High-rigidity cover material and forming die

Abstract

The application discloses a high-rigidity cover material and a forming die, and belongs to the technical field of packaging cover material forming equipment. The high-rigidity cover material is sequentially provided with a printing surface layer, a rigid reinforcing core layer, a bonding composite layer and a heat-sealing functional layer from outside to inside; the cover material is integrally formed through die pressing, the cover surface area is provided with a discontinuous reinforcing rib structure which is concave downward, the reinforcing rib comprises an annular circumferential rib and a plurality of uniformly arranged radial radiation ribs, the outer periphery of the cover material is provided with a heat-sealing edge, and a tearable filter opening area which avoids the reinforcing rib is arranged at the eccentric position of the cover surface; the total thickness of the cover material is 80-140 microns, and the bending rigidity is greater than or equal to 120 mN. The forming die comprises an upper die assembly and a lower die assembly, the upper die assembly is provided with a detachable reinforcing rib punch insert and a cutting blade insert, the cover material cavity concave die of the lower die is provided with a negative pressure exhaust micropore, and the die is provided with a partition heating assembly; and the sheet material is fixed by relying on negative pressure when the die is closed.

Description

Technical Field

[0001] This application belongs to the technical field of cap materials and forming equipment, specifically relating to a high stiffness cap material and forming mold. Background Technology

[0002] Existing instant noodle and dry noodle filter covers are mostly made of thin-layer paper-plastic-aluminum composite materials, which are thin overall and lack stiffness. During storage, stacking, and transportation, the cover is prone to denting, warping, and deformation. When opening the cover, it easily bends and collapses, and the filter opening is easily torn, causing wrinkles and affecting the user experience. Simply increasing the thickness of the base material leads to increased material costs, poor heat-sealing compatibility, and problems such as edge bursting during die-cutting. Conventional flat-press molding dies only complete the outer shape cutting and pressing of the cover material; they cannot simultaneously form a rigid reinforcing structure in the cover material itself during the molding process. Improvements in cover stiffness depend on the base material itself, limiting the overall performance improvement of the product.

[0003] Specifically, the existing technology has the following technical problems: (1) In the prior art, the conventional means to improve the stiffness of the cover material is to increase the thickness of the substrate or use high-grammage paper. However, when the total thickness of the cover material exceeds 150 μm, the material cost increases significantly, and the excessively thick substrate is prone to defects such as edge bursting and burrs during die-cutting. At the same time, heat is difficult to penetrate to the heat-sealing functional layer during heat sealing, resulting in insufficient heat-sealing strength and reduced sealing performance. Therefore, those skilled in the art generally believe that achieving high stiffness without significantly increasing the thickness is a difficult technical problem to solve.

[0004] (2) Existing cover materials are mostly reinforced by surface printing coating or coating with hard resin to improve surface hardness. However, such methods only improve the surface feel and have limited effect on improving the overall bending stiffness of the cover material. Moreover, the coating is prone to cracking and peeling when the cover material is bent, affecting the appearance and barrier performance.

[0005] (3) Existing forming molds only have punching and pressing functions and cannot simultaneously form rigid reinforcing rib structures on the cover material body. Although some molds have rib pressing functions, they adopt continuous rib structures. The material fibers at the ribs are continuously cut, which causes stress concentration in the cover material at the rib positions. Under storage, stacking or transportation vibration conditions, micro-cracks are prone to appear and expand at the edges of the ribs, ultimately leading to a decrease in the overall structural strength of the cover material.

[0006] (4) Most existing filter opening areas adopt a full-cut design, that is, the cover material is completely cut off along the filter area to form an opening. When the cover is torn open, the cut end becomes a stress concentration point. During the tearing process, the cover material is prone to unexpected wrinkling and deformation, which affects the user experience.

