A high-strength, low-precipitation halogen-free flame-retardant polyamide composition and preparation method thereof

Abstract

The present invention discloses a high-strength, low-precipitation halogen-free flame-retardant polyamide composition and its preparation method. The composition comprises the following raw materials, measured by weight: 26-89.98% polyamide resin; 10-35% filler; 0.01-25% flame retardant; 0.01-10% modified synergistic flame retardant; 0-1% antioxidant; 0-2% processing aid; and 0-1% masterbatch. This invention addresses the "pain point" of halogen-free flame-retardant nylon materials, which are prone to precipitation. Based on the structural characteristics of nylon materials, the present invention introduces a flame retardant with a novel structure in the formulation design to balance the char layer thickness and char layer fluidity during the combustion process, thereby improving the flame retardant efficiency. Furthermore, a modified synergist is introduced, and the synergistic effect of the synergist and the flame retardant further enhances the flame retardant efficiency. Surface treatment of the synergist increases its compatibility with the polyamide resin, avoiding the risk of precipitation.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a high-strength, low-precipitation halogen-free flame-retardant polyamide composition and a preparation method thereof. Background Art

[0002] Polyamide (nylon) has a history of over 80 years since its commercialization by DuPont, and over 60 years of use as an engineering plastic. Polyamide boasts excellent properties such as high strength, wear resistance, heat resistance, and solvent resistance, making it widely used in automobiles, electronics, civil aircraft, and home appliances. It ranks first among general-purpose engineering plastics (PA, PC, POM, PBT / PET, and PPO). The application of polyamide in engineering plastics often requires resin modification based on the required operating conditions.

[0003] Flame-retardant polyamide materials are widely used in power batteries, high-speed railways, civil aircraft and other fields. The flame-retardant paths of polymers include: grafting and cross-linking modification technology, gas-phase flame-retardant technology, free radical inhibitors in the condensed phase, catalytic carbonization technology, flame-resistant coating technology, cooling flame-retardant technology, etc. In the preparation process of flame-retardant nylon materials, the flame retardancy of nylon materials is usually achieved by mechanically blending flame retardants in the preparation process of composite materials, grafting or bonding flame-retardant groups on the polymer chain or surface, and copolymerization with flame-retardant monomers. The mechanical blending of flame retardants is the most widely used method in the preparation process of composite materials.

[0004] Chinese patent CN202210816927 discloses a halogen-free intumescent flame-retardant nylon 66 composition, a nylon 66 composite material, and methods for preparing the same. The halogen-free intumescent flame retardant comprises a phosphorus-based flame retardant, a nitrogen-based flame retardant, and nano-montmorillonite. The phosphorus-based and nitrogen-based flame retardants react to form a cross-linked coating containing P-N bonds. The presence of the nano-montmorillonite promotes the formation of a carbonized layer during combustion, improving the flame retardancy of PA66. Chinese patent CN202210998254 discloses a flame-retardant nylon material and a method for preparing the same. The steps involve melting nylon and filling the melted nylon with chiral helical silica nanotubes. The nylon-filled chiral helical silica nanotubes, glass fiber, modified asbestos, a compatibilizer, and an anti-aging agent are then mixed, heated, and kneaded in a kneader for at least 10 minutes to obtain a mixture. The resulting mixture is then melt-extruded through a twin-screw extruder to obtain composite particles. The composite particles exhibit certain flame retardant properties. Chinese patent CN202210666576 discloses a high-glow-wire halogen-free, environmentally friendly flame-retardant nylon 66. This flame-retardant material utilizes a combination of phosphorus and nitrogen-based halogen-free flame retardants, which together form a gas-phase and condensed-phase flame-retardant mechanism. The flaky α-zirconium phosphate loaded onto the surface of graphene oxide not only increases the thermal oxidative stability of the graphene oxide but also catalyzes carbonization, contributing to a synergistic improvement in the thermal stability and flame retardancy of the polymer composite. This addresses the complex preparation process and high energy consumption associated with graphene-loaded zirconium phosphate composites, enabling large-scale production. Recent patents have focused on the development of halogen-free flame-retardant nylon materials composed of phosphorus-based flame retardants and synergists. While these systems offer environmental advantages over halogen-based flame-retardant systems, they are susceptible to precipitation during the injection molding process and in high-temperature, high-humidity environments, limiting their application. Furthermore, most published research focuses on mechanical blending and modification of flame retardants, with relatively little research on the molecular structure design of flame retardants, hindering the advancement of halogen-free flame-retardant nylon technology. Summary of the Invention

