Phosphorus-containing bridging agent mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 master batch and preparation method thereof

Abstract

The invention belongs to the technical field of composite material polymer synthesis, and particularly relates to a phosphorus-containing bridging agent mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 master batch and a preparation method thereof. According to the flame-retardant nylon 6 master batch and the preparation method thereof, an enhanced phosphorus-nitrogen-inorganic synergistic flame-retardant system is constructed through a chemical bonding compound system mediated by the red phosphorus coated SiO / MF chemical bonding type double-layer shell microcapsule and a phosphorus-containing bridging agent, the flame-retardant nylon 6 master batch is prepared, the LOI of flame-retardant nylon 6 fibers prepared from the flame-retardant nylon 6 master batch and pure nylon 6 through melt spinning reaches 31% or above, the UL94 grade is V-0, vertical combustion is achieved, and the flame-retardant nylon 6 fibers have good flame retardance. And the molten drop phenomenon is avoided. According to the preparation method disclosed by the invention, Si-O-C covalent bonds between shell layers avoid layering and cracking, the phosphorus-containing bridging agent ensures that flame-retardant components are uniformly dispersed, cracking and leakage are avoided in a high-temperature spinning process at 230-260 DEG C, the problems that the existing microcapsules are poor in temperature resistance, red phosphorus is easy to oxidize and the compounding synergism is poor are solved, and the preparation method is safe and reliable and meets the environmental protection requirement.

Description

Technical Field

[0001] This invention belongs to the field of composite material polymer synthesis technology, specifically relating to a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch and its preparation method. Background Technology

[0002] Nylon 6 (Polyamide 6, PA6), as an important engineering plastic and fiber raw material, is severely limited in its application in safety-sensitive fields such as electronics, automotive, and high-end textiles due to its flammability (limiting oxygen index LOI of only about 24%). Developing a highly efficient, environmentally friendly flame-retardant nylon 6 that balances material mechanical and processing properties is a continuous pursuit of the industry. Among these, halogen-free phosphorus-based flame-retardant systems, with red phosphorus as their core, are considered one of the most promising technological approaches due to their significant advantages of high flame-retardant efficiency, low addition amount, and low smoke emission.

[0003] The flame-retardant mechanism of red phosphorus mainly lies in its ability to generate substances such as polymetaphosphoric acid during combustion, which form a dense, carbonized protective layer on the polymer surface, providing heat insulation and oxygen barrier properties. However, ordinary red phosphorus has a series of inherent defects, including easy moisture absorption and oxidation, release of highly toxic phosphine (PH3) gas, poor compatibility with the polymer matrix, dark color, and negative impact on the electrical properties of materials. Surface modification is necessary for practical application. Microencapsulation is an effective means to solve these problems. Under the protection of capsule walls formed by melamine-formaldehyde resin (MF), phenolic resin, or inorganic materials, the stability, ignition point, and compatibility with resins of red phosphorus are significantly improved.

[0004] To further improve flame retardant efficiency and enhance the overall performance of composite materials, the combination of microencapsulated red phosphorus with inorganic synergists such as metal hydroxides (e.g., magnesium hydroxide, aluminum hydroxide) and hypophosphite has become a mainstream research direction. This combination aims to leverage the synergistic effect of different flame retardant mechanisms: red phosphorus promotes char formation in the condensed phase, while metal hydroxides function through decomposition endothermic reactions, dilution of combustible gases, and smoke suppression. However, a deeper analysis of existing technologies reveals that current mainstream solutions still face fundamental technical bottlenecks in achieving efficient, stable, and long-lasting synergy in the following three dimensions: First, the "pseudo-synergy" and interface defects caused by physical compounding. Most current technical solutions, such as those disclosed in patents CN101684196A and CN120158088A, essentially involve mechanically and physically blending pre-prepared microcapsule red phosphorus with modified inorganic powders (such as magnesium hydroxide and aluminum hypophosphite). This simple physical mixing cannot achieve a strong bond between the two components at the microscale. During the high-shear processing of nylon 6 melt, flame retardant particles with vastly different densities and surface properties are prone to phase separation and localized agglomeration, forming microscopic "island structures." This not only leads to uneven distribution of the flame retardant components in the matrix, affecting the stable performance of flame retardant efficiency, but also creates numerous stress concentration points at the heterogeneous phase interface, severely damaging the mechanical properties of the composite material, especially impact strength and tensile strength. To solve the dispersion problem, existing technologies generally rely on general-purpose coupling agents such as silanes and aluminates for surface pretreatment of the inorganic powders. However, the coupling agent lacks specific chemical interaction with organic wall materials such as MF on the surface of microcapsule red phosphorus, resulting in limited and difficult-to-control modification effects.

[0005] Second, there is a lack of "directional chemical bridging" designed specifically for flame-retardant functionality. The more fundamental problem lies in the difficulty of achieving instantaneous and efficient intrinsic synergy between physically mixed flame-retardant components under extreme combustion conditions. Red phosphorus and metal hydroxides need to be in close contact and undergo a chemical reaction at the combustion front to maximize the synergistic char-forming effect. The random distribution of physically mixed components leads to a large amount of effective components being isolated by the polymer matrix, reducing the reaction probability and significantly diminishing the synergistic efficiency.

