PVDF Foam Structure with Dense Skin for Self-Supporting Pipes
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Solution Overview
Problem
The challenge is to create a self-supporting, sized polyvinylidene fluoride (PVDF) foam structure with a dense skin, as existing methods face issues with poor melt strength and difficulty in controlling cell formation, limiting the production of hollow or long articles like pipes without external support.
Innovation Solution
A process involving a master batch with nucleating agents and blowing agents is used to achieve high melt viscosity, allowing for the production of PVDF foam with a dense skin, which is then sized and cooled to maintain stability and shape without external support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If PVDF is foamed to reduce density and cost, then density reduction is achieved, but poor melt strength and difficulty in controlling cell formation occur
Solution Approach 1:
The patent changes the chemical composition parameters of PVDF by incorporating specific copolymers (VDF-HFP-CTFE with 5-20% HFP and 5-15% CTFE) and additives (nucleating agents, blowing agents, plasticizers) to achieve the desired balance between melt strength and foamability. This compositional parameter adjustment allows the material to maintain sufficient melt strength while enabling controlled cell formation during foaming.
Solution Approach 2:
The patent creates a composite PVDF material system that combines PVDF homopolymer or copolymer with specific additives including nucleating agents (such as calcium carbonate, titanium dioxide), blowing agents (such as azodicarbonamide, water), and plasticizers. This composite formulation synergistically improves melt strength and controls cell formation while maintaining density reduction benefits.
2Weight of moving object
If PVDF is foamed to reduce density, then weight reduction is achieved, but difficulty in producing hollow or long articles without external support occurs
Solution Approach 1:
The patent adjusts processing parameters including temperature profiles (heating to 150-200°C for foaming), pressure conditions, and residence time in the extruder to optimize melt strength during processing. These parameter changes enable the foamed PVDF to maintain structural integrity sufficient for producing hollow and long articles without external support.
Solution Approach 2:
The composite PVDF formulation with enhanced melt strength properties allows the material to support its own weight and maintain shape during processing of complex geometries. The specific copolymer composition and additive package provide the necessary rheological properties for manufacturing hollow pipes and long profiles without carrier support.
3Ease of manufacture
If PVDF alloy is formed with other polymers to improve foaming process, then foaming process is improved, but advantageous properties of PVDF related to high crystallinity are compromised
Solution Approach 1:
The patent carefully controls the composition parameters by limiting HFP content to 5-20% and CTFE content to 5-15%, ensuring that the copolymer structure maintains sufficient crystallinity (30-70%) while enabling improved foaming. This precise parameter control allows the material to exhibit both good processability and the desired crystalline properties for chemical resistance and mechanical strength.
Solution Approach 2:
The patent introduces functional additives (nucleating agents, blowing agents) in specific quantities (0.1-5% each) to locally enhance foaming properties without affecting the bulk crystalline structure of PVDF. These additives create localized effects that improve cell formation and distribution while the majority of the material maintains its crystalline PVDF characteristics for property retention.
4Ease of manufacture
If self-supporting foamed PVDF structure is created, then external support is eliminated, but high melt viscosity is required which is not seen in existing art
Solution Approach 1:
The patent formulates a composite PVDF system with specific copolymers and additives that collectively provide the required melt viscosity for self-supporting foam formation. The combination of VDF-HFP-CTFE copolymer, nucleating agents, and plasticizers creates a material with enhanced rheological properties that maintain high melt viscosity sufficient for supporting the foam structure during and after formation.
Solution Approach 2:
The patent optimizes processing temperature parameters (maintaining 150-200°C during extrusion and foaming) to preserve high melt viscosity throughout the critical foaming process. This temperature control ensures the material remains viscous enough to support cell structure formation and maintain shape without collapsing, achieving self-supporting capability.
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 PVDF foam structure has a density reduction of at least 3% and a dense skin with fewer than 20 voids per mm², enabling the creation of self-supporting shapes like pipes and tubes with improved mechanical and chemical properties.
Implementation Method 1
Nucleating agents are also required for good, homogeneous foam formation
Implementation Method 2
a process using foaming agents and nucleating agents
Implementation Method 3
cooling the PVDF /gas mixture in the extruder end, adapter, and/or die
Implementation Method 4
passing the PVDF foam through a sizer to form a shaped PVDF foam structure having a dense skin
Data Source
Figure 1
AI summary
The invention relates to a foamed fluoropolymer, preferably a polyvinylidene fluoride (PVDF) structure, such as from Kynar® resins. The foamed structure is continuous self-supporting, sized, and has a dense skin. The foamed structure is manufactured in a process using foaming agents and nucleating agents. The structure is sized into a specific shape during the manufacturing process - requiring a good melt viscosity of the PVDF foam. In one process, a master batch containing the nucleating agent is used. The foamed article could be a sheet, film, profile, tube, pipe, article, rod foam-core structure, or other self-supporting shape. Foamed tubes, pipes, rods, sheets and conduit are especially useful. The foamed structure of the invention provides added value by being lighter weight, more flexible, and more impact resistant than a comparable non-foamed PVDF structure. It also has increased hysteresis, increased insulation properties, reduced dielectric constant, and increased compressibility.