Printability of paper and its effect on print quality

There are many factors that affect the printability of paper, including the following:

Silk paper

It refers to the direction in which most of the fibers are arranged in the paper. Generally, the direction of the fibers is perpendicular to the long side of the plate.

Paper is a substance that is very sensitive to moisture. Due to changes in temperature and humidity, the retractability of paper in different directions varies greatly. Therefore, in the printing or post-printing process, the influence of the paper web on the quality of the printed matter should be considered. In the book binding, the book block is best to choose straight-lined paper, that is, the paper silk is parallel to the back of the book, and the silk cover of the soft-cover paper is perpendicular to the back of the book to ensure the flatness of the book.

Paper tensile strength

Refers to the maximum tension that paper or paper can withstand, expressed as absolute tension or broken length. Roll paper In high-speed rotary printing, if the tensile strength of the paper is lower than the longitudinal tension applied to the paper, a paper breakage failure occurs. The faster the printing speed, the greater the tensile strength of the paper used for printing should be.

Surface strength of paper

Refers to the paper in the printing process, by the ink stripping tension effect, the resistance to off powder, lint, blistering and tearing performance, with the paper's pull speed to express, the unit is m / s. When high-speed printing machine is printing or printing with high-viscosity ink, paper with high surface strength should be selected. Otherwise, the problems of paper lint and powder falling are easy to occur. The fine fibers, fillers and coating particles that are detached from the paper surface are easy to be used. The web of images on the plate clogs or accumulates on the blanket, causing a "stencil" and degrading the plate's resistance to printing.

Water content of paper

Refers to the ratio of the reduced mass to the original paper quality when the sample is dried to constant weight at the specified drying temperature, expressed as a percentage. The water content of general paper is between 6% and 8%, and the water content is too low. Electrostatic adsorption may occur during the printing process, resulting in difficulties in paper feeding and blemishes on the back of printed products. The ideal moisture content of paper is 5.5%~6.0%. The printing shop temperature should be controlled at 18~24°C, and the relative humidity should be controlled between 60%~65%.

Paper smoothness

Refers to the degree of unevenness of the paper surface, using a Baker smoothness meter for testing. The longer the volume of air that passes through the paper, the higher the smoothness. Uses smoother paper for printing. The ink on the printing plate or blanket can come into contact with it with a large area, which results in high smoothness on the paper. This enables the screen to be clear, rich in tone, and colorful. .

Ink absorption of paper

It refers to the paper's ability to absorb ink, or the penetrability of ink on paper. The strength of paper absorbability mainly depends on the type and ratio of paper fibers and the gap between fibers. In addition, there is a close relationship between the size of the printing pressure during the printing process, the length of the imprinting time, and the adhesiveness and permeability of the ink. Paper absorbing ink quickly, will make the print matt, imprinted powder, printing dots increase, but also lead to ink penetration into the back of the paper, resulting in through-print failure. Absorption of ink on the paper is too fast, which slows down the drying of the ink, which can easily cause the back of the printed material to become dirty, and in severe cases, the adhesion of the printed sheet occurs. It can be seen that the ink absorption of paper is either too fast or too slow, which is not good for printing. Therefore, to obtain high-quality prints with vivid colors and realistic images, only the use of paper with moderate ink absorbability can meet the requirements.

Acidity of paper

The acidity and alkalinity of paper has a great deal to do with lithography. Lithography offset paper commonly used acidic. The acidity and alkalinity of the paper has a great influence on the drying performance of the blot. The ink dries slowly on acidic paper and dries quickly on alkaline paper.