[0006] Third, there is a contradiction between the performance limitations and long-term effectiveness of existing microcapsule wall materials. Currently, most microcapsule red phosphorus wall materials use single materials such as MF resin, which are at risk of degradation under long-term thermal aging or humid and hot environments. This may lead to a decline in the protective function of the capsule wall, slow exposure of red phosphorus, and consequently, decreased material weather resistance, deterioration of electrical properties (reduction in the tracking index CTI), and a decline in mechanical properties over time. Patent CN120158088A attempts to mitigate the negative impact of red phosphorus decomposition on acidic substances by adding additional acid scavengers and water scavengers, but this is a passive remedial measure that increases the complexity and cost of the formulation and fails to enhance the barrier stability of the microcapsule wall material itself and its binding force with synergists from the source. In summary, existing technologies have failed to address the three core contradictions in the combination system of microencapsulated red phosphorus and inorganic synergists: "weak interfacial bonding," "non-synergistic function," and "unstable long-term effect." Therefore, there is an urgent need in this field for an innovative technical solution that should not be limited to the later physical assembly of independent components, but rather should start from the molecular design of the flame-retardant system to construct an integrated composite flame-retardant unit linked by chemical bonds and guided by synergistic flame-retardant function. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch and its preparation method, and to provide a flame-retardant masterbatch technical solution that is suitable for spinning process and takes into account high efficiency flame retardancy, excellent mechanical properties, good stability and environmental protection.

[0008] The technical solution adopted is as follows: A method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch includes the following steps: (1) Preparation of red phosphorus@SiO2 / MF double-shell microcapsules ① The industrial red phosphorus powder was ball-milled to obtain submicron-sized red phosphorus powder, which was then sealed and stored for later use. ② Add styrene-maleic anhydride copolymer (SMA) and sodium hydroxide to deionized water, heat and stir until completely dissolved to obtain a styrene-maleic anhydride copolymer emulsifier solution, and cool to room temperature for later use. ③ Submicron-sized red phosphorus powder and tetraethyl orthosilicate (TEOS) are placed in a reactor and stirred until homogeneous. A styrene-maleic anhydride copolymer emulsifier solution is added and stirred until homogeneous to obtain an oil-in-water (O / W) emulsion. The emulsion is then transferred to a constant temperature water bath, heated, and stirred to allow the tetraethyl orthosilicate to undergo preliminary hydrolysis, forming a SiO2 precursor shell rich in silanol groups on the surface of the red phosphorus, thus obtaining a SiO2 precursor emulsion coated with red phosphorus. ④ Add melamine, formaldehyde solution, urea and deionized water to a three-necked flask, stir to dissolve, then adjust the pH value of the system, raise the temperature and stir to obtain a transparent and viscous melamine-formaldehyde (MF) prepolymer solution, and cool for later use. ⑤ Slowly add the prepolymer solution prepared in step ④ to the SiO2 precursor emulsion in step ③ while stirring; after the addition is complete, adjust the pH value of the system, raise the temperature and stir and continue the reaction to make the prepolymer solution crosslink and polymerize on the surface of the SiO2 precursor emulsion. After the reaction was completed, the pH of the system was adjusted to neutral to terminate the reaction and obtain the microcapsule suspension. The pH of the microcapsule suspension was adjusted to alkaline, and the mixture was heated in a water bath with stirring to promote the solidification of the SiO2 shell. The product was centrifuged, the precipitate was collected, washed, dried and sieved to remove large agglomerated particles, and red phosphorus@SiO2 / MF double-shell microcapsules were obtained. (2) Preparation of DOPO-epoxypropyl ether (DOPO-GE) Under nitrogen protection, DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and toluene were mixed evenly, and the temperature was raised to completely dissolve DOPO. After adding the catalyst and stirring until homogeneous, epichlorohydrin was added dropwise. After the addition was complete, the mixture was heated and refluxed. After reflux was complete, the reaction solution was cooled and NaOH aqueous solution was added dropwise. After the addition was complete, the reaction was kept at the temperature to carry out the dehydrochlorination ring-closure reaction. After the reaction was complete, the target product was collected to obtain a pale yellow transparent liquid, which is DOPO-epoxypropyl ether. (3) Linkage between red phosphorus@SiO2 / MF double-shell microcapsules and Mg(OH)2 nanoparticles The red phosphorus@SiO2 / MF double-shell microcapsules and nano magnesium hydroxide particles were dried separately. Dried DOPO-glycidyl ether was diluted, and dried red phosphorus@SiO2 / MF double-shell microcapsules were weighed and added to a high-speed mixer. The mixture was heated and stirred, and the diluted DOPO-glycidyl ether was evenly sprayed onto the surface of the red phosphorus@SiO2 / MF double-shell microcapsules using a sprayer. Dried nano-magnesium hydroxide was added and stirring was continued. The high-speed mixer was turned off, and the material was allowed to cool to room temperature. The material was then removed and passed through a 500-mesh vibrating sieve, and the sieve residue was collected. The sieve residue was dried to obtain a compound flame retardant powder with "magnesium hydroxide fixed on the surface of the microcapsules", namely, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant. (4) Preparation of flame-retardant nylon 6 masterbatch a. Dry PA6 slices, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, zinc stearate, antioxidant, and polyethylene wax separately; b. Weigh the dried PA6 chips, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, zinc stearate, antioxidant, and polyethylene wax, add them to a high-speed mixer, and stir at room temperature to obtain a uniform mixture. c. The mixture is added to a twin-screw extruder. After melt blending, the material is extruded into strips through the die head and cooled to room temperature by an air-cooled conveyor belt. d. The cooled strips are fed into a pelletizer and cut into masterbatches; the masterbatches are then screened by a vibrating screen to remove powder and irregular particles, dried, and sealed in packaging to obtain flame-retardant nylon 6 masterbatches. The flame-retardant nylon 6 masterbatch is mixed with pure nylon 6 chips and then melt-spun to obtain flame-retardant nylon 6 fibers.

[0009] Preferably, in step (1), industrial red phosphorus powder is placed into a ball mill jar lined with zirconia, nitrogen is injected to replace the air in the jar, and zirconia balls are added, wherein the ball-to-material ratio is 8:1; The powder was pulverized using a planetary ball mill at a speed of 400–450 r / min for 4–6 h. The pulverized powder was then passed through a 1000-mesh standard sieve to remove large particles and impurities. The sieve-underfill material was collected to obtain submicron-sized ultrafine red phosphorus powder with a particle size of 0.5–1.0 μm.

