Biaxially Oriented Polypropylene Pipe With Low High-Temperature Shrinkage
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Solution Overview
Problem
Biaxially oriented polypropylene pipes face challenges in maintaining low shrinkage at elevated temperatures while enhancing other properties such as long-term hydrostatic pressure performance and impact resistance.
Innovation Solution
A biaxially oriented pipe is produced using a propylene-based or ethylene-based polymer composition, where the polymer is formed into a tube and heated to a drawing temperature equal to or higher than its melting temperature, then stretched in both the axial and hoop directions to achieve the desired orientation, utilizing a heterophasic propylene copolymer or random copolymer with specific comonomer content and draw ratios to minimize shrinkage and maximize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If biaxial orientation is applied to improve long-term hydrostatic pressure performance and impact resistance, then these mechanical properties are enhanced, but shrinkage at elevated temperatures increases
Solution Approach 1:
The patent changes the drawing temperature parameter to be equal to or higher than the melting temperature Tm, which fundamentally alters the orientation mechanism. This parameter change enables the polymer chains to orient without excessive crystallinity development, reducing shrinkage while maintaining mechanical properties enhancement from biaxial orientation.
Solution Approach 2:
The patent employs dynamic control of the drawing process by applying biaxial stretching at elevated temperatures (Td ≥ Tm) where the polymer is in a more flexible state. This dynamic approach allows simultaneous achievement of molecular orientation for improved mechanical properties and controlled dimensional stability through temperature management.
2Stability of the object's composition
If drawing temperature is increased to reduce shrinkage, then shrinkage decreases, but manufacturing complexity increases
Solution Approach 1:
The patent simplifies the manufacturing process by establishing a clear parameter threshold (Td ≥ Tm) for drawing temperature. This parameter change eliminates the need for complex multi-stage temperature control systems, as the process can be executed in a single heating and drawing step at the specified temperature range.
Solution Approach 2:
The patent applies preliminary heating to bring the polymer to the required drawing temperature (Td ≥ Tm) before biaxial stretching. This preliminary action ensures the polymer is in the optimal state for orientation, simplifying the overall process by preparing the material in advance rather than requiring complex in-process temperature adjustments.
3Strength
If heterophasic propylene copolymer with dispersed ethylene-α-olefin copolymer is used to improve impact resistance, then low temperature impact performance is enhanced, but manufacturing precision decreases
Solution Approach 1:
The patent uses heterophasic propylene copolymer containing dispersed ethylene-α-olefin copolymer particles (2.0-30 wt%) to create a composite structure. The dispersed rubber particles act as impact modifiers while the propylene matrix provides structural integrity. This composite approach enhances low-temperature impact resistance while the controlled particle distribution maintains manufacturing precision.
Solution Approach 2:
The patent applies local quality by incorporating dispersed ethylene-α-olefin copolymer particles specifically in the propylene matrix. These dispersed phases are strategically positioned to provide localized impact resistance where needed, while the continuous propylene matrix maintains overall dimensional stability and uniformity during manufacturing.
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 process results in a pipe with significantly reduced shrinkage at elevated temperatures, maintaining or enhancing other desired properties like hydrostatic pressure performance and impact resistance, while allowing for uniform wall thickness and excellent long-term performance.
Implementation Method 1
heating the tube such that the tube has a drawing temperature Td (° C.) wherein Td is equal to or higher than Tm
Implementation Method 2
heating the tube such that the tube has a drawing temperature Td (° C.)
Implementation Method 3
stretching the tube of step a) in the axial direction and in the peripheral direction at Td to obtain the biaxially oriented pipe
Data Source
AI summary
The disclosure relates to a biaxially oriented pipe made of a polymer composition comprising a propylene-based polymer, wherein the pipe is made by a process comprising the steps of: •a) forming the polymer composition having a melting temperature Tm (° C.) into a tube, •b) heating the tube such that the tube has a drawing temperature Td (° C.) and •c) stretching the tube of step a) in the axial direction and in the peripheral direction at Td to obtain the biaxially oriented pipe, wherein Td is equal to or higher than Tm, wherein •i) the propylene-based polymer comprises (A1) a heterophasic propylene copolymer, wherein the heterophasic propylene copolymer consists of (a1) a propylene-based matrix, wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least 70 wt % of propylene monomer units and at most 30 wt % of ethylene and/or α-olefin monomer units, based on the total weight of the propylene-based matrix and (a2) a dispersed ethylene-α-olefin copolymer, wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer is 100 wt %, wherein the amount of (a2) with respect to the propylene-based polymer is 2.0 to 30 wt % or ii) the propylene-based polymer comprises (B) a random copolymer of propylene and a comonomer which is ethylene and/or an α-olefin having 4 to 10 carbon atoms, wherein when the pipe has an outer diameter of less than 40 mm, the propylene-based polymer comprising (B) has a comonomer content of 0.1 to 3.8 wt % based on the propylene-based polymer.