Dynamic rolling compensation sintering method for preparing expanded polytetrafluoroethylene plate

Abstract

The invention provides a dynamic rolling compensation sintering method for preparing an expanded polytetrafluoroethylene plate, which comprises the following steps: coating a biaxially oriented polytetrafluoroethylene film on a steel roller from an unreeling machine, and controlling the rotating speed of the steel roller and the advancing speed of the film on the unreeling machine, so that the expanded polytetrafluoroethylene film has a certain tension force; therefore, the steel roller is tightly coated with the thin film, and the thin film layers are tightly attached to each other. After wrapping is finished, the steel roller coated with the polytetrafluoroethylene film is put into a sintering furnace to be sintered, during sintering, the expanded polytetrafluoroethylene film is continuously rolled through a pressure roller above the steel roller, parameters such as the thickness and the surface density of the expanded polytetrafluoroethylene film are corrected in real time, and the expanded polytetrafluoroethylene film is obtained. Therefore, the consistency of the performance indexes of the expanded polytetrafluoroethylene plate is realized. The expanded polytetrafluoroethylene plate or strip produced by the method is simple in process requirement and high in production efficiency.

Description

A dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a method for preparing expanded polytetrafluoroethylene sealing material, and more particularly to a method for improving the consistency of plate thickness, density and interlayer bonding by implementing dynamic roll pressure compensation during sintering. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is known as the "King of Plastics" due to its excellent chemical stability, resistance to high and low temperatures, and low coefficient of friction, and is widely used in high-end sealing applications. Expanded polytetrafluoroethylene (ePTFE), while retaining the excellent properties of PTFE, forms a microporous structure through stretching, resulting in lower density and excellent creep resistance, making it the preferred material for high-performance gaskets and fillers.

[0003] Currently, the mainstream process for preparing expanded polytetrafluoroethylene (PTFE) sheets or strips is the "film wrapping-sintering" method. For example, US Patent 5964465 describes a method for forming a continuous long low-creep PTFE sealing strip, in which a film is wrapped around a cylinder, sintered, and then spirally cut into a continuous long strip. Chinese Patent Application No. 201110098806.5 discloses a method for preparing a continuous long expanded PTFE sealing sheet by wrapping a film onto a steel strip with a ring structure.

[0004] However, all of the aforementioned existing technologies suffer from a long-standing, unresolved core defect: the thickness, density, and interlayer peel strength of the final product exhibit uneven distribution and poor consistency on a macroscopic scale. The root cause lies in the fact that during the wrapping stage, tension fluctuations in the film result in inconsistent interlayer bonding; simultaneously, the inherent microscopic fluctuations in the thickness and areal density of the raw material film itself are amplified layer by layer during the wrapping process. Structural defects formed at this stage cannot be corrected during subsequent static sintering, resulting in these defects being "solidified" in the final product. To improve consistency, the industry typically addresses this by significantly increasing the thickness accuracy and areal density uniformity of the raw material film. This directly leads to a sharp increase in film manufacturing costs, creating an industry dilemma of "sacrificing economic efficiency in pursuit of product uniformity."

[0005] Therefore, there is an urgent need in this field for a new method that can actively compensate for raw material defects and process fluctuations during processing, so as to achieve the homogeneous production of high-performance ePTFE sheets at low cost. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of the prior art and provide a dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene (PTFE) sheets. The core objective of this method is to fundamentally solve the problems of uneven distribution of finished product thickness, density, and interlayer bonding force by introducing a real-time, dynamic mechanical compensation mechanism at key stages of material forming, without demanding ultra-high precision raw materials, through innovative process design, thereby achieving a balance between high performance and low cost.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is a sintering integrated method with dynamic roll pressure compensation. Its core lies in creatively integrating the continuous roll pressure function with the sintering process in time and space to form a closed-loop process unit with "online compensation" capability.

