Double casting device and double casting preparation method of film

Abstract

The present invention relates to C08J, and more specifically, to a double casting device and a double casting preparation method for a film. It includes: a first windshield and a second windshield. By arranging a support roller at the support body just below the film falling position of the second die head, a supporting force facing the direction of the casting die head is applied to the support body, so that the strip support body and the roller have a certain fitting area. The fitting area is at the film falling position of the casting. Since the strip support body and the roller are completely fitted, the position stability of the strip support body at this position can be provided. At the same time, a windshield device is arranged before and after the second die head casting direction, and a suction device is arranged on the outside of the die head relative to the windshield device in the casting direction of the second casting nozzle. The inventor found that the lateral difference and unevenness of the film falling can be avoided, so that the local thickness of the film finally formed is uniform, the film is flat, and the peeling is stable. It can be used for -micron thickness casting film, as a TAC film for polarizer.

Description

Technical Field

[0001] The present invention relates to C08J, and more specifically, to a double casting device and a double casting preparation method for a film. Background Art

[0002] The cellulose film produced by the solution casting method has excellent optical properties and surface properties, and has stable mechanical properties. It is particularly suitable for the preparation of TAC films for polarizers, where the cellulose film for polarizers has strict difference requirements for the uniformity of the overall thickness to ensure the display characteristics. The preparation method of cellulose lipid film is shown in CN103950136A, which generally includes the processes of casting, drying, and winding. However, in the process of drying the 80-300 micron thick cast film with the belt-shaped support, the drying rate of the film surface in contact with the air is greater than the contact surface of the support, which makes the cast film dry unevenly, resulting in abnormal conditions such as large curling, uneven film surface, and unstable peeling, affecting production stability and product quality.

[0003] In the process of two-time casting film making, the process of the second die spitting out the solution and casting it on the base cast film is the key factor to ensure the uniformity of thickness. However, after the second die is cast, when the second stage of drying is completed by the air supply port and return air port behind the second die, an airflow running in the opposite direction of the casting direction will appear at the second die. Due to the interference of the die and other equipment, a turbulent wind field around the second die is formed during the film casting process. This causes lateral differences and unevenness in the film. As a result, the apparent defects such as orthogonal transverse lines, longitudinal lines, and oblique lines relative to the casting direction are formed. For this reason, the usual method for controlling the wind field around the casting die is to adjust the surrounding process wind pressure and try to achieve a windless or zero pressure wind state, which is difficult to achieve in a large process production environment; another conventional measure is to set a wind shield device around the die. Because the film and the support are in operation, the wind shield cannot achieve a complete wind blocking effect, and at the same time causes wind field turbulence inside the shield, exacerbating the instability of the film.

[0004] In addition, for the stability of the second casting process, the position stability of the belt-shaped support at the second casting is also an important factor in the uniformity of film forming. If the running speed of the support fluctuates, the discharged solution will accumulate or stretch locally on the support, resulting in an abnormal situation of excessive or insufficient local thickness. At the same time, if the distance between the die head and the support changes, the film will stretch or accumulate during the film casting process due to the viscosity of the solution, which will eventually cause the local thickness of the film to be uneven. Summary of the invention

[0005] To overcome the above technical problems. The present invention adopts the form of double casting. The specific process is that the cellulose solution is prepared by a dissolving and mixing device, and is continuously and evenly cast onto a stainless steel mirror-finished endless belt support through a primary casting die. During the operation of the support, it is displaced and heated by the parallel circulating wind, and is initially dried to form a base cast film. A secondary casting die is arranged at the position after the base film is dried, and the cellulose solution is cast through the secondary casting die to the top of the cast film of the support below, and is fused into a thick cast film. The double-layer cast film runs with the support and is dried into a semi-dry film. By peeling, further stretching, drying and winding, a cast film is finally formed, which can effectively solve the problems of support body shaking and process wind field turbulence during the film falling process, and the surface uniformity and surface flatness of the product are good. The first aspect of the present invention provides a double casting device, including:

[0006] An annular belt-shaped support body; a first rotating drum and a second rotating drum are respectively arranged inside the two sides of the annular belt-shaped support body, and the first rotating drum and the second rotating drum are tensioned and driven to rotate periodically.

