Self-adhesive protective film for peep-proof film

Abstract

The invention relates to a self-adhesive protective film for a peep-proof film. The self-adhesive protective film is composed of an adhesive layer, a core layer and a surface layer. The adhesive layer is composed of a block copolymer, a first block copolymer is fused with an aromatic vinyl compound structural unit and an alkyl (meth) acrylate structural unit, and a second block copolymer is combined with an acrylate structural unit and a methacrylate structural unit. In the aspect of material selection and proportioning, the mass content of the diblock copolymer and the mass ratio of the polystyrene (methyl) acrylate compound to the acrylic block copolymer in the adhesive layer are accurately controlled. The core layer is made of olefin-styrene copolymer or cyclic olefin polymer, and the bonding layer is composed of a specific composition, so that the hardness of the bonding layer and the cohesive force of the adhesive layer are effectively controlled. The adhesive force of the protective film changes slightly along with temperature, the adhesive force is stable at high temperature and high pressure, and the protective film is easy to tear without residual glue. The surface roughness is controlled through formula design, and good winding and unwinding characteristics can be achieved.

Description

Technical Field

[0001] The present application relates to the technical field of protective film materials, and in particular to a self-adhesive protective film for a privacy film. Background Art

[0002] With the rapid development of consumer and industrial electronic products, protective films have become an indispensable component of electronic display panels, widely used in mobile phones, computers, LCD TVs, automotive electronics, medical devices, instrumentation, and other infrastructure. Their primary function is to effectively prevent scratches and foreign matter from entering products during transportation, storage, and processing, thereby ensuring product integrity and display quality. In recent years, market demand for electronic products such as televisions, tablets, and smartphones has continued to grow, and screen sizes have continued to expand, further driving the stable development of the global display panel industry.

[0003] However, with the expansion of screen viewing angles, users face the risk of information leakage when using mobile phones and other electronic devices to browse personal information in public places. To meet this challenge, anti-peep film is used to solve related problems. Specifically, by adopting ultra-fine blinds optical patented technology, it can achieve an anti-peep effect that only allows users to read from the front, and bystanders can only see a dark screen, effectively protecting the privacy of users. In the production process of anti-peep film, in order to prevent the adhesive surface from being scratched and foreign matter from being mixed in during the process, it is usually necessary to apply a protective film for protection. However, the protective film of the anti-peep film must meet a series of strict requirements, including optical grade cleanliness, moderate viscosity, slow viscosity increase at high temperature and high humidity, no precipitation contamination of the adhered object, smooth surface without grain defects, no stretching and deformation when unwinding during roll storage, and easy peeling, etc.

[0004] Despite the availability of a wide variety of protective film products on the market, numerous practical challenges remain. In particular, after the privacy film is applied to the protective film, a subsequent high-temperature adhesive coating process (e.g., 140°C for 1-2 minutes) is required. This process places extremely high demands on the protective film's heat resistance, adhesive stability, and lack of precipitation. While currently used protective films achieve basic protection, the adhesive layer commonly suffers from precipitation and insufficient heat resistance. Some manufacturers have attempted to improve heat resistance by adding crystalline PP or PE, but this approach often results in increased hardness, which in turn affects adhesion and versatility. Improving adhesion through adhesive coating often faces challenges such as increased peel force, poor stability, and difficulty removing residual adhesive during heat treatment. Therefore, developing a self-adhesive protective film that effectively protects the privacy film's microstructure and improves product yield while also meeting the requirements of high-temperature adhesive coating, eliminating precipitation contamination, and maintaining stable adhesion and easy peelability has become a pressing technical challenge. Summary of the Invention

[0005] The purpose of this application is to provide a self-adhesive protective film for privacy films. In addition to having the functions of ordinary protective films, this protective film has the following characteristics: low crystal point, high cleanliness, good appearance, soft and compliant, automatic adsorption and degassing, good adhesion stability, no floating during baking with the film, no residual adhesive and pause marks, etc. It can automatically adsorb and degas, and its adhesion strength changes little with temperature and time. The self-adhesive protective film for privacy films of this application includes an adhesive layer, a core layer and a surface layer; The adhesive layer includes a first block copolymer and a second block copolymer, wherein the mass content ratio of the second block copolymer to the first block copolymer is in the range of 60:40 to 95:5, the first block copolymer includes a first polymer block and a second polymer block, and the second block copolymer includes a third polymer block and a fourth polymer block; The first polymer block contains an aromatic vinyl compound structural unit, the second polymer block contains an alkyl (meth)acrylate structural unit, the third polymer block contains an acrylate structural unit, and the fourth polymer block contains a methacrylate structural unit.

[0006] In one embodiment, the melt index of the first block copolymer and the second block copolymer is 1-30 g / 10 min.

[0007] In one embodiment, the weight average molecular weight of the first block copolymer is in the range of 40,000-140,000.

[0008] In one embodiment, in the first block copolymer, the content of the first polymer block is in the range of 10 wt % to 70 wt %.

