A plastic housing for protecting electrical appliances and a manufacturing method thereof

Abstract

The present invention relates to the technical field of plastic shells, and discloses a plastic shell for protecting electrical appliances and a manufacturing method thereof. The plastic shell comprises the following raw materials: polypropylene, a compound flame retardant, a reinforcing additive, sodium dodecylbenzenesulfonate, antioxidant 1076, oxidized polyethylene wax; wherein the compound flame retardant uses polylactic acid-glycolic acid copolymer as a carbon source, 2-amino-4,6-dihydroxypyrimidine as a gas source, and ethyl dichlorophosphate as an acid source to synthesize a "three-source integrated" intumescent flame retardant, significantly improving the flame retardant performance of the plastic shell; the reinforcing additive is prepared by grafting 7-hydroxycoumarin onto the surface of sisal fiber, effectively enhancing the mechanical strength of the plastic shell. The comprehensive exertion of these properties greatly broadens the application field of the plastic shell and extends the overall service life of the electrical appliance.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic shells, and particularly relates to a plastic shell for protecting electrical appliances and a manufacturing method thereof. Background Art

[0002] With the progress of technology and the improvement of people's living standards, electrical appliances have gradually become an integral part of people's lives. Plastics are widely used in electrical equipment due to their unique performance advantages and processing convenience. The shell is an important component of an electrical appliance, and its main function is to provide physical protection for the electrical appliance. Currently, most electrical appliance shells are plastic shells. By wrapping the internal components and circuit boards of the electrical appliance, the plastic shell can prevent environmental factors such as external impacts, dust, and moisture from damaging the electrical appliance, thereby extending the service life and stability of the electrical appliance.

[0003] Polypropylene has become the preferred material for preparing electrical appliance shells due to its advantages such as light weight, non-toxicity, odorlessness, good insulation, low price, and easy processing. With the development of science and technology, people's performance requirements for electrical appliance shells have become increasingly strict. During the use of electrical appliances, open flames or high temperatures may be generated due to situations such as electric arcs, sparks, or short circuits. Polypropylene is a flammable material, and during the combustion process, it will produce molten droplets, releasing a large amount of heat and toxic gases, thus causing fire accidents and restricting its application in a wider range of fields. Therefore, the plastic shell needs to have excellent flame retardant properties. In addition, the existing plastic shells of electrical appliances need to have excellent mechanical strength to resist external impacts and extrusion, prevent damage to the electrical appliance caused by collisions or extrusion during transportation, installation, and use, better isolate and protect the circuits and components inside the electrical appliance, and thus extend the overall service life of the electrical appliance.

[0004] In the prior art, optimizing the base material is one of the main ways to improve the performance of plastic shells. For example, the invention patent with the publication number CN113444317B discloses a preparation method of a high-gloss flame-retardant polypropylene material. The invention uses the prepared 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide grafted glycidyl as a flame retardant component and participates in the preparation process of the polypropylene material, making the prepared polypropylene material have relatively excellent flame retardancy and can be widely used in manufacturing electrical appliance shells such as household appliances, outdoor electrical appliances, and industrial and mining electrical appliances, with high economic value and social benefits. Therefore, the plastic shell can be modified by preparing a filling component with excellent flame retardant properties and mechanical strength to obtain a high-performance plastic shell. Summary of the Invention

[0005] In order to solve the problems mentioned in the background art, the purpose of the present invention is to provide a plastic shell for protecting electrical appliances and a manufacturing method thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A plastic shell for protecting electrical appliances, comprising raw materials in the following parts by weight: 60-70 parts of polypropylene, 4-6 parts of compound flame retardant, 5-9 parts of reinforcing additive, 1-3 parts of sodium dodecylbenzenesulfonate, 1-2 parts of antioxidant 1076, and 2-3 parts of oxidized polyethylene wax.

