1,000 Offset Printing (214-226)

214. What are the basic requirements for chemical properties of offset printing paper?
A: During the offset printing process, it is required that the paper does not chemically react with the wetting fluid and graphic ink film transferred from the printing plate to the surface of the blanket, in order to ensure the normal transfer of printing images, and Fix, dry, and color on paper.

215. What is the physical and mechanical properties of paper? What are the technical indicators?
Answer: The physical properties of paper are the main basis for determining the quality of paper and the grade of grade. The mechanical properties of paper refer to the resistance of paper to external forces under certain conditions. The physical and mechanical properties of paper are specifically expressed in eight technical indicators such as paper skewness, thickness, tightness, transparency, dust degree, tensile strength, folding resistance, and tearing degree.

216. What is paper skewness? What does it mean for offset printing?
A: Skewness is the maximum deviation of the long edge (or short edge) of the flat sheet from the long edge (or short edge) of the corresponding rectangle. If the paper is skewed, the paper size is locally insufficient or excessive. At this time, the four edges of the base paper must be trimmed before printing to ensure the offset accuracy of offset printing. However, if the paper size deviation is seriously insufficient, it cannot be applied.

217. What is the thickness of paper? What does it mean for offset printing?
A: The paper thickness refers to the thickness of the paper. The thickness of the paper should be uniform, if the paper thickness is not uniform, its printing effect will inevitably produce a significant difference.

218. What is the paper tightness? What does it mean for offset printing?
A: The paper tightness refers to the degree of looseness or tightness of the paper structure, which is also called the specific gravity volume weight. That is, the heavier the weight of the same volume of paper is, the tighter the structure of the paper is, and the looser it is. The tightness of paper is closely related to the ink absorption and smoothness of the paper. In general, the ink absorption of the paper decreases with the increase of the paper tightness, and the smoothness of the paper increases with the increase of the paper tightness.

219. What is the transparency of paper? What does it mean for offset printing?
A: Paper transparency refers to the degree of transparency of the paper when light passes through the paper. All kinds of printing paper should have opacity, that is, one side of the printed imprint can not be printed on the other side, otherwise it will affect the clarity of the other side.

220. What is the paper dust degree? What does it mean for offset printing?
A: The degree of paper dust refers to the presence of black and non-black spots on the surface of the paper that are inconsistent with the paper color, which is different from the large and relatively dense dust that is indicated in the appearance paper disease. The degree of dust on the paper is represented by the total number of dust in an area of ​​1 square meter. In offset printing, the requirements for the degree of paper dust are mainly determined by the requirements of the printed matter, and prints such as portraits and maps do not allow the paper to have a large degree of dust.

221. What is the tensile strength of paper? What does it mean for offset printing?
A: The paper tensile strength refers to the maximum tension that the paper can withstand. The corresponding value is called tensile strength. In order to avoid the influence of the paper quantification, the tensile strength of the paper is generally expressed by the length of the paper (ie, the length of the paper when it breaks due to its own weight), the surface strength of the paper, the structure of the paper fibers, and the fibers. The strength of the bond, as well as the moisture content of the paper.
Web offset presses have higher requirements on the tensile strength of webs. The webs are under tension during continuous operation and are subjected to a certain tension in the longitudinal direction. When the tensile strength is lower than the tension of the web, When the tape breaks, it will appear. For flat paper, offset printing generally provides a certain average split length and the ratio of longitudinal and transverse tension.

222. What is the paper folding degree? What does it mean for offset printing?
A: The paper folding resistance refers to the number of times that the paper can withstand 180° reciprocating folding under a certain tension, and is used to express the ability of the paper to resist folding. In general, the folding-resistance requirement for offset printing paper is related to the use of the printed product. In the process of use, maps, traffic maps, cover sheets, and wrapping papers that need to be folded repeatedly require higher endurance, and offset book and periodical papers also need to have a certain ability to resist folding.

223. What is paper tear? What does it mean for offset printing?
A: The paper tearing degree refers to the force required when a previously cut paper sample is ruptured to a certain length. It indicates the external force required to tear the paper, which is also known as tearing force, and the arrangement of fibers and fibers of the paper. There is a lot of connection between them. In general, paper tears more easily in the longitudinal direction than in the transverse direction. For webs, tearing is an important strength indicator. In a variety of printing operations, such as mechanical folding operations, there are certain requirements for the tear of the paper.

224. What is the appearance of paper?
A: The appearance of paper is the quality of the appearance of the paper that can pass the sensory test. The actual appearance of paper for offset printing is the uniformity, cleanliness, and flatness.

225. What is the paper uniformity?
A: Paper uniformity refers to the uniform nature of the distribution of fibers in the paper and the thickness of the cross-web. When the light is checked on the light, if there are clear or dark transparent or transparent spots on the surface of the paper, it is indicated that the thickness of the paper is uneven, the fibers are unevenly interwoven, and the structural condition is poor.

226. What is the cleanliness of paper?
A: Paper cleanliness refers to the cleanliness of the paper surface. When you look at or look at the paper obliquely, if you find that the surface of the paper has bright and dark spots, reflective spots, or dust that is different from the paper, it indicates that the surface of the paper is unclean.

Excerpt from---<Printing Technology>