Defoaming device for polyamide acid solution

Abstract

The utility model discloses a polyamide acid solution defoaming device which comprises a defoaming kettle, a feeding pipe, a discharging pipe, a gas access pipe and an emptying pipe are arranged on the defoaming kettle, and a grooved thin-layer distributor is arranged in the defoaming kettle. The grooved thin-layer distributor comprises a spherical crown and a plurality of through grooves which are formed in the spherical crown and penetrate through the thickness of the spherical crown, a rotating shaft and a center line of the spherical crown coincide with a rotating shaft and a center line of the defoaming kettle respectively, the through grooves are arranged on the spherical crown in a manner of forming a closed loop, and the center of the formed closed loop coincide with the center of the spherical crown; a gap exists between the outer side surface of the grooved thin-layer distributor and the inner wall of the kettle body, and the lower edge of the grooved thin-layer distributor is fixedly connected with the inner wall of the kettle body; the width of the through groove in the radial direction of the spherical crown is smaller than or equal to a gap between the outer side surface of the grooved thin-layer distributor and the inner wall of the kettle body. The defoaming device disclosed by the utility model is larger in treatment capacity, shorter in defoaming time and good in defoaming effect.

Description

Technical Field

[0001] The utility model relates to the technical field of polyimide films, and particularly relates to a defoaming device for polyamic acid solution. Background Art

[0002] Polyimide films are widely used in the electrical and electronic fields due to their excellent mechanical properties, high temperature resistance, corrosion resistance, electrical insulation and dimensional stability.

[0003] At present, the production and forming process of polyimide films uses polyamic acid solution (also known as polyamic acid resin solution) as the raw material, and a self-supporting polyamic acid thick film is obtained by casting and coating on a casting machine, and then through heating and tensioning (stretching) in the longitudinal and transverse directions, imidization, and shaping processes to obtain polyimide films.

[0004] The conventional method for synthesizing polyamic acid solution is to place a polar aprotic solvent (such as N,N-dimethylacetamide, etc.) in a reaction kettle, add dianhydride and diamine, and carry out polycondensation reaction under normal pressure or negative pressure conditions. The polycondensation reaction is usually accompanied by stirring and homogenization, and the operation of stirring in the reaction kettle will increase the amount of air involved in the solution system, resulting in a large number of bubbles in the synthesized polyamide acid solution, especially micro-nano sized bubbles in a high-viscosity solution system. As is well known, the tiny bubbles and impurities in the polyamide acid solution will cause defects on the surface of the cast and formed film. These defects not only affect the appearance of the film, but more importantly, weak points are easily formed at the defect positions and are broken down by high voltage, resulting in the failure of insulation applications and affecting the effective application of downstream electrical and electronic products. Therefore, defoaming the polyamide acid solution before subsequent casting has become a necessary step in the production and processing technology of polyimide films.

[0005] Defoaming is usually carried out in a defoaming kettle. The traditional defoaming kettle is an ordinary vertical or horizontal tank container. The traditional defoaming process is to send the polyamide acid solution that has completed batching and fully reacted in the reaction kettle into the defoaming kettle and let it stand or maintain a vacuum state for several hours to allow natural defoaming or negative pressure defoaming. However, this traditional defoaming device and method are difficult to eliminate tiny bubbles, especially micro-nano sized bubbles, in a short time. The inventor team of this application previously provided a defoaming kettle for polyamide acid solution and the corresponding defoaming method. Specifically, it can be seen in the invention patent with publication number CN104107565A. The defoaming kettle mentioned therein is equipped with a thin-layer distributor on the basis of a conventional tank container. Through the cooperation of the thin-layer distributor and the designed defoaming method, the technical effect of eliminating bubbles (including micron-sized and even nano-sized bubbles) in a short time (less than 1 hour) can be achieved, and the defoaming effect is good. As a result, the apparent defects of the polyimide film products prepared from the defoamed polyamide acid solution are significantly reduced. The applicant found in subsequent practical applications that this technical solution has the following deficiencies: (1) The thin-layer distributor only plays a role in distributing the polyamide acid solution to form a thin layer and can only flow downward from the lower edge of the thin-layer distributor and the inner wall of the tank, with a small throughput, and the overall defoaming time is still long. Especially when the viscosity of the polyamide acid solution is high (greater than or equal to 150,000 cps), even multiple sets of defoaming kettles need to be configured; (2) The height of the rotating surface of the thin-layer distributor is relatively large, and the polyamide acid solution slides down faster on the thin-layer distributor (especially for low-viscosity polyamide acid solution (less than or equal to 150,000 cps)), which is not conducive to forming a thinner thin layer and is also prone to accumulation at the lower edge of the thin-layer distributor and the inner wall of the tank, weakening the defoaming effect; in addition, the large height of the rotating surface will also increase the space it occupies in the kettle and increase the equipment investment; (3) During the defoaming process, it is necessary to control the thickness of the polyamide acid solution layer on the thin-layer distributor to achieve an ideal defoaming effect. The defoaming process overly relies on the flow rate control process of the polyamide acid solution, increasing the complexity of defoaming; (4) When the preparation amount of a single batch of polyamide acid solution increases, it will be affected by the throughput, resulting in an extended defoaming time, reduced production efficiency, or an increase in the number of configured defoaming kettles. Summary of the Utility Model

