Rear cover laminated board with improved bending performance and preparation method thereof

Abstract

The invention discloses a rear cover laminated board with improved bending performance and a preparation method thereof, relates to the technical field of electronic product shells, and provides the rear cover laminated board with improved bending performance and the preparation method thereof. The silicon carbide fiber is used as a base material, the tensile strength of the silicon carbide fiber is high, and excellent rigid support can be provided for the laminated board, so that the bending strength of the epoxy composite material is improved, and the performance requirement of a 3C shell is met. The modified epoxy resin is used as a matrix, the silicon carbide ceramic fiber cloth coated with dopamine is doped, and the cobalt hydroxide nanosheets are loaded on the silicon carbide ceramic fiber cloth, so that the strength of the laminated board is enhanced. Then, dopamine is used for coating, and a silicon dioxide aqueous solution is used for forming a silicon dioxide-containing micro-nano structure on the surface, so that the surface hydrophobicity is enhanced. The prepared shell material not only has enough rigidity, but also has excellent toughness, and meets the requirements of'deformation resistance 'and'fracture resistance'.

Description

Technical Field

[0001] This invention relates to the field of electronic product housing technology, specifically to a back cover laminate with improved bending performance and its preparation method. Background Technology

[0002] In the rapidly evolving consumer electronics industry, the casing materials for 3C devices such as mobile phones, tablets, and laptops are undergoing a transformation from traditional metals (such as aluminum alloys and stainless steel) to epoxy composite materials. While traditional metal casings possess excellent mechanical properties, they are also dense and heavy. Furthermore, the electromagnetic shielding properties of metals increasingly clash with the compatibility of wireless charging and 5G signal transmission. Epoxy composite materials, with their advantages of only 50%-70% the density of aluminum alloys, flexible molding processes, and customizable electromagnetic parameters, are gradually becoming the mainstream choice for high-end 3C device casings.

[0003] However, the widespread application of epoxy composite materials has also presented new challenges to their mechanical properties, such as bending properties. For handheld devices such as mobile phones and tablets, the casing is constantly subjected to complex bending stresses during daily use: when holding a mobile phone with one hand, the mid-frame area needs to resist the radial bending moment applied by the fingers; when a tablet is placed on a table, the edges may experience local bending deformation due to external impact; during the opening and closing of a laptop, the casing part where the screen connects to the body is under alternating bending loads for a long time.

[0004] To address the aforementioned issues and improve bending performance, this application provides a back cover laminate with improved bending performance and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a back cover laminate with improved bending performance and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A back cover laminate with improved bending performance, wherein the back cover laminate comprises, from the inside out, a silicon carbide prepreg layer, a puncture-resistant layer, another silicon carbide prepreg layer, a base layer, a pad printing layer, an encapsulation layer, and a protective layer, wherein the puncture-resistant layer and the silicon carbide prepreg layer are cured together with epoxy resin.

[0007] In a more optimized manner, the silicon carbide prepreg layer is composed of silicon carbide fiber cloth impregnated with epoxy resin.

[0008] More preferably, the silicon carbide fiber cloth is a dopamine-coated silicon carbide ceramic fiber cloth, and its preparation method includes the following steps: S1: Silicon carbide ceramic fibers are arranged in an aqueous solution of cobalt hydroxide nanosheets, immersed for 2-3 hours, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take silica and deionized water, disperse them evenly to obtain a silica aqueous solution; take tris(hydroxymethyl)aminomethane hydrochloride and deionized water, add sodium hydroxide solution, adjust the pH to 8.5 to obtain Tris buffer, add dopamine hydrochloride, stir evenly to obtain a mixed solution; S3: Add silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets to deionized water and soak for 1-2 hours. Then add a mixed solution and soak for 22-26 hours. Take it out and coat the surface with a silica aqueous solution. Place it in an environment with a humidity of 30% for 24-26 hours to obtain silicon carbide ceramic fiber cloth coated with dopamine.

[0009] A more optimized method for preparing the silicon carbide ceramic fiber cloth is as follows: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide is taken; polyaluminum carbide silane is added to the mixed solution and stirred for 6-7 hours; then 3-aminopropyltriethoxysilane and polyvinylpyrrolidone are added and stirred until homogeneous to obtain a polyaluminum carbide silane solution; the polyaluminum carbide silane solution is subjected to electrospinning with an output voltage of 20 kV, an injection flow rate of 2 mL / h, a roller receiving distance of 8 cm, and a spinning time of 2 hours; the solution is dried, heated to 200-210℃ and held for 3-3.5 hours, and then pyrolyzed under a nitrogen atmosphere; followed by washing and drying to obtain the silicon carbide ceramic fiber cloth.

