Dry End Polymer Coating for Paper Strength

The patent applies strength additives at the dry end of the papermaking process after sheet formation has occurred, rather than at the wet end during fiber suspension. This preliminary action (applying after formation) allows the additives to bond to formed fibers without interfering with fiber quality, machine drainage, or operational processes that occur during wet end papermaking.

The patent extracts the strength enhancement function from the wet end process and separates it into a distinct dry end application step. By taking out the strength additive application from the wet end fiber suspension process, the harmful interferences with fiber quality and machine operations are eliminated while preserving the beneficial paper strength improvement.

The patent employs a composite additive system comprising multiple components: a cationic polymer (such as polydiallyldimethylammonium chloride), an acrylamide polymer, and optionally a starch component. This composite material approach creates synergistic interactions between components that enhance dry strength while the specific composition ratios and molecular characteristics maintain solution stability, preventing precipitation and excessive viscosity buildup during application.

The patent optimizes specific parameters of the additive components including charge density, molecular weight, and composition ratios. By carefully controlling these parameters (e.g., using cationic polymers with specific charge densities and acrylamide polymers with controlled molecular weights), the system achieves both improved dry strength and maintained solution stability, avoiding precipitation and viscosity issues that plague other surface applied additives.