Flame-retardant polypropylene wire rod as well as preparation method and application thereof

Abstract

The invention relates to a flame-retardant polypropylene wire rod and a preparation method and application thereof, the flame-retardant polypropylene wire rod has a core-shell structure, and the shell structure comprises polypropylene, MCA, tetrapod-like zinc oxide, an antioxidant and a lubricant; the core layer structure is prepared from polypropylene, piperazine pyrophosphate, melamine polyphosphate, tetrapod-like zinc oxide, an antioxidant and a lubricant. According to the invention, by controlling the type and content of the flame retardant in the shell layer of the wire rod, the interlayer binding force is not influenced during high-temperature fused deposition printing, a workpiece with relatively high mechanical property can be prepared, and the core layer material of the wire rod has relatively high flame retardant property, so that the prepared workpiece has relatively good flame retardant property. The preparation method of the flame-retardant polypropylene wire rod is simple, electronic and electric appliance structural parts which are complex in structure, difficult to design mold parting surface injection molding, high in mechanical property requirement and high in flame retardant property requirement can be prepared through 3D printing forming, and the flame-retardant polypropylene wire rod has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer composite materials, and particularly relates to a flame-retardant polypropylene wire and a preparation method and application thereof. Background Art

[0002] 3D printing is a rapid prototyping technology. The wire melt deposition molding technology is one of the 3D printing technologies. It uses a printing nozzle to heat the material to the melting temperature, and the melt solidifies layer by layer after flowing out to form the required printed part. Compared with traditional injection molding, 3D printing technology can quickly manufacture three-dimensional solid parts with complex structures without molds, which can greatly shorten the product development cycle and reduce the product development cost.

[0003] As one of the five general-purpose resins, polypropylene resin is one of the polymer materials with the largest production, consumption and the widest application fields in the world today. Polypropylene has the advantages of low density, high strength, good heat resistance and insulation, low price, and excellent chemical stability, and is widely favored in the fields of household appliances, automobiles, electronic appliances, medical treatment, etc.

[0004] Polypropylene resin has a low limiting oxygen index and is accompanied by intense melting droplets during combustion, which cannot meet the application fields with high flame-retardant performance requirements. Therefore, a relatively high content of flame retardant needs to be added to achieve better flame-retardant performance. However, adding a relatively high content of flame retardant will affect the polymer interaction and reduce the entanglement of molecular chains, often resulting in a decrease in the mechanical properties of the prepared parts.

[0005] Therefore, it is necessary to develop a polypropylene wire with excellent flame-retardant performance, and the parts prepared by 3D printing still have good mechanical properties to solve the technical deficiencies of existing materials. Summary of the Invention

[0006] To solve the above technical problems, the present invention controls the types and contents of the flame retardants on the surface layer of the wire, so that it does not affect the interlayer bonding force during high-temperature melt deposition printing, and parts with relatively high mechanical properties can be prepared. The core layer material of the wire has high flame-retardant performance, and the shell layer material of the wire has excellent synergistic flame-retardant performance, so that the prepared parts have good flame-retardant performance.

[0007] The technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention provides a flame-retardant polypropylene wire with a core-shell structure, which includes a shell layer resin and a core layer resin. Among them,

[0009] The shell layer resin contains the following raw materials in parts by mass:

[0010] Polypropylene: 90-96 parts;

[0011] Melamine cyanurate (MCA): 2 - 5 parts;

[0012] Tetrapod - shaped zinc oxide: 1 - 5 parts;

[0013] Antioxidant: 0.2 - 1 part;

[0014] Lubricant: 0.2 - 0.5 part;

[0015] The core - layer resin comprises raw materials in the following parts by mass:

[0016] Polypropylene: 66 - 80 parts;

[0017] Piperazine pyrophosphate: 12 - 18 parts;

[0018] Melamine polyphosphate: 6 - 10 parts;

[0019] Tetrapod - shaped zinc oxide: 1.5 - 5 parts;

[0020] Antioxidant: 0.2 - 1 part;

[0021] Lubricant: 0.2 - 0.5 part.

[0022] The total mass of the flame - retardant polypropylene wire is the sum of the masses of the shell - layer resin and the core - layer resin, wherein the shell - layer resin accounts for 10 - 20% of the total mass of the wire, and the core - layer resin accounts for 80 - 90% of the total mass of the wire.

[0023] In the present invention, the melting point of the polypropylene in the raw materials of the core and shell resins is 130 - 165 °C, and its melt index is 5 - 15 g / 10 min (230 °C, 2.16 kg).

