Low hygroexpansivity paper sheet
A paper sheet is providing having a basis weight of 50 to 80 g/m 2 , and having a top surface and a bottom surface, said paper sheet comprising 10%-80% by weight of hardwood kraft pulp; and 10%-70% by weight of sulfite pulp; wherein the paper sheet has an MD/CD TSI ratio of 1.25 to 2.15, and a fiber hygroexpansion stress transfer parameter (ω) of less than 0.1.
1. A single ply paper sheet of 50 to 80 g/m 2 basis weight having a top surface and a bottom surface, said paper sheet comprising:
a. 10%-80% by weight of hardwood kraft pulp; and
b. 10%-70% by weight of sulfite pulp;
and wherein the paper sheet has an MD/CD TSI ratio of 1.25 to 2.15, and a fiber hygroexpansion stress transfer parameter (w) of less than 0.1.
2. A paper sheet according to claim 1 , wherein the w is less than 0.08.
3. A paper sheet according to claim 1 , wherein the hardwood kraft pulp comprises eucalyptus.
4. A paper sheet according to claim 1 , having a MD/CD TSI ratio of 1.5 to 1.9.
5. A paper sheet according to claim 4 , wherein the hardwood kraft pulp comprises eucalyptus.
6. A paper sheet according to claim 1 further comprises:
c. 5%-50% by weight of softwood kraft pulp.
7. A paper sheet according to claim 6 , wherein the hardwood kraft pulp comprises eucalyptus.
8. A paper sheet according to claim 7 comprising 3-15% pulp fines having a fiber length less than 0.4 mm.
9. A paper sheet according to claim 7 comprising 4-25% filler.
10. A paper sheet according to claim 9 , wherein the filler comprises titanium dioxide, calcium carbonate, clay, aluminum trihydrate, or satin white.
11. A paper sheet according to claim 7 , said paper sheet having a basis weight of 55 to 65 g/m 2 .
12. A paper sheet according to claim 7 , said paper sheet having a pre-set dryer bias curl of 5 to 15 mm.
13. The paper sheet of claim 12 , wherein the dryer bias curl is set to a surface corresponding to a top side of the paper sheet.
14. A paper sheet according to claim 7 , wherein the sulfite pulp comprises ammonia-based bisulfite pulp.
15. A paper sheet according to claim 14 , wherein the ammonia-based bisulfite pulp comprises hardwood pulp and softwood pulp.
16. A paper sheet according to claim 7 , said paper sheet having a caliper of 68 to 94 μm.
17. A paper sheet according to claim 7 , wherein the ω is less than 0.06.
18. A paper sheet according to claim 6 , having a MD/CD TSI ratio of 1.5 to 1.9.
19. A paper sheet according to claim 18 , wherein the hardwood kraft pulp comprises eucalyptus.
20. A paper sheet according to claim 19 , having a MD/CD TSI ratio of 1.6 to 1.8.