DISINTEGRATABLE BROWN SACK PAPER

Abstract

The present invention includes a method of manufacturing a sack paper having a Gurley porosity (ISO 5636-5) of less than 25 s, comprising the steps of: a) mixing an unbleached pulp with a bleached pulp to obtain a pulp mixture in such proportions that the dry weight ratio of unbleached pulp to bleached pulp in the pulp mixture is between 7:1 and 1:1; and b) forming the sack paper from said pulp mixture, wherein starch is added in an amount of 1-7 kg/ton paper.

Claims

1-15. (canceled)

16. A method of manufacturing a sack paper having a Gurley porosity (ISO 5636-5) of less than 25 s, comprising the steps of: a) providing a pulp having a Kappa number (SCAN-C 1:00) of 15-40; b) subjecting the pulp to high consistency (HC) refining and optionally low consistency (LC) refining to obtain refined pulp, wherein the energy supply of the LC refining is less than 120 kWh/ton paper; and c) forming the sack paper from said pulp mixture, wherein the amount of starch added in the method is 1-7 kg/ton paper and the amount of hydrophobic size added in the method is less than 2 kg/ton.

17. The method of claim 16, wherein the Gurley porosity (ISO 5636-5) of the sack paper is less than 20 s.

18. The method of claim 16, wherein the Kappa number (SCAN-C 1:00) of the pulp provided in step a) is 20-35.

19. The method of claim 16, wherein the geometric tensile energy absorption index (ISO 1924-3) of the sack paper is at least 2 J/g.

20. The method of claim 16, wherein the grammage (ISO 536) of the sack paper is 50-140 g/m.sup.2, such as 60-120 g/m.sup.2.

21. The method of claim 16, wherein the pulp provided in step a) is a chemical pulp.

22. The method of claim 16, wherein at least 50% of the dry weight of the pulp provided in step a) is softwood pulp.

23. The method of claim 16, wherein step c) comprises creping.

24. The method of claim 16, wherein the amount of hydrophobic size is less than 1.5 kg/ton paper.

25. The method of claim 16, wherein the amount of starch is 1-5 kg/ton paper.

26. The method of claim 16, wherein step a) comprises conversion of wood into a pulp having a Kappa number (SCAN-C 1:00) of 25-40 using Kraft pulping.

27. The method of claim 16, wherein the energy supply of the LC refining is less than 110 kWh/ton paper.

28. The method of claim 17, wherein the Gurley porosity (ISO 5636-5) of the sack paper is less than 15 s.

29. The method of claim 17, wherein the Gurley porosity (ISO 5636-5) of the sack paper is less than 10 s.

30. The method of claim 19, wherein the geometric tensile energy absorption index (ISO 1924-3) of the sack paper is at least 2.8 J/g.

31. The method of claim 20, wherein the grammage (ISO 536) of the sack paper is 60-120 g/m.sup.2.

32. The method of claim 20, wherein the grammage (ISO 536) of the sack paper is 70-110 g/m.sup.2.

33. The method of claim 21, wherein the chemical pulp is Kraft pulp.

34. The method of claim 22, wherein at least 90% of the dry weight of the pulp provided in step a) is softwood pulp.

35. The method of claim 24, wherein the amount of hydrophobic size is less than 1.0 kg/ton paper.

36. The method of claim 24, wherein the amount of hydrophobic size is less than 0.5 kg/ton paper.

37. The method of claim 24, wherein the amount of hydrophobic size is less than 0.3 kg/ton paper.

38. The method of claim 24, wherein the amount of hydrophobic size is 0 kg/ton paper.

39. The method of claim 25, wherein the amount of starch is 1-5 kg/ton paper.

40. The method of claim 25, wherein the amount of starch is 2-5 kg/ton paper.

41. The method of claim 27, wherein the energy supply of the LC refining is less than 100 kWh/ton paper.

Description

BRIEF DESCRIPTION OF THE FIGURE

[0160] FIG. 1 is a plot showing the disintegratability of various papers.