[0010] Preferably, in step (1) when preparing the emulsifier, the maleic anhydride content in the styrene-maleic anhydride copolymer is 30-40 wt%; the mass ratio of the styrene-maleic anhydride copolymer, the mass of sodium hydroxide, and the volume ratio of deionized water is 1-2 g: 0.8-1.5 g: 100 mL. The heating temperature is 70-80℃, the rotation speed is 250-300 r / min, and the stirring time is 2-3 h.

[0011] Preferably, in step (1) when preparing the SiO2 precursor emulsion, the mass ratio of submicron red phosphorus powder to tetraethyl orthosilicate is 1:1; The pH of the styrene-maleic anhydride copolymer emulsifier solution was adjusted to 4-5 with citric acid; the speed of the high-speed homogenizer was 10000-15000 r / min, and the emulsification time was 30-50 min; The resulting oil-in-water emulsion was reacted in a constant temperature water bath at 50–60°C with stirring at 200 r / min for 1–2 h.

[0012] Preferably, in step (1) when preparing the melamine-formaldehyde prepolymer, the mass ratio of melamine, formaldehyde solution and urea is 1:2-5:0.2-0.5, wherein the mass fraction of formaldehyde in the formaldehyde solution is 37%; the mass ratio of melamine to deionized water is 1g:10-15mL. After stirring and dissolving, adjust the pH of the system to 8-9 with triethanolamine, then heat to 60-70℃ and stir for 1-2 hours. The prepared melamine-formaldehyde prepolymer solution was added dropwise to the SiO2 precursor emulsion at a rate of 1–5 mL / min, while stirring at 200–300 r / min. After the addition was complete, the pH of the system was adjusted to 4–5 with citric acid, the temperature was raised to 50–60℃ and stirred for 20–30 min, and then the temperature was raised to 70℃ at a rate of 1–5℃ / min, and the reaction was continued for 1–2 h. After the reaction was completed, 20% sodium hydroxide solution was added to adjust the pH of the system to neutral. The pH of the obtained microcapsule suspension was adjusted to 10-11 with ammonia water. The suspension was stirred at 80 r / min for 2 h in a 60℃ water bath to promote the solidification of the SiO2 shell. The obtained product was centrifuged at 2000-3000 r / min for 10-15 min, the precipitate was collected, washed 2-3 times with deionized water and 1-2 times with anhydrous ethanol, dried and then passed through a 500-mesh sieve.

[0013] Preferably, in step (2), the mass ratio of DOPO to toluene is 2-3 g: 5 mL; Heat to 80-90℃ to completely dissolve DOPO; The catalyst added was benzyltriethylammonium chloride, wherein the mass ratio of DOPO to the catalyst was 30-50:1; The volume ratio of epichlorohydrin to toluene added was 11:10, the dropping rate was 1-5 mL / min, and the temperature was maintained at 85-95℃. After the dropping was completed, the temperature was raised to 100-110℃ and the reaction was refluxed for 6-8 h. After reflux, the reaction solution is cooled to 40-50°C, and 50% NaOH aqueous solution is added dropwise at a rate of 1-5 mL / min for 30 min, with the temperature controlled at 45-55°C. After the addition is complete, the reaction is kept at 50°C for 4-6 h to carry out the dehydrochlorination ring-closing reaction. The target product was collected by vacuum distillation at a vacuum level of 0.01 MPa and a temperature of 180–190 °C.

[0014] Preferably, in step (3), the moisture content of the red phosphorus@SiO2 / MF double-shell microcapsules and nano magnesium hydroxide particles is controlled to be ≤0.1% after drying; DOPO-epoxypropyl ether is diluted with anhydrous ethanol or methanol to a mass fraction of 10% to 15%. In a high-speed mixer, the temperature is set to 80℃ and the stirring speed to 600 r / min, and preheating is performed for 5 min. When spraying, the amount of DOPO-epoxypropyl ether is 3% to 5% of the total mass of red phosphorus@SiO2 / MF double-shell microcapsules and magnesium hydroxide. The stirring time is 25 to 30 min.

[0015] As a further preferred option, the mass ratio of red phosphorus@SiO2 / MF double-shell microcapsules to nano-magnesium hydroxide is 2-3:1.

[0016] Preferably, in step (4), the antioxidant is antioxidant 1010; by weight, 50-60 parts of nylon 6 chips, 35-40 parts of modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, 2-3 parts of zinc stearate, 1-2 parts of antioxidant 1010, and 1-2 parts of polyethylene wax. In the twin-screw extruder, the extrusion process parameters are set as follows: zone 1 temperature 220℃, zone 2 temperature 235℃, zone 3 temperature 245℃, zone 4 temperature 250℃, die head temperature 248℃, and screw speed 300 r / min.

[0017] Preferably, in step (4), the material strip is cut into masterbatch with a length of 2-3 mm; The flame-retardant nylon 6 masterbatch and pure nylon 6 chips are mixed at a mass ratio of 1:2 to 5 and then melt-spun, with a preferred mass ratio of 1:4 to 5. The spinning temperature is 230–260℃ and the draw ratio is 3–5 times.

[0018] The present invention also provides a flame-retardant nylon 6 masterbatch, which is prepared by a method for preparing a flame-retardant nylon 6 masterbatch synergistically using red phosphorus microcapsules mediated by a phosphorus-containing bridging agent according to the present invention.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, the phosphorus element provided by red phosphorus and the nitrogen element provided by MF form a classic phosphorus-nitrogen synergistic system: the nitrogen element promotes the oxidative decomposition of red phosphorus and accelerates the generation of phosphoric acid substances; the phosphorus element promotes the char formation reaction of MF and forms a denser phosphorus-nitrogen composite char layer, with a flame retardant efficiency far higher than that of single red phosphorus or single MF system.

[0020] (2) In this invention, the organic MF layer and the inorganic SiO2 layer form a "soft and hard combination" double-wall structure: the inner shell of SiO2 has excellent mechanical strength and thermal stability (resisting high-temperature shearing during spinning), and the outer shell of MF has good coating and char-forming properties (forming a dense char layer during combustion). The combination of the two not only solves the problem of poor shear resistance of pure MF wall material, but also makes up for the defect of loose coating of pure SiO2 wall material, ensuring the structural stability of the double-shell microcapsules during extrusion processing and combustion.

