PTFE Fine Powder Coagulation Surfactant Timing
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Solution Overview
Problem
Polytetrafluoroethylene (PTFE) fine powder tends to aggregate during production, transport, and molding processes, leading to reduced molding properties and deteriorated appearance of molded articles, which impairs handling characteristics and requires sieve removal, decreasing productivity.
Innovation Solution
A process involving the addition of a surfactant at a specific time during coagulation in the production of PTFE fine powder, specifically a nonionic surfactant added after initiating coagulation, to improve handling characteristics by reducing aggregate formation and maintaining low apparent density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If secondary particle powder is formed by coagulation of PTFE aqueous dispersions, then fibrillating properties are improved, but aggregate formation increases and handling characteristics deteriorate
Solution Approach 1:
A surfactant is introduced as an intermediary substance during the coagulation process. The surfactant modifies the interaction between PTFE particles and water, enabling controlled coagulation that preserves fibrillating properties while preventing excessive aggregate formation. This mediator allows the system to achieve both fibrillation and improved handling characteristics simultaneously.
Solution Approach 2:
The patent changes physical-chemical parameters of the aqueous dispersion by adding a surfactant, which alters the surface tension and interfacial properties. This parameter change enables optimized coagulation behavior, producing secondary particles with appropriate fibrillating properties while controlling aggregate size and distribution to maintain good handling characteristics.
2Reliability
If aggregates are removed with a sieve during production, then molding properties are improved, but productivity decreases
Solution Approach 1:
The surfactant is added during the coagulation step to preliminarily control aggregate formation. By preventing excessive aggregation at the source, the need for subsequent sieve removal is reduced or eliminated. This preliminary action ensures that particles coagulate into appropriate sizes without forming large aggregates that would require removal, thereby maintaining productivity while ensuring good molding properties.
3Quantity of substance
If fluorine-containing anionic surfactant is added to PTFE aqueous dispersion, then apparent density and flowability are improved, but extrusion pressure increases
Solution Approach 1:
The patent changes the type of surfactant from fluorine-containing anionic to a different class of surfactant (such as nonionic or cationic), which alters the parameter of particle interaction. This change enables the maintenance of appropriate apparent density and flowability while avoiding the harmful effect of excessive extrusion pressure. The specific surfactant class selected provides the right balance between particle aggregation and flow characteristics.
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 produces PTFE fine powder with superior handling characteristics, achieving a low compression ratio and high aggregate disintegration degree, equivalent to conventional fine powders, while maintaining equivalent apparent density, thus enhancing molding properties and productivity.
Implementation Method 1
a step of adding a surfactant (B) after the step (2)
Implementation Method 2
When a high shear force is applied to PTFE aqueous dispersions, primary particles are aggregated and secondary particles having average particle size of 100 to 1000 μm are formed (coagulation)
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(d)
AI summary
The present invention provides a process for producing a PTFE fine powder having superior handling characteristics despite of a low apparent density. The present invention relates to a process for producing a polytetrafluoroethylene fine powder characterized by including: (1) a step of preparing an aqueous dispersion containing polytetrafluoroethylene, water and a surfactant (A); (2) a step of initiating coagulation of the polytetrafluoroethylene in said aqueous dispersion by agitating said aqueous dispersion; (3) a step of adding a surfactant (B) after the step (2); (4) a step of terminating coagulation after the step (3); (5) a step of collecting a wet powder of the polytetrafluoroethylene; and (6) a step of drying the wet powder of the polytetrafluoroethylene.