Flexible Polyurethane Skin Formulation for Low Flexural Modulus
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Solution Overview
Problem
Current methods for producing flexible polyurethane skins with a flexural modulus below 30 MPa face challenges due to the use of organolead catalysts, which are environmentally regulated, and result in increased volatile organic compound emissions and stiffness when replaced by alternative catalysts, while aromatic polyurethane formulations require light-stability coatings and have processing issues.
Innovation Solution
A method involving a polyurethane reaction mixture with a flexibiliser and an NCO-index higher than 90, combined with a second aromatic polyurethane layer to achieve a composite skin with a flexural modulus below 30 MPa, reducing emissions and eliminating the need for light-stability coatings by accelerating the curing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If organolead catalysts are used to produce flexible polyurethane skins with short cure times, then the flexural modulus is reduced and productivity is improved, but environmental regulations forbid their use and they increase volatile organic compound emissions
Solution Approach 1:
The patent removes the harmful organolead catalyst from the system while maintaining the desired flexible properties through alternative catalysis approaches using organobismuth and organotin catalysts in combination with specific polyol and isocyanate formulations
Solution Approach 2:
The patent modifies the chemical parameters of the polyurethane formulation, specifically using aliphatic isocyanates with controlled NCO-index and specific polyol combinations to achieve flexible skins without organolead catalysts, thereby reducing VOC emissions while maintaining flexibility
2Object-affected harmful factors
If alternative catalysts (organobismuth and organotin) are used to replace organolead catalysts, then environmental compliance is improved, but the polyurethane skins become stiffer with higher flexural modulus
Solution Approach 1:
The patent adjusts the NCO-index parameter to be higher than 90 and uses specific combinations of polyols and isocyanates to control the crosslinking density and network structure, achieving flexible skins (flexural modulus below 30 MPa) with alternative catalysts
Solution Approach 2:
The patent employs composite catalytic systems combining organobismuth and organotin catalysts with specific polyol-isocyanate formulations to achieve the desired balance between environmental compliance and flexible mechanical properties
3Object-affected harmful factors
If the NCO-index is increased to reduce volatile organic compound emissions, then emissions are reduced, but the polyurethane elastomers become stiffer with higher flexural modulus
Solution Approach 1:
The patent optimizes the NCO-index to be higher than 90 while compensating for the stiffening effect through careful selection of polyol molecular weight, functionality, and isocyanate type to maintain flexible properties
Solution Approach 2:
The patent creates a balanced formulation where the high NCO-index provides emission control while the specific polyol-isocyanate combination ensures local flexibility in the final elastomer network
4Productivity
If aromatic polyisocyanates are used instead of aliphatic polyisocyanates, then cure rate and productivity are improved and cost is reduced, but light stability deteriorates requiring additional coating layers
Solution Approach 1:
The patent removes the need for additional light-stability coating layers by using aliphatic polyisocyanates that inherently provide light stability, eliminating the complex multi-layer structure
Solution Approach 2:
The patent creates a composite approach by combining aliphatic polyisocyanates with high NCO-index formulations to achieve both fast enough cure rates and inherent light stability without requiring aromatic isocyanates or additional coatings
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 method produces a flexible composite polyurethane skin with reduced volatile organic compound emissions and no requirement for light-stability coatings, achieving a flexural modulus below 30 MPa while minimizing the use of organometal catalysts and maintaining adequate curing times.
Implementation Method 1
a catalyst component, the isocyanate component being composed of at least one isocyanate having at least two NCO-groups
Implementation Method 2
the polyurethane reaction mixture is sprayed onto a mould surface and the polyurethane reaction mixture is allowed to cure to produce the skin layer
Data Source
Figure 1~4
AI summary
The present invention relates to a method for producing a flexible elastomeric composite polyurethane skin wherein a polyurethane reaction mixture is sprayed onto a mould surface and the polyurethane reaction mixture is allowed to cure to produce the skin layer. The polyurethane reaction mixture is composed of components comprising at least an isocyanate component, isocyanate-reactive components and a catalyst component and the isocyanate component is composed of at least one isocyanate having at least two NCO-groups which are not directly attached to an aromatic group. The catalyst component is substantially free of lead, which leads to a lower flexibility. In accordance with the invention, the flexibility of the polyurethane skin is increased by means of at least one flexibiliser which reduces the flexural modulus of the skin and which comprises at least one isocyanate-reactive group. The flexibiliser is preferably a monofunctional flexibiliser which comprises only one isocyanate-reactive group.