Rebound composite sheet and preparation method thereof

Abstract

The invention discloses a springback type composite sheet and a preparation method thereof, and belongs to the technical field of composite sheets. The sheet comprises an inner layer, a springback layer, a blocking layer and an outer layer which are sequentially arranged in a stacked mode. The base material of the rebound layer is polyester or polyamide, the tensile strength of the rebound layer is limited to be larger than or equal to 150 MPa, the elongation at break of the rebound layer is larger than or equal to 50%, the thickness of the rebound layer is 10-30 microns, meanwhile, the melt flow rate of the polyester under the condition of 275 DEG C / 2.16 kg is controlled to be 5-20 g / 10 min, and / or the melt flow rate of the polyamide under the condition of 235 DEG C / 2.16 kg is controlled to be 5-18 g / 10 min. The springback layer further comprises functional auxiliaries such as maleic anhydride grafted polyethylene and oxazoline grafted polyolefin, and polyester or polyamide is preferably subjected to two-way stretching treatment. The preparation method comprises the following steps: performing corona treatment on each layer of substrate film, sequentially compounding each layer at different temperatures and pressures by adopting a step-by-step dry-method compounding process, and finally performing curing treatment. The method is used for improving the rebound resilience of the composite sheet packaging.

Description

Technical Field

[0001] This invention relates to the field of composite sheet technology, and specifically to a resilient composite sheet and its preparation method. Background Technology

[0002] In the field of daily chemical product packaging, packaging toothpaste, cosmetics, and other products in tube form has become the industry mainstream. The core requirements for this packaging include good flexibility, barrier properties, formability, and, crucially, resilience. Ideally, after the contents are extruded, the pressed area of ​​the tube should quickly and completely spring back to its initial shape. This not only effectively reduces the entry of external air and moisture into the tube, preventing oxidation and deterioration of the contents, but also maintains the tube's aesthetic appearance and enhances the user experience.

[0003] Currently, most commercially available flexible tubing sheets use polyethylene as the base material and are composited with barrier materials. While this structure can meet basic packaging and barrier requirements, its resilience is generally poor: the compressed tubing is prone to collapse and deformation, unable to quickly return to its original shape, and may even develop permanent deformation after long-term use, affecting the reliability and appearance of the packaging.

[0004] To overcome the rebound problem, existing technologies typically take two approaches: one is to simply increase the overall thickness of the sheet, but this directly leads to a decrease in the flexibility of the hose and a stiff feel when extruding the contents; the other is to try to modify PE by mixing rubber-like elastomers, but due to the poor compatibility between the two, it is easy to cause problems such as interlayer separation and material embrittlement, while also increasing production costs.

[0005] Therefore, developing a new composite material structure that can improve the resilience of hoses without sacrificing flexibility and economy has become an urgent technical need in the industry. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and solve at least one of the problems in the background art.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0008] A resilient composite sheet includes an inner layer, a resilient layer, a barrier layer, and an outer layer stacked sequentially; the substrate of the resilient layer is selected from at least one of polyester or polyamide, with a tensile strength ≥150MPa, an elongation at break ≥50%, and a thickness of 10~30μm; the polyester has a melt flow rate of 5~20g / 10min at 275℃ / 2.16kg, and / or the polyamide has a melt flow rate of 5~18g / 10min at 235℃ / 2.16kg.

[0009] As a preferred technical solution, the rebound layer comprises, by mass percentage, 72%~88% polyester and / or polyamide, 6%~15% maleic anhydride-grafted polyethylene, 3%~8% oxazoline-grafted polyolefin, 0.2%~2% flow promoter, and 0.2%~2% foaming agent.

[0010] As a preferred technical solution, the preparation method of the oxazoline-grafted polyolefin includes carrying out a free radical grafting reaction of polyolefin resin and oxazoline monomer in the presence of an organic peroxide initiator during melt extrusion. The amount of initiator added is 0.1% to 1% of the mass of the polyolefin resin, and the reaction temperature is 180 to 220°C.

[0011] As a preferred technical solution, the oxazoline monomer in the oxazoline-grafted polyolefin is selected from at least one of 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline.

[0012] As a preferred technical solution, in the elastic layer, the polyester is selected from at least one of polyethylene terephthalate, polybutylene terephthalate, and polybutylene naphthalate treated by biaxial stretching process; the polyamide is selected from at least one of polycaprolactam, polyhexamethylene adipamide, and polydodecanoic acid lactam treated by biaxial stretching process.

