Continuous production method of modified nylon 6 by directly adding fibers into melt

Abstract

The invention provides a continuous production method of modified nylon 6 by directly adding fibers into a melt, which comprises the following steps: directly conveying a nylon 6 melt from which volatile monomers and oligomers are removed by a devolatilization tower into a screw extruder, and adding fibers and auxiliaries into a feed port of the screw extruder, and carrying out strip casting and pelletizing on the modified nylon 6 melt fully and uniformly mixed by the screw extruder, or directly conveying the modified nylon 6 melt into a forming processing device to obtain a modified nylon 6 product. According to the method, the extraction procedure in various nylon 6 products and the melting section in modification are omitted, the nylon 6 products with excellent mechanical properties are obtained by directly adding fibers into the melt, the production procedures are remarkably saved, the production efficiency is improved, and the production energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to a method for continuously producing modified nylon 6 by direct melt fiber addition. Background Art

[0002] Nylon 6 (PA6) is the largest and most widely used variety of nylon in the world. It has excellent mechanical properties such as high surface hardness, high strength, and wear resistance. It can be used to produce automotive parts, rail transportation, and power tools. With the development of science and technology and the expansion of material application fields, the product market has higher and higher requirements for material performance. Pure PA6 can no longer meet the needs of many product applications. Modified PA6 has been modified to obtain higher performance modified nylon materials continue to emerge. Modifying nylon 6 with fibers with good mechanical and heat resistance and stable dimensions is one of the common methods.

[0003] When nylon 6 is polymerized, a large amount (about 10%) of monomers and oligomers will remain due to its reaction equilibrium characteristics. Hot water extraction is required to remove a large amount of volatiles before modification. A large number of glass fiber modified nylon 6 material production technologies are based on the addition of glass fiber to the nylon 6 particles after extraction (such as patents CN118725562A, CN113881076B). This process involves melt cooling and pelletizing, hot water extraction, drying, melting and other processes that take a long time and consume high energy. Recently, a nylon 6 melt modification continuous production method (patent CN116162346A) proposed directly introducing nylon 6 melt into a twin-screw extruder for blending and modification with glass fiber and modifier, but it still needs to go through the extraction step after modification. This method omits the granulation, drying and melting steps before modification, reducing production costs. However, the extraction step after modification still results in insufficient energy consumption in the modified particle production process. The devolatilization efficiency directly carried out in the twin-screw extruder is low and affects the homogenization process of the nylon 6 melt and other components. In addition, the performance uniformity of the modified chips after extraction is difficult to guarantee, which can easily cause undesirable phenomena such as floating fibers in the product. Summary of the invention

[0004] The purpose of the present invention is to provide a method for continuous production of modified nylon 6 by direct melt fiber addition, so as to overcome the deficiencies of the above-mentioned prior art and realize high-efficiency, low-consumption and continuous production of high-quality fiber-modified nylon 6 material.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for continuously producing modified nylon 6 by direct melt fiber addition comprises the following steps:

[0007] A method for continuous production of modified nylon 6 by direct melt fiber addition, characterized in that it comprises the following steps:

[0008] (1) The nylon 6 melt containing monomers and oligomers obtained after the polymerization of caprolactam enters the devolatilization tower for devolatilization and viscosity growth;

[0009] (2) conveying the metered nylon 6 melt from the devolatilization tower into a screw extruder; and, adding fiber through another feed port on the screw extruder, and controlling the fiber addition ratio by adjusting the screw extruder process;

[0010] The screw extruder is equipped with an additive adding system, including a power delivery and metering device to control the additive content, and the additive can be added on the screw extruder;

[0011] (3) The nylon 6 melt containing fibers and additives after being fully mixed by a screw extruder is directly pelletized without extraction to obtain modified nylon 6 chips; or the melt after being fully mixed by a screw extruder is directly conveyed into a molding processing device without extraction to obtain a modified nylon 6 product.

