A method for improving the thickness uniformity of expanded polytetrafluoroethylene film and its application

Abstract

The present invention relates to the technical field of expanded polytetrafluoroethylene membranes, and more specifically, to a method for improving the thickness uniformity of expanded polytetrafluoroethylene membranes and its application. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membranes comprises the following steps: longitudinally stretching a thick polytetrafluoroethylene sheet to obtain a polytetrafluoroethylene tape; transversely stretching the polytetrafluoroethylene tape, and heating the middle position of the polytetrafluoroethylene tape along the transverse stretching direction, so that the middle temperature of the polytetrafluoroethylene tape is higher than the temperature at both ends, and after the transverse stretching is completed, an expanded polytetrafluoroethylene membrane is obtained. The method provided by the present invention can significantly improve the thickness uniformity and pore size uniformity of an expanded polytetrafluoroethylene membrane.

Description

Technical Field

[0001] The invention relates to the technical field of expanded polytetrafluoroethylene membranes, and in particular to a method for improving the thickness uniformity of expanded polytetrafluoroethylene membranes and an application thereof. Background Art

[0002] In the aerospace industry, although traditional sealing materials such as rubber, polycarbonate and vulcanized rubber are widely used in the sealing needs of aerospace equipment, their performance limitations are becoming increasingly prominent and it is difficult to meet the high requirements of modern civil aircraft design for sealing materials. To this end, the industry urgently needs a sealing solution that is both versatile and easy to use, and has excellent performance to reduce the weight of aircraft and optimize maintenance processes. As a popular polymer material, polytetrafluoroethylene stands out for its excellent chemical resistance. Through advanced expansion modification technology, polytetrafluoroethylene resin is converted into expanded polytetrafluoroethylene. This new material not only retains the excellent properties of polytetrafluoroethylene, but also has a unique microporous structure, high toughness and low density. These characteristics make expanded polytetrafluoroethylene an ideal sealing material choice in the aerospace field. It can effectively meet the industry's stringent requirements for sealing materials in terms of weight control and ease of maintenance.

[0003] However, during the stretching preparation process of the existing expanded polytetrafluoroethylene film, due to problems such as the internal temperature control technology of the stretching equipment and the stretching rate, the expanded polytetrafluoroethylene film after stretching has a problem of poor thickness uniformity. It is impossible to effectively control the thickness uniformity of the expanded polytetrafluoroethylene film during the production process, resulting in fluctuations in product thickness, affecting the overall quality and performance of the product.

[0004] In addition, the pore structure and porosity of the expanded polytetrafluoroethylene membrane are crucial to its performance. However, the pore size and distribution of the expanded polytetrafluoroethylene membrane prepared by the prior art are uneven, resulting in a decrease in the overall performance of the expanded polytetrafluoroethylene membrane.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first purpose of the present invention is to provide a method for improving the thickness uniformity of expanded polytetrafluoroethylene membranes, which can significantly improve the thickness uniformity and pore size uniformity of expanded polytetrafluoroethylene membranes, thereby solving the problems of poor thickness uniformity and uneven pore size and distribution of existing expanded polytetrafluoroethylene films.

[0007] The second object of the present invention is to provide a method for improving the thickness uniformity of an expanded polytetrafluoroethylene membrane and its application in preparing an expanded polytetrafluoroethylene membrane.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] The present invention first provides a method for improving the thickness uniformity of an expanded polytetrafluoroethylene membrane, comprising the following steps: longitudinally stretching a polytetrafluoroethylene thick sheet to obtain a polytetrafluoroethylene tape; transversely stretching the polytetrafluoroethylene tape, and heating the middle position of the polytetrafluoroethylene tape along the transverse stretching direction so that the middle temperature of the polytetrafluoroethylene tape is higher than the temperatures at both ends, and obtaining an expanded polytetrafluoroethylene membrane after the transverse stretching is completed.