[0013] As a preferred technical solution, the biaxial stretching treatment of the polyester in the elastic layer includes: stretching the polyester longitudinally by 3 to 4 times and then stretching it transversely by 3 to 4 times above the glass transition temperature and below the melting point, followed by heat setting treatment; the biaxial stretching treatment of the polyamide includes: stretching the polyamide longitudinally by 2.5 to 3.5 times and then stretching it transversely by 2.5 to 3.5 times above the glass transition temperature and below the melting point, followed by heat setting treatment.

[0014] As a preferred technical solution, the substrate of the inner layer and / or outer layer is selected from at least one of low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and polyolefin elastomer; the thickness of the inner layer is 50-80 μm, and the thickness of the outer layer is 80-140 μm.

[0015] As a preferred technical solution, the substrate of the barrier layer is selected from at least one of ethylene-vinyl alcohol copolymer, polyvinylidene chloride, aluminized polyester film, and silica-coated polyester film; the thickness of the barrier layer is 10~25μm.

[0016] As a preferred technical solution, the inner layer and / or outer layer are made of embossed film, and the surface of the embossed film is provided with an embossed pattern with a depth of 5~20μm and a line density of 80~200 lines / inch.

[0017] In a second aspect, the present invention provides a method for preparing a resilient composite sheet as described in any of the preceding claims, characterized by comprising the following steps: S01. Corona treatment is performed on the inner layer, the elastic layer, the barrier layer and the outer layer substrate film respectively to make their surface tension ≥38mN / m; S02. Apply an adhesive to one side of the resilient layer and dry-laminate it with the inner substrate film. The lamination temperature is 60~75℃ and the lamination pressure is 0.3~0.5MPa. S03. Apply an adhesive to the other side of the rebound layer and dry-laminate it with the barrier layer substrate film. The lamination temperature is 70~80℃ and the lamination pressure is 0.35~0.45MPa. S04. Apply an adhesive to the other side of the barrier layer and dry-laminate it with the outer substrate film. The lamination temperature is 65~80℃ and the lamination pressure is 0.4~0.5MPa. S05. The composite sheet is cured at 40~50℃ for 24~48 hours to obtain the elastic composite sheet.

[0018] The advantages and beneficial effects of this invention are as follows: Through a multi-layer structural design, a balanced optimization of flexibility, barrier properties, and high resilience is achieved in the flexible sheet material. This invention uses polyester or polyamide as the substrate for the resilience layer, utilizing its strong molecular chain rigidity and high crystallinity to form an ordered microstructure under biaxial stretching, thereby endowing the material with excellent elastic recovery capabilities. By introducing maleic anhydride-grafted polyethylene and oxazoline-grafted polyolefin, the interfacial compatibility and bonding strength between the polyester / polyamide and polyethylene inner and outer layers are improved. Their reactive functional groups can chemically react with the polyester end groups and polyamide amide bonds, constructing a stable cross-linked network between layers, effectively inhibiting delamination and improving the overall structural durability.

[0019] Furthermore, this invention, through a dry composite process, achieves a strong bond between layers while preserving the orientation structure and mechanical properties of the resilience layer to the maximum extent. The resulting composite sheet exhibits superior resilience performance under simulated usage conditions compared to traditional composite structures, overcoming problems such as decreased flexibility and poor compatibility caused by simply increasing thickness or adding elastomers. Detailed Implementation

[0020] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. It is to be understood that the specific embodiments described herein are merely illustrative of this application and not intended to limit it. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0021] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] This invention provides a resilient composite sheet and its preparation method. This sheet can be used for tube packaging in toothpaste, cosmetics, etc., solving the technical problems of insufficient resilience and easy deformation in existing tube sheets, while maintaining good flexibility, barrier properties, and formability. The sheet comprises an inner layer, a resilient layer, a barrier layer, and an outer layer stacked sequentially. The substrate of the resilient layer is selected from at least one of polyester or polyamide, and it must meet the key performance indicators of tensile strength ≥150MPa, elongation at break ≥50%, and thickness of 10~30μm. Furthermore, the melt flow rate (MFR) of the polyester at 275℃ / 2.16kg is limited to 5~20g / 10min, and / or the MFR of the polyamide at 235℃ / 2.16kg is limited to 5~18g / 10min.

[0024] This invention selects polyester or polyamide as the main material for the resilience layer, primarily based on their high molecular chain rigidity and ease of crystallization. The material should have a tensile strength ≥150MPa to indicate its basic resilience and prevent yielding or breakage of the resulting product during extrusion. An elongation at break ≥50% indicates good basic ductility and toughness of the surface material. The thickness selection considers the balance between overall sheet thickness, resilience, and flexibility. Too thin a sheet results in insufficient mechanical support and weak resilience; too thick a sheet may lead to excessive overall rigidity and reduced flexibility.

