Offset Printing 1000 Questions (114-128)

114. How to arrange the offset printing color sequence according to the ink stickiness?

Answer: Generally in multi-color continuous overprinting, the printing color sequence should be arranged in descending order of ink viscosity. This is because in multi-color continuous printing, the ink is wet and wet, and only when the second color ink is sticky. When the ink is smaller than the previous color ink and larger than the latter color ink, good overprint performance and printing effect can be obtained. In addition, in the offset printing, the viscosity of the used ink should be determined according to the actual conditions such as the printing pressure, the printing speed, the ink supply amount, the paper properties, etc., so as to prevent the past color from being adhered to the previous color ink layer.

115. What is the relationship between ink viscosity and printing speed?

A: For domestic inks, the general sheetfed offset press has a viscosity of 7 to 13 at a speed of 5000 to 10,000 rpm and a viscosity of 4 to 5 at a speed of 20,000 rpm. When the web offset press has a speed of more than 20,000 rpm, the ink viscosity is 3 to 5.

116. How to measure the viscosity of ink?

A: The viscosity of the ink is usually measured by the ink stickiness tester. After the instrument is adjusted to the horizontal state, the ink is evenly coated on the ink roller with the ink absorber to transfer it. The ink is produced due to the viscosity. Torque destabilizes the lever and deviates from an inclined state. When the lever is balanced to the horizontal state, the arm scale shown by the lever is the viscosity value of the test ink.

117. What is the viscosity increase value of ink?

A: The viscosity increase value of the ink refers to the difference between the viscosity at the 15th minute and the viscosity at the 1st minute when measuring the viscosity of the ink. It is mainly used to describe the stability of the ink stickiness on the printing press. The large increase in the viscosity of the ink indicates that the ink is not sticky on the machine, resulting in poor transfer transfer, or even damage to the paper surface, such as lint-free, powder-flooding, and scumming. In addition, the ink viscosity growth value also changes with the ambient temperature or face problems, generally, every increase or decrease of 3°C, the viscosity changes by 1 unit. In actual printing, the ink viscosity growth is generally about 1. For the value-added of stickiness caused by other factors in the printing press, it should be strictly controlled. The smaller the value, the better.

118. What is the viscoelasticity of ink?

A: Viscoelasticity refers to the viscous and elastic phenomenon that occurs when the ink flows. It is the viscoelastic property that appears when the ink thread breaks during the separation process of the ink layer. The viscoelasticity of the ink depends mainly on the viscoelasticity of the binder used in the ink.

119. What are the factors that affect the viscoelasticity of ink?

A: The viscoelasticity of an ink depends mainly on the viscoelasticity of the binder used. In the printing process, when the ink is transferred, due to the relationship of viscosity and viscosity, the ink is pulled into filament under a certain tension, and when the separation breaks, the ink shrinks rapidly, this shrinkage phenomenon and the deformation speed and force. The time of action is related. In the rapidly deformed condition, the action time is short, it looks like a solid elastic phenomenon, and under the condition of slow deformation, the action time is long, it will almost change into a liquid-like viscous flow. The length of the ink depends mainly on printing. The faster the speed, the faster the printing speed, the shorter the ink. The ink is short, the ink layer is thick, and the picture is clear, but if the ink is too short, the ink is not good; but if the ink is too long, it is easy to fly.

120. What is the thixotropy of ink?

A: Ink thixotropy refers to the property that the ink causes fluidity change under external force. Offset ink is a plastic fluid, and thixotropy is one of its rheological properties. In the process of ink adjustment, the ink becomes hard and soft, thick and thin, and the viscosity decreases and the fluidity increases when the ink is stirred; when the stirring is stopped or the ink is left standing, the ink body is softened and then hardened. Thick, viscosity increases, fluidity decreases.

121. What are the factors that affect the thixotropy of ink?

A: The thixotropy of offset printing ink is not related to the change of temperature and humidity in the work environment. It is mainly due to the flocculation of the pigment in the ink, and the flocculation process is reversible. In general, the thixotropy of the ink is mainly determined by the nature of the pigment and the binder used in the ink, and the pigment particles, the surface properties and the volume occupied by the ink are greatly affected.

122. What is the relationship between thixotropic offset printing and offset printing?

A: The thixotropy of offset inks plays an important role in the offset printing process. In the offset printing process, due to the action of the ink roller, the fluidity and ductility of the ink are also increased. After the transfer to the printed sheet, the fluidity and ductility are reduced due to the disappearance of the external force. Dilute thicker to ensure the accuracy and clarity of blotting dots.

123. What is the yield value of ink and its influencing factors?

A: The ink yield value refers to the minimum external force required for the ink to start flowing. It is used to characterize the viscous phenomenon and properties of the ink from the elastic deformation to the flow deformation process. It mainly depends on the rheology of the binder used in the ink. Nature and its own viscosity.

124. What is the relationship between the yield value of offset ink and offset printing?

A: In the process of ink transfer or offset printing, when the ink begins to deform under the action of shear force, it does not immediately flow. It only begins to flow when the shear force is greater than the theoretical yield value of the ink. Therefore, the yield value of the ink is Affects the flow of ink. In addition, the yield value of the ink can also indicate the consistency and soft and hard characteristics of the ink body. Generally, the larger the yield value, the harder the ink body; otherwise, it is soft. Therefore, when the ink enters the ink-distribution process from the ink fountain, the yield value is often too large to be evenly opened. If the ink is not agitated, the ink is not smoothly applied.

125. What are the properties of the offset ink chemistry?

A: The chemical properties of offset inks mainly refer to the resistance of inks to printing inks during the printing process or after printing. The resistance to chemicals includes water resistance, acid resistance, alkali resistance, solvent resistance, wax resistance, and light resistance. Sex etc.

126. What is the water resistance of offset ink? What are the influencing factors?

A: The water resistance of ink is the ability of the ink to resist water infiltration. Mainly depends on the stability of the ink structure, and the stability of the ink structure depends on the combination of the pigment and the binder used, and the water-resistant properties of the pigment. The water resistance of the print indicates the water resistance of the ink film.

127. What is the relationship between ink water resistance and offset printing quality?

A: In the offset printing process, the fountain solution and the ink alternately contact the printing plate. Since the fountain solution contains a certain amount of surface active material, the water resistance of the ink is often affected. The poor water resistance of the ink leads to poor fluidity of the ink, deterioration of the transferability, failure of the ink roller, and less and less printing of the printing plate, so that the fountain solution and the entire printing plate are stained with a colored liquid. The layer, while reducing the viscosity and viscosity of the ink, the color of the imprint also changes, the gloss decreases, and the ink curing time is delayed. In severe cases, there will be forced shutdowns or large amounts of waste. For blotting ink films, poor water resistance causes bleeding.

128. What is the acid resistance of the ink? What does it have to do with offset printing quality?

A: The ink's resistance to acidic substances is called the acid resistance of the ink.

The acid resistance of the ink depends on the acid resistance of the pigment and binder used in the ink. In the offset printing process, if the ink is in contact with the fountain solution, it will dissolve in the fountain solution if the ink is not in contact with the fountain solution, or the fountain solution will gradually enter. In the ink, it causes troubles such as floating. The acid resistance of the ink is not only related to the printing process, but also to the conditions of use of the printed product. For example, when the printing bottle labels, packaging papers, paper boxes, etc., if the ink has poor acid resistance, an acidic adhesive or packaging material is used. Acidic substances, etc., will cause the imprint to fade or discolor, causing the devaluation of the product and affecting sales.

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