[0021] (3) In this invention, the gas phase flame retardancy of double-shell microencapsulated red phosphorus and the condensed phase flame retardancy of nano-magnesium hydroxide complement each other: red phosphorus inhibits the gas phase combustion chain reaction, while magnesium hydroxide inhibits the heat transfer of the condensed phase by absorbing heat and forming a barrier; at the same time, the MgO produced by decomposition can neutralize the acidic phosphorus oxides produced by the combustion of red phosphorus, reduce the emission of corrosive gases, and achieve the triple effect of "flame retardancy + smoke suppression + toxicity reduction".

[0022] (4) In this invention, the phosphorus-containing bridging agent realizes the covalent bond connection between the red phosphorus@SiO2 / MF double-shell microcapsule and magnesium hydroxide. The dual action constructs a multi-dimensional bonding network of "powder-bridging agent-coupling agent-matrix", which greatly improves the dispersibility of inorganic powder in nylon matrix and enhances the interfacial bonding force, thereby achieving a balance between flame retardant performance and mechanical properties, thus ensuring the long-term flame retardant performance.

[0023] (5) The flame-retardant PA6 masterbatch prepared by the present invention is mixed with pure PA6 and spun. The stability of the chemical bond enhances the long-term weather resistance of the entire flame-retardant system. Finally, with a low total addition amount, nylon 6 obtains excellent and long-lasting flame-retardant properties, while retaining its inherent mechanical and processing properties to the greatest extent. Attached Figure Description

[0024] Figure 1 This invention describes the preparation mechanism of red phosphorus@SiO2 / MF double-shell microcapsules.

[0025] Figure 2 This is the preparation process of DOPO-GE according to the present invention.

[0026] Figure 3 This invention describes the reaction process of DOPO-GE with red phosphorus@SiO2 / MF double-shell microcapsules and Mg(OH)2. Detailed Implementation

[0027] The accompanying drawings are for illustrative purposes only; to enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples, but should not be construed as limiting the present patent.

[0028] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods or obtained from conventional commercial sources.

[0029] Example 1 A method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch includes the following steps: (1) Preparation of red phosphorus@SiO2 / MF double-shell microcapsules ① Preparation of submicron-sized red phosphorus powder Industrial red phosphorus powder was placed in a zirconia-lined ball mill jar, and nitrogen was injected to replace the air inside the jar (to ensure an oxygen-free environment and prevent red phosphorus oxidation). Zirconia balls (ball-to-powder ratio 8:1) were added, and the mixture was pulverized for 5 hours using a planetary ball mill at a speed of 450 r / min. The pulverized powder was then passed through a 1000-mesh standard sieve to remove large particles and impurities. The sieve-passing material was collected to obtain submicron-sized ultrafine red phosphorus powder with a particle size of 0.5–1.0 μm, which was then sealed and stored for later use.

[0030] ② Preparation of SMA emulsifier solution Add 2 g of styrene-maleic anhydride copolymer (SMA, maleic anhydride content 30%) and 1.5 g of sodium hydroxide to 100 mL of deionized water. Heat at 80 °C and stir at 300 r / min for 3 h until SMA is completely dissolved to obtain a 2 wt.% SMA emulsifier solution. Cool to room temperature for later use.

[0031] ③ Preparation of SiO2 precursor emulsion Take 10 g of the submicron-sized red phosphorus powder prepared in step ① and 10 g of tetraethyl orthosilicate (TEOS) and place them in a beaker. Stir at 500 r / min for 15 min to mix evenly. Adjust the pH of the SMA emulsifier solution to 4.5 with citric acid and pour it into the above red phosphorus / TEOS mixture. Transfer it to a high-speed homogenizer and emulsify at 15000 r / min for 30 min to obtain a uniform oil-in-water (O / W) emulsion. Transfer the emulsion to a constant temperature water bath and stir at 200 r / min for 2 h at 60℃ to allow TEOS to undergo preliminary hydrolysis and form a SiO2 precursor shell rich in silanol groups (-Si-OH) on the surface of red phosphorus to obtain a SiO2 precursor emulsion coated with red phosphorus.

[0032] ④ Preparation of melamine-formaldehyde (MF) prepolymer Add 4 g of melamine, 15 g of formaldehyde solution (37% by mass), 1.25 g of urea and 50 mL of deionized water to a three-necked flask, stir to dissolve, adjust the pH of the system to 8.5 with triethanolamine, raise the temperature to 70°C, stir at 250 r / min for 1 h to obtain a transparent and viscous MF prepolymer solution, and cool to 40°C for later use.

[0033] ⑤ Preparation of red phosphorus@SiO2 / MF double-shell microcapsules The MF prepolymer solution prepared in step ④ was slowly added dropwise to the SiO2 precursor emulsion in step ③, while stirring at 300 r / min. After the addition was complete, the pH of the system was adjusted to 4.5 with citric acid, the temperature was raised to 55℃ and stirred for 30 min, and then the temperature was slowly raised to 70℃ and the reaction was continued for 2 h to allow the MF prepolymer to crosslink and polymerize on the surface of the SiO2 precursor. After the reaction was completed, 20% sodium hydroxide solution was added to adjust the pH of the system to 7.0, and the reaction was terminated to obtain the microcapsule suspension. The pH of the suspension was adjusted to 11 with ammonia water, and stirred at 80 r / min for 2 h in a 60℃ water bath to promote the solidification of the SiO2 shell. The product was centrifuged (3000 r / min, 15 min), the precipitate was collected, washed 3 times with deionized water and 1 time with anhydrous ethanol, dried in a vacuum drying oven at 60℃ for 12 h, and then passed through a 500-mesh sieve to remove large agglomerated particles, thus obtaining red phosphorus@SiO2 / MF double-shell microcapsules.