[0007] A first die head is located above one side of the annular belt-shaped support body;

[0008] A second die head is located above the middle of the annular belt-shaped support body;

[0009] The drying assembly is located at the periphery of the annular belt-shaped support body; the present invention does not specifically limit the drying assembly, which is generally composed of an air supply port and an air return port. The number of drying assemblies of the present invention can be selected according to the circumference of the annular belt-shaped support body and the drying speed, and is not specifically limited; along the casting direction, the drying assembly is sequentially provided with a first air supply port and a first air return port; the first air supply port and the first air return port are located between the first die head and the second die head;

[0010] The peeling roller is located on one side of the annular belt-shaped support body close to the first die head.

[0011] As a preferred technical solution of the present invention, along the casting direction, a first windshield and a second windshield are respectively provided on both sides of the second die head; the first windshield and the second windshield are preferably plate-shaped;

[0012] The first windshield is located between the second die head and the first windshield;

[0013] A secondary air return port is provided on a side of the second air shield away from the second die head.

[0014] As a preferred technical solution of the present invention, the center distance between the secondary return air port and the second die head is 300-500mm, and the center distances thereof include 300mm, 350mm, 400mm, 450mm, and 500mm. The center distance between the first return air port 42 and the second die head 27 is 300-500mm, and the center distances thereof include 300mm, 350mm, 400mm, 450mm, and 500mm.

[0015] As a preferred technical solution of the present invention, the first return air outlet and the secondary return air outlet can be in the form of an air collecting hood, etc., and their projection shape can be rectangular, circular, etc., and the number can be one arrangement, two side by side arrangements, etc. In the overall projection shape, the length of the orthogonal direction of the casting is greater than the width of the support body in the same direction, that is, the width of the first return air outlet or the secondary return air outlet is greater than the width of the support body.

[0016] As a preferred technical solution of the present invention, the two-time casting device further includes a casting heat preservation box;

[0017] The annular belt-shaped support body is arranged in the casting heat preservation box; the first die head and the second die head are arranged in the casting heat preservation box.

[0018] As a preferred technical solution of the present invention, along the casting direction, the distance between the first return air outlet and the first wind shield is 0-100 mm, and the distance between the secondary return air outlet 47 and the second wind shield is 0-100 mm.

[0019] The first return air inlet and / or the secondary return air inlet are respectively installed on the upper part of the casting insulation box body, and the lower end surface of the first return air inlet and / or the secondary return air inlet does not protrude from the plane of the upper inner wall of the box body. The lower end surface of the first return air inlet and / or the secondary return air inlet is a perforated plate, and the perforated plate is provided with a plurality of holes, and the shape of the holes is selected from at least one of a long hole, a round hole, and a rectangular hole, preferably a round hole, and the hole area of ​​the perforated plate accounts for 30-80% of the overall area of ​​the perforated plate, preferably 60-80%, and can be listed as 30%, 40%, 50%, 60%, 70%, 80%.

[0020] As a preferred technical solution of the present invention, the thickness of the first windshield is 50-150mm, preferably 75-125mm, the thickness of the second windshield is 50-150mm, preferably 75-125mm, the first windshield and the second windshield are arranged orthogonally to the casting direction, along the casting direction, the first windshield is 1-3mm away from the support, and the distance from the second die is 0.025-0.05 times the operating speed of the support, for example, the operating speed of the vehicle is 12m / min The distance between the second windshield and the second die head is 0.025-0.05 times of the running speed of the support body, for example, at a running speed of 12 m / min, the distance between the second windshield and the second die head can be maintained at 300-600 mm; preferably, the distance between the secondary air return port and the center of the second die head is 300-500 mm, and the distance between the first air return port and the center of the second die head is 300-500 mm. The first windshield and the second windshield are fixed in the casting insulation box and are sealed to the box.

