A mobile phone film base film with angle color change and blue light prevention effect and a preparation method thereof

Abstract

The application relates to the technical field of optical films, and specifically discloses a mobile phone film base film with angle color change and blue light prevention effects and a preparation method thereof. The mobile phone film base film is composed of high-refractive layers and low-refractive layers which are alternately stacked, the high-refractive layers are PET layers, and the low-refractive layers are PMMA layers; the optical layer thickness of the base film is in gradient distribution, so that the main reflection peak of the base film under a 0-degree viewing angle is located in the near-infrared wave band of 740 nm-980 nm, and the main reflection peak moves to a short-wave direction with the increase of the observation viewing angle. The application can not only provide a unique and soft viewing angle color change effect to meet individualized needs, but also ensure that the base film has high light transmission and low reflection at a normal viewing angle to guarantee a clear screen reading experience, and on this basis, the base film can be conveniently integrated with beneficial optical functions such as blue light prevention.

Description

Technical Field

[0001] This application relates to the technical field of optical thin films, and in particular to a mobile phone film base film with angle-changing color and blue light blocking effects, and its preparation method. Background Technology

[0002] With the widespread use of smartphones, screen protectors have become an important accessory in the consumer electronics field. Users' requirements for screen protectors have gradually expanded from simple scratch and drop protection to a higher level of pursuit of optical performance and visual effects.

[0003] Currently, most screen protectors on the market that achieve iridescent effects use magnetron sputtering technology to deposit multiple layers of metal or metal oxide films on the substrate surface. Iridescent films prepared using this process can display rich metallic luster and colors at specific angles. However, these films have significant drawbacks: First, at a normal viewing angle, especially in strong outdoor sunlight, their reflectivity of visible light is usually high, creating strong specular reflections that severely interfere with reading the screen content and can easily cause eye fatigue with prolonged use, affecting the user experience. Second, their iridescent effects largely rely on the metal film layer, resulting in often harsh colors, and it's difficult to integrate eye-protection functions while achieving personalized visual effects.

[0004] Other optical film products achieve color changes through the interference of multiple polymer layers. For example, some commercially available products appear purplish-red at a direct viewing angle and gold at a side viewing angle. While these products achieve color change at a certain viewing angle, the color at a direct viewing angle is rather abrupt when the screen is off, and the color shift is aggravated in strong outdoor light, affecting the original white balance of the screen display and also negatively impacting reading comfort.

[0005] Therefore, how to develop a new type of mobile phone screen protector base film that can provide a unique and gentle viewing angle color-changing effect to meet personalized needs, while ensuring high light transmittance and low reflection under normal viewing angle to guarantee a clear screen reading experience, and on this basis, can easily integrate beneficial optical functions such as blue light protection, while taking into account production costs and environmental friendliness, is an urgent problem to be solved. Summary of the Invention

[0006] In order to enable mobile phone screen protectors to provide a unique and gentle viewing angle color-changing effect to meet personalized needs, while ensuring high light transmittance and low reflection at the normal viewing angle to guarantee a clear screen reading experience, and on this basis, to easily integrate beneficial optical functions such as blue light protection, this application provides a mobile phone screen protector base film with viewing angle color-changing and blue light protection effects and its preparation method.

[0007] In a first aspect, this application provides a mobile phone screen protector base film with angle-changing color and blue light blocking effects, employing the following technical solution: A mobile phone screen protector base film with angle-changing color and blue light blocking effects includes a base film composed of alternating high refractive index layers and low refractive index layers. The high refractive index layer is a PET layer with a refractive index of 1.57-1.60, and the low refractive index layer is a PMMA layer with a refractive index of 1.49. The optical layer thickness of the base film is gradient-distributed, so that the main reflection peak of the base film at a 0° viewing angle is located in the near-infrared band of 740nm-980nm, and the main reflection peak shifts towards the short-wave direction as the viewing angle increases.

[0008] By adopting the above technical solution, PET is selected as the high refractive index layer and PMMA as the low refractive index layer to form an alternating stacked optical interference structure. By designing the thickness of the optical layer to be gradient distributed, the main reflection peak is located in the near-infrared band of 740-980nm at a 0° viewing angle, thereby achieving a colorless and transparent visual effect at a positive viewing angle and avoiding interference with screen reading. At the same time, the main reflection peak moves towards the short-wave direction as the viewing angle increases, entering the visible light band, and achieving a color gradient effect at a side viewing angle, meeting the user's demand for personalized visual effects when the screen is off.

