Lightweight high-strength micro-textured composite mobile phone back cover and preparation method

Abstract

This invention discloses a lightweight, high-strength micro-textured composite mobile phone back cover and its preparation method. The back cover includes a surface-hardening layer, a substrate layer, and a functional coating layer stacked sequentially from the outside to the inside. This invention adopts a multi-layer structure consisting of a surface-hardening layer, a PMMA and PC composite substrate, an optical texture layer, and an inner functional coating layer, which balances strength, toughness, and appearance under relatively thin thickness conditions. At the same time, this invention adopts a process path of forming a microstructure array on a mold, simultaneously replicating the microtexture during the molding process, online spraying of the surface-hardening coating after demolding, and implementing magnetron sputtering of the functional coating on the inner side, which orderly connects the shape forming, microstructure construction, and functional film deposition in a unified production process.

Description

Technical Field

[0001] This invention relates to the field of mobile terminal structural components technology, specifically to a lightweight, high-strength micro-textured composite mobile phone back cover and its preparation method. Background Technology

[0002] Currently, common forms of smartphone back covers include glass back covers, metal back covers, ceramic back covers, and plastic back covers, represented by polycarbonate and polymethyl methacrylate composite boards. Glass and ceramics excel in transparency, gloss, and appearance, but they are heavy, fragile, and have low processing yields; metal back covers have high strength and rigidity, but they significantly shield communication, Wi-Fi, near-field communication, and wireless charging; plastic composite back covers are lightweight, have good signal reception, and offer high molding flexibility, but there is still room for improvement in scratch resistance, high-end decorative effects, and overall mechanical performance.

[0003] Existing composite back cover decoration technologies mostly rely on ink printing, gradient coating, spraying, or lamination to obtain colors and macroscopic patterns. They enhance wear resistance by applying a hardened coating to the outer surface and achieve iridescent or brushed metal effects by layering textured layers, metal or metal oxide coatings, and ink layers on the inner surface. The optical response of these solutions mainly stems from film interference or large-area gradient coatings, resulting in relatively simple designs at the microscopic geometric level. To achieve complex decorative effects, multiple intermediate layers are often layered, increasing the number of interfaces and structural thickness. This hinders further improvements in bending and drop resistance while maintaining a thinner profile and can easily lead to reliability issues such as warping, cracking, and delamination.

[0004] Therefore, there is an urgent need in this field for a technical solution that can directly construct a fine microstructure optical layer inside the substrate while maintaining the lightweight and high strength of the mobile phone back cover, and form a compact composite structure with the inner functional coating. This solution can organically integrate the surface hardening layer, substrate layer, microtextured optical layer and functional layer in structure, and achieve stable mass production through reasonable mold design and molding process, thereby improving the appearance, signal compatibility and overall mechanical reliability at the same time.

[0005] Chinese patent literature discloses a back cover for an electronic product [Application No.: 202221928944.1, Publication No.: CN218140396U]. This patent discloses a multi-layer back cover structure with PMMA / PC composite board as the substrate. Although it can achieve a similar decorative purpose as the present invention by using PMMA / PC composite board in combination with a double texture layer, PVD layer and ink layer, the present invention directly replicates optical microstructures such as prism array, microlens array or grating array on the PC surface of the substrate through micro-nano texture on the mold cavity, and integrally forms the micro-texture layer with the substrate layer. At the same time, a thin metal oxide or magnetic wave-absorbing functional coating is tightly attached to the inner side to form a compact multi-layer composite structure. The comparative patent does not have this feature of synergistic design of the substrate-embedded micro-texture optical layer and functional coating. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a lightweight, high-strength micro-textured composite mobile phone back cover.

[0007] A lightweight, high-strength micro-textured composite mobile phone back cover is characterized by comprising a surface-hardening layer, a substrate layer, and a functional coating layer stacked sequentially from the outside to the inside. The substrate layer includes a first resin sublayer disposed on the outer side and a second resin sublayer disposed on the inner side. An optical texture layer is formed on the surface of the second resin sublayer facing the functional coating. The optical texture layer is a microstructure array composed of multiple concave and convex geometric units, and the optical texture layer and the second resin sublayer are integrally formed. The surface-hardening layer is applied to the side of the first resin sublayer facing away from the second resin sublayer, and the functional coating layer is applied to the side of the optical texture layer facing away from the second resin sublayer.

