Anti-ultraviolet all-plastic sheet and preparation method thereof

Abstract

The invention discloses an anti-ultraviolet all-plastic sheet and a preparation method thereof. The sheet is of a multi-layer co-extrusion structure and sequentially comprises a core layer, a blocking layer, a bonding layer and a surface layer from inside to outside. Wherein the core layer contains polyolefin and a light stabilizer, the surface layer contains polyolefin and an ultraviolet absorbent, and the spectrum of the polyolefin and the spectrum of the ultraviolet absorbent are complementary within the range of 200400 nm; the barrier layer is selected from aromatic polyamide, aromatic polyester or ethylene-vinyl alcohol copolymer; the bonding layer comprises maleic anhydride grafted polyethylene. According to the invention, molding is carried out through a co-extrusion film blowing process, and the prepared sheet keeps good transparency and full-plastic recoverability, realizes effective shielding of ultraviolet rays and obstruction of gases such as oxygen and the like, and is suitable for packaging contents sensitive to light and oxygen.

Description

Technical Field

[0001] This invention relates to the field of composite sheet technology, specifically to an anti-ultraviolet all-plastic sheet and its preparation method. Background Technology

[0002] In the daily chemical packaging industry, cosmetics, toothpaste, and other products often use tube packaging. These sheet materials need to possess both barrier properties and UV resistance. They must prevent oxygen penetration that could lead to oxidation of the contents and prevent internal ingredients from escaping; simultaneously, they must effectively shield against ultraviolet rays to prevent photochemical degradation, discoloration, or deterioration of the contents caused by light. Traditional aluminum-plastic composite sheets meet these requirements through an aluminum foil layer. However, the opacity of aluminum foil affects the packaging's display effect; as a metal material, aluminum foil is difficult to separate efficiently from plastic after disposal, hindering the overall recycling of the packaging.

[0003] In search of recyclable alternatives, the industry is turning to all-plastic structures. Common technical approaches to achieving barrier properties include using functional resins such as polyvinylidene chloride (PVDC) or ethylene-vinyl alcohol copolymer (EVOH). The former faces environmental and incineration controversies due to its chlorine content, while the latter's barrier performance degrades under high temperature and humidity conditions. Another approach is to add nano-inorganic particles to the substrate or coat the surface with a barrier coating; however, the former is prone to particle agglomeration affecting material transparency and mechanical properties, while the latter often faces challenges related to coating adhesion, scratch resistance, and process complexity.

[0004] To achieve UV protection, the common practice is to add organic or inorganic UV absorbers to the plastic matrix. However, many traditional UV absorbers suffer from insufficient heat resistance, easy decomposition during processing, and the risk of migration during use, posing safety hazards. Particularly noteworthy is that many absorbers have insufficient blocking efficiency in the near-ultraviolet region (380-400 nm), failing to provide long-term and adequate protection for photosensitive contents.

[0005] Therefore, existing all-plastic sheet technologies often struggle to achieve a balance between multiple indicators such as barrier properties, recyclability, and UV resistance. 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 described in the background art.

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

[0008] In a first aspect, the present invention provides an anti-ultraviolet all-plastic sheet, comprising a barrier layer, an adhesive layer and a surface layer that are sequentially stacked and fully covered on both sides of a core layer; The core layer comprises polyolefin and light stabilizer, with a haze value of 4.0-15.0%; Each of the two barrier layers independently comprises at least one of aromatic polyamide, aromatic polyester, and ethylene-vinyl alcohol copolymer, with a haze value of 1.0-8.0%; Both adhesive layers comprise maleic anhydride-grafted polyethylene with a haze value of 5-20.0%; At least one of the two surface layers comprises a polyolefin and a UV absorber, with a haze value of 3.0%-12.0%; The barrier layer encapsulates the core layer, and the barrier layer is connected to the surface layer by the adhesive layer. The light stabilizer and the ultraviolet absorber have complementary spectra in the wavelength range of 200~400nm.

[0009] As a preferred technical solution, the adhesive layer, by weight, comprises 30-70 parts of matrix resin, 20-50 parts of maleic anhydride-grafted polyethylene, 5-10 parts of polyolefin elastomer, 0.5-5 parts of heterocyclic compound, and 0.1-2 parts of processing aid.

