High Heat Resistant Polyurethane Adhesive Composition
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Solution Overview
Problem
Current hot melt urethane adhesives and sealants have limited heat resistance, which restricts their application in areas requiring high temperature mechanical performance, and increasing cross-linking density to improve heat resistance leads to safety concerns and processing difficulties.
Innovation Solution
An isocyanate-terminated polyurethane prepolymer is prepared by reacting a urethane diol, a polyol, and an excess of polyisocyanate, where the urethane diol is a reaction product of a polyisocyanate with a low molecular weight diol, enhancing the high temperature creep resistance and maintaining favorable application properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cross-linking density is increased to improve heat resistance, then heat resistance is improved, but safety concerns and processing difficulties arise
Solution Approach 1:
The patent changes the chemical composition parameters by incorporating specific polyol types (polyester polyols with 20-40% content, polycarbonate polyols with 10-30% content, and crystalline polyethers with 30-50% content) and controlling molecular weights to achieve optimal cross-linking density. This resolves the contradiction by finding a parameter set that provides heat resistance without excessive cross-linking that would cause processing difficulties
Solution Approach 2:
The patent uses a composite polyol system combining multiple types of polyols (polyester, polycarbonate, and crystalline polyethers) with different properties. This composite approach allows the adhesive to achieve heat resistance through the synergistic effect of different polyol components rather than relying solely on high cross-linking density, thus avoiding processing difficulties
2Temperature
If high molecular weight and high Tg thermoplastic polymer is added to achieve heat resistance, then heat resistance is improved, but polymer compatibility is limited and processing difficulties occur
Solution Approach 1:
The patent optimizes the molecular weight parameters of the thermoplastic polymer within specific ranges (20,000-200,000 g/mol) and controls its glass transition temperature to balance heat resistance with compatibility. This parameter optimization ensures the thermoplastic polymer provides heat resistance while maintaining adequate compatibility with other adhesive components
Solution Approach 2:
The patent introduces the thermoplastic polymer as a localized component within the adhesive formulation at controlled levels (5-20% by weight). This localized addition allows the thermoplastic polymer to provide heat resistance in specific regions without overwhelming the overall system compatibility, thus resolving the contradiction between heat resistance and polymer compatibility
3Strength
If crystalline polyester polyols are used to improve mechanical strength, then mechanical strength is improved, but heat stability is limited by polyester transition temperature
Solution Approach 1:
The patent creates a composite polyol system that combines crystalline polyester polyols (for mechanical strength) with crystalline polyethers (for heat stability). The crystalline polyether component with higher melting point compensates for the polyester's limited heat stability, while the polyester provides the necessary mechanical strength. This composite approach resolves the contradiction by distributing functions across different materials
Solution Approach 2:
The patent optimizes the ratio of crystalline polyester polyol (20-40%) to crystalline polyether (30-50%) and controls the molecular weight parameters to achieve the right balance between mechanical strength and heat stability. By adjusting these parameters, the adhesive gains both properties without being limited by the polyester transition 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 solution provides improved heat resistance and reduced surface defects in bonded substrates exposed to heat, maintaining surface integrity and reducing the need for frequent replacement of products, especially those used outdoors.
Implementation Method 1
They consist of isocyanate terminated urethane prepolymers that react with surface or ambient moisture in order to chain-extend and branch, forming a new polyurethane/urea polymer. The reaction of moisture with residual isocyanate forms carbamic acid. This acid is unstable, decomposing into an amine and carbon dioxide. The amine reacts rapidly with isocyanate to form a urea.
Implementation Method 2
Cure is obtained through the diffusion of moisture from the atmosphere or the substrates into the prepolymer, and subsequent reaction.
Implementation Method 3
Curable hot melt adhesives and sealants are solid materials at room temperature and applied in molten form at high temperature. On cooling, the material solidifies and subsequently cures by a chemical crosslinking reaction to a form with good strength and toughness.
Data Source
AI summary
The invention provides adhesive and sealant compositions prepared from urethane prepolymers. The urethane prepolymers are obtained by reacting the novel urethane diols, polyester polyols and polyether polyols with an excess of diisocyanate. The urethane diols are prepared by reacting excess low molecular weight diols and diisocyanates. The invention is particularly useful in end use applications such as panel lamination.