PET sheet production line and production method

Abstract

The application relates to a PET plate production line and a production method. The PET plate production line comprises an extruder, a die and a calender arranged along a processing direction, the extruder comprises a cylinder and a double-screw assembly arranged in the cylinder; the double-screw assembly comprises two intermeshing screws, the outer diameter of each screw decreases along the processing direction, the included angle between the central axes of the two screws is 10'-1°20', and the rotating directions of the two screws are opposite. The application improves the production line according to the characteristics of PET material, improves the plasticizing effect of the PET material, guarantees the quality of the PET plate, improves the production capacity of the production line and reduces the energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of plate manufacturing, and in particular relates to a PET plate production line and a production method. Background Art

[0002] PVC sheets, currently widely used in the market, have numerous shortcomings. First, PVC materials are environmentally unfriendly and can release harmful substances during production and use, impacting indoor air quality. Second, PVC sheets have relatively low wear and heat resistance, making them prone to fading and deformation after long-term use. Furthermore, the recycling rate of PVC sheets is low, leading to resource waste and environmental pollution. Therefore, the search for more environmentally friendly and durable alternative materials has become a pressing need for industry development.

[0003] Polyester (PET) is an emerging alternative material with superior performance. Firstly, PET excels in environmental protection, with extremely low emissions and harmful substances released during production, meeting the requirements of modern green buildings. Secondly, PET's wear and pressure resistance surpasses that of traditional PVC, resulting in a longer service life. PET also exhibits excellent heat resistance. Furthermore, PET's high recyclability reduces the environmental impact of production, aligning with the concept of sustainable development.

[0004] Despite the numerous advantages of PET, there are currently no high-capacity production lines suitable for PET sheet. This is primarily due to the fact that the equipment and processes of existing high-capacity production lines are primarily designed for other types of materials. Due to the unique physical properties of PET, when using existing high-capacity production lines for production, the mixing, extrusion, and molding processes may not meet the plasticization requirements of PET material, resulting in unstable product quality and low output. Furthermore, existing PET sheet production lines use co-rotating parallel twin-screw extruders, which require high-speed operation but have low production capacity and high power consumption. This makes it impossible to achieve high-capacity production of PET sheet, limiting its promotion and application. Summary of the Invention

[0005] In response to at least one shortcoming in the related art, the present invention provides a PET sheet production line and production method, which improves the production line based on the characteristics of PET materials, enhances the plasticizing effect of PET materials, ensures the quality of PET sheets, increases the production capacity of the production line and reduces energy consumption.

[0006] On the one hand, the present application provides a PET sheet production line, comprising an extruder, a die, and a calender arranged along a processing direction, wherein the extruder comprises:

[0007] barrel;

[0008] The twin-screw assembly is arranged in the barrel, and the twin-screw assembly comprises two intermeshing screws, the outer diameter of each screw decreases along the processing direction, and the included angle between the central axes of the two screws is 10′-1°

[0009] 20′, the rotating directions of the two screws are opposite.

[0010] In some embodiments of the first aspect, the two screws are identical in size, the average of the maximum value and the minimum value of the outer diameter of each screw is the mean diameter, the ratio of the length of each screw to the mean diameter is 25:1-35:1, and the length of each screw is 3-7 m.

[0011] In some embodiments of the first aspect, each screw sequentially comprises a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharge section along the processing direction; the preheating section is used for stirring the material and cooperating with the barrel to heat the material; the first mixing section and the second mixing section are used for mixing and finely processing the material; the barrel is provided with exhaust devices corresponding to the first exhaust section and the second exhaust section, respectively, which are in communication with the inside of the barrel for exhausting the waste gas generated during the extrusion molding of the material; the compression section is used for applying pressure to the material to compress the material; the plasticizing section is used for providing shear force to make the compressed material in a molten state; and the discharge section is used for outputting the material in a molten state from the extruder into a mold.

[0012] In some embodiments of the first aspect, the calender comprises a rack and a plurality of calender roller groups arranged on the rack along the processing direction, and the web molded by the mold enters the calender for calendering, wherein the calender roller above the web conveying path is an upper calender roller, the calender roller below the web conveying path is a lower calender roller, each calender roller group comprises one upper calender roller and one lower calender roller arranged correspondingly, or only one lower calender roller, and a conveying device is arranged between at least two adjacent calender roller groups; the conveying device comprises a plurality of rollers arranged between the two adjacent calender roller groups and a conveying belt surrounding the plurality of rollers, the upper end surfaces of the plurality of rollers are located on the same plane to make the upper surface of the conveying belt form a plane, and the plane where the upper surface of the conveying belt is located is tangent to the roller surface of the lower calender roller in the two adjacent calender roller groups, respectively.

[0013] In some embodiments of the first aspect, the conveying device further comprises a roller mounting member, the two ends of each roller are mounted on the rack via the roller mounting member, the roller mounting member is formed with a mounting groove, the two ends of each roller are formed with a mounting shaft, respectively, the mounting shaft is arranged in the mounting groove and supported by the bottom of the mounting groove to mount the roller on the rack; a bolt hole is formed in the roller mounting member and communicates with the bottom of the mounting groove, an adjusting bolt is threadedly mounted in the bolt hole, and the end of the adjusting bolt extends into the mounting groove from the bottom of the mounting groove and supports the roller.

[0014] In some embodiments of the first aspect, at least one of the multiple calendering roller groups includes only one lower calendering roller, and a first baking device is arranged above the calendering roller group that includes only one lower calendering roller to heat the slab.

