Polysiloxane Acrylate Copolymers for Coating Flow Modification
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Solution Overview
Problem
Existing flow modifiers for coating compositions, such as poly(meth)acrylate and polysiloxane-based additives, often lead to surface irregularities like 'orange peel' due to incompatibility with binders, and conventional polymerization methods like RAFT are inefficient and produce undesirable byproducts.
Innovation Solution
Copolymers comprising vinyl-terminated polysiloxanes, two or more alkyl esters of olefinically unsaturated carboxylic acids with varying alkyl chain lengths, and hydroxyalkyl esters, synthesized through radically initiated polymerization, are used as flow modifiers to promote leveling and smooth coating films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polysiloxane-based flow modifiers are used to improve surface smoothness, then levelling performance is improved, but surface irregularities such as craters and clouding occur due to incompatibility with binder
Solution Approach 1:
The invention uses block copolymers comprising both polysiloxane moieties (for levelling) and poly(meth)acrylate moieties (for binder compatibility). This composite structure allows the flow modifier to simultaneously achieve smooth surface formation while maintaining compatibility with the coating binder, preventing craters and clouding.
Solution Approach 2:
Different blocks of the copolymer perform different functions: the polysiloxane blocks provide levelling action at the liquid-gas interface, while the poly(meth)acrylate blocks ensure compatibility with the binder. This local differentiation of function within the single additive resolves the contradiction between levelling performance and compatibility.
2Manufacturing precision
If RAFT polymerisation is used to produce low polydispersity polymers, then molecular weight control is improved, but sulfur contamination and colour issues arise from the RAFT agent
Solution Approach 1:
The invention removes the harmful RAFT agent (with sulfur and colour issues) from the final polymer structure while retaining the benefits of controlled polymerisation. This is achieved by using a chain transfer agent that does not leave unwanted residues, thereby extracting the harmful sulfur-containing components from the system.
Solution Approach 2:
The invention uses a conventional radical initiator instead of RAFT agents, accepting that the initiator will be consumed and decompose during polymerisation. This disposable approach avoids the long-term stability and contamination issues of RAFT agents while achieving sufficient molecular weight control.
3Manufacturing precision
If flow modifier mass fraction is increased to improve levelling, then surface smoothness is improved, but incompatibility effects and surface irregularities worsen
Solution Approach 1:
The invention changes the chemical composition parameters of the flow modifier by using block copolymers with specific ratios of polysiloxane to poly(meth)acrylate blocks. This parameter optimization allows effective levelling at lower mass fractions while maintaining binder compatibility, avoiding the worsening of incompatibility effects.
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
These copolymers effectively improve surface smoothness and wetting while avoiding surface irregularities, with a conventional polymerization process that eliminates sulfur and color issues, achieving optimal mass fractions for enhanced performance in coating compositions.
Implementation Method 1
The effect of these flow modifiers is presumably also based on their effect on the liquid-gas interface, where these products are accumulated owing to a certain incompatibility with the binder of the coating system
Implementation Method 2
All these different words describe different aspects of an additive that modifies the flow behaviour including shear and elongational viscosity, interfacial adhesion, and also surface tension, of a paint composition or coating composition
Data Source
AI summary
This invention relates to copolymers AB having moieties derived from vinyl-terminated polysiloxanes A with more than one vinyl group bound to the polysiloxane, and moieties derived from two or more alkyl esters B of an olefinically unsaturated carboxylic acid, wherein at least two different alkyl esters B1 and B2 are used; the alkyl group of the first alkyl ester B1 of an olefinically unsaturated carboxylic acid has from one to five carbon atoms, the alkyl group of the second alkyl ester B2 of an olefinically unsaturated carboxylic acid has from six to thirty carbon atoms, and moieties derived from at least one hydroxyalkyl ester B3 of an olefinically unsaturated carboxylic acid, the ester B3 having at least one hydroxyl group in the alkyl group, and from two to six carbon atoms in the alkyl group, to a process for their preparation, and to a method of use thereof as flow modifiers in coating compositions.