Bopp film adjustable multi-stage forming automation equipment and forming method

Abstract

An adjustable multi-stage automated forming equipment and method for BOPP film is disclosed. This invention employs an adjustable three-stage gradient multi-stage stretching technology for BOPP film. Each stage of the stretching roller assembly utilizes seven or more independently driven roller segments, achieving axial active stretching of the film rollers along the same axis with differentiated speeds. Combined with a controllable relaxation coupling structure between stages, multiple small-ratio step-by-step stretching is performed, along with a stress relaxation process. This enables precise control of stretching parameters in various regions of the film width, significantly improving the optical uniformity and dimensional stability of the BOPP film. The finished product quality and production yield of the BOPP film are also improved, making it suitable for producing high-end optical and high-uniformity BOPP films.

Description

Technical Field

[0001] This invention relates to a film forming equipment and forming method, and more particularly to an adjustable multi-stage automated forming equipment and forming method for BOPP film, belonging to the field of automated production line technology. Background Technology

[0002] Biaxially oriented polypropylene (BOPP) film is widely used in packaging, printing, electronics, and optics due to its excellent mechanical, optical, and barrier properties. The production process of BOPP film mainly includes core steps such as casting, longitudinal stretching (MDO), transverse stretching (TDO), and traction winding. Among these, the transverse stretching process is crucial in determining the film's thickness uniformity, optical isotropy, and dimensional stability along its width. In existing BOPP film biaxial stretching production processes, film forming is mainly divided into two core steps: longitudinal stretching (MDO) and transverse stretching (TDO). In existing industrial production lines, transverse stretching commonly uses a chain-type tenter frame, relying on clamps on both sides to hold the film edges and move them outwards to achieve width expansion and stretching. This technical solution has revealed several shortcomings in actual production.

[0003] First, chain-type tenter frames have a large footprint and high equipment cost. The accompanying drying oven consumes a significant amount of energy, and the clamps and chains are prone to wear. Daily debugging and maintenance are also labor-intensive, resulting in high production costs. Second, the chain only clamps the film edges, leading to uneven stress distribution across the film's width. This easily causes quality defects such as arcing distortion, thick edges, and thin areas in the center of the film, directly reducing the film's optical uniformity and thermal dimensional stability. Third, traditional tenter frames often use a single, high-ratio lateral stretching mode. The film undergoes large deformation in a short time, resulting in localized stress concentration, which easily leads to necking, microcracks, and film breakage, causing downtime and limiting product yield.

[0004] The existing ordinary conveyor rollers and longitudinal stretching rollers have completely consistent linear speeds in each section, and the rollers do not have active stretching capabilities in the axial direction. The casting and MDO processes cannot complete pre-expansion and stress release, and all transverse stretching loads are concentrated in the rear TDO tenter frame, which further increases the difficulty of tenter frame process debugging and imposes stringent requirements on the quality of the casting substrate.

[0005] In some existing tensioning testing equipment, rigid screw and crank-connecting rod tensioning mechanisms have high transmission stiffness. The stroke, rate, tension, and holding time parameters of longitudinal and transverse tensioning are coupled together, making it impossible to achieve independent and differentiated control in both directions. The impact force generated during equipment start-up, shutdown, and reversal can induce microcracks, local thinning, or even film rupture for low-modulus and brittle BOPP films, making it difficult to achieve multiple progressive tensioning processes. Simple cylinder tensioning equipment is mostly driven as a whole with a shared air circuit, and the process parameters in each direction cannot be adjusted independently in a closed loop. The clamping force of the matching fixtures cannot be precisely controlled. Excessive clamping force will damage the film edge, while insufficient clamping force will cause film slippage, resulting in dispersion of the stretch ratio and deterioration of thickness uniformity.

[0006] There is a long-standing technological bias within the industry: to achieve high-precision biaxial stretching, rigid screw mechanical transmission is required; pneumatic drives are difficult to achieve precise closed-loop control of multiple parameters. Current technology lacks fixture-free, segmented, independently driven axial pre-stretching equipment, making it impossible to achieve multi-stage gradient lateral pre-stretching without clamping the film edges. It also lacks a complete technical solution for inter-stage stress relaxation and full-width online closed-loop control. Ordinary solid cylindrical rollers lack axial speed differences and cannot produce axial stretching effects; single-stage, high-ratio axial stretching results in significant stress concentration, easily causing necking and localized over-stretching of BOPP films, further worsening the thickness difference.

[0007] In summary, developing a novel BOPP film forming equipment that can eliminate the need for clamping, achieve non-contact active stretching in the width direction, decompose a single high-ratio stretching into multiple low-ratio gradient stretchings, and possess online stress relaxation and closed-loop control capabilities has become the key to solving this technical challenge in this field. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing BOPP film transverse stretching systems, which rely on chain tenter frame machines. These machines are bulky, have low stretching accuracy, produce poor film surface quality, require clamping and fixing at the film edges, and are prone to film indentation and damage. Furthermore, they suffer from uneven stress distribution during the stretching process and low production efficiency. This invention provides an adjustable multi-stage automated BOPP film forming device. Through segmented, independently driven roller sections, it achieves clamp-free, multi-stage, gradient active stretching and forming of the film width. Multiple small-ratio step-by-step stretching, combined with a stress relaxation buffering process, releases residual stress during film forming. This enables precise control of stretching parameters in different areas of the film width, significantly improving the optical uniformity and dimensional stability of the BOPP film, and also increasing the finished product quality and yield.

