Glass fiber plate mobile phone rear cover and preparation method thereof

Abstract

The invention relates to the field of mobile phone materials, in particular to a glass fiber plate mobile phone rear cover and a preparation method thereof. The glass fiber plate mobile phone rear cover is formed by compounding and curing a glass fiber reinforced framework and a special epoxy resin composition; the special epoxy resin composition comprises the following components in parts by weight: 60-85 parts of an epoxy resin matrix, 5-15 parts of an alicyclic epoxy resin intermediate, 8-20 parts of a toughening agent, 20-35 parts of a composite curing agent, 0.1-0.5 part of a defoaming agent and 0.5-1 part of a flatting agent. According to the preparation method, a sectional process of prepreg-preforming-compression molding is adopted, the resin flowability can be controlled in the pre-curing step, resin loss in the subsequent molding process is avoided, air between laminates can be fully discharged in the pre-pressing step, the material can be fully cured in a sectional temperature and pressure control mode of compression molding, and the product quality is improved. And the density and the size precision of the product are improved, the product percent of pass is remarkably improved, and large-scale industrial production is facilitated.

Description

Technical Field

[0001] This invention relates to the field of mobile phone materials, specifically to a fiberglass mobile phone back cover and its preparation method. Background Technology

[0002] With the widespread adoption of 5G communication technology and wireless charging, consumer electronics devices are placing higher demands on back cover materials: they must possess excellent electromagnetic signal transmittance, structural strength, lightweight design, and a superior aesthetic appeal. Glass fiber reinforced composite materials, due to their excellent mechanical properties, dimensional stability, and designability, have become one of the ideal alternatives to metal back covers.

[0003] Epoxy resin is often considered an ideal matrix resin for high-performance glass fiber composites due to its excellent bonding strength, dimensional stability, chemical resistance, and insulation properties. However, directly applying conventional epoxy resin / glass fiber composites to mobile phone back covers, which have extremely high requirements for aesthetics, feel, reliability, and dielectric properties, has significant drawbacks. For example, traditional epoxy-based composites are prone to microcracks or even brittle fracture during drop impacts; direct spraying of conventional epoxy glass fiber sheets can lead to paint film adhesion issues, which are easily affected by the glass fiber texture and the surface energy of the resin matrix, resulting in a risk of paint film peeling over long-term use; and ordinary epoxy glass fiber composites may undergo plasticization and hydrolysis in high-temperature and high-humidity environments, leading to decreased strength and dimensional changes.

[0004] Therefore, there is a lack of an epoxy resin / glass fiber composite material system and its supporting preparation process specifically designed for high-end mobile phone back covers. This system needs to maintain the inherent advantages of high strength and lightweight materials while simultaneously addressing key issues such as high toughness, low dielectric constant, low stress, excellent surface compatibility, and long-term environmental reliability in order to meet the stringent comprehensive performance requirements of consumer electronics products. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a fiberglass mobile phone back cover and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention discloses a fiberglass mobile phone back cover, which is formed by composite curing of a fiberglass reinforced skeleton and a special epoxy resin composition; the special epoxy resin composition comprises the following components by weight: 60-85 parts epoxy resin matrix, 5-15 parts alicyclic epoxy resin intermediate, 8-20 parts toughening agent, 20-35 parts composite curing agent, 0.1-0.5 parts defoamer and 0.5-1 part leveling agent.

[0007] Preferably, the epoxy resin matrix is ​​a bisphenol A type epoxy resin, including E51 or E44.

[0008] Preferably, the alicyclic epoxy resin intermediate is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate.

[0009] Preferably, the composite curing agent comprises an aromatic amine curing agent and a biomass curing agent; the weight ratio of the aromatic amine curing agent to the biomass curing agent is 7-8:2-3.

[0010] Preferably, the aromatic amine curing agent is 4,4'-diaminodiphenyl sulfone; the biomass curing agent is the product of resveratrol and D-dibenzoyl tartaric anhydride via an anhydride-phenol hydroxyl esterification reaction.

