Caprolactam and fiber reaction pultrusion method

Abstract

The invention provides a caprolactam and fiber reaction pultrusion method, in the caprolactam and fiber reaction pultrusion method, before nitrogen serving as protective gas is introduced into a filling section, the nitrogen needs to be heated, and compared with the mode that unheated nitrogen is directly introduced into the filling section in the related technology, the nitrogen is heated, so that the heating efficiency is greatly improved. Due to the fact that the nitrogen fed into the filling section is heated, it can be guaranteed that the mixing temperature in the mixing process of the fibers and the caprolactam entering the filling section meets the mixing temperature required by the technology; the condition that the fibers mixed with caprolactam cannot meet the process requirement due to the fact that the mixing temperature in the process of mixing the fibers and the caprolactam is lower than the mixing temperature required by the process when normal-temperature nitrogen is introduced into the filling section is avoided, and the yield of the caprolactam and fiber reaction pultrusion process is improved.

Description

Technical Field

[0001] This application relates to the field of composite material molding technology, and more specifically, to a method for pultrusion molding of caprolactam and fiber. Background Technology

[0002] Currently, pultrusion is an automated production process for forming pultruded products. Pultruded profiles have higher tensile strength and are lighter than ordinary steel. Therefore, pultruded profiles are rapidly replacing ordinary steel and are widely used in various fields. Summary of the Invention

[0003] To address the aforementioned problems, the purpose of this application is to provide a pultrusion molding method for reacting caprolactam with fibers.

[0004] In a first aspect, embodiments of this application provide a method for pultruding caprolactam and fiber, used to pultrude caprolactam and fiber in a pultrusion molding apparatus; the pultrusion molding apparatus includes: a first heating section, a filling section, a second heating section, and a cooling section connected in sequence; the method includes:

[0005] In the pultrusion molding equipment, when the fiber enters the first heating section, the first heating section heats the fiber at a preset first temperature and then conveys the heated fiber to the filling section;

[0006] The nitrogen gas, which is used as a protective gas, is heated to a preset second temperature, and then the nitrogen gas heated to the second temperature is introduced into the filling section.

[0007] Heated nitrogen gas is introduced into the filling section at a preset third temperature, and caprolactam is introduced into the filling section at the same time as the fiber enters the filling section, so that the fiber entering the filling section mixes with the introduced caprolactam to obtain the fiber mixed with caprolactam, wherein the third temperature is 121 degrees to 140 degrees; and the length of the filling section is 45 cm to 70 cm.

[0008] The fiber mixed with caprolactam is conveyed to the second heating section, where it is heated at a curing reaction temperature to cause the caprolactam to cure and solidify onto the fiber, forming a composite material containing the caprolactam and the fiber. The composite material is then conveyed to the cooling section; wherein the curing reaction temperature is 140 to 160 degrees Celsius.

[0009] In the cooling section, the composite material that has undergone the curing reaction is cooled and shaped to obtain a profile of the composite material.

[0010] In the solution provided by the first aspect of the present application embodiments, in the method of pultrusion molding of caprolactam and fiber, the nitrogen gas, which serves as a protective gas, needs to be heated before being introduced into the filling section. Compared with the related technology of directly introducing unheated nitrogen gas into the filling section, since the nitrogen gas introduced into the filling section is heated, it can ensure that the mixing temperature during the mixing process of fiber and caprolactam in the filling section meets the mixing temperature required by the process. This avoids the situation where the mixing temperature during the mixing process of fiber and caprolactam is lower than the mixing temperature required by the process due to the introduction of room temperature nitrogen gas into the filling section, resulting in the fiber mixed with caprolactam failing to meet the process requirements. This improves the yield of the caprolactam and fiber reaction pultrusion molding process.

[0011] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 A flowchart of a pultrusion molding method for reacting caprolactam with fibers, provided in an embodiment of this application, is shown. Detailed Implementation

[0014] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0015] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0016] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0017] Currently, pultrusion is an automated production process for forming pultruded products. Pultruded profiles have higher tensile strength and are lighter than ordinary steel. Therefore, pultruded profiles are rapidly replacing ordinary steel and are widely used in various fields.

