Double-sided printed polyester base film and preparation method thereof

Abstract

The invention provides a double-sided printed polyester base film and a preparation method thereof, the polyester base film is an A-B-A structure, the A structure is a composite layer, and the B structure is a support layer; the composite layer sequentially comprises a light absorption layer, a transition layer and a light reflection layer in the direction away from the supporting layer; the composite layer comprises a light absorption material; wherein the content of the light-absorbing material in unit volume is gt of the light-absorbing layer; a transition layer gt; a reflective layer; the reflective layer comprises a reflective material. In the scheme, due to the design of the A-B-A structure, both sides of the film can be printed, and the application flexibility is improved, especially in a scene needing double-side pattern printing. And on the other hand, through the light absorption, transition and light reflection design of the composite layer, the film has the effects of low light transmission and high reflection, so that the visual effect of pattern printing is better.

Description

Technical Field

[0001] The invention relates to the technical field of polyester base films, and in particular to a double-sided printed polyester base film and a preparation method thereof. Background Art

[0002] Polyester-based films are widely used in many fields due to their excellent physical and chemical properties. For example, polyester films have excellent sealing, barrier and transparency properties, and can be used for food packaging to protect food from the effects of air, moisture and light, and extend the shelf life of food. In addition, polyester films are also widely used in labels, advertising posters, commercial signs and other fields because of their smooth surface, suitable for high-quality printing, and good durability.

[0003] However, in the process of poster printing, for hanging posters, a double-sided printing effect is required, so there are certain requirements for the light transmittance of the film material, which is often difficult to meet with the existing technology. Summary of the invention

[0004] In order to solve at least one of the above problems, the present invention provides a double-sided printed polyester base film, wherein the polyester base film is an ABA structure, wherein the A structure is a composite layer and the B structure is a support layer; along the direction away from the support layer, the composite layer includes a light-absorbing layer, a transition layer and a light-reflecting layer in sequence; the composite layer includes a light-absorbing material; wherein the content of the light-absorbing material per unit volume is: light-absorbing layer>transition layer>reflecting layer; and the reflective layer includes a reflective material.

[0005] In this technical solution, the structure of the polyester base film is presented as three layers, the outer side is a composite layer (including a light-absorbing layer, a transition layer and a reflective layer), and the middle is a support layer. This structure is conducive to double-sided printing. Among them, the support layer selects PET film as the base material, which mainly plays a supporting role. The composite layer includes a light-absorbing layer, a transition layer and a reflective layer. The effect of low light transmittance and high reflection is achieved by setting the structure. On the one hand, the light transmittance of the film material is reduced, and on the other hand, the reflection of light is increased, which can make the printing effect better. Specifically, the effect of low light transmittance is achieved by light-absorbing materials. The light-absorbing layer contains light-absorbing materials, and the content of light-absorbing materials per unit volume gradually decreases along the direction away from the support layer; the brightening effect is mainly achieved by setting a reflective layer. The reflective layer contains reflective materials. Therefore, when the light reaches the surface of the polyester base film, part of the light is reflected, and the remaining light enters the transition layer and the light-absorbing layer. Since the mass proportion of the light-absorbing material in each layer is increasing, it cannot pass through the film material, thereby ensuring the low light transmittance of the film material. In the above scheme, the content of the light-absorbing material is decreasing, that is, the light-absorbing layer is higher than the transition layer, and the transition layer is higher than the reflective layer. Such a design can make the light gradually absorbed or reflected in the structure of the film, thereby enhancing the overall printing effect of the film material.

[0006] The benefits of adopting this technical solution are: 1. Due to the design of the ABA structure, both sides of the film can be printed, which increases the flexibility of application, especially in scenarios where double-sided pattern printing is required. 2. Through the light absorption, transition and reflective design of the composite layer, the film has the effect of low light transmittance and high reflection, so the visual effect of pattern printing is better.

[0007] Furthermore, the light-absorbing material is selected from at least one of carbon black, graphene, carbon nanotubes, black titanium, and ceramic materials; and / or the light-reflecting material is hollow glass microbeads.