[0025] The molecular weight ratio (MFR) of polyester and polyamide were limited to the above ranges. A low MFR indicates high melt viscosity and poor flowability, which can easily lead to uneven plasticization, film defects, and stress concentration during subsequent film preparation or co-extrusion lamination, affecting the uniformity of the rebound layer and its final mechanical properties. A high MFR, on the other hand, indicates a low molecular weight or insufficient branching. While this makes processing easier, the tensile strength, toughness, and creep resistance of the finished product will decrease accordingly, resulting in a weakened shape recovery effect of the rebound layer and an inability to provide rapid and strong recovery force after extrusion.

[0026] In this invention, the inner layer, which directly contacts the contents, must possess good chemical stability, flexibility, and heat-sealing properties; the outer layer, serving as the printing and appearance layer, must provide wear resistance, weather resistance, and aesthetics; the barrier layer is used to block oxygen and water vapor, protecting the contents. The intermediate rebound layer, located in the middle, serves the structural function of providing elastic recovery force.

[0027] In some embodiments, the resilient layer comprises, by weight percentage, 72% to 88% polyester and / or polyamide; 6% to 15% maleic anhydride-grafted polyethylene; 3% to 8% oxazoline-grafted polyolefin; 0.2% to 2% flow promoter; and 0.2% to 2% foaming agent.

[0028] As a continuous phase, the content of polyester / polyamide determines the matrix strength and elastic modulus of the resilience layer; if the content is too low, the matrix properties will be excessively diluted, and sufficient strength and resilience cannot be guaranteed; if the content is too high, the addition of other functional additives will not be sufficient to achieve the modification target.

[0029] Maleic anhydride-grafted polyethylene (MAH-g-PE) primarily functions as a compatibilizer and toughening agent. The polyolefin segments of MAH-g-PE exhibit good compatibility with non-polar polyethylene inner / outer layer materials. Furthermore, the grafted maleic anhydride groups (-CO-O-CO-) can chemically react with the terminal hydroxyl (-OH), terminal carboxyl (-COOH), or terminal amino (-NH2) groups of the polyester or polyamide at processing temperatures, forming chemical bonds or strong hydrogen bonds. This improves the interfacial adhesion between the polar polyester / polyamide matrix and the non-polar polyolefin inner and outer layers, mitigating to some extent the problem of delamination in traditional composite structures due to poor interfacial compatibility. Simultaneously, as an elastomer dispersed within a rigid matrix, MAH-g-PE can induce crazes and shear bands, absorbing impact energy and enhancing the material's toughness without excessively reducing its modulus.

[0030] Oxazoline-grafted polyolefins are used to construct moderate intermolecular crosslinking networks to enhance resilience. The oxazoline group (especially 2-oxazoline) is a highly reactive heterocycle that, at melt blending temperatures, can undergo ring-opening addition reactions with the carboxyl groups of polyesters and the amino or carboxyl groups of polyamides, forming amide ester bonds or diamide bonds. This reaction introduces controllable chemical crosslinking points between the polyester / polyamide molecular chains. This crosslinking network forms a loose physicochemical crosslinking structure. On the one hand, it increases the entanglement density between molecular chains, improving melt strength and creep resistance, making the material more likely to recover to its initial low entropy state after deformation; on the other hand, these crosslinking points can act as temporary crosslinking points, storing elastic potential energy during material compression deformation, driving rapid chain retraction when the external force is removed. Therefore, the introduction of oxazoline-grafted polyolefins can enhance the elastic recovery driving force of the material.

[0031] Flow promoters are used to improve the processing performance of composite sheets in subsequent thermoforming processes (such as hose forming). In processes like high-frequency heat sealing and shoulder forming of hoses, the sheet needs to undergo plastic flow under specific temperature and pressure to form a particular shape. Adding appropriate amounts of flow promoters (such as low molecular weight polyethylene wax, stearates, or specific polymer processing aids) can reduce melt viscosity, decrease friction between polymer chains, and improve melt uniformity and flowability. This ensures that during thermoforming, the layers deform more harmoniously, avoiding stress concentration, interlayer delamination, or poor forming due to differences in flowability.