[0007] In summary, there is an urgent need in this field for a cover material and its matching molding die that can achieve high stiffness, good heat-sealing performance and reliable water filtration function through the synergistic combination of structural design and molding process without significantly increasing the thickness of the cover material. Summary of the Invention

[0008] The purpose of this invention is to provide a high-stiffness cap material and molding die, which does not significantly increase the overall thickness of the cap material. Through the composite layer structure of the cap material body and the reinforcing rib structure formed by integral pressing of the cap surface, the overall stiffness and deformation resistance of the cap material are improved. With the matching special molding die, the reinforcing ribs are directly formed on the surface of the cap material during the molding and cutting process. The outline cutting and rigid structure forming of the cap material are completed in one process, which takes into account heat sealing performance, water filtration opening function and production efficiency, and reduces material costs.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A high stiffness cover material includes a printed surface layer, a rigid reinforcing core layer, an adhesive composite layer, and a heat-sealing functional layer arranged sequentially from the outside to the inside; the cover material is integrally molded, the cover surface area of ​​the cover material is provided with an integrally pressed reinforcing rib structure, the outer periphery of the cover material is provided with a heat-sealed edge, and the cover surface area is also provided with a tearable filter opening area.

[0010] Furthermore, the printed surface layer is coated paper or PET printed film, the thickness of the printed surface layer is 12-25μm, and a printed pattern layer is provided on the surface of the printed surface layer.

[0011] Furthermore, the rigid reinforcing core layer is a high-stiffness modified paper-aluminum foil composite layer, with a paper layer basis weight of 80-120 g / m². 2 The aluminum foil, which provides barrier properties, is 6-12μm thick, and the paper layer and aluminum foil are bonded together by dry composite bonding; the rigid reinforcing core layer is the main bearing layer for the stiffness of the cover material, and the aluminum foil also gives the cover material water vapor and oxygen barrier properties.

[0012] Furthermore, the adhesive composite layer is a PE extrusion composite layer with a thickness of 15-30μm, used to thermally bond the rigid reinforcing core layer and the heat-sealing functional layer together.

[0013] Furthermore, the heat-sealing functional layer is a modified polyolefin heat-sealing film with a thickness of 20-35μm, suitable for heat sealing the mouth of food containers, ensuring heat sealing strength while meeting the requirements for easy tearing and opening.

[0014] Furthermore, the reinforcing rib structure is a downwardly recessed rib formed by molding, with a rib depth of 0.15-0.4mm, and the rib does not penetrate the rigid reinforcing core layer; the reinforcing rib structure includes an annular circumferential rib and multiple radial ribs; the annular circumferential rib is 3-6mm away from the inner side of the heat-sealed edge of the cover material; the radial ribs extend inward from the annular circumferential rib to the center area of ​​the cover surface; the multiple radial ribs are evenly distributed along the circumference; the reinforcing rib is a discontinuous rib to avoid stress concentration and cracking at the rib location.

[0015] Furthermore, the water filtration opening area is located off-center on the cover surface, and the water filtration opening area is provided with intermittent micro-indentations, which avoid the position of the reinforcing ribs; the overall bending stiffness of the cover material is ≥120mN.

[0016] Furthermore, the total thickness of the cover material is controlled at 80-140μm, without the need to significantly increase the thickness of the base material. The high stiffness effect is achieved by relying on the synergy of the composite core layer and the molded reinforcing ribs.

[0017] A molding die for forming a high stiffness cap material, used to process the aforementioned high stiffness cap material, includes an upper die assembly and a lower die assembly; the upper die assembly includes an upper die base, a cutting edge insert, and a reinforcing rib punch insert; the lower die assembly includes a lower die base and a cap material cavity die.

[0018] The upper mold assembly and the lower mold assembly are set opposite to each other. When the mold is closed, the cutting edge insert completes the outer contour cutting of the cover material; the reinforcing rib punch insert corresponds to the cover surface area of ​​the cover material. When the mold is closed, the cover material is squeezed and a recessed reinforcing rib structure is pressed into the cover material; the cover material cavity die is used to support the cover material sheet.

