Infiltration of ink during printing (3)

The surface smoothness of non-coated paper is relatively low, and the surface smoothness of the paper is usually measured with a Baker smoothness meter. The resulting bake smoothness is obtained, and the becker smoothness of domestic newsprint is approximately 25 to 50 s. In order to increase the contact area between the paper and the ink, a higher pressure must be applied to the non-coating paper with a lower smoothness. Therefore, the ink permeation is performed under a high printing pressure, and the ink penetration time is The time during which the printing pressure is applied, ie the time the paper passes through the embossing area. Such as. If the permeation time of the fruit ink is constant, the greater the printing pressure, the faster the ink permeation speed and the greater the penetration depth. Therefore, the printing pressure measured at a fixed penetration time can be used to characterize the penetration of non-coated paper under high printing pressure.

In this way, the penetration is due to the penetration of the ink during the printing process, so it is called the printing penetration of the ink. The printing penetration of the ink is represented by the P' value, and the P' value is measured on the printability tester. Fixed imprinting (ie, printing penetration) time, change the size of the printing pressure, so that a volume of 0.006cm3, a viscosity of 0.0203Pa · s of a dibutyl phthalate dyeing liquid scooped into an oil mark on the paper surface, If the length L of the oil mark is measured, the P' value can be expressed as:

The unit of L in the formula is mm, and the unit of P' is m-1. The greater the printing pressure, the more the ink penetrates, and the shorter the length of the formed oil trace, the larger the P′ value; conversely, the lower the printing pressure is, the less the ink penetrates, and the longer the ink length is formed, the smaller the P′ value. Therefore, the P' value can be used to indicate the printing penetration of the ink. The print penetration values ​​listed in Table 7-5 are measured on the AIC2-5 printability tester at a printing speed of 0.2 m/s with three different printing pressures, as described above. Paper has different Baker smoothness.

The experimental data listed in Table 7-5 indicate that the printing penetration of the ink of the same non-coated paper increases with the increase of the printing pressure; under the same printing pressure, the penetration of ink increases with the increase of the unevenness of the paper surface.

In the printing of books and periodicals, most of the paper used is uncoated paper with low smoothness. When printing with letterpress paper or newsprint with a basis weight of 50 to 60 g/m2, the paper itself absorbs oil. Better performance, longer press time, higher printing pressure, and the occurrence of ink blemishes and print-through phenomena, so the use of inks with higher viscosity is advantageous for preventing the excessive penetration of ink into the interior of the paper.