[0008] The present invention also provides a method for preparing the polyester base film, comprising the following steps: S10: obtaining a support layer, and performing surface treatment on one side of the support layer; S20: sequentially coating the surface-treated support layer with a light-absorbing layer slurry, a transition layer slurry, and a light-reflecting layer slurry; wherein the light-absorbing layer slurry contains a light-absorbing material, and the light-reflecting layer slurry contains a light-reflecting material; S30: performing surface treatment on the other side of the support layer, and repeating step S20 to obtain a polyester base film.

[0009] Furthermore, in step S10 and step S30, the surface treatment is corona treatment, and the discharge intensity is controlled to be 4-10 kV.

[0010] Further, step S20 includes coating the light absorbing layer slurry; specifically includes the following steps: A: Obtain a light-absorbing material and perform ball-milling treatment, disperse the ball-milled light-absorbing material in sodium alginate and an organic solvent, and filter and dry after ultrasonic stirring to obtain a modified light-absorbing material; B: Prepare the light absorbing layer slurry according to the ratio of 80-90 parts of PET resin, 5-10 parts of modified light absorbing material, and 0-3 parts of auxiliary agent; C: Apply the light absorbing layer slurry to the surface of the support layer to obtain the light absorbing layer. The coating temperature is controlled to be 5-10°C and the coating amount is 4-6g / m 2 .

[0011] Furthermore, in terms of mass, the ratio of the light absorbing material, sodium alginate and the organic solvent is 1:(0.2-0.5):(3-4); and / or The ultrasonic power of ultrasonic stirring is 30-50w, and the stirring time is 2-3h.

[0012] Further, step S20 includes coating the transition layer slurry; specifically includes the following steps: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times. After the spraying is completed, the slurry is kept at the spraying temperature of the second spraying for 15-30 minutes to obtain the transition layer.

[0013] In the first spraying, the transition layer slurry includes 100 parts of PET resin, 0.5-0.8 parts of calcium sulfate dihydrate, and 0-3 parts of additives according to mass parts; the spraying temperature is 40-45℃, and the spraying amount is 2-3g / m 2 ; In the second spraying, the transition layer slurry includes 80-90 parts of PET resin, 0.1-0.3 parts of calcium sulfate dihydrate, and 0-3 parts of additives according to mass parts; the spraying temperature is room temperature, and the spraying amount is 1-1.5g / m 2 .

[0014] Furthermore, step S20 includes coating a reflective layer slurry; specifically, the following steps are included: Prepare the reflective layer slurry according to 60-70 parts of PET resin, 15-20 parts of UV varnish, 10-12 parts of reflective material and 0-3 parts of additives; Apply the reflective layer slurry to the surface of the transition layer, let it stand for 15-30 minutes, and cure it with ultraviolet light to obtain the reflective layer; The coating amount of the reflective layer slurry is 3-5 g / m 2 .

[0015] Furthermore, the reflective material is hollow glass microspheres, and the particle size of the hollow glass microspheres is 20-50 microns. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0017] Figure 1 This is a schematic structural diagram of a polyester base film provided in Example 1 of the present invention.

[0018] Reference numerals: 1-support layer; 2-light-absorbing layer; 21-light-absorbing material; 3-transition layer; 4-light-reflecting layer; 41-light-reflecting material. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] See also Figure 1The present invention provides a double-sided printed polyester base film, the polyester base film is an ABA structure, wherein the A structure is a composite layer, and the B structure is a support layer 1; along the direction away from the support layer 1, the composite layer sequentially includes a light absorbing layer 2, a transition layer 3 and a light reflecting layer 4; the composite layer includes a light absorbing material 21; wherein the content of the light absorbing material 21 per unit volume is: light absorbing layer 2>transition layer 3>reflecting layer 4; the reflective layer 4 includes a reflective material 41.