[0009] To achieve the above objectives, the technical solution of the present invention is: an adjustable multi-stage forming automated equipment for BOPP film, comprising a frame, wherein a feeding preheating unit is installed on the frame and located at the BOPP film forming inlet, and a first-stage stretching roller group, a second-stage stretching roller group, and a third-stage stretching roller group are sequentially installed on the frame along the film-moving direction of the BOPP film. Each stretching roller group includes a central stationary shaft, a reference roller section, four or more transition roller sections, and edge roller sections located at both ends. The central stationary shaft is horizontally fixed on the frame by a mounting base. A reference roller section is set at the axial center of the central stationary shaft. Transition roller sections are symmetrically arranged on the central stationary shaft on both sides of the reference roller section. An edge roller section is set at each end of the central stationary shaft. A servo drive component is independently installed between the central stationary shaft and each roller section, which can realize stepless adjustment of the rotation speed of a single roller section, so that the single-stage stretching roller group forms a linear velocity gradient that gradually increases from the center to both sides, thereby realizing active axial stretching of the film.

[0010] Interstage relaxation buffer units are installed on the frame between the primary and secondary stretching roller groups and between the secondary and tertiary stretching roller groups to achieve controllable stress relaxation of the film after stretching. Above each segmented stretching roller group is a set of pressing and bonding units to tightly adhere the film to the surface of the roller segment. An online detection closed-loop control unit is installed at the discharge end of the tertiary stretching roller group. The online detection closed-loop control unit is electrically linked with each servo drive component, temperature control component, interstage relaxation buffer unit and pressing and bonding unit to form a closed-loop control system.

[0011] Furthermore, the feeding preheating unit includes three series-connected constant temperature preheating rollers and symmetrical hot air rectifier outlets at the top and bottom. The preheating temperature can be controlled at 90-110℃, and the heat field uniformity is ≤±0.5℃.

[0012] Furthermore, the transition roller sections installed on the primary stretching roller group, the secondary stretching roller group, and the tertiary stretching roller group are of the same length. In the reference roller section, the transition roller section, and the edge roller section located on the same central static shaft, a gap of 0.2 mm to 0.5 mm is reserved between adjacent roller sections, and an isolation gasket is installed in the gap.

[0013] Furthermore, the three-stage segmented stretching roller group—the primary stretching roller group, the secondary stretching roller group, and the tertiary stretching roller group—is configured with a gradient stretching ratio. The speed difference between the reference roller section and the edge roller section on the primary stretching roller group is 5%-8%, with a single-stage stretching ratio of 1.05-1.08. The speed difference between the reference roller section and the edge roller section on the secondary stretching roller group is 10%-12%, with a single-stage stretching ratio of 1.10-1.12. The speed difference between the reference roller section and the edge roller section on the tertiary stretching roller group is 13%-15%, with a single-stage stretching ratio of 1.13-1.15 and a cumulative three-stage stretching ratio of 1.3-1.45.

[0014] Furthermore, the base of the roller section is made of hard anodized aluminum alloy, and the outer surface of the roller section is sprayed with a micron-level ceramic wear-resistant coating with a coating friction coefficient controlled at 0.35-0.4; each roller section is equipped with a constant temperature heat transfer oil circulation heating device or a constant temperature electric heating device, and a temperature detection module is installed on the roller section.

[0015] Furthermore, the interstage relaxation buffer unit includes a mirror-finish constant temperature buffer roller, a vertical lifting servo module, and a tension detection sensor. The mirror-finish constant temperature buffer roller is mounted on the vertical lifting servo module. By finely adjusting the height through the vertical lifting servo module, the controllable relaxation amount of the film is 1%-3%. A tension detection sensor is installed in the bearing mounting seat of the mirror-finish constant temperature buffer roller. The mirror-finish constant temperature buffer roller has a built-in heating module to maintain a constant film surface stretching temperature.

[0016] Furthermore, the pressing and bonding unit includes a silicone pressure roller and a pneumatic pressure regulating component. The silicone pressure roller is mounted on the pneumatic pressure regulating component and is positioned parallel to the corresponding stretching roller group directly above it. The axis of the silicone pressure roller is parallel to the axis of the stretching roller group. The pressing pressure of the silicone pressure roller is 0.2–0.6 MPa and is steplessly adjustable. Pressure sensors are provided at both ends of the silicone pressure roller for real-time feedback of pressing parameters and linkage closed-loop control.

[0017] Furthermore, the online detection closed-loop control unit includes multiple sets of online detection probes and a transverse tension array sensor. The online detection probes are arranged one-to-one with the multiple roller segments on each stretching roller group, and are used to collect the film width segment thickness and tension data in real time, and to correct the rotation speed, temperature and pressing pressure of each roller segment in conjunction with the data.