[0008] Further, the preparation method of the compound flame retardant comprises the following steps:

[0009] A1: Under nitrogen protection, mix polylactic acid-glycolic acid copolymer, 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution, stir evenly, then add an activator and a condensing agent. After adding, raise the temperature to 65-75 °C, keep stirring for 4-7 h, stop heating and remove nitrogen, and discharge after cooling to room temperature to obtain an intermediate material;

[0010] A2: Add the intermediate material and ethyl acetate into a reactor filled with nitrogen in sequence. After stirring evenly, add ethyl dichlorophosphate and a promoter, and raise the temperature of the system to 60-70 °C under stirring conditions, keep warm for 3-6 h, wait for the material to cool naturally, and discharge to obtain the compound flame retardant.

[0011] Further, in step A1, the activator is any one of 1-hydroxybenzotriazole, 4-dimethylaminopyridine or N-hydroxysuccinimide.

[0012] Further, in step A1, the condensing agent is any one of N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N,N'-diisopropylcarbodiimide.

[0013] Further, in step A2, the promoter is any one of pyridine or triethylamine.

[0014] Further, the preparation method of the reinforcing additive comprises the following steps:

[0015] AA1: Ultrasonically disperse sisal fibers in toluene solution to form a dispersion liquid. Under continuous nitrogen conditions, add halogenated isocyanate and dibutyltin dilaurate to the dispersion liquid, stir evenly, react at 50-70 °C for 2-4 h. After the reaction is completed, centrifuge to separate the solid material, wash the solid material, and dry it under vacuum to obtain modified sisal fibers;

[0016] AA2: Add the modified sisal fibers into N,N-dimethylformamide, ultrasonically treat for 20-40 min, introduce nitrogen, then add 7-hydroxycoumarin and triethylamine. After adding, turn on the heating. After the temperature of the system reaches 70-80 °C, keep stirring at a constant temperature for 5-7 h, filter, collect the product, wash it, and dry it to obtain the reinforcing additive.

[0017] Further, in step AA1, the halo isocyanate is any one of 2-chloroethyl isocyanate or 3-chloropropyl isocyanate.

[0018] Further, in step AA2, the mass ratio of the modified sisal fiber to 7-hydroxycoumarin is 1:0.1 - 0.3.

[0019] A method for manufacturing a plastic shell for protecting electrical appliances includes the following steps:

[0020] Step 1: Add polypropylene, a compound flame retardant, a reinforcing additive, sodium dodecylbenzenesulfonate, antioxidant 1076, and oxidized polyethylene wax into a high-speed kneader, knead at 110 - 120 °C for 30 - 50 min, and then place it in a cooling mixer to cool to 30 - 40 °C to obtain a mixed material.

[0021] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel at 80 - 90 °C, the second zone at 130 - 160 °C, the third zone at 170 - 180 °C, the fourth zone at 120 - 140 °C, and the head temperature at 170 - 180 °C to obtain masterbatch.

[0022] Step 3: Inject mold the masterbatch obtained above through an injection molding machine to obtain a plastic shell.

[0023] Further, in step 3, the process conditions for the injection molding are: control the material temperature for injection at 180 - 220 °C, the injection pressure at 40 - 60 MPa, and the injection speed at 20 - 40 mm / s.

[0024] Advantages of the present invention:

[0025] (1) By adding a compound flame retardant and a reinforcing additive during the preparation of the plastic shell, the limiting oxygen index of the prepared plastic shell can reach up to 32.6%, the tensile strength can reach up to 53.4 MPa, and the impact strength can reach up to 32.6 KJ / m 2 , having good flame retardant properties and mechanical strength, greatly broadening the application field of the plastic shell and extending the overall service life of the electrical appliance.

