A double-sided printing film and its preparation method

Abstract

The present application discloses a double-sided printed film and a preparation method thereof. The double-sided printed film is composed of three layers of composites, with the middle layer being the core layer and the two sides of the core layer being the surface layers. The surface layer is prepared from polyethylene terephthalate, polypropylene, modified titanium dioxide, and additives. The core layer is prepared from polyethylene terephthalate, polypropylene, and modified titanium dioxide. The preparation method includes the steps of: mixing modified titanium dioxide, additives, polyethylene terephthalate, and polypropylene and then injecting them to obtain the surface layer; mixing modified titanium dioxide, polyethylene terephthalate, and polypropylene and then injecting them to obtain the core layer; and co-extruding the surface layer and the core layer to obtain the double-sided printed film. The double-sided printed film provided by the present application has extremely low light transmittance, weather resistance, tensile properties, and puncture resistance, improves the printing effect and aesthetics, and thus enhances the market competitiveness.

Description

Technical Field

[0001] This application relates to the field of polyester-based film manufacturing, and particularly to a double-sided printed film and a preparation method thereof. Background Art

[0002] The double-sided printed film is a material with broad application prospects, and its uses are extensive and diverse. Such products are mainly used in the fields of packaging, printing, advertising, electronic devices, etc. For example, the double-sided printed film is widely used in the packaging field for automatic packaging materials, food packaging materials, mask packaging materials, etc., further enhancing the safety and aesthetics of products. In addition, the double-sided printed film is also applied to the screen protection of smart devices, the plastic sealing of gift boxes, and the production of various labels and advertising light boxes.

[0003] Among them, the double-sided printed low light transmittance film is a high-performance thin film material with broad application prospects. Due to the good printability of such materials, it is suitable for the production of hanging printed posters, and the low light transmittance of the printed film ensures that the patterns printed on both sides do not affect each other, with good visual effects.

[0004] However, at present, there is an urgent need to optimize and improve the double-sided printed film products with good light transmittance, better mechanical properties and weather resistance, as well as the preparation methods. Summary of the Invention

[0005] One object of this application is to provide a double-sided printed film and a preparation method thereof, which are beneficial to reducing the light transmittance of the double-sided printed film and improving the printing effect and aesthetics of printed products.

[0006] Another object of this application is to provide a double-sided printed film and a preparation method thereof, which are beneficial to enhancing the tensile properties and weather resistance of the double-sided printed film and strengthening the service performance of printed products.

[0007] Another object of this application is to provide a double-sided printed film and a preparation method thereof, which are beneficial to enhancing the adhesion between layers of the double-sided printed film, further strengthening the puncture resistance, and enhancing the market competitiveness of printed products.

[0008] To achieve the above purposes, the technical solution adopted in this application is: a double-sided printed film, which is composed of a three-layer composite, wherein the middle layer is the core layer, and both sides of the core layer are the surface layers;

[0009] The surface layer is prepared from polyethylene terephthalate, polypropylene, modified titanium dioxide, and additives.

[0010] The core layer is prepared from polyethylene terephthalate, polypropylene, and modified titanium dioxide.

[0011] In some embodiments, the modified titanium dioxide is titanium dioxide grafted with polypropylene grafted maleic anhydride on its surface.

[0012] In some embodiments, the preparation steps of the modified titanium dioxide are as follows:

[0013] S100, Put titanium dioxide powder into absolute ethanol and perform ultrasonic treatment for 10 min to 30 min to obtain a first solution;

[0014] S200, Place the first solution into a mixed solution of a silane coupling agent and absolute ethanol, stir and react for 1 h to 3 h to obtain a first mixture;

[0015] S300, Centrifuge the first mixture, wash and dry the solid matter obtained by centrifugation to obtain a first powder;

[0016] S400, Provide a mixed solution of xylene and ethanol, put the first powder and polypropylene grafted maleic anhydride into the mixed solution to obtain a second mixture;

[0017] S500, Add benzoyl peroxide to the second mixture, raise the temperature to a first temperature for grafting reaction to obtain a third mixture;

[0018] S600, Centrifuge the third mixture, wash and dry the solid matter obtained by centrifugation to obtain the modified titanium dioxide.

[0019] In some embodiments, the ratio of the molar number n1 of maleic anhydride groups in the polypropylene grafted maleic anhydride to the molar number n2 of epoxy groups in the first powder is: 1 / 10 ≤ n1:n2 ≤ 1 / 2.