[0018] Furthermore, a machine vision camera is installed on the outside of the composite processing module and the automatic hook-up device.

[0019] A method for adjustable multi-stage molding of BOPP film includes the following steps:

[0020] A. Preheating feeding: The BOPP film casting to be stretched is introduced into the feeding preheating unit and uniformly preheated through three series constant temperature preheating rollers and symmetrical hot air rectifiers at the top and bottom. The preheating temperature is controlled at 90-110℃ and the thermal uniformity is ≤±0.5℃.

[0021] B. First-stage small-ratio stretching: The preheated film enters the first-stage stretching roller group and is tightly bonded to the roller surface under the action of the pressing and bonding unit; each section of the first-stage stretching roller group, driven by an independent servo drive component, forms a gradually increasing linear velocity gradient from the reference roller section to the two edge roller sections, performing the first small-ratio gradient stretching of the film in the width direction, with a single-stage stretching ratio of 1.05-1.08;

[0022] C. First-stage stress relaxation: The film that has completed the first-stage stretching enters the interstage relaxation buffer unit between the first-stage and second-stage stretching roller groups. The height of the mirror constant temperature buffer roller is finely adjusted by the vertical lifting servo module, so that the film undergoes 1%-3% controlled shrinkage under constant temperature conditions to release some of the tensile internal stress.

[0023] D. Secondary medium-ratio stretching: After stress relaxation, the film enters the secondary stretching roller group and repeats the gradient stretching process of step B. The second gradient stretching is performed with a higher speed difference, and the single-stage stretching ratio is 1.10-1.12.

[0024] E. Secondary stress relaxation: The film that has completed secondary stretching enters the interstage relaxation buffer unit between the secondary and tertiary stretching roller groups, and repeats the stress relaxation process in step C.

[0025] F. Three-stage high-ratio stretching: After stress relaxation, the film enters the three-stage stretching roller group and repeats the gradient stretching process in step B. The third gradient stretching is performed with the highest speed difference. The single-stage stretching ratio is 1.13-1.15, and the cumulative stretching ratio of the three stages reaches 1.3-1.45.

[0026] G. Online detection and closed-loop control: During the three-stage stretching and the entire forming process, the online detection closed-loop control unit located at the discharge end of the three-stage stretching roller group collects the thickness and tension data of each segment of the film width in real time through multiple sets of online detection probes, and feeds the data back to the control system. The control system links and corrects the rotation speed, temperature of each roller segment of each stage of the stretching roller group and the pressing pressure of the pressing and bonding unit according to the preset process parameters, forming a closed-loop control of the entire process.

[0027] The beneficial effects of this invention are:

[0028] 1. This invention breaks through the technical limitation of traditional BOPP film production equipment rollers that can only perform longitudinal stretching. It cleverly adopts a coaxial segmented independent drive structure to achieve axial active stretching of film rollers with the same outer diameter, coaxial axis, and differentiated speeds. It eliminates the need for edge clamping with a chain, avoiding film indentation and damage caused by edge clamping and fixing. At the same time, it can also significantly reduce the equipment size and energy consumption of traditional tenter frames, and reduce production and maintenance costs.

[0029] 2. This invention adopts a three-level gradient multi-stage stretching + inter-stage controllable relaxation coupling structure, which decomposes a single high-ratio stretching into multiple low-ratio step-by-step stretchings. Combined with stress relaxation process, it completely solves problems such as necking, stress concentration and film breakage in the axial stretching process of BOPP film, and improves production stability and yield.

[0030] 3. The present invention adopts a closed-loop control mode of independent speed regulation, overall temperature control and segmented precise detection for each roller section, which realizes the fine control of the stretching parameters of each region of the film width, effectively improves the defects of uneven film thickness, bow-shaped deformation and inconsistent shrinkage rate, and greatly improves the optical uniformity and dimensional stability of BOPP film.

[0031] 4. The equipment of this invention can be flexibly integrated between the casting and longitudinal stretching (MDO) processes, serving as a pre-stretching and stress relief unit. By pre-expanding and stress homogenizing the cast film, the stretching load and process difficulty of the subsequent transverse stretching (TDO) tenter frame are effectively reduced, optimizing the overall stretching process compatibility. This provides a new, efficient, and high-precision solution for the industrial production of high-end optical and high-uniformity BOPP films. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structural layout of the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the inter-stage relaxation buffer unit of the present invention.

[0034] Figure 3 This is a schematic diagram of the structure of the stretching roller assembly of the present invention.

[0035] Figure 4 This is a schematic diagram of the structure of the stretching roller unit of the present invention.

[0036] Figure 5 This is a schematic diagram of the structure of the tension roller unit of the present invention exploding.

[0037] Figure 6 This is a schematic diagram of the planar structure of the stretching roller unit of the present invention.

