Electronic paper protective film

Abstract

An electronic paper protective film includes a substrate layer, an inorganic silicon-containing layer is sputtered on one side of the substrate layer by magnetron sputtering, and a hardening liquid layer is coated on the other side of the substrate layer. It realizes the integrated coating of ultraviolet cutoff function and hardening function, reduces the coating process, and reduces the production cost.

Description

Technical Field

[0001] The present invention relates to the field of thin film optical technology, and in particular to an electronic paper protective film. Background Art

[0002] Electronic Paper Display (EPD) is a special thin display screen, also known as "electronic ink screen". Different from traditional display screens, electronic ink screens do not emit light themselves, but rely on reflecting ambient light to display images, so there is no backlight or backlight module. Electronic ink screens are widely used due to their low power consumption, large viewing angle, eye protection and reusability. The components of electronic ink screens include substrates, electronic paper, protective films and electronic components, among which the protective film plays a vital role in protecting electronic paper.

[0003] When electronic ink screens are used in outdoor displays, such as bus stops and billboards, the ultraviolet rays in sunlight will seriously age the electronic ink and materials, so the adhesive layer of the protective film must have the ability to cut off ultraviolet rays. The greatest threat to the material comes from the UV-A band (315nm-380nm) and UV-B band (280nm-315nm) in sunlight. Adding ultraviolet absorbers to the protective film is an effective method to protect the electronic ink material from damage.

[0004] The existing electronic paper protective film is made of anti-glare film and water vapor barrier film, and the UV cutoff function is added to the laminating adhesive. This process is more complicated and increases the product quality risk in the multi-step process. There is also a technology that realizes the anti-glare function and water vapor barrier function in the same PET (polyethylene terephthalate), but the UV cutoff coating needs to be completed before the anti-glare coating is applied. This technical method not only has many coating times, but also a complex process and high cost. The UV absorber coating is thin and has a high concentration, which is prone to saturation precipitation under reliability conditions.

[0005] CN201920173900.4 discloses a protective film, comprising: a substrate layer, which is composed of a transparent material and has no birefringence; a hardening coating for scratch prevention; the hardening coating is a cross-linked polyacrylate coating; an isolation layer, which is arranged between the substrate layer and the hardening coating and is used to isolate the substrate layer from the hardening coating; the isolation layer is composed of a polyacrylate material or a polyester material.

[0006] CN201210204968.7 discloses an anti-glare screen protective film, whose main structure includes: a main film, an installation glue layer, an installation glue protective film, an anti-glare and scratch-resistant layer, a protective film glue layer and an anti-scratch layer protective film; wherein the main film, the installation glue protective film and the anti-scratch layer protective film are film structures made of PET material, and the installation glue layer, the anti-glare and scratch-resistant layer and the protective film glue layer are glue structures of different properties.

[0007] CN202123428316.5 discloses a barrier film structure for electronic paper packaging, comprising a polymer substrate layer, a barrier layer is provided on one side of the polymer substrate layer, and a diffusion layer is provided on the other side of the polymer substrate layer; the barrier layer has a single layer, a double layer or multiple layers.

[0008] In the prior art, the ultraviolet absorber is added to the diffusion layer or anti-glare coating. The diffusion layer or anti-glare layer is relatively thin, and a high concentration of ultraviolet absorber needs to be added to meet the ultraviolet cut-off requirements, which is prone to the problem of high-concentration crystal precipitation. If the thickness of the diffusion layer or anti-glare layer is increased, after the photocuring process, the thick diffusion layer or AG layer will cause warping problems. Summary of the invention

[0009] In order to solve the above problems, the present invention first provides an electronic paper protective film, which includes a substrate layer, an inorganic silicon-containing layer is sputtered on one side of the substrate layer by magnetron sputtering, and a hardening liquid layer is coated on the other side of the substrate layer, and the hardening layer coating liquid contains a main agent, a curing agent, an ultraviolet absorber and a solvent, wherein the main agent is 40-50 parts, the curing agent is 2-3 parts, the ultraviolet absorber is 2-3 parts, and the solvent is 44-56 parts, totaling 100 parts and all are parts by weight.

[0010] Furthermore, the substrate layer is selected from polyethylene terephthalate (PET) or triacetate cellulose film (TAC).

[0011] Furthermore, the thickness of the substrate layer is 50-100 μm, or 60 μm, 80 μm, or 90 μm.

[0012] Furthermore, the inorganic silicon-containing layer is a water vapor barrier layer.

[0013] Furthermore, the inorganic silicon-containing layer is a silicon oxide layer or a silicon nitride layer.