[0009] Optionally, the base film has a visible light transmittance of ≥86% and a visible light reflectance of ≤13.5% at a 0° viewing angle.

[0010] Optionally, the base film has a short-wave reflection peak in the 400-450nm band to block harmful blue light.

[0011] Optionally, the reflectivity of the short-wavelength reflection peak is 20%-35%, and the blue light blocking rate is ≥15%.

[0012] By adopting the above technical solution, a short-wave reflection peak is introduced in the 400-450nm band in the multi-layer interference structure. Under the premise of ensuring that the main reflection peak is still mainly located in the near-infrared band at a 0° viewing angle, the harmful blue light is effectively blocked. The reflectivity of the short-wave reflection peak is controlled at 20%-35%, and the blue light blocking rate is controlled at ≥15%. This achieves effective filtering of harmful blue light and avoids unnecessary color interference at the positive viewing angle due to excessively strong reflection peaks. It achieves a balance between the blue light protection function and the colorless and transparent effect at the positive viewing angle.

[0013] Optionally, the wavelength shift range of the main reflection peak under a viewing angle change of 0°-60° covers 600-980nm.

[0014] Optionally, the total number of alternating high-refractive-index and low-refractive-index layers is 200-350 layers, the thickness of a single high-refractive-index layer in each cycle is 50-150 nm, the thickness of a single low-refractive-index layer in each cycle is 50-150 nm, and the thicknesses of the high-refractive-index and low-refractive-index layers exhibit a linear increasing or non-linear gradient distribution.

[0015] By adopting the above technical solution, the total number of layers is controlled at 200-350 layers, and the single-layer thickness of each periodic optical layer is controlled at 50-150nm and distributed in a gradient. This design ensures that the multilayer film structure can generate an adjustable main reflection peak, while ensuring the continuity and uniformity of the color-changing effect.

[0016] Optionally, a protective layer is provided on both sides of the base film, the thickness of the protective layer is 1-3 μm, and the total thickness of the base film and the protective layer is 25-40 μm.

[0017] Secondly, this application provides a method for preparing a mobile phone screen protector base film with angle-changing color and blue light blocking effects, using the following technical solution: A method for preparing a mobile phone screen protector base film with angle-changing color and blue light blocking effects includes the following steps: S1. Prepare PET material and PMMA material as raw materials for the high refractive index layer and low refractive index layer, respectively; S2. PET and PMMA are alternately stacked using a circular casting distributor or a composite distributor to form a multi-layered structure with a gradient thickness distribution. S3. The superimposed melt is extruded through a die to form a casting sheet with a width of 400-800mm; S4. Electrostatic bonding or airflow cooling is used to ensure close contact between the cast sheet and the cooling drum, achieving rapid curing; S5. The cooled casting sheet is stretched synchronously to obtain a mobile phone film base film with angle-changing color and blue light protection effect.

[0018] Optionally, in step S2, by controlling the melt flow rate and distributor parameters of each layer, the thickness of the optical layer increases linearly from the starting layer to the ending layer, with the thickness varying from 68 nm to 125 nm.

[0019] Optionally, in step S5, the process parameters for synchronous stretching are: longitudinal stretching ratio 1:4 to 1:6, transverse shrinkage ratio 1:0.6 to 1:0.8, and stretching temperature 100-110℃.

[0020] In summary, this application includes at least one of the following beneficial technical effects: 1. PET is selected as the high-refractive-index layer and PMMA as the low-refractive-index layer to form an alternating stacked optical interference structure. By designing the thickness of the optical layer as a gradient distribution, the main reflection peak is located in the near-infrared band of 740-980nm at a 0° viewing angle, thus achieving a colorless and transparent visual effect at a frontal viewing angle and avoiding interference with screen reading. At the same time, the main reflection peak shifts towards shorter wavelengths as the viewing angle increases, entering the visible light band, achieving a color gradient effect at a side viewing angle, and meeting users' needs for personalized visual effects when the screen is off. 2. By introducing a short-wavelength reflection peak in the 400-450nm band within the multi-layer interference structure, and ensuring that the main reflection peak remains primarily located in the near-infrared band at a 0° viewing angle, effective blocking of harmful blue light is achieved. The reflectivity of the short-wavelength reflection peak is controlled at 20%-35%, and the blue light blocking rate is controlled at ≥15%. This achieves effective filtering of harmful blue light while avoiding unnecessary color interference at the positive viewing angle due to excessively strong reflection peaks, thus achieving a balance between blue light protection and colorless transparency at the positive viewing angle. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the reflection spectrum changes of Embodiment 1 of this application under different viewing angles.