[0008] A dynamic roll-compensated sintering method for preparing expanded polytetrafluoroethylene (PTFE) sheets includes the following steps: (1) Providing raw materials: Selecting commercial-grade expanded PTFE film with a width of 195±10 cm, a thickness of 10-20 μm, and a surface density of 5-10 g / m²; (2) Controllable wrapping: Wrapping the film on a uniformly rotating steel roller at a speed of 5-15 m / min using an unwinding machine. By precisely matching the unwinding speed with the rotation speed of the steel roller, the film obtains a stable and appropriate tension during the wrapping process, thereby achieving initial tight bonding between layers. The number of layers is determined based on the target plate thickness, film thickness and a coefficient (1.5-2.5); (3) Construct an integrated sintering-rolling system: After the wrapping is completed, fix the end of the film. Crucially, set a pressure roller parallel to the steel roller covering the film. Adjust the gap between the pressure roller and the steel roller to the preset value (the gap = target plate thickness × coefficient, the coefficient is 0.5-1.1). Then, put the "steel roller-film-pressure roller" as a whole system into the sintering furnace.

[0009] (4) Dynamic roller pressure compensation sintering: Start the sintering program while keeping the steel roller rotating at a constant speed of 8-12 rpm. Under the action of gravity and the preset gap, the pressure roller applies a constant and uniform linear pressure to the continuously rotating film coating below. This process runs through the entire sintering cycle: heat up to 150-220℃ (film softening preheating section) in 0.5-1.5 hours and hold for 0.5 hours; continue to heat up to the crystallization melting zone of 350-370℃ and hold at this critical temperature for 2-4 hours. During the entire holding stage, the continuous roller pressure of the pressure roller is carried out synchronously with the plasticizing and melting process of the material; (5) Cooling and cutting: After the holding is completed, stop heating and let the system cool naturally to room temperature with the furnace. Stop the rotation of the steel roller, take out the product, and cut it axially to obtain a plate or radially spirally to obtain a continuous strip as required.

[0010] A roll pressing sintering system for implementing a dynamic roll pressing compensation sintering method for expanded polytetrafluoroethylene (PTFE) sheets includes a sintering furnace equipped with a temperature control device. A steel roller is rotatably mounted inside the sintering furnace. The steel roller is used to wrap an expanded PTFE film. The steel roller is connected to a drive mechanism via a steel roller drive shaft and a chain. The drive mechanism drives the steel roller to rotate at a uniform speed during the sintering process. A pressure roller is arranged parallel to the steel roller, located above the steel roller and adjustablely positioned within the sintering furnace. The pressure roller applies continuous roll pressing to the film wrapped on the steel roller during the sintering process. Preferably, the pressure roller is mounted with an adjustable bracket via a slide rail to precisely control the gap between itself and the steel roller.

[0011] Compared with existing technologies, the dynamic roll-pressure compensation sintering method provided by this invention produces the following synergistic and unexpected technical effects: 1. This invention introduces an active physical correction mechanism at the critical stage (sintering) where defects may be solidified. The continuous action of the pressure roller is equivalent to an "online leveler," which can compensate in real time for the macroscopic thickness differences accumulated due to uneven initial film thickness and fluctuations in wrapping gap, transforming the traditional "open-loop" process into a "quasi-closed-loop" process with self-compensation capabilities.

[0012] 2. This invention significantly improves the uniformity and consistency of product performance. Dynamic rolling can effectively smooth out local high points and low filling points, greatly reducing the thickness deviation and density fluctuation of the entire product area (as shown in the example, the thickness deviation can be controlled within ±0.1mm). Applying continuous pressure when the material is in the optimal plasticized state (around 370℃) greatly promotes the mutual diffusion and entanglement of PTFE molecules between layers, which not only improves the average peel strength, but also makes the peel strength value more concentrated across the entire board.

[0013] 3. Because the process itself possesses strong defect compensation capabilities, the requirements for the thickness and areal density accuracy of the upstream raw material film can be significantly relaxed. This allows the use of lower-cost commercial-grade films to manufacture high-end sealing products with performance consistency comparable to or even superior to high-cost films, achieving the dual goals of cost reduction and efficiency improvement.

