Three-layer composite film blow molding device based on die spiral topological surface

Abstract

The application discloses a three-layer composite film blow molding device based on a die spiral topological surface, which comprises a blow molding die head and a cooling integrated system; the blow molding die head comprises a die core and an outer die body, the die core is arranged in the outer die body, a compressed air flow channel is arranged in the die core, a spiral differential flow channel is arranged in the die core and the outer die body, and the spiral differential flow channel is used for spirally differentiating the material flowing through the blow molding die head and extruding the material into a tubular film blank with a spiral lift angle, and the inner and outer surfaces of the spiral differential flow channel are processed into reverse spiral topological surfaces; the cooling integrated system comprises a ring-shaped pressure stabilizing cavity and a water cooling system, the ring-shaped pressure stabilizing cavity is arranged at the end of the spiral differential flow channel, the ring-shaped pressure stabilizing cavity is communicated with the compressed air flow channel, and the water cooling system is connected with the ring-shaped pressure stabilizing cavity. The application simplifies the equipment for blow molding of the multi-layer composite film and can realize continuous production.

Description

Technical Field

[0001] This invention relates to the field of plastic processing technology, and more specifically to a three-layer composite film blow molding apparatus based on a die spiral topological surface. Background Technology

[0002] Multilayer composite films possess excellent functionality, giving them superior tear strength, dimensional stability, puncture resistance, and barrier properties compared to conventional single-layer films. As a result, they are widely used in food packaging, agricultural films, and other fields.

[0003] Blown film is one of the plastic film forming methods. This method involves melting and plasticizing the material using an extruder, then extruding it through the die gap into a tubular preform. The preform is then inflated by compressed gas, and finally, under the action of a traction device, it is cooled and shaped into a film.

[0004] However, current blow molding methods for multilayer composite films rely on multilayer co-extrusion dies and multiple extruders. Precise control of the flow path and extrusion rate of each layer is crucial for achieving uniform composite formation. Multiple extruders, each responsible for melting, plasticizing, and extruding different layers, not only make the equipment system large and complex, increasing purchase and maintenance costs, but also incurring high costs for process adjustments and upgrades. Furthermore, this process is extremely demanding in its matching of extrusion parameters. Even slight deviations in parameters such as melt temperature, extrusion speed, and pressure of different layers can easily lead to melt cross-lamination, severely compromising the structural integrity and performance stability of the multilayer composite film. Existing single-layer blow molding dies can only produce films with a single structure, failing to meet the functional requirements of multilayer composite films. Therefore, how to cost-effectively modify single-layer dies to achieve efficient molding of multilayer composite structures has become a critical challenge that the film manufacturing industry urgently needs to overcome.

[0005] Chinese invention patent CN114643696B discloses "a cross-film inner and outer die spiral micro-channel blow molding device and method", which has the advantages of simple molding, convenient operation, continuous production and no waste generation. However, this solution has the problem of film distortion during blow molding and poor mechanical properties of the product. Summary of the Invention

[0006] To address at least one of the technical problems existing in the prior art, this invention provides a three-layer composite film blow molding device based on a single-layer die head with a spiral topological curved surface structure. This device enables rapid blow molding of multi-layer composite films using a single-layer die head, producing a "sandwich"-like composite cross-oriented bubble structure. This simplifies the equipment for multi-layer composite film blow molding and allows for continuous production. The spiral topological curved surface structure of the single-layer blow molding die head enables the blow molding of three-layer composite films, making it suitable for processing polymer materials such as packaging and agricultural films.

[0007] This invention, through a ring-shaped pressure stabilizing chamber and a water cooling system, can ensure the interlayer interface fusion strength and effectively prevent molecular chain degradation caused by shear overheating.

[0008] To achieve the objectives of this invention, the present invention provides a three-layer composite film blow molding device based on a die spiral topological surface, comprising a blow molding die head and a cooling integrated system;

[0009] The blow molding die head includes a core and an outer mold body. The core is located inside the outer mold body and has a compressed air flow channel. The core and the outer mold body are provided with a spiral micro-flow channel, which is used to spirally divide the material flowing through the blow molding die head and extrude it into a tubular film preform with a spiral helix angle.

[0010] The integrated cooling system includes an annular pressure regulating chamber and a water cooling system for controlling the cooling rate. The annular pressure regulating chamber is located at the end of the spiral micro-channel to balance the difference in centrifugal force between the inside and outside. The annular pressure regulating chamber is connected to the compressed air channel, and the water cooling system is connected to the annular pressure regulating chamber.