[0015] In some embodiments of the first aspect, a displacement sensor for measuring the lifting distance of the upper calendering roller is provided corresponding to each upper calendering roller, and a second drive motor for controlling the lifting and lowering of the upper calendering roller is provided on the frame. The displacement sensor is connected to the second drive motor and is configured to send a signal to the second drive motor to lift the upper calendering roller to a set position.

[0016] In some embodiments of the first aspect, a cooling bracket, a traction machine and a cutting device are provided at the rear end of the calender, and a second baking device is provided at the front end of the traction machine, and the second baking device is used to heat the PET sheet before cutting.

[0017] A second aspect of the present application provides a method for producing a PET sheet, which is produced using any PET sheet production line of the first aspect, comprising the following steps:

[0018] Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2-5;

[0019] The mixed material is fed into the extruder for extrusion molding. The two screws of the extruder rotate in opposite directions and the speed is 10-40r / min.

[0020] The material plasticized by the extruder enters the mold for molding;

[0021] The formed slab enters the calender for calendering;

[0022] The slabs output from the calender are cut into PET sheets.

[0023] In some embodiments of the second aspect, the screw of the extruder includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharge section in sequence along the processing direction. The temperature of the extruder in the preheating section is 210-260°C, the temperature from the first mixing section to the plasticizing section is 230-280°C, the temperature in the second exhaust section and the discharge section is 190-250°C, and the temperature decreases from the second exhaust section to the discharge section; the temperature of the mold is 220-260°C; and the temperature of the calendering roller in the calender is 180-250°C.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] (1) The PET sheet production line provided by at least one embodiment of the present invention improves the screw structure in the extruder according to the characteristics of the PET material, thereby providing a suitable shear force for plasticizing the PET material, improving the plasticizing effect and efficiency, and reducing the energy consumption of the extrusion process;

[0026] (2) The production line for PET sheets provided by at least one embodiment of the present invention comprises a conveying device provided between adjacent calendering roller groups. The conveying device uses a conveyor belt to convey the slabs, and the inclination of the conveyor belt is adjustable, which can effectively prevent deformation of the slab surface and ensure the flatness of the final PET sheet.

[0027] (3) The PET sheet production line provided by at least one embodiment of the present invention is provided with baking devices in the calender and before the tractor, respectively, based on the changes in material properties during the PET sheet production process. The slabs can be heated as needed to avoid the problem of sheet cracking caused by excessive brittleness of the slabs during the calendering and cutting processes.

[0028] (4) The production method of PET sheets provided by at least one embodiment of the present invention adopts an improved production line to produce PET sheets and increases the proportion of calcium powder in the material, thereby realizing low-speed heterogeneous extrusion. At the same time, the temperature of the mold and the temperature of the calendering roller are limited to a suitable range according to the characteristics of the PET material, thereby ensuring the quality of the finished PET sheets, improving production capacity and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1a A side view of a PET sheet production line provided in an embodiment of the present application;

[0031] Figure 1b A top view of the PET sheet production line provided in an embodiment of the present application;

[0032] Figure 2 This is a schematic structural diagram of an extruder in an embodiment of the present application;

[0033] Figure 3 This is a schematic structural diagram of a twin-screw assembly in an embodiment of the present application;

[0034] Figure 4a This is a schematic diagram of the distribution of various sections along the axial direction of the screw in the embodiment of the present application;

[0035] Figure 4b for Figure 4aCross-sectional view of the middle AA site;

[0036] Figure 4c for Figure 4a Cross-sectional view of the mid-BB area;

[0037] Figure 5a This is a structural diagram 1 of a calender in an embodiment of the present application;

[0038] Figure 5b The structure of the calender in the embodiment of this application is shown in FIG. Figure 2 ;

[0039] Figure 5c A side view of a calender in an embodiment of the present application;

[0040] Figure 6 for Figure 5c A partial enlarged view of the middle part C;

[0041] Figure 7 This is a structural diagram 1 of the conveying device in an embodiment of the present application;

[0042] Figure 8 This is a schematic diagram of the structure of the transmission device in the embodiment of the present application. Figure 2 ;

[0043] Figure 9a This is a schematic diagram of the structure of the conveying device after the conveyor belt is removed in an embodiment of the present application, so as to fully illustrate the structure of the roller mounting member;

[0044] Figure 9b for Figure 9a A partial enlarged view of the middle portion D, wherein the roller mounting portion is partially cut away to show the internal bolt holes;

[0045] Figure 10 This is a schematic diagram of one side of the calender equipped with a displacement sensor in an embodiment of the present application.

[0046] In the picture:

[0047] 1. Loading machine;

[0048] 2. Extruder; 21. Barrel; 211. Barrel sleeve; 22. Screw; 221. Preheating section; 2211. Feeding section; 2212. First heating section; 2213. Second heating section; 222. First mixing section; 223. First exhaust section; 224. Compression section; 225. Second mixing section; 226. Plasticizing section; 2261. Reflux section; 2262. Baffle section; 2263. Reflux trough; 227. Second exhaust section; 228. Discharge section; 2281. First discharge section; 2282. Second discharge section; 229. First transition section; 2210. Second transition section; 23. Agitation assembly; 231. Toothed protrusion; 24. Exhaust device; 25. Heating coil;

[0049] 3. Mould;

[0050] 4. Calender; 41. Frame; 42. Calendering roller assembly; 421. Upper calendering roller; 422. Lower calendering roller; 43. Conveyor; 431. Support roller; 4311. Mounting shaft; 432. Conveyor belt; 433. Support roller mounting member; 4331. Mounting slot; 4332. Bolt hole; 434. Adjustment bolt; 435. First drive motor; 436. Drive roller; 437. Guide roller; 44. First baking device; 45. Elevator; 46. Connecting rod; 47. Displacement sensor; 48. Second drive motor;

[0051] 5. Cooling bracket;

[0052] 6. Second baking device;

[0053] 7. Traction machine;

[0054] 8. Cutting device;

[0055] 9. Ground running track. DETAILED DESCRIPTION

[0056] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0057] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0058] In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "back," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features referred to.

