A core-shell structure flame retardant, a preparation method thereof and an application thereof in preparing a low smoke density material

Abstract

The present invention discloses a core-shell structure flame retardant, a preparation method thereof and an application thereof in the preparation of a low smoke density material. The flame retardant comprises a structure with polytetrafluoroethylene as the core and styrene-polymerized PAN-based carbon fiber as the shell. In the present invention, the flame retardant has styrene-polymerized PAN-based carbon fiber as the shell and polytetrafluoroethylene as the core, which can not only accelerate the formation of a carbon layer during combustion, but also improve the dispersion ability of polytetrafluoroethylene in the matrix resin and improve the mechanical properties of the PC material.

Description

Technical Field

[0001] The present invention relates to a flame retardant, and particularly to a core-shell structure flame retardant, a preparation method thereof, and an application thereof in the preparation of a low-smoke density material. Background Art

[0002] Polycarbonate (PC) is an engineering plastic with very wide applications, having excellent impact toughness, flame retardancy, electrical insulation, heat resistance, gloss, and dimensional stability. In addition to being used in the manufacture of traditional products such as electronic and electrical appliances, 3C products, and household appliances, some modified polycarbonates are also applied in high-end fields such as aerospace and rail transit. These fields pay particular attention to safety, so the requirements for the smoke density index of the used PC alloy materials are very high. Since PC contains a relatively high proportion of benzene rings in its molecular structure and has a low oxygen index, it is extremely prone to incomplete combustion and generate a large amount of smoke during the combustion process; in addition, PC softens when burning and is prone to curling under the action of strong thermal radiation, thereby increasing the heating and combustion area, making the combustion intense and the smoke generation more severe.

[0003] Currently, there are mainly three types of methods to reduce the smoke density of PC materials. One is to increase the oxygen index of the material, such as PC + filler, PC + PEI, PC + PEEK; the second is to introduce an intumescent flame retardant to inhibit smoke generation, such as PC + phosphorus-based flame retardant; the third is to use special copolymerized PC. These methods not only have limited effects on improving the smoke density, but also cause a decline in the performance of PC materials or an increase in cost to varying degrees. Introducing fillers and phosphorus-based flame retardants will reduce the mechanical properties of PC materials; introducing PEI (polyethyleneimine) and PEEK (polyetheretherketone) will reduce the fluidity of PC materials and significantly increase the cost; using special copolymerized PC requires design and adjustment at the polymerization end, making the product customization difficult and the use very limited.

[0004] Patent CN102863770A discloses a low-smoke density PC / ABS alloy and a preparation method thereof, which introduces nano-hydrotalcite to make the smoke density of the product less than 75. However, this patent does not mention that the introduction of nano-hydrotalcite will reduce the mechanical properties of the material. The loss of the mechanical properties of PC materials will limit their applications very much, and improving the mechanical properties by introducing auxiliaries such as toughening agents will further exacerbate the smoke generation during combustion.

[0005] Patent CN106488954A discloses a polycarbonate composition, a preparation method thereof, and articles thereof, which introduce enhanced mineral fillers, phosphorus-containing flame retardants, and polyetherimide to make the smoke density and heat release rate of the product reach the HL2 level. However, the introduction of the above substances inevitably causes a decline in the fluidity, heat resistance, and mechanical properties of PC products, and the cost will also increase significantly.

[0006] There is no report on jointly improving combustion state and accelerating carbon formation while well maintaining the mechanical properties of PC materials. Summary of the Invention

[0007] To solve the above technical problems, the present invention first proposes a core-shell structure flame retardant and its preparation method. In the flame retardant of the present invention, polytetrafluoroethylene is used as the core and styrene-polymerized PAN-based carbon fiber is used as the shell, which can not only accelerate the formation of a carbon layer during combustion, but also improve the dispersion ability of polytetrafluoroethylene in the matrix resin and improve the mechanical properties of PC materials.

[0008] The present invention also proposes an application of the core-shell structure flame retardant in the preparation of low-smoke density materials, especially PC alloys. By introducing the above core-shell structure flame retardant into the PC resin, the obtained PC alloy has a very low smoke density and well retains the mechanical properties and heat resistance of the PC material.

[0009] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0010] A core-shell structure flame retardant, comprising a structure with polytetrafluoroethylene as the core and styrene-polymerized PAN-based carbon fiber as the shell.

[0011] As a preferred embodiment, the mass ratio of the core to the shell structure in the flame retardant is (4-28):(60-100).

