Nano-silver aluminum oxide composite particles, antibacterial cover plate and preparation method and application of nano-silver aluminum oxide composite particles and antibacterial cover plate

Abstract

The invention relates to the technical field of nano-composite materials, in particular to nano-silver aluminum oxide composite particles, an antibacterial cover plate and a preparation method and application of the antibacterial cover plate. The nano-silver aluminum oxide composite particles are prepared from aluminum salt, tetramethylammonium hydroxide, ammonia water, silver nitrate, gelatin, tea polyphenol and a mixed solvent through a specific process, and a supported structure in which the nano-silver particles are supported on an aluminum oxide carrier is formed. The composite particles, polyimide varnish, a silane coupling agent, a plasticizer, a defoaming agent and a solvent are prepared into coating slurry according to a specific proportion, and the antibacterial cover plate with long-acting antibacterial property, high hardness, high light transmittance and excellent durability can be prepared through a step heating curing procedure. The antibacterial cover plate is suitable for electronic equipment such as smart phones and tablet personal computers, and effectively solves the technical problems that an existing cover plate is not lasting in antibacterial performance, and mechanical and optical properties are difficult to consider at the same time.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite materials technology, and in particular to a nano-silver alumina composite particle, an antibacterial cover plate, its preparation method and application. Background Technology

[0002] The cover surfaces of electronic devices such as smartphones and tablets are the areas most frequently touched by users, making them highly susceptible to the growth and adhesion of pathogenic microorganisms such as Escherichia coli and Staphylococcus aureus, posing hygiene risks. Therefore, endowing cover surfaces with antibacterial properties has become an important requirement.

[0003] In existing technologies, a common approach is to coat the cover plate surface with a coating containing antibacterial agents such as nano-silver, or to directly blend the antibacterial agent into the matrix resin. However, surface coatings suffer from poor adhesion, poor abrasion resistance, and easy peeling, leading to antibacterial failure. Simple blending of nano-silver, due to its extremely high surface energy, easily leads to aggregation in the resin matrix, affecting the optical uniformity of the material (resulting in increased haze). Furthermore, the weak bond between nano-silver and the matrix results in rapid and uncontrollable release of silver ions, often causing a rapid decline in antibacterial activity after initial high performance, failing to achieve long-lasting antibacterial effects. In addition, increasing the surface hardness of the cover plate usually requires adding inorganic fillers such as alumina and silica, but increasing the amount of filler often compromises light transmittance. How to achieve high hardness and long-lasting antibacterial effects while maintaining high light transmittance remains a current technical challenge.

[0004] Therefore, the antibacterial function of electronic device covers in existing technologies mainly faces two key contradictions: first, the contradiction between the decline in optical performance caused by the aggregation of silver nanoparticles and the short-lasting antibacterial effect due to the rapid release of silver ions; second, the contradiction between increasing hardness by adding inorganic fillers and the damage to the material's light transmittance by the fillers. How to develop a cover material that can simultaneously achieve long-lasting antibacterial effect, high hardness, high light transmittance, and excellent durability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the existing electronic device cover plate, such as the lack of long-lasting antibacterial effect, poor wear resistance, and difficulty in taking into account both optical and mechanical properties. The present invention provides nano-silver alumina composite particles, antibacterial cover plate, preparation method and application thereof.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] In a first aspect, this application provides a nano-silver alumina composite particle, characterized in that it comprises the following raw materials in parts by weight: 5-10 parts aluminum salt, 2-5 parts tetramethylammonium hydroxide, 1-3 parts ammonia water, 5-10 parts silver nitrate, 1-5 parts gelatin, 0.5-2.5 parts tea polyphenols, and 64.5-85.5 parts mixed solvent.

[0008] The nano-silver alumina composite particles of this application form a supported structure in which nano-silver particles are loaded onto the surface of nano-alumina particles. The nano-silver particles are uniformly anchored on the surface of the nano-alumina carrier with a small nano-size. The two are firmly bonded by the bridging and reduction effects of gelatin and tea polyphenols. This structure can effectively prevent the agglomeration of nano-silver particles and achieve the slow and sustained release of silver ions in subsequent application environments.

[0009] Furthermore, the amount of the tetramethylammonium hydroxide used is 3 to 4 parts by weight.

[0010] Furthermore, the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0011] Furthermore, the mixed solvent preferably consists of at least two of anhydrous ethanol, n-hexane, and deionized water.

[0012] Secondly, this application provides a method for preparing the above-mentioned nano-silver alumina composite particles, comprising the following steps:

[0013] S11. The aluminum salt, tetramethylammonium hydroxide, ammonia water and the first solvent are mixed, and after stirring and heating, solid-liquid separation and drying are carried out to obtain nano-alumina particles;

[0014] S12. The gelatin, tea polyphenols and the second solvent are mixed, and the silver nitrate is added for heating reaction. Then the nano-alumina particles are added for loading reaction. After the reaction is completed, the nano-silver alumina composite particles are obtained through post-processing. The first solvent and the second solvent are used together as the mixed solvent.

[0015] Furthermore, the first solvent comprises anhydrous ethanol, n-hexane, and deionized water.