[0009] In one embodiment, the weight average molecular weight of the second block copolymer is in the range of 10,000-100,000.

[0010] In one embodiment, the second block copolymer includes a hard segment formed by an alkyl methacrylate having an alkyl group with 1 to 3 carbon atoms and a soft segment formed by an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms.

[0011] In one embodiment, the main material of the core layer includes one or more of polypropylene resin, polyethylene resin, styrene copolymer resin, and cyclic olefin resin.

[0012] In one embodiment, the main material of the core layer includes polypropylene resin and styrene copolymer resin, and the styrene copolymer resin is preferably a styrene-butylene block copolymer elastomer.

[0013] In one embodiment, the main material of the surface layer is polyolefin resin.

[0014] In one embodiment, the thickness of the protective film is in the range of 30-80 μm, the thickness of the adhesive layer is in the range of 10-20% of the overall thickness of the protective film, the thickness of the core layer is in the range of 60-80% of the overall thickness of the protective film, and the thickness of the surface layer is in the range of 10-20% of the overall thickness of the protective film.

[0015] Compared with the prior art, this application has the following beneficial effects: The specific block copolymers in the adhesive layer impart automatic adsorption and rapid degassing capabilities to the protective film. During the lamination process, the protective film adheres quickly and tightly to the surface of the privacy film while simultaneously excluding trapped air, preventing air bubbles and improving lamination efficiency and product quality. The adhesive layer, composed of a first block copolymer and a second block copolymer, achieves excellent adhesion strength with minimal temperature and time variations by controlling the mass content and weight-average molecular weight of each block copolymer, as well as the content and molecular weight of the polymer blocks. This ensures that the protective film exhibits a slow increase in viscosity in high-temperature and high-humidity environments, with no precipitation and contamination of the adhered object. Furthermore, during the film-baking process, the film does not float, leaving no adhesive residue or lag marks, significantly improving product reliability and service life.

[0016] The core layer is primarily made of one or more of polypropylene resin, polyethylene resin, styrene copolymer resin, and cyclic olefin resin, while the surface layer is primarily made of polyolefin resin. This combination ensures the protective film has low crystal defects and high cleanliness, meeting the requirements of optical-grade applications and effectively preventing the degradation of optical performance caused by crystals and impurities. The special material formula results in a smooth surface, free of lines, defects, and other anomalies. It adheres perfectly to the surface of the privacy film, providing an excellent appearance and conformability, preventing defects from transferring to the adhesive surface of the privacy film, and ensuring the film's optical properties.

[0017] The overall design of the protective film takes into account the needs of flexibility and adaptability. Styrene-butylene block copolymer is added to the core layer, so that the protective film has excellent flexibility and tensile resistance while maintaining good adhesion properties. When the roll sample is stored, it will not be stretched and deformed when unrolled, and it is easy to peel off, which facilitates the processing and use of the product. The protective film of the present application adopts a multi-layer structure design of an adhesive layer, a core layer and a surface layer. The layers work together to play a role. The synergistic effect of the multi-layer structure enables the protective film to achieve a high level in various performance indicators. In summary, the self-adhesive protective film for anti-peep film of the present application has achieved many excellent properties such as low crystal point, high cleanliness, good appearance, soft fit, automatic adsorption and exhaust, good adhesion stability, no floating when baked with the film, no residual glue and pause printing through material selection and structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the self-adhesive protective film for the privacy film according to the embodiment of the present application.

[0019] Description of reference numerals: 100, adhesive layer; 200, core layer; 300, surface layer. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the accompanying drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0021] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0022] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0023] At a time when electronic display technology is developing rapidly, anti-peep film, as a key product to protect personal privacy and information security, is being widely used in screens of various electronic devices. However, during the production, transportation and use of anti-peep film, it is easily affected by external environmental factors, such as scratches and pollution, which affects its anti-peep performance and service life. Therefore, how to provide reliable and effective protection for anti-peep film has become an important issue that the industry needs to solve urgently. The present application provides a self-adhesive protective film for anti-peep film, which not only inherits the basic functions of ordinary protective films, but also achieves innovative breakthroughs in material selection and structural design. It has the characteristics of low crystal point, high cleanliness, good appearance, soft fit, automatic adsorption and exhaust, good adhesion stability, etc., providing a full-range, high-quality protection solution for anti-peep film. Next, the specific composition and unique advantages of the self-adhesive protective film will be introduced in detail. Please refer to Figure 1A self-adhesive protective film for a privacy film in a preferred embodiment of the present application includes an adhesive layer 100, a core layer 200, and a surface layer 300. The adhesive layer 100 includes a first block copolymer and a second block copolymer, and the mass content ratio of the second block copolymer to the first block copolymer is in the range of 60:40 to 95:5. The first block copolymer includes a first polymer block and a second polymer block, and the second block copolymer includes a third polymer block and a fourth polymer block, wherein the first polymer block contains an aromatic vinyl compound structural unit, the second polymer block contains an alkyl (meth)acrylate structural unit, the third polymer block contains an acrylate structural unit, and the fourth polymer block contains a methacrylate structural unit.