[0010] As a preferred technical solution, the heterocyclic compound includes at least one of nicotinamide, L-ascorbyl palmitate, and aminotrimethylenephosphonic acid.

[0011] As a preferred technical solution, the thickness ratio of the core layer, barrier layer, adhesive layer and surface layer is (10~30):(5~20):(5~15):(15~35) respectively, and the total thickness of the UV-resistant all-plastic sheet is 100-500μm.

[0012] As a preferred technical solution, the polyolefin in the core layer and / or surface layer includes at least one of homopolymer polypropylene, copolymer polypropylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, and ethylene-methacrylic acid copolymer.

[0013] As a preferred technical solution, the light stabilizer in the core layer includes at least one or any combination of hindered amine light stabilizers, hindered phenolic light stabilizers, benzoate light stabilizers, oxalamide light stabilizers, or organophosphorus light stabilizers.

[0014] As a preferred technical solution, the ultraviolet absorber in the surface layer includes benzotriazole compounds, benzophenone compounds, salicylate compounds, triazine compounds, substituted acrylonitrile compounds, cyanoacrylate compounds, or malonate compounds, or combinations thereof.

[0015] As a preferred technical solution, the concentration of the ultraviolet absorber and / or the light stabilizer decreases along the light transmission direction of the sheet.

[0016] Secondly, the present invention provides a method for preparing an anti-ultraviolet all-plastic sheet having any of the above-mentioned technical features, comprising the following steps: S1. Prepare molten materials for forming the core layer, barrier layer, adhesive layer and surface layer respectively; S2. Feed each layer of molten material into a co-extrusion die having at least seven extrusion channels; S3. Extruding through the co-extrusion die to form a composite preform; S4. The composite membrane preform is inflated, cooled, and drawn to form a tubular film. S5. The tubular film is cut open along the traction direction, heated, flattened, and rolled up to obtain the UV-resistant all-plastic sheet.

[0017] As a preferred technical solution In step S3, the extrusion temperature of the co-extrusion die is 180℃~250℃; and / or In step S4, the inflation ratio is 1.0~3.5, and cooling is achieved using an air ring with a temperature of 5℃~30℃; and / or In step S4, the traction ratio of the traction is 5~15; and / or In step S5, the heating and flattening process uses an infrared heating device with an infrared wavelength of 2.0 μm to 5.0 μm and a heating temperature of 60℃ to 90℃; and / or In step S5, the heating and flattening process uses a hot oil heating device with a heating temperature of 70℃~120℃.

[0018] The advantages and beneficial effects of this invention are as follows: By combining a surface layer containing an ultraviolet absorber with a core layer containing a light stabilizer and physically encapsulating it with barrier layers on both sides, not only is stable resistance to 200-400nm ultraviolet light achieved, but the migration of functional additives into the contents or environment is also inhibited, ensuring safe use and long-lasting performance. Along the light transmission direction, the intensity of incident light in the sheet prepared by this invention gradually decreases due to the action of the light stabilizer and ultraviolet absorber. The sheet adopts an all-plastic structure, ensuring high barrier and ultraviolet resistance while possessing good transparency and flatness. The polyolefin, maleic anhydride-grafted polyethylene adhesive layer, and barrier resin used in the entire sheet are all easily recyclable plastic materials and do not contain difficult-to-recycle components such as aluminum foil and PVDC.

[0019] This invention introduces heterocyclic compounds into the adhesive layer. These compounds can interact with maleic anhydride-grafted polyethylene to enhance interlayer adhesion. They also have antioxidant properties and can be used as auxiliary stabilizers during processing and use to inhibit the thermo-oxidative aging of the material. 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 an anti-UV all-plastic sheet and its preparation method. The sheet has a multi-layer co-extrusion structure, including a barrier layer, an adhesive layer, and a surface layer stacked sequentially on both sides of the core layer. It is formed in one step by a co-extrusion blown film process, achieving efficient shielding against ultraviolet rays and effective blocking of gases such as oxygen. At the same time, it has good transparency, mechanical properties, and all-plastic recyclability, making it particularly suitable for high-end soft tube packaging of cosmetics, pharmaceuticals, food, and other light- and oxygen-sensitive contents.