[0016] Furthermore, in step S11, the amount of tetramethylammonium hydroxide added is 3 to 4 parts by weight, and the hydrolysis time of the heating reaction is 3 to 4 hours; even further, the amount of tetramethylammonium hydroxide added is 4 parts, and the hydrolysis time is 3 hours. These conditions are conducive to forming nano-alumina carriers with small particle size (e.g., 50-70 nm), narrow distribution, and excellent dispersibility.

[0017] Thirdly, this application provides an antibacterial cover plate, comprising the following raw materials in parts by weight: 70-90 parts polyimide varnish, 0.01-0.1 parts of the nano-silver alumina composite particles, 0.1-5 parts silane coupling agent, 0.1-3 parts plasticizer, 0.1-0.3 parts defoamer, and 10-20 parts solvent.

[0018] Further, the solvent is preferably at least one selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and γ-butyrolactone.

[0019] Fourthly, this application also provides a method for preparing the above-mentioned antibacterial cover plate, comprising the following steps: S21. Mixing the nano-silver alumina composite particles, silane coupling agent and solvent, and performing ultrasonic pretreatment to obtain a pre-dispersion liquid;

[0020] S22. Mix the pre-dispersed liquid, polyimide varnish, plasticizer, defoamer and solvent, and stir evenly to obtain a coating slurry;

[0021] S23. The coating slurry is coated onto the substrate, cured by a stepped heating process, demolded and dried to obtain the antibacterial cover plate.

[0022] Further, in step S23, the stepped heating program is as follows: first, cure at 80-90℃ for 0.5-1 hour, then cure at 120-130℃, 150-160℃, and 200-220℃ for 0.5-1 hour each, and finally cure at 240-260℃ for 1-2 hours.

[0023] Furthermore, the stepped heating program is as follows: 80℃ / 0.5h → 120℃ / 0.5h → 150℃ / 0.5h → 200℃ / 0.5h → 250℃ / 1h. This program facilitates the gradual evaporation of the solvent, ensures the complete imidization reaction of the polyimide, and promotes the stable bonding between the composite particles and the matrix, thereby obtaining a cover plate with excellent optical properties and stable performance.

[0024] Fifthly, this application also provides an application of the above-mentioned antibacterial cover in the protective cover of electronic devices, including but not limited to smartphones, tablets, laptops, wearable devices and other portable electronic devices with screens.

[0025] Using the antibacterial cover described in this application as the outermost screen protection cover of the aforementioned electronic devices can significantly reduce the risk of microbial growth on the user's contact surface by utilizing its long-lasting antibacterial properties. At the same time, with its comprehensive performance of high hardness, scratch resistance, high light transmittance and low haze, it provides reliable surface protection and excellent visual experience for electronic devices, meeting the combined requirements of hygiene and safety, durability and display effect in the consumer electronics field.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Balancing mechanical and optical properties: This application organically combines the antibacterial function of nano-silver with the reinforcing effect of nano-alumina. The alumina carrier not only stably loads nano-silver, but also significantly improves the surface hardness, wear resistance and durability of the cover plate as a reinforcing phase. The unique load-type structure and surface treatment technology ensure that the composite particles are highly uniformly dispersed in the matrix, thereby greatly improving the mechanical properties of the cover plate while maintaining excellent high light transmittance and low haze, successfully solving the technical problem of high hardness and high light transmittance.

[0028] (2) Achieved long-lasting and efficient antibacterial properties: This application constructs a supported composite structure of nano-silver and alumina and adopts a mild reduction process to enable the slow and controllable release of silver ions in the application environment. This result significantly prolongs the duration of antibacterial effect and overcomes the problem of rapid decay of antibacterial performance caused by the initial explosive release of silver ions in the prior art, thereby providing long-lasting and stable antibacterial protection.

[0029] (3) Excellent overall durability: The antibacterial cover of this application has undergone rigorous reliability testing, and its key performance (including optical performance, mechanical strength and antibacterial function) has shown good retention rate, demonstrating excellent environmental stability and long-term reliability, meeting the needs of electronic device covers for long-term protection.

[0030] (4) The process is controllable and easy to industrialize: The preparation method provided in this application has clear steps, optimized process conditions, and is mild and controllable. The raw materials used are common and readily available, the overall process is mature, and it is easy to implement on a large scale, which has significant practical value and market prospects. Detailed Implementation

[0031] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0032] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “an embodiment,” “an example,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0033] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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 protection scope of the present invention.

[0034] Unless otherwise specified, the raw materials, equipment and methods used in this invention can be obtained from publicly available commercial channels.

[0035] Example 1

[0036] This embodiment provides a nano-silver alumina composite particle, the raw material composition of which is prepared in laboratory scale according to the following parts by weight and a ratio of 1 part corresponding to 50 grams: 5.0 parts aluminum salt (calculated as Al(NO3)3·9H2O), 2.0 parts tetramethylammonium hydroxide (TMAOH), 1.0 part ammonia water (25-28%), 5.0 parts silver nitrate, 1.0 part gelatin, 0.5 parts tea polyphenols, and 85.5 parts mixed solvent.