[0059] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0060] The first aspect of the present application provides a PET sheet production line, which is particularly suitable for producing PET sheets, but it is understandable that other types of sheets can also be produced according to actual conditions. Figure 1a and Figure 1b As shown, in some embodiments, the PET production line includes a feeder 1, an extruder 2, a mold 3, a calender 4, a cooling bracket 5, a traction machine 7, a cutting device 8, etc. along the processing direction.

[0061] The material is mixed by the feeder 1 and then enters the extruder 2 for processing. The extruder 2 used in the embodiment of the present application is a twin-screw extruder. The material is transported forward in the extruder 2 by the rotation of the screw. During the forward movement of the material, the material is heated, sheared and compressed by the screw so that the material is fully mixed, melted and plasticized, providing the prerequisite for the subsequent forming of the plate.

[0062] Different materials present different characteristics in the process of processing, for example, PET material has higher hardness and intensity, makes it more brittle and rigidity is large, and glass transition temperature is higher, needs higher processing temperature, but good environmental protection.When adopting existing forcing machine to extrude at PET material, plasticizing process is difficult to control, and the problem of plasticizing is not enough or over-plasticizing occurs easily, and current fluctuation is large, and product quality is unstable and production capacity is low.For the problems referred to above, the application first starts with forcing machine 2 and improves production line, improves the plasticizing effect of PET material, is conducive to improving the quality of follow-up sheet material forming.

[0063] like Figure 2 and Figure 3 As shown, the extruder 2 includes a barrel 21 and a twin-screw assembly disposed in the barrel 21. The twin-screw assembly includes two screws 22 that mesh with each other. The outer diameter of each screw 22 gradually decreases along the processing direction, and the angle α between the central axes of the two screws 22 is 10′ to 1°20′. The two screws 22 rotate in opposite directions, that is, one screw 22 rotates clockwise and the other screw 22 rotates counterclockwise. Figure 3 The structure diagram of the twin-screw assembly is shown in FIG. 2. In order to more clearly illustrate the degree of inclination of the screw 22, Figure 3 The threads on the screw 22 are not shown. Figure 3As shown, the two screws 22 have a very small taper close to that of a flat screw (i.e., a cylindrical screw of equal outer diameter). This taper is very small relative to the length of the screws 22. The angle between the central axes of the two screws 22 is α, and the value of α ranges from 10′ to 1°20′. The final value of α can be determined based on the composition of the material and processing conditions. For example, α can also be 30′, 35′, 40′, 1°, 1°10′, etc. Optionally, α is 10′ to 1°.

[0064] In some embodiments, the two screws 22 have the same dimensions. The median diameter is the average of the maximum and minimum outer diameters of each screw 22. The ratio of the length to the median diameter of each screw 22 is 25:1 to 35:1, and the length of each screw 22 is 3 to 7 meters. In this embodiment, the taper and length of the screws 22 are limited. Compared to existing tapered screws, this screw 22 has a longer length and a smaller taper. This optimizes the combination of the shear force provided by the screw 22 and the duration of its action on the PET material, resulting in a more complete plasticization process for the PET material, improved plasticization results, and the desired processing state. For example, the ratio of the length to the median diameter of each screw 22 can be 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, etc., and the length can be 3.5m, 4m, 4.5m, 5m, 5.5m, 6m, 6.5m, etc. According to the length of the screw and the ratio of the length to the median diameter, the outer diameter value (maximum outer diameter) of the feeding end and the outer diameter value (minimum outer diameter) of the discharge end of the screw 22 can be determined, thereby determining the external dimensions of the screw 22.

[0065] The twin-screw assembly used in the extruder 2 is a novel screw structure, intermediate between a flat twin-screw and a conical twin-screw. Existing conical twin-screws have a large taper, with the screw diameter varying significantly from the feed end to the discharge end. For example, the maximum diameter is approximately twice the minimum diameter. They are relatively short, with an aspect ratio between 22:1 and 28:1. As the material moves forward within the screw, the space becomes increasingly smaller, and the pressure on the material increases. While this provides good plasticizing capabilities, it can be prone to over-plasticization or paste formation when used to process PET materials if not properly controlled. Furthermore, pressure control is required during the production process, which can cause fluctuations and poor stability. Existing parallel twin-screws have equal outer diameters and no taper. Compared with conical twin-screws, their plasticizing capacity is slightly inferior. Therefore, it is necessary to increase the screw length to improve the plasticizing effect. The aspect ratio of existing parallel twin-screws is generally above 30:1, and some may reach 38:1 or even above 40:1. Since parallel twin-screws do not have taper, the material does not generate pressure and fluctuations during the forward propulsion process. Therefore, the production process is relatively easy to control and has good stability. However, when used to process PET materials, the plasticizing process will not be sufficient, and the PET material cannot reach a good plasticized state. The twin-screw assembly designed in this application is designed and developed based on the above two existing screw structures. By retaining and reducing the appropriate taper of the conical twin screw, the disadvantage of the conical twin screw being easily over-plasticized is avoided, and the appropriate pressure is retained to control the advantage of the conical twin screw being easy to plasticize within an appropriate range. Accordingly, due to the reduction in taper, the plasticizing ability is relatively weakened. The required degree of plasticization is achieved by appropriately increasing the length of the screw. Compared with the existing conical screw, it has a smaller taper and a longer length, which can provide suitable shear force for the plasticization of PET materials, so that the PET material can be more fully plasticized without over-plasticization. It is easier to control during the production process and has good stability. At the same time, it combines the advantages of conical twin screws and flat twin screws.

