A long-acting ultraviolet blocking bio-based film and a preparation method thereof

Abstract

The application relates to the technical field of optical films, and specifically discloses a long-acting ultraviolet-blocking bio-based film and a preparation method thereof. The long-acting ultraviolet-blocking bio-based film comprises, from top to bottom, an upper protective layer which is a bio-based polyester layer, an ultraviolet reflection layer which is a multilayer optical film formed by alternately stacking at least a first bio-based polyester and a second resin and used for reflecting ultraviolet light in the 315-400 nm wave band through interference, and a lower protective layer which is a bio-based polyester layer containing an organic ultraviolet absorber. The average reflectivity R of the ultraviolet reflection layer in the 315-400 nm wave band is greater than or equal to 90%, the maximum absorbance A of the organic ultraviolet absorber in the 300-400 nm wave band is greater than or equal to 2, and the proportion of bio-based carbon content in the total carbon content in the bio-based film is greater than or equal to 60%. Through the synergistic effect of the ultraviolet reflection layer and the lower protective layer and in combination with the excellent gas barrier property of the bio-based polyester, the application realizes an ultraviolet blocking rate of more than 99% in the 315-400 nm wave band, and the performance retention rate is extremely high after accelerated aging.

Description

Technical Field

[0001] This application relates to the technical field of optical thin films, and in particular to a long-lasting ultraviolet-blocking biofilm and its preparation method. Background Technology

[0002] Ultraviolet (UV) radiation from sunlight, especially long-wave UV rays, has strong penetrating power, capable of reaching deep into materials or the dermis of the skin. It is a major cause of aging, fading, performance degradation in polymer materials, and skin damage. Therefore, there is an urgent need for optical films with efficient and long-lasting UV blocking capabilities in many fields, such as outdoor building materials, photovoltaic module backsheets, automotive window films, high-end packaging, and cultural relic preservation.

[0003] Common UV-blocking films mainly rely on two technical approaches. One approach involves incorporating small-molecule organic UV absorbers, such as benzophenone or benzotriazole compounds, into the film matrix. While this method provides good initial blocking performance, the doped molecules are prone to migration and volatilization under long-term use or light exposure, especially irreversible photochemical decomposition. This results in a significant degradation of UV protection performance within hundreds of hours, failing to meet the requirement of outdoor durability for several years.

[0004] Another approach utilizes the principle of optical interference, alternatingly stacking two polymers with different refractive indices, such as polyethylene terephthalate and polymethyl methacrylate, into a structure of tens to hundreds of layers to achieve high reflectivity within a specific wavelength range. This method itself does not involve photosensitive materials and theoretically has a longer lifespan. However, this technology generally relies on petroleum-based polymer raw materials, resulting in high carbon emissions during production, constraints from non-renewable resources, and poor compatibility with green circular economy systems. Furthermore, these petroleum-based polymer materials typically have poor oxygen and water vapor barrier properties, which may reduce the overall protective effectiveness of the film in humid or high-oxygen environments, making it difficult to apply in scenarios with stringent permeability requirements.

[0005] Therefore, there is an urgent need to develop an ultraviolet barrier film that combines excellent initial performance, long-term stability, and superior environmental barrier properties, and is environmentally friendly and based on renewable raw materials, in order to overcome the aforementioned technical bottlenecks. Summary of the Invention

[0006] This application provides a long-lasting UV-blocking bio-based membrane and its preparation method. Through the synergistic effect of the UV-reflecting layer and the absorbing layer, combined with the excellent gas barrier properties of bio-based polyester, a UV blocking rate of over 99% is achieved in the 315-400nm wavelength range, with extremely high performance retention after accelerated aging. Simultaneously, the membrane material has a high bio-based content, good environmental friendliness, and excellent oxygen and water vapor blocking performance, making it suitable for fields requiring long-lasting UV protection.

[0007] In a first aspect, this application provides a long-lasting ultraviolet-blocking bio-based membrane, employing the following technical solution: A long-lasting ultraviolet-blocking bio-based membrane, comprising, from top to bottom: The upper protective layer is a bio-based polyester layer; The ultraviolet reflective layer is a multilayer optical film formed by alternating superposition of at least a first bio-based polyester and a second resin, used to reflect ultraviolet light through interference in the 315-400nm wavelength band; The lower protective layer is a bio-based polyester layer containing organic ultraviolet absorbers; The ultraviolet reflective layer has an average reflectivity R ≥ 90% in the 315-400nm wavelength band; the organic ultraviolet absorber has a maximum absorbance A ≥ 2 in the 300-400nm wavelength band; and the bio-based carbon content in the bio-based membrane accounts for ≥ 60% of the total carbon content.