[0012] On the basis of adopting the above technical solutions, the present invention may also adopt the following further technical solutions, or use these further technical solutions in combination:

[0013] In the present invention, the screw extruder is preferably a twin-screw extruder

[0014] The devolatilization tower has a temperature working range of 235-280°C and a pressure working range of 1-3000Pa, which can achieve rapid removal of monomers and oligomers and increase in melt viscosity; preferably, the devolatilization tower has a temperature working range of 240-260°C and a pressure working range of 1-200Pa;

[0015] The liquid level of the devolatilization tower is accurately controlled by a gamma-ray level meter, which is used to accurately control the liquid level and adjust the melt residence time;

[0016] The devolatilization tower has a stirrer at the bottom to homogenize the material so that the material in the devolatilization tower is heated and reacts evenly, which is beneficial to improving the quality of the melt.

[0017] The devolatilization tower adopts a screw discharge method to ensure stable discharge under high vacuum;

[0018] The devolatilization tower is equipped with a vacuum pump and a volatile separation system, which can ensure the required devolatilization vacuum degree when the melt is continuously in and out, and the volatile separation system can cool and separate the devolatilized components for reuse;

[0019] The relative viscosity of nylon 6 entering the screw extruder is 2.2-3.6, and the sum of hot water extractables in the nylon 6 melt does not exceed 2% of the total mass of the melt.

[0020] The added fibers are inorganic fibers, including glass fibers, carbon fibers, basalt fibers, or mixtures thereof. The inorganic fibers are preferably glass fiber filaments, the moisture content of which is not more than 0.15%; particularly preferably, glass fiber direct untwisted roving is selected.

[0021] The additives include one or more of antioxidants, anti-aging agents, flame retardants, compatibilizers, flow aids, lubricants, and masterbatches; preferably, when the additives include both granules and powders, the additive adding system is provided with no less than 2 sets;

[0022] By weight, 100 parts of nylon 6, 10 to 80 parts of fiber, and no more than 5 parts of the additives are fed into the twin-screw extruder;

[0023] Preferably, when the added fiber is glass fiber, the weight ratio of nylon to glass fiber is 10:3 to 10:7;

[0024] Preferably, when the fiber added is carbon fiber, the weight ratio of nylon to carbon fiber is 10:1 to 10:6;

[0025] Preferably, when the auxiliary agents are both antioxidants and anti-aging agents, the ratio of the two is 0.5:1 to 1:1.5.

[0026] The twin-screw extruder is provided with multi-stage functional areas with different structures for strengthening the shear flow, kneading and homogenization of the molten material. The temperature of each section of the twin-screw extruder is 225-275°C, the main engine speed is 100-1000r / min, and the auxiliary agent feeding speed is 50-1000r / min. By setting the speed of the twin-screw extruder and the temperature configuration of each section of the screw, the fiber addition speed is controlled to adjust the weight proportion of the fiber in the nylon melt.

[0027] The twin-screw extruder is also provided with an extraction port, which can extract dust, particles generated during mixing and modification and vaporized volatiles in the melt.

[0028] The modified nylon is easy to demould, has a smooth surface and no floating fibers, has a moisture content of no more than 0.3%, a tensile strength of 150 to 800 MPa, a flexural strength of 200 to 800 MPa, a flexural modulus of 9 to 35 GPa, and a notched impact strength of 10 to 40 kJ / m 2 , the melt flow index is 2 to 20 g / 10 min.

[0029] The beneficial effects of the present invention are:

[0030] Before the nylon 6 melt enters the screw extruder for mixing and modification with the fiber, a large amount of volatile monomers and oligomers in the nylon 6 melt are directly removed by a devolatilization tower. Compared with the operation of removing monomers in a screw extruder with vacuum devolatilization, the devolatilization efficiency is high and a large amount of oligomers can be effectively removed, which effectively avoids the volatiles escaping to various parts of the screw to form dust, the unstable flow of the melt caused by the volatilization of a large amount of monomers, and the uneven mixing of the melt with other components, which affects the product quality.

