A polyimide composite helmet and a method of making the same

Abstract

The application provides a polyimide composite helmet and a preparation method thereof, and comprises the following steps: spraying a release agent in an upper and lower mold, laying a release cloth on the inner mold after the release agent volatilizes, placing polyimide needle-punched felt on the release cloth of the lower mold, covering the upper mold and fixing; injecting polyurethane resin into the cavity of the upper and lower mold by using a vacuum assisted forming process, so that the polyurethane resin infiltrates the polyimide needle-punched felt; mixing high-toughness and high-strength polyimide short fibers and polyurethane resin, adding an additive and a curing agent, and stirring uniformly to form a mixture; injecting the mixture into the cavity of the upper and lower mold by using a vacuum assisted forming process; transferring the upper and lower mold to a hot press tank platform for processing and molding to obtain the polyimide composite helmet. The polyimide composite helmet prepared by the application has the advantages of high toughness and high strength, light weight, excellent impact resistance and the like, and ensures that the helmet has better aging resistance under long-term use conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of safety helmets, and more particularly to a polyimide composite helmet and a preparation method thereof. BACKGROUND

[0002] It is well known that the head is the most vulnerable part of the human body and is also the most susceptible to fatal injuries. In the event of an accident, the head is prone to skull fractures, intracranial hemorrhage and other injuries, which endanger life. A safety helmet is a hat that protects the human head from injuries caused by falling objects and other specific factors. Most of the safety helmets on the market have the disadvantages of low strength, low wear resistance, poor temperature resistance, serious aging, high water absorption, and heavy weight.

[0003] For example, Chinese patent CN207411572U discloses a safety helmet with high safety, which comprises a safety helmet body, a brim is arranged on one side of the safety helmet body, the safety helmet body is arc-shaped, front buckles are fixedly connected to both sides of the safety helmet body, rear buckles are fixedly connected to one side of the front buckles and located on the safety helmet body, buckles are fixedly connected to the bottoms of the front buckles and the rear buckles, an air bag is arranged on one side of the inner wall of the safety helmet body, and a baffle is fixedly connected to the bottom of the air bag and located between the inner walls of the safety helmet body. The utility model relates to safety equipment technical field, and the safety helmet with high safety has the air bag arranged on one side of the inner wall of the safety helmet body, the safety helmet has multiple layers of protection, the safety of the safety helmet is improved, and safety protection is provided for the wearer of the safety helmet. The top of the safety helmet body is fixedly connected with a solar panel, so that the wearer feels cool when wearing the safety helmet, and the comfort of wearing is improved. However, the technical scheme has the following disadvantages: the safety helmet improves the safety by arranging the air bag and the baffle, but the buffer protection of the safety helmet when resisting impact is relatively insufficient, and the safety protection performance of the safety helmet cannot be assisted and improved, which has certain optimization space.

[0004] Chinese patent 218303614U discloses a continuous basalt fiber composite material safety helmet, which comprises a mounting helmet, a protection mechanism and a buffer mechanism. The continuous basalt fiber composite material safety helmet can block rainwater in rainy days through the protection cover, reduce water droplets on the face when wearing, reduce the influence on work, improve work efficiency, and the installation plate, the baffle and the buffer plate can buffer the friction force when an accident occurs, reduce safety hazards, have high practicality, can buffer the impact on the face and the face through the sponge, buffer the impact on the head through the foam and the air bag, reduce the harm to the head, effectively protect the head, protect the neck through the telescopic sleeve and the rubber sleeve, protect the wearer in all directions, reduce wearing accessories, reduce labor burden, have simple structure and convenient use, and are conducive to promotion and use. However, the safety helmet made of the composite material has the following disadvantages: the safety helmet is heavy, and the personnel bear heavy burden during work.

[0005] At present, in high-rise buildings, metallurgical high-temperature operations, coal mine chemical industry and other industries, there is an urgent need for an anti-impact safety helmet which combines good impact resistance, light weight, wear resistance and temperature resistance. SUMMARY

[0006] The application aims to provide a polyimide composite helmet and a preparation method thereof, so as to solve the technical problems of poor impact resistance and heavy weight of the helmet in the prior art.

