Paper and printing suitability and related processes

First, printing represents the process of copying many sheets from a printing plate on a printing press. The printing industry is the largest concentrated consumer of paper products.

In order to provide paper products suitable for printing, manufacturers must understand and value the printer's requirements for paper. The two most important factors must be regarded as "operational" (run
Ability) and printability.

1, runability (runability)

The operation of the paper web on the printing press can be considered as a combination of all properties. Poor operation can cause web breaks, stoppages, or a decrease in the speed of the printing press, which has a large impact on the economic benefits of printing. The operability of the paper is manifested in strength, uniformity, no paper disease, and good mechanical conditions of the paper roll or paper.
Poor runnability appears on the press as break or relaxation tension, resulting in inaccurate wrinkling and overprinting. For newsprint, when the moisture content is high, its operability will be improved.

2, printability (printability)

Printability can also be referred to as print quality, but it is the effect of paper on the exact reproduction of the print. Paper properties: Whiteness, ink absorption, water opacity, color, gloss, smoothness, air permeability and degree of sizing are all important for printing. However, different printing methods require different papers. In general, coated paper is better than uncoated paper because of its smoothness, whiteness, gloss, and other properties. Therefore, it has a good appearance after printing.

Second, commercial printing has four main methods, which are classified as follows:

1. Letterpress (Letter)

The printing on raised surfaces, also known as relief printing, involves the use of rotary presses, including the printing of newspapers and magazines, as well as advertising leaflets. Intensity and ink strength are high. No paper breakage, wrinkling, or other problems that cause the printer to shut down are not allowed. At the same time, paper should not be allowed to lose hair, powder, blisters, soluble substances and Friction material.

2. Lithograph printing on a flat surface, also known as lithography (Plano
Graphic). Most of the lithographic methods are printed and printed on the plate to a blanket cylinder and then transferred to the substrate. This type of printing can also be referred to as Offset, commonly known as offset printing. Because the ink used for lithography is quite viscous, when the paper is peeled from the blanket, there is a large pulling force on the surface of the paper and a peeling force is generated (Picking)

Therefore, the paper used for this type of printing must be clean, free of paper, and strong in surface strength. At the same time, this printing method can easily damage the coating layer of the coated paper, and does not require a high degree of smoothness on the surface of the paper. The paper can also print good results.

3, Gravure (Gravure) to send ink to the substrate on the concave surface, also known as Intaglio. Gravureplate's remarkable feature is that the ink is directly applied to the substrate by the concave portion of the printing plate. The surface of the printing plate is flat, and only the graphic portion is concave. This printing method requires a relatively high level of paper smoothness. This type of printing is commonly used in cigarette pack printing.

4. Screen printing This printing method is mainly used for the production of artworks. The amount of paper used is negligible. Therefore, it is not discussed here.

Third, the printability of paper


In order to obtain prints with excellent print quality, paper and ink must be suitable materials. In other words, the requirements of the paper must be easy to print, in addition to the ink color is bright, strong coloring, but also must have good and proper permeability, volatility and the ability to conjunctiva. In addition, the rubber rollers, blankets, plates used in printing, and the conditions in the printing shop and the operation of the printing process must also be compatible with the need to print excellent works.

The printability of paper means that the paper can adapt to the requirements of the ink, printing plate, and printing conditions to ensure the smooth operation of the print job and obtain the necessary conditions for excellent prints. The printability of the paper is not a fixed property, but a performance that is compatible with different printing conditions and different print characteristics. (For reasons of space, we will briefly introduce some of the more important paper properties):

1. Brightness: In order to draw reader's attention to the strong printing contrast, you can use high-white paper, while low-white paper is more suitable for reading, books that are not easy to make your eyes tired. In Europe and the United States, books printed on low-white paper are very popular, and children's books in our country are moving closer to this aspect.

2, Color Colour: For different uses of paper, there are different requirements on the color, for industrial printing, except for special purposes, generally used are white paper.

3, gloss Gloss: Gloss changes will affect the color printing of color uniformity and print after print gloss. Uneven glossiness of the paper can cause prints to have different glosses, resulting in poor uniformity in reflection of the visual effects of the image. Too low gloss will result in prints with low gloss, poor color reproduction and dullness. The gloss is too high to affect the ink penetration, resulting in different drying speeds and back-printing problems (and back blemishes).

4, opacity Opacity: Grams weighing less than 105 grams of paper on the opacity is relatively high. If the opacity is too low, the image of the printed product may be easily printed. When the two sides are printed, the front and back images and characters may interfere with each other, affecting the visual effect. In particular, color printing may cause color cast, which may make color adjustment difficult.

5, ink absorption: ink absorption directly affects the quality of printed products, is one of the important properties of paper. For the same manufacturer, the absorbability of each batch of paper products must be uniform, and the same brand of paper products must also be consistent. Absorption of the ink is too small to cause printing dot enlargement, prone to print hair, back stains and long drying time; ink absorption is too high, will result in print penetration, ink pulverization, color change and deep image, clear Differences and other issues.

6. Surface strength: The higher the surface strength, the better. It is very important for offset printing. It includes the strength of IGT and the strength of wax extraction. If the surface strength is too low, the paint or fibers on the surface of the paper will be pulled up during printing. The surface of the print will cause spots and pits, foreign bodies on the surface of the blanket, and foreign matter in the ink fountain. In severe cases, the plate will wear. Due to the low surface strength caused by the waste and paper dust, cut paper powder, dust caused by the appearance of waste products have similarities, the difference in appearance is an important basis for the former can be found in the original point on the print, and the original point Concave, and the latter does not.

7. Moisture: Moisture content affects the change in size and curling of the paper. High moisture content also increases the runnability of uncoated paper. If the moisture content of coated paper is too high, blistering may occur on commercial web machines. At the same time, the moisture content of the paper must match that of the printing environment, otherwise curling of the single copper, the scalloping and the tight edge of the double copper offset paper may occur, and the overprint and the tight edges may cause overprinting. And printing folds and other issues. Excessive moisture in the paper can cause difficulties in feeding the paper, printing wrinkles, back-printing, curling, long drying time, and reduced stiffness; problems such as low water content can cause curling, difficulty in feeding paper, printing wrinkles, static electricity, and paper strength. Reduced and easily retractable issues.

8, smoothness smoothness roughness roughness: smoothness and roughness are the metrics of the micro-planarity of the paper surface, but the focus and the detection method is different. In gravure printing, the smoothness of the paper is required to be relatively high. If the smoothness is not enough, some dots cannot be transferred to the surface of the paper, resulting in dew point.

9, oil immersion foaming temperature: For commercial rotary coated paper, this physical property is very important. If the oil immersion foaming temperature does not reach a certain requirement, it cannot be used for rotary printing. Otherwise, blistering may easily occur during printing, resulting in the rejection of a large amount of printed matter.