Preparation method of reinforced flame-retardant PP plastic

Abstract

The invention relates to a preparation method of reinforced flame-retardant PP plastic, and belongs to the technical field of high polymer materials, and the preparation method comprises the following steps: S1, raw material preparation and pretreatment; s2, preparation of a functional premix: adding the preheated halogen-free flame retardant, synergistic flame retardant and surface modified glass fiber into a high-speed mixer together to obtain the uniform functional premix; s3, preparing a main premix: obtaining the main premix with uniformly distributed components; and S4, melt blending and underwater pelletizing: feeding the main premix obtained in S3 into a co-rotating twin-screw extruder through a weightlessness type feeder to obtain the reinforced flame-retardant PP plastic particles. According to the preparation method of the reinforced flame-retardant PP plastic, ammonium polyphosphate and melamine cyanurate subjected to surface treatment are adopted to form a non-classical composite flame-retardant system, a carbon layer is high in strength and not prone to being broken through by flames, the oxygen and heat isolation efficiency of the carbon layer is far higher than that of a traditional IFR system, the high flame-retardant standard is met, and the environment-friendly requirement is met.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a method for preparing reinforced flame-retardant PP plastic. Background Technology

[0002] Polypropylene (PP), as a general-purpose plastic with excellent overall performance and low price, is widely used in electronics, automobiles, and home appliances. However, PP itself is extremely flammable (limiting oxygen index LOI is only about 17%), and the combustion process is violent and accompanied by melting and dripping, which greatly limits its application in situations with strict fire safety requirements.

[0003] To address the flammability issue of PP, traditional technologies mainly fall into two categories:

[0004] Halogenated flame retardant systems: such as synergistic effects of brominated flame retardants and antimony trioxide. These systems have high flame retardant efficiency, but they produce a large amount of toxic and corrosive fumes during combustion, leading to "secondary disasters." Moreover, they are environmentally unfriendly after disposal and are being gradually restricted and phased out by global environmental regulations (such as RoHS and REACH).

[0005] Halogen-free flame retardant system:

[0006] Single-filler type: such as high-filler aluminum hydroxide (ATH) or magnesium hydroxide (MH). These flame retardants require very high addition levels (usually >60%) to achieve a certain flame retardant effect, which will severely damage the mechanical properties of PP, especially impact strength and processing flowability, causing the material to become brittle and unable to be injection molded into complex structural parts.

[0007] Traditional halogen-free synergistic systems include classic intumescent flame retardant (IFR) systems composed of ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL). While this system forms a dense char layer during combustion and exhibits good flame retardant properties, it has significant drawbacks:

[0008] Hygroscopicity: APP and PER are prone to absorbing moisture, which leads to a decrease in the electrical properties of the products and easy precipitation in humid environments.

[0009] Poor compatibility: IFR has poor compatibility with PP matrix and is prone to migration and precipitation to the surface of the product, causing "blooming" phenomenon, affecting appearance and long-term flame retardancy.

[0010] Deterioration of mechanical properties: Higher addition amounts are also required, resulting in a loss of the material's toughness and strength.

[0011] Reinforcement Modification: Glass fiber (GF) is often added to improve mechanical properties. However, ordinary GF has weak bonding with the plastic matrix and is more likely to become a defect point in the IFR system, leading to a sharp decline in impact performance. At the same time, the "wick effect" of GF can sometimes even intensify combustion, which runs counter to the goal of flame retardancy.

[0012] Therefore, there is an urgent need in this field to develop a new preparation method that can organically combine halogen-free flame retardant technology with reinforcement technology, so as to endow PP material with efficient, stable and environmentally friendly flame retardant properties without sacrificing the mechanical and processing properties of PP material. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention provides a method for preparing reinforced flame-retardant PP plastic. This method, through innovative flame-retardant formulation design and precise processing control, produces PP composite materials that combine excellent flame retardancy, high mechanical strength, and good processing performance.

