Surface protective film for prism sheet and method for manufacturing the same

Abstract

The application discloses a surface protective film of a prism sheet and a preparation method thereof, and belongs to the technical field of protective films. The specific hydrogenated styrene copolymer, tackifying resin and monomer resin are compounded to achieve good wettability and initial adhesion of the prism sheet. The metallocene-catalyzed polypropylene and the cyclic olefin copolymer are compounded in the core layer to effectively reduce the interface light reflection loss. The antistatic composition composed of polyether amide copolymer, ethoxylated amine and glycerol monostearate is added to achieve certain antistatic effect. The composite light stabilizer is further added to build a double protection system and improve the aging resistance. The back unrolling layer, the core layer and the adhesive layer are designed as a whole, and the preparation raw materials are optimized, and the formula synergistic effect can be achieved. The prism sheet surface protective film with excellent comprehensive performance, such as excellent initial adhesion, low unrolling force, slow adhesive force growth, antistatic property, aging resistance and optical matching, can be prepared, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of protective film technology, and more specifically, to a surface protective film for a prism sheet and its preparation method. Background Technology

[0002] Prism sheets are key optical components in backlight modules. Their surface features a micro-prism structure at the micrometer level (typically 20-50 μm), which uses geometric optics principles to focus light emitted from the backlight towards the viewing direction, significantly improving display brightness. During production, storage, and transportation, prism sheets are susceptible to dust, foreign matter contamination, or mechanical scratches. Therefore, a protective film must be applied to their surface to ensure optical performance. However, due to the microstructure of the prism sheet surface, the actual contact area with the protective film is small, making it difficult for traditional low-adhesion protective films to adhere effectively. To solve this problem, the industry widely adopts high-adhesion self-adhesive protective films (self-adhesive films) to avoid the contamination risks such as delamination and exudation that may occur with adhesive-coated protective films.

[0003] Currently, commonly used high-adhesion self-adhesive films typically employ hydrogenated styrene block copolymers (such as SEBS and SEPS) as the adhesive layer material, and are modified by adding tackifiers or softeners such as aromatic hydrocarbon oils, naphthenic oils, and paraffin oils to improve their initial adhesion to prism sheets. However, these materials present the following problems in practical applications: Difficult unwinding: Due to the strong adhesion between the adhesive layer and the backing layer, the unwinding force after film winding is significant, affecting efficiency. Rapid increase in adhesion: Over time, the adhesive layer material undergoes creep, leading to a significant increase in peel force after application, reaching 50% to 100%, causing difficulty in downstream film removal. Uneven unwinding force: Large-diameter inorganic particles are often added to the backing layer to reduce the contact area, but after winding, especially at the bottom of the roll, the adhesive layer material is pressed into "pits" by the particles under pressure and creep, resulting in an uneven adhesive surface and uneven adhesion distribution after unwinding, affecting consistency in use. Poor storage modulus matching: Traditional styrene block copolymers have a high storage modulus at room temperature, resulting in insufficient initial tack. While modification with tackifiers or filler oils can improve initial tack, it often leads to drastic changes in storage modulus at low or high temperatures, affecting the material's adhesion stability and unwinding performance over a wide temperature range. To address one of these technical problems, existing technologies have introduced materials such as Kraton MD6666 and MD6700, but these still struggle to balance initial tack, unwinding force, and temperature resistance, especially given the conflict between high tack requirements and long-term stability.

[0004] Therefore, there is an urgent need to develop a self-adhesive protective film that has good initial tack, low unwinding force, slow tack growth, and is suitable for the protection of prism sheet surfaces. Summary of the Invention

[0005] Based on this, in order to solve one of the above-mentioned technical problems, the present invention provides a surface protective film for a prism sheet and a method for preparing the same. The specific technical solution is as follows: a surface protective film for a prism sheet, wherein the surface protective film is a three-layer co-extruded cast film, including a back unwinding layer, a core layer and an adhesive layer;

[0006] By weight, the core layer comprises the following raw materials: 70-90 parts metallocene-catalyzed polypropylene, 10-20 parts cyclic olefin copolymer, 5-15 parts hydrogenated petroleum resin, 1-5 parts antistatic composition, 1-10 parts composite light stabilizer, 0.5-3 parts β-crystal nucleating agent, 0.5-1 part microcrystalline wax, and 0.5-2 parts dispersant.

