Polyvinyl alcohol film, its drying method and application, drying device for polyvinyl alcohol film and application

Abstract

This invention relates to the field of polyvinyl alcohol (PVA) optical film processing technology, and discloses a PVA film, its drying method and application, and a PVA film drying apparatus and application. The method includes: S1, performing a first drying of a PVA solution to obtain a PVA film I; S2, under the action of an inlet traction roller and an outlet traction roller, performing a second drying of the upper and lower surfaces of the PVA film I using thermal radiation to obtain a PVA film; wherein, in step S2, the linear velocity between the inlet traction roller and the outlet traction roller decreases along the running direction of the PVA film I. The thermal radiation heating method can simultaneously adjust the temperature of both sides of the film, control the water content of both sides of the film to be more uniform, avoid film shrinkage and curling, and simultaneously control the rate of decrease in linear velocity between the inlet traction roller and the adjacent outlet traction roller, ensuring that the dried film has excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl alcohol films, specifically to a polyvinyl alcohol film and its drying method and application, as well as a drying apparatus and application for polyvinyl alcohol films. Background Technology

[0002] Polyvinyl alcohol (PVA) optical film is currently the only functional material that can be processed into polarizing properties. Polarizing films made from PVA through dyeing, stretching, and top and bottom lamination can be widely used in testing instruments, polarizing microscopes, automotive headlight anti-glare devices, LCD / OLED displays, sunglasses, anti-glare goggles, and polarizing filters for cameras and camcorders. The market applications of polarizing films are constantly expanding, and the demand for PVA optical films is also increasing, thus PVA optical films have a promising market outlook.

[0003] Currently, the primary method for preparing PVA optical films involves aqueous solution casting followed by drying to produce the final film product; the drying method is typically roller drying. During the drying process, both the roller temperature and roller speed must be strictly controlled. Furthermore, the surface of the film adhering to the roller is heated more than the outer surface, resulting in uneven water loss on both sides of the film. During drying, longitudinal shrinkage and transverse shrinkage from the film edges towards the center occur. Unevenness in these two types of shrinkage directly affects the elongation at break during stretching and the film surface curling. Therefore, there is an urgent need to develop a novel drying method for PVA optical films to address the problems of low elongation at break and film surface curling caused by uneven drying. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems in the prior art where the drying method of polyvinyl alcohol film causes film shrinkage and curling, and the excessive stretching during the drying process results in a low elongation at break of the product film. This invention provides a polyvinyl alcohol film, its drying method and application, and a drying device and application for polyvinyl alcohol film. The drying method can simultaneously adjust the temperature on both sides of the film, control the moisture content on both sides of the film to be more uniform, avoid film shrinkage and curling, and ensure that the dried film has excellent mechanical properties.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for drying a polyvinyl alcohol film, wherein the method includes:

[0006] S1. The polyvinyl alcohol solution is first dried to obtain polyvinyl alcohol film I;

[0007] S2. Under the action of the inlet traction roller and the outlet traction roller, the upper and lower surfaces of the polyvinyl alcohol film I are dried by thermal radiation to obtain a polyvinyl alcohol film.

[0008] In step S2, the linear velocity between the inlet traction roller and the outlet traction roller decreases along the running direction of the polyvinyl alcohol film I.

[0009] A second aspect of the present invention provides a polyvinyl alcohol film dried by the method described in the first aspect of the present invention.

[0010] A third aspect of the present invention provides a drying apparatus for polyvinyl alcohol film, wherein the apparatus includes an inlet traction roller 1, a first thermal radiation heater 3-1, a second thermal radiation heater 3-2, and an outlet traction roller 4;

[0011] The first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 are located above and below the polyvinyl alcohol film, respectively;

[0012] The polyethylene film is conveyed by an inlet traction roller 1 and an outlet traction roller 4, with the linear velocity decreasing between the inlet traction roller 1 and the adjacent outlet traction roller 4.