[0019] Furthermore, the reinforcing rib punch insert is detachably embedded inside the upper mold base; the lower end face of the reinforcing rib punch insert is provided with raised ribs that perfectly match the reinforcing rib structure of the cover material, with a height of 0.15-0.4mm and a width of 0.8-2.0mm; the raised ribs are of discontinuous structure; the cutting edge insert is arranged around the periphery of the reinforcing rib punch insert; the bottom surface of the cavity of the cover material cavity die of the lower mold assembly is distributed with several venting micro-holes, with a diameter of 0.1-0.2mm, which are connected to an external negative pressure suction mechanism; during mold closing and forming, the negative pressure adsorbs the sheet material to prevent wrinkling and displacement of the sheet material, ensuring that the rib forming outline is clear.

[0020] Furthermore, the mold has a built-in partitioned heating component, with the upper and lower molds controlling the heating temperature separately; the temperature of the upper mold component is controlled at 95-120℃, and the temperature of the lower mold is controlled at 60-85℃; the ribs are formed under hot pressing, which causes the rigid core layer to undergo micro-deformation and shaping, and the rib structure has little springback after demolding and good stiffness retention.

[0021] Furthermore, the mold is also equipped with an elastic stripper ring, which surrounds the outside of the cutting edge insert; when the mold opens, the elastic stripper ring pushes the cover material out of the mold cavity, preventing the cover material from sticking to the upper mold.

[0022] Compared with the prior art, the present invention has the following outstanding substantive features and significant progress: (1) Synergistic effect of layered composite structure and molded reinforcing ribs: This invention combines a rigid reinforcing core layer (paper-aluminum foil composite layer) with a molded annular + radially radial discontinuous reinforcing rib structure. The two are not simply superimposed functions, but produce a significant synergistic effect. The aluminum foil layer in the rigid reinforcing core layer undergoes microscopic plastic deformation during the molding process, forming a tighter entanglement structure with the paper fibers. At the same time, the bottom of the pits of the discontinuous reinforcing ribs generates pre-compressive stress on the aluminum foil layer, which significantly enhances the aluminum foil layer's ability to resist external loads in subsequent use. Experiments show that, under the condition of similar total thickness of the cover material, the bending stiffness of the cover material of this invention is increased by about 45%-70% compared with the control sample that only increases the thickness of the substrate, while the material cost only increases by about 8%-15%.

[0023] (2) The non-obviousness of the discontinuous reinforcing rib structure: In the prior art, if a reinforcing rib structure is adopted, a continuous rib design is generally used. However, the present invention creatively discovers that designing the reinforcing rib as discontinuous (each rib segment is 8-12mm long, with a 2-3mm gap between segments) can simultaneously achieve three technical effects: First, it eliminates stress concentration caused by continuous long ribs, preventing the cover material from cracking at the rib position; second, the gap forms a weak "flexible hinge" effect, making the cover material less prone to overall collapse when manually opening and bending; third, the discontinuous structure reduces the local deformation resistance during molding, making the rib forming clearer and the demolding springback smaller. Those skilled in the art could not have foreseen that the discontinuous structure could simultaneously solve the above three technical problems based on the prior art, and this design choice exceeds the conventional design capabilities of those skilled in the art.

[0024] (3) Layout of the water-filtering opening area and the reinforcing ribs: This invention creatively places the water-filtering opening area at an off-center position on the cover surface, and ensures that the micro-indentation completely avoids the reinforcing rib structure. This layout design solves the technical problem of mutual interference between the water-filtering cut and the reinforcing rib in the prior art—if the micro-indentation passes through the reinforcing rib area, the microstructure of the material at the rib has been altered by molding (change in fiber orientation, pre-compression of aluminum foil). Setting a cut in this area will cause the crack to extend along the direction of the rib during tearing, resulting in an unexpected tearing path and wrinkles on the cover surface. Through the off-center layout and the micro-indentation avoidance design, this invention maintains the overall structural integrity of the cover material while ensuring the water-filtering function.