[0012] As a preferred embodiment, in the styrene-polymerized PAN-based carbon fiber, the mass ratio of styrene to PAN-based carbon fiber is (30-40):(30-60).

[0013] As a preferred embodiment, the PAN-based carbon fiber is selected from one or a mixture of more of homopolymer polyacrylonitrile-based carbon fiber and copolymer polyacrylonitrile-based carbon fiber;

[0014] Preferably, the carbon content of the PAN-based carbon fiber is 50-90 wt%, preferably 60-80 wt%; the average particle size is 10-80 μm, preferably 40-60 μm.

[0015] As a preferred embodiment, the molecular weight of the polytetrafluoroethylene is between 500,000 and 2 million, preferably 800,000 and 1.5 million.

[0016] When the shell layer of the flame retardant provided by the present invention is subjected to shear force during the modification process, it will crack, and the internal polytetrafluoroethylene will be fibrillated to achieve the coating of carbon fibers. When the product burns, the carbon fibers are rearranged to play a role of skeleton support, and the polytetrafluoroethylene shrinks around the direction of the carbon fibers when heated, maintaining the flatness of the product and being able to efficiently reduce smoke generation. It has the characteristic of low smoke density when applied in PC alloys, and can retain the mechanical properties and heat resistance of PC alloys.

[0017] The present invention also provides a preparation method of a core-shell structure flame retardant, which includes the following steps:

[0018] 1) Add polytetrafluoroethylene emulsion, initiator A, emulsifier and water into a reaction kettle, heat up to 70-80 °C under an inert gas atmosphere, stir well for 10-40 min, then add a small amount of styrene monomer, control the temperature at 75-90 °C and the pressure at 2-4 Mpa, and discharge the pressure and release the material after reacting for 1-3 h to obtain a core layer emulsion;

[0019] 2) Add styrene, PAN-based carbon fiber, initiator A, initiator B, and catalyst to the core layer emulsion prepared in step 1) and mix and heat them. A core-shell structure emulsion is obtained through atom transfer radical polymerization (ATRP method); the reaction temperature is 60-80 °C, preferably 65-75 °C; the reaction time is 0.5-3 h, preferably 1-2 h; the polymerization reaction is carried out under an inert gas atmosphere, and the reaction pressure is 1-2 MPa;

[0020] 3) Add a demulsifier to the core-shell structure copolymer emulsion prepared in step 2) and stir to demulsify it. Then, after washing, separating, and drying, add it to acetone to dissolve and refine it, and finally dropwise add ethanol to precipitate, obtaining a core-shell structure flame retardant.

[0021] As a preferred embodiment, in the method, the dosage of each raw material is specifically as follows by mass parts:

[0022]

[0023] Among them, the solid content of the polytetrafluoroethylene emulsion is 40-70%, and the preferred particle size is 20-40 μm;

[0024] Preferably, the dosage of styrene in step 1) accounts for 1 / 6-1 / 3 of its total mass;

[0025] Preferably, the dosage of initiator A in step 1) accounts for 1 / 4-1 / 2 of its total mass.

[0026] Preferably, the dosage of water in step 1) is 4-8 times the mass of the polytetrafluoroethylene emulsion, preferably 5-6 times.

[0027] Preferably, in step 3), the addition amount of acetone is 20 - 50 times the mass of the core - shell structure copolymer, the addition amount of ethanol is 1 / 10 - 1 / 2 of the volume of acetone, the system temperature is controlled at 10 - 30 °C when adding ethanol dropwise, and the precipitation time is 1 - 5 h.

[0028] As a preferred embodiment, the emulsifier is selected from any one or more of styrene - maleic anhydride copolymer, fatty acid polyoxyethylene ether, polyvinyl alcohol, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecyl sulfonate, and alkyl polyether;

[0029] Preferably, the initiator A is selected from any one or more of potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile, benzoyl peroxide, di - tert - butyl peroxide, potassium ammonium persulfate, sodium bisulfite, or ammonium bisulfite;

[0030] Preferably, the initiator B is selected from one or more of carbon tetrachloride, tert - butyl bromoisobutyrate, and polyazoester;

[0031] Preferably, the catalyst is one or two of the complex of ferric chloride and succinic acid and the complex of cuprous bromide and bipyridine; the dosage of the catalyst is preferably 0.1 - 1.5 wt% of the mass of the PAN - based carbon fiber, preferably 0.5 - 1 wt%;

[0032] Preferably, the demulsifier is selected from sulfate solutions of alkali metals or alkaline earth metals, preferably aqueous solutions of potassium sulfate, sodium sulfate, and magnesium sulfate, more preferably an aqueous solution of magnesium sulfate with a concentration of 1 - 3 mol / L; further preferably, the dosage of the demulsifier is 1 - 5 wt% of the mass of the polytetrafluoroethylene emulsion.