[0014] To achieve the above objectives, the present invention provides the following technical solution:

[0015] A method for preparing reinforced flame-retardant PP plastic, comprising raw materials comprising the following parts by weight and prepared by the following method:

[0016] Polypropylene resin: 78 parts;

[0017] Halogen-free flame retardant (APP): 12 parts;

[0018] Synergistic flame retardant (MCA): 8 parts;

[0019] Surface-modified glass fiber: 20 parts;

[0020] Compatibilizer (PP-g-MAH): 5 parts;

[0021] Antioxidant: 0.5 parts;

[0022] Lubricant (calcium stearate): 1 part;

[0023] The method includes the following steps:

[0024] S1. Raw material preparation and pretreatment:

[0025] S1-1: Dry the polypropylene resin in a forced-air oven at 80-90℃ for 2-3 hours to reduce its moisture content to below 0.03%;

[0026] S1-2: Preheat and dry the halogen-free flame retardant and the synergistic flame retardant at 55-65°C for 1-2 hours;

[0027] S2. Preparation of functional premixes:

[0028] The preheated halogen-free flame retardant, synergistic flame retardant and surface-modified glass fiber are added to a high-speed mixer. At a mixing temperature of 40-60℃, the mixture is first mixed at a speed of 500-800 rpm for 3-5 minutes, and then the speed is reduced to 200-300 rpm for 2-4 minutes, for a total time of 5-9 minutes, to obtain a uniform functional premix.

[0029] S3. Preparation of main premix:

[0030] S3-1: Add the dried PP resin, half the amount of compatibilizer, and half the amount of lubricant into a high-speed mixer and mix at 300-400 rpm for 3-5 minutes to initially coat the surface of the resin particles.

[0031] S3-2: Add all the functional premixes obtained from S2, increase the rotation speed to 600-800 rpm, mix for 8-12 minutes, and use high shear force to embed the functional powders and fibers into and adhere to the resin surface.

[0032] S3-3: Add the remaining half of the compatibilizer and lubricant, as well as all of the antioxidant. Reduce the speed to 400-500 rpm and continue mixing for 3-5 minutes to obtain a premixed material with uniformly distributed components.

[0033] S4. Melt blending and underwater pelletizing:

[0034] The main premix obtained from S3 is fed into a co-rotating twin-screw extruder via a loss-in-weight feeder;

[0035] The temperature of the eight temperature control zones of the twin-screw extruder from the feeding section to the die head is set as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, Zone 5 200℃, Zone 6 205℃, Zone 7 200℃, and Zone 8 195℃.

[0036] The screw speed is set to 380-420 rpm, and the die head pressure is maintained at 3.0-3.8 MPa.

[0037] The melt-extruded strips are cooled in a cooling water tank, and surface moisture is removed by a blower-type dewatering device. Then, they are granulated by an underwater pelletizer to obtain the reinforced flame-retardant PP plastic granules.

[0038] Furthermore, the halogen-free flame retardant is ammonium polyphosphate (APP) or melamine polyphosphate (MPP).

[0039] Furthermore, the synergistic flame retardant is melamine cyanurate (MCA) treated with silane coupling agent KH-560, with a particle size D50 ≤ 15 μm.

[0040] Furthermore, the mass ratio of the halogen-free flame retardant to the synergistic flame retardant is (2:1) to (1.5:1).

[0041] Furthermore, the surface-modified glass fiber is a short-cut alkali-free glass fiber that has been surface-treated with an epoxy silane coupling agent KH-560, with a fiber diameter of 10-13 μm and a length of 4-5 mm.

[0042] Furthermore, the mixing temperature in S2 is controlled at 50±2℃, and the total mixing time is 7 minutes.

[0043] Furthermore, the compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 1.0%-1.2% and a melt flow rate of 50-80 g / 10 min (190℃, 2.16 kg).

[0044] Furthermore, the screw configuration of the twin-screw extruder includes 5 sets of kneading blocks and 3 reverse thread elements; wherein, the kneading blocks located in the melting zone adopt a 45° staggered angle, and the kneading blocks located in the homogenization zone adopt a 60° staggered angle.

[0045] Furthermore, the water temperature in the cooling water tank is controlled at 25-35℃, and the immersion length of the material strip in the water tank is greater than 2 meters.

