Offset Printing 1000 Questions (250-260)

250. How to avoid paper lint, powder off?

A: Generally speaking, the paper binding force is a constant, but due to improper storage and storage, it will be reduced due to changes in water content. Therefore, if the above conditions cannot be satisfied during the offset printing process, any one of the right side of the inequality will cause the paper to have different degrees of powder-off, lint-free, stripping, or peeling. Therefore, according to the actual situation of offset printing, make appropriate adjustments to ensure the quality of printed products. Specific adjustment method:
1 Reduce the adhesion of the ink to the paper surface. Under the premise of ensuring the ink color saturation, the viscosity of the ink is reduced and the thickness of the ink layer is reduced.
2 According to the size of the impression cylinder radius and printing speed to adjust to reduce the stripping tension. When the printing speed is constant, the smaller the radius of the impression cylinder is, the larger the peeling tension is, and vice versa; when the radius of the impression cylinder is constant, the higher the printing speed is, the larger the peeling tension is, and vice versa.
3 reduce the stickiness of the blanket. Under normal circumstances, generally do not need to consider the viscosity of the blanket, but if the blanket appears improper maintenance or desulfurization and sticky situation, it should consider reducing the viscosity of the blanket.
In actual offset printing, the method of reducing the printing speed or the viscosity of the ink is usually used to make up for the lack of paper strength, and to reduce the loss of paper and powder.

251. What is paper absorption? What does it mean for offset printing?

A: Paper absorbency refers to the paper's ability to absorb ink. In offset printing, the process of ink-absorption of paper is accomplished under the combined effect of printing pressure, inter-fiber voids, and capillary tubes. The size of the ink-absorbing properties of offset printing paper is mainly determined by the tightness and firmness of the fibrous tissue structure of the paper and the strength of the ink penetrating the paper. In general, loose paper structure, the fiber gap is large, the capillary effect is strong, the ability to absorb ink is strong; paper structure is tight, the fiber gap is small, the capillary effect is weak, the ink absorption ability is weak.
If the ink absorption capacity of the offset printing paper is too large or too small, it will cause the imprint of the print to be dull, or the phenomena of overprinting, chalking and dripping will occur. Therefore, the ink absorption of the offset printing paper is crucial to the offset printing process.

252. What is the paper smoothness? What does it mean for offset printing?

A: Paper smoothness refers to the smoothness or roughness of the surface of the paper, which depends mainly on the structure of the paper itself, the evenness of the tissue, and the compressibility. Paper smoothness plays a decisive role in the uniformity of ink transfer and penetration. Paper with high smoothness can be uniformly inked, and it is easy to obtain a clear graphic effect. If not, it is easy to cause the graphic imprinting to be unclear.
In the actual offset printing, when the paper smoothness can not meet the printing requirements, it is often adjusted by adjusting printing pressure or ink viscosity.

253. What is the paper gloss? What is the difference between it and paper smoothness?

A: Paper gloss refers to the ability of the paper surface to reflect light, which is used to evaluate paper properties. Paper with high smoothness has strong gloss, but glossy paper does not necessarily have high smoothness.

254. What is the paper opacity? What does it mean for offset printing?

A: The paper opacity refers to the degree of opacity of the paper when the incident light is irradiated, which is used to describe the light blocking ability of the printing paper. Paper opacity describes the imprinting properties of the paper during the printing process. If the paper has low opacity, different degrees of print-through will occur during printing, affecting the clarity of the text. Therefore, for offset printing paper, especially for low-volume double-sided printing paper, the higher the paper opacity, the better.

255. What is the paper pH? How does it affect the drying of printing inks?

A: Paper pH refers to the degree of acidity or alkalinity of the base paper and coating layer. The acidity of the paper inhibits the curing of the ink film and affects the drying speed of the ink film on the surface. Offset papers are mostly weakly acidic because the offset fountain solution is acidic. If the paper is also acidic, it will significantly affect the drying of the blotting ink film. The paper's alkalinity has a certain squeezing effect on the ink, and at the same time it also affects the dosage control of the fountain solution. If it is too high, it will promote the emulsification of the ink and cause printing failure.