[0007] To achieve the above-mentioned purpose, the first aspect of the application provides a preparation method of a polyimide composite helmet, comprising the following steps:

[0008] Spray a release agent inside the upper and lower molds, and after the release agent volatilizes, lay a release cloth on the inner mold, place the polyimide needle felt on the release cloth of the lower mold, cover the upper mold and fix it;

[0009] Inject polyurethane resin into the cavity of the upper and lower molds by using a vacuum assisted forming process, so that the polyurethane resin infiltrates the polyimide needle felt;

[0010] Mix high-toughness and high-strength polyimide short fibers and polyurethane resin, and after adding additives and curing agents, stir uniformly to form a mixture, and inject the mixture into the cavity of the upper and lower molds by using a vacuum assisted forming process;

[0011] Transfer the upper and lower molds to a hot press tank platform for processing and molding to obtain a polyimide composite helmet.

[0012] Further, the polyimide needle felt has a grammage of 450 g / m 2 , and a fineness of 300-900 dtex; the polyimide needle felt is laid flat and overlapped on the release cloth of the lower mold in 2-5 layers, and has a thickness of 0.25-0.8 mm.

[0013] Further, the infiltration degree of the polyurethane resin to the polyimide needle felt is 60%-75%.

[0014] Further, the high-toughness and high-strength polyimide short fibers have a linear density of 470-500 dtex, a breaking strength of 9000-11000 cn, a breaking strength of 19-23 CN / dtex, an elongation at break of 3.4-3.7%, and an initial modulus of 590-760 cN / dtex.

[0015] Further, the polyurethane resin has a viscosity of 2.99-5.8 Pa.s, a flexural modulus ≥ 3.5 Gpa, an elongation at break of 70%, and a total volume rate after curing of 99%.

[0016] Further, the autoclave process is: heating to 80℃ at 1-3℃ / min and keeping for 60min, then heating to 180℃ at 1.5-3℃ / min and keeping for 360min; when heating to 70-80℃, increasing to 0.45-0.7MPa at 0.02-0.05MPa / min.

[0017] Further, the high-toughness high-strength polyimide chopped fiber is treated by an antistatic agent and a treating agent, and the treating agent is used to enhance the bonding strength between the polyimide needle felt and the high-toughness high-strength polyimide chopped fiber layer.

[0018] Further, the antistatic agent is HQ-11 antistatic agent; and / or the treating agent is AS460.

[0019] Further, the method further comprises the step of spraying an outer decorative layer on the surface of the polyimide composite helmet.

[0020] In a second aspect, the application provides a polyimide composite helmet prepared by the method described in any one of the above.

[0021] Compared with the prior art, the application has the following technical effects:

[0022] The method for preparing a polyimide composite helmet of the application can enhance the impact resistance of the prepared helmet by setting the polyimide needle felt, ensure the safety of use, and the helmet is light in weight, more convenient to use, resistant to high and low temperatures, has no smoldering, and permanent flame retardancy can be ensured, even if the helmet reaches high temperature in an instant, combustion will not occur. The polyimide needle felt is compounded with high-toughness high-strength polyimide chopped fiber, so that the prepared helmet has better mechanical properties, electrical insulation properties and radiation resistance; and the polyimide needle felt can effectively disperse the buffering force to each part of the helmet, and has good buffering effect. The use of polyurethane resin as an adhesive makes the prepared helmet resistant to high and low temperatures, can reach -200℃-250℃, and is more suitable for working in various different temperature environments; in addition, as a filling inner layer, it can increase the bending modulus, shear properties and the like of the helmet.