[0032] Foaming agents need to be combined with specific vacuum treatment processes. Vacuum treatment is required during the mixing process of sheet extrusion or calendering. During this process, the foaming agent (such as sodium bicarbonate or azodicarbonamide) decomposes upon heating, generating trace amounts of gas. The instantaneous gas flow and weak volumetric disturbances generated by this decomposition create microscopic turbulence and shear fields in the melt. This can break up any localized component agglomeration or concentration gradients that may exist in the melt, promoting the uniform dispersion of substances such as maleic anhydride-grafted polyethylene and oxazoline-grafted polyolefins in the polyester / polyamide continuous phase. Under vacuum, these gases cannot form macroscopic bubbles. Adding a foaming agent to improve dispersion can reduce defects to some extent, thereby alleviating and preventing film warping or deformation.

[0033] It should be noted that if the microporous structure is found to limit the implementation of the biaxial stretching process during processing, it is necessary to reduce the amount of foaming agent, or to overcome this by increasing the vacuum level or extending the mixing time.

[0034] In some embodiments, the preparation method of oxazoline-grafted polyolefins includes: subjecting a polyolefin resin (such as polyethylene, polypropylene, or ethylene-octene copolymer) to an oxazoline monomer (such as 2-vinyl-2-oxazoline) in a twin-screw extruder at a melt temperature of 180-220°C in the presence of an organic peroxide initiator (such as dicumyl peroxide DCP). The amount of initiator added is 0.1%-1% of the mass of the polyolefin resin. This method utilizes free radicals to abstract tertiary hydrogen atoms from the polyolefin chain, forming macromolecular free radicals, which then undergo graft copolymerization with the vinyl groups of the oxazoline monomer. The resulting product is mainly a polyolefin with highly active oxazoline groups on its side chains.

[0035] In some embodiments, to further improve the orientation and mechanical isotropy of the resilient layer, the polyester or polyamide is preferably treated with a biaxial stretching process. Specifically: The polyester is selected from polyethylene terephthalate (BOPET) and polybutylene terephthalate (BOPBT) processed by biaxial stretching. The biaxial stretching process typically involves: first, longitudinal stretching of 3-4 times within a temperature range (e.g., 90-120°C) above its glass transition temperature (approximately 70-80°C) and below its melting point (approximately 250-260°C), to initially orient the molecular chains along the extrusion direction; then, transverse stretching of 3-4 times at a higher temperature (e.g., 110-130°C), to bidirectionally orient the molecular chains in the plane; finally, heat setting at a temperature above the stretching temperature but below the melting point (e.g., 200-230°C) to eliminate internal stress, fix the orientation structure, and improve crystallinity and dimensional stability. BOPET films treated in this way have highly oriented and crystalline molecular chains, exhibiting considerable tensile strength and modulus in the film plane. Furthermore, due to the entropic elasticity of the orientation structure, they exhibit a tendency to spring back when compressed in a direction perpendicular to the film plane.

[0036] Polyamides are selected from polycaprolactam (BOPA) and other materials processed by biaxial stretching. The biaxial stretching process window differs from that of polyesters, typically occurring at temperatures higher than its glass transition temperature (approximately 40-50°C) but much lower than its melting point (approximately 220°C). For example, longitudinal stretching of 2.5-3.5 times is performed first at 60-90°C, followed by transverse stretching of 2.5-3.5 times within a similar temperature range. Due to the strong hydrogen bonds between polyamide molecules, its heat setting temperature is usually set at (e.g., 100-130°C) for heat relaxation treatment to improve crystallization and stabilize dimensions.

[0037] In some embodiments, the substrate of the inner and / or outer layers is selected from at least one of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and polyolefin elastomer (POE). These materials have good flexibility, low-temperature resistance, excellent processability, and moderate cost. The inner layer thickness is preferably 50-80 μm to ensure sufficient sealing strength and compatibility with the contents; the outer layer thickness is preferably 80-140 μm to provide good mechanical protection, printability, and appearance.

[0038] In some embodiments, the substrate of the barrier layer is selected from ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), aluminized polyester film (VMPET), and silica-coated polyester film (SiO2). x At least one of (PET).

[0039] In some embodiments, to increase the friction of the hose surface and improve the user experience, the inner and / or outer layers may be made of embossed film. The surface of the embossed film has a fine embossed pattern with a depth of 5-20 μm and a linear density of 80-200 lines per inch (LPI). This embossing is typically formed online or offline using a dedicated embossing roller after the sheet is laminated and cured.

[0040] The present invention also provides a method for preparing the above-mentioned resilient composite sheet, comprising the following steps: S01. Corona treatment is performed on the inner layer, the elastic layer, the barrier layer and the outer layer substrate film respectively to make their surface tension ≥38mN / m.

[0041] S02. Apply polyurethane adhesive (or acrylate or epoxy adhesive) to one side of the rebound layer, and then dry-laminate it with the inner substrate film that has been corona-treated.