[0037] Its preparation method includes the following steps:

[0038] (I) Preparation of nano-alumina particles

[0039] First, add 1075g of anhydrous ethanol, 700g of deionized water and 50g of ammonia to the reaction vessel. Weigh out 250g of aluminum nitrate [Al(NO3)3·9H2O] and 100g of tetramethylammonium hydroxide (TMAOH) and add them to the reaction vessel. Stir vigorously at 800 rpm for 3 hours until completely dissolved to form transparent sol A.

[0040] Then, 500g of n-hexane and 500g of anhydrous ethanol were mixed to prepare a mixed solution B. Solution A and solution B were mixed at a volume ratio of 3:7 and labeled as solution C. The mixture was heated for 3 hours while stirring.

[0041] Finally, take 500g of solution C, centrifuge at 6000rpm for 10min to obtain alumina precipitate, then transfer it to a petri dish, cover it with perforated aluminum foil, and dry it in a vacuum drying oven at 60℃ to obtain nano-alumina powder.

[0042] (II) Preparation of nano-silver alumina composite particles

[0043] Add 50g of gelatin, 1500g of deionized water, and 25g of tea polyphenols to a reaction vessel and stir to dissolve. Then add 250g of silver nitrate (AgNO3) and stir to dissolve. The stirring speed is 500rpm, and the temperature is raised to 135℃. React for 10h. After the reaction is complete, add all the nano-alumina powder prepared in step one to the solution. After reacting for 5h, filter, wash three times with anhydrous ethanol, and dry under vacuum at 60℃ to obtain nano-silver alumina composite particle powder (Ag@Al2O3), which is a supported structure of nano-silver particles loaded on an alumina carrier.

[0044] Example 2

[0045] This embodiment provides a nano-silver alumina composite particle, the raw material composition of which is prepared in laboratory scale according to the ratio of 1 part corresponding to 50 grams: 7.5 parts aluminum salt, 3.0 parts tetramethylammonium hydroxide, 2.0 parts ammonia water, 7.5 parts silver nitrate, 3.0 parts gelatin, 1.0 part tea polyphenols, and 76.0 parts mixed solvent.

[0046] Its preparation method includes the following steps:

[0047] (I) Preparation of nano-alumina particles

[0048] First, add 1000g of anhydrous ethanol, 550g of deionized water and 100g of ammonia water to the reaction vessel. Weigh out 375g of aluminum nitrate [Al(NO3)3·9H2O] and 150g of tetramethylammonium hydroxide (TMAOH) and add them to the reaction vessel. Stir vigorously at 800 rpm for 3 hours until completely dissolved to form transparent sol A.

[0049] Then, 500g of n-hexane and 500g of anhydrous ethanol were mixed to prepare a mixed solution B. Solution A and solution B were mixed at a volume ratio of 3:7 and labeled as solution C. The mixture was heated for 3 hours while stirring.

[0050] Finally, take 500g of solution C, centrifuge at 6000rpm for 10min to obtain alumina precipitate, then transfer it to a petri dish, cover it with perforated aluminum foil, and dry it in a vacuum drying oven at 60℃ to obtain nano-alumina powder.

[0051] (II) Preparation of nano-silver alumina composite particles

[0052] Add 150g of gelatin, 1250g of deionized water, and 50g of tea polyphenols to a reaction vessel and stir to dissolve. Then add 375g of silver nitrate (AgNO3) and stir to dissolve. The stirring speed is 500rpm, and the temperature is raised to 135℃. React for 10h. After the reaction is complete, add all the nano-alumina powder prepared in step one to the solution. After reacting for 5h, filter, wash three times with anhydrous ethanol, and dry under vacuum at 60℃ to obtain nano-silver alumina composite particle powder (Ag@Al2O3), which is a supported structure of silver nanoparticles loaded on an alumina carrier.

[0053] Example 3

[0054] This embodiment provides a nano-silver alumina composite particle, comprising the following raw materials in parts by weight: 10.0 parts aluminum salt, 5.0 parts tetramethylammonium hydroxide, 3.0 parts ammonia, 10.0 parts silver nitrate, 5.0 parts gelatin, 2.5 parts tea polyphenols, and 64.5 parts mixed solvent.

[0055] Its preparation method includes the following steps:

[0056] (I) Preparation of nano-alumina particles

[0057] First, add 900g of anhydrous ethanol, 300g of deionized water and 150g of ammonia water to the reaction vessel. Weigh out 500g of aluminum nitrate [Al(NO3)3·9H2O] and 250g of tetramethylammonium hydroxide (TMAOH) and add them to the reaction vessel. Stir vigorously at 800 rpm for 3 hours until completely dissolved to form transparent sol A.

[0058] Then, 500g of n-hexane and 500g of anhydrous ethanol were mixed to prepare a mixed solution B. Solution A and solution B were mixed at a volume ratio of 3:7 and labeled as solution C. The mixture was heated for 3 hours while stirring.

[0059] Finally, take 500g of solution C, centrifuge at 6000rpm for 10min to obtain alumina precipitate, then transfer it to a petri dish, cover it with perforated aluminum foil, and dry it in a vacuum drying oven at 60℃ to obtain nano-alumina powder.

