Polymer Dispersion Particle Size Control for Coating Adhesion
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Solution Overview
Problem
Current polymer dispersions used for coating metal food and drink containers are unsuitable for thin film applications due to large particle sizes, leading to uneven coatings and poor adhesion, which affects the shelf life and safety of the contents.
Innovation Solution
A process involving a mixture of polypropylene polymer with carboxylic acid groups and a second polymer, melted under high shear in an extruder, followed by rapid cooling and dispersion in an organic liquid, to produce small particle size polymer dispersions with a narrow particle size distribution, ensuring stability and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polymer dispersions are used for coating metal containers, then the coating can be applied, but the particle size is too large causing uneven coatings and poor adhesion
Solution Approach 1:
The patent applies parameter changes by controlling the particle size distribution of the polymer dispersion to achieve mean particle sizes between 0.1-10 μm with narrow distributions (P90/P10 ratio < 2.0). This parameter optimization resolves the contradiction by ensuring both coating uniformity and adhesion quality are achieved simultaneously through precise control of dispersion characteristics
Solution Approach 2:
The patent employs preliminary action by pre-treating the polymer particles through controlled polymerization and dispersion formation before application. The narrow particle size distribution is established in advance during manufacturing, ensuring that when the coating is applied to metal containers, both uniformity and adhesion are achieved without requiring additional processing steps
2Ease of manufacture
If polymer dispersions with large particles are used, then the coating can be applied to metal containers, but the coating becomes uneven and adhesion is poor
Solution Approach 1:
The patent resolves this contradiction by changing the particle size parameters to mean sizes of 0.1-10 μm with narrow distributions (P90/P10 < 2.0). This parameter optimization allows the coating to be applied easily while achieving uniform coverage, as the smaller, more uniformly sized particles flow and distribute more evenly across the metal surface
3Length of stationary object
If polymer dispersions are used for thin film coatings, then the coating thickness can be reduced, but particles greater than 10 μm cause uneven surfaces
Solution Approach 1:
The patent applies parameter changes by limiting particle sizes to 0.1-10 μm with narrow distributions, which enables thin film coatings (≤10 μm) to be achieved with uniform surfaces. The controlled particle size ensures that even at reduced thicknesses, the coating maintains surface uniformity without the roughness caused by larger particles
4Productivity
If conventional polymer dispersions are used, then the coating can be applied, but filtration losses occur and storage stability is reduced
Solution Approach 1:
The patent resolves this contradiction by optimizing particle size parameters to mean sizes of 0.1-10 μm with narrow distributions (P90/P10 < 2.0). This parameter control reduces filtration losses by preventing particle aggregation and maintains storage stability by ensuring uniform particle sizes that resist sedimentation and phase separation, while still allowing adequate coating application rates
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 polymer dispersions with mean particle sizes less than 5 μm, enhancing storage stability and minimizing filtration losses, while providing coatings with improved adhesion and flexibility for metal containers.
Implementation Method 1
causing some of the carboxylic acid and/or carboxylic acid anhydride groups of the polypropylene to react with at least some of the functional groups of the second polymer to form a reaction mixture
Implementation Method 2
causing the polymers to melt at a chosen temperature under conditions of high shear in an extruder to form an intimate mixture of the polymers
Implementation Method 3
rapidly cooling the reaction mixture outside the extruder to form a solid product
Implementation Method 4
contacting the solid product with an organic liquid wherein the organic liquid is chosen to be a good solvent for the second polymer and a poor solvent for the polypropylene polymer whereby a dispersion comprising polypropylene particles in a solution of the second polymer dissolved in the organic liquid is formed
Data Source
AI summary
A process for the manufacture of a polymer dispersion from a mixture of a first polypropylene polymer having sufficient carboxylic acid and/or carboxylic acid anhydride groups equivalent to an acid value of from 2 to 50 mg KOH/g nv polymer and a second polymer having a molar excess of functional groups capable of reacting with the carboxylic acid and/or carboxylic acid anhydride groups of the polypropylene is provided. Also provided herein are polypropylene dispersions in organic carrier liquid prepared by such method, as well as coating compositions comprising the dispersion and articles coated with the coating composition.