[0021] As a preferred technical solution of the present invention, the device further comprises a support roller; the support roller is located below the position where the second die head falls the film to the annular belt support body, and the support roller is in contact with the annular belt support body to provide a certain tension force, such as Figure 3 As shown, after the belt-shaped support body is supported by the supporting roller, the belt-shaped supporting plane behind the roller in the casting direction is as shown in Figure B, and the length of the contact surface between the annular belt-shaped support body and the supporting roller in the circumferential direction of the roller is 4-10 times, preferably 5-7 times, of the distance A between the second die head and the annular belt-shaped support body, wherein the distance A is determined by the process conditions. Preferably, the length of the contact surface between the annular belt-shaped support body and the supporting roller in the circumferential direction of the roller is 4-8mm, and a temperature-controlled water flow channel is provided inside the supporting roller, and the roller can be driven to rotate by the rotation of the supporting body or driven to rotate by a motor.

[0022] The present invention arranges a support roller at the film-casting position of the second die head, and provides support and tensioning force to the support body to ensure that the support body is not subject to position jitter or fluctuation caused by external forces. In addition, in the present invention, windshields are arranged in front and behind the second die head respectively to block the front and rear airflows from flowing through the secondary casting position, thereby maintaining the stability of the secondary casting film-casting process. At the same time, in order to reduce or eliminate the influence of the turbulent wind field formed by the air supply and return ports of the dry wind near the second die head, a windshield device of a certain thickness is arranged in front and behind the die head to block the wind flow to the die head and avoid the influence of the air flow on the film-casting process; because the strip support body with the solution film attached is in a continuous operation state, the windshield needs to maintain a certain safety distance from the strip support body, thereby causing the wind flow to be rapid and eddy at the safety distance. Therefore, the method provided by the present invention further optimizes the wind field state outside the windshield, that is, a negative pressure return air port is arranged on the outside of the windshield relative to the die head, and the return air port is provided with negative pressure by an external fan, thereby absorbing the gas turbulence formed by the windshield blocking, avoiding the surface defects such as lines formed on the film surface by the airflow sweeping, and further stabilizing the airflow around the die head. Through the above device, the stability of the die head film falling process is guaranteed, thereby achieving a uniform film thickness effect and improving product quality.

[0023] In order to further promote the drying of the film after the secondary casting, the drying assembly also includes a plurality of air supply ports and air return ports along the casting direction. Without specific limitation, in one example, along the casting line, the drying assembly includes a first air supply port, a first air return port, a secondary air return port, a second air supply port, a second air return port, a third air supply port and a fourth air return port. The casting direction is the rotation direction of the annular belt-shaped support body.

[0024] The second aspect of the present invention provides a method for preparing a film by double casting, comprising: preparing a casting solution by the double casting device as described above.

[0025] As a preferred technical solution of the present invention, the preparation method comprises:

[0026] The cellulose solution 1 is cast through the first die head onto the annular belt support to form a base cast film. The base cast film is dried by the drying air from the first air supply port and the first air return port during the process of running with the annular belt support to the bottom of the second die head to form a base semi-dry film. The cellulose solution 2 is cast through the second die head onto the surface of the base film below and adheres to each other to form a cast film. After the cast film continues to run with the annular belt support and is dried by the second air supply port, it is peeled off from the surface of the annular belt support at the peeling roller and enters the subsequent stretching, drying and winding process.

[0027] As a preferred technical solution of the present invention, the preparation method comprises:

[0028] The cellulose solution a is cast through the first die head onto the annular belt-shaped support to form a base cast film. The base cast film is dried by the drying air from the first air supply port and the first air return port as the annular belt-shaped support moves to the bottom of the second die head to form a base semi-dry film. The cellulose solution a is cast through the second die head onto the surface of the base film below and adheres to each other to form a cast film. The cast film continues to move with the annular belt-shaped support and is dried twice by the second air supply port and the second air return port, the third air supply port and the fourth air return port, and then is peeled off from the surface of the support at the peeling roller and enters the subsequent stretching, drying and winding process.