[0005] In order to fill the gap in the prior art, the present invention provides a high-strength, low-precipitation halogen-free flame-retardant polyamide composition and a preparation method thereof. Through the design of the flame retardant molecular structure, a flame retardant with a completely new structure is introduced, which improves the flame retardant efficiency and reduces the amount of flame retardant added, thereby achieving the high strength of the flame-retardant polyamide material. The amount of flame retardant added is further reduced by adding a modified synergistic flame retardant, and the precipitation of the synergistic flame retardant is avoided by pretreatment, thereby achieving the high strength and low precipitation characteristics of the flame-retardant polyamide material.

[0006] The present invention is achieved through the following technical solutions:

[0007] A high-strength, low-elution halogen-free flame-retardant polyamide composition, comprising the following raw materials in parts by weight:

[0008]

[0009] The polyamide resin may be one or more of PA6, PA56, PA66, PA6 / 66, PA66 / 6, PA66 / 6T, PA6T / X, PA10T, PA10T / X, PA9T, PA46, PA4T, PA5T, PA5T / X, etc.;

[0010] The filler can be fibrous or non-fibrous according to its form. The fibrous filler can be one or more of glass fiber, aramid fiber, carbon fiber, basalt fiber, etc., and the non-fibrous filler can be one or more of whiskers, wollastonite, mica, kaolin, talc, glass beads, and calcium carbonate.

[0011] The preferred filler of the present invention is glass fiber, with an alkali content of less than 0.8%, a bulk density of 0.6-0.8 g / cm3, a monofilament fiber diameter of 7-13 μm, a short cut length of 2-5 mm, and a moisture content of ≤0.05%.

[0012] The flame retardant is diethyl hypophosphite ethyl aluminum diphosphate. It has a whiteness greater than 95%, moisture less than 0.3%, a pH greater than 4, a phosphorus content of 25-28%, an aluminum content of 7-8%, a density of 1.34-1.38 g / cm³, and a particle size (D50) of 10-20 μm. The flame retardant has the following structural formula:

[0013]

[0014] The synergistic flame retardant is modified zinc aluminum tripolyphosphate with a whiteness greater than 90%, an effective content of P2O5 of 48-52%, an effective content of Al2O3 of 13-15%, an effective content of ZnO of 18-22%, a pH value of 5-7%, and a particle size (D50) less than 5 μm.

[0015] The modified aluminum tripolyphosphate is prepared by treating the above-mentioned aluminum zinc tripolyphosphate with a surface treatment agent and using foamed nylon as a carrier.

[0016] The antioxidant is a mixture of a phosphite antioxidant and a hindered phenol antioxidant in a ratio of 1:1 (by weight), wherein the phosphite antioxidant can be tris[2,4-di-tert-butylphenyl]phosphite, CAS No. 31570-04-4; 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, CAS No. 154862-43-8; the hindered phenol antioxidant can be N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, CAS No. 23128-74-7; triethylene glycol ether-bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, CAS No. No.36443-68-2; at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, CAS No.6683-19-8, etc.

[0017] The hindered phenol antioxidant of the present invention is preferably N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, and the phosphite antioxidant is preferably tris[2,4-di-tert-butylphenyl]phosphite.

[0018] The processing aid is an organic additive that can provide both internal and external lubrication without affecting flame retardancy, and can be one or more of silicone powder, silicone masterbatch, PETS, montan wax, polyethylene wax, oxidized polyethylene wax, calcium stearate, and the like.

[0019] The processing aid of the present invention is preferably a mixture of silicone powder, phenyl silicone and silicon dioxide in a ratio of 1:1.

[0020] The color masterbatch has a carbon black content of 10-99% and a carrier of PA6 or a lubricant.