[0007] By weight, the adhesive layer comprises the following raw materials: 100 parts of hydrogenated styrene copolymer, 1-30 parts of tackifying resin, and 1-20 parts of monomer resin.

[0008] Furthermore, the antistatic composition is a mixture of polyether amide copolymer, amine ethoxide and glyceryl monostearate in a mass ratio of (1~3):(1~5):(1~5).

[0009] Furthermore, the composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octoxybenzophenone in a mass ratio of (3~7):(1~3):(1~5).

[0010] Furthermore, the total styrene content in the hydrogenated styrene copolymer is 35-55%, and the styrene content at the ends of the molecular chains is 13-20%, with the remaining styrene evenly distributed in the soft segments of the molecular chains.

[0011] Furthermore, the tackifying resin is at least one of hydrogenated C5 resin, hydrogenated C9 resin, and terpene resin.

[0012] Furthermore, the monomer resin is obtained by polymerization of aromatic hydrocarbon monomers, and the softening point of the monomer resin is greater than 140°C.

[0013] Furthermore, the dispersant is polyethylene wax.

[0014] Furthermore, the raw material for preparing the back unwinding layer is copolymer polypropylene, and the surface roughness of the back unwinding layer is 400~800nm.

[0015] Furthermore, in the three-layer co-extruded cast film, the thickness of the back unwinding layer accounts for 15-20% of the total thickness, the thickness of the core layer accounts for 60-70% of the total thickness, and the thickness of the adhesive layer accounts for 15-20% of the total thickness.

[0016] In addition, the present invention also provides a method for preparing a surface protective film on a prism sheet, the method comprising the following steps:

[0017] S1. After drying the raw materials for the back unwinding layer, core layer and adhesive layer respectively, they are extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film;

[0018] S2. After the composite film is cooled by the casting roller, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

[0019] Compared with existing technologies, its beneficial effects include:

[0020] 1. This invention utilizes a specific hydrogenated styrene copolymer, combined with tackifying resin and monomer resin, to achieve excellent wettability and initial adhesion of the microprism structure of the prism sheet, preventing excessively rapid increase in adhesion and solving the problem of difficulty in tearing the film due to a significant increase in adhesion over time in existing technologies. Furthermore, by controlling the surface roughness of the back unwinding layer and utilizing the lubricating effect of microcrystalline wax, the unwinding force is significantly reduced, improving ease of use.

[0021] 2. The core layer of this invention incorporates a metallocene-catalyzed polypropylene and cyclic olefin copolymer, which effectively reduces interfacial light reflection loss and optical distortion caused by protective film stress, ensuring that the optical performance of the prism is not affected during the application of the protective film. An antistatic composition consisting of polyether amide copolymer, amine ethoxide, and glyceryl monostearate is then added. Through the synergistic effect of migratory antistatic agents, excellent antistatic properties are achieved, effectively preventing electrostatic adsorption during the processing and use of the protective film. Furthermore, a composite light stabilizer consisting of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168), and 2-hydroxy-4-n-octyloxybenzophenone (UV-531) is added to the core layer to construct a dual-protection system and improve the overall aging resistance of the protective film.

[0022] 3. Through the structural design of the back unwinding layer, core layer and adhesive layer, and the optimization of raw materials and synergistic formulation, this invention can prepare a prism sheet surface protective film with excellent comprehensive performance, including excellent initial tack, low unwinding force, slow tack growth, antistatic properties, aging resistance and optical matching, and has good prospects for industrial application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] A surface protective film for a prism sheet according to one embodiment of the present invention is a three-layer co-extruded cast film, comprising a back unwinding layer, a core layer and an adhesive layer;

[0026] By weight, the core layer comprises the following raw materials: 70-90 parts metallocene-catalyzed polypropylene, 10-20 parts cyclic olefin copolymer, 5-15 parts hydrogenated petroleum resin, 1-5 parts antistatic composition, 1-10 parts composite light stabilizer, 0.5-3 parts β-crystal nucleating agent, 0.5-1 part microcrystalline wax, and 0.5-2 parts dispersant.

[0027] By weight, the adhesive layer comprises the following raw materials: 100 parts of hydrogenated styrene copolymer, 1-30 parts of tackifying resin, and 1-20 parts of monomer resin.