[0010] Furthermore, the middle temperature of the polytetrafluoroethylene-based tape is 10° C. to 20° C. higher than the temperatures at both ends.

[0011] Furthermore, the temperature of the transverse stretching is 260°C to 280°C.

[0012] Furthermore, the transverse stretching multiple W is 3.5 to 5 times.

[0013] Furthermore, the stretching rate of the transverse stretching is 30 to 32 m / min.

[0014] Furthermore, the longitudinal stretching temperature is 220°C to 230°C.

[0015] Furthermore, the longitudinal stretching multiple L is 4.5 to 5.5 times.

[0016] Furthermore, the stretching rate of the longitudinal stretching is 10% / s to 30% / s.

[0017] Furthermore, the ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.8-0.9:1.

[0018] Furthermore, the thickness of the polytetrafluoroethylene thick sheet is 0.5 mm to 1 mm, and the width is 10 cm to 20 cm.

[0019] Furthermore, the polytetrafluoroethylene tape has a thickness of 0.4 mm to 0.5 mm and a width of 10 cm to 20 cm.

[0020] The present invention also provides application of the method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane in preparing expanded polytetrafluoroethylene membrane.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The method for improving the thickness uniformity of the expanded polytetrafluoroethylene film provided by the present invention helps the film material maintain consistent ductility during stretching, thereby improving the thickness uniformity of the expanded polytetrafluoroethylene film.

[0023] (2) The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention can promote the uniformity of the pore size and the uniform porosity distribution of the expanded polytetrafluoroethylene membrane.

[0024] (3) The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention further improves the thickness uniformity of the expanded polytetrafluoroethylene membrane and the distribution uniformity of its pore structure and porosity by heating the middle position of the polytetrafluoroethylene-based tape and coordinating the process parameters such as the stretching temperature, stretching ratio, and stretching rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A schematic diagram of arranging a heating tube at a middle position along the transverse stretching direction provided by the present invention;

[0027] Figure 2 This is a comparison chart of the pore sizes at different positions of the expanded polytetrafluoroethylene membranes of Example 1 and Comparative Examples 1 to 4 provided by the present invention. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0029] If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0030] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0031] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0032] In a first aspect, the present invention provides a method for improving the thickness uniformity of an expanded polytetrafluoroethylene membrane, or a method for preparing an expanded polytetrafluoroethylene membrane with uniform thickness, which specifically comprises the following steps:

[0033] First, a polytetrafluoroethylene thick sheet is longitudinally stretched, and after the longitudinal stretching is completed, a polytetrafluoroethylene tape is obtained.

[0034] Then the polytetrafluoroethylene tape is stretched transversely. During the transverse stretching process, the heating device located at the center line of the polytetrafluoroethylene tape (the center line in the direction of transverse stretching) is turned on to heat the middle position of the polytetrafluoroethylene tape in the direction of transverse stretching, so that the middle temperature of the polytetrafluoroethylene tape is slightly higher than the temperature at both ends. After the transverse stretching is completed, an expanded polytetrafluoroethylene film is obtained. The middle position refers to the vicinity of the center line position of the polytetrafluoroethylene tape in the direction of transverse stretching.

[0035] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene film provided by the present invention sequentially performs longitudinal stretching and transverse stretching, and heats the middle position of the polytetrafluoroethylene-based tape, which can improve the thickness uniformity of the expanded polytetrafluoroethylene film and ensure that each batch of products can meet the predetermined thickness standard. Among them, the improvement of thickness uniformity means the enhancement of product quality stability and reliability, and reduces performance fluctuations and scrap rates caused by uneven thickness.

[0036] In addition, the method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention can also promote the uniform distribution of the pore size and porosity of the expanded polytetrafluoroethylene membrane. Among them, the uniform distribution of pore size and porosity has an important influence on the mechanical strength and other properties of the material, which is conducive to broadening the application field of the expanded polytetrafluoroethylene membrane.

