A bidirectional synchronous stretching and retracting device

Abstract

The application discloses a bidirectional synchronous stretching and retracting device, which comprises two chain clamp devices, and a processing channel is arranged between the two chain clamp devices; each chain clamp device comprises a chain clamp assembly and a plurality of chain disc components for driving the chain clamp assembly, the chain clamp assembly is provided with a preheating zone and a plurality of stretching and retracting zones, one of the stretching and retracting zones is referred to as a stretching first zone, and the stretching first zone extends obliquely from the rear end of the preheating zone to the side away from the processing channel; one of the chain disc components is arranged between the preheating zone and the stretching first zone. By arranging the first chain disc between the preheating zone and the stretching first zone, the transmission direction of the chain disc component is aligned with the running direction of the chain clamp component in the area with relatively large running resistance, so that the running load of the chain clamp device is reduced. Therefore, in the case that the same number of chain clamp assemblies is maintained, higher running speed can be realized, the production efficiency is improved, and the production demand is met.

Description

Technical Field

[0001] This invention relates to the field of plastics processing, and in particular to a bidirectional synchronous stretching and retraction device. Background Technology

[0002] Biaxial stretching equipment is the core device for producing biaxially oriented plastic films. It holds a crucial position in the manufacturing of mid-to-high-end functional films, especially those requiring thinness, high specific strength, and high uniformity. Biaxial stretching equipment is mainly divided into two categories: asynchronous stretching and synchronous stretching, each with its own advantages and disadvantages.

[0003] Asynchronous stretching employs a method of first stretching longitudinally and then stretching laterally. Its advantages include simple structure, flexible adjustment, and a wide range of film specifications adaptable. It is widely used in large-width, high-speed, and high-volume extrusion production lines, and has a high overall industry share. However, due to the combination of longitudinal stretching using a pressure roller and laterally stretching using a chain-clamped track oven, the orientation of the finished film material is predominantly laterally oriented. Most products exhibit a trend of high lateral strength and modulus but low elongation, and relatively low longitudinal strength and modulus but high elongation. Furthermore, excessive crystallization induced by stretching during the initial longitudinal stretching stage can increase the film breakage rate during laterally stretching, making it difficult to produce ultrathin films. The roller-type longitudinal stretching method, due to the need for anti-sticking rollers and suppressing necking, requires a stretching temperature at least 30°C lower than the clamped stretching method, preventing the longitudinal stretching ratio from being increased indefinitely. For polypropylene stretching, a stable longitudinal stretching ratio is generally below 7 times. These disadvantages make it difficult to meet the product requirements of some ultrathin films with high requirements for longitudinal strength and modulus.

[0004] Synchronous stretching employs a production method that simultaneously stretches both longitudinally and transversely. Its advantage lies in allowing polymer materials to be stretched in both directions simultaneously, avoiding over-orientation in a single direction. This results in films with relatively strong isotropy, which is advantageous for improving longitudinal strength and modulus, and provides higher stability and consistency when preparing ultrathin films. However, synchronous stretching systems also suffer from drawbacks, such as lower adjustment flexibility and slower operating speed due to their higher equipment complexity. For example, in linkage-type synchronous stretching equipment, longitudinal adjustment relies primarily on changes in the distance between the two tracks, significantly limiting the flexibility and adjustability of the longitudinal stretching ratio. Linear motor-type synchronous stretching systems are even more complex, with an excessive number of motors and a high error rate. While their longitudinal stretching is flexible within a certain range, they do not support excessively large longitudinal stretching ratios (such as those exceeding 8 times).

[0005] There are also cases in the industry where combined stretching is achieved by using small longitudinal stretching machines in conjunction with synchronous stretching machines. For example, in the diaphragm field, there are cases of trying to increase the longitudinal stretching ratio by using a small longitudinal stretching machine combined with a large synchronous stretching machine with a fixed longitudinal ratio (longitudinal stretching ratio ≥ 5 times). However, this approach does not completely solve the problem. For example, for materials such as polypropylene, there is a clear minimum limit to the longitudinal stretching ratio it can support. When the longitudinal stretching is below about 4 times, the material will exhibit transversely uneven stripes due to its intrinsic properties. If a longitudinal stretching machine combined with synchronous stretching is used, the longitudinal stretching ratio of the synchronous stretching machine cannot be too high. Otherwise, based on the calculation of the minimum longitudinal stretching ratio of 4 times and the minimum longitudinal stretching ratio of 5 times by a biaxial stretching machine, the minimum longitudinal stretching ratio of the membrane material would need to exceed 20 times. An excessively high unidirectional stretching ratio obviously cannot meet the overall requirements of the product, such as biaxially oriented polypropylene (BOPP) film. As is well known, the lower the longitudinal stretching ratio of the synchronous stretching machine, the more clamps are required, the greater the load on the equipment, and it is difficult to achieve high production speeds. The various contradictions between the above processes and equipment have led to an urgent need in the industry to improve biaxial stretching equipment in order to meet the development requirements of efficient production of ultra-thin and ultra-high strength films. At the same time, the equipment also needs to adapt to different process requirements and take into account the feasibility of flexible adjustment. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a bidirectional synchronous stretching and retraction device.

