1,000 offset printing

248. What is paper elasticity? What does it mean for offset printing?
A: Usually the paper has both elasticity and plasticity. Elasto-plasticity of paper refers to the elastic and plastic deformation of the paper when it is subjected to a certain external force. During the offset printing process, a certain pressure must be applied, and the graphic ink film on the printing plate can be transferred to the paper indirectly through the blanket. Paper will produce compression deformation at the moment of pressure action. When the force disappears, it can be restored to the original state of deformation, that is, elastic deformation; and the deformation still exists after the pressure disappears, that is, plastic deformation.
In multi-color, high-speed offset printing, the elastic deformation of the paper will continue to occur repeatedly, so the elasto-plasticity of the paper is very important for offset printing and the clarity of the graphic imprinting. Fullness and so on are related to the elasticity of the paper.
249. What is the surface strength of the paper? What is the reason for falling powder?
A: The paper surface strength refers to the fibers in the paper. The binding fastness between the filler and the compound or between the paint layer and the base paper.
In offset printing, there is a more complex mechanical force relationship between paper and ink. In order to ensure that the ink is transferred to the paper normally and the structure of the printed sheet is not damaged when it is peeled off, the following conditions should be satisfied.
The binding force between the fiber, the filler and the rubber (or coating layer) in the paper ≥ the adhesion of the ink to the paper + the peeling tension + the adhesiveness of the blanket. Otherwise, paper lint and powder fallout will occur during the printing process.
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 condition cannot be satisfied during the offset printing process, any one of the right sides of the inequality will cause the paper to have a different degree of powder loss. Hair loss, peeling, or delamination. 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 Adjust the radius of the impression cylinder and the printing speed to reduce the peeling 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 and what does it mean for offset printing?
Answer: Paper sucks ink, 1 wow 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.
Offset ink absorption capacity of offset printing paper is too large or too small. The phenomenon of chalking, dinging, etc., so the ink absorption of offset printing paper is critical for the offset printing process.
252. What is paper smoothness and 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 paper gloss and 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 paper opacity and 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 pH of paper and what is its effect on 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. Alkaline paper, wow, for the ink has a certain reminder 1000, but also affect the amount of fountain solution control, too high will also promote the emulsification of ink and cause printing failures.
256. What are the common offset printing papers, and what are their characteristics and printability?
A: Common offset printing papers include offset newsprint, offset book and offset printing paper. Writing paper. Book paper, offset printing paper, white paperboard, etc.
1 Offset newsprint. Paper soft, uniform organization, soft colors, quantitative. Uniform moisture, good stiffness, opacity, moderate smoothness, tensile strength, and high 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. But when the roll is not tight. It is easy to wrinkle. Misregistration is not allowed.
2 offset printing paper. The paper is soft, uniform in texture, uniform in hue, weight 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 tissue is uniform and the texture is tight and white. Smooth, strong water resistance, small flexibility. High opacity, high surface strength, moderate ink absorption.
4 writing paper. Uniform fibrous tissue. Close, smooth, with 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 and tight. Smooth, consistent color, good water resistance, folding 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. close. Smooth, low elasticity, good resistance to wet friction, moderate ink absorption, 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.