A bio-based laminated film and preparation method thereof

Abstract

The present invention relates to the technical field of optical films, and specifically discloses a bio-based laminated film and a preparation method thereof. The laminated film is obtained by alternately laminating two resins with different refractive indices, one of which is a bio-based polyester resin, and the difference in refractive index between the two resins is ≥0.05, and the laminated film reflects light with a wavelength range of 300 to 1200 nm; the bio-based polyester resin is polyethylene 2,5-furandicarboxylate or polyhydroxyalkanoate; the laminated film has the characteristics of biodegradability, and can also take into account the improvement of the mechanical properties and optical properties of the laminated film.

Description

Technical Field

[0001] The present invention relates to the technical field of optical films, and more particularly to a bio-based laminated film and a preparation method thereof. Background Art

[0002] Laminated film technology is achieved by alternately laminating two or more materials with different optical properties. By designing the optical thickness of the film layer, the reflection of sunlight passing through multiple interfaces in the laminated film can appear in different wavelength ranges. On this basis, through the matching of different materials and the design of film layer structure, more and more films with different optical properties are gradually being developed and applied, such as infrared reflective film, polarized reflective film, etc.

[0003] At present, the resin used in laminated films is generally a petrochemical product and is not biodegradable. As the use of laminated films increases, resin recycling becomes difficult, which is easy to pollute the environment and is not conducive to sustainable development. Summary of the invention

[0004] In order to solve the problem that traditional laminated films are derived from petrochemical raw materials and are not environmentally friendly, the present application provides a bio-based laminated film and a preparation method thereof. The laminated film has biodegradable properties and can also have low haze and excellent mechanical properties.

[0005] In a first aspect, the present application provides a bio-based laminated membrane, which adopts the following technical solution:

[0006] A bio-based laminated film, obtained by alternately laminating two resins with different refractive indices, one of which is a bio-based polyester resin, and the difference in refractive index between the two resins is ≥0.05, and the laminated film reflects light with a wavelength range of 300 to 1200 nm;

[0007] The bio-based polyester resin is polyethylene 2,5-furandicarboxylate or polyhydroxyalkanoate.

[0008] Furthermore, one resin in the laminated film is polyethylene 2,5-furandicarboxylate, and the other resin is selected from polymethyl methacrylate, polyethylene naphthalate, polyethylene terephthalate-1,4-cyclohexane dimethanol or polyhydroxyalkanoate.

[0009] Furthermore, the number of alternating layers of the bio-based laminated membrane is 231 to 401.

[0010] Furthermore, the intrinsic viscosity of the resin is 0.8-1.0 dL / g.

[0011] Furthermore, the optical thickness of a single layer of the resin is 20 to 200 nm.

[0012] Furthermore, in the reflectance spectrum curve of the bio-based laminated film in the wavelength range of 300 to 1200 nm, the difference between the highest reflectivity and the lowest reflectivity is more than 50%.

[0013] In a second aspect, the present application provides a method for preparing a bio-based laminated membrane, using the following technical solution:

[0014] A method for preparing a bio-based laminated film comprises the following steps:

[0015] Pretreatment: vacuum drying and pre-crystallization of the two resin particles;

[0016] Co-extrusion film forming: The resin particles after pre-crystallization treatment are melted separately, enter the distributor, and are extruded together. The temperature during extrusion is 255-265°C to obtain a cast sheet;

[0017] Stretching and shaping: the cast sheet is stretched at a stretching temperature of 95 to 105°C, and after stretching, it is placed in a heating box for shaping at a heating temperature of 105 to 115°C to obtain a bio-based laminated film.

[0018] Furthermore, in the pretreatment step, the pre-crystallization temperature is 120-140° C., the pre-crystallization vacuum is 0.1-1 Torr, and the pre-crystallization time is 10-24 hours.

[0019] Furthermore, in the stretching and shaping step, the stretching multiple is 3 to 5 times, and the stretching rate is 30 to 50 mm / s.

[0020] Furthermore, in the stretching and shaping step, the blowing speed of the heating box is 60 to 80 mm / s.

