Aqueous Polymer Latex Feed Method for TiO2 Hiding Power
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Solution Overview
Problem
Existing methods for improving the hiding or opacifying efficacy of titanium dioxide (TiO2) pigments in water-borne coatings are unsatisfactory, often requiring expensive phosphorous-containing monomers or complex dispersants, and result in instability and grit formation.
Innovation Solution
Aqueous polymer latex is prepared by radical emulsion polymerization of a monomer composition consisting of ethylenically unsaturated monomers, monoethylenically unsaturated monocarboxylic acids, and non-ionic monomers, with a specific feed method where the relative amount of acidic monomers is increased during certain periods of the polymerization process, allowing for effective adsorption of TiO2 particles without the need for expensive phosphorous-containing monomers and improving stability and scrub resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If phosphorous-containing monomers are used to improve TiO2 particle spacing and hiding power, then opacifying capacity is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive phosphorous-containing monomers with cheaper carboxylic acid monomers (acrylic acid, methacrylic acid, itaconic acid, fumaric acid) that achieve the same TiO2 spacing effect. These conventional monomers are more economical and widely available, reducing manufacturing cost while maintaining hiding power.
Solution Approach 2:
The patent changes the chemical parameter of the adsorbing groups from phosphorous-based to carboxylic acid-based functional groups. This parameter change maintains the ability to adsorb TiO2 particles and improve spacing while using more cost-effective materials.
2Illumination intensity
If phosphorous-containing monomers are used to improve TiO2 particle spacing, then hiding power is improved, but coating stability deteriorates due to flocculation and grit formation
Solution Approach 1:
The patent replaces phosphorous-containing monomers with conventional carboxylic acid monomers that do not cause flocculation and grit formation. These alternative monomers provide stable coating formulations while achieving the desired TiO2 particle spacing and hiding power.
Solution Approach 2:
The patent converts the potential harm of using conventional carboxylic acid monomers (which might be expected to cause instability) into a benefit by demonstrating that these monomers actually provide both good hiding power and stable coating formulations without flocculation or grit formation.
3Illumination intensity
If TiO2 pigment levels are increased to improve hiding power, then opacifying capacity is improved, but light scattering efficiency decreases due to particle crowding
Solution Approach 1:
The patent introduces carboxylic acid-containing polymer as an intermediary substance that adsorbs onto TiO2 particle surfaces. This intermediary layer prevents direct particle-to-particle contact and maintains optimal spacing, allowing high TiO2 levels to be used without crowding effects, thereby preserving light scattering efficiency.
Solution Approach 2:
The patent changes the surface chemistry parameter of TiO2 particles by introducing carboxylic acid groups that adsorb onto the particle surfaces. This parameter change creates electrostatic or steric repulsion between particles, maintaining uniform spacing even at high pigment concentrations.
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 achieves good hiding and opacifying efficacy, stability, and scrub resistance in water-borne coatings without using expensive phosphorous-containing monomers, reducing grit formation and enhancing the compatibility of TiO2 particles.
Implementation Method 1
a polymer latex which is capable of adsorbing the TiO2 particles on the surface of the polymer latex particles
Implementation Method 2
coatings containing a titanium dioxide pigment and use of said aqueous polymer latex as a binder or co-binder in a water-borne coating composition which contains a titanium dioxide pigment
Data Source
AI summary
Disclosed herein is a process for preparing an aqueous polymer latex by polymerising a monomer composition M by a radical emulsion polymerisation, where at least 95% of the monomer composition M is metered during a period P to the polymerisation reaction under polymerisation conditions, such that during at least one period P(n) within the period P, the relative amount of monomers M2, which are metered to the polymerisation reaction during the periods P(n), to the total amount of the monomer composition M, which is metered to the polymerisation reaction during said period P(n), is at least 1% by weight higher than the relative amount of monomers M2, which are metered to the polymerisation reaction outside of each of said periods P(n), to the total amount of the monomer composition M, which is metered to the polymerisation reaction outside of each of said periods P(n).