[0026] (2) During the preparation process of the plastic shell of the present invention, a compound flame retardant is added, which can significantly improve the flame retardant performance of the plastic shell. The poly(lactic-co-glycolic acid) copolymer in the compound flame retardant can serve as a carbon source, 2-amino-4,6-dihydroxypyrimidine can serve as a gas source, and diethyl chlorophosphate can serve as an acid source to synthesize an intumescent flame retardant of "three sources in one". During a fire, a dense foam carbon layer can be formed, generating a large amount of non-toxic and non-combustible gases. Through adsorption, these gases are added to the foam carbon layer, making this layer flame-retardant, heat-insulating, and oxygen-insulating, ultimately preventing the spread and propagation of the flame, avoiding fire accidents caused by the combustion of the plastic shell due to electric arcs, sparks, or short circuits during the use of electrical appliances, and broadening its application in a wider range of fields.

[0027] (3) By preparing a reinforcing additive as an enhancer for the plastic shell, after the sisal fiber is organically modified, it has good interfacial properties with the polypropylene matrix and can be relatively uniformly dispersed in the polypropylene matrix, forming a good filling effect. On the one hand, by utilizing the advantages of the sisal fiber, the mechanical strength of the plastic shell can be effectively improved, avoiding damage to the electrical appliance caused by collision or extrusion during transportation, installation, and use, and better isolating and protecting the circuits and components inside the electrical appliance. On the other hand, the rigid rings grafted on the surface of the sisal fiber can further play a strengthening role, enabling the prepared plastic shell to have excellent mechanical strength, thereby extending the overall service life of the electrical appliance.

[0028] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 It is the infrared spectrum test chart of the intermediate material and the compound flame retardant prepared in Example 1 of the present invention.

[0031] Figure 2 It is the infrared spectrum test chart of the reinforcing additive prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Example 1

[0034] I. Preparation of compound flame retardant

[0035] A1: Under nitrogen protection, 5 g of poly (lactic-co-glycolic acid), 1.2 g of 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution were mixed and stirred evenly. Then, 0.08 g of 4-dimethylaminopyridine and 0.05 g of N,N'-diisopropylcarbodiimide were added. After the addition, the temperature was raised to 70 °C, and the mixture was stirred for 6 h. The heating was stopped and the nitrogen was removed. After cooling to room temperature, the intermediate material was discharged.

[0036] A2: 5 g of the intermediate material and ethyl acetate were successively added to a reactor filled with nitrogen. After stirring evenly, 1.4 g of ethyl dichlorophosphate and 0.1 g of triethylamine were added. Under stirring conditions, the temperature of the system was raised to 65 °C and kept for 4 h. After the material was naturally cooled, it was discharged to obtain the compound flame retardant.

[0037] The intermediate material and the compound flame retardant were analyzed by infrared spectroscopy using a WQF-200 Fourier transform infrared spectrometer from Beijing Rayleigh Analytical Instrument Co., Ltd. As Figure 1 shown, it can be seen from Figure 1 that in the infrared spectrum of the intermediate material, an absorption peak of the hydroxyl group O-H appears at 3280 cm -1 , an absorption peak of N-H in the amide bond appears at 3324 cm -1 , an absorption peak of C=O in the amide bond appears at 1655 cm -1 , an absorption peak of C=O of the ester group appears at 1760 cm -1 , an absorption peak of C-N appears at 1409 cm -1 , and an absorption peak of C=N appears at 1605 cm -1 ; in the infrared spectrum of the compound flame retardant, an absorption peak of N-H in the amide bond appears at 3310 cm -1 , an absorption peak of C=O in the amide bond appears at 1650 cm -1 , an absorption peak of C=O of the ester group appears at 1765 cm -1 , an absorption peak of C-N appears at 1415 cm -1 , an absorption peak of C=N appears at 1610 cm -1 and an absorption peak appears at 1280 cm-1 An absorption peak of P=O appeared at 1061 cm -1 An absorption peak characteristic of P-O-C appeared at this position.