[0011] Preferably, the preparation method of the biomass solidification agent includes: S1. Add resveratrol, catalyst and solvent to the flask and stir until completely dissolved to obtain solution A; dissolve D-dibenzoyl tartaric anhydride in the solvent and slowly add it dropwise through a constant pressure dropping funnel under ice bath for 30 minutes to obtain solution B; S2. After the addition is complete, slowly heat to room temperature and react for 4 hours, then heat to 50-60℃ and react for 6-8 hours. Cool the reaction solution to room temperature and after post-treatment, a light yellow viscous substance is obtained, which is the biomass modified curing agent.

[0012] Preferably, in the preparation process of the biomass modified curing agent, the molar ratio of resveratrol and D-dibenzoyl tartaric anhydride is 1:1-1.2.

[0013] Preferably, in the preparation process of the biomass modified curing agent, the catalyst is 4-dimethylaminopyridine (DMAP), and the molar ratio of the catalyst to resveratrol is 0.01-0.1:1.

[0014] Preferably, the defoamer is BYK-055 and the leveling agent is BYK-310.

[0015] Preferably, the glass fiber reinforced skeleton is glass fiber cloth treated with silane coupling agent KH-560.

[0016] Preferably, the fiberglass cloth is a plain or twill fiberglass cloth with a thickness of 0.05-0.15 mm and an areal density of 50-150 g / m². 2 .

[0017] Preferably, the preparation process of the glass fiber reinforced skeleton includes: KH-560 coupling agent was mixed with ethanol to prepare a 5% (w / w) solution. The cleaned glass fiber cloth was completely immersed in the prepared KH-560 solution for 1-2 hours. After soaking, the fiber cloth was removed and air-dried in a ventilated place. After the solvent evaporated, it was baked at 40-60℃ until completely dry to obtain a glass fiber reinforced skeleton.

[0018] Secondly, this invention discloses a method for preparing a fiberglass board mobile phone back cover, comprising the following steps: (1) Prepreg: Mix the components of the special epoxy resin composition evenly to make a liquid. Use impregnation or scraping process to fully wet the glass fiber reinforcement skeleton. Control the resin content to 35%-45%. Then pre-cur it in the drying tunnel at 80-110℃ to obtain the prepreg. (2) Preforming: According to the design requirements of the back cover, the prepreg is laid in a predetermined direction and then placed in a mold preheated at 60-80℃ for low-pressure pre-pressing to pre-shape the layers and remove air, thus obtaining a preformed blank; (3) Molding: The preformed blank is transferred to the mold and hot-pressed to obtain the fiberglass mobile phone back cover.

[0019] Preferably, the molding process includes: first, maintaining the temperature at 100-120℃ and the pressure at 5-15MPa for 2-5 minutes; then raising the temperature to 150-180℃ and the pressure to 15-30 MPa, maintaining the temperature for 5-15 minutes, and then demolding after holding the pressure and cooling to below 80℃.

[0020] The beneficial effects of this invention are as follows: 1. This invention significantly improves the tensile strength, flexural strength, and impact resistance of the back cover material by compounding an epoxy resin matrix with an alicyclic epoxy resin intermediate and combining it with the reinforcing effect of a glass fiber reinforced skeleton. Specifically, the introduction of the alicyclic epoxy resin intermediate 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate optimizes the crosslinking structure of the epoxy resin matrix and enhances the interfacial bonding between the matrix and glass fiber. The composite curing agent utilizes the synergistic effect of an aromatic amine curing agent and a biomass curing agent, retaining the advantages of high crosslinking density and high heat resistance of the cured material after 4,4'-diaminodiphenyl sulfone curing, while also improving the toughness of the cured system through the modification effect of the biomass curing agent. This solves the problem of insufficient brittleness and hardness in traditional epoxy resin-based composite materials, enabling the prepared glass fiberboard mobile phone back cover to effectively resist daily drops, collisions, and other external impacts, providing reliable protection for the internal components of the mobile phone.