EXAMPLES

[0161] For the trials presented below, kg/ton refers to kg/ton paper

[0162] Full Scale Trial

[0163] A full scale trial was carried out on paper machine 9 (PM9) at BillerudKorsn?s AB's mill in Sk?rblacka, Sweden. In the trial, the disintegratability of a paper obtained from a mixture of an unbleached pulp (57 wt. %) and a bleached pulp (43 wt. %) was compared to the disintegratability of a reference paper obtained from the unbleached pulp only. The grammage of the papers was 90 g/m.sup.2.

[0164] Both pulps were softwood kraft pulps subjected to HC refining (about 120 kWh/ton) and LC refining (20 kWh/ton), to which starch (8 kg/ton), Fennosil 517 (0.25 kg/ton) and ASA size (1 kg/ton) had been added. The Kappa number (SCAN-C 1:00) of the unbleached pulp was 50. The ISO brightness (ISO 2470-1) of the bleached pulp was 90.

[0165] The disintegratability of the papers was tested according to the following protocol:

[0166] 1. Cut paper (dry weight 30.0 g) into pieces of about 1.5 cm?1.5 cm and add them to 2 l of water having a temperature of 20? C.;

[0167] 2. After 2 minutes, add the paper-water mixture to a laboratory defibrator (L&W);

[0168] 3. Run 5000 revolutions;

[0169] 4. Add the contents from the defibrator to a laboratory sieve equipment having sieve openings of 0.15 mm and run the sieve for 15 minutes;

[0170] 5. After completed filtration, collect the retentate;

[0171] 6. Dry the retentate at 105? C.;

[0172] 7. Weigh the dried retentate; and

[0173] 8. Calculate the disintegratability (%) using the formula ((30?w)/30)*100, wherein w is the weight (g) of the dried retentate.

[0174] The Gurley porosity was also measured. The results are shown in table 1 below.

TABLE-US-00001 TABLE 1 Unbleached Bleached Gurley pulp pulp (ISO 5636-5) Disintegratability Reference 100 wt. % 0 wt. % 5 s 30% paper Inventive 57 wt. % 43 wt. % 5-3 s 93% paper

[0175] Laboratory Trials

[0176] The laboratory trial set-up was first evaluated and found to have a sufficient correlation with the full scale trial.

[0177] In the laboratory trials, bleached and unbleached pulps were obtained from paper mills.

[0178] Trial 1

[0179] The unbleached pulp was unbleached softwood kraft pulp subjected to HC refining (250 kWh/ton) and LC refining (18 kWh/ton). The Kappa number (SCAN-C 1:00) of the unbleached pulp was 50. The bleached pulp was bleached softwood kraft pulp subjected to HC refining (150 kWh/ton) and LC refining (16 kWh/ton). The ISO brightness (ISO 2470-1) of the bleached pulp was 90.

[0180] Different pulps for sheet forming were prepared according to table 2 below. Laboratory sheets having a grammage of 80 g/m.sup.2 were prepared in a dynamic sheet former according to BillerudKorsn?s' internal method. The disintegratability of the sheets, which is also shown in table 2 below, was tested as in the full scale trial described above.

TABLE-US-00002 TABLE 2 Reference Test 1 Test 2 Test 3 Test 4 Unbleached pulp 100 100 90 68 57 (wt. %) Bleached pulp 0 0 10 32 43 (wt. %) Starch (kg/ton) 8 8 8 8 8 Fennosil 517 0.25 0.25 0.25 0.25 0.25 (kg/ton) ASA (kg/ton) 1 0 0 0 0 Disintegratability 41% 60% 62% 88% 96%

[0181] From tables 1 and 2, it can be concluded that an addition of bleached pulp to unbleached pulp significantly improves the disintegratability of the resulting paper, in particular if the pulp mixture from which the paper is formed comprises more than 10% bleached pulp, such as at least 20% bleached pulp. Further, table 2 shows that the disintegratability is significantly improved by reducing the amount of ASA size (an hydrophobic size) added to the pulp.

[0182] The results from tables 1 and 2 are also presented in FIG. 1.

[0183] Trial 2

[0184] The unbleached pulp and the bleached pulp were the same as in trial 1 with the exception that for the unbleached pulp, the degree of HC refining was 258 kWh/ton and the degree of LC refining was 41 kWh/ton.