[0013] The fourth aspect of the present invention provides the application of the method described in the first aspect and the apparatus described in the third aspect in the preparation of polyvinyl alcohol films.

[0014] Through the above technical solutions, the polyvinyl alcohol film and its drying method and application, as well as the polyvinyl alcohol film drying device and application provided by the present invention, achieve the following beneficial effects:

[0015] (1) The heat radiation heating method can penetrate into the film for heating. The heating speed is fast and uniform, which further ensures that the film is heated evenly and avoids the film curling. Moreover, the drying method can adjust the temperature of both sides of the film at the same time, control the moisture content of both sides of the film to be more uniform, avoid the film shrinking and curling, and ensure that the dried film has excellent mechanical properties.

[0016] (2) Controlling the linear velocity reduction rate between the inlet traction roller and the adjacent outlet traction roller can reduce the stretching of the film caused by elastic shrinkage during the drying process and ensure that the film has a high elongation at break. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the drying apparatus for polyvinyl alcohol film provided by the present invention.

[0018] Explanation of reference numerals in the attached figures

[0019] 1. Inlet traction roller; 1-1. First inlet traction roller; 1-2. Second inlet traction roller; 2-1. First pressure roller; 2-2. Second pressure roller; 3-1. First thermal radiation heater; 3-2. Second thermal radiation heater; 4. Outlet traction roller; 4-1. First outlet traction roller; 4-2. Second outlet traction roller. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of the present invention provides a method for drying a polyvinyl alcohol film, wherein the method includes:

[0022] S1. The polyvinyl alcohol solution is first dried to obtain polyvinyl alcohol film I;

[0023] S2. Under the action of the inlet traction roller and the outlet traction roller, the upper and lower surfaces of the polyvinyl alcohol film I are dried by thermal radiation to obtain a polyvinyl alcohol film.

[0024] Along the running direction of the polyvinyl alcohol film I, the linear velocity between the inlet traction roller and the outlet traction roller decreases.

[0025] In this invention, the linear velocity refers to the instantaneous velocity of the traction roller when it rotates.

[0026] In this invention, the drying method described above allows for simultaneous temperature adjustment on both sides of the film, resulting in more uniform moisture content, preventing shrinkage and curling, and ensuring excellent mechanical properties after drying. Furthermore, the thermal radiation heating method penetrates deep into the film, providing rapid and uniform heating, further ensuring even heating and preventing edge curling. Controlling the decreasing linear speed between the infeed and outfeed traction rollers reduces stretching caused by elastic shrinkage during drying, ensuring a high elongation at break.

[0027] In this invention, the polyvinyl alcohol solution is preferably dried on a casting roller, and after drying, molding, and peeling, a polyvinyl alcohol film I is formed. The concentration of the polyvinyl alcohol solution is not particularly limited and can be a concentration conventional in the art, such as 10-35 wt%.

[0028] In this invention, it should be noted that the guide traction roller refers to a traction roller positioned opposite to the film running direction, such as... Figure 1 The traction rollers on the left side of the first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 are specifically the first inlet traction roller 1-1 and the second inlet traction roller 1-2. The outlet traction roller refers to the traction roller positioned in the same direction as the film's running direction, such as... Figure 1In the middle, the traction rollers on the right side of the first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 are specifically the first outgoing traction roller 4-1 and the second outgoing traction roller 4-2.

[0029] According to the present invention, in step S2, the number of the inlet traction rollers is not less than 2, and the number of the outlet traction rollers is not less than 2.

[0030] According to some preferred embodiments of the present invention, the linear velocity between adjacent infeed traction rollers decreases, and the linear velocity between adjacent outfeed traction rollers decreases.

[0031] In this invention, such as Figure 1 In this context, the linear velocity between adjacent guide traction rollers refers to the linear velocity between the first guide traction roller 1-1 and the second guide traction roller 1-2. The linear velocity between adjacent exit traction rollers refers to the linear velocity between the first exit traction roller 4-1 and the second exit traction roller 4-2.

