Aliphatic Thermoplastic Polyurethane for Light Directing Articles
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Solution Overview
Problem
Light directing articles, particularly those used in retroreflective applications, face challenges with temperature stability during manufacturing and usage, as linear, non-branched thermoplastic polyurethane films have low cross-over temperatures, causing them to soften and flow, while highly crosslinked thermoset polyurethanes are too stiff and rigid.
Innovation Solution
An aliphatic thermoplastic polyurethane composition with a cross-over temperature greater than 110°C and a glass transition temperature between 35°C and 70°C is used as a body layer in light directing articles, providing thermal stability without excessive rigidity, allowing the articles to withstand higher temperatures during processing and use while maintaining flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If linear, non-branched thermoplastic polyurethane films are used, then flexibility and ease of processing are improved, but thermal stability deteriorates due to low cross-over temperatures causing softening and flow
Solution Approach 1:
The patent introduces branching structures into the polyurethane film, fundamentally changing the molecular architecture parameter. This branching increases the cross-over temperature from below 100°C to above 110°C while preserving flexibility, as the branched structure creates physical entanglements that raise the thermal transition point without forming rigid crosslinks
Solution Approach 2:
The patent creates a composite polyurethane system combining linear and branched molecular structures. The linear segments provide flexibility and processability, while the branched segments elevate the cross-over temperature. This composite approach allows the film to maintain both thermal stability and flexibility simultaneously
2Temperature
If highly crosslinked thermoset polyurethanes are used, then thermal stability is improved, but flexibility deteriorates due to excessive rigidity
Solution Approach 1:
The patent applies local quality by introducing branching at specific molecular locations rather than creating uniform crosslinks throughout the polymer network. The branched structures provide localized thermal stability enhancement without creating the extensive rigid network characteristic of thermosets, thus maintaining overall film flexibility
Solution Approach 2:
The patent maintains dynamic molecular characteristics by using thermoplastic branched polyurethane rather than thermoset crosslinked structures. The material retains its ability to flow and deform under stress above the glass transition temperature, providing dynamic flexibility that thermosets lack, while the branching elevates the operational temperature range
3Ease of operation
If the polyurethane film is made thinner to improve flexibility, then ease of operation is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent changes the molecular architecture parameter by introducing branching, which increases the cross-over temperature and enhances mechanical strength. This allows the film to be made thinner for improved flexibility while the branched structure compensates for the reduced thickness by providing superior thermal and mechanical stability at the thinner gauge
Data Source
AI summary
The disclosed aliphatic thermoplastic polyurethane composition is well suited for use in thin, flexible light directing articles to impart flexibility, toughness, or protection to the light directing articles that contain optically active elements. The disclosed aliphatic thermoplastic polyurethanes have improved thermostability at higher temperatures. Specifically, the disclosed aliphatic thermoplastic polyurethanes have a cross-over temperature greater than 110° C. In one embodiment, the cross-over temperature is greater than 130° C. In one embodiment, the cross-over temperature is less than 170° C. and a Tg greater than 35° C. and less than 70° C.