[0033] In the preparation method of the core - shell structure flame retardant provided by the present invention, the PAN - based carbon fiber is selected from one or more mixtures of homopolymer polyacrylonitrile - based carbon fiber and copolymer polyacrylonitrile - based carbon fiber; preferably, the carbon content of the PAN - based carbon fiber is 50 - 90 wt%, preferably 60 - 80 wt%; the average particle size is 10 - 80 μm, preferably 40 - 60 μm. Preferably, the molecular weight of the polytetrafluoroethylene is between 500,000 and 2,000,000, preferably 800,000 - 1,500,000.

[0034] Through the preparation method of the core - shell structure flame retardant provided by the present invention, the core - shell structure flame retardant has a powdery solid appearance and a particle size of 300 - 800 nm.

[0035] The present invention also provides an application of the core - shell structure flame retardant as described above or the core - shell structure flame retardant prepared by the method as described above in the preparation of low - smoke - density materials, especially in PC alloys.

[0036] The present invention also provides a low-smoke-density PC alloy, which comprises the following component raw materials by weight:

[0037] PC resin, 80-95 parts, preferably 85-90 parts;

[0038] Flame retardant, 2-20 parts, preferably 5-15 parts;

[0039] Antioxidant, 0-1 part, preferably 0.1-0.3 part;

[0040] Lubricant, 0-1 part, preferably 0.1-0.4 part,

[0041] The flame retardant is the core-shell structure flame retardant described above or the core-shell structure flame retardant prepared by the method described above;

[0042] Preferably, the PC resin is selected from any one or more of aromatic polycarbonates and aliphatic polycarbonates. Preferably, under the test conditions of 300 °C and a load of 1.2 kg, the melt flow index MFR is between 3-30 g / 10 min, preferably between 5-25 g / 10 min, more preferably between 7-15 g / 10 min. Further preferably, it is bisphenol A type PC resin, and even more preferably any one or more of Wanhua Chemical 2070, 2100, 2150, and 2220;

[0043] Preferably, the antioxidant is selected from any one or more of hindered phenols, phosphites, thioesters, benzofurans, acryloyl-modified phenols, and hydroxylamines. Preferably, it is any one or more of Irganox 1076, Irganox1010, and Irganox 168;

[0044] Preferably, the lubricant is selected from any one or more of fatty alcohols, metal soaps, fatty acids, fatty acid esters, montanic acid and its derivatives, amide waxes, saturated hydrocarbons, polyolefin waxes and their derivatives, organosilicons and silicone powders, and organofluorines. Preferably, it is any one or at least two combinations of fatty acid esters and organosilicons, and more preferably fatty acid esters.

[0045] As a feasible implementation scheme for preparing the low-smoke-density PC alloy in the present invention, for example:

[0046] 1) Mix the PC resin, core-shell structure flame retardant, antioxidant, and lubricant evenly with a high-speed mixer;

[0047] 2) Add the mixture in step 1) to the main feed hopper, and melt-extrude and pelletize it through a twin-screw extruder to obtain the PC alloy.

[0048] Preferably, the PC resin is dried before use. The drying temperature of the material is 80-120°C, preferably 100-120°C, and it is dried until the water content is less than 0.5wt%, preferably less than 0.3wt%.

[0049] Preferably, the mixing speed in the high-speed mixer is 200-600 rpm, and the mixing time is 30-90 s.

[0050] Preferably, the temperature of the twin-screw extrusion is 240-310°C. The temperature is set in sections from the feeding port to the die head as follows: the feeding port is 240-260°C, each of the first to fourth sections is independently 280-290°C, and each of the fifth to seventh sections is independently 290-310°C. Preferably, the first to fourth sections are 285°C, and the fifth to seventh sections are 295°C.

[0051] For the extrusion operation, the screw speed can be controlled at 400-800 rpm, the vacuum degree of the vacuum device in the metering section of the twin-screw is controlled to be less than -0.4 Mpa, and the temperature of the cooling water tank is 40-80°C.

