Method for preparing continuous-length fluororesin casting film through multi-time casting process

Abstract

The invention provides a method for preparing a continuous-length fluororesin casting film, which comprises the following steps of: arranging a plurality of dipping tanks which are arranged in sequence and are filled with fluororesin emulsion, enabling a continuously moving metal mold belt to pass through the dipping tanks in sequence for dipping, and coating the fluororesin emulsion on the surface of the metal mold belt after dipping each time; after the coated metal mold belt leaves each dipping tank, drying treatment and roasting treatment are carried out on the metal mold belt; the dipping, drying treatment and roasting treatment processes are repeated until the metal mold belt is dipped in the last dipping tank and subjected to drying treatment and roasting treatment, the continuous-length fluororesin film is obtained, and before the metal mold belt is dipped for the first time, texturing treatment is conducted on the edge areas of the two sides of the metal mold belt through laser. The method can be used for producing the fluororesin film with the thickness of more than 50 microns, is high in automation degree, low in labor intensity and suitable for industrial production, avoids the generation of waste residues and scraps through laser treatment, and simplifies the process and equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of fluororesin film processing and molding, and in particular relates to a method for preparing a continuous-length fluororesin casting film through multiple casting processes. Background Art

[0002] The perfluororesin emulsion is coated on a metal mold belt such as stainless steel or aluminum alloy, evaporated and subjected to high-temperature heat treatment, and then peeled off from the metal mold belt to obtain an isotropic, high-strength perfluororesin film. Since fluororesins have high melt viscosity, especially polytetrafluoroethylene, which is a representative perfluororesin, is in a gel state above the melting point and has a high thermal expansion coefficient. When sintered at high temperature, this will cause the film to form cracks. Therefore, the thickness of the film without penetrating cracks obtained by a single emulsion casting, that is, the limit film crack thickness of the perfluororesin, is generally 5-20 μm. To obtain a thicker and denser film, multiple casting processes must be used.

[0003] Perfluororesin has low surface energy and unique amphiphilicity, making it difficult to bond. In addition, the linear expansion coefficient of perfluororesin is much greater than that of metal mold tape. During the film sintering process, there is a large stress between the interfaces of the two, and the stress is proportional to the film thickness. Therefore, when the film thickness reaches about 50 μm, the deformation stress generated by heat will cause the casting film to fall off from the edge of the mold tape. In severe cases, the entire film will fall off from the mold tape and cannot be cast any more. Therefore, in order to achieve the production of perfluororesin casting films with a thickness of more than 50 μm, the edge of the mold tape must be processed to improve its adhesion to the fluororesin film.

[0004] Conventional use of grinding wheels and sandpaper to process the edge areas of metal mold belts is labor-intensive and produces a large amount of waste slag and waste chips, which will significantly reduce the strength of the metal casting film. In addition, this treatment method is difficult to ensure the uniformity of edge treatment and cannot effectively process the four edge areas of the metal mold belt at the same time. Summary of the invention

[0005] In view of the technical difficulty of producing casting films with a thickness of more than 50μm due to the significantly increased deformation stress at the interface between the metal mold belt and the casting film due to the increase in film thickness, as well as the limitations of traditional grinding wheels and sandpaper in processing the edge area of ​​the metal mold belt, the applicant proposed a method for preparing a continuous length of fluororesin casting film through multiple casting processes. The core of this method is to use laser technology to roughen the edge area of ​​the metal mold belt, thereby significantly enhancing the adhesion between the edge area of ​​the metal mold belt and the fluororesin film. This measure not only successfully overcomes the above-mentioned technical difficulties, but also effectively makes up for the shortcomings of traditional processing methods, providing a practical solution for the production of high-thickness continuous length fluororesin casting films.

[0006] Specifically, the present application provides a method for preparing a continuous length fluororesin casting film by a multiple casting process, the method comprising providing a plurality of sequentially arranged dipping tanks filled with fluororesin emulsion, allowing a continuously moving metal mold belt to pass through the dipping tanks in sequence for dipping, and after each dipping, the surface of the metal mold belt is coated with fluororesin emulsion; after the metal mold belt coated with fluororesin emulsion leaves each dipping tank, drying and baking the metal mold belt; repeating the above-mentioned dipping, drying and baking processes until the metal mold belt is dipped in the last dipping tank and subjected to drying and baking, thereby obtaining a continuous length fluororesin film, Before the first dipping of the metal mold belt, the edge areas on both sides of the two surfaces of the metal mold belt determined by its length and width are roughened by laser, preferably, the edge areas on both sides refer to the areas in the two surfaces from the edge of the metal mold belt to 0.3% to 4% of the width of the metal mold belt from the edge in the width direction, and the edge areas extend along the length direction of the metal mold belt. The thickness of the obtained continuous length fluororesin film is 50 μm or more, preferably 50 to 500 μm, more preferably 50 to 200 μm.