[0020] In some embodiments, the mass fraction of polyethylene terephthalate in the surface layer is 50 wt.% to 60 wt.%, the mass fraction of polypropylene is 10 wt.% to 20 wt.%, the mass fraction of the modified titanium dioxide is 5 wt.% to 15 wt.%, and the mass fraction of the auxiliary agent is 5 wt.% to 10 wt.%.

[0021] In some embodiments, the mass fraction of polyethylene terephthalate in the core layer is 50 wt.% to 60 wt.%, the mass fraction of polypropylene is 20 wt.% to 30 wt.%, and the mass fraction of the modified titanium dioxide is 10 wt.% to 20 wt.%.

[0022] In some embodiments, the mass fraction of the modified titanium dioxide in the core layer is greater than the mass fraction of the modified titanium dioxide in the surface layer.

[0023] In some embodiments, the particle size of the modified titanium dioxide is 30 nm to 60 nm.

[0024] In some embodiments, the additives include fluorescent brighteners, stearic acid amide, oleic acid amide, nano calcium carbonate, and zinc oxide.

[0025] In some embodiments, among the additives, the mass fraction of the fluorescent brightener is 10 wt.% to 20 wt.%, the mass fraction of the stearic acid amide is 10 wt.% to 20 wt.%, the mass fraction of the oleic acid amide is 5 wt.% to 15 wt.%, the mass fraction of the nano calcium carbonate is 30 wt.% to 45 wt.%, and the mass fraction of the zinc oxide is 15 wt.% to 25 wt.%.

[0026] In some embodiments, the thickness of the surface layer is 40 μm to 80 μm, and the thickness of the core layer is 200 μm to 400 μm.

[0027] According to another aspect of the present application, there is also provided a method for preparing a double-sided printing film, including the steps:

[0028] A100, mixing the modified titanium dioxide and the additives by a high-speed mixer to obtain a first filler;

[0029] A200, mixing the first filler, polyethylene terephthalate, and polypropylene by a high-speed mixer and then performing injection molding to obtain a surface layer;

[0030] A300, mixing the modified titanium dioxide, polyethylene terephthalate, and polypropylene by a high-speed mixer and then performing injection molding to obtain a core layer;

[0031] A400, performing co-extrusion treatment on the surface layer and the core layer to obtain the double-sided printing film.

[0032] Compared with the prior art, the beneficial effects of the present application are as follows:

[0033] (1) A double-sided printing film and a preparation method thereof provided by the present invention, by constructing a double-sided printing film with a three-layer composite layer, including a surface layer with a low light transmittance and a core layer with an ultra-low light transmittance, further reduce the overall light transmittance of the printing film, and improve the printing effect and aesthetics of the printed product.

[0034] (2) A double-sided printing film and a preparation method thereof provided by the present invention, by modifying titanium dioxide, enhance the bonding performance between the three-layer composite layers, enable the modified titanium dioxide to be stably distributed between the layers, while enhancing the interfacial interaction between the layers, and enhance the tensile performance and puncture resistance of the printing film, thereby reducing damage phenomena during use.

[0035] (3) A double-sided printing film and its preparation method provided by the present invention add polypropylene to the printing film matrix to increase the weather resistance of the printing film, and show better stability under ultraviolet irradiation and high-temperature environments, thereby extending the service life. Specific Embodiments

[0036] Next, in combination with specific embodiments, the present application will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0037] In the description of the present application, it should be noted that for orientation terms, such as the terms "center", "horizontal", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicating orientation and positional relationships, are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of the present application.

[0038] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence.

[0039] The terms "comprising" and "having" in the description and claims of the present application, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0040] According to one aspect of the present invention, a double-sided printing film is composed of a three-layer composite, wherein the middle layer is the core layer, and the two sides of the core layer are the surface layers;

[0041] The surface layer is prepared from polyethylene terephthalate, polypropylene, modified titanium dioxide, and additives;

[0042] The core layer is prepared from polyethylene terephthalate, polypropylene, and modified titanium dioxide.

[0043] By constructing a three-layer composite layer structure in the double-sided printing film, it is convenient to regulate the performance of the printing film. The core layer has an ultra-low light transmittance, and the surface layers with low light transmittance are distributed on both sides, further reducing the overall light transmittance of the printing film and improving the printing effect and aesthetics of the printed product. In the blend system of polyethylene terephthalate (PET) and polypropylene (PP), modified titanium dioxide grafted with polypropylene grafted maleic anhydride (PP-g-MAH) is added. The grafted PP-g-MAH serves as a good compatibilizer, while improving the compatibility of PET and PP, enhancing the interfacial force, making the bonding performance between each phase region and each layer stronger, and being beneficial to improving the tensile and puncture resistance of the double-sided printing film. Further, the addition of modified titanium dioxide grafted with PP-g-MAH is beneficial to improving the defects in the blend system, further enhancing the oxygen barrier and water vapor barrier properties of the printing film, and being beneficial to improving the weather resistance during outdoor use.