[0052] Compared with the prior art, the present invention has the following technical advantages:

[0053] In the existing low-smoke-density PC, the smoke suppression effect is not obvious, and it inevitably causes the attenuation of other properties of the PC material. The PC alloy synthesized in the present invention solves this problem in two aspects: First, the PAN-based carbon fiber shell layer of the synthesized core-shell structure flame retardant rearranges when heated, playing a role of skeleton support, avoiding the problem of softening and curling of the PC material during combustion, reducing the heating and combustion area, and at the same time better ensuring the mechanical properties of the material; Second, the synthesized core-shell structure flame retardant enables the better dispersion of the core layer of polytetrafluoroethylene. Polytetrafluoroethylene shrinks around the carbon fiber direction during combustion, accelerating carbon formation and suppressing smoke generation. Description of the Drawings

[0054] Figure 1 It is the combustion morphology diagram of the samples prepared in Example 4 and Comparative Examples 5-9 after the smoke density test. Detailed Embodiments

[0055] The following further illustrates the present invention through specific embodiments. The embodiments described in the present invention are only for the illustration of the present invention and do not limit the scope of the present invention.

[0056] I. In the examples and comparative examples, the sources of the main raw materials are as shown in Table 1 below:

[0057] Table 1 Information on the Sources of Raw Materials

[0058]

[0059]

[0060] Unless otherwise specified, other raw materials and reagents were obtained through commercial channels on the market.

[0061] Second, in the examples and comparative examples, the performance test parameters of the PC alloy and the corresponding test methods are as follows:

[0062] The processing equipment used was: a twin-screw extruder, KraussMaffei ZE28 x40D BD, with a length-to-diameter ratio of 40 and a screw diameter of 28 cm;

[0063] The injection molding equipment used was: Haitian injection molding machine MA600 / 100, with a length-to-diameter ratio of 24 and a screw diameter of 22 cm.

[0064] The performance test parameters of the PC alloy and the corresponding test methods are as follows:

[0065] Particle size: Measured using a particle size analyzer: During the propagation of light, it is calculated by the limitation of the wavefront by pores or particles on the order of the wavelength scale;

[0066] Impact strength (MPa): Measured using ISO 180-2000 "Plastics - Determination of Izod impact strength";

[0067] Heat distortion temperature (°C): Measured using ISO 75 / B "Plastics - Methods of test for heat distortion temperature";

[0068] Heat release rate (kW / m 2 ): Measured using ISO 5660-1 "Heat release rate (cone calorimeter method)" for "50 KW / m 2 radiant heat, non-flaming combustion mode";

[0069] Smoke density: Measured using ISO 5659-2 "Determination of optical density in a single smoke chamber" for "50 KW / m 2 radiant heat, non-flaming combustion mode";

[0070] Combustion morphology: After the smoke density test, the combustion morphology of the sample was photographed and recorded. The higher the bulge of the sample, the more intense the combustion.

[0071] Characterization method for the core-shell structure flame retardant: The prepared core-shell structure toughener was observed using a transmission electron microscope. Before the test, the toughener was diluted and mixed with distilled water. A small amount of the mixed solution was sucked with a pipette and dropped onto a copper mesh, stained with a 2% phosphotungstic acid solution, the excess stain was blotted with filter paper, and after natural drying, the structure and particle size were observed under the transmission electron microscope.

[0072]

Example 1

[0073] The method for preparing the core-shell structure flame retardant (T1) was:

[0074] 1) Add 12 g of polytetrafluoroethylene emulsion (solid content 70%), 0.3 g of potassium persulfate, 6 g of sodium dodecylbenzenesulfonate, and 72 g of water into a 1000 ml three-necked flask equipped with a stirrer. Heat it to 70 °C under an inert gas atmosphere, stir thoroughly for 40 min, then add 6 g of styrene monomer, heat it to 80 °C, control the pressure at 2 Mpa, relieve the pressure and discharge the material after reacting for 1 h to obtain the core layer emulsion;

[0075] 2) Add 12 g of styrene monomer, 24 g of homopolymer PAN-based carbon fiber, 0.3 g of potassium persulfate, 0.6 g of carbon tetrachloride, 0.03 g of a catalyst of ferric chloride and succinic acid complex (mass ratio 1:1) into the flask in step 1). Heat it to 70 °C under an argon atmosphere, control the pressure at 1 MPa, and carry out polymerization reaction for 1 h by ATRP method to obtain a core-shell structure emulsion;