[0037] Therefore, the thickness uniformity and pore structure of the expanded polytetrafluoroethylene film prepared by the present invention are significantly improved, which directly improves the overall performance of the product. The expanded polytetrafluoroethylene film with better performance has a wider application prospect in the fields of aerospace, chemical industry, and medical treatment, and can meet higher requirements of application scenarios.

[0038] Specifically, the temperature control inside the conventional transverse stretching box is relatively uniform, but the transverse stretching makes the equipment clamp the edge of the base tape and pull it, which makes it easier to stretch the two sides and difficult to stretch the middle, resulting in uneven thickness. Therefore, the present invention heats the middle position of the polytetrafluoroethylene-based tape to make the temperature in the middle higher than the two ends, promote the softening of the middle material, improve the fluidity of the middle material, and make it easier to stretch, thereby achieving the uniformity of the thickness of the expanded polytetrafluoroethylene membrane and the uniformity of the pore size. The synergistic effect of heating and stretching is the key to achieving uniform thickness of the membrane material and uniform pore structure.

[0039] In some specific embodiments, a heating device, such as a heating tube, may be provided at an intermediate position along the transverse stretching direction, see Figure 1 As shown, to increase the temperature in the middle of the PTFE tape. Figure 1 As shown in the figure, F represents the stretching force, and the direction extending toward the two ends indicated by F is the direction of transverse stretching. It can be understood that the middle of the middle in the transverse stretching direction is relative to the two ends, and the heating position can be the position where the center line of the polytetrafluoroethylene tape in the transverse stretching direction is 1 / 3 to 1 / 2 times the width of the polytetrafluoroethylene tape at the two ends.

[0040] In some specific implementations, the temperature of the heating device can be controlled by a thermostat.

[0041] It can be understood that the stretching is more uniform during longitudinal stretching, so heating equipment may not be required.

[0042] In some specific embodiments, the middle temperature of the polytetrafluoroethylene based tape is 10°C to 20°C higher than the temperatures at both ends, including but not limited to any point value of 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, and 20°C, or a range value between any two of them.

[0043] In some specific embodiments, the temperature of the transverse stretching is 260°C to 280°C, including but not limited to any point value of 260°C, 263°C, 265°C, 268°C, 270°C, 271°C, 272°C, 273°C, 274°C, 275°C, 276°C, 277°C, 278°C, 279°C, and 280°C, or a range value between any two of them.

[0044] It can be understood that this temperature refers to the heating temperature of the stretching equipment and also the temperature at both ends of the polytetrafluoroethylene tape.

[0045] In some specific embodiments, the transverse stretching multiple W is 3.5 to 5 times, including but not limited to any point value of 3.5, 3.6, 3.8, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.7, and 5 times, or a range value between any two of them.

[0046] In the forward moving process, the transverse stretching is W times at a constant temperature, and the transverse stretching multiple W is controlled by the transverse expansion width. For example, if the width of the polytetrafluoroethylene tape is 15cm to 18cm, the width is stretched to 67.5cm to 81cm by 4.5 times.

[0047] In some specific embodiments, the stretching rate (i.e., the forward advancing rate) of the transverse stretching is 30-32 m / min, for example, 31 m / min, wherein m / min refers to the number of meters that the polytetrafluoroethylene-based tape advances forward per minute.

[0048] Under the same conditions (heating temperature, stretching ratio, etc.) and within a suitable stretching rate range, the faster the stretching rate, the better the thickness uniformity of the obtained expanded polytetrafluoroethylene membrane.

[0049] In some specific embodiments, the temperature of the longitudinal stretching is 220°C to 230°C, including but not limited to any point value of 220°C, 221°C, 222°C, 223°C, 224°C, 225°C, 226°C, 227°C, 228°C, 229°C, and 230°C, or a range value between any two of them.

[0050] In some specific embodiments, the longitudinal stretching multiple L is 4.5 to 5.5 times; including but not limited to 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5 times, any one of the point values ​​or any range value between two of them.