[0066] In one embodiment of the present application, the twin-screw assembly is designed based on the existing 92 conical twin-screw. The maximum diameter of the existing 92 conical twin-screw is 188 mm and the minimum diameter is 92 mm. The average value of the maximum diameter and the minimum diameter of the existing conical twin-screw is (188+92) / 2=140. Optionally, 190 mm and 145 mm are respectively taken as the minimum diameter of the maximum diameter of the screw in the twin-screw assembly in one embodiment of the present application, and the ratio of length to median diameter is taken as 33:1. The length of the screw is (190+145) / 2*33=5527.5 mm. Therefore, the length is taken as 5527 mm, and this form of twin-screw assembly is named 168 light conical flat twin-screw.

[0067] In addition, the existing PET material extrusion molding process is subject to the structure of the screw, both screws of the extruder are rotated in the same direction and must be operated at a high speed, so that the energy consumption is large but the production capacity is low. The improvement of the screw structure of the above-mentioned extruder 2 can adopt a counter-rotation scheme in which the rotation directions of the two screws 22 are opposite. Compared with the existing same direction scheme, the rotation speed can be lower, for example, the rotation speed can be 25-40 r / min, so that the energy consumption is smaller but the production capacity is improved.

[0068] In some embodiments, as shown in Figure 4a The initial state of the material when added to the extruder 2 is solid or granular or powdery, and the barrel 21 of the extruder 2 is provided with a heating ring 25 corresponding to each section of the screw 22 to control the temperature inside the barrel 21. In this embodiment, based on the improvement of the screw structure, the functions of each section of the screw from the material inlet end to the material outlet end are rearranged, and two mixing sections and two exhaust sections are provided, so that the mixing of the PET material before entering the plasticizing section is more sufficient, and the exhaust is more thorough.

[0069] The functions of each section of the screw 22 are realized by the design of the screw flight on the screw 22 in cooperation with the temperature control of the barrel 21. It can be understood that the present application focuses on the adjustment of the distribution of each functional section on the screw based on the improvement of the screw structure, and does not focus on how to realize the functions of each section. For the scheme for realizing the functions of each section, those skilled in the art can realize it by referring to the prior art, and the part not described in the present application should not be considered as insufficient disclosure.

[0070] The barrel 21 continuously heats the material in the preheating section 221, and the preheating section 221 of the screw 22 uniformly heats the material by continuously stirring the material, so as to ensure the preheating effect. The first mixing section 222 and the second mixing section 225 are used for mixing and fine crushing the material, so that the size of the dispersed phase of the material is smaller and the distribution is more uniform. In the process of rotating the screw 22, the material is subjected to shear force between the screw 22 and the barrel 21 and between different flow layers inside the material, so as to realize mixing. In the process of processing the material, air, steam and low molecular volatile substances entrained in the material are discharged, if not discharged in time, air bubbles, cavities and other defects will be formed in the product, which will cause the quality of the product to decrease, such as Figure 2As shown, the barrel 21 is provided with exhaust devices 24 at positions corresponding to the first exhaust section 223 and the second exhaust section 227. The exhaust device 24 is connected to the interior of the barrel 21 and is used to discharge the waste gas generated during the extrusion molding process of the material. The screw 22 adopts a large pitch in the first exhaust section 223 and the second exhaust section 227 to make the material loose, increase the contact area between the material and the air, and facilitate exhaust. The compression section 224 compresses the material to increase the density of the material. The screw 22 has a smaller pitch and a shallower thread depth in the compression section 224, which reduces the space occupied by the material and realizes the compression function. After preheating and compression, the material enters the plasticizing section 226 for further heating and shearing, so that the material is completely melted, forming a uniform viscous flow state, and achieving the plasticizing effect. The plasticized material is smoothly conveyed forward through the discharge section 228, output from the extruder 2 and enters the mold 3.

[0071] In some embodiments, as Figure 4a and Figure 4b As shown, the first mixing section 222 and the second mixing section 225 have multiple groups of stirring assemblies 23 spaced axially on the outer surface of the screw 22. Each group of stirring assemblies 23 includes multiple tooth-like protrusions 231 distributed along the circumference of the screw 22. The spacing between adjacent stirring assemblies 23 is 20 to 35 mm, and the length of each tooth-like protrusion 231 in the axial direction of the screw 22 is 20 to 35 mm. The distribution and size of the stirring assemblies 23 in the first mixing section 222 and the second mixing section 225 are the same, and the length of the second mixing section 225 is greater than that of the first mixing section 222. In this embodiment, the design of the stirring assemblies 23 in the mixing section of the screw 22 disrupts the flow of the material and increases the lateral mixing of the material. The two-stage mixing before plasticization ensures that the material is more thoroughly mixed, preparing for plasticization.

[0072] It is understandable that, except for the first mixing section 222 and the second mixing section 225 , the outer surfaces of the other sections of the screw 22 are provided with helical threads, and the corresponding functions are achieved by designing the pitch, lead, screw ridges, etc. of the helical threads.

