Preparation process of antibacterial and anti-cracking plastic accessory for refrigerator accessory

Abstract

The invention discloses a preparation process of an antibacterial and anti-cracking plastic part for a refrigerator part. The preparation process comprises the following steps: preparing Ag ion antibacterial particles; the preparation method comprises the following steps: uniformly mixing transparent PP resin, Ag ion antibacterial particles, a styrene-ethylene-butylene-styrene block copolymer and a functional aid according to different proportions to respectively obtain a blend of a surface layer, a transition layer and a core layer; a five-layer co-extrusion die head is used for co-extrusion, all the layers are arranged in a surface layer-transition layer-core layer-transition layer-surface layer mode, and an extruded sheet is obtained; carrying out hot-pressing treatment on the extruded sheet, and inducing interlayer diffusion to form a blank with gradient change of the doping amount of the Ag ion antibacterial particles; and taking the blank, and carrying out post-treatment. The doping amount of the Ag ion antibacterial particles is changed in a gradient mode through multi-layer co-extrusion and hot pressing treatment, namely, the doping amount is gradually reduced from the surface layer to the core layer in the thickness direction, the doping amount in the same thickness plane is equal, the accessory has the advantages of being good in antibacterial performance and excellent in transparency, meanwhile, the usage amount of Ag is reduced, and cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigerator accessories, and particularly relates to a preparation process for an antibacterial and crack-resistant plastic accessory for a refrigerator accessory. Background Art

[0002] Although a refrigerator uses low temperature to inhibit the growth and reproduction of bacteria, at refrigeration temperature, the metabolic activities of bacteria decrease or nearly stop, but they are not completely dead. Once encountering a suitable temperature, the bacteria will quickly grow and reproduce. Plastic accessories such as the sealing strip, door handle, and fresh-keeping box in the refrigerator are prone to accumulating bacteria because they often come into contact with food and hands. These bacteria not only affect the fresh-keeping effect of food but may also become a potential safety hazard, causing various health problems such as gastroenteritis and sore throat. Accessories made of antibacterial plastic can effectively inhibit the growth of bacteria, reduce the source of "secondary pollution", and ensure the hygienic safety of food. In addition, the plastic accessories used in the refrigerator also have a requirement for crack resistance because the plastic accessories inside the refrigerator need to withstand low-temperature and ultra-low-temperature working environments. If the material is not tough enough, problems such as cracking and deformation are likely to occur.

[0003] Currently, the main raw materials of refrigerator plastic accessories are polystyrene (PS) and polypropylene (PP), which have the characteristics of high transparency, high hardness, simple production process, and low price, and are widely used in the production of accessories such as drawers and linings inside the refrigerator. However, these plastic accessories only have the advantages of general plastics and do not have the above-mentioned antibacterial and crack-resistant properties, and cannot meet the daily antibacterial and crack-resistant requirements of the refrigerator, especially for some high-end refrigerators. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation process for an antibacterial and crack-resistant plastic accessory for a refrigerator accessory, which solves the defect that the existing plastic accessories mainly made of polystyrene (PS) and polypropylene (PP) cannot meet the daily antibacterial and crack-resistant requirements of the refrigerator.

[0005] The present invention realizes the above purpose through the following technical solutions:

[0006] A preparation process for an antibacterial and crack-resistant plastic accessory for a refrigerator accessory, the steps include:

[0007] S1. Prepare Ag ion antibacterial particles for later use;

[0008] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, and functional additives, and mix them evenly in different proportions to obtain the blend materials for the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend material is 2.8 - 3.2%, the mass ratio in the transition layer blend material is 1.2 - 1.8%, and the mass ratio in the core layer blend material is 0.2 - 0.5%;

[0009] S3. Use a five-layer coextrusion die of a screw extruder for coextrusion, and the layers are arranged as skin layer - transition layer - core layer - transition layer - skin layer. The thickness ratios of each layer are 8 - 12%, 13 - 17%, 42 - 58%, 13 - 17%, and 8 - 12% respectively to obtain an extruded sheet;

[0010] S4. Take the extruded sheet and send it into a hot press. After hot pressing treatment, induce interlayer diffusion to form a blank with a gradient change in the doping amount of Ag ion antibacterial particles;

[0011] S5. Take the blank and through post-treatment, the antibacterial and crack-resistant plastic fitting is obtained.

[0012] The further improvement lies in that the specific operation of step S1 is as follows:

[0013] S1-1. Zeolite pretreatment

[0014] Take zeolite powder and soak it in an AgNO3 aqueous solution. Stir and react at 58 - 62 °C for 4 - 6 h. Through ion exchange, Ag ions are loaded on the surface of the zeolite powder, and then centrifuge and wash to remove free Ag ions. After drying, Ag@zeolite is obtained;

[0015] S1-2. SiO2 coating

[0016] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 12 - 14 h to generate a coated sphere with a core of Ag@zeolite and a mesoporous SiO2 coating layer on the shell;

[0017] S1-3. Surface modification

[0018] Soak the coated sphere in a 3-aminopropyltrimethoxysilane / ethanol solution, stir and react at 75 - 85 °C for 3 - 4 h to graft amino groups on the surface of the coated sphere. Then immerse the coated sphere in an AgNO3 aqueous solution and stir and react at room temperature for 2 - 3 h to adsorb Ag ions on the amino group-modified shell surface. Then centrifuge and wash to remove free Ag ions. After drying, Ag ion antibacterial particles are obtained.

[0019] The further improvement lies in that the particle size of the zeolite powder is 80 - 100 nm.