[0010] A more optimized method for preparing the cobalt hydroxide nanosheets is as follows: take cobalt nitrate hexahydrate and deionized water, stir evenly, add triethylamine, heat to 175-180℃, react for 6-7 hours, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets.

[0011] A more optimized method for preparing the epoxy resin solution is as follows: Under nitrogen protection, modified epoxy resin was melted, and amino-terminated hyperbranched polyamide and 2,5-dipyridine carboxylic acid were added and stirred evenly to obtain modified epoxy resin; isocyanate-modified epoxy resin, modified epoxy resin and dicyandiamide were mixed evenly to obtain epoxy resin solution.

[0012] More optimally, the puncture-resistant layer is composed of Cordura fiber woven fabric impregnated with epoxy resin.

[0013] Ideally, the pad printing layer is one of a textured epoxy resin layer, a polyurethane layer, or an acrylic layer.

[0014] Ideally, the encapsulation layer is one of a transparent epoxy resin layer, a polyurethane layer, or an acrylic layer.

[0015] A method for preparing a back cover laminate with improved bending performance includes the following steps: Step 1: Apply epoxy resin solution evenly to the surface of dopamine-coated silicon carbide ceramic fiber cloth, and dry it to obtain a silicon carbide prepreg layer. Step 2: Apply epoxy resin solution evenly to the surface of Cordura fiber woven fabric and allow it to dry to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them to obtain a laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This application provides a back cover laminate with improved bending performance and its preparation method. Silicon carbide fiber is used as the substrate. Silicon carbide fiber has high tensile strength and can provide excellent rigid support for the laminate, thereby improving the bending strength of the epoxy composite material and meeting the performance requirements of 3C shells.

[0017] This application uses modified epoxy resin as the matrix and incorporates silicon carbide ceramic fiber cloth coated with dopamine, so that the shell material not only has sufficient rigidity to avoid significant deformation during use, but also has excellent toughness to prevent sudden brittle fracture, thus meeting the requirements of "deformation resistance" and "fracture resistance".

[0018] 2. This application loads cobalt hydroxide nanosheets onto silicon carbide ceramic fiber cloth to enhance the strength of the laminate. Then, dopamine is used to coat it, and a silica-containing micro / nano structure is formed on it using an aqueous silica solution, thereby enhancing the surface hydrophobicity. The dopamine-coated silicon carbide ceramic fiber cloth has amino groups that can react with the amino and epoxy groups in the modified epoxy resin, enhancing the bonding force between the two.

[0019] 3. This application enhances the flame retardant properties of epoxy resin by adding 2,5-dipyridinecarboxylic acid to introduce pyridine groups into the modified epoxy resin. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0021] The sources and types of substances involved in the embodiments of this application are not specifically limited. Exemplary examples include: epoxy resin: bisphenol A type epoxy resin: grade E-51, purchased from Baling Petrochemical; isocyanate modified epoxy resin: grade A-IME AER4152 from Asahi Kasei Corporation of Japan; silica: type ML-SiO2-N07, particle size: 7nm; Cordura fiber woven fabric: Cordura 1000D nylon, thickness 0.1mm, purchased from Dongguan Tongli Textile Co., Ltd.; underlay: PU502; pad printing layer: textured epoxy resin adhesive layer, Loctite EA 3423 epoxy resin adhesive; encapsulation layer: transparent epoxy resin adhesive layer, type LOCTITEEA E-30CL; protective layer: acrylic resin, type FD-508PA, purchased from Suzhou Kostar Electronic Materials Co., Ltd.