[0007] The two side edge regions may refer to the regions from the edge of the metal mold belt to 0.5% to 3.5% or 2.8-3.0% of the width of the metal mold belt from the edge in the width direction of the two surfaces. For example, taking a metal mold belt with a width of 1.22 m as an example, the two side edge regions may refer to the regions from the edge of the metal mold belt to 1-4 cm (e.g., 1 cm, 2 cm, 3 cm, or 4 cm) from the edge in the width direction of the two surfaces.

[0008] The metal mold belt is selected from stainless steel mold belt, aluminum and aluminum alloy mold belt and copper foil mold belt, preferably, the stainless steel mold belt is an acid-washed stainless steel mold belt. More preferably, the metal mold belt is an acid-washed 316L stainless steel mold belt.

[0009] The metal mold belt can be selected from 304 and 316 pickled stainless steel mold belts with a thickness of 0.1-0.15 mm, aluminum and aluminum alloy mold belts with a thickness of 0.12-0.20 mm, and copper foil mold belts with a thickness of 0.1-0.2 mm.

[0010] The width of the metal mold belt is 0.5-3.0 m, more preferably 1.0-1.6 m, and most preferably 1.22 m.

[0011] Before the first dipping of the metal mold belt, a laser marking machine can be used to roughen the edge areas of both sides of the two surfaces of the continuously moving metal mold belt determined by its length and width. Preferably, the laser power is 20-30 W / cm 2 The moving speed of the metal mold belt is 0.5-2 m / min, preferably 1.0-1.8 m / min.

[0012] Preferably, the metal mold tape is fed out by an unwinding device into which the metal mold tape roll is placed, and is pulled by a traction mechanism to move continuously. The laser marking machine can be placed between the unwinding device and the first immersion tank, more preferably, at the unwinding position of the metal mold tape. A laser marking machine equipped with four laser heads can be used, and the positions of the laser heads are adjusted so that the lasers are respectively aimed at the edge areas on both sides of the two surfaces of the metal mold tape, and when the metal mold tape starts to move continuously, the laser is turned on to perform a roughening treatment on the edge areas of the metal mold tape. Preferably, the laser processing width is set to 1-3 cm, and the marking area is set to be a rectangle along the moving direction of the metal mold tape, and the rectangle is 1-3 cm wide and 2-5 cm long.

[0013] The fluororesin emulsion in each dipping tank may be the same or different. The drying treatment and calcination treatment after each dipping may be the same or different.

[0014] Preferably, the fluororesin emulsion in each dipping tank is independently selected from polytetrafluoroethylene emulsion, fusible polytetrafluoroethylene emulsion, polychlorotrifluoroethylene emulsion, perfluoroethylene-propylene emulsion or a mixture of two or more thereof.

[0015] Preferably, the fluororesin emulsion has a limiting film-breaking thickness greater than or equal to 15 μm, and more preferably, greater than or equal to 20 μm.

[0016] Preferably, the fluororesin emulsion has a surface energy of less than 26 J / m², and more preferably, the fluororesin emulsion has a surface energy of less than 24 J / m².

[0017] The thickness of the continuous length fluororesin film is determined by the moving speed of the metal mold belt and the number of dipping times (number of dipping tanks). The film thickness increases by 10-15 μm after a single dipping.

[0018] The number of immersions may be 2-20 times, more preferably 4-10 times, and more preferably 5-6 times.

[0019] The drying temperature is 80-120°C for 1-5 min, and the calcination temperature is 300-400°C for 2-10 min.