[0023] The polyimide composite helmet prepared by the application has the advantages of high toughness and high strength, light weight, excellent impact resistance, corrosion resistance, ultraviolet resistance, and extremely low water absorption, and ensures that the helmet has better aging resistance under long-term use conditions, and has excellent size stability and safety performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0025] Figure 1 A flow chart of a preparation method of a polyimide composite helmet provided in the embodiments of the present application. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application more clear, the present application will be further described in detail in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0027] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following three cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0028] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0029] The embodiments of the present application provide a preparation method of a polyimide composite helmet, and the flow is as shown in the figure Figure 1 The preparation method comprises the following steps:

[0030] (1) Spray a release agent in the upper and lower mold cavities, and after the release agent volatilizes, lay a release cloth on the inner mold. Place the polyimide needle felt on the release cloth of the lower mold, cover the upper mold and fix it, and connect the reserved vacuum interface;

[0031] (2) Inject polyurethane resin into the cavity of the upper and lower molds by using vacuum assisted forming process (VARI), so that the polyurethane resin infiltrates the polyimide needle felt;

[0032] (3) Mix high-toughness and high-strength polyimide chopped fibers and polyurethane resin, and after adding additives and curing agents, stir uniformly to form a mixture. Inject the mixture into the cavity of the upper and lower molds by using vacuum assisted forming process;

[0033] (4) The upper and lower molds are transferred to the hot press tank platform for processing and molding to obtain a polyimide composite helmet.

[0034] Further steps (5) can be included to spray an outer decorative layer on the surface of the polyimide composite helmet and polish it.

[0035] In the above step (1), the release agent is sprayed at 0.01-0.05 mm, and the volatilization time is 5-10 min. The release agent can be 770NC, the polyimide needle felt model is ASP016, and the grammage is 450 g / m 2 . The fineness is 300-900 dtex, and the layers are overlapped in a flat laying manner. The polyimide needle felt is overlapped on the release cloth of the lower mold for 2-5 layers, and the thickness is controlled to be 0.25-0.8 mm.

[0036] In the above step (2), the polyurethane resin is first stirred uniformly in the stirred tank, and the resin is defoamed by VARI vacuum. The mixed resin is injected into the mold cavity through the conveying pipeline according to the temperature, flow rate, and pressure requirements, so that the resin infiltrates the polyimide needle felt. The infiltration degree is 60%-75%, and the remaining 25%-40% of the infiltration allowance is used for subsequent infiltration of high-toughness and high-strength polyimide short fibers. The air permeability of the polyimide needle felt is 14-18 m 3 / m 2 / min. The present application first makes the infiltration degree of the polyurethane resin to the polyimide needle felt reach 60%-75%, and then injects the mixture of high-toughness and high-strength polyimide short fibers and polyurethane resin, which facilitates the rapid and uniform integration of the high-toughness and high-strength polyimide short fibers into the pores of the polyimide needle felt. The viscosity of the polyurethane resin is 2.99-5.8 Pa.s, the flexural modulus is ≥3.5 Gpa, the elongation at break is 70%, and the total volume rate after curing is 99%.

[0037] In the above step (3), preferably, the high-toughness and high-strength polyimide short fibers are treated with an antistatic agent and a treatment agent. The treatment agent is used to enhance the bonding strength between the polyimide needle felt and the high-toughness and high-strength polyimide short fiber layer, and to improve the mechanical properties of the helmet. Specifically, the antistatic agent can be HQ-11 antistatic agent (HQ-11 antistatic agent is an oil agent for synthetic fiber filaments, provided by Zhuben Oil Fat (Suzhou) Co., Ltd.); the treatment agent is AS460 (AS460 is a silane coupling agent KH-550).

[0038] The high-toughness and high-strength polyimide chopped fiber can be treated by the following steps: first, mixing HQ-11 sizing agent with deionized water in a cleaning tank, the content of HQ-11 sizing agent being 0.5-2 wt%, and then putting the high-toughness and high-strength polyimide chopped fiber into the cleaning tank, and heating the deionized water in the cleaning tank to 60-80°C, and ultrasonic cleaning for 15-20 minutes. Too low or too high water temperature will affect the oil removal effect, and too high temperature will also cause deformation of the high-toughness and high-strength polyimide chopped fiber, affecting the performance. After cleaning, the high-toughness and high-strength polyimide chopped fiber is taken out and washed clean with clean water. This treatment process can clean the silicone oil attached to the surface of the high-toughness and high-strength polyimide chopped fiber, to enhance the adhesion of the high-toughness and high-strength polyimide chopped fiber to the polyurethane resin, and improve the adhesion of the polymer coating to the polymer surface. The use of deionized water and HQ-11 sizing agent treatment can more effectively remove silicone oil than ordinary water under the premise of ensuring production safety, and eliminate static charge, and can more effectively impregnate in subsequent processing. After cleaning, the high-toughness and high-strength polyimide chopped fiber is put into an oven for drying, and the temperature is not allowed to exceed 80°C.