[0014] Furthermore, the thickness of the inorganic silicon-containing layer is 60-120 nm, or 80 nm, 100 nm, or 110 nm.

[0015] Furthermore, the silicon oxide layer or silicon nitride layer is deposited by reactive sputtering using a high-purity silicon target in a mixed atmosphere of argon, oxygen or nitrogen, and the power of the silicon target is 12-22 kW, or 15 kW, 18 kW, or 20 kW.

[0016] Furthermore, the main agent of the hardening layer coating liquid is selected from one of acrylic resin, polyurethane, propylene polyol and epoxy resin.

[0017] Furthermore, the weight proportion of the main agent of the hardening layer coating liquid is 42 parts, 45 parts, or 48 parts.

[0018] Furthermore, the curing agent of the hardening layer coating solution is selected from one of toluene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, and trimethylcyclohexyl diisocyanate.

[0019] Furthermore, the weight proportion of the curing agent in the hardened layer coating liquid is 2.2 parts, 2.5 parts, or 2.8 parts.

[0020] Furthermore, the ultraviolet absorber of the hardening layer coating solution is selected from one of benzophenone, salicylate, benzotriazole and triazine.

[0021] Furthermore, the weight proportion of the ultraviolet absorber in the hardening layer coating liquid is 2.2 parts, 2.5 parts, or 2.8 parts.

[0022] Furthermore, the organic solvent of the hardening layer coating solution is one of ethyl acetate, butyl acetate and cyclohexanone.

[0023] Furthermore, the weight proportion of the organic solvent in the hardening layer coating liquid is 48 parts, 50 parts, or 54 parts.

[0024] The present invention also provides a method for preparing an electronic paper protective film, comprising:

[0025] Step (1), selecting a substrate layer: selecting a polyethylene terephthalate (PET) or triacetate cellulose film (TAC) substrate as the substrate layer;

[0026] Step (2), sputtering an inorganic silicon-containing layer: magnetron sputtering an inorganic silicon-containing layer on one side of the substrate layer;

[0027] Step (3), preparing a hardening layer coating liquid: mixing a main agent, a curing agent, an ultraviolet absorber, and a solvent, and stirring the mixture sufficiently to obtain a hardening layer coating liquid;

[0028] Step (4), coating a hardening layer: coating the hardening layer coating liquid on the other side of the substrate layer, and curing it to obtain an electronic paper protective film.

[0029] Furthermore, in step (1), the substrate layer is selected from polyethylene terephthalate (PET) or triacetate cellulose film (TAC).

[0030] Furthermore, in step (1), the thickness of the substrate layer is 50-100 μm, or 60 μm, 80 μm, or 90 μm.

[0031] Furthermore, in step (2), the inorganic silicon-containing layer is a water vapor barrier layer.

[0032] Furthermore, in step (2), the inorganic silicon-containing layer is a silicon oxide layer or a silicon nitride layer.

[0033] Furthermore, in step (2), the thickness of the inorganic silicon-containing layer is 60-120 nm, or 80 nm, 100 nm, or 110 nm.

[0034] Furthermore, in step (2), the silicon oxide layer or silicon nitride layer is deposited by reactive sputtering using a high-purity silicon target in an argon, oxygen or nitrogen mixed atmosphere, and the power of the silicon target is 12-22 kW, or 15 kW, 18 kW, or 20 kW.

[0035] Furthermore, in step (2), a high-purity silicon target power supply is used, with a power of 12-22 kW, or 15 kW, 18 kW, or 20 kW.

[0036] Furthermore, in step (3), the main agent of the hardening layer coating liquid is selected from one of acrylic resin, polyurethane, propylene polyol, and epoxy resin.

[0037] Furthermore, in step (3), the weight proportion of the main agent of the hardening layer coating liquid is 42 parts, 45 parts, or 48 parts.

[0038] Furthermore, in step (3), the curing agent of the hardened layer coating solution is selected from one of toluene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, and trimethylcyclohexyl diisocyanate.

[0039] Furthermore, in step (3), the weight proportion of the curing agent in the hardened layer coating liquid is 2.2 parts, 2.5 parts, or 2.8 parts.

[0040] Furthermore, in step (3), the ultraviolet absorber of the hardening layer coating solution is selected from one of benzophenone, salicylate, benzotriazole and triazine.

[0041] Furthermore, in step (3), the weight proportion of the ultraviolet absorber in the hardening layer coating solution is 2.2 parts, 2.5 parts, or 2.8 parts.

[0042] Furthermore, in step (3), the organic solvent of the hardening layer coating solution is one of ethyl acetate, butyl acetate and cyclohexanone.

