Polyurethane Gel Coats with Polycyclic Polyether Polyols for FRP

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Solution Overview

Problem

Existing gel coats for glass fiber reinforced plastics (FRPs) are brittle and prone to cracking, and polyaspartate-based gel coats exhibit incompatibility with unsaturated polyester resin, leading to poor interfacial curing and delamination.

Innovation Solution

A polyurethane coating composition comprising a polycyclic polyether polyol derived from a polycyclic polyol starter and alkylene oxide, combined with a non-aromatic polyisocyanate, which provides a tough and UV-resistant gel coat compatible with unsaturated polyester resin.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If unsaturated polyester resin is used for gel coat, then hardness is improved, but toughness deteriorates and cracking susceptibility increases

Engineering Contradiction:

ImprovehardnessVSAvoidcracking resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent employs a composite coating system consisting of a polyurethane gel coat layer formulated with specific polyols and isocyanates, combined with an unsaturated polyester resin backing layer. This composite structure allows the gel coat to provide toughness and flexibility while the backing layer provides structural hardness and strength, resolving the contradiction between hardness and cracking resistance.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the chemical composition parameters of the gel coat by using specific polyols (such as polyether polyols with controlled molecular weight and functionality) and isocyanates in optimized ratios. This changes the crosslink density and network structure of the cured coating, achieving a balance between hardness and toughness that prevents cracking while maintaining durability.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If polyaspartate based gel coat is used, then toughness and elongation are improved, but compatibility with unsaturated polyester resin deteriorates

Engineering Contradiction:

ImprovetoughnessVSAvoidinterfacial compatibility

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent introduces a compatibility layer or modification at the interface between the gel coat and unsaturated polyester resin backing. This intermediary composition, containing specific functional groups that can interact with both polyurethane and polyester systems, ensures proper adhesion and interfacial curing, preventing delamination while maintaining the toughness benefits of polyaspartate-based formulations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies different compositional qualities to different regions of the coating system. The gel coat layer itself maintains its tough, flexible polyurethane formulation, while the region adjacent to the polyester resin backing contains modified components that ensure compatibility and proper curing at the interface, thus achieving both toughness and interfacial stability.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If traditional gel coat formulations are used, then ease of manufacture is improved, but UV degradation resistance deteriorates

Engineering Contradiction:

Improveformulation simplicityVSAvoidUV degradation

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent modifies the chemical structure parameters of the polyol components by selecting specific cyclic polyether structures and controlling molecular weight distributions. These parameter changes enhance UV stability and hydrolysis resistance while maintaining the ease of manufacturing through conventional coating processes and standard catalyst systems.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces traditional unsaturated polyester resin in the gel coat with polyurethane chemistry that offers superior weatherability and UV resistance. While the chemistry is slightly more complex, it eliminates the need for frequent repainting or maintenance, effectively trading minor formulation complexity for long-term durability and resistance to environmental degradation.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 offers enhanced toughness, reduced cracking susceptibility, and compatibility with unsaturated polyester resin, while maintaining aesthetic appeal and durability.

Implementation Method 1

a polycyclic polyether polyol that is the reaction product of a reaction mixture that includes a polycyclic polyol starter and an alkylene oxide

Methodology Applied

Scientific EffectEtherification: Chemical Bonding

Implementation Method 2

coating compositions comprising: (a) a isocyanate-reactive component comprising a polycyclic polyether polyol... and (b) an isocyanate-functional component comprising a non-aromatic polyisocyanate

Methodology Applied

Scientific EffectPolyaddition: Chemical Bonding

Data Source

PatentEP3938416B1Polyurethane coating compositions and their use as gel coats

Publication Date: 2025.09.10 COVESTRO LLC

AI summary

Polyurethane coating compositions are disclosed that include an isocyanate-reactive component that includes a polycyclic polyether polyol that is the reaction product of a reaction mixture that includes a polycyclic polyol starter, and an alkylene oxide, as well as an isocyanate-functional component that includes a non-aromatic polyisocyanate. The polyurethane coating compositions may be particularly useful as a gel coat in the manufacture of glass fiber reinforced plastics.