[0008] By adopting the above technical solution, most of the ultraviolet light is first blocked by the high-reflectivity layer, and then the remaining part is treated by the absorption layer, so that the film can obtain extremely high initial blocking efficiency in the ultraviolet band. At the same time, the high-reflectivity layer greatly reduces the intensity of ultraviolet irradiation reaching the absorption layer, significantly delays the photodecomposition of the absorber, and ensures long-term stability. The selected bio-based polyester is not only renewable and reduces carbon emissions, but its excellent gas barrier properties also provide a stable internal environment for the entire system.

[0009] Optionally, the first bio-based polyester is polyethylene furanate.

[0010] By adopting the above technical solutions, PEF not only meets the requirements of bio-based materials, but the furan ring structure in its molecular chain brings higher chain segment rigidity and stronger intermolecular forces, making its oxygen and water vapor barrier performance significantly better than that of traditional petroleum-based polyesters such as PET. This fundamentally improves the environmental barrier capability and durability of the film.

[0011] Optionally, the second resin is selected from at least one of polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, and polyethylene terephthalate-1,4-cyclohexanediol.

[0012] Optionally, the organic ultraviolet absorber is a benzophenone or benzotriazole ultraviolet absorber.

[0013] Optionally, the number of ultraviolet reflective layers is 50-300.

[0014] Optionally, the oxygen permeability of the bio-based membrane is less than 1 cm. 3 / (m 2 •day), water vapor transmission rate less than 0.5g / (m 2 ·day).

[0015] Optionally, the bio-based membrane has an average UV blocking rate of ≥99% in the 315-400nm wavelength band, and an average UV blocking rate retention rate of ≥98% after 4000 hours of QUV accelerated aging test.

[0016] Secondly, this application provides a method for preparing a long-lasting ultraviolet-blocking bio-based membrane, employing the following technical solution: A method for preparing a long-lasting ultraviolet-blocking bio-based membrane includes the following steps: S1. Preparation of lower protective layer resin containing organic ultraviolet absorber: Bio-based polyester, organic ultraviolet absorber and additives for the lower protective layer are mixed and granulated by melt extrusion to obtain lower protective layer resin particles. S2, Co-extrusion Casting: Bio-based polyester for forming the upper protective layer, a first bio-based polyester and a second resin for forming the ultraviolet reflective layer, and the lower protective layer resin particles are melted and conveyed to a multilayer co-extrusion die; wherein, the first bio-based polyester and the second resin are alternately stacked and distributed by a distributor to form an ultraviolet reflective layer structure; the upper protective layer melt, the ultraviolet reflective layer melt, and the lower protective layer melt are compounded in the die and cooled by casting rollers to form a cast sheet. S3. Biaxial stretching: The cast sheet is stretched longitudinally and laterally to obtain a long-lasting ultraviolet-blocking biofilm.

[0017] Optionally, in step S1, the melt extrusion granulation uses a twin-screw extruder with a feed section temperature of 180-190℃, a plasticizing section temperature of 200-210℃, a homogenizing section temperature of 220-230℃, and a die head temperature of 215-220℃; the screw speed is 200-300 rpm, and a vacuum devouring device is provided with a vacuum degree of -0.10 MPa to -0.06 MPa.

[0018] Optionally, in step S3, the longitudinal stretching ratio is 3.0-4.0 times, and the stretching temperature is 90-110℃; the transverse stretching ratio is 3.5-4.5 times, and the stretching temperature is 100-120℃; followed by heat setting at 200-230℃.

[0019] In summary, this application includes at least one of the following beneficial technical effects: 1. First, a high-reflectivity layer blocks most of the ultraviolet light, and then an absorption layer treats the remaining portion, thereby enabling the film to achieve extremely high initial blocking efficiency in the ultraviolet band. At the same time, the high-reflectivity layer greatly reduces the intensity of ultraviolet irradiation reaching the absorption layer, significantly delays the photodecomposition of the absorber, and ensures long-term stability. The selected bio-based polyester is not only renewable and reduces carbon emissions, but its excellent gas barrier properties also provide a stable internal environment for the entire system. 2. PEF not only meets the requirements of bio-based materials, but the furan ring structure in its molecular chain brings higher chain segment rigidity and stronger intermolecular forces, making its oxygen and water vapor barrier performance significantly better than that of traditional petroleum-based polyesters such as PET. This fundamentally improves the environmental barrier capability and durability of the film. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the ultraviolet blocking rate spectrum of the PEF / PMMA reflective film in Comparative Example 1.