[0008] Preferably, the first resin sublayer is a PMMA layer containing a core-shell toughening agent, and the second resin sublayer is a PC layer containing a core-shell toughening agent. The first resin sublayer and the second resin sublayer constitute an integral composite board, and the core-shell toughening agent has a mass percentage content of 5% in the composite board.

[0009] The above technical solution significantly improves the overall toughness and impact resistance of the substrate layer while maintaining the lightweight and highly transparent appearance of the phone back cover. The first resin sublayer uses PMMA with a core-shell toughening agent, and the second resin sublayer uses PC with a core-shell toughening agent. They exist in the form of an integrated composite board with the front and back laminated together, so that the two resins form a stable bond at the interface. The core-shell toughening agent is distributed in the entire composite board at a mass percentage of about 5%, which improves the material's resistance to crack propagation and drop resistance without significantly sacrificing rigidity.

[0010] Specifically, the core-shell toughening agent is finely dispersed in the PMMA and PC resin matrix. When the back cover is subjected to external impact or bending load, local yielding and creasing deformation easily occur around the core-shell particles, which can absorb and dissipate some impact energy, slow down the concentrated propagation of stress in the matrix, and thus reduce the tendency of microcrack initiation and rapid propagation. At the same time, the outer PMMA sublayer provides better surface hardness and optical effects, while the inner PC sublayer provides higher matrix strength and dimensional stability. The two work together through the integrated composite plate structure, which is conducive to achieving a comprehensive balance of strength and toughness under relatively small thickness conditions.

[0011] In practical applications, this integrated composite substrate containing a uniform amount of core-shell toughening agent helps improve the reliability of mobile phone back covers under daily use, assembly clips, drop impacts, and bending deformation conditions, reducing the risk of corner cracking, stress whitening, and interlayer delamination. At the same time, the stable mechanical response can also work with subsequent microtexture replication and functional coating deposition processes to reduce deformation and cracking during molding and use, providing a solid substrate foundation for achieving lightweight, high-strength, and aesthetically stable microtextured composite mobile phone back covers.

[0012] Preferably, the microstructure array of the optical texture layer is at least one of the following structures: a prism array structure arranged side by side along a predetermined direction, a microlens array structure composed of multiple microlens units, and a grating structure composed of multiple periodic stripe units.

[0013] The above technical solutions enable flexible configuration of multiple optical response forms on the same optical texture layer. By selecting or combining prism array structures, microlens array structures, and grating structures, not only can directional highlight and brightness variation effects be obtained, but also a stronger sense of depth effect and color variation effect that changes with the viewing angle can be introduced. Thus, while maintaining the lightweight and high strength of the substrate, a richer and more customizable decorative appearance and optical performance can be achieved.

[0014] Specifically, the prism array structure, through geometric refraction and reflection, produces striped highlights and anisotropic gloss effects on incident light in a predetermined direction, which is beneficial for creating light and shadow variations similar to straight lines or diagonal brushed lines; the microlens array structure, composed of a large number of tiny lens units, can locally focus and scatter incident light, making the pattern or functional coating on the back appear magnified, suspended, or layered in a three-dimensional way; the grating structure, composed of periodic stripe units, produces diffraction and interference phenomena dependent on the incident angle and viewing angle under white light illumination, thus creating color gradients and dynamic effects that change with the viewing angle. By using different types of microstructure arrays in sections on the same back cover, or by orderly combining them in local areas, the overall optical style and detail expression can be customized according to the product positioning.

[0015] In practical applications, this optical texture layer design, which allows for flexible selection and combination of prism arrays, microlens arrays, and grating structures, helps mobile phone back covers achieve multi-series and multi-style appearance differentiation under the same substrate and process platform. It enhances the overall performance of the product in terms of light and shadow performance, visual layering, and brand recognition. At the same time, it maintains the integrated molding structure of the optical texture layer and the substrate, which facilitates the stable replication of complex microstructures during mass production, reduces the dependence on additional decorative film layers, and provides greater space for the design and superposition of subsequent functional coatings.