[0020] A heating device may be provided above each impregnation tank. Preferably, the heating device is a vertical drying furnace, the inner wall of which is provided with a heater. A drying section and a sintering section are provided in the drying furnace from bottom to top. After each impregnation in the impregnation tank, the metal mold belt enters from the lower part of the heating device corresponding to the impregnation tank, and passes through the drying section and the sintering section of the drying furnace from bottom to top for the drying treatment and the sintering treatment. In addition, a turning roller may be provided at the end of the sintering section, so that the metal mold belt passes through the drying section and the sintering section again from top to bottom along the turning direction of the turning roller.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The method of the present application uses laser to roughen the four edge areas of the metal mold belt, thereby solving the technical problem of difficulty in producing a casting film with a thickness exceeding 50 μm in a multiple casting process.

[0022] Compared with the traditional grinding process using sandpaper and grinding wheels, the method of the present application uses laser marking to roughen the edge area of ​​the metal mold belt. The degree of roughening can be effectively controlled by controlling the laser power and marking frequency, and it is easier to realize automation. Moreover, the process of the method of the present application has low labor intensity and does not require manual interference, which is particularly suitable for the needs of industrial continuous production. In addition, after the grinding process using sandpaper and grinding wheels, a large amount of waste slag and waste chips will be generated, and the fine particles remaining on the metal will eventually enter the fluororesin mold, which will not only reduce the strength of the film, but most importantly, cause pollution to the film. In the method of the present application, basically no fine powder is generated after laser treatment, and the mold belt does not need to be cleaned, which can simplify the processing of the mold belt and facilitate the design of processes and equipment. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific examples. This implementation case is implemented based on the technology of the present invention, and a detailed implementation method and specific operation process are now given. The protection scope of the present invention is not limited to the following examples. In addition, any resin range recorded in the specification of this application includes any numerical value within the range and the numerical range formed by any combination of these numerical values.

[0024] The multiple casting film production device used in the following embodiments of the present application includes a traction structure, a reeling device, a laser marking machine, several dipping tanks placed in sequence (the number of dipping tanks is determined by the number of dipping times), a heating device and a reeling machine arranged above each dipping tank, wherein the heating device is a vertical drying furnace arranged above each dipping tank, the inner wall of the drying furnace is provided with a heater, and the drying furnace is sequentially arranged from bottom to top with a drying section with a specific temperature and a sintering section with a specific temperature, the laser marking machine is arranged at the unwinding position of the metal mold belt, the laser marking machine has 4 laser heads, and the positions of the 4 laser heads can be adjusted so that they are respectively aligned with the four edge areas of the released metal mold belt (that is, in the two surfaces determined by the length and width of the metal mold belt, from the edge of the metal mold belt to the area at a certain distance from the edge in the width direction), the traction structure includes a heating device arranged between the reeling device and the first dipping tank, between the dipping tank and the heating device arranged above it, between the heating device above the dipping tank and the previous or next dipping tank of the dipping tank, and between the heating device The guide roller between the heating device of the last dipping tank and the winding machine, the dipping guide roller arranged at the bottom of each dipping tank, the steering roller arranged at the end of the sintering section of each heating device, the traction structure also includes a guide belt, after the metal mold belt is placed in the unwinding device and the metal mold belt is welded with the guide belt (such as a guide steel belt, a guide aluminum alloy belt), the traction mechanism can drive the metal mold belt to be roughened at a certain forward speed by the laser marking machine, and then move along the corresponding guide roller and the dipping guide roller to pass through the first dipping tank for dipping, It enters from the lower part of the heating device corresponding to the impregnation tank, passes through the drying section and sintering section of the drying furnace from bottom to top, then turns back along the turning roller at the end of the sintering section, passes through the sintering section and drying section of the drying furnace again from top to bottom, and leaves the drying furnace, then follows the corresponding guide rollers and impregnation guide rollers, passes through the second impregnation tank and repeats the same path until it leaves the drying furnace corresponding to the last impregnation tank. After the last impregnation and heat treatment, the fluororesin film is peeled off from the upper and lower sides of the metal mold belt, and is introduced into the winder to wind the film, and the mold belt is recovered at the same time.

[0025] When the multiple casting film production device is used to prepare a fluororesin film, the laser intensity and the roughening treatment area of ​​the laser marking machine are set, and the laser is turned on to perform continuous roughening treatment on the edge of the metal mold belt when the metal mold belt is turned on to advance, so that the metal mold belt can be impregnated after the roughening treatment. In addition, the time and temperature of the drying and calcining treatment after each impregnation recorded in the following examples can be achieved by adjusting the temperature and length of the drying section and the calcining section in the drying furnace. Those skilled in the art can easily achieve such adjustment.