[0044] It can be understood that when using PET as the matrix of the printing film, the advantages of PET such as high transparency, relatively high gloss, chemical stability, thermal stability, and environmental sustainability have made it widely used in the printing products industry. However, the high processing difficulty and high cost of PET have restricted its application. Further, PP has good toughness and impact resistance. Blending with PET can significantly improve the impact strength and tensile strength of the printing film, and improve the processing performance and reduce the processing difficulty. Especially when used outdoors, the good water resistance, gas barrier property, and heat resistance of PP reduce the sensitivity of the PET component in the system to moisture, improve the stability of the PET component when used in a humid or hot environment, and thus enhance the performance of the double-sided printing film. Further, using PP is beneficial to reducing the production cost of the printing film and has good economic benefits.

[0045] In some embodiments, the modified titanium dioxide is titanium dioxide grafted with polypropylene grafted maleic anhydride on the surface.

[0046] It can be understood that titanium dioxide powder is a white filler with excellent performance. Its high hiding power, high whiteness, and high refractive index endow it with strong scattering ability in the visible light range, which helps to improve the whiteness of the printing film and reduce the light transmittance. Further, by grafting PP-g-MAH onto the titanium dioxide powder, the interfacial compatibility between the PET and PP components in the printing film matrix is increased. While optimizing the processing performance of the blend system, the stress concentration phenomenon at the interface is reduced, thereby improving the elongation at break and tensile strength of the printing film. In other words, the titanium dioxide powder grafted with PP-g-MAH is beneficial to enhancing the bonding force between itself and the matrix and reducing the phenomenon of shedding. Moreover, the modified titanium dioxide is distributed in both the surface layer and the core layer. Due to the action of the modified titanium dioxide, the interlayer adhesion performance becomes better, further improving the tensile and puncture resistance of the printing film, so that it has good performance in various usage environments.

[0047] In some embodiments, the preparation steps of the modified titanium dioxide are as follows:

[0048] S100, Put the titanium dioxide powder into anhydrous ethanol and perform ultrasonic treatment for 10 min to 30 min to obtain the first solution;

[0049] S200, Place the first solution into a mixed solution of silane coupling agent and anhydrous ethanol, stir and react for 1 h to 3 h to obtain the first mixture;

[0050] S300, Centrifuge the first mixture, wash and dry the solid matter obtained by centrifugation to obtain the first powder;

[0051] S400, Provide a mixed solution of xylene and ethanol, put the first powder and polypropylene grafted maleic anhydride into the mixed solution to obtain the second mixture;

[0052] S500, Add benzoyl peroxide to the second mixture, heat up to the first temperature for grafting reaction to obtain the third mixture;

[0053] S600, Centrifuge the third mixture, wash and dry the solid matter obtained by centrifugation to obtain the modified titanium dioxide.

[0054] Through the preparation steps of the modified titanium dioxide provided by this application, it has the advantages of simple preparation method, fewer operation steps, and higher production efficiency, which is conducive to large-scale production.

[0055] In some embodiments, the ratio of the number of moles n1 of maleic anhydride groups in polypropylene grafted maleic anhydride to the number of moles n2 of epoxy groups in the first powder is: 1 / 10 ≤ n1:n2 ≤ 1 / 2. Specifically, the ratio of n1:n2 can be 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 1 / 4, 1 / 3, 1 / 2. Further preferably, the ratio of the number of moles n1 of maleic anhydride groups in polypropylene grafted maleic anhydride to the number of moles n2 of epoxy groups in the first powder is: 1 / 6 ≤ n1:n2 ≤ 1 / 2. It can be understood that the first powder obtained by treatment with a silane coupling agent has a relatively large number of epoxy groups, and a part of the epoxy groups react with the maleic anhydride groups in PP-g-MAH, causing PP-g-MAH to graft onto the first powder, thereby preparing modified titanium dioxide. The remaining epoxy groups react with the terminal carboxyl groups in PET, increasing the adhesion force between PET, PP, and modified titanium dioxide in each layer while increasing compatibility, so that the printed film maintains good mechanical stability during use.