[0007] According to an embodiment of the present invention, a bidirectional synchronous stretching and retraction device includes two chain clamping devices arranged in a left-right mirror symmetrical configuration, with a processing channel between the two chain clamping devices, the front end of the processing channel being a starting end; each chain clamping device includes a chain clamping assembly and multiple chain disc components for driving the chain clamping assembly, the chain clamping assembly having a preheating zone and several stretching and retraction zones from front to back from the starting end of the processing channel, the preheating zone extending front to back, one of the stretching and retraction zones being called the stretching head zone, the stretching head zone extending obliquely from the rear end of the preheating zone towards the side away from the processing channel; one of the chain disc components is located between the preheating zone and the stretching head zone.

[0008] The bidirectional synchronous stretching and retraction device according to a first aspect embodiment of the present invention has at least the following technical advantages: by setting a first chain disc between the preheating zone and the stretching first zone, the transmission direction of the chain disc component is aligned with the running direction of the chain clamp component in the area of ​​high running resistance, which helps to reduce the operating load of the chain clamp device. Therefore, while maintaining the same number of chain clamp components, a higher operating speed can be achieved, thereby improving production efficiency and meeting production needs.

[0009] According to some embodiments of the present invention, the chain clamp assembly includes a plurality of chain clamp components, each of the chain clamp components having a width dimension of at least 40 mm and a width dimension of no more than 120 mm.

[0010] According to some embodiments of the present invention, the chain clamp component has a clamping seat and a clamping block disposed on the upper side of the clamping seat, the bottom surface of the clamping block is curved, and a clamping space for clamping a plastic film is provided between the clamping seat and the clamping block.

[0011] According to some embodiments of the present invention, each of the chain clamp assemblies includes a plurality of stretch retraction zones, which are arranged sequentially from front to back, and two adjacent stretch retraction zones form an included angle.

[0012] According to some embodiments of the present invention, two adjacent stretching and retraction zones are collectively referred to as a turning unit, and the included angle between the two stretching and retraction zones of the turning unit is called a turning angle. The turning angle is located on the side of the turning unit away from the processing channel. For any turning unit where the turning angle is a minor angle, one of the chain drive components is provided between the two stretching and retraction zones.

[0013] According to some embodiments of the present invention, the number of stretching and retraction zones is four, wherein three of the stretching and retraction zones are respectively referred to as stretching and retraction zone two, stretching and retraction zone three, and stretching and retraction zone four. The stretching and retraction zone two extends obliquely from the rear end of the stretching zone three toward the side closer to the processing channel. The stretching and retraction zone three extends obliquely from the rear end of the stretching and retraction zone two toward the side farther away from the processing channel. The stretching and retraction zone four extends obliquely from the rear end of the stretching and retraction zone three toward the side closer to the processing channel.

[0014] According to some embodiments of the present invention, the chain clamp assembly further includes a shaping region that extends rearward from the rear end of all the stretch retraction regions.

[0015] According to some embodiments of the present invention, the bidirectional synchronous stretching and retraction device further includes a heating box, the heating box having a heating channel extending forward and backward, and the preheating zone, all the stretching and retraction zones, the shaping zone and the processing channel are all located within the heating channel.

[0016] According to some embodiments of the present invention, one of the chain disk components is provided at the front end of the preheating zone, and one of the chain disk components is provided at the rear end of the shaping zone.

