How paper performance affects print quality

At present, the inspection of imported paper and board is based on the ZBY32033-90 People's Republic of China industry standard "Inspection Rules for Imported Paper and Paperboard". The author hereby discusses and analyzes the suitability of imported paper and paperboard in printing, and is now described as follows.

From the perspective of physical performance

Quantitative: It refers to the mass per square meter of paper or paper, commonly known as grammage, and its unit is g/m2. If the basis weight is low, problems such as print-through may occur during printing. When the same batch of paper is not evenly distributed, the printed matter is prone to misprints and shades.

Thickness: It refers to the distance from the surface to the other side of the paper or board measured under a constant grammage and is expressed in mm. If the thickness is too small, printing problems such as print-through may occur. The uneven thickness of the same paper will lead to deep paper-thickness prints and shallow prints in thin places.

Tightness: refers to the mass of paper or board per cubic meter, expressed in g/m3, which is a measure of the density of paper structure. The tightness is too great, the paper is brittle and the ink absorption will be significantly reduced.

Smoothness: There are three methods for determining the smoothness of the Buick method, the roughness of the Bentzheim method, and the smoothness of the Smother method. To put it mildly, it is to assess the degree of surface roughness of the paper. If the smoothness is high, the printed product can be faithfully reproduced, especially the accurate reproduction of the small dots, the smoothness is low, the small dots will fall to the low depressions of the paper and cannot be printed, and the level of the prints will not be clear.

Hardness: It indicates the strength of the paper compressively concavity of another object, and also indicates the coarseness of fibers and other fibers in the paper. Low hardness, more suitable for printing, prints can be accurately reproduced.

Degree of dust: It is a measure of how much paper surface impurities. That is, on the surface of paper or paperboard, impurities such as black, yellow, or brown fiber bundles that are visible to the naked eye and are significantly different from the paper surface color. Dust is high, and many print spots are dirty, affecting the appearance.

Ink absorption: It is the ability of the paper to absorb ink. The ink absorption is strong, the printed matter is easy to dry, the ink-absorbing property is poor, the printed matter is slow to dry, and the printed product is prone to blemishes.

Analysis from the perspective of mechanical properties

Tensile strength: It refers to the maximum tension that a unit width paper or cardboard can withstand before breaking. It is expressed in KN/m. It is a measure of the resistance of a paper to its tensile strength, and it is also a very important index of a web. The tensile strength is low, and paper breaks and the like easily occur during printing.

Tear: This is the force required to continue tearing the cut paper or paperboard to a certain degree, expressed in m/N or g/f. It is the ability to assess the paper's resistance to shear. The tearing is small and the paper is easily damaged during printing.

Folding resistance: refers to the ability of paper or paperboard to withstand the reciprocal folding at an angle of 135 degrees under a certain tension. It is expressed as the number of double folds. It is the ability to express the paper's ability to resist rubbing. With low folding resistance, the paper cannot withstand folding and is easily broken.

Stiffness: It refers to the bending distance of a 38mm wide paperboard to a 15 degree angle under a certain condition, expressed in g?cm, indicating the paper's resistance to bending.

Analysis from the perspective of optical performance

Whiteness: Refers to the reflectance factor of a white or near-white paper or paperboard surface with a dominant wavelength of 457mm blue light. Simply put, it means the degree of innocence of the paper. The whiteness is too low, and the prints appear gray and incompetent; the whiteness is too high, making people easily tired when reading.

Opacity: refers to the ratio of the reflectance of green light when a single sample is lined with a fully-absorbed black mat to the corresponding reflectance of several layers of samples that are completely opaque, ie, the ability of the paper to resist light transmission. Opacity is low and prints are easily printed.

Glossiness: It can reflect the quality of the paper light color and print color, and it can also reflect the image quality of the paper surface. Gloss prints should be shiny, but not as high gloss as possible. Text-based, it is appropriate to use low gloss paper to prevent eye fatigue and lower costs, and the main picture-based, should choose a higher gloss paper, so that the prints are bright and pleasing.

From the perspective of chemical properties

The moisture content of the paper: expressed as a percentage of the paper's weight in water and paper. The moisture of the printing paper is generally about 4 to 8%, the moisture content in the paper is too low, the paper is brittle, and static electricity is easily generated during printing; moisture in the paper is too high, and printing is difficult to dry.

Paper ash content: It is used to measure the amount of inorganic matter in paper. With more ash content, the printing rate of the printing plate will be reduced; conversely, the plate printing rate will increase.

The degree of sizing of the paper: There are two methods for detecting the degree of sizing by the cobb sizing method and the liquid infiltration method. It indicates the degree of sizing of the paper, the degree of sizing is too high, the print is dried slowly, and the sizing degree If it is too low, problems such as print-through may occur during printing.

Paper acidity and pH: In general, the paper's PH value is neutral, but in fact, offset paper, offset paper and other non-coated printing paper PH value between 4.5 to 7.0, weak Alkali; while the pH value of coated paper is mostly between 7 and 9 and it is weakly acidic. However, the pH of the coated or non-coated paper decreases with the increase of storage time. When the PH value of the paper is low, the drying time of the printed matter is longer; otherwise, the drying time of the printed matter is short.

Durability of paper: It is the service life of printed matter. The durability of the paper is poor and the print preservation time is short. (Wang Zhixing)

Reproduced from: Shanghai Packaging