The influence of the most popular ink types and de

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The influence of ink type and deinking method (II)

II. The influence of printing method on ink characteristics and flotation deinking

the basic requirement of ink brushing is to meet the needs of printing method. For different printing methods, the contact path between ink and fiber is different, and different changes are produced to the physical and chemical properties of ink. These changes in ink characteristics directly affect the efficiency of flotation deinking

according to the ink solidification mechanism, printing methods can be divided into two categories

the first type is the printing method of ink adhesion through absorption and evaporation. In this case, the ink adapts to different printing needs with different viscosity

lithographic printing method is based on the principle that ink and water cannot be mixed. The image area on the printing plate is made into acceptable oil-based ink rather than water. Lithographic printing ink is often called offset plate, which has been certified by CNAs and other series of authoritative certification oil-based ink. It is based on water-resistant color carrier (bonding agent) and pigment water or ethanol, which cannot flow out. This method is used for brush paper, glossy magazines, books and photographic reproductions. In this method, the offset cold set ink is simply absorbed by the pores of the paper at room temperature, and the pigment then stays on the surface of the paper without additional drying, that is, the liquid component of the ink penetrates into the paper, leaving the solid component on the paper. Even if the adhesion is carried out under drying or chemical reaction, it still has absorption effect. Therefore, there is no obvious change in the properties of offset cold set oil-based ink during the printing process

letterpress printing and its improved printing. Aniline letterpress printing is this kind of printing method. Its ink is used for the protruding surface on the printing plate. When the printing plate is pressed on the paper, the ink on the protruding surface of the printing plate is transferred to the paper. Letterpress printing inks have medium or low viscosity and fast drying performance. Commonly used oil-based and water-based inks. This method is a typical method of printing newspapers and magazines

rotogravure printing uses the recessed area of the printing plate to form an image. The ink, such as temperature, pressure and the state under different productivity conditions, fills the recessed area. The paper is pressed to the recessed area by the elastic rubber roller to contact the ink. Rotogravure printing is typically used to print color newspapers and magazines

in letterpress and gravure printing, water-based ink and oil-based offset thermosetting ink are dried by evaporating volatile solvents (such as water or low boiling organic solvents, such as aromatic hydrocarbons or esters) at 60 ℃, and resins and other boring materials are combined with pigments and left on paper. Since there is no chemical reaction during printing, the oil-based offset thermosetting ink and the dried water-based ink maintain their original hydrophobic properties after printing

the second important printing method is indirect printing. Printing requires relatively high temperature to make the ink adhere to the fiber. When fine powder solid ink is used, these printing methods are photocopying and laser printing

Photocopying method, the latent image is formed on the charged photoconductive surface and then transferred to the paper, that is, the charged surface receives light to reflect the recorded latent image for copying. The light reflected from the non printing area forms a surface charge and dissipates, while the area without light retains its original charge. These charged areas are exposed to pigment particles with opposite charges, and the pigment particles adhere to the charged area to form a visible image. Finally, the image is transferred to paper. When the pigment particles are heated to 200 ℃, the styrene diselenate will melt and the pigment will melt, and combine with the paper fiber to form mm diameter polymer particles to form an image. These particle size changes can be clearly seen from scanning electron microscope (SEM) photos and optical microscope (OM) photos. At the same time, the atomic force microscope (AFM) photos can also clearly see the change range of the small particles of the primaries after melting

laser printing is an image formed with the help of laser beam, and its printing principle is similar to photocopying. The laser beam neutralizes the charge on the charged drum and forms a latent image on the non image area. After the pigment particles arrive on the drum, they adhere to the charged image area and form a visible image. The image is then transferred to the paper crown, and the pigment particles melt on the surface of the paper. Therefore, as mentioned above, the composition of laser printing pigment is similar to that of photocopying pigment. During the reprinting process, laser printing particles also undergo similar physical and chemical changes. After reprinting, laser printing pigment particles change from 25 to 150 effective working space × one hundred and fifty × 240mm0 μ M increases to several mm (see Figure 4)

due to the short-term action of heat (melting), light and oxygen (air) in the printing process of the above two printing pigments, the styrene group, especially the styrene group on the surface of the pigment particles, oxidizes and polymerizes to form peroxides. During printing, the pigment polymerizes to form larger particles, which makes the cellulose chemically combine with it, and also makes the cellulose fiber surrounded by the pigment ink particles; In addition, oxidation produces greater polarity (magnetism) on the ink surface, which makes flotation more difficult. Even if the ink can be separated from the fiber into the flotation slurry, there will still be some cellulose fibers bonded with the ink particles. These two effects will make the color ink particles more hydrophilic, which is the reason why the flotation deinking efficiency of office waste paper is low. Therefore, it is necessary to design improved deinking methods, such as magnetic separation technology; Specific pigment particles can also be designed

in a word, the oil-based (offset cold set and offset hot set) ink for paper printing contains w = 45% - 60% oil and w = 5% - 35% resin, and the water-based ink contains w = 40% water and w = 30% resin (polystyrene). Laser printing and photocopying pigments contain styrene acrylate copolymer with w = 60% - 90%. Except that water-based inks are dissolved in water (but the residue after drying is hydrophobic), other inks (including dried water-based inks) are originally hydrophobic. Therefore, ink can be separated from hydrophilic cellulose fibers by foam flotation

because of different printing methods, the ink has different physical and chemical surface properties during the printing process. The oil-based offset cold set ink for paper is simply absorbed by the pores of the paper to complete the printing, while the water-based ink and oil-based offset hot set ink complete the printing by physical drying (evaporation) when the temperature is lower than 60 ℃. Therefore, these inks have no significant changes in their chemical properties, especially in their hydrophobic properties, which makes them easy to separate from cellulose during flotation. Corresponding safety protection devices have been added to the positions where the machine may be damaged due to misoperation. During the printing process of photocopying and laser printing, the pigment particles are heated and fused to the cellulose dimension by the action of heat/light. Due to exposure to heat (up to 200 ℃), light and oxygen (air), the pigment particles polymerize and oxidize, and then form peroxide to connect with the fiber. This polymerization forms a strong physical combination of tiger's den and produces larger particles. Oxidation makes the surface of pigment particles produce greater polarity (magnetism) and reduces the efficiency of flotation deinking, which also proves that the printing method changes the surface chemical and physical properties of printing ink and has a decisive impact on the effect of flotation deinking

in order to improve the flotation deinking efficiency of laser printing photocopy waste paper, the design of new pigment particles and the surface properties of printing pigment particles must be considered

source: Spark design

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