[0017] According to some embodiments of the present invention, the bidirectional synchronous stretching and retraction device further includes a longitudinal stretching machine, which is located in front of the processing channel.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a schematic diagram of the bidirectional synchronous stretching and retraction device according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the chain clamp assembly in the preheating zone according to one embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the chain clamp component in the preheating zone according to one embodiment of the present invention;

[0023] In the attached image:

[0024] 001-Processing channel; 110-Preheating zone; 121-Stretching first zone; 122-Stretching and retraction second zone; 123-Stretching and retraction third zone; 124-Stretching and retraction fourth zone; 140-Shaping zone; 150-First return section; 160-Second return section; 170-Third return section; 210-First chain disc; 220-Second chain disc; 230-Third chain disc; 240-Fourth chain disc; 300-Heating box; 410-Inner guide rail; 411-Inner sliding block; 412-Inner hinge shaft; 420-Outer guide rail; 421-Chain clamp component; 422-Outer hinge shaft; 423-Clamping seat; 424-Clamping block; 500-Longitudinal stretching machine. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the invention and for simplifying the description, and do not indicate that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc., are understood to exclude the stated number, while "above," "below," "within," etc., are understood to include the stated number. If "first" or "second" is used, it is only for the purpose of distinguishing technical features and should not be construed as indicating relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0027] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0028] The following is for reference. Figures 1 to 3 This invention describes a bidirectional synchronous stretching and retraction device according to an embodiment of the present invention.

[0029] The bidirectional synchronous stretching and retraction device of this invention, as described in this embodiment, refers to... Figure 1 As shown, it includes two chain clamp devices, which are arranged in a mirror image symmetrically. A processing channel 001 is provided between the two chain clamp devices. The front end of the processing channel 001 is the starting end. When the bidirectional synchronous stretching and retracting device is running, the plastic film passes through the processing channel 001 from front to back. The chain clamp device includes a chain clamp assembly and multiple chain disk components for driving the chain clamp assembly.

[0030] The chain clamp assembly is ring-shaped, with a working part that contacts the plastic film and a return part that does not contact the plastic film. The working part and the return part are connected end to end to form a ring. Taking the chain clamp device on the right side of the two chain clamp devices as an example, the working part is located on the left side of the chain clamp assembly, and the return part is located on the rear, right and front sides of the chain clamp assembly.

[0031] The chain clamp assembly has a preheating zone 110 and several stretching and retraction zones from front to back at the starting end of the processing channel 001. The preheating zone 110 and the first stretching zone 121 are both part of the working part. The preheating zone 110 extends front to back. One of the stretching and retraction zones is called the first stretching zone 121. The first stretching zone 121 extends obliquely from the rear end of the preheating zone 110 to the side away from the processing channel 001. That is, the first stretching zone 121 extends obliquely to the right rear from the rear end of the preheating zone 110. The working part also includes a second stretching and retraction zone 122, a third stretching and retraction zone 123, a fourth stretching and retraction zone 124 and a shaping zone 140 connected in sequence to the rear end of the first stretching zone 121. The width of the processing channel 001 at the shaping zone 140 is greater than its width at the preheating zone 110.

[0032] The return section includes a first return segment 150, a second return segment 160, and a third return segment 170. The first return segment 150 extends from the rear end of the working section to the right front, and the third return segment 170 extends from the front end of the working section to the right rear. The second return segment 160 connects the right end of the first return segment 150 and the right end of the third return segment 170.

[0033] Each chain clamp device may contain up to six chain disc components. All chain disc components are located inside the annular structure formed by the chain clamp assembly. One chain disc component, referred to as the first chain disc 210, is located between the preheating zone 110 and the first stretching zone 121. Another chain disc component, referred to as the second chain disc 220, is located between the second stretching and retraction zone 122 and the third stretching and retraction zone 123. The remaining four chain disc components are located between the working part and the first return section 150, between the first return section 150 and the second return section 160, between the second return section 160 and the third return section 170, and between the third return section 170 and the working part, respectively. All chain disc components are active chain discs driven by an electric motor.