[0006] The technical problem to be solved by this utility model is to provide a defoaming device for polyamide acid solution with a larger throughput, a shorter defoaming time, and a good defoaming effect.

[0007] To solve the above technical problems, this utility model adopts the following technical solutions:

[0008] A defoaming device for a polyamic acid solution comprises a defoaming kettle for containing a polyamic acid solution, wherein the defoaming kettle is provided with a feed pipe, a discharge pipe, a gas access pipe and an emptying pipe, and a slotted thin layer distributor is provided in the defoaming kettle, wherein the slotted thin layer distributor comprises a spherical cap and a plurality of through slots which are provided on the spherical cap and penetrate the thickness of the spherical cap, the rotation axis and the center line of the spherical cap respectively coincide with the rotation axis and the center line of the defoaming kettle, the through slots are arranged on the spherical cap in a manner of forming a closed loop, and the center of the formed closed loop coincides with the center of the spherical cap; there is a gap between the outer side surface of the slotted thin layer distributor and the inner wall of the kettle body, and the lower edge of the slotted thin layer distributor is fixedly connected to the inner wall of the kettle body at one or more places; the width of the through slot in the radial direction of the spherical cap is less than or equal to the gap between the outer side surface of the slotted thin layer distributor and the inner wall of the kettle body.

[0009] Furthermore, the number of the closed loops is one or more than two, preferably 2 to 6, and is evenly arranged on the spherical cap. The number of through grooves forming a closed loop is at least 2, preferably 2 to 4.

[0010] Furthermore, the through grooves may be arranged on the spherical cap in a closed loop in a circular, square or elliptical shape.

[0011] Furthermore, the width of each through groove in the radial direction of the spherical crown is preferably 0.2 to 2.5 mm.

[0012] Furthermore, the height of the spherical cap is 1 / 5 to 1 / 12 of the diameter of the sphere where the spherical cap is located. This height combined with the design of opening a through groove on the spherical cap can effectively reduce the accumulation of polyamic acid solution on the outer side of the slotted thin layer distributor and the inner wall of the kettle. More importantly, such a design does not need to control the thickness of the polyamic acid solution layer on the slotted thin layer distributor, and the expected defoaming effect can be achieved regardless of the thickness of the liquid layer. Moreover, such a design is also conducive to forming a thinner and more evenly dispersed liquid thin layer, which is conducive to the elimination of bubbles, especially micro-nano-sized bubbles; in addition, the spherical cap design of the above height will also reduce the space occupied by it in the kettle.

[0013] The gap between the outer side surface of the grooved thin layer distributor and the inner wall of the kettle body is 0.1-5 mm.

[0014] Furthermore, a stirrer can be provided in the defoaming kettle, and the stirrer is located below the slotted thin layer distributor. In this case, a motor capable of driving the stirrer needs to be provided on the defoaming kettle. The thin liquid curtain formed by the downward flow of the slotted thin layer distributor can better eliminate bubbles under the action of the stirrer; at the same time, the stirring of the stirrer can also make the polyamic acid solution system gathered at the bottom of the kettle reach temperature uniformity in a shorter time.

[0015] Furthermore, the defoaming kettle is also provided with a pressure detection device and a temperature detection device for obtaining the pressure and temperature in the kettle.

[0016] Furthermore, the defoaming kettle body is provided with a jacket, and the jacket is provided with a medium inlet and a medium outlet, and the temperature of the polyamic acid solution system in the kettle is reduced by conveying cooling medium into the jacket.