[0024] In the sheet structure of this invention, the core layer comprises polyolefin and a light stabilizer, with its haze value controlled within the range of 4.0-15.0%. This ensures sufficient light transmittance and visual comfort for the entire sheet, while the moderate light scattering effect allows the light stabilizer in the core layer to function more uniformly and persistently. As the main support layer of the sheet, the polyolefin matrix of the core layer provides basic mechanical strength and thermoforming properties. The added light stabilizer absorbs or quenches ultraviolet energy, inhibits the photo-oxidative degradation of polymer chains, and forms a spectral complement with the ultraviolet absorbers in the surface layer, thus constructing multi-layered ultraviolet protection throughout the material's thickness. If the core layer haze is too low, although the transparency is extremely high, the dispersion and light path management effects of the light stabilizer may be insufficient, and the stiffness of the sheet may be affected. If the haze is too high, it may significantly sacrifice the display clarity of the packaging, affecting its aesthetics.

[0025] A barrier layer is fully covered on the outer sides of both core layers. This barrier layer is independently selected from at least one of aromatic polyamides (such as nylon 6), aromatic polyesters (such as polyethylene terephthalate, PET), or ethylene-vinyl alcohol copolymer (EVOH), with a haze value controlled between 1.0% and 8.0%. The barrier layer material contains a rigid aromatic ring structure or strongly polar hydroxyl groups, which can effectively reduce the permeability of small molecule gases such as oxygen and water vapor. A haze value within this range means that the barrier layer achieves high barrier function while having a low impact on overall transparency, ensuring the visibility of the package contents. Although the barrier properties of EVOH decrease at high temperatures, in the multi-layer structure of this invention, it is protected by the core and surface layers, resulting in a relatively mild working environment and stable performance.

[0026] The barrier layer is firmly bonded to the core layer and the surface layer via two adhesive layers. The adhesive layers are primarily composed of maleic anhydride-grafted polyethylene (MAH-g-PE), with a haze value of 5-20.0%. The maleic anhydride polar functional groups on the MAH-g-PE molecular chain can chemically bond (e.g., through hydrogen bonding, and even possible esterification / amidation reactions) and physically entangle with the barrier layer material. Simultaneously, its polyethylene backbone exhibits excellent compatibility with the polyolefin matrix of both the core and surface layers. This creates a strong and durable bond between the polarity-differentiated layers, preventing interlayer delamination due to stress or environmental changes during use.

[0027] In the two outermost layers, at least one layer contains a polyolefin and a UV absorber, with a haze value of 3.0%–12.0%. These layers are directly exposed to light and serve to protect against ultraviolet radiation. The added UV absorber efficiently absorbs ultraviolet light in the 200–400 nm wavelength range and converts it into dissipation. The moderate haze of the layers helps soften light, reduce glare, and may work in conjunction with the UV absorber to optimize the light absorption path. The light stabilizer in the core layer and the UV absorber in the surface layer have complementary absorption or stabilization mechanisms in the 200–400 nm UV spectral range; for example, the UV absorber primarily shields short-wave ultraviolet light, while the light stabilizer focuses on inhibiting free radical reactions initiated by long-wave ultraviolet light.

[0028] In a preferred embodiment, the adhesive layer comprises, by weight, 30-70 parts of matrix resin, 20-50 parts of maleic anhydride-grafted polyethylene, 5-10 parts of polyolefin elastomer, 0.5-5 parts of heterocyclic compound, and 0.1-2 parts of processing aid. The matrix resin is typically a polyolefin compatible with the core / surface layer, such as LDPE or LLDPE, providing basic adhesive properties and processing flowability. The addition of a polyolefin elastomer (such as POE) improves the flexibility and impact resistance of the adhesive layer, enabling it to better buffer stress and prevent brittle cracking during subsequent tube making, folding, and extrusion of the sheet.