[0039] Then, AS460 treating agent and anhydrous ethanol are mixed and stirred in a reaction kettle, the content of AS460 treating agent being 2-7 wt%, and acetic acid is added to adjust the PH value to 4 to hydrolyze the AS460 treating agent. Then the high-toughness and high-strength polyimide chopped fiber is put into the reaction kettle for continuous stirring for 15-30 minutes, and then taken out after the AS460 treating agent fully infiltrates the surface of the high-toughness and high-strength polyimide chopped fiber, and naturally air-dried or put into an oven for drying at 50-80°C. In this treatment process, the AS460 treating agent stretches the high-toughness and high-strength polyimide chopped fiber in an infiltrating manner, increases the fiber strength, and makes the performance of helmet interlayer shear more excellent.

[0040] The treating agent selected by the embodiments of the present application is AS460, in addition to which, the embodiments of the present application also use PRIMER-N0.34T, KBE-903, KH602 and KH-560 as treating agents for further treating the high-toughness and high-strength polyimide chopped fiber treated by the antistatic agent.

[0041] PRIMER-N0.34T is a primer provided by Shinkol Chemical Industry Co., Ltd., and the main components are 2-propanol and toluene, and the decomposition product is methanol; KBE-903 is provided by Shinkol Chemical Industry Co., Ltd., and the main component contains an amino functional group; KH602 and KH-560 are provided by Nanjing Xiangqian Chemical Co., Ltd.

[0042] It is found in the experiment that using PRIMER-N0.34T as the treating agent can improve the bonding performance of high-toughness and high-strength polyimide short fibers and polyurethane resin, but at the same time, it will reduce the compression strength index of the helmet, and the compression strength is about 120 MPa. Since the decomposition product of PRIMER-N0.34T is methanol, long-term inhalation is harmful to the human body. Using KBE-903 as the treating agent, white precipitates will be produced during the production process, the minimum coverage area of high-toughness and high-strength polyimide short fibers is 353 m 2 / g, and the tensile strength is only 840 MPa. The minimum coverage area of high-toughness and high-strength polyimide short fibers is 410 m 2 / g, the tensile strength is about 940 MPa, the compression strength is about 200 MPa, and the bending strength is about 500 MPa. Using KH602 or KH-560 as the treating agent can make the high-toughness and high-strength polyimide short fibers softer, and improve the elongation at break of the test sample, but the bending strength is lower, only 350 MPa. Through the comparison of the effects of various treating agents, it is found that using AS460 can achieve the best test results, therefore, the embodiment of the present application uses AS460 as the treating agent.

[0043] The high-toughness and high-strength polyimide short fibers and the polyurethane resin after treatment are stirred in a stirred tank, and after adding the additives and the curing agent, the mixture is uniformly stirred to form a mixed material. In the mixed material, the volume content of the polyimide short fibers, the polyurethane resin and the curing agent is respectively 50%-75%, 20-45% and 5%-15%, and the rest is the additive. Rapid cooling is used to control the internal expansion of the high-toughness and high-strength polyimide short fibers, and vacuum pumping is used to defoam the resin and the curing agent in the stirred tank, so that the resin and the short fibers are uniformly dispersed. The dispersion degree is determined by the dispersion test method, and the mixed material is fully injected into the mold cavity by stamping.

