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

The Effect of Refining,Forming,and Pressing on Fine Paperquality
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 weaker 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. 1 The test piece of premium paper was made from 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 changed to Bel-Form. Spray forming machine. The headbox concentration was 055% on the upper spray former and 0.50% on the longliner. 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 (Figure 1). 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 of FIG. 1 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 single press of the single felt while bypassing the first press nip (see Figure 1). Table 1 Overview of Test Conditions Shaper Pulp Freeness ml CSF
Press nip load, kN/m nip pulse sum, kPa, s 1st, 2nd, 3rd, 4th paper forming machine, broadleaf, 350 coniferous, 550 0 70 88 105 22.5 35 70 88 105 25.5 53 70 88 105 27.1 70 70 88 105 28.5 105 70 88 105 31.5 Injection Molding Machine Hardwood, 250 Softwood, 550 53 70 88 9 18.9 53 70 88 53 22.6 53 70 88 175 33.1
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. 2 Results and discussion 2.1 Solids content of the paper web The impact of the press nip load on the solids content of the upper shotcreper former is shown in Table 2 and Figure 2. When the load of the first press is increased from 0 or 35 kN/m to 105 kN/m, the solid content of the paper web made from the low-prepared ingredients is increased by more than 1%, which is made from the high-grade ingredients The solids content of the web is only increased by a very small percentage. Increasing the nip load of the 4th press from 9 or 53 kN/m to 175 kN/m, the solids content of the paper web made from the low-grade semi-slurry is increased by 1%, and the finished product is made of a high-grade finish. The solid content of the paper web increased by 2%. Table 2 Effect of the first and fourth press loads on the paper web made of the upper shot former The first press nip load, kN/m 0 (0) 35 (200) 53 (300) 70 (400) 105 ( 600) Solids content, % (Hardwood, 350 ml CSF) 40.2 NA* NA NA 41.5 Solids content, % (Hardwood, 250 ml CSF) NA 37.5 37.2 37.4 38.0 Fourth press nip load, 9 53 105 175 kN/m ( 50) (300) (600) (1000) Solids content, % (Hardwood, 350 ml CSF) 40.5 NA NA 41.7 Solids content, % (Hardwood, 250 ml CSF) NA 36.5 37.2 38.4
* Invalid Figure 2 The solids content of the web is a function of the total nip pulse for all presses. Black grid indicates Bel-Form paper; white grid indicates long web paper machine paper. Hardwood Kraft Pulp Freeness is 250ml CSF
Figure 2 shows that the solids content of the hardwood pulp formed from seminal plasma to 250 ml of CSF after pressing is the function of the total nip pulse for all the presses (see Table 1). This figure shows that increasing the load of the fourth press can improve dewatering more than increasing the load of the first press. It is likely that the fourth press rewetting the sheet when the nip load of the fourth press is lower than the nip load of the third press. These results show that the reduction of the final press load in order to increase the bulk of the paper will increase the burden of drying.
Seminal plasma has an important influence on dehydration. By increasing the degree of seminal plasma, the freeness of hardwood pulp was reduced from 350 to 250 ml of CSF, and the solid content in the pressed sheet could be reduced by about 2% under any squeezing conditions. 2.2 Looseness of uncalendered and calendered paper The degree of seminal pulp has little effect on the bulk of uncalendered paper (Table 3). The difference in bulkiness in the ten sheets of paper with two refiners under the same conditions is negligible. The distribution of fines and fillers (see the distribution of fines and fillers below) shows that seminal pulp only slightly changed the structure of the paper. However, sheets made from pulp with a low degree of fineness contain more filler, which can increase the density of the paper. Our test was conducted on a test paper machine at a speed similar to that of an industrial paper machine. Under these conditions, paper with a high degree of fineness, after pressing, has higher moisture than paper with a low degree of fineness, and the large moisture content helps maintain the bulk of the paper. When the freeness is less than 350 mlCSF, the seminal plasma has little effect on the bulk, so reducing the seminal plasma does not significantly increase the bulk. Table 3 Looseness of uncalendered paper after pressing at different nips * Shaper hardwood mlCSF Press with adjusted nip load Looseness in the following nip load cm3/g 0 53 105 175 (0 (300) (600) (1000) Upper Spray Former 350 Fourth - 1.64 1.65 1.61 250 Fourth - 1.64 1.65 1.62 350 First 1.70 - 1.63 - 250 First 1.70 - 1.65 - Longnet 350 Fourth - 1.71 1.70 1.37 250 Fourth - 1.70 1.68 1.67 350 First 1.76 - 1.66 - 250 First 1.77 - 1.66 -
Figure 3 shows that the bulk of the uncalendered paper can be a function of the total nip pulse for all presses. This figure shows that the bulk is only moderately affected by the press nip load. For example, the diamond symbol represents the press condition where the fourth press load is increased from 53 to 175 kN/m (300 to 1000 lb/in). This dramatic change in the final press nip load produces only a slight reduction in the bulk of the paper. Therefore, reducing the load on the final press nip is not an effective way to increase the bulk of the sheet. Surprisingly, it is much more effective to reduce the load on the first press. (See Table 3 and Table 4). The load of the first press was increased from 0 to 53 kN/m (0 to 400 lb/in), and at both finishes, the bulk was reduced by 0.1 m3/g, or 6%. Therefore, on a four-press paper machine, canceling the first nip can increase the bulk of the paper more than reducing the load of the last press. Table 4 Different nip load Pressure after pressing Calendered paper * Shaper Hardwood Slurry ml CSF Press with adjusted nip load Pinch under the following nip load cm3/g 0 53 105 175 (0) (300) (600) (1000) Upper Spray Former 350 Fourth - 1.47 1.43 1.42 First 1.47 - 1.39 - Fourdrinier 350 Fourth - 1.55 1.50 1.46 First 1.54 - 1.46 - Figure 3 The bulk of the uncalendered paper can be a function of the total nip pulse for all presses. Black Grid indicates Bel-Form, and White Grid indicates the Long Paper machine paper. Hardwood Kraft Pulp to (a) 250ml CSF and (b) 350ml CSF
The test data obtained when the total press pulse value is close to 22.5 kPa·s can better understand the influence of the press nip load on the bulk of the paper. In FIG. 3, the diamond marks indicate the press loads of 53, 70, 88 and 53 kN/m, and the square marks indicate the pressing load of 0, 70, 88, and 105 kN/m (see Table 1). The bulk of the samples represented by the squares was higher than the bulk of the samples represented by the rhombuses, although the highest nip load that these samples passed was greater (105:88 kN/m). There are two explanations for this finding: either the double blanket first nip can reduce the bulk more than the single nip first nip, or the bulk when the same press pulse is distributed in more press nips Decline more.
In FIG. 4, an attempt was made to find the relationship between the bulk of the uncalendered paper and the solids content of the press web. For paper made from pulp with a low degree of seminal pulp, the bulkiness of the paper after solids content is low after pressing, but paper made from ingredients with a high degree of refinement does not have this relationship. Even if the press nip uses a high-pressure zone load, the high-precision paper web still has a solid content after being pressed.