[0029] Heterocyclic compounds such as nicotinamide, L-ascorbyl palmitate, or aminotrimethylenephosphonic acid. These molecules have aromatic or saturated cyclic structures containing heteroatoms such as N and O. On the one hand, the lone pairs of electrons on their heteroatoms can generate strong polar interactions with the anhydride groups or carboxyl groups in maleic anhydride-grafted polyethylene, and may even participate in the formation of ion pairs. This not only further enhances the polarity of MAH-g-PE itself and its bonding force with the barrier layer, but may also promote the formation of a denser physical cross-linking network within the adhesive layer, improving interlayer adhesion strength and resistance to media. On the other hand, these heterocyclic compounds themselves mostly have excellent antioxidant or metal ion chelating abilities. They can act as auxiliary stabilizers during the high-temperature melting stage of co-extrusion processing and during long-term use of sheets, effectively capturing free radicals generated by heat or shear, or passivating trace metal ions that may catalyze the degradation of polyolefins, thereby inhibiting the thermo-oxidative aging of the adhesive layer itself and adjacent layers, ensuring the long-term stability of the multilayer structure performance at the interface level.

[0030] In one embodiment, the thickness ratio of the core layer, barrier layer, adhesive layer, and surface layer is (10~30):(5~20):(5~15):(15~35), with a total sheet thickness of 100-500 μm. The core layer has the largest proportion, ensuring the overall rigidity and strength of the sheet. Although the barrier layer is thin, it is sufficient to provide an effective barrier; too thick a layer would increase cost and haze, while too thin a layer might lead to barrier failure due to defects. The adhesive layer is extremely thin, achieving the strongest adhesion with the lowest possible thickness. The surface layer has a moderate thickness, sufficient to hold the UV absorber without excessively affecting the feel or cost. The total thickness of 100-500 μm takes into account the flexibility, barrier properties, and economy required for tube packaging.

[0031] In terms of material selection, the polyolefins of the core layer and / or surface layer can be widely selected from at least one of homopolymer polypropylene, copolymer polypropylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, and ethylene-methacrylic acid copolymer. These materials can be flexibly combined according to different requirements for transparency, flexibility, heat resistance, crystallinity, etc. The light stabilizers of the core layer include hindered amine light stabilizers, hindered phenolic light stabilizers, benzoate light stabilizers, oxalamide light stabilizers, or organophosphorus light stabilizers, or combinations thereof. The UV absorbers of the surface layer include benzotriazole compounds, benzophenone compounds, salicylates, triazine compounds, substituted acrylonitrile compounds, cyanoacrylate compounds, or malonate compounds, or combinations thereof. They have different UV absorption bands and weather resistance, and can be selected as needed.

[0032] In one embodiment, the concentration of the UV absorber and / or the light stabilizer in the sheet can be set as a decreasing gradient along the light transmission direction. This means that the concentration of the UV absorber / light stabilizer gradually decreases from the outermost surface layer to the inner core layer, and then to another surface layer. This gradient distribution satisfies the Lambert-Beer law. Placing the highest concentration of UV absorber on the surface layer where the incident light is strongest allows for rapid and efficient initial absorption; as the light penetrates deeper and its intensity weakens, the required concentration of light stabilizer inside also decreases accordingly. This maximizes protective efficiency while reducing the total amount of functional additives used, thereby reducing the risk of additive migration from the surface layer to the contents, while ensuring overall protective effectiveness.

[0033] This invention also provides a method for preparing the above-mentioned UV-resistant all-plastic sheet, comprising the following steps: S1. Prepare the molten materials for forming the core layer, barrier layer, adhesive layer, and surface layer separately. Each layer material needs to be melt-plasticized and mixed in a separate extruder. The temperature setting must ensure that it is higher than the melting point of the highest melting point plastic in each component. For example, if polypropylene is used as the core layer substrate, and it also contains a barrier material with a higher melting point such as PET, the temperature of the melting and metering sections of the corresponding extruder should be set above 250°C, typically within the range of 180°C to 250°C, to ensure that all polymers are fully melted, functional additives are uniformly dispersed, and good melt flowability is maintained. Too low a temperature will lead to uneven plasticization and extrusion fluctuations; too high a temperature may cause thermal degradation of the polymer, especially heat-sensitive light stabilizers and UV absorbers.

[0034] S2. The molten material of each layer is fed into a co-extrusion die with at least seven extrusion channels. The at least seven channels correspond to the double-sided symmetrical structure of the sheet: two surface layers, two adhesive layers, two barrier layers, and one core layer or composite core layer. The co-extrusion die ensures that the molten material of each layer is stacked and composited within the die at a stable flow rate, pressure, and temperature, forming a clear interface.

