Terms in offset printing (top)

The specific meaning of some terms in packaging offset printing 175. What is oxidative polymerization drying?
The dry vegetable oil molecules in the ink binder contain unsaturated double bonds, and they react with oxygen in the air to cause oxidative polymerization reactions. Many dry three-dimensionally distributed plant oil molecules turn into a three-dimensional network structure. The huge molecules lose their fluidity and dry on the surface of the substrate. This dry form is called oxidative polymerization drying.
176. What is a driers?
Dry vegetable oils are mixed with trace amounts of organic antioxidants and affect the absorption of oxygen. As a result, the hydrogenation polymerization reaction rate is slow and cannot meet the needs of normal printing. In order to speed up the drying of ink, driers must be added. The driers on the one hand react with the antioxidants to form precipitates, which exclude the influence of antioxidants; on the other hand, they also directly promote the polymerization of dry vegetable oil molecules. Therefore, the drying speed can be greatly accelerated.
177. What are the commonly used driers? What are the characteristics of each?
The commonly used driers are white dry oil and red dry oil. White kerosene is a milky white paste fluid made of metal aluminum, manganese and cobalt. It is characterized by promoting the oxidation and polymerization of salty solid film on the ink layer from top to bottom, inside and outside, and is a commonly used driers in offset printing. Red dry oil is a purple-brown liquid fluid characterized by the surface oxidation of the main conjunctiva, gradually drying inwards, drying faster, but because of its own color, generally only put in magenta, black ink used.
178. Use driers should pay attention to what the problem?
1 Pressing is a powerful emulsifier, adding a certain amount of driers can accelerate the drying of the ink, but adding too much will cause serious emulsification of the ink, not only can not play a role in accelerating the drying, and even cause the ink roller to slip, difficult to transfer ink . In this case, only the original ink can be added to dilute the concentration of the driers or to switch directly to the new ink.
2 Excessive driers may cause ink crystallization. What is imprint crystallization? What harm does it have?
The blots on the paper are completely dried and solidified, and the surface is bright and smooth, with no fine irregularities and glassy shapes. The main hazards of crystallization and crystallization are that, if other colors need to be superimposed on this color, poor adhesion will occur. Nowadays, resin-based offset printing inks should not crystallize under normal use conditions. However, if excessive driers are added, this may occur.
180. What is osmotic drying?
After the ink is transferred to the paper, due to the effect of the printing pressure and the capillary adsorption of the paper fiber, some of the ink infiltrate into the paper, and the other part of the ink is fixed on the surface of the paper together with the pigment. This kind of drying method is called penetration. dry.
181. What is pass through?
When printing on thin, loose, uncoated paper, the ink may permeate through the paper and reach the back of the paper, causing smudges on the back, called through-print.
182. How to avoid printing?
Overprinting is caused by the excessive penetration of the binder in the ink. The methods to avoid it are:
1 The depth of penetration of the linking material is related to the size of the aperture of the paper woven tube. For printing thin non-coated paper, the paper should not be too loose.
2 Because the depth of penetration is inversely proportional to the square root of the viscosity of the ink, the viscosity of the ink should be controlled and the ink cannot be adjusted too thin.
3 The pressure permeation caused by the printing pressure is proportional to the square root of the pressure, so the pressure knife should not be too large.
183. What is imprinting powder?
When printing with coating paper C, the linking material in the ink penetrates too much into the paper, and an excessive amount of pigment particles remains on the surface of the printed matter to cause the imprinted powder to become powdery.
184. What are the factors that affect the imprinting powder?
The most important factors affecting chalking are the size of the capillary pore size of the paper and whether the ink pigment particle size distribution is reasonable. So choosing the right paper and ink is the key. In addition, pulverization is also related to the excessive penetration of the binder. To reduce excessive penetration of the binder, it is necessary to increase the viscosity of the ink and reduce the printing pressure.
185. What are the factors that affect the drying rate of blots?
The factors that affect the drying rate of the imprint are: ink, paper, ink layer thickness, wetting fluid, ambient temperature and humidity, and production process.
186. What are the influencing factors on the drying speed of the imprinting ink?
1 The composition and ratio of the binder. The different ingredients in the binder dry in different ways. Dry vegetable oils are dried by oxidative polymerization, and the drying rate is slow. Other ingredients are dried by infiltration and dry quickly. Therefore, if the amount of oil in the ink is large, the drying speed is slow. The dry vegetable oil contains many different components. The greater the degree of unsaturation of the oil, the faster the oxidative polymerization will dry.
2 Ingredients of pigments, some inorganic pigments are metal salts and oxides, generally have a drying effect on the drying value of the material oil, drying speed. Organic pigments for the production of colored inks do not have a squeezing effect, and they sometimes inhibit hydrogenation drying and slow drying.
2 ink viscosity. The ink has a large viscosity, shortens the time for thickening of the ink, accelerates the oxidation polymerization, and is advantageous for drying. (To be continued)