[0020] The further improvement lies in that in step S1-1, for every 1 g of zeolite powder, 90 - 120 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used;

[0021] In step S1-2, for every 1 g of Ag@zeolite, 480 - 520 mL of an ethanol / water solution with a volume concentration of 80% is used, 10 - 12 g of tetraethyl orthosilicate and 10 - 12 mL of ammonia water with a mass concentration of 28% are used;

[0022] In step S1-3, for every 1 g of the coated spheres, 10-12 mL of a 1% 3-aminopropyltrimethoxysilane / ethanol solution and 45-50 mL of an aqueous AgNO3 solution with a molar concentration of 0.01 M are used.

[0023] Further improvement lies in that the thickness of the mesoporous SiO2 coating layer is 18-25 nm, the pore diameter is 2-8 nm, and the porosity is 8-12%.

[0024] Further improvement lies in that in step S2, the so-called "mixing evenly" means adding each raw material into a high-speed mixer, first mixing at a speed of 300-400 rpm for 4-6 min, and then mixing at a speed of 800-1000 rpm for 8-12 min.

[0025] Further improvement lies in that in step S2, the functional aids include one or more of a transparent nucleating agent, a transparent antistatic agent, a transparent antioxidant, and a transparent lubricant.

[0026] Further improvement lies in that in step S3, the co-extrusion temperature is 180-220 °C and the screw speed is 200-300 rpm.

[0027] Further improvement lies in that in step S4, the temperature of the hot pressing treatment is 170-180 °C, the pressure is 8-12 MPa, and the heat preservation and pressure holding time is 4-6 min.

[0028] Further improvement lies in that in step S5, the post-treatment means annealing the billet in an oven at 70-80 °C for 1-2 h to eliminate internal stress, and then taking it out and naturally cooling it to room temperature.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) In the present invention, through multi-layer co-extrusion and hot pressing treatment, the doping amount of Ag ion antibacterial particles changes in a gradient manner, that is, the doping amount gradually decreases from the surface layer to the core layer in the thickness direction, while the doping amount is basically the same within the same thickness plane, making the fittings have both good antibacterial performance and excellent transparency, and at the same time reducing the Ag usage amount and lowering the cost;

[0031] (2) The present invention uses styrene-ethylene-butene-styrene block copolymer as a toughening agent, which has a refractive index close to that of the PP resin and good compatibility, making the anti-cracking effect of the fittings prominent and the transparency can be guaranteed at the same time;

[0032] (3) The present invention uses special Ag ion antibacterial particles, which have a core-shell double-layer structure and are loaded with Ag ions both inside and outside. Among them, the zeolite powder core is loaded with a large amount of Ag ions through ion exchange for reserve, and the mesoporous SiO2 shell with specific pore size, thickness and porosity serves as a slow-release channel and protective layer, enabling the reserved Ag ions to be released evenly. At the same time, the shell is surface-modified with 3-aminopropyltriethoxysilane, providing stable coordination sites to temporarily store the released Ag ions to meet the daily response antibacterial requirements, thereby enhancing the overall antibacterial effect; in addition, the SiO2 shell, as a low-refractive-index transition material, can reduce the overall scattering, further improve the transparency, and at the same time improve the compatibility with the matrix, enhancing the mechanical properties. Detailed implementation manners

[0033] The following further describes the present application in detail. It is necessary to point out here that the following specific implementation manners are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0034] I. Main raw materials:

[0035] Transparent PP resin: Select Metocene X50109 from BASF;

[0036] Styrene-ethylene-butene-styrene block copolymer: Select Kraton MD6932;

[0037] Transparent nucleating agent: Millad 3988;

[0038] Transparent antistatic agent: PELESTAT 230;

[0039] Transparent antioxidant: Irganox 1010;

[0040] Transparent lubricant: Butyl stearate.

[0041] II. Specific implementation experiments

[0042] The present invention sets the following Examples 1-3, and the raw material ratios in each example refer to Table 1 below:

[0043] Table 1: Raw material ratio table of Examples 1-3

[0044]

[0045] The specific process steps of Examples 1-3 are as follows:

[0046] Example 1

[0047] A preparation process for an antibacterial and crack-resistant plastic fitting for a refrigerator fitting, the steps including:

[0048] S1. Prepare Ag ion antibacterial particles for later use. The specific operation is as follows:

[0049] S1-1. Pretreatment of zeolite

[0050] Take zeolite powder with a particle size of 80±2 nm, soak it in an AgNO3 aqueous solution, stir and react at 58°C for 4 h. Through ion exchange, Ag ions are loaded on the surface of the zeolite powder, and then centrifugally washed to remove free Ag ions. After drying, Ag@zeolite is obtained; among them, for every 1 g of zeolite powder, 90 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used;

[0051] S1-2. SiO2 coating

[0052] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 12 h to generate a coated sphere with an inner core of Ag@zeolite and an outer shell of a mesoporous SiO2 coating layer; among them, for every 1 g of Ag@zeolite, 480 mL of an ethanol / water solution with a volume concentration of 80% is used, 10 g of tetraethyl orthosilicate and 10 mL of ammonia water with a mass concentration of 28% are used;

[0053] After detection, the thickness of the mesoporous SiO2 coating layer is 18±1 nm, the pore size distribution is 2-4 nm, and the porosity is 8.3%;

[0054] S1-3. Surface modification

[0055] Soak the coated sphere in a 3-aminopropyltrimethoxysilane / ethanol solution, stir and react at 75°C for 3 h to graft amino groups on the surface of the coated sphere, then immerse the coated sphere in an AgNO3 aqueous solution, stir and react at room temperature for 2 h to adsorb Ag ions on the amino-modified shell surface, and then centrifugally wash to remove free Ag ions. After drying, Ag ion antibacterial particles are obtained; among them, for every 1 g of the coated sphere, 10 mL of a 3-aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1% is used, and 45 mL of an AgNO3 aqueous solution with a molar concentration of 0.01 M is used.