[0029] Compared with the prior art, the present invention has the following beneficial effects: in the process of preparing the two-time film flow, the first die head casts the base film and runs it to the second die head, and the film is dried by parallel circulating air. The drying principle is that after the first film flow, the air supply port sends out a non-concentration dry air parallel to the casting direction. The solvent in the base film volatilizes and diffuses to the low-concentration area and runs with the dry air to the return air port before the second film flow. The return air outlet is controlled by an external fan to generate a negative pressure area to absorb the concentrated gas. After the preliminary drying of the base film, the solution is superimposed and cast through the second die head above the preliminary dried base film to obtain a double-layer cast film, and the final product is obtained through the peeling, stretching, drying and winding processes; wherein a supporting roller is arranged at the support body just below the film falling position of the second die head, and a supporting force facing the direction of the casting die head is applied to the support body, so that the strip support body and the roller have a certain fitting area, and the fitting area is at the film falling position of the casting. Since the strip support body and the roller are completely fitted, the position stability of the strip support body at this position can be provided. At the same time, a wind shield is arranged before and after the second die head in the casting direction, and a suction device is arranged outside the die head relative to the wind shield in the casting direction of the second casting nozzle. The inventor found that the lateral difference and unevenness of the film falling can be avoided, so that the local thickness of the film finally formed is uniform, the film is flat, and the peeling is stable, which can be used for -micron thickness cast film as TAC film for polarizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the casting device of the present invention.

[0031] Figure 2 It is a schematic diagram of the device of the method of the present invention.

[0032] Figure 3 This is the layout diagram of the wind shield and return air outlet of the present invention

[0033] Figure 4 Schematic diagram of the support tube of the present invention

[0034] Figure 5 It is a schematic diagram of the test of horizontal stripes and wavy membrane surface.

[0035] Among them, the first die head 22, the annular belt support body 23, the first drum 24 and the second drum 25, the second die head 27, the first wind shield 11 and the second wind shield 12, the first air supply port 41, the first return air port 42, the second air supply port 43, the second return air port 44, the third air supply port 46, the fourth return air port 45, the first drum 24, the second drum 25, the peeling roller 32a, the support roller 28, the secondary return air port 47. Cellulose solution one 31, cellulose solution two 31a, and a film 36. DETAILED DESCRIPTION

[0036] Example

[0037] Example 1

[0038] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 60% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 100 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 5 mm long in the circumferential direction of the roller.

[0039] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0040] The cellulose solution 1 31 is cast through the first die head 22 to the annular belt-shaped support body 23 to form a base cast film. At this time, the film 36 has a thickness of 120 microns. When the base cast film moves with the annular belt-shaped support body 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast through the second die head 27 to the surface of the base film below and adheres to each other to form a cast film. At this time, the film thickness is 200 microns. The cast film continues to run with the annular belt-shaped support body 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45. The thickness is reduced to 175 microns, and it is peeled off from the surface of the support body 23 at the peeling roller 32a, and enters the subsequent stretching, drying and winding process.

[0041] Example 2

[0042] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 80% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 100 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 5 mm long in the circumferential direction of the roller.

[0043] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0044] The cellulose solution 1 31 is cast through the first die head 22 to the annular belt-shaped support body 23 to form a base cast film. At this time, the film 36 has a thickness of 120 microns. When the base cast film moves with the annular belt-shaped support body 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast through the second die head 27 to the surface of the base film below and adheres to each other to form a cast film. At this time, the film thickness is 200 microns. The cast film continues to run with the annular belt-shaped support body 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45. The thickness is reduced to 175 microns, and it is peeled off from the surface of the support body 23 at the peeling roller 32a, and enters the subsequent stretching, drying and winding process.

[0045] Example 3

[0046] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 80% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 100 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 7 mm long in the circumferential direction of the roller.