[0022] Figure 2 This is a schematic diagram of the reflection spectrum changes under different viewing angles in Embodiment 2 of this application.

[0023] Figure 3 For comparison of reading in sunlight between Comparative Example 1 and Example 1.

[0024] Figure 4 The reflectance spectrum of Comparative Example 1 at 0° is shown. Numbered 1-6 correspond to samples 1-6 of Comparative Example 1.

[0025] Figure 5 The image shows the reflectance spectrum of Comparative Example 2 at 0°.

[0026] Figure 6 This is a comparison of reading in sunlight between Comparative Example 1 and Comparative Example 2. Detailed Implementation

[0027] Example

[0028] This application discloses a mobile phone film base film with angle-changing color and blue light blocking effects.

[0029] Example 1: Gold Gradient Effect Mobile Phone Base Film High refractive index layer material: optical grade PET slices with a refractive index of 1.59 are used.

[0030] Low refractive index layer material: optical grade PMMA slices with a refractive index of 1.49 are used.

[0031] The stacked structure design consists of a total of 280 layers, namely 140 PET / PMMA repeating units. The thickness increases linearly from the starting layer near the protective layer to the middle layer, with a specific thickness range of 68-125nm. On both sides of the alternating stacked structure, a PET protective layer is set, with each protective layer having a thickness of 2μm. The overall thickness of the base film is controlled at 31μm.

[0032] A mobile phone screen protector base film with angle-changing color and blue light blocking effects is prepared by the following steps: S1. Dry the PET and PMMA raw materials at 120℃ and 90℃ respectively for 4 hours to remove moisture; S2. The dried raw materials are fed into two extruders for melting and plasticizing, and the melt temperature is controlled at 260-270℃. S3. PET melt and PMMA melt are alternately superimposed through a circular casting distributor to form a multi-layer melt flow of 280 layers. By controlling the melt flow rate of each layer and the distributor parameters, a linearly increasing gradient distribution of optical layer thickness from 68nm to 125nm is achieved. S4. The superimposed multi-layer melt is extruded through a T-die to form a casting sheet with a width of 600mm; S5. Electrostatic bonding is used to ensure close contact between the cast sheet and the cooling drum at 25°C, enabling rapid curing and shaping. S6. The cooled casting is fed into a synchronous stretching machine for stretching. The stretching process parameters are: longitudinal stretching ratio 1:5, transverse shrinkage ratio 1:0.7, stretching temperature 105℃. The film thickness is uniform and the optical performance is stable after stretching.

[0033] Optical performance testing: The optical performance of the mobile phone film base film prepared in Example 1 was tested using a PerkinElmer Lambda 750 UV / Vis / NIR spectrophotometer. The test results are shown in Table 1 below: Table 1

[0034] Example 1: Changes in reflectance spectrum at different viewing angles, as shown below Figure 1 As shown.

[0035] This embodiment prepares a mobile phone film base film with angle-changing color and blue light protection effects. It is colorless and transparent from the front view and has a gold gradient from the side view. The 0° main reflection peak is located in the near-infrared band of 800-980nm, avoiding visible light reflection interference. The visible light transmittance reaches 89.74%, and the reflectance is only 10.48%, which is significantly better than traditional magnetron sputtering films, ensuring screen readability under strong outdoor light.

[0036] Example 2: Gold Gradient Effect Mobile Phone Screen Protector Base Film with Integrated Blue Light Protection Function High refractive index layer material: optical grade PET slices with a refractive index of 1.59 are used.

[0037] Low refractive index layer material: optical grade PMMA slices with a refractive index of 1.49 are used.

[0038] Layered structure design: PET and PMMA layers are alternately stacked, with a total of 320 layers, or 160 repeating PET / PMMA units. This ensures the main reflection band is located in the near-infrared to visible long-wavelength range, while simultaneously forming a relatively broad short-wavelength reflection peak in the short-wavelength direction. The optical layer thickness distribution is as follows: Layers 1-100, with a single-layer thickness increasing from 68nm to 75nm, corresponding to a short-wavelength reflection peak of 420-440nm; Layers 101-150, with a single-layer thickness increasing from 75nm to 115nm, avoiding excessive optical interference and preventing unnecessary stray peaks between the main and secondary peaks; Layers 151-320, with a single-layer thickness increasing from 115nm to 145nm, corresponding to a main peak of 740-880nm. A PET protective layer is placed on each side of the alternating stacked structure, with each protective layer having a thickness of 2μm, resulting in an overall base film thickness of 36μm.

