Vinyl Polymer Dispersion for Low VOC Coatings
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Solution Overview
Problem
Current waterborne coatings lack in-can clarity and film-forming properties at low temperatures, often requiring high levels of volatile organic compounds (VOC) to achieve proper film formation, which is undesirable due to environmental regulations and affects coating quality such as transparency and chemical resistance.
Innovation Solution
A process for preparing an aqueous dispersion of hydroplasticisable multiphase vinyl polymer particles through a two-stage emulsion polymerization, using a sulfur-based anionic surfactant and controlled inorganic salt content, with specific monomer mixtures and polymerization conditions to achieve particles with low particle size and high transparency, allowing for improved film-forming and coating properties without high VOC levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If waterborne coatings use dispersed polymer particles to achieve environmental compliance, then VOC content is reduced, but in-can clarity and transparency are worsened due to light scattering
Solution Approach 1:
The patent changes the particle size parameter to below 50 nm and controls the particle size distribution to achieve a balance between reduced VOC content and improved in-can clarity. This parameter optimization allows waterborne coatings to maintain transparency while complying with environmental regulations.
Solution Approach 2:
The patent creates a core-shell structure where the core contains dispersed polymer particles and the shell provides a transparent interface. This local quality differentiation allows the coating to maintain both environmental compliance and optical clarity by optimizing the properties of different regions within the coating structure.
2Strength
If polymer dispersion has high Tg to achieve good hardness and block resistance, then coating durability is improved, but film formation at ambient temperature deteriorates due to insufficient coalescence
Solution Approach 1:
The patent segments the polymer structure into core and shell phases with different Tg values. The core contains high Tg polymer for hardness and block resistance, while the shell contains lower Tg polymer that facilitates film formation at ambient temperature. This segmentation allows both contradictory requirements to be satisfied simultaneously.
Solution Approach 2:
The patent creates a composite polymer structure combining high Tg and low Tg polymer phases. The high Tg phase provides mechanical properties (hardness, block resistance) while the low Tg phase enables film formation. This composite approach resolves the contradiction between durability and film formation capability.
3Reliability
If low molecular weight hydrophilic oligomer is used to improve film formation, then coalescence is enhanced, but coating properties such as chemical resistance and hardness deteriorate
Solution Approach 1:
The patent segments the functional roles into different polymer phases: the low Tg phase (5-30 wt%) provides film formation capability while the high Tg phase (70-95 wt%) maintains chemical resistance and hardness. This segmentation prevents the low molecular weight oligomer from dominating the entire coating structure.
Solution Approach 2:
The patent precisely controls the molecular weight and concentration of the hydrophilic oligomer phase, limiting it to 5-30 wt% of the total polymer composition. This parameter control ensures sufficient film formation while preventing excessive softening that would compromise chemical resistance and hardness.
4Reliability
If base is added to hydroplasticise the polymer dispersion, then film formation at ambient temperature is improved, but pH control becomes problematic for alkali sensitive substrates
Solution Approach 1:
The patent segments the functional requirements by incorporating film formation capability directly into the polymer structure through the low Tg phase, rather than relying on base addition. This allows the coating to achieve good film formation at lower pH levels suitable for alkali-sensitive substrates.
Solution Approach 2:
The patent creates a polymer structure that copies the film formation function of high pH dispersions but achieves it through structural design (core-shell morphology and Tg differentiation) rather than chemical modification via base addition. This structural copying enables film formation without the harmful high pH effect.
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 results in a vinyl polymer dispersion with excellent in-can clarity and film-forming properties at high solid contents, maintaining coating quality while reducing VOC requirements, suitable for applications like clear wood-coatings and sensitive substrates.
Implementation Method 1
wherein surfactant (1a2) is a sulfur based anionic surfactant containing less than 60 wt% ethylene oxide
Implementation Method 2
a first polymerization step comprising (1a) preparing an emulsion (1A) in water of a first monomer mixture (1a1), a surfactant (1a2) and a water soluble inorganic salt (1a3)... (1b) emulsion polymerizing the obtained emulsion 1A forming a hydroplasticisable first stage polymer particle dispersion (1B)
Implementation Method 3
wherein the water soluble inorganic salt (1a3) content at the start of polymerization (1b) is between 0.01 and 3 g/kg water
Data Source
AI summary
The invention relates to a process for the preparation of aqueous vinyl polymer dispersions having good film forming properties, good stability and in can clarity, to the polymer dispersions obtainable by the process and coating compositions prepared from said polymer dispersions and the use thereof, said process comprising a first emulsion polymerisation step of a first monomer mixture, a sulfur based anionic surfactant containing less than 60 wt% ethylene oxide and a salt content at the start of polymerization is between 0.01 and 3 gr/kg water and a second polymerization step of a second monomer mixture wherein carboxylic acid functional monomers is present in an amount such that the acid value of the resulting polymer is less than 23 KOH/g.