[0018] Based on this, the following embodiments of this application propose a method for pultrusion molding of caprolactam and fiber. In the method of pultrusion molding of caprolactam and fiber, before introducing nitrogen gas as a protective gas into the filling section, the nitrogen gas needs to be heated. Since the nitrogen gas introduced into the filling section is heated, it can ensure that the mixing temperature of the fiber and caprolactam in the filling section meets the mixing temperature required by the process. This avoids the situation where the mixing temperature of the fiber and caprolactam is lower than the mixing temperature required by the process due to the introduction of room temperature nitrogen gas into the filling section, resulting in the fiber mixed with caprolactam not meeting the process requirements. This improves the yield of the pultrusion molding process of caprolactam and fiber.

[0019] In the following embodiments, the fiber may be, but is not limited to, glass fiber yarn, glass fiber cloth, or glass fiber mat.

[0020] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example

[0022] See Figure 1The flowchart shown is a method for pultrusion molding of caprolactam and fiber. This embodiment proposes a method for pultrusion molding of caprolactam and fiber, which is used to pultrude caprolactam and fiber in a pultrusion molding equipment. The pultrusion molding equipment includes a first heating section, a filling section, a second heating section and a cooling section connected in sequence.

[0023] The pultrusion molding equipment includes at least four sequentially connected processing sections: a first heating section, a filling section, a second heating section, and a cooling section. Each processing section forms a closed processing channel with two ports.

[0024] The first heating section is used to heat the fibers.

[0025] The dispensing section is used to mix caprolactam with the heated fibers.

[0026] The second heating section is used to cure the fibers mixed with caprolactam.

[0027] The cooling section is used to cool and shape the composite material after the curing reaction.

[0028] In one embodiment, a front guide plate and a rear guide plate are respectively provided at both ends of the first heating section, and a plurality of guide rollers are arranged at intervals in the fiber processing direction and orthogonal to the fiber processing direction; the first heating section is provided with a hot air inlet and a hot air outlet. Each of the plurality of guide rollers transfers heat to the fiber when it comes into contact with the fiber.

[0029] The processing channel of the filling section has a tapered cross-section along the fiber processing direction. This makes the contact between the fiber and caprolactam within the filling section more compact.

[0030] In one embodiment, the processing channel of the filling section forms an angle of 12°-15° with the horizontal plane from one end near the first heating section to the other end away from the first heating section. This facilitates the flow of caprolactam along the fiber processing direction, improving the mixing speed and efficiency of caprolactam and fiber.

[0031] Preferably, the lower part of the filling section near the first heating section is provided with an overflow port for allowing resin that has not been mixed with caprolactam to flow out of the filling section.

[0032] In order to introduce nitrogen gas as a protective gas into the filling section, a protective gas inlet is provided at one end of the filling section near the first heating section. Nitrogen gas is introduced into the filling section so that the nitrogen gas can protect the caprolactam resin.

[0033] The protective gas inlet can be connected to a nitrogen tank containing nitrogen, so that nitrogen can be introduced into the filling section. Of course, other types of protective gases besides nitrogen can also be used according to actual process needs, which will not be elaborated here.

[0034] The filling section is equipped with a resin injection inlet; there can be one or more resin injection inlets, and the resin injection inlets can be set at the top, bottom or side of the filling section depending on the different profile cross-sections.

[0035] In one embodiment, the pultrusion molding apparatus further includes a resin supply unit for supplying resin, the resin supply unit comprising a resin tank, a static mixer, and a heating and insulation unit. The resin tank, the static mixer, and the heating and insulation unit are connected by pipelines.

[0036] A pipeline is provided to connect the resin unit and the filling section.

[0037] The pultrusion equipment also includes a yarn rack for supplying fibers, on which the fibers are drawn through a processing channel into the first heating section.

[0038] Pultrusion equipment also includes a vacuum pump for evacuating the resin supply unit.