[0073] In some embodiments, the length of the preheating section 221 accounts for 30% to 40% of the total length of the screw 22, and the pitch of the preheating section 221 is 50 to 65 mm. The preheating section 221 includes, in the processing direction, a feed section 2211, a first temperature rising section 2212, and a second temperature rising section 2213. The length of the feed section 2211 is greater than or equal to the length of the first temperature rising section 2212, and the length of the first temperature rising section 2212 is greater than the length of the second temperature rising section 2213. The number of threads in the feed section 2211, the first temperature rising section 2212, and the second temperature rising section 2213 is equal, and the pitch and flight dimensions decrease in the axial direction of the screw 22. In this embodiment, the long length of the preheating section 221 allows the material to be fully heated before mixing. By dividing the preheating section 221 into three functional sections with successively decreasing pitch and flight dimensions in each section, the material can be more fully heated and better transitioned to the mixing section.

[0074] In some embodiments, the pitch of the compression section 224 is smaller than the pitch of the first exhaust section 223 and larger than the spacing between the agitating assemblies 23 of the first mixing section 222 and the second mixing section 225. The dimension of the screw flight of the compression section 224 in the axial direction of the screw 22 is smaller than the length of the tooth-like protrusions 231 of the first mixing section 222 and the second mixing section 225 in the axial direction of the screw 22. The small pitch and small dimension of the screw flight of the compression section 224 can enhance the extrusion of the material, thereby compressing the material more tightly.

[0075] In some embodiments, the pitch and flight dimensions of the first venting section 223 and the second venting section 227 are identical, and the pitch and flight dimensions of the first venting section 223 and the second venting section 227 in the axial direction of the screw 22 are both greater than those of the other sections of the screw 22. The length of the second venting section 227 is greater than the length of the first venting section 223 but less than twice the length of the first venting section 223. The large pitch and flight dimensions of the venting section increase the residence time of the material in the venting section and reduce pressure, thereby facilitating the discharge of gas from the material out of the barrel 21. Furthermore, the design of two venting sections, one at the rear end of the first mixing section 222 and the other at the rear end of the plasticizing section 226, helps improve the plasticization of the PET material. The longer length of the second venting section 227 facilitates the full discharge of gas from the plasticized material, further reducing defects such as bubbles in the product.

[0076] In some embodiments, three exhaust devices 24 are provided, wherein one exhaust device 24 is provided at the first exhaust section 223, and two exhaust devices 24 are provided side by side in the processing direction at the second exhaust section 227. The exhaust device 24 can be any device in the prior art that can achieve extruder exhaust, for example, reference can be made to the solution provided in Chinese patent application 202422531684.X.

[0077] In some embodiments, the plasticizing section 226 includes a reflux section 2261 and a material blocking section 2262. Figure 4c As shown, a reflow groove 2263 is formed on at least part of the spiral fins in the reflow section 2261, the lead of the material blocking section 2262 is smaller than the lead of the reflow section 2261, and the length of the reflow section 2261 is greater than the length of the material blocking section 2262 and less than twice the length of the material blocking section 2262. The reflux section 2261 can cause some of the material to reflux in the screw 22. During the reflux process, materials entering the screw 22 at different levels and times can be fully mixed, increasing the residence time of the material in the plasticizing section 226, promoting heat transfer, further promoting the plasticization of the material, and ensuring that the material reaches a good plasticized state. The lead of the reflux section 2261 can be 80 to 100 mm (e.g., 90 mm), and the lead of the stop section 2262 is smaller, which can be 40 to 55 mm (e.g., 50 mm). The axial propulsion speed of the material in the stop section 2262 is relatively slow, and the pressure can be adjusted to prevent excessive reflux of the material. The material flowing out of the reflux section 2261 can be propulsed in an orderly and stable manner in the stop section 2262 in a predetermined direction, making the plasticizing process more stable. In addition, the design of the length of the reflux section 2261 and the stop section 2262 can find a balance between plasticizing efficiency and plasticizing effect, so that the material can be fully processed and the extrusion process can be completed efficiently.

[0078] In some embodiments, a first transition section 229 is further provided between the first mixing section 222 and the first exhaust section 223, and a second transition section 2210 is further provided between the second mixing section 225 and the plasticizing section 226; the pitch of the first transition section 229 is greater than the spacing of the stirring components 23 of the first mixing section 222 and smaller than the pitch of the first exhaust section 223; the pitch of the second transition section 2210 is greater than the spacing of the stirring components 23 of the second mixing section 225 and greater than the pitch of the plasticizing section 226.

[0079] In some embodiments, the discharge section 228 includes a first discharge section 2281 and a second discharge section 2282, which are located at the rear end of the second exhaust section 227 along the processing direction. The pitch of the first discharge section 2281 is greater than the pitch of the second discharge section 2282, the number of threads in the first discharge section 2281 is less than the number of threads in the second discharge section 2282, and the length of the first discharge section 2281 is greater than twice the length of the second discharge section 2282. The design of the first discharge section 2281 and the second discharge section 2282 in the discharge section 228 can efficiently convey materials and establish stable pressure, smoothly conveying the materials forward and avoiding pressure fluctuations that may cause product quality problems.