[0056] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, and mix them evenly in different proportions. That is, add each raw material to a high-speed mixer, first mix at a speed of 300 rpm for 6 min, and then mix at a speed of 800 rpm for 12 min to obtain the blend materials for the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend material is 2.8%, the mass ratio in the transition layer blend material is 1.2%, and the mass ratio in the core layer blend material is 0.2%.

[0057] S3. Use a five-layer coextrusion die head of a screw extruder for coextrusion. The temperature settings for each coextrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 200 rpm, and the layer arrangement is surface layer - transition layer - core layer - transition layer - surface layer. The thickness ratios of each layer are 8%, 13%, 58%, 13%, and 8% respectively to obtain an extruded sheet.

[0058] S4. Take the extruded sheet and send it into a hot press for hot pressing treatment. The temperature of the hot pressing treatment is 170 °C, the pressure is 8 MPa, and the heat preservation and pressure holding time is 6 min to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles.

[0059] S5. Take the blank, put the blank into an oven at 70 °C for annealing for 2 h to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack-resistant plastic fitting.

[0060] Example 2

[0061] A preparation process for an antibacterial and crack-resistant plastic fitting for a refrigerator fitting, the steps include:

[0062] S1. Prepare Ag ion antibacterial particles for use. The specific operation is as follows:

[0063] S1-1. Zeolite pretreatment

[0064] Take zeolite powder with a particle size of 90 ± 2 nm, soak it in an AgNO3 aqueous solution, stir and react at 60 °C for 5 h, load Ag ions on the surface of the zeolite powder through ion exchange, then centrifuge and wash to remove free Ag ions, and dry to obtain Ag@zeolite; among them, for every 1 g of zeolite powder, 100 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used.

[0065] S1-2. SiO2 coating

[0066] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 13 h to form a coated sphere with an Ag@zeolite core and a mesoporous SiO2 coating layer; among them, for every 1 g of Ag@zeolite, 500 mL of an ethanol / water solution with a volume concentration of 80% is used, 11 g of tetraethyl orthosilicate and 11 mL of ammonia water with a mass concentration of 28% are used;

[0067] After testing, the thickness of the mesoporous SiO2 coating layer is 22 ± 1 nm, the pore size distribution is 3 - 5 nm, and the porosity is 9.2%;

[0068] S1-3. Surface modification

[0069] Immerse the coated sphere in a 3-aminopropyltrimethoxysilane / ethanol solution, stir and react at 80 °C for 3.5 h to graft amino groups on the surface of the coated sphere, then immerse the coated sphere in an AgNO3 aqueous solution, stir and react at room temperature for 2.5 h to adsorb Ag ions on the surface of the amino-modified shell layer, and then centrifuge and wash to remove free Ag ions. After drying, Ag ion antibacterial particles are obtained; among them, for every 1 g of the coated sphere, 11 mL of a 3-aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1% is used, and 48 mL of an AgNO3 aqueous solution with a molar concentration of 0.01 M is used.

[0070] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, mix them evenly in different proportions, that is, add each raw material to a high-speed mixer, first mix at a speed of 350 rpm for 5 min, and then mix at a speed of 900 rpm for 10 min to obtain the blends of the surface layer, transition layer, and core layer respectively. Among them, the mass proportion of the Ag ion antibacterial particles in the surface layer blend is 3.0%, in the transition layer blend is 1.5%, and in the core layer blend is 0.3%;

[0071] S3. Use a five-layer coextrusion die head of a screw extruder for coextrusion. The temperature settings of each coextrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 250 rpm, and the layer arrangement is surface layer - transition layer - core layer - transition layer - surface layer. The thickness ratios of each layer are 10%, 15%, 50%, 15%, and 10% respectively to obtain an extruded sheet;

[0072] S4. Take the extruded sheet and send it to a hot press for hot pressing treatment. The temperature of the hot pressing treatment is 175 °C, the pressure is 10 MPa, and the heat preservation and pressure holding time is 5 min to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles;

[0073] S5. Take the blank, put it into an oven at 75 °C for annealing for 1.5 h to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack-resistant plastic fitting.

[0074] Example 3

[0075] A preparation process for an antibacterial and crack-resistant plastic fitting for a refrigerator fitting, the steps include:

[0076] S1. Prepare Ag ion antibacterial particles for later use. The specific operation is as follows:

[0077] S1-1. Pretreatment of zeolite

[0078] Take zeolite powder with a particle size of 100 ± 2 nm, soak it in an AgNO3 aqueous solution, stir and react at 62 °C for 6 h, and load Ag ions on the surface of the zeolite powder through ion exchange. Then, centrifuge and wash to remove free Ag ions, and dry to obtain Ag@zeolite; among them, for every 1 g of zeolite powder, use 120 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M.

[0079] S1-2. SiO2 coating

[0080] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 14 h to generate a coated sphere with an Ag@zeolite core and a mesoporous SiO2 coating layer; among them, for every 1 g of Ag@zeolite, use 520 mL of an ethanol / water solution with a volume concentration of 80%, use 12 g of tetraethyl orthosilicate and 12 mL of ammonia water with a mass concentration of 28%.