[0021] In this technical solution, the structure of the polyester base film is three layers, the outer side is a composite layer (including a light-absorbing layer 2, a transition layer 3 and a light-reflecting layer 4), and the middle is a support layer 1. This structure is conducive to double-sided printing. Among them, the support layer 1 selects PET film as the base material, which mainly plays a supporting role. The composite layer includes a light-absorbing layer 2, a transition layer 3 and a light-reflecting layer 4. The effect of low light transmittance and high reflection is achieved by setting the structure. On the one hand, the light transmittance of the film material is reduced, and on the other hand, the reflection of light is increased, which can make the printing effect better. Specifically, the effect of low light transmittance is achieved by the light-absorbing material 21. The light-absorbing layer 2 contains the light-absorbing material 21, and the mass proportion of the light-absorbing material 21 gradually decreases along the direction away from the support layer 1; the brightening effect is mainly achieved by setting the reflective layer 4. The reflective layer 4 contains the reflective material 41, so when the light reaches the surface of the polyester base film, part of the light is reflected, and the remaining light enters the transition layer 3 and the light-absorbing layer 2. Due to the increasing content of the light-absorbing material 21, it cannot pass through the film material, thereby ensuring the low light transmittance of the film material. In the above scheme, the content of the light absorbing material 21 is decreasing, that is, the light absorbing layer 2 is higher than the transition layer 3, and the transition layer 3 is higher than the reflective layer 4. Such a design allows light to be gradually absorbed or reflected in the film structure, thereby enhancing the overall printing effect of the film material.

[0022] Furthermore, the light-absorbing material is selected from at least one of carbon black, graphene, carbon nanotubes, black titanium, and ceramic materials; and / or the light-reflecting material is hollow glass microbeads.

[0023] The present invention also provides a method for preparing the polyester base film, comprising the following steps: S10: obtaining a support layer, and performing surface treatment on one side of the support layer; S20: sequentially coating the surface-treated support layer with a light-absorbing layer slurry, a transition layer slurry, and a light-reflecting layer slurry; wherein the light-absorbing layer slurry contains a light-absorbing material, and the light-reflecting layer slurry contains a light-reflecting material; S30: performing surface treatment on the other side of the support layer, and repeating step S20 to obtain a polyester base film.

[0024] In the above technical solution, the preparation method adopts a process combining surface treatment and coating to ensure that the various layers of the polyester base film can be evenly attached and work effectively. Specifically: by treating the surface of the support layer, the adhesion between the support layer and the coating layer (such as the light-absorbing layer, transition layer, and reflective layer) is improved, and the shedding or peeling of the coating layer is avoided. Coating the light-absorbing layer, transition layer, and reflective layer: The coating of each layer is carried out in sequence to ensure that the composite structure of the film can be stably formed. The different material selections for the light-absorbing layer, transition layer, and reflective layer give the film excellent comprehensive properties.

[0025] Furthermore, in step S10 and step S30, the surface treatment is corona treatment, and the discharge intensity is controlled to be 4-10 kV.

[0026] Among them, corona treatment is a common surface treatment technology. The ionized air generated by high-voltage corona discharge interacts with the surface of the support layer, causing the surface molecular structure to change and forming a surface with polar groups. This process can significantly increase the hydrophilicity or lipophilicity of the material surface, giving it a higher surface energy, thereby improving the adhesion of the coating layer (such as the light-absorbing layer, transition layer and reflective layer).

[0027] Further, step S20 includes coating the light absorbing layer slurry; specifically includes the following steps: A: Obtain a light-absorbing material and perform ball-milling treatment, disperse the ball-milled light-absorbing material in sodium alginate and an organic solvent, and filter and dry after ultrasonic stirring to obtain a modified light-absorbing material; B: Prepare the light absorbing layer slurry according to the ratio of 80-90 parts of PET resin, 5-10 parts of modified light absorbing material, and 0-3 parts of auxiliary agent; C: Apply the light absorbing layer slurry to the surface of the support layer to obtain the light absorbing layer. The coating temperature is controlled to be 5-10°C and the coating amount is 4-6g / m 2 .