[0056] In some embodiments, the mass fraction of polyethylene terephthalate in the surface layer is 50 wt.% - 60 wt.%. Specifically, the mass fraction of polyethylene terephthalate in the surface layer is 50 wt.%, 51 wt.%, 52 wt.%, 53 wt.%, 54 wt.%, 55 wt.%, 56 wt.%, 57 wt.%, 58 wt.%, 59 wt.%, 60 wt.%. It can be understood that the PET material has good dimensional stability, is not easily deformed or shrunk, and is suitable for printing and packaging applications that require high precision. Moreover, the PET material has good weather resistance and can be used outdoors for a long time without easily aging or discoloring.

[0057] In some embodiments, the mass fraction of polypropylene in the surface layer is 10 wt.% - 20 wt.%. Specifically, the mass fraction of polypropylene in the surface layer is 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%. In other words, after blending PP with good toughness and impact resistance with PET, the tensile strength of the printed film can be enhanced, and the processing performance can be improved while reducing the processing difficulty. Especially when used outdoors, PP has good water resistance, gas barrier properties, and heat resistance, thereby reducing the sensitivity of the PET component to moisture and improving the stability of the PET component when used in a humid or hot environment, thus enhancing the performance of the double-sided printed film.

[0058] In some embodiments, the mass fraction of the modified titanium dioxide in the surface layer is 5 wt.% to 15 wt.%. Specifically, the mass fraction of the modified titanium dioxide in the surface layer can be 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%. Further preferably, the mass fraction of the modified titanium dioxide in the surface layer is 5 wt.% to 10 wt.%. By adding an appropriate amount of modified titanium dioxide to the surface layer, while enhancing the service performance of the printing film, the light transmittance of the printing film is reduced, thereby improving the clarity of the printed pattern and the printing quality, and further enhancing the market competitiveness of the product. Moreover, the modified titanium dioxide in the surface layer can interact with the core layer, enhancing the interfacial adhesion force and thus improving the tensile property and puncture resistance of the printing film.

[0059] In some embodiments, the mass fraction of the additive in the surface layer is 5 wt.% to 10 wt.%. Specifically, the mass fraction of the additive in the surface layer can be 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%. By adding an appropriate additive to the printing film, the surface smoothness of the printing film is improved, which is beneficial to the printed pattern and improves the printing quality. Moreover, the added additive can also be an additive with a whitening effect, so as to achieve the improvement of the super-white property of the printing film while improving the processing performance and facilitating the blending process.

[0060] In some embodiments, the mass fraction of polyethylene terephthalate in the core layer is 50 wt.% to 60 wt.%. Specifically, the mass fraction of polyethylene terephthalate in the surface layer can be 50 wt.%, 51 wt.%, 52 wt.%, 53 wt.%, 54 wt.%, 55 wt.%, 56 wt.%, 57 wt.%, 58 wt.%, 59 wt.%, 60 wt.%. It can be understood that PET materials have broad application prospects in the fields of printing and packaging. Their good mechanical properties, chemical stability, thermal stability and environmental protection characteristics make them an ideal raw material for printing products.

[0061] In some embodiments, the mass fraction of polypropylene in the core layer is 20 wt.% to 30 wt.%. Specifically, the mass fraction of polypropylene in the core layer can be 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, 30 wt.%. By adding more PP to the core layer, the mechanical properties and weather resistance of the support layer are enhanced, and further the stability of the printing film during use is enhanced.

[0062] In some embodiments, the mass fraction of the modified titanium dioxide in the core layer is 10 wt.% to 20 wt.%. Specifically, the mass fraction of the modified titanium dioxide in the core layer is 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%. Further preferably, the mass fraction of the modified titanium dioxide in the core layer is 15 wt.% to 20 wt.%. By adding more modified titanium dioxide to the core layer, the super-white performance of the core layer is enhanced, the light transmittance of the printing film is further reduced, and the printing effect of the printing film as a raw material for printing products is improved.

[0063] In some embodiments, the mass fraction of the modified titanium dioxide in the core layer is greater than that in the surface layer. Since the relatively large amount of modified titanium dioxide in the core layer can interact with the surface layers provided on both sides, the interfacial adhesion force is enhanced, the bonding effect between the two surface layers and the core layer is increased, and the tensile strength and puncture resistance of the printing film are further enhanced.