[0080] This application also improves the calender 4 in the plate production line to make it more suitable for producing PET plates. Figure 5a-5cAs shown, the calender 4 includes a frame 41 and multiple groups of calendering rollers 42 arranged on the frame 41 along the processing direction. The slab formed by the mold 3 enters the calender 4 for calendering. The calendering rollers located above the slab conveying path are upper calendering rollers 421, and the calendering rollers located below the slab conveying path are lower calendering rollers 422. Each group of calendering rollers 42 includes an upper calendering roller 421 and a lower calendering roller 422 correspondingly arranged above and below, or only includes one lower calendering roller 422. A conveying device 43 is provided between at least two adjacent calendering roller groups 42. Figure 6-Figure 8 The conveying device 43 includes a plurality of rollers 431 arranged between two adjacent calendering roller groups 42 and a conveyor belt 432 surrounding the plurality of rollers 431. The upper end surfaces of the plurality of rollers 431 are located on the same plane so that the upper surface of the conveyor belt 432 constitutes a plane. The upper surface of the conveyor belt 432 is tangent to the roller surface of the lower calendering roller 422 in the two adjacent calendering roller groups 42.

[0081] In the above embodiment, one or more conveying devices 43 may be provided, depending on the distance between adjacent calendering roller sets 42. For example, if the distance between two adjacent calendering roller sets 42 is large, a conveying device 43 may be provided. If the distance between two adjacent calendering roller sets 42 is small, a conveying device 43 may not be provided. The conveying device 43 takes the form of a conveyor belt 432 wrapped around multiple rollers 431. The upper surface of the conveyor belt 432 supported above the multiple rollers 431 is flat. Due to the high rigidity of the PET slab, the temperature of the calender 4 is high during the calendering process, keeping it in a relatively soft and easily deformable state. While the PET slab is being transported between the calendering roller sets 42, the flat conveyor belt 432 provides flat support for the PET slab, preventing corrugated deformation and ensuring the flatness of the PET sheet.

[0082] The plane of the upper surface of the conveyor belt 432 is tangential to the roller surfaces of the lower calendering rollers 422 in the two adjacent calendering roller groups 42, ensuring that the conveyor belt 432 forms a good connection with the calendering rollers at its ends. The slab discharged from one calendering roller group 42 can be conveyed to the top of the conveyor belt 432 in a flat state, and then conveyed from the top of the conveyor belt 432 to the next calendering roller group 42 in a flat state, thereby ensuring the flatness of the slab. The upper surface of the conveyor belt 432 can be horizontal or inclined, depending on the height of the lower calendering rollers 422 at its front and rear ends. The inclination of the upper surface of the conveyor belt 432 is determined by the arrangement height of the multiple rollers 431.

[0083] In some embodiments, as Figure 9a and Figure 9bAs shown, the conveying device 43 further includes a roller mounting member 433, and both ends of each roller 431 are respectively mounted on the frame 41 via the roller mounting member 433. The roller mounting member 433 is formed with a mounting groove 4331. Both ends of each roller 431 are respectively formed with a mounting shaft 4311, and the mounting shaft 4311 is disposed in the mounting groove 4331 to mount the roller 431 on the frame 41. The roller mounting member 433 can be a sheet-like structure or a block-like structure, and the mounting groove 4331 is formed through the sheet-like structure or the block-like structure. The shape of the mounting groove 4331 can be an upward opening or a hole.

[0084] In some embodiments, as Figure 9a and Figure 9b The roller mounting member 433 has a bolt hole 4332 in communication with the bottom of the mounting slot 4331. An adjustment bolt 434 is threadedly mounted within the bolt hole 4332. The end of the adjustment bolt 434 extends from the bottom of the mounting slot 4331 into the mounting slot 4331 and supports the mounting shaft 4311 of the roller 431. To adjust the height of the roller 431 to adjust the flatness and inclination of the upper surface of the conveyor belt 432, the height of the roller 431 can be adjusted simply by rotating the adjustment bolt 434 to adjust the height at which the end of the adjustment bolt 434 is exposed from the bottom of the mounting slot 4331. This is simple and easy to do.

[0085] In some embodiments, as Figure 5c-Figure 8 As shown, the conveyor 43 also includes a first drive motor 435 and drive rollers 436 mounted on the frame 41. The conveyor belt 432 is wrapped around multiple rollers 431 and drive rollers 436. The output shaft of the first drive motor 435 is connected to the drive rollers 436. The first drive motor 435 rotates the drive rollers 436 to drive the conveyor belt 432. In this embodiment, the first drive motor 435 only needs to drive the rotation of one drive roller 436 to achieve conveyance of the entire conveyor 43, eliminating the need to drive the rotation of each roller 431 separately. This improves drive efficiency and ensures stable slab conveying. The first drive motor 435 can be a servo motor, etc.

[0086] In some embodiments, the conveyor 43 further includes two guide rollers 437, which are mounted between the drive roller 436 and the plurality of idler rollers 431. The two guide rollers 437 are located between the two lower calendering rollers 422 in two adjacent calendering roller groups 42. The conveyor belt 432 wraps around the plurality of idler rollers 431 and is guided to the drive roller 436 via opposite sides of the two guide rollers 437. In this embodiment, the drive roller 436 is mounted on the frame 41 near the bottom of the frame 41. The guide rollers 437 are used to adjust the direction of the conveyor belt 432 to prevent interference between the conveyor belt 432 and the calendering rollers.

[0087] In some embodiments, as Figure 5a-5cAs shown, at least one of the multiple calendering roller groups 42 includes only a single lower calendering roller 422. A first baking device 44 is positioned above the calendering roller group 42 that includes only a single lower calendering roller 422 to heat the slab. The first baking device 44 can be a heating device such as an oven or a heat lamp. The length of the first baking device 44 can be comparable to the length of the calendering rollers, thereby covering the entire width of the slab and ensuring uniform heating. Due to the high rigidity of PET, it can become brittle as the temperature decreases during processing. To prevent the PET slab from becoming brittle and developing defects such as cracks during the calendering process, the first baking device 44 is positioned within the calender 4 to allow heating to be applied as needed based on changes in the PET slab's properties during calendering.