[0016] Preferably, the functional coating is a metal oxide film deposited on the inner side of the back cover of the mobile phone, wherein the metal oxide film is an indium tin oxide film.

[0017] The above technical solution can introduce a stable and controllable metal oxide functional layer without significantly increasing the thickness and weight of the phone's back cover structure. This allows a continuous and dense indium tin oxide film to be formed on the back side of the micro-textured optical layer, thereby ensuring overall light transmittance and decorative effect while giving the back cover excellent optical control capabilities and electrical properties. This is beneficial for achieving fine adjustment of reflection, highlights, light transmittance uniformity, and local brightness.

[0018] Specifically, indium tin oxide (ITO) thin films, as transparent conductive metal oxides, possess high visible light transmittance and a certain refractive index. They can modulate the light transmitted or reflected by the microstructure array, creating softer, more layered light spots and transitions between light and dark areas when combined with prism arrays, microlens arrays, or grating structures. Simultaneously, the thin layer can improve the optical matching of the substrate-air interface to some extent, mitigating glare or "bright spots" caused by abrupt changes in interface reflection. Furthermore, ITO thin films exhibit surface conductivity, which facilitates the introduction of antistatic, charge-dissipating, or electromagnetic property modulation techniques into the back cover structure.

[0019] In practical applications, this indium tin oxide functional coating, located on the inside of the phone's back cover, helps to differentiate the optical styles and expand the functions of different series of models under a unified process platform. On the one hand, it allows for precise control of reflectivity, transmittance, and hue by adjusting the film thickness and deposition process parameters, enabling the back cover to maintain a high-end and stable visual performance while remaining lightweight and strong. On the other hand, the thin metal oxide layer adheres closely to the substrate and optical texture layer, which helps to improve the environmental stability and reliability of the overall structure, providing a reliable interface foundation for the subsequent collaborative design with functional structures such as touch, electromagnetic shielding, or sensing modules.

[0020] A method for preparing a lightweight, high-strength micro-textured composite mobile phone back cover, characterized in that the mobile phone back cover is the lightweight, high-strength micro-textured composite mobile phone back cover as described in claim 1, and the preparation method includes the following steps: S1 Mold Pre-processing: Micro-nano textures are processed on the surface of the mold cavity used to form the shape of the back cover of the mobile phone in a predetermined pattern, so that the surface of the mold cavity corresponding to the non-logo area of ​​the back cover of the mobile phone has a microstructure array. S2 Substrate Molding and Micro Imprinting: A composite board consisting of a first resin sublayer and a second resin sublayer is placed in the mold cavity. Under heating and pressurization conditions, the second resin sublayer is softened and adhered to the surface of the mold cavity, thereby replicating an optical texture layer on the second resin sublayer towards the functional coating side and obtaining a semi-finished back cover integrally formed with the substrate layer. S3 Surface hardening layer formation: After removing the semi-finished cover from the mold, a surface hardening coating is applied to the outer surface of its first resin sublayer and cured to form a surface hardening layer; S4 Functional Coating Formation: A functional coating is deposited on the inner side of the optical texture layer of the semi-finished back cover, and the obtained product is subjected to edge trimming, pore opening and cleaning treatment.

[0021] Preferably, in step S1, the micro-nano texture is obtained by etching the surface of the mold cavity with a femtosecond laser, and the microstructure array is an isosceles triangular prism array structure.

[0022] The above technical solution enables the high-precision construction of an array of isosceles triangular prism microstructures on the surface of the mold cavity. This allows the substrate layer to stably replicate micro-nano textures with clear geometric contours during the subsequent molding process, thereby ensuring that the optical texture layer achieves a high level of consistency in morphology, clarity of boundaries, and integrity of edges and corners. This lays the foundation for achieving stable and controllable optical and decorative effects.

[0023] Specifically, femtosecond laser processing, characterized by low single-pulse energy and an extremely narrow heat-affected zone, avoids significant melt collapse and burrs during etching of metal mold surfaces. This facilitates the formation of sharp-edged, smooth-surfaced isosceles triangular prism structures. The cross-sectional shape and arrangement of the prisms can be precisely controlled through laser scanning paths and parameters, ensuring high consistency in the period, angles, and depth of the microstructure array on the mold surface. The micro- and nano-textures obtained in this way can be completely transferred to the back of the substrate during injection molding or hot pressing replication, improving the geometric accuracy and replication stability of the microtexture layer.

