Epoxy Coating Gloss Retention via Cross-Link Density
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Solution Overview
Problem
Current car wash-resistant coatings suffer from a loss of gloss due to mechanical damage during car washing, and existing solutions often require expensive inorganic additives or result in coatings with poor water resistance.
Innovation Solution
A coating composition comprising an epoxy-functional binder and an acid- or anhydride functional cross-linker, optimized to achieve a high gloss and low loss of gloss through careful selection of cross-link density and glass transition temperature parameters, without the need for polysiloxane binders or inorganic nanoscopic particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inorganic additives like polysiloxane binders or inorganic nanoscopic particles are used to improve car wash resistance, then car wash resistance is improved, but processing becomes difficult and expensive
Solution Approach 1:
The patent removes inorganic additives (polysiloxane binders and inorganic nanoscopic particles) from the coating system, achieving car wash resistance through the organic polymer network structure alone. This extraction of harmful/expensive components simplifies processing and reduces cost while maintaining the desired protective function.
Solution Approach 2:
The patent modifies the chemical parameters of the coating system by adjusting the cross-link density (X) and glass transition temperature (Tg) of the polymer network. By optimizing these parameters, the coating achieves car wash resistance through its inherent molecular structure rather than relying on inorganic additives, thereby improving ease of manufacture.
2Strength
If binders with high number of hydroxyl groups are used to achieve high cross-link density, then cross-link density is improved, but the coating becomes hydrophilic with poor water resistance
Solution Approach 1:
The patent carefully controls the hydroxyl value parameter of the binder to achieve an optimal balance. By selecting binders with moderate hydroxyl content and compensating through cross-linker selection and cross-link density optimization, the coating achieves high mechanical strength while maintaining hydrophobicity and water resistance.
Solution Approach 2:
The patent creates a composite polymer network system combining binder and cross-linker components in optimized proportions. This composite structure allows the coating to achieve high cross-link density for strength while the overall composition maintains hydrophobicity through the specific combination of organic polymer components.
3Strength
If cured coatings are optimised for very good dry scratch resistance, then dry scratch resistance is improved, but car wash resistance may not be optimal
Solution Approach 1:
The patent adjusts the glass transition temperature (Tg) and cross-link density (X) parameters to achieve a balanced performance profile. By optimizing Tg to be in the range of -50°C to 50°C and controlling cross-link density, the coating simultaneously achieves good dry scratch resistance and car wash resistance, resolving the trade-off between these two properties.
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 coating composition maintains a high gloss of at least 81 GU with a loss of gloss of less than 0.25, providing excellent car wash resistance and water resistance without the use of costly additives, while ensuring a homogeneous polymer network for improved durability.
Implementation Method 1
one or more cross-linkers reactive with the reactive groups of the binder
Implementation Method 2
after curing of the coating
Data Source
AI summary
The invention relates to a high gloss car wash-resistant coating composition comprising an epoxy-functional binder and a cross-linker reactive with the epoxy groups of the binder and a method to prepare such a car wash-resistant coating. The invention further relates to the use of said coating composition, as a pigment-free top coat or a clear coat, in the finishing and refinishing of articles, for example motorcycles, cars, trains, buses, trucks, and aeroplanes. The coating composition after curing forms a coating having an initial gloss of at least 81 GU and a loss of gloss (LoG) of less than 0.25, the loss of gloss being determined by the formula (I)LoG =(1−e(A/X)/(1+eK)+(1−eD*ΔTg) (I)wherein K=B*(Tgonset−C)In formula I A=−8.03, B=−0.21, C=328 and D=−0.00304.X reflects the cross-link density parameter in kPa/K, Tgonset the onset temperature of the Tg transition in K and ΔTg the width of the glass transition temperature in K, all three parameters determined in a dynamic mechanical thermal analysis test (hereinafter “DMTA”) at 11 Hz and a heating rate of 5° C./min.