[0024] In the present invention, the antioxidant in the raw materials of the core and shell resins is selected from one or more of hindered phenol antioxidants, phosphite antioxidants and thioester antioxidants;

[0025] Preferably, the hindered phenol antioxidants are such as 1010, 330, 1790; the phosphite antioxidants are such as 168, 626; the thioester antioxidants are such as DSTDP, 412S, DLTDP.

[0026] In the present invention, the lubricant in the raw materials of the core and shell resins is selected from one or more of zinc stearate and ethylene bisstearamide.

[0027] In the second aspect of the present invention, there is provided a method for preparing the above - mentioned flame - retardant polypropylene material, comprising the following steps:

[0028] (1) Placing the raw materials of the shell - layer resin in a twin - screw extruder for high - temperature melting and dispersion, and extruding and pelletizing to obtain the shell - layer resin;

[0029] (2) Place the raw materials of the core-layer resin in a twin-screw extruder for high-temperature melting and dispersion, and extrude and pelletize to obtain the core-layer resin;

[0030] (3) Place the shell-layer resin and the core-layer resin in two single-screw extruders respectively for plasticization, and obtain the flame-retardant polypropylene wire with a core-shell structure by co-extruding through a die head and drawing, and collect the formed wire through a disc device winding. Among them, the shell-layer resin accounts for 10-20% of the total mass of the wire, and the core-layer resin accounts for 80-90% of the total mass of the wire.

[0031] In the present invention, the length-diameter ratio of the screw of the twin-screw extruder in the steps (1) and (2) is (40-52):1, the screw speed is 100-300 r / min, and the extrusion temperature is 180-190 °C.

[0032] In the present invention, the length-diameter ratio of the screw of the single-screw extruder in the step (3) is (25-35):1, the screw speed is 100-300 r / min, and the extrusion temperature is 180-190 °C.

[0033] In the third aspect of the present invention, an application of the above-mentioned flame-retardant polypropylene wire is provided. The flame-retardant polypropylene wire with a core-shell structure of the present invention can be used to prepare 3D printing parts with excellent flame-retardant performance and good mechanical properties.

[0034] The technical solution of the present invention has the following beneficial effects compared with the prior art:

[0035] 1. The flame-retardant polypropylene wire in the present invention adopts a core-shell structure. The shell-layer resin contains a small amount of synergistic flame retardant MCA and co-catalyst tetrapod-shaped zinc oxide, and its addition amount is low, which will not affect the bonding strength and elongation at break between the resin layers after printing. Moreover, compared with traditional particulate zinc oxide, tetrapod-shaped zinc oxide has a higher specific surface area and more excellent co-catalytic effect, which is beneficial to the rapid decomposition of MCA to generate gas to achieve a gas-phase flame-retardant effect. And the needle-shaped zinc oxide structure has a strong anchoring effect on the matrix resin, which can improve the melt strength of the resin. Without adding polytetrafluoroethylene-based anti-dripping agents, it can achieve the phenomenon that the resin does not drip when burning.

[0036] 2. The flame-retardant polypropylene wire in the present invention adopts a core-shell structure, and the core layer resin adopts a pyrophosphate piperazine + melamine polyphosphate flame retardant system, which has excellent precipitation resistance and hydrolysis resistance. The shell layer resin is used to cover the flame-retardant core layer during the extrusion process, so that the prepared flame-retardant polypropylene wire still has excellent flame retardant effect after long-term storage. At the same time, the core layer also uses four needle-shaped zinc oxide as a co-catalyst, which quickly promotes the decomposition of melamine polyphosphate and pyrophosphate piperazine to produce acid source and gas source during the combustion process, thereby accelerating the carbonization of pyrophosphate piperazine, making the carbon layer produced by combustion dense, and the needle-shaped zinc oxide itself has an anti-dripping effect, so there is no need to add polytetrafluoroethylene anti-dripping agents, and the material has good tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of flame retardant polypropylene wire;

[0038] Figure 2 Schematic diagram of interlayer bonding force of 3D printing test;

[0039] Figure 3 Schematic diagram of flame retardancy testing for 3D printing. DETAILED DESCRIPTION

[0040] In order to better understand the technical solution of the present invention, the content of the present invention is further described below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0041] The devices and main raw material sources used in the embodiments and comparative examples of the present invention are as follows:

[0042] Twin-screw extruder: Model SK-26, screw length-diameter ratio 50:1; Nanjing Keya Chemical Equipment Co., Ltd.;

[0043] Single screw co-extrusion equipment: model HRJSJ-35, screw length-diameter ratio 28:1, Foshan Hai Ruijia Precision Extrusion Machinery Co., Ltd.