[0043] Furthermore, in step (3), the weight proportion of the organic solvent in the hardening layer coating solution is 48 parts, 50 parts, or 54 parts.

[0044] Furthermore, in step (4), the aging temperature is 50-70°C, or 60°C.

[0045] Furthermore, in step (4), the aging time is 10-36 hours, or 15 hours, 20 hours, 25 hours, or 30 hours.

[0046] Compared with the prior art, the beneficial effects of this technical solution are as follows:

[0047] 1. Simplified manufacturing process: The present invention realizes the integrated coating of UV cutoff and hardening functions by coating an acrylic resin layer with UV cutoff on one side of PET and using magnetron sputtering to sputter an inorganic layer as a water vapor barrier on the other side of PET, which reduces the coating process, reduces production costs, and also reduces quality risks in the process. This innovation solves the problem that the UV cutoff layer and the hardening layer need to be coated separately in the prior art, simplifies the manufacturing process, and improves production efficiency.

[0048] 2. Improve the anti-precipitation performance: The present invention directly adds BASF UV400 ultraviolet absorber (hydroxyphenyl triazine, a mixture) to the acrylic hardening resin. Compared with other powdered ultraviolet absorbers, the liquid BASF UV400 ultraviolet absorber has better anti-precipitation performance. After reliability, the liquid absorber does not have the problem of crystallization, thereby ensuring the performance stability and service life of the protective film. This innovation solves the problem of easy crystallization of ultraviolet absorbers at high temperatures in the prior art.

[0049] 3. Enhanced water vapor barrier performance: The present invention magnetron sputters an inorganic layer on the other side of PET as a water vapor barrier layer. This inorganic layer can effectively block the penetration of water vapor, thereby improving the waterproof performance of the electronic paper protective film. This innovation solves the problem in the prior art that water vapor penetration may cause the display effect of electronic paper to decline, and enhances the service life of electronic paper.

[0050] In general, this technical solution not only improves the performance of the electronic paper protective film by optimizing material selection and simplifying the manufacturing process, but also reduces production costs and reduces quality risks in the production process, and has significant advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The figure is a schematic diagram of the structure of an electronic paper protective film of the present invention.

[0052] Among them, 04 is the protective film of the present invention, 01 is the hardening layer, 02 is the substrate layer, and 03 is the barrier layer.

[0053] Figure 2 This is a photo of the electronic paper protective film of Example 1.

[0054] Figure 3 This is a photo of the electronic paper protective film of Example 1. DETAILED DESCRIPTION

[0055] In order to make it easier to understand the structure of the present invention and the functional features and advantages that can be achieved, the preferred embodiments of the present invention are described in detail with the help of the accompanying drawings as follows:

[0056] Example 1

[0057] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 12 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 60 nm.

[0058] Prepare the hardening layer coating liquid, add 50 parts of main agent acrylic resin, 3 parts of curing agent toluene diisocyanate, 2 parts of BASF UV400 ultraviolet absorber, and 45 parts of solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it for coating the hardening layer.

[0059] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0060] Example 2

[0061] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 22 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 120 nm.

[0062] Prepare the hardening layer coating liquid, add 40 parts of main agent acrylic resin, 2 parts of curing agent toluene diisocyanate, 3 parts of BASF UV400 ultraviolet absorber, and 45 parts of solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it for coating the hardening layer.

[0063] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0064] Example 3

[0065] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon nitride layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 12 kW, the argon and nitrogen atmospheres were turned on, and the silicon nitride coating was deposited. After the deposition, the thickness of the silicon nitride layer was 60 nm.

[0066] Prepare the hardening layer coating liquid, add 50 parts of main agent acrylic resin, 2 parts of curing agent toluene diisocyanate, 3 parts of BASF UV400 ultraviolet absorber, 45 parts of solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it for coating the hardening layer.

[0067] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0068] Example 4

[0069] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 12 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 60 nm.

[0070] Prepare the hardening layer coating liquid, add 50 parts of the main agent propylene polyol resin, 2 parts of the curing agent xylene diisocyanate, 3 parts of BASF UV400 ultraviolet absorber, and 45 parts of the solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it for coating the hardening layer.

[0071] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0072] Comparative Example 1

[0073] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 22 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 120 nm.

[0074] Prepare the hardening layer coating liquid, add 50 parts of main agent acrylic resin, 2 parts of curing agent toluene diisocyanate, without adding any UV absorber, and 48 parts of solvent ethyl acetate, a total of 100 parts, all of which are parts by weight. After mixing, stir thoroughly for 60 minutes and use it for coating the hardening layer.

[0075] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0076] Comparative Example 2

[0077] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 22 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 120 nm.

