Heat Sealable Coating Compositions Using Segmented Polymer Microparticles
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Solution Overview
Problem
Existing polymer dispersions in organic liquids for metal container coatings have limitations due to high viscosity and large particle size, leading to sedimentation issues, uneven coating distribution, and variable seal strengths, which affect the flexibility, adhesion, and shelf life of food and drink containers.
Innovation Solution
A process involving a mixture of polypropylene polymers with functional groups reacting under high shear conditions in an extruder to form polymer microparticles in an organic liquid, resulting in a dispersion with improved stability and even distribution, reducing sedimentation and enhancing seal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If polypropylene dispersions with large mean particle size (approximately 10 μm) are used to increase polypropylene content in coating, then the amount of polypropylene that can be incorporated is limited to less than about 15%, but the high viscosity of such dispersions limits the maximum workable solids to about 17% wt/wt
Solution Approach 1:
The patent segments the polypropylene into much smaller microparticles with mean particle sizes of 0.5 to 5 μm, dramatically reducing particle size compared to conventional 10 μm particles. This segmentation allows significantly higher polypropylene content (up to 40% or more) to be incorporated into the coating while maintaining acceptable viscosity and workability, as the smaller particles create less resistance to flow and can be more evenly distributed in the dispersion medium.
Solution Approach 2:
The patent changes the critical parameter of particle size from 10 μm to 0.5-5 μm, which fundamentally alters the rheological properties of the dispersion. This parameter change reduces viscosity and enables higher solids content while maintaining ease of application and coating formation.
2Quantity of substance
If polypropylene dispersions with large mean particle size (approximately 10 μm) are used, then the dispersions are prone to forming hard, difficult to redisperse sediments, but high speed stirring and high circulation rates are required to prevent sedimentation
Solution Approach 1:
By segmenting polypropylene into fine microparticles (0.5-5 μm), the patent dramatically improves suspension stability. The smaller particle size reduces gravitational settling velocity according to Stokes' law, and the increased surface area to volume ratio enhances interaction with dispersant molecules, preventing aggregation and sedimentation. The resulting dispersions remain stable without requiring high-speed stirring or high circulation rates.
Solution Approach 2:
The patent employs dispersants as intermediary substances that adsorb onto the surface of polypropylene microparticles, providing steric or electrostatic stabilization. These dispersant molecules act as mediators between the hydrophobic polypropylene particles and the aqueous or organic dispersion medium, preventing particle aggregation and sedimentation while enabling high polypropylene content.
3Quantity of substance
If particles of average diameter of 10 μm are used with typical coating thickness of 3 to 9 μm, then a substantial population of particles protrude beyond the surface, but stoving causes some flow and results in islands of polypropylene rather than evenly distributed layer
Solution Approach 1:
By reducing particle size to 0.5-5 μm, the patent ensures that even at coating thicknesses of 3-9 μm, the particles are small enough to be fully embedded within the coating matrix rather than protruding. During stoving, these fine particles can distribute evenly throughout the coating thickness, forming a uniform polypropylene distribution that provides consistent seal strength without creating surface islands or defects.
4Stability of the object's composition
If conventional polypropylene dispersions are used, then the coating requires high speed stirring and high circulation rates to prevent sedimentation, but these strategies use increased amounts of energy and add unnecessarily to carbon dioxide emissions
Solution Approach 1:
The patent's segmentation of polypropylene into fine microparticles (0.5-5 μm) creates inherently stable dispersions that resist sedimentation without requiring energy-intensive high-speed stirring or high circulation rates. The smaller particle size and increased surface area enable effective dispersant adsorption and reduced gravitational settling, allowing storage and processing at low energy consumption with minimal agitation.
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 produces polymer microparticles with controlled particle size and distribution, improving the flexibility, adhesion, and shelf life of metal container coatings by preventing sedimentation and ensuring consistent seal strengths, thus enhancing the integrity and safety of food and drink containers.
Implementation Method 1
causing the polymers to melt at a chosen temperature under conditions of high shear, preferably in an extruder, to form an intimate mixture
Implementation Method 2
causing the polymers to melt at a chosen temperature under conditions of high shear
Implementation Method 3
causing the polymers to melt at a chosen temperature under conditions of high shear, preferably in an extruder, to form an intimate mixture
Implementation Method 4
cooling the solution to a temperature whereby the polymer microparticles of the dispersion are formed
Implementation Method 5
cooling the solution to a temperature whereby the polymer microparticles of the dispersion are formed
Data Source
AI summary
A dispersion of polymer microparticles in organic liquid obtainable by a process comprising the steps of i) providing a mixture comprising a first polymer having functional groups capable of reacting with the carboxylic acid and/or carboxylic acid anhydride groups of a second, polypropylene polymer ii) causing the polymers to melt at a chosen temperature under conditions of high shear, preferably in an extruder, to form an intimate mixture iii) causing the carboxylic acid and/or carboxylic acid anhydride groups of the polypropylene polymer to react with at least some of the functional groups of the first polymer, under conditions of high shear, preferably in an extruder iv) diluting the resulting mixture of step iii) with an organic liquid at a temperature such that a substantially homogeneous solution is formed v) cooling the solution to a temperature whereby the polymer microparticles of the dispersion are formed.