[0021] Figure 2 This is a schematic diagram of the ultraviolet blocking rate spectrum of the PEF / PMMA / PEF-A composite film in the embodiment. Detailed Implementation

[0022] Preparation Example

[0023] Preparation Example 1 A functional masterbatch containing a UV absorber was prepared by weighing 93.5 kg of dry PEF resin, 6 kg of benzotriazole UV absorber, and 0.5 kg of antioxidant 1010, and adding them to a high-speed mixer. The mixture was then mixed for 12 minutes at 70°C and 1000 rpm. The premix was fed into a co-rotating twin-screw extruder. The extruder temperatures were set as follows: feed section 185°C, plasticizing section 205°C, homogenizing section 225°C, and die head 218°C. The screw speed was 250 rpm, and a vacuum of -0.08 MPa was maintained in the melting section. The extruded melt was then pelletized in a water ring and vacuum dried at 80°C for 5 hours to obtain PEF-A masterbatch, which was then sealed for later use.

[0024] Example

[0025] This application discloses a long-lasting ultraviolet-blocking biofilm.

[0026] A long-lasting UV-blocking bio-based film comprises, from top to bottom, an upper protective layer, a UV-reflective layer, and a lower protective layer. The upper protective layer, composed of pure bio-based polyester, provides physical protection and initial barrier against environmental water and oxygen. The UV-reflective layer is a multi-layered alternating stacked structure formed by precision co-extrusion of the first bio-based polyester with another resin having different optical properties. The number of layers typically ranges from 50 to 300. By designing the optical thickness of each layer, an average reflectivity of over 90% is achieved in the wavelength range of 315 nm to 400 nm. The lower protective layer is composed of a blend of bio-based polyester and a highly efficient organic UV absorber, used to absorb the small amount of residual UV light after passing through the reflective layer.

[0027] The advantage of this structure lies in the fact that the incident ultraviolet light is first largely blocked by the highly reflective layer, leaving less than 10% of the ultraviolet light energy to reach the lower absorption layer. Because the intensity of ultraviolet radiation experienced by the absorber is greatly reduced, its photodecomposition rate is significantly suppressed, thus achieving long-term stability of the film's ultraviolet blocking performance. Simultaneously, the selected bio-based polyester, especially polyethylene furanate, has a high molecular chain rigidity and inherently possesses oxygen and water vapor barrier properties far superior to ordinary petroleum-based polyesters, providing a stable internal microenvironment for the entire film system and further ensuring functional durability.

[0028] Example 1

[0029] A long-lasting ultraviolet-blocking bio-based membrane is prepared by the following steps: P1. Vacuum dry PEF resin and PMMA resin at 80℃ for 6 hours and 4 hours respectively. Vacuum dry PEF-A masterbatch at 80℃ for 4 hours before use; P2. The raw materials are melted separately and then conveyed to the multi-layer co-extrusion die. The upper protective layer uses pure PEF resin and the melt temperature is set to 235°C. The reflective layer uses PEF resin and PMMA resin and the melt temperatures are set to 235°C and 240°C, respectively. The lower protective layer uses the PEF-A masterbatch obtained in Preparation Example 1 and the melt temperature is set to 235°C. The reflective layer is formed into 50 cycles, i.e., 100 alternating layers, through a distributor. P3. The upper protective layer PEF melt flow, the reflective layer melt flow, and the lower protective layer PEF-A melt flow are simultaneously introduced into a three-layer co-extrusion T-die for merging. The merged melt is extruded from the die and cast onto a cooling roller with a surface temperature of 25°C to form a uniform casting sheet. P4. The casting is fed into the stretching equipment. First, it is stretched longitudinally at 100°C with a stretching ratio of 3.5 times. Then, it is stretched transversely at 110°C with a stretching ratio of 4.0 times. P5. The biaxially stretched film was heat-set at 210℃, cooled, and then wound up to obtain a long-lasting UV-blocking bio-based film with a total thickness of approximately 22 μm. The reflective layer thickness was approximately 20 μm, the PEF to PMMA thickness ratio for each cycle was 0.98, the thickness for the first cycle was 0.3 μm, the thickness for the fiftieth cycle was 0.5 μm, and the thickness of both the upper and lower protective layers was 1 μm.