[0024] In practical applications, this mold structure, which uses femtosecond laser etching to form an isosceles triangular prism array, helps to achieve optical texture consistency and appearance stability among mass-produced mobile phone back cover products, reducing batch differences caused by mold wear and processing errors. At the same time, the anisotropic characteristics of the prism array in the reflection and refraction directions can combine incident light at different angles to form directional highlight stripes and light and dark variation effects, enabling products to obtain a more distinctive and layered decorative appearance while ensuring dimensional accuracy and molding efficiency.

[0025] Preferably, in step S2, the composite board is held under pressure for 30 seconds at a mold temperature of 220℃-255℃ and a pressure of 60MPa, and then cooled and demolded to obtain the semi-finished back cover.

[0026] The above technical solution can ensure that the composite board is fully softened and flowed in the mold cavity while reasonably controlling the molding cycle, so that the substrate layer and the micro-nano texture of the mold surface can be fully adhered and replicated, resulting in a semi-finished back cover with uniform structure and stable morphology, providing a substrate with good dimensional accuracy for the subsequent deposition of surface hardening layer and functional coating.

[0027] Specifically, under the conditions of mold temperature controlled at 220 to 255 degrees Celsius, molding pressure maintained at 60 MPa and held for 30 seconds, the inner resin sublayer can be fully softened without significant decomposition. Under high pressure, the melt fills the mold cavity and closely adheres to the mold surface with microstructure array. During the holding pressure stage, melt shrinkage is effectively compensated, and relatively uniform solidification and shaping are achieved through temperature control of the mold wall during cooling, thereby reducing internal stress and warping risk, while ensuring that details such as microstructure edges and slopes are clearly replicated.

[0028] In practical applications, the setting of these molding process parameters helps to stably obtain semi-finished back covers with consistent thickness, low warpage, and high micro-texture replication accuracy in mass production, reducing the occurrence of molding defects such as flow marks, shrinkage, and silver streaks, and lowering the risk of subsequent cracking and deformation caused by molding stress. At the same time, the improved consistency of size and morphology also facilitates the alignment and coverage of subsequent online surface hardening and internal functional coating processes, improving the consistency of overall assembly and the yield of finished products.

[0029] Preferably, in step S3, a surface hardening layer is formed on the outer surface of the first resin sublayer by ultrasonic spraying, the wet film thickness of the coating is 20 μm, and it is cured under UV energy of 800 mJ / cm²; in step S4, an indium tin oxide functional coating with a thickness of 100 nm is formed by magnetron sputtering, wherein the vacuum degree of the coating chamber is 5.0 × 10⁻³ Pa and the working pressure is 0.5 Pa.

[0030] Through the above technical solution, a stable surface hardening layer and an indium tin oxide functional coating can be constructed on the outer and inner sides of the molded substrate, respectively. By using ultrasonic spraying combined with controlled wet film thickness and setting UV curing energy, a good balance can be achieved between adhesion, density and surface hardness of the surface hardening layer. At the same time, by magnetron sputtering under the conditions of vacuum degree of 5.0 x 10^-3 Pa and working pressure of 0.5 Pa, an indium tin oxide thin film with a thickness of about 100 nanometers is formed, so that the functional coating has good consistency in terms of optical uniformity, electrical properties and film stability, thereby improving the wear resistance, appearance texture and functional integration of the entire mobile phone back cover.

[0031] Specifically, ultrasonic spraying atomizes the hardened coating into small, uniformly distributed droplets, forming a wet film approximately 20 micrometers thick on the outer surface of the first resin sublayer. This helps reduce defects such as sagging, orange peel, and pinholes. By controlling the ultraviolet irradiation energy at approximately 800 millijoules per square centimeter, the cross-linking reaction within the coating is fully carried out, resulting in high surface hardness and good scratch resistance, while ensuring adhesion to the substrate interface. During magnetron sputtering, the high vacuum reduces the content of impurity gases, and the stable plasma discharge at a suitable working pressure facilitates uniform sputtering of the indium tin oxide target and the formation of a dense, continuous film on the back side of the optical texture layer. This results in a uniform film thickness distribution, stable refractive index, and a balance between light transmittance and conductivity.