[0046] Compared with the prior art, the present invention provides a method for preparing reinforced flame-retardant PP plastic, which has the following beneficial effects:

[0047] 1. The preparation method of this reinforced flame-retardant PP plastic adopts a non-classical composite flame-retardant system by using "ammonium polyphosphate (APP)" and "surface-treated melamine cyanurate (MCA)". APP promotes dehydration and carbonization in the early stage of combustion, while MCA can not only efficiently gasify and absorb heat, dilute oxygen and combustible gases, but its cyanurate structure can also interact with the degradation products of APP to catalyze the formation of a denser and more stable three-dimensional network-like expanded char layer. This char layer has high strength and is not easily broken by the flame. Its efficiency in isolating oxygen and heat is far superior to the traditional IFR system, thus achieving the high flame-retardant standard of UL94 V-0 (1.6mm) with a lower total addition amount. The entire system is halogen-free and meets environmental protection requirements.

[0048] 2. The key to the preparation method of this reinforced flame-retardant PP plastic lies in the use of surface-modified glass fibers. The glass fiber surface treated with silane coupling agents contains active groups, which not only form strong chemical bonds with the PP matrix through compatibilizers, greatly improving interfacial bonding and preventing stress concentration; but also some of its surface active sites can generate certain physical / chemical adsorption interactions with flame retardant molecules such as APP and MCA. This interaction allows the glass fiber to act as a "skeleton" supporting the expanded char layer during combustion, much like the reinforcing steel in reinforced concrete, significantly enhancing the strength, density, and integrity of the char layer, effectively resisting flame impact and airflow erosion, resulting in a more durable and stable flame-retardant effect.

[0049] 3. The preparation method of this reinforced flame-retardant PP plastic involves pre-combining flame retardant powder with surface-modified glass fiber under mild heating at 40-60℃, allowing some of the flame retardant to be "anchored" on the GF surface; by pre-constructing "flame retardant-reinforcement" units at the microscopic level, it lays the foundation for uniform dispersion and synergistic effect in the final product; through the combination of kneading blocks and anti-threading elements, a strong and controllable shear field and backflow are generated in the melt, ensuring that the fibers are fully dispersed, wetted, and maintain a reasonable length, while forcing the flame retardant particles to achieve uniform distribution at the nanometer / micrometer level; the unique "high at the front and low at the back" temperature curve (the die head temperature is lower than the homogenization section) helps the melt to moderately thicken before exiting, reducing melt fracture caused by the presence of flame retardant and GF, ensuring a smooth and flat granule appearance, and facilitating rapid filling of the mold during injection molding.

[0050] 4. The preparation method of this reinforced flame-retardant PP plastic, through the synergy of the above components and processes, the final material achieves the UL94 V-0 flame retardant rating while maintaining high impact strength and flexural modulus, moderate melt flow rate, and excellent processing performance. It is very suitable for manufacturing complex thin-walled electronic and electrical housings, automotive parts requiring high strength and flame retardancy, etc., through injection molding. Attached Figure Description

[0051] Figure 1 This is a process flow diagram of a method for preparing reinforced flame-retardant PP plastic according to the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Example 1:

[0054] Please see Figure 1The preparation method of reinforced flame-retardant PP plastic in this embodiment includes the following steps:

[0055] S1. Raw material preparation and pretreatment:

[0056] Weigh out 78 parts by weight of polypropylene resin and dry it in an 85℃ forced-air oven for 2.5 hours until its moisture content is ≤0.03%.

[0057] Weigh out 12 parts by weight of ammonium polyphosphate (APP) and 8 parts by weight of melamine cyanurate (MCA) treated with KH-560, and preheat and dry at 60°C for 1.5 hours.

[0058] Surface-modified glass fiber (KH-560 treatment, diameter 12μm, length 4.5mm): 20 parts by weight;

[0059] Maleic anhydride-grafted polypropylene (PP-g-MAH, grafting rate 1.1%): 5 parts by weight;

[0060] Antioxidant: 0.5 parts by weight, calcium stearate: 1 part by weight.

[0061] S2. Preparation of functional premixes:

[0062] The preheated APP, MCA and surface-modified glass fiber were put into a high-speed mixer and mixed at 600 rpm for 4 minutes at 50°C, and then mixed at 250 rpm for 3 minutes, for a total mixing time of 7 minutes, to obtain the functional premix.