[0042] S03. Apply an adhesive to the other side of the rebound layer and dry-laminate it with the corona-treated barrier layer substrate film.

[0043] S04. Apply an adhesive to the other side of the barrier layer and dry-laminate it with the corona-treated outer substrate film.

[0044] S05. The composite sheet is introduced into the curing chamber and cured at 40~50℃ for 24~48 hours.

[0045] The curing process allows the -NCO groups in the polyurethane adhesive to undergo a full cross-linking reaction with the film surface or the adhesive itself, generating a polyurethane network structure, thereby maximizing the interlayer peel strength.

[0046] In some production embodiments, the above-mentioned lamination process can be continuously completed on a multi-functional tandem dry lamination production line. This production line sequentially includes: a multi-axis unwinding unit, an online corona treatment unit, a multi-station coating unit, a multi-stage lamination unit, a guiding and drawing unit, and a rewinding unit. The laminated rolls are then transferred to a separate tunnel-type curing chamber for batch curing.

[0047] The present invention will be explained and described in detail below with reference to the embodiments.

[0048] Example 1 This embodiment provides a resilient composite sheet. The resilient layer is made of PET film with a tensile strength of 155 MPa, an elongation at break of 65%, and a thickness of 15 μm. The melt flow rate of the raw material under the conditions of 275℃ / 2.16 kg is 8 g / 10 min.

[0049] The preparation method is as follows: S01. Corona treatment was performed on the inner layer LLDPE film with a thickness of 60 μm, the barrier layer EVOH film with a thickness of 15 μm, the resilience layer, and the outer layer LDPE film with a thickness of 100 μm.

[0050] S02. Coat one side of the resilient PET film with polyurethane adhesive, and then feed it together with the inner LLDPE film into a dry laminating machine. Set the laminating roller temperature to 65℃ and the laminating pressure to 0.35MPa for lamination.

[0051] S03. Coat the other side of the resilient PET film with polyurethane adhesive, and then feed it together with the barrier layer EVOH film into a dry laminating machine. Set the laminating roller temperature to 75℃ and the laminating pressure to 0.38MPa for lamination.

[0052] S04. Coat the other side of the barrier layer EVOH film with polyurethane adhesive, and then feed it together with the outer LDPE film into a dry laminating machine. Set the laminating roller temperature to 70℃ and the laminating pressure to 0.42MPa for lamination.

[0053] S05. Place the composite sheet in a curing chamber at 45°C and cure for 30 hours to obtain a resilient composite sheet.

[0054] The composite sheet prepared in this embodiment has a resilience layer composed of a single, unstretched PET film. Testing showed a resilience rate of 72% and an interlayer peel strength of 3.8 N / 15 mm.

[0055] Example 2 This embodiment provides a resilient composite sheet, the inner layer of which is made of LLDPE and prepared into a film with a thickness of 60μm.

[0056] The rebound layer raw materials, by mass percentage, consist of: 78% PET resin, 10% MAH-g-PE, 4% oxazoline-grafted polyolefin, 0.8% flow promoter (polyethylene wax), and 0.5% foaming agent (sodium bicarbonate). The melt flow rate of the PET raw material at 275℃ / 2.16kg is 12g / 10min. The oxazoline-grafted polyolefin is obtained by melt extrusion grafting of ethylene-octene copolymer (POE), 2-vinyl-2-oxazoline monomer, and dicumyl peroxide (DCP) at 0.3% of the POE mass at 195℃. All the above raw materials are melt-blended in a twin-screw extruder at 200-220℃, and finally cast and cooled through a T-die to obtain a rebound layer film with a tensile strength of 158MPa, an elongation at break of 62%, and a thickness of 20μm.

[0057] The barrier layer is made of EVOH and is a 15μm thick film.

[0058] The outer layer is made of LDPE and is a 100μm thick film.

[0059] Its preparation method includes the following steps: S01. Corona treatment is performed on the inner LLDPE film, the resilience film, the barrier EVOH film, and the outer LDPE film respectively to make their surface tension reach 40mN / m.

[0060] S02. Coat one side of the resilient film with polyurethane adhesive, and then feed it together with the inner LLDPE film into a dry laminating machine. Set the laminating roller temperature to 65℃ and the laminating pressure to 0.35MPa for lamination.

[0061] S03. Coat the other side of the resilient layer film with polyurethane adhesive, and then introduce it together with the barrier layer EVOH film into a dry laminating machine. Set the laminating roller temperature to 75℃ and the laminating pressure to 0.38MPa for lamination.