[0028] In one embodiment, the viscous layer, under dynamic thermomechanical analysis testing at a frequency of 1 Hz and a deformation of 0.05%, satisfies the following condition: a storage modulus of 5 × 10⁻⁶ at 25°C. 5 ~1×10 6 Pa, energy storage modulus at -30℃ greater than 3×10 8 Pa, energy storage modulus greater than 1×10 5 The upper limit temperature of Pa is greater than 110℃. The viscous layer of this invention has a storage modulus greater than 3×10 at -30℃. 8 Pa ensures sufficient rigidity even at low temperatures, preventing excessive deformation of the adhesive layer during unwinding; storage modulus greater than 1×10⁻⁶. 5 The upper limit temperature of Pa is greater than 110℃, which ensures that the adhesive layer does not soften or creep under high temperature storage conditions, maintains structural stability, and prevents delamination or residual adhesive problems.

[0029] In one embodiment, the antistatic composition is a mixture of a polyether amide copolymer, amine ethoxylate, and glyceryl monostearate in a mass ratio of (1~3):(1~5):(1~5).

[0030] In one embodiment, the composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of (3~7):(1~3):(1~5).

[0031] In one embodiment, the hydrogenated styrene copolymer is a styrene-(ethylene-butene-styrene copolymer)-styrene block copolymer or a styrene-(ethylene-butene)-styrene block copolymer.

[0032] In one embodiment, the total styrene content in the hydrogenated styrene copolymer is 35-55%, and the styrene content at the ends of the molecular chains is 13-20%, with the remaining styrene evenly distributed in the soft segments of the molecular chains.

[0033] In one embodiment, the tackifying resin is at least one of hydrogenated C5 resin, hydrogenated C9 resin, and terpene resin.

[0034] In one embodiment, the tackifying resin has a softening point greater than 140°C.

[0035] In one embodiment, the monomer resin is obtained by polymerization of aromatic hydrocarbon monomers, and the softening point of the monomer resin is greater than 140°C.

[0036] In one embodiment, the pure monomer resin is a polymer of styrene and / or α-methylstyrene.

[0037] In one embodiment, the dispersant is polyethylene wax.

[0038] In one embodiment, the back unwinding layer is prepared from copolymer polypropylene, and the surface roughness of the back unwinding layer is 400-800 nm. The back unwinding layer of this invention uses copolymer polypropylene, with a surface roughness controlled at 400-800 nm, ensuring good bonding with the core layer and providing a suitable unwinding interface for the adhesive layer. Compared to existing technologies that increase roughness by adding large-diameter inorganic particles, this invention achieves suitable surface roughness without adding inorganic particles, avoiding the problem of indentations and pits caused by inorganic particles to the adhesive layer during winding.

[0039] In one embodiment, in the three-layer co-extruded cast film, the thickness of the back unwinding layer accounts for 15-20% of the total thickness, the thickness of the core layer accounts for 60-70% of the total thickness, and the thickness of the adhesive layer accounts for 15-20% of the total thickness.

[0040] In addition, the present invention also provides a method for preparing a surface protective film on a prism sheet, the method comprising the following steps:

[0041] S1. After drying the raw materials for the back unwinding layer, core layer and adhesive layer respectively, they are extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film;

[0042] S2. After the composite film is cooled by the casting roller, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

[0043] In one embodiment, in step S1, the back unwinding layer material, core layer material, and adhesive layer material are filtered through a 30-50μm disc filter before extrusion. This invention utilizes a 30-50μm disc filter to effectively remove impurities and gel particles from the raw materials, ensuring the optical-grade cleanliness of the protective film and preventing impurities from damaging the prism sheet surface.

[0044] In one embodiment, in step S2, the temperature of the casting roller is 20~40℃, and the distance between the die head and the casting roller is 50~150mm.

[0045] The above-mentioned scheme, through the structural design of the back unwinding layer, core layer and adhesive layer, and the optimization of raw materials and synergistic effects of the formulation, can produce a prism sheet surface protective film with excellent comprehensive performance, including excellent initial tack, low unwinding force, slow tack growth, antistatic properties, weather resistance and optical matching, and has good prospects for industrial application.

[0046] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0047] Example 1:

[0048] A method for preparing a surface protective film on a prism sheet includes the following steps:

[0049] S1. The raw materials for preparing the back unwinding layer, core layer and adhesive layer are dried separately, filtered through a 45μm disc filter, and then extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film.