256. What are the common offset papers? What are its characteristics and printability?

Answer: Common offset printing papers include offset newsprint, offset book, offset printing, writing paper, cover paper, offset printing coating paper, and white paperboard.
1 Offset newsprint. The paper is soft, uniform in texture, soft in color, uniform in quantity and moisture, good in stiffness and opacity, moderate in smoothness, high in tensile strength and high in tear. It can be used with web offset presses and resin type non-heat-set web offset printing inks with a printing speed of 10,000 prints/hour or more. However, when the roll is not tight, it is easy to produce wrinkles, color misregistration and other faults.
2 offset printing paper. The paper is soft, uniform in texture, uniform in hue, quantity, and moisture, good in opacity, high in smoothness, high in tensile strength, and high in tear. It can be used with web offset printing machines with a printing speed of 10,000 or more/hr and resin type non-heat-set web offset printing inks, or high-speed multi-color single-sheet offset printing machines and ordinary resin type offset printing inks.
3 Offset printing paper. The fibrous structure is uniform, the texture is compact, white and smooth, the water resistance is strong, the stretchability is small, the opacity is large, the surface strength is high, and the ink absorption is moderate.
4 writing paper. The fibrous tissue is uniform, tight, smooth and has good water resistance. Compatible with monochrome or multicolor sheetfed offset and resin offset inks with print speeds up to 10,000 prints/hour.
5 book cover paper. The fibrous tissue is uniform, tight, smooth, consistent in color tone, and has good water resistance, folding resistance, and abrasion resistance. It can be matched with single-color or multi-color sheet-fed offset presses and resin-type offset printing inks with a printing speed of 10,000 or less/hr.
6 offset printing coating paper. The surface is white, tight, smooth, with low stretchability, good resistance to wet friction, moderate ink absorption, and high surface strength. It can be used with sheet-fed offset presses and resin-based light fast-drying offset printing inks with printing speeds up to 10,000 prints/hour.
7 white cardboard. The paper is tight, tough, uniform in thickness, white and smooth, with low stretchability, good water resistance, moderate ink absorption, and high surface strength. It can be used with single-color or two-color offset printing machines and resin-based bright fast-drying offset printing inks with a printing speed of 10,000 prints/hour.

257. What is offset printing plate?

A: Offset printing plate is a type of printing plate in which the graphic part and the blank part (non-graphic part) are almost on the same plane. Its use of oil-water incompatibility principle, graphic part of the oil-and water-repellent and adsorptive ink, blank part of the hydrophilic and oil-repellent and adsorption of water (fluid solution), when the offset printing plate is printed on the first water after the ink, through selectively Adsorption finishes printing. At present, the most commonly used offset printing plate is the PS plate.

258. What is the basic structure of offset printing plate?

A: The offset printing plate consists of a base plate and a printing section. Plate base is the support of the printing part, generally consists of materials with certain mechanical strength and chemical stability; the printing part is the working surface in the printing process, there are two parts of the graphic part and the blank part, it is through the coating of the photosensitive liquid. , After exposure, development, fixing, processing and other processing after processing.

259. What are the classifications of offset printing plates?

answer:
1 According to the different structure of the printing plate, the offset printing plate is divided into a plano-convex type and a concave type;
2 According to the different materials of the base plate, offset printing plates include lithographs, metal plates, glass plates (plates) and paper base plates;
3 According to the structural pattern of the base material, the offset printing plate is divided into a single flat printing plate and a roller printing plate;
4 According to the roughening state of the surface of the substrate, the offset printing plate is divided into ordinary sand and sandless printing plates;
5 According to the different graphic basis, the offset printing plate has a protein plate, photosensitive resin plate, multi-layer metal plate, etc.;
6 According to the blank basis, the offset printing plate is divided into ordinary type and anhydrous type;
7 According to different uses, offset printing plates have proofing plates, printing plates, etc.

260. What is the PS version?

A: PS version (Presensitized Offset Plates) is the abbreviation of pre-coated photosensitive resin plate. It is a kind of offset printing plate formed by pre-coating the photosensitive liquid on the surface of the plate base. Currently widely used in China is aluminum-based positive PS version.

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