Use of cellulosic fibre pulp

Abstract

Use of cellulosic fibre pulp having a Schopper-Riegler number according to ISO 5267-1 of about 70 or more as an additive to papermaking pulp for enhancing compressive strength of paper or board manufactured from the papermaking pulp. A process for enhancing compressive strength of paper or board manufactured from a papermaking pulp, comprising use of a cellulosic fibre pulp having a Schopper-Riegler number according to ISO 5267-1 of about 70 or more as a component of the papermaking pulp.

Claims

1. A process for manufacturing paper or board, comprising: preparing a cellulosic fibre pulp by beating or refining a woodpulp or recycled fibre pulp to obtain a Schopper-Riegler number according to ISO 5267-1 of 70 or more; using the cellulosic fibre pulp having a Schopper-Riegler number according to ISO 5267-1 of about 70 or more as a component of a papermaking pulp, wherein the cellulosic fibre pulp is used in the papermaking pulp in such amount that fibre originating from the cellulosic fibre pulp constitutes up to about 25 wt %, determined on a dry matter basis, of the fibre composition of the papermaking pulp and/or of the paper or board to be manufactured; and manufacturing paper or board from the papermaking pulp.

2. The process according to claim 1, wherein the Schopper-Riegler number of the cellulosic fibre pulp is about 70-79.

3. The process according to claim 1, wherein a filler is added to the papermaking pulp.

Description

EXAMPLES

(1) In the following examples, use of a cellulosic fibre pulp having a Schopper-Riegler number of about 70 or more is exemplified by the use of a highly refined cellulosic fibre pulp (ORK, ORE or ORR, as further laid out below.

Laboratory Examples

(2) In laboratory examples 1, 2, 3 and 5 below, paper hand-sheets were prepared from pulp mixtures comprising as one of their components a highly refined cellulosic fibre pulp. Physical properties, in particular strength properties, of the hand-sheets were subsequently tested. The laboratory examples were planned and evaluated using a mixture design with three mixture components, the proportions of the mixture components summing to 100%. The mixture design enabled prediction of responses, i.e. paper properties, for other combinations of the pulp mixture components than for the tested mixtures, and facilitated up-scaling to mill trials. A mixture design provides an estimate of how well the components can model a certain response. The most basic approach is to create a model by linearly fitting coefficients (coeff) to the proportion of each mixture component (comp).
Response=Coeff1*Comp1+Coeff2*Comp2+Coeff3*Comp3

(3) When possible, responses for the tested mixtures were additionally evaluated by direct comparison.

(4) The highly refined cellulosic fibre component was obtained by refining of a pulp as defined below to achieve a desired Schopper-Riegler number. Refining was performed with an Escher Wyss conical lab refiner run at a constant edge load of 1.5 J/m and a constant power of 1.05 kW. The desired refining energy was accomplished by recirculation of a pulp batch of around 0.5 kg.

(5) A pulp mixture for hand-sheet preparation was obtained by mixing of pulp components as defined below and subsequent dilution with tap water to a pulp consistency of 0.2%. To the pulp mixture was added 1% of a cationic starch as a retention aid. Paper hand-sheets were produced from the pulp mixture in a Formette Dynamique sheet former at a drum speed of 1200 rpm. The formation took place at a pressure of 2.8 bar, with a MEG 2510TC nozzle having a 25 spray angle, and at a jet-to-drum angle of 35 against the cover plate tangent. The hand-sheets formed were passed three times through a roll press, at a pressure of 3, 6 and 6 bar, respectively. Drying of the pressed hand-sheets was performed by restrained drying in an L&W Rapid Dryer type 3-1. The drying time amounted to 14 minutes.

(6) The following methods were used for testing of pulp. Drainability (Schopper-Riegler number, SR): ISO 5267-1 Fibre length (Lorentzen/Wettre Fiber Tester Plus): ISO 16065-2

(7) The following methods were used for testing of paper hand-sheets. Grammage: ISO 536 Compressive strengthShort-span test (SCT): ISO 9895 Ash 525 C.: ISO 1762

(8) Experimental results presented herein are average values of several measurements. Unless otherwise stated, the grammage is provided in g/m.sup.2, the SCT CD (SCT cross direction) is provided in kN/m, and the SCT CD index (SCT cross direction index) is provided in kNm/kg. Herein, response models fitted to SCT CD index are based on averages of several measurements.