[0050] The raw material for preparing the back unwinding layer is copolymer polypropylene, and the surface roughness of the back unwinding layer is 600 nm.

[0051] The core layer comprises the following raw materials in parts by weight: 85 parts metallocene-catalyzed polypropylene, 10 parts cyclic olefin copolymer, 5 parts hydrogenated petroleum resin, 3 parts antistatic composition, 4 parts composite light stabilizer, 0.5 parts β crystal nucleating agent, 0.5 parts microcrystalline wax, and 1 part polyethylene wax.

[0052] The antistatic composition is a mixture of polyether amide copolymer, amine ethoxylate, and glyceryl monostearate in a mass ratio of 2:5:3;

[0053] The composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of 5:2:3.

[0054] The adhesive layer comprises the following raw materials in parts by weight: 100 parts hydrogenated styrene copolymer, 25 parts hydrogenated C5 resin, and 15 parts monomer resin.

[0055] The hydrogenated styrene copolymer is a styrene-(ethylene-butene-styrene copolymer)-styrene block copolymer, wherein the total styrene content is 50%, the styrene content at the end of the molecular chain is 13%, and the remaining 37% of styrene is uniformly distributed in the soft segments of the molecular chain.

[0056] The monomer resin is a copolymer of styrene and α-methylstyrene, and the softening point of the monomer resin is 145°C.

[0057] S2. After the composite film is cooled by the casting roller at a temperature of 25°C and the distance between the die and the casting roller is 80mm, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

[0058] Example 2:

[0059] A method for preparing a surface protective film on a prism sheet includes the following steps:

[0060] S1. The raw materials for preparing the back unwinding layer, core layer and adhesive layer are dried separately, filtered through a 45μm disc filter, and then extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film.

[0061] The raw material for preparing the back unwinding layer is copolymer polypropylene, and the surface roughness of the back unwinding layer is 600 nm.

[0062] The core layer comprises the following raw materials in parts by weight: 80 parts metallocene-catalyzed polypropylene, 15 parts cyclic olefin copolymer, 5 parts hydrogenated petroleum resin, 4 parts antistatic composition, 5 parts composite light stabilizer, 0.6 parts β crystal nucleating agent, 0.5 parts microcrystalline wax, and 1 part polyethylene wax.

[0063] The antistatic composition is a mixture of polyether amide copolymer, ethoxylated amine and glyceryl monostearate in a mass ratio of 3:4:3;

[0064] The composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of 5:3:2.

[0065] The adhesive layer comprises the following raw materials in parts by weight: 100 parts hydrogenated styrene copolymer, 20 parts hydrogenated C5 resin, and 20 parts monomer resin.

[0066] The hydrogenated styrene copolymer is a styrene-(ethylene-butene-styrene copolymer)-styrene block copolymer, wherein the total styrene content is 50%, the styrene content at the end of the molecular chain is 13%, and the remaining 37% of styrene is uniformly distributed in the soft segments of the molecular chain.

[0067] The monomer resin is a copolymer of styrene and α-methylstyrene, and the softening point of the monomer resin is 145°C.

[0068] S2. After the composite film is cooled by the casting roller at a temperature of 25°C and the distance between the die and the casting roller is 80mm, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

[0069] Example 3:

[0070] A method for preparing a surface protective film on a prism sheet includes the following steps:

[0071] S1. The raw materials for preparing the back unwinding layer, core layer and adhesive layer are dried separately, filtered through a 45μm disc filter, and then extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film.

[0072] The raw material for preparing the back unwinding layer is copolymer polypropylene, and the surface roughness of the back unwinding layer is 600 nm.

[0073] The core layer comprises the following raw materials in parts by weight: 85 parts metallocene-catalyzed polypropylene, 10 parts cyclic olefin copolymer, 5 parts hydrogenated petroleum resin, 5 parts antistatic composition, 6 parts composite light stabilizer, 1 part β crystal nucleating agent, 0.6 parts microcrystalline wax, and 1 part polyethylene wax.

[0074] The antistatic composition is a mixture of polyether amide copolymer, amine ethoxylate, and glyceryl monostearate in a mass ratio of 2:5:3;

[0075] The composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of 4:2:4.