[0021] Furthermore, the heating and heat preservation time of the heating box in the stretching and shaping step is 70 to 90 seconds.

[0022] This application has at least the following advantages:

[0023] First, this application selects a specific bio-based polyester resin as one of the main raw materials for the laminated film. Polyethylene 2,5-furandicarboxylate (PEF) can be degraded into dicarboxylic acid and furan glycol under the action of microorganisms, and polyhydroxyalkanoate (PHA) is a bio-based material. The two resins are one of the main raw materials for the laminated film, giving the laminated film biodegradable properties, which is conducive to the later recycling of the bio-based laminated film.

[0024] Secondly, the traditional multilayer polyethylene 2,5-furandicarboxylate has poor light transmittance. By adopting this lamination technology and casting and stretching at an appropriate temperature, interference occurs between the reflected light at the interface between the two resins of the laminated film and the reflected light at the interface between the laminated film and the air, thereby improving the light transmittance of the laminated film, thereby solving the problem of poor light transmittance of polyethylene 2,5-furandicarboxylate.

[0025] Furthermore, the refractive index difference between PEF and PMMA, PEN, PETG and PHA in bio-based polyester resins is large, which meets the needs of optical application scenarios. The above-mentioned resins have similar intrinsic viscosities, and the flow speed of the resins in the dispenser is similar. The resin with high intrinsic viscosity is not easy to stretch the resin with low intrinsic viscosity, and the interface of the two resins is not easy to be irregularly distorted. The transmittance of the laminated film is increased, which is beneficial to improve the optical performance of the laminated film.

[0026] The above resins all contain ester groups, have good compatibility, and have moderate bonding forces between layers. When the resins are melt-laminated, the thermal stress and mechanical stress at the interface between the two are good, and the laminated film has good mechanical properties. At the same time, due to the structural characteristics of the resin itself, when the resins are melt-laminated, the surface tension at the interface between the two is different, and mutual diffusion is not easy to occur.

[0027] Finally, improvements are made to the preparation method of the laminated film. The resin particles are first pre-crystallized to make the molecular arrangement of the resin particles more orderly, thereby improving the strength, stiffness, heat resistance, weather resistance, chemical corrosion resistance and other properties of the laminated film; the temperature during extrusion is controlled. When the extrusion temperature is within this range, the pellets are completely crystallized, the probability of bubbles forming between the laminated films is reduced, and the light transmittance of the laminated film is improved, which helps to improve the optical and mechanical properties of the laminated film; the stretching temperature and the temperature of the heating box are controlled so that the macromolecular chains of the resin are fully oriented and crystallized, which greatly improves the comprehensive mechanical properties of the stretched laminated film, and the bonding strength between the layers is also greatly improved, taking into account the improvement of both the optical and mechanical properties of the laminated film. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the reflection spectrum diagram of Example 2 in the visible light and near-infrared light bands. DETAILED DESCRIPTION

[0029] Unless otherwise specified, the sources of raw materials for each preparation example and embodiment in this application are as follows:

[0030] PEF: refractive index 1.63, intrinsic viscosity 0.85dL / g, customized by Zhejiang Wankai New Materials Co., Ltd.

[0031] PMMA: brand HBS006H, from Mitsubishi;

[0032] PET: Brand FG612, from Yizheng Chemical Fiber;

[0033] PEN: Brand 8050SC, from Teijin of Japan;

[0034] PHA: Brand BP330-05, derived from blue crystal microorganisms;

[0035] PETG: Brand S2008, from SK, South Korea.

