Polylactic Acid Film Heat Resistance via Crystallization Control
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Solution Overview
Problem
Conventional polylactic acid based films lack heat resistance and maintain their shape poorly at temperatures above the glass transition temperature, leading to deformation and whitening due to recrystallization, which complicates the production of adhesive tapes.
Innovation Solution
Incorporating an acidic functional group-denatured olefin based polymer and a tetrafluoroethylene based polymer into the polylactic acid resin composition, along with a crystallization promoting step at the crystallization temperature, to enhance melt tension and crystallization, allowing film formation between specific temperature ranges for improved heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If polylactic acid is cooled immediately after melt film formation to maintain film shape, then the film shape is maintained, but crystallization is suppressed and heat resistance is poor
Solution Approach 1:
The patent applies preliminary crystallization action by providing a heating step at 60-100°C after film formation to promote crystal growth before final cooling. This preliminary crystallization develops the crystal structure in advance, enabling the film to maintain its shape and resist heat deformation at higher temperatures without requiring immediate cooling that would suppress crystallization.
2Temperature
If biaxial stretching is performed to achieve stretch-oriented crystallization and heat resistance, then heat resistance is improved, but residual internal stress causes extreme heat shrinkage
Solution Approach 1:
The patent changes the temperature parameter profile by implementing a two-stage thermal process: first heating to 60-100°C to promote crystallization, then cooling to solidify. This parameter change enables crystallization without biaxial stretching, avoiding the residual internal stress that causes heat shrinkage while still achieving heat resistance through crystal structure development.
3Temperature
If high melting point materials are blended with polylactic acid to express heat resistance, then heat resistance is improved, but transparency decreases and biomass ratio is reduced
Solution Approach 1:
The patent changes the thermal processing parameters (heating to 60-100°C for crystallization, then cooling) rather than changing the material composition. This approach achieves heat resistance through crystal structure development in pure polylactic acid, avoiding the need to blend high melting point materials that would reduce transparency and biomass content.
4Reliability
If heating is applied at 60-100°C after film formation to suppress deformation, then detachment failure is suppressed, but the process is inefficient due to reheating after cooling
Solution Approach 1:
The patent implements preliminary crystallization action during the film formation process itself by controlling the temperature profile (heating to 60-100°C then cooling in sequence). This preliminary crystallization develops the crystal structure and improves detachment reliability in one integrated step, eliminating the need for separate reheating operations and improving overall process efficiency.
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 polylactic acid based film exhibits improved heat resistance, maintaining shape and transparency with reduced heat shrinkage, enabling the production of adhesive tapes without separate adhesive preparation and offering increased freedom in product constitution.
Implementation Method 1
addition of a tetrafluoroethylene based polymer (C) facilitates promoted crystallization of polylactic acid
Implementation Method 2
solidifying the resin composition melt-formed in a film state by cooling after a crystallization promoting step
Data Source
AI summary
A method of producing a polylactic acid based film or sheet with improved heat resistance and comprised of a resin composition containing a polylactic acid according to a melt film forming method, wherein the resin composition comprises polylactic acid (A), an acidic functional group-denatured olefin based polymer (B) containing an acidic functional group, and having an acid number of 10-70 mg KOH/g and a weight average molecular weight of 10,000-80,000, and a tetrafluoroethylene based polymer (C), which method comprises performing melt film formation at a temperature of the resin composition between the crystallization temperature (Tc) in a decreasing temperature process of the resin composition +15° C. and the melting temperature (Tm) in a raising temperature process −5° C., or solidifying the resin composition melt-formed in a film state by cooling after a temperature controllable step at crystallization temperature (Tc) in the decreasing temperature process ±10° C.