[0025] (4) Synergy of zoned temperature control and negative pressure adsorption in the molding die: The mold of this invention adopts a zoned heating scheme with the upper mold at 95-120℃ and the lower mold at 60-85℃, combined with the negative pressure venting micropores of the cavity mold to adsorb and fix the sheet material. This combination scheme solves the contradiction between the positioning accuracy and the forming quality of the ribs in the high-speed molding process of thin sheets (80-140μm): negative pressure adsorption ensures that the sheet material is completely attached to the cavity before mold closing, eliminating wrinkles and offset; zoned temperature control makes the temperature of the upper mold higher than that of the lower mold, ensuring that the cover material is fully softened in the rib area to complete plastic deformation, while the relatively low temperature of the lower mold can prevent the heat-sealing functional layer from excessive melting and sticking to the mold cavity, ensuring smooth demolding. Those skilled in the art would find it difficult to obtain the technical inspiration for this specific temperature gradient and negative pressure adsorption combination from the prior art.

[0026] Compared with the prior art, the present invention has the following advantages: (1) Synergistic achievement of high stiffness and lightweight: This cover material adopts a rigid reinforced core paper-aluminum composite structure, combined with a ring-shaped and radial discontinuous reinforcing ribs molded in one piece. Without significantly increasing the total thickness of the cover material (80-140μm), the bending stiffness of the cover material is greatly improved (≥120mN), and it is not easy to dent or warp under pressure when stacked. According to the test, in Example 1 with a total thickness of 112μm, the bending stiffness reached 145mN, which is about 71% higher than that of conventional plain paper aluminum-plastic cover material of the same thickness (about 85mN); in Example 3 with a thickness of 138μm, the bending stiffness reached 168mN, which is about 60% higher than that of conventional products of the same thickness (about 105mN).

[0027] (2) Significantly improved opening and filtration performance: The cover material is less prone to collapsing and wrinkling when opening the cover or tearing the filter outlet, improving the user experience. The micro-indentation of the filter avoids the reinforcing ribs, ensuring smooth opening and controllable tearing path without abnormal tearing.

[0028] (3) One process completes two functions: matching molding mold, one mold closing simultaneously completes two processes: cover material punching and cutting, and reinforcing rib hot pressing and shaping; the reinforcing rib insert is detachable, and different rib layout inserts can be quickly replaced to adapt to different specifications of cover material; the cavity is negative pressure exhaust, the hot pressing zone temperature control, the rib forming is clear, the springback after demolding is small, and it is suitable for high-speed continuous die cutting production of roll material, with a production speed of 80-120 times / minute.

[0029] (4) Compatible with existing production lines and controllable costs: The lid material retains good heat-sealing performance and is compatible with existing high-speed heat-sealing production lines for barrelled food. It does not require modification of the heat-sealing equipment, and takes into account barrier properties, easy-tear and water-filtering functions, while controlling material costs. Compared with the solution of simply thickening the base material, the material cost increases by no more than 15%, while the stiffness is improved by more than 45%. Attached Figure Description

[0030] Figure 1This is a structural schematic diagram of the high stiffness cover material of this application; Figure 2 This is a top view of the cover material; Figure 3 This is a schematic diagram of the molding die structure for the cover material; Figure 4 for Figure 3 A schematic diagram of direction A; Figure 5 This is a schematic diagram of the raised ribs of the upper mold and the groove structure of the lower mold.

[0031] In the attached diagram, 1-Printed surface layer; 2-Rigid reinforcing core layer; 3-Adhesive composite layer; 4-Heat-sealing functional layer; 6-Annular circumferential rib; 7-Radial radial rib; 8-Upper mold base; 9-Reinforcing rib punch insert; 10-Cutting edge insert; 11-Lower mold base; 12-Cutting edge; 13-Cover material cavity die; 91-Raised rib; 92-Exhaust micropore. Detailed Implementation

[0032] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Those skilled in the art should understand that the following embodiments are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention. The raw materials of the cover material of the present invention are all food packaging grade materials. The composite processing is completed by using existing paper-aluminum-plastic composite equipment to complete the layer-to-layer composite. The forming process uses the special forming mold of the present invention to perform hot pressing and die cutting on the composite roll and sheet material.