[0031] The melt produced by the devolatilization tower process is mixed and modified by a twin-screw extruder to obtain nylon 6, which has a low oligomer content and does not require an extraction step. It can be directly transported to a molding processing device to obtain a modified nylon 6 product, or it can be directly pelletized after cooling (such as water cooling), thereby avoiding stress concentration in subsequent processing caused by extraction after nylon 6 modification, as well as adverse phenomena such as floating fibers that affect product performance; and the water-passing time for pelletizing is short, and only simple surface moisture removal is required, without the need for conventional drying tower nitrogen drying, which greatly improves production efficiency, saves energy, and improves the performance of modified nylon;

[0032] The nylon 6 material entering the screw extruder is the melt directly from the devolatilization tower. There is no need to set up a melting section in the screw extruder, which avoids the screw link caused by insufficient material drying or exposure to the air to absorb moisture, or improper process settings. In addition, no melting is required, which can save production energy consumption.

[0033] In the present invention, the content of fiber and additive components and the mixing efficiency are flexibly adjusted by directly regulating the process parameter combination of the twin-screw extruder and the process of the auxiliary agent adding system, thereby reducing the operation process and improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0035] The following is a further detailed description of the specific implementation of the present invention in conjunction with the examples. The examples are only for further describing the implementation process of the present invention and do not limit the present invention. The test reference standard for hot water extractable content is GB / T38138-2019. The tensile strength test reference standard ISO527-2, the test rate is 50mm / min; the flexural strength and flexural modulus test reference standard ISO178, the test rate is 2mm / min; the cantilever beam notched impact strength test reference standard ISO180; the melt flow rate test reference standard ISO527-2, the test temperature is 250°C, and the load is 2.16kg.

[0036] Example 1

[0037] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 500Pa, the temperature is 260℃, the relative viscosity of the melt discharged from the devolatilization tower is 2.48, and the mass of hot water extractables accounts for 1.5%. The nylon 6 melt is transported into a twin-screw extruder, and the tube-wound glass fiber filament is added into the twin-screw extruder. The speed of the twin-screw extruder is controlled to be 300r / min, the temperature of each zone is 250-260℃, and the auxiliary agent feeding speed is 200r / min. The mass of the glass fiber and antioxidant particles added to the side of the twin-screw extruder is 32% and 0.8% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0038] Example 2

[0039] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 200Pa, the temperature is 260℃, the relative viscosity of the melt discharged from the devolatilization tower is 2.62, and the mass of hot water extractables accounts for 1.1%. The nylon 6 melt is transported into a twin-screw extruder, and the tube-wound glass fiber filament is added into the twin-screw extruder. The speed of the twin-screw extruder is controlled to be 300r / min, the temperature of each zone is 250-260℃, and the auxiliary agent feeding speed is 200r / min. The mass of the glass fiber and antioxidant particles added to the side of the twin-screw extruder is 32% and 0.8% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0040] Example 3

[0041] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 100Pa, the temperature is 255℃, the relative viscosity of the melt discharged from the devolatilization tower is 3.01, and the mass of hot water extractables accounts for 0.82%. The nylon 6 melt is transported into a twin-screw extruder, and the tube-wound glass fiber filament is added into the twin-screw extruder. The speed of the twin-screw extruder is controlled to be 300r / min, the temperature of each zone is 250-260℃, and the auxiliary agent feeding speed is 200r / min. The mass of the glass fiber and antioxidant particles added to the side of the twin-screw extruder is 32% and 0.8% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0042] Example 4

[0043] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 50-80Pa, the temperature is 250℃, the relative viscosity of the melt discharged from the devolatilization tower is 3.35, the mass of hot water extractables accounts for 0.46%, the nylon 6 melt is transported into a twin-screw extruder, the tube-wound glass fiber filament is added into the twin-screw extruder, the speed of the twin-screw extruder is controlled to be 510r / min, the temperature of each zone is 250-260℃, the auxiliary agent feeding speed is 200r / min, the glass fiber added to the side of the twin-screw extruder is 51% of the mass of the pure nylon 6 melt, the added auxiliary agents are antioxidant particles and anti-aging agent particles, and the masses are 0.8% and 1.2% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0044] Example 5