[0035] S3. The composite preform is extruded through the co-extrusion die to form a composite film preform. The die temperature of each layer is controlled between 180°C and 250°C. At this temperature, the melt elasticity and surface tension of each polymer layer reach a balance state that is conducive to interlayer spreading and adhesion. For the adhesive layer, this temperature is also sufficient to activate the interaction between the polar groups of maleic anhydride-grafted polyethylene and the adjacent layer materials.

[0036] S4. The composite preform is inflated, cooled, and drawn to form a tubular film. The tubular preform extruded from the die is immediately inflated with compressed air, and the inflation ratio (bubble diameter / die diameter) is controlled between 1.0 and 3.5. The inflation ratio directly affects the transverse tensile orientation, thickness uniformity, and mechanical properties of the sheet. After inflating, the bubble is rapidly cooled and solidified by an air ring at a temperature of 5°C to 30°C. Simultaneously, longitudinal stretching is applied to the bubble by traction rollers, and the traction ratio (traction speed / extrusion speed) is controlled between 5 and 15.

[0037] S5. The tubular film is cut open along the traction direction, heated, flattened, and then wound up to obtain the UV-resistant all-plastic sheet. The cut film needs to be heated and flattened to eliminate internal stress and wrinkles caused by inflation and traction. An infrared heating device with an infrared wavelength of 2.0μm~5.0μm can be used. This wavelength can be effectively absorbed by plastic molecules and converted into heat energy. The heating temperature is controlled at 60℃~90℃ to achieve rapid and uniform surface heating and stress relaxation. Alternatively, a hot oil heating roller with a heating temperature of 70℃~120℃ can be used for more uniform volume heating through contact conduction. The flattened sheet has high flatness, facilitating subsequent printing, lamination, or tube manufacturing. Finally, it is wound up to obtain the finished product.

[0038] The present invention will be further explained and illustrated below with reference to the embodiments.

[0039] [Example 1] A method for preparing an UV-resistant all-plastic sheet includes the following steps: S1. Prepare seven layers of molten material for forming the core layer, the first barrier layer, the second barrier layer, the first adhesive layer, the second adhesive layer, the first surface layer, and the second surface layer.

[0040] The core layer is made by uniformly mixing PP granules with hindered amine light stabilizer (HALS) in a high-speed mixer, wherein the amount of light stabilizer added is 0.8% of the total mass of the core layer. The mixture is fed into the core layer extruder and melt-mixed at a set melt temperature of 210°C.

[0041] The materials for the first and second barrier layers are EVOH, which are fed into two barrier layer extruders and the melting temperature is set to 200℃.

[0042] Materials for the first and second adhesive layers: LLDPE, as the matrix resin, MAH-g-PE, and POE (ethylene-octene copolymer) are mixed in a mass ratio of 65:20:7, and 1 part of processing aid (calcium stearate) is added. The mixture is divided into two equal parts and fed into two adhesive layer extruders respectively, with the melt temperature set at 190℃.

[0043] First surface layer material: PP granules are mixed evenly with benzotriazole UV absorber (UV-327) in a high-speed mixer, wherein the amount of UV absorber added is 1.2% of the total mass of the surface layer. The mixture is fed into the first surface layer extruder, and the melt temperature is set to 205℃.

[0044] Second surface material: Only PP granules are used, fed into the second surface extruder, and the melt temperature is set to 205℃.

[0045] S2. The seven-layer molten material prepared in step S1 is precisely metered by seven independent metering pumps and then fed into a multi-layer co-extrusion blown film die with seven concentric annular flow channels. The material layers are arranged from the inside out as follows: first surface layer, first adhesive layer, first barrier layer, core layer, second barrier layer, second adhesive layer, and second surface layer.

[0046] S3. Set the overall extrusion temperature of the co-extrusion die to 200°C. At this temperature, the melt viscosity of each layer is well matched, and a seven-layer composite tubular preform is co-extruded through the die lip.

[0047] S4. Compressed air is introduced into the composite membrane preform for inflation, with the inflation ratio controlled at 2.5. The inflated membrane bubble is immediately subjected to rapid cooling and solidification through a dual-air-outlet cooling ring at a temperature of 20°C. Simultaneously, the cooling membrane bubble is longitudinally stretched by traction rollers, with the traction ratio controlled at 10.