[0060] (II) Preparation of nano-silver alumina composite particles

[0061] 250g of gelatin, 1025g of deionized water, and 125g of tea polyphenols were added to a reaction vessel and stirred until dissolved. Then, 500g of silver nitrate (AgNO3) was added and stirred until dissolved at 500 rpm. Simultaneously, the temperature was raised to 135℃ and the reaction was allowed to proceed for 10 hours. After the reaction was complete, all the prepared alumina powder was added to the solution, and the reaction was allowed to proceed for 5 hours. The mixture was then filtered, washed three times with anhydrous ethanol, and dried under vacuum at 60℃ to obtain nano-silver alumina composite particle powder (Ag@Al2O3), a supported structure of silver nanoparticles on an alumina carrier.

[0062] Example 4: Study on the effect of TMAOH concentration on the morphology of nano-alumina carriers

[0063] This embodiment aims to study the key role of tetramethylammonium hydroxide (TMAOH) concentration in the preparation of nano-alumina particle carriers, using different weight parts of TMAOH (relative to aluminum salts).

[0064] The preparation method is similar to step (I) of Example 1, which involves preparing nano-alumina particles. Other conditions are kept constant, only the amount of TMAOH added is changed to 2, 3, 4, and 5 parts by weight, with the hydrolysis reaction time adjusted accordingly (3-5 hours). The reaction is stirred at 800 rpm for a specific time to form a sol, which is then further processed to obtain nano-alumina powder. Dynamic light scattering (DLS) was used to characterize its particle size and dispersibility, and the results are as follows:

[0065] Table 1 Effects of TMAOH concentration and hydrolysis time on the properties of alumina particles

[0066] TMAOH content (parts by weight) Hydrolysis time (h) Average particle size (nm) Dynamic light scattering dispersion index (PDI) Alumina particle distribution 2 3 80-120 >0.25 Severe aggregation, wide distribution, and unstable. 3 4 70-100 0.10-0.20 Good dispersion, moderate particle size 4 3 50-70 0.10-0.18 It is well dispersed and has a small particle size and narrow distribution. 5 5 80-120 >0.25 Increased particle size and wider distribution

[0067] As shown in the table above, the alumina particles exhibit the best performance when the TMAOH content is 4 parts by weight and the hydrolysis time is 3 hours, with the smallest average particle size (50-70 nm), the lowest PDI value (0.10-0.18), good dispersibility, and a narrow particle size distribution. When the TMAOH content is too low (2 parts) or too high (5 parts), severe particle agglomeration, increased particle size, and wider particle size distribution occur. Even at a moderate TMAOH content (3 parts), if the hydrolysis time is not optimized (e.g., extended to 4 hours), the particle size is still relatively large (70-100 nm). This indicates that selecting 4 parts by weight of TMAOH combined with a 3-hour hydrolysis time is the key process condition for obtaining an ideal nano-alumina carrier.

[0068] Example 5

[0069] This embodiment provides an antibacterial cover plate, the raw material composition of which is prepared in laboratory scale according to the ratio of 1 part to 10 grams by weight: 85 parts of polyimide slurry (solid content 15%, prepared according to the method of announcement number CN114276541A) (based on solids), 0.01 parts of nano silver alumina composite particles (Ag@Al2O3) prepared in Example 2, 0.5 parts of silane coupling agent KH-550, 1.5 parts of dioctyl phthalate (plasticizer), 0.2 parts of defoamer BYK3451, and 12.79 parts of solvent N-methylpyrrolidone (NMP).

[0070] Its preparation method includes the following steps:

[0071] (1) Preparation of pretreatment solution: Weigh 0.1g of the composite particles (Ag@Al2O3) prepared in Example 2, 5g of silane coupling agent KH550 and 50g of NMP, mix them, and sonicate for 30 minutes for pre-dispersion and surface treatment.

[0072] (2) Slurry preparation: Add the above pretreatment liquid to 850g (based on solids) of polyimide slurry, and add 15g of dioctyl phthalate (plasticizer), 2g of defoamer BYK3451 and 77.9g of NMP at the same time. Stir at 2000rpm for 1 hour in a high-speed homogenizer to obtain a uniform slurry.

[0073] (3) Coating and curing: Take 4cm 2 The glass substrate (silicon wafer or glass) was cleaned sequentially with deionized water, acetone, and ethanol. The above slurry was applied to a clean glass plate using a Mayer wire rod coater, with a wet film thickness of 150 μm. The coated glass plate was then placed in a forced-air oven and cured according to the following step sequence: 80℃ / 0.5h → 120℃ / 0.5h → 150℃ / 0.5h → 200℃ / 0.5h → 250℃ / 1h. After natural cooling, the film was demolded from the glass plate with 80℃ deionized water and then dried in a 120℃ oven for 10 minutes to obtain a transparent cover film with a thickness of approximately 22.5 μm, denoted as sample S1.

[0074] Example 6

[0075] This embodiment provides an antibacterial cover plate, whose raw material ratio and preparation method are basically the same as those in Example 5. The difference is that the amount of composite particles (Ag@Al2O3) is increased to 0.05g, and the amounts of other components are adjusted accordingly to maintain the total weight parts unchanged, and finally a transparent cover plate film sample S2 is obtained.