[0014] 4. This method requires no complex online monitoring or feedback system; stable compensation can be achieved simply by setting a pre-defined gap and rotating at a uniform speed. The device is easy to retrofit and integrate into existing sintering furnaces, making it ideal for large-scale continuous production. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the structure of the roll pressing sintering system of the present invention; Figure 2 is a right view of Figure 1 of the present invention; Figure 3 is a schematic diagram of the internal structure of the roll pressing sintering system of the present invention; Figure 4 is a right view of Figure 3 of the present invention.

[0016] Parts Description: 1. Temperature control device, 2. Steel roller drive shaft, 3. Chain, 4. Drive mechanism, 5. Pressure roller, 6. Steel roller, 7. Support, 8. Slide rail, 9. Sintering furnace. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0018] A roll-pressing sintering system used in the dynamic roll-pressing compensation sintering method for preparing expanded polytetrafluoroethylene (PTFE) sheets includes a sintering furnace 9, which is equipped with a temperature control device 1. A steel roller 6 is rotatably mounted inside the sintering furnace 9. The steel roller 6 is used to wrap the expanded PTFE film. The steel roller 6 is connected to a drive mechanism motor 4 via a steel roller drive shaft 2 and a chain 3. The motor 4 drives the steel roller 6 to rotate at a uniform speed during the sintering process. A pressure roller 5 is arranged parallel to the steel roller 6, located above the steel roller 6 and adjustable within the sintering furnace 9. The pressure roller 5 is used to apply continuous roll pressure to the film wrapped on the steel roller 6 during the sintering process. An adjustable bracket 7 is mounted on the pressure roller 5 via a slide rail 8 to precisely control the gap between the pressure roller 5 and the steel roller 6.

[0019] Example 1: Preparation of a homogeneous plate with a thickness of 1.0 mm (1) Raw materials: Commercial ePTFE film with a thickness of about 10 μm, a surface density of 5-10 g / m², and a width of about 200 cm was selected.

[0020] (2) Wrapping: The film is wrapped around a steel roller 6 with a diameter of 500 mm at a speed of 5 m / min. The number of layers is calculated as 1.0 mm / 10 μm × 1.5 = 150 layers. The tension is adjusted to make the film flat and adhered.

[0021] (3) System settings: Set the gap between the pressure roller and the steel roller to 1.0 mm × 0.5 = 0.5 mm. Push the assembled roller system into the large through-type sintering furnace.

[0022] (4) Dynamic sintering: Close the furnace door and start the steel roller rotation (10 revolutions / minute). Heat up according to the program: 1 hour to 170℃, hold for 0.5 hours; then heat up to 360℃ and hold at this temperature for 2 hours, during which the pressure roller continuously performs roller pressure compensation; then stop heating and cool with the furnace.

[0023] (5) Cutting: After cooling, the plate is cut off along the axial direction of the steel roller.

[0024] Results: The resulting board has a size of approximately 4.5m × 1.5m, a thickness of 1.0±0.1mm, a density of 0.6±0.05g / cm³, a tensile strength at all points of the board within the range of 22-26MPa, and an interlayer peel strength that is stable at 0.35-0.40 N / mm. The product has excellent uniformity.

[0025] Example 2: Preparation of a continuous sealing tape with a thickness of 3.9 mm (1) Raw materials: Commercial ePTFE film with a thickness of about 20 μm and a surface density of 6-8 g / m² was selected.

[0026] (2) Wrapping: The film is wrapped at a speed of 10 m / min, with 390 layers: 3.9 mm / 20 μm × 2.0 = 390 layers.

[0027] (3) System settings: The pressure roller gap is set to 3.9 mm × 1.1 ≈ 4.3 mm. Then, the material is fed into the furnace.