[0064] In some embodiments, the particle size of the modified titanium dioxide is 30 nm to 60 nm. It can be understood that titanium dioxide with a nano-sized particle diameter has a high refractive index and can effectively scatter and absorb light. This makes the printing film added with nano-sized titanium dioxide exhibit a low light transmittance in the visible light range. Further, nano-sized titanium dioxide has a strong absorption capacity for ultraviolet rays and can effectively block the penetration of ultraviolet rays. This not only improves the light-tightness of the printing film, but also protects the printing film from degradation caused by ultraviolet rays, and further extends the service life of the printing film.

[0065] In other words, nano-sized titanium dioxide, as a common filler used in polymers, can improve the tensile strength and toughness of the printing film, and the nano-sized titanium dioxide has good dispersibility in the printing film, enhancing the overall uniformity and use stability of the printing film. Further, nano-sized titanium dioxide can also improve the flatness and glossiness of the surface of the printing film, which is beneficial to printing patterns on the printing film, making the appearance of the printed product more uniform and beautiful. This is very important for application fields with high surface quality requirements, such as advertising films, decorative films, and other application scenarios.

[0066] In some embodiments, the additives include fluorescent whitening agents, stearic acid amide, oleic acid amide, nano calcium carbonate, and zinc oxide. It can be understood that using fluorescent whitening agents in the surface layer can significantly improve the whiteness and brightness of the printing film, and is beneficial to enhancing weather resistance and thermal stability, maintaining a stable whitening effect under high temperature and light conditions, thereby reducing the light transmittance of the printing film, and further enhancing the use stability of the printed product.

[0067] By adding stearamide and oleamide, the smoothness and flatness of the printed film can be improved preferably, and the processing performance can be improved during the processing, the melt viscosity can be reduced, and the dispersion uniformity of the other components can be improved. Further, stearamide and oleamide have a certain antistatic effect, which can reduce the accumulation of dust and other impurities on the surface of the printed product, and at the same time improve the waterproof and moisture-proof performance of the printed film, thereby enhancing the service performance of the printed film.

[0068] By adding nano calcium carbonate and zinc oxide, light can be effectively scattered, light penetration can be reduced, the whiteness and glossiness of the printed film can be improved, thereby improving the light impermeability of the printed film. Further, adding nano calcium carbonate and zinc oxide can also improve the toughness, tensile strength and wear resistance of the printed film, and improve the service performance of the film.

[0069] In some embodiments, the mass fraction of the fluorescent whitening agent in the additive is 10wt.% - 20wt.%. Specifically, the mass fraction of the fluorescent whitening agent in the additive is 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.%, 20wt.%. The fluorescent whitening agent has a good whitening effect, can significantly improve the whiteness and brightness of the printed film, and can achieve an ideal whitening effect even at a low addition amount, further improving the light impermeability of the printed film.

[0070] In some embodiments, the fluorescent whitening agent includes one or more of fluorescent whitening agent OB, fluorescent whitening agent OB-1 and fluorescent whitening agent KSN. By selecting a fluorescent whitening agent with good heat resistance and weather resistance, while extending the service life of the printed film, the service performance of the printed film can be improved.

[0071] In some embodiments, the mass fraction of stearamide in the additive is 10wt.% - 20wt.%. Specifically, the mass fraction of stearamide in the additive is 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.%, 20wt.%. By adding stearamide, the smoothness and flatness of the printed film can be improved preferably, and the processing performance can be improved during the processing, the melt viscosity can be reduced, and the dispersion uniformity of the other components can be improved.

[0072] In some embodiments, the mass fraction of oleic acid amide in the additive is 5wt.% - 15wt.%. Specifically, the mass fraction of oleic acid amide in the additive is 5wt.%, 6wt.%, 7wt.%, 8wt.%, 9wt.%, 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%. By adding oleic acid amide, the smoothness and flatness of the printed film can be improved, and the processing performance can be improved during the processing, the melt viscosity can be reduced, and the dispersion uniformity of the other components can be improved.

[0073] In some embodiments, the mass fraction of nano calcium carbonate in the additive is 30wt.% - 45wt.%. Specifically, the mass fraction of nano calcium carbonate in the additive is 30wt.%, 32wt.%, 34wt.%, 36wt.%, 38wt.%, 40wt.%, 42wt.%, 44wt.%, 45wt.%. Nano calcium carbonate has a high specific surface area and good dispersibility, and can effectively scatter light and reduce the penetration of light, thereby improving the light impermeability of the printed film.