[0076] This embodiment provides an antibacterial cover plate, the raw material composition of which is prepared in laboratory scale according to the ratio of 1 part to 10 grams by weight: 80 parts of polyimide slurry (solid content 15%, prepared according to the method of announcement number CN114276541A) (based on solids), 0.05 parts of nano silver alumina composite particles (Ag@Al2O3) prepared in Example 2, 1.5 parts of silane coupling agent KH-550, 2.5 parts of dioctyl phthalate (plasticizer), 0.95 parts of defoamer BYK3451, and 15 parts of solvent N-methylpyrrolidone (NMP).

[0077] Its preparation method includes the following steps:

[0078] (1) Preparation of pretreatment solution: Weigh 0.5g of the composite particles (Ag@Al2O3) prepared in Example 2, 15g of silane coupling agent KH550 and 70g of NMP, mix them, and sonicate for 30 minutes for pre-dispersion and surface treatment.

[0079] (2) Slurry preparation: Add the above pretreatment liquid to 800g (based on solids) of polyimide slurry, and add 25g of dioctyl phthalate (plasticizer), 9.5g of defoamer BYK3451 and 80g of NMP. Stir at 2000rpm for 1 hour in a high-speed homogenizer to obtain a uniform slurry.

[0080] (3) Coating and curing: Take a 4cm2 glass substrate (silicon wafer or glass) and clean it with deionized water, acetone and ethanol in sequence; use a Mayer wire bar coater to coat the above slurry onto a clean glass plate with a wet film thickness of 150μm; then place the coated glass plate in a forced-air oven and cure it according to the following step program: 80℃ / 0.5h→120℃ / 0.5h→150℃ / 0.5h→200℃ / 0.5h→250℃ / 1h; after natural cooling, use 80℃ deionized water to demold the film from the glass plate, and then dry it in a 120℃ oven for 10 minutes to obtain a transparent cover film with a thickness of about 22.5μm, which is recorded as sample S2.

[0081] Example 7

[0082] This embodiment provides an antibacterial cover plate, whose raw material ratio and preparation method are basically the same as those in Example 5. The difference is that the amount of composite particles (Ag@Al2O3) is increased to 0.10g, and the amount of other components is adjusted accordingly to maintain the total weight unchanged, and finally a transparent cover plate film sample S3 is obtained.

[0083] This embodiment provides an antibacterial cover plate, the raw material composition of which is prepared in laboratory scale according to the ratio of 1 part to 10 grams by weight: 85 parts of polyimide slurry (solid content 15%, prepared according to the method of announcement number CN114276541A) (based on solids), 0.1 parts of nano silver alumina composite particles (Ag@Al2O3) prepared in Example 2, 2.0 parts of silane coupling agent KH-550, 2.1 parts of dioctyl phthalate (plasticizer), 0.3 parts of defoamer BYK3451, and 10.5 parts of solvent N-methylpyrrolidone (NMP).

[0084] Its preparation method includes the following steps:

[0085] (1) Preparation of pretreatment solution: Weigh 1g of the composite particles (Ag@Al2O3) prepared in Example 2, 20g of silane coupling agent KH550 and 50g of NMP, mix them, and sonicate for 30 minutes for pre-dispersion and surface treatment.

[0086] (2) Slurry preparation: Add the above pretreatment liquid to 850g (based on solids) of polyimide slurry, and add 21g of dioctyl phthalate (plasticizer), 3g of defoamer BYK3451 and 55g of NMP at the same time. Stir at 2000rpm for 1 hour in a high-speed homogenizer to obtain a uniform slurry.

[0087] (3) Coating and curing: Take 4cm 2 The glass substrate (silicon wafer or glass) was cleaned sequentially with deionized water, acetone, and ethanol. The slurry was then applied to a clean glass plate using a Mayer wire rod coater, resulting in a wet film thickness of 150 μm. The coated glass plate was then placed in a forced-air oven and cured according to the following step sequence: 80℃ / 0.5h → 120℃ / 0.5h → 150℃ / 0.5h → 200℃ / 0.5h → 250℃ / 1h. After natural cooling, the film was demolded from the glass plate using 80℃ deionized water and then dried in a 120℃ oven for 10 minutes to obtain a transparent cover film with a thickness of approximately 22.5 μm, denoted as sample S3.

[0088] Comparative Example 1 (Pure Polyimide Cover Plate)

[0089] This comparative example provides an antibacterial cover plate, the formulation of which does not contain composite particles (Ag@Al2O3) and silane coupling agent, and the remaining components and preparation process are the same as in Example 5, resulting in a transparent cover plate film sample D1.

[0090] Comparative Example 2 (Cover plate of physically mixed nano-silver and alumina)

[0091] This comparative example provides an antibacterial cover plate. Commercially available silver nanoparticles with an average particle size of approximately 30 nm and alumina nanoparticles with an average particle size of approximately 80 nm were physically mixed at a silver / alumina mass ratio of approximately 1:8 and ball-milled for 2 hours to obtain a mixed powder. 0.05 g of this mixed powder was used to replace the composite particles (Ag@Al2O3) in Example 6. All other raw materials and preparation processes were identical to those in Example 6. The resulting cover plate film sample was designated as Sample D2.