[0032] According to some preferred embodiments of the present invention, the linear velocity reduction rate between adjacent guide traction rollers is 0-0.2%, preferably 0.1-0.2%, and the linear velocity reduction rate between adjacent exit traction rollers is 0-0.2%, preferably 0.1-0.2%.

[0033] According to some preferred embodiments of the present invention, the linear velocity between the inlet traction roller and the adjacent outlet traction roller decreases by 0.2-5%.

[0034] In this invention, by way of example, reference is made to Figure 1 "The decrease in linear velocity between the inlet traction roller and the adjacent outlet traction roller" refers to the decrease in linear velocity between the second inlet traction roller 1-2 and the first outlet traction roller 4-1.

[0035] In this invention, the linear velocity reduction rate between the inlet traction roller and the adjacent outlet traction roller meets the above-mentioned range, which ensures that the film will not be stretched due to elastic shrinkage during the film drying process, thereby giving the film a higher elongation at break during the stretching process.

[0036] In this invention, it should be noted that the reduction rate I between the first inlet traction roller 1-1 and the second inlet traction roller 1-2, and the linear velocity reduction rate between the first outlet traction roller 4-1 and the second outlet traction roller 4-2 can be the same or different, but preferably the same.

[0037] According to some preferred embodiments of the present invention, the linear velocity reduction rate between adjacent infeed traction rollers and outfeed traction rollers is preferably 0.2-2%.

[0038] According to the present invention, the conditions for the first drying include: a drying temperature of 60-98°C and a drying time of 21-90 seconds.

[0039] The inventors of this invention have shown that excessively high drying temperatures in the first drying stage can lead to rapid water loss in the polyvinyl alcohol film, resulting in an uneven film surface and affecting the film's tensile strength and elongation at break. Conversely, excessively low drying temperatures can cause difficulties in molding and prolong the drying time. In this invention, the conditions for the first drying stage meet the aforementioned ranges, which can reduce film shrinkage and curling, and ensure that the film has a high elongation at break.

[0040] Furthermore, according to a preferred embodiment of the present invention, the conditions for the first drying include: a drying temperature of 60-75°C and a drying time of 30-60 seconds.

[0041] According to the present invention, the water content of the polyvinyl alcohol film I is 5-40 wt%.

[0042] In this invention, the first drying conditions ensure that the moisture content of the polyvinyl alcohol film I meets the above-mentioned range, and the second drying conditions described below can work together to ensure that the moisture content of the polyvinyl alcohol film meets the requirements (1-5 wt%), thereby preventing film curling and improving its tensile properties.

[0043] Furthermore, the water content of the polyvinyl alcohol film I is 5-25 wt%.

[0044] According to the present invention, the conditions for the thermal radiation include: a power of 30-150kW and an air volume of 500-1500m³. 3 / h.

[0045] In this invention, the power and air volume meet the above-mentioned range, which can adjust the moisture content of the film and avoid the defect of uneven film surface caused by excessive water loss.

[0046] Furthermore, the conditions for the heat radiation include: a power of 80-150kW and an air volume of 1000-1500m³. 3 / h.

[0047] According to the present invention, the conditions for the second drying include: a drying temperature of 60-140°C and a drying time of 100-200 seconds.

[0048] In this invention, the second drying conditions satisfy the above-mentioned range, and can work together with the first drying conditions to adjust the moisture content in the film. This can improve the overall uniformity of the film and enhance the tensile properties of the film while avoiding unevenness on the film surface.

[0049] Furthermore, the conditions for the second drying process include: a drying temperature of 95-110°C and a drying time of 120-160 seconds.

[0050] According to the present invention, the vertical distance between the heat source of the thermal radiation and the upper and lower surfaces of the polyvinyl alcohol film I is independently 10-40 cm.