[0034] Reference Figure 2The chain clamp assembly includes an inner guide rail 410, an outer guide rail 420, a plurality of inner sliding blocks 411 slidably disposed on the inner guide rail 410, and a plurality of chain clamp components 421 slidably disposed on the outer guide rail 420. The inner sliding blocks 411 and chain clamp components 421 are alternately arranged, and a connecting rod connects adjacent inner sliding blocks 411 and chain clamp components 421. Each chain clamp component 421 is provided with an outer hinge shaft 422, and each inner sliding block 411 is provided with an inner hinge shaft 412. The two ends of the connecting rod are hinged to the inner hinge shaft 412 and the outer hinge shaft 422, respectively. Each chain clamp component 421 is equipped with a clamp for holding the plastic film. This allows the chain clamp component 421 to hold the plastic film while conveying it along the guide rail. When the inner guide rail 410 and outer guide rail 420 move closer or further apart, the distance between adjacent chain clamp components 421 increases or decreases, thereby achieving longitudinal stretching of the film. The structure of the chain clamp assembly, the connection method between the chain disc component and the chain clamp assembly, and the structure of the chain clamp component 421 in the bidirectional synchronous stretching and retraction device are all conventional technologies in the field, and their specific structures will not be described in detail here. The lateral stretching and contraction of the film is controlled by the distance between the two chain clamp components, and the longitudinal stretching and contraction of the film is controlled by the distance between the inner guide rail 410 and the outer guide rail 420 of the chain clamp assembly. The lateral and longitudinal stretching and contraction of the film do not affect each other, enabling simultaneous lateral and longitudinal stretching, as well as simultaneous lateral and longitudinal contraction, lateral and longitudinal contraction, and lateral and longitudinal contraction.

[0035] Understandably, the smaller the longitudinal stretching ratio of the bidirectional synchronous stretching and retraction device, the more chain clamp components 421 are contained in each chain clamp assembly of the same length, the greater the load on the equipment, and the more difficult it is to achieve a high production speed. This is the main factor restricting the increase in production output.

[0036] Since the working part needs to clamp the plastic film for stretching, the running resistance of the chain clamp assembly mainly comes from the working part. In the preheating zone 110, the thrust direction of the chain disc component at the front end of the preheating zone 110 is consistent with the running direction of the chain clamp component 421, and it is not subjected to tangential force, so the resistance is acceptable. However, when it reaches the stretching first zone 121, the thrust direction of the chain disc component at the front end of the preheating zone 110 is at an angle to the running direction of the chain clamp component 421. The force component effect and the increase in tangential friction caused by the tangential force result in a significant decrease in the force transmission efficiency and a rapid increase in running resistance. This can easily lead to excessive equipment load and the inability to further increase the running speed. The connection between the preheating zone 110 and the stretching first zone 121 is the core bottleneck.

[0037] In this embodiment, by setting a first chain disc 210 between the preheating zone 110 and the stretching zone 121, the transmission direction of the chain disc component is aligned with the running direction of the chain clamp component 421 in an area with high running resistance. This helps to reduce the operating load of the chain clamp device. Therefore, while maintaining the same number of chain clamp components, a higher operating speed can be achieved, thereby improving production efficiency and meeting production needs.

[0038] In some embodiments of the present invention, the longitudinal stretching ratio of the bidirectional synchronous stretching and retraction device is no greater than 4 times. This, combined with the longitudinal stretching machine 500 at the front of the processing channel 001, which has a stretching ratio of no less than 4 times, provides the production line with a wider process window, meeting the needs of different product manufacturing processes.

[0039] In some embodiments of the present invention, the width of each chain clamp component is at least 40 mm and does not exceed 120 mm. The dimension of the chain clamp component along its direction of movement is the width of the chain clamp component, and the distance between two chain clamp components is the distance between the axes of the outer hinge shafts of the two chain clamp components. In the preheating zone, adjacent chain clamp components abut each other, that is, the width of the chain clamp component is equal to the distance between two adjacent chain clamp components. In the stretching and retraction zone, the shaping zone, and the return section, adjacent chain clamp components separate from each other, that is, the width of the chain clamp component is less than the distance between two adjacent chain clamp components. The width of the chain clamp components of the synchronous stretching machine in the related art is generally less than 30 mm, and the width of the chain clamp components of the asynchronous stretching machine in the related art is generally more than 120 mm.

[0040] With the maximum longitudinal tensile ratio б max Taking 2, 2.5, and 3 as examples, the dimensions of each part corresponding to different chain clamp component widths D are shown in Tables 1 to 3.

[0041] Table 1: Maximum Longitudinal Tension Ratio б max =2 hours

[0042]

[0043]

[0044] Table 2: Maximum Longitudinal Tension Ratio б max =2.5

[0045]

[0046] Table 3: Maximum Longitudinal Tension Ratio б max =3 hours

[0047]

[0048] According to the data in the table above:

[0049] When the maximum longitudinal tensile ratio is б during synchronous stretching max At the same time, the larger the width D of the chain clamp component, the larger the distance H between the inner and outer guide rails.