[0045] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 50-80Pa, the temperature is 255°C, the relative viscosity of the melt discharged from the devolatilization tower is 3.37, the mass of hot water extractables accounts for 0.45%, the nylon 6 melt is transported into a twin-screw extruder, the tube-wound glass fiber filament is added into the twin-screw extruder, the speed of the twin-screw extruder is controlled to be 650r / min, the temperature of each zone is 250-258°C, the auxiliary agent feeding speed is 200r / min, the glass fiber added to the side of the twin-screw extruder is 60% of the mass of the pure nylon 6 melt, the added auxiliary agents are antioxidant particles, anti-aging agent particles and flow aid powder, and the masses are 0.8%, 1.2% and 0.2% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0046] Example 6

[0047] The polymerized nylon 6 melt is introduced into a devolatilization tower, the working pressure of the devolatilization tower is 50-80Pa, the temperature is 255℃, the relative viscosity of the melt discharged from the devolatilization tower is 3.35, the mass of hot water extractables accounts for 0.47%, the nylon 6 melt is transported into a twin-screw extruder, the tube-wound glass fiber filament is added into the twin-screw extruder, the speed of the twin-screw extruder is controlled to be 650r / min, the temperature of each zone is 250-258℃, the auxiliary agent feeding speed is 200r / min, the continuous carbon fiber added to the side of the twin-screw extruder is 30% of the mass of the pure nylon 6 melt, the added auxiliary agents are antioxidant particles, anti-aging agent particles and flow aid powder, and the masses are 0.8%, 1.2% and 0.2% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled and cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0048] Comparative Example 1

[0049] The polymerized nylon 6 melt is cooled and pelletized, and then dried after hot water extraction. The relative viscosity of the nylon 6 pellets is 2.48, and the mass of the hot water extractable matter is 0.31%. The nylon 6 pellets are transported into a twin-screw extruder to be melted and mixed, and the tube-wound glass fiber filaments are added to the twin-screw extruder. The speed of the twin-screw extruder is controlled to be 300r / min, the temperature of each zone is 250-260°C, and the auxiliary agent feeding speed is 200r / min. The mass of the glass fiber and antioxidant particles added to the side of the twin-screw extruder is 32% and 0.8% of the mass of the pure nylon 6 melt, respectively. After the modified nylon 6 melt comes out of the twin-screw extruder, it is water-cooled, cast-belt pelletized, and then transported to a dryer to remove surface moisture to obtain modified nylon 6 particles.

[0050] Comparative Example 2

[0051] The nylon 6 melt with a relative viscosity of 2.25 and a hot water extractable mass of 8.81% after polymerization is transported into a twin-screw extruder with a vacuum devolatilization system for mixing and adding glass fiber; the vacuum degree of the vacuum suction system of the twin-screw extruder is controlled to be 100-150Pa; the tube-wound glass fiber filament is added into the twin-screw extruder, the speed of the twin-screw extruder is controlled to be 300r / min, the temperature of each zone is 250-260℃, the auxiliary agent feeding speed is 200r / min, the mass of the glass fiber and antioxidant particles added to the twin-screw extruder is 32% and 0.8% of the mass of the pure nylon 6 melt, respectively; the modified nylon 6 melt is water-cooled and cast-strip pelletized after coming out of the twin-screw extruder, and then enters a hot water extraction tower, the hot water extraction water bath ratio is 1.36:1, the temperature is 115℃, and the extraction time is 36h, and after extraction, it is sent to a dryer with nitrogen, and the modified nylon 6 particle product is obtained after discharging.

[0052] The technical index test results of the above embodiments and control examples are shown in Table 1.