[0036] Example 1

[0037] A bio-based laminated membrane is prepared according to the following steps:

[0038] Material selection: PEF resin particles with a refractive index of 1.63 and PMMA resin particles with a refractive index of 1.49 are selected as the main raw materials of the laminated film; the intrinsic viscosity of the PEF resin particles is 0.85 dL / g, and the intrinsic viscosity of the PMMA resin particles is 0.9 dL / g;

[0039] Pretreatment: PEF resin particles and PMMA resin particles were vacuum dried and pre-crystallized in different vacuum drying ovens at a ratio of 56:44; the vacuum pre-crystallization temperature of PEF resin particles was 120°C, the vacuum degree was 0.5 Torr, and the vacuum time was 12h; the vacuum pre-crystallization temperature of PMMA resin particles was 140°C, the vacuum degree was 0.5 Torr, and the vacuum time was 12h;

[0040] Co-extrusion film forming: The pre-crystallized particles are pumped to the extruder's extraction funnel through an insulated pipe, and the pellets are co-extruded using different twin-screw extruders. After passing through a melt metering pump and a filter, they are transferred to a designed multi-layer feed block. The PET and PMMA resins in the molten state in the feed block will be alternately stacked in sequence; the multiplier behind the feed block will cut and stack the alternately stacked melts in the feed block again, doubling the original number of layers to form a 231-layer optical thickness cast sheet with a total thickness of 26μm;

[0041] The laminated melt will then enter the wedge-shaped die for confluence, and will be extruded from the die lip after being horizontally stretched in the die. The molten resin temperature of the melt tube is set at 255°C, the molten resin temperature at the metering pump is set at 255°C, and the molten resin temperature before the filter is set at 255°C; the molten resin temperature after the filter is set at 260°C, the molten resin temperature of the distributor is set at 260°C, and the molten resin temperature at the die is set at 260°C;

[0042] The sheet flowing out of the extruder die is cooled and stretched by the traction roller and the cooling roller. The electrostatic effect of the electrostatic wire at the die makes the sheet flowing out of the die completely adhere to the surface of the cooling roller. By adjusting the rotation speed of the cooling and stretching roller, a film of the required thickness is formed.

[0043] Stretching and shaping: the cooled film is cut into squares of 110×110 mm and subjected to biaxial stretching and shaping by a stretching machine. When the stretching ratio is 4.5 times, the specific stretching parameters are: stretching temperature 95°C, stretching rate 30 mm / s, cavity temperature of the heating box 105°C, blowing speed of the heating box 60 mm / s, and insulation time 70s, to obtain a bio-based laminated film.

[0044] Example 2

[0045] A bio-based laminated film, which is different from Example 1 in that the number of laminated layers in the co-extrusion film-forming step is 401 and the film layer thickness is 38 μm.

[0046] Example 3

[0047] A bio-based laminated film, which differs from Example 1 in that the stretching ratio, stretching temperature and shaping parameters in the stretching shaping step are different, as follows:

[0048] The cooled film was cut into squares of 110×110 mm and biaxially stretched by a stretching machine. When the stretching ratio was 5 times, the specific stretching parameters were: stretching temperature 105°C, stretching rate 50 mm / s, cavity temperature of the heating box 115°C, blast speed of the heating box 80 mm / s, and insulation time 90 s.

[0049] Example 4

[0050] A bio-based laminated film, which is different from Example 1 in that in this example, PEF resin particles with a refractive index of 1.63 and PETG resin particles with a refractive index of 1.57 are selected as main raw materials for the laminated film; the intrinsic viscosity of the PEF resin particles is 0.85 dL / g, and the intrinsic viscosity of the PETG resin particles is 0.85 dL / g.

[0051] Example 5

[0052] A bio-based laminated film, which differs from Example 1 in that in this example, PHA resin particles with a refractive index of 1.49 and PETG resin particles with a refractive index of 1.57 are selected as main raw materials for the laminated film; the intrinsic viscosity of the PHA resin particles is 1 dL / g, and the intrinsic viscosity of the PETG resin particles is 0.85 dL / g.