[0044] 3D printer: Finder, Zhejiang Flashforge 3D Technology Co., Ltd.;

[0045] Polypropylene: FL7540L, melting point 135°C, melt index 7g / 10min (230°C, 2.16kg), Singapore Polyolefins Pte Ltd;

[0046] Tetrapod-shaped zinc oxide: SS-ZJ52, Hangzhou Jikang New Materials Co., Ltd.;

[0047] MCA: melamine cyanurate, Shandong Shian Chemical Co., Ltd.;

[0048] Lubricant: zinc stearate;

[0049] Primary antioxidant: hindered phenol antioxidant, 1010, XinXiu Chemical;

[0050] Co - antioxidant: phosphite antioxidant, 168, XinXiu Chemical;

[0051] Other raw materials are all commercially available raw materials of analytical purity.

[0052] The performance characterization method of the flame - retardant polypropylene material of the present invention is as follows:

[0053] Tensile strength: ISO 527;

[0054] Flame - retardant performance: UL - 94;

[0055] The printing method of the flame - retardant polypropylene wire is as follows:

[0056] The printing conditions of the polypropylene wire are: the forming layer thickness is 0.17 mm, the scanning speed is 40 cm 3 / h, the nozzle temperature is 200 - 220 °C, the temperature of the forming chamber is 60 - 80 °C, and other parameters are formed using the system - default parameters.

[0057] Test method for the interlayer bonding strength of polypropylene printing:

[0058] Use the Finder 3D printer to print a 3D printing sample of 200 mm * 150 mm * 4 mm perpendicular to the bottom plate with the polypropylene wire, and cut out a tensile test specimen in accordance with the ISO527 standard along the Z - axis direction through a cutting machine (see Figure 2 ), and conduct tensile property testing.

[0059] Test method for polypropylene printing flame - retardancy:

[0060] Use the Finder 3D printer to print 3D printing samples of 200 mm * 150 mm * 1.6 mm and 200 mm * 150 mm * 3.2 mm perpendicular to the bottom plate with the polypropylene wire, and cut out flame - retardant test specimens in accordance with the UL - 94 standard along the Z - axis direction through a cutting machine (see Figure 3 ), and conduct vertical burning testing.

[0061] Test method for the long - term storage stability of the flame - retardant polypropylene wire:

[0062] Place the wire in a damp - heat aging oven at 50 °C and 85% humidity for 7 days, and then print and cut the flame - retardant sample (see Figure 3 ) and conduct flame - retardancy testing.

[0063] Examples 1 - 5 (i.e., S1 - 5) and Comparative Examples 1 - 5 (i.e., D1 - 5) are used to prepare 3D - printed polypropylene wires according to the raw materials and dosages in Table 1.

[0064] The preparation method of the shell resin is as follows: Weigh each raw material according to the weight ratio, then put them into a high-speed mixer and mix for 3 minutes. Then feed them into the main feeding port of a twin-screw extruder. The screw speed is 300 r / min, and the extrusion temperature is 190 °C. After high-temperature melting and dispersion, extrusion granulation is carried out to obtain the shell resin.

[0065] The preparation method of the core resin is as follows: Weigh each raw material according to the weight ratio, then put them into a high-speed mixer and mix for 3 minutes. Then feed them into the main feeding port of a twin-screw extruder. The screw speed is 300 r / min, and the extrusion temperature is 190 °C. After high-temperature melting and dispersion, extrusion granulation is carried out to obtain the core resin.

[0066] The preparation method of the flame-retardant polypropylene wire is as follows: Place the shell resin and the core resin in two single-screw extruders respectively for plasticization. The extrusion temperature is 190 °C. Through co-extrusion, an extrusion die head is used to extrude to prepare a core-shell composite polypropylene wire. The wire diameter is 1.75 ± 0.05 mm, and the formed wire is collected and formed by a disc device.

[0067] Table 1 Raw material usage amounts of examples and comparative examples and properties of their printed parts (parts by weight)

[0068]

[0069] It can be found from Table 1 that the polypropylene wires of Examples 1-5 adopt a core-shell structure. The tensile splines prepared by 3D printing have excellent tensile strength performance and elongation at break. The flame-retardant splines prepared by 3D printing pass the V0 flame-retardant tests of 1.6 mm and 3.2 mm and have excellent flame-retardant performance.