[0028] (4) Dynamic sintering: steel rollers rotate at 10 revolutions per minute. Heat up to 220°C in 1.5 hours and hold for 0.5 hours; continue heating to 370°C and hold at this core temperature for 4 hours, implementing full roller pressure compensation; then cool naturally.

[0029] (5) Cutting: A spiral cutting machine is used to produce continuous strips with a width of 3 cm and a length of more than 300 meters.

[0030] Results: The strip has a total thickness of 3.9±0.2mm and a density of 0.6±0.05g / cm³. The fluctuation range of tensile strength and peel strength is less than 10%, achieving high stability of performance for long-size products.

[0031] Comparative Example 1: Traditional static sintering (without pressure rollers) was used. The same raw materials and wrapping parameters as in Example 1 were used. After wrapping, the steel roller was placed separately in the sintering furnace and sintered under the same temperature program. However, there were no pressure rollers in the furnace and the steel rollers did not rotate.

[0032] Results: The board size is approximately 4.5m × 1.5m, the thickness ranges from 0.89 to 1.15mm, and the density is 0.6 ± 0.2g / cm³. The uniformity of the product's thickness and density is poor.

Claims

1. A dynamic roll-compensated sintering method for preparing expanded polytetrafluoroethylene (PTFE) sheets, characterized in that, The method includes the following steps: (1) providing an expanded polytetrafluoroethylene film; (2) continuously wrapping the film around a rotating steel roller to form a multi-layer coating structure; (3) setting a pressure roller above the steel roller and adjusting the gap between the pressure roller and the steel roller to a preset value, thereby forming a roll pressing sintering system integrating the coated film steel roller and the pressure roller; (4) placing the roll pressing sintering system as a whole in a sintering furnace, and keeping the steel roller rotating continuously at a uniform speed throughout the sintering process, so that the pressure roller applies continuous and dynamic line contact roll pressing to the coating structure, and the sintering process includes at least a heat preservation stage in the temperature range of 350-370℃; (5) after sintering, cooling and cutting to obtain an expanded polytetrafluoroethylene product.

2. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1, characterized in that, In step (4), the continuous and dynamic line contact roller pressing is carried out throughout the entire sintering cycle: the temperature is raised to 150-220°C within 0.5-1.5 hours and held for 0.5 hours; the temperature is then raised to the crystallization melting zone of 350-370°C and held at this temperature for 2-4 hours.

3. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (2), the number of film layers is determined according to the following formula: number of layers = thickness of sealing plate / thickness of film × coefficient, where the coefficient is 1.5-2.

5.

4. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (3), the preset gap is determined according to the following formula: gap = plate thickness × coefficient, where the coefficient is 0.5-1.

1.

5. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (2), the wrapping speed of the film is 5-15 meters per minute.

6. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (4), the rotation speed of the steel roller is 8-12 revolutions per minute.

7. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (1), the expanded polytetrafluoroethylene film has a width of 195±10 cm, a thickness of 10-20 μm, and a surface density of 5-10 g / m².

8. The dynamic roll-compensation sintering method for preparing expanded polytetrafluoroethylene sheets as described in claim 1 or 2, characterized in that, In step (5), the cutting is performed by cutting along the axial direction of the steel roller to obtain a sheet material, or by spiral cutting along the radial direction of the steel roller to obtain a continuous strip.

9. A roll pressing sintering system for implementing the method according to any one of claims 1-8, characterized in that, include: Sintering furnace; A steel roller rotatably disposed within the sintering furnace is used to wrap an expanded polytetrafluoroethylene film. A pressure roller, arranged parallel to the steel roller, is located above the steel roller and adjustablely positioned inside the sintering furnace, and is used to apply continuous roller pressure to the film covering the steel roller during the sintering process. A drive mechanism is used to drive the steel roller to rotate at a constant speed during the sintering process.

10. The roll pressing sintering system as described in claim 9, characterized in that, The pressure roller is mounted via an adjustable bracket to precisely control the gap between it and the steel roller.

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