[0021] 2. The biomass curing agent prepared by the esterification reaction of resveratrol and D-dibenzoyl tartaric anhydride in this invention is a multifunctional curing agent containing carboxyl and ester groups. When compounded with the aromatic amine curing agent 4,4'-diaminodiphenyl sulfone (DDS), it can effectively delay and regulate the curing reaction rate, prolonging the gel time of the resin system and reducing the curing exothermic peak. This allows the resin to maintain its fluidity for a longer period during curing, fully wetting the fibers, and significantly reducing internal stress caused by the intense reaction and mismatch in thermal expansion coefficients during temperature curing, fundamentally reducing warping deformation of the product. Furthermore, the glass fiber reinforced skeleton is made from conventional glass fiber cloth treated with the silane coupling agent KH-560. The raw materials are readily available and the cost is controllable, giving it a better prospect for industrial application compared to high-end reinforcing materials such as carbon fiber.

[0022] 3. The preparation method of the present invention adopts a segmented process of "prepreg-preforming-compression molding". The pre-curing step can control the resin flowability and avoid resin loss during subsequent molding. The pre-compression step can fully expel the air between the layers. The segmented temperature and pressure control method of compression molding can achieve full curing of the material, improve the density and dimensional accuracy of the product, significantly improve the product qualification rate, and is suitable for large-scale industrial production. Detailed Implementation

[0023] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0024] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0025] The present invention will be further described below with reference to the following embodiments.

[0026] Example 1 A method for preparing a fiberglass mobile phone back cover includes the following steps: (1) Preparation of special epoxy resin composition: According to the weight parts, weigh epoxy resin matrix E51 (75 parts), alicyclic epoxy resin intermediate 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarboxylate (10 parts), toughening agent (14 parts), composite curing agent (28 parts, of which the weight ratio of 4,4'-diaminodiphenyl sulfone to biomass curing agent is 7:3), defoamer BYK-055 (0.3 parts), leveling agent BYK-310 (0.8 parts), add the above components to the mixer in sequence, stir and mix evenly to make a glue solution; (2) Preparation of glass fiber reinforced skeleton: KH-560 coupling agent was mixed with ethanol to prepare a solution with a mass concentration of 5%; a thickness of 0.1 mm and a surface density of 100 g / m³ were selected. 2 Plain fiberglass cloth was cleaned and then completely immersed in the prepared KH-560 solution for 1.5 hours. After soaking, the fiberglass cloth was removed and air-dried in a ventilated place until the solvent evaporated completely. Then it was placed in a 50°C oven and baked until completely dry to obtain a glass fiber reinforced skeleton. (3) Prepreg preparation: The above-mentioned adhesive solution is fully impregnated into the glass fiber reinforced skeleton by impregnation process, and the resin content is controlled to be 40%. Then the impregnated skeleton is sent into the drying tunnel and pre-cured at 95°C to obtain the prepreg. (4) Preforming: According to the design dimensions of the mobile phone back cover, the prepreg is laid in the predetermined direction and placed in a mold preheated at 70°C for low-pressure pre-pressing (pressure 3MPa, time 5min) to pre-shape the layers and remove air, thus obtaining the preformed blank. (5) Molding: Transfer the preformed blank to the mold of the molding machine, first keep it at a temperature of 110℃ and a pressure of 10MPa for 3 minutes; then raise the temperature to 165℃ and the pressure to 22MPa, keep it for 10 minutes; after molding, keep the pressure and cool to below 80℃ to demold, and obtain the glass fiber board mobile phone back cover.

