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Abstract: Paper is the most commonly used material for packaging printing. Its physical properties have a direct or indirect impact on the printing quality. Correct understanding and mastering the nature of paper, according to the characteristics of the product, reasonable use of paper to improve the quality of printing products, will play a positive role in promoting. This paper to share the characteristics of the paper related content, for friends reference:

Printing paper

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Any of various types of printed paper that has specific properties, depending on the printing method.

Paper specially used for printing. According to the use can be divided into: newsprint, books and periodicals paper, cover paper, securities paper and so on. According to the different printing methods can be divided into letterpress printing paper, gravure printing paper, offset printing paper and so on.

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1 Quantitative

It refers to the weight of paper per unit area, expressed by g/㎡, that is, the gram weight of 1 square meter paper. The quantitative level of paper determines the physical properties of paper, such as tensile strength, tearing degree, tightness, stiffness and thickness. This is also the main reason why the high-speed printing machine is not good for the quantitative paper below 35g/㎡, so that it is easy to appear abnormal paper, overprint is not allowed and other reasons. Therefore, according to the characteristics of the equipment, the quantitative arrangement of the printing parts corresponding to its performance can be produced, in order to better reduce consumption, improve the quality of products and the printing efficiency of the equipment.

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2 Thickness

Is the thickness of paper, the unit of measurement is usually expressed in μm or mm. Thickness and quantitative and compactness has a close relationship, in general, the paper thickness is large, its quantitative corresponding high, but the relationship between the two is not absolute. Some paper, though thin, equals or exceeds the thickness. This shows that the tightness of the paper fiber structure determines the quantity and thickness of the paper. From the point of view of printing and packaging quality, uniform thickness of paper is very important. Otherwise, it will affect the automatic renewal paper, printing pressure and ink quality. If you use different thickness of paper printed books, will make the finished book produced significant thickness difference.

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3 Tightness

It refers to the weight of paper per cubic centimeter, expressed in g/C㎡. The tightness of paper is calculated by the quantity and thickness according to the following formula: D=G/ D ×1000, where: G represents the quantity of paper; D is the thickness of the paper. Tightness is a measure of the density of the paper structure, if too tight, paper brittle crack, opacity and ink absorption will be significantly reduced, imprinting is not easy to dry, and easy to produce sticky dirty bottom phenomenon. Therefore, when printing paper with high tightness, attention should be paid to the reasonable control of the amount of ink coating, and the choice of dryness and the corresponding ink.

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4 Hardness

Is the performance of paper resistance to another object compression, but also the paper fiber tissue rough performance. The paper hardness is low, can obtain more clear mark. The letterpress printing process is generally more suitable for printing with paper with low hardness, so that the printing ink quality is good, and the printing plate resistance rate is also high.

 

5 Smoothness

Refers to the degree of paper surface bump, unit in seconds, measurable. The detection principle is: under a certain vacuum and pressure, a certain volume of air through the glass surface and the sample surface gap between the time taken. The smoother the paper is, the slower the air moves through it, and vice versa. Printing requires paper with moderate smoothness, high smoothness, small dot will faithfully reproduce, but the full print should pay attention to prevent the back sticky. If the paper smoothness is low, the required printing pressure is large, ink consumption is also large.

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6 Dust Degrees

Refers to the impurities on the surface of the paper spots, color and paper color there is an obvious difference. Dust degree is a measure of the impurities on paper, expressed by the number of dust areas in a certain range per square meter of paper area. Paper dust is high, printing ink, dot reproduction effect is poor, dirty spots affect the beauty of the product.

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7 Sizing Degree

Usually the paper surface of writing paper, coating paper and packaging paper is formed by sizing a protective layer with water resistance. How to apply sizing, commonly used duck pen dipped in special standard ink in a few seconds, draw a line on the paper, see the maximum width of its non-proliferation, impermeability, the unit is mm. Paper surface sizing is high, printing ink layer brightness is high, less ink consumption.

 

8 Absorbency

It is the ability of a paper to absorb ink. Smoothness, sizing good paper, ink absorption is weak, ink layer dry slow, and easy to stick dirty printing. On the contrary, ink absorption is strong, printing is easy to dry.

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9 Lateral

It refers to the paper fiber organization arrangement direction. In the process of making paper, the fiber runs along the longitudinal direction of the paper machine. It can be recognized by the sharp Angle of the net marks. Vertical to vertical is transverse. The deformation value of longitudinal paper grain printing is small. In the process of transverse paper grain printing, the variation of expansion is large, and the tensile strength and tear degree are poor.

 

10 Expansion Rate

It refers to the paper in the moisture absorption or moisture loss after the size of the variation. The softer the fiber tissue of the paper, the lower the tightness, the higher the expansion rate of the paper; Conversely, the lower the scaling rate. In addition, smoothness, sizing good paper, its expansion rate is small. Such as double-sided coated paper, glass card and A offset paper, etc.

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11 Porosity

In general, the thinner and less tight the paper, the more breathable it will be. The unit of breath ability is ml/min(milliliter per minute) or s/100ml(second /100ml), which refers to the amount of air passed through the paper in 1 minute or the time required to pass through 100ml of air. The paper with large air permeability is prone to double paper suction in the printing process.

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12 White Degree

It refers to the brightness of the paper, if all the light reflected from the paper, the naked eye can see that is white. Determination of the whiteness of paper, usually the whiteness of magnesium oxide is 100% as a standard, take the paper sample by blue light irradiation, the whiteness of small reflectivity is bad. Photoelectric whiteness meter can also be used to measure the whiteness. The units of whiteness are 11 percent. High whiteness paper, printing ink appears dark, and easy to produce through the phenomenon.

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13 Front and Back

In paper making, pulp is shaped by filtration and dehydration by adhering to a steel mesh. In this way, as the side of the net due to the loss of fine fibers and fillers with water, so leaving net marks, the paper surface is thicker. And the other side without the net is finer. Smooth, so that the paper forms a difference between the two sides, although the production of drying, pressure light, there are still differences between the two sides. The gloss of paper is different, which directly affects the absorption of ink and the quality of printing products. If the letterpress process uses paper printing with thick back side, the plate wear will be significantly increased. The front of the paper printing pressure is light, ink consumption is less.

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Post time: Jul-07-2021