[0062] S04. Coat the other side of the barrier layer EVOH film with polyurethane adhesive, and then feed it together with the outer LDPE film into a dry laminating machine. Set the laminating roller temperature to 70℃ and the laminating pressure to 0.42MPa for lamination.

[0063] S05. Place the composite sheet in a curing chamber at 45°C and cure for 30 hours to obtain a resilient composite sheet.

[0064] The composite sheet prepared in this embodiment has a resilience layer that is a blend film containing various functional additives. Testing showed that its resilience rate was 85% and its interlayer peel strength was 5.2 N / 15 mm.

[0065] Example 3 This embodiment provides a resilient composite sheet, with the inner layer made of LLDPE and a 60μm thick film.

[0066] The resilience layer uses commercially available BOPET film. The film is prepared by melting and extruding PET raw material with an intrinsic viscosity of 0.72 dL / g into a cast sheet, first stretching it longitudinally by 3.2 times at 95℃, then stretching it transversely by 3.5 times at 120℃, and finally heat-setting it at 210℃. The resulting BOPET film has a tensile strength of 180 MPa, an elongation at break of 55%, a thickness of 12 μm, and a melt flow rate of 10 g / 10 min at 275℃ / 2.16 kg.

[0067] The barrier layer is made of PVDC and is a thin film with a thickness of 18μm.

[0068] The outer layer is made of LDPE and is a 100μm thick film.

[0069] Its preparation method includes the following steps: S01. Corona treatment is performed on the inner LLDPE film, the resilient BOPET film, the barrier PVDC film, and the outer LDPE film to make their surface tension reach 40mN / m.

[0070] S02. Coat one side of the resilient BOPET film with polyurethane adhesive, and then feed it together with the inner LLDPE film into a dry laminating machine. Set the laminating roller temperature to 68°C and the laminating pressure to 0.32MPa for lamination.

[0071] S03. Coat the other side of the BOPET film with polyurethane adhesive, and then feed it together with the PVDC film of the barrier layer into a dry laminating machine. Set the laminating roller temperature to 78°C and the laminating pressure to 0.40MPa for lamination.

[0072] S04. Coat the other side of the barrier layer PVDC film with polyurethane adhesive, and then feed it together with the outer layer LDPE film into a dry laminating machine. Set the laminating roller temperature to 72℃ and the laminating pressure to 0.45MPa for lamination.

[0073] S05. Place the composite sheet in a curing chamber at 45°C and cure for 30 hours to obtain a resilient composite sheet.

[0074] The composite sheet prepared in this embodiment has a highly oriented BOPET film as its resilience layer. Testing showed a resilience rate of 91% and an interlayer peel strength of 4.5 N / 15 mm.

[0075] Example 4 This embodiment provides a resilient composite sheet, with the inner layer made of EVA and a 70μm thick film.

[0076] The rebound layer raw materials, by mass percentage, consist of: 82% PA6 resin, 8% MAH-g-PE, 6% oxazoline-grafted polyolefin, 1.2% flow promoter (calcium stearate), and 0.3% foaming agent (azodicarbonamide). The PA6 raw material has a melt flow rate of 10 g / 10 min at 235℃ / 2.16 kg. The oxazoline monomer in the oxazoline-grafted polyolefin is 2-isopropenyl-2-oxazoline. After blending the above raw materials, the mixture is melt-extruded into a cast sheet, stretched longitudinally by 3.0 times at 65℃, stretched transversely by 3.0 times at 85℃, and then heat-set at 110℃ to obtain a rebound layer film with a tensile strength of 165 MPa, an elongation at break of 58%, and a thickness of 25 μm.

[0077] The barrier layer is made of aluminized polyester (VMPET) and is a 12μm thick film.

[0078] The outer layer is made of polyolefin elastomer (POE), with a thickness of 120μm, an embossed film, an embossing depth of 12μm, and a linear density of 120 lines per inch.

[0079] Its preparation method includes the following steps: S01. The inner EVA film, the resilience film, the barrier VMPET film, and the outer POE embossed film are subjected to corona treatment to make their surface tension reach 40mN / m.

[0080] S02. Coat one side of the resilient layer film with polyurethane adhesive, and then feed it together with the inner EVA film into a dry laminating machine. Set the laminating roller temperature to 62℃ and the laminating pressure to 0.40MPa for lamination.

[0081] S03. Coat the other side of the resilient layer film with polyurethane adhesive, and then feed it together with the barrier layer VMPET film into a dry laminating machine. Set the laminating roller temperature to 72°C and the laminating pressure to 0.42MPa for lamination.