[0032] In practical applications, this approach, which combines ultrasonic spraying with UV curing and hardening with indium tin oxide magnetron sputtering under controlled process parameters, helps to stably obtain mobile phone back cover products with good surface wear resistance, consistent optical performance, and reliable film adhesion in mass production. It reduces appearance defects and performance fluctuations caused by cracking, peeling, or uneven thickness of the hardened layer or functional coating, improves the overall assembly yield and appearance durability during long-term use, and provides a feasible process basis for the industrialization of lightweight, high-strength micro-textured composite mobile phone back covers.

[0033] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a multi-layer structure consisting of a surface-hardened layer, a PMMA / PC composite substrate, an optical texture layer, and an inner functional coating, achieving a balance of strength, toughness, and aesthetics with a relatively thin thickness. A core-shell toughening agent is introduced into the composite substrate. The outer PMMA layer, in conjunction with the hardened coating, provides transparency and scratch resistance, while the inner PC layer provides support and deformation resistance. The optical texture is formed directly on the back of the substrate and tightly adheres to the functional coating, reducing intermediate adhesive layers and excess film layers, which improves bending resistance and appearance stability under drop conditions.

[0034] 2. This invention employs a process path that involves forming a microstructure array on a mold, simultaneously replicating microtextures during molding, and applying a surface-hardening coating online after demolding, followed by magnetron sputtering of a functional coating on the inner side. This method seamlessly integrates shape forming, microstructure construction, and functional film deposition into a unified production process. This approach avoids multiple bonding and transfer processes, reduces the impact of repeated heating on the substrate, and lowers the likelihood of defects such as warping and cracking. It facilitates the production of mobile phone back covers with consistent dimensions and stable optical performance under continuous production conditions, providing a better technological foundation for serialized products. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The present invention will be described in detail below through multiple embodiments and comparative examples. These embodiments are intended to further illustrate the technical solutions and beneficial effects of the present invention, and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, all parts mentioned in the present invention are parts by weight, and the process equipment mentioned is conventional equipment in the art.

[0038] Example 1: Lightweight, high-strength micro-textured composite mobile phone back cover based on prism array optical effects I. Material Preparation This embodiment provides a lightweight, high-strength micro-textured composite mobile phone back cover based on the optical effect of a prism array. The back cover comprises, from the outside in, a surface hardening layer, a substrate layer, an optical texture layer, and a functional coating. The substrate layer consists of a first resin sublayer facing outwards and a second resin sublayer facing inwards. The first resin sublayer is a PMMA layer containing a core-shell toughening agent, and the second resin sublayer is a PC layer containing a core-shell toughening agent. These two layers form a single composite material, with 5% core-shell toughening agent uniformly incorporated throughout the composite material. This formulation, while ensuring transparency and molding flowability, improves the toughness of the mobile phone back cover under drop impact and bending loads, thus helping to slow down crack initiation and propagation.

[0039] See product structure stacking. Figure 1 , Figure 1In the design, the L1 structural layer is a surface-hardened coating, the L2 structural layer is a polymethyl methacrylate layer containing a core-shell toughening agent, the L3 structural layer is a polycarbonate layer containing a core-shell toughening agent, and the L4 structural layer is a functional coating.

[0040] The surface-hardening coating is a UV-curable siloxane-modified acrylic coating with a solid content greater than 90%. The high solid content formulation can form a dense cross-linked network with a relatively thin dry film thickness, reducing pinholes and shrinkage defects caused by volatile components, and is conducive to obtaining a surface pencil hardness close to 7H, meeting the scratch resistance requirements during daily handling and storage.

[0041] The functional coating target is indium tin oxide (ITO), used to deposit transparent metal oxide thin films on the inside of the mobile phone back cover using magnetron sputtering. ITO thin films have high visible light transmittance and a suitable refractive index, and their surface possesses a certain degree of conductivity. This allows them to work in synergy with the optical texture layer to control reflection and transmission effects, and also provides the foundation for subsequent integration of functions such as antistatic properties and electromagnetic property modulation.