[0024] The combination of aromatic vinyl compound structural units and (meth) alkyl acrylate structural units in the first block copolymer in the adhesive layer 100, and the combination of acrylate structural units and methacrylate structural units in the second block copolymer, make the adhesive layer 100 have excellent adhesion properties, can form a strong adhesion with the surface of the anti-peep film, and ensure that the protective film will not fall off easily under various conditions of use. The structural design of the block copolymer makes the adhesive layer 100 have good flexibility and adaptability, can adapt to the surface of the anti-peep film of different shapes and curvatures, achieve a tight fit, avoid the generation of bubbles and wrinkles, and improve the quality of the fit. The characteristics imparted by different block copolymers make the adhesive layer 100 have good weather resistance and chemical stability, can maintain stable adhesion properties under different environmental conditions, and is not easily affected by environmental factors such as temperature and humidity. At the same time, it has good tolerance to common chemical substances and is not prone to aging, deterioration and other problems.

[0025] Specifically, in the adhesive layer 100, the mass content of the first block copolymer and the second block copolymer is set within a precise and specific range. The mass content ratio of the second block copolymer to the mass content of the first block copolymer is in the range of 60:40 to 95:5. In terms of the thermoplastic elastomer composition involved in this application, the first block copolymer and the second block copolymer are formulated in a specific mass ratio. In specific applications, taking the first block copolymer and the second block copolymer as a whole, the addition ratio of the polystyrene (meth)acrylate compound (first block copolymer) is preferably set between 5% and 40%. To further optimize performance, the more preferred addition ratio range is 10% to 30%. Correspondingly, the addition ratio of the acrylic block copolymer (second block copolymer) is preferably in the range of 60% to 95%. To achieve better results, the more preferred addition ratio range is 70% to 90%. In this application, the melt index of the first block copolymer is 1-30 g / 10 min, and the melt index of the second block copolymer is also 1-30 g / 10 min. By precisely controlling the content of the first block copolymer, the hardness of the adhesive layer and the cohesion of the adhesive layer can be effectively controlled, significantly improving the temperature resistance of the protective film. This also ensures a good connection between the adhesive layer and the core layer of 200SBC (styrene-based thermoplastic elastomer), ensuring the stability and reliability of the overall performance of the protective film.

[0026] The weight-average molecular weight of the first block copolymer is precisely controlled within the range of 40,000-140,000 and comprises two or more first polymer blocks and one or more second polymer blocks. The first polymer block is rich in structural units derived from aromatic vinyl compounds, such as styrene and various alkyl-substituted styrenes, such as α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene. Styrene is a more preferred choice from the perspectives of raw material transparency and improved heat resistance. The second polymer block is composed of structural units of alkyl (meth)acrylates. There are a wide variety of alkyl (meth)acrylates, including methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, pentyl (meth)acrylate, neopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, cyclohexyl (meth)acrylate, and dicyclopentane (meth)acrylate. Among polystyrene (meth)acrylates, copolymers of styrene and methyl methacrylate are the preferred choice due to their excellent performance.

[0027] In the first block copolymer, the content of the first polymer block is in the range of 10 wt% to 70 wt%, preferably in the range of 15 wt% to 60 wt%. In the field of polystyrene (meth)acrylate compounds, there are many representative commercial products, including Delpet 980N manufactured by Asahi Kasei Corporation, MS 600 and MS 800 manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., and TX-100S manufactured by Denka Company Limited.

[0028] The weight average molecular weight of the second block copolymer is in the range of 10,000 to 100,000. The molecular weight of the acrylic block copolymer (second block copolymer), measured by weight average molecular weight (Mw), is preferably in the range of 10,000 to 100,000, more preferably 10,000 to 70,000.

[0029] This acrylic block copolymer comprises one or more third polymer blocks and one or more fourth polymer blocks. The third polymer blocks contain structural units derived from acrylic acid esters, while the fourth polymer blocks contain structural units derived from methacrylic acid esters. When the weight-average molecular weight of the acrylic block copolymer is set above 10,000, sufficient bonding strength is achieved. While keeping it below 70,000 maintains a suitable viscosity range, this molecular weight setting also effectively reduces precipitation and adhesive residue. To prevent adhesive residue, the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) is preferably in the range of 1.0-2.0.