[0038] In the diagram: 1. Frame; 2. Feeding preheating unit; 3. Primary stretching roller group; 4. Secondary stretching roller group; 5. Tertiary stretching roller group; 6. Interstage relaxation buffer unit; 7. Pressing and bonding unit; 8. Mounting base; 9. Central stationary shaft; 10. Reference roller section; 11. Transition roller section; 12. Edge roller section; 13. Servo drive assembly; 14. Isolation gasket; 15. Silicone pressure roller; 16. Pneumatic pressure regulating assembly; 17. Mirror constant temperature buffer roller; 18. Vertical lifting servo module; 19. Tension detection sensor; 20. Temperature detection module; 21. Online detection probe; 22. Control box. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] See Figures 1 to 6This invention discloses an adjustable multi-stage automated BOPP film forming equipment, comprising a frame 1. The equipment is characterized by: a feeding preheating unit 2 installed on the frame 1 at the BOPP film forming inlet; a primary stretching roller group 3, a secondary stretching roller group 4, and a tertiary stretching roller group 5 sequentially installed on the frame 1 along the BOPP film feeding direction; each stretching roller group includes a central stationary shaft 9, a reference roller section 10, four or more transition roller sections 11, and edge roller sections 12 at both ends; the central stationary shaft 9 is horizontally fixed to the frame 1 via a mounting base 8; a reference roller section 10 is located at the axial center of the central stationary shaft 9; transition roller sections 11 are symmetrically arranged on the central stationary shaft 9 on both sides of the reference roller section 10; and an edge roller section 12 is located at each end of the central stationary shaft 9; a servo drive component 13 is independently installed between the central stationary shaft 9 and each roller section, enabling stepless adjustment of the rotational speed of a single roller section, thus forming a linear velocity gradient that gradually increases from the center to both sides of the single-stage stretching roller group, achieving active axial stretching of the film.

[0041] Interstage relaxation buffer units 6 are respectively installed on the frame 1 between the first-stage stretching roller group 3 and the second-stage stretching roller group 4, and between the second-stage stretching roller group 4 and the third-stage stretching roller group 5, to achieve controllable stress relaxation of the film after stretching. Above each segmented stretching roller group, a set of pressing and bonding units 7 is respectively installed to tightly adhere the film to the surface of the roller section. The discharge end of the third-stage stretching roller group is equipped with an online detection closed-loop control unit. The online detection closed-loop control unit is electrically linked with each servo drive component, temperature control component, interstage relaxation buffer unit 6 and pressing and bonding unit 7 to form a closed-loop control system.

[0042] The feeding preheating unit 2 includes three series-connected constant temperature preheating rollers and symmetrical hot air rectifier outlets at the top and bottom. The preheating temperature can be controlled at 90-110℃, and the heat field uniformity is ≤±0.5℃.

[0043] The transition roller sections 11 installed on the first-stage stretching roller group 3, the second-stage stretching roller group 4, and the third-stage stretching roller group 5 are of the same length. Among the reference roller section 10, the transition roller section 11, and the edge roller section 12 located on the same central static shaft 9, a gap of 0.2 mm to 0.5 mm is reserved between adjacent roller sections, and an isolation washer 14 is installed in the gap.

[0044] The three-stage segmented stretching roller group, consisting of primary stretching roller group 3, secondary stretching roller group 4, and tertiary stretching roller group 5, adopts a gradient stretching ratio setting. The speed difference between the reference roller section 10 and the edge roller section 12 on the primary stretching roller group 3 is 5%-8%, and the single-stage stretching ratio is 1.05-1.08. The speed difference between the reference roller section 10 and the edge roller section 12 on the secondary stretching roller group 4 is 10%-12%, and the single-stage stretching ratio is 1.10-1.12. The speed difference between the reference roller section 10 and the edge roller section 12 on the tertiary stretching roller group 5 is 13%-15%, the single-stage stretching ratio is 1.13-1.15, and the cumulative stretching ratio of the three stages is 1.3-1.45.

[0045] The base of the roller section is made of hard anodized aluminum alloy. The outer surface of the roller section is coated with a micron-level ceramic wear-resistant coating with a friction coefficient controlled at 0.35-0.4. Each roller section is equipped with a constant temperature heat transfer oil circulation heating device or a constant temperature electric heating device. A temperature detection module 20 is installed on the roller section.

[0046] The interstage relaxation buffer unit 6 includes a mirror-finish constant temperature buffer roller 17, a vertical lifting servo module 18, and a tension detection sensor 19. The mirror-finish constant temperature buffer roller 17 is mounted on the vertical lifting servo module 18. By finely adjusting the height through the vertical lifting servo module 18, the controllable relaxation amount of the film is 1%-3%. The tension detection sensor 19 is installed in the bearing mounting seat of the mirror-finish constant temperature buffer roller 17. The mirror-finish constant temperature buffer roller 17 has a built-in heating module to maintain a constant film surface stretching temperature.

[0047] The pressing and bonding unit 7 includes a silicone pressure roller 15 and a pneumatic pressure regulating component 16. The silicone pressure roller 15 is mounted on the pneumatic pressure regulating component 16 and is positioned parallel to the corresponding stretching roller group directly above it. The axis of the silicone pressure roller 15 is parallel to the axis of the stretching roller group. The pressing pressure of the silicone pressure roller 15 is 0.2–0.6 MPa and is steplessly adjustable. Pressure sensors are provided at both ends of the silicone pressure roller 15 for real-time feedback of pressing parameters and linkage closed-loop control.