[0017] The above defoaming device has a good defoaming effect on polyamic acid solutions with a viscosity of 80,000 to 1,000,000 cps (test temperature condition is 25°C, the same below), and is particularly suitable for high-viscosity polyamic acid solutions with a viscosity of 180,000 to 600,000 cps.

[0018] The method for defoaming a polyamic acid solution by using the above-mentioned polyamic acid solution defoaming device comprises: controlling the pressure in the defoaming kettle to be negative pressure, conveying the polyamic acid solution into the defoaming kettle through the feeding pipe on the defoaming kettle, controlling the temperature of the polyamic acid solution to be less than or equal to 65°C, the polyamic acid solution falling on the top of the spherical cap of the slotted thin layer distributor, uniformly dispersing and flowing along the radial direction of the spherical cap to form a thin layer, when passing through the through groove on the spherical cap, part of the polyamic acid solution flows downward to form at least one circle of liquid thin curtain concentric with the spherical cap, and the remaining polyamic acid solution continues to disperse and form a thin layer, until the formed thin layer flows downward along the gap between the outer side surface of the slotted thin layer distributor and the inner wall of the defoaming kettle, and finally gathers at the bottom of the defoaming kettle; after stopping conveying the polyamic acid solution and the polyamic acid solution on the slotted thin layer distributor is dispersed, cooling the defoaming kettle until the temperature of the polyamic acid solution system in the kettle is less than or equal to 15°C; when the liquid level of the polyamic acid solution in the defoaming kettle is stable, standing for a period of time, the defoaming of the polyamic acid solution is completed.

[0019] Compared with the prior art, the utility model adopts a special structure of a slotted thin layer distributor in a conventional defoaming kettle body. On the one hand, by opening through slots on the spherical crown of the slotted thin layer distributor and arranging the through slots on the spherical crown in a manner of arranging a closed loop, the processing volume of the polyamic acid solution per unit time is effectively increased, and the defoaming time is further shortened; on the other hand, by controlling the height of the spherical crown, the accumulation of the polyamic acid solution on the outer side of the slotted thin layer distributor and the inner wall of the kettle body can be effectively reduced, and the thickness of the polyamic acid solution liquid layer on the slotted thin layer distributor does not need to be controlled. Regardless of the thickness of the liquid layer, the expected defoaming effect can be achieved. The combination of the above two aspects can form multiple layers of thinner liquid curtain-like thin layers that are concentric with the spherical crown, further improving the defoaming effect, thereby further reducing the apparent defects of the polyimide film product prepared from the polyamic acid solution after defoaming using the defoaming device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of an implementation mode of the polyamic acid solution defoaming device described in the utility model.

[0021] Figure 2 In Figure 1 the top view of the grooved dispenser in the illustrated embodiment.

[0022] Figure 3 It is a schematic structural diagram of another embodiment of the polyamic acid solution defoaming device of the present utility model.

[0023] The reference numerals in the figure are:

[0024] 1 feed pipe, 2 emptying pipe, 3 grooved thin-layer dispenser, 3-1 spherical crown, 3-2 through groove, 4 temperature detection device, 5 medium inlet, 6 discharge pipe, 7 medium outlet, 8 pressure detection device, 9 gas access pipe, 10 stirrer. Specific embodiments

[0025] In order to better explain the technical solution of the present utility model, the present utility model will be further described in detail below with reference to the accompanying drawings, but the embodiments of the present utility model are not limited thereto.

[0026] See Figure 1 and Figure 2 The polyamic acid solution defoaming device of the present utility model includes a defoaming kettle for containing polyamic acid solution. A feed pipe 1, a discharge pipe 6, a gas access pipe 9 and an emptying pipe 2 are provided on the defoaming kettle. A grooved thin-layer dispenser 3 is provided directly below the feed inlet in the defoaming kettle. There is a gap between the outer side surface of the grooved thin-layer dispenser 3 and the inner wall of the defoaming kettle body. The size of this gap is set as required. Usually, the distance of this gap in the radial direction of the defoaming kettle is 0.1-5 mm; one or more than two places at the lower edge of the grooved thin-layer dispenser 3 are fixedly connected to the inner wall of the defoaming kettle body.