[0030] The second block copolymer has various structural forms, including a hard segment (H) formed by an alkyl methacrylate with 1-3 carbon atoms and a soft segment (S) formed by an alkyl acrylate with 1-8 carbon atoms. Specifically, there are triblock polymers with an HSH structure and diblock polymers with an SH structure. In practical applications, triblock and diblock polymers can be mixed to achieve even better performance. Regarding the monomers used to form the block copolymer, for the hard segment (H), alkyl methacrylates with 1-3 carbon atoms are preferred, such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate. These monomers have high glass transition temperatures and impart good hardness and strength to the copolymer. For the soft segment (S), alkyl acrylates with 1-8 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, isoamyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate. These monomers have low glass transition temperatures, increasing the flexibility and ductility of the copolymer. In actual products, a variety of specific block copolymers are available, such as KURARITY® LA2140E, KURARITY® LA2250, KURARITY® LA2330, KURARITY® LA3320, KURARITY® LA3170, KURARITY® LA2270, KURARITY® LA4285, KURARITY® LA1892, KURARITY® LK9243, and KURARITY® KLLK9333. Considering both heat resistance and viscosity requirements, KURARITY® LA2250 is a preferred choice for grades requiring moderate hardness and suitability for cast film processes. This product offers excellent overall performance, meeting temperature resistance requirements while providing good viscosity and processing properties.

[0031] The core layer 200, which serves as the intermediate layer, can be made of polypropylene resin, polyethylene resin, styrene copolymer resin, or cyclic olefin resin, either singly or as a blend. Considering the self-adhesive film's application characteristics, flexibility, and adhesion to the various layers, blends of olefin resins and styrene copolymer resins are preferred. Examples of olefin resins include polyethylene resin and polypropylene resin, with polypropylene being particularly preferred. Block polypropylene (block PP) is particularly preferred for its heat resistance. Its melting point should preferably be above 150°C, more preferably above 155°C, and even more preferably above 160°C, with a higher melting point being more beneficial. Differential scanning calorimetry (DSC) testing requires that the second melting curve contain no sub-peaks with a peak temperature below 150°C. The melting enthalpy should generally be above 50 J / g, more preferably above 60 J / g, and even more preferably above 70 J / g. On the other hand, although the specific value of the melting enthalpy is affected by the ratio of the crystalline polypropylene resin to the olefin elastomer, from the perspective of softness, the melting enthalpy should preferably be controlled below 110 J / g, more preferably below 100 J / g.

[0032] In order to ensure good adhesion with the adhesive layer and achieve soft properties, it is necessary to add an olefin elastomer to the core layer 200. Any suitable olefin elastomer can be used, without affecting the desired effects of the present application, such as α-olefin elastomers, olefin block copolymers, olefin random copolymers, and styrene elastomers. From the perspective of fully demonstrating the advantages of the present application, styrene-butadiene block copolymer elastomers are preferred, as they have good connection properties with the adhesive layer type.

[0033] The above-mentioned styrene-butadiene block copolymers cover various types of block copolymers, including linear, diblock, radial, and branched block copolymers. Among them, the diblock linear block copolymer is preferably prepared by anionic polymerization. The styrene-butadiene block copolymer is composed of at least one block S and at least one block B and / or block B / S, preferably a block B / S. Block S forms a hard phase, and block B and / or block B / S forms a soft phase. Specifically, block S contains structural units of at least one vinyl aromatic monomer; block B and / or block B / S contain structural units of conjugated dienes, and the B / S block also contains structural units of at least one vinyl aromatic monomer. Considering the structural characteristics and performance requirements, it is preferred that no separate B block is contained, and the linear structure of random B / S blocks is predominant. In styrene-butadiene block copolymers, the hard phase content should be between 30% and 95% for both heat resistance and wettability. If the hard phase content exceeds 95%, the material's hardness and elastic modulus will be too high, hindering its flexibility. If the hard phase content is less than 30%, the material's heat resistance and adhesion to the adhesive layer will not meet the desired requirements. The preferred range is 40% to 90%. The content of this aromatic olefin compound monomer can be determined by 1H nuclear magnetic resonance (1H-NMR) or infrared spectroscopy.

[0034] The molecular weight (Mw) of the styrene-butadiene block copolymer should be controlled between 30,000 and 200,000. An Mw greater than 30,000 facilitates polymerization and industrial production; an Mw less than 200,000 provides adequate adhesion to rough surfaces. Furthermore, the block copolymer's melt flow rate (MFR) should preferably be controlled between 1 and 30 g / 10 min to facilitate melt extrusion and film formation. Its density can preferably be controlled between 0.930 and 1.10 g / cm³. Considering processability and the impact on material properties, its content is preferably controlled below 40 wt% and above 10%, with a more preferred range of 10-30%.

[0035] In addition, the core layer 200 may further include any other suitable components, such as tackifiers, plasticizers, antidegradants, various pigments, dyes, antioxidants, antistatic agents, lubricants, foaming agents, heat stabilizers, light stabilizers, inorganic fillers, and organic fillers. These components may be present in one type or in two or more types. To minimize the impact on the overall performance of the material, their content is preferably controlled to be less than 10 wt%, more preferably less than 7 wt%, further preferably less than 5 wt%, particularly preferably less than 2 wt%, and even more preferably less than 1 wt%.