[0028] In the above scheme, the ball milling treatment of the light absorbing material reduces its particle size and increases the specific surface area of ​​the material. This physical modification can improve the uniformity of the particle size of the light absorbing material, which is beneficial to its dispersion effect. Ultrasonic stirring is used to ensure good dispersion of the light absorbing material and avoid material agglomeration, which is crucial to ensure the uniformity and stability of the film. Among them, the organic solvent can be selected from acetone, tetrahydrofuran, n-propanol, etc.

[0029] In the preparation of the light-absorbing layer slurry, the selection of PET resin provides basic structural support. Since the support layer selects PET film, the main body of the slurry is also preferably PET resin, wherein the role of the modified light-absorbing material is to reduce the light transmittance of the film material. Whether to add auxiliary agents or not, those skilled in the art can choose according to common knowledge and actual needs, such as adding leveling agents, defoaming agents, dispersants, surfactants or other auxiliary agents. Among them, the leveling agent can select silane leveling agents and acrylic leveling agents, the defoaming agent can select silicone oil defoaming agents, the dispersant can select fatty acid salts and polyurethane defoaming agents, and the surfactant can select epoxy acrylic acid and silane coupling agents.

[0030] Furthermore, in terms of weight, the ratio of the light absorbing material, sodium alginate and the organic solvent is 1:(0.2-0.5):(3-4); and / or the ultrasonic power of the ultrasonic stirring is 30-50w, and the stirring time is 2-3h.

[0031] In this embodiment, sodium alginate is used to modify the surface of the light-absorbing material, and the surface of the light-absorbing material is coated with sodium alginate through ultrasonic dispersion and drying processes, and a transition layer slurry is further sprayed. The transition layer slurry contains calcium sulfate dihydrate, and calcium ions can be cross-linked and chelated with sodium alginate, thereby achieving the traction of the light-absorbing material and the change of its concentration gradient. Specifically, through two sprayings, and setting different concentrations of calcium sulfate dihydrate and spraying conditions, the content of the light-absorbing material per unit volume in the prepared composite layer is: light-absorbing layer>transition layer>reflective layer.

[0032] Further, step S20 includes coating the transition layer slurry; specifically includes the following steps: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times. After the spraying is completed, the slurry is kept at the spraying temperature of the second spraying for 15-30 minutes to obtain the transition layer.

[0033] In the first spraying, the transition layer slurry includes 100 parts of PET resin, 0.5-0.8 parts of calcium sulfate dihydrate, and 0-3 parts of additives according to mass parts; the spraying temperature is 40-45℃, and the spraying amount is 2-3g / m 2 ; In the second spraying, the transition layer slurry includes 80-90 parts of PET resin, 0.1-0.3 parts of calcium sulfate dihydrate, and 0-3 parts of additives according to mass parts; the spraying temperature is room temperature, and the spraying amount is 1-1.5g / m 2 .

[0034] Furthermore, step S20 includes coating a reflective layer slurry; specifically, the following steps are included: Prepare the reflective layer slurry according to 60-70 parts of PET resin, 15-20 parts of UV varnish, 10-12 parts of reflective material and 0-3 parts of additives; Apply the reflective layer slurry to the surface of the transition layer, let it stand for 15-30 minutes, and cure it with ultraviolet light to obtain the reflective layer; The coating amount of the reflective layer slurry is 3-5 g / m 2 .

[0035] This technical solution is to further add the coating process of the reflective layer on the basis of the aforementioned transition layer. The ratio of the reflective layer slurry contains PET resin as the main base material, UV varnish is used to accelerate the curing process, and the reflective material is the key component to improve the light reflection effect. Through UV curing, the reflective layer is cured and formed in a short time, and its adhesion and durability are ensured. The coating amount is controlled at 3-5 g / m², and the two-step operation of static and UV curing is used to ensure that the coating is uniform, stable and has a good reflective effect.

[0036] Furthermore, the reflective material is hollow glass microspheres, and the particle size of the hollow glass microspheres is 20-50 microns.