[0050] When the maximum longitudinal tensile ratio is б during synchronous stretching max The same and the equipment is running until б=б max When the width D of the chain clamp component is larger, the spacing A between adjacent chain clamp components is larger, that is, the number of chain clamp components in the same length chain clamp assembly is smaller, and the torque required to operate the bidirectional synchronous stretching and retraction device is smaller.

[0051] This embodiment uses a wider chain clamp component, which reduces the number of chain clamp components without changing the longitudinal stretching ratio. Simultaneously, a wider chain clamp component also improves the strength and stability of the clamp itself. Theoretically, the wider the clamp and the larger the spacing, the greater the distance between the inner and outer guide rails of the synchronous stretching device at the same longitudinal stretching ratio. This means that the adjustment range of the longitudinal stretching ratio by the rail spacing is larger during the longitudinal stretching process, thus improving the control accuracy of the longitudinal stretching ratio and ensuring the stability and reliability of the process.

[0052] With the maximum longitudinal tensile ratio б max Taking 2, 2.5, and 3 as examples, the influence of the increase in the distance between the inner and outer guide rails ΔH on the increase in the center distance ΔA of the chain clamp component under different maximum longitudinal stretching ratios, that is, the influence on the longitudinal stretching ratio control accuracy, is shown in Table 4.

[0053] Table 4:

[0054]

[0055]

[0056] According to the data in Table 4, the maximum longitudinal tensile ratio б during synchronous stretching is... max Under the same conditions, the closer the actual longitudinal tensile stretch ratio б is to the maximum longitudinal tensile stretch ratio б, the better. max The higher the accuracy of its longitudinal tension adjustment, the greater the longitudinal tension ratio б under the same synchronous tensioning actual longitudinal tension ratio б. max The smaller the value, the higher the precision of its longitudinal stretching ratio adjustment.

[0057] In some embodiments of the present invention, the chain clamp component 421 has a clamping seat 423 and a clamping block 424 disposed on the upper side of the clamping seat 423. The bottom surface of the clamping block 424 is curved, similar to the bottom surface of a basin or a hemisphere. A clamping space for clamping a plastic film is provided between the clamping seat 423 and the clamping block 424, and the actual clamping area is less than or equal to one-third of the lower surface area of ​​the clamping block 424. (Refer to...) Figure 3The bottom surface of the clamping block 424 extends upwards from the center outwards. It is understandable that a typical clamping block 424 has a flat bottom surface. If a wider chain clamping component 421 is used without changing the bottom surface design of the clamping block 424, this would result in a large dead volume in the clamping area (the clamping position cannot achieve longitudinal dimensional changes), reducing the local uniformity of the film. This embodiment uses a curved contact area, which can maximize clamping strength without excessively sacrificing the clamping area, while minimizing the adverse effects of the dead volume in the clamping area on the uniform stretching of the film.

[0058] In some embodiments of the present invention, each chain clamp assembly includes multiple stretching and retraction zones, which are arranged sequentially from front to back, with adjacent stretching and retraction zones forming an included angle. This allows for the configuration of multiple stretching and retraction zones with different inclinations according to actual production needs. As the film is conveyed along the processing channel 001, it is stretched or retracted sequentially at different lateral stretch ratios, allowing the stress accumulated during stretching to be released and alleviated, preventing or delaying stress hardening, and achieving a stable and higher areal stretch ratio.

[0059] In some embodiments of the present invention, two adjacent stretching and retraction zones are collectively referred to as a turning unit, and the included angle between the two stretching and retraction zones of the turning unit is called a turning angle. The turning angle is located on the side of the turning unit away from the processing channel 001. For any turning unit with a minor turning angle, one of the chain disk components is provided between the two stretching and retraction zones. When the turning angle is a minor angle, the current stretching and retraction zone extends further away from the rear end of the previous stretching and retraction zone in an inclined direction away from the processing channel 001, which will also form a position with greater resistance. In this embodiment, by providing a chain disk component at each position with greater resistance, it is beneficial to reduce the operating load of the chain clamping device.