[0076] 3) Add the core-shell structure copolymer emulsion in step 2) into 5 g of an aqueous solution of MgSO4 with a concentration of 1 mol / L, carry out demulsification by mechanical stirring at a rotation speed of 300 rpm at a temperature of 75 °C, then wash, filter by suction, and dry to obtain a pre-product; Add all the pre-product into 200 ml of acetone until it is completely dissolved, control the temperature at 30 °C, dropwise add 50 ml of an ethanol solution with a purity of 80 wt% to precipitate the product, carry out suction filtration and drying after precipitation for 2 h to obtain the core-shell structure flame retardant powder T1.

[0077] Transmission electron microscopy (TEM) shows that the T1 flame retardant has an obvious core-shell structure, the dark part is the shell, the light part is the core, and the particle size is uniform, with an average particle size of about 350 nm.

[0078]

Example 2

[0079] The method for preparing the core-shell structure flame retardant (T2) is as follows:

[0080] 1) Add 13.5 g of polytetrafluoroethylene emulsion (solid content 50%), 0.2 g of sodium persulfate, 18 g of sodium dodecyl sulfate, and 108 g of water into a 1000 ml three-necked flask equipped with a stirrer. Heat it to 75 °C under an inert gas atmosphere, stir thoroughly for 20 min, then add 7.2 g of styrene monomer, heat it to 90 °C, control the pressure at 3 Mpa, relieve the pressure and discharge the material after reacting for 2 h to obtain the core layer emulsion;

[0081] 2) Add 21.6 g of styrene monomer, 49.5 g of copolymer PAN-based carbon fiber, 0.3 g of sodium persulfate, 0.2 g of tert-butyl bromoisobutyrate, 0.05 g of copper bromide and bipyridine complex catalyst (mass ratio 1:1) into the flask in step 1). Heat it to 60 °C under an argon atmosphere, control the pressure at 2 Mpa, and carry out polymerization reaction for 2 h by ATRP method to obtain a core-shell structure emulsion;

[0082] 3) Add the core-shell structured copolymer emulsion from step 2) to 4 g of an aqueous solution of NaSO4 with a concentration of 2 mol / L, and carry out demulsification by mechanical stirring at a rotation speed of 200 rpm at a temperature of 85 °C. Then, through washing with water, suction filtration, and drying, a pre-product is obtained; add all of the pre-product to 300 ml of acetone until it is completely dissolved, control the temperature at 20 °C, and dropwise add 150 ml of an ethanol solution with a purity of 85 wt% to precipitate the product. After precipitation for 3 h, carry out suction filtration and drying to obtain the core-shell structured flame retardant powder T2.

[0083] Transmission electron microscopy (TEM) shows that the T2 flame retardant has an obvious core-shell structure, with the dark part being the shell and the light part being the core, and the particle size is uniform, with an average particle size of about 400 nm.

[0084]

Example 3

[0085] The method for preparing the core-shell structured flame retardant (T3) is as follows:

[0086] 1) Add 36 g of polytetrafluoroethylene emulsion (solid content 40%), 0.6 g of ammonium persulfate, 6 g of sodium dodecyl sulfonate, and 144 g of water to a 1000 ml three-necked flask equipped with a stirrer. Under an inert gas atmosphere, heat up to 80 °C, stir well for 10 min, then add 9.6 g of styrene monomer, heat up to 70 °C, control the pressure at 4 Mpa, and after reacting for 3 h, relieve the pressure and discharge the material to obtain the core layer emulsion;

[0087] 2) Add 38.4 g of styrene monomer, 36 g of homopolymer PAN-based carbon fiber, 1.8 g of ammonium persulfate, 1.8 g of polyazoester, 0.12 g of copper bromide and bipyridine complex catalyst (mass ratio 1:1) to the flask in step 1). Under an argon atmosphere, heat up to 80 °C, control the pressure at 1.5 MPa, and carry out polymerization reaction for 1 h by ATRP method to obtain the core-shell structured emulsion;

[0088] 3) Add the core-shell structured copolymer emulsion from step 2) to 10 g of an aqueous solution of K2SO4 with a concentration of 3 mol / L, and carry out demulsification by mechanical stirring at a rotation speed of 100 rpm at a temperature of 65 °C. Then, through washing with water, suction filtration, and drying, a pre-product is obtained; add all of the pre-product to 400 ml of acetone until it is completely dissolved, control the temperature at 10 °C, and dropwise add 80 ml of an ethanol solution with a purity of 90 wt% to precipitate the product. After precipitation for 4 h, carry out suction filtration and drying to obtain the core-shell structured flame retardant powder T3.