[0033] Example 1

[0034] like Figures 1-4 As shown, this embodiment is a conventional commercial containerized noodle filter cover, and the finished cover is suitable for food containers with a diameter of 162mm.

[0035] The cover material consists of, from the outside in, a printed surface layer 1, a rigid reinforcing core layer 2, an adhesive composite layer 3, and a heat-sealing functional layer 4. The printed surface layer 1 is made of food-grade PET printing film, 18μm thick, with product patterns and text printed on the surface using water-based inks. It is abrasion-resistant and meets the visual display requirements of the outer packaging. The rigid reinforcing core layer 2 is the core load-bearing layer for the stiffness of this cover material. It uses a modified paper-aluminum foil dry composite, with the paper layer made of high-stiffness food packaging paper with a basis weight of 100g / m². 2The aluminum foil is made of soft food-grade aluminum foil with a thickness of 8μm. The paper layer and aluminum foil are dry-laminated using a dry-bonding adhesive. The aluminum foil effectively blocks oxygen and moisture, preventing the dough inside the container from becoming damp and spoiling. The bonding composite layer 3 is a PE extrusion composite layer with a thickness of 22μm. Through an extrusion thermal lamination process, the rigid reinforcing core layer 2 and the heat-sealing functional layer 4 are firmly bonded together as a whole, with an interlayer peel force ≥2.5N / 15mm, preventing the multi-layer structure from delaminating during use. The heat-sealing functional layer 4 is a modified polyolefin heat-sealing film with a thickness of 28μm. This material has good heat-sealing compatibility with PP and PE container openings. After heat sealing, the peel force of the heat-sealed edge is in the range of 8-15N / 15mm, ensuring a leak-proof seal during transportation while also allowing for easy manual tearing. In this embodiment, the total thickness of the lid material is 112μm, and the measured bending stiffness is 145mN.

[0036] The cover area is provided with a discontinuous reinforcing rib structure formed by molding, including annular circumferential ribs 6 and radial radial ribs 7; The reinforcing ribs are a downwardly recessed structure with a depth of 0.25mm. Strict control is maintained to prevent the ribs from penetrating the rigid reinforcing core layer 2, thus preventing aluminum foil layer breakage and barrier performance failure. The annular circumferential ribs 6 are 4mm from the inner side of the heat-sealing edge. There are a total of 12 radial ribs 7, evenly distributed at equal angles along the circumference. Each radial rib 7 extends inward from the annular circumferential rib 6 to the center area of ​​the cover. All ribs adopt a discontinuous segmented structure, with each segment 8-12mm long and a 2-3mm gap between segments to eliminate stress concentration caused by continuous long ribs and prevent cracking of the cover material at the rib locations. The drainage opening area is located off-center on the cover, avoiding the center of the cover material and the reinforcing rib area. The drainage opening area has discontinuous micro-indentations that completely avoid all reinforcing ribs. The micro-indentations only weaken the local material strength without cutting the cover material. Users can tear along the micro-indentations to create a drainage notch for mixing and draining the noodles. The outermost ring of the lid is a heat-sealing edge, used to complete the heat-sealing welding with the mouth of the barrel.

[0037] This embodiment is equipped with a molding die, including an upper die assembly and a lower die assembly. The upper die assembly consists of an upper die base 8, a reinforcing rib punch insert 9, and a cutting edge insert 10. The reinforcing rib punch insert 9 is detachably embedded in the upper die base using screws, facilitating later maintenance and replacement of inserts with different rib types. The lower end face of the reinforcing rib punch insert 9 is machined with discontinuous raised ribs 91 that perfectly match the reinforcing ribs of the cover material. The raised ribs 91 have a height of 0.25mm and a width of 1.2mm. The raised ribs 91 have a discontinuous structure.

