Viscosity is one of the important properties of fluids, when a liquid is agitated, the speed of its flow is proportional to the force used, namely:
 
Force used (shear stress) = constant * shear velocity.
 
This constant is the viscosity of the liquid, which is a measure of the interaction between the molecules of the fluid and the ability to hinder the relative motion of the molecules, that is, the resistance of the fluid flow. The unit of viscosity is PASCAL o second (Paos), and viscosity is also known as viscosity.
 
The viscosity of ink is the most important property of ink fluidity. The size of the viscosity is mainly determined by the composition of the ink itself. If the viscosity of the ink binder is large, the viscosity of the ink is also large, the type and amount of the solvent in the ink, the proportion of the pigment and the particle size and its dispersion in the binder, the sum of these factors forms the difference in ink viscosity. Such as a large amount of paint. The viscosity of the ink made is large, the viscosity of the ink with large pigment particles is small, and the viscosity of the good ink with pigment dispersion is small.
 
1. the relationship between viscosity and printing
Generally, the higher the speed of the printing press, the lower the viscosity should be, usually the speed is 600EP/h, and the viscosity is 20 to 50 Paos.
 
2.the relationship between ink viscosity and the type of substrate
Due to the different surface strength of different substrates, they can withstand different ink viscosity values at the same printing speed. Such as low surface strength can only be used with relatively low viscosity ink.
 
3. the relationship between viscosity and temperature
Generally, the higher the temperature, the lower the viscosity.
 
Viscosity can be defined as the stickiness of a substance. It can also be said that at a given speed, the force separating two planes of a certain unit area (they are stuck to each other by the liquid) is generally called the Taek value. Viscosity is a relative value, dimensionless ink on the press, from the ink roller to the plate, from the plate to the substrate each transfer, the ink layer is stripped. The viscosity of the ink is the ability to hinder the stripping of the ink layer.
 
The relationship between viscosity and ink to substrate
Especially in high-speed printing, the viscosity of the ink must be below the critical value, otherwise the ink cannot be transferred and attached to the substrate. If the general conditions allow, the higher the viscosity of the ink, the better, the higher the viscosity of the ink in the printing of small text, the impression is clear, the dot is sharp. According to the printing order, the viscosity of the first color ink is maximum and gradually reduced to facilitate overprinting, and the measurement of viscosity can be measured by the viscosity meter.
 
 
Viscosity is the internal impedance of the molecule, and the viscosity is related to the separation proportion of the ink film, low viscosity ink viscosity and viscosity there is a linear relationship, that is, the greater the viscosity of the ink, the greater the viscosity.
 
Test method for ink viscosity
Apply No. 4 cup (QND-4) and add a drop of the tested ink. At a temperature of 25 ° C ±1 ° C, release the small hole switch at the lower end and let the ink flow freely. When the ink flow line is interrupted, the timing is stopped, and the seconds indicated by the stopwatch are viscosity data.
 
Viscosity index: 25~70s/25 ℃, the general ink factory control viscosity between 30~60s.
 
The viscosity change of ink is related to the following points:
※ Ink at a certain temperature (25 ℃) has a certain viscosity, the viscosity of the ink is reduced with the rise of the temperature, the temperature decreases and the viscosity increases such an inverse property.
 
The change in viscosity has a subtle effect on the drift area of the ink or the flow mode of the dot, especially in multi-color printing. If the room temperature changes greatly, the shifting state will change, and the tone will often change, which is because the temperature change affects the change of ink viscosity.
 
※ The fluidity of ink is usually referred to as the fluidity of ink under the action of external force and gravity. Ink fluidity and viscosity have a close relationship, ink will increase the viscosity at the same time will reduce its fluidity, on the contrary, improve fluidity.
 
※ The consistency of the ink is not equal to the viscosity of the high viscosity of the ink is not necessarily thick. Only inks with the same viscosity, the greater the consistency, the worse the fluidity.
 
The fluidity is too small, so that the spread of ink is not smooth, uneven, resulting in the same printing in front of the light and deep;
 
The fluidity is too large, so that the spread of ink is uneven, the printing level is not clear, the ink color is not full, and the dot is expanded.

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