[0074] In some embodiments, the mass fraction of zinc oxide in the additive is 15wt.% - 25wt.%. Specifically, the mass fraction of zinc oxide in the additive is 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.%, 20wt.%, 21wt.%, 22wt.%, 23wt.%, 24wt.%, 25wt.%. Zinc oxide has a high refractive index and good photocatalytic activity, and can absorb ultraviolet light and scatter visible light, further reducing the light transmittance of the printed film.

[0075] In some embodiments, the first temperature in step S500 is 140°C - 200°C. Specifically, the first temperature is 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C. Further preferably, the first temperature is 140°C - 180°C. By selecting an appropriate grafting reaction temperature, the grafting efficiency of the modified titanium dioxide can be further improved.

[0076] In some embodiments, the reaction time of the grafting reaction in step S500 is 40min - 80min. Specifically, the reaction time is 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min. Further preferably, the reaction time is 50min - 70min. By selecting an appropriate grafting reaction time, the grafting efficiency of the modified titanium dioxide can be further improved.

[0077] In some embodiments, the thickness of the surface layer is 40 μm to 80 μm. Specifically, the thickness of the surface layer is 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm. By selecting an appropriate thickness of the surface layer, it is beneficial to improve the printing pattern effect of the printing film, maintain good mechanical properties and service performance, and reduce the possibility of damage.

[0078] In some embodiments, the thickness of the core layer is 200 μm to 400 μm. Specifically, the thickness of the core layer is 200 μm, 250 μm, 300 μm, 350 μm, 400 μm. By selecting an appropriate thickness of the core layer, the mechanical strength as the support layer is improved, and thus the tensile strength and puncture resistance of the printing film are enhanced.

[0079] According to another aspect of the present application, there is also provided a method for preparing a double-sided printing film, including the steps of:

[0080] A100, mixing modified titanium dioxide and an auxiliary agent by a high-speed mixer to obtain a first filler;

[0081] A200, mixing the first filler, polyethylene terephthalate and polypropylene by a high-speed mixer and then injecting them to obtain a surface layer;

[0082] A300, mixing modified titanium dioxide, polyethylene terephthalate and polypropylene by a high-speed mixer and then injecting them to obtain a core layer;

[0083] A400, co-extruding the surface layer and the core layer to obtain a double-sided printing film.

[0084] The double-sided printing film prepared by co-extruding the surface layer and the core layer has good interfacial adhesion, and thus enhances the tensile strength and puncture resistance of the double-sided printing film, and is suitable for maintaining good use stability in various application environments. The preparation method provided by the present application has simple steps, has the potential for large-scale production, increases production efficiency and thus enhances market competitiveness.

[0085] Example 1

[0086] A double-sided printing film is composed of a three-layer composite. The middle layer is the core layer, and both sides of the core layer are surface layers. The surface layer includes the following components by weight percentage: the mass fraction of PET is 58wt.%, the mass fraction of PP is 20wt.%, the mass fraction of modified titanium dioxide is 14wt.%, the mass fraction of nano calcium carbonate is 3.5wt.%, the mass fraction of zinc oxide is 2.5wt.%, the mass fraction of stearic acid amide is 1.5wt.%, the mass fraction of oleic acid amide is 1.5wt.%, and the mass fraction of fluorescent brightener is 1wt.%. The core layer includes the following components by weight percentage: the mass fraction of PET is 55wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 17wt.%.

[0087] Example 2

[0088] The difference between Example 2 and Example 1 is that the surface layer includes the following components by weight percentage: the mass fraction of PET is 59wt.%, the mass fraction of PP is 20wt.%, the mass fraction of modified titanium dioxide is 13wt.%, the mass fraction of nano calcium carbonate is 3.5wt.%, the mass fraction of zinc oxide is 2.5wt.%, the mass fraction of stearic acid amide is 1.5wt.%, the mass fraction of oleic acid amide is 1.5wt.%, and the mass fraction of fluorescent brightener is 1wt.%.

[0089] Example 3

[0090] The difference between Example 3 and Example 1 is that the surface layer includes the following components by weight percentage: the mass fraction of PET is 57wt.%, the mass fraction of PP is 20wt.%, the mass fraction of modified titanium dioxide is 15wt.%, the mass fraction of nano calcium carbonate is 3.5wt.%, the mass fraction of zinc oxide is 2.5wt.%, the mass fraction of stearic acid amide is 1.5wt.%, the mass fraction of oleic acid amide is 1.5wt.%, and the mass fraction of fluorescent brightener is 1wt.%.

[0091] Example 4

[0092] The difference between Example 4 and Example 1 is that the core layer includes the following components by weight percentage: the mass fraction of PET is 57wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 15wt.%.