[0021] The high-strength, low-precipitation halogen-free flame-retardant polyamide composition and the preparation method thereof comprise the following steps:

[0022] (1) The moisture content of the polyamide resin is not higher than 2000 ppm;

[0023] (2) Weighing various dried raw materials according to the formula ratio; mixing the polyamide resin, flame retardant, modified synergistic flame retardant, antioxidant, processing aid, and masterbatch uniformly with a high-speed mixer and setting aside; weighing the filler according to the ratio and setting aside;

[0024] (3) The resin and additive mixture is added through the main feed port of a twin-screw extruder, and the filler is added from the side feed port of the twin-screw extruder. After melt extrusion, granulation, drying and other processes at 260°C, the halogen-free flame retardant polyamide composition is obtained.

[0025] The above-mentioned halogen-free polyamide composition can be used in the fields of new energy vehicles, electronic appliances, connectors, etc.

[0026] Beneficial effects of the present invention:

[0027] 1) Aluminum diethyl hypophosphite (ADP) has a low carbon residue, allowing for a certain degree of fluidity in the initial carbon film formed upon combustion. However, this low carbon residue requires a high addition level to form a stable, sufficiently thick carbon film. Aluminum phosphate has a very high carbon residue, exceeding 50% even at 800°C, but the carbon film is very hard and lacks fluidity. The optimal performance is achieved when both are added in a specific ratio. By combining these two in a molecular structure design, a novel flame retardant, ethyl aluminum diethyl hypophosphite (EDP), has been introduced. This novel flame retardant, EDP, combines the effects of ADP and aluminum phosphate on carbon residue and carbon film fluidity, resulting in excellent flame retardancy. Furthermore, compared to ADP combined with aluminum phosphate or aluminum phosphite synergists, it is more efficient and requires a lower addition level, resulting in more favorable mechanical properties and low extractables. Compared to commercial products such as EDP, its unique structure allows it to achieve UL94 V0 flame retardancy even at low addition levels without the need for synergists.

[0028] 2) Modified zinc aluminum tripolyphosphate is used as a synergist. To achieve excellent flame retardancy, the content of each element of zinc aluminum tripolyphosphate is limited. To achieve a low precipitation effect, the zinc aluminum tripolyphosphate is surface-modified. The silane coupling agent in the surface treatment agent improves the compatibility of the synergistic flame retardant with nylon. The ethylene maleic anhydride copolymer in the surface treatment agent can chemically connect the synergist to the resin interface, and the foamed nylon is used as a carrier to increase the dispersibility of the synergistic flame retardant. The three work together to eliminate the risk of easy precipitation of the synergistic flame retardant, increase its flame retardant efficiency, and reduce the added amount.

[0029] 3) Usually, a multi-component compound of halogen-free flame retardants can achieve V0 flame retardancy of reinforced nylon under the UL94 standard. The diethyl hypophosphite ethyl dialuminum phosphate flame retardant used in the present invention can achieve V0 flame retardancy when added alone at a low addition amount, and has high flame retardancy efficiency.

[0030] 4) Modified aluminum zinc tripolyphosphate as a synergist reduces the amount of flame retardant added without affecting flame retardancy and precipitation, reduces the overall cost of materials, and improves product competitiveness.

[0031] The above-mentioned beneficial effects achieve the excellent flame retardant properties, low cost, low precipitation and high strength characteristics of the polyamide composition, thereby enhancing the market competitiveness of the product. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] The following materials are used in the examples and comparative examples of the present invention, but are not limited to the following materials:

[0034] Polyamide resin, trade name EPR27, produced by Shenma;

[0035] Flame retardant, trade name OP1230, produced by CLARIANT;

[0036] Flame retardant, trade name HR8900, produced by Weihai Hairun;

[0037] Glass fiber, trade name ECS301HP-3, produced by Chongqing International Composite Materials Co., Ltd.;

[0038] Flame retardant: diethyl hypophosphite ethyl aluminum diphosphate, commercially available;

[0039] Synergistic flame retardant, zinc aluminum tripolyphosphate, commercially available;