[0185] Different pulps for sheet forming were prepared according to table 3 below. As in Trial 1, Fennosil 517 (kg/ton) was added in an amount of 0.25 kg/ton. No ASA was added in trial 2. Laboratory sheets having a grammage of 80 g/m.sup.2 were prepared in a dynamic sheet former according to BillerudKorsn?s' internal method. The disintegratability of the sheets, which is also shown in table 3 below, was tested as in the full scale trial described above.

TABLE-US-00003 TABLE 3 UBP refers to the unbleached pulp (wt. %). BP refers to the bleached pulp (wt. %). S refers to starch (kg/ton). D refers to disintegratability (%). Test 1 2 3 4 5 6 7 8 9 10 11 12 UBP 100 90 68 57 100 90 68 57 100 90 68 57 BP 0 10 32 43 0 10 32 43 0 10 32 43 S 8 8 8 8 5 5 5 5 2 2 2 2 D 19 59 74 84 58 62 85 92 76 85 95 98

[0186] In table 3, it is verified that an addition of bleached pulp (BP) to unbleached pulp (UBP) significantly improves the disintegratability (D) of the resulting paper. Further, table 3 shows that the disintegratability (D) is significantly improved by reducing the amount of starch (S) added to the pulp. Finally, a comparison of the values for 8 kg/ton starch in table 3 to those of table 2 shows that the disintegratability (D) was lower when the degree of LC refining of the unbleached pulp was higher.

[0187] Trials 3 and 4

[0188] In trial 3, the unbleached pulp was unbleached softwood kraft pulp subjected to 177 kWh/ton HC refining and 131 kWh/ton LC refining. In trial 4, the unbleached pulp was the same type of unbleached softwood kraft pulp subjected to 210 kWh/ton HC refining and 95 kWh/ton LC refining. The Kappa number (SCAN-C 1:00) of the unbleached pulp was 30 in both trial 3 and trial 4. The bleached pulp was the same as in trial 1.

[0189] Trial 3 and trial 4 were carried at different occasions.

[0190] Different pulps for sheet forming were prepared according to table 4 and 5 below. As in Trial 1, Fennosil 517 (kg/ton) was added in an amount of 0.25 kg/ton. No ASA was added in trials 3 and 4. Laboratory sheets having a grammage of 80 g/m.sup.2 were prepared in a dynamic sheet former according to BillerudKorsn?s' internal method. The disintegratability of the sheets, which is also shown in tables 4 and 5 below, was tested as in the full scale trial described above.

TABLE-US-00004 TABLE 4 Trial 3. UBP refers to the unbleached pulp (wt. %). BP refers to the bleached pulp (wt. %). S refers to starch (kg/ton). D refers to disintegratability (%). Test 1 2 3 4 5 6 7 8 9 10 UBP 100 90 80 68 57 100 80 68 100 80 BP 0 10 20 32 43 0 20 32 0 20 S 8 8 8 8 8 5 5 5 2 2 D 49 66 79 89 97 82 95 95 86 97

[0191] In table 4, it is verified that an addition of bleached pulp (BP) to unbleached pulp (UBP) significantly improves the disintegratability (D) of the resulting paper and that the disintegratability (D) is significantly improved by reducing the amount of starch (S) added to the pulp. It is also notable that the disintegratability (D) of table 4, which were obtained with an unbleached pulp having a Kappa number of 30, are generally higher than those of table 3, which were obtained with an unbleached pulp having a Kappa number of 50. As an example, the disintegratability for 32% bleached pulp and 5 kg/ton starch is 95% in table 4 compared to 85% in table 3.

TABLE-US-00005 TABLE 5 Trial 4. UBP refers to the unbleached pulp (wt. %). BP refers to the bleached pulp (wt. %). S refers to starch (kg/ton). D refers to disintegratability (%). Test 1 2 3 4 5 UBP 100 100 80 68 57 BP 0 0 20 32 43 S 2 2 2 2 2 D 96 99 100 100 100

[0192] A comparison of the values in table 5 to those of table 4 shows that the disintegratability (D) was higher when the degree of LC refining of the unbleached pulp was lower. Further, it is shown in table 5 that when the kappa number, degree of LC refining and the amount of starch are all kept relatively low, it is not necessary to add bleached pulp to reach high (>95%) disintegratability values. However, a positive effect of additions of bleached pulp is still observed in table 5.