[0093] Example 5

[0094] The difference between Example 5 and Example 1 is that the core layer includes the following components by weight percentage: the mass fraction of PET is 53wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 19wt.%.

[0095] Example 6

[0096] The difference between Example 6 and Example 1 is that the core layer comprises the following components by weight percentage: the mass fraction of PET is 60wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 19wt.%.

[0097] Example 7

[0098] The difference between Example 7 and Example 1 is that the core layer comprises the following components by weight percentage: the mass fraction of PET is 53wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 19wt.%.

[0099] Example 8

[0100] The difference between Example 8 and Example 1 is that the core layer comprises the following components by weight percentage: the mass fraction of PET is 53wt.%, the mass fraction of PP is 28wt.%, and the mass fraction of modified titanium dioxide is 19wt.%.

[0101] Example 9

[0102] The difference between Example 9 and Example 1 is that the surface layer comprises the following components by weight percentage: the mass fraction of PET is 68wt.%, the mass fraction of PP is 10wt.%, and the mass fraction of modified titanium dioxide is 14wt.%.

[0103] Example 10

[0104] The difference between Example 10 and Example 1 is that the core layer comprises the following components by weight percentage: the mass fraction of PET is 48wt.%, the mass fraction of PP is 30wt.%, and the mass fraction of modified titanium dioxide is 14wt.%.

[0105] Example 11

[0106] The difference between Example 11 and Example 1 is that the core layer comprises the following components by weight percentage: the mass fraction of PET is 58wt.%, the mass fraction of PP is 20wt.%, and the mass fraction of modified titanium dioxide is 14wt.%.

[0107] Comparative Example 1

[0108] The difference between Comparative Example 1 and Example 1 is that the titanium dioxide used is not modified.

[0109] Performance Evaluation

[0110] The tensile strength of the double-sided printed films in Examples 1 to 11 and Comparative Example 1 was detected in accordance with GB / T 1040.3, the haze was detected in accordance with GB / T 2410, the light transmittance of each group of films was analyzed using an ultraviolet-visible spectrophotometer with a scanning wavelength of 200 nm to 800 nm, the oxygen transmission rate was detected in accordance with ASTM D1434-23, and the water vapor transmission rate was detected in accordance with ASTM E96. The test results are shown in Table 1.

[0111] Table 1: Performance Tests of Double-Sided Printed Films

[0112]

[0113] It can be understood that different contents of modified titanium dioxide result in different properties of the prepared double-sided printed films. Referring to Examples 1, 2, and 4, when the content of modified titanium dioxide in the surface layer or the core layer is low, the tensile strength of the double-sided printed film is low, the haze decreases, and the light transmittance increases somewhat, indicating that the light-blocking property of the double-sided printed film is poor. Referring to Examples 1, 3, and 5, when the content of modified titanium dioxide in the surface layer or the core layer is high, the filler is prone to uneven dispersion, reducing the toughness of the printed film and thus the mechanical strength of the printed film. Further, due to the good interfacial adhesion between layers, the barrier properties against oxygen and water vapor are enhanced. The lower oxygen transmission rate and water vapor transmission rate in Table 1 also indicate that the printed film after using modified titanium dioxide has good weather resistance, is suitable for various usage environments, and enhances market competitiveness.

[0114] From Examples 1, 6, 7, and 8, it can be seen that when the content of modified titanium dioxide in the core layer is less than that in the surface layer, since the modified titanium dioxide in the core layer is difficult to generate good adhesion with the surface layer, the bonding performance between the core layer and the surface layer is reduced. Further, due to the decrease in the content of modified titanium dioxide, the light-blocking property of the printed film decreases accordingly.

[0115] Referring to Examples 1, 9, and 10, by regulating the component ratio between PET and PP in the surface layer, when the proportion of PP reaches 30%, it may lead to a small interfacial force between the two phases, large and unevenly distributed dispersed phase sizes, thus reducing the adhesion between the modified titanium dioxide and the PP component, and further reducing the mechanical properties of the printed film. On the one hand, the light-blocking performance of the printed film decreases somewhat. On the other hand, due to the decrease in the bonding performance, the barrier properties of the layer against water vapor and oxygen decrease accordingly. In other words, when the proportion of PP is low, since PET dominates in the system, it may lead to a decrease in the toughness and elongation at break of the printed film.