[0044] The high-toughness and high-strength polyimide short fibers used in the embodiment of the present application have a linear density of 470-500 dtex, a breaking strength of 9000-11000 cn, a breaking strength of 19-23 CN / dtex, an elongation at break of 3.4-3.7%, and an initial modulus of 590-760 cN / dtex, and a length of 0.5-1 cm. The curing agent is composed of Urepu12115LV polyol combination and BX30 isofluoroformic acid combination, and the additive is silane coupling agent KH560. The high-toughness and high-strength polyimide short fibers, the polyurethane resin, the additive and the curing agent are stirred in the stirring tank for 10-20 min, the stirring speed is 20-40 revolutions / min, after uniform stirring, the negative pressure value of vacuum pumping is 0.45-0.6 MPa, the conveying pipe is kept at 60-80°C, and the conveying speed into the mold cavity is 80-150 ml / min.

[0045] In the step (4), the autoclave heat pressing process is as follows: heating to 80℃ at a rate of 1-3℃ / min and holding for 60min, then heating to 180℃ at a rate of 1.5-3℃ / min and holding for 360min; when heating to 70-80℃, the pressure is increased to 0.45-0.7MPa at a rate of 0.02-0.05MPa / min. Specifically, the upper and lower molds are transferred to the platform of the autoclave by using a crane, and the vacuum pipe on the autoclave is connected during the process. The autoclave process is adjusted, and the surface vacuum auxiliary material is removed after the autoclave is taken out. The movable block is pried to open the mold, and the main part of the lightweight safety helmet is obtained.

[0046] In the step (5), an abrasive head spraying machine is used to spray an outer decorative layer on the surface of the polyimide composite helmet. The outer decorative layer is dyed polytetrafluoroethylene, and the surface spraying amount is 60-120g / m 2 . The polytetrafluoroethylene has excellent chemical corrosion resistance, strong acid, strong base, strong oxidizing agent, etc., has outstanding heat resistance, heat resistance, cold resistance and wear resistance, long-term use temperature range -200℃-250℃, and has excellent electrical insulation and is not affected by temperature and frequency. The sprayed helmet is placed in an oven and set to a certain temperature and time for curing, and then a sander is used to polish the surface to obtain a lightweight safety helmet. Further, conventional hat bands, top belts and sweat-absorbing bands and other components can be installed on the helmet.

[0047] The release cloth of the embodiment of the application adopts a four-fluorine release cloth or a nylon 66 release cloth, model F4T09 and NSPA66, and the release agent model is 770NC. The release agent is provided by Hebei Fiome Composite Material Co., Ltd., the release cloth, polyurethane resin and curing agent are provided by the technical department of Jiangsu Aoshen New Material Co., Ltd., and the polyimide high-toughness high-strength filament chopped fiber model is ASPI091, provided by Jiangsu Aoshen New Material Co., Ltd.

[0048] The preparation method of the polyimide composite helmet of the embodiment of the application can enhance the impact resistance of the prepared helmet by setting the polyimide needle felt, ensure safety in use, and the helmet is light in weight, more convenient to use, resistant to high and low temperature, no smoldering, permanent flame retardancy can be guaranteed, even if the helmet reaches high temperature in an instant, it will not burn. By compounding high-toughness high-strength polyimide chopped fiber on the polyimide needle felt, the prepared helmet has better mechanical properties, electrical insulation properties and radiation resistance; and the polyimide needle felt can effectively disperse the buffering force to each part of the helmet, playing a good buffering role. By using polyurethane resin as an adhesive, the prepared helmet is resistant to high and low temperature, can reach -200℃-250℃, making it more suitable for working in various different temperature environments; in addition, as a filling inner layer, it can increase the bending modulus, shear properties, etc. of the helmet. By setting an outer decorative layer, the wear resistance and easy coloring of the helmet can be improved, and secondary processing such as electroplating, welding and heat pressing can also be used.

[0049] The polyimide composite helmet prepared by the embodiment of the application has the advantages of high toughness and high strength, light weight, excellent impact resistance, corrosion resistance, ultraviolet resistance, and extremely low water absorption, and ensures better aging resistance of the helmet under long-term use conditions, and excellent size stability and safety performance.