[0047] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0048] The cellulose solution 1 31 is cast through the first die head 22 to the annular belt-shaped support body 23 to form a base cast film. At this time, the film 36 has a thickness of 120 microns. When the base cast film moves with the annular belt-shaped support body 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast through the second die head 27 to the surface of the base film below and adheres to each other to form a cast film. At this time, the film thickness is 200 microns. The cast film continues to run with the annular belt-shaped support body 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45. The thickness is reduced to 175 microns, and it is peeled off from the surface of the support body 23 at the peeling roller 32a, and enters the subsequent stretching, drying and winding process.

[0049] Example 4

[0050] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 80% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 600 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 7 mm long in the circumferential direction of the roller.

[0051] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0052] The cellulose solution 1 31 is cast through the first die head 22 to the annular belt-shaped support body 23 to form a base cast film. At this time, the film 36 has a thickness of 120 microns. When the base cast film moves with the annular belt-shaped support body 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast through the second die head 27 to the surface of the base film below and adheres to each other to form a cast film. At this time, the film thickness is 200 microns. The cast film continues to run with the annular belt-shaped support body 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45. The thickness is reduced to 175 microns, and it is peeled off from the surface of the support body 23 at the peeling roller 32a, and enters the subsequent stretching, drying and winding process.

[0053] Example 5

[0054] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 80% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 100 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 7 mm long in the circumferential direction of the roller.

[0055] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0056] The cellulose solution 1 31 is cast through the first die head 22 to the annular belt-shaped support body 23 to form a base cast film. At this time, the film 36 has a thickness of 40 microns. When the base cast film moves with the annular belt-shaped support body 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast through the second die head 27 to the surface of the base film below and adheres to each other to form a cast film. At this time, the film thickness is 100 microns. The cast film continues to run with the annular belt-shaped support body 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45, and the thickness is reduced to 85 microns. It is peeled off from the surface of the support body 23 at the peeling roller 32a and enters the subsequent stretching, drying and winding process.

[0057] Example 6

[0058] like Figures 1 to 4As shown, this example provides a two-time casting device, comprising: an annular belt-shaped support body 23; a first rotating drum 24 and a second rotating drum 25 are respectively arranged inside the two sides of the annular belt-shaped support body 23; a first die head 22, located above one side of the annular belt-shaped support body 23; a second die head 27, located above the middle of the annular belt-shaped support body 23; a drying component, located at the periphery of the annular belt-shaped support body 23, along the casting defense line, the drying component comprises a first air supply port 41, a first return air port 42, a secondary return air port 47, a second air supply port 43, a second return air port 44, a third air supply port 46 and a fourth return air port 45; the first air supply port 41 and the first return air port 42 are located between the first die head 22 and the second die head 27, and the secondary return air port 47, the second air supply port 43, the second return air port 44, the third air supply port 46 and the fourth return air port 45 are located between the first die head 22 and the second die head 2 7, a peeling roller 32a is arranged on the outside; it is located on the side of the annular belt-shaped support body 23 close to the first die head 22; along the casting direction, the first wind shield 11 and the second wind shield 12 are respectively arranged on both sides of the second die head 27; the first wind shield 11 is located between the second die head 27 and the first wind shield 11; the second wind shield 12 is provided with a secondary return air port 47 on the side away from the second die head 27; the projection shape of the first return air port 42 and the secondary return air port 47 is a rectangle; the two casting device also includes a casting insulation box; the annular belt-shaped support body 23 is arranged in the casting insulation box; the first die head 22 and the second die head 27 are arranged in the casting insulation box; along the casting direction; the first return air port 42 and the secondary return air port 47 are respectively installed on the upper part of the casting insulation box, and the lower end faces of the first return air port 42 and the secondary return air port 47 do not protrude from the plane of the inner wall of the upper part of the box. The lower end faces of the first return air port 42 and the secondary return air port 47 are orifice plates, which are provided with a plurality of holes, the shape of the holes being selected from uniformly long strip holes, and the hole area of ​​the orifice plate accounts for 80% of the overall area of ​​the orifice plate; the first wind shield 11 is 1 mm away from the support body 23, and is 100 mm away from the first return air port 42; the second wind shield 12 is 1 mm away from the support body 23, and is 100 mm away from the secondary return air port 47; the first return air port 42 is 100 mm away from the first wind shield 11, and the secondary return air port 47 is 100 mm away from the second wind shield 12; the device also includes a support roller 28 with a diameter of 300 mm; the support roller 28 is located below the position where the second die head 27 falls the film to the annular belt-shaped support body 23, and the support roller 28 is in contact with the annular belt-shaped support body 23; the contact surface between the annular belt-shaped support body 23 and the support roller 28 is 7 mm long in the circumferential direction of the roller.