[0011] Furthermore, the outer mold body and the mold core are connected by bolts and are respectively mounted on the outer mold body mounting base and the mold core mounting base.

[0012] Furthermore, reverse spiral topological surfaces are machined on the inner and outer surfaces of the annular flow channel of the single-layer die head. The inner wall is a left-hand spiral groove and the outer wall is a right-hand spiral groove. The inner and outer layers are reverse spirally layered by the difference in melt flow shear force in the annular flow channel of the die head, and the neutral layer maintains longitudinal flow, thereby forming a "sandwich" composite cross-oriented bubble structure.

[0013] Furthermore, the reverse spiral flow channel has a processing accuracy tolerance of ≤0.01mm and a surface roughness Ra≤0.2μm, and is treated with chrome plating or mirror polishing to ensure the accuracy of the thin film products.

[0014] Furthermore, the inner and outer surfaces of the annular flow channel of the single-layer die head are machined with reverse spiral topological surfaces. The spiral helix angle Φ of the inner and outer walls is 15°-45°, the wedge angle β is 5°-20°, and the settling angle ψ is 3°-10°. By changing the spiral helix angle of the die core and the die head, as well as the width of the spiral micro-flow channel, the thickness ratio of each layer (1:1:1 to 1:2:1) and the orientation direction of the cross-orientation can be effectively controlled. Moreover, since the topological surface has no sharp corners, the prepared product has no weld lines.

[0015] Furthermore, heating modules (heating elements) are installed on the outer mold body and the mold core respectively, so that the temperature of the two can be controlled separately.

[0016] Furthermore, an annular pressure stabilizing chamber is set at the end of the spiral flow channel, and the air pressure is adjusted to 0.1-0.5MPa by compressed air to balance the difference in centrifugal force between the inner and outer layers.

[0017] Furthermore, the cooling rate controlled by the water cooling system is 10℃ / s-30℃ / s to prevent molecular chain degradation.

[0018] Furthermore, the temperature of the outer mold body is 5℃-20℃ higher than that of the mold core, or the temperature of the mold core is 5℃-20℃ higher than that of the outer mold body. This can create a viscosity gradient along the radial direction of the die to enhance the layering effect.

[0019] Furthermore, the device is capable of upward or downward blow molding.

[0020] The present invention also provides a three-layer composite film blow molding method based on the helical topological surface of the die.

[0021] This invention provides a method for easily achieving continuous processing and self-reinforcing of polymer films using a simple mechanical device. This invention is simple, effective, convenient, quick, requires no additional fillers, and is environmentally friendly.

[0022] This invention utilizes a single-layer blow molding die to complete the blow molding of multi-layer composite films, improving upon the shortcomings of traditional processes such as low mechanical strength, large differences in transverse and longitudinal mechanical properties, low tear resistance, and low puncture resistance. By optimizing the die head flow channel structure and process parameters, the invention achieves the spontaneous generation of a three-layer composite structure from a single-layer bubble. The beneficial effects of this invention include the following:

[0023] 1. The equipment has a simple structure and is easy to promote. Compared with traditional single-layer blow molding dies, this die head can realize the blow molding of multi-layer composite films. Compared with traditional multi-layer blow molding dies, this die head has a simple structure and does not require multiple extruders, saving a lot of floor space and energy consumption. Equipment modification costs are reduced by more than 30%, and production efficiency is increased by 10%-20%.

[0024] 2. This invention, by setting up an annular pressure-stabilizing chamber, can balance the difference in centrifugal force between the inner and outer layers, promote the interlayer interface fusion strength, prevent peeling, avoid film distortion during blow molding, and improve product performance. Simultaneously, the water-cooling system can effectively control the cooling rate, preventing molecular chain degradation caused by shear overheating.

[0025] 3. No external filler is required, making it green and environmentally friendly. This invention achieves self-reinforcement of polymer films using pure materials, further improving the transverse mechanical properties, puncture resistance, and tear resistance of the products.

[0026] 4. The sandwich structure of the present invention helps to improve the mechanical properties of the product, such as tensile strength and puncture strength. Attached Figure Description

[0027] Figure 1This is a schematic diagram of the structure of the outer mold body and the mold core provided in the embodiment of the present invention, wherein (a) is a schematic diagram of the outer mold body and (b) is a schematic diagram of the mold core.

[0028] Figure 2 This is a schematic diagram of melt layering flow and molecular chain orientation in an embodiment of the present invention (the dark gray part is the blown product, and the light gray and white parts are the perspective of the product cut open).