[0048] S5. The cooled and shaped cylindrical film is cut open along the traction direction to obtain a flat film. An infrared heating device is used to flatten the film; the infrared wavelength is 3.5 μm, and the heating temperature is set to 80℃. After static electricity is eliminated, the flattened film is wound up to obtain the UV-resistant all-plastic sheet.

[0049] In the structure of the UV-resistant all-plastic sheet prepared in this embodiment, the haze value of the core layer is 8.5%, the haze value of the barrier layer is 3.0%, the haze value of the adhesive layer is 18%, and the haze value of the surface layer containing the UV absorber is 6.0%. The spectral absorption curves of the core layer light stabilizer and the surface layer UV absorber are complementary in the 200-400nm wavelength range.

[0050] The UV-resistant all-plastic sheet prepared in this embodiment was tested using conventional testing methods, and its light transmittance was approximately 82%. Oxygen transmittance (OTR, 23°C, 0%RH): approximately 8.5 cm⁻¹. 3 / (m 2 (day / atm). UV blocking rate (200-400nm): approximately 99.2%.

[0051] [Example 2] A method for preparing an anti-ultraviolet all-plastic sheet, the basic steps are the same as in Example 1, the difference being: The adhesive layers, specifically the first and second adhesive layers, are composed (by weight): 80 parts LLDPE matrix resin, 12 parts maleic anhydride-grafted polyethylene, 8 parts polyolefin elastomer POE, 2.5 parts heterocyclic compound (nicotinamide), and 1 part processing aid (calcium stearate). The melting temperature is set at 195℃.

[0052] The first and second barrier layers in the barrier layer are made of aromatic polyamide (nylon MXD6), and the melting temperature is set to 235℃.

[0053] By adjusting the screw speed of each extruder, the thickness ratio of each layer of the final sheet is controlled to be approximately: core layer: barrier layer: adhesive layer: surface layer = 15:8:5.0:15. The total thickness is approximately 300μm.

[0054] Surface UV absorber concentration gradient: In the first surface (outer) molten material, the concentration of UV absorber (UV-327) is 1.5% (mass fraction), while in the second surface (inner, closer to the contents) molten material, the concentration of UV absorber decreases to 0.8% (mass fraction).

[0055] In the performance test results of the sheet in this embodiment, the light transmittance is approximately 85%. Oxygen transmittance (OTR, 23°C, 0%RH): approximately 4.2 cm. 3 / (m 2 (day / atm). Ultraviolet blocking rate (200-400nm) is approximately 99.5%.

[0056] [Example 3] A method for preparing an anti-ultraviolet all-plastic sheet, the basic steps are the same as in Example 2, the difference being: The heterocyclic compound in the adhesive layer was replaced with L-ascorbate palmitate, with an addition amount of 1.0 part.

[0057] The matrix resin for both the core layer and the two surface layers is mPE to improve the material's flexibility and optical properties. The light stabilizer for the core layer is a benzoate, and the UV absorber for the surface layers is a benzophenone (UV-531).

[0058] The co-extrusion die temperature is adjusted to 185℃. The blow-up ratio is adjusted to 1.8, and the traction ratio is adjusted to 8. The infrared flattening temperature is adjusted to 70℃.

[0059] The thickness ratio of each layer is controlled as follows: core layer: barrier layer: adhesive layer: surface layer = 12:10:1.2:15. The total thickness is approximately 180μm.

[0060] The performance test results for this embodiment include: light transmittance of approximately 88%; oxygen transmittance (OTR, 23°C, 0%RH): approximately 5.8 cm⁻¹. 3 / (m 2(day / atm). Ultraviolet blocking rate (200-400nm) 98.8%.

[0061] [Example 4] A method for preparing an anti-ultraviolet all-plastic sheet, the basic steps are the same as in Example 2, the difference being: The heterocyclic compound in the adhesive layer was replaced with aminotrimethylenephosphonic acid, with an addition amount of 4.0 parts.

[0062] The first and second barrier layers are made of aromatic polyester (PET), and the melting temperature is set at 250℃.

[0063] The surface UV absorber has a concentration gradient (1.8% on the outer side and 0.5% on the inner side), and the light stabilizer (organophosphorus) in the core layer is also designed with a concentration gradient. Specifically, a two-color masterbatch feeding system is set in the feed section of the core layer extruder, so that the light stabilizer concentration is higher (about 1.2%) in the core layer area near the two side barrier layers, while the concentration is lower (about 0.6%) in the central area of ​​the core layer.