[0051] In this invention, the vertical distance between the heat source of the thermal radiation and the polyvinyl alcohol film I meets the above-mentioned range, which enables the film to dry more uniformly, the film thickness to be more uniform, and avoids the film curling.

[0052] Furthermore, the vertical distance between the heat source of the thermal radiation and the upper and lower surfaces of the polyvinyl alcohol film I is independently 10-40 cm.

[0053] A second aspect of the present invention provides a polyvinyl alcohol film dried by the method described in the first aspect of the present invention.

[0054] According to the present invention, the water content of the polyvinyl alcohol film is 1-5 wt%.

[0055] In this invention, by controlling the moisture content to meet the above-mentioned range, a polyvinyl alcohol film with a smooth surface, high uniformity, and good tensile properties can be obtained.

[0056] Furthermore, the water content of the polyvinyl alcohol film is 2-3 wt%.

[0057] In this invention, there is no particular limitation on the thickness of the polyvinyl alcohol film, for example, it can be 20-75 μm.

[0058] According to a preferred embodiment of the present invention, the tensile strength of the polyvinyl alcohol film is 62-78 MPa, preferably 70-78 MPa, the elongation at break is 550-720%, preferably 620-720%, the film thickness range is not greater than 6, preferably 0.5-1, the film thickness standard deviation is not greater than 1.5, preferably 0-1, and the warpage angle is not greater than 10°, preferably 0-1°.

[0059] A third aspect of the present invention provides a drying apparatus for polyvinyl alcohol film, wherein the apparatus includes an inlet traction roller 1, a first thermal radiation heater 3-1, a second thermal radiation heater 3-2, and an outlet traction roller 4;

[0060] The first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 are located above and below the polyvinyl alcohol film, respectively;

[0061] The polyethylene film is conveyed by an inlet traction roller 1 and an outlet traction roller 4, with the linear velocity decreasing between the inlet traction roller 1 and the adjacent outlet traction roller 4.

[0062] In this invention, the first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 can simultaneously adjust the temperature of both sides of the film (the temperatures can be different), controlling the water content of both sides of the film to be more uniform, resulting in a greater elongation at break when the film is stretched. This further solves the curling problem caused by uneven water loss on the film surface. It also allows for more precise control of the film surface water content.

[0063] Furthermore, by using the first thermal radiation heater 3-1 and the second thermal radiation heater 3-2 for heating from both sides, the heat can penetrate into the interior of the film, resulting in fast and uniform heating. In order to further adapt to the scheme of the present invention, thermal radiation heaters that are small in size, have high power, and are easy to install are preferred.

[0064] According to some preferred embodiments of the present invention, the number of the inlet traction rollers 1 is not less than 2, and the number of the outlet traction rollers 4 is not less than 2.

[0065] According to some preferred embodiments of the present invention, the inlet traction roller 1 includes a first inlet traction roller 1-1 and a second inlet traction roller 1-2, and the outlet traction roller 4 includes a first outlet traction roller 4-1 and a second outlet traction roller 4-2.

[0066] According to some preferred embodiments of the present invention, the device further includes a pressure roller 2.

[0067] According to some preferred embodiments of the present invention, the number of the pressing rollers 2 is not less than 2.

[0068] According to some preferred embodiments of the present invention, the device further includes a first pressing roller 2-1 and a second pressing roller 2-2, wherein the first pressing roller 2-1 is disposed above the second inlet traction roller 1-2 and the second pressing roller 2-2 is disposed above the first outlet traction roller 4-1, for pressing the polyvinyl alcohol film.

[0069] According to the present invention, the vertical distance between the thermal radiation heater and the polyvinyl alcohol film is independently 10-40 cm, preferably 10-20 cm.

[0070] In this invention, the thermal radiator refers to the aforementioned first thermal radiant heater 3-1 and second thermal radiant heater 3-2. The distances between the first thermal radiant heater 3-1 and the second thermal radiant heater 3-2 and the two sides of the film can be the same or different, but preferably the same.