[0039] In order to support and fix the processing section formed by the sequentially connected first heating section, filling section, second heating section and cooling section, the extrusion molding equipment also includes: a support frame for placing the sequentially connected first heating section, filling section, second heating section and cooling section.

[0040] After introducing the pultrusion equipment above, we will now introduce the pultrusion method of reacting caprolactam with fibers:

[0041] The caprolactam-fiber reaction pultrusion molding method proposed in this embodiment includes the following specific steps:

[0042] Step 100: In the pultrusion molding equipment, when the fiber enters the first heating section, the first heating section heats the fiber at a preset first temperature and conveys the heated fiber to the filling section.

[0043] In step 100 above, the first heating device heats the fiber at a preset first temperature, including:

[0044] The first heating device uses hot air flowing into the first heating device at a preset first temperature to heat the fiber to 140 to 160 degrees; wherein the first temperature is 190 degrees.

[0045] Step 102: Heat the nitrogen gas used as a protective gas to a preset second temperature, and then introduce the nitrogen gas heated to the second temperature into the filling section.

[0046] In step 102 above, the pultrusion molding equipment further includes a heating device connected to the injection section.

[0047] Heating the nitrogen gas to a preset second temperature includes the following steps (1) to (2):

[0048] (1) Control the temperature of the heating equipment to rise to 180 degrees to 200 degrees;

[0049] (2) Using a heating device that raises the temperature to 180 to 200 degrees, the nitrogen gas is heated to the second temperature, wherein the second temperature is 150 to 170 degrees.

[0050] Step 104: In the filling section with a preset third temperature, heated nitrogen gas is introduced, and caprolactam is introduced into the filling section at the same time as the fiber enters the filling section, so that the fiber entering the filling section mixes with the introduced caprolactam to obtain the fiber mixed with the caprolactam, wherein the third temperature is 121 degrees to 140 degrees; and the length of the filling section is 45 cm to 70 cm.

[0051] In step 104 above, the caprolactam is a mixture of a first caprolactam and a second caprolactam.

[0052] The third temperature mentioned above is 121 to 140 degrees Celsius. Excessively high temperatures will cause the caprolactam to solidify prematurely in the dispensing section, clogging the mold. Conversely, excessively low temperatures will reduce the material's reaction rate and decrease its physical and mechanical properties. Selecting a suitable temperature range ensures the product achieves good surface quality and physical properties.

[0053] The length of the filling section is set to 45 to 70 centimeters to ensure that the fibers are fully impregnated in the filling section and caprolactam, preventing dry fibers from forming. If the filling section is too short, dry fibers will result. If the filling section is too long, the material will solidify prematurely, causing yarn breakage and clogging of the filling section.

[0054] The process of introducing caprolactam into the injection section includes the following steps (1) to (3):

[0055] (1) The first caprolactam is subjected to vacuum dehydration treatment at a first vacuum dehydration treatment temperature, and the second caprolactam is subjected to vacuum dehydration treatment at a second vacuum dehydration treatment temperature, wherein the first vacuum dehydration treatment temperature is 120 degrees to 140 degrees; and the second vacuum dehydration treatment temperature is 100 degrees to 120 degrees.

[0056] (2) Under the protection of an inert gas, the first caprolactam and the second caprolactam after vacuum dehydration are mixed to obtain a mixture of the first caprolactam and the second caprolactam as the caprolactam;

[0057] (3) After heating the caprolactam to 140 to 150 degrees, caprolactam is introduced into the injection section.

[0058] In step (1) above, in the resin supply unit, the first caprolactam and the second caprolactam are vacuum dehydrated in different resin tanks, and after vacuum dehydration, they are transported to a static mixer for mixing.

[0059] The first caprolactam comprises: polyamide 6, a catalyst, and an internal release agent;

[0060] The second caprolactam comprises: polyamide 6, an activator, and an internal release agent.

[0061] In one embodiment, the polyamide 6 in the first caprolactam comprises 86.21%-97.08% by mass; the catalyst comprises 0.98%-5.17% by mass; and the internal release agent comprises 1.94%-8.62% by mass.