[0037] Example 1 This embodiment provides a method for preparing a double-sided printed polyester base film, comprising the following steps: 1. Obtain a support layer and perform corona treatment on one side of the support layer, controlling the discharge intensity to 10 kV.

[0038] 2. Apply the light absorbing layer slurry on the surface treated support layer: Obtain light-absorbing material and perform ball milling, disperse the ball-milled light-absorbing material in sodium alginate and an organic solvent, and filter and dry after ultrasonic stirring to obtain a modified light-absorbing material; the ultrasonic power of ultrasonic stirring is 50w, and the stirring time is 3h. Among them, in terms of mass, the ratio of light-absorbing material, sodium alginate and organic solvent is 1:0.5:4; the light-absorbing material is carbon black.

[0039] Prepare the light absorbing layer slurry according to the ratio of 90 parts of PET resin and 10 parts of modified light absorbing material; The light absorbing layer slurry was coated on the surface of the support layer to obtain a light absorbing layer. The coating temperature was controlled to be 10°C and the coating amount was 6 g / m 2 .

[0040] 3. Apply transition layer slurry: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times. After the spraying is completed, the slurry is kept at the spraying temperature of the second spraying for 30 minutes to obtain the transition layer.

[0041] In the first spraying, the transition layer slurry includes 100 parts of PET resin and 0.8 parts of calcium sulfate dihydrate by weight; the spraying temperature is 45°C and the spraying amount is 3g / m 2 ; In the second spraying, the transition layer slurry includes 90 parts of PET resin, 0.3 parts of calcium sulfate dihydrate, and 3 parts of additives according to mass. The spraying temperature is room temperature and the spraying amount is 1.5g / m 2 .

[0042] 4. Coating reflective layer slurry: The reflective layer slurry is prepared according to 70 parts of PET resin, 20 parts of UV varnish, 12 parts of reflective material and 3 parts of additives; the reflective material is hollow glass microbeads, and the particle size of the hollow glass microbeads is 50 microns.

[0043] The reflective layer slurry was coated on the surface of the transition layer, left to stand for 30 minutes, and cured by ultraviolet light to obtain the reflective layer; the coating amount of the reflective layer slurry was 5 g / m 2 .

[0044] 5. Perform surface treatment on the other side of the support layer and repeat steps 2-4 to obtain a polyester base film.

[0045] Example 2 The present invention provides a method for preparing a double-sided printed polyester base film, comprising the following steps: 1. Obtain a support layer and perform corona treatment on one side of the support layer, controlling the discharge intensity to 4 kV.

[0046] 2. Apply the light absorbing layer slurry on the surface treated support layer: Obtain light-absorbing material and perform ball milling, disperse the ball-milled light-absorbing material in sodium alginate and an organic solvent, and filter and dry after ultrasonic stirring to obtain a modified light-absorbing material; the ultrasonic power of ultrasonic stirring is 30w, and the stirring time is 2h. Among them, in terms of mass, the ratio of light-absorbing material, sodium alginate and organic solvent is 1:0.2:3; the light-absorbing material is graphene.

[0047] Prepare the light absorbing layer slurry according to the ratio of 80 parts of PET resin and 5 parts of modified light absorbing material; The light absorbing layer slurry was coated on the surface of the support layer to obtain a light absorbing layer. The coating temperature was controlled to be 5°C and the coating amount was 4 g / m 2 .

[0048] 3. Apply transition layer slurry: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times. After the spraying is completed, the slurry is kept at the spraying temperature of the second spraying for 15 minutes to obtain the transition layer.

[0049] In the first spraying, the transition layer slurry includes 100 parts of PET resin and 0.5 parts of calcium sulfate dihydrate by weight; the spraying temperature is 40°C and the spraying amount is 2g / m 2 ; In the second spraying, the transition layer slurry includes 80 parts of PET resin and 0.1 parts of calcium sulfate dihydrate according to mass. The spraying temperature is room temperature and the spraying amount is 1g / m 2 .