[0029] Figure 3 This is a schematic diagram of the integration of the annular pressure stabilizing cavity and the water cooling system in an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the structure of a three-layer composite film blow molding device for blow molding polyethylene (upward blow molding) in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the structure of a three-layer composite film blow molding device for blow molding polypropylene (downward blow molding) in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the velocity distribution along the thickness direction of the flow channel in the annular gap of the die in an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] like Figures 1-5 As shown in the figure, an embodiment of the present invention provides a three-layer composite film blow molding device based on a die spiral topological surface, including a blow molding die head and a cooling integrated system.

[0035] The blow molding die head includes a die core 1, an outer die body 2, a die core mounting base 3, and an outer die body mounting base 4. The die core 1 is mounted on the die core mounting base 3, and the outer die body 2 is mounted on the outer die body mounting base 4. The die core 1 is located inside the outer die body 2, and the die core 1 and the outer die body 2 are coaxial, with a gap between them. A compressed air flow channel 8 is provided inside the die core 1. Both the die core 1 and the outer die body 2 are provided with a spiral micro-flow channel 10, i.e., a die annular gap flow channel, which is used to spirally micro-extrude the material flowing through the blow molding die head into a tubular preform with a spiral helix angle.

[0036] In one embodiment of the invention, the inner wall is a left-handed spiral groove and the outer wall is a right-handed spiral groove. The inner and outer layers are reverse spirally layered by the difference in melt flow shear force in the die annular gap flow channel, and the neutral layer maintains longitudinal flow, thereby forming a "sandwich" composite cross-oriented bubble structure.

[0037] In one embodiment of the present invention, the outer mold body 2 and the mold core 1 are connected by bolts and are respectively mounted on the outer mold body mounting base 4 and the mold core mounting base 3.

[0038] The integrated cooling system includes an annular pressure-stabilizing chamber 5 and a water-cooling system 6 connected to the annular pressure-stabilizing chamber 5. The annular pressure-stabilizing chamber 5 is located at the end of the spiral micro-channel 10 and is connected to the compressed air channel 8. The annular pressure-stabilizing chamber 5 is used to stabilize the melt pressure and the blow molding pressure. The water-cooling system 6 is used to control the cooling rate. In one embodiment of the invention, as... Figure 3 As shown, some of the flow channels in the water-cooling system 6 are arranged in a labyrinthine pattern, which helps to increase the contact area and make the cooling rate faster. The annular pressure regulating cavity 5 is a hollow cylindrical shape.

[0039] In one embodiment of the present invention, the inner and outer walls of the reverse spiral topological surface processed on the inner and outer surfaces of the single-layer die head have a spiral helix angle Φ of 15°-45°, a wedge angle β of 5°-20°, and a settling angle ψ of 3°-10°. By changing the spiral helix angle of the die core and the die head, as well as the flow channel gap of the die annular surface, the thickness ratio of each layer (1:1:1 to 1:2:1) and the orientation direction of the cross-orientation can be effectively controlled. Furthermore, since the topological surface has no sharp corners, the prepared product has no weld lines.

[0040] In one embodiment of the present invention, the pressure is adjusted to 0.1-0.5 MPa by compressed air through an annular pressure stabilizing chamber 5 to balance the difference in centrifugal force between the inner and outer layers.

[0041] In one embodiment of the present invention, the cooling rate is controlled at 10°C / s-30°C / s by the water cooling system 6, so that the product is rapidly cooled and shaped and the molecular chain is prevented from degrading.

[0042] In one embodiment of the present invention, the temperatures of the outer mold body 2 and the mold core 1 are individually controlled by segmented heating of the mold head. Preferably, the outer mold body 2 and the mold core 1 are each thermally connected to a heating element, and are heated separately by corresponding heaters.

[0043] In one embodiment of the present invention, the temperature of the outer mold body 2 is 5°C-20°C higher than that of the mold core 1, or the temperature of the mold core 1 is 5°C-20°C higher than that of the outer mold body 2, which can form a viscosity gradient along the radial direction of the die to enhance the layering effect.

[0044] In one embodiment of the present invention, the processing accuracy tolerance of the finger mold annular gap flow channel is ≤0.01mm, the surface roughness Ra is ≤0.2μm, and chrome plating or mirror polishing is adopted to ensure the accuracy of the thin film product.