[0036] The core layer material of this application provides structural support for the protective film, ensuring that it will not deform or crack under various usage environments, thereby effectively protecting the internal privacy film from external physical damage. Both materials have excellent optical transparency and will not interfere with the optical properties of the privacy film, ensuring the film's anti-peeping effect and display clarity.

[0037] The polyolefin resin in the surface layer 300 material has excellent wear resistance, chemical corrosion resistance, and aging resistance. It can effectively prevent external scratches, chemical corrosion, and ultraviolet radiation, extending the service life of the protective film and anti-peep film. The surface of the surface layer 300 material is smooth and flat, with good gloss, which can improve the overall appearance quality of the protective film. The thickness of the protective film is in the range of 30-80μm. Among them, the thickness of the adhesive layer 100 accounts for 10%-20% of the total thickness of the protective film, the thickness of the core layer 200 accounts for 60%-80% of the total thickness of the protective film, and the thickness of the surface layer 300 accounts for 10%-20% of the total thickness of the protective film.

[0038] In order to give the film sufficient softness and ensure that it has sufficient anti-adhesion properties, the surface of the film needs to be matte treated. After matte treatment, the glossiness of the film should generally be controlled below 40%, and the arithmetic average roughness (Ra) of its surface is preferably in the range of 0.2-0.4μm. Matt surface treatment can be achieved by adjusting the raw material formula or using an anilox roller. From the perspective of softness, in this application, the tensile elastic modulus of the film should generally be controlled below 500MPa, and more preferably below 350MPa. From the perspective of film formation stability, the tensile elastic modulus of the film should generally be not less than 100MPa, preferably not less than 200MPa.

[0039] The self-adhesive protective film in this application is produced in a dust-free workshop using high-precision equipment using a three-layer co-extrusion casting process. A supercritical nitrogen fluid delivery system is introduced during the production process, effectively reducing the generation of crystal points at the source. Furthermore, advanced defect detectors and beta-ray thickness testers are used to conduct online tracking inspections of the film's appearance defects and thickness, ensuring that the film produced has excellent properties such as uniform thickness, high cleanliness, absence of impurities, smooth surface, and low crystal points.

[0040] The adhesive strength of this self-adhesive protective film varies minimally with temperature. Even under high-temperature and high-pressure processing conditions, the adhesive strength remains stable within a certain range, making it easy to tear without residual adhesive. At room temperature, the adhesive strength of the conductive film is 1-10 gf / 25 mm, preferably 3-10 gf / 25 mm. After treatment at 140°C for 5 minutes, the adhesive strength is 3-20 gf / 25 mm, with no floating or bubbles. The surface and core layers of the self-adhesive protective film are primarily made of polyolefin resin. For heat resistance, the polyolefin resin for the surface and core layers is preferably polypropylene. Common types of polypropylene resins include homopolypropylene, block polypropylene, and random copolymer polypropylene. For heat and solvent resistance, the melting point of polypropylene is preferably above 150°C, more preferably above 155°C, and even more preferably above 160°C. The higher the melting point of the polypropylene resin, the better its heat and solvent resistance. Furthermore, no sub-peak with a peak top temperature below 150°C should appear in the second melting curve. The melting enthalpy of polypropylene resin should generally be 50 J / g or higher, more preferably 60 J / g or higher, and even more preferably 70 J / g or higher. However, from the perspective of flexibility, the melting enthalpy should be controlled below 110 J / g, more preferably below 100 J / g.

[0041] To achieve excellent winding and unwinding properties, surface roughness must be precisely controlled through formulation design, typically within the range of 0.2-0.4μm (Ra). Additionally, when preparing the surface layer composition, additives such as antistatic agents, antioxidants, nucleating agents, weathering agents, processing aids, and wax powder may be added in appropriate amounts, provided they do not affect the required properties.

[0042] Specific implementation cases: Some specific implementation methods will be further introduced below to further explain the technical solution of this application in detail.

[0043] Example 1 The rough surface layer A is selected from CF330 with a thickness of 6 μm, the core layer B functional layer is selected from F8403 / TR2000 = 8 / 2 blend, with a layer thickness of 28 μm, and the adhesive layer C material is compounded with KURARITY 2250 / MS-200 = 9 / 1, with a layer thickness of 6 μm. The ratio here is the mass content ratio.