[0051] In some specific embodiments, the stretching rate of the longitudinal stretching is 10% / s to 30% / s, including but not limited to any point value of 10% / s, 11% / s, 12% / s, 13% / s, 14% / s, 15% / s, 16% / s, 18% / s, 20% / s, 23% / s, 25% / s, 28% / s, and 30% / s, or a range value between any two of them. The unit % / s refers to the strain per second, for example, if the stretching rate of the longitudinal stretching is 10% / s, the initial length of the material is 1 meter, and after stretching for 1 second, the length of the material is 1.1 meters.

[0052] In some specific embodiments, the ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.8 to 0.9:1, including but not limited to any point value of 0.8:1, 0.81:1, 0.82:1, 0.83:1, 0.85:1, 0.87:1, 0.88:1, and 0.9:1, or a range value between any two of them.

[0053] Under the premise of heating the middle position of the polytetrafluoroethylene-based tape, the present invention can ensure that the film material is uniformly stressed during the stretching process by accurately controlling the temperature, stretching multiple, stretching rate and other process parameters of the longitudinal stretching and the transverse stretching, thereby avoiding uneven thickness or changes in pore structure caused by temperature or speed fluctuations. This can not only further improve the thickness uniformity of the expanded polytetrafluoroethylene membrane, but also further promote the uniform distribution of the pore size and porosity of the expanded polytetrafluoroethylene membrane, thereby improving the overall performance of the expanded polytetrafluoroethylene membrane, including mechanical strength, chemical resistance, thermal stability, etc., so that it can be more adapted to the application requirements of high-end fields such as aerospace.

[0054] In some specific embodiments, the thickness of the polytetrafluoroethylene thick sheet is 0.5 mm to 1 mm, including but not limited to any one of 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, and 1 mm, or a range between any two of them; the width of the polytetrafluoroethylene thick sheet is 10 cm to 20 cm, including but not limited to any one of 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, and 20 cm, or a range between any two of them.

[0055] In some specific embodiments, the thickness of the polytetrafluoroethylene based tape is 0.4 mm to 0.5 mm, including but not limited to any one of 0.4 mm, 0.41 mm, 0.42 mm, 0.43 mm, 0.44 mm, 0.45 mm, 0.46 mm, 0.48 mm, and 0.5 mm, or a range between any two of them; the width of the polytetrafluoroethylene based tape is 10 cm to 20 cm, including but not limited to any one of 0 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, and 20 cm, or a range between any two of them.

[0056] In some specific embodiments, the expanded polytetrafluoroethylene membrane has a thickness of 0.08 mm to 0.09 mm, such as 0.083 mm, 0.085 mm or 0.088 mm.

[0057] In some specific embodiments, the method for preparing the polytetrafluoroethylene thick sheet includes any method commonly used in the art, and the present invention is not limited thereto. For example, a polytetrafluoroethylene dispersed resin is used as a raw material, a liquid extrusion aid is added, and after uniform mixing, the mixture is pre-pressed into a green body, and the green body is extruded into a rod-shaped product as required, and then the rod-shaped product is subjected to calendering, drying to remove the extrusion aid, and stretching to prepare a polytetrafluoroethylene thick sheet.

[0058] In a second aspect, the present invention provides application of the method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane in preparing expanded polytetrafluoroethylene membrane.

[0059] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention not only improves the thickness uniformity of the expanded polytetrafluoroethylene membrane, but also improves the uniformity of the pore size of the expanded polytetrafluoroethylene membrane and the uniform distribution of the porosity. Among them, the improvement of thickness uniformity means the enhancement of the stability and reliability of product quality, which is conducive to improving the product quality rate and product performance. The uniform distribution of pore size and porosity has an important influence on the mechanical strength and other properties of the material, which is conducive to broadening the application field of the expanded polytetrafluoroethylene membrane.

[0060] Therefore, the method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention and the expanded polytetrafluoroethylene membrane prepared by the method have broad application prospects, for example, they can be used in the fields of aerospace, chemical industry, medical treatment, etc.