[0062] In the second caprolactam, the mass percentage of polyamide 6 is 81.97%-96.9%; the mass percentage of the activator is 1.16%-9.83%; and the mass percentage of the internal release agent is 1.93%-8.2%.

[0063] The mixing ratio of the first caprolactam and the second caprolactam is 1:2 or 1:3.

[0064] The activator is polyisocyanate or toluene diisocyanate.

[0065] The internal release agent is No. 46 machine oil, graphite, or molybdenum disulfide.

[0066] In step (2) above, the inert gas can be nitrogen.

[0067] The first caprolactam and the second caprolactam, after vacuum dehydration, are mixed in a static mixer.

[0068] The pultrusion molding equipment further includes a heat insulation section disposed between the injection section and the second heating section.

[0069] The fiber mixed with the caprolactam is conveyed to the second heating section, including:

[0070] The fiber mixed with caprolactam is then conveyed to the second heating section after passing through the heat insulation section.

[0071] Optionally, the length of the insulation section is between 21 and 23 millimeters.

[0072] Step 106: The fiber mixed with caprolactam is conveyed to the second heating section, where the fiber mixed with caprolactam is heated at the curing reaction temperature to cause the caprolactam to undergo a curing reaction and be cured on the fiber, forming a composite material containing the caprolactam and the fiber. The composite material is then conveyed to the cooling section; wherein the curing reaction temperature is 140 degrees to 160 degrees.

[0073] Step 108: In the cooling section, the composite material after the curing reaction is cooled and shaped to obtain a profile of the composite material.

[0074] Here, the composite material profile refers to the composite material profile of caprolactam and fiber.

[0075] The following example further illustrates the caprolactam-fiber reactive pultrusion molding method proposed in this embodiment:

[0076] Example 1

[0077] 97.08% polyamide 6, 0.98% catalyst, and 1.94% internal release agent by mass were placed into one of the two resin tanks in the resin supply unit. 96.9% polyamide 6, 1.16% activator, and 1.93% internal release agent by mass were placed into the other resin tank in the resin supply unit. Then, 97.08% polyamide 6, 0.98% catalyst, and 1.94% internal release agent by mass were placed into the other resin tank in the resin supply unit. A resin tank containing 1.94% internal release agent was heated to 140°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain first caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the first caprolactam for protection. Meanwhile, a resin tank containing 96.9% polyamide 6, 1.16% activator, and 1.93% internal release agent was heated to 120°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain second caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the second caprolactam for protection.

[0078] After being pre-arranged, the fibers pass sequentially through the first heating section, the filling section, and the second heating section.

[0079] The cooling section is finally fixed to the traction machine. Connect the injection gun and nitrogen pipeline to the injection section.

[0080] Nitrogen gas is introduced, and the plunger metering pump and traction machine are started to begin producing fiber-caprolactam composite materials. Finally, after cutting, continuous fiber-caprolactam composite materials are obtained.

[0081] The first heating section has a hot air flow temperature of 190℃ and a residence time of 15 minutes. The filling section has a temperature of 140℃. The second heating section has a temperature of 160℃. The cooling section has a temperature of 115℃. The fiber traction speed is 20 cm / min. The filling section is 50 cm long. The processing channel has an inclination angle of 15° to the horizontal plane. The insulation section is 23 mm long. The second heating section is 60 cm long. The cooling section is 30 cm long.

[0082] The obtained continuous fiber-caprolactam composite material conforms to standards GB / T 1040-2006 and GB / T 9341-2000.

[0083] Example 2

[0084] 86.21% polyamide 6, 5.17% catalyst, and 8.62% internal release agent by mass were placed into one of the two resin tanks in the resin supply unit. 81.97% polyamide 6, 9.83% activator, and 8.2% internal release agent by mass were placed into the other resin tank in the resin supply unit. Then, 86.21% polyamide 6, 5.17% catalyst, and 8.62% internal release agent by mass were placed into the other resin tank in the resin supply unit. A resin tank containing 8.62% internal release agent was heated to 120°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain first caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the first caprolactam for protection. Meanwhile, a resin tank containing 81.97% polyamide 6, 9.83% activator, and 8.2% internal release agent was heated to 100°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain second caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the second caprolactam for protection.