[0040] Synergistic flame retardant, modified zinc aluminum tripolyphosphate, homemade;

[0041] Processing aid, commercially available under the trade name silicone powder;

[0042] Antioxidant 1098, hindered phenol antioxidant, commercially available;

[0043] Antioxidant 168, a phosphite antioxidant, commercially available;

[0044] Black masterbatch, PA6-2015, commercially available;

[0045] Silane coupling agent: trade name A1100, produced by Momentive;

[0046] Ethylene maleic anhydride copolymer, trade name E60P, from Vertellus;

[0047] Adsorbent, trade name Accurel XP700, produced by 3M

[0048] Preparation of modified synergistic flame retardant:

[0049] 1) E60P and A1100 were added and mixed evenly in a ratio of 1:15 to prepare a surface treatment agent;

[0050] 2) preheating aluminum zinc tripolyphosphate to 100-110° C., adding the zinc tripolyphosphate to a high-speed mixer, stirring and drying for 10-15 minutes to ensure that the moisture content of the filler is less than 0.2%, adding a surface treatment agent to the aluminum zinc tripolyphosphate for activation modification for 5 minutes to prepare surface-treated aluminum zinc tripolyphosphate;

[0051] 3) The surface-treated aluminum zinc tripolyphosphate and Accurel XP700 were mixed in a ratio of 1:1 and mixed in a high-speed mixer for 10 minutes to prepare a modified synergistic flame retardant.

[0052] Preparation methods of Examples 1-10 and Comparative Examples 1-7:

[0053] Preparation of halogen-free flame retardant polyamide composition:

[0054] Weigh various dried raw materials according to the formula ratio; mix the polyamide resin, flame retardant, modified synergistic flame retardant, antioxidant, processing aid, and masterbatch uniformly with a high-speed stirrer and set aside; weigh the filler according to the ratio and set aside; add the above-mentioned resin and additive mixed raw materials through the main feeding port of the twin-screw extruder, and add the filler through the side feeding port of the twin-screw extruder; after melt extrusion, granulation, drying and other processes at 260°C, the halogen-free flame retardant polyamide composition is obtained.

[0055] Preparation of halogen-free flame retardant polyamide composition test specimens:

[0056] The above materials were dried in a forced air drying oven at 120° C. for 4 hours and then injection molded into standard specimens at an injection molding temperature of 280-300° C. The mechanical properties of the injection molded specimens were conditioned in a standard laboratory environment (23° C., 50% RH) for 24 hours before testing.

[0057] Test methods for various performance indicators:

[0058] Tensile properties: According to ISO 527 method, specimen size: 170*10*4mm, test speed 5mm / min.

[0059] Bending properties: According to ISO 178 method, specimen size: 80*10*4mm, test speed 2mm / min.

[0060] Notched impact performance: According to ISO 179 method, sample size: 80*10*4mm.

[0061] Flame retardant performance: According to UL94 method, sample size: 127*12.7*1.6mm.

[0062] Precipitation resistance: A sample of 150*100*3.2 mm was placed in an environmental chamber with the following settings: temperature: 85°C, humidity 85% RH, time: 200 h, and the state of the surface precipitates was visually evaluated.

[0063] Table 1: Composition and properties of halogen-free flame-retardant polyamide compositions of Examples 1-11:

[0064]

[0065] Table 2: Composition and properties of halogen-free flame retardant polyamide compositions of Comparative Examples 1-7:

[0066]

[0067] As can be seen from Tables 1 and 2, compared with other similar products commercialized on the market, diethyl hypophosphite ethyl dialuminum can effectively reduce the amount of flame retardant added (Examples 2-4 and Comparative Examples 6-7), which shows that the flame retardant efficiency of the flame retardant is high, while the effect on mechanical properties is small, and the prepared halogen-free flame retardant polyamide has the characteristics of high strength. Modified zinc aluminum tripolyphosphate replaces diethyl hypophosphite ethyl dialuminum diphosphate in the same proportion and can still achieve the same flame retardant effect (Examples 2-10), solving the risk of unmodified zinc aluminum tripolyphosphate easily precipitating and having a large impact on mechanical properties (Examples 5-7, Examples 10-11 and Comparative Examples 1-5), and the preparation method of modified zinc aluminum tripolyphosphate is simple and low in cost, which can enhance the market competitiveness of halogen-free flame retardant polyamide materials. The halogen-free flame retardant polyamide composition prepared by the present invention can be applied in the fields of energy vehicles, electronic appliances, connectors, etc.