[0026] Generally speaking, the metal mold belt can be reused when it is not severely deformed, and can generally be recycled more than 10 times. The thickness of the prepared film is adjusted by adjusting the dipping rate and the number of dipping times (ie, the number of dipping tanks).

[0027] In the embodiments of the present application, with regard to the length of the drying section (used to dry moisture), since in the above-mentioned production device, when the impregnated metal mold belt passes through the drying section in the drying furnace again from top to bottom along the turning roller, the sintered film will no longer be dried. Therefore, the length of the drying section is calculated as the drying time recorded in the embodiments × the forward speed of the metal mold belt (i.e., the moving speed).

[0028] As for the length of the firing section (used for sintering to form a layer of fluororesin film on the surface of the material), since the impregnated metal mold belt passes through the firing section twice along the turning roller from bottom to top and from top to bottom, the length of the firing section is (the firing time recorded in the embodiment × the forward speed of the metal mold belt) / 2.

[0029] Example 1: Preparation of 80 μm polytetrafluoroethylene casting film by laser processing 304 stainless steel strip A 304 stainless steel strip with an acid passivation thickness of 0.1 mm and a width of 1.22 m was selected. The steel strip was placed in the unwinding device of the multiple casting film production device and welded to the guide steel strip (a scrap steel strip after use). In order to achieve the required film thickness, 6 dippings were required, and the forward speed of the steel strip was 1.5 m / min. After each dipping, it was necessary to dry at 120°C for 2 min, and then calcined at 360°C for 4 min. High molecular weight and high limit film crack thickness polytetrafluoroethylene concentrated emulsion (60% solid content) (emulsion grade: PTFE SNF-1HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to all 6 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was adjusted so that the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 1.5 cm away from the edge), and the laser intensity was set to 25 w / cm 2 The roughening treatment area is 1.5 cm × 3 cm. After setting, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The thickness of the prepared film is 78 μm to 82 μm, with a tolerance of ±2 μm, and two polytetrafluoroethylene casting films can be obtained from both sides.

[0030] Example 2: Preparation of 100 μm polytetrafluoroethylene casting film by laser treatment of 304 stainless steel strip Acid-passivated 304 stainless steel strip with a thickness of 0.1 mm and a width of 1.22 m was selected. The steel strip was placed in the unwinding device of the multiple casting film production device and welded with the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 6 dippings were required, and the steel strip forward speed was 1.2 m / min. After each dipping, it was dried at 120°C for 2 min and then baked at 360°C for 4 min. High molecular weight and high limit film crack thickness polytetrafluoroethylene concentrated emulsion (60% solid content) (emulsion grade: PTFE SNF-1HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to all 6 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was adjusted so that the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 1.5 cm away from the edge), and the laser intensity was set to 27w / cm 2 The processing area is 1.5cm×3cm. After setting, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The thickness of the prepared film is 97 μm to 103 μm, with a tolerance of ±3 μm, and two polytetrafluoroethylene casting films can be obtained from both sides.

[0031] Example 3: Preparation of 75 μm polytetrafluoroethylene casting film by laser treatment of aluminum alloy strip A common aluminum alloy strip with a thickness of 0.2 mm and a width of 1.22 m was selected. The aluminum alloy strip was placed in the unwinding device of the multiple casting film production device and welded with the guide aluminum alloy strip (a scrap aluminum alloy strip after use). In order to achieve the required thickness, 6 dippings were required, and the steel strip forward speed was 1.6 m / min. After each dipping, it was necessary to dry at 120°C for 2 min and then bake at 360°C for 4 min. A high molecular weight and high limit film crack thickness polytetrafluoroethylene concentrated emulsion (60% solid content) (emulsion grade: PTFE SNF-1HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to all 6 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was adjusted so that the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 2.0 cm away from the edge), and the laser intensity was set to 21 w / cm 2The processing area is 2.0 cm×4.0 cm. After setting up, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The prepared film thickness is 73 μm to 77 μm, with a tolerance of ±2 μm, and two polytetrafluoroethylene casting films can be obtained from both sides.