[0081] After detection, the thickness of the mesoporous SiO2 coating layer is 25 ± 2 nm, the pore size distribution is 6 - 8 nm, and the porosity is 11.7%.

[0082] S1-3. Surface modification

[0083] Soak the coated sphere in a 3-aminopropyltrimethoxysilane / ethanol solution, stir and react at 85 °C for 4 h to graft amino groups on the surface of the coated sphere. Then, immerse the coated sphere in an AgNO3 aqueous solution, stir and react at room temperature for 3 h to adsorb Ag ions on the amino-modified shell surface. Then, centrifuge and wash to remove free Ag ions, and dry to obtain Ag ion antibacterial particles; among them, for every 1 g of the coated sphere, use 12 mL of a 3-aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1%, and use 50 mL of an AgNO3 aqueous solution with a molar concentration of 0.01 M.

[0084] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, and mix them evenly in different proportions. That is, add each raw material to a high-speed mixer, first mix at a speed of 400 rpm for 4 minutes, and then mix at a speed of 1000 rpm for 8 minutes to obtain the blends of the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend is 3.2%, the mass ratio in the transition layer blend is 1.8%, and the mass ratio in the core layer blend is 0.5%.

[0085] S3. Use a five-layer coextrusion die head of a screw extruder for coextrusion. The temperatures of each coextrusion zone are set to 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 300 rpm, and the arrangement of each layer is surface layer - transition layer - core layer - transition layer - surface layer. The thickness ratios of each layer are 12%, 17%, 42%, 17%, and 12% respectively to obtain an extruded sheet.

[0086] S4. Take the extruded sheet and send it into a hot press. After hot pressing treatment, the temperature of the hot pressing treatment is 180 °C, the pressure is 12 MPa, and the heat preservation and pressure holding time is 4 minutes to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles.

[0087] S5. Take the blank, put the blank into an 80 °C oven for annealing for 1 hour to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack-resistant plastic fitting.

[0088] On the basis of Example 2, adjust the raw material ratio and control all other process parameters unchanged to obtain the following Comparative Examples 1-3:

[0089] Table 2: Raw material ratios of Comparative Examples 1-3

[0090]

[0091] Comparative Example 4

[0092] A preparation process for an antibacterial and crack-resistant plastic fitting for a refrigerator fitting, the steps include:

[0093] S1. Prepare Ag ion antibacterial particles for use. The specific operation is as follows:

[0094] S1-1. Zeolite pretreatment

[0095] Take zeolite powder with a particle size of 90 ± 2 nm, soak it in an aqueous AgNO3 solution, stir and react at 60 °C for 5 h. Through ion exchange, Ag ions are loaded on the surface of the zeolite powder, and then centrifuged and washed to remove free Ag ions. After drying, Ag@zeolite is obtained; among them, for every 1 g of zeolite powder, 100 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used;

[0096] S1-2, SiO2 coating

[0097] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 13 h to form a coated sphere with an Ag@zeolite core and a mesoporous SiO2 coating layer on the shell; among them, for every 1 g of Ag@zeolite, 500 mL of an ethanol / water solution with a volume concentration of 80% is used, 11 g of tetraethyl orthosilicate and 11 mL of ammonia water with a mass concentration of 28% are used;

[0098] After testing, the thickness of the mesoporous SiO2 coating layer is 22 ± 1 nm, the pore size distribution is 3 - 5 nm, and the porosity is 9.2%;

[0099] S1-3, surface modification

[0100] Soak the coated sphere in a 3-aminopropyltrimethoxysilane / ethanol solution, stir and react at 80 °C for 3.5 h to graft amino groups on the surface of the coated sphere, and then immerse the coated sphere in an AgNO3 aqueous solution, stir and react at room temperature for 2.5 h to adsorb Ag ions on the surface of the amino-modified shell layer, and then centrifuge and wash to remove free Ag ions. After drying, Ag ion antibacterial particles are obtained; among them, for every 1 g of the coated sphere, 11 mL of a 3-aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1% is used, and 48 mL of an AgNO3 aqueous solution with a molar concentration of 0.01 M is used.

[0101] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, mix them evenly in different proportions, that is, add each raw material to a high-speed mixer, first mix at a speed of 350 rpm for 5 min, and then mix at a speed of 900 rpm for 10 min to obtain blends for the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend is 3.0%, in the transition layer blend is 1.5%, and in the core layer blend is 0.3%;

[0102] S3. Co - extrusion is carried out using a five - layer co - extrusion die head of a screw extruder. The temperature settings for each co - extrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 250 rpm, and the layer arrangement is skin - transition layer - core layer - transition layer - skin. The thickness ratios of each layer are 20%, 20%, 20%, 20%, and 20% respectively, to obtain an extruded sheet;

[0103] S4. Take the extruded sheet and send it into a hot press. After hot - pressing treatment, the temperature of the hot - pressing treatment is 175 °C, the pressure is 10 MPa, and the heat - preservation and pressure - holding time is 5 min to induce inter - layer diffusion and form a blank with a gradient change in the doping amount of Ag - ion antibacterial particles;

[0104] S5. Take the blank, put the blank into an oven at 75 °C for annealing for 1.5 h to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack - resistant plastic fitting.