(9) Unless otherwise stated, proportions of pulp mixture components given in % refer to weight % of the respective pulp component calculated as dry pulp.

Example 1

Laboratory Example

(10) This example is based on a three component mixture design, the components being kraft pulp (kraft), recycled fibre pulp (RCF) and highly refined kraft pulp (ORK).

(11) The kraft pulp was a softwood pulp drawn from a paper mill at a Schopper-Riegler number of 13 (day average value) and a Kappa number of 85.7. The average fibre length was 2.298 mm.

(12) The recycled fibre pulp was drawn from a paper mill at a Schopper-Riegler number of 46 (calculated from a modified Schopper-Riegler number obtained with a larger orifice than prescribed by ISO 5267-1). The ash content (as tested on hand-sheets made from the recycled fibre pulp) was 9 wt %. The average fibre length was 1.275 mm.

(13) The highly refined kraft pulp was prepared by refining, as described above, the kraft pulp to a Schopper-Riegler number of 77.5 using a specific refining energy of 600 kWh/ton. The fibre length was not measured.

(14) The mixing plan, setting out the relative proportions (wt %) of the components, and the results are shown in table 1. A highly refined kraft pulp is hard to dewater and may not be used without mixing with other pulps. Hence the maximum dosage was set to 20%.

(15) TABLE-US-00001 TABLE 1 Mixing plan and results SCT CD Kraft RCF ORK SCT CT Grammage index 100 0 0 0.84 103.9 8.1 90 0 10 1.13 102.2 11.1 80 0 20 1.36 104.2 13.1 40 40 20 1.75 97.6 17.9 45 45 10 1.51 99.8 15.1 50 50 0 1.26 100 12.6 0 80 20 2.04 98.4 20.7 0 90 10 1.82 98.9 18.4 0 100 0 1.55 98 15.8

(16) Table 2 shows a statistical evaluation of the results, by which a model, as set out above, was created for SCT CD index. Neither the model nor the components have any risk for non-significance, according to the statistical tests performed as part of the evaluation (F and t tests with 95% confidence limits).

(17) TABLE-US-00002 TABLE 2 Statistical evaluation of SCT CD index Model Adjusted R.sup.2 0.80 Risk for no significance (F test) 0.000 Coefficient (importance) Kraft 0.080 RCF 0.164 ORK 0.377 Coeff. Risk for no significance (t test) Kraft 3.86E05 RCF 2.28E07 ORK 2.51E05

(18) Table 2 shows that ORK is by far the most important component for SCT CD index (coefficient 0.337). It is apparent that kraft pulp having a Schopper-Riegler number of 13 has a poor SCT strength and is not suited for paper making without additional refining, as its coefficient is lower than the coefficient for RCF. This manifests itself such that recycled fibre pulp contributes twice as much to the SCT CD index as the kraft pulp.

(19) For strength comparisons, predicted results for two hypothetical mixtures with different amounts of kraft pulp, with and without highly refined pulp are shown in table 3. Experimental results for the same mixtures are shown in table 4.

(20) TABLE-US-00003 TABLE 3 Predicted results for hypothetical mixtures Mixture Kraft 100 RCF 0 ORK 0 SCT CD index 8.04 Kraft 90 RCF 0 ORK 10 SCT CD index Model 11.0 Change (improvement with 10% ORK) 36.8%

(21) TABLE-US-00004 TABLE 4 Experimental results Mixture Kraft 100 RCF 0 ORK 0 SCT CD index Experiment 8.08 Kraft 90 RCF 0 ORK 10 SCT CD index Experiment 11.1 Change (improvement with 10% ORK) 37.4%

(22) It is to be noted that the experimental results originates from the same population as was used for building the model.

Example 2

Laboratory Example

(23) This example is based on a three component mixture design, the components being refined kraft pulp (kraft), recycled fibre pulp (RCF) and highly refined kraft pulp (ORK).

