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Treatment method for fading and discoloration of printed products

     In the packaging and printing industry, there are various types of paper products. Under the irradiation of sunlight, sunlight, incandescent lamps and other light sources, printed products such as books, picture albums, newspapers, advertising recruitment pictures and New Year pictures can show bright and colorful colors through the selective absorption and reflection of ink materials.Treatment method for fading and discoloration of printed products.

    The fading and discoloration of printed matter are caused by many factors, such as light resistance of ink, acid-base of paper, temperature, printing color sequence and so on.Treatment method for fading and discoloration of printed products.

Treatment method for fading and discoloration of printed products

1. Discoloration during ink drying.

    In the process of printing, the ink color of the newly printed ink is compared with that of the dried ink. The ink color of the newly printed ink is relatively deep. After a period of time, the ink color will become lighter after the imprinting is dry. This is not the problem that the ink is not resistant to light fading and discoloration. It is mainly the discoloration caused by the penetration and oxidation of the conjunctiva during the drying process. Relief ink is mainly osmotic drying.

     The ink layer of the products just printed from the printing machine is relatively thick. At this time, it will take some time for infiltration and oxidation conjunctiva drying. Moreover, most of the connecting materials in the ink penetrate into the interior of the paper fiber. It is inevitable that the ink layer becomes thinner and the color changes after the oxidized conjunctiva is dried. During printing, the ink color shall be controlled to be slightly darker than that of the original printing sample, and the ink shall meet the ink color requirements of the sample after drying.

     The color mechanism of printed matter is carried out by subtraction. Sunlight, sunlight and incandescent lamp irradiate the small particles of ink pigment from the light source, and absorb the color light selectively reflected by the pigment. The deeper the light passes through the ink film, the more saturated the reflected color light, the thicker the ink layer, and the darker the color.Treatment method for fading and discoloration of printed products.

2. Ink itself is not resistant to light and fades.

     It is inevitable for ink to fade and change color after encountering light. All ink will fade and change color to a certain extent after encountering light. The light ink fades and discolors seriously after a long time of light irradiation. Yellow, magenta and green fade quickly, while green, blue and black fade slowly. When adjusting the ink in the actual work, we should try to choose the ink with good light fastness.Treatment method for fading and discoloration of printed products.

    When adjusting the light color, we should pay attention to the light resistance of the ink after desalination. When adjusting the ink, we should consider the consistency of the light fastness of several kinds of ink. Outdoor advertising contribution paintings are easy to fade when exposed to the sun. The light resistance of ink must be considered. 

      The same blue ink, phthalocyanine blue is more light resistant than light lake blue and Malachite blue. Gray can add a little black ink and o-benzene essential oil ink to white ink; For green, you can use monochrome o-benzene essential oil.Treatment method for fading and discoloration of printed products.

     If it is not yellow enough, you can add lit resin yellow ink. If you add a little white ink, the color will be more bright. If Malachite blue and chrome yellow ink are used, it is easy to fade, change color and turn yellow for a long time.Treatment method for fading and discoloration of printed products.

3. The influence of paper acidity and alkalinity on ink packaging and discoloration.

     Generally speaking, paper is weakly alkaline. The ideal pH value of paper is 7 and neutral. Chemicals such as alkali (NaOH), sulfide and chlorine need to be added in the papermaking process. If they are not handled properly in the pulping and papermaking process, the paper may be acidic or alkaline. There are some residual chlorine and organic acids in the slurry. If not properly treated, the paper is acidic; If alkaline fillers and pigments are used in the papermaking process, and there is residual alkali solution in the slurry without necessary treatment, the resulting paper is alkaline.Treatment method for fading and discoloration of printed products.

     ① The acid-base property of paper has a great influence on the printing technology and the color durability of printed matter. The acidity and alkalinity of paper directly affects the oxidation conjunctiva drying of printing. The printing drying of paper with high acidity is particularly slow because acidic substances can inhibit the oxidation conjunctiva drying of printing.Treatment method for fading and discoloration of printed products.

      ② The acidity and alkalinity of paper will also cause the fading and discoloration of ink. The pH value of raw material paper below 7 is acidic, and above 7 is alkaline. The paper and bucket solution with strong acidity are also weakly acidic, which affect the ink and discoloration, such as malachite blue, acid and green.

      ③ The alkali resistance of ink is worse. Basically all inks will be discolored or discolored by alkali. Chrome yellow ink turns red with alkali, and the medium basket encounters paper fading with greater alkali. In particular, gold ink, silver ink and electrochemical aluminum foil bronzing will lose their original luster when encountering alkaline substances, the golden brilliant color will turn into ancient Yellow, the silver ink will turn black and not bright, the adhesion will decline, and the printed matter is often discarded.Treatment method for fading and discoloration of printed products.

    The alkalinity of paper comes from the papermaking technology itself, as well as the adhesive containing alkaline substances used in subsequent binding production. If foamed alkali and other alkaline adhesives are used, the alkaline substances will penetrate into the paper fibers and chemically react with the ink pigment particles on the paper surface to make them fade and change color.

     When selecting raw materials and adhesives, first analyze the effects of physical and chemical properties and acid-base properties of adhesives and paper on ink, paper, electrochemical aluminum foil, gold powder, silver powder and film.Treatment method for fading and discoloration of printed products.   

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