[0034] (2) Preparation of DOPO-epoxypropyl ether (DOPO-GE) Under nitrogen protection, 21.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 50 mL of toluene were uniformly mixed and heated to 90 °C to completely dissolve the DOPO. 0.5 g of benzyltriethylammonium chloride (TEBA) catalyst was added, and after stirring, epichlorohydrin (55 mL, 0.69 mol) was slowly added dropwise while maintaining the temperature at 85-95 °C. After the addition was complete, the temperature was raised to 100 °C and refluxed for 6 h. After reflux, the reaction solution was cooled to 45 °C, and 50% NaOH aqueous solution was slowly added dropwise over 30 min at a controlled temperature of 50 °C. After the addition was complete, the reaction was maintained at 50 °C for 6 h to carry out the dehydrochlorination ring-closure reaction. The target product was collected by vacuum distillation at 0.01 MPa and 185 °C, yielding a pale yellow transparent liquid, which is DOPO-GE.

[0035] (3) Linkage between red phosphorus@SiO2 / MF double-shell microcapsules and Mg(OH)2 nanoparticles Modified red phosphorus@SiO2 / MF double-shell microcapsules and nano-magnesium hydroxide particles (20-40 nm) were placed in a vacuum drying oven and dried at 80℃ for 12 h, controlling the moisture content to ≤0.1%. The dried DOPO-GE was diluted with anhydrous ethanol to a mass fraction of 10%-15%. The dried red phosphorus@SiO2 / MF double-shell microcapsules were weighed and added to a high-speed mixer. The temperature was set to 80℃ and the stirring speed to 600 r / min. After preheating for 5 min, the diluted DOPO-GE (red phosphorus@SiO2 / MF double-shell microcapsules: DOPO-GE dilution = 3:1) was evenly sprayed onto the surface of the red phosphorus@SiO2 / MF double-shell microcapsules using a sprayer, and stirring was continued for 15 min. Maintaining the high-speed mixer temperature at 80℃ and the speed at 600 r / min, the dried nano-magnesium hydroxide was added according to the ratio (keeping the ratio of red phosphorus@SiO2 / MF double-shell microcapsules: Mg(OH)2 = 3:1), and stirring was continued for 25-30 min. After min, turn off the high-speed mixer and wait for the material to cool to room temperature. Take it out and pass it through a 500-mesh vibrating screen to remove a small amount of unreacted agglomerated particles and collect the sieve material. Put the sieved material into a vacuum drying oven and dry it at 60℃ for 8 h to remove the trace amount of moisture generated by the reaction and obtain the compound flame retardant powder of "magnesium hydroxide fixed on the surface of microcapsules", namely modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant.

[0036] (4) Preparation of flame-retardant nylon 6 masterbatch ① Raw material drying PA6 chips, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, zinc stearate, antioxidant 1010, and polyethylene wax were placed in a vacuum drying oven and dried at 80℃ for 12 h to ensure that the moisture content of each raw material was ≤0.1% and to avoid the generation of air bubbles during extrusion.

[0037] ② Mixing ingredients Weigh out 55 parts by weight of dried PA6 chips, 40 parts of modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, 2 parts of zinc stearate, 1 part of antioxidant 1010, and 2 parts of polyethylene wax, add them to a high-speed mixer, and stir at 800 r / min for 20 min at room temperature to obtain a homogeneous mixture.

[0038] ③ Melt blending extrusion The mixture is added to a twin-screw extruder, and the extrusion process parameters are set as follows: zone 1 temperature 220℃, zone 2 temperature 235℃, zone 3 temperature 245℃, zone 4 temperature 250℃, die head temperature 248℃, and screw speed 300 r / min. After the material is melt-blended, it is extruded into strips through the die head and cooled to room temperature by an air-cooled conveyor belt.

[0039] ④ Pelletizing and drying The cooled strips are fed into a pelletizer and cut into masterbatches of 2-3 mm in length. The masterbatches are then screened to remove powder and irregular particles, dried in a vacuum drying oven at 60°C for 8 hours, and sealed in packaging to obtain flame-retardant nylon 6 masterbatches.

[0040] The above-mentioned flame-retardant nylon 6 masterbatch was mixed with pure PA6 chips at a mass ratio of 1:4, and then melt-spun (spinning temperature 240℃, draw ratio 4 times) to obtain flame-retardant nylon 6 fiber for testing fiber properties.

[0041] Synthesis and preparation principles: ① The formation principle of double-shell microcapsules like Figure 1As shown, SMA, as an amphiphilic emulsifier, adsorbs onto the surface of red phosphorus-TEOS mixed particles under high-speed shearing, forming a stable oil-in-water (O / W) emulsion. TEOS hydrolyzes under acidic conditions, forming a SiO2 precursor shell rich in silanol groups (-Si-OH). The MF prepolymer, positively charged under acidic conditions, interacts with the carboxyl groups (negatively charged) on the SMA molecular chain through electrostatic attraction, causing it to adsorb onto the precursor surface. The hydroxymethyl groups (-CH2OH) in the MF prepolymer undergo dehydration condensation with the silanol groups (-Si-OH) on the SiO2 precursor surface, forming Si-OC covalent bonds, achieving chemical bonding between the SiO2 inner layer and the MF outer layer. By adjusting the pH of the system, the MF prepolymer further condenses to form a three-dimensional network cross-linked shell. Water can penetrate the MF resin shell and contact the SiO2 precursor; this water is rich in OH groups. − 、 or H + This promotes further hydrolysis and condensation of the precursor. OH − or H + The melamine resin gradually diffuses into the aqueous layer, forming a SiO2 shell with melamine resin as the hard template. This ultimately results in a double-shell flame-retardant microcapsule with red phosphorus as the core material, SiO2 as the first shell, and MF resin as the second shell. Finally, a high-performance microphase change material is obtained by adjusting the MF / TEOS ratio, and the moisture in the microcapsules is evaporated by freeze-drying. The core of MF prepolymer preparation is the addition-condensation reaction between melamine and formaldehyde. However, to ensure sufficient hydroxymethylation of melamine (generating reactive sites), formaldehyde is usually added in excess, resulting in unreacted "free formaldehyde" remaining in the system after the reaction. Urea's role is to react with free formaldehyde through its own amino groups (−NH2), converting it into a non-volatile, chemically stable product, thus preventing formaldehyde release during subsequent high-temperature spinning (230-260℃) or product use.