[0027] The said grooved thin-layer dispenser 3 is as Figure 2As shown, it includes a spherical cap 3-1 and multiple through grooves 3-2 opened on the spherical cap 3-1 and penetrating the thickness of the spherical cap 3-1. The rotation axis and center line of the spherical cap 3-1 coincide with the rotation axis and center line of the defoaming kettle respectively. The height of the spherical cap 3-1 is 1 / 5 to 1 / 12 of the diameter of the sphere where the spherical cap 3-1 is located. This height combined with the design of opening the through grooves 3-2 on the spherical cap 3-1 can effectively reduce the accumulation of polyamic acid solution on the outer side of the slotted thin layer distributor 3 and the inner wall of the kettle body. More importantly, such a design does not need to control the thickness of the polyamic acid solution layer on the slotted thin layer distributor 3, and the expected defoaming effect can be achieved regardless of the thickness of the liquid layer. Moreover, such a design is also conducive to forming a thinner and more evenly dispersed liquid thin layer, which is conducive to the elimination of bubbles, especially micro-nano-sized bubbles. The through grooves 3-2 are arranged on the spherical crown 3-1 in a manner of forming a closed loop. The closed loop formed is usually a centrally symmetrical figure, and the center of the closed loop formed coincides with the center of the spherical crown 3-1; and the width of the through grooves 3-2 in the radial direction of the spherical crown 3-1 is less than or equal to the gap between the outer side of the slotted thin layer distributor 3 and the inner wall of the kettle body. Preferably, the width of the through grooves 3-2 in the radial direction of the spherical crown 3-1 is 0.2 to 2.5 mm. Specifically, the through grooves 3-2 can be arranged on the spherical crown 3-1 in a manner of forming a closed loop in a circular, square or elliptical shape. The number of the closed loops can be one or more than two, preferably 2 to 6, and more preferably, the closed loops are arranged equidistantly in the radial direction of the spherical crown 3-1. The number of through grooves 3-2 forming a closed loop is at least 2 (i.e., there must be a physical connection between two adjacent through grooves 3-2 constituting the same closed loop), preferably 2 to 4; the length of the through grooves 3-2 can be determined as needed. For example, when the closed loop is a circle, the length of each through groove 3-2 forming a circular closed loop can be evenly divided by the circumference of the circle.

[0028] The defoaming kettle is also provided with a pressure detection device 8 and a temperature detection device 4 for obtaining the pressure and temperature in the kettle. The defoaming kettle body is provided with a jacket, and the jacket is provided with a medium inlet 5 and a medium outlet 7. The temperature in the kettle is lowered by conveying cooling medium into the jacket.

[0029] The feed pipe 1 on the defoaming kettle is used to transport the synthesized polyamic acid solution into the defoaming kettle. It is usually set at the top of the defoaming kettle, preferably directly above the grooved thin-layer distributor 3. A delivery pump (such as a gear metering pump, etc.) is usually installed on this pipeline path to meter the polyamic acid solution entering the defoaming kettle; the discharge pipe 6 is used for discharging after defoaming is completed and is usually set at the bottom of the defoaming kettle; the gas access pipe 9 is used to connect with a vacuum pump to create a negative pressure environment inside the defoaming kettle, or to introduce carbon dioxide or inert gas (such as nitrogen, etc.) into the defoaming kettle during the defoaming process. It is usually set at the top of the defoaming kettle; the vent pipe 2 is used to discharge the gas inside the kettle and is usually set at the top of the defoaming kettle. The vent pipe 2 cooperates with an electromagnetic on-off valve to regulate the negative pressure inside the kettle.

[0030] The defoaming device described in the present utility model has a good defoaming effect on polyamic acid solutions with viscosities of 8 to 1,000,000 cps, and is especially suitable for defoaming high-viscosity polyamic acid solutions with viscosities of 18 to 600,000 cps.