[0064] Due to the high melting point of PET, the co-extrusion die temperature was adjusted to 240℃. The blow-up ratio was adjusted to 3.2, and the traction ratio was adjusted to 13. Hot oil-heated rollers were used for heating and flattening at a temperature of 110℃.

[0065] The thickness ratio of each layer is controlled as follows: core layer: barrier layer: adhesive layer: surface layer = 20: 5: 15: 35. The total thickness is approximately 480 μm.

[0066] The performance test results of this embodiment include: Light transmittance is approximately 78%. Oxygen transmittance (OTR, 23℃, 0%RH) is approximately 3.0 cm. 3 / (m 2 (day / atm). Ultraviolet blocking rate (200-400nm) is approximately 99.8%.

[0067] [Example 5] A method for preparing an anti-ultraviolet all-plastic sheet, the basic steps are the same as in Example 2, the difference being: The core layer is made of copolymer polypropylene, and the surface layer is made of ethylene-vinyl acetate copolymer to improve heat-sealing performance.

[0068] The surface UV absorber uses triazine compounds.

[0069] The co-extrusion die temperature was adjusted to 215℃. The blow-up ratio was adjusted to 2.0, and the traction ratio was adjusted to 6. The air ring cooling temperature was adjusted to 12℃.

[0070] Both surfaces were treated with UV absorbers at the same concentration of 1.0%.

[0071] The thickness ratio of each layer is controlled as follows: core layer: barrier layer: adhesive layer: surface layer = 10:12:1.5:35. The total thickness is approximately 120μm.

[0072] The performance test results of this embodiment include: light transmittance of approximately 80%; oxygen transmittance (OTR, 23°C, 0%RH): approximately 6.5 cm⁻¹. 3 / (m 2 (day / atm). UV blocking rate (200-400nm): approximately 99.0%.

[0073] [Comparative Example 1] The product uses a commercially available five-layer transparent composite sheet. Its performance test results include: light transmittance of approximately 86% and oxygen transmittance (OTR, 23℃, 0%RH): approximately 9.0 cm⁻¹. 3 / (m 2 (day / atm). Ultraviolet blocking rate (200-400nm) is approximately 15%.

[0074] [Comparative Example 2] The preparation of an anti-UV all-plastic sheet follows the same steps as in Example 2, except that no heterocyclic compounds (nicotinamide) are added to the materials of the first and second adhesive layers. The materials only contain LLDPE matrix resin, maleic anhydride-grafted polyethylene, POE polyolefin elastomer, and processing aids.

[0075] Its performance test results include a light transmittance of approximately 84% and an oxygen transmittance (OTR, 23°C, 0%RH) of approximately 4.5 cm. 3 / (m 2 (day / atm). Ultraviolet blocking rate (200-400nm) is approximately 99.4%.

[0076] The interlaminar peel strength (N / 15mm) of Comparative Example 2 was 2.5. After 7 days of heat aging at 80°C, slight delamination appeared at the edge of the sheet, while the sample of Example 2 showed no obvious changes.

[0077] [Comparative Example 3] The preparation of an anti-UV all-plastic sheet is basically the same as that in Example 1, except that the light stabilizer (HALS) in the core layer is completely replaced with the same type of UV absorber (UV-327) as the surface layer, and the amount added is the same as that of the light stabilizer in the core layer in Example 1.

[0078] In the performance test results of Comparative Example 3, the light transmittance was approximately 80%. Oxygen transmittance (OTR, 23℃, 0%RH): approximately 8.8 cm⁻¹ 3 / (m 2 (day atm). Initial UV blocking rate (200-400nm): approximately 99.0%.

[0079] The UV blocking rate of Comparative Example 3 decreased to approximately 85% after 500 hours of accelerated aging (380-400nm long-wave UV blocking rate dropped to approximately 85%). In contrast, the UV blocking rate of Sample 1 remained above 97% after the same aging process. Comparative Example 3 exhibited good UV blocking rate initially, but its shielding ability against long-wave UV decreased after aging. This is because UV absorbers primarily function by absorbing and converting UV energy. Under prolonged, high-intensity light exposure, their molecular structure may undergo photo-fatigue or decomposition, leading to performance degradation. In contrast, the light stabilizer used in the core layer of Example 1 primarily works by capturing free radicals generated by UV radiation, interrupting the photo-oxidative degradation chain reaction. This absorption and stabilization mechanism makes its UV resistance more durable and stable.