[0022] Example 1: A method for preparing a back cover laminate with improved bending performance, comprising the following steps: Step 1: Apply epoxy resin evenly to the surface of the dopamine-coated silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2 The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 6.5h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of cobalt hydroxide nanosheets: Take 1g of cobalt nitrate hexahydrate and 65mL of deionized water, stir well, add triethylamine, adjust the pH to 12, heat to 178℃, react for 6.5h, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets. Preparation of dopamine-coated silicon carbide ceramic fiber cloth: S1: Silicon carbide ceramic fibers were placed in an aqueous solution of cobalt hydroxide nanosheets with a concentration of 20 g / L, immersed for 2.5 h, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take 4g of silica and 100mL of deionized water, disperse them evenly to obtain a silica aqueous solution; take 0.2g of tris(hydroxymethyl)aminomethane hydrochloride and 150mL of deionized water, add a 0.1mol / L sodium hydroxide solution, adjust the pH to 8.5 to obtain a Tris buffer solution, add 0.5g of dopamine hydrochloride, stir evenly to obtain a mixed solution; take 2g of silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets and add it to 30mL of deionized water, soak for 1.5h, then add the mixed solution, soak for 24h, take it out, then coat the surface with a silica aqueous solution with a thickness of 8µm, and place it in an environment with a humidity of 30% for 25h to obtain a dopamine-coated silicon carbide ceramic fiber cloth; Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0023] Example 2: A method for preparing a back cover laminate with improved bending performance, comprising the following steps: Step 1: Apply epoxy resin evenly to the surface of the dopamine-coated silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2 The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 6h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of cobalt hydroxide nanosheets: Take 1g of cobalt nitrate hexahydrate and 65mL of deionized water, stir well, add triethylamine, adjust the pH to 12, heat to 175℃, react for 6h, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets. Preparation of dopamine-coated silicon carbide ceramic fiber cloth: S1: Silicon carbide ceramic fibers were placed in an aqueous solution of cobalt hydroxide nanosheets with a concentration of 20 g / L, immersed for 2 h, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets. S2: Take 4g of silica and 100mL of deionized water, disperse them evenly to obtain a silica aqueous solution; take 0.2g of tris(hydroxymethyl)aminomethane hydrochloride and 150mL of deionized water, add a 0.1mol / L sodium hydroxide solution, adjust the pH to 8.5 to obtain a Tris buffer solution, add 0.5g of dopamine hydrochloride, stir evenly to obtain a mixed solution; take 2g of silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets and add it to 30mL of deionized water, soak for 1h, then add the mixed solution, soak for 22h, take it out, and then coat the surface with a silica aqueous solution with a thickness of 8µm, place it in an environment with a humidity of 30% for 24h to obtain a dopamine-coated silicon carbide ceramic fiber cloth; Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0024] Example 3: A method for preparing a back cover laminate with improved bending performance, comprising the following steps: Step 1: Apply epoxy resin evenly to the surface of the dopamine-coated silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 7h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of cobalt hydroxide nanosheets: Take 1g of cobalt nitrate hexahydrate and 65mL of deionized water, stir well, add triethylamine, adjust the pH to 12, heat to 180℃, react for 7h, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets. Preparation of dopamine-coated silicon carbide ceramic fiber cloth: S1: Silicon carbide ceramic fibers were placed in an aqueous solution of cobalt hydroxide nanosheets with a concentration of 20 g / L, immersed for 3 h, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take 4g of silica and 100mL of deionized water, disperse them evenly to obtain a silica aqueous solution; take 0.2g of tris(hydroxymethyl)aminomethane hydrochloride and 150mL of deionized water, add a 0.1mol / L sodium hydroxide solution, adjust the pH to 8.5 to obtain a Tris buffer solution, add 0.5g of dopamine hydrochloride, stir evenly to obtain a mixed solution; take 2g of silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets and add it to 30mL of deionized water, soak for 2h, then add the mixed solution, soak for 26h, take it out, then coat the surface with a silica aqueous solution with a thickness of 8µm, and place it in an environment with a humidity of 30% for 26h to obtain a dopamine-coated silicon carbide ceramic fiber cloth; Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0025] Comparative Example 1: No cobalt hydroxide nanosheets added; otherwise, the same as in Example 1. Step 1: Apply epoxy resin evenly to the surface of the dopamine-coated silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2 The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 6.5h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of dopamine-coated silicon carbide ceramic fiber cloth: Take 4g of silica and 100mL of deionized water, disperse them evenly to obtain a silica aqueous solution; take 0.2g of tris(hydroxymethyl)aminomethane hydrochloride and 150mL of deionized water, add a 0.1mol / L sodium hydroxide solution, adjust the pH to 8.5 to obtain a Tris buffer solution, add 0.5g of dopamine hydrochloride, stir evenly to obtain a mixed solution; take 2g of silicon carbide ceramic fiber cloth and add it to 30mL of deionized water, soak for 1.5h, then add the mixed solution, soak for 24h, take it out, and then coat the surface with a silica aqueous solution with a thickness of 8µm, place it in an environment with a humidity of 30% for 25h to obtain a silicon carbide ceramic fiber cloth coated with dopamine; Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0026] Comparative Example 2: No dopamine modification was used; all other aspects were the same as in Example 1. Step 1: Apply epoxy resin evenly to the surface of the modified silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2 The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 6.5h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of cobalt hydroxide nanosheets: Take 1g of cobalt nitrate hexahydrate and 65mL of deionized water, stir well, add triethylamine, adjust the pH to 12, heat to 178℃, react for 6.5h, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets. Preparation of modified silicon carbide ceramic fiber cloth: S1: Silicon carbide ceramic fibers were placed in an aqueous solution of cobalt hydroxide nanosheets with a concentration of 20 g / L, immersed for 2.5 h, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take 4g of silicon dioxide and 100mL of deionized water, disperse them evenly to obtain a silicon dioxide aqueous solution; take 2g of silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets and add it to 30mL of deionized water, soak for 1.5h, then coat the surface with a silicon dioxide aqueous solution with a thickness of 8µm, and place it in an environment with a humidity of 30% for 25h to obtain modified silicon carbide ceramic fiber cloth. Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0027] Comparative Example 3: No silica was added; all other aspects were the same as in Example 1. Step 1: Apply epoxy resin evenly to the surface of the dopamine-coated silicon carbide ceramic fiber cloth, with a coating amount of 150g / m² on one side. 2 The silicon carbide prepreg layer was obtained by drying at 110℃ for 20 min. Step 2: Apply epoxy resin evenly to the surface of the Cordura fiber woven fabric, with a coating amount of 150g / m² on one side. 2 Dry at 110℃ for 20 min to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them at 160°C and 10MPa to obtain the laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate; Preparation of silicon carbide ceramic fibers: A mixed solution of xylene, tetrahydrofuran, and dimethylformamide in a volume ratio of 3:1:1 was prepared. 10g of polyaluminum carbide was added to 10mL of the mixed solution and stirred for 6.5h. Then, 0.1g of 3-aminopropyltriethoxysilane and 0.5g of polyvinylpyrrolidone were added and stirred until homogeneous to obtain a polyaluminum carbide solution. The polyaluminum carbide solution was subjected to electrospinning with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2h. After drying, the solution was heated to 200℃ and held for 3h. Then, it was pyrolyzed at 1000℃ under a nitrogen atmosphere. After washing and drying, silicon carbide ceramic fiber cloth was obtained. Preparation of cobalt hydroxide nanosheets: Take 1g of cobalt nitrate hexahydrate and 65mL of deionized water, stir well, add triethylamine, adjust the pH to 12, heat to 178℃, react for 6.5h, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets. Preparation of dopamine-coated silicon carbide ceramic fiber cloth: S1: Silicon carbide ceramic fibers were placed in an aqueous solution of cobalt hydroxide nanosheets with a concentration of 20 g / L, immersed for 2.5 h, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take 0.2g of tris(hydroxymethyl)aminomethane hydrochloride and 150mL of deionized water, add 0.1mol / L sodium hydroxide solution, adjust the pH to 8.5 to obtain Tris buffer, add 0.5g of dopamine hydrochloride, stir well to obtain a mixed solution; take 2g of silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets and add it to 30mL of deionized water, soak for 1.5h, then add the mixed solution, soak for 24h, take it out, let it stand, and obtain silicon carbide ceramic fiber cloth coated with dopamine; Preparation of modified epoxy resins: Under nitrogen protection, 120g of modified epoxy resin was melted, and 90g of amino-terminated hyperbranched polyamide and 7.5g of 2,5-dipyridinecarboxylic acid were added. The mixture was stirred until homogeneous to obtain the modified epoxy resin. Preparation of epoxy resin solution: Take 15 parts of isocyanate-modified epoxy resin, 70 parts of modified epoxy resin, and 6.5 parts of dicyandiamide, mix them evenly to obtain epoxy resin solution.