[0031] In Figure 1 In the shown embodiment, the specifications of the defoaming kettle are 1600 mm × 2650 mm (inner diameter × height) (capacity of 2500 L). The distance between the outer side of the grooved thin-layer distributor 3 and the inner wall of the defoaming kettle body in the radial direction of the defoaming kettle is 1.5 mm. The height of the spherical crown 3-1 of the grooved thin-layer distributor 3 is 1 / 12 of the diameter of the sphere where the spherical crown 3-1 is located (i.e., 30 mm). There are two places at the lower edge of the grooved thin-layer distributor 3 that are fixedly connected to the inner wall of the defoaming kettle body. After the grooved thin-layer distributor 3 is fixed, the distance between the top of the spherical crown 3-1 and the lower port of the feed pipe 1 extending into the kettle body is the same as the height of the spherical crown 3-1 itself, that is, 30 mm. There are 3 circular closed loops formed by arranging through grooves 3-2 on the spherical crown 3-1 of the grooved thin-layer distributor 3. These 3 circular closed loops are equidistantly arranged in the radial direction of the spherical crown 3-1 (the distance between adjacent two circular closed loops is about 400 mm). Each closed loop is composed of 3 arc-shaped through grooves 3-2, and the lengths of the through grooves 3-2 that make up each circular closed loop are evenly divided according to the circumferential length of the circle they form. The width of all through grooves 3-2 in the radial direction of the spherical crown 3-1 is 1.5 mm.

[0032] Figure 3 This is another embodiment of the polyamic acid solution defoaming device described in the present utility model, and the difference from the Figure 1 shown embodiment is that: a stirrer 10 is further provided below the grooved thin-layer distributor 3 inside the defoaming kettle body, and a motor capable of driving the stirrer 10 to work is also provided on the defoaming kettle. The liquid-like thin curtain flowing downward through the grooved thin-layer distributor 3 can better eliminate bubbles under the action of the stirrer 10; at the same time, the stirring of the stirrer 10 can also make the polyamic acid solution system aggregated at the bottom of the kettle body reach temperature uniformity in a shorter time.

[0033] A method for defoaming a polyamic acid solution by using the polyamic acid solution defoaming device of the present utility model is specifically as follows:

[0034] Control the pressure inside the defoaming kettle to be negative pressure, and convey the polyamic acid solution into the defoaming kettle through the feed pipe 1 on the defoaming kettle. The temperature of the polyamic acid solution is controlled to be less than or equal to 65 °C. The polyamic acid solution falls on the top of the spherical crown 3-1 of the grooved thin-layer distributor 3 and is evenly distributed and dispersed along the radial direction of the spherical crown 3-1 to form a thin layer. When passing through the through groove 3-2 on the spherical crown 3-1, part of the polyamic acid solution flows downward to form at least one circle of liquid thin curtain concentric with the spherical crown 3-1, and the remaining polyamic acid solution continues to be dispersed to form a thin layer until the formed thin layer flows downward along the gap between the outer side surface of the grooved thin-layer distributor 3 and the inner wall of the defoaming kettle body, and finally gathers at the bottom of the defoaming kettle; after stopping the conveyance of the polyamic acid solution and the polyamic acid solution on the grooved thin-layer distributor 3 is dispersed, cool down the defoaming kettle until the temperature of the liquid inside the kettle is less than or equal to 15 °C; when the liquid level inside the defoaming kettle is stable, let it stand for a period of time, and the defoaming of the polyamic acid solution is completed.

[0035] When there are as many closed loops on the spherical crown 3-1 of the grooved thin-layer distributor 3, there will be as many layers (circles) of liquid thin curtains concentric with the spherical crown 3-1 formed, and the shape of the liquid thin curtain is determined by the closed loops and shape on the grooved thin-layer distributor 3. The synthesized polyamic acid solution is dispersed into multiple layers (multiple circles) of liquid thin curtains and flows downward through the grooved thin-layer distributor 3 to achieve the purpose of eliminating bubbles, especially micro-nano sized bubbles, and further significantly reducing the apparent defects of the self-supporting polyamic acid thick film obtained by casting the defoamed polyamic acid solution. Taking Figure 1 the defoaming device of the shown embodiment as an example, 3 circles of cylindrical liquid thin curtain layers concentric with the spherical crown 3-1 will be formed. In addition, a circle of cylindrical liquid thin curtain layer will also be formed at the gap between the outer side surface of the grooved thin-layer distributor 3 and the inner wall of the defoaming kettle body.

