Curable Coating Composition for Weathering Resistance
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Solution Overview
Problem
Current methods for improving the weatherability and mar resistance of polycarbonate resins, such as lamination with acrylic films or UV absorber-containing coatings, face issues like UV absorber volatilization, adhesion problems, and long-term cracking due to incomplete crosslinking and temperature changes.
Innovation Solution
A curable composition comprising an organic/inorganic composite with hydrolyzable silyl groups or SiOH groups bonded to a vinyl polymer through a Si—C bond, combined with a UV absorber of molecular weight at least 500 and high weight retentivity, forms a dense siloxane crosslinked network, preventing UV absorber migration and enhancing adhesion and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heavy loading of UV absorber is added to the undercoat layer to improve weatherability, then the weatherability is improved, but the adhesion of the undercoat layer to the substrate and protective coating deteriorates, and the UV absorber volatilizes during heat curing and bleeds out over time causing cracking and yellowing
Solution Approach 1:
The patent introduces a silane coupling agent as an intermediary substance between the UV absorber and the polycarbonate substrate. The silane coupling agent contains both organofunctional groups that interact with the UV absorber and inorganic silyl groups that bond to the substrate, thereby mediating the adhesion problem caused by heavy UV absorber loading while maintaining weatherability protection
Solution Approach 2:
The patent creates a composite undercoat layer combining UV absorber, silane coupling agent, and polycarbonate resin. This composite structure allows the UV absorber to provide weatherability while the silane coupling agent provides adhesion, resolving the contradiction between these two properties through material composition design
2Reliability
If a vinyl polymer protective coating is used to provide UV absorption and weatherability, then the weatherability is improved, but the mar resistance remains limited
Solution Approach 1:
The patent develops a composite protective coating system combining silane-crosslinked polymer and colloidal silica-laden polysiloxane. The silane-crosslinked polymer provides UV absorption and weatherability, while the polysiloxane layer provides enhanced mar resistance, achieving both properties through composite material design
3Strength
If alkoxysilyl groups are used for crosslinking in the undercoat to improve adhesion and weatherability, then the adhesion is improved, but post-crosslinking occurs with passage of time causing strain and defects like cracks and delamination
Solution Approach 1:
The patent applies a silane coupling agent during the initial coating formulation that undergoes crosslinking reaction upon application. This preliminary crosslinking action creates a stable network structure before the coating is subjected to environmental conditions, preventing post-crosslinking strain and related defects like cracks and delamination
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 a durable, weather-resistant coating with improved water and solvent resistance, maintaining initial UV absorber loading and preventing cracking, suitable for outdoor applications like vehicle windows and building materials.
Implementation Method 1
an organic/inorganic composite in which a hydrolyzable silyl group and/or SiOH group-containing polysiloxane is bonded to a vinyl polymer through a Si—C bond
Implementation Method 2
forms a dense siloxane crosslinked network
Implementation Method 3
a curable composition comprising an organic/inorganic composite with hydrolyzable silyl groups or SiOH groups bonded to a vinyl polymer through a Si—C bond, combined with a UV absorber of molecular weight at least 500 and high weight retentivity
Data Source
AI summary
A curable composition comprises (A) an organic/inorganic composite in which a hydrolyzable silyl group and/or SiOH group-containing polysiloxane is bonded to a vinyl polymer through a Si—C bond, and (B) an organic UV absorber having a molecular weight of at least 500 and a weight retentivity of at least 95% when held at 150° C. for 24 hours in an open state. The curable composition is coated and cured to an article, whereby the article is endowed with satisfactory weathering resistance while minimizing coloration or degradation.