[0028] experiment: The laminates obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. A three-point bending test was performed on the samples according to GB / T 3356-2014 to test the bending performance of the laminates. The laminates were made into 50mm × 10mm samples, and the mass m1 before immersion was recorded. The samples were then immersed in deionized water for 24 hours at a test temperature of 25℃. After removal and drying, the mass m2 after immersion was recorded, and the water absorption rate was calculated. The test results are shown in Table 1. Table 1: Conclusion: The data comparison in the table shows that, in Comparative Example 1, without the addition of cobalt hydroxide nanosheets, the mechanical properties of the laminate decreased. In Comparative Example 2, without the addition of dopamine for modification, the mechanical properties of the laminate decreased, but the surface water absorption rate increased. In Comparative Example 3, without the addition of silica, the mechanical properties of the laminate decreased, but the surface water absorption rate increased. The hydrophobic properties of the laminate deteriorated. The laminates prepared in Examples 1-3 had cobalt hydroxide nanosheets loaded onto silicon carbide ceramic fiber cloth, which enhanced the strength of the laminate. Then, dopamine was used to coat it, and a silica-containing micro / nano structure was formed on it using a silica aqueous solution, which enhanced the surface hydrophobicity. Therefore, the laminates exhibited good mechanical properties and good hydrophobicity.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A back cover laminate with improved bending performance, characterized in that: The back cover laminate consists of, from the inside out, a silicon carbide prepreg layer, a puncture-resistant layer, another silicon carbide prepreg layer, a base layer, a pad printing layer, an encapsulation layer, and a protective layer. The puncture-resistant layer and the silicon carbide prepreg layer are cured together with epoxy resin.