[0082] S04. Coat the other side of the barrier layer VMPET film with polyurethane adhesive, and then feed it together with the outer POE embossed film into a dry laminating machine. Set the laminating roller temperature to 68°C and the laminating pressure to 0.48MPa for lamination.

[0083] S05. Place the composite sheet in a curing chamber at 48°C and cure for 36 hours to obtain a resilient composite sheet.

[0084] The composite sheet prepared in this embodiment has a resilient layer of biaxially oriented nylon film and an outer layer of embossed film. Testing showed a resilience rate of 89% and an interlayer peel strength of 5.8 N / 15 mm.

[0085] Example 5 This embodiment provides a resilient composite sheet, with the inner layer made of LDPE and a 55μm thick film.

[0086] The resilient layer raw materials, by mass percentage, comprise: 75% PBT resin, 12% MAH-g-PE, 5% oxazoline grafted polyolefin, 1.5% flow promoter, and 0.4% foaming agent. The PBT raw material has a melt flow rate of 18 g / 10 min at 275℃ / 2.16 kg. After melt blending and vacuum devolatilization of the above raw materials, the mixture is cast into a thick sheet, then stretched longitudinally by 3.8 times at 80℃, and transversely by 3.8 times at 105℃. Finally, it is heat-set at 190℃ to obtain a resilient layer film with a tensile strength of 175 MPa, an elongation at break of 50%, and a thickness of 10 μm.

[0087] The barrier layer is made of silicon oxide-coated polyester, and is a 22μm thick film.

[0088] The outer layer is made of LLDPE and is a 135μm thick film.

[0089] Its preparation method includes the following steps: S01. Corona treatment is performed on the inner LDPE film, the resilience film, the barrier film and the outer LLDPE film respectively to make their surface tension reach 40mN / m.

[0090] S02. Coat one side of the resilient film with an epoxy adhesive, and then feed it together with the inner LDPE film into a dry laminating machine. Set the laminating roller temperature to 68°C and the laminating pressure to 0.32MPa for lamination.

[0091] S03. Coat the other side of the resilient layer film with an epoxy adhesive, and then feed it together with the barrier layer SiOx PET film into a dry laminating machine. Set the laminating roller temperature to 78°C and the laminating pressure to 0.40MPa for lamination.

[0092] S04. Coat the other side of the barrier layer film with an epoxy adhesive, and then feed it together with the outer LLDPE film into a dry laminating machine. Set the laminating roller temperature to 72°C and the laminating pressure to 0.45MPa for lamination.

[0093] S05. Place the composite sheet in a curing chamber at 42°C and cure for 40 hours to obtain a resilient composite sheet.

[0094] The composite sheet prepared in this embodiment has an ultra-thin biaxially oriented PBT film as its resilience layer. Testing showed a resilience rate of 94% and an interlayer peel strength of 5.0 N / 15 mm.

[0095] Comparative Example 1 This comparative example is a commercially available five-layer co-extruded composite sheet for toothpaste tubes, with a typical structure of PE / Tie / EVOH / Tie / PE and a total thickness of approximately 300 μm. The sheet uses PE as the substrate and EVOH as the barrier layer.

[0096] Tests showed that its resilience was 48% and its interlayer peel strength was 3.0 N / 15mm.

[0097] Comparative Example 2 This comparative example provides a resilient composite sheet, with the inner layer made of LLDPE and a 60μm thick film.

[0098] The rebound layer raw materials, by mass percentage, consist of: 98.7% PET resin, 10% MAH-g-PE, 0.8% flow promoter (polyethylene wax), and 0.5% foaming agent (sodium bicarbonate). The melt flow rate of the PET raw material at 275℃ / 2.16kg is 12g / 10min. The above raw materials are melt-blended in a twin-screw extruder, vacuum devolatilized, and then cast to obtain a rebound layer film with a tensile strength of 160MPa, an elongation at break of 63%, and a thickness of 20μm. The barrier layer is made of EVOH and has a thickness of 15μm; the outer layer is made of LDPE and has a thickness of 100μm.

[0099] Its preparation method is exactly the same as that in Example 2.

[0100] The test results showed that the resilience of the resulting composite sheet was 78%, and the interlayer peel strength was 4.1 N / 15mm.

[0101] Comparative Example 3 This comparative example provides a resilient composite sheet. The inner layer is made of LLDPE and is a 60μm thick film. The resilient layer material, by mass percentage, comprises: 78% PET resin, 10% MAH-g-PE, 4% oxazoline grafted polyolefin, and 0.8% flow promoter (polyethylene wax). The melt flow rate of the PET material at 275℃ / 2.16kg is 12g / 10min. The above materials are melt-blended in a twin-screw extruder at 200-220℃ without vacuum devolatilization, followed by casting to obtain a resilient film with a tensile strength of 156MPa, an elongation at break of 61%, and a thickness of 20μm.