[0044] Among them, acrylic block copolymers (including but not limited to the following brands): 1) KURARITY 2250 (Kuraray Co., Ltd.), type: methyl methacrylate / n-butyl acrylate / methyl methacrylate triblock copolymer; molecular weight: 65,000; molecular weight distribution: 1.2; PMMA content: 30%; 2) KURARITY 4285 (Kuraray Co., Ltd.); Type: Methyl methacrylate / n-butyl acrylate / methyl methacrylate triblock copolymer; Molecular weight: 67,000; Molecular weight distribution: 1.2; PMMA content: 50%; Polystyrene (meth)acrylate compound; Estyrene MS-200 (Nippon Steel & Sumikin Chemical Co., Ltd); Density: 1.13 g / cm³; Test conditions: 230°C; Melt flow rate (MFR): 3-5 g / 10 min; Vicat softening point: 103°C; Polystyrene-butadiene block copolymer: SBR: styrene-butadiene copolymer; Manufacturer: JSR Corporation; Product name: "TR2000"; Styrene / butadiene mass ratio: 40 / 60; SBC: styrene-butadiene copolymer; Manufacturer: Denka Co., Ltd.; Product name: "CLEAREN 170ZR"; Styrene / butadiene mass ratio: 83 / 17; Block polypropylene: CF330 (Hanwha); density: 0.90 g / cm³; test conditions: 230°C; melt flow rate (MFR): 3-5 g / 10min; melting point: 165°C; Block polypropylene: F8403 (Yanshan Petrochemical); density: 0.90 g / cm³; test conditions: 230°C; melt flow rate (MFR): 2-3 g / 10min; melting point: 163°C; MLLDPE: EG8200G (DOW Affinity); Density: 0.87 g / cm³; Test conditions: 190°C; Melt flow rate (MFR): 5 g / 10min; Melting point: 63°C The surface layers and core layers of the remaining embodiments are the same as those of Example 1, and the adhesive layer is changed as follows: Example 2: KURARITY 2250 / MS-200 are compounded in a ratio of 8 / 2, and the layer thickness is 6 μm.

[0045] Example 3: KURARITY 2250 / MS-200 are compounded in a ratio of 7 / 3, and the layer thickness is 6 μm.

[0046] Example 4: KURARITY 2250 / MS-200 are compounded in a ratio of 6 / 4, and the layer thickness is 6 μm.

[0047] Example 5: KURARITY 4285 / MS-200 are compounded in a ratio of 9 / 1, and the layer thickness is 6 μm.

[0048] Example 6: KURARITY 4285 / MS-200 are compounded in a ratio of 8 / 2, and the layer thickness is 6 μm.

[0049] Example 7: KURARITY 4285 / MS-200 are compounded in a ratio of 7 / 3, and the layer thickness is 6 μm.

[0050] The surface layer and adhesive layer are the same as in Example 2, and the core layer is changed as follows: Example 8: F8403 / TR2000=7 / 3 is compounded, and the layer thickness is 28μm.

[0051] Example 9: F8403 / 170ZR=8 / 2 is compounded, and the layer thickness is 28 μm.

[0052] Example 10: F8403 / 170ZR=7 / 3 is compounded, and the layer thickness is 28 μm.

[0053] The comparative examples are as follows: Comparative Example 1: Surface layer CF330 core layer F8403 adhesive layer EG8200G, interlayer setting: 6μm / 28μm / 6μm Specific process: After the above components are mixed in a specific ratio, the film is produced using a heated casting process. The specific process is as follows: extrusion through an extruder → casting through a T-die → air knife treatment → casting roll forming → cooling through a chill roll → thickness measurement using a beta-ray thickness gauge → trimming of scrap edges → inspection using a defect detector → winding. The T-die and chill roll are key production equipment in the melt casting process. The T-die design ensures uniform material flow across the entire width of the die lip, and its temperature is generally set at 220°C. The casting roll surface is precision machined, ensuring a stable rotational speed to minimize axial temperature fluctuations. The casting roll temperature should be controlled at around 30°C, and the chill roll temperature should also be maintained at 30°C. The temperatures of the casting and chill rolls must be properly regulated. Excessive cooling or overheating can negatively impact the film's mechanical properties, transparency, and haze. The difference between the die head and chill roll temperatures is a key parameter determining the film's crystallinity. Increasing the temperature difference reduces crystallinity, thereby improving the film's transparency and toughness.

[0054] An air knife device is installed above the casting roll, and a vacuum box is located below the die head. When the air knife's blowing power is controlled at 40% and the vacuum suction power is controlled at 20%, the molten material immediately adheres to the casting roll surface. This not only improves the cooling effect, but also makes the plastic film surface smoother and reduces necking at the ends of the cast film. Simultaneously, controlling the die head's suction power at 60% removes low-molecular-weight volatiles, preventing their accumulation on the casting roll, thereby better ensuring the film's appearance quality.

[0055] After the film passes through the cooling rollers, a beta-ray thickness gauge automatically adjusts the T-die gap, keeping the average error in cast film thickness within 2%. Furthermore, the winding tension must be adjusted based on factors such as film thickness and production speed, maintaining a constant 90N. Excessive or insufficient winding tension can cause wrinkles on the film surface, affecting film flatness.