[0038] Technical principle: In the compound flame retardant, first, due to the presence of an active amino substituent in the structure of 2-amino-4,6-dihydroxypyrimidine, under the action of 4-dimethylaminopyridine and N,N'-diisopropylcarbodiimide, it can undergo an amidation reaction with the carboxyl active functional group in the structure of poly(lactic-co-glycolic acid) copolymer, thereby introducing 2-amino-4,6-dihydroxypyrimidine into the structure of poly(lactic-co-glycolic acid) copolymer to obtain an intermediate material; second, under the action of triethylamine, the hydroxyl group in the structure of the intermediate material can further react with the phosphoryl chloride group in the structure of ethyl dichlorophosphate to obtain the compound flame retardant.

[0039] II. Preparation of the reinforcing additive

[0040] AA1: Ultrasonically disperse 3 g of sisal fiber in a toluene solution to form a dispersion. Under a continuous nitrogen atmosphere, add 0.8 g of 2-chloroethyl isocyanate and 0.03 g of dibutyltin dilaurate to the dispersion, stir evenly, react at 60 °C for 3 h. After the reaction is completed, centrifuge to separate the solid material, wash the solid material, and dry it under vacuum to obtain modified sisal fiber;

[0041] AA2: Add 3 g of modified sisal fiber to N,N-dimethylformamide, ultrasonically treat for 30 min, introduce nitrogen, then add 1 g of 7-hydroxycoumarin and 0.05 g of triethylamine. After adding, start heating. After the system temperature reaches 75 °C, stir at a constant temperature for 6 h, filter, collect the product, wash it, and dry it to obtain the reinforcing additive.

[0042] Use the WQF-200 Fourier transform infrared spectrometer of Beijing Rayleigh Analytical Instrument Co., Ltd. to perform infrared spectral analysis on the reinforcing additive. As Figure 2 shown, it can be seen from Figure 2 that in the infrared spectrum of the reinforcing additive, an absorption peak of -NH in the urethane group appeared at 3330 cm -1 An absorption peak of C=O in the urethane group appeared at 1691 cm -1 An absorption peak of C-H on the benzene ring appeared at 3050 cm -1 An absorption peak of ether bond C-O-C appeared at 1040 cm -1 at this position.

[0043] Technical principle: In the reinforcing additive, first, under the catalysis of dibutyltin dilaurate, the hydroxyl groups on the surface of sisal fibers react with the isocyanate groups in the structure of 2-chloroethyl isocyanate, thereby modifying halogen functional groups on the surface of sisal fibers to obtain modified sisal fibers; second, under the action of triethylamine, using the halogen functional groups on the surface of sisal fibers as active sites, and based on the mechanism that halogen functional groups can undergo substitution reactions with the hydroxyl groups in the structure of 7-hydroxycoumarin, 7-hydroxycoumarin is grafted onto the surface of sisal fibers to prepare the reinforcing additive.

[0044] III. Preparation of Plastic Shell

[0045] Step 1: Add 60 g of polypropylene, 4 g of compound flame retardant, 5 g of reinforcing additive, 1 g of sodium dodecylbenzenesulfonate, 1 g of antioxidant 1076, and 2 g of oxidized polyethylene wax into a high-speed kneader, knead at 110 °C for 30 min, and then place it in a cooling mixer to cool to 30 °C to obtain a mixed material.

[0046] Step 2: Add the above-obtained mixed material into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel to 80 °C, the second zone to 130 °C, the third zone to 170 °C, the fourth zone to 120 °C, and the head temperature to 170 °C to obtain masterbatch.

[0047] Step 3: Inject and mold the above-obtained masterbatch through an injection molding machine, control the material temperature of injection to be 180 °C, the injection pressure to be 40 MPa, and the injection speed to be 40 mm / s to obtain a plastic shell.

[0048] Example 2

[0049] Preparation of Plastic Shell

[0050] Step 1: Add 65 g of polypropylene, 5 g of compound flame retardant, 7 g of reinforcing additive, 2 g of sodium dodecylbenzenesulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115 °C for 40 min, and then place it in a cooling mixer to cool to 35 °C to obtain a mixed material.