[0092] Comparative Example 3 (Ag@Al2O3 composite particle cover plate prepared by sodium borohydride reduction method)

[0093] This comparative example provides an antibacterial cover plate, the preparation method of which includes the following steps: S1. Prepare alumina sol (not dried) as in step (1) of Example 1; S2. Concentrate and disperse the above alumina sol in water, add an equal amount of silver nitrate as in Example 2, and rapidly add an excess of sodium borohydride aqueous solution dropwise while stirring vigorously in an ice-water bath. After reacting for 1 hour, centrifuge, wash, and dry to obtain composite particles. Using this composite particle at an addition amount of 0.05 parts by weight, a cover plate film is prepared according to the method of Example 6, and is denoted as sample D3.

[0094] Comparative Example 4 (Supported nano-silver-silica composite particle cover plate)

[0095] This comparative example provides an antibacterial cover plate. Silica microspheres with a particle size of approximately 60 nm were prepared using the Stöber method, and then silver nanoparticles were loaded using a method similar to that in Example 2, yielding Ag@SiO2 composite particles. Using these particles added at 0.05 parts by weight, a cover plate film was prepared according to the method in Example 6, denoted as sample D4.

[0096] Comparative Example 5 (High Additive Content Composite Particle Cover)

[0097] This comparative example provides an antibacterial cover plate, whose formulation and preparation method are basically the same as those in Example 6. The difference is that the amount of Ag@SiO2 composite particles added is significantly increased to 0.50 parts by weight, and the resulting cover plate film is designated as sample D5.

[0098] Comparative Example 6 (Cover plate prepared by a one-step high-temperature curing process)

[0099] This comparative example provides an antibacterial cover plate with the same formulation as Example 6, but the stepped heating procedure is omitted. Instead, the coated wet film is placed in a 250°C oven for 2 hours to cure. The resulting cover plate film is denoted as sample D6.

[0100] Performance testing

[0101] The cover film samples obtained in Examples 5-7 (S1-S3) and Comparative Examples 1-6 (D1-D6) were subjected to comprehensive performance tests, including basic optical and mechanical properties, antibacterial and silver ion release properties, and durability and reliability. The results are summarized in Tables 2, 3 and 4 below.

[0102] Test 1: Optical and Mechanical Properties Test of Antibacterial Cover

[0103] The basic optical and mechanical properties of each cover plate film sample were tested, and the results are summarized in Table 2 below. Transmittance and haze were tested using a BYK haze meter (light source D65) at a wavelength of 550 nm; pencil hardness was tested according to GB / T 6739-2006 standard; and water contact angle was tested using a contact angle meter.

[0104] Table 2 Summary of basic optical and mechanical test data for cover plates of each embodiment and comparative example

[0105] illustration Transmittance @ 550 nm (%) Haze (%) Pencil hardness Water contact angle (°) Example 5 (S1) 90.61 0.57 3H 103.18 Example 6 (S2) 90.17 0.63 4H 105.32 Example 6 (S3) 89.86 0.72 5H 108.57 Comparative Example 1 (D1) 91.21 0.55 HB 90.23 Comparative Example 2 (D2) 89.32 1.92 3H 99.16 Comparative Example 3 (D3) 88.72 1.58 3H 100.09 Comparative Example 4 (D4) 90.93 0.61 2H 103.5 Comparative Example 5 (D5) 88.56 2.37 6H 110.16 Comparative Example 6 (D6) 89.75 1.12 4H 101.95

[0106] Test 2: Antibacterial rate and silver ion release rate test

[0107] The antibacterial rates of the cover film sample S2 prepared in Preferred Example 6 and key comparative examples 2-4 (cover films D2-D4) against *Escherichia coli* and *Staphylococcus aureus* were tested at different time points of 24, 48, 72, and 96 hours. Simultaneously, the release rate of silver ions in the initial (0-24 h) and long-term (24-96 h) phases was determined using ICP-MS, and the test results are shown in Table 3 below. For a more comprehensive evaluation, the performance of commercially available surface antibacterial coatings was also tested as a reference.

[0108] Table 3 Antibacterial rate and silver ion release rate of different examples

[0109] illustration 24h antibacterial rate (%) 48h antibacterial rate (%) 72h antibacterial rate (%) 96h antibacterial rate (%) Initial average rate (0-24h) Long-term average rate (24-96h) Example 6 (S2) 99.99 99.99 99.9 99.9 2.2 ppb / h 0.7ppb / h Comparative Example 2 (D2) 90 82 75 55 8.1 ppb / h 0.4 ppb / h Comparative Example 3 (D3) 99.9 99 97 94 5.2 ppb / h 1.3ppb / h Comparative Example 4 (D4) 99.99 99.99 99.9 99.5 1.7ppb / h 0.6ppb / h Commercially available antibacterial coatings 99.9 88 90 80 14ppb / h 4.1 ppb / h

[0110] Test 3: Durability and Reliability Testing

[0111] To simulate harsh operating environments, durability and reliability tests were conducted on the cover film sample S2 prepared in Preferred Example 6 and the cover film samples D2 and D4 prepared in Key Comparative Examples 2 and 4. The results are shown in Table 4 below. The double 85 test was conducted for 500 hours at 85°C / 85%RH. The abrasion resistance test involved 100 cycles of reciprocating friction with steel wool (#0000) under a 500g load.