[0085] After pre-arrangement, the fibers sequentially pass through the first heating section, the filling section, the second heating section, and the cooling section, finally being fixed onto the traction machine. The injection gun and nitrogen pipeline are connected to the filling section, nitrogen is introduced, and the plunger-type metering pump and traction machine are started to begin producing the fiber-caprolactam composite material. Finally, after cutting, a continuous fiber-caprolactam composite material is obtained. Specifically, the first heating section has a hot airflow temperature of 190℃ and a residence time of 15 minutes; the filling section temperature is 121℃; the second heating section temperature is 140℃; the cooling section temperature is 110℃; the fiber traction speed is 20 cm / min; the filling section length is 30 cm; the processing channel angle with the horizontal plane is 12°; the insulation section length is 21 mm; the second heating section length is 50 cm; and the cooling section length is 20 cm.

[0086] The obtained continuous fiber-caprolactam composite material conforms to standards GB / T 1040-2006 and GB / T 9341-2000.

[0087] Example 3

[0088] 90% polyamide 6, 3% catalyst, and 7% internal release agent by mass are placed into one of the two resin tanks in the resin supply unit. 88% polyamide 6, 4% activator, and 8% internal release agent by mass are placed into the other resin tank in the resin supply unit. Then, 90% polyamide 6, 3% catalyst, and 7% internal release agent by mass are placed into the other resin tank in the resin supply unit. The resin tank containing the agent was heated to 130°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain the first caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the first caprolactam for protection. Meanwhile, a resin tank containing 88% polyamide 6, 4% activator, and 8% internal release agent was heated to 110°C, vacuum dehydrated for 10 minutes while maintaining stirring, to obtain the second caprolactam. After vacuum dehydration, nitrogen gas was introduced into the resin tank containing the second caprolactam for protection.

[0089] After pre-arrangement, the fibers sequentially pass through the first heating section, the injection section, the second heating section, and the cooling section, finally being fixed onto the traction machine. The injection gun and nitrogen pipeline are connected to the injection section, nitrogen is introduced, and the plunger-type metering pump and traction machine are started to begin producing the fiber-caprolactam composite material. Finally, after cutting, a continuous fiber-caprolactam composite material is obtained.

[0090] The first heating section has a hot air flow temperature of 190℃ and a residence time of 15 minutes. The filling section temperature is 131℃, the second heating section temperature is 152℃, the cooling section temperature is 113℃, the fiber traction speed is 20 cm / min, the filling section length is 40 cm, the processing channel angle with the horizontal plane is 13.5°, the insulation section length is 22.5 mm, the second heating section length is 55 cm, and the cooling section length is 22 cm.

[0091] The obtained continuous fiber-caprolactam composite material conforms to standards GB / T 1040-2006 and GB / T 9341-2000.

[0092] In summary, this embodiment proposes a method for reactive pultrusion molding of caprolactam and fibers. In this method, nitrogen gas, used as a protective gas, needs to be heated before being introduced into the filling section. Compared with the related technology of directly introducing unheated nitrogen gas into the filling section, the nitrogen gas introduced into the filling section is heated, which ensures that the mixing temperature of the fiber and caprolactam during the mixing process meets the process requirements. This avoids the situation where introducing room temperature nitrogen gas into the filling section results in a mixing temperature of fiber and caprolactam that is lower than the process requirements, leading to the fiber mixed with caprolactam failing to meet the process requirements. This improves the yield of the reactive pultrusion molding process of caprolactam and fibers.