[0051] Step 2: Add the above-obtained mixed material into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel to 85 °C, the second zone to 145 °C, the third zone to 175 °C, the fourth zone to 130 °C, and the head temperature to 175 °C to obtain masterbatch.

[0052] Step 3: Inject and mold the above-obtained masterbatch through an injection molding machine, control the material temperature of injection to be 200 °C, the injection pressure to be 50 MPa, and the injection speed to be 50 mm / s to obtain a plastic shell.

[0053] The preparation methods of the compound flame retardant and the reinforcing additive are the same as those in Example 1.

[0054] Example 3

[0055] Preparation of the plastic shell

[0056] Step 1: Add 70 g of polypropylene, 6 g of the compound flame retardant, 9 g of the reinforcing additive, 3 g of sodium dodecylbenzenesulfonate, 2 g of antioxidant 1076, and 3 g of oxidized polyethylene wax into a high-speed kneader, knead at 120 °C for 50 min, and then place it in a cooling mixer to cool to 40 °C to obtain a mixed material.

[0057] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel to 90 °C, the second zone to 160 °C, the third zone to 180 °C, the fourth zone to 140 °C, and the head temperature to 180 °C to obtain masterbatch.

[0058] Step 3: Inject and mold the masterbatch obtained above through an injection molding machine. Control the material temperature of injection to be 220 °C, the injection pressure to be 60 MPa, and the injection speed to be 60 mm / s to obtain the plastic shell.

[0059] The preparation methods of the compound flame retardant and the reinforcing additive are the same as those in Example 1.

[0060] Comparative Example 1

[0061] Preparation of the plastic shell

[0062] Step 1: Add 65 g of polypropylene, 5 g of the compound flame retardant, 2 g of sodium dodecylbenzenesulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115 °C for 40 min, and then place it in a cooling mixer to cool to 35 °C to obtain a mixed material.

[0063] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel to 85 °C, the second zone to 145 °C, the third zone to 175 °C, the fourth zone to 130 °C, and the head temperature to 175 °C to obtain masterbatch.

[0064] Step 3: Inject and mold the masterbatch obtained above through an injection molding machine. Control the material temperature of injection to be 200 °C, the injection pressure to be 50 MPa, and the injection speed to be 50 mm / s to obtain the plastic shell.

[0065] The preparation method of the compound flame retardant is the same as that in Example 1.

[0066] Comparative Example 2

[0067] Preparation of the plastic shell

[0068] Step 1: Add 65 g of polypropylene, 7 g of reinforcing additive, 2 g of sodium dodecylbenzenesulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115°C for 40 min, and then place it in a cooling mixer to cool to 35°C to obtain a mixed material;

[0069] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel at 85°C, the second zone at 145°C, the third zone at 175°C, the fourth zone at 130°C, and the head temperature at 175°C to obtain masterbatch;

[0070] Step 3: Inject and mold the masterbatch obtained above through an injection molding machine, control the material temperature of injection at 200°C, the injection pressure at 50 MPa, and the injection speed at 50 mm / s to obtain a plastic shell.

[0071] The preparation method of the reinforcing additive is the same as that in Example 1.

[0072] Comparative Example 3

[0073] Preparation of Plastic Shell

[0074] Step 1: Add 65 g of polypropylene, 5 g of compound flame retardant, 5 g of sisal fiber, 2 g of 7-hydroxycoumarin, 2 g of sodium dodecylbenzenesulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115°C for 40 min, and then place it in a cooling mixer to cool to 35°C to obtain a mixed material;

[0075] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel at 85°C, the second zone at 145°C, the third zone at 175°C, the fourth zone at 130°C, and the head temperature at 175°C to obtain masterbatch;

[0076] Step 3: Inject and mold the masterbatch obtained above through an injection molding machine, control the material temperature of injection at 200°C, the injection pressure at 50 MPa, and the injection speed at 50 mm / s to obtain a plastic shell.