[0078] Prepare the hardening layer coating liquid, add 50 parts of main agent acrylic resin, 2 parts of curing agent toluene diisocyanate, 48 parts of solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it for coating the hardening layer.

[0079] Prepare the UV cut-off layer coating liquid, add 3 parts of UV absorber Eversorb 109 (Eversorb, Taiwan, China, powdered solid) into 97 parts of ethyl acetate solvent, stir well for 30 minutes and then prepare for coating.

[0080] The UV cutoff layer coating solution was coated on the other side (non-water vapor barrier layer) of the PET substrate using a 4# wire rod, and the coating solution was placed in an oven at 85° C. for 3 minutes.

[0081] Then use a 4# wire rod to apply the above hardening layer coating on the surface of the UV cutoff layer, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0082] Comparative Example 3

[0083] A PET substrate with a thickness of 100 μm was used to magnetron sputter a silicon dioxide layer on one side of the PET substrate. The high-purity silicon target power supply was turned on, the power was set to 22 kW, the argon and oxygen atmospheres were turned on, and the silicon dioxide coating was deposited. After the deposition, the thickness of the silicon dioxide layer was 120 nm.

[0084] Prepare a hardening layer coating liquid, add 50 parts of the main agent acrylic resin, 2 parts of the curing agent toluene diisocyanate, 3 parts of the UV absorber Eversorb 109 (Yongguang, Taiwan, China, powdered solid), 45 parts of the solvent ethyl acetate, a total of 100 parts (all parts by weight), mix and stir thoroughly for 60 minutes, and then use it to apply the hardening layer.

[0085] Use a 4# wire rod to apply the hardening layer coating liquid on the other side (non-water vapor barrier layer) of the PET substrate, place it in an 85°C oven for 3 minutes, and then place it in a 60°C oven for aging for 24 hours for subsequent performance testing.

[0086] The finished products provided in the embodiments and comparative examples were tested for performance according to the following standards:

[0087] Hardening layer UV absorber precipitation test: The finished diaphragms prepared above were placed in a high temperature testing machine at 65°C, 95% RH and 85°C, and the precipitation on the diaphragm surface was observed after 500 hours, which were divided into "no precipitation", "slight precipitation" and "serious precipitation", among which "no precipitation" was a qualified product of the present invention.

[0088] 200nm-780nm transmittance test: According to ASTM D1003 standard, the finished film was optically tested using Agilent Cary5000 UV-visible near-infrared spectrophotometer, where the visible light band transmittance is the average transmittance of 381nm-780nm. The visible light transmittance is greater than 88%, the transmittance at 280nm and 370nm is less than 1%, and the transmittance at 380nm is less than 6%, which is a qualified product of the present invention.

[0089] The water vapor transmission rate test uses a water vapor transmission rate tester and refers to the ASTM F1249 standard to test the water vapor transmission rate of the product, where the water vapor transmission rate is less than 8mg / (m 2 ·day) is a qualified product of the present invention.

[0090] Adhesion test: According to GB 1720-1979 "Determination of film adhesion", the coating adhesion is tested, where 100 / 100 means no film peeling, and 60 / 100 means 40% peeling. Only those with adhesion reaching 100 / 100 are qualified.

[0091] Table 1 is the test results of the finished products provided in the embodiments and comparative examples:

[0092]

[0093] It can be seen from the test results of the above embodiments and comparative examples that comparative example 1 does not add any ultraviolet absorber, so there is no absorption at 370nm and 380nm, and the low transmittance at 280nm is due to the absorption of this wavelength by the PET substrate.

[0094] In Comparative Example 2, the commercially available Eversorb 109 absorber needs to be dissolved and coated on the PET surface to form a UV cutoff layer, and then a hardening layer is coated on the surface of the UV cutoff layer. From the results, the adhesion between the hardening layer and the UV cutoff layer is poor, and serious precipitation occurs. This is because the high concentration of UV absorber encounters crystallization nuclei under the driving force of high temperature or high temperature and high humidity, and forms crystals, which manifests as precipitation on the surface. The precipitation on the surface further leads to poor adhesion with the hardening layer.

[0095] In Comparative Example 3, commercially available Eversorb 109 is dissolved in the hardening layer resin and mixed, and then the hardening layer is coated and cured. From the results, the adhesion is significantly improved compared with Comparative Example 2. However, since the Eversorb 109 ultraviolet absorber itself is in powder form and has poor miscibility with the hardening layer resin, under the driving force of high temperature or high temperature and high humidity, the crystals formed after encountering the crystallization nucleus manifest as precipitation on the surface. However, since its migration and crystallization are a process, it shows obvious precipitation instead of the severe precipitation in Comparative Example 2.