[0039] The difference between the preparation process of Example 2 and Example 1 is that in step S3, the parameters of the circular casting distributor are adjusted to achieve precise control over the thickness distribution of the optical layer, so that it simultaneously meets the design requirements of the main reflection peak and the short-wave reflection peak. The specific process parameters are: melt temperature 260-270℃, cooling drum temperature 25℃, longitudinal stretching ratio 1:5, transverse shrinkage ratio 1:0.7, and stretching temperature 105℃.

[0040] Optical performance testing: The optical performance of the mobile phone film base film prepared in Example 2 was tested using a PerkinElmer Lambda 750 UV / Vis / NIR spectrophotometer. The test results are shown in Table 2 below. Table 2

[0041] Example 2: Changes in reflectance spectrum at different viewing angles, as shown below Figure 2 As shown.

[0042] Example 2, while achieving the gold gradient effect of Example 1, integrates blue light blocking functionality. The 0° main reflection peak is located at 740-880nm, and the short-wavelength reflection peak is located at 420-440nm, achieving a 17% blue light blocking rate while maintaining a visible light transmittance of 87.28%. This design achieves a harmonious balance between visual appeal and eye health protection.

[0043] Example 3

[0044] The difference between Example 3 and Example 1 is that the total number of alternating layers is 200, and the thickness of the optical layer exhibits a non-linear gradient distribution from the starting layer to the ending layer, ranging from 50 nm to 150 nm. The PET protective layers on both sides are 1 μm each, and the overall thickness of the base film is 25 μm. In the fabrication process, the stretching parameters were adjusted to a longitudinal stretching ratio of 1:4, a transverse shrinkage ratio of 1:0.8, and a stretching temperature of 100℃. Test results show that the base film prepared in this example also achieves a colorless and transparent effect from the front view and a golden gradient effect from the side view, with a visible light transmittance of 88.9% and a visible light reflectance of 11.2% at 0°.

[0045] Example 4

[0046] The difference between Example 4 and Example 2 is that the synchronous stretching process parameters were adjusted to a longitudinal stretching ratio of 1:6, a transverse shrinkage ratio of 1:0.6, and a stretching temperature of 110℃. Test results show that the base film prepared in this example also achieved a gold gradient effect and blue light blocking function. The 0° main reflection peak is located at 750-890nm, the short-wave reflection peak is located at 420-440nm, the reflectivity is approximately 25%, the blue light blocking rate is 15.5%, the visible light transmittance is 86.9%, and the visible light reflectivity is 13.5%.

[0047] Comparative Example

[0048] Comparative Example 1: Traditional magnetron sputtering colored mobile phone film Sample source: Six commercially available iridescent mobile phone screen protector base films prepared using magnetron sputtering technology, labeled as Sample 1-6.

[0049] Optical performance testing: The visible light reflectance of six samples at a 0° viewing angle was tested using a PerkinElmer Lambda 750 UV / Vis / NIR spectrophotometer. The test results are shown in Table 3 below. Table 3

[0050] The reflectance spectra of samples 1-6 at 0° are shown below. Figure 4 As shown.

[0051] Test results show that traditional magnetron sputtered color films generally have high visible light reflectance at a normal viewing angle, with some samples exhibiting local peak reflectance exceeding 30%. While this can achieve a certain level of vibrant color, the excessively high reflectance at a normal viewing angle severely impacts the outdoor reading experience and fails to meet users' requirements for screen clarity.

[0052] Comparison Example 2: Commercially available screen protectors, purplish-red when viewed from the front and gold when viewed from the side. Sample source: Commercially available mobile phone screen protector base film, with an optical effect of purplish-red from the front view and gold from the side view.

[0053] The reflectance spectra of the samples at a 0° viewing angle were measured using a PerkinElmer Lambda 750 UV / Vis / NIR spectrophotometer. The test results are shown in Table 4 below. Table 4

[0054] Comparative Example 2: Reflectance spectrum at 0° as shown below Figure 5 As shown.

[0055] Although the commercially available product achieves a color-changing effect from a viewing angle, it has a reflection peak in the visible light range at a normal viewing angle, resulting in a noticeable purplish-red hue on the film layer. This affects the screen display effect under strong light and fails to solve the technical problems of colorless transparency and low reflectivity at a normal viewing angle.