[0089] Transmission electron microscopy (TEM) shows that the T3 flame retardant has an obvious core-shell structure, with the dark part being the shell and the light part being the core, and the particle size is uniform, with an average particle size of about 600 nm.

[0090]

Example 4

[0091] Prepare a low-smoke density PC alloy using the core-shell structure flame retardant (T1) prepared in Example 1. The raw material composition is as follows:

[0092]

[0093] The preparation method is as follows:

[0094] Dry the PC resin 2220 at 100 °C until the moisture content is less than 0.3 wt%.

[0095] 1) Mix the PC resin 2220, the core-shell structure flame retardant T1, antioxidant 1010, antioxidant 168, and lubricant PETS in a high-speed mixer. Set the rotation speed to 200 rpm and mix at room temperature for 30 s to obtain a mixed material.

[0096] 2) Add the mixed material from step 1) to the main feed hopper and melt-extrude and pelletize it through a twin-screw extruder. The extrusion conditions are as follows: control the vacuum degree of the vacuum device in the metering section of the twin-screw to be less than -0.06 MPa, the screw rotation speed to be 400 rpm, and the screw temperature to be set in sections from the feeding port to the die head as: 240 °C, 280 °C, 280 °C, 280 °C, 280 °C, 290 °C, 290 °C, 290 °C. Cool the extruded material in the extruder water tank at 60 °C, pelletize it, and obtain the PC alloy.

[0097]

Example 5

[0098] Prepare a low-smoke density PC alloy using the core-shell structure flame retardant (T2) prepared in Example 2. The raw material composition is as follows:

[0099]

[0100] The preparation method refers to the preparation method of Example 4, and the extrusion process is the same as that of Example 4.

[0101]

Example 6

[0102] Prepare a low-smoke density PC alloy using the core-shell structure flame retardant (T3) prepared in Example 3. The raw material composition is as follows:

[0103]

[0104] The preparation method refers to the preparation method of Example 4, and the extrusion process is the same as that of Example 4.

[0105]

Comparative Example 1

[0106] Prepare a core layer emulsion in the same method as step 1) of Example 1 and directly use it as a flame retardant (D1).

[0107]

Comparative Example 2

[0108] The flame retardant (D2) was prepared in substantially the same manner as in Example 1, except that the homopolymerized PAN-based carbon fiber in step 2) was replaced with the same mass of polyacrylonitrile.

[0109]

Comparative Example 3

[0110] The flame retardant (D3) was prepared in substantially the same manner as in Example 1, except that the homopolymerized PAN-based carbon fiber in step 2) was replaced with the same mass of carbon fiber.

[0111]

Comparative Example 4

[0112] 72 g of water, 12 g of polytetrafluoroethylene emulsion (solid content 70%), 18 g of styrene monomer, and 24 g of homopolymerized PAN-based carbon fiber were added to a 1000 ml three-necked flask equipped with a stirrer, and the temperature was raised to 70 °C under an inert gas atmosphere. Then 0.3 g of potassium persulfate and 6 g of sodium dodecylbenzenesulfonate were further added, and the mixture was stirred thoroughly for 40 min.

[0113] 5 g of an aqueous solution of MgSO4 with a concentration of 1 mol / L was added to the above emulsion, and demulsification was achieved by mechanical stirring at a rotation speed of 300 rpm at a temperature of 75 °C. Then, after washing with water, suction filtration, and drying, a pre-product was obtained; all of the pre-product was added to 200 ml of acetone until completely dissolved, the temperature was controlled at 30 °C, and 50 ml of an ethanol solution with a purity of 80 wt% was added dropwise to precipitate the product. After precipitation for 2 h, suction filtration and drying were carried out to obtain the non-core-shell structure flame retardant powder D4.

[0114]

Comparative Example 5

[0115] The PC alloy was prepared according to the PC alloy raw material formula and method in Example 4, except that the core-shell structure flame retardant T1 was replaced with the flame retardant D1 of the same mass.

[0116]

Comparative Example 6

[0117] The PC alloy was prepared according to the PC alloy raw material formula and method in Example 4, except that the core-shell structure flame retardant T1 was replaced with the flame retardant D2 of the same mass.