[0059] This example also provides a two-casting method for preparing a film, comprising: preparing a cellulose solution through the two-casting device as described above.

[0060] The cellulose solution 1 31 is cast and spit out to the annular belt-shaped support 23 through the first die head 22 to form a base cast film. At this time, the film 36 has a thickness of 120 microns. When the base cast film moves with the annular belt-shaped support 23 to the bottom of the second die head 27, it is dried by the drying air of the first air supply port 41 and the first return air port 42 to form a base semi-dry film. The cellulose solution 2 31a is cast to the surface of the base film below through the second die head 27 and adheres to each other to form a cast film. At this time, the film thickness is 220 microns. The cast film continues to run with the annular belt-shaped support 23 and is dried twice by the second air supply port 43 and the second return air port 44, the third air supply port 46 and the fourth return air port 45, and the thickness is reduced to 200 microns. It is peeled off from the surface of the support 23 at the peeling roller 32a and enters the subsequent stretching, drying and winding process.

[0061] Comparative Example 1

[0062] like Figures 1 to 4 As shown, this example provides a double casting device and a double casting preparation method for a film thereof, and its specific implementation method is the same as Example 2, except that there is no secondary return air port 47, the first wind shield plate 11, the second wind shield plate 12, and the support roller 28.

[0063] Comparative Example 2

[0064] like Figures 1 to 4 As shown, this example provides a double casting device and a double casting method for preparing a film thereof, and its specific implementation method is the same as that of Example 2, except that there is no support roller 28.

[0065] Comparative Example 3

[0066] like Figures 1 to 4 As shown, this example provides a double casting device and a double casting method for preparing a film thereof. The specific implementation method is the same as that of Example 3, except that there is no secondary return air port 47, the first wind shield plate 11 and the second wind shield plate 12.

[0067] Performance Evaluation

[0068] For the film products obtained in the examples, a single-layer film of a certain size was taken as a sample, and the quality of the transverse stripes and wavy film surface was evaluated using the following method. The evaluation results are shown in Table 1.

[0069] 1. Horizontal stripes

[0070] refer to Figure 5Sample 36 is evaluated for the quality of horizontal stripes. First, a bracket 51 is prepared to fix one edge of the sample 35, which is the orthogonal edge in the casting direction. The fixing method is to press or clamp the fixing plate 53. A fluorescent tube 52 is arranged above the bracket 51, and the length of the tube is required to be greater than the width of the product 35. The fluorescent tube 52 is 1m high from the fixing plate and parallel to the fixed edge of the sample 35. The height of the bracket is 1-1.2m from the ground, and a dark flannel 54 is laid on the ground. The inspector P stands 1-1.5m away from the bracket, pinches the two corners of the edge of the sample with both hands and flattens the sample, so that the reflected light 57 of the fluorescent tube 52 in the sample 35 can be observed horizontally. Personnel P tightens the sample 35 and swings it up and down at an angle β. During the swinging process, if the sample 35 has a horizontal stripe defect, the deformation of the reflected light 57 will appear, which is mainly characterized by a change in thickness. In a sample 35 of a certain width, the number of changes in the emitted light 57 is used as the evaluation standard. The width is usually 100mm.

