How much is the packaging offset? (61-70)

61. What are the disadvantages of waterless offset printing?

1 Waterless offset printing is very harsh on the ambient temperature and requires that the temperature of the printing shop must be maintained at 23 ~ 25 °C. The temperature is low, the ink will freeze, and the temperature will be high and a paste failure will occur.

2 After the waterless offset printing plate is dirty, decontamination is more difficult.

3 Waterless offset printing plate is more expensive than ordinary PS plate.

62. What type of print is suitable for waterless offset printing?

Waterless offset printing is suitable for products with high product quality requirements, low number of prints, and short construction time requirements. Waterless offset printing develops faster in Japan and Europe and the United States, and is less used for commercial printing in China.

63. What are the basic principles of lithographic offset printing?

Offset offset printing is mainly based on the following four basic principles: the principle of oil-water immiscibility, the principle of selective adsorption of printing plates, the principle of dot coloration, and the principle of indirect printing.

64. What is the principle of similar dissolution?

There is a general rule that whether the two substances are mutually soluble or not, ie, the polar solvent is compatible with the polar solvent, the nonpolar solvent is compatible with the nonpolar solvent, and the polar solvent is incompatible with the nonpolar solvent. When two different polar solvents are put together, since both are polar molecules, in addition to the orientation forces between the respective molecules, there are also alignment forces between the two different molecules. Relying on the orientation forces between different molecules, two different polar solvents are miscible with each other. Combining two different non-polar solvents, there is no orientation force and inducing force between the same molecules or between different molecules, the intermolecular force is weak, and both molecules tend to disperse disorderly to reach the maximum Confusion, eventually forming a homogeneous solution. When a polar solvent and a non-polar solvent are put together, the polar molecules themselves have an orientation force, an inducing force, and a dispersive force, while there is no molecular orientation force between the polar solvent and the non-polar solution, and only the induction occurs. Force and dispersion force, and the attraction between polar solvent molecules is greater than the attraction between polar solvents and non-polar solvent molecules, so the two are immiscible.

65. What kind of chemical structure does the water have?

The formula of water is H2O, and one water molecule is composed of two hydrogen atoms and one oxygen atom combined with polar covalent bonds through a common electron pair. The molecular structure of water is asymmetrical. Three atoms are separated into three corners of a triangle. The two HO bonds form a 104° 45′ angle. Therefore, water molecules belong to polar molecules. There are orientation forces and induction between water molecules. Force, dispersive force, and hydrogen bonding have a strong intermolecular attraction.

66. What kind of chemical structure does oil have?

Oil is a generic term for organic liquids. A variety of saturated hydrocarbons, benzene and other organic liquids, although the molecules have polar bonds, but the entire molecule has a symmetrical structure, and therefore are non-polar molecules. The commonly used ink binders, such as linseed oil, have polar carboxyl groups (-COOH), but due to their long non-polar carbon chain, they dominate the molecule and play a leading role in the polarity of hydrophilicity. The group is almost ineffective, so linseed oil, etc. can also be considered non-polar molecules.

What is the principle of immiscibility between ink and fountain solution?

What factors affect the surface tension and interfacial tension

What is the approximate surface tension of the ink and fountain solution?

Which kinds of plates are used for packaging offset printing?

What is a high-energy surface and a low-energy surface?

67. What is the principle of ink and fountain solution immiscible?

The liquid part of the offset ink is a binder, and the binder is composed of dry vegetable oil and synthetic resin. The binders in offset inks have one thing in common: The non-polar hydrocarbon chains are dominant in the molecule and play a dominant role, so the ink can be viewed approximately as a non-polar liquid. Most of the fountain solution is water, other additives are mostly polar molecules, so the fountain solution can be seen as a polar liquid, according to the similar principle of dissolving, ink and water are immiscible.

68. What is interfacial tension?

At the interface between the solid and liquid phases, or at the interface between two different liquid phases, the molecules of the two substances in a unit area, each relative to the sum of the excess free energy of the same number of molecules in the interior of the phase, It is called interfacial tension.

69. What are the factors affecting the liquid surface tension and interfacial tension in the printing industry?

1 kind of liquid. Different liquids have different intermolecular forces, and the intermolecular forces are large and the surface tension is large. Water has a large surface tension, while oil has a small surface tension.

2 temperature. When the temperature rises, the attraction between the liquid molecules weakens, and the density of the coexisting vapor increases. The surface molecules are reduced by the attraction force of the molecules inside the liquid, and the gravity of gas molecules increases, and the surface tension decreases. As the temperature of the printing shop increases, or the machine heats up during the printing process, the temperature of the ink and fountain solution will increase, causing the surface tension of the ink and the fountain solution and the interfacial tension between them to decrease.

3 A solvent dissolves in other substances and the surface tension changes. If you add a small amount of surfactant in pure water, the surface tension will drop sharply.

70. What is the approximate surface tension of the ink and fountain solution?

The surface tension of the ink is generally 0.03 to 0.036 N/m, and the surface tension of the fountain solution is approximately 0.04 to 0.07 N/m. The surface tension of the fountain solution is due to the variety and concentration of various additives added in the fountain solution. Sizes also vary.

(Qufu Normal University, Yu Tianjian, Tian Peijuan)