[0050] 4. Coating reflective layer slurry: The reflective layer slurry is prepared according to 60 parts of PET resin, 15 parts of UV varnish and 10 parts of reflective material; the reflective material is hollow glass microbeads, and the particle size of the hollow glass microbeads is 20 microns.

[0051] The reflective layer slurry was coated on the surface of the transition layer, left to stand for 15 minutes, and cured by ultraviolet light to obtain the reflective layer; the coating amount of the reflective layer slurry was 3g / m 2 .

[0052] 5. Perform surface treatment on the other side of the support layer and repeat steps 2-4 to obtain a polyester base film.

[0053] Example 3 The present invention provides a method for preparing a double-sided printed polyester base film, comprising the following steps: 1. Obtain a support layer and perform corona treatment on one side of the support layer, controlling the discharge intensity to 6 kV.

[0054] 2. Apply the light absorbing layer slurry on the surface treated support layer: The light-absorbing material is obtained and ball-milled, and the ball-milled light-absorbing material is dispersed in sodium alginate and an organic solvent, and filtered and dried after ultrasonic stirring to obtain a modified light-absorbing material; the ultrasonic power of the ultrasonic stirring is 40w, and the stirring time is 3h. Among them, in terms of mass, the ratio of the light-absorbing material, sodium alginate and the organic solvent is 1:0.3:3; the light-absorbing material is black titanium.

[0055] Prepare the light absorbing layer slurry according to the ratio of 85 parts of PET resin, 7 parts of modified light absorbing material and 3 parts of auxiliary agent; The light absorbing layer slurry was coated on the surface of the support layer to obtain a light absorbing layer. The coating temperature was controlled to be 6°C and the coating amount was 5 g / m 2 .

[0056] 3. Apply transition layer slurry: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times. After the spraying is completed, the slurry is kept at the spraying temperature of the second spraying for 18 minutes to obtain the transition layer.

[0057] In the first spraying, the transition layer slurry includes 100 parts of PET resin, 0.6 parts of calcium sulfate dihydrate, and 3 parts of additives according to mass parts; the spraying temperature is 42°C, and the spraying amount is 2g / m 2 ; In the second spraying, the transition layer slurry includes 87 parts of PET resin, 0.2 parts of calcium sulfate dihydrate, and 3 parts of additives according to mass. The spraying temperature is room temperature and the spraying amount is 1g / m 2 .

[0058] 4. Coating reflective layer slurry: The reflective layer slurry is prepared according to 66 parts of PET resin, 17 parts of UV varnish, 11 parts of reflective material and 3 parts of additives; the reflective material is hollow glass microbeads, and the particle size of the hollow glass microbeads is 40 microns.

[0059] The reflective layer slurry was coated on the surface of the transition layer, left to stand for 20 minutes, and cured by ultraviolet light to obtain the reflective layer; the coating amount of the reflective layer slurry was 4g / m 2 .

[0060] 5. Perform surface treatment on the other side of the support layer and repeat steps 2-4 to obtain a polyester base film.

[0061] In the above steps, the auxiliary agent includes 1 part of silane leveling agent, 1 part of polyurethane defoaming agent, and 1 part of silane coupling agent.

[0062] Comparative Example 1 This comparative example provides a method for preparing a double-sided printed polyester base film. The preparation process thereof is similar to that of Example 1, except that no light absorbing material is added.

[0063] Comparative Example 2 This comparative example provides a method for preparing a double-sided printed polyester base film. The preparation process thereof is similar to that of Example 1, except that the light absorbing material is not modified.

[0064] Comparative Example 3 This comparative example provides a method for preparing a double-sided printed polyester base film. The preparation process thereof is similar to that of Example 1, except that no transition layer is coated.

[0065] Comparative Example 4 This comparative example provides a method for preparing a double-sided printed polyester base film. The preparation process thereof is similar to that of Example 1, except that no reflective material is added.

[0066] The polyester base films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Table 1. The test of light transmittance is shown in GB / T 2410, and the test of glossiness is shown in GB / T 9754. As can be seen from Table 1, the technical solution provided by the present invention significantly improves the glossiness of the polyester base film and reduces its light transmittance.

