Polyurethane Urea Film Preparation via Staged Viscosity Control
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Solution Overview
Problem
Conventional methods for preparing polyurethane-containing films face challenges such as low gel time and high viscosity, making it difficult to achieve films with acceptable optical properties and durability, particularly for polarizing optical elements.
Innovation Solution
A method involving the reaction of a polyurethane material with isocyanate functional groups and a material with active hydrogen functional groups, forming a reaction mixture that increases viscosity, which is then dispensed onto a support substrate and cured to produce a non-elastomeric, polyurethane-containing free film with improved optical and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyurethane-containing materials are used for film manufacturing, then optical properties and mechanical durability are improved, but processing difficulty increases due to low gel time and high viscosity
Solution Approach 1:
The patent applies preliminary action by pre-reacting the polyisocyanate with a portion of the polyol to form a polyurethane prepolymer before final film formation. This preliminary reaction reduces the gel time during film casting by having part of the crosslinking already initiated, while the remaining polyol is added during dispensing to complete the reaction and achieve final cure. This resolves the contradiction by preparing the system in advance to improve processability without sacrificing the final optical and mechanical properties.
Solution Approach 2:
The patent segments the polyol component into two portions: a first portion reacted with polyisocyanate to form prepolymer, and a second portion added during film formation. This segmentation allows the reaction to be controlled in stages - the first portion provides initial structure formation with reduced viscosity for easier processing, while the second portion completes the network formation for final mechanical durability and optical properties.
2Ease of manufacture
If polymer orientation occurs during manufacturing, then film formation is achieved, but birefringence increases reducing optical quality
Solution Approach 1:
The patent changes the rheological parameters of the reaction mixture by controlling the viscosity development through staged reaction. By allowing viscosity to increase to at least 300 cps before dispensing, the material becomes sufficiently viscous to maintain orientation without excessive flow that would cause birefringence. The heating step then cures the film while minimizing further orientation changes, thus achieving film formation with reduced birefringence.
3Manufacturing precision
If reaction mixture viscosity is increased to at least 300 cps before dispensing, then film uniformity is improved, but reaction time is extended
Solution Approach 1:
The patent uses preliminary action by pre-forming the polyurethane prepolymer before film dispensing. This preliminary reaction allows the system to reach the required viscosity of at least 300 cps in advance, ensuring uniform film formation during dispensing. The remaining reaction completes during the heating/curing step, thus achieving film uniformity without excessively extending the overall process time.
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 enables the production of non-birefringent polyurethane films with high stress at break and strain, suitable for use in polarizing optical elements like liquid crystal displays, offering enhanced optical and mechanical performance.
Implementation Method 1
combining the first component with a portion of the second component to form a first reaction mixture; allowing the first reaction mixture to react for a time sufficient to increase the viscosity of the reaction mixture to at least 300 cps
Implementation Method 2
heating the film on the support substrate to a temperature and for a time sufficient to yield a cured film
Data Source
AI summary
A method of preparing a polyurethane-containing film including:(a) providing as a first component a polyurethane material having isocyanate functional groups;(b) providing as a second component a material having active hydrogen functional groups reactive with isocyanate;(c) combining the first component with a portion of the second component to form a first reaction mixture;(d) allowing the first reaction mixture to react for a time sufficient to increase the viscosity to at least 300 cps;(e) adding the remainder of the second component to the first reaction mixture to form a second reaction mixture;(f) dispensing the reaction mixture onto a support substrate in a substantially uniform thickness to form an at least partial film thereon;(g) heating the film on the support substrate to a temperature and for a time sufficient to yield a cured film; and(h) removing the cured film from the support substrate to yield a non-elastomeric polyurethane-containing free film.