[0061] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0062] The preparation method of the polytetrafluoroethylene thick sheet used in each embodiment and each comparative example of the present invention is: using polytetrafluoroethylene dispersed resin as raw material, adding liquid extrusion aid, mixing evenly, pre-pressing into a green body, extruding the green body into a rod-shaped product, and then calendering, drying to remove the extrusion aid, and stretching the rod-shaped product in sequence to prepare the polytetrafluoroethylene thick sheet.

[0063] Example 1

[0064] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene film provided in this embodiment comprises the following steps:

[0065] A polytetrafluoroethylene thick sheet with a thickness of 0.55 mm and a width of 18 cm was longitudinally stretched to obtain a polytetrafluoroethylene tape with a thickness of 0.5 mm and a width of 17 cm; wherein the longitudinal stretching multiple L was 5 times, the longitudinal stretching temperature was 230°C, and the longitudinal stretching rate was 30% / s.

[0066] Turn on the heating tube located at the center line of the polytetrafluoroethylene tape (the center line in the transverse stretching direction) (see Figure 1 ), the middle position of the polytetrafluoroethylene-based tape along the transverse stretching direction is heated so that the middle temperature of the polytetrafluoroethylene-based tape is higher than the temperature at both ends, and transverse stretching is performed ( Figure 1 The direction of extension toward both ends indicated by F is the direction of transverse stretching), wherein the transverse stretching temperature (i.e., the temperature at both ends of the polytetrafluoroethylene tape) is 280°C, the middle temperature of the polytetrafluoroethylene tape is 20°C higher than the temperature at both ends, the transverse stretching multiple W is 4.5 times, and the transverse stretching rate (forward advancement rate) is 32m / min. After the transverse stretching is completed, an expanded polytetrafluoroethylene membrane is obtained.

[0067] The ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.9:1.

[0068] The expanded polytetrafluoroethylene membrane prepared in this embodiment has a smooth surface and a thickness of 0.08±0.005 mm, which is very uniform.

[0069] Example 2

[0070] The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in embodiment 1, except that the middle temperature of the polytetrafluoroethylene tape is 10° C. higher than the temperature at both ends.

[0071] Example 3

[0072] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that the transverse stretching rate (forward advancing rate) is 30 m / min.

[0073] Example 4

[0074] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that the temperature for transverse stretching is 270°C.

[0075] Example 5

[0076] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene film provided in this embodiment is basically the same as that in embodiment 1, except that the transverse stretching multiple W is 4 times, that is, the ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.8:1.

[0077] Example 6

[0078] The method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that the longitudinal stretching multiple L is 5.5 times, the longitudinal stretching temperature is 220°C, and the longitudinal stretching rate is 10% / s, that is, the ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.82:1.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 1 is that the heating tube is not turned on, that is, the middle position of the polytetrafluoroethylene tape along the transverse stretching direction is not heated.

[0081] The expanded polytetrafluoroethylene membrane obtained in this comparative example has a smooth surface and a thickness of 0.08±0.01 mm. The thickness is uneven, being thick in the middle and thin at both sides.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is that the transverse stretching rate (forward advancing rate) is 20 m / min.

[0084] The expanded polytetrafluoroethylene membrane obtained in this comparative example has a smooth surface and a thickness of 0.08±0.01 mm, with some locations suddenly increasing in thickness.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 1 is that the middle temperature of the polytetrafluoroethylene tape is 30° C. higher than the temperature at both ends.

[0087] The expanded polytetrafluoroethylene membrane obtained in this comparative example is thin in the middle and partially damaged in the middle.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 1 is that the longitudinal stretching multiple L is 7 times, the longitudinal stretching temperature is 200° C., the longitudinal stretching rate is 5% / s, and the transverse stretching multiple W is 7 times, and the transverse stretching temperature (i.e., the temperature at both ends of the polytetrafluoroethylene-based tape) is 250° C. That is, the ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 1:1.