[0105] Comparative Example 5

[0106] A preparation process for an antibacterial and crack - resistant plastic fitting for a refrigerator fitting, the steps include:

[0107] S1. Prepare Ag - ion antibacterial particles for use. The specific operation is as follows:

[0108] Take zeolite powder with a particle size of 90 ± 2 nm, soak it in an AgNO3 aqueous solution, stir and react at 60 °C for 5 h. Through ion exchange, Ag ions are loaded on the surface of the zeolite powder, and then centrifuged and washed to remove free Ag ions. After drying, Ag@zeolite is obtained and directly used as Ag - ion antibacterial particles; among them, for every 1 g of zeolite powder, 100 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used;

[0109] S2. Take transparent PP resin, Ag - ion antibacterial particles, styrene - ethylene - butene - styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, and mix them evenly in different proportions. That is, add each raw material to a high - speed mixer, first mix at a speed of 350 rpm for 5 min, and then mix at a speed of 900 rpm for 10 min to obtain the blends for the skin layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag - ion antibacterial particles in the skin - layer blend is 3.0%, the mass ratio in the transition - layer blend is 1.5%, and the mass ratio in the core - layer blend is 0.3%;

[0110] S3. Co - extrusion is carried out using a five - layer co - extrusion die head of a screw extruder. The temperature settings for each co - extrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 250 rpm, and the layer arrangement is skin - transition layer - core layer - transition layer - skin. The thickness ratios of each layer are 10%, 15%, 50%, 15%, and 10% respectively, to obtain an extruded sheet;

[0111] S4. Feed the extruded sheet into a hot press for hot pressing treatment at a temperature of 175 °C, a pressure of 10 MPa, and a heat preservation and pressure holding time of 5 min to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles;

[0112] S5. Take the blank, put it into an oven at 75 °C for annealing for 1.5 h to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack - resistant plastic fitting.

[0113] Comparative Example 6

[0114] A preparation process of an antibacterial and crack - resistant plastic fitting for refrigerator fittings, the steps include:

[0115] S1. Prepare Ag ion antibacterial particles for use. The specific operation is as follows:

[0116] S1 - 1. Zeolite pretreatment

[0117] Take zeolite powder with a particle size of 90 ± 2 nm, soak it in an AgNO3 aqueous solution, stir and react at 60 °C for 5 h, load Ag ions on the surface of the zeolite powder through ion exchange, then centrifuge and wash to remove free Ag ions, and dry to obtain Ag@zeolite; among them, for every 1 g of zeolite powder, 100 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used;

[0118] S1 - 2. SiO2 coating

[0119] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 13 h to generate a coated sphere with a core of Ag@zeolite and a mesoporous SiO2 coating layer on the shell; among them, for every 1 g of Ag@zeolite, 500 mL of an ethanol / water solution with a volume concentration of 80% is used, 11 g of tetraethyl orthosilicate and 11 mL of ammonia water with a mass concentration of 28% are used;

[0120] After detection, the thickness of the mesoporous SiO2 coating layer is 22 ± 1 nm, the pore size distribution is 3 - 5 nm, and the porosity is 9.2%;

[0121] S1 - 3. Surface modification

[0122] Soak the coated sphere in a 3 - aminopropyltrimethoxysilane / ethanol solution, stir and react at 80 °C for 3.5 h to graft amino groups on the surface of the coated sphere, and then wash and dry to obtain Ag ion antibacterial particles; among them, for every 1 g of the coated sphere, 11 mL of a 3 - aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1% is used.

[0123] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, and mix them evenly in different proportions. That is, add each raw material to a high-speed mixer, first mix at a speed of 350 rpm for 5 minutes, and then mix at a speed of 900 rpm for 10 minutes to obtain the blends of the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend is 3.0%, the mass ratio in the transition layer blend is 1.5%, and the mass ratio in the core layer blend is 0.3%.

[0124] S3. Use a five-layer coextrusion die of a screw extruder for coextrusion. The temperature settings of each coextrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 250 rpm, and the arrangement of each layer is surface layer - transition layer - core layer - transition layer - surface layer. The thickness ratios of each layer are 10%, 15%, 50%, 15%, and 10% respectively to obtain an extruded sheet.

[0125] S4. Take the extruded sheet and send it to a hot press. After hot pressing treatment, the temperature of the hot pressing treatment is 175 °C, the pressure is 10 MPa, and the heat preservation and pressure holding time is 5 minutes to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles.

[0126] S5. Take the blank, put the blank in an oven at 75 °C for annealing for 1.5 hours to eliminate internal stress, and then take it out and cool it naturally to room temperature to obtain the antibacterial and crack-resistant plastic fitting.

[0127] Comparative Example 7

[0128] A preparation process for an antibacterial and crack-resistant plastic fitting for a refrigerator fitting, the steps include:

[0129] S1. Prepare Ag ion antibacterial particles for use. The specific operation is as follows:

[0130] S1-1. Zeolite pretreatment

[0131] Take zeolite powder with a particle size of 90 ± 2 nm, soak it in an AgNO3 aqueous solution, stir and react at 60 °C for 5 hours, load Ag ions on the surface of the zeolite powder through ion exchange, and then centrifuge and wash to remove free Ag ions, and dry to obtain Ag@zeolite; among them, for every 1 g of zeolite powder, 100 mL of an AgNO3 aqueous solution with a molar concentration of 0.1 M is used.

[0132] S1-2. SiO2 coating

[0133] Disperse the Ag@zeolite in an ethanol / water solution, add tetraethyl orthosilicate and ammonia water, and stir and react at room temperature for 13 h to form a coated sphere with an Ag@zeolite core and a mesoporous SiO2 coating layer; among them, for every 1 g of Ag@zeolite, 500 mL of an ethanol / water solution with a volume concentration of 80% is used, 11 g of tetraethyl orthosilicate and 11 mL of ammonia water with a mass concentration of 28% are used;

[0134] After testing, the thickness of the mesoporous SiO2 coating layer is 22 ± 1 nm, the pore size distribution is 3 - 5 nm, and the porosity is 9.2%;

[0135] S1-3. Surface loading

[0136] Immerse the coated spheres in an AgNO3 aqueous solution, stir and react at room temperature for 2.5 h to adsorb Ag ions on the surface of the shell layer, then centrifuge and wash to remove free Ag ions, and obtain Ag ion antibacterial particles after drying; among them, for every 1 g of coated spheres, 48 mL of an AgNO3 aqueous solution with a molar concentration of 0.01 M is used.

