The influence of seminal pulp, forming and pressing processes on paper quality

In the press nip of the paper machine, during the compression of the fibers, the cellulose web is reduced in thickness because the cellulose is flattened and permanently deformed. The pressed paper expands after passing through the nip but does not fully recover its original bulk. Therefore, the dryness of the dry paper is related to the strength of the wet press.
The tight state of the web during the wet pressing increases the binding area of ​​the fibers and strengthens the strength properties of the dried product. Reducing the bulk of the paper is suitable for some products, but fine paper does not want this, and the minimum bulk is specified for this paper. If the required paper bulkiness cannot be achieved by modifying the operating conditions, it is necessary to greatly increase the paper ration to meet the requirements.
The density of the paper depends on the nature of the pulp and several operating parameters. The effect of seminal plasma and calendering on the bulk and other properties of fine paper has been extensively studied. The effect of wet pressing on the reduction of bulk is more pronounced than that of mechanical pulp.
Paper mill practical experience and test paper machine studies show that under the same line pressure load, the shorter but stronger maximum pressure produced by the hard nip is better than that produced by the soft nip or the shoe press. Long, but less intense pressure pulses can reduce the bulk more dramatically. However, the effect of the nip load on the bulk of the paper at different press positions has not been systematically studied.
The purpose of this study was to determine how the amplitude of pressure pulses applied to the first and last press nips can affect the moisture removal and dry bulk of fine paper, and how these effects can be combined with the degree of seminal plasma.
The wet paper web may be embossed in the press nip, leaving the front of the single-blanket pressed paper to be rougher than the roll surface. Premium paper made from soft chemical pulp is more embossed than news paper made from hard mechanical pulp. Another purpose of this study was to determine the two-sidedness of the roughness produced by the fine paper during the pressing process.
It has previously been reported that in the first blanket-free press zone, the paper facing the felt has a better print quality than the roll surface, although the reason for this improvement is still unclear. This better print quality may be the result of a greater positive effect on the front side of the paper.
This stacking effect is more evident on high-quantitative paperboard than on low-quantitative printing paper. The displacement of the front side of the paper and the fine fibers can also improve the printing properties of the paper surface. The displacement of the fine fiber material during the pressing of the vacuum press has been reported, but it has not been confirmed that the fine fibers and the Z-direction of the filler are redistributed during the pressing. In this study, evidence of Z-direction movement of fine fibers and fillers under strong press conditions was found.
The effect of the wet press on both sides of the paper is compatible with the web properties formed during the forming process. The effect of long web and double web formation on the properties of paper is well known. However, as far as we know, the comprehensive effect of successive changes in forming and pressing conditions on the properties of the paper has not been studied. In this study, we used a series of identical pressing conditions to study the fine paper made by the four-wire machine and the upper spray former.
The test section premium paper was made from a bleached kraft pulp containing 80% poplar and 20% black spruce. Both types of pulp are produced in the eastern part of Canada; hardwood pulp is shipped in the form of a non-dried wet pulp sheet, whereas softwood pulp is in the fully dry form. Conifer wood was ground to Canadian Standard Freeness 550 ml CSF. Hardwood pulp was ground to two different freeness: 350 ml CSF and 250 ml CSF. Paper with a precipitated calcium carbonate in the range of 60 to 70 g/m2 was copied under alkaline conditions at a speed of 700 m/min.
In these experiments, the No. 3 experimental paper machine at Beloit's Research and Development Center was equipped with a Concept III headbox and a former. It was first applied to a fourdrinier machine and then immediately switched to the Bel Form. Slurry shaper. The headbox concentration was 0.55% on the upper shot former and 0.50% on the fourdrinier former. For the low-grade ingredients, the retention rate on both formers was 84%. For the high-grade ingredients, the retention rate of the upper spray former was 85%, and that of the permanent-grinding machine was 77%. .
The press section includes a four-roll press followed by a fourth press. A special enclosed traction system including a vacuum pick-up roller and a pick-up web guides the paper from a four-high press to a fourth press felt. The two finely refined pulps were made into fine papers on a fourdrinier paper machine and an upper spray former, respectively. In the four trials, eight different press conditions were used in each group, for a total of 32 different test conditions.
The press section of the test paper machine includes a four-roll press followed by a fourth press. When the nip load was zero, the first double felt nip was opened. After the paper entered the press section, the press nip load used in the first press test in the second nip of the single felt was shown in Table 1. The paper is first pressed in the double blanket nip unless the paper is first pressed within the second press of the single felt while bypassing the first press nip.
The pilot paper machine had no drying section and the pressed paper was rolled up without being dried. The wet paper rolls for each condition were collected and dried on a separate 14-cylinder dryer. The dry paper was calendered in a single pressure zone of a Paprican laboratory calender, the calender speed was 50 m/min, the nip load was 10 kN/m, and the roll temperature was 50°C.
Paper was measured using standard procedures and the results are shown below. The roughness of the paper was measured immediately before and after calendering. When the load was 1000 kPa (S10), it was measured using a Parker Print-Surf (PPS) instrument with a soft paper blank. The print quality was determined using a field version on a laboratory IGT printer and the ink concentration was determined according to the procedures described in the literature.