Aqueous Binder Composition for Sag-Resistant Coatings
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Solution Overview
Problem
Aqueous binder compositions colloidally stabilized with low molecular weight and acid-containing polymers exhibit poor interaction with thickening agents, resulting in low viscosity at high shear and slow build-up of low-shear viscosity, leading to sagging issues during coating applications.
Innovation Solution
An aqueous binder composition is prepared through a process involving the sequential emulsion polymerization of carboxylic acid-functional vinyl polymer and vinyl polymer, where the acid value of the latter is lower and the molecular weight is higher than the former, with specific chain transfer agents used in each stage to achieve the desired properties, allowing for low viscosity at high shear and high viscosity at low shear with rapid build-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If aqueous binder compositions are stabilized using low molecular weight and acid containing polymers, then colloidal stability is improved, but interaction with thickening agents deteriorates resulting in low viscosity and slow build-up of low-shear viscosity
Solution Approach 1:
The invention segments the polymer stabilizer into two distinct components: a first vinyl polymer with high acid value (30-130 mg KOH/g) and low molecular weight (5,000-70,000 Da) for colloidal stability, and a second vinyl polymer with low acid value (0-25 mg KOH/g) and high molecular weight (100,000-1,000,000 Da) for thickening agent interaction. This segmentation allows each polymer to perform its specific function optimally without compromise.
Solution Approach 2:
The invention creates a composite polymer system where two vinyl polymers with different molecular weights and acid values work synergistically. The composite nature of the stabilizer system enables both colloidal stability (from the low molecular weight high acid polymer) and good interaction with thickening agents (from the high molecular weight low acid polymer), resolving the contradiction between these two requirements.
2Ease of operation
If low viscosity at high shear is achieved for easy application, then coating application efficiency is improved, but sagging resistance deteriorates
Solution Approach 1:
The invention employs dynamic viscosity control through the use of associative thickening agents that interact with the high molecular weight vinyl polymer. This creates a shear-dependent viscosity profile where the coating shows low viscosity under high shear stress during application (enabling easy spraying/brushing) but rapidly builds high viscosity at low shear stress after application (preventing sagging).
Solution Approach 2:
The invention changes the viscosity parameter dynamically by selecting polymers with specific molecular weights and acid values that enable rapid viscosity build-up. The high molecular weight second polymer (100,000-1,000,000 Da) with low acid value creates strong interactions with thickening agents, enabling the viscosity to change from low (during application) to high (after application) based on shear rate conditions.
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 high viscosity at low shear rates, reducing sagging and improving coating application efficiency while maintaining low viscosity at high shear rates, thus enhancing the coating process.
Implementation Method 1
The polymer particles comprise at least two vinyl polymers obtained by emulsion polymerisation
Implementation Method 2
aqueous binder compositions containing polymer emulsions that are colloidally stabilized using low molecular weight and acid containing polymers
Data Source
AI summary
The current invention relates to a process for preparing an aqueous binder composition, the process comprising at least the following steps A) and B): A) preparing carboxylic acid-functional vinyl polymer (Polymer A) by emulsion polymerisation of a monomer composition A comprising the following monomers: Ai) at least one carboxylic acid functional olefinically unsaturated monomer; and Aii) at least one olefinically unsaturated monomer different than Ai); B) preparing vinyl polymer (Polymer B) by emulsion polymerization of a monomer composition B in the presence of Polymer A where the monomer composition B comprises the following monomer(s): Bi) at least one olefinically unsaturated monomer; Bii) optionally carboxylic acid functional olefinically unsaturated monomer different than Bi); where at least part of the carboxylic acid groups of Polymer A are deprotonated to obtain ionic or potentially ionic water-dispersing groups; where the acid value of Polymer B is lower than the acid value of Polymer A; where the weight average molecular weight (Mw) of Polymer B is higher than the weight average molecular weight (Mw) of Polymer A; where the glass transition temperature of Polymer B is equal to or lower than that of Polymer A; where the weight ratio of Polymer A to Polymer B is in the range of from 5:95 to 95:5; and whereby step A) comprises at least a first polymerisation stage of a monomer composition A1 effected in the presence of a chain transfer agent C1 having a water solubility of at least 5 g/L and a subsequent second polymerisation stage of a monomer composition A2 effected in the presence of a chain transfer agent C2 having a water solubility of at most 0.5 g/L, and whereby the second polymerisation stage of step A) is effected in the optional further presence of chain transfer agent C1 having a water solubility of at least 5 g/L whereby the concentration of chain transfer agent C1 having a water solubility of at least 5 g/L in the second polymerisation stage of step A) is at most 35 mole-%, relative to the total molar concentration of chain transfer agent C1 and chain transfer agent C2 present in the second polymerisation stage of step A).