[0032] Example 4: Preparation of 75 μm fusible polytetrafluoroethylene (PFA) casting film by laser treatment of aluminum alloy strip A common aluminum alloy strip with a thickness of 0.2 mm and a width of 1.22 m was selected. The aluminum alloy strip was placed in the unwinding device of the multiple casting film production device and welded with the guide aluminum alloy strip (a scrap aluminum alloy strip after use). In order to achieve the required thickness, 6 dippings were required, and the steel strip forward speed was 1.4 m / min. After each dipping, it was necessary to dry at 120°C for 2 min and then bake at 360°C for 4 min. A high molecular weight and high limit film crack thickness PFA concentrated emulsion (50% solid content) (emulsion grade: PFA-E50H, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to all 6 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was adjusted so that the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 2.0 cm away from the edge), and the laser intensity was set to 21 w / cm 2 The processing area is 2.0 cm × 4.0 cm. After setting up, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The prepared film thickness is 72 μm to 78 μm, with a tolerance of ±3 μm, and two polytetrafluoroethylene casting films can be obtained from both sides.

[0033] Example 5: Preparation of 75 μm fusible polytetrafluoroethylene casting film by laser processing 316L stainless steel strip Acid-treated 316L stainless steel strip with a thickness of 0.08 mm and a width of 1.22 m was selected. The stainless steel strip was placed in the unwinding device of the multiple casting film production device and welded with the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 5 dippings were required, and the steel strip forward speed was 1.2 m / min. After each dipping, it was dried at 120°C for 2 min and then baked at 360°C for 4 min. PFA concentrated emulsion (50% solid content) with high molecular weight and high limit film crack thickness (emulsion grade: PFA-E50H, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to all 5 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was adjusted so that the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 2.0 cm away from the edge), and the laser intensity was set to 30 w / cm 2 The treatment area is 2.0 cm × 4.0 cm. After setting up, continuous laser treatment is carried out to continuously prepare polytetrafluoroethylene casting films. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The prepared film thickness is 72 μm to 78 μm, with a tolerance of ±3 μm, and two polytetrafluoroethylene casting films can be obtained from both sides. The experiment found that although the 316L stainless steel belt is expensive, it can be reused more than 10 times, and the edge of the steel belt needs to be processed by laser only for the first time.

[0034] Example 6: Preparation of 100 μm fusible polytetrafluoroethylene and tetrafluoroethylene uniform composite film by laser treatment of 304 stainless steel strip Acid-treated 304 stainless steel strip with a thickness of 0.1 μm and a width of 1.22 m was selected. The stainless steel strip was placed in the unwinding device of the multiple casting film production device and welded with the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 5 dippings were required, and the steel strip forward speed was 1.4 m / min. After each dipping, it was dried at 120°C for 2 min and then baked at 310°C for 4 min. The 5 dipping tanks were all added with a high molecular weight and high limit film crack thickness PFA concentrated emulsion (50% solid content) (emulsion grade: PFA-E50H, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) and a high molecular weight and high limit film crack thickness polytetrafluoroethylene concentrated emulsion (60%) (emulsion grade: PTFE SFN-1HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) prepared in a mass ratio of 1:4. Adjust the laser marking machine set at the unwinding position of the metal mold tape so that the positions of the four laser heads of the laser marking machine are respectively aligned with the four edge areas of the metal mold tape (i.e., the area from the edge of the metal mold tape to 2.0 cm away from the edge in the width direction of the two surfaces determined by the length and width of the metal mold tape), and set the laser intensity to 26 w / cm 2 The processing area is 2.0 cm × 4.0 cm. After setting up, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The prepared film thickness is 97 μm to 103 μm, with a tolerance of ±3 μm, and two PFA and polytetrafluoroethylene composite films can be obtained from the front and back sides. The tensile strength of the film is higher and the gas barrier property is better, but the tear resistance is reduced.