(24) The refined kraft pulp was prepared by refining, as described above, a softwood kraft pulp drawn from a paper mill at a Schopper-Riegler number of 13 (day average value) to a Schopper Riegler number of 20 using a specific refining energy of 100 kWh/ton. The average fibre length after refining was 2.242 mm.

(25) The recycled fibre pulp was drawn from the same mill. Its Schopper-Riegler number was not measured. The ash content (as tested on hand-sheets made from the recycled fibre pulp) was 9.75 wt %. The average fibre length was 1.20 mm.

(26) The highly refined kraft pulp was prepared by refining, as described above, a softwood kraft pulp drawn from a paper mill at a Schopper-Riegler number of 13 (day average value) to a Schopper Riegler number of 76 using a specific refining energy of 450 kWh/ton. The average fibre length after refining was 1.831 mm.

(27) The mixing plan, setting out the relative proportions (wt %) of the components, and the results are shown in table 5. A highly refined kraft is hard to dewater and may not be used without mixing with other pulps. Hence maximum dosage is set to 20%.

(28) TABLE-US-00005 TABLE 5 Mixing plan and results SCT CD Kraft RCF ORK SCT CD Grammage index 100 0 0 1.62 106.2 15.25 90 0 10 1.74 103.8 16.76 80 0 20 2.01 103.3 19.46 50 50 0 1.51 101.5 14.88 45 45 10 1.66 101 16.44 40 40 20 1.84 100.8 18.25 0 80 20 1.78 99 17.98 0 90 10 1.58 98.9 15.98 0 100 0 1.38 97.7 14.12

(29) Table 6 shows a statistical evaluation of the results, by which a model, as set out above, was created for SCT CD index. Neither the model nor the components have any risk for non-significance according to the statistical tests performed as part of the evaluation (F and t tests with 95% confidence limits).

(30) TABLE-US-00006 TABLE 6 Statistical evaluation of SCT CD index Model Adjusted R.sup.2 0.83 Risk for no significance (F test) 0.000 Coefficient (importance) Kraft 0.153 RCF 0.140 ORK 0.337 Coeff. Risk for no significance (t test) Kraft 3.24E10 RCF 5.36E10 ORK 6.23E08

(31) ORK is the superior pulp component in contributing to a high SCT CD index, as shown by the high coefficient in table 6 (0.337). The kraft component has gained strength potential with refining (having a Schopper-Riegler number of 20), and is slightly better than RCF in contributing to SCT CD index, as compared to the kraft component of laboratory example 1 (having a Schopper-Riegler number of 13).

(32) For strength comparisons, predicted results for hypothetical mixtures of respectively pure kraft and a 90/10% kraft/ORK mixture are shown in table 7. A 12% improvement of SCT CD index is shown. Experimental results for the same mixtures are shown in table 8.

(33) TABLE-US-00007 TABLE 7 Predicted results for hypothetical mixtures Mixture Kraft 100 RCF 0 ORK 0 SCT CD index Model 15.3 Kraft 90 RCF 0 ORK 10 SCT CD index Model 17.1 Change 12%

(34) TABLE-US-00008 TABLE 8 Experimental results Mixture Kraft 100 RCF 0 ORK 0 SCT CD index Experiment 15.25 Kraft 90 RCF 0 ORK 10 SCT CD index Experiment 16.8 Change 10%

(35) It is again to be noted that the same population was used for experimental results and for building the model.

Example 3

Laboratory Example

(36) This example is based on a three component mixture design, the components being bleached eucalyptus (hardwood) kraft pulp (kraft), filler and highly refined bleached eucalyptus (hardwood) kraft pulp (ORE).

(37) The bleached eucalyptus kraft pulp was prepared by refining, as described above, a dry market pulp obtained from Suzano at a Schopper-Riegler number of 17.5 to a Schopper-Riegler number of 30. The average fibre length after refining was 0.741 mm.

(38) The filler was CaCO.sub.3 (Hydrocarb 60-ME obtained from Omya).