[0070] The polypropylene wire of Comparative Example 1 adopts a core-shell structure, but four-needle zinc oxide is not added to the shell layer as a co-catalyst, and dripping occurs during the flame-retardant test, resulting in its failure to pass the V0 flame-retardant in the flame-retardant test; Comparative Example 2 does not adopt a core-shell structure. Its formulation system has good flame-retardant performance, but the high addition amount of the flame retardant affects the entanglement and crystallization of polypropylene molecular chains during printing, resulting in poor interlayer bonding force and low elongation at break of the tensile spline. Comparative Example 3 does not add the piperazine pyrophosphate flame-retardant system. The mechanical properties of the printed parts are good, but the flame-retardant test cannot pass the V0 flame-retardant. In Comparative Example 4, only four-needle zinc oxide is added to the shell layer, and MCA (gas-phase flame retardant) that provides a rich gas source is not added, resulting in its failure to reach V0 flame-retardant during combustion. In Comparative Example 5, the content of the shell resin is relatively high. During high-temperature combustion, the gas-phase flame retardant provided by itself cannot offset the side effect of easy dripping caused by its too high content, so that it can only meet the V2 flame-retardant effect of 3.2 mm.

[0071] For the wire rods prepared in Example 1 and Example 5, after placing the materials at high temperature and high humidity, printing the parts and cutting samples for flame retardancy testing, they still have excellent flame retardancy performance; in Comparative Example 2, the shell resin embedding was not used, and the flame retardancy performance of the samples after high temperature and high humidity testing deteriorated.

[0072] The above description of the embodiments is to facilitate those skilled in the art of this technology to understand and apply the present invention. Those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the embodiments here, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A flame-retardant polypropylene wire, characterized in that: It has a core-shell structure, including a shell resin and a core resin, where The shell resin contains raw materials in the following parts by mass: Polypropylene: 90 - 96 parts; MCA: 2 - 5 parts; Tetrapod-shaped zinc oxide: 1 - 5 parts; Antioxidant: 0.2 - 1 part; Lubricant: 0.2 - 0.5 part; The core resin contains raw materials in the following parts by mass: Polypropylene: 66 - 80 parts; Piperazine pyrophosphate: 12 - 18 parts; Melamine polyphosphate: 6 - 10 parts; Tetrapod-shaped zinc oxide: 1.5 - 5 parts; Antioxidant: 0.2 - 1 part; Lubricant: 0.2 - 0.5 part; Among them, the shell resin accounts for 10 - 20% of the total mass of the wire, and the core resin accounts for 80 - 90% of the total mass of the wire.

2. The flame-retardant polypropylene wire according to claim 1, wherein, The melting point of polypropylene in the core and shell resins is 130 - 165 °C, and the melt index is 5 - 15 g / 10 min under the conditions of 230 °C and 2.16 kg.

3. The flame-retardant polypropylene wire according to claim 1, wherein The antioxidant in the core and shell resins is any one or more of hindered phenol antioxidants, phosphite antioxidants, and thioester antioxidants.

4. The flame-retardant polypropylene wire according to claim 1, characterized in that The lubricant in the core and shell resins is any one or more of zinc stearate and ethylene bisstearamide.

5. A method for preparing the flame-retardant polypropylene wire according to any one of claims 1 - 4, comprising the following steps: (1) Place the raw materials of the shell layer in a twin-screw extruder for high-temperature melting and dispersion, and extrude and pelletize to obtain the shell resin; (2) Place the raw materials of the core layer in a twin-screw extruder for high-temperature melting and dispersion, and extrude and pelletize to obtain the core resin; (3) Place the shell resin and the core resin in two single-screw extruders for plasticization respectively, and obtain the flame-retardant polypropylene wire with a core-shell structure by co-extruding through a die head and drawing.

6. The preparation method according to claim 5, characterized in that The length-diameter ratio of the screw of the twin-screw extruder in steps (1) and (2) is (40 - 52):1, the screw speed is 100 - 300 r / min, and the extrusion temperature is 180 - 190 °C.

7. The preparation method according to claim 5, characterized in that, The length-diameter ratio of the screw of the single-screw extruder in step (3) is (25 - 35):1, the screw speed is 100 - 300 r / min, and the extrusion temperature is 180 - 190 °C.

8. An application of the flame-retardant polypropylene wire according to any one of claims 1 - 4 or the flame-retardant polypropylene wire prepared by the preparation method according to any one of claims 5 - 7 in 3D printing.

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