[0096] In Example 1-2, BASF UV400 ultraviolet absorber is mixed with the hardening layer resin coating liquid, and after being fully stirred, it is coated on the PET surface at one time, which not only reduces the number of coating times, but also reduces the quality risk. The liquid UV400 absorber has better compatibility with the hardening layer resin. Therefore, under high temperature or high temperature and high humidity conditions, no precipitation is found and other performance requirements of the protective film are met.

[0097] Example 2 has the highest cutoff performance at 380nm, the ultraviolet absorber does not precipitate under high temperature or high temperature and high humidity conditions, and the water vapor permeability is the lowest, which is the optimal embodiment of the present invention.

[0098] The transmittance of the electronic paper protective film of the present invention at 280nm is not higher than 0.6%, or 0.4%, or 0.3%. The transmittance at 370nm is not higher than 0.80%, or 0.70%, or 0.66%. The transmittance at 380nm is not higher than 4.0%, or 3.5%, or 3.3%. In the precipitation test of the ultraviolet absorber of the hardening layer, precipitation is found.

[0099] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. All equivalent changes and modifications made according to the content of the present invention are included in the patent scope of the present invention.

Claims

1. An electronic paper protective film, comprising a substrate layer, an inorganic silicon-containing layer is sputtered on one side of the substrate layer by magnetron sputtering, and a hardening liquid layer is coated on the other side of the substrate layer, wherein the hardening layer coating liquid comprises a main agent, a curing agent, an ultraviolet absorber and a solvent, wherein the main agent is 40-50 parts, the curing agent is 2-3 parts, the ultraviolet absorber is 2-3 parts, and the solvent is 44-56 parts, a total of 100 parts, and all are parts by weight.

2. The electronic paper protective film according to claim 1, characterized in that: The substrate layer is selected from polyethylene terephthalate (PET) or triacetate cellulose film (TAC).

3. The electronic paper protective film according to claim 1, characterized in that: The thickness of the substrate layer is 50-100 μm.

4. The electronic paper protective film according to claim 1, characterized in that: The inorganic silicon-containing layer is a silicon oxide layer or a silicon nitride layer.

5. The electronic paper protective film according to claim 1, characterized in that: The thickness of the inorganic silicon-containing layer is 60-120 nm.

6. The electronic paper protective film according to claim 1, characterized in that: The silicon oxide layer or silicon nitride layer is deposited by reactive sputtering of a high-purity silicon target in a mixed atmosphere of argon, oxygen or nitrogen, with the power of the silicon target being 12-22 kW.

7. The electronic paper protective film according to claim 1, characterized in that: The main agent of the hardening layer coating liquid is selected from one of acrylic resin, polyurethane, propylene polyol and epoxy resin.

8. The electronic paper protective film according to claim 1, characterized in that: The curing agent of the hardening layer coating solution is selected from one of toluene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate and trimethylcyclohexyl diisocyanate.

9. The electronic paper protective film according to claim 1, characterized in that: The ultraviolet absorber of the hardening layer coating solution is selected from benzophenone, salicylate, benzotriazole and triazine.

10. The electronic paper protective film according to claim 1, characterized in that: The organic solvent of the hardening layer coating solution is one of ethyl acetate, butyl acetate and cyclohexanone.

11. A method for preparing an electronic paper protective film according to any one of claims 1 to 10, comprising: Step (1), selecting a substrate layer: selecting a polyethylene terephthalate (PET) or triacetate cellulose film (TAC) substrate as the substrate layer; Step (2), sputtering an inorganic silicon-containing layer: magnetron sputtering an inorganic silicon-containing layer on one side of the substrate layer; Step (3), preparing a hardening layer coating liquid: mixing a main agent, a curing agent, an ultraviolet absorber, and a solvent, and stirring the mixture sufficiently to obtain a hardening layer coating liquid; Step (4), coating a hardening layer: coating the hardening layer coating liquid on the other side of the substrate layer, and curing it to obtain an electronic paper protective film.

12. The preparation method according to claim 11, characterized in that: Step (2), use a high purity silicon target power supply with a power of 12-22 kW.

13. The preparation method according to claim 11, characterized in that: In step (4), the aging temperature is 50-70°C, or 60°C.

14. The preparation method according to claim 11, characterized in that: Step (4), the aging time is 10-36 hours.

15. The preparation method according to claim 11, characterized in that: In step (3), the ultraviolet absorber of the hardening layer coating solution is selected from one of benzophenone, salicylate, benzotriazole and triazine.

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