[0045] In one embodiment of the present invention, high-density polyethylene (HDPE) is selected as the raw material, such as... Figure 4 As shown, in upward blow molding, the material is melted and plasticized by a single extruder with an extrusion pressure of 20 MPa and then enters the blow molding die. The outer mold body 2, located on the outside of the blow molding die, is heated to 220°C, and the inner mold core 1, located on the inside, is heated to 210°C. The material flows along the direction of the spiral micro-channel. The annular channel gap of the die is set to 1.2 mm, the helix angle Φ = 30°, the wedge angle β = 10°, and the settling angle ψ = 5°. The outer layer of the material flow is in the same direction as the spiral micro-channel, and the inner layer is in the same direction as the flow of the mold core 1. The velocity gradients at the outer mold body 2 and the mold core 1 are opposite. The middle layer (neutral layer) of the gap between the outer mold body 2 and the mold core 1 has only upward flow in the thickness direction and no horizontal velocity component. The neutral layer maintains a vertically upward flow direction. The material flow forms a "sandwich" composite cross-oriented preform with a certain helix angle in the axial direction.

[0046] The preform passes through the annular pressure-stabilizing cavity 5 located at the end of the spiral micro-channel. The air pressure in the annular pressure-stabilizing cavity 5 is regulated to 0.3 MPa by compressed air in the compressed air channel 8 (compressed gas is blown out from the mold core 1 through the compressed air channel 8 to inflate the product, thereby regulating the air pressure in the annular pressure-stabilizing cavity 5), thus balancing the centrifugal forces of the inner and outer layers. The preform is then inflated by compressed air. The water-cooling system 6 introduces cooling water into the annular pressure-stabilizing cavity 5 for water cooling, so that the inflated preform, after a cooling rate of 15℃ / s, becomes a "sandwich" composite cross-oriented film 7 with a certain spiral angle. The thickness ratio of the inner layer: neutral layer: outer layer is 1:1:1.

[0047] In one embodiment of the present invention, the performance comparison of the formed film is shown in Table 1. As can be seen from Table 1, the performance of the film product prepared by this device is better than that of existing film products.

[0048] Table 1

[0049]

[0050] In one embodiment of the present invention, such as Figure 5 As shown, a three-layer composite film blow molding device based on the spiral topological surface of the die is used to blow mold polypropylene, including a blow molding die head and a cooling integrated system.

[0051] The blow molding die head includes a die core 1, an outer die body 2, a die core mounting base 3, and a die mounting base 4. The integrated cooling system includes an annular pressure stabilizing chamber 5 and a water cooling system 6. The die core 1 is mounted on the die core mounting base 3, and the outer die body 2 is mounted on the die mounting base 4. The die core 1 and the outer die body 2 are coaxial, and a gap is left between them. A compressed air flow channel 8 is provided inside the die core 1. Spiral micro-flow channels, i.e., die annular gap flow channels, are provided inside the die core 1 and the outer die body 2 to spirally micro-extrude the material flowing through the blow molding die head into a tubular preform with a helical helix angle.

[0052] In this embodiment, polypropylene (PP) is used as the raw material, and the molding process is downward blow molding, that is, the mold core 1 and the outer mold body 2 are set downwards, and a water tank 9 is set below the mold core 1 and the outer mold body 2, and the water tank 9 is connected to the water cooling system.

[0053] After being melted and plasticized by a single extruder with an extrusion pressure of 20 MPa, the material enters the blow molding die. The outer mold body 2 of the blow molding die is heated to 220°C, and the core 1 is heated to 210°C. The material flows along the spiral micro-channel direction. The annular channel gap of the die is set to 0.8 mm, the helix angle Φ = 25°, the wedge angle β = 10°, and the settling angle ψ = 5°. The outer layer of the material flows in the same direction as the helical direction of the die, the inner layer flows in the same direction as the core, and the neutral layer maintains a vertically upward flow direction. The material flows in the axial direction to form a "sandwich" composite cross-oriented preform with a certain helix angle.

[0054] The preform passes through the annular pressure-stabilizing chamber 5 located at the end of the spiral flow channel. The air pressure in the annular pressure-stabilizing chamber 5 is regulated to 0.2 MPa by compressed air in the compressed air flow channel 8, balancing the centrifugal forces of the inner and outer layers. The preform is then inflated by compressed air. The water cooling system 6 introduces cooling water into the annular pressure-stabilizing chamber 5. The inflated preform is cooled by water spray at a cooling rate of 25℃ / s, forming a "sandwich" composite cross-oriented film 7 with a certain spiral angle. The cooling water flows from the annular pressure-stabilizing chamber 5 onto the film product and then flows along the film product into the water tank 9 for recycling. The thickness ratio of the inner layer: neutral layer: outer layer is 1:2:1.