[0048] The online detection closed-loop control unit includes multiple sets of online detection probes 21 and a transverse tension array sensor. The online detection probes 21 are arranged one-to-one with multiple roller segments on each stretching roller group, and are used to collect film width segment thickness and tension data in real time, and to correct the rotation speed, temperature and pressing pressure of each roller segment in conjunction with the data.

[0049] The servo drive assembly 13 consists of a ring servo motor and a drive module, and the isolation gasket 14 is a polytetrafluoroethylene isolation gasket.

[0050] See Figures 1 to 5This invention employs an adjustable three-stage gradient multi-stage stretching technology for BOPP films. Each stage of the stretching roller assembly utilizes seven or more independently driven roller segments, achieving axial active stretching of the film rollers along the same axis with differentiated speeds. Combined with a controllable relaxation coupling structure between stages, it enables multiple small-ratio step-by-step stretching processes, along with stress relaxation technology. This allows for precise control of stretching parameters in various regions of the film width, significantly improving the optical uniformity and dimensional stability of the BOPP film, achieving excellent technical results, and making it suitable for producing high-end optical, high-uniformity BOPP films. The structure and working principle of this invention are as follows:

[0051] This invention includes a feeding preheating unit 2 installed at the BOPP film forming inlet. The feeding preheating unit 2 comprises three series-connected constant-temperature preheating rollers and symmetrical hot air rectifier outlets. The BOPP film to be stretched and formed achieves stable preheating during its passage through the feeding preheating unit 2, with a controllable preheating temperature of 90-110℃ and a thermal uniformity of ≤±0.5℃. Behind the feeding preheating unit 2, a primary stretching roller group 3, a secondary stretching roller group 4, and a tertiary stretching roller group 5 are sequentially installed on the frame 1 along the BOPP film's direction of travel. These three stretching roller groups are spaced apart, facilitating equipment layout and providing sufficient space for the transverse stretching and forming of the film.

[0052] Each stretching roller assembly includes a central stationary shaft 9, a reference roller section 10, four or more transition roller sections 11, and edge roller sections 12 located at both ends. The central stationary shaft 9 is a rigid shaft and is horizontally fixed to the frame 1 by mounting base 8. The central stationary shaft 9 does not rotate. The reference roller section 10 is provided in the central section of the central stationary shaft 9. The reference roller section 10 is located on the transverse axis of film stretching. Transition roller sections 11 are symmetrically arranged on the central stationary shaft 9 on both sides of the reference roller section 10. There are at least two transition roller sections 11 located on one side of the reference roller section 10. An edge roller section 12 is provided at each end of the central stationary shaft 9. A servo drive assembly 13 is independently installed between the central stationary shaft 9 and each roller segment. The servo drive assembly 13 consists of a ring servo motor and a drive module, which can realize stepless adjustment of the rotation speed of a single roller segment, so that the single-stage stretching roller group forms a linear velocity gradient that gradually increases from the center to both sides. Each roller segment is driven independently, and the roller segments on the same central stationary shaft 9 are precisely coordinated, thereby realizing the active and uniform axial stretching of the film.

[0053] The three-stage segmented stretching roller group, consisting of primary stretching roller group 3, secondary stretching roller group 4, and tertiary stretching roller group 5, adopts a gradient stretching ratio setting. Specifically, the speed difference between the reference roller section 10 and the edge roller section 12 on the primary stretching roller group 3 is 5%-8%, with a single-stage stretching ratio of 1.05-1.08; the speed difference between the reference roller section 10 and the edge roller section 12 on the secondary stretching roller group 4 is 10%-12%, with a single-stage stretching ratio of 1.10-1.12; and the speed difference between the reference roller section 10 and the edge roller section 12 on the tertiary stretching roller group 5 is 13%-15%, with a single-stage stretching ratio of 1.13-1.15 and a cumulative three-stage stretching ratio of 1.3-1.45.

[0054] The base of the roller section is made of hard anodized aluminum alloy, and the outer surface of the roller section is coated with a micron-level ceramic wear-resistant coating with a friction coefficient controlled between 0.35 and 0.4. Each roller section is equipped with a constant-temperature heat transfer oil circulation heating device or a constant-temperature electric heating device, and a temperature detection module 20 is installed on the roller section.

[0055] Interstage relaxation buffer units 6 are respectively installed on the frame 1 between the primary stretching roller group 3 and the secondary stretching roller group 4, and between the secondary stretching roller group 4 and the tertiary stretching roller group 5. This controllable relaxation coupling structure can achieve stress relaxation and completely solve the problems of necking, stress concentration, and film breakage during the axial stretching process of BOPP film. The interstage relaxation buffer unit 6 includes a mirror-finish constant temperature buffer roller 17, a vertical lifting servo module 18, and a tension detection sensor 19. The mirror-finish constant temperature buffer roller 17 is installed on the vertical lifting servo module 18. By finely adjusting the height through the vertical lifting servo module 18, the controllable relaxation amount of the film is 1%-3%. The tension detection sensor 19 is installed in the bearing mounting seat of the mirror-finish constant temperature buffer roller 17 and can realize closed-loop control.