[0053] Comparative Example 1

[0054] A bio-based laminated film, which differs from Example 1 in that the process parameters of the co-extrusion film-forming step are different, specifically:

[0055] Co-extrusion film forming: The pre-crystallized particles are pumped to the extruder's extraction funnel through an insulated pipe, and the pellets are co-extruded using different twin-screw extruders. After passing through a melt metering pump and a filter, they are transferred to a designed multi-layer feed block. The PET and PMMA resins in the molten state in the feed block will be alternately stacked in sequence; the multiplier behind the feed block will cut and stack the alternately stacked melts in the feed block again, doubling the original number of layers to form a 231-layer optical thickness cast sheet with a total thickness of 26μm;

[0056] The laminated melt will then enter the wedge-shaped die for confluence, and will be extruded from the die lip after being horizontally stretched in the die. The molten resin temperature of the melt tube is set at 230°C, the molten resin temperature at the metering pump is set at 230°C, and the molten resin temperature before the filter is set at 230°C; the molten resin temperature after the filter is set at 240°C, the molten resin temperature of the distributor is set at 240°C, and the molten resin temperature at the die is set at 240°C;

[0057] The sheet flowing out of the extruder die is cooled and stretched by traction rollers and cooling rollers. The electrostatic effect of the electrostatic wire at the die allows the sheet flowing out of the die to completely adhere to the surface of the cooling roller. By adjusting the rotation speed of the cooling and stretching roller, a film of the desired thickness can be formed.

[0058] Comparative Example 2

[0059] A bio-based laminated film, which differs from Example 1 in that the process parameters of the stretching and shaping step are different, specifically:

[0060] Stretching and shaping: the cooled film is cut into squares of 110×110 mm and subjected to biaxial stretching and shaping by a stretching machine. When the stretching ratio is 4.5 times, the specific stretching parameters are: stretching temperature 85°C, stretching rate 30 mm / s, cavity temperature of the heating box 95°C, blowing speed of the heating box 60 mm / s, and insulation time 60 s to obtain a bio-based laminated film.

[0061] Comparative Example 3

[0062] A laminated film, which differs from Example 1 in that PEF lipid particles with a refractive index of 1.63 and PET resin particles with a refractive index of 1.65 are selected as main raw materials of the laminated film.

[0063] Comparative Example 4

[0064] A laminated film, which is different from Example 1 in that PET resin particles with a refractive index of 1.65 and PMMA resin particles with a refractive index of 1.49 are selected as main raw materials of the laminated film.

[0065] Test data

[0066] The optical properties and mechanical properties of Examples 1-5 and Comparative Examples 1-4 were tested below, and the test results are as follows:

[0067] Table 1. Test data of Examples 1-5

[0068]

[0069] Table 2. Test data of comparative examples 1-4

[0070]

[0071] Note: The haze is measured by HAM-200 remote haze meter; the visible light transmittance, visible light reflectance and infrared reflectance are measured by Shimadzu spectrometer model 3600; Figure 1 Obtained using the software Essential Macleod.

[0072] Example 1 and Comparative Example 1 form a single contrast, and the difference between them is that the extrusion temperature in the co-extrusion film-forming step is relatively low. The haze of Comparative Example 1 is high, and the visible light transmittance and infrared reflectivity are low, and the optical performance is poor. The reason is that: the co-extrusion temperature is low, the pellets are not completely crystallized, more bubbles are formed between the laminated films, and the film surface of the laminated film is foggy, resulting in a decrease in the optical performance of the laminated film.

[0073] Example 1 and Comparative Example 2 form a single comparison, the difference between them is that the stretching and shaping temperature in the stretching and shaping step is relatively low, the crystal orientation of the macromolecules in the film is incomplete, resulting in a significant decrease in the mechanical properties of the laminated film, and the infrared reflectivity is also relatively low.

[0074] Example 1 and Comparative Example 3 form a single comparison. The difference between them is that two resins with a refractive index difference of less than 0.05 are used for lamination. After actual testing, the visible light reflectance ratio of the laminated film is small, the infrared reflectivity is low, and the haze is large, which does not meet the needs of optical application scenarios such as heat insulation.

[0075] Example 1 and Comparative Example 4 form a single comparison. The difference between them is that the two materials of traditional PET and PMMA are used for lamination. The PET and PMMA used in Comparative Example 4 are traditional polyester materials and do not have biodegradable properties. At the same time, its mechanical properties are poor, and its tensile strength and elongation at break are low; in terms of optical properties, its infrared reflectivity is low, and it needs to be further improved in optical application scenarios such as heat insulation.