[0042] The substrate composite sheet is cut into flat blanks according to the external dimensions of the target model. The total thickness of the sheet is predetermined according to the overall machine structure design to control the overall machine quality while meeting the requirements of bending stiffness and impact resistance. After cutting, the edges of the sheet are deburred and cleaned to prevent burrs from scratching the mold microstructure during the forming process and to reduce the risk of edge stress concentration.

[0043] II. Mold Preparation The mold is made of mold steel suitable for high-precision machining. First, the overall three-dimensional contour of the phone's back cover is machined using an ultra-precision CNC milling machine, including the back curvature, corner transitions, and mating parts with the mid-frame and sealing structure. For local areas requiring high precision, wire EDM can be used for further finishing to ensure that the cavity dimensions after the mold is closed meet the design tolerance requirements.

[0044] In the mold cavity, corresponding to the non-marked area of ​​the phone's back cover, an array of isosceles triangular prism microstructures is etched using femtosecond laser processing technology. Before laser processing, the mold surface is finely polished to control the surface roughness within a range suitable for replicating the microstructures. During processing, by setting appropriate single-pulse energy, scanning speed, and scanning spacing, the period of the microstructure is approximately 5μm, the depth is approximately 1.5μm, and the cross-section of each prism approximates an ideal isosceles triangle with sharp edges and smooth, continuous slopes. The prisms are arranged side-by-side along a predetermined direction. After processing, the mold is deburred and ultrasonically cleaned to ensure that there are no residual particles or contaminants in the cavity, avoiding damage to the microstructures during replication or the formation of local defects on the finished product surface.

[0045] III. Preparation Steps Step 1: Integrated molding and micro-imprinting The aforementioned polymethyl methacrylate (PMMA) and polycarbonate composite sheet was placed in a preheated mold cavity. The mold temperature was controlled within the range of 220℃-255℃. After mold closing, a molding pressure of 60MPa was applied and maintained for 30 seconds. Within this process window, the inner polycarbonate sublayer was in a molten and softened state, fully filling the mold cavity under high pressure and tightly adhering to the microstructure region with the isosceles triangular prism array, thereby achieving precise replication of the prism geometry.

[0046] During the pressure holding stage, controlled cooling is achieved through the internal cooling water channels of the mold, allowing the molten substrate to solidify and set under a relatively uniform temperature gradient, reducing internal residual stress and the risk of warping. Once the mold temperature drops to the set demolding temperature, the mold opens, and the molded part is ejected by the ejection mechanism, resulting in a semi-finished mobile phone back cover with the substrate layer and optical texture layer integrally formed. At this point, the outer surface is a flat polymethyl methacrylate surface, while the inner surface features a prism microstructure array with clearly defined geometric contours, laying the foundation for subsequent optical effects.

[0047] Step 2: Online surface hardening treatment After mold opening, a robotic arm is used to transfer the semi-finished mobile phone back cover to a dust-free coating station. Before coating, the dust and fine particles attached to the outer surface are removed by electrostatic dust removal or ion air device, and the workpiece is preheated appropriately to ensure that the surface temperature is within a range conducive to paint wetting and leveling.

[0048] Subsequently, ultrasonic spraying technology was used to uniformly spray a UV-curable siloxane-modified acrylate coating onto the outer surface of polymethyl methacrylate. By controlling the spray gun's movement speed, spray path, and reciprocating strokes, the wet film thickness of the coating was achieved to approximately 20 μm. The high-solids content formulation can form a continuous and dense dry film at this wet film thickness, reducing the occurrence of defects such as sagging, craters, and pinholes.

[0049] Immediately after spraying, the workpiece is placed in a UV curing device and cured under UV energy of 800 mJ·cm⁻². This allows the active groups within the coating to fully cross-link, forming a transparent, well-adhesive, and high-hardness surface-hardened layer. During the curing process, the volume shrinkage and internal stress level of the coating are controlled by adjusting the conveyor speed and irradiation time to avoid problems such as cracking or localized haze. After curing, a visual inspection is performed to confirm that the surface is smooth, has a uniform gloss, and is free of obvious particles and pinholes.