[0027] The preparation method of the above-mentioned biomass solidification agent includes the following steps: S1. Add resveratrol (10 mmol, 2.28 g), catalyst 4-dimethylaminopyridine (DMAP, 0.5 mmol, 0.06 g), and solvent THF (50 mL) to a three-necked flask. Turn on the stirrer and stir until the materials are completely dissolved to obtain solution A. Dissolve D-dibenzoyl tartaric anhydride (11 mmol, 3.98 g) in solvent THF (20 mL) and transfer it to a constant pressure dropping funnel. Slowly add the solution to solution A under ice bath conditions, controlling the dropping time to 30 min. After the dropping is completed, solution B is obtained. S2. After the addition is complete, slowly raise the temperature to room temperature and react at this temperature for 4 hours. Then, continue to raise the temperature to 55°C and react at this temperature for 7 hours. After the reaction is complete, cool the reaction solution to room temperature and slowly add 20 mL of saturated sodium bicarbonate solution to quench excess acid anhydride. Transfer the mixture to a separatory funnel and add 50 mL of dichloromethane for extraction. Repeat the extraction 3 times and combine the organic phases. Wash the organic phase twice with 30 mL of saturated saline solution. Add anhydrous sodium sulfate to the washed organic phase and dry for 4 hours. Filter to remove anhydrous sodium sulfate. Distill the filtrate under reduced pressure to remove the solvent and obtain a pale yellow viscous substance, which is the biomass solidification agent.

[0028] Example 2 A method for preparing a fiberglass mobile phone back cover includes the following steps: (1) Preparation of special epoxy resin composition: According to the weight parts, weigh epoxy resin matrix E44 (65 parts), alicyclic epoxy resin intermediate 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarboxylate (8 parts), toughening agent (10 parts), composite curing agent (22 parts, of which the weight ratio of 4,4'-diaminodiphenyl sulfone to the biomass curing agent prepared in Example 1 is 8:2), defoamer BYK-055 (0.2 parts), leveling agent BYK-310 (0.6 parts), and mix them evenly to prepare an adhesive solution; (2) Preparation of glass fiber reinforced skeleton: Select a thickness of 0.08 mm and a surface density of 80 g / m³. 2 Twill fiberglass cloth, after being treated with KH-560 solution in the same manner as in Example 1, yields a glass fiber reinforced skeleton. (3) Prepreg preparation: The glass fiber reinforcement skeleton is impregnated with adhesive by a scraping process, the resin content is controlled at 36%, and the prepreg is pre-cured in an 85℃ oven to obtain the prepreg; (4) Preforming: After the prepreg is laid out, it is placed in a preheated mold at 65°C and pre-pressed under low pressure (pressure 2MPa, time 4min) to obtain the preformed blank; (5) Molding: First, maintain the temperature at 105℃ and the pressure at 8MPa for 2 minutes; then raise the temperature to 155℃ and the pressure to 18MPa, and maintain for 8 minutes; hold the pressure and cool to below 80℃ to demold and obtain the fiberglass mobile phone back cover.

[0029] Example 3 A method for preparing a fiberglass mobile phone back cover includes the following steps: (1) Preparation of special epoxy resin composition: According to the weight parts, weigh epoxy resin matrix E51 (82 parts), alicyclic epoxy resin intermediate 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarboxylate (14 parts), toughening agent (18 parts), composite curing agent (33 parts, of which the weight ratio of 4,4'-diaminodiphenyl sulfone to the biomass curing agent prepared in Example 1 is 7.5:2.5), defoamer BYK-055 (0.4 parts), leveling agent BYK-310 (0.9 parts), and mix them evenly to prepare an adhesive solution; (2) Preparation of glass fiber reinforced skeleton: a thickness of 0.12 mm and a surface density of 120 g / m² were selected. 2 Plain-weave fiberglass cloth, treated with KH-560 solution according to the same method as in Example 1, yields a glass fiber reinforced skeleton. (3) Prepreg preparation: The glass fiber reinforcement skeleton is impregnated with the adhesive solution using an impregnation process, the resin content is controlled to be 43%, and the prepreg is pre-cured in a drying oven at 105℃ to obtain the prepreg. (4) Preforming: After the prepreg is laid out, it is placed in a preheated mold at 75°C and pre-pressed under low pressure (pressure 4MPa, time 6min) to obtain the preformed blank; (5) Molding: First, maintain the temperature at 115℃ and the pressure at 13MPa for 4 minutes; then raise the temperature to 175℃ and the pressure to 28MPa, and maintain for 13 minutes; hold the pressure and cool to below 80℃ to demold and obtain the fiberglass mobile phone back cover.