[0056] Each embodiment was tested, including film appearance, tensile elastic modulus, resin melting point, melt flow rate, friction coefficient, roughness, adhesion, contamination, temperature resistance, light transmittance and haze test. The specific test contents are as follows: 1. Film appearance The laminated sealing film of the present application is required to have generally uniform properties and excellent appearance. For example, preferably, the film has minimal thickness variation, few fisheyes, foreign matter, streaks, or scratches, and is free of color unevenness, wrinkles, and pinholes. When measured using the method described in the Examples, the number of crystal points with a diameter of 0.1 mm or greater but less than 0.15 mm is preferably less than 100 per square meter, and the number of crystal points with a diameter of 0.15 mm or greater but less than 0.2 mm is preferably less than 10 per square meter. Foreign matter and impurities are not permitted.

[0057] 2. Tensile elastic modulus In the laminated sealing film of this application, the "longitudinal direction" refers to the direction corresponding to the direction of movement during the film manufacturing process, and the "width direction" refers to the direction perpendicular to the direction of movement during the film manufacturing process. Hereinafter, the "longitudinal direction" will sometimes be referred to as the "MD direction," and the "width direction" as the "TD direction." The laminated sealing film of this application preferably has a tensile modulus in the MD / TD directions between 200 and 350 MPa. This facilitates production and processing while ensuring the film's soft, conformable properties.

[0058] The tensile modulus of the film in MD / TD was measured three times with a sample length of 100 mm, a sample width of 25 mm, a chuck distance of 50 mm, and a speed of 300 mm / min, and the average value was taken as the tensile modulus in each direction.

[0059] 3. Melting point of resin The melting point of the resin was measured using a differential scanning calorimeter in accordance with JIS K7121. Specifically, approximately 5 mg of sample was placed in an aluminum pan and heated from room temperature to 200°C at a heating rate of 10°C / min. The sample was held at 200°C for 3 minutes, cooled to 23°C, held at 23°C for 3 minutes, and then heated again to 200°C. The melting point was determined as the maximum melting endothermic peak temperature. If two or more melting endothermic peaks were present, the highest melting endothermic peak was used as the melting point.

[0060] 4. Melt flow rate The polypropylene-based and adhesive layer resins were measured at a temperature of 230° C. using a thermal flow evaluation device (Shimadzu Corporation, capillary rheometer, CFT500D). 5. Friction coefficient The dynamic friction coefficient of the laminated sealing film of this application is preferably 0.5 or less at a load of 2 N, and the non-stick surface friction coefficient is preferably 0.5 or less. This provides sufficient slippage between the films and facilitates satisfactory winding and unwinding characteristics. The dynamic and static friction coefficients are determined in accordance with JIS K7125 at 23°C and 65% RH.

[0061] 6. Roughness In order to suppress the peeling force between the protective film surface and the adhesive layer, it is preferred that the surface has a concave-convex structure to reduce the contact area with the adhesive layer. The haze of the film is basically proportional to the surface roughness, so a suitable formula combination is required to achieve the appropriate haze, balancing the film's own fisheyes, other foreign matter and the film detection requirements. The arithmetic average surface roughness is measured using an optical profilometer. 7. Adhesion The peel force of the privacy film attached to the protective film was measured at a peeling speed of 300 mm / min (peeling at 180°C). The peel force across a 25 mm width was used as the adhesion force. The peeling operation was performed at 23°C and 65% RH. A Kejian tensile testing machine was used, referring to GB / T2792.

[0062] 8. Pollution After attaching the privacy film to the protective film, cut it into A4 size, bake it in a blast drying oven at 120℃ for 10 minutes, take it out and cool it down, tear off the protective film, and observe the pause position under a strong light in a dark room to see if there is a white or dark pause mark. 9. Temperature resistance The sample prepared in method 7 was placed in a forced air drying oven at 140°C for 2 minutes. After being taken out, a peeling force test was performed to observe whether it floated.

[0063] 10. Light transmittance and haze test The haze of the film is preferably 30% or less, more preferably 25% or less. A haze exceeding 25% often results in streaking and scratching of the film, making it difficult to visually identify the contents. The haze of the film is preferably 10% or greater. A haze of 10% or greater minimizes the loss of adhesion strength. The AT-4725 transmission haze meter from BYK Chemie GmbH, Germany, was used, with reference to GB / T2410. The specific compositions and test results for each example are shown in Table 1.

[0064] Table 1 Specific composition and test results of each embodiment As can be seen from the foregoing, this application provides an innovative self-adhesive protective film for privacy films, achieving breakthroughs in material selection and structural design. It exhibits outstanding properties such as low crystal point, high cleanliness, excellent appearance, conformable and soft structure, automatic adsorption and degassing, and good adhesive stability, providing a comprehensive, high-quality protection solution for privacy films. The protective film consists of a three-layer structure: an adhesive layer, a core layer, and a surface layer. The adhesive layer, a key component, is composed of a specific block copolymer. The first block copolymer combines aromatic vinyl compound structural units with (meth)acrylate structural units, while the second block copolymer combines acrylate structural units with methacrylate structural units. This unique combination gives the adhesive layer excellent adhesion, flexibility, and adaptability, allowing it to tightly conform to privacy film surfaces of varying shapes and curvatures, effectively preventing the formation of bubbles and wrinkles, and exhibiting excellent weather resistance and chemical stability. In terms of material selection and proportioning, the weight content of the first block copolymer and the second block copolymer in the adhesive layer is set within the ranges of 5%-40% and 60%-95%, respectively. At the same time, polystyrene (meth)acrylate compounds and acrylic block copolymers are formulated in a specific mass ratio to further optimize the performance of the protective film.