[0090] The expanded polytetrafluoroethylene film obtained in this comparative example has uneven thickness, and the film is partially torn.

[0091] The thickness of the expanded polytetrafluoroethylene membranes prepared in each embodiment and each comparative example was tested respectively, wherein 5 positions (denoted as position 1, position 2, position 3, position 4 and position 5) were dispersedly taken on each expanded polytetrafluoroethylene membrane and the membrane thickness at these 5 positions was tested respectively, and the results are shown in Table 1.

[0092] Table 1 Thickness values ​​of each expanded polytetrafluoroethylene film at different positions

[0093]

[0094]

[0095] It can be seen from Table 1 that the thickness of the expanded polytetrafluoroethylene membrane obtained in each embodiment is more uniform. However, since the middle position of the polytetrafluoroethylene-based tape in Comparative Example 1 was not heated, the thickness of the expanded polytetrafluoroethylene membrane obtained was uneven, thick in the middle and thin on both sides. Since the transverse stretching rate of Comparative Example 2 was too low, the thickness suddenly increased in some positions and the thickness was uneven. Since the middle temperature of Comparative Example 3 was much higher than the temperature at both ends, the middle position was thin and the middle film was damaged. Since the longitudinal stretching speed of Comparative Example 4 was slow and the longitudinal stretching temperature was low, the porosity of the membrane was small and the thickness was uneven. In addition, the transverse stretching multiple W of Comparative Example 4 was the same as the longitudinal stretching multiple L, which caused the film to be torn.

[0096] Furthermore, the pore sizes of the expanded polytetrafluoroethylene membranes obtained in Example 1 and Comparative Examples 1 to 4 at different positions (5 positions were selected in a dispersed manner) were tested and statistically analyzed. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the pore sizes of the expanded polytetrafluoroethylene membrane of Example 1 are very uniform, while the pore sizes of Comparative Examples 1 to 4 are uneven, with a significant difference.

[0097] In summary, the method for improving the thickness uniformity of the expanded polytetrafluoroethylene membrane provided by the present invention can improve the thickness uniformity of the expanded polytetrafluoroethylene membrane, and can promote the uniformity of the pore size and the uniform porosity distribution of the expanded polytetrafluoroethylene membrane.

[0098] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane, characterized in that: The steps include: The polytetrafluoroethylene thick sheet is longitudinally stretched to obtain a polytetrafluoroethylene tape; The polytetrafluoroethylene tape is stretched transversely, and the middle position of the polytetrafluoroethylene tape along the transverse stretching direction is heated to make the middle temperature of the polytetrafluoroethylene tape higher than the temperatures at both ends, and after the transverse stretching is completed, an expanded polytetrafluoroethylene film is obtained.

2. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The middle temperature of the polytetrafluoroethylene-based tape is 10° C. to 20° C. higher than the temperatures at both ends.

3. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The temperature of the transverse stretching is 260°C to 280°C.

4. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The transverse stretching multiple W is 3.5 to 5 times.

5. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The stretching rate of the transverse stretching is 30-32 m / min.

6. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The longitudinal stretching temperature is 220°C to 230°C; (2) The longitudinal stretching multiple L is 4.5 to 5.5 times; (3) The stretching rate of the longitudinal stretching is 10% / s to 30% / s.

7. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The ratio of the transverse stretching multiple W to the longitudinal stretching multiple L is 0.8-0.9:

1.

8. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The thickness of the polytetrafluoroethylene thick sheet is 0.5 mm to 1 mm, and the width is 10 cm to 20 cm.

9. The method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: The polytetrafluoroethylene tape has a thickness of 0.4 mm to 0.5 mm and a width of 10 cm to 20 cm.

10. Use of the method for improving the thickness uniformity of expanded polytetrafluoroethylene membrane according to any one of claims 1 to 9 in the preparation of expanded polytetrafluoroethylene membrane.

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