[0102] The barrier layer is made of EVOH and is a 15μm thick film.

[0103] The outer layer is made of LDPE and is a 100μm thick film.

[0104] Its preparation method is exactly the same as that in Example 2.

[0105] The test results showed that the resilience of the resulting composite sheet was 81%, and the interlayer peel strength was 4.3 N / 15mm.

[0106] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A resilient composite sheet, characterized in that, The material comprises an inner layer, a resilient layer, a barrier layer, and an outer layer stacked sequentially. The substrate of the resilient layer is selected from at least one of polyester or polyamide, with a tensile strength ≥150MPa, an elongation at break ≥50%, and a thickness of 10~30μm. The melt flow rate of the polyester at 275℃ / 2.16kg is 5~20g / 10min, and / or the melt flow rate of the polyamide at 235℃ / 2.16kg is 5~18g / 10min.

2. The resilient composite sheet according to claim 1, characterized in that, The resilient layer comprises, by mass percentage: 72% to 88% polyester and / or polyamide, 6% to 15% maleic anhydride-grafted polyethylene, 3% to 8% oxazoline-grafted polyolefin, 0.2% to 2% flow promoter, and 0.2% to 2% foaming agent.

3. The resilient composite sheet according to claim 2, characterized in that, The method for preparing the oxazoline-grafted polyolefin includes: performing a free radical grafting reaction between the polyolefin resin and the oxazoline monomer in the presence of an organic peroxide initiator during melt extrusion; the amount of the initiator added is 0.1% to 1% of the mass of the polyolefin resin, and the reaction temperature is 180 to 220°C.

4. The resilient composite sheet according to claim 3, characterized in that, The oxazoline monomer is selected from at least one of 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline.

5. The resilient composite sheet according to claim 1 or 2, characterized in that, In the rebound layer The polyester is selected from at least one of polyethylene terephthalate, polybutylene terephthalate, and polybutylene naphthalate treated by biaxial stretching process; The polyamide is selected from at least one of polycaprolactam, polyhexamethylene adipamide, and polydodecanoic acid that have been treated by biaxial stretching.

6. The resilient composite sheet according to claim 5, characterized in that, The biaxial stretching treatment of the polyester includes: stretching the polyester longitudinally by 3 to 4 times above its glass transition temperature and below its melting point, then stretching it transversely by 3 to 4 times, followed by heat setting. The biaxial stretching treatment of the polyamide includes: stretching it longitudinally by 2.5 to 3.5 times above the glass transition temperature and below the melting point, followed by stretching it transversely by 2.5 to 3.5 times, and then heat setting.

7. The resilient composite sheet according to claim 1, characterized in that, The substrate of the inner and / or outer layers is selected from at least one of low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and polyolefin elastomer; and / or The thickness of the inner layer is 50~80μm, and the thickness of the outer layer is 80~140μm.

8. The resilient composite sheet according to claim 1, characterized in that, The substrate of the barrier layer is selected from at least one of ethylene-vinyl alcohol copolymer, polyvinylidene chloride, aluminized polyester film, and silica-coated polyester film; and / or The thickness of the barrier layer is 10~25μm.

9. The resilient composite sheet according to claim 1, characterized in that, The inner and / or outer layers are made of embossed film, and the surface of the embossed film is provided with an embossed pattern with a depth of 5~20μm and a line density of 80~200 lines / inch.

10. A method for preparing a resilient composite sheet according to any one of claims 1 to 9, characterized in that, Includes the following steps: S01. Corona treatment is performed on the inner layer, the elastic layer, the barrier layer and the outer layer substrate film respectively to make their surface tension ≥38mN / m; S02. Apply an adhesive to one side of the resilient layer and dry-laminate it with the inner substrate film. The lamination temperature is 60~75℃ and the lamination pressure is 0.3~0.5MPa. S03. Apply an adhesive to the other side of the rebound layer and dry-laminate it with the barrier layer substrate film. The lamination temperature is 70~80℃ and the lamination pressure is 0.35~0.45MPa. S04. Apply an adhesive to the other side of the barrier layer and dry-laminate it with the outer substrate film. The lamination temperature is 65~80℃ and the lamination pressure is 0.4~0.5MPa. S05. The composite sheet is cured at 40~50℃ for 24~48 hours to obtain the elastic composite sheet.