Process for making a stiffened paper
View Patent ↗A process for making a stiffened and rigid paper includes preparing a pulp slurry consisting essentially of water, a cellulosic pulp, a crosslinker, and a starch, and optionally a binder; draining the liquid from the pulp slurry to form a web; and drying the web. Alternatively, a process for making a stiffened and rigid paper includes the step of adding at least one crosslinker at one or more locations, such as at the wet-end, dry-end, or at both ends of the papermaking process. Suitable crosslinkers include a glyoxal-containing crosslinker, a gluteraldehyde, a polyfunctional aziridine, a zirconium-containing crosslinker, a titanium-containing crosslinker, and an epichlorohydrin, and mixtures thereof. When a binder is employed, it can be added either in the dry or wet form. Provided is a neutral or alkaline process to produce a paper product having the improved mechanical properties of a laminated product in the Z-direction, without a lamination step.
1. A process for making rigid paper, the process comprising:
preparing an aqueous slurry comprising cellulosic pulp and starch;
draining the slurry to form a web;
adding a crosslinker selected from the group consisting of glyoxal-containing crosslinkers, gluteraldehydes, and polyfunctional aziridines in an amount of about 0.3 to about 20 weight percent based on the weight of solids in the pulp slurry or web, wherein the crosslinker is added to the slurry, or to the web; and
drying the web to produce a paper product,
wherein the process does not include use of a hydrophilic polyacrylamide applied to the web; and
wherein the paper product is a single ply paper having a basis weight in the range of about 65 lbs/3000 ft^2 to about 165 lbs/3000 ft^2, a folding endurance as measured by M.I.T. in the range of up to about 22.9, and a normalized Gurley stiffness in the range of about 369 to 4747.
2. The process of claim 1 , wherein the crosslinker is glyoxal-containing crosslinker in an amount between 0.3 to about 10 weight percent.
3. The process of claim 1 , wherein the cellulosic pulp comprises recycled pulp.
4. The process of claim 1 , wherein the paper has a basis weight of about 65 lbs/3000 ft^2.
5. The process of claim 4 , wherein the paper has an M.I.T. Fold in the range of about 1.0 to 22.9 and a normalized to basis weight Gurley stiffness of about 369 to 406.
6. The process of claim 1 , wherein the paper has a basis weight of about 115 lbs/3000 ft^2.
7. The process of claim 6 , wherein the paper has an M.I.T. Fold of about 0 and a normalized to basis weight Gurley stiffness of about 1902 to 1990.
8. The process of claim 1 , wherein the paper has a basis weight of about 165 lbs/3000 ft^2.
9. The process of claim 8 , wherein the paper has an M.I.T. Fold in the range of about 0.8 to 1.0 and a normalized to basis weight Gurley stiffness of about 4633 to 4747.
10. The process of claim 1 , wherein the process does not include use of a mix of hydrophobic surface size agent with polyacrylamide.
11. The process of claim 1 , wherein the paper product has a water Cobb value greater than 233.
12. The process of claim 1 , further comprising spraying a crosslinker onto the web.
13. The process of claim 1 , further comprising adding a crosslinker at a size press.
14. The process of claim 1 , wherein the crosslinker is added in an amount effective to provide an unlaminated sheet of paper having a stiffness and a rigidity at least equal to an equal caliper laminated sheet.