[0030] Comparative Example 1 The difference between this comparative example and Example 1 is that no alicyclic epoxy resin intermediate was added to the special epoxy resin composition, while the remaining components and preparation process are exactly the same as in Example 1.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that the composite curing agent is a single 4,4'-diaminodiphenyl sulfone, and no biomass curing agent is added. The remaining components and preparation process are exactly the same as in Example 1.

[0032] Comparative Example 3 The difference between this comparative example and Example 1 is that the glass fiber reinforced skeleton was not treated with silane coupling agent KH-560, while the remaining components and preparation process are exactly the same as in Example 1.

[0033] Comparative Example 4 The difference between this comparative example and Example 1 is that the compression molding adopts a single temperature and pressure condition, that is, it is directly held at a temperature of 165°C and a pressure of 22MPa for 13 minutes. The rest of the preparation process and components are exactly the same as those in Example 1.

[0034] Comparative Example 5 This comparative example is a conventional fiberglass mobile phone back cover, using bisphenol A type epoxy resin E51 as the matrix and 4,4'-diaminodiphenyl sulfone as the curing agent. No alicyclic epoxy resin intermediates or toughening agents were added, and the fiberglass cloth was not treated with coupling agents. The preparation process was conventional impregnation-molding (single temperature and pressure conditions).

[0035] Experimental testing The mobile phone back cover samples prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests according to the following standards: Tensile strength: Tested according to GB / T 1447-2005 "Test Method for Tensile Properties of Fiber Reinforced Plastics"; Flexural strength: Tested according to GB / T 1449-2005 "Test Method for Flexural Properties of Fiber Reinforced Plastics"; Impact strength: Tested according to GB / T 1451-2005 "Impact Test Method for Fiber Reinforced Plastics Simply Supported Beams"; Heat distortion temperature: Tested in accordance with GB / T 1634.2-2004 "Determination of load distortion temperature of plastics - Part 2: Plastics, hard rubber and long fiber reinforced composites"; Appearance quality and pass rate: The appearance of 50 samples prepared in each group was observed, and the number of samples with defects such as air holes, insufficient glue, and warping was counted. The pass rate was calculated (pass rate = number of qualified samples / total number of samples × 100%). Aging resistance: The sample was placed in a high and low temperature alternating test chamber and subjected to high and low temperature cycle tests at -40℃ (2h) and 85℃ (2h) for a total of 50 cycles. The flexural strength retention rate after the cycle was tested (flexural strength retention rate = flexural strength after cycle / flexural strength before cycle × 100%).

[0036] The experimental results are shown in the table below:

[0037] The above results show that: Compared with the comparative products, the tensile strength, bending strength, impact strength, heat distortion temperature, pass rate, and bending strength retention rate after high and low temperature cycling of the products in the embodiments of the present invention are significantly improved. This fully demonstrates that the technical solution of the present invention can comprehensively improve the overall performance of fiberglass mobile phone back covers and has significant technical advantages and industrialization value.

[0038] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A fiberglass board mobile phone back cover, characterized in that, It is formed by composite curing of a glass fiber reinforced skeleton and a special epoxy resin composition; the glass fiber reinforced skeleton is glass fiber cloth treated with a silane coupling agent; the special epoxy resin composition contains the following components by weight: 60-85 parts epoxy resin matrix, 5-15 parts alicyclic epoxy resin intermediate, 8-20 parts toughening agent, 20-35 parts composite curing agent, 0.1-0.5 parts defoamer and 0.5-1 part leveling agent; The aromatic amine curing agent is 4,4'-diaminodiphenyl sulfone; the biomass curing agent is the product of resveratrol and D-dibenzoyl tartaric anhydride via an anhydride-phenol hydroxyl esterification reaction.