[0118]

Comparative Example 7

[0119] The PC alloy was prepared according to the PC alloy raw material formula and method in Example 4, except that the core-shell structure flame retardant T1 was replaced with the flame retardant D3 of the same mass.

[0120]

Comparative Example 8

[0121] The PC alloy was prepared according to the PC alloy raw material formula and method in Example 4, except that the core-shell structure flame retardant T1 was replaced with the flame retardant D4 of the same mass.

[0122]

Comparative Example 9

[0123] The PC alloy was prepared according to the PC alloy raw material formula and method in Example 4, with the only difference being that the core-shell structure flame retardant T1 was replaced with an equal mass of the phosphorus-based flame retardant PX-200 (Daihachi, Japan).

[0124] The PC alloys prepared in Examples 4-6 (S4-S6) and Comparative Examples 5-9 (D5-D9) were subjected to cantilever beam notch impact test, heat distortion temperature test, heat release rate test, and smoke density test. The relevant properties are shown in Table 2.

[0125] Table 2. Performance test results

[0126]

[0127] In addition, the combustion morphologies of the PC alloy samples prepared in Example 4 and Comparative Examples 5-9 after the smoke density test were photographed as Figure 1 shown. It can be seen from Figure 1 this that the PC alloy products prepared in the examples of the present invention maintain the best flatness of the samples after combustion in the smoke density test, and there are obvious bulges on the surfaces of the comparative examples. This indicates that the products of the present invention have the ability to rapidly form carbon and maintain the flatness of the structure, effectively blocking the contact between the internal PC resin and air, thereby achieving the effect of flame retardancy and smoke suppression.

[0128] It can be seen from Table 2 that the PC alloy products prepared in the examples of the present invention have obvious effects on suppressing smoke density and heat release rate, and well retain the toughness and heat resistance of the PC resin; the smoke suppression effect of the comparative examples is not significantly improved, and it will cause a decrease in the mechanical properties and thermal properties of the products to varying degrees.

[0129] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a core-shell structure flame retardant, characterized in that, It includes the following steps: 1) Add polytetrafluoroethylene emulsion, initiator A, emulsifier and water into a reaction kettle, heat up to 70 - 80 °C under an inert gas atmosphere, stir thoroughly for 10 - 40 min, then add styrene monomer, control the temperature at 75 - 90 °C and the pressure at 2 - 4 Mpa, discharge the pressure and release the material after reacting for 1 - 3 h to obtain the core layer emulsion; the dosage of styrene accounts for 1 / 6 - 1 / 3 of its total mass. 2) Add styrene, PAN - based carbon fiber, initiator A, initiator B and catalyst into the core layer emulsion prepared in step 1), blend and heat them, and obtain the core - shell structure emulsion through atom transfer radical polymerization; the reaction temperature is 60 - 80 °C; the reaction time is 0.5 - 3 h; the polymerization reaction is carried out under an inert gas atmosphere, and the reaction pressure is 1 - 2 MPa. 3) Add a demulsifier to the core - shell structure copolymer emulsion prepared in step 2) and stir to demulsify, then after washing with water, separating and drying, add it to acetone for dissolution and purification, and finally drop - wise add ethanol to precipitate to obtain the core - shell structure flame retardant.

2. The preparation method of the core-shell structure flame retardant according to claim 1, characterized in that, In step 2), the reaction temperature is 65 - 75 °C; the reaction time is 1 - 2 h.

3. The preparation method of the core-shell structure flame retardant according to claim 1, wherein, In the said method, the dosages of each raw material are specifically as follows by mass parts: Among them, the solid content of the polytetrafluoroethylene emulsion is 40 - 70%.

4. The preparation method of the core-shell structure flame retardant according to claim 3, characterized in that, In the said method, the dosages of each raw material are specifically as follows by mass parts:

5. The preparation method of the core-shell structure flame retardant according to claim 3, wherein, Among them, the particle size of the polytetrafluoroethylene emulsion is 20 - 40 μm.

6. The preparation method of the core-shell structure flame retardant according to claim 3, characterized in that, In step 1), the dosage of initiator A accounts for 1 / 4 - 1 / 2 of its total mass.

7. The preparation method of the core-shell structure flame retardant according to any one of claims 1-6, characterized in that, The emulsifier is selected from any one or more of styrene - maleic anhydride copolymer, fatty acid polyoxyethylene ether, polyvinyl alcohol, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium dodecyl sulfonate, alkyl polyether.