[0137] S2. Take transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butene-styrene block copolymer, transparent nucleating agent, transparent antistatic agent, transparent antioxidant, and transparent lubricant, mix them evenly in different proportions, that is, add each raw material to a high-speed mixer, first mix at a speed of 350 rpm for 5 min, and then mix at a speed of 900 rpm for 10 min to obtain blends for the surface layer, transition layer, and core layer respectively. Among them, the mass ratio of the Ag ion antibacterial particles in the surface layer blend is 3.0%, the mass ratio in the transition layer blend is 1.5%, and the mass ratio in the core layer blend is 0.3%;

[0138] S3. Use a five-layer coextrusion die head of a screw extruder for coextrusion. The temperature settings for each coextrusion zone are 180 °C, 200 °C, and 220 °C in sequence, the screw speed is 250 rpm, and the layer arrangement is surface layer - transition layer - core layer - transition layer - surface layer. The thickness ratios of each layer are 10%, 15%, 50%, 15%, and 10% respectively to obtain an extruded sheet;

[0139] S4. Take the extruded sheet and send it to a hot press for hot pressing treatment. The temperature of the hot pressing treatment is 175 °C, the pressure is 10 MPa, and the heat preservation and pressure holding time is 5 min to induce interlayer diffusion and form a blank with a gradient change in the doping amount of Ag ion antibacterial particles;

[0140] S5. Take the blank, place the blank in an oven at 75 °C for annealing for 1.5 h to eliminate internal stress, and then take it out and cool naturally to room temperature to obtain the antibacterial and crack-resistant plastic fitting.

[0141] III. Performance testing

[0142] (1) Antibacterial performance test

[0143] Test equipment and reagents: Bacterial strains: Staphylococcus aureus (ATCC6538) and Escherichia coli (ATCC 25922); Strain culture: Nutrient Broth and Nutrient Agar; Phosphate Buffered Saline (PBS, pH 7.2): used to dilute the bacterial suspension; PBS neutralizing solution containing 0.5% Tween 80: used to terminate the action of the antibacterial agent; Test container: 90mm Petri dish; Incubator: Temperature control: 35 ± 1°C, humidity ≥ 90% RH (for incubation contact).

[0144] Specific test steps: Take the plastic samples prepared in Examples 1 - 3 and Comparative Examples 1 - 7, cut them into sheets of 50×50×1mm, clean the sample surface with ethanol to remove contaminants, and air dry for later use; Inoculate the bacterial strain in Nutrient Broth and culture it at 37°C for 25h, take the culture solution and dilute it with PBS to a concentration of 1×10 5 CFU / mL; Divide the samples into two groups, one group is placed in a low-temperature box at -20 ± 1°C for 1h after preparation, and the other group is placed in a low-temperature box at -20 ± 1°C for 30 days after preparation; Put the two groups of samples into sterile Petri dishes respectively, evenly drop 0.4mL of the bacterial suspension on the sample surface, with a coverage area of about 40×40mm, cover the liquid drop with a sterile polyethylene film to avoid evaporation, ensure full contact between the bacteria and the material surface, and place the Petri dish in an incubator at 35 ± 1°C and humidity ≥ 90% for 24h; After incubation, add 10mL of the neutralizing solution, scrape the bacteria on the sample surface with a sterile cotton swab and elute them, dilute the eluate by 10 -1 times, take 1mL of the diluted solution and spread it on a Nutrient Agar plate, culture the plate at 37°C for 36h, and count the number of colonies CFU. In addition, set a positive control group (sterile glass slide instead of the sample) to conduct the same test.

[0145] Calculate the antibacterial rate of each sample, and the calculation results are statistically obtained in Table 3 below. The calculation formula is as follows:

[0146]

[0147] In the formula: U t is the number of bacteria in the positive control; A t is the number of bacteria after contact with the sample.

[0148] (2) Anti-cracking performance test

[0149] Test equipment: Instron Ceast 9050 pendulum impact tester, low-temperature environmental chamber (temperature control range at least -40°C to room temperature, accuracy ±1°C).

[0150] Specific test steps: Take the plastic samples prepared in Examples 1-3 and Comparative Examples 1-7, with at least 5 samples in each group. Cut each group of samples into plates with a length of 63.5 mm, a width of 12.5 mm, and a thickness of 3.0 mm, and cut an A-type notch (radius 0.25 mm, depth 2.54 mm) at the middle position of the sample length edge; then place all the samples in a low-temperature chamber at -20 ± 1°C for 36 h to simulate the environment of a refrigerator freezer; take out the samples from the low-temperature chamber and install them on the fixture within 10 seconds, ensuring that the notch faces away from the pendulum impact direction, and the long axis of the sample is perpendicular to the impact direction, and clamp the sample; then release the pendulum to freely fall and impact the back of the sample notch, and record the impact energy value (the energy absorbed by the pendulum during the complete fracture of the sample).