2. The fiberglass board mobile phone back cover according to claim 1, characterized in that, The epoxy resin matrix is ​​a bisphenol A type epoxy resin, including E51 or E44.

3. A fiberglass board mobile phone back cover according to claim 1, characterized in that, The alicyclic epoxy resin intermediate is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate.

4. A fiberglass board mobile phone back cover according to claim 1, characterized in that, The composite curing agent includes an aromatic amine curing agent and a biomass curing agent; the weight ratio of the aromatic amine curing agent to the biomass curing agent is 7-8:2-3.

5. A fiberglass board mobile phone back cover according to claim 1, characterized in that, The preparation method of the biomass solidification agent includes: S1. Add resveratrol, catalyst and solvent to the flask and stir until completely dissolved to obtain solution A; dissolve D-dibenzoyl tartaric anhydride in the solvent and slowly add it dropwise through a constant pressure dropping funnel under ice bath for 30 minutes to obtain solution B; S2. After the addition is complete, slowly heat to room temperature and react for 4 hours, then heat to 50-60℃ and react for 6-8 hours. Cool the reaction solution to room temperature and after post-treatment, a light yellow viscous substance is obtained, which is the biomass modified curing agent.

6. A fiberglass board mobile phone back cover according to claim 5, characterized in that, In the preparation process of the biomass modified curing agent, the molar ratio of resveratrol to D-dibenzoyl tartaric anhydride is 1:1-1.2; the catalyst is 4-dimethylaminopyridine (DMAP), and the molar ratio of the catalyst to resveratrol is 0.01-0.1:

1.

7. A fiberglass board mobile phone back cover according to claim 1, characterized in that, The defoamer is BYK-055, and the leveling agent is BYK-310.

8. A fiberglass mobile phone back cover according to claim 1, characterized in that, The fiberglass cloth is a plain or twill fiberglass cloth with a thickness of 0.05-0.15 mm and an areal density of 50-150 g / m². 2 .

9. A fiberglass board mobile phone back cover according to claim 1, characterized in that, The preparation process of the glass fiber reinforced skeleton includes: KH-560 coupling agent was mixed with ethanol to prepare a 5% (w / w) solution. The cleaned glass fiber cloth was completely immersed in the prepared KH-560 solution for 1-2 hours. After soaking, the fiber cloth was removed and air-dried in a ventilated place. After the solvent evaporated, it was baked at 40-60℃ until completely dry to obtain a glass fiber reinforced skeleton.

10. A method for preparing a fiberglass mobile phone back cover according to claim 1, characterized in that, Includes the following steps: (1) Prepreg: Mix the components of the special epoxy resin composition evenly to make a liquid. Use impregnation or scraping process to fully wet the glass fiber reinforcement skeleton. Control the resin content to 35%-45%. Then pre-cur it in the drying tunnel at 80-110℃ to obtain the prepreg. (2) Preforming: According to the design requirements of the back cover, the prepreg is laid in a predetermined direction and then placed in a mold preheated at 60-80℃ for low-pressure pre-pressing to pre-shape the layers and remove air, thus obtaining a preformed blank; (3) Molding: The preformed blank is transferred to the mold and hot-pressed to obtain the fiberglass mobile phone back cover. Preferably, the compression molding process includes: maintaining the temperature at 100-120℃ and the pressure at 5-15MPa for 2-5 minutes; Then raise the temperature to 150-180℃ and the pressure to 15-30 MPa, hold for 5-15 minutes, and after molding, keep the pressure and cool to below 80℃ before demolding.

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