[0050] The cavity of the upper and lower molds used in the embodiment of the application is consistent with the shape of the semicircular helmet, and a semicircular (or spherical) composite helmet is prepared. The smooth semispherical shell can evenly disperse the concentrated impact force along the spherical surface, and the prepared helmet is more solid and can provide better impact and penetration protection.

[0051] The following illustrates a polyimide composite helmet and a preparation method thereof by multiple specific embodiments.

[0052] Embodiment 1

[0053] The embodiment 1 of the application provides a polyimide composite helmet and a preparation method thereof, which comprises the following steps:

[0054] (1) Spray a release agent 770NC in the upper and lower molds, and after the release agent volatilizes, lay a nylon 66 release cloth on the inner mold, and then lay three layers of polyimide needle-punched felt on the release cloth of the lower mold, cover the upper mold and fix it, and connect the reserved vacuum interface;

[0055] (2) Inject polyurethane resin into the cavity of the upper and lower molds by using a vacuum assisted forming process (VARI) to make the polyurethane resin infiltrate the polyimide needle-punched felt, and the infiltration degree is 60%;

[0056] (3) Mix the high-toughness and high-strength polyimide chopped fibers treated with an antistatic agent and a treating agent with the polyurethane resin, and after adding an additive and a curing agent, stir uniformly to form a mixture. In the mixture, the volume content of the polyimide chopped fibers, the polyurethane resin, and the curing agent is 55%, 25%, and 10%, respectively, and the rest is the additive. Inject the mixture into the cavity of the upper and lower molds by using a vacuum assisted forming process. The high-toughness and high-strength polyimide chopped fibers, the polyurethane resin, the additive, and the curing agent are stirred in a stirring tank for 10 minutes at a stirring speed of 20 revolutions per minute. After uniform stirring, the negative pressure value of vacuum extraction is 0.4 Mpa;

[0057] The specific treatment process of the high-toughness and high-strength polyimide chopped fibers is as follows: first, mix HQ-11 antistatic agent with deionized water in a cleaning tank, and the content of HQ-11 antistatic agent is 1 wt%, and then put the high-toughness and high-strength polyimide chopped fibers into the cleaning tank, and at the same time, heat the deionized water in the cleaning tank to 80℃, and ultrasonic clean for 20 minutes.

[0058] Afterwards, the AS460 treating agent and anhydrous ethanol are mixed and stirred in a reaction kettle, the AS460 treating agent content is 5wt%, and acetic acid is added to adjust the PH value to 4 to hydrolyze the AS460 treating agent. Then the high-toughness and high-strength polyimide chopped fibers are put into the reaction kettle to continue stirring for 30 minutes, and the high-toughness and high-strength polyimide chopped fibers are taken out after the surface treatment, and are put into a 50℃ oven for drying.

[0059] (4) The upper and lower mold transfer is transferred to the hot press tank platform for processing and molding to obtain a polyimide composite helmet. The hot pressing process is: heating to 80℃ at 1℃ / min, holding for 60min, then heating to 180℃ at 1.5℃ / min, holding for 360min; when heating to 70℃, increasing to 0.45MPa at 0.02MPa / min.

[0060] (5) Spraying a dyed polytetrafluoroethylene outer decorative layer on the surface of the polyimide composite helmet, the surface spraying amount is 60g / m 2 .

[0061] Example 2

[0062] The example 2 of the present application provides a polyimide composite helmet and a preparation method thereof, comprising the following steps:

[0063] (1) Spraying a release agent 770NC in the upper and lower mold, after the release agent volatilizes, laying a nylon 66 release cloth on the inner mold, laying 5 layers of polyimide needle punched felt on the release cloth of the lower mold, covering the upper mold and fixing, connecting the reserved vacuum interface;

[0064] (2) Using a vacuum assisted forming process (VARI) to inject polyurethane resin into the cavity of the upper and lower mold, so that the polyurethane resin infiltrates the polyimide needle punched felt, and the infiltration degree is 65%;