[0036] In the above method, increasing the feeding temperature of the polyamic acid solution can reduce the viscosity of the solution, which is beneficial to the subsequent bursting of bubbles, especially micro-nano sized bubbles, and also beneficial to the flow of the solution. It is preferred to control the temperature of the polyamic acid solution at 35-60°C. When defoaming, the pressure in the defoaming kettle is negative pressure, and it is preferably controlled at -0.01 to -0.1 MPa. To achieve the above negative pressure environment, usually before or while feeding the polyamic acid solution into the defoaming kettle, the gas access pipe 9 is connected to a vacuum pump for vacuum pumping operation until the vacuum environment in the defoaming kettle reaches the expected value. After stopping the feeding of the polyamic acid solution and when the polyamic acid solution on the grooved thin layer distributor 3 is completely dispersed, the defoaming kettle is cooled down, effectively reducing the incidence of catalytic hydrolysis of the polyamic acid solution under high temperature conditions. Usually, the temperature is reduced to 5-15°C of the polyamic acid solution system in the kettle. The cooling of the defoaming kettle is achieved by introducing a cooling medium (such as chilled water) into the medium inlet 5 of the jacket.

[0037] In the above method, when the liquid layer thickness of the polyamic acid solution on the grooved thin layer distributor 3 is less than or equal to 3 mm, it can be regarded as the polyamic acid solution on the grooved thin layer distributor 3 being completely dispersed. When the change in the liquid level height in the defoaming kettle does not exceed 1 mm within 5 minutes, it is regarded as the liquid level in the defoaming kettle being stable. After the liquid level in the defoaming kettle is stable, it is left standing for 3-8 minutes to complete the defoaming of the polyamic acid solution, and then it can be discharged to the subsequent casting process. The apparent defects such as surface bubbles of the cast film (self-supporting polyamic acid thick film) obtained from the polyamic acid solution treated by this defoaming method are further reduced, and can be controlled within 0.0002-0.0008 per m 2 (that is, the number of bubbles on a 3000 m long and 1.6 m wide film roll is less than 5), and the size of each bubble is not greater than 0.05 mm. The standing time can be extended, but the extension cannot bring a significant reduction in apparent defects. Therefore, the standing time is usually controlled at 5-8 minutes.

[0038] The polyamic acid solution fed into the defoaming kettle can be directly supplied by the reaction kettle or supplied by a storage kettle (previously synthesized and stored in the storage kettle) (in this case, the polyamic acid solution in the storage kettle needs to be heated to the corresponding temperature in advance). When feeding, usually the flow rate is controlled at 1.5-150 kg / min, preferably 15-100 kg / min, and more preferably 30-60 kg / min. Using the defoaming device of the present invention and under the above-mentioned feeding flow rate conditions, after the feeding of the polyamic acid solution into the defoaming kettle is completed and the polyamic acid solution on the grooved thin layer distributor 3 is completely dispersed, it is left standing for 3-8 minutes to complete the defoaming of the polyamic acid solution. After defoaming is completed, the vacuum pump is turned off, and carbon dioxide or an inert gas is introduced into the kettle through the gas access pipe 9 (the gas flow rate is 0.1-0.08 m 3( / min). When discharging, first adjust the electromagnetic proportional valve on the emptying pipe 2 to control the pressure in the defoaming kettle to be maintained at 0.4 - 0.8 MPa.

[0039] Application experiment: Use the Figure 1 shown defoaming device to defoam the synthesized polyamic acid solution.

[0040] The device used in the experiment is the defoaming device shown in Figure 1 . The polyamic acid solution synthesized by the reaction kettle is used as the supply input to the defoaming kettle, and the total delivery volume of the polyamic acid solution is 1500 Kg.

[0041] The temperature of the polyamic acid solution entering the defoaming kettle is controlled at 50 °C, and the flow rate of the polyamic acid solution entering the defoaming kettle is 15 kg / min. The polyamic acid solution entering the defoaming kettle through the feed pipe 1 falls on the spherical crown 3-1 of the grooved thin-layer distributor 3, and forms a thin layer flowing dispersedly from the center of the spherical crown 3-1 to the outside on the spherical crown 3-1 of the grooved thin-layer distributor 3. When passing through the circular closed loop formed by the through grooves 3-2 arranged on the spherical crown 3-1 of the thin-layer distributor, three cylindrical liquid thin curtain layers concentric with the spherical crown 3-1 are formed. Then, the thin layer of the polyamic acid solution flows downward through the gap between the outer side of the grooved thin-layer distributor 3 and the inner wall of the defoaming kettle body to form another cylindrical liquid thin curtain layer, and finally gathers at the bottom of the kettle body.

[0042] When the polyamic acid solution enters the defoaming kettle, evacuate to make the vacuum degree in the defoaming kettle -0.1 MPa. After the pressure feeding is completed, stop passing the heat-conducting medium and then switch to cooling, and control the temperature in the defoaming kettle body to be 5 °C.