[0063] S3. Preparation of main premix:

[0064] Mix the dried PP resin with half of the compatibilizer and half of the lubricant at 350 rpm for 4 minutes;

[0065] Add all functional premixes, increase the speed to 700 rpm, and mix for 10 minutes;

[0066] Add the remaining compatibilizer, lubricant and all antioxidants, reduce the speed to 450 rpm and continue mixing for 4 minutes to obtain the main premix.

[0067] S4. Melt blending and underwater pelletizing:

[0068] The main premix is ​​fed into the co-rotating twin-screw extruder through a loss-in-weight feeder. The temperature of each zone is set as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, Zone 5 200℃, Zone 6 205℃, Zone 7 200℃, and Zone 8 195℃.

[0069] The screw speed is 400 rpm, and the die pressure is 3.5 MPa.

[0070] The extruded strip is cooled in a 25°C cooling water tank, and after being blown dry, it is cut into pellets underwater to obtain reinforced flame-retardant PP plastic pellets.

[0071] Example 2:

[0072] A method for preparing reinforced flame-retardant PP plastic includes the following steps:

[0073] A1. Raw material preparation and pretreatment:

[0074] Polypropylene resin: 78 parts by weight, dried at 90°C for 2 hours;

[0075] Melamine polyphosphate (MPP): 12 parts by weight, MCA: 8 parts by weight, preheated and dried at 65°C for 1 hour;

[0076] Surface-modified glass fiber: 20 parts by weight;

[0077] PP-g-MAH: 5 parts, antioxidant: 0.5 parts by weight, calcium stearate: 1 part by weight.

[0078] A2. Preparation of functional premixes:

[0079] Mix at 700 rpm for 3 minutes at 55°C, then mix at 300 rpm for 2 minutes, for a total of 5 minutes.

[0080] A3. Preparation of main premix:

[0081] Mix the PP resin and half of the additives at 300 rpm for 5 minutes;

[0082] Add the premix and mix at 800 rpm for 8 minutes;

[0083] Add the remaining additives and mix at 500 rpm for 3 minutes.

[0084] A4. Extrusion and pelletizing:

[0085] The extruder temperature setting is the same as in Example 1;

[0086] The screw speed is 420 rpm, and the die pressure is 3.8 MPa.

[0087] Cooling water temperature 30℃, immersion length 2.5 meters.

[0088] Example 3:

[0089] A method for preparing reinforced flame-retardant PP plastic includes the following steps:

[0090] B1. Raw material preparation and pretreatment:

[0091] Polypropylene resin: 78 parts by weight, dried at 80°C for 3 hours;

[0092] APP: 10 parts by weight, MCA: 10 parts by weight (mass ratio 1:1), preheat and dry at 55°C for 2 hours;

[0093] Surface-modified glass fiber: 20 parts by weight;

[0094] PP-g-MAH: 5 parts by weight, antioxidant: 0.5 parts by weight, calcium stearate: 1 part by weight.

[0095] B2. Preparation of functional premixes:

[0096] Mix at 45°C for 5 minutes at 500 rpm, then mix at 200 rpm for 4 minutes, for a total of 9 minutes.

[0097] B3. Preparation of main premix:

[0098] Mix the PP resin and half of the additives at 400 rpm for 3 minutes;

[0099] Add the premix and mix at 600 rpm for 12 minutes;

[0100] Add the remaining additives and mix at 400 rpm for 5 minutes.

[0101] B4. Extrusion and pelletizing:

[0102] The extruder temperature setting is the same as in Example 1;

[0103] The screw speed is 380 rpm, and the die pressure is 3.0 MPa.

[0104] Cooling water temperature 35℃, immersion length 2.2 meters.

[0105] The beneficial effects of this invention are:

[0106] The reinforced flame-retardant PP plastic prepared through the above embodiments, as tested, shows that:

[0107] It achieves UL94 V-0 flame retardant rating (1.6mm), produces no molten droplets, and generates low smoke.

[0108] Excellent mechanical properties: cantilever beam impact strength ≥12kJ / m², flexural modulus ≥4500MPa;

[0109] The melt flow rate is maintained at 15-25 g / 10 min, which is suitable for injection molding of complex structures;

[0110] The glass fiber is tightly bonded to the matrix, with no exudation or frosting, resulting in a smooth product appearance.

