SU550581A1 - Method for determining uniformity of paper surface - Google Patents

Description

one

The invention relates to the pulp and paper industry and can be used in determining the quality of the paper surface.

To determine the printed paper smoothness, a Chapman device is used, which works on the principle of full reflection of a ray of light that falls on a three-sided irisma, and a sample of paper is pressed against the base of the prism. In those places where the paper and the face of the prism are in contact with each other, the beam is not reflected. The value of the printed paper smoothness is the contact surface area.

The disadvantage of this method is that the heterogeneity of the paper surface is not measured and the elastoplastic properties of the paper are not taken into account.

The known method of determining the uniformity of the paper surface using a differential pneumatic profilograph 1. The method is based on scanning the surface of the paper with a thin needle at a pressure of not more than 0.1 gf and recording surface irregularities in the diagram.

The disadvantage of this method is that the surface structure of the paper is determined in a limited area and without taking into account the elastic-plastic properties of the paper. Besides

In addition, the resulting profile diagrams are difficult to interpret and turn into a form suitable for application, for example, to printing conditions.

In order to improve the accuracy of determining the uniformity of the paper surface according to the proposed method, copy paper and metal are preliminarily applied to the test paper, and then contact is made by passing the resulting bag between two rotating metal shafts under a pressure of 1-100 kgf / cm and the required value is judged by the degree propechatnosti mortar points on the sample. The degree of propelling is determined by known photometric techniques or visually. The choice of the grid number is determined by the printing method for which the paper is intended.

This method was used to determine the uniformity of the surface of the paper samples.

The results of the determination are given below in the examples and in the table, which summarizes the data obtained according to the invention and the method for determining the quality of the paper using a profilograph.

Example. Test the paper for gravure printing grade "A GOST 9168-70. To do this, take four samples of the specified paper having the same Becku smoothness for 160 s, but different in fiber composition, namely: sample No. 1-80% sulfite softwood pulp

20% sulphate hardwood pulp

sample No. 2-60% sulfite coniferous cellulose

40% sulphate hardwood pulp

sample number 3-40% sulfite coniferous cellulose

60% sulfate hardwood pulp sample No. 4-100% softwood sulphite

pulp.

The last sample is subjected to surface sizing with carboxymethyl cellulose. The determination of the surface uniformity of each sample is carried out as follows.

On a sample of paper impose a strip of carbon paper with a copy layer to the sample, and on a copy sheet - a metal grid with a cell size of 70 lines / cm. The choice of cell size is determined by the method of printing (in addition, the method of gravure printing).

The resulting packet is passed between two metal shafts with a smooth surface on the Fogra instrument with a shaft speed of 1.5 m / s.

Three parallel seals were made for each paper sample, respectively, at a pressure of 1, 50, 100 kgf / cm.

The uniformity of the printing of the grid cells on the paper sample is determined on a scanning microphotometer with a chart recorder for a 10 cm scan area. The results of the microphotometric scanning are recorded in a diagram where the unprinted intensity and the number of unprinted sections are recorded. The diagram determines the integral component of the oscillations of print unevenness 5 (V / mm) and the arithmetic average value of absolute

fluctuations - Ra (B). 5 and c) d t about equal to the dimension of the paper surface. Improving the quality of the paper surface corresponds to a decrease in the values of indicators 5 and Ra- The analysis results are shown in Table. one.

For comparison, the uniformity of the paper surface is determined by a known method (prototype) on a profilometer by scaling the surface of the paper with a thin sheet under a pressure of 0.1 kg. With this measurement

for the profilometer, the maximum possible distance is 6 mm. The arithmetic average value of the depth of the irregularities on the surface of the paper Ra (μm) is read from the indicating device. The measurement data was carried out on three strips of each paper sample, in five points, and then the average value was calculated (see Table 1).

Table 1

To find out which of the methods (proposed or known) accurately characterizes the behavior of paper during printing, printing irregularity is determined on a scanning microphotometer.

Printing is carried out in an innately intaglio printing machine. Unprinted strips were cut out of the sheets on which the yache was made for definitions using the proposed method and on a profilometer.

Print irregularities are determined for halftones. S (B / mm) and Ra (B), as determined by the method described above, are used to characterize the printing accuracy (see Table 1).

Since the results of measuring the unevenness of the paper surface according to the proposed method and the prototype, as well as the unevenness of printing cannot be compared by their absolute values of indicators, ranking according to ranks is carried out, and the paper with the best indicators is assigned the rank 1, the paper with the worst indicators is rank 4. At the same time, for indicators S (V / mm) and Ra (B), the total rank of the ranks for each indicator is determined, i.e. a distribution by rank is obtained taking into account two indicators. The ranking results are shown in Table. 2

The rank correlation coefficient was calculated for the proposed and known methods with respect to print unevenness using the formula:

16 S (K.-Kg)

N (I)

Y is the rank of the reference sample;

1/2 - the rank of the compared sample;

N is the number of compared values in

rank sequence. The rank correlation coefficient for uniformity of the paper surface by a known method (prototype) is (-) 0.55, which indicates an inverse relationship. But since the uniformity of the surface of unprinted paper does not depend on the uniformity of printing, it can be said that the uniformity of the surface of the paper, determined on a profilometer (according to the prototype), does not characterize the behavior of paper during printing. For the proposed method, the rank correlation coefficient for pressures is 1.0; 50 and 100 kgf / cm is 0.95, respectively; 0.65 and 0.85, which indicates a close correlation of the proposed method with the result of printing on an industrial intaglio printing machine.

From tab. 2 shows that the proposed method more accurately describes the behavior of paper during printing, as evidenced by the coincidence of the ranking sequences for the proposed method and the uniformity of printing, whereas the coincidence of the ranks by a known method and uniformity of printing is absent.

table 2

The method makes it possible to determine the uniformity of the paper surface over a sufficiently large area, to vary widely over pressure and speed during printing, which makes it possible to bring the test conditions as close as possible to workers when processing paper under industrial conditions. The method allows one to take into account the effect of the elastoplastic properties of paper and to evaluate the surface structure both visually and with the use of appropriate devices, for example, using a scanning microscope.

The method provides a more complete assessment of the structure of the paper and its printing properties.

Claims (1)

1. "Control of the working properties of printing materials, M., publishing house" Book, 1971, p. 451-455 (prototype).