[0065] The core layer is made of one or more of polypropylene resin, polyethylene resin, styrene copolymer resin, and cyclic olefin resin, ensuring the film's high strength and optical transparency, effectively resisting external physical damage while maintaining the film's privacy protection and display clarity. The surface layer is made of polyolefin resin, imparting excellent wear resistance, chemical corrosion resistance, and aging resistance. Its smooth surface enhances the overall appearance.

[0066] In terms of molecular weight control of the block copolymers, the weight-average molecular weight of the first block copolymer is precisely controlled within the range of 40,000-140,000, while the weight-average molecular weight of the second block copolymer is within the range of 10,000-100,000. By precisely controlling the molecular weight, the protective film is ensured to have sufficient bonding strength and appropriate viscosity, while effectively improving the problems of precipitation and residual glue. The thickness of the protective film is controlled within the range of 30-80 μm, of which the thicknesses of the adhesive layer, core layer, and surface layer account for 10%-20%, 60%-80%, and 10%-20%, respectively. The adhesive layer is composed of a specific composition. By precisely controlling the content of styrene-methyl methacrylate copolymer, the hardness of the adhesive layer and the cohesion of the adhesive layer are effectively controlled, which significantly improves the temperature resistance of the protective film and achieves good connection characteristics between the adhesive layer and the core layer SBC.

[0067] During the production process, this application utilizes a three-layer co-extrusion casting process and introduces a supercritical nitrogen fluid delivery system to reduce the generation of crystal points at the source. At the same time, advanced defect detectors and beta-ray thickness testers are used to conduct online tracking and detection of film appearance defects and thickness, ensuring that the produced film has excellent properties such as uniform thickness, high cleanliness, no impurities, smooth surface, and low crystal points.

[0068] The adhesion of this self-adhesive protective film varies minimally with temperature, maintaining stable adhesion even under high-temperature and high-pressure processing conditions. It is easy to tear without residual adhesive. At room temperature, its adhesion to conductive film is 3-10gf / 25mm; after treatment at 140°C for 5 minutes, the adhesion is 3-20gf / 25mm, with no floating or bubbles. To achieve excellent winding and unwinding properties, this application precisely controls the surface roughness through formulation design, and appropriately adds antistatic agents, antioxidants, and other additives to further enhance the performance of the protective film.

[0069] The above is only a specific implementation of the present application. Any other improvements made based on the concept of the present application are considered to be within the scope of protection of the present application.

Claims

1. A self-adhesive protective film for a privacy film, characterized in that: Including adhesive layer, core layer and surface layer; The adhesive layer includes a first block copolymer and a second block copolymer, wherein the mass content ratio of the second block copolymer to the first block copolymer is in the range of 60:40 to 95:5, the first block copolymer includes a first polymer block and a second polymer block, and the second block copolymer includes a third polymer block and a fourth polymer block; The first polymer block contains an aromatic vinyl compound structural unit, the second polymer block contains an alkyl (meth)acrylate structural unit, the third polymer block contains an acrylate structural unit, and the fourth polymer block contains a methacrylate structural unit.

2. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The melt index of the first block copolymer and the second block copolymer is 1-30 g / 10 min.

3. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The weight average molecular weight of the first block copolymer is in the range of 40,000-140,000.

4. The self-adhesive protective film for privacy film according to claim 1, characterized in that: In the first block copolymer, the content of the first polymer block is in the range of 10 wt % to 70 wt %.

5. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The weight average molecular weight of the second block copolymer is in the range of 10,000 to 100,000.

6. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The second block copolymer includes a hard segment formed by an alkyl methacrylate having an alkyl group with 1 to 3 carbon atoms and a soft segment formed by an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms.

7. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The main material of the core layer includes one or more of polypropylene resin, polyethylene resin, styrene copolymer resin, and cyclic olefin resin.

8. The self-adhesive protective film for privacy film according to claim 7, characterized in that: The main material of the core layer includes polypropylene resin and styrene copolymer resin, and the styrene copolymer resin is preferably a styrene-butylene block copolymer elastomer.

9. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The main material of the surface layer is polyolefin resin.

10. The self-adhesive protective film for privacy film according to claim 1, characterized in that: The thickness of the protective film is in the range of 30-80 μm, the thickness of the adhesive layer is in the range of 10-20% of the overall thickness of the protective film, the thickness of the core layer is in the range of 60-80% of the overall thickness of the protective film, and the thickness of the surface layer is in the range of 10-20% of the overall thickness of the protective film.

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