Discussion on ink adhesion and yield value

2022-07-23
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Brief discussion: ink adhesion and yield value

tinting power refers to the ability of the ink layer to display the color intensity on the substrate. It is one of the quality indicators that characterize the ink concentration or saturation

the tinting power of ink is not only determined by the pigment concentration, content and dispersion in its structure, but also related to the selective absorption and reflection of light waves by the ink film. Generally speaking, when the pigment content is large and the dispersion is large, its coloring power is strong; On the contrary, its coloring power is weak. As offset lithography is an indirect printing method, the thickness of the ink film on the sheet is thin, so it needs to be compensated by the coloring force of the ink. In the process of offset printing, the tinting force of ink is not only directly related to the printing effect and print quality, but also closely related to the amount of ink per unit area. If the ink with strong coloring power is selected, the consumption is less than that with weak coloring power, and good printing effect can be obtained. For the choice of ink tinting power, it is usually determined by the graphic nature of the printed matter. If the printing color line is the main one, the one with strong coloring force shall be used, which is beneficial to the small reaction point. However, when the printing is full-scale, the one with weaker coloring power shall be applied

in the process of offset printing, the strength of ink coloring can usually be judged from the ink transfer on the surface of the ink roller and the coloring concentration of the printed matter. If the amount of ink transfer is large, and the print concentration is insufficient, it indicates that its coloring power is weak; Otherwise, it is strong

viscosity refers to the viscosity of ink when flowing. It is an indicator of the resistance (or internal friction) of ink flow

the viscosity of offset printing ink mainly depends on the inherent properties of the binder used, the particle size and content of pigment (including filler), and its dispersion in the binder. High pigment content and high viscosity; Large pigment particles and low viscosity; The pigment has good dispersion and low viscosity

in the offset printing process, a certain viscosity is the main condition to maintain the normal transmission and transfer of ink, and it is also an important condition to determine the imprint fastness, clarity and gloss. When the ink viscosity is too large, it is difficult to transfer and transfer, resulting in insufficient ink volume in the layout, resulting in the bare graphic foundation and the formation of a pattern. Similarly, the viscosity is too large, it is also easy to cause the paper to be roughened, de powdered, or cause the stripping of the printing sheet. However, if the viscosity is too small, it is easy to produce floating dirt. In serious cases, it will cause ink emulsification. If it cannot maintain normal transmission and transfer, it will gradually accumulate on the ink roller, printing plate and blanket to avoid affecting the measurement accuracy of the equipment; From the pigment particles, when the accumulation reaches a certain degree, it will cause paste

during offset printing, the viscosity should be controlled according to the tightness of the paper used and the printing speed. If the tightness is large, the viscosity can be larger, otherwise it should be smaller. The printing speed is slow, the viscosity should be large, and the printing speed is fast, the viscosity should be small

stickiness refers to the process of ink transfer, transfer and distribution. The resistance produced when the ink layers are separated, broken (or pulled apart), which is a characteristic of the adhesion and cohesion of the ink, so it is usually also called adhesion

the viscosity of ink is affected by its own viscosity, elasticity, surface tension and other factors. Generally, the viscosity is directly proportional to the viscosity, but it is not an absolute linear relationship. Viscosity data only provides a reference range. Because it is greatly affected by factors such as paper, printing machine speed, and printing conditions, it often occurs that the viscosity is not too large but the viscosity is large, or that the viscosity is large and the piston rises for a period of time at a small interval

in the offset printing process, the ink viscosity is mainly related to the thickness of the ink layer and the speed of the ink layer separation. The thick ink layer has high viscosity, and the high speed and viscosity are also large; Thin ink layer, low viscosity, low speed and low viscosity. If the stickiness is too small and the anti separation force is small, the distributed ink layer is too thin, the color of the printed product is easy to fade, and the dot imprinting tends to expand. Viscosity is small, water resistance is generally poor, so it is easy to cause dirty version. If the viscosity is too large, the anti separation force is large, resulting in poor transmission and transfer, and uneven ink layer distribution. Plastic uses synthetic resin, pigments, fillers and additives as raw materials to make the color of the printed sheet different. Even cause streaks. When the blanket is peeled off from the printing sheet, if the surface strength of the paper is insufficient and the viscosity of the ink is large, roughening will occur, which will cause paper stripping failure in serious cases

generally speaking, in wet overprint, the viscosity of the ink should decrease correspondingly according to the color sequence. This is because in multi-color (such as four-color or five color) continuous printing, because the ink is wet press wet overprint, its viscosity should be determined according to the actual conditions such as printing pressure, printing speed, ink supply, paper properties, etc., so as to ensure that it can obtain good overprint performance and printing effect, and prevent the latter color from being well adhered to the previous color ink layer during overprint. According to the manager, in wet overprint, only when the viscosity of the second color ink is less than that of the first color, but greater than that of the third color, can the ink layer overprint well. Therefore, generally speaking, the viscosity between colors should meet the following requirements: T1 T2 T3 T4

yield value refers to the minimum external force required when the ink starts to flow. It is used to characterize the viscous phenomenon and properties of ink from elastic deformation to flow deformation

offset printing inks are mostly plastic fluids. Their yield value mainly depends on the flow value property of the binder used and its viscosity

in the process of ink blending or offset printing, when the ink begins to deform under the shear force, it does not flow immediately, but only when the shear force gradually increases. Then, when the shear force exceeds the theoretical yield value, the verifier has little understanding of adding 1 increment, and the laminar flow phenomenon appears. It is called the minimum yield value when it is actually observed that the ink starts to flow; When laminar flow occurs, it is called the maximum yield value

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