[0088] In some embodiments, a lift 45 is installed on the first baking device 44. The lift 45 is mounted on the frame 41. Activating the lift 45 adjusts the distance between the oven and the slab, thereby adjusting the heating effect. Because the first baking device 44 is relatively long, two lifts 45 can be provided at each end of its length. The two lifts 45 are connected by a connecting rod 46 to ensure synchronous movement. The lifts can be implemented using any commonly available structure capable of performing a lifting function.

[0089] In some embodiments, the frame 41 of the calender 4 is installed on the ground running rail 9 to facilitate the adjustment of the position of the calender 4 in the production line.

[0090] In some embodiments, as Figure 10 As shown, a displacement sensor 47 for measuring the lifting distance of the upper calendering roller 421 is provided corresponding to each upper calendering roller 421, and a second drive motor 48 for controlling the lifting of the upper calendering roller 421 is provided on the frame 41. The displacement sensor 47 is connected to the second drive motor 48 and is configured to send a signal to the second drive motor 48 to lift the upper calendering roller 421 to a set position, thereby realizing precise adjustment of the gap between the calendering roller group 42.

[0091] In some embodiments, as Figure 1a and Figure 1b As shown, a cooling bracket 5, a haul-off machine 7, and a cutting device 8 are installed at the rear end of the calender 4. A second baking device 6 is also installed at the front end of the haul-off machine 7. This second baking device 6 is used to heat the PET sheet before cutting. Considering that the PET sheet may become brittle after passing through the cooling bracket 5, heating the PET sheet before cutting is necessary to prevent defects such as cracks during cutting and ensure optimal cutting. The specific configuration of the second baking device 6 can be referred to above as the first baking device 44 and will not be further described here.

[0092] In some embodiments, a film coating assembly (not shown in the figure) can also be provided at the rear end of the calender 4 for film coating treatment of the PET plate blank, and the film coating assembly can be provided with one or more sets of film coating rollers as needed, which can be referred to in the prior art.

[0093] The PET plate production line provided by the embodiments of the present application improves the extruder 2 and the calender 4 in combination with the characteristics of PET material, and the production capacity of the production line can reach a high capacity of 1600 kg / h or more, and the quality of the obtained PET plate is stable, has few defects, and has a high yield.

[0094] The second aspect of the present application provides a production method of a PET plate, which is produced by using the PET plate production line according to any one of the first aspect, and includes the following steps:

[0095] The mixture of PET material and auxiliary materials is mixed with calcium powder at a ratio of 1:2-5;

[0096] The mixed material is sent to the extruder 2 for extrusion molding, and the rotation directions of the two screws 22 of the extruder 2 are opposite and the rotation speed is 10-40 r / min;

[0097] The material plasticized by the extruder 2 enters the mold 3 for molding;

[0098] The molded plate blank enters the calender 4 for calendering treatment;

[0099] The plate blank output by the calender 4 is cut to form a PET plate.

[0100] In the above production method of the PET plate, the production is carried out based on the improved PET plate production line, the mixing ratio of calcium powder can be adjusted to adjust the state of the material in the extruder 2, the two screws 22 of the extruder 2 can rotate at a low speed in opposite directions to improve the plasticizing effect, reduce energy consumption and increase the yield, and the molding and calendering effect of the plate can be improved under the premise that the material has a good plasticizing state, and the quality of the finished PET plate is ensured.

[0101] In the above embodiments, the mixing ratio of the mixture of PET material and auxiliary materials to calcium powder can be 1:3-5, and specifically can be 1:4; the auxiliary materials can include, for example, one or a combination of two or more of plasticizers, heat stabilizers, lubricants, and flame retardants, which can be determined as needed. The rotation speed of the screw 22 during extrusion molding can be 15 r / min, 18 r / min, 20 r / min, 25 r / min, 28 r / min, 30 r / min, 35 r / min, etc., which can be determined by a person skilled in the art according to actual needs.

[0102] In some embodiments, the temperature of the extruder 2 is 190-280° C. Specifically, the extruder 2 is provided with a barrel sleeve 211 corresponding to each section of the screw 22, and a heating ring 25 is provided on the barrel sleeve 211 for heating the barrel 21, wherein the temperature of the extruder 2 in the preheating section 221 is 210-260° C. (for example, 220° C., 230° C., 240° C., 250° C., etc.), the temperature from the first mixing section 222 to the plasticizing section 226 is 230-280° C. (for example, 240° C., 250° C., 260° C., 270° C., etc.), the temperature in the second exhaust section 227 and the discharge section 228 is 190-250° C. (for example, 200° C., 210° C., 220° C., 230° C., 240° C., etc.), and the temperature decreases from the second exhaust section 227 to the discharge section 228. The extruder 2 sets corresponding temperatures for each functional section of the screw 22 so that each section of the screw 22 can better perform its function at the corresponding temperature, so that the material is fully mixed and plasticized.

[0103] In some embodiments, when the material extruded by the extruder 2 enters the mold 3 for molding, the temperature of the mold 3 is 220-260°C, for example, it can be 230°C, 240°C, 250°C, etc., and those skilled in the art can adjust it according to the state of the material after extrusion.

[0104] In some embodiments, the temperature of the calendering roller in the calendering machine 4 is 180-250°C, for example, it can be 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, etc., and those skilled in the art can adjust it according to the state of the slab after forming.

[0105] According to the characteristics of the PET material during processing, the temperature of the mold 3 and the temperature of the calendering roller 4 are limited to a suitable range, thereby adjusting the temperature according to the state of the PET sheet during production, improving the quality of the finished sheet, reducing the occurrence of defects, and further increasing the production line's capacity.