[0042] The specific chemical reaction equation is as follows: (NH2)2CO+HCHO→HOCH2NHCONH2 (monohydroxymethylurea); HOCH2NHCONH2+HCHO→(HOCH2)2NHCONH2 (dihydroxymethylurea); HOCH2NHCONH2+H2NCONH2→NH2CONHCH2NHCONH2+H2O.

[0043] ② Bonding of red phosphorus@SiO2 / MF double-shell microcapsules and nanoparticles like Figure 2 , 3The reaction between DOPO and epichlorohydrin introduces an epoxy group (-CH2-CH(O)-CH2-) into the DOPO molecule, forming DOPO-GE. This molecule contains a phosphorus-phenanthroline ring and epoxy groups (highly reactive functional groups). The epoxy group can undergo a ring-opening addition reaction with hydroxyl groups (-OH) at relatively low temperatures, without the need for an additional catalyst (the -OH on the surface of red phosphorus@SiO2 / MF double-shell microcapsules / Mg(OH)2 can act as a nucleophile to initiate ring opening), forming a stable CO-covalent bond. The hydroxyl group (-CH(OH)-) generated after the epoxy group ring-opening can further form hydrogen bonds with the hydroxyl groups on the surface of unreacted particles. Simultaneously, the rigid ring structure of DOPO prevents close packing between particles, reducing agglomeration and allowing the compounded flame-retardant powder to be more evenly dispersed in the nylon 6 melt. Furthermore, the organic cyclic chain of DOPO-GE can form weak hydrogen bonds with the amide bonds of nylon 6, maximizing the retention of the fiber's original strength and further reducing the number of filament breakages during spinning.

[0044] Comparative Example 1: Red phosphorus@SiO2 / MF microcapsules were prepared without the addition of TEOS.

[0045] Except for omitting the TEOS, raw material, and SiO2 precursor emulsion preparation steps in the preparation of red phosphorus@SiO2 / MF microcapsules, the other raw materials, ratios, and preparation processes are the same as in Example 1; specifically, submicron-sized red phosphorus powder is directly mixed and emulsified with SMA emulsifier solution, and then MF prepolymer is added for encapsulation, forming only red phosphorus@MF single-layer shell microcapsules.

[0046] Comparative Example 2: Red phosphorus@SiO2 / MF microcapsules were hydrolyzed under different pH conditions during preparation.

[0047] During the preparation of red phosphorus@SiO2 / MF double-shell microcapsules, the system was adjusted to different pH values ​​during the solidification of the SiO2 shell. The remaining raw materials, proportions, and preparation processes were the same as in Example 1. Specifically, the pH of the red phosphorus@SiO2 / MF microcapsule suspension was adjusted to 5.0 using acetic acid, and the mixture was stirred in a 60°C water bath for 2 hours.

[0048] Comparative Example 3, without the addition of magnesium hydroxide.

[0049] Ten parts of modified nano magnesium hydroxide were removed from the raw material ratio, and the remaining raw materials, ratios and preparation processes were the same as in Example 1; that is, the raw material composition was: 55 parts of PA6 chips, 40 parts of modified red phosphorus@SiO2 / MF double-shell microcapsules, 2 parts of zinc stearate, 1 part of antioxidant 1010, and 2 parts of polyethylene wax.

[0050] Comparative Example 5: Simple compounding, no double shell + no bridging agent.

[0051] The microcapsules use a red phosphorus@MF single-layer shell (without TEOS). The microcapsules are physically blended with Mg(OH)2. No phosphorus-containing bridging agent is added during the compounding process (physical mixing). The remaining raw materials, proportions and preparation process are the same as in Example 1.

[0052] Comparative Example 6: It has a double shell and no bridging agent.

[0053] The preparation process of the double-shell microcapsules and the modification process of the double-shell microcapsules and magnesium hydroxide are the same as in Example 1 (SiO2 and MF are chemically combined), but no phosphorus-containing bridging agent is added during the compounding process. The microcapsules and magnesium hydroxide are only physically mixed. The other raw materials, ratios and preparation processes are the same as in Example 1.

[0054] The flame-retardant nylon 6 fiber samples prepared in Example 1 and Comparative Examples 1-6 were subjected to performance tests, and the results are shown in Table 1.

[0055] Table 1. Performance comparison of flame-retardant nylon 6 fiber samples prepared in Example 1 and Comparative Examples 1-6 As can be seen from Table 1, the fibers with the flame-retardant nylon 6 masterbatch prepared in this invention have the following effects: (1) Excellent flame retardant performance and significantly improved stability: Through the chemical bonding compound system mediated by red phosphorus@SiO2 / MF chemically bonded double-shell microcapsules and phosphorus-containing bridging agent, a reinforced phosphorus-nitrogen-inorganic synergistic flame retardant system is constructed, which makes the LOI of flame retardant nylon 6 fiber reach more than 31%, UL94 rating V-0, vertical burning GB 8410-2017 B1 level, and no dripping phenomenon; the Si-OC covalent bond between the shell layers avoids delamination and breakage, and the phosphorus-containing bridging agent ensures uniform dispersion of flame retardant components. There is no breakage and leakage during high-temperature spinning at 230-260℃, which solves the problems of poor temperature resistance of existing microcapsules, easy oxidation of red phosphorus, and poor compound synergy.

