some adjustments to the color tone, viscosity, consistency, dryness, and fluidity of the ink.

　　 Requirements for auxiliary materials:

　　①The fineness of the particles must be similar to that of the ink, not too thick;

　　②Can not affect the coloring power, adhesion and other properties of the ink;

　　③It can blend well with ink without any chemical reaction;

　　④Can not corrode and chemically react to the printing plate.

　　 2. The cause of ink fading and discoloration

The fading and discoloration of printed products are mainly caused by the performance of the ink, but some are also caused by the art of printing, and the ink encounters acid, alkali, sulfide, alcohol, such as: methanol, ethanol (alcohol), glycerol, surface activity Chemical substances such as substances are also very easy to cause fading and discoloration problems:

  1. Ink penetration and discoloration in the conjunctival process: In the printing process, the ink color is darker when the printed matter is printed, but the color of the ink will become lighter after a period of time. This is not the reason that the ink is not light-resistant, mainly the ink Causes of penetration and conjunctiva during drying. The light is irradiated on the pigment particles through the connecting material, and the color light that is reflected by the pigment to the sunlight is selected to show the color. The deeper the light penetrates the ink film, the more saturated the color light reflected. Therefore, a thicker ink layer has a thicker color, and a transparent ink layer has a brighter color. The printed product just printed has a thicker ink layer. However, after drying, a large part of the binder in the ink will penetrate into the inside of the paper fiber, so the ink layer after drying should be shallower, so that the color will become lighter. When printing, the color should be controlled to be slightly thicker than the original color sample, so that the original color will be met after the ink is dried.

  2. Fading of ink due to light resistance: When we adjust the ink, we should choose ink with good light resistance as much as possible. Any ink will fade in different degrees under sunlight or other light sources. It should be estimated when mixing light color inks. The light resistance of the ink after being diluted. For example, it is best to use phthalocyanine blue for pale lake blue, not peacock blue, because phthalocyanine blue is more resistant to light and not easy to change color. Gray ink can be mixed with white ink with black ink and phthalocyanine ink; emerald color can be monochromatic phthalocyanine green, if yellow is not enough, bright resin yellow ink can be added, and white ink can be added if it is brighter, if you use peacock blue and chrome yellow ink , It is prone to yellowing for a long time.

If the products we print are outdoor advertising posters, posters, New Year pictures, etc., because these products are posted outdoors and are directly exposed to sunlight, under the action of ultraviolet rays in the sun, wind and rain will last a long time. Bright colors are easy to fade, and it is found that only black and blue inks still exist. Light colors, yellow and red inks are all fading, so in order to reduce the fading after the sun's ultraviolet rays, it is best to print the two colors y and m first in the color sequence during four-color overprinting, and the two colors C and BK are placed After printing, in this way, the two colors of C and BK that are superimposed at the end have the effect of light and heat resistance, thereby reducing the fading phenomenon of the printed product.

　　3. Loose paper and rough discoloration: If the printed paper has poor smoothness, the surface of the paper is rough, loose offset paper, letterpress paper, newsprint, kraft paper, etc., the paper has high absorbency, and the ink and pigment particles are fine, and the drying process is slow. The medium is gradually absorbed by the paper along with the binder, so the ink color becomes lighter. The absorption of ink by paper and the increase in penetration of ink into paper will cause the separation of the binder and the pigment, which will cause the ink film to become thinner, discolored, and poor in gloss. To reduce the absorption and penetration time of the paper, it must be increased accordingly. Drying speed, increase the amount of red and white dry oil in the ink.

　　4. The ink is not resistant to acid and alkali fading and discoloration: peacock blue ink will turn green when exposed to acid. The wetting fluid for offset printing is often acidic, and the pH value is controlled between 4.5-6. The acidic wetting fluid will affect the discoloration of the ink. , The ideal wetting fluid has a pH value of 7, which is neutral. Acidic paper and wetting fluid also have the effect of resisting ink drying.

