1,000 Offset Printing (107-113)

107. How to measure the flow of ink?

A: The measurement of ink flow is currently widely used in the determination of the flow meter. The specific method is: place the sample ink and flow meter in a 25±1°C incubator and remove it after 20 minutes of incubation. Then, 0.1 ml of ink is sucked with a blotter, placed in the center of the lower glass plate, covered with a glass plate and a weight, and placed in a 25°C thermostat. After 15 minutes of incubation, the weight is removed, and the weight is removed. The spread diameter (mm) of the test ink was measured with a transparency scale, which is the fluidity of the ink.

108. What is the viscosity of ink? What is its effect on offset printing?

A: Ink viscosity refers to the viscosity of ink flow, it is an indicator of the size of the ink fluid flow resistance. The viscosity of offset inks depends primarily on the inherent properties of the binder used, the size and content of the pigment particles, and their dispersion in the binder. High pigment content, high ink viscosity; large pigment particles, low ink viscosity; good pigment dispersion and low ink viscosity.

In the offset printing process, a certain viscosity is the main condition for ensuring the normal transfer and transfer of the ink, and is also an important condition for determining the fastness, sharpness and gloss of the ink blot. When the viscosity of the ink is too high, the ink is difficult to transfer and transfer, which may cause the printing plate to be insufficient in quantity, resulting in a flower pattern. When the viscosity is too small, it is easy to cause turbidity. In severe cases, the ink may be excessively emulsified, or the ink may not be transferred normally. Transfer, and gradually pile up on the ink roller, printing plate and blanket, when it is accumulated to a certain extent, it will cause paste.

109. How to choose the viscosity of ink in offset printing?

A: In offset printing, the selection and control of ink viscosity should be based on the absorbency and the printing speed of the paper used. When printing good absorbing paper, you can use ink with higher viscosity; otherwise, you can use ink with lower viscosity. When the printing speed is slow, the viscosity of the selected ink is larger; when the printing speed is fast, the viscosity of the selected ink is smaller. In addition, the viscosity of the ink is also affected by the influence of the ambient temperature and the working surface temperature. When the viscosity of the ink changes, it also causes changes in the flow, consistency, and viscoelasticity of the ink.

110. How to determine the viscosity of offset ink?

A: The determination of offset ink viscosity usually uses the following two methods:

1 dropstick viscometer method: 1ml of ink sample is placed in the gap between the long rod and the short cylinder of the instrument. When the round rod is dropped 10cm vertically, the time required for the round rod to fall is recorded to calculate the thin layer of ink. Shear rate. The viscosity of the ink can be determined by measuring the three or four pairs of data by using different load rates at different shear rates, using the instrument chart.

2 Parallel Plate Viscometer Method: Place approximately 0.5 ml of the test ink sample on the lower sample plate of the instrument and wipe the test ink to clean the remaining ink around the hole. Then place the upper load plate on top of the support rod and push the piston up to push the ink onto the mounting plate. At the same time, the drop stick and the load plate press the ink between the fixed plate and the load plate, and begin to record the extended diameter of the flat cylindrical shape at different times, and calculate the viscosity value. The diameter of the expanded flat cylinder is generally measured at different times such as 10 seconds, 100 seconds, and 30 minutes.

111. What is the viscosity of ink?

A: The viscosity of ink refers to the magnitude of the resistance generated when the ink is separated and broken during the transfer, transfer and distribution of the ink. It is a physical quantity used to characterize the adhesion and cohesion of the ink. It is usually called Adhesion.

112. What are the influencing factors of ink viscosity?

A: The factors that affect the viscosity of the ink include the viscosity, elasticity, surface tension of the ink, the printing paper, the speed of the printing press, and the condition of the printed product. In general, the ink viscosity is proportional to the viscosity, but it is not an absolute linear relationship. In the printing process, there are often cases where the viscosity is not large but the viscosity is large, or the viscosity is large and the viscosity is not large.

113. What is the effect of ink stickiness on offset printing?

A: The viscosity of the ink in the offset printing process is mainly related to the thickness of the ink layer and the speed at which the ink layer is separated. The thick layer of viscous ink is thick, and the viscosity is small; the viscous ink is thin, and the viscosity is large and slow. When the viscosity of the ink is too small, the ink layer is too thin, the color of the printed material is easy to light, the dots are easy to increase, and the water resistance is also poor, and the ink emulsification easily occurs, resulting in a dirty plate; when the viscosity is too large, the water resistance of the ink It is generally poor. When the viscosity of the ink is too high, its resistance to separation is large, resulting in poor transfer and transfer, uneven distribution of the ink layer, and unevenness of the color of the printed sheets, and even the occurrence of streaks. When the blanket and the printed sheet are peeled, if the paper If the surface strength is insufficient, and the viscosity of the ink is large, the pulling hair may be generated, and the paper peeling failure may be caused in severe cases.

(Author/Drilling)