[0106] In some embodiments, the calender 4 is provided with a first baking device 44, which heats the slab during the slab calendering process. The temperature of the first baking device 44 is 180-220°C. The temperature of the first baking device 44 can be 190°C, 200°C, 210°C, etc. After the slab is heated by the first baking device 44, the temperature increases, the brittleness decreases, and the risk of fracturing during the calendering process is reduced.

[0107] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to preferred embodiments, persons skilled in the art should understand that the specific implementation methods of the present invention may still be modified or some technical features may be replaced by equivalents without departing from the spirit of the technical solutions of the present invention, and all of these should fall within the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A PET sheet production line, comprising an extruder, a die and a calender arranged along a processing direction, characterized in that: The extruder comprises: barrel; a twin-screw assembly disposed in the barrel, the twin-screw assembly comprising two intermeshing screws, the outer diameter of each screw decreasing along the processing direction, the angle between the central axes of the two screws being 10′ to 1°20′, and the two screws rotating in opposite directions; Each of the screws includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharge section in sequence along the processing direction; The pitch and flight dimensions of the first exhaust section and the second exhaust section are the same, and the pitch and flight dimensions of the first exhaust section and the second exhaust section in the axial direction of the screw are both larger than the pitch and flight dimensions of the other sections of the screw in the axial direction of the screw, and the length of the second exhaust section is larger than the length of the first exhaust section and less than twice the length of the first exhaust section; The plasticizing section includes a reflux section and a material-blocking section, a reflux groove is formed on at least part of the screw fins in the reflux section, the lead of the material-blocking section is smaller than the lead of the reflux section, and the length of the reflux section is greater than the length of the material-blocking section and less than twice the length of the material-blocking section.

2. The PET sheet production line according to claim 1, characterized in that: The two screws have the same size, the average of the maximum and minimum values ​​of the outer diameter of each screw is the median diameter, the ratio of the length to the median diameter of each screw is 25:1~35:1, and the length of each screw is 3~7 m.

3. The PET sheet production line according to claim 1, characterized in that: The calendering machine includes a frame and multiple groups of calendering rollers arranged on the frame along the processing direction. The slab formed by the mold enters the calendering machine for calendering, wherein the calendering roller located above the slab conveying path is the upper calendering roller, and the calendering roller located below the slab conveying path is the lower calendering roller. Each group of calendering rollers includes an upper calendering roller and a lower calendering roller correspondingly arranged above and below, or only includes one lower calendering roller. A conveying device is provided between at least two adjacent calendering roller groups; the conveying device includes multiple rollers arranged between the two adjacent calendering roller groups and a conveyor belt surrounding the multiple rollers, the upper end surfaces of the multiple rollers are located on the same plane so that the upper surface of the conveyor belt constitutes a plane, and the plane where the upper surface of the conveyor belt is located is tangent to the roller surface of the lower calendering roller in the two adjacent calendering roller groups.

4. The PET sheet production line according to claim 3, characterized in that: The conveying device also includes a roller mounting member, and both ends of each roller are respectively mounted on the frame via the roller mounting member, the roller mounting member is formed with a mounting groove, and both ends of each roller are respectively formed with a mounting shaft, the mounting shaft is arranged in the mounting groove and supported by the bottom of the mounting groove to mount the roller on the frame; a bolt hole connected to the bottom of the mounting groove is opened in the roller mounting member, and an adjusting bolt is threadedly mounted in the bolt hole, and the end of the adjusting bolt extends into the mounting groove from the bottom of the mounting groove and supports the roller.

5. The PET sheet production line according to claim 3, characterized in that: At least one of the multiple calendering roller groups includes only one lower calendering roller, and a first baking device is provided above the calendering roller group including only one lower calendering roller for heating the slab.

6. The PET sheet production line according to claim 3, characterized in that: A displacement sensor for measuring the lifting distance of the upper calendering roller is provided corresponding to each upper calendering roller. The frame is provided with a second drive motor for controlling the lifting and lowering of the upper calendering roller. The displacement sensor is connected to the second drive motor and is configured to send a signal to the second drive motor to lift the upper calendering roller to a set position.

7. The PET sheet production line according to claim 1, characterized in that: A cooling bracket, a haul-off machine and a cutting device are provided at the rear end of the calender, and a second baking device is provided at the front end of the haul-off machine. The second baking device is used to heat the PET sheet before cutting.

8. A method for producing PET sheets, which is produced using the PET sheet production line described in any one of 1 to 7 above, characterized in that: The following steps are involved: Mix the mixture of PET material and auxiliary materials with calcium powder in a ratio of 1:2-5; The mixed material is fed into the extruder for extrusion molding, and the two screws of the extruder rotate in opposite directions and at a speed of 10-40 r / min; The material plasticized by the extruder enters the mold for molding; The formed slab enters the calender for calendering; The slabs output from the calender are cut into PET sheets.

9. The method for producing a PET sheet according to claim 8, wherein: The screw of the extruder includes a preheating section, a first mixing section, a first exhaust section, a compression section, a second mixing section, a plasticizing section, a second exhaust section and a discharge section in sequence along the processing direction. The temperature of the extruder in the preheating section is 210-260°C, the temperature from the first mixing section to the plasticizing section is 230-280°C, the temperature in the second exhaust section and the discharge section is 190-250°C, and the temperature decreases from the second exhaust section to the discharge section; the temperature of the mold is 220-260°C; and the temperature of the calendering roller in the calendering machine is 180-250°C.

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