[0077] The preparation method of the compound flame retardant is the same as that in Example 1.

[0078] Comparative Example 4

[0079] Preparation of Plastic Shell

[0080] Step 1: Add 65 g of polypropylene, 2 g of sodium dodecylbenzenesulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115 °C for 40 min, and then place it in a cooling mixer and cool to 35 °C to obtain a mixed material;

[0081] Step 2: Add the mixed material obtained above into a granulator for extrusion granulation. Set the temperature of the first zone of the granulator barrel to 85 °C, the second zone to 145 °C, the third zone to 175 °C, the fourth zone to 130 °C, and the head temperature to 175 °C to obtain masterbatch;

[0082] Step 3: Inject the masterbatch obtained above through an injection molding machine. Control the material temperature of injection molding to 200 °C, the injection pressure to 50 MPa, and the injection speed to 50 mm / s to obtain a plastic shell.

[0083] Performance testing:

[0084] Make the plastic shells prepared in Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention into samples that meet the specifications. According to GB / T 2406.2-2009 "Plastics - Determination of burning behavior by the oxygen index method - Part 2: Room temperature test", conduct combustion performance tests on the samples to evaluate the flame retardant performance of the plastic shells; according to GB / T 1040.1-2018 "Plastics - Determination of tensile properties - Part 1: General principles", conduct tensile strength tests on the samples; according to GB / T1843-2008 "Plastics - Determination of Izod impact strength", conduct impact strength tests on the samples. The specific test results are shown in Table 1:

[0085] Table 1 - Performance test

[0086] Limiting oxygen index (%) Tensile strength (MPa) <![CDATA[Impact strength (KJ / m 2 )]]> Example 1 32.3 52.6 32.1 Example 2 32.6 53.4 32.6 Example 3 31.9 52.1 31.8 Comparative example 1 29.4 41.8 22.9 Comparative example 2 22.5 49.5 29.7 Comparative example 3 30.2 44.3 25.3 Comparative example 4 19.7 39.7 20.2

[0087] It can be seen from the test results in Table 1 that the plastic shells prepared in Examples 1 to 3 are added with a compound flame retardant and a reinforcing additive. The limiting oxygen index of the plastic shells is higher than 30%, the tensile strength is higher than 50 MPa, and the impact strength is higher than 30 KJ / m 2, all have excellent flame retardancy and mechanical strength; in the plastic shell prepared in Comparative Example 1, no reinforcing additive was added, and compared with the examples, the mechanical strength of the plastic shell was relatively poor; in the plastic shell prepared in Comparative Example 2, no compound flame retardant was added, and the limiting oxygen index decreased significantly, and the flame retardancy of the plastic shell was inferior to that of the examples; in the plastic shell prepared in Comparative Example 3, a compound flame retardant, sisal fiber and 7-hydroxycoumarin were added. Compared with the examples, the plastic shell had better flame retardancy, but the mechanical strength was average. It is speculated that this may be because the surface of the sisal fiber was not modified, and its compatibility with the matrix was poor, resulting in a decrease in the mechanical strength of the plastic shell; in the plastic shell prepared in Comparative Example 4, no compound flame retardant and reinforcing additive were added, so the flame retardancy and mechanical strength of this plastic shell were the worst.

