Core-Shell Polymer Dispersion for Aluminum Heat Sealing
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Solution Overview
Problem
Existing heat-sealing lacquers for aluminum and food packaging materials lack adequate corrosion protection and blocking resistance, requiring improved formulations that are free from PVC and polyvinylchloride, with a need for higher heat-seal-seam strengths and better peelability.
Innovation Solution
An aqueous dispersion comprising particles with a specific monomer composition and particle size, produced through emulsion polymerization, is used in a heat-sealing lacquer that includes a first polymer phase with a glass transition temperature of -20 to 30°C and a second phase with a glass transition temperature of 20 to 50°C, featuring a core-shell structure and the use of a chain-transfer agent, which is applied as a single layer for sealing aluminum and polylactide surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing heat-sealing lacquers are used for aluminum and food packaging materials, then heat-sealing function is achieved, but corrosion protection is inadequate and blocking resistance is poor
Solution Approach 1:
The patent divides the polymer system into two distinct polymer phases with different glass transition temperatures (Tg1: -20 to 30°C and Tg2: 20 to 50°C). This segmentation allows each phase to contribute different properties: the lower Tg phase provides flexibility and corrosion resistance, while the higher Tg phase provides structural integrity and blocking resistance, resolving the contradiction between these two properties.
Solution Approach 2:
The invention creates a composite polymer system combining two copolymers with specific monomer compositions and Tg ranges. This composite structure integrates the beneficial properties of both phases: the first copolymer (with acrylic acid and hydroxy-functional monomers) provides corrosion protection and flexibility, while the second copolymer (with itaconic acid and higher Tg) provides blocking resistance, achieving both properties simultaneously.
2Strength
If PVC and polyvinylchloride are used in heat-sealing lacquers, then heat-seal-seam strength is achieved, but corrosion protection deteriorates
Solution Approach 1:
The patent explicitly removes PVC and polyvinylchloride from the formulation, replacing them with a two-phase polymer system based on acrylic and methacrylic copolymers. This extraction eliminates the corrosive effects of PVC while maintaining heat-sealing functionality through the synergistic combination of two polymer phases with complementary Tg ranges and monomer compositions.
Solution Approach 2:
The invention changes the chemical composition parameters by using specific monomer ratios: the first copolymer contains 3-15% acrylic acid and 2-10% hydroxy-functional monomers with Tg1 of -20 to 30°C, while the second copolymer contains 3-15% itaconic acid with Tg2 of 20 to 50°C. These parameter changes create a non-corrosive system that achieves adequate heat-seal-seam strength through the dual-phase architecture.
3Strength
If heat-seal-seam strength is increased, then sealing performance is improved, but peelability deteriorates
Solution Approach 1:
The patent creates a dynamic polymer system with two distinct glass transition temperatures that allow the material to exhibit different mechanical properties at different temperatures. At sealing temperature, the higher Tg phase provides strength for adequate seal-seam strength, while at lower temperatures (including room temperature), the lower Tg phase provides flexibility and peelability, enabling easy peeling of the sealing.
Solution Approach 2:
The invention uses specific Tg ranges (Tg1: -20 to 30°C, Tg2: 20 to 50°C) and monomer compositions to create a polymer system where the lower Tg phase ensures peelability at ambient conditions while the higher Tg phase contributes to seal strength during the heating process. The hydroxy-functional monomers (3-15%) and carboxylic acid groups enhance adhesion control, allowing optimization of both seal strength and peelability.
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 solution provides enhanced corrosion protection, improved blocking resistance, and high heat-seal-seam strengths without the need for PVC or plasticizers, allowing for easy-to-peel sealings with a low initial sealing temperature, suitable for food packaging applications.
Implementation Method 1
The aqueous dispersion is produced by means of emulsion polymerization, where a first monomer mixture which leads to the first polymer phase is used as or charged together with an initial charge into a reactor and, after polymerization of the first monomer mixture, a second monomer mixture which leads to the second polymer phase is added to the reaction mixture and polymerized
Implementation Method 2
characterized in that a chain-transfer agent is added to both monomer mixtures
Data Source
AI summary
The present invention is directed to an aqueous dispersion comprising particles comprising a first polymer phase and a second polymer phase, where the second polymer phase comprises from 2 to 10% by weight of units based on acids copolymerizable with methacrylates, based on the entirety of the two polymer phases, and wherein the particles have a particle size dso, determined as given in the description, of from 100 to 150 nm, and wherein the entirety of the polymers comprised in the particles comprise of from 49 to 65% by weight of units based on methyl methacrylate and/or butyl methacrylate, of from 22 to 33% by weight of units based on a C1-C4-alkyl ester of acrylic acid, of from 3 to 7% by weight of units based on a hydroxy-functional (meth)acrylate, of from 2 to 8% by weight of units based on (meth)acrylic acid, and of from 5 to 15% by weight of units based on styrene, based on the total weight of the polymers, to a process for preparing an aqueous dispersion comprising a first polymer phase and a second polymer phase, where the second polymer phase comprises of from 2 to 10% by weight of units based on acids copolymerizable with methacrylates, based on the entirety of the monomers used to prepare the two polymer phases, wherein the aqueous dispersion is produced by means of emulsion polymerization, where a first monomer mixture which leads to the first polymer phase is used as or charged together with an initial charge into a reactor and, after polymerization of the first monomer mixture, a second monomer mixture which leads to the second polymer phase is added to the reaction mixture and polymerized, characterized in that a chain-transfer agent is added to both monomer mixtures, and wherein the entirety of monomers used is composed of from 49 to 65% by weight of methyl methacrylate and n-butyl methacrylate, of from 22 to 33% by weight of n-butyl acrylate, of from 3 to 7% by weight of hydroxy-ethyl acrylate, of from 2 to 8% by weight of acrylic acid, and of from 5 to 15% by weight of units based on styrene, based on the total amount of monomers present in both monomer mixtures, and to the use of an aqueous dispersion according to the invention or obtained by a process according to the invention in a heat-sealing lacquer for the sealing of aluminum surfaces with respect to aluminum, polystyrene (PS), polylactide (PLA), or other polymer materials used in food packaging, and to a heat-sealing lacquer for the sealing of aluminum surfaces with respect to aluminum, polystyrene (PS), polylactide (PLA), or other polymer materials used in food packaging, comprising at least 50% by weight of the aqueous dispersion according to the invention or obtained by a process according to the invention.