[0056] Above each segmented stretching roller assembly is a set of pressing and bonding units 7 for tightly bonding the film to the surface of the roller segment. The pressing and bonding unit 7 includes a silicone pressure roller 15 and a pneumatic pressure regulating component 16. The silicone pressure roller 15 is mounted on the pneumatic pressure regulating component 16 and is arranged parallel to the corresponding stretching roller assembly directly above it. The axis of the silicone pressure roller 15 is parallel to the axis of the stretching roller assembly. The pressing pressure of the silicone pressure roller 15 is 0.2–0.6 MPa and is steplessly adjustable. Pressure sensors are equipped at both ends of the silicone pressure roller 15 for real-time feedback of pressing parameters and linkage closed-loop control.

[0057] In addition, the present invention employs a line detection closed-loop control unit, which is electrically linked with each servo drive component, temperature control component, interstage relaxation buffer unit 6 and pressing and bonding unit 7. The controller is set in the control box 22 for centralized control, forming a closed-loop control system.

[0058] The following explanation is provided in conjunction with specific embodiments:

[0059] Example 1:

[0060] The three-stage stretching roller group adopts a gradient ratio setting. The speed difference between the reference roller section 10 and the edge roller section 12 of the first-stage stretching roller group 3 is 6%, with a single-stage stretching ratio of 1.06; the speed difference of the second-stage stretching roller group 4 is 11%, with a single-stage stretching ratio of 1.11; and the speed difference of the third-stage stretching roller group 5 is 14%, with a single-stage stretching ratio of 1.14. The cumulative stretching ratio of the three stages is approximately 1.34.

[0061] Example 2:

[0062] The difference between this embodiment and Embodiment 1 lies in the setting of the stretching ratio and relaxation amount, in order to adapt to the production needs of films of different specifications.

[0063] The speed difference between the reference roller section 10 and the edge roller section 12 of the first-stage stretching roller group 3 is 8%, with a single-stage stretching ratio of 1.08; the speed difference of the second-stage stretching roller group 4 is 12%, with a single-stage stretching ratio of 1.12; and the speed difference of the third-stage stretching roller group 5 is 15%, with a single-stage stretching ratio of 1.15. The cumulative stretching ratio of the three stages reaches 1.45.

[0064] The controllable relaxation amount of the thin film in the interstage relaxation buffer unit 6 is set to 3%.

[0065] The pressing pressure of the silicone roller 15 is adjusted to 0.6 MPa.

[0066] The remaining structure and molding method steps are the same as in Example 1.

[0067] Example 3:

[0068] The difference between this embodiment and Embodiment 1 lies in the configuration of the number of roller segments, in order to demonstrate the structural flexibility of the present invention.

[0069] Each stretching roll group consists of 7 roll segments: 1 reference roll segment 10, 4 transition roll segments 11, and 2 edge roll segments 12. The gap between adjacent roll segments is 0.5 mm.

[0070] The speed difference of the first-stage stretching roller group 3 is 5%, and the single-stage stretching ratio is 1.05; the speed difference of the second-stage stretching roller group 4 is 10%, and the single-stage stretching ratio is 1.10; the speed difference of the third-stage stretching roller group 5 is 13%, and the single-stage stretching ratio is 1.13. The cumulative stretching ratio of the three stages is 1.3.

[0071] The controllable relaxation amount of the thin film in the interstage relaxation buffer unit 6 is set to 1%.

[0072] The pressing pressure of the silicone roller 15 is adjusted to 0.2 MPa.

[0073] The remaining structure and molding method steps are the same as in Example 1.

[0074] The specific steps of the adjustable multi-stage molding method for BOPP film of the present invention are as follows:

[0075] Before production, the equipment is powered on for self-test and preheating. The whole machine is powered on, and the control system detects the working status of each servo drive component, temperature control component, pressing and bonding unit, inter-stage relaxation buffer unit, and online detection closed-loop control unit. The feeding preheating unit and the heating system of each stage stretching roller group are started to raise the temperature of the preheating unit, roller section and mirror constant temperature buffer roller to the process set temperature. After the thermal field is stable, the material is fed and threaded through the film.

