Multistage Vinyl Ester Emulsion for Exterior Wood Coatings
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Solution Overview
Problem
Current vinyl ester-ethylene/acrylic multistage emulsions used in wood protection paints suffer from issues such as high water uptake, algal and fungal growth, blistering, and dirt pick-up, while also exhibiting insufficient elasticity and high dirt pick behavior when used in exterior wood coatings.
Innovation Solution
A multistage emulsion polymerization process is employed, where a first monomer composition comprising 60-95 weight percent vinyl ester and 5-40 weight percent ethylene is polymerized under ethylene pressure to produce a first stage product with a glass transition temperature (Tg) of less than 25°C, followed by a second stage polymerization in the presence of the first stage product, using a second monomer composition with a Tg of at least 95°C, typically comprising 90 weight percent or more of (meth)acrylic esters, to create a copolymer emulsion suitable for wood protection paints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If current VAE dispersions are used in binder-rich coatings, then the coating can be formulated with lower pigment volume concentration, but the coating exhibits higher water uptake, higher algal and fungal growth, blistering and higher dirt pick-up
Solution Approach 1:
The patent changes the chemical composition parameters of the polymer dispersion by incorporating specific comonomers (carboxylic acid comonomers with carboxyl groups and hydrophobic comonomers) to modify the properties of the VAE dispersion. This allows achieving both low pigment volume concentration and improved coating performance by altering the polymer structure rather than changing the application parameters
Solution Approach 2:
The patent creates a composite polymer system by copolymerizing vinyl acetate/ethylene with additional comonomers (carboxylic acid comonomers and hydrophobic comonomers). This composite approach combines the benefits of VAE (low cost, good adhesion) with the advantages of the added comonomers (reduced water uptake, improved weathering resistance, reduced blistering) to achieve superior overall performance
2Reliability
If polyvinyl ester dispersions with polymerized silanes and epoxides are used, then weathering resistance is improved, but water permeability increases
Solution Approach 1:
The patent modifies the chemical structure of the polyvinyl ester dispersion by incorporating hydrophobic comonomers (such as long-chain alkyl acrylates or methacrylates) alongside the crosslinking agents. This structural modification reduces water permeability while maintaining the weathering resistance provided by the polymerized silanes and epoxides, effectively decoupling these two properties
3Reliability
If APEO-free emulsifiers are used to eliminate health and environmental concerns, then wood protection is improved, but the dispersion exhibits insufficient elasticity when used with pigments and more than 5% fillers
Solution Approach 1:
The patent compensates for the loss of elasticity from APEO-free emulsifiers by incorporating specific comonomers that enhance polymer chain flexibility and interparticle bonding. The carboxylic acid comonomers form hydrogen bonds and the hydrophobic comonomers provide steric stabilization, both of which maintain elasticity without requiring APEO-containing emulsifiers
4Productivity
If vinyl ester copolymers with high solid content are used, then coating efficiency is improved, but dirt pick behavior increases
Solution Approach 1:
The patent modifies the surface properties of the high solid content vinyl ester copolymer by incorporating hydrophobic comonomers that create a water-repellent surface. This surface modification reduces dirt pick behavior by preventing water and water-soluble contaminants from adhering to the coating, while maintaining the high solid content for coating efficiency
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 resulting copolymer emulsion provides a wood protection paint that is resistant to blistering, exhibits low water uptake, low algal and fungal growth, low dirt pick-up, high color retention, and sufficient elasticity, enhancing the performance of exterior wood coatings.
Implementation Method 1
a copolymer emulsion prepared by an emulsion polymerization process comprising: (a) polymerizing, in a first stage and under ethylene pressure, a first monomer composition comprising from 60 weight percent to 95 weight percent of at least one vinyl ester, and from 5 weight percent to 40 weight percent ethylene
Implementation Method 2
In the polymerization processes which have become known to date, monomer mixtures are converted by free-radical polymerization by addition of initiators in the presence of protective colloids and/ or emulsifiers
Implementation Method 3
produce a first stage product having a glass transition temperature Tg of less than 25 °C, such as from 5 to 15 °C; and (b) polymerizing, in a second stage and in the presence of said first stage product, a second monomer composition such that the polymer produced by said second monomer composition has a glass transition temperature Tg of at least 95 °C
Data Source
AI summary
A wood protection paint comprises a copolymer emulsion prepared by an emulsion polymerization process, in which a first monomer composition comprising from 60 weight percent to 95 weight percent of at least one vinyl ester, and from 5 weight percent to 40 weight percent ethylene is polymerized in a first stage under ethylene pressure to produce a first stage product having a Tg of less than 25 °C. Then, in a second stage, a second monomer composition selected such that the polymer produced by the second monomer composition has a Tg of at least 95 °C.