[0055] As shown in Table 2, the performance of the thin film products prepared by this device is superior to that of existing thin film products.

[0056] Table 2

[0057]

[0058] The foregoing embodiments of this invention, by processing reverse spiral topological surfaces on the inner and outer surfaces of the die annular channel, combined with temperature gradient control and pressure balance design, enable the melt to automatically differentiate into inner and outer reverse spiral layers and an intermediate longitudinal layer through the die channel, forming a "sandwich" composite foam structure. This method eliminates the need for complex multi-layer co-extrusion equipment, has low modification costs, and high production efficiency, making it suitable for high-barrier packaging, agricultural films, and other fields.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this invention may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-layer composite film blow molding device based on a helical topological surface of a die, characterized in that, Includes blow molding die head and integrated cooling system; The blow molding die head includes a core and an outer mold body. The core is located inside the outer mold body and has a compressed air flow channel. The core and the outer mold body are provided with a spiral micro-flow channel, which is used to spirally differentiate the material flowing through the blow molding die head and extrude it into a tubular film preform with a spiral helix angle. The inner and outer surfaces of the spiral micro-flow channel are machined with reverse spiral topological curved surfaces. The cooling integrated system includes an annular pressure regulating chamber and a water cooling system. The annular pressure regulating chamber is located at the end of the spiral micro-channel and is connected to the compressed air channel. The water cooling system is connected to the annular pressure regulating chamber. The inner and outer layers are separated by reverse spiral stratification through the difference in melt flow shear force in the spiral micro-channel, while the neutral layer maintains longitudinal flow, thus forming a "sandwich" composite cross-oriented bubble structure. The spiral helix angle Φ of the reverse spiral topological surface is 15°-45°, the wedge angle β is 5°-20°, and the receding angle ψ is 3°-10°. The thickness ratio of each layer and the orientation direction of the cross orientation are controlled by adjusting the spiral helix angle of the mold core and the outer mold body as well as the channel gap. The inner wall of the die annular gap channel is a left-hand spiral groove, and the outer wall is a right-hand spiral groove.

2. The three-layer composite film blow molding apparatus based on the helical topological surface of the die according to claim 1, characterized in that, The machining accuracy tolerance of the reverse spiral flow channel is ≤0.01mm, the surface roughness Ra≤0.2μm, and it is polished.

3. The three-layer composite film blow molding apparatus based on the helical topological surface of the die according to claim 1, characterized in that, The mold core and outer mold body are each connected to a heating element for individual temperature control.

4. The three-layer composite film blow molding device based on the helical topological surface of the die according to claim 1, characterized in that, The water cooling system controls the cooling rate to be 10°C / s-30°C / s.

5. The three-layer composite film blow molding apparatus based on the helical topological surface of the die according to claim 1, characterized in that, The temperature of the outer mold body is 5°C-20°C higher than the temperature of the mold core, or the temperature of the mold core is 5°C-20°C higher than the temperature of the outer mold body.

6. The three-layer composite film blow molding apparatus based on a helical topological surface of a die according to any one of claims 1-5, characterized in that, The device is capable of upward or downward blow molding.

7. A three-layer composite film blow molding method based on a helical topological surface of a die, characterized in that, The method, employing the apparatus according to any one of claims 1-6, comprises the steps of: After the material is melted and plasticized, it enters the blow molding die. The material flows along the direction of the spiral micro-channel. The outer layer of the material flow flows in the same direction as the spiral micro-channel, while the inner layer flows in the same direction as the core. The velocity gradients at the outer mold body and the core are opposite. The middle of the gap between the outer mold body and the core has only upward flow in the thickness direction, without any horizontal velocity component. The neutral layer maintains a vertically upward flow direction. The material flow forms a "sandwich" composite cross-oriented preform with a certain spiral angle in the axial direction. The membrane preform passes through the annular pressure stabilizing chamber, and the air pressure in the annular pressure stabilizing chamber is regulated by the compressed air in the compressed air flow channel, so that the centrifugal force of the inner and outer layers is balanced, and the membrane preform is inflated by the compressed air. The water cooling system introduces cooling water into the annular pressure stabilizing chamber for water cooling, so that the blown preform becomes a "sandwich" composite cross-oriented film with a certain helical angle after cooling.

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