[0060] In some embodiments of the present invention, there are four stretching and retraction zones, three of which are referred to as stretching and retraction zone two 122, stretching and retraction zone three 123, and stretching and retraction zone four 124, respectively. Stretching and retraction zone two 122 extends obliquely from the rear end of stretching zone one 121 toward the side closer to the processing channel 001. Stretching and retraction zone three 123 extends obliquely from the rear end of stretching and retraction zone two 122 toward the side farther from the processing channel 001. Stretching and retraction zone four 124 extends obliquely from the rear end of stretching and retraction zone three 123 toward the side closer to the processing channel 001. The included angle between stretching and retraction zone two 122 and stretching and retraction zone three 123 is a minor angle, therefore a second chain plate 220 is provided.

[0061] The first stretching zone 121 is used for transverse stretching and longitudinal retraction of the film; the second stretching and retraction zone 122 is used for transverse retraction and longitudinal stretching of the film; the third stretching and retraction zone 123 is used for transverse stretching and longitudinal retraction of the film; and the fourth stretching and retraction zone 124 is used for transverse retraction and longitudinal stretching of the film. The retraction function eliminates bowing and improves the flatness of the film. This embodiment, by adding a combined stretching and retraction process, performs multi-stage series processing on the semi-finished film. During each stage of transverse / longitudinal stretching, a suitable amount of active longitudinal / transverse retraction is simultaneously performed, allowing the stress accumulated during stretching to be released and alleviated, avoiding or delaying stress hardening, achieving a stable and higher surface stretching ratio. This is suitable for preparing thinner films and also improves tensile strength, while allowing for flexible adjustment of transverse and longitudinal orientation and tensile strength.

[0062] In some embodiments of the invention, the chain clamp assembly further includes a shaping region 140 that extends rearward from the rear end of all stretch retraction regions. This facilitates the shaping of the stretched film.

[0063] In some embodiments of the present invention, the bidirectional synchronous stretching and retraction device further includes a heating chamber 300, which has a front-to-back extending heating channel. The preheating zone 110, all stretching and retraction zones, the shaping zone 140, and the processing channel 001 are all located within the heating channel. The heating channel extends through the heating chamber 300 in the front-to-back direction, allowing the plastic film to be continuously conveyed. The preheating zone 110, all stretching and retraction zones, and the shaping zone 140 of the two chain clamp devices are all located within the heating channel. This improves the plasticity and stretchability of the film.

[0064] In some embodiments of the present invention, the front end of the preheating zone 110 is provided with one chain disk component, referred to as the third chain disk 230, and the rear end of the shaping zone 140 is provided with one chain disk component, referred to as the fourth chain disk 240. The working part containing the preheating zone 110, all stretching and retraction zones, and the shaping zone 140 is a part with high running resistance. By providing chain disk components at both ends of the working part, it is beneficial to the stable operation of the chain clamp device. Specifically, the front end of the preheating zone 110 can be configured to extend forward and protrude beyond the heating box 300, and the rear end of the shaping zone 140 can be configured to extend rearward and protrude beyond the heating box 300, so that the third chain disk 230 and the fourth chain disk 240 are both located outside the heating box 300 and do not need to be heated by the heating box 300, which is beneficial to stable operation.

[0065] In some embodiments of the present invention, the bidirectional synchronous stretching and retraction device further includes a longitudinal stretching machine 500, which is located in front of the processing channel 001. The longitudinal stretching machine 500 can be a pressure roller type longitudinal stretching machine. The longitudinal stretching machine 500 is conventional equipment in the art and can be purchased directly. Its specific structure will not be described in detail here. Its maximum longitudinal stretching ratio can reach ten. In use, the film first passes through the longitudinal stretching machine 500 and then through the bidirectional synchronous stretching and retraction device. The longitudinal stretching machine 500 can provide a longitudinal stretching ratio with a large adjustable range. When combined with the stretching device formed by the two chain clamping devices with smaller longitudinal stretching ratios of the present invention, the BOPP film stretching production line using this embodiment can support a large longitudinal stretching ratio (≥8 times the total longitudinal stretching ratio) while ensuring that its minimum longitudinal stretching ratio is within a reasonable range (≤5 times the total longitudinal stretching ratio), so that the production line has a wider process window to meet the usage requirements.

[0066] In some embodiments of the present invention, the stretching ratio of the longitudinal stretching machine 500 is not less than four. This avoids the film material exhibiting transversely uneven stripes due to its intrinsic properties.

