Paper roughness test and printability

Practice has proved that in the routine detection and study of surface properties of paper, roughness tester has the best correlation with printing. In this paper, we will use Messmer Parker Print-Surf Roughness Tester as an example to introduce the impact of the printing process in detail. Slab roughness of paper roughness and method of measuring the roughness of paper using air leakage method to simulate printing conditions.

introduction

Ideally, both sides of the paper should be smooth, flat, and uniform in thickness so that it can make good contact with the flat surface of the contact (such as liners, blankets, plates, etc.). However, in reality, most papers are not ideal. They are mainly manifested in the following: uneven thickness, resulting in the printing plate being accessible only at the place where the thickness is the greatest; uniform thickness, but the paper is undulating and can only touch one side of the plate; The surface of the paper is rough and can only have a small, discrete contact with the plate. Therefore, we can define the paper rent roughness as the deviation between a test surface and an ideal reference plane.

In general, paper with a undulating surface but a uniform thickness can be brought into good contact with the printing plate by adjusting the printing pressure. However, if the unevenness of the paper is poor, it cannot be adjusted in this way. However, if the paper is flat on one side, it can be lined with a cushion to make good contact with the plate. Both of these methods cause the paper itself to stretch or bend, and the pressure required is adjusted according to the amplitude, frequency, unevenness of the paper surface, and the hardness of the paper.

At present, the main method for measuring paper roughness internationally is the air leakage method, which measures the speed of air leakage between the paper surface and the reference plane. There are several types of instruments used in the air leakage method. They all have advantages and disadvantages. However, the test instruments must be easy to use, the readings must be consistent, they cannot change over time, they do not change due to differences in the skills of the operators, and are not due to test sites. The difference varies; the deviation of each instrument is within a reasonable range; and the most important point is that the test instrument must be able to test the printing performance of the paper, and this is also the most difficult to evaluate.

Development of measuring instruments for air leakage

Instruments using the air leakage method have essentially the same apparatus: a hard, annular pad is pressed against the paper, and is applied to the annular pad with different pressure, and the flow velocity between the paper surface and the annular pad is measured.

1. Buick smoothness meter

As early as 1927, the Buick Smoothness Tester applied air leakage to measure roughness (or smoothness) and applied it to the paper industry. It uses the glass as the reference plane, and under the pattern of the paper, a rubber pad is placed on it to apply a pressure of 100 kg in an area of ​​10 cm2 to form a semi-vacuum state, thereby drawing in air and passing through the contact surface. At this time, the measurement vacuum is within the specified range. The time required for internal change, the test result is in seconds.

However, the disadvantages of the Buick Smoothness Meter are also becoming increasingly apparent - the pressure is too low, and the test results are obviously low for microscopic smoothness, poor macro smoothness, uneven thickness, or undulating patterns (especially paperboard); It is a test that the ring surface is too wide, which leads to pits on the surface, such as felt marks, and rough paper on the surface of the paper, resulting in high measurement results. However, these results are exactly the opposite of the printing effect. In addition, when measuring the smoothness with a Buick smoothness meter, the measurement error caused by the air flow is also large.