[0050] Step 3: Preparation of the inner functional coating The semi-finished mobile phone back cover, after surface hardening treatment, is fixed onto the fixture of the magnetron sputtering equipment, with the inner side featuring the prism microstructure facing the target. The vacuum system is activated, and the vacuum level in the coating chamber is evacuated to 5.0 × 10⁻³ Pa to reduce the impact of residual gas and impurities on the composition and density of the thin film. Subsequently, an inert gas is introduced to establish a working pressure of 0.5 Pa, stabilizing the plasma discharge and ensuring a smooth and controllable sputtering process.

[0051] Under the above conditions, magnetron sputtering deposition was performed using an indium tin oxide target to gradually form a transparent metal oxide thin film on the inner surface of the mobile phone back cover. By setting appropriate target power and sputtering time, the film thickness was controlled to approximately 100 nm. Within this thickness range, the film maintains both high visible light transmittance and a certain degree of surface conductivity, which is beneficial for optical effect control and suppression of electrostatic accumulation. After coating, the film was allowed to cool naturally to the set temperature in the equipment before being removed, and the film appearance, film thickness uniformity, and surface resistance were randomly inspected.

[0052] Step 4: Subsequent machining and cleaning The completed functional coating on the phone back cover is transferred to a CNC precision carving machine. The edges of the back cover are machined according to the overall structural design requirements to ensure that its dimensions meet assembly tolerances with the mid-frame and seals. Subsequently, drilling or milling is performed in areas such as the camera window, flash window, and microphone location. Reinforcing ribs or positioning structures are added to the inner areas as needed to improve assembly positioning accuracy and overall strength.

[0053] After machining, the phone back cover is thoroughly cleaned and dried to remove cutting debris and dust, and then subjected to another visual inspection and dimensional measurement. Qualified products undergo reliability sampling tests according to regulations before being packaged and stored.

[0054] IV. Effects and Comparison The lightweight, high-strength micro-textured composite mobile phone back cover prepared using the process described in this embodiment exhibits excellent performance in terms of weight, surface abrasion resistance, and thermal shock reliability.

[0055] The results of this implementation comparing the product with traditional glass back cover products are shown in Table 1.

[0056] Table 1 project Comparative product: Polyethylene terephthalate film composite back cover This embodiment features a lightweight, high-strength, micro-textured composite mobile phone back cover. Structural form Decorative films are laminated to the outside of the substrate and printed with patterns. An integrated structure comprising a surface hardening layer, a substrate layer, a prism optical texture layer, and a functional coating. weight Nearly the same size glass back cover Approximately 30% of the size of a glass back cover. Surface abrasion resistance The steel wool showed obvious scratches and decreased gloss after the abrasion resistance test. Fewer scratches and stable optical performance under the same conditions thermal shock reliability Warping and bubbling appeared at the edges after repeated thermal shocks. No warping or bubbles were observed under the same conditions. Process and cost It requires processes such as film preparation, optical adhesive application, and film lamination, and involves many interfaces. The texture is integrally molded with the substrate, eliminating the need for film and lamination processes, thus significantly reducing costs. Under the same size conditions, compared with traditional glass back covers, the weight of the phone back cover in this embodiment is approximately 30% of that of a glass back cover of the same size, significantly reducing the overall weight of the device while maintaining sufficient rigidity and bending resistance. The surface hardening layer can reach a level close to 7H in pencil hardness testing under certain load conditions, and is not prone to obvious scratches in scenarios simulating daily placement and friction.

[0057] In the steel wool abrasion test, the outer surface of the back cover was subjected to a high number of reciprocating rubs with a fixed load. The comparative product was a traditional composite board back cover with a polyethylene terephthalate decorative film bonded to the outside of the substrate. After the test, the surface of the comparative product showed more scratches, a significant decrease in gloss, and localized areas of gloss loss. Under the same conditions, the back cover of this embodiment only showed a few minor scratches, and the overall gloss and optical texture effect remained stable.

[0058] In the thermal shock test, the back cover of the mobile phone in this embodiment and the comparative product were placed in the test chamber at the same time. After multiple impacts under the condition of cyclical temperature change between -85 degrees Celsius and 85 degrees Celsius, the comparative product showed defects such as warping and bubbles at the edge, while the edge bonding state and surface optical effect of the back cover of the mobile phone in this embodiment did not show any obvious abnormalities, and the structural stability was better.

