Weatherable and durable coating compositions
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Solution Overview
Problem
Existing coatings, such as isocyanate-containing polyurethane and epoxy coatings, face issues with moisture stability, brittleness, and the need for additional layers due to limited chemical cross-linking, while isocyanate-free alternatives are sought for better weatherability and durability.
Innovation Solution
A curable coating composition comprising an amino-functional silicone resin with Si-O-C bonded amine functionality and an acrylic copolymer with epoxy functionalized groups, offering a balanced molar ratio of amine to epoxy functionality for improved moisture stability and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isocyanate-containing polyurethane coatings are used to achieve superior weatherability and durability, then weatherability and durability are improved, but health and safety concerns arise due to isocyanate exposure
Solution Approach 1:
The patent removes isocyanate from the coating system and replaces it with amino-functional silicone resin that cures via hydrolysis and condensation of alkoxy groups. This extraction eliminates the harmful isocyanate component while preserving the desired weatherability and durability through alternative curing chemistry.
Solution Approach 2:
The patent changes the curing mechanism from isocyanate-based polyaddition to hydrolysis and condensation of alkoxy-functional silicone resin. This parameter change in the chemical reaction pathway eliminates isocyanate exposure while maintaining coating performance through different chemical mechanisms.
2Reliability
If epoxy coatings are used to protect metal with good color and gloss retention, then corrosion resistance and appearance are improved, but the coating becomes brittle as it continues to cure
Solution Approach 1:
The patent creates a composite coating system combining amino-functional silicone resin with acrylic copolymer containing epoxy groups. This composite approach integrates the flexibility and moisture stability of silicone with the corrosion resistance and appearance properties of epoxy, eliminating brittleness while maintaining performance.
Solution Approach 2:
The patent changes the cross-linking density and molecular architecture by using amino-functional silicone resin with controlled amine content (5-50 mole percent). This parameter change in the curing system produces a more flexible and less brittle network compared to conventional epoxy coatings, while maintaining corrosion resistance and appearance.
3Device complexity
If amino-functional polysiloxanes with Si-O-C bonds are used, then coating composition is simplified, but the bonds are susceptible to hydrolysis resulting in regeneration of amine alcohol and silanol
Solution Approach 1:
The patent changes the alkoxy groups in the silicone resin to sterically hindered alkoxy groups (e.g., t-butoxy, sec-butoxy). This parameter change in the molecular structure provides steric protection against hydrolysis of the Si-O-C bonds, improving moisture stability while maintaining the simplified coating composition and curing mechanism.
4Device complexity
If hydrolysis occurs in amino-functional polysiloxanes, then the SiOC bond is severed, but this greatly limits the level of chemical cross-linking
Solution Approach 1:
The patent changes the alkoxy groups to sterically hindered varieties that resist hydrolysis. This parameter change protects the Si-O-C bonds from cleavage, thereby maintaining high levels of chemical cross-linking while preserving the simplicity of the amino-functional polysiloxane coating composition.
Solution Approach 2:
The patent incorporates sterically hindered alkoxy groups beforehand in the silicone resin structure to prevent hydrolysis of the Si-O-C bonds during service. This prior protective measure ensures that the bonds remain intact and maintain chemical cross-linking, avoiding the need for more complex bond protection strategies.
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 composition provides superior weatherability, corrosion resistance, and chemical resistance with a balanced amine-epoxy ratio, eliminating the need for additional layers and maintaining coating performance.
Implementation Method 1
a curable coating composition comprising: (1) an amino-functional silicone resin comprising in polymerized form, structural units of: (i) (R3SiO1/2)a; (ii) (R2Si(OR')xO(2-x)/2)b; (iii) (RSi(OR')y,O(3-y)/2)c; and (iv) (Si(OR')zO(4-z)/2)d wherein each R' is hydrogen, an alkyl group or a functionalized alkyl group, provided that at least 5 mole percent of all R' groups are amine containing groups
Implementation Method 2
the SiOC bond is susceptible to hydrolysis resulting in regeneration of the original amine alcohol and silanol
Data Source
AI summary
A curable coating composition is provided having multi-functionalized acrylic copolymer and amino-functional silicone resin curing agents. The acrylic copolymer of the curable coating composition has, in polymerized form, epoxy functionalized groups and cure compatibility groups and the amino-functional silicone resin is an alkoxy functional siloxane, which optionally is derived from sterically hindered alcohol-amine precursor moieties. The coating compositions are useful in the field of superior weatherable and durable coatings and are useful to replace isocyanate-containing polyurethane based coatings. Also provided are coated articles produced from the curable composition.