8. The preparation method of the core-shell structure flame retardant according to claim 7, characterized in that, The initiator A is selected from any one or more of potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile, benzoyl peroxide, di - tert - butyl peroxide, ammonium potassium persulfate, sodium bisulfite or ammonium bisulfite.

9. The preparation method of the core-shell structure flame retardant according to claim 7, characterized in that, The initiator B is selected from one or more of carbon tetrachloride, tert - butyl bromo - isobutyrate, polyazo ester.

10. The preparation method of the core-shell structure flame retardant according to claim 7, characterized in that, The catalyst is one or two of the complex of ferric chloride and succinic acid, the complex of cuprous bromide and bipyridine.

11. The preparation method of the core-shell structure flame retardant according to claim 7, wherein, The dosage of the catalyst is 0.1 - 1.5 wt% of the mass of PAN - based carbon fiber.

12. The preparation method of the core-shell structure flame retardant according to claim 11, characterized in that, The dosage of the catalyst is 0.5 - 1 wt% of the mass of PAN - based carbon fiber.

13. The preparation method of the core-shell structure flame retardant according to claim 7, characterized in that, The demulsifier is selected from sulfate solutions of alkali metals or alkaline earth metals.

14. The preparation method of the core-shell structure flame retardant according to claim 13, wherein, The demulsifier is selected from aqueous solutions of potassium sulfate, sodium sulfate, magnesium sulfate.

15. The preparation method of the core-shell structure flame retardant according to claim 14, wherein, The demulsifier is selected from an aqueous solution of magnesium sulfate with a concentration of 1 - 3 mol / L.

16. The preparation method of the core-shell structure flame retardant according to claim 13, characterized in that, The dosage of the demulsifier is 1 - 5 wt% of the mass of the polytetrafluoroethylene emulsion.

17. Application of the core - shell structure flame retardant prepared by the method according to any one of claims 1 - 16 in the preparation of low - smoke density materials.

18. Application of the core - shell structure flame retardant prepared by the method according to any one of claims 1 - 16 in PC alloy.

19. A low-smoke-density PC alloy, characterized in that, By weight parts, it includes the following component raw materials: PC resin, 80 - 95 parts, Flame retardant, 2 - 20 parts, Antioxidant, 0 - 1 part, Lubricant, 0 - 1 part, The flame retardant is a core-shell structure flame retardant prepared by the method described in any one of claims 1-16.

20. The low-smoke-density PC alloy according to claim 19, wherein By weight, it comprises the following component raw materials: PC resin, 85-90 parts; Flame retardant, 5-15 parts; Antioxidant, 0.1-0.3 parts; Lubricant, 0.1-0.4 parts.

21. The low-smoke-density PC alloy according to claim 19, characterized in that, The PC resin is selected from any one or more of aromatic polycarbonates and aliphatic polycarbonates.

22. The low-smoke-density PC alloy according to claim 21, wherein, The PC resin is selected as the PC resin with a melt flow index MFR between 3-30 g / 10 min under the test conditions of 300 °C and a load of 1.2 kg.

23. The low-smoke-density PC alloy according to claim 22, wherein The PC resin is selected as the PC resin with a melt flow index MFR between 5-25 g / 10 min under the test conditions of 300 °C and a load of 1.2 kg.

24. The low-smoke-density PC alloy according to claim 22, wherein The PC resin is selected as the PC resin with a melt flow index MFR between 7-15 g / 10 min under the test conditions of 300 °C and a load of 1.2 kg.

25. The low-smoke-density PC alloy according to claim 22, wherein, The PC resin is a bisphenol A type PC resin.

26. The low-smoke-density PC alloy according to claim 20, wherein The antioxidant is selected from any one or more of hindered phenols, phosphite esters, thioesters, benzofurans, acryloyl-modified phenols, and hydroxylamines.

27. The low-smoke-density PC alloy according to claim 26, wherein, The antioxidant is selected from any one or more of Irganox1076, Irganox 1010, and Irganox 168.

28. The low-smoke-density PC alloy according to claim 27, wherein, The lubricant is selected from any one or more of fatty alcohols, metal soaps, fatty acids, fatty acid esters, montanic acid and its derivatives, amide waxes, saturated hydrocarbons, polyolefin waxes and their derivatives, organosilicons and silicone powders, and organofluorines.

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