[0088] The above content is only an example and explanation of the concept of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution. As long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A plastic casing for protecting an electrical appliance, characterized in that: The invention comprises the following raw materials in parts by weight: 60 to 70 parts of polypropylene, 4 to 6 parts of compound flame retardant, 5 to 9 parts of reinforcing additive, 1 to 3 parts of sodium dodecylbenzene sulfonate, 1 to 2 parts of antioxidant 1076, and 2 to 3 parts of oxidized polyethylene wax; The composite flame retardant is firstly prepared by using 2-amino-4,6-dihydroxypyrimidine to react with the carboxyl active functional group in the structure of polylactic acid-glycolic acid copolymer to obtain an intermediate material, and the intermediate material is further reacted with ethyl dichlorophosphate to obtain the intermediate material; The reinforcing additive is firstly obtained by reacting the hydroxyl group on the surface of the sisal fiber with the isocyanate group in the structure of 2-chloroethyl isocyanate to obtain modified sisal fiber, and the modified sisal fiber is further obtained by substitution reaction with 7-hydroxycoumarin.

2. A plastic casing for protecting an electrical appliance according to claim 1, characterized in that: The preparation method of the composite flame retardant comprises the following steps: A1: Under nitrogen protection, polylactic acid-glycolic acid copolymer, 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution are mixed and stirred evenly, and then an activator and a condensing agent are added. After the addition is completed, the temperature is raised to 65-75°C, and the mixture is stirred for 4-7 hours at the same temperature. The heating is stopped and the nitrogen is removed. The mixture is cooled to room temperature and then discharged to obtain an intermediate material. A2: The intermediate material and ethyl acetate are added to a reactor filled with nitrogen in sequence. After stirring evenly, ethyl dichlorophosphate and an accelerator are added. Under stirring conditions, the system temperature is raised to 60-70°C and kept warm for 3-6 hours. After the material is cooled naturally, the material is discharged to obtain a compound flame retardant.

3. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A1, the activator is any one of 1-hydroxybenzotriazole, 4-dimethylaminopyridine or N-hydroxysuccinimide.

4. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A1, the condensing agent is any one of N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N,N'-diisopropylcarbodiimide.

5. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A2, the promoter is any one of pyridine or triethylamine.

6. A plastic casing for protecting an electrical appliance according to claim 1, characterized in that: The preparation method of the reinforcing additive comprises the following steps: AA1: ultrasonically dispersing sisal fiber in a toluene solution to form a dispersion, adding 2-chloroethyl isocyanate and dibutyltin dilaurate to the dispersion under continuous nitrogen conditions, stirring evenly, reacting at 50-70° C. for 2-4 hours, and after the reaction is completed, centrifuging to separate solid materials, washing the solid materials, and vacuum drying to obtain modified sisal fiber; AA2: Add modified sisal fiber to N,N-dimethylformamide, ultrasonically treat for 20 to 40 minutes, introduce nitrogen, and then add 7-hydroxycoumarin and triethylamine. After the addition is completed, turn on the heating. After the system temperature reaches 70 to 80°C, stir at a constant temperature for 5 to 7 hours, filter, collect the product, wash, and dry to obtain a reinforcing additive.

7. A plastic casing for protecting an electrical appliance according to claim 6, characterized in that: In step AA2, the mass ratio of the modified sisal fiber to 7-hydroxycoumarin is 1:0.1-0.

3.

8. A method for manufacturing a plastic casing for protecting an electrical appliance as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Add polypropylene, compound flame retardant, reinforcing additive, sodium dodecylbenzene sulfonate, antioxidant 1076, and oxidized polyethylene wax into a high-speed kneader, knead at 110-120° C. for 30-50 minutes, and then place in a cooling mixer and cool to 30-40° C. to obtain a mixed material; Step 2: Add the obtained mixture into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 80-90°C, the temperature of the second zone to 130-160°C, the temperature of the third zone to 170-180°C, the temperature of the fourth zone to 120-140°C, and the head temperature to 170-180°C to obtain masterbatch; Step 3: The masterbatch obtained above is injection molded by an injection molding machine to obtain a plastic shell.

9. A method for manufacturing a plastic casing for protecting an electrical appliance according to claim 8, characterized in that: In step three, the process conditions of the injection molding are: controlling the injection material temperature to be 180-220° C., the injection pressure to be 40-60 MPa, and the injection speed to be 20-40 mm / s.

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