Low-Temperature Powder Coating with Stable Poly(Ester-Anhydride) Resin
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Solution Overview
Problem
Existing low temperature curable powder coatings suffer from poor storage stability and agglomeration due to the use of anhydrides like trimellitic anhydride, which also require high curing temperatures and are unsuitable for heat-sensitive substrates.
Innovation Solution
A method involving reactive extrusion of a poly(ester-anhydride) using a multi-functional aromatic dianhydride and carboxylic acid terminated polyester without acetic anhydride, followed by mixing with an epoxy resin and a catalyst, then extruding and pulverizing the mixture to form a stable powder coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low molecular weight resins are used to achieve low curing temperature, then curing temperature is reduced to 120-140°C, but storage stability deteriorates due to agglomeration of powder particles
Solution Approach 1:
The patent changes the chemical structure parameters of the polyester resin by introducing cyclic anhydride groups at the chain ends through controlled reaction with excess anhydride. This structural modification increases the glass transition temperature and molecular weight while maintaining low curing temperature capability, thereby resolving the contradiction between low curing temperature and storage stability
Solution Approach 2:
The patent creates a composite resin system combining polyester backbone with cyclic anhydride end groups, forming a poly(ester-anhydride) structure. This composite structure provides both the low curing temperature characteristics of low molecular weight resins and the storage stability of higher molecular weight polymers
2Reliability
If molecular weight of polyester is increased to improve storage stability, then agglomeration tendency is reduced, but curing temperature increases beyond the desired low temperature range
Solution Approach 1:
The patent applies local quality modification by introducing cyclic anhydride groups specifically at the chain ends of the polyester molecules rather than throughout the entire chain. This localized structural change provides the necessary molecular weight and glass transition temperature for storage stability while keeping the bulk polymer structure suitable for low temperature curing
3Strength
If traditional anhydrides like trimellitic anhydride are used to synthesize multi-carboxylic acid functional polyesters, then crosslinking capability is improved, but curing temperature increases and storage stability deteriorates
Solution Approach 1:
The patent inverts the traditional approach by not fully reacting the anhydride groups to form multi-carboxylic acid polyesters, but instead leaving excess cyclic anhydride groups at the chain ends. This inverted strategy creates poly(ester-anhydride) structures that maintain crosslinking capability through the anhydride groups while avoiding the high curing temperatures associated with traditional multi-carboxylic acid polyester formulations
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 powder coating composition exhibits excellent storage stability and appearance properties at low curing temperatures, suitable for heat-sensitive substrates.
Implementation Method 1
preparing a poly(ester-anhydride) by reactive extrusion in the absence of acetic anhydride and epoxy compounds in a first separate step, said poly(ester-anhydride) being produced by the reaction of a carboxylic acid terminated polyester and a multi-functional aromatic dianhydride
Implementation Method 2
A successfully employed low temperature curable powder coating formulation usually comprises an epoxy resin (ER) and a carboxylic acid terminated polyester (PE) component where the two components crosslink through an epoxy/carboxylic acid reaction
Data Source
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AI summary
The present invention relates to a method for producing a low temperature curable powder coating composition and such low temperature curable powder coating composition obtainable by such method.