[0076] Preheating feeding: The BOPP film casting to be stretched is introduced into the feeding preheating unit and preheated evenly through three series constant temperature preheating rollers and symmetrical hot air rectifiers at the top and bottom. The preheating temperature is controlled at 90-110℃ and the heat field uniformity is ≤±0.5℃. First-stage low-ratio stretching: The preheated film enters the first-stage stretching roller group and is tightly bonded to the roller surface under the action of the pressing and bonding unit. Driven by independent servo drive components, each section of the first-stage stretching roller group forms a gradually increasing linear velocity gradient from the reference roller section to the two edge roller sections, performing the first low-ratio gradient stretching of the film in the width direction, with a single-stage stretching ratio of 1.05-1.08. First-stage stress relaxation: The film that has completed the first-stage stretching enters the interstage relaxation buffer unit between the first-stage and second-stage stretching roller groups. The height of the mirror constant temperature buffer roller is finely adjusted by the vertical lifting servo module, so that the film undergoes a controlled shrinkage of 1%-3% under constant temperature conditions to release some of the tensile internal stress. Second-stage medium-ratio stretching: The stress-relaxed film enters the second-stage stretching roller group and repeats the gradient stretching process of step B, performing a second gradient stretching with a higher speed difference, with a single-stage stretching ratio of 1. 10-1.12; Secondary stress relaxation: The film after secondary stretching enters the interstage relaxation buffer unit between the secondary and tertiary stretching roller groups, repeating the stress relaxation process in step C; Tertiary high-ratio stretching: The stress-relaxed film enters the tertiary stretching roller group, repeating the gradient stretching process in step B, performing a third gradient stretching with the highest speed difference, with a single-stage stretching ratio of 1.13-1.15, and a cumulative stretching ratio of 1.3-1.45 for the three stages; Online detection and closed-loop control: During the tertiary stretching and the entire forming process, the online detection closed-loop control unit located at the discharge end of the tertiary stretching roller group collects the thickness and tension data of each segment of the film width in real time through multiple sets of online detection probes, and feeds the data back to the control system. The control system links and corrects the speed, temperature, and pressing pressure of each roller segment of each stretching roller group and the pressing and bonding unit according to the preset process parameters, forming a closed-loop control throughout the entire process.

[0077] The above description is a further detailed explanation of the present invention in conjunction with specific embodiments. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, any simple modifications and substitutions made without departing from the concept of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. An adjustable multi-stage automated BOPP film forming equipment, comprising a frame (1), characterized in that: A feeding preheating unit (2) is installed on the frame (1) at the BOPP film forming inlet. A first-stage stretching roller group (3), a second-stage stretching roller group (4), and a third-stage stretching roller group (5) are sequentially installed on the frame (1) along the BOPP film feeding direction. Each stretching roller group includes a central stationary shaft (9), a reference roller section (10), four or more transition roller sections (11), and edge roller sections (12) located at both ends. The central stationary shaft (9) is horizontally fixed on the frame (1) by a mounting base (8). A reference roller section (10) is provided at the axial center of the central static shaft (9). Transition roller sections (11) are symmetrically provided on the central static shaft (9) on both sides of the reference roller section (10). An edge roller section (12) is provided at each end of the central static shaft (9). A servo drive component (13) is independently installed between the central static shaft (9) and each roller section. The stepless adjustment of the rotation speed of a single roller section can be realized, so that the single-stage stretching roller group forms a linear velocity gradient that gradually increases from the center to both sides, thereby realizing the active axial stretching of the film. Interstage relaxation buffer units (6) are respectively installed on the frame (1) between the first-stage stretching roller group (3) and the second-stage stretching roller group (4), and between the second-stage stretching roller group (4) and the third-stage stretching roller group (5) to achieve controllable stress relaxation of the film after stretching. Each segmented stretching roller group is provided with a set of pressing and bonding units (7) for tightly bonding the film to the surface of the roller section. The discharge end of the third-stage stretching roller group is provided with an online detection closed-loop control unit. The online detection closed-loop control unit is electrically linked with each servo drive component, temperature control component, interstage relaxation buffer unit (6) and pressing and bonding unit (7) to form a closed-loop control system.

2. The adjustable multi-stage automated BOPP film forming equipment according to claim 1, characterized in that: The feeding preheating unit (2) includes three series constant temperature preheating rollers and symmetrical hot air rectifiers at the top and bottom. The preheating temperature can be controlled at 90-110℃ and the heat field uniformity is ≤±0.5℃.

3. The adjustable multi-stage automated BOPP film forming equipment according to claim 2, characterized in that: The transition roller sections (11) installed on the first-level stretching roller group (3), the second-level stretching roller group (4) and the third-level stretching roller group (5) are of the same length. The reference roller section (10), the transition roller section (11) and the edge roller section (12) located on the same central static shaft (9) have a gap of 0.2 mm to 0.5 mm between adjacent roller sections, and an isolation washer (14) is installed in the gap.

4. The adjustable multi-stage automated BOPP film forming equipment according to claim 1 or 3, characterized in that: The three-stage segmented stretching roller group (3), the second-stage stretching roller group (4), and the third-stage stretching roller group (5) are set with gradient stretching ratios. The speed difference between the reference roller section (10) and the edge roller section (12) on the first-stage stretching roller group (3) is 5%-8%, and the single-stage stretching ratio is 1.05-1.

08. The speed difference between the reference roller section (10) and the edge roller section (12) on the second-stage stretching roller group (4) is 10%-12%, and the single-stage stretching ratio is 1.10-1.

12. The speed difference between the reference roller section (10) and the edge roller section (12) on the third-stage stretching roller group (5) is 13%-15%, the single-stage stretching ratio is 1.13-1.15, and the three-stage cumulative stretching ratio is 1.3-1.