[0112] Table 4. Durability and reliability test results for different examples

[0113] Test Project Test conditions Example 6 (S2) Comparative Example 2 (D2) Comparative Example 4 (D4) Double 85 test 85°C / 85%RH, 500h Transmittance >89.5%, hardness maintained at 4H, antibacterial rate >99.99%. With a transmittance of 85%, a hardness reduced to 2H, and an antibacterial rate of <50%, this material exhibits these characteristics. Transmittance >90%, hardness reduced to 1H, antibacterial rate >99%. Abrasion resistance test Steel wool #0000, 500g load, 100 cycles No visible scratches Dense fine scratches appeared Minor scratches Bending test R=3mm, 100,000 cycles. No cracks Microcracks appeared after 50,000 cycles. No cracks Chemical-resistant wipes 75% ethanol, wipe 500 times. No surface changes; antibacterial rate >99.9%. Surface atomization significantly reduces antibacterial rate. The surface is slightly misted, maintaining an antibacterial rate of >90%.

[0114] Based on the test data in Tables 2-4, the technical effects of the present invention are analyzed as follows:

[0115] 1. Long-lasting and highly effective antibacterial performance: In the embodiments of this invention (S1-S3), with extremely low addition amounts of composite particles Ag@Al2O3 (0.01-0.05g), the 24-hour antibacterial rate against Escherichia coli and Staphylococcus aureus reached 99.99%, demonstrating immediate high efficiency. More importantly, its long-lasting effect is evident: Example 6 (S2, addition amount 0.05g) maintained an antibacterial rate of 99.9% after 96 hours; in contrast, the antibacterial rate of Comparative Example 2 (D2, physical mixing) dropped sharply to 55% after 96 hours, and commercially available antibacterial coatings also decreased to 80%. This directly proves the success of the controlled slow release mechanism of silver ions achieved by this invention through a "supported structure" and a "gelatin-tea polyphenol mild reduction process." Table 3 shows that the silver ion release of sample S2 exhibits a "moderate initial release, gradual long-term release" characteristic (2.2 ppb / h initially, 0.7 ppb / h in the long term). In contrast, the physically mixed sample D2 shows an initial explosive release (8.1 ppb / h), leading to eventual failure. Sample D3, rapidly reduced with sodium borohydride, still shows a relatively high long-term release rate (1.3 ppb / h), and its antibacterial rate drops to 94% after 96 hours, indicating unstable binding and rapid, continuous loss of silver ions, resulting in lower durability compared to this invention. This demonstrates that the composite particle structure of this invention effectively prevents premature consumption of silver ions, ensuring a sustained and stable antibacterial effect.

[0116] 2. Perfect Balance of Excellent Mechanical and Optical Properties: This invention significantly improves the hardness of the cover plate while maintaining excellent optical properties. For example, the pencil hardness of Example 6 (S2) reaches 4H, far exceeding that of the pure polyimide cover plate (D1, HB), while the light transmittance is still as high as 90.17% and the haze is only 0.63%. This balance is attributed to: ① The reinforcing effect of the alumina carrier: As a high-hardness nanoparticle, alumina acts as a reinforcing phase in the matrix, directly improving the film hardness (S3 hardness reaches 5H). Comparative Example 4 (D4, Ag@SiO2) has a cover plate hardness of only 2H due to the lower hardness of silicon dioxide, confirming the unique advantage of the alumina carrier in improving mechanical properties. ② Good dispersibility: The supported structure and silane coupling agent treatment ensure uniform dispersion of the composite particles in the resin matrix, avoiding the aggravation of light scattering caused by agglomeration. Comparative Example 2 (D2, physical mixture) had a haze as high as 1.92% due to uneven dispersion; Comparative Example 5 (D5, high addition amount of 0.5g) achieved a hardness of 6H, but the haze deteriorated to 2.37%, and the optical performance was severely degraded. This proves the importance of the preferred addition range of Ag@Al2O3 composite particles (0.01-0.1 parts by weight) in balancing hardness and light transmittance.

[0117] Furthermore, as shown in Table 2, in Examples 5-7 (S1-S3), as the amount of Ag@Al2O3 composite particles added increased within the range of 0.01-0.1 parts by weight, the pencil hardness of the cover film significantly improved from 3H to 5H, and the water contact angle increased, demonstrating that the alumina carrier effectively enhanced the mechanical properties and hydrophobicity of the material. Crucially, during this process, the transmittance only slightly decreased from 90.61% to 89.86%, and the haze slightly increased from 0.57% to 0.72%, resulting in minimal loss of optical performance. This indicates that the supported structure of the present invention effectively prevents the aggregation of nano-silver and alumina, enabling them to be uniformly dispersed, significantly improving mechanical properties while minimizing the impact on optical performance. Among these, Example 6 (S2, Ag@Al2O3 addition amount 0.05g) exhibited the best overall performance balance and is considered the optimal example.

[0118] 3. Excellent Overall Durability and Reliability: After rigorous accelerated aging tests, the product of this invention exhibits strong environmental stability. As shown in Table 4, after the double 85 test (85℃ / 85%RH, 500h), the transmittance, hardness, and antibacterial rate of Example 6 (S2) remained at high levels. In contrast, the control sample D2 (physical mixture) showed decreased transmittance, reduced hardness, and near-complete loss of antibacterial performance. In the abrasion resistance test, sample S2 showed no visible scratches, while D2 and D4 showed varying degrees of scratches, demonstrating the excellent surface abrasion resistance of the cover plate of this invention. Furthermore, sample S2 also performed well in bending and chemical wiping tests. These results collectively indicate that the antibacterial cover plate prepared by this invention not only has superior initial performance but also possesses long-term reliability, enabling it to adapt to complex and harsh operating environments.