[0053] Table 1 Technical indicators of modified nylon 6 in the examples and control examples

[0054]

[0055] (MPa) (MPa) (GPa) <![CDATA[(kJ / m 2 )]]> (g / 10min) Example 1 181 251 9.7 17.3 15.1 Example 2 197 262 9.8 18.1 14.5 Example 3 324 415 13.5 25.8 11.6 Example 4 419 502 16.9 31.5 8.3 Example 5 538 641 25.4 36 6.5 Example 6 650 251 32.1 38 4.2 Comparative Example 1 165 230 9.3 17 16.5 Comparative Example 2 180 247 9.5 17 15.3

[0056] As can be seen from the above table, by implementing the technology of the present invention, a modified nylon 6 product with significantly improved mechanical properties can be obtained. The above is a preferred implementation case of the present invention and does not limit the present invention in any way. The changes derived from this are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for continuous production of modified nylon 6 by direct melt fiber addition, characterized in that: The following steps are involved: (1) The nylon 6 melt containing monomers and oligomers obtained after the polymerization of caprolactam enters the devolatilization tower for devolatilization and viscosity growth; (2) conveying the metered nylon 6 melt from the devolatilization tower into a screw extruder; and, adding fiber through another feed port on the screw extruder, and controlling the fiber addition ratio by adjusting the screw extruder process; The screw extruder is equipped with an additive adding system, including a power delivery and metering device to control the additive content, and the additive can be added on the screw extruder; (3) The nylon 6 melt containing fibers and additives, which has been fully mixed by a screw extruder, is pelletized into a cast strip to obtain modified nylon 6 slices; or the melt, which has been fully mixed by a screw extruder, is conveyed into a molding processing device to obtain a modified nylon 6 product.

2. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The devolatilization tower has a temperature operating range of 235-280° C. and a pressure operating range of 1-3000 Pa. A gamma-ray level gauge for controlling the liquid level is provided in the tower to accurately control the liquid level and adjust the residence time of the melt.

3. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The relative viscosity of nylon 6 entering the screw extruder is 2.2-3.6, and the hot water extractable matter in the nylon 6 melt accounts for no more than 2% of the total mass of the melt.

4. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The added fibers are inorganic fibers, including glass fibers, carbon fibers, basalt fibers or any mixture thereof; The inorganic fibers are preferably glass fiber filaments, and the moisture content of the glass fiber is not more than 0.15%; particularly preferably, glass fiber direct untwisted roving is selected.

5. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The additives include one or more of antioxidants, anti-aging agents, flame retardants, compatibilizers, flow aids, lubricants, and masterbatches; preferably, when the additives include both granules and powders, at least two sets of additive adding systems are provided.

6. A method for continuous production of modified nylon 6 by direct melt fiber addition as claimed in claim 1 or 5, characterized in that: By weight, the weight of nylon 6 is 100 parts, the fiber is 10-80 parts, and the auxiliary agent is no more than 5 parts; preferably, when the auxiliary agents are both an antioxidant and an anti-aging agent, the ratio of the antioxidant to the antioxidant is 1:0.5-1.

5.

7. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The screw extruder is a twin-screw extruder; the working temperature of the twin-screw extruder is 225-275°C, the main engine speed is 100-1000r / min, and the auxiliary agent feeding speed is 50-1000r / min.

8. A method for continuous production of modified nylon 6 by direct melt fiber addition as claimed in claim 1 or 7, characterized in that: The screw extruder is also provided with an extraction port, which can extract dust, particles and vaporized volatiles in the melt.

9. The method for continuous production of modified nylon 6 by direct melt fiber addition according to claim 1, characterized in that: The modified nylon 6 is easy to demould, has a smooth surface and no floating fibers, has a moisture content of no more than 0.3%, a tensile strength of 150 to 800 MPa, a flexural strength of 200 to 800 MPa, a flexural modulus of 9 to 35 GPa, and a notched impact strength of 10 to 40 kJ / m 2 , the melt flow index is 2 to 20 g / 10 min.

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