(39) The highly refined bleached eucalyptus kraft pulp was prepared by refining, as described above, a dry market pulp obtained from Suzano at a Schopper-Riegler number of 17.5 to a Schopper-Riegler number of 75. The average fibre length after refining was 0.688 mm

(40) The mixing plan, setting out the relative proportions (wt %) of the components, and the results are shown in table 9. As a filler does generally not contribute to strength, the maximum dosage is set to 12%. For the same reason as in laboratory examples 1 and 2, the maximum dosage of ORE is set to 20%.

(41) TABLE-US-00009 TABLE 9 Mixing plan and results SCT CD Kraft ORE Filler Grammage SCT CD index 88 0 12 69.5 1.3 18.7 78.8 9.2 12 69.4 1.42 20.5 70.1 17.9 12 70.1 1.49 21.3 94 0 6 69.9 1.42 20.3 84.2 9.8 6 68.6 1.47 21.4 74.9 19.1 6 69.8 1.59 22.8 100 0 0 70.9 1.49 21 89.6 10.4 0 70.4 1.59 22.6 79.7 20.3 0 69.9 1.66 23.7

(42) Table 10 shows a statistical evaluation of the results, by which a model, as set out above, was created for SCT CD index. The significance test of filler influence on SCT CD index barely makes it below the 5% limit. Values lower than 5% can be regarded as significant.

(43) TABLE-US-00010 TABLE 10 Statistical evaluation of SCT CD index Model Adjusted R.sup.2 0.83 Risk for no significance (F test) 0.000 Coefficient (importance) Kraft 0.211 Filler 0.036 ORE 0.347 Coeff. Risk for no significance (t test) Kraft 0.000 Filler 0.049 ORE 0.000

(44) As can be seen in table 10, ORE is the component contributing the most to SCT CD index (0.347). Also the kraft component contributes to SCT CD index. The filler has a very small influence on SCT CD index.

(45) Utilising hypothetic mixtures of respectively pure kraft and a kraft/ORE mixture of 90/10%, no filler, predicted results are shown in table 11. Strength improvement amounts to about 6.5% increase for SCT CD index. Experimental results for the same mixtures are shown in table 12.

(46) TABLE-US-00011 TABLE 11 Predicted results for hypothetical mixtures Mixture Kraft 100 RCF 0 ORE 0 SCT CD index Model 21.1 Kraft 90 RCF 0 ORE 10 SCT CD index Model 22.5 Change 6.4%

(47) TABLE-US-00012 TABLE 12 Experimental results Mixture Kraft 100 RCF 0 ORE 0 SCT CD index Experiment 21.00 Kraft 90 RCF 0 ORE 10 SCT CD index Experiment 22.6 Change 7.62%

(48) It is again to be noted that the same population was used for experimental results and for building the model.

Example 4

Factory Example

(49) Full scale production of two-ply kraftliner was performed at Smurfit Kappa's facilities (PM6) in Facture, France. A trial two-ply kraftliner in which the bottom ply was produced from a pulp composition of 50 wt % of an ordinary kraft softwood pulp, 30 wt % of a recycled fibre pulp and 20 wt % of a highly refined softwood pulp (ORK) was compared to a control two-ply kraftliner in which the bottom ply was produced from a pulp composition of 75 wt % of the ordinary kraft softwood pulp and 25 wt % of the recycled fibre pulp. The ordinary kraft softwood pulp had been brought to a Schopper-Riegler number of 16-20 by passing it through an ordinary refiner for bottom ply pulp. The highly refined softwood pulp for the trial kraftliner had been prepared by passing an amount of the ordinary kraft softwood pulp in a loop through an ordinary refiner for bottom ply pulp until a Schopper-Riegler number of 75 was reached. For the trial kraftliner the top layer constituted 30% of the total kraftliner, whereas for the control craftliner the top layer constituted 20% of the total kraftliner.

(50) The trial kraftliner was found to have a SCT CD index of 19.3 whereas the control kraftliner had a SCT CD index of 18.0 (both values being average values of several measurements), indicating an increase by 7%.