[0071] In this invention, it is worth noting that the position of the thermal radiation heater should be kept parallel to the surface of the film, and the heating power of the thermal radiation heater should be infinitely adjustable to ensure uniform temperature distribution in the transverse and longitudinal directions of the film.

[0072] In this invention, the pressing roller 2 refers to the first pressing roller 2-1 and the second pressing roller 2-2. The pressing roller is preferably a rubber pressing roller, i.e., a roller covered with high-temperature resistant silicone rubber. During operation, the pressing roller, driven by a cylinder, presses down on the film to prevent slippage and ensure constant elastic shrinkage of the film.

[0073] In this invention, the distance between adjacent guide traction rollers is 0.5-2m, the distance between the guide traction roller and the adjacent exit traction roller is 10-20m, and the distance between adjacent exit rollers is 0.5-2m.

[0074] In this invention, the distance between adjacent inlet traction rollers and the distance between adjacent outlet rollers can be the same or different, but are preferably the same.

[0075] The fourth aspect of the present invention provides the application of the method described in the first aspect and the apparatus described in the third aspect in the preparation of polyvinyl alcohol films.

[0076] The present invention will be described in detail below through embodiments.

[0077] In the following embodiments, the moisture content was obtained in real time by an infrared water content analyzer;

[0078] The performance evaluation indicators are tensile strength and elongation at break. Both were tested using a CMT6104 microcomputer-controlled electronic universal testing machine according to GB / T13022-1991. Each group underwent three repeated tests, and the results are expressed as the average value.

[0079] The thickness of the film was measured using an online thickness gauge;

[0080] The range and standard deviation of the film thickness are calculated using the following formulas:

[0081] R = X Max -X Min Equation (1)

[0082] In equation (1): R is the range of film thickness, X Max X represents the maximum film thickness. Min This represents the minimum film thickness.

[0083]

[0084] In equation (2): S is the standard deviation of the film thickness, and X is a single measured value. is the average of a set of measurements, where n is the number of measurements.

[0085] In the following examples and comparative examples, the concentration of the polyvinyl alcohol solution is 20 wt%, the distance between the first inlet traction roller 1-1 and the second inlet traction roller 1-2, the distance between the first outlet traction roller 4-1 and the second outlet traction roller 4-2 are all 1 m, and the distance between the second inlet traction roller 1-2 and the first outlet traction roller 4-1 is 12 m.

[0086] Example 1

[0087] S1. The polyvinyl alcohol solution is first dried on the casting roller at a temperature of 68°C for 50 seconds to obtain polyvinyl alcohol film I with a water content of 15%.

[0088] S2, such as Figure 1 As shown, under the action of the first inlet traction roller 1-1 and the second inlet traction roller 1-2, the above-mentioned polyvinyl alcohol film I is introduced into a thermal radiation oven (containing a first thermal radiation heater 3-1 and a second thermal radiation heater 3-2) for a second drying process. The power is 100kW and the air volume is 1000m³ / h. 3 / h, the upper and lower surfaces of the polyvinyl alcohol film are subjected to a second drying process at a drying temperature of 95°C and a drying time of 150s. At the same time, the first pressing roller 2-1 and the second pressing roller 2-2 are pressed down on the film by the push of two cylinders to prevent the film from slipping. The film is then exported under the action of the first export traction roller 4-1 and the second export traction roller 4-2 to obtain a polyvinyl alcohol film with a water content of 3%.

[0089] Along the running direction of the polyvinyl alcohol film I, the linear velocity decrease rate between the second inlet traction roller 1-2 and the first outlet traction roller 4-1 is 0.2%, the linear velocity decrease rate between the first inlet traction roller 1-1 and the second inlet traction roller 1-2 is 0.2%, and the linear velocity decrease rate between the first outlet traction roller 4-1 and the second outlet traction roller 4-2 is 0.2%.