[0093] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for pultrusion molding of caprolactam and fiber, characterized in that, Used for pultruding caprolactam and fibers in pultrusion equipment; The pultrusion molding equipment includes: a first heating section, a feeding section, a second heating section, and a cooling section connected in sequence; the method includes: In the pultrusion molding equipment, when the fiber enters the first heating section, the first heating section heats the fiber at a preset first temperature and then conveys the heated fiber to the filling section; The nitrogen gas, which is used as a protective gas, is heated to a preset second temperature, and the nitrogen gas heated to the second temperature is introduced into the filling section. Heated nitrogen gas is introduced into the filling section at a preset third temperature, and caprolactam is introduced into the filling section at the same time as the fiber enters the filling section, so that the fiber entering the filling section mixes with the introduced caprolactam to obtain the fiber mixed with caprolactam, wherein the third temperature is 121 degrees to 140 degrees; and the length of the filling section is 45 cm to 70 cm. The fiber mixed with caprolactam is conveyed to the second heating section, where it is heated at a curing reaction temperature to cause the caprolactam to cure and solidify onto the fiber, forming a composite material containing the caprolactam and the fiber. The composite material is then conveyed to the cooling section; wherein the curing reaction temperature is 140 to 160 degrees Celsius. In the cooling section, the composite material that has undergone the curing reaction is cooled and shaped to obtain a profile of the composite material.

2. The method according to claim 1, characterized in that, The first heating device heats the fiber at a preset first temperature, including: The first heating device uses hot air flowing into the first heating device at a preset first temperature to heat the fiber to 140 to 160 degrees; wherein the first temperature is 190 degrees.

3. The method according to claim 1, characterized in that, The pultrusion molding equipment further includes: a heating device connected to the injection section; Heating the nitrogen gas to a preset second temperature includes: The temperature of the heating device is controlled to rise to 180 to 200 degrees Celsius; The nitrogen gas is heated to the second temperature, which is 150 to 170 degrees Celsius, using a heating device that raises the temperature to 180 to 200 degrees Celsius.

4. The method according to claim 1, characterized in that, The pultrusion molding equipment further includes: a heat insulation section disposed between the injection section and the second heating section; The fiber mixed with the caprolactam is conveyed to the second heating section, including: The fiber mixed with caprolactam is then conveyed to the second heating section after passing through the heat insulation section.

5. The method according to claim 1, characterized in that, The caprolactam is a mixture of a first caprolactam and a second caprolactam; The process of introducing caprolactam into the injection section includes: The first caprolactam is subjected to vacuum dehydration treatment at a first vacuum dehydration treatment temperature, and the second caprolactam is subjected to vacuum dehydration treatment at a second vacuum dehydration treatment temperature, wherein the first vacuum dehydration treatment temperature is 120 degrees to 140 degrees; and the second vacuum dehydration treatment temperature is 100 degrees to 120 degrees. Under the protection of an inert gas, the first caprolactam and the second caprolactam after vacuum dehydration are mixed to obtain a mixture of the first caprolactam and the second caprolactam as the caprolactam; After heating the caprolactam to 140 to 150 degrees Celsius, caprolactam is introduced into the injection section.

6. The method according to claim 5, characterized in that, The first caprolactam comprises: polyamide 6, a catalyst, and an internal release agent; The second caprolactam comprises: polyamide 6, an activator, and an internal release agent.

7. The method according to claim 6, characterized in that, In the first caprolactam, the mass percentage of polyamide 6 is 86.21%-97.08%; the mass percentage of the catalyst is 0.98%-5.17%; and the mass percentage of the internal release agent is 1.94%-8.62%. In the second caprolactam, the mass percentage of polyamide 6 is 81.97%-96.9%; the mass percentage of the activator is 1.16%-9.83%; and the mass percentage of the internal release agent is 1.93%-8.2%.

8. The method according to claim 6, characterized in that, In the caprolactam, the mixing ratio of the first caprolactam and the second caprolactam is 1:2 or 1:

3.

9. The method according to any one of claims 5-8, characterized in that, The activator is polyisocyanate or toluene diisocyanate.

10. The method according to any one of claims 5-8, characterized in that, The internal release agent is No. 46 machine oil, graphite, or molybdenum disulfide.

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