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5. The adjustable multi-stage automated BOPP film forming equipment according to claim 1, characterized in that: The base of the roller section is made of hard anodized aluminum alloy. The outer surface of the roller section is sprayed with a micron-level ceramic wear-resistant coating, and the coefficient of friction of the coating is controlled at 0.35-0.

4. Each roller section is equipped with a constant temperature heat transfer oil circulation heating device or a constant temperature electric heating device, and a temperature detection module (20) is installed on the roller section.

6. The adjustable multi-stage automated BOPP film forming equipment according to claim 2, characterized in that: The interstage relaxation buffer unit (6) includes a mirror constant temperature buffer roller (17), a vertical lifting servo module (18), and a tension detection sensor (19). The mirror constant temperature buffer roller (17) is mounted on the vertical lifting servo module (18). The height is finely adjusted by the vertical lifting servo module (18), and the controllable relaxation amount of the film is 1%-3%. The tension detection sensor (19) is installed in the bearing mounting seat of the mirror constant temperature buffer roller (17). The mirror constant temperature buffer roller (17) has a built-in heating module to maintain a constant film surface stretching temperature.

7. The adjustable multi-stage automated BOPP film forming equipment according to claim 1, characterized in that: The pressing and bonding unit (7) includes a silicone pressure roller (15) and a pneumatic pressure regulating component (16). The silicone pressure roller (15) is mounted on the pneumatic pressure regulating component (16). The silicone pressure roller (15) is arranged parallel to the corresponding stretching roller group directly above it. The axis of the silicone pressure roller (15) is parallel to the axis of the stretching roller group. The pressing pressure of the silicone pressure roller (15) is 0.2–0.6 MPa and is steplessly adjustable. Pressure sensors are provided at both ends of the silicone pressure roller (15) for real-time feedback of pressing parameters and linkage closed-loop control.

8. The adjustable multi-stage automated BOPP film forming equipment according to claim 1, characterized in that: The online detection closed-loop control unit includes multiple sets of online detection probes (21) and a transverse tension array sensor. The online detection probes (21) are arranged one-to-one with multiple roller segments on each stretching roller group, and are used to collect the thickness and tension data of the film width segments in real time, and to correct the rotation speed, temperature and pressing pressure of each roller segment in conjunction with the roller pressing.

9. The adjustable multi-stage automated BOPP film forming equipment according to claim 1, characterized in that: The servo drive assembly (13) consists of a ring servo motor and a drive module, and the isolation gasket (14) is made of polytetrafluoroethylene.

10. A molding method for producing BOPP film using the automated equipment as described in claim 1, characterized in that... Includes the following steps: A. Preheating feeding: The BOPP film casting to be stretched is introduced into the feeding preheating unit (2), and uniformly preheated by three series constant temperature preheating rollers and symmetrical hot air rectifiers at the top and bottom. The preheating temperature is controlled at 90-110℃, and the uniformity of the heat field is ≤±0.5℃. B. First-stage small-ratio stretching: The preheated film enters the first-stage stretching roller group (3) and is tightly bonded to the roller surface under the action of the pressing and bonding unit (7); each section of the roller group (3) is driven by an independent servo drive component, with the reference roller section as the reference, and forms a gradually increasing linear velocity gradient towards the two side edge roller sections to perform the first small-ratio gradient stretching of the film in the width direction, with a single-stage stretching ratio of 1.05-1.08; C. First-stage stress relaxation: The film that has completed the first-stage stretching enters the interstage relaxation buffer unit between the first-stage and second-stage stretching roller groups. The height of the mirror constant temperature buffer roller is finely adjusted by the vertical lifting servo module, so that the film undergoes 1%-3% controlled shrinkage under constant temperature conditions to release some of the tensile internal stress. D. Secondary medium-ratio stretching: After stress relaxation, the film enters the secondary stretching roller group (4) and repeats the gradient stretching process of step B. The second gradient stretching is performed with a higher speed difference, and the single-stage stretching ratio is 1.10-1.

12. E. Secondary stress relaxation: The film that has completed secondary stretching enters the interstage relaxation buffer unit between the secondary and tertiary stretching roller groups, and repeats the stress relaxation process in step C. F. Three-stage high-ratio stretching: After stress relaxation, the film enters the three-stage stretching roller group (5) and repeats the gradient stretching process of step B. The third gradient stretching is performed with the highest speed difference. The single-stage stretching ratio is 1.13-1.15, and the cumulative stretching ratio of the three stages reaches 1.3-1.

45. G. Online detection and closed-loop control: During the three-stage stretching and the entire forming process, the online detection closed-loop control unit located at the discharge end of the three-stage stretching roller group (5) collects the thickness and tension data of each segment of the film width in real time through multiple online detection probes, and feeds the data back to the control system. The control system corrects the rotation speed, temperature and pressing pressure of each roller segment of each stage of the stretching roller group and the pressing and bonding unit according to the preset process parameters, forming a closed-loop control of the entire process.

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