Wood Coating Sequence Using Anionic Polymers to Block Knot Staining
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Solution Overview
Problem
Existing cationic coating compositions for wood coatings suffer from production issues and high susceptibility to staining and discoloration due to the migration of wood extractives, particularly in softwood species like pine, leading to knot-bleeding and staining.
Innovation Solution
A two-step process involving the application of anionic polymers with specific Hansch parameters, where Polymer A has a Hansch parameter ≤1.6 and Polymer B ≥1.7, is used to form a coating system that prevents staining and discoloration by entrapping extractives, using free radical aqueous emulsion polymerization of ethylenically unsaturated monomers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If cationic coating compositions are used to block stains, then staining resistance is improved, but production reliability deteriorates due to agglomerations and impurities
Solution Approach 1:
The patent inverts the conventional approach by using anionic polymers instead of cationic polymers. This reversal eliminates the aggregation and impurity problems associated with cationic formulations while maintaining effective stain blocking through the anionic polymer's ability to interact with chromophoric constituents
Solution Approach 2:
The patent changes the charge parameter of the polymer from cationic to anionic, fundamentally altering the chemical properties and interaction mechanisms. This parameter change resolves the production issues while preserving the stain blocking function through different chemical pathways
2Ease of manufacture
If anionic coating compositions are used to improve production compatibility, then manufacturing ease is improved, but staining resistance deteriorates
Solution Approach 1:
The patent modifies the molecular structure parameters of the anionic polymer, specifically incorporating functional groups with appropriate Hansch parameters (≤1.6) that provide both water solubility and chromophore interaction capability, thereby achieving both manufacturing ease and staining resistance
Solution Approach 2:
The patent creates a composite functional system within the anionic polymer by combining hydrophilic segments for water solubility and anionic charge with hydrophobic segments and specific functional groups for chromophore interaction, achieving dual functionality in a single material
3Productivity
If water-based coating compositions are used, then environmental compatibility is improved, but extractive migration increases causing discoloration
Solution Approach 1:
The anionic polymer acts as an intermediary substance that intercepts chromophoric constituents before they can migrate to the coating surface. The polymer's functional groups bind to these extractives, preventing their migration while maintaining the water-based formulation's environmental benefits
4Reliability
If primers are applied to seal wood and improve adhesion, then coating performance is improved, but water stability deteriorates due to leaching
Solution Approach 1:
The patent adjusts the polymer's hydrophobicity parameter (Hansch parameter ≤1.6) to optimize the balance between water solubility for application and water resistance for stability. This parameter optimization prevents excessive water sensitivity while maintaining coating performance
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 process effectively prevents staining and discoloration on wood surfaces, particularly over pine knots, by creating a stable coating system that minimizes the migration of wood extractives, ensuring high water stability and resistance to soiling.
Implementation Method 1
the anionic polymer A with a Hansch parameter ≤1.6... the anionic polymer B with a Hansch parameter ≥1.7... prevents the migration of stains like a marking pen or tannins from wooden substrates to the top of the coating by complexation of the stain by the phosphoethyl methacrylate group in the hydrophobic polymer
Implementation Method 2
the anionic polymer A is obtained by free radical aqueous emulsion polymerization of a mixture comprising ethylenically unsaturated monomers A, and wherein the anionic polymer B is obtained by free radical aqueous emulsion polymerization of a mixture comprising ethylenically unsaturated monomers B
Data Source
AI summary
The present invention relates to a process of coating wood with at least two waterbased coating compositions the process comprising: a) applying a coating composition A comprising at least one anionic polymer A with a Hansch parameter ≤1.6, and drying or allowing to dry said aqueous coating composition A, b) applying a coating composition B comprising at least one anionic polymer B with a Hansch parameter ≥1.7 and pigment, and drying or allowing to dry said aqueous coating composition B, with the proviso that the difference of the Hansch Parameters of anionic polymer B and anionic polymer A is at least 0.5. The invention also relates to wood coated accordingly, and the use of a coating composition A, comprising an aqueous anionic polymer A with a Hansch parameter ≤1.6, as an undercoat for coating wood.