[0038] The cutting edge insert 10 is arranged around the reinforcing rib punch insert 9 to punch out the outer contour of the circular cover material. The lower die assembly includes a lower die base 11 and a cover material cavity die 13; the bottom surface of the cavity die is densely covered with venting micro-holes 92 and grooves, the grooves corresponding to the raised ribs 91, the micro-hole diameter is 0.15mm, and all venting micro-holes 92 are connected to an external negative pressure suction mechanism. The mold is equipped with an independent zone heating assembly, the upper die assembly temperature is set to 105℃, and the lower die temperature is set to 72℃; an elastic stripper ring is arranged around the outer side of the cutting edge insert 10.

[0039] Actual production process: The completed capping material roll is continuously conveyed into the mold station, and the sheet is laid flat on the capping material cavity die 13. The external negative pressure suction mechanism is activated, and the sheet is tightly adsorbed and attached to the surface of the cavity through the exhaust micro-holes 92, eliminating defects such as wrinkles and misalignment of the sheet. Then, the upper mold closes downward as a whole, and the cutting edge insert 10 first contacts the sheet to complete the punching of the outer contour of the capping material. At the same time, the reinforcing rib punch insert 9 applies hot pressure to the capping material surface, pressing out discontinuous reinforcing ribs that are recessed downward on the surface of the capping material. Under the action of hot pressing temperature, the internal fibers of the rigid reinforcing core layer 2 and the aluminum foil undergo micro-plastic deformation, realizing the shaping of the rib structure. After a holding time of 0.3-0.5s, the upper mold opens upward, and the elastic unloading ring around the outside pushes the formed capping material out of the mold cavity, preventing the capping material from adhering to the upper mold insert, completing a single-cycle cutting-rib forming. The roll material continues to be fed into the next forming cycle, which is compatible with high-speed roll die-cutting production lines, with a production speed of 80-120 times / minute.

[0040] Example 2

[0041] This embodiment focuses on lightweight and economical water filter cover materials, suitable for small-sized bucket-packaged noodles. The overall structure is largely the same as in Embodiment 1, with the difference lying in the material parameters and mold process parameters. The printed surface layer 1 is made of food-grade coated paper with a thickness of 15μm; the rigid reinforcing core layer 2 has a paper weight of 80g / m². 2 The aluminum foil thickness is 6μm; the adhesive composite layer 3 is 15μm thick; the heat-sealing functional layer 4 is 20μm thick; the total thickness of the cover material is 86μm, and the measured bending stiffness is 122mN, which meets the deformation resistance requirements of basic stacking. The rib depth is set to 0.15mm, and the rib width is 0.8mm. The mold heating parameters are adjusted to 95℃ for the upper mold and 60℃ for the lower mold, with a holding time of 0.25s. This embodiment uses less material and has a lower material cost, making it suitable for low-end economical products. Because the overall substrate thickness is relatively small, the rib depth is correspondingly reduced to avoid excessive rib pressure causing the aluminum foil layer to be crushed; the negative pressure adsorption pressure is moderately increased to ensure that the thin sheet material is fully attached to the cavity die 13, preventing the rib forming outline from becoming blurred. In this embodiment, the bending stiffness of the cover material just reaches the lower limit of the index of 120mN, which can meet the conditions of conventional warehouse stacking, but is not suitable for ultra-high stacking conditions.

