Smoothness: It refers to the degree of surface roughness of the paper, expressed in seconds. The detection principle is: the time it takes for a certain volume of air to pass through the gap between the surface of the glass plate and the surface of the sample under a certain degree of vacuum and pressure. The smoother the paper surface, the slower the speed at which the air passes, and vice versa, the faster the air passes through. Printing requires moderate smoothness, high smoothness, and fine dot reproduction. However, full-printing should be done to prevent the back side from becoming dirty. If the smoothness of the paper is low, the required printing pressure is large and the ink consumption is also large.
Tear: It refers to the force required to tear a pre-notched specimen to a certain length, expressed in kilotons (tons). The degree of paper breakage is the ability of paper and paperboard to resist tearing. There is a certain relationship with the degree of folding of the paper. The degree of tearing also depends on the fiber length and its internal tissue direction and the strength of the fiber itself.
Degree of dust: It refers to the impurity spots on the paper, and there is a clear difference between the color and the paper color. The degree of dust is an index for measuring the amount of paper surface impurities, and is expressed as the number of dust areas within a certain range on a paper surface per square meter area. The degree of paper dust is high, and the ink and the dot reproduction effect of the printed product are poor. Dirty spots affect the appearance of the product.
Ink absorption: It is the ability of the paper to absorb ink. Paper with good smoothness and sizing degree has weak ink absorption, and the ink layer dries slowly, and it is easy to stick dirty prints. On the contrary, ink absorption is strong and the printed products are easy to dry.
Air permeability: In general, the thinner the paper, the lower the tightness, the greater the air permeability. The unit of air permeability is ml / min (milliliters per minute) or s / 100 ml (seconds / 100 ml), which means the amount of air that passes through the paper in one minute or the time required to permeate 100 ml of air. Paper with high air permeability is prone to attract double paper during the printing process.
Whiteness: It refers to the brightness of the paper. If the paper reflects all the light, it can be seen by the naked eye as white. To determine the whiteness of paper, the whiteness of magnesia is usually defined as 100 % as the standard. The paper is treated with blue light, and the whiteness of the small reflectance is poor. Optical whiteness meter can also be used to measure whiteness. The unit of whiteness is 11 %. Paper with high whiteness appears dark in printing ink and is prone to print-through phenomena.
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