Polyolefin Microporous Films via Sequential Cold and Hot Stretching
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Solution Overview
Problem
Existing polyolefin-based films lack effective methods to achieve porosity without using inorganic fillers or extensive annealing, and there is a need for breathable films that balance water vapor permeability with liquid impermeability for applications like housewrap, roof membranes, and hygiene products.
Innovation Solution
Microporous films are produced using polypropylene copolymers with polypropylene homopolymer and ethylene-containing copolymer segments, achieved through sequential cold and hot stretching without annealing, creating microphase segregation for pore formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional methods (inorganic filler, hole punching, extensive pre-annealing) are used to achieve porosity in polyolefin films, then pore formation is achieved, but process complexity and manufacturing cost increase
Solution Approach 1:
The invention extracts and eliminates the need for inorganic fillers and extensive annealing steps from the traditional pore formation process. By using copolymer blends with microphase segregation, the patent achieves pore formation through the intrinsic phase separation of copolymer components during stretching, removing the need for external additives or complex pre-treatment steps.
Solution Approach 2:
The invention uses copolymer blends consisting of polypropylene homopolymer and polypropylene copolymer with ethylene-containing segments. This composite material system creates microphase segregation during stretching, where the different copolymer phases separate to form pores, enabling pore formation through material composition rather than mechanical or chemical processing complexity.
2Quantity of substance
If breathable films are designed to allow water vapor passage, then water vapor permeability is improved, but liquid water barrier properties may deteriorate
Solution Approach 1:
The invention creates a controlled porous structure through copolymer microphase segregation, where the pore size and distribution are determined by the copolymer morphology. The pores are sufficiently small to allow water vapor molecules to pass through while being too small to permit liquid water penetration, achieving selective permeability based on the phase-separated copolymer structure.
Solution Approach 2:
The copolymer blend creates local phase-separated regions with distinct properties. The microphase segregated structure provides different functional zones: the copolymer-rich phases form the pore structure for vapor transmission, while the polypropylene homopolymer matrix maintains the liquid water barrier, allowing different regions of the film to perform different functions simultaneously.
3Manufacturing precision
If sequential cold and hot stretching is applied to copolymer films, then microporous structure is formed, but processing time and temperature control complexity increase
Solution Approach 1:
The copolymer film is prepared with a specific microphase-separated morphology during extrusion and casting, creating a pre-organized structure that facilitates subsequent pore formation. The preliminary phase separation during film production sets the stage for efficient pore development during stretching, reducing the need for extended processing times compared to random copolymer systems.
Solution Approach 2:
The stretching process uses periodic temperature variation with a cold stretching step followed by a hot stretching step. This periodic thermal treatment allows controlled pore development at different stages: initial pore nucleation during cold stretching and pore expansion/ stabilization during hot stretching, achieving efficient microporous structure formation through staged processing.
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 films exhibit tunable water vapor permeability and barrier properties, suitable for applications requiring breathability and mechanical strength, such as housewrap, roof membranes, and hygiene products, while avoiding the use of inorganic fillers.
Implementation Method 1
film porosity is achieved through the use of specific types of PP copolymer to make non-porous films, followed by a sequential cold/hot stretching process, which effects a microphase segregation induced pore formation in the polyolefin-based film
Implementation Method 2
sequential cold and hot stretching steps comprising: (i) at least one cold stretching step at a temperature in a range of from -20 °C to 50 °C; and (ii) at least one hot stretching step at a temperature in a range of from 50 °C to 150 °C
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3D
AI summary
Microporous polymer films and methods of making same are disclosed. The microporous polymer film comprises: one or more polypropylene copolymer, said polypropylene copolymer comprising one or more polypropylene homopolymer chain segments and one or more ethylene-containing copolymer chain segments; wherein the microporous polymer film comprises: (i) polypropylene homopolymer chain segments in total amount of from 50-82 wt.%, based on the weight of the microporous polymer film; (ii) one or more ethylene-containing copolymer chain segments in total amount of from 18-50 wt.%, based on the weight of the microporous polymer film, wherein at least a portion of the ethylene-containing copolymer chain segments comprises polymerized units of ethylene in an amount of at least 45 wt.%, based on the weight of the ethylene-containing copolymer chain segments.