Example 5

Laboratory Example

(51) This example is based on a three component mixture design, the components being refined kraft pulp (kraft), recycled fibre pulp (RCF) and highly refined recycled pulp (ORR).

(52) The refined kraft pulp was a softwood kraft pulp drawn from a paper mill at a Schopper-Riegler number of 15. The average fibre length was 2.246 mm and the ash content was 0.9 wt %.

(53) The recycled fibre pulp was drawn from a paper mill at a Schopper-Riegler number of 32. The ash content (as tested on hand-sheets made from the recycled fibre pulp) was 9.7 wt %. The average fibre length was 1.298 mm.

(54) The highly refined recycled pulp was prepared by refining, as described above, the recycled fibre pulp to a Schopper Riegler number of 74 using a specific refining energy of 215 kWh/ton. The average fibre length after refining was 1.084 mm.

(55) The mixing plan, setting out the relative proportions (wt %) of the components, and the results are shown in table 13. A highly refined recycled pulp is hard to dewater and may not be used without mixing with other pulps. Hence maximum dosage is set to 20%.

(56) TABLE-US-00013 TABLE 13 Mixing plan and results SCT CD Kraft RCF ORR SCT CD Grammage index 100 0 0 1.9 104.4 18.2 90 0 10 2.02 101.8 19.8 80 0 20 2 100.2 20 50 50 0 1.75 102.5 17.1 45 45 10 1.79 102.1 17.5 40 40 20 1.95 101.3 19.2 0 80 20 1.76 100.8 17.5 0 90 10 1.67 100 16.7 0 100 0 1.64 104.3 15.7

(57) Table 14 shows a statistical evaluation of the results, by which a model, as set out above, was created for SCT CD index. Neither the model nor the components have any risk for non-significance according to the statistical tests performed as part of the evaluation (F and t tests with 95% confidence limits).

(58) TABLE-US-00014 TABLE 14 Statistical evaluation of SCT CD index Model Adjusted R.sup.2 0.83 Risk for no significance (F test) 0.000 Coefficient (importance) Kraft 0.185 RCF 0.155 ORR 0.265 Coeff. Risk for no significance (t test) Kraft 3.51E10 RCF 1.00E09 ORR 8.82E07

(59) ORR is the superior pulp component for SCT CD index as shown by the high coefficient (0.265) in table 14.

(60) For strength comparisons, predicted results for hypothetical mixtures of respectively pure kraft and a 90/10% kraft/ORR mixture are shown in table 15. A 4.3% improvement of SCT CD index is shown. Experimental results for the same mixtures are shown in table 16.

(61) TABLE-US-00015 TABLE 15 Predicted results for hypothetical mixtures Mixture Kraft 100 RCF 0 ORR 0 SCT CD index Model 18.5 Kraft 90 RCF 0 ORR 10 SCT CD index Model 19.3 Change 4.3%

(62) TABLE-US-00016 TABLE 16 Experimental results Mixture Kraft 100 RCF 0 ORR 0 SCT CD index Experiment 18.2 Kraft 90 RCF 0 ORR 10 SCT CD index Experiment 19.3 Change 8.79%

(63) It is again to be noted that the same population was used for experimental results and for building the model.

Example 6

Possible Industrial Application

(64) The exemplary mixtures of table 17 are proposed for industrial application in the manufacture of paper or board having a high compressive strength. Kraft=kraft pulp, RCF=recycled fibre pulp, ORR=highly refined recycled fibre pulp (Schopper-Riegler number 70), ORK=highly refined kraft pulp (Schopper-Riegler number 70).

(65) TABLE-US-00017 TABLE 17 Exemplary mixtures (wt % on a dry matter basis) Kraft 60 50 50 70 70 RCF 30 30 30 20 10 ORR 10 20 0 10 20 ORK 0 0 20 0 0

DISCUSSION

(66) The laboratory and factory examples laid out above confirm that addition of an extensively refined cellulosic fibre pulp to a papermaking pulp enhances the compressive strength, in particular the SCT CD, of paper or board manufactured from the papermaking pulp. An extensively refined cellulosic fibre pulp may thus be used to allow higher recycled content as well as higher filler content in a papermaking pulp.