[0090] Example 2-11

[0091] The method is the same as in Example 1, except that some operating parameters are different, as detailed in Table 1 and Table 1 Continued. Here, moisture content 1 refers to the moisture content of the polyvinyl alcohol film I after the first drying; moisture content 2 refers to the moisture content of the polyvinyl alcohol film after the second drying; the decrease rate refers to the linear velocity decrease rate between adjacent traction rollers; vertical distance 1 refers to the distance between the thermal radiation heater and the upper surface of the polyvinyl alcohol film; and vertical distance 2 refers to the distance between the thermal radiation heater and the lower surface of the polyvinyl alcohol film.

[0092] Example 12

[0093] The method is the same as in Example 1, except that, along the running direction of the polyvinyl alcohol film I, the linear velocity decrease rate between the second inlet traction roller 1-2 and the first outlet traction roller 4-1 is 0.2%, and the linear velocity decrease rate between the first inlet traction roller 1-1 and the second inlet traction roller 1-2, and the linear velocity decrease rate between the first outlet traction roller 4-1 and the second outlet traction roller 4-2 are both 0.

[0094] Example 13

[0095] The method is the same as in Example 1, except that, along the running direction of the polyvinyl alcohol film I, the linear velocity reduction rate between the second inlet traction roller 1-2 and the first outlet traction roller 4-1 is 0.5%, and the linear velocity reduction rate between the first inlet traction roller 1-1 and the second inlet traction roller 1-2, and the linear velocity reduction rate between the first outlet traction roller 4-1 and the second outlet traction roller 4-2 are both 0.2%.

[0096] Comparative Example 1

[0097] The method is the same as in Example 1, except that the polyvinyl alcohol film I obtained in step S1 is placed in an oven for a second drying (without a thermal radiation heater), and the conditions for the second drying are the same as in Example 1.

[0098] Comparative Example 2

[0099] The method is the same as in Example 1, except that the polyvinyl alcohol film I obtained in step S1 is dried a second time on a roller under the same drying conditions as in Example 1.

[0100] Comparative Example 3

[0101] The method is the same as in Example 1, except that the linear velocity between the second inlet traction roller 1-2 and the first outlet traction roller 4-1 is the same, that is, the decrease rate is 0.

[0102] Table 1

[0103]

[0104]

[0105] Table 1 (continued)

[0106]

[0107]

[0108] Decline rate a This refers to the rate of decrease in linear velocity between the second inlet traction roller 1-2 and the first outlet traction roller 4-1. bThis refers to the linear velocity reduction rate between the first inlet traction roller 1-1 and the second inlet traction roller 1-2.

[0109] Test case

[0110] The polyvinyl alcohol films prepared in the examples and comparative examples were subjected to tensile property tests, and the results are shown in Table 2.

[0111] Edge curling test: The polyvinyl alcohol films in the above examples and comparative examples were immersed in 50°C water for 5 minutes, taken out and placed on a table to observe the edge curling, and the angle between the tangent at the warped part of the film and the horizontal direction of the ground was measured. The larger the angle, the more serious the edge curling.

[0112] Table 2

[0113]

[0114]

[0115] As can be seen from the results in Table 1, the polyvinyl alcohol film treated by the drying method of the present invention has excellent performance, uniform film thickness, and ideal tensile strength and elongation at break, which basically meets the requirements for use in preparing polyvinyl alcohol film products.

[0116] The preferred embodiments 1-4 have significantly better technical effects, with tensile strength not less than 70 MPa, elongation at break not less than 180%, film thickness range not greater than 1, standard deviation not greater than 0.42, and warpage angle not greater than 1°.

[0117] Comparative Example 1 uses a combination of traditional casting rollers and traditional oven drying, Comparative Example 2 uses casting roller drying, and Comparative Example 3 uses the same linear speed between the second inlet traction roller 1-2 and the first outlet traction roller 4-1. All of these methods result in a significant reduction in tensile strength and elongation at break, while also increasing the film thickness range and standard deviation, resulting in poor film uniformity and film curling.