Claims

1. A high-strength, low-precipitation halogen-free flame-retardant polyamide composition, characterized by: It is composed of the following raw materials in parts by weight: Polyamide resin 26-89.98%; Filler 10-35%; Flame retardant: 0.01-25%; Modified synergistic flame retardant: 0.01-10%; Antioxidants: 0-1%; Processing aids: 0-2%; Masterbatch: 0-1%; The flame retardant is diethyl hypophosphite ethyl diphosphate aluminum; whiteness> 95%, moisture < 0.3%, pH> 4, phosphorus content: 25-28%, aluminum content: 7-8%; density 1.34-1.38g / cm 3 ; Particle size D50 is 10-20μm; The structural formula of the flame retardant is as follows: ； The synergistic flame retardant is modified zinc aluminum tripolyphosphate, with whiteness greater than 90%, P2O5 effective content of 48-52%, Al2O3 effective content of 13-15%, ZnO effective content of 18-22%, pH value of 5-7%, and particle size D50 less than 5μm; the modified aluminum tripolyphosphate is prepared by treating the above zinc aluminum tripolyphosphate with a surface treatment agent and using foamed nylon as a carrier.

2. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The polyamide resin is one or more of PA6, PA56, PA66, PA6 / 66, PA66 / 6T, PA6T / X, PA10T, PA10T / X, PA9T, PA46, PA4T, PA5T, and PA5T / X.

3. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The filler is selected from fibrous or non-fibrous fillers according to its form. The fibrous filler is selected from one or more of glass fiber, aramid fiber, carbon fiber, and basalt fiber. The non-fibrous filler is selected from one or more of whiskers, wollastonite, mica, kaolin, talc, glass beads, and calcium carbonate.

4. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The filler is glass fiber, with an alkali content of less than 0.8%, a bulk density of 0.6-0.8 g / cm3, a single fiber diameter of 7-13 μm, a short cut length of 2-5 mm, and a moisture content of ≤0.05%.

5. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The antioxidant is a mixture of a phosphite antioxidant and a hindered phenol antioxidant in a weight ratio of 1:1, wherein the phosphite antioxidant is selected from at least one of tris[2,4-di-tert-butylphenyl]phosphite; 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane; and the hindered phenol antioxidant is selected from at least one of N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine; triethylene glycol ether-bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate; and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

6. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 5, characterized in that: The hindered phenol antioxidant is selected from N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, and the phosphite antioxidant is selected from tris[2,4-di-tert-butylphenyl]phosphite.

7. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The processing aid is an organic additive that can take into account both internal and external lubrication and does not affect the flame retardant performance; it is selected from one or more of silicone powder, silicone masterbatch, PETS, montan wax, polyethylene wax, oxidized polyethylene wax, and calcium stearate.

8. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The processing aid is silicone powder, which is composed of phenyl silicone and silicon dioxide, and the mass ratio of phenyl silicone to silicon dioxide is 1:

1.

9. The high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to claim 1, characterized in that: The masterbatch has a carbon black content of 10-99%, and the carrier is PA6 or a lubricant.

10. The method for preparing the high-strength, low-precipitation halogen-free flame-retardant polyamide composition according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) The moisture content of polyamide resin is not higher than 2000ppm; (2) Weigh the dried raw materials according to the formula ratio; mix the polyamide resin, flame retardant, modified synergistic flame retardant, antioxidant, processing aid, and masterbatch uniformly through a high-speed mixer and set aside; weigh the filler according to the ratio and set aside; (3) The resin and additive mixture is added through the main feed port of a twin-screw extruder, and the filler is added through the side feed port of the twin-screw extruder. After melt extrusion, granulation, and drying at 260°C, the halogen-free flame-retardant polyamide composition is obtained.

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