[0056] Reference Figure 3 The reading effect of Example 1 and Comparative Example 1 under outdoor sunlight was compared. The results showed that the mobile phone film base film prepared in Example 1 was clear and transparent under a normal viewing angle, and the screen content was easy to see; while the magnetron sputtering film of Comparative Example 1 had strong specular reflection, and the screen content was almost unreadable.

[0057] Reference Figure 6 The reading effects of Comparative Example 1 and Comparative Example 2 under outdoor sunlight were compared. The results showed that: Comparative Example 1 had a generally high visible light reflectivity at the normal viewing angle, which caused specular reflection under outdoor sunlight, making the screen content difficult to read; Although Comparative Example 2 avoided the high reflectivity problem of magnetron sputtering film, it had a reflection peak in the visible light range at the normal viewing angle, which caused the film layer to have an obvious purplish-red color, which also affected the screen display content under strong light.

[0058] The key optical performance of Examples 1-2 and Comparative Example 2 of this application is compared, and the results are shown in Table 5 below: Table 5

[0059] Both Examples 1 and 2 achieved a colorless and transparent effect from a positive viewing angle, with the 0° main reflection peak located in or primarily in the near-infrared band, avoiding visible light interference. In contrast, the 0° main reflection peak in Comparative Example 2 was located in the visible light band, resulting in a purplish-red hue on the film. Furthermore, Example 2 successfully integrated blue light protection while maintaining excellent visual effects.

[0060] All equivalent changes made to the structure, shape, and principle of this application shall be covered within the scope of protection of this application.

Claims

1. A mobile phone screen protector base film with angle-changing color and blue light blocking effects, characterized in that: The film includes a base film, which is composed of alternating high-refractive-index layers and low-refractive-index layers. The high-refractive-index layers are PET layers with a refractive index of 1.57-1.60, and the low-refractive-index layers are PMMA layers with a refractive index of 1.

49. The thickness of the optical layer of the base film is gradient-distributed, so that the main reflection peak of the base film at a 0° viewing angle is located in the near-infrared band of 740nm-980nm, and the main reflection peak shifts towards the short-wave direction as the viewing angle increases. The base film also has a short-wave reflection peak in the 400-450nm wavelength range, which is used to block harmful blue light.

2. The mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 1, characterized in that: The base film has a visible light transmittance of ≥86% and a visible light reflectance of ≤13.5% at a 0° viewing angle.

3. The mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 1, characterized in that: The short-wavelength reflection peak has a reflectivity of 20%-35% and a blue light blocking rate of ≥15%.

4. The mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 1, characterized in that: The wavelength shift range of the main reflection peak under a viewing angle change of 0°-60° covers 600-980nm.

5. A mobile phone screen protector base film with angle-changing color and blue light blocking effects according to claim 1, characterized in that: The total number of alternating high-refractive-index and low-refractive-index layers is 200-350. The thickness of a single high-refractive-index layer in each cycle is 50-150 nm, and the thickness of a single low-refractive-index layer in each cycle is 50-150 nm. The thicknesses of the high-refractive-index and low-refractive-index layers increase linearly or exhibit a non-linear gradient distribution.

6. The mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 1, characterized in that: The base film has protective layers on both sides, the thickness of the protective layers is 1-3 μm, and the total thickness of the base film and the protective layers is 25-40 μm.

7. A method for preparing a mobile phone screen protector base film with angle-changing color and blue light blocking effects as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Prepare PET material and PMMA material as raw materials for the high refractive index layer and low refractive index layer, respectively; S2. PET and PMMA are alternately stacked using a circular casting distributor or a composite distributor to form a multi-layered structure with a gradient thickness distribution. S3. The superimposed melt is extruded through a die to form a casting sheet with a width of 400-800mm; S4. Electrostatic bonding or airflow cooling is used to ensure close contact between the cast sheet and the cooling drum, achieving rapid curing; S5. The cooled casting sheet is stretched synchronously to obtain a mobile phone film base film with angle-changing color and blue light protection effect.

8. The method for preparing a mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 7, characterized in that: In step S2, by controlling the melt flow rate and distributor parameters of each layer, the thickness of the optical layer increases linearly from the starting layer to the ending layer, with a thickness variation range of 68nm to 125nm.

9. The method for preparing a mobile phone screen protector base film with angle-changing color and blue light blocking effect according to claim 7, characterized in that: In step S5, the process parameters for synchronous stretching are: longitudinal stretching ratio 1:4 to 1:6, transverse shrinkage ratio 1:0.6 to 1:0.8, and stretching temperature 100-110℃.

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