[0071] The evaluation criteria are:

[0072] A: 0;

[0073] B: 1-10;

[0074] C:>10.

[0075] 2. Wave-shaped membrane surface

[0076] refer to Figure 5 The horizontal stripe quality evaluation was performed on sample 35. The evaluation device and operation process were the same as those for the horizontal stripes.

[0077] The evaluation standard is to observe the linearity of the reflected light 55 from the fluorescent lamp 52 on the sample 36. The evaluation standard is whether the linearity of the reflected light 55 is continuous, intermittent, or cannot form an image.

[0078] A: Continuous;

[0079] B: intermittent;

[0080] C: Unable to image.

[0081] 3. The comprehensive quality assessment results are based on the poorer ratings in the horizontal stripes and wavy film surface tests.

[0082] Table 1

[0083]

[0084]

[0085] It can be seen from the test results in Table 1 that when the device provided by the present invention is used for casting, transverse stripes and wavy film surfaces can be reduced to obtain a film with uniform thickness.

Claims

1. A double casting device, characterized in that: include: An annular belt-shaped support body (23); A first die head (22) is located above one side of the annular belt-shaped support body (23); A second die head (27) is located above the middle of the annular belt-shaped support body (23); A drying component is located outside the annular belt-shaped support body (23); along the casting direction, the drying component is provided with a first air supply port (41) and a first air return port (42) in sequence; the first air supply port (41) and the first air return port (42) are located between the first die head (22) and the second die head (27); A peeling roller; located on one side of the annular belt-shaped support body close to the first die head; Along the casting direction, a first windshield and a second windshield are respectively provided on both sides of the second die head; The first wind shield is located between the second die head and the first air return port; A secondary air return port is provided on a side of the second air shield away from the second die head.

2. The double casting device according to claim 1, characterized in that: Along the casting direction, the distance between the first air return port and the first wind shield is 0-100 mm, and the distance between the secondary air return port (47) and the second wind shield is 0-100 mm.

3. The double casting device according to claim 1, characterized in that: The lower end surface of the first return air outlet and / or the secondary return air outlet is a perforated plate, and the hole area of ​​the perforated plate accounts for 30-80% of the overall area of ​​the perforated plate.

4. The double casting device according to claim 1, characterized in that: The first windshield is 1-3 mm away from the support, and the distance from the second die is 0.025-0.05 times the operating speed of the support. The second windshield is 1-5 mm away from the support, and the distance from the second die is 0.025-0.05 times the operating speed of the support.

5. The double casting device according to any one of claims 1 to 4, characterized in that: The device also includes a supporting roller; the supporting roller is located below the position where the second die head falls the film onto the annular belt-shaped support body, and the supporting roller is in contact with the annular belt-shaped support body.

6. The double casting device according to claim 5, characterized in that: The contact surface between the annular belt-shaped support body and the support roller has a length of 4-8 mm in the circumferential direction of the roller.

7. The double casting device according to claim 5, characterized in that: The length of the contact surface between the annular belt-shaped support body and the support roller in the circumferential direction of the roller is 4-10 times the distance A between the second die head and the annular belt-shaped support body.

8. A method for preparing a film by double casting, characterized in that: include: The casting solution is prepared by the double casting device according to any one of claims 1 to 7.

9. The twice casting method for preparing a film according to claim 8, characterized in that: include: The cellulose solution 1 is cast through the first die head onto an annular belt-shaped support to form a base cast film. During the process of the base cast film running with the annular belt-shaped support to the bottom of the second die head, it is dried by the drying air from the first air supply port and the first return air port to form a base semi-dry film. The cellulose solution 2 is cast through the second die head onto the surface of the base film below and adheres to each other to form a cast film. After the cast film continues to run with the annular belt-shaped support and is dried by the second air supply port, it is peeled off from the surface of the annular belt-shaped support at the peeling roller and enters the subsequent stretching, drying and winding processes.

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