[0119] 4. Necessity of the "Step-by-Step Temperature Curing Process": Data from Tables 2 and 3 show that the comparison between Comparative Example 6 (D6, one-step high-temperature curing process) and Example 6 (S2, step-by-step temperature curing process) highlights the necessity of the step-by-step temperature curing procedure. The haze of sample D6 (1.12%) was significantly higher than that of S2 (0.63%), and its 96-hour antibacterial rate (approximately 98.2%) was slightly lower than that of S2 (99.9%). This indicates that step-by-step temperature curing facilitates the gradual evaporation of solvents, the full imidization reaction of polyimide, and the stable shaping of composite particles in the matrix, which is an important guarantee for obtaining low haze and long-lasting antibacterial properties.

[0120] 5. Necessity of Nano-Alumina Carrier: The comparison between Comparative Example 4 (D4, Ag@SiO2) and Example 6 (S2) demonstrates the non-obviousness of the carrier material selection. Both exhibit similar optical and antibacterial properties, but S2 has a significantly higher pencil hardness (4H) than D4 (2H). In durability testing, S2 maintained a hardness of 4H without scratches after the double 85 test, while D4's hardness decreased to 1H and showed a few scratches. This clearly shows that choosing alumina as a carrier not only provides load-bearing capacity but also, as a high-hardness reinforcing phase, brings superior surface hardness, wear resistance, and overall durability to the cover plate, qualities that silica lacks.

[0121] In summary, this invention, by designing and preparing supported nano-silver alumina composite particles and applying them to polyimide antibacterial covers, successfully solves the technical problems of insufficient antibacterial performance, poor wear resistance, and difficulty in balancing high hardness and high light transmittance in existing technologies. Test data fully demonstrates that this application achieves a high degree of unity between long-lasting antibacterial effect, high hardness, high light transmittance, and excellent durability. Its comprehensive performance is significantly superior to comparative examples using physical mixing, different preparation processes, or different carrier materials, demonstrating outstanding technological progress and practical application value.

[0122] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A nano-silver alumina composite particle, characterized in that, The raw materials include the following parts by weight: 5-10 parts aluminum salt, 2-5 parts tetramethylammonium hydroxide, 1-3 parts ammonia, 5-10 parts silver nitrate, 1-5 parts gelatin, 0.5-2.5 parts tea polyphenols, and 64.5-85.5 parts mixed solvent.

2. The nano-silver alumina composite particles according to claim 1, characterized in that, The aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

3. The nano-silver alumina composite particles according to claim 1, characterized in that, The mixed solvent is composed of at least two of anhydrous ethanol, n-hexane, and deionized water.

4. A method for preparing nano-silver alumina composite particles as described in any one of claims 1-3, characterized in that, Includes the following steps: S11. The aluminum salt, tetramethylammonium hydroxide, ammonia water and the first solvent are mixed, and after stirring and heating, solid-liquid separation and drying are carried out to obtain nano-alumina particles; S12. The gelatin, tea polyphenols and the second solvent are mixed, and the silver nitrate is added for heating and reaction. Then the nano-alumina particles are added for loading and reaction. After the reaction is completed, the nano-silver alumina composite particles are obtained through post-processing. The first solvent and the second solvent together constitute the mixed solvent.

5. The preparation method according to claim 4, characterized in that, In step S11, the amount of tetramethylammonium hydroxide added is 3 to 4 parts by weight, and the hydrolysis time of the heating reaction is 3 to 4 hours.

6. An antibacterial cover, characterized in that, The raw materials comprise the following parts by weight: 70-90 parts polyimide varnish, 0.01-0.1 parts nano-silver alumina composite particles as described in any one of claims 1-3, 0.1-5 parts silane coupling agent, 0.1-3 parts plasticizer, 0.1-0.3 parts defoamer, and 10-20 parts solvent.

7. The antibacterial cover plate according to claim 6, characterized in that, The solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and γ-butyrolactone.

8. A method for preparing an antibacterial cover plate as described in claim 6 or 7, characterized in that, Includes the following steps: S21. The nano-silver alumina composite particles, silane coupling agent and part of the solvent are mixed and subjected to ultrasonic pretreatment to obtain a pre-dispersion; S22. Mix the pre-dispersed liquid, polyimide varnish, plasticizer, defoamer and solvent, and stir evenly to obtain a coating slurry; S23. The coating slurry is coated onto the substrate, cured by a stepped heating process, demolded and dried to obtain the antibacterial cover plate.

9. The preparation method according to claim 8, characterized in that, In step S23, the stepped heating program is as follows: first, cure at 80-90℃ for 0.5-1 hour, then cure at 120-130℃, 150-160℃, and 200-220℃ for 0.5-1 hour each, and finally cure at 240-260℃ for 1-2 hours.

10. The application of an antibacterial cover as described in claim 6 or 7 in a protective cover for electronic devices.