[0035] Example 7: Preparation of 100 μm fusible polytetrafluoroethylene and tetrafluoroethylene sandwich film by laser treatment of 304 stainless steel strip Acid-treated 304 stainless steel strip with a thickness of 0.1 mm and a width of 1.22 m was selected. The stainless steel strip was placed in the unwinding device of the multiple casting film production device and welded to the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 5 dippings were required, and the steel strip forward speed was 1.4 m / min. After each dipping, it was dried at 120°C for 2 min and then baked at 360°C for 4 min. The 1st, 4th and 5th dipping tanks were filled with high molecular weight and high limit film crack thickness polytetrafluoroethylene emulsion (60% solid content) (emulsion grade: PTFE SFN-1HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.), while the 2nd and 3rd dipping tanks were filled with high molecular weight and high limit film crack thickness PFA concentrated emulsion (50% solid content) (emulsion grade: PFA-E50HG, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.). The laser marking machine set at the unwinding position of the metal mold tape was adjusted so that the positions of the four laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold tape (i.e., the area from the edge of the metal mold tape to 1.5 cm away from the edge in the width direction of the two surfaces determined by the length and width of the metal mold tape), and the laser intensity was set to 25 w / cm 2 The processing area is 1.5 cm × 3.0 cm. After setting up, continuous laser treatment is carried out to start the continuous preparation of polytetrafluoroethylene casting film. During the whole process, polytetrafluoroethylene does not fall off from the stainless steel mold belt. The prepared film thickness is 97 μm to 103 μm, with a tolerance of ±3 μm, and an interlayer composite film can be obtained from both sides. This film has good temperature resistance, high strength and excellent barrier properties.

[0036] Example 9: Preparation of 100 μm perfluoroethylene propylene film by laser treatment of 304 stainless steel strip Acid-treated 304 stainless steel strip with a thickness of 0.1 mm and a width of 1.22 m was selected. The stainless steel strip was placed in the unwinding device of the multiple casting film production device and welded with the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 5 dippings were required, and the steel strip forward speed was 1.4 m / min. After each dipping, it was necessary to dry at 120°C for 2 min and then bake at 360°C for 4 min. High molecular weight and high limit film crack thickness perfluoroethylene propylene emulsion (solid content 55%) (emulsion grade: FEP-E50H, purchased from Zhonghao Chenguang Chemical Research Institute Co., Ltd.) was added to the 5 dipping tanks. The laser marking machine set at the unwinding position of the metal mold belt was aligned with the positions of the 4 laser heads of the laser marking machine to the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 1.5 cm away from the edge), and the laser intensity was set to 25 w / cm 2The processing area was 1.5 cm × 3.0 cm. After setting up, continuous laser treatment was carried out to start preparing the FEP casting film. During the whole process, the FEP did not fall off the stainless steel mold belt. The thickness of the prepared film was 97 μm to 103 μm, with a tolerance of ±3 μm.

[0037] Example 10: Preparation of 120 μm polychlorotrifluoroethylene film by laser treatment of 304 stainless steel strip Acid-treated 304 stainless steel strip with a thickness of 0.1 mm and a width of 1.3 m was selected. The stainless steel strip was placed in the unwinding device of the multiple casting film production device and welded to the guide steel strip (a scrap steel strip after use). In order to achieve the required thickness, 5 dippings were required, and the steel strip forward speed was 1.0 m / min. After each dipping, it was dried at 120°C for 2 min and then baked at 320°C for 4 min. A high molecular weight, high limit film crack thickness trifluoroethylene dispersion (ethanol-dispersed trifluoroethylene dispersion, purchased from Zhejiang Chemical Research Institute) was added to the 5 dipping tanks. The laser marking machine was set at the unwinding position of the metal mold belt, and the positions of the 4 laser heads of the laser marking machine were respectively aligned with the four edge areas of the metal mold belt (i.e., in the two surfaces determined by the length and width of the metal mold belt, in the width direction from the edge of the metal mold belt to the area 1.5 cm away from the edge), and the laser intensity was set to 25 w / cm 2 The processing area is 1.5 cm × 3.0 cm. After setting up, continuous laser treatment is carried out to start the continuous preparation of polytrifluorochloroethylene casting film. During the whole process, the polytrifluorochloroethylene film did not fall off the stainless steel mold belt. The thickness of the prepared film was 117 μm to 123 μm, with a tolerance of ±3 μm.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a continuous length fluororesin casting film by a multiple casting process, the method comprising providing a plurality of sequentially arranged dipping tanks filled with fluororesin emulsion, allowing a continuously moving metal mold belt to pass through the dipping tanks in sequence for dipping, and the surface of the metal mold belt is coated with fluororesin emulsion after each dipping; drying and baking the metal mold belt coated with fluororesin emulsion after leaving each dipping tank; repeating the above-mentioned dipping, drying and baking processes until the metal mold belt is dipped in the last dipping tank and subjected to drying and baking, thereby obtaining a continuous length fluororesin film, Before the first dipping of the metal mold belt, the edge areas on both sides of the two surfaces of the metal mold belt determined by its length and width are roughened by laser, preferably, the edge areas on both sides refer to the areas in the two surfaces from the edge of the metal mold belt to 0.3% to 4% of the width of the metal mold belt from the edge in the width direction, and the edge areas extend along the length direction of the metal mold belt. The thickness of the obtained continuous length fluororesin film is 50 μm or more, preferably 50 to 500 μm, more preferably 50 to 200 μm.