[0080] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, 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 UV-resistant all-plastic sheet, characterized in that, It includes a barrier layer, an adhesive layer, and a surface layer that are stacked and fully covered on both sides of the core layer; The core layer comprises polyolefin and light stabilizer, with a haze value of 4.0-15.0%; Each of the two barrier layers independently comprises at least one of aromatic polyamide, aromatic polyester, and ethylene-vinyl alcohol copolymer, with a haze value of 1.0-8.0%; Both adhesive layers comprise maleic anhydride-grafted polyethylene with a haze value of 5.0-20.0%; At least one of the two surface layers comprises a polyolefin and a UV absorber, with a haze value of 3.0%-12.0%; The barrier layer encapsulates the core layer, and the barrier layer is connected to the surface layer by the adhesive layer. The light stabilizer and the ultraviolet absorber have complementary spectra in the wavelength range of 200~400nm.

2. The UV-resistant all-plastic sheet according to claim 1, characterized in that, The adhesive layer, by weight, comprises 30-70 parts of matrix resin, 20-50 parts of maleic anhydride-grafted polyethylene, 5-10 parts of polyolefin elastomer, 0.5-5 parts of heterocyclic compound, and 0.1-2 parts of processing aid.

3. The UV-resistant all-plastic sheet according to claim 2, characterized in that, The heterocyclic compounds include at least one of nicotinamide, L-ascorbyl palmitate, and aminotrimethylenephosphonic acid.

4. The UV-resistant all-plastic sheet according to claim 3, characterized in that, The thickness ratio of the core layer, barrier layer, adhesive layer and surface layer is (10~30):(5~20):(5~15):(15~35) respectively, and the total thickness of the UV-resistant all-plastic sheet is 100-500μm.

5. The UV-resistant all-plastic sheet according to claim 1, characterized in that, In the core layer and / or surface layer, the polyolefin includes at least one of homopolymer polypropylene, copolymer polypropylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, and ethylene-methacrylic acid copolymer.

6. The UV-resistant all-plastic sheet according to claim 1, characterized in that, In the core layer, the light stabilizer includes hindered amine light stabilizers, hindered phenolic light stabilizers, benzoate light stabilizers, oxalamide light stabilizers, or organophosphorus light stabilizers or combinations thereof.

7. The UV-resistant all-plastic sheet according to claim 1, characterized in that, The ultraviolet absorber in the surface layer includes at least one or any combination of benzotriazole compounds, benzophenone compounds, salicylates, triazine compounds, substituted acrylonitrile compounds, cyanoacrylate compounds, or malonates.

8. The UV-resistant all-plastic sheet according to claim 4, characterized in that, Along the direction of light transmission, the concentration of the ultraviolet absorber and / or the light stabilizer decreases in the sheet.

9. A method for preparing an anti-ultraviolet all-plastic sheet as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Prepare molten materials for forming the core layer, barrier layer, adhesive layer and surface layer respectively; S2. Feed each layer of molten material into a co-extrusion die having at least seven extrusion channels; S3. The composite film preform is extruded through the co-extrusion die and formed. S4. The composite membrane preform is inflated, cooled, and drawn to form a tubular film. S5. The tubular film is cut open along the traction direction, heated, flattened, and rolled up to obtain the UV-resistant all-plastic sheet.

10. The method for preparing the UV-resistant all-plastic sheet according to claim 9, characterized in that, In step S3, the extrusion temperature of the co-extrusion die is 180℃~250℃; and / or In step S4, the inflation ratio is 1.0~3.5, and cooling is achieved using an air ring with a temperature of 5℃~30℃; and / or In step S4, the traction ratio of the traction is 5~15; and / or In step S5, the heating and flattening process uses an infrared heating device with an infrared wavelength of 2.0 μm to 5.0 μm and a heating temperature of 60℃ to 90℃; and / or In step S5, the heating and flattening is carried out using a hot oil heating device, with a heating temperature of 70℃~120℃.