Formulation design principle of the hottest flexog

2022-09-23
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Formulation design principle of flexographic printing ink

release date: 2 source of relaxation: China paper

flexographic printing principle:

image transmission in the process of flexographic printing is completed through a flexible photosensitive resin plate obtained by photochemical reaction. The ink is in an ink tank, Through the grain transfer ink roller (ANI transports a certain volume of ink to the printing plate. The ink transfer roller is composed of chromium alloy, and the surface is plated with ceramic wear-resistant layer or ceramic wear-resistant layer by ion spraying. The amount of ink transferred is determined by the number of lines on the surface of the ink transfer roller. The surface of the thick ink transfer roller has about 120 lines per inch, while the ink transfer roller used for printing fine patterns can reach lines per inch. Today, China's paper industry takes you into flexible packaging printing technology, see Introduce the relevant contents in detail

technical requirements of flexographic printing ink:

◆ relatively low viscosity: the viscosity of standard UV flexographic printing ink under the shear rate of 2500s-1 is 0 5Pa. s. The printing speed is determined by the construction conditions (in the open air or in a closed room), and also determines the viscosity of the final ink. If the viscosity is too high, the ink will accumulate between the ink roller and the doctor blade, so the printed pattern will have some discontinuous ink accumulation stains. If the viscosity of the ink is very low, the problem will be smaller. However, due to the small amount of ink in flexographic printing itself, the transmission of ink will be affected. UV flexo ink curing speed requirements will also affect the viscosity of the ink, because most of the high-level official group products are very high viscosity. In order to improve the curing speed of the ink without affecting the viscosity, the amount of photoinitiator must be increased, but this will affect the odor and the cost of the ink at the same time. Therefore, the formulation designer must find the best combination point of ink viscosity and other characteristics. UV flexo printing ink has higher viscosity than water-based flexo printing ink, so compared with water-based flexo printing ink, UV flexo printing ink can achieve a printing effect closer to offset printing and gravure printing

◆ pigment wettability and color strength: flexo printing inks require a very high pigment content, often 15% to 20%. When the pore density on the surface of the ink transfer roller is very low, a very high pigment content will cause many small and discontinuous printing spots. The viscosity is closely related to the wetting of pigments; If the pigment is not wetted well, it will not reflect the characteristics of Newtonian fluid, and the ink will also have corresponding flow difficulties. In addition, because the pigment is not dispersed well, the color intensity will also weaken

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◆ rheology: ink with good fluidity will have good gloss. Newtonian fluid has the characteristic that the viscosity does not change with the shear rate, which not only determines whether the ink transmission is good, but also is equally important for the transmission of ink on the ink roller. When the ink passes through the roller, the bubbles extruded will enter the remaining ink. In this way, too many bubbles will offset the Newtonian rheology of the ink and lead to printing failure

◆ curing speed: at present, the commonly used printing speed is 70m. Since the surface of the elastic element is pasted with a strain gauge -150m/min, the requirements for the curing speed of the ink are increased

◆ adhesion on various substrates: since UV flexo printing ink is mainly used to print various very soft labels and packages, the ink must have good adhesion on various soft substrates such as PP, PE, pet, PVC, and PA

◆ other requirements: the ink should have scratch resistance, chemical and bacterial resistance, flexibility and low odor

manufacturing process of flexographic printing ink:

general manufacturing method of UV flexographic printing ink:

a the application of polyester acrylate or epoxy acrylate and a certain amount of pigment mainly includes grinding together on a three roller machine. During the grinding process, some active monomers and dispersing additives will be added to make a color paste

b ink is made by diluting the color paste with a low viscosity mixture containing active monomer, initiator and leveling agent

application example of flexographic printing ink:

material percentage

pigment 12%

polyurethane acrylate 24%

polyester acrylate 10%

diluent 42%

photoinitiator 10%

auxiliary 2%

note:

magenta flexographic printing ink

for magenta pigment 57:1, you must mix and grind with polyester acrylate to get the best rheological behavior. Due to the high polarity of polyurethane acrylate, the viscosity of ink at low shear rate will be too high

black flexo printing ink

for black flexo printing ink, in order to improve the curing speed of the ink, epoxy acrylate can be appropriately used in the formula to replace polyurethane acrylate. Using oxidized carbon black pigment to disperse in epoxy acrylate will have different effects. The epoxy acrylic resin often used is based on bisphenol A epoxy resin

influence of active monomers and dispersants:

if the viscosity reducing components in the system are not selected well, the proper pigment content will not achieve good results. Viscosity reducing components include active monomers used to adjust viscosity. Of course, monomers also play a role in coordinating other aspects of performance. In addition, photoinitiators and additives are also essential. When the dispersant is added in the grinding stage of the pigment, the rheology of the ink tends to Newtonian fluid, and the optical density also increases

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