Aqueous Antimicrobial Coating with Silver Color Stability
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Solution Overview
Problem
Aqueous binder and coating compositions containing inorganic microbiocides with metal ions undergo conspicuous coloration changes upon exposure to heat or sunlight, limiting their use, and increasing silver content for antiviral properties exacerbates this issue, while traditional polymerization processes lead to high coagulum formation.
Innovation Solution
An aqueous antimicrobial composition comprising a multistage polymer with imidazole pendant groups and silver, stabilized by a multistage free-radical polymerization process, achieving less than 500 ppm coagulum and improved coloration stability with a heterocyclic to silver mole ratio greater than 4:1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver content is increased to provide antiviral properties, then antimicrobial efficacy is improved, but coloration stability deteriorates
Solution Approach 1:
The patent introduces heterocyclic groups (such as imidazole, benzotriazole, or benzimidazole) as intermediary ligands that complex with silver ions. These heterocyclic groups act as mediators between the silver ions and the polymer binder, forming stable coordination complexes that prevent direct interaction between silver ions and the binder that would cause discoloration. The heterocyclic groups stabilize the silver ions while maintaining their antimicrobial and antiviral activities.
Solution Approach 2:
The patent creates a composite structure where silver ions are complexed with heterocyclic-containing polymer binders. This composite material combines the antimicrobial properties of silver with the stabilizing effect of heterocyclic groups, achieving both high efficacy and coloration stability. The composite approach allows the system to benefit from multiple functional components working together.
2Stability of the object's composition
If imidazole monomer content is increased to improve coloration stability, then coloration stability is improved, but polymerization process stability deteriorates
Solution Approach 1:
The patent optimizes the concentration parameter of heterocyclic monomers to a specific range (0.1-10% by weight, preferably 0.5-5%). This parameter change balances two competing requirements: sufficient heterocyclic groups to complex with silver ions and stabilize coloration, while maintaining low enough concentration to avoid excessive coagulum formation during polymerization. The patent also controls the molecular weight of the polymer (10,000-1,000,000) as another parameter to ensure process stability.
Solution Approach 2:
The patent applies partial action by using a moderate amount of heterocyclic monomers (not excessive amounts) to achieve the necessary stabilization effect. This partial approach prevents the excessive coagulum formation that would occur with high monomer concentrations while still providing sufficient heterocyclic groups for silver complexation and coloration stability.
3Reliability
If silver content is increased for antiviral properties, then antimicrobial and antiviral efficacy are improved, but coagulum formation increases
Solution Approach 1:
The heterocyclic groups serve as intermediaries that complex with silver ions, preventing direct aggregation of silver particles that would lead to coagulum formation. The heterocyclic-containing polymer chains act as steric barriers and solubilizing agents, keeping silver ions dispersed in the aqueous medium while maintaining their bioactive state for antimicrobial and antiviral efficacy.
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 provides good process stability and improved coloration stability upon exposure to heat, suitable for coating applications with antimicrobial properties.
Implementation Method 1
silver complexed with polymers bearing imidazole pendant groups
Implementation Method 2
multistage free-radical polymerization process
Data Source
AI summary
Discloses an aqueous antimicrobial coating composition comprising: (A) a polymer obtained by a multistage polymerisation and composed of: 75% to 95% of a first-stage polymer and from 5% to 25% of a second-stage polymer; wherein the first-stage polymer comprises: monoethylenically unsaturated functional monomers carrying at least one functional group selected from a carboxyl, carboxylic anhydride, sulfonic acid, amide, sulfonate, phosphoric acid, phosphonate, phosphate, or hydroxyl group (e.g. acrylic acid, acrylamide); <1.0% of a monomers bearing imidazole, benzotriazole, or benzimidazole; and monoethylenically unsaturated nonionic monomers (e.g. alkyl acrylate); wherein the second-stage polymer has MW=8000 to 30000 g/mol and comprises: residues of C6-C24 alkyl thiol (e.g. dodecyl mercaptan); monomers bearing imidazole, benzotriazole, or benzimidazole (e.g. vinyl imidazole); and monomers of alkyl acrylate; wherein the monomers bearing imidazole, benzotriazole, or benzimidazole in a multistage polymer are present at a total concentration of 0.5% to 8%; and (B) 1 to 10000 ppm of a silver, wherein the mol ratio of monomers bearing imidazole, benzotriazole, or benzimidazole to silver is greater than 4; and (C) <500 ppm of coagulum (coagulates having diameter>44 micrometers); and a method of preparing such aqueous antimicrobial composition and a coating composition comprising such aqueous antimicrobial composition and a pigment.