[0118] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for drying a polyvinyl alcohol film, characterized in that, The method includes: S1. The polyvinyl alcohol solution is first dried to obtain polyvinyl alcohol film I; S2. Under the action of the inlet traction roller and the outlet traction roller, the upper and lower surfaces of the polyvinyl alcohol film I are dried by thermal radiation to obtain a polyvinyl alcohol film. In step S2, the linear velocity between the inlet traction roller and the outlet traction roller decreases along the running direction of the polyvinyl alcohol film I.

2. The drying method according to claim 1, wherein, The number of the inlet traction rollers is not less than 2, and the number of the outlet traction rollers is not less than 2; Preferably, the linear velocity decrease rate between adjacent guide traction rollers is 0-0.2%; Preferably, the linear velocity decrease rate between adjacent lead-out traction rollers is 0-0.2%; Preferably, the linear velocity decrease rate between the inlet traction roller and the adjacent outlet traction roller is 0.2-5%, more preferably 0.2-2%.

3. The drying method according to claim 1 or 2, wherein, The first drying conditions include: a drying temperature of 60-98℃ and a drying time of 21-90s; Preferably, the water content of the polyvinyl alcohol film I is 5-40 wt%.

4. The drying method according to claim 1 or 2, wherein, The conditions for the heat radiation include: power of 30-150kW and air volume of 500-1500m³. 3 / h; Preferably, the conditions for the second drying include: a drying temperature of 60-140°C and a drying time of 100-200 seconds.

5. The drying method according to claim 1 or 2, wherein, The vertical distance between the heat source of the thermal radiation and the upper and lower surfaces of the polyvinyl alcohol film I is 10-40 cm, preferably 10-20 cm.

6. A polyvinyl alcohol film obtained by the drying method according to any one of claims 1-5.

7. The polyvinyl alcohol film according to claim 6, wherein, The water content of the polyvinyl alcohol film is 1-5 wt%, preferably 2-3 wt%.

8. A drying apparatus for polyvinyl alcohol film, characterized in that, The device includes an inlet traction roller (1), a first thermal radiation heater (3-1), a second thermal radiation heater (3-2), and an outlet traction roller (4); The first thermal radiation heater (3-1) and the second thermal radiation heater (3-2) are located above and below the polyvinyl alcohol film, respectively; The polyethylene film is conveyed by an inlet traction roller (1) and an outlet traction roller (4), with the linear velocity decreasing between the inlet traction roller (1) and the adjacent outlet traction roller (4).

9. The drying apparatus according to claim 8, wherein, The number of the inlet traction rollers (1) is not less than 2; Preferably, the number of the outgoing traction rollers (4) is not less than two; Preferably, the inlet traction roller (1) includes a first inlet traction roller (1-1) and a second inlet traction roller (1-2), and the outlet traction roller (4) includes a first outlet traction roller (4-1) and a second outlet traction roller (4-2); Preferably, the drying device further includes a pressure roller (2); Preferably, the number of the pressing rollers (2) is not less than two; Preferably, the device further includes a first pressing roller (2-1) and a second pressing roller (2-2); Preferably, the first pressing roller (2-1) is disposed above the second inlet traction roller (1-2), and the second pressing roller (2-2) is disposed above the outlet first outlet traction roller (4-1), for pressing the polyvinyl alcohol film; Preferably, during the thermal radiation heating process, the linear velocity decrease rate between the inlet traction roller (1) and the adjacent outlet traction roller (4) is 0.2-5%, preferably 0.2-2%. Preferably, the vertical distance between the first thermal radiation heater (3-1) and the second thermal radiation heater (3-2) and the polyvinyl alcohol film is 10-40 cm, more preferably 10-20 cm.

10. The use of the method according to any one of claims 1-5 and the drying apparatus according to claim 8 or 9 in the preparation of polyvinyl alcohol films.

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