[0076] The adhesive layer comprises the following raw materials in parts by weight: 100 parts hydrogenated styrene copolymer, 25 parts hydrogenated C5 resin, and 15 parts monomer resin.

[0077] The hydrogenated styrene copolymer is a styrene-(ethylene-butene-styrene copolymer)-styrene block copolymer, wherein the total styrene content is 50%, the styrene content at the end of the molecular chain is 13%, and the remaining 37% of styrene is uniformly distributed in the soft segments of the molecular chain.

[0078] The monomer resin is a copolymer of styrene and α-methylstyrene, and the softening point of the monomer resin is 145°C.

[0079] S2. After the composite film is cooled by the casting roller at a temperature of 25°C and the distance between the die and the casting roller is 80mm, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

[0080] Comparative Example 1:

[0081] Compared with Example 3, Comparative Example 1 differs in that the back unwinding layer in Comparative Example 1 includes the following raw materials by weight: 60 parts copolymer polypropylene material and 40 parts inorganic additives (hydrotalcite powder); the rest is the same as in Example 3.

[0082] Comparative Example 2:

[0083] Compared with Example 3, Comparative Example 2 differs in that the core layer of Comparative Example 2 includes the following raw materials in parts by weight: 100 parts low-density polyethylene, 5 parts antistatic composition, 6 parts composite light stabilizer, 1 part β crystal nucleating agent, 0.6 parts microcrystalline wax and 1 part polyethylene wax.

[0084] Everything else is the same as in Example 3.

[0085] Comparative Example 3:

[0086] The difference between Comparative Example 3 and Example 3 is that the antistatic composition in the raw materials for preparing the core layer of Comparative Example 3 is a single amine ethoxide, while the rest is the same as in Example 3.

[0087] Comparative Example 4:

[0088] The difference between Comparative Example 4 and Example 4 is that the antistatic composition in the core layer of Comparative Example 4 is a mixture of polyether amide copolymer and glycerol monostearate in a mass ratio of 1:1, while the rest is the same as in Example 3.

[0089] Comparative Example 5:

[0090] Compared with Example 3, Comparative Example 5 differs in that the core layer of Comparative Example 5 uses a single tris(2,4-di-tert-butylphenyl) phosphite instead of the composite light stabilizer; otherwise, it is the same as Example 3.

[0091] Comparative Example 6:

[0092] Compared with Example 3, Comparative Example 6 differs in that the composite light stabilizer in the raw materials for preparing the core layer of Comparative Example 6 is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1:1.

[0093] Comparative Example 7:

[0094] The difference between Comparative Example 7 and Example 3 is that hydrogenated styrene copolymer was not added to the raw materials for preparing the adhesive layer of Comparative Example 7, but otherwise it was the same as Example 3.

[0095] Comparative Example 8:

[0096] Compared with Example 3, Comparative Example 8 differs in that the hydrogenated styrene copolymer in the raw materials for preparing the adhesive layer of Comparative Example 8 is a styrene-(ethylene-butene-styrene copolymer)-styrene block copolymer, wherein the total styrene content is 13% and the styrene content at the end of the molecular chain is 13%, and the rest is the same as that of Example 3.

[0097] Comparative Example 9:

[0098] The difference between Comparative Example 9 and Example 3 is that no monomer resin was added in Comparative Example 9, but otherwise it is the same as Example 3.

[0099] It should be noted that the thickness ratio of the back unwinding layer, core layer and adhesive layer of the surface protective film of the prism sheets prepared in Examples 1-3 and Comparative Examples 1-9 is 15:70:15, and the total thickness is 40 μm.

[0100] Peeling force and unwinding force tests were conducted on the surface protective film samples of prism sheets from Examples 1 to 3 and the surface protective films of prism sheets from Comparative Examples 1 to 9. The results are shown in Table 1 below.

[0101] Peel strength test method: The sample was attached to the prism sheet and cut into strips 25mm wide. The strips were then rolled back and forth once with a 2kg rubber roller with a hardness of Hs80±5. The 180° peel strength between the protective film and the prism sheet was tested under laboratory conditions of 23℃ and 50% humidity for 30 minutes and 80℃ for 30 minutes.