[0065] (3) Mixing the high-toughness and high-strength polyimide chopped fibers treated by the antistatic agent and the treating agent with the polyurethane resin, adding the additives and the curing agent to stir uniformly to form a mixture, in the mixture, the volume content ratio of the polyimide chopped fibers, the polyurethane resin, and the curing agent is respectively: 65%, 20%, and 10%, and the rest is the additive. Using a vacuum assisted forming process to inject the mixture into the cavity of the upper and lower mold; the high-toughness and high-strength polyimide chopped fibers, the polyurethane resin, and the additives and the curing agent are stirred in the stirring tank for 15min at a stirring speed of 30r / min, and after uniform stirring, the negative pressure value of vacuumizing is 0.5Mpa;

[0066] The specific treatment of the high-toughness and high-strength polyimide chopped fibers is the same as that in example 1.

[0067] (4) transfer the upper and lower mold to the hot press tank platform for processing and molding to obtain the polyimide composite helmet. The hot pressing process is: heating to 80℃ at 2℃ / min, keeping for 60min, then heating to 180℃ at 2℃ / min, keeping for 360min; when heating to 75℃, increasing to 0.6MPa at 0.03MPa / min.

[0068] (5) spraying a dyed polytetrafluoroethylene outer decorative layer on the surface of the polyimide composite helmet, the surface spraying amount being 80g / m 2 .

[0069] Example 3

[0070] The example 3 of the present application provides a polyimide composite helmet and a preparation method thereof, comprising the following steps:

[0071] (1) spraying a release agent 770NC in the upper and lower mold, laying a nylon 66 release cloth on the inner mold after the release agent volatilizes, laying 3 layers of polyimide needle-punched felt on the release cloth of the lower mold, covering the upper mold and fixing, and connecting the reserved vacuum interface;

[0072] (2) injecting polyurethane resin into the cavity of the upper and lower mold by using a vacuum assisted forming process (VARI) to make the polyurethane resin infiltrate the polyimide needle-punched felt, and the infiltration degree is 75%;

[0073] (3) mixing high-toughness and high-strength polyimide chopped fibers treated by an antistatic agent and a treatment agent with polyurethane resin, adding an additive and a curing agent, and stirring uniformly to form a mixture, in the mixture, the volume content ratio of the polyimide chopped fibers, the polyurethane resin and the curing agent is respectively: 70%, 22% and 5%, and the rest is the additive. The mixture is injected into the cavity of the upper and lower mold by using a vacuum assisted forming process. The stirring time of the high-toughness and high-strength polyimide chopped fibers, the polyurethane resin, the additive and the curing agent in the stirring tank is 20min, the stirring speed is 40r / min, and the negative pressure value of vacuumizing after uniform stirring is 0.6Mpa;

[0074] The specific treatment process of the high-toughness and high-strength polyimide chopped fibers is the same as that in example 1.

[0075] (4) transferring the upper and lower mold to the hot press tank platform for processing and molding to obtain the polyimide composite helmet. The hot pressing process is: heating to 80℃ at 3℃ / min, keeping for 60min, then heating to 180℃ at 3℃ / min, keeping for 360min; when heating to 80℃, increasing to 0.7MPa at 0.05MPa / min.

[0076] (5) spraying a dyed polytetrafluoroethylene outer decorative layer on the surface of the polyimide composite helmet, the surface spraying amount being 120g / m 2 .

[0077] Comparative Example 1

[0078] The difference between it and Example 1 is that the high-toughness high-strength polyimide short-cut fiber in step (3) is not treated with antistatic agent and treatment agent, and other process conditions are the same.

[0079] The weight, absolute water absorption, interlaminar shear short beam strength, impact performance, etc. of the composite helmet prepared in Example 1-Example 3 and Comparative Example 1 of the present application were tested, and the standards followed in the test were GB / T2812, GB / T2811-2019, ISO3873-1977, and the test results are shown in Table 1, Table 2.