[0151] Calculate the impact strength of each sample to evaluate its low-temperature impact fracture resistance. The greater the impact strength, the better the low-temperature impact fracture resistance of the sample. The calculation results are statistically obtained in Table 4 below. The calculation formula is as follows:

[0152]

[0153] (3) Transparency test

[0154] Test equipment: Use a UV-Vis spectrophotometer (PerkinElmer Lambda 950) for detection.

[0155] Specific test steps: Take the plastic samples prepared in the examples and comparative examples. Cut each group of samples into specimens with a size of 50×50 mm and a thickness of 2 mm, and polish the surface to Ra < 0.1 μm. Under the condition of no sample, use air as a reference to calibrate the instrument to 100% transmittance. Then place each specimen in the sample holder, ensure that the light beam is perpendicular to the incidence, scan the full wavelength range, and record the transmittance and haze value at 550 nm (the wavelength sensitive to the human eye). The recorded results are statistically obtained in Table 5 below.

[0156] IV. Result analysis

[0157] (1) Test results of antibacterial performance

[0158] Table 3: Test results of antibacterial performance

[0159]

[0160]

[0161] (2) Test results of anti-cracking performance

[0162] Table 4: Results of anti-cracking performance test

[0163]

[0164] (3) Results of transparency test

[0165] Table 5: Results of transparency test

[0166]

[0167]

[0168] Result analysis:

[0169] Examples 1 - 3 of the present invention all show good performance in antibacterial property, anti-cracking property and transparency. Especially for Example 2, in terms of antibacterial property, the antibacterial rate reaches 99.9% after 1 hour, and the decrease of antibacterial rate is not obvious after 30 days. Analyzing the reason, it is found that through the adjustment of process parameters in Example 2, a mesoporous SiO2 shell with appropriate pore size, thickness and porosity is formed, which is used as a slow-release channel and protective layer, so that the antibacterial rate can be maintained for a long time; the impact strength of Example 2 reaches 213.5 J / m, which is relatively leading in the industry. In terms of transparency, the light transmittance can reach 92.0% and the haze value is 8.4%, which is also very excellent, minimizing the impact of adding antibacterial particles with zeolite powder as the carrier on transparency.

[0170] Comparative Examples 1 - 7 are all adjustments made on the basis of Example 2, among which:

[0171] Comparative Example 1 still adopts the five-layer co-extrusion technology, but the ratio of all raw materials including Ag ion antibacterial particles in each layer is the same, and the dosage of each raw material is the weighted (thickness) average value of each layer in Example 2, that is, the overall raw material ratio of the sample is the same, only the distribution of raw materials is different. From the results, compared with Example 2, the antibacterial rate at 1 hour and after 30 days has decreased to a certain extent, which is due to the lower content distribution of Ag ion antibacterial particles on the surface layer, while the anti-cracking property and transparency change not significantly. This shows that the scheme of gradient distribution of Ag ion antibacterial particles adopted in the present invention can improve the antibacterial property of plastic fittings, and at the same time can maintain high anti-cracking property and transparency.

[0172] Comparative Example 2 only increases the dosage of Ag ion antibacterial particles in each layer on the basis of Example 2. It is found that the improvement of its antibacterial rate is not obvious compared with Example 2, indicating that too many Ag ion antibacterial particles have little effect, but its anti-cracking property decreases and the transparency also decreases significantly. This shows that even if the gradient distribution scheme is adopted, an appropriate doping amount of Ag ion antibacterial particles still needs to be taken. An excessive doping amount is obviously not beneficial and the cost increases.

[0173] In Comparative Example 3, only the dosage of Ag ion antibacterial particles in each layer was reduced as a whole on the basis of Example 2. It was found that its antibacterial rate decreased significantly compared with Example 2. At the same time, its anti-cracking performance and transparency improved, but not significantly. This shows that too small a doping amount of Ag ion antibacterial particles will seriously affect the antibacterial rate.

[0174] In Comparative Example 4, the five-layer coextrusion technology was still used, and the doping amount of Ag ion antibacterial particles in each layer was distributed in a gradient manner. However, the thickness of each layer was equal, that is, the thickness ratios of the surface layer and the transition layer were significantly increased compared with Example 2. It was found that its antibacterial rate was comparable to that of Example 2, but its anti-cracking performance decreased, and its transparency decreased significantly. This shows that an appropriate thickness ratio is also very crucial.

[0175] In Comparative Example 5, Ag@zeolite was not coated and modified, but directly used as Ag ion antibacterial particles. As a result, its antibacterial performance at 1 h was better, but the antibacterial rate after 30 days decreased significantly, indicating that its antibacterial performance could not be maintained for a long time. In addition, its anti-cracking performance and transparency also decreased significantly. The reason was analyzed that the loss of the SiO2 outer shell as a transition material increased the overall scattering, decreased the transparency, and the fusion effect between materials also became worse, affecting the mechanical properties. This shows that the Ag ion antibacterial particles with a core-shell structure adopted in the present invention have achieved unexpected technical effects.

[0176] In Comparative Example 6, the SiO2 outer shell of the Ag ion antibacterial particles was not secondarily loaded with Ag ions, resulting in a significant decrease in its antibacterial rate (Staphylococcus aureus) at 1 h to 91.2%, and the antibacterial rate after 30 days increased to 96.2%. The reason was analyzed that there was no Ag ion loading on the outer surface of the initial particles, and only a small amount of released Ag ions, resulting in insufficient antibacterial performance. After 30 days, the Ag ions were stably released, and the antibacterial effect recovered, but it was still lower than the level of Example 2. This shows that the secondary loading of Ag ions is very important for the initial antibacterial rate.

