Phosphated Epoxy Resin Coating for Hydrolytic Stability and Low-Temperature Cure
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Solution Overview
Problem
Existing electrodepositable coating compositions either lack stability to hydrolysis, leading to degradation of the coating film upon exposure to water, or require high heating temperatures for curing, which is undesirable.
Innovation Solution
A phosphated epoxy resin with terminal groups containing a phosphorous atom covalently bonded through carbon-phosphorous bonds or phosphoester linkages, combined with carbamate functional groups, is used to create an aqueous resinous dispersion that can be electrodeposited and cured at low temperatures while maintaining hydrolytic stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional electrodepositable coating compositions are used to achieve ease of application, then coating stability to hydrolysis deteriorates, leading to degradation of the coating film upon exposure to water
Solution Approach 1:
The invention uses a composite resin system combining epoxide-functional polymer, phosphorous acid (or phosphonic/phosphinic acid), and blocked polyisocyanate in specific ratios. This composite material provides both electrodepositability and hydrolytic stability through the synergistic interaction of phosphorous-containing groups that resist hydrolysis while maintaining coating film integrity
Solution Approach 2:
The invention changes the chemical composition parameters by incorporating specific amounts of phosphorous acid (0.1-10 eq per epoxide group) and blocked polyisocyanate (0.1-5 eq per hydroxyl group). These parameter changes enable the coating to maintain stability to hydrolysis while remaining electrodepositable, resolving the contradiction between ease of application and coating reliability
2Ease of operation
If conventional electrodepositable coating compositions are used to achieve ease of application, then curing temperature requirement increases, requiring high heating temperatures to cure the electrodeposited coating
Solution Approach 1:
The invention changes the curing mechanism by using blocked polyisocyanate that releases the blocking group at lower temperatures, enabling cure at 70-150°C instead of higher temperatures. The blocked polyisocyanate (0.1-5 eq per hydroxyl group) provides latent reactivity that activates at moderate temperatures, reducing energy requirements while maintaining ease of electrodeposition application
Solution Approach 2:
The blocked polyisocyanate acts as an intermediary curing agent that mediates between the epoxide-functional polymer and the curing process. The blocking group temporarily deactivates the isocyanate reactivity during application, then releases it during curing at lower temperatures, enabling both ease of application and effective curing at reduced temperature
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 phosphated epoxy resin-based coating composition achieves hydrolytic stability and can cure at low temperatures, addressing the issues of degradation and high curing temperatures in existing coatings.
Implementation Method 1
at least one terminal group comprising a phosphorous atom covalently bonded to the resin by a carbon-phosphorous bond or by a phosphoester linkage
Implementation Method 2
electrophoretically depositing an aqueous resinous dispersion onto the substrate to form a coating on the substrate
Implementation Method 3
at least one carbamate functional group...cure at low temperatures
Data Source
AI summary
The present invention is directed to a phosphated epoxy resin comprising at least one terminal group comprising a phosphorous atom covalently bonded to the resin by a carbon-phosphorous bond or by a phosphoester linkage; and at least one carbamate functional group. The present invention is also directed towards aqueous resinous dispersions comprising the phosphated epoxy resin, methods of coating a substrate, coated substrates, and methods of making a phosphated epoxy resin.