Under normal circumstances, the inks are not alkali resistant. The gold ink for printing gold and the electrochemical aluminum foil for bronzing will turn into pale yellow when exposed to alkali, and will be dull and dull. The alkali color turns red, so it can't be used to print the packaging prints of alkali substances. Peach red, emerald green, green lotus, royal blue, light blue and other inks are not alkali resistant. Peacock blue has better alkali resistance. Most of the paper is weakly alkaline. If printing soap, toilet soap, white alkali and other alkalis For packaging products with sexual substances, it is necessary to consider the alkali resistance and saponification resistance of the printed product.

In the post-printing process, avoid the influence of alkaline adhesives on the discoloration of the printed product ink. For example, the sorophylline adhesive is alkaline and cannot be used, otherwise it is easy to change color. Choose those pure natural, non-polluting, PH value=7, neutral and environmentally friendly adhesives are suitable.

　　 5. The ink is not resistant to alcohol and changes color: There are ethanol and isopropanol in the offset printing wetting fluid. Alcohol wetting has: ①Good wetting performance and good spreading performance on the layout; ②Because alcohol has a certain volatility, the moisture of the layout will be volatilized to a certain extent after transferring to the blanket, so the water absorption of the paper will be reduced. Reduce; ③When the alcohol evaporates, it can take away a lot of heat, so that the temperature of the printing plate is reduced, and the fluidity of the ink is guaranteed.

　　In addition to ethanol, the offset printing wetting fluid also uses alcohols such as glycerol and polyethylene glycol. The printed products printed by the alcohol wetting fluid will change color after a long time, indicating that the ink's alcohol resistance is poor.

　　 6. The ink is not heat-resistant and discolors and fades: In general, the heat resistance of the ink is about 120°C, and the gold-red ink has worse heat resistance, only about 70°C. During the printing process, the ink is on the ink roller and the plate surface 5000 sheets When running at high speed per hour, friction will generate heat generally at 40~50℃, and the ink will release heat during the drying process. Therefore, the printed products should not be piled up too thick, and should be ventilated to reduce the temperature to prevent heat discoloration. If the printed product is too thick and too thick during the stacking and drying process, when it is close to 60~70℃, the gold-red ink will change and fade. It is brighter when printed, and after a period of time, the light flesh color will turn into yellowish color. This is because the gold-red ink is not heat-resistant. Pressure cookers, stoves, rice cookers and other kitchen utensils are often packaged when the ink color is not heat-resistant and discolors and fades.

　　7. The discoloration caused by the drying oil of the desiccant added in the ink: red dry oil should be added to the dark color ink, white dry oil should be added to the light color ink, the amount of dry oil added should not exceed 5% of the ink volume, if the amount exceeds 20% The above causes the ink to change color. If the golden red ink is added to the red dry oil, it will easily turn brown. The red dry oil itself has a darker purple red color. The blending of light inks will have some influence, but the small amount of dry oil will not have much effect. The white dry oil does not seem to have any color, and its essence is light brown after the conjunctiva. Therefore, when a lot of white dry oil is used to adjust the light color ink, it accelerates the drying of the oxidized conjunctiva of the ink film, and the color looks bright, but after drying, it will Yellowish brown.

  8. Discoloration caused by chemical substances in paper: During papermaking, sulfide or other compounds are often contained in pulp due to rinsing and processing. Due to different manufacturing methods, some papers are acidic or alkaline, and the ideal paper pH value =7, neutral, the acidity and alkalinity of the paper will affect the ink color, especially the light color ink.

The sulfide or acid substances in the paper react with the inorganic pigments in the ink. When the ink binders and pigments penetrate into the paper fibers and the oxidized conjunctiva on the surface of the paper, they will change color and darken the color.

　　 The iron compound in the paper can make the light-colored ink brown, and the gold ink for printing gold and the anodized aluminum foil for bronzing are easily blackened by sulfide corrosion and have poor gloss. If the white paint and sizing material on the surface of the coated paper are strongly alkaline, they will react with the acidic pigment iron blue, etc., which will easily cause discoloration.