[0102] Test method for unwinding force: The sample is wound up to 500m using the same linear speed, tension, and back pressure of the pressure roller. The roll film is then cut into 50mm wide pieces using a cutter. The roll film is placed in a 40℃ oven for one month. Using a Kejian KJ-6088 high-speed unwinding force testing machine at an unwinding speed of 30m / min, the average unwinding peel force is tested, and the unwinding force at 10m on the roll surface, 100m in the middle of the roll, and 100m at the bottom of the roll is recorded.

[0103] Table 1: Test results of peel force and unwinding force

[0104]

[0105] Analysis of the data in Table 1 shows that the surface protective film prepared by this invention has good wettability and initial adhesion to the microstructure of the prism sheet and exhibits temperature stability; the unwinding force is within the ideal range, facilitating automatic film tearing during production; and the overall structure is uniform and stable. Compared with Example 3, the back unwinding layer in Comparative Example 1 uses 60 parts of copolymer polypropylene and 40 parts of inorganic additives (hydrotalcite powder) as raw materials. The inorganic particles increase the surface roughness of the back layer and reduce the initial contact area, thus reducing the unwinding force. After winding, under pressure and long-term storage, the hard inorganic particles of the back layer press out "pits" on the surface of the adhesive layer, resulting in an uneven surface. During unwinding, stress concentration occurs at the edges of these pits, increasing unwinding resistance and exhibiting a particle indentation effect. The core layer in Comparative Example 2 uses different raw materials and cannot provide sufficient support for the adhesive layer. During application, the adhesive layer is prone to excessive deformation, resulting in a reduced actual contact area with the prism sheet. This leads to a decrease in peel force and insufficient rigidity, causing the film to creep under winding pressure. The bottom of the roll experiences the greatest pressure, resulting in severe deformation of the adhesive layer and a significant increase in unwinding resistance. In Comparative Example 3, the single amine oxide lacks the lubricating effect of glyceryl monostearate, increasing the interfacial friction between the core layer and the adhesive layer, thus affecting the performance of the protective film. In Comparative Example 4, the absence of amine oxide has little impact on peel and unwinding performance. Comparative Example 5 uses a single tri(2,4-di)phosphite. The composite light stabilizer replaced by tert-butylphenyl ester underwent thermo-oxidative aging in the 80°C test, resulting in molecular chain breakage or cross-linking, leading to performance inferior to Example 3. The composite light stabilizer in Comparative Example 6, composed of a 1:1 mass ratio of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite, exhibited insufficient high-temperature anti-aging properties, resulting in performance inferior to Example 3. This demonstrates that the composite light stabilizer of the present invention has a synergistic effect among its components, resulting in superior anti-aging properties of the protective film. The adhesive layer of Comparative Example 7, lacking hydrogenated styrene copolymer, showed significantly worse wettability and adhesion to the microstructure of the prism sheet compared to Example 3. Comparative Example 8, with added hydrogenated styrene copolymer, had a different structure, failing to balance adhesion and stability. It had an excessively high content of hard segments at the ends, resulting in an overly rigid adhesive layer. The lack of styrene distribution in the soft segments led to insufficient viscoelasticity and easy creep at high temperatures, resulting in performance inferior to Example 3. The adhesive layer of Comparative Example 9, lacking monomer resin, exhibited high-temperature creep, and its stability was inferior to Example 3.

[0106] In addition, the surface resistivity and aging resistance of the surface protective film samples of the prism sheets of Examples 1-3 and the surface protective films of the prism sheets of Comparative Examples 1-9 were tested, and the results are shown in Table 2 below.

[0107] Surface resistance test method: The test was conducted using a Keithley 6517B surface resistance meter according to the method specified in GB / T31838.3-2019.

[0108] UV accelerated aging test method: Samples with dimensions of 50mm × 50mm were placed in a QUV testing machine for UV aging resistance testing. The UV aging test standard adopted was GB / T16422.3-2014. The lamp source was a fluorescent UV lamp (UVA-340), with a peak wavelength of 340nm and an average radiation intensity of 0.76W / m². 2 The temperature inside the chamber was controlled at 50±2℃, the relative humidity was not controlled, and the distance between the sample and the light source was 30mm. After 14 days, the tensile strength retention rate of the samples was as follows.