[0059] In terms of process and cost, the comparative product requires additional procurement of polyethylene terephthalate decorative film and optical adhesive, and adds processes such as film application and curing, increasing the number of interface layers and making it prone to delamination risk. This embodiment integrates the substrate layer and the prism optical texture layer, and directly deposits an indium tin oxide functional coating on the inner side, eliminating the film and adhesive-related steps, simplifying the process flow, and resulting in a significant decrease in overall production cost compared to the comparative solution.

[0060] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lightweight, high-strength micro-textured composite mobile phone back cover, characterized in that, The material comprises a surface-hardening layer, a substrate layer, and a functional coating, which are stacked sequentially from the outside to the inside. The substrate layer includes a first resin sublayer disposed on the outer side and a second resin sublayer disposed on the inner side. An optical texture layer is formed on the surface of the second resin sublayer facing the functional coating. The optical texture layer is a microstructure array composed of multiple concave and convex geometric units, and the optical texture layer and the second resin sublayer are integrally formed. The surface-hardening layer is applied to the side of the first resin sublayer facing away from the second resin sublayer, and the functional coating is applied to the side of the optical texture layer facing away from the second resin sublayer.

2. The lightweight, high-strength micro-textured composite mobile phone back cover according to claim 1, characterized in that, The first resin sublayer is a PMMA layer containing a core-shell toughening agent, and the second resin sublayer is a PC layer containing a core-shell toughening agent. The first resin sublayer and the second resin sublayer constitute an integral composite board, and the core-shell toughening agent has a mass percentage content of 5% in the composite board.

3. The lightweight, high-strength micro-textured composite mobile phone back cover according to claim 1, characterized in that, The microstructure array of the optical texture layer is at least one of the following structures: a prism array structure arranged side by side along a predetermined direction, a microlens array structure composed of multiple microlens units, and a grating structure composed of multiple periodic stripe units.

4. The lightweight, high-strength micro-textured composite mobile phone back cover according to claim 1, characterized in that, The functional coating is a metal oxide film deposited on the inside of the back cover of the mobile phone, and the metal oxide film is an indium tin oxide film.

5. A method for preparing a lightweight, high-strength micro-textured composite mobile phone back cover, characterized in that, The mobile phone back cover is the lightweight, high-strength micro-textured composite mobile phone back cover as described in claim 1, and the preparation method includes the following steps: S1 Mold Pre-processing: Micro-nano textures are processed on the surface of the mold cavity used to form the shape of the back cover of the mobile phone in a predetermined pattern, so that the surface of the mold cavity corresponding to the non-logo area of ​​the back cover of the mobile phone has a microstructure array. S2 Substrate Molding and Micro Imprinting: A composite board consisting of a first resin sublayer and a second resin sublayer is placed in the mold cavity. Under heating and pressurization conditions, the second resin sublayer is softened and adhered to the surface of the mold cavity, thereby replicating an optical texture layer on the second resin sublayer towards the functional coating side and obtaining a semi-finished back cover integrally formed with the substrate layer. S3 Surface hardening layer formation: After removing the semi-finished cover from the mold, a surface hardening coating is applied to the outer surface of its first resin sublayer and cured to form a surface hardening layer; S4 Functional Coating Formation: A functional coating is deposited on the inner side of the optical texture layer of the semi-finished back cover, and the obtained product is subjected to edge trimming, pore opening and cleaning treatment.

6. The preparation method according to claim 5, characterized in that, In step S1, the micro-nano texture is obtained by etching the surface of the mold cavity with a femtosecond laser, and the microstructure array is an isosceles triangular prism array structure.

7. The preparation method according to claim 5, characterized in that, In step S2, the composite board is held under pressure for 30 seconds at a mold temperature of 220℃-255℃ and a pressure of 60MPa, and then cooled and demolded to obtain the semi-finished back cover.

8. The preparation method according to claim 5, characterized in that, In step S3, a surface hardening layer is formed on the outer surface of the first resin sublayer by ultrasonic spraying. The wet film thickness of the coating is 20 μm, and it is cured under UV energy of 800 mJ / cm². In step S4, an indium tin oxide functional coating with a thickness of 100 nm is formed by magnetron sputtering. The vacuum degree of the coating chamber is 5.0 × 10⁻³ Pa, and the working pressure is 0.5 Pa.

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