[0043] Stop transporting the polyamic acid solution to the defoaming kettle and wait until the polyamic acid solution on the grooved thin-layer distributor 3 is dispersed completely (when the liquid layer thickness of the polyamic acid solution on the grooved thin-layer distributor 3 is 3 mm, it is regarded as the polyamic acid solution on the grooved thin-layer distributor 3 being dispersed completely), then let it stand for 5 min, and close the vacuum pump. Pass nitrogen into the defoaming kettle through the gas connection pipe, with the gas flow rate being 0.5 m 3 / min. Adjust the electromagnetic proportional valve on the emptying pipe 2 to keep the pressure in the kettle at 0.6 MPa. Transport the polyamic acid solution in the defoaming kettle to the casting machine to cast into a film. Detect the apparent quality of the obtained cast film. The number of bubbles on the surface of the cast film is 0.0006 per m 2 , and the color difference (ΔE value) of the cast film is 0.03.

[0044] It can be seen that when using the defoaming device of the present utility model to defoam the polyamic acid solution, there is no need to consider the accumulation amount of the polyamide amine solution on the trough thin-layer distributor when transporting the polyamic acid solution to the defoaming kettle. On the premise of large-flow input, the defoaming treatment of the input polyamic acid solution can be ensured, and the required standing time is also short, only 3-8 minutes, which shortens the entire defoaming time, and can ensure the defoaming effect. Finally, the obtained casting film has a low color difference value and a further reduced number of surface bubbles.

Claims

1. A defoaming device for a polyamic acid solution, comprising a defoaming kettle for containing the polyamic acid solution. The defoaming kettle is provided with a feed pipe (1), a discharge pipe (6), a gas access pipe (9) and a vent pipe (2). A grooved thin layer distributor (3) is arranged in the defoaming kettle, wherein, The described grooved thin-layer distributor (3) includes a spherical crown (3-1) and multiple through grooves (3-2) formed on the spherical crown (3-1) and penetrating the thickness of the spherical crown (3-1). The rotation axis and the center line of the spherical crown (3-1) coincide with the rotation axis and the center line of the defoaming kettle respectively. The through grooves (3-2) are arranged on the spherical crown (3-1) in a way that forms a closed loop, and the center of the formed closed loop coincides with the center of the spherical crown (3-1); there is a gap between the outer side surface of the grooved thin-layer distributor (3) and the inner wall of the kettle body, and one or more than two positions along the lower edge of the grooved thin-layer distributor (3) are fixedly connected to the inner wall of the kettle body; the width of the through groove (3-2) in the radial direction of the spherical crown (3-1) is less than or equal to the gap between the outer side surface of the grooved thin-layer distributor (3) and the inner wall of the kettle body.

2. The polyamic acid solution defoaming device according to claim 1, characterized in that, The number of the described closed loops is one or more than two.

3. The polyamic acid solution defoaming device according to claim 1, characterized in that, The through grooves (3-2) are arranged on the spherical crown (3-1) in a way that forms a closed loop arranged in a circular, square or elliptical shape.

4. The polyamic acid solution defoaming device according to claim 1, characterized in that, The width of each through groove (3-2) in the radial direction of the spherical crown (3-1) is 0.2 - 2.5 mm.

5. The polyamic acid solution defoaming device according to any one of claims 1 to 4, characterized in that, The height of the spherical crown (3-1) is 1 / 5 - 1 / 12 of the diameter of the sphere where the spherical crown (3-1) is located.

6. The polyamic acid solution defoaming device according to any one of claims 1 to 4, characterized in that, The gap between the outer side surface of the grooved thin-layer distributor (3) and the inner wall of the kettle body is 0.1 - 5 mm.

7. The polyamic acid solution defoaming device according to any one of claims 1 to 4, characterized in that, A stirrer (10) is further provided in the defoaming kettle.

8. The polyamic acid solution defoaming device according to any one of claims 1 to 4, characterized in that, A pressure detection device (8) and a temperature detection device (4) are further provided on the defoaming kettle.

9. The polyamic acid solution defoaming device according to any one of claims 1 to 4, characterized in that, The kettle body of the defoaming kettle is equipped with a jacket, and a medium inlet (5) and a medium outlet (7) are provided on the jacket.

Images