[0076] In contrast to Example 1 and Example 2, increasing the number of layers of the laminated film helps improve the infrared reflectivity, the heat insulation performance of the laminated film, and the mechanical properties of the laminated film, but the haze of the laminated film also increases significantly, the visible light transmittance decreases, the film surface of the laminated film is foggy, and the optical requirements of heat insulation and high definition cannot be taken into account. Figure 1 The reflectance spectrum of Example 2 in the visible light and near infrared light bands is shown in the following figure. Figure 1 The vertical axis is reflectivity. The minimum reflectivity is obtained at 350-450nm, and the minimum reflectivity is 45%. The maximum reflectivity is obtained at 650-900nm, and the maximum reflectivity reaches 100%. The difference between the maximum reflectivity and the minimum reflectivity is greater than 50%.

[0077] In contrast to Example 1 and Example 3, increasing the stretching ratio, stretching temperature and shaping temperature of the laminated film accelerates the growth of the crystal nuclei in the film, improves the density between the layers of the laminated film, reduces the haze of the laminated film, increases the visible light transmittance and infrared reflectivity, and improves the optical properties of the laminated film. However, due to the excessively rapid formation of the crystal nuclei, the crystallinity decreases, resulting in poor mechanical properties of the laminated film.

[0078] Example 1 and Example 4 form a single comparison. In Example 4, PETG with a refractive index of 1.57 is used instead of PMMA with a refractive index of 1.49. Although the intrinsic viscosity of the two is the same, the difference in refractive index is small, resulting in increased haze in the laminated film of Example 4, reduced infrared reflectivity, and decreased optical performance.

[0079] In a single comparison between Example 1 and Example 5, PETG and PHA resin combination is selected to replace PEF and PMMA resin combination. In Example 5, the refractive index difference is smaller, and the intrinsic viscosity difference is larger, resulting in increased haze, reduced infrared reflectivity, and decreased optical performance in Example 5.

[0080] In summary, the present application produces a bio-based laminate film, which has biodegradable properties, a haze lower than 1.5, an infrared reflectivity higher than 35%, a tensile strength greater than 150 MPa, an elongation at break greater than 90%, and both optical application scenarios and mechanical properties meet the requirements.

[0081] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] Moreover, the above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A bio-based laminated film, characterized in that : It is obtained by alternately laminating two resins with different refractive indices, the refractive index difference between the two resins is ≥0.05, and the infrared reflectivity of the laminated film is higher than 35%; One resin in the laminated film is polyethylene 2,5-furandicarboxylate, and the other resin is polymethyl methacrylate; The method for preparing the bio-based laminated film comprises the following steps: Pretreatment: vacuum drying and pre-crystallization of the two resin particles, the pre-crystallization temperature is 120-140°C, the pre-crystallization vacuum degree is 0.1-1 Torr, and the pre-crystallization time is 10-24h; Co-extrusion film forming: The resin particles after pre-crystallization treatment are melted separately, enter the distributor, and are extruded together. The temperature during extrusion is 255-265°C to obtain a cast sheet; Stretching and shaping: the cast sheet is stretched at a stretching temperature of 95 to 105°C, and after stretching, it is placed in a heating box for shaping at a heating temperature of 105 to 115°C. The heating and insulation time of the heating box is 70 to 90s to obtain a bio-based laminated film.

2. A bio-based laminated membrane as claimed in claim 1, characterized in that The intrinsic viscosities of the polyethylene 2,5-furandicarboxylate resin and the polymethyl methacrylate resin are both 0.8 to 1.0 dL / g.

3. A bio-based laminated membrane as claimed in claim 1, characterized in that :The number of alternating layers of the bio-based laminated membrane is 231 to 401.

4. The method for preparing a bio-based laminated membrane according to claim 1, characterized in that In the stretching and shaping step, the stretching multiple is 3 to 5 times, and the stretching rate is 30 to 50 mm / s.

5. The method for preparing a bio-based laminated membrane according to claim 1, characterized in that : The blast speed of the heating box in the stretching and shaping step is 60 to 80 mm / s.

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