[0080] Table 1

[0081]

[0082]

[0083] Table 2

[0084]

[0085] From the above Table 1, Table 2, it can be seen that the helmet made in Example 1-Example 3 of the present application has small damage deformation and higher overall protection performance than the comparative example helmet, indicating that the helmet can provide better protection; it has excellent anti-static and insulation performance, and is basically non-flammable, while the conventional safety helmet cannot achieve the flame retardant performance, indicating that the helmet of the present application can protect the user's safety even in a fire operation; whether in high and low temperature or in water immersion, the impact performance of the helmet of the present application is very good, and can maintain the shape when subjected to impact load; the anti-static performance index shows that the helmet of the present application is a low static material, has excellent anti-static performance, and is not easy to generate static electricity, and is suitable for ultra-high anti-static requirements.

[0086] The physical properties shown in Table 2 show that the safety helmet prepared in the present application has very low absolute water absorption, indicating that the safety helmet has high density and fewer fine pores in the helmet, and the interlaminar shear short beam strength performance is almost twice that of the conventional safety helmet, showing that its resistance to damage is much higher than that of the conventional safety helmet. High impact performance and bending strength indicate that the stress and deformation caused by instantaneous impact are also small when subjected to impact load. Its temperature resistance is much higher than that of the conventional helmet, and the safety helmet prepared in the present application can be applied to various high-temperature environments. In addition, the helmet of the present application has higher strength and better durability, and the higher compression strength indicates that it has good pressure resistance; and the breaking strength can reach 3-4 times that of iron, significantly improving the tearing strength of the safety helmet and prolonging the service life of the helmet.

[0087] The above embodiments only express several implementation ways of the present application, and the description is specific and detailed, but it should not be understood as a limitation to the patent scope of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a polyimide composite helmet, characterized in that, Includes the following steps: Spray a release agent inside the upper and lower molds. After the release agent evaporates, lay a release cloth in the inner mold. Place the polyimide needle-punched felt on the release cloth of the lower mold, cover it with the upper mold and fix it. Polyurethane resin is injected into the cavity of the upper and lower molds using a vacuum-assisted molding process, so that the polyurethane resin impregnates the polyimide needle-punched felt. High-toughness and high-strength polyimide short-cut fibers and polyurethane resin are mixed, and additives and curing agents are added and stirred evenly to form a mixture. The mixture is then injected into the cavity of the upper and lower molds using a vacuum-assisted molding process. The upper and lower molds are transferred to a hot autoclave platform for processing and molding to obtain a polyimide composite helmet.

2. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The polyimide needle-punched felt has a basis weight of 450 g / m². 2 The fineness is 300-900 dtex; the polyimide needle-punched felt is laid flat and stacked in 2-5 layers on the release cloth of the lower mold, with a thickness of 0.25-0.8 mm.

3. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The polyurethane resin has a wettability of 60%-75% on the polyimide needle-punched felt.

4. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The high-toughness and high-strength polyimide chopped fibers have a linear density of 470-500 dtex, a breaking strength of 9000-11000 cn, a breaking strength of 19-23 CN / dtex, a breaking elongation of 3.4-3.7%, and an initial modulus of 590-760 cN / dtex.

5. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The polyurethane resin has a viscosity of 2.99-5.8 Pa·s, a flexural modulus ≥3.5 GPa, an elongation at break of 70%, and a total volume fraction of 99% after curing.

6. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The hot pressing process of the autoclave is as follows: heat up to 80℃ at 1-3℃ / min and hold for 60min, then heat up to 180℃ at 1.5-3℃ / min and hold for 360min; when the temperature reaches 70-80℃, increase the pressure to 0.45-0.7MPa at 0.02-0.05MPa / min.

7. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, The high-toughness and high-strength polyimide chopped fibers are treated with an antistatic agent and a treatment agent to enhance the interlayer bonding strength between the polyimide needle-punched felt and the high-toughness and high-strength polyimide chopped fibers.

8. The method for preparing a polyimide composite helmet as described in claim 7, characterized in that, The antistatic agent is HQ-11; and / or the treatment agent is AS460.

9. The method for preparing a polyimide composite helmet as described in claim 1, characterized in that, It also includes the step of spraying an outer coating onto the surface of the polyimide composite helmet.

10. A polyimide composite helmet, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

Images