[0042] Example 3

[0043] This embodiment is designed for high-stack storage conditions, specifically for large-capacity, bulk-packaged ready-to-eat products, where the lid material requires high resistance to denting and warping. The printed surface layer 1 is made of PET printing film with a thickness of 25μm; the rigid reinforcing core layer 2 is a paper layer with a basis weight of 120g / m². 2 The aluminum foil thickness is 12μm; the adhesive composite layer 3 thickness is 30μm; the heat-sealing functional layer 4 thickness is 35μm; the total thickness of the cover material is 138μm, and the measured bending stiffness is 168mN. The rib depth is 0.4mm, and the rib width is 2.0mm; 16 radial ribs are set to further improve the rigidity of the cover surface. The mold zone heating component is adjusted to the upper mold temperature of 120℃ and the lower mold temperature of 85℃, and the mold closing pressure holding time is extended to 0.5-0.7s to ensure that the rigidity-enhancing core layer 2 undergoes sufficient micro-plastic deformation and reduce the springback after the ribs are demolded. The reinforcing rib punch insert 9 is made of high-strength mold steel to withstand greater hot pressure loads; the negative pressure suction mechanism maintains normal operation to ensure accurate positioning of the thick sheet material. The cover material of this embodiment has strong resistance to pressure deformation and can withstand higher storage stacking layers. The cover surface is not prone to denting under transportation bumps, but the material cost is higher than that of Embodiment 1.

[0044] Example 4

[0045] This embodiment, based on Embodiment 1, features a variant design for the reinforcing rib layout. The radial ribs 7 are arranged in a staggered pattern of long and short ribs, with some radial ribs extending only to half the length of the lid surface and not directly reaching the center. The annular circumferential ribs 6 are positioned 6mm from the inner side of the heat-sealing edge. The indentation depth of the micro-indentation in the filter opening area is reduced, further enhancing the overall crack resistance of the lid material. The thickness of the remaining material layers and the mold temperature parameters remain consistent with Embodiment 1. This layout is suitable for large-diameter lid materials, effectively alleviating stress concentration at the center of the lid material, and is suitable for large-size food container lid materials with a diameter greater than 170mm.

[0046] Comparative Example 1 A commercially available ordinary paper-aluminum-plastic filter cover with a total thickness of 110μm was selected. Its layer structure is similar to that of the cover material of this invention, but it lacks the molded reinforcing ribs. Testing revealed that this conventional cover material has a bending stiffness of only 85mN; in a simulated warehouse stacking test, after being stacked at a height of 1.2m for 72 hours, the cover surface showed significant indentation and warping; when the filter was manually opened, the cover material collapsed, and the surface wrinkled and deformed, resulting in a poor user experience. The comparison shows that, with a similar total thickness, this invention, through a composite layer combined with a molded reinforcing rib structure, significantly improves the stiffness of the cover material and its resistance to deformation.

[0047] Comparative Example 2 To verify the inventiveness of the discontinuous stiffener structure compared to the continuous structure, a comparative example 2 was set up: based on the material system and mold of Example 1, the stiffeners were changed from discontinuous to continuous (i.e., the stiffeners have no gaps, forming a complete ring + continuous radial stiffeners), while other parameters remained unchanged. Test results showed that the initial bending stiffness of the cover material in Comparative Example 2 was comparable to that of Example 1 (approximately 142 mN vs 145 mN). However, after a simulated transportation vibration test (amplitude 5 mm, frequency 10 Hz, duration 2 h), visible microcracks appeared at the edges of the stiffeners in Comparative Example 2, and the bending stiffness decreased to 118 mN, a decrease of approximately 17%; while the bending stiffness of Example 1 only decreased to 138 mN after the same vibration test, a decrease of approximately 5%. This result fully demonstrates that the structural stability of the discontinuous stiffener structure under long-term dynamic loads is significantly better than that of the continuous structure, an effect that cannot be foreseen by those skilled in the art through conventional design choices.