[0030] Example 2

[0031] The difference between Example 2 and Example 1 is that in Example 2, the reflective layer is composed of 200 layers of PEF and PMMA alternately stacked, so that the total thickness of the reflective layer of the final film is about 23 μm, the thickness of the upper protective layer PEF is adjusted to about 1.2 μm, and the thickness of the lower protective layer PEF-A is adjusted to about 1.2 μm.

[0032] Example 3

[0033] The difference between Example 3 and Example 2 is that in Example 3, the reflective layer uses PEF and PEN resin, the drying conditions of PEN resin are 120°C for 6 hours, and the melt temperature of PEN resin is set to 285°C.

[0034] Example 4

[0035] The difference between Example 4 and Example 2 is that in Example 4, the reflective layer uses 300 layers of PEF and PETG resins alternately stacked. The drying conditions for PETG resin are 80°C for 4 hours, the melt temperature of PETG is set to 225°C, and the final total thickness of the reflective layer of the film is about 26μm. The thickness of the upper protective layer PEF is adjusted to about 1.5μm, and the thickness of the lower protective layer PEF-A is adjusted to about 1.5μm.

[0036] Example 5

[0037] The difference between Example 5 and Example 1 is that in Example 5, the reflective layer is composed of 50 layers of PEF and PMMA alternately stacked, so that the total thickness of the reflective layer of the final film is about 10 μm, the thickness of the upper protective layer PEF is adjusted to about 0.5 μm, and the thickness of the lower protective layer PEF-A is adjusted to about 0.5 μm.

[0038] Comparative Example

[0039] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, both the upper and lower protective layers are PET layers, the reflective layer is composed of 100 layers of alternating PET and PMMA, the drying conditions of the PET resin are 120°C for 4 hours, and the melt temperature of the PET resin is 265°C.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the lower protective layer is a PEF layer.

[0041] Performance testing and effect analysis

[0042] The performance of the films prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

[0043] Table 1

[0044] The films provided in Examples 1-4 all achieved an initial UV blocking rate of over 99%, which is significantly higher than that of Comparative Examples 1-2, demonstrating the design advantages of the reflection-absorption synergistic structure.

[0045] Regarding long-term effectiveness, Examples 1-4 exhibited extremely high UV blocking rates and minimal performance degradation after 4000 hours of QUV accelerated aging. In contrast, Comparative Example 1 showed a significant performance decline. Example 5, due to its thin reflective layer with a reflectivity of less than 90%, experienced reduced effectiveness of the underlying absorbent during aging, resulting in poorer long-term protection. This confirms the crucial role of a high-reflectivity reflective layer in achieving long-term protection.

[0046] Films with PEF as the main substrate all exhibited excellent oxygen and water vapor barrier properties, significantly better than petroleum-based comparative film 1, which is attributed to the high barrier properties of PEF material itself.

[0047] Examples 1-4 maintain a high bio-based carbon content while exhibiting excellent optical and barrier properties.

[0048] Based on the above data, it can be seen that, firstly, the irreplaceable nature of the layer sequence determines the performance quality. Comparative Example 2 provides the same reflective layer structure and PEF as Example 1, but omits the lower protective layer containing the UV absorber. Although its water vapor and oxygen blocking properties are also excellent, its UV blocking rate is low, indicating that a single reflective structure has a certain reflection blind zone in the wide-band UV region, making it difficult to achieve full-band blocking. In contrast, Examples 1-4 fill the performance gap of the reflective layer by introducing an absorption layer in the lower layer, achieving an initial blocking rate of over 99%.

[0049] Secondly, high reflectivity effectively protects the absorption layer, ensuring the longevity of the film. The only difference between Example 5 and Examples 1-4 is the reduced thickness of the reflective layer, resulting in a decrease in reflectivity to 65%. Although the lower layer still contains UV absorbers, the reflective layer fails to effectively weaken the intensity of incident UV light, causing the absorbers to decompose rapidly under illumination. This leads to a significant decrease in the blocking rate after QUV aging to 88%, resulting in a marked deterioration in longevity. This result demonstrates that the lower layer absorber is effectively protected only when the reflectivity is ≥90%, highlighting the importance of the layering design with the reflective layer on the outside and the absorption layer on the inside.