[0111] Therefore, this invention successfully provides a reinforced flame-retardant PP plastic with high flame retardancy, excellent mechanical properties, good processability, and environmental friendliness, as well as its preparation method.

[0112] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing reinforced flame-retardant PP plastic, characterized in that, It is prepared from the following raw materials in parts by weight by the following method: Polypropylene resin: 78 parts; Halogen-free flame retardant (APP): 12 parts; Synergistic flame retardant (MCA): 8 parts; Surface-modified glass fiber: 20 parts; Compatibilizer (PP-g-MAH): 5 parts; Antioxidant: 0.5 parts; Lubricant (calcium stearate): 1 part; The method includes the following steps: S1. Raw material preparation and pretreatment: S1-1: Dry the polypropylene resin in a forced-air oven at 80-90℃ for 2-3 hours to reduce its moisture content to below 0.03%; S1-2: Preheat and dry the halogen-free flame retardant and the synergistic flame retardant at 55-65°C for 1-2 hours; S2. Preparation of functional premixes: The preheated halogen-free flame retardant, synergistic flame retardant and surface-modified glass fiber are added to a high-speed mixer. At a mixing temperature of 40-60℃, the mixture is first mixed at a speed of 500-800 rpm for 3-5 minutes, and then the speed is reduced to 200-300 rpm for 2-4 minutes, for a total time of 5-9 minutes, to obtain a uniform functional premix. S3. Preparation of main premix: S3-1: Add the dried PP resin, half the amount of compatibilizer, and half the amount of lubricant into a high-speed mixer and mix at 300-400 rpm for 3-5 minutes to initially coat the surface of the resin particles. S3-2: Add all the functional premixes obtained from S2, increase the rotation speed to 600-800 rpm, mix for 8-12 minutes, and use high shear force to embed the functional powders and fibers into and adhere to the resin surface. S3-3: Add the remaining half of the compatibilizer and lubricant, as well as all of the antioxidant. Reduce the speed to 400-500 rpm and continue mixing for 3-5 minutes to obtain a premixed material with uniformly distributed components. S4. Melt blending and underwater pelletizing: The main premix obtained from S3 is fed into a co-rotating twin-screw extruder via a loss-in-weight feeder; The temperature of the eight temperature control zones of the twin-screw extruder from the feeding section to the die head is set as follows: Zone 1 170℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, Zone 5 200℃, Zone 6 205℃, Zone 7 200℃, and Zone 8 195℃. The screw speed is set to 380-420 rpm, and the die head pressure is maintained at 3.0-3.8 MPa. The melt-extruded strips are cooled in a cooling water tank, and surface moisture is removed by a blower-type dewatering device. Then, they are granulated by an underwater pelletizer to obtain the reinforced flame-retardant PP plastic granules.

2. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The halogen-free flame retardant is ammonium polyphosphate (APP) or melamine polyphosphate (MPP).

3. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The synergistic flame retardant is melamine cyanurate (MCA) treated with silane coupling agent KH-560, with a particle size D50 ≤ 15 μm.

4. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The mass ratio of the halogen-free flame retardant to the synergistic flame retardant is (2:1) to (1.5:1).

5. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The surface-modified glass fiber is a short, alkali-free glass fiber that has been surface-treated with an epoxy silane coupling agent KH-560. The fiber diameter is 10-13 μm and the length is 4-5 mm.

6. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The mixing temperature in S2 is controlled at 50±2℃, and the total mixing time is 7 minutes.

7. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 1.0%-1.2% and a melt flow rate of 50-80 g / 10 min (190℃, 2.16 kg).

8. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The screw configuration of the twin-screw extruder includes 5 sets of kneading blocks and 3 reverse screw elements; wherein, the kneading blocks located in the melting zone adopt a 45° staggered angle, and the kneading blocks located in the homogenization zone adopt a 60° staggered angle.

9. The method for preparing reinforced flame-retardant PP plastic according to claim 1, characterized in that: The water temperature in the cooling water tank is controlled at 25-35℃, and the immersion length of the material strip in the water tank is greater than 2 meters.

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