Polyurethane Power Transmission Belt Viscosity Strength Trade-off
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Solution Overview
Problem
Existing polyurethane prepolymers with added plasticizers compromise the hardness, tensile modulus, and tear strength of polyurethane elastomers, which are essential for dynamic applications like power transmission belts, while also facing challenges in processing due to increased viscosity.
Innovation Solution
A polyisocyanate prepolymer composition is developed, incorporating a diisocyanate, a polyol, a triol crosslinker, and a plasticizer, along with a chain extender, to create a thermally stable polyurethane/urea elastomer that maintains low temperature flexibility and improves flex fatigue resistance, using a two-step reaction process that includes standard molding techniques and embedding textile reinforcement within the elastomer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plasticizers are added to polyurethane prepolymers to reduce viscosity, then ease of manufacture is improved, but tensile strength and hardness deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the polyol component by selecting specific molecular weights (500-4000) and types (polycarbonate, polyester, or their mixtures), and by controlling the diisocyanate to polyol ratio (1.8:1 to 2.4:1), to achieve optimal balance between viscosity reduction and tensile strength retention in the plasticized polyurethane elastomer
Solution Approach 2:
The patent creates a composite elastomeric material system combining polyurethane and urea phases through reaction of polyisocyanate prepolymers with diamine chain extenders, forming a plasticized polyurethane/urea elastomer composite that achieves both processability and mechanical strength
2Ease of manufacture
If plasticizers are added to polyurethane prepolymers to reduce viscosity, then ease of manufacture is improved, but tear strength deteriorates
Solution Approach 1:
The patent optimizes the plasticizer content parameter within specific ranges (5-30% by weight of prepolymer) and selects plasticizers with specific molecular weights (300-800 for polyethylene glycol di-2-ethylhexoate) to minimize the negative impact on tear strength while maintaining viscosity reduction benefits
3Productivity
If plasticized polyurethane elastomers are used to improve processing, then mold filling rate is improved, but flex fatigue resistance deteriorates
Solution Approach 1:
The patent develops a plasticized polyurethane/urea elastomer composite material that combines the processing advantages of plasticized polyurethane with the enhanced flex fatigue resistance of urea-containing elastomers, achieving both high mold filling rate and superior flex fatigue performance
Solution Approach 2:
The patent adjusts the chemical composition parameters including the use of specific diisocyanates (PPDI, 2,6-TDI, or cycloaliphatic), polyols (polycarbonate, polyester, or mixtures), and plasticizers to optimize the balance between mold filling rate and flex fatigue resistance
4Ease of manufacture
If standard plasticizers are used to reduce prepolymer viscosity, then ease of manufacture is improved, but composite integrity deteriorates
Solution Approach 1:
The patent selects plasticizers with specific molecular weight ranges (300-800 for polyethylene glycol di-2-ethylhexoate, 400-800 for triethylene glycol di-2-ethylhexoate) to ensure compatibility with the polyurethane matrix and maintain composite integrity while achieving viscosity reduction
Solution Approach 2:
The patent replaces conventional plasticizers with polyethylene glycol di-2-ethylhexoate and related compounds that provide both viscosity reduction and enhanced composite integrity, eliminating the need for separate integrity-enhancing additives
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 resulting polyurethane/urea elastomers exhibit improved pot life, mold filling rate, tensile cord strength retention, and belt durability, with enhanced flex fatigue resistance and composite integrity, even at high temperatures, despite some reduction in physical properties.
Implementation Method 1
the reaction product of: (A) a polyisocyanate prepolymer composition prepared by reacting (i) a diisocyanate... (ii) a polyol... and (iii) a triol crosslinker
Implementation Method 2
certain additives, known as plasticizers or diluents, when added to polyurethane prepolymers will reduce the viscosity of these prepolymers
Implementation Method 3
reacting polyisocyanate prepolymers with symmetric primary diamine chain extenders, mixtures of symmetric primary diamine chain extenders and secondary diamine chain extenders
Implementation Method 4
are subsequently cured at the appropriate temperature and time to create a finished product
Data Source
Figure 1~3
Figure 4
Figure 5~6
AI summary
A power transmission belt having a main belt body portion of elastomeric material, a tensile reinforcement such as carbon fiber cord, disposed in said body portion, and a sheave contact portion integral with said main body portion. The elastomeric material includes the reaction product of a polyisocyanate prepolymer composition and a chain extender. The polyisocyanate prepolymer composition is prepared by reacting a diisocyanate and a polyol substantially free of moieties oxidative at less than about 1500C and at least one triol crosslinker selected from the same group of polyols. Either before or after reacting the prepolymer, a plasticizer selected from the group consisting of alkyl-ether di-alkylesters such as polyethylene glycol di-alkylester is added thereto. The chain extender is an aromatic symmetric primary or secondary diamine chain extender.