[0109] Table 2: Results of surface resistivity and tensile strength retention

[0110]

[0111] Analysis of the data in Table 2 shows that the protective film of the present invention has excellent antistatic properties and resistance to light aging, and has better applicability. Compared with Example 3, the addition of inorganic additives (hydrotalcite powder) to the back unwinding layer in Comparative Example 1 disrupts the interfacial continuity between the core layer and the back unwinding layer, affecting the migration of the antistatic agent to the surface of the protective film and the formation of conductive pathways, resulting in a decrease in overall antistatic performance. This indicates that sacrificing antistatic performance and roll bottom unwinding uniformity for low roll surface unwinding force is not advisable, while the present invention achieves excellent antistatic performance while maintaining overall unwinding uniformity. In Comparative Example 2, the raw materials for the preparation of the core layer were changed, and the overall compatibility was not as good as in Example 3, resulting in performance inferior to Example 3. In Comparative Example 3, the addition of a single amine oxyacetoxide, a single migratory antistatic agent (amine oxyacetoxide), can achieve a certain level of antistatic effect. The effect was not as good as in Example 3; Comparative Example 4 lacked the migrating antistatic agent amine ethoxide, and its antistatic effect was not as good as in Example 3, indicating that the antistatic composition of the present invention can play a certain synergistic role and form a better antistatic effect; the components of the composite light stabilizer in Comparative Examples 5 and 6 were different, resulting in a lower tensile strength retention rate than in Example 3, indicating that photo-oxidative degradation led to a decrease in mechanical properties, while the present invention has a significant synergistic effect through the ternary composite light stabilizer system, effectively inhibiting thermal oxidative degradation during processing and use; the raw materials for preparing the adhesive layer in Comparative Examples 7 to 9 were changed, making the stability of the adhesive layer less than that of Example 3, resulting in slightly worse performance than in Example 3.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A surface protective film for a prism sheet, characterized in that, The surface protective film is a three-layer co-extruded cast film, including a back unwinding layer, a core layer, and an adhesive layer; The raw material for preparing the back unwinding layer is copolymer polypropylene, and the surface roughness of the back unwinding layer is 400~800nm; the copolymer polypropylene does not contain inorganic particles. By weight, the core layer comprises the following raw materials: 70-90 parts metallocene-catalyzed polypropylene, 10-20 parts cyclic olefin copolymer, 5-15 parts hydrogenated petroleum resin, 1-5 parts antistatic composition, 1-10 parts composite light stabilizer, 0.5-3 parts β-crystal nucleating agent, 0.5-1 part microcrystalline wax, and 0.5-2 parts dispersant; wherein, the antistatic composition is a mixture of polyether amide copolymer, amine ethoxide, and glyceryl monostearate in a mass ratio of (1-3):(1-5):(1-5); the composite light stabilizer is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of (3-7):(1-3):(1-5); By weight, the adhesive layer comprises the following raw materials: 100 parts of hydrogenated styrene copolymer, 1-30 parts of tackifying resin, and 1-20 parts of monomer resin; the total styrene content in the hydrogenated styrene copolymer is 35-55%, and the styrene content at the ends of the molecular chains is 13-20%, with the remaining styrene uniformly distributed in the soft segments of the molecular chains; the monomer resin is obtained by polymerization of aromatic hydrocarbon monomers, and the softening point of the monomer resin is greater than 140°C.

2. The surface protective film of the prism sheet according to claim 1, characterized in that, The tackifying resin is at least one of hydrogenated C5 resin, hydrogenated C9 resin, and terpene resin.

3. The surface protective film of the prism sheet according to claim 1, characterized in that, The dispersant is polyethylene wax.

4. The surface protective film of the prism sheet according to claim 1, characterized in that, In the three-layer co-extruded cast film, the thickness of the back unwinding layer accounts for 15-20% of the total thickness, the thickness of the core layer accounts for 60-70% of the total thickness, and the thickness of the adhesive layer accounts for 15-20% of the total thickness.

5. A method for preparing a surface protective film on a prism sheet, characterized in that, The preparation method is used to prepare a surface protective film for a prism sheet as described in any one of claims 1 to 4, and the preparation method includes the following steps: S1. After drying the raw materials for the back unwinding layer, core layer and adhesive layer respectively, they are extruded through a multi-cavity co-extrusion die by a three-layer co-extrusion casting extrusion method to obtain a composite film; S2. After the composite film is cooled by the casting roller, it is shaped by the annealing roller and then wound up to obtain the surface protective film of the prism sheet.

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