[0116] Furthermore, as can be seen from Example 1 and Example 11, when the PET and PP component ratios of the core layer and the surface layer are the same, at this time, the printing film prepared in Example 1 has a slight advantage over the printing film prepared in Example 11 in terms of mechanical strength and light-tightness. However, since the price of PP is lower than that of PET, the printing film prepared in Example 1 has the advantage of lower price, which is beneficial to reducing the production cost.

[0117] As can be seen from Example 1 and Comparative Example 1, since modified titanium dioxide that can react with PET and PP is not introduced into the printing film, the compatibility and adhesion between the components and between the layers in Comparative Example 1 are poor, thus significantly reducing the mechanical strength of the printing film. Further, due to the poor adhesion between the layers, the oxygen transmission rate and the water vapor transmission rate are high, indicating that the printing film in Comparative Example 1 has poor weather resistance and service performance.

[0118] The foregoing describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments. The above embodiments and the principles described in the specification are only for the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed. The scope of protection required by the present application is defined by the appended claims and their equivalents.

Claims

1. A double-sided printing film, characterized in that: The double-sided printing film is composed of a three-layer composite material, wherein the middle layer is a core layer, and both sides of the core layer are surface layers; The surface layer is prepared from polyethylene terephthalate, polypropylene, modified titanium dioxide and additives, wherein the mass fraction of polyethylene terephthalate in the surface layer is 50wt.%-60wt.%, the mass fraction of polypropylene is 10wt.%-20wt.%, the mass fraction of modified titanium dioxide is 5wt.%-15wt.%, and the mass fraction of the additive is 5wt.%-10wt.%; The core layer is prepared from polyethylene terephthalate, polypropylene and modified titanium dioxide, wherein the mass fraction of polyethylene terephthalate in the core layer is 50wt.%-60wt.%, the mass fraction of polypropylene is 20wt.%-30wt.%, and the mass fraction of modified titanium dioxide is 10wt.%-20wt.%; Wherein, the modified titanium dioxide is titanium dioxide with polypropylene grafted maleic anhydride on the surface, the mass fraction of the modified titanium dioxide in the core layer is greater than the mass fraction of the modified titanium dioxide in the surface layer, and the preparation steps of the modified titanium dioxide are: S100, putting titanium dioxide powder into anhydrous ethanol and performing ultrasonic treatment for 10 min to 30 min to obtain a first solution; S200, placing the first solution into a mixed solution of a silane coupling agent and anhydrous ethanol, stirring and reacting for 1 h to 3 h to obtain a first mixture; S300, centrifugally treating the first mixture, washing and drying the solid matter obtained by the centrifugation to obtain a first powder; S400, providing a mixed solution of xylene and ethanol, and placing the first powder and polypropylene grafted maleic anhydride into the mixed solution to obtain a second mixture; S500, adding dibenzoyl peroxide to the second mixture, raising the temperature to perform a grafting reaction, and obtaining a third mixture; S600, centrifugally treating the third mixture, washing and drying the solid matter obtained by the centrifugation to obtain modified titanium dioxide; The ratio of the molar number n1 of maleic anhydride groups in the polypropylene grafted maleic anhydride to the molar number n2 of epoxy groups in the first powder is: 1 / 10≤n1:n2≤1 / 2.

2. The double-sided printing film according to claim 1, characterized in that: The thickness of the surface layer is 40 μm to 80 μm, the thickness of the core layer is 200 μm to 400 μm, the particle size of the modified titanium dioxide is 30 nm to 60 nm, and the auxiliary agents include fluorescent whitening agent, stearic acid amide, oleic acid amide, nano calcium carbonate and zinc oxide.

3. The double-sided printing film according to claim 2, characterized in that: Among the auxiliary agents, the mass fraction of the fluorescent whitening agent is 10wt.%~20wt.%, the mass fraction of the stearic acid amide is 10wt.%~20wt.%, the mass fraction of the oleic acid amide is 5wt.%~15wt.%, the mass fraction of the nano-calcium carbonate is 30wt.%~45wt.%, and the mass fraction of the zinc oxide is 15wt.%~25wt.%.

4. A method for preparing a double-sided printed film, characterized in that: Includes steps: A100, mixing the modified titanium dioxide and the additive by a high-speed mixer to obtain a first filler; A200, mixing the first filler, polyethylene terephthalate and polypropylene by a high-speed mixer and then performing injection molding to obtain a surface layer; A300, the modified titanium dioxide, polyethylene terephthalate and polypropylene are mixed by a high-speed mixer and then injection molded to obtain a core layer; A400, the surface layer and the core layer are co-extruded to obtain the double-sided printed film.

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