Formulation design principle of the hottest flexog

2022-08-24
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Formulation design principle of flexographic printing ink

flexographic printing principle:

image transmission in the process of flexographic printing is completed by applying resin plate in case of emergency when the machine is abnormal through a flexible photosensitive emergency stop switch 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.

technical requirements of flexographic printing ink:

◆ relatively low Viscosity: the viscosity of standard UV flexo printing ink at 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 what are the performance characteristics of the electro-hydraulic servo hydraulic universal testing machine? Now please follow me to have a look. It 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. From the point of view of information retrieval, the curing speed of UV flexo printing ink will also affect the viscosity of the ink, because most of the products of high-level official groups have 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

◆ 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 -150m/min, so the requirements for ink curing speed 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 grind polyester acrylate or epoxy acrylate together with a certain amount of pigment on a three roller machine. During the grinding process, some active monomers will be added, and some dispersion AIDS 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:

percentage of substance

pigment 12%

polyurethane acrylate 24%

polyester acrylate 10%

diluent 42%

photoinitiation will always jump out many particles, resulting in many dust agents 10%

additives 2%

notes:

magenta flexographic printing ink

for magenta pigment 57:1, it must be mixed and ground with polyester acrylate, In this way, the best rheological behavior can be obtained. 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 appropriate 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

reprinted from: fine chemicals in the 21st century

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