[0067] This multi-stage combined bidirectional synchronous stretching and retraction device combines a clamping synchronous stretching machine with a conventional roller-type longitudinal stretching machine 500, using the multiplicative relationship of the longitudinal stretching ratios to achieve flexible adjustment of the longitudinal stretching ratio. The clamping chain component 421 of this multi-stage combined bidirectional synchronous stretching and retraction device features a wider clamping body design and a curved clamping surface design to ensure the strength of the chain component 421, reduce the number of chain components 421, and minimize the impact of dead volume during longitudinal stretching and retraction. This multi-stage combined bidirectional synchronous stretching and retraction device can achieve multiple longitudinal and transverse stretching and retraction operations. It not only allows for flexible adjustment of the longitudinal and transverse orientation and strength of the film material without changing the overall surface stretching ratio, but also enables active stress relaxation in the tangential direction while stretching in one direction. Through repeated operations of unidirectional stretching and vertical retraction relaxation, a stable and larger surface stretching ratio is achieved, thereby improving the strength and stability of ultra-thin films, representing a groundbreaking innovation.

[0068] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A bidirectional synchronous stretching and retraction device, characterized in that: The device includes two chain clamping devices arranged in a mirror image symmetrically. A processing channel (001) is provided between the two chain clamping devices, with the front end of the processing channel (001) being the starting end. Each chain clamping device includes a chain clamping assembly and multiple chain disc components for driving the chain clamping assembly. The chain clamping assembly has a preheating zone (110) and several stretching and retraction zones extending from the starting end of the processing channel (001) from front to back. The preheating zone (110) extends front to back. One of the stretching and retraction zones is called the stretching head zone (121). The stretching head zone (121) extends obliquely from the rear end of the preheating zone (110) to the side away from the processing channel (001). One of the chain disc components is provided between the preheating zone (110) and the stretching head zone (121).

2. The bidirectional synchronous stretching and retraction device according to claim 1, characterized in that: The chain clamp assembly includes a plurality of chain clamp components (421), each chain clamp component (421) having a width dimension of at least 40 mm and a width dimension of no more than 120 mm.

3. The bidirectional synchronous stretching and retraction device according to claim 2, characterized in that: The chain clamp component (421) has a clamping seat (423) and a clamping block (424) disposed on the upper side of the clamping seat (423). The bottom surface of the clamping block (424) is curved. A clamping space for clamping plastic film is provided between the clamping seat (423) and the clamping block (424).

4. The bidirectional synchronous stretching and retraction device according to claim 1, characterized in that: Each of the chain clamp assemblies includes a plurality of stretch retraction zones, which are arranged sequentially from front to back, with adjacent stretch retraction zones forming an angle.

5. The bidirectional synchronous stretching and retraction device according to claim 4, characterized in that: Two adjacent stretching and retraction zones are collectively referred to as a turning unit. The angle between the two stretching and retraction zones of the turning unit is called the turning angle. The turning angle is located on the side of the turning unit away from the processing channel (001). For any turning unit with a minor turning angle, one of the chain disk components is provided between the two stretching and retraction zones.

6. The bidirectional synchronous stretching and retraction device according to claim 5, characterized in that: The number of stretching and retraction zones is four, of which three stretching and retraction zones are respectively called stretching and retraction zone two (122), stretching and retraction zone three (123) and stretching and retraction zone four (124). The stretching and retraction zone two (122) extends obliquely from the rear end of the stretching zone one (121) toward the side closer to the processing channel (001). The stretching and retraction zone three (123) extends obliquely from the rear end of the stretching and retraction zone two (122) toward the side away from the processing channel (001). The stretching and retraction zone four (124) extends obliquely from the rear end of the stretching and retraction zone three (123) toward the side closer to the processing channel (001).

7. The bidirectional synchronous stretching and retraction device according to claim 1, characterized in that: The chain clamp assembly also includes a shaping area (140) that extends rearward from the rear end of all the stretch retraction areas.

8. The bidirectional synchronous stretching and retraction device according to claim 7, characterized in that: The bidirectional synchronous stretching and retraction device also includes a heating box (300), which is provided with a heating channel extending forward and backward. The preheating zone (110), all the stretching and retraction zones, the shaping zone (140) and the processing channel (001) are all located in the heating channel.

9. The bidirectional synchronous stretching and retraction device according to claim 7, characterized in that: One of the chain disk components is provided at the front end of the preheating zone (110), and one of the chain disk components is provided at the rear end of the shaping zone (140).

10. The bidirectional synchronous stretching and retraction device according to claim 7, characterized in that: The bidirectional synchronous stretching and retraction device also includes a longitudinal stretching machine (500), which is located in front of the processing channel (001).

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