[0048] The lids prepared in Examples 1-3 were selected for comprehensive performance testing, including interlayer peel strength, heat seal strength, flexural stiffness, drop stacking test, and filter opening performance. The interlayer peel strength of the lids in Examples 1-3 was greater than 2.3 N / 15 mm, with no delamination; the heat seal strength met the sealing requirements for barrelled food; after the stacking simulation test, the lids showed no obvious dents or warping; the filter opening area was easily torn without abnormal tearing, fully meeting the actual usage requirements of ready-to-eat barrelled products.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-stiffness cover material, characterized in that, It includes a printed surface layer (1), a rigid reinforcing core layer (2), an adhesive composite layer (3), and a heat-sealing functional layer (4) arranged sequentially from the outside to the inside; the cover material is molded as a whole, and the cover area of ​​the cover material is provided with an integrally pressed reinforcing rib structure, the outer periphery of the cover material is provided with a heat-sealed edge, and the cover area is also provided with a tearable filter opening area.

2. The high stiffness cover material according to claim 1, characterized in that, The printed surface layer (1) is coated paper or PET printing film, the thickness of the printed surface layer (1) is 12-25μm, and a printed pattern layer is provided on the surface of the printed surface layer (1).

3. The high stiffness cover material according to claim 2, characterized in that, The rigid reinforced core layer (2) is a high stiffness modified paper-aluminum foil composite layer with a paper layer basis weight of 80-120 g / m². 2 The aluminum foil thickness providing barrier properties is 6-12μm, and the paper layer and aluminum foil are bonded together by dry composite bonding.

4. The high stiffness cover material according to claim 3, characterized in that, The adhesive composite layer (3), which thermally combines the rigid reinforcing core layer and the heat-sealing functional layer, is a PE extrusion composite layer with a thickness of 15-30μm.

5. A high stiffness cover material according to claim 3, characterized in that, The heat-sealing functional layer (4) is a modified polyolefin heat-sealing film with a thickness of 20-35 μm.

6. A high stiffness cover material according to claim 5, characterized in that, The reinforcing rib structure is a downwardly recessed rib formed by molding, with a rib depth of 0.15-0.4mm. The rib does not penetrate the rigid reinforcing core layer (2). The reinforcing rib structure includes an annular circumferential rib (6) and multiple radial ribs (7). The annular circumferential rib (6) is 3-6mm away from the inner side of the heat-sealed edge of the cover material. The radial ribs (7) extend inward from the annular circumferential rib to the center area of ​​the cover surface. The multiple radial ribs (7) are evenly arranged along the circumference. The reinforcing rib is a discontinuous rib.

7. A high stiffness cover material according to claim 6, characterized in that, The total thickness of the cover material is controlled between 80-140μm.

8. A molding die for a high-stiffness cap material, using the high-stiffness cap material according to any one of claims 1-7, characterized in that, It includes an upper mold assembly and a lower mold assembly; the upper mold assembly includes an upper mold base (8), a cutting edge insert (10), and a reinforcing rib punch insert (9); the lower mold assembly includes a lower mold base (11) and a cover material cavity die (13).

9. The molding die for a high stiffness cap material according to claim 8, characterized in that, The reinforcing rib punch insert (9) is detachably embedded inside the upper mold base (8); the lower end face of the reinforcing rib punch insert (9) is provided with a raised rib that is completely matched with the reinforcing rib structure of the cover material, the raised rib height is 0.15-0.4mm and the rib width is 0.8-2.0mm; the raised rib is a discontinuous structure; the cutting edge insert (10) is arranged around the periphery of the reinforcing rib punch insert (9); the bottom surface of the cavity of the cover material cavity die (13) of the lower mold assembly is distributed with several exhaust micro-holes, the diameter of the exhaust micro-holes is 0.1-0.2mm, and they are connected to the external negative pressure suction mechanism; when the mold is closed, the negative pressure adsorbs the sheet material to prevent the sheet material from wrinkling or shifting, and ensures that the outline of the rib forming is clear.

10. The molding die for a high stiffness cap material according to claim 9, characterized in that, The mold has a built-in partitioned heating component; the temperature of the upper mold component is controlled at 95-120℃, and the temperature of the lower mold is 60-85℃; the rib forming is completed under hot pressing, so that the rigid reinforced core layer (2) undergoes micro-deformation and shaping.

Images