Polyelectrolyte Additive for Gravure Coating Stability
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Solution Overview
Problem
The Gravure printing process faces issues with core wrinkling and bursts due to static electricity and pigment agglomeration, which are exacerbated by high solids content and the use of polyvinyl alcohol (PVOH) in coating compositions, leading to increased costs and reduced process stability.
Innovation Solution
A composition comprising a pigment, polyvinyl alcohol, and a novel polyelectrolyte additive with ionisable carboxylate groups and amine functional groups, produced by polymerizing acrylic acid in the presence of hydroxyalkyl amines, acts as a steric stabilizer to prevent agglomeration and reduce static charge, allowing for high solids content and cost-effective processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high solids content is used in coating composition, then energy savings during drying and reduced binder quantity are achieved, but particle stability decreases and pigment particles agglomerate
Solution Approach 1:
The patent introduces a specific polyelectrolyte additive with amine terminal groups and carboxylate backbone groups as an intermediary substance. This additive mediates between the conflicting requirements of high solids content and particle stability by adsorbing onto pigment surfaces and providing electrostatic repulsion, preventing agglomeration even at high pigment concentrations and low water content.
Solution Approach 2:
The patent changes the chemical parameters of the coating system by incorporating a polyelectrolyte with specific molecular weight (500-4000 Daltons) and specific functional groups (amine terminals, carboxylate backbone). This parameter change enables the system to maintain stability at high solids content by modifying the electrostatic interactions between pigment particles.
2Illumination intensity
If polyvinyl alcohol is used as binder, then bright white coated paper is achieved, but pigment agglomeration increases due to interaction with optical brighteners at pH 7 and above
Solution Approach 1:
The polyelectrolyte additive acts as an intermediary that competes with PVOH for interaction with optical brighteners and pigment surfaces. The amine terminal groups of the polyelectrolyte interact with carboxyl groups of optical brighteners, preventing PVOH-brightener-pigment aggregation and maintaining pigment dispersion stability while allowing PVOH to provide brightness enhancement.
Solution Approach 2:
The patent changes the pH-sensitive interaction parameters by introducing a polyelectrolyte with amine groups that remain protonated and interactive at pH 7 and above. This parameter change allows the system to maintain stability in the alkaline pH range where PVOH would otherwise cause agglomeration through interaction with optical brighteners.
3Stability of the object's composition
If conventional polycarboxylates are used to stabilize pigment, then pigment dispersion is improved, but static charge dissipation occurs rapidly reducing process stability
Solution Approach 1:
The patent changes the molecular weight parameter of the polycarboxylate stabilizer from conventional high molecular weight to low molecular weight (500-4000 Daltons), and changes the terminal group from hydroxyl to amine. This parameter change results in reduced conductivity of the coating slurry, allowing static charge to be retained longer and improving process stability while maintaining pigment dispersion.
4Quantity of substance
If larger or coarser pigments are used, then cost is reduced, but manufacturing precision decreases due to increased agglomeration tendency
Solution Approach 1:
The polyelectrolyte additive serves as an intermediary that provides enhanced steric and electrostatic stabilization for coarse pigment particles. The low molecular weight and specific functional groups allow the additive to effectively adsorb onto larger pigment surfaces, preventing agglomeration and maintaining coating uniformity even when using cost-effective coarse pigments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition achieves improved stability, reduced shear viscosity, and enhanced process efficiency, enabling the production of wide, large-diameter paper rolls without wrinkles or core bursts, while using less expensive pigments and reducing the need for high additive quantities.
Implementation Method 1
the polyelectrolyte having amine functional groups at at least some of the terminals... acts as a steric stabilizer to prevent agglomeration
Implementation Method 2
decreases conductivity of the coating layer and contributes to increased static charge build up
Data Source
AI summary
The present invention relates to a composition comprising: (a) at least one pigment; (b) at least one binder including polyvinylalcohol; and (c) an additive, wherein the additive is a polyelectrolyte with a backbone that comprises ionisable carboxylate groups, the polyelectrolyte having amine functional groups at at least some of the terminals, and wherein the polyelectrolyte has an average molecular weight in the region of 500 to 4000 Daltons. The composition of the present invention is particularly useful for coating a paper product and Gravure printing processes.