[0177] In Comparative Example 7, the SiO2 outer shell of the Ag ion antibacterial particles was not surface grafted and modified with 3-aminopropyltrimethoxysilane. The results showed that the antibacterial rate after 30 days decreased significantly. The reason was analyzed that the outer surface lost the ligand sites, and the Ag ions released through the channels could not be stably retained, resulting in the lack of the action of Ag ions when sterilization was required. In addition, in terms of anti-cracking performance and transparency, Comparative Example 7 was basically equivalent to Example 2, without obvious disadvantages.

[0178] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A process for preparing antibacterial and anti-cracking plastic accessories for refrigerator accessories, characterized in that the steps include: S1, preparing Ag ion antibacterial particles for later use; S2, taking transparent PP resin, Ag ion antibacterial particles, styrene-ethylene-butylene-styrene block copolymer and functional additives, mixing them evenly in different proportions to obtain blends of the surface layer, transition layer and core layer, wherein the mass proportion of the Ag ion antibacterial particles in the surface layer blend is 2.8-3.2%, the mass proportion in the transition layer blend is 1.2-1.8%, and the mass proportion in the core layer blend is 0.2-0.5%; S3, using a five-layer co-extrusion die head of a screw extruder for co-extrusion, and the layers are arranged as surface layer-transition layer-core layer-transition layer-surface layer, and the thickness of each layer accounts for 8-12%, 13-17%, 42-58%, 13-17%, and 8-12%, respectively, to obtain an extruded sheet; S4, taking the extruded sheet and feeding it into a hot press, and subjecting it to hot pressing treatment to induce interlayer diffusion, thereby forming a blank with a gradient change in the doping amount of Ag ion antibacterial particles; S5. Take the blank and perform post-processing to obtain the antibacterial and anti-cracking plastic accessory.

2. The process for preparing an antibacterial and anti-cracking plastic accessory for refrigerator accessories according to claim 1, characterized in that: The specific operations of step S1 are: S1-1. Zeolite pretreatment Take zeolite powder, soak it in AgNO3 aqueous solution, stir and react at 58-62℃ for 4-6h, load Ag ions on the surface of zeolite powder by ion exchange, then centrifuge and wash to remove free Ag ions, and obtain Ag@zeolite after drying; S1-2, SiO2 coating The Ag@zeolite is dispersed in an ethanol / water solution, ethyl orthosilicate and ammonia water are added, and the mixture is stirred at room temperature for 12-14 hours to generate a coated sphere having an Ag@zeolite core and a mesoporous SiO2 coating layer as an outer shell; S1-3. Surface modification The coated balls are immersed in 3-aminopropyltrimethoxysilane / ethanol solution, stirred and reacted at 75-85°C for 3-4 hours to graft amino groups on the surface of the coated balls. The coated balls are then immersed in AgNO3 aqueous solution, stirred and reacted at room temperature for 2-3 hours to allow Ag ions to adsorb on the surface of the amino-modified shell layer. The free Ag ions are removed by centrifugal washing, and Ag ion antibacterial particles are obtained after drying.

3. The process for preparing an antibacterial and anti-cracking plastic accessory for a refrigerator accessory according to claim 2, characterized in that: The particle size of the zeolite powder is 80-100 nm.

4. The process for preparing an antibacterial and anti-cracking plastic accessory for a refrigerator accessory according to claim 2, characterized in that: In step S1-1, for every 1 g of zeolite powder, 90-120 mL of an aqueous solution of AgNO3 having a molar concentration of 0.1 M is used; In step S1-2, for every 1 g of Ag@zeolite, 480-520 mL of 80% ethanol / water solution by volume, 10-12 g of ethyl orthosilicate and 10-12 mL of 28% ammonia water by mass are used; In step S1-3, for every 1 g of coated spheres, 10-12 mL of 3-aminopropyltrimethoxysilane / ethanol solution with a mass concentration of 1% and 45-50 mL of AgNO3 aqueous solution with a molar concentration of 0.01 M are used.

5. The process for preparing an antibacterial and anti-cracking plastic accessory for refrigerator accessories according to claim 2, characterized in that: The thickness of the mesoporous SiO2 coating layer is 18-25 nm, the pore diameter is 2-8 nm, and the porosity is 8-12%.

6. The process for preparing an antibacterial and anti-cracking plastic accessory for a refrigerator accessory according to claim 1, characterized in that: The uniform mixing in step S2 refers to adding the raw materials into a high-speed mixer, first mixing at a speed of 300-400 rpm for 4-6 min, and then mixing at a speed of 800-1000 rpm for 8-12 min.

7. The process for preparing an antibacterial and anti-cracking plastic accessory for refrigerator accessories according to claim 1, characterized in that: In step S2, the functional additive includes one or more of a transparent nucleating agent, a transparent antistatic agent, a transparent antioxidant, and a transparent lubricant.

8. The process for preparing an antibacterial and anti-cracking plastic accessory for a refrigerator accessory according to claim 1, characterized in that: In step S3, the co-extrusion temperature is 180-220°C, and the screw speed is 200-300rpm.

9. The process for preparing an antibacterial and anti-cracking plastic accessory for a refrigerator accessory according to claim 1, characterized in that: In step S4, the temperature of the hot pressing treatment is 170-180°C, the pressure is 8-12MPa, and the heat preservation and pressure holding time is 4-6min.

10. The process for preparing an antibacterial and anti-cracking plastic accessory for refrigerator accessories according to claim 1, characterized in that: In step S5, the post-treatment refers to placing the blank in a 70-80°C oven for annealing for 1-2 hours to eliminate internal stress, and then taking it out and naturally cooling it to room temperature.

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