[0050] In summary, this application has developed a UV barrier film that combines high initial efficiency, long-term stability, excellent environmental barrier properties, and good environmental protection characteristics through the layer structure design of a specific combination of bio-based materials.

[0051] All equivalent changes made to the structure, shape, and principle of this application shall be covered within the scope of protection of this application.

Claims

1. A long-lasting ultraviolet-barrier bio-based membrane, characterized in that, From top to bottom, they include: The upper protective layer is a bio-based polyester layer; The ultraviolet reflective layer is a multilayer optical film formed by alternating superposition of at least a first bio-based polyester and a second resin, used to reflect ultraviolet light through interference in the 315-400nm wavelength band; The lower protective layer is a bio-based polyester layer containing organic ultraviolet absorbers; The ultraviolet reflective layer has an average reflectivity R ≥ 90% in the 315-400nm wavelength band; the organic ultraviolet absorber has a maximum absorbance A ≥ 2 in the 300-400nm wavelength band; and the bio-based carbon content in the bio-based membrane accounts for ≥ 60% of the total carbon content.

2. The long-lasting ultraviolet-blocking bio-based membrane according to claim 1, characterized in that: The first bio-based polyester is polyethylene furanate.

3. The long-lasting ultraviolet-blocking bio-based membrane according to claim 2, characterized in that: The second resin is selected from at least one of polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polyethylene naphthalate and polyethylene terephthalate-1,4-cyclohexanediol ester.

4. The long-lasting ultraviolet-blocking bio-based membrane according to claim 1, characterized in that: The organic ultraviolet absorber is a benzophenone or benzotriazole ultraviolet absorber.

5. The long-lasting ultraviolet-barrier bio-based membrane according to claim 1, characterized in that: The number of layers in the ultraviolet reflective layer is 50-300.

6. The long-lasting ultraviolet-blocking bio-based membrane according to claim 1, characterized in that: The oxygen permeability of the bio-based membrane is less than 1 cm. 3 / (m 2 •day), water vapor transmission rate less than 0.5 g / (m 2 ·day).

7. The long-lasting ultraviolet-blocking bio-based membrane according to claim 1, characterized in that: The bio-based membrane has an average UV blocking rate of ≥99% in the 315-400nm wavelength band, and after 4000 hours of QUV accelerated aging test, the average UV blocking rate retention rate is ≥98%.

8. A method for preparing a long-lasting ultraviolet-barrier bio-based membrane according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of lower protective layer resin containing organic ultraviolet absorber: Bio-based polyester, organic ultraviolet absorber and additives for the lower protective layer are mixed and granulated by melt extrusion to obtain lower protective layer resin particles. S2, Co-extrusion Casting: Bio-based polyester for forming the upper protective layer, a first bio-based polyester and a second resin for forming the ultraviolet reflective layer, and the lower protective layer resin particles are melted and conveyed to a multilayer co-extrusion die; wherein, the first bio-based polyester and the second resin are alternately stacked and distributed by a distributor to form an ultraviolet reflective layer structure; the upper protective layer melt, the ultraviolet reflective layer melt, and the lower protective layer melt are compounded in the die and cooled by casting rollers to form a cast sheet. S3. Biaxial stretching: The cast sheet is stretched longitudinally and laterally to obtain a long-lasting ultraviolet-blocking biofilm.

9. The method for preparing a long-lasting ultraviolet-barrier bio-based membrane according to claim 8, characterized in that: In step S1, the melt extrusion granulation uses a twin-screw extruder with a feed section temperature of 180-190℃, a plasticizing section temperature of 200-210℃, a homogenizing section temperature of 220-230℃, and a die head temperature of 215-220℃; the screw speed is 200-300 rpm, and a vacuum devouring device is provided with a vacuum degree of -0.10 MPa to -0.06 MPa.

10. The method for preparing a long-lasting ultraviolet-barrier biofilm according to claim 8, characterized in that: In step S3, the longitudinal stretching ratio is 3.0-4.0 times, and the stretching temperature is 90-110℃; the transverse stretching ratio is 3.5-4.5 times, and the stretching temperature is 100-120℃; then heat setting is performed at 200-230℃.

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