2. The back cover laminate with improved bending performance according to claim 1, characterized in that: The silicon carbide prepreg layer is composed of silicon carbide fiber cloth impregnated with epoxy resin.

3. The back cover laminate with improved bending performance according to claim 2, characterized in that: The silicon carbide fiber cloth is a dopamine-coated silicon carbide ceramic fiber cloth, and its preparation method includes the following steps: S1: Silicon carbide ceramic fibers are arranged in an aqueous solution of cobalt hydroxide nanosheets, immersed for 2-3 hours, removed and dried to obtain silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets; S2: Take silica and deionized water, disperse them evenly to obtain a silica aqueous solution; take tris(hydroxymethyl)aminomethane hydrochloride and deionized water, add sodium hydroxide solution, adjust the pH to 8.5 to obtain Tris buffer, add dopamine hydrochloride, stir evenly to obtain a mixed solution; S3: Add silicon carbide ceramic fiber cloth loaded with cobalt hydroxide nanosheets to deionized water and soak for 1-2 hours. Then add a mixed solution and soak for 22-26 hours. Take it out and coat the surface with a silica aqueous solution. Place it in an environment with a humidity of 30% for 24-26 hours to obtain silicon carbide ceramic fiber cloth coated with dopamine.

4. A back cover laminate with improved bending performance according to claim 3, characterized in that: The preparation method of the silicon carbide ceramic fiber cloth is as follows: Take a mixed solution of xylene, tetrahydrofuran, and dimethylformamide; add polyaluminosilane to the mixed solution and stir for 6-7 hours; add 3-aminopropyltriethoxysilane and polyvinylpyrrolidone and stir evenly to obtain a polyaluminosilane solution; electrospin the polyaluminosilane solution with an output voltage of 20kV, an injection flow rate of 2mL / h, a roller receiving distance of 8cm, and a spinning time of 2 hours; dry the solution; heat it to 200-210℃ and keep it at that temperature for 3-3.5 hours; then pyrolyze it under a nitrogen atmosphere; wash and dry the solution to obtain silicon carbide ceramic fiber cloth.

5. A back cover laminate with improved bending performance according to claim 3, characterized in that: The preparation method of the cobalt hydroxide nanosheets is as follows: take cobalt nitrate hexahydrate and deionized water, stir evenly, add triethylamine, heat to 175-180℃, react for 6-7 hours, cool to room temperature, wash and dry to obtain cobalt hydroxide nanosheets.

6. A back cover laminate for improving bending performance according to claim 1, characterized in that: The preparation method of the epoxy resin solution is as follows: under nitrogen protection, take modified epoxy resin, melt it, add terminal amino hyperbranched polyamide and 2,5-dipyridine carboxylic acid, stir evenly to obtain modified epoxy resin; take isocyanate modified epoxy resin, modified epoxy resin and dicyandiamide, mix evenly to obtain epoxy resin solution.

7. A back cover laminate for improving bending performance according to claim 1, characterized in that: The puncture-resistant layer is composed of Cordura fiber woven fabric impregnated with epoxy resin.

8. A back cover laminate for improving bending performance according to claim 1, characterized in that: The pad printing layer is one of the following: a textured epoxy resin layer, a polyurethane layer, or an acrylic layer.

9. A back cover laminate for improving bending performance according to claim 1, characterized in that: The encapsulation layer is one of a transparent epoxy resin layer, a polyurethane layer, or an acrylic layer.

10. A method for preparing a back cover laminate with improved bending performance according to any one of claims 1-9, characterized in that: Includes the following steps: Step 1: Apply epoxy resin solution evenly to the surface of dopamine-coated silicon carbide ceramic fiber cloth, and dry it to obtain a silicon carbide prepreg layer. Step 2: Apply epoxy resin solution evenly to the surface of Cordura fiber woven fabric and allow it to dry to obtain a puncture-resistant layer; Step 3: Stack the silicon carbide prepreg layer, the puncture-resistant layer, and the silicon carbide prepreg layer in sequence, and hot press them to obtain a laminate. Step 4: Sequentially apply the underlayer, pad printing layer, encapsulation layer, and protective layer to the laminate to obtain the mobile phone back cover laminate.

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