[0056] (2) The mechanical properties are well preserved and more stable: the benzene ring in the phosphorus bridging agent forms hydrogen bonds with the amide bond in nylon 6, which greatly improves the compatibility and dispersibility of inorganic flame retardant powder with nylon 6 matrix. The fiber breaking strength reaches more than 4.5 cN / dtex and the breaking elongation is 31%, which is not much different from the mechanical properties of pure nylon 6 fiber. This alleviates the defect of the fiber mechanical properties being greatly reduced due to the addition of flame retardant in the existing technology.

[0057] (3) Stronger processing adaptability: The total amount of flame retardant added is controlled within 30%, and the chemical bonding compound avoids agglomeration. The melt viscosity of Nylon 6 is more stable, the number of filament breakages during spinning is ≤2 times / 10 h, there is no clogging of the spinneret, it is fully compatible with melt spinning and high-speed spinning processes, and it is easy to carry out large-scale industrial production.

[0058] (4) Significantly improved water resistance: The modified flame retardant component is tightly bonded to the nylon 6 matrix through chemical bonding (coupling agent + bridging agent). After 50 washes, the LOI remains above 31.8%, and the flame retardant performance is almost unaffected, meeting the long-term use needs of clothing, home textiles and industrial textiles, and solving the problem of poor water resistance of existing flame retardant fibers.

[0059] (5) Excellent environmental performance and more efficient flame retardant synergy: The halogen-free flame retardant system is adopted, and there are no harmful gases or wastewater emissions during the production process; the phosphorus-containing bridging agent achieves both chemical bonding and participates in flame retardant synergy, which improves flame retardant efficiency while reducing the total amount added. The flame retardant components are stably bonded to the matrix, and there is no risk of migration and precipitation during use. It is safe and reliable and meets the requirements of global environmental regulations.

[0060] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch, characterized in that, Includes the following steps: (1) Preparation of red phosphorus@SiO2 / MF double-shell microcapsules ① The industrial red phosphorus powder was ball-milled to obtain submicron-sized red phosphorus powder, which was then sealed and stored for later use. ② Add styrene-maleic anhydride copolymer and sodium hydroxide to deionized water, heat and stir until completely dissolved to obtain styrene-maleic anhydride copolymer emulsifier solution, cool to room temperature for later use; ③ Place submicron-sized red phosphorus powder and tetraethyl orthosilicate in a reactor, stir and mix evenly, add styrene-maleic anhydride copolymer emulsifier solution, stir evenly to obtain an oil-in-water emulsion; transfer the emulsion to a constant temperature water bath, heat and stir to allow tetraethyl orthosilicate to undergo preliminary hydrolysis, forming a SiO2 precursor shell rich in silanol groups on the surface of red phosphorus, to obtain a SiO2 precursor emulsion coated with red phosphorus; ④ Add melamine, formaldehyde solution, urea and deionized water to a three-necked flask, stir to dissolve, then adjust the pH value of the system, raise the temperature and stir to obtain a transparent and viscous melamine-formaldehyde prepolymer solution, and cool it for later use. ⑤ Slowly add the prepolymer solution prepared in step ④ to the SiO2 precursor emulsion in step ③ while stirring; after the addition is complete, adjust the pH value of the system, raise the temperature and stir and continue the reaction to make the prepolymer solution crosslink and polymerize on the surface of the SiO2 precursor emulsion. After the reaction was completed, the pH of the system was adjusted to neutral to terminate the reaction and obtain the microcapsule suspension. The pH of the microcapsule suspension was adjusted to alkaline, and the mixture was heated in a water bath with stirring to promote the solidification of the SiO2 shell. The product was centrifuged, the precipitate was collected, washed, dried and sieved to remove large agglomerated particles, and red phosphorus@SiO2 / MF double-shell microcapsules were obtained. (2) Preparation of DOPO-epoxypropyl ether Under nitrogen protection, DOPO and toluene are mixed evenly, and the temperature is increased to completely dissolve DOPO; After adding the catalyst and stirring until homogeneous, epichlorohydrin was added dropwise. After the addition was complete, the mixture was heated and refluxed. After reflux was complete, the reaction solution was cooled and NaOH aqueous solution was added dropwise. After the addition was complete, the reaction was kept at the temperature to carry out the dehydrochlorination ring-closure reaction. After the reaction was complete, the target product was collected to obtain a pale yellow transparent liquid, which is DOPO-epoxypropyl ether. (3) Linkage between red phosphorus@SiO2 / MF double-shell microcapsules and Mg(OH)2 nanoparticles The red phosphorus@SiO2 / MF double-shell microcapsules and nano magnesium hydroxide particles were dried separately. Dried DOPO-glycidyl ether was diluted, and dried red phosphorus@SiO2 / MF double-shell microcapsules were weighed and added to a high-speed mixer. The mixture was heated and stirred, and the diluted DOPO-glycidyl ether was evenly sprayed onto the surface of the microcapsules using a sprayer. Dried nano-magnesium hydroxide was added and stirring was continued. The high-speed mixer was turned off, and the material was allowed to cool to room temperature. The material was then removed and passed through a 500-mesh vibrating sieve, and the sieve residue was collected. The sieve residue was dried to obtain a compound flame retardant powder with "magnesium hydroxide fixed on the surface of the microcapsules", namely, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant. (4) Preparation of flame-retardant nylon 6 masterbatch a. Dry PA6 slices, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, zinc stearate, antioxidant, and polyethylene wax separately; b. Weigh the dried PA6 chips, modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, zinc stearate, antioxidant, and polyethylene wax, add them to a high-speed mixer, and stir at room temperature to obtain a uniform mixture. c. The mixture is added to a twin-screw extruder. After melt blending, the material is extruded into strips through the die head and cooled to room temperature by an air-cooled conveyor belt. d. The cooled strips are fed into a pelletizer and cut into masterbatches; the masterbatches are then screened by a vibrating screen to remove powder and irregular particles, dried, and sealed in packaging to obtain flame-retardant nylon 6 masterbatches. The flame-retardant nylon 6 masterbatch is mixed with pure nylon 6 chips and then melt-spun to obtain flame-retardant nylon 6 fibers.

2. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (1), industrial red phosphorus powder is placed into a ball mill jar lined with zirconia, nitrogen is injected to replace the air in the jar, and zirconia balls are added, wherein the ball-to-material ratio is 8:

1. The powder was pulverized using a planetary ball mill at a speed of 400–450 r / min for 4–6 h. The pulverized powder was then passed through a 1000-mesh standard sieve to remove large particles and impurities. The sieve-underfill material was collected to obtain submicron-sized ultrafine red phosphorus powder with a particle size of 0.5–1.0 μm.

3. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (1), when preparing the emulsifier, the maleic anhydride content in the styrene-maleic anhydride copolymer is 30-40 wt%; the mass ratio of the styrene-maleic anhydride copolymer, the mass of sodium hydroxide, and the volume ratio of deionized water is 1-2 g: 0.8-1.5 g: 100 mL. The heating temperature is 70-80℃, the rotation speed is 250-300 r / min, and the stirring time is 2-3 h.

4. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (1), when preparing the SiO2 precursor emulsion, the mass ratio of submicron red phosphorus powder to tetraethyl orthosilicate is 1:

1. The pH of the styrene-maleic anhydride copolymer emulsifier solution was adjusted to 4-5 with citric acid; the speed of the high-speed homogenizer was 10000-15000 r / min, and the emulsification time was 30-50 min; The resulting oil-in-water emulsion was reacted in a constant temperature water bath at 50–60°C with stirring at 200 r / min for 1–2 h.

5. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (1), when preparing the melamine-formaldehyde prepolymer, the mass ratio of melamine, formaldehyde solution, and urea is 1:2-5:0.2-0.5, wherein the mass fraction of formaldehyde in the formaldehyde solution is 37%; the mass ratio of melamine to deionized water is 1g:10-15mL. After stirring and dissolving, adjust the pH of the system to 8-9 with triethanolamine, then heat to 60-70℃ and stir for 1-2 hours. The prepared melamine-formaldehyde prepolymer solution was added dropwise to the SiO2 precursor emulsion at a rate of 1–5 mL / min, while stirring at 200–300 r / min. After the addition was complete, the pH of the system was adjusted to 4–5 with citric acid, the temperature was raised to 50–60℃ and stirred for 20–30 min, and then the temperature was raised to 70℃ at a rate of 1–5℃ / min, and the reaction was continued for 1–2 h. After the reaction was completed, 20% sodium hydroxide solution was added to adjust the pH of the system to neutral. The pH of the obtained microcapsule suspension was adjusted to 10-11 with ammonia water. The suspension was stirred at 80 r / min for 2 h in a 60℃ water bath to promote the solidification of the SiO2 shell. The obtained product was centrifuged at 2000-3000 r / min for 10-15 min, the precipitate was collected, washed 2-3 times with deionized water and 1-2 times with anhydrous ethanol, dried and then passed through a 500-mesh sieve.

6. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (2), the mass ratio of DOPO to toluene is 2-3 g: 5 mL; Heat to 80-90℃ to completely dissolve DOPO; The catalyst added was benzyltriethylammonium chloride, wherein the mass ratio of DOPO to the catalyst was 30-50:1; The volume ratio of epichlorohydrin to toluene added was 11:10, the dropping rate was 1-5 mL / min, and the temperature was maintained at 85-95℃. After the dropping was completed, the temperature was raised to 100-110℃ and the reaction was refluxed for 6-8 h. After reflux, the reaction solution is cooled to 40-50°C, and 50% NaOH aqueous solution is added dropwise at a rate of 1-5 mL / min for 30 min, with the temperature controlled at 45-55°C. After the addition is complete, the reaction is kept at 50°C for 4-6 h to carry out the dehydrochlorination ring-closing reaction. The target product was collected by vacuum distillation at a vacuum level of 0.01 MPa and a temperature of 180–190 °C.

7. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (3), the red phosphorus@SiO2 / MF double-shell microcapsules and nano magnesium hydroxide particles are dried and the moisture content is controlled to be ≤0.1%; DOPO-epoxypropyl ether is diluted with anhydrous ethanol or methanol to a mass fraction of 10% to 15%. In a high-speed mixer, the temperature is set to 80℃ and the stirring speed to 600 r / min, and preheating is performed for 5 min. When spraying, the amount of DOPO-epoxypropyl ether is 3% to 5% of the total mass of red phosphorus@SiO2 / MF double-shell microcapsules and magnesium hydroxide. The stirring time is 25 to 30 min. The mass ratio of red phosphorus@SiO2 / MF double-shell microcapsules to nano-magnesium hydroxide is 2-3:

1.

8. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (4), the antioxidant is antioxidant 1010; by weight, 50-60 parts of nylon 6 chips, 35-40 parts of modified red phosphorus@SiO2 / MF-Mg(OH)2 microcapsule flame retardant, 2-3 parts of zinc stearate, 1-2 parts of antioxidant 1010, and 1-2 parts of polyethylene wax. In the twin-screw extruder, the extrusion process parameters are set as follows: zone 1 temperature 220℃, zone 2 temperature 235℃, zone 3 temperature 245℃, zone 4 temperature 250℃, die head temperature 248℃, and screw speed 300 r / min.

9. The method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch according to claim 1, characterized in that, In step (4), the material strip is cut into masterbatch with a length of 2-3 mm; The flame-retardant nylon 6 masterbatch and pure nylon 6 chips are mixed at a mass ratio of 1:2 to 5 and then melt-spun; wherein the spinning temperature is 230 to 260°C and the draw ratio is 3 to 5 times.

10. The flame-retardant nylon 6 masterbatch prepared by the method for preparing a phosphorus-containing bridging agent-mediated red phosphorus microcapsule synergistic flame-retardant nylon 6 masterbatch as described in any one of claims 1-9.

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