[0067] Table 1

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double-sided printed polyester base film, characterized in that: The polyester base film is an ABA structure, wherein the A structure is a composite layer and the B structure is a support layer; Along the direction away from the support layer, the composite layer includes a light absorbing layer, a transition layer and a light reflecting layer in sequence; The composite layer includes a light-absorbing material; wherein the content of the light-absorbing material per unit volume is: light-absorbing layer>transition layer>reflective layer; The reflective layer includes reflective material.

2. The polyester base film according to claim 1, characterized in that The light absorbing material is selected from at least one of carbon black, graphene, carbon nanotubes, black titanium, and ceramic materials; and / or The reflective material is hollow glass microspheres.

3. A method for preparing a polyester base film as claimed in claim 1 or 2, characterized in that: The following steps are involved: S10: obtaining a support layer, and performing surface treatment on one side of the support layer; S20: sequentially coating the light absorbing layer slurry, the transition layer slurry and the light reflecting layer slurry on the surface treated support layer; Wherein, the light-absorbing layer slurry contains the light-absorbing material, and the light-reflecting layer slurry contains the light-reflecting material; S30: performing surface treatment on the other side of the support layer, and repeating step S20 to obtain the polyester base film.

4. The preparation method according to claim 3, characterized in that: In step S10 and step S30, the surface treatment is corona treatment, and the discharge intensity is controlled to be 4-10 kV.

5. The preparation method according to claim 3, characterized in that: Step S20 includes coating the light absorbing layer slurry; specifically includes the following steps: A: obtaining a light-absorbing material and subjecting it to ball-milling treatment, dispersing the light-absorbing material after ball-milling in sodium alginate and an organic solvent, and filtering and drying after ultrasonic stirring to obtain a modified light-absorbing material; B: Prepare the light absorbing layer slurry according to the ratio of 80-90 parts of PET resin, 5-10 parts of modified light absorbing material, and 0-3 parts of auxiliary agent; C: coating the light absorbing layer slurry onto the surface of the support layer to obtain the light absorbing layer, controlling the coating temperature to be 5-10°C and the coating amount to be 4-6 g / m 2 .

6. The preparation method according to claim 5, characterized in that: In terms of parts by mass, the ratio of the light absorbing material, the sodium alginate and the organic solvent is 1:(0.2-0.5):(3-4); and / or The ultrasonic power of the ultrasonic stirring is 30-50w, and the stirring time is 2-3h.

7. The preparation method according to claim 3, characterized in that: Step S20 includes applying a transition layer slurry; specifically includes the following steps: The transition layer slurry is sprayed onto the surface of the light absorbing layer for two times, and after the spraying is completed, the transition layer is kept at the spraying temperature of the second spraying for 15-30 minutes to obtain the transition layer; In the first spraying, the transition layer slurry includes 100 parts of PET resin, 0.5-0.8 parts of calcium sulfate dihydrate, and 0-3 parts of additives according to mass parts; the spraying temperature is 40-45°C, and the spraying amount is 2-3g / m 2 ; During the second spraying, the transition layer slurry includes 80-90 parts of PET resin, 0.1-0.3 parts of calcium sulfate dihydrate, and 0-3 parts of additives, according to mass parts; the spraying temperature is room temperature, and the spraying amount is 1-1.5g / m 2 .

8. The preparation method according to claim 3, characterized in that: Step S20 includes coating the reflective layer slurry; specifically includes the following steps: The reflective layer slurry is prepared according to 60-70 parts of PET resin, 15-20 parts of UV varnish, 10-12 parts of reflective material and 0-3 parts of additives; The reflective layer slurry is applied to the surface of the transition layer, left to stand for 15-30 minutes, and cured by ultraviolet light to obtain the reflective layer; The coating amount of the reflective layer slurry is 3-5 g / m 2 .

9. The preparation method according to claim 8, characterized in that: The reflective material is hollow glass microspheres, and the particle size of the hollow glass microspheres is 20-50 microns.

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