2. The method according to claim 1, wherein the metal mold belt is selected from stainless steel mold belt, aluminum and aluminum alloy mold belt and copper foil mold belt, preferably, the stainless steel mold belt is a pickled stainless steel mold belt, more preferably, the metal mold belt is selected from 304 and 316 pickled stainless steel mold belts with a thickness of 0.1-0.15 mm, aluminum and aluminum alloy mold belts with a thickness of 0.12-0.20 mm and copper foil mold belts with a thickness of 0.1-0.2 mm, preferably, the width of the metal mold belt is 0.5-3.0 m, more preferably 1.0-1.6 m, and most preferably 1.22 m.

3. The method according to claim 1, wherein the metal mold belt is an acid washed 316L stainless steel mold belt.

4. The method according to claim 1, wherein before the first dipping of the metal mold belt, the edge areas on both sides of the two surfaces of the continuously moving metal mold belt determined by its length and width are roughened by a laser marking machine, preferably, the laser power is 20-30 W / cm 2 , the moving speed of the metal mold belt is 0.5-2 m / min.

5. The method according to claim 4, wherein the metal mold tape is sent out by an unwinding device for placing a metal mold tape roll, and is pulled by a traction mechanism to move continuously. Preferably, a laser marking machine is placed between the unwinding device and the first immersion tank. More preferably, a laser marking machine with four laser heads is provided at the unwinding position of the metal mold tape, and the positions of the laser heads are adjusted so that the lasers are respectively aimed at the edge areas on both sides of the two surfaces of the metal mold tape. When the metal mold tape starts to move continuously, the laser is turned on to roughen the edge areas of the metal mold tape, the laser processing width is set to 1-3 cm, and the marking area is set to a rectangle along the moving direction of the metal mold tape, the rectangle is 1-3 cm wide and 2-5 cm long.

6. The method according to claim 1, wherein the fluororesin emulsions in each dipping tank are the same or different, and the drying treatment and calcination treatment performed after each dipping are the same or different. Preferably, the fluororesin emulsion in each dipping tank is independently selected from polytetrafluoroethylene emulsion, fusible polytetrafluoroethylene emulsion, polytrifluorochloroethylene emulsion, perfluoroethylene propylene emulsion or a mixture of two or more thereof, and the fluororesin emulsion has a limiting film crack thickness greater than or equal to 18 μm, more preferably, a limiting film crack thickness greater than or equal to 20 μm, and the fluororesin emulsion has a surface energy less than 26 J / m², more preferably, the fluororesin emulsion has a surface energy less than 24 J / m².

7. The method according to claim 1, wherein the thickness of the continuous length fluororesin film is determined by the moving speed of the metal mold belt and the number of dipping times, and the film thickness increases by 10-15 μm after a single dipping.

8. The method according to claim 1, wherein the drying treatment is carried out at a temperature of 80-120°C for 1-5 min, and the calcination treatment is carried out at a temperature of 300-400°C for 2-10 min.

9. The method according to claim 1, wherein the number of dipping is 2-20 times, more preferably 4-10 times, more preferably 5-6 times.

10. According to the method of claim 1, a heating device is arranged above each impregnation tank. More preferably, the heating device is a vertical drying furnace, the inner wall of the drying furnace is provided with a heater, and a drying section and a sintering section are arranged in sequence from bottom to top in the drying furnace. After each impregnation in the impregnation tank, the metal mold belt enters from the lower part of the heating device corresponding to the impregnation tank, and passes through the drying section and sintering section of the drying furnace from bottom to top to perform the drying treatment and roasting treatment. Most preferably, a turning roller is arranged at the end of the sintering section, so that the metal mold belt passes through the drying section and sintering section again from top to bottom along the turning direction of the turning roller.