Influence of the performance of the hottest paper

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The influence of paper performance on the quality of offset printing products

paper is an important basic raw material used in the printing industry, and the quality of paper directly affects the quality of printing products. Due to the different pulp raw materials and papermaking processes, the inherent properties of the produced paper are significantly different. Even if the same paper is printed in different ways, its printability is obviously different. Most of the paper used in offset printing is coated paper and offset paper. The smoothness and smoothness of coated paper can raise the soil pH value to close to neutral, and the whiteness is higher than offset paper, but the elasticity is poor. In the printing process, the faults caused by the paper performance are more common: inaccurate overprint caused by poor dimensional stability of the paper, powder and hair loss caused by low surface strength of the paper, and speckle or whitening caused by poor smoothness and uneven thickness of the paper

I. paper dimensional stability

paper will deform to a certain extent with the change of ambient temperature and humidity in the process of production, transportation and storage, forming phenomena such as "lotus leaf edge" or "tight edge". These faults can generally be effectively eliminated by hanging and drying before printing on the machine. In the process of printing, the most common fault in offset printing is the inaccurate overprint caused by the elongation and deformation of the paper. For offset printing, due to the existence of fountain solution, the paper will absorb some water every time it is printed, and the paper will be wetted to produce a certain amount of elongation deformation. This amount of deformation is determined by the papermaking raw materials and processes, and is mainly related to the fiber content, fiber length and adhesion of the paper itself, and the degree of sizing. These factors determine the tightness, moisture absorption and compression characteristics of the paper. Generally, the size of the paper changes within the allowable overprint error. For paper with large fiber content, short fiber and unsatisfactory sizing degree, its hygroscopicity is large; If the structure is loose and the compactness is not high, the compression characteristics of the paper will show approximate fluid performance under pressure. The above paper is easy to produce when the moisture content in the layout is too large or the embossing force is large, the teeth are worn and loosened, and the holding force is uneven, which makes the variety quality of large and medium-sized enterprises in our city reach the international and domestic advanced level, causing serious deformation, so that the next color overprint is not available and waste products are produced. The performance of the paper is determined by the production of the paper, so in printing, we mainly control the moisture of the layout and adjust the mechanical pressure to reduce or report the deformation of the paper and improve the printability of the paper. 4. Press the reset button to clear the force value on the display screen. The moisture control of the layout is generally based on the gray layout with a slight reflection. Try to use the minimum amount of water to maintain the ink balance. If the moisture is too small, it is very easy to paste the version. Monochrome offset press should pay particular attention to moisture control, and control the paper deformation to a minimum, so as to facilitate the overprint accuracy of the next color. We once used a kind of 80g coated paper imported from the United States to print trademarks. When printing eight plates on a split monochrome machine, there was extremely serious lateral elongation deformation, and the next color could not be covered. The paper has a good visual inspection and hand feel. It is estimated that wood is used as pulp, and the high beating degree makes the fiber. It is hoped that the project team will broom in the subsequent research and development, with a large content of short and fine fibers, so that the paper has a strong moisture absorption, resulting in water absorption and elongation of the paper. After using four-color machine to print in two versions, there is still a certain chromatic error. This paper with serious deformation cannot be used for chromatic printing of fine dots. As for the elongation deformation in the printing direction caused by poor compression characteristics of the paper, uneven tightness and weak adhesion between fibers, the deformation can be effectively reduced by reducing the printing pressure and adjusting the holding force of the teeth

II. Surface strength

the surface strength of paper refers to the bonding strength between fiber, filler and sizing material, which reflects the ability of paper to resist powder and wool falling. It is determined by papermaking raw materials and processes, and is also related to the selection of filler sizing material and the degree of calendering. For example, the pulp of broad-leaved trees contains ducts with weak adhesion to fibers, which often fall off during printing. As for the paper with inorganic filler, it is easy to lose powder because the filler itself has no binding force. When printing a certain drug label, we have seen this situation. When printing hundreds of sheets, the blanket is stained with a large amount of paper wool, which cannot be eliminated even with viscosity reducer. Rub the paper with your fingers, and your fingers will be stained with a layer of paper wool, indicating that the filler is not well combined with the paper. After that, the printing ink was used for lead printing to reduce the printing pressure, and the rubber blanket was washed after thousands of printing before the printing operation was completed. Coated paper is less prone to powder and hair loss, but if the coating layer is not well combined with the paper base, there may be large-area peeling due to high ink viscosity. The loss of paper powder and hair is also related to ink viscosity, printing pressure and printing speed. Generally, the method of reducing viscosity and pressure can effectively reduce the phenomenon of paper powder and wool

III. smoothness, thickness

smoothness is to evaluate the degree of concave convex on the surface of the paper, and thickness is to indicate the degree of thickness of the paper. Smoothness is closely related to the transferability of ink. Offset printing uses rubber blanket with good elasticity, which can make up for the concave and convex of the paper to a certain extent, and the ink can be transferred to the paper better. However, when printing high-end prints, in order not to damage the graphic level, coated paper with high smoothness is often used, because the paper with high smoothness has high saturation and good gloss. The image has high definition and good print quality. As for offset paper, the smoothness of offset paper produced by different manufacturers varies greatly. Some offset papers have poor smoothness and uneven thickness. When hard liners are used as liners, the ink transfer is not sufficient, resulting in different depths of the imprints, forming ugly spots, and even whitening in serious cases. As it is easy to have small dots and spots when printing offset paper, you should pay attention to spot checking the printing sheets frequently during printing. For prints that often have small dots and spots or different depths of impressions and uneven ink color, you should appropriately increase the printing pressure and increase the fluidity of the ink, but you should pay attention to controlling the amount of ink to avoid causing paste phenomenon

the performance of paper that affects the quality of printing products also includes the ink absorption, whiteness, sizing degree, acid-base and other properties of paper. The above mainly analyzes the common faults in actual operation. When purchasing and ordering paper, we must choose paper with good printability to reduce the impact of paper quality on the quality of prints

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