Process for Enhancing Dry Strength of Paper by Treatment with Vinylamine-Containing Polymers and Acrylamide-Containing Polymers

Abstract

A process is disclosed for the production of paper with enhanced dry strength comprising adding to the wet end of a paper machine, (a) a vinylamine-containing aqueous solution polymer having a molecular weight of from 75,000 daltons to 750,000 daltons and (b) an amphoteric or cationic acrylamide-containing aqueous solution polymer having a molecular weight of from 75,000 daltons to 1,500,000 daltons, wherein the sum of the anionic and cationic monomers comprises at least 5% on a molar basis of the composition of the acrylamide-containing polymer.

Description

[0001]This Application claims priority of U.S. Provisional Application No. 61 / 290,670, filed Dec. 29, 2009, the entire contents of which are herein incorporated by reference.FIELD OF THE INVENTION[0002]This invention relates to enhanced dry strength in paper using a process of treating a pulp slurry with a combination of a vinylamine-containing polymer and a cationic or amphoteric acrylamide-containing polymer.BACKGROUND OF THE INVENTION[0003]The papermaking industry is constantly seeking new synthetic additives to improve the dry strength of paper products. Improved dry strength can give a higher performance product, but also may allow the papermaker to use less cellulosic fiber to achieve a particular performance target. Furthermore, the increased usage of recycled fiber results in a weaker sheet, forcing the papermaker to either increase basis weight of the sheet or employ synthetic strength additives. The options that are known have various economic and technical limitations. Fo...

AI Technical Summary

Benefits of technology

[0012]Treatment of a pulp slurry with a vinylamine-containing aqueous solution polymer in combination with a ca

Problems solved by technology

Furthermore, the increased usage of recycled fiber results in a weaker sheet, forcing the papermaker to either increase basis weight of the sheet or employ synthetic strength additives.

The options that are known have various economic and technical limitations.

However, these combinations also may elevate the wet strength of the resultant paper to the point that repulping broke paper is extremely difficult and inefficient.

Polymers of acrylamide or copolymers incorporating acrylamide and a monomer such as diallyldimethylammonium chloride, when treated with a dialdehyde compound such as glyoxal, are widely known to result in resins that can also enhance the dry strength of paper significantly, yet have very limited permanent wet strength properties, allowing the papermaker to easily repulp broke paper.

However, these resins also have their limitations.

These additives either have a very short shelf-life due to viscosity instability, or are shipped at very low active solids content.

Furthermore, when added in the larger amounts, the performance of such dialdehyde-modified acrylamide-containing polymers tends to reach a plateau, making a high-performance product difficult to manufacture.

However, when added in ever increasing amounts, they have the negative effect of overflocculating the sheet because of the heavy cationic charge these resins carry.

Overflocculation results in a poorly formed, weaker finished product.

However, the aforementioned drawbacks of glyoxalated polyacrylamides, namely low active solids of the product and limited viscosity stability of the product, are clearly in play.

However, examples from the prior art that may include these polymers have significant drawbacks.

For instance, previous examples may require special metering apparatuses, additional steps for treating starch prior to addition to the pulp slurry, or high molar mass polymers that may result in overflocculation of the pulp slurry when added in sufficient amounts to affect dry strength.