Polymer forming body and preparation method thereof

Abstract

The invention relates to a preparation method of a polymer molded body, which comprises the following steps: heating and melting raw materials in a mold, carrying out rotational molding, and carrying out at least one step of firstly vacuumizing and then pressurizing before cooling the mold. The polymer forming body prepared according to the invention can be used for a high-pressure hydrogen tank inner container, has good internal compactness, almost has no change in density before and after hydrogen circulation, has high appearance quality, does not have bubbles inside, and has good stability. The adverse effects on the mechanical strength, hydrogen permeation resistance, hydrogen circulation stability and service life of the product caused by bubbles in the forming body can be effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoplastic materials. Specifically, the present invention relates to a polymer molding and a preparation method thereof, and in particular to a polyamide molding suitable for a high-pressure hydrogen storage tank lining profile and a preparation method thereof. Background Art

[0002] Nowadays, the technology of green energy vehicles is developing rapidly, among which the research on hydrogen fuel cell vehicles has also attracted much attention. Hydrogen fuel cell vehicles are fuel cells that pass hydrogen into the car, and then hydrogen and oxygen react in the fuel cell to generate electricity, which is then used to drive the car forward. Compared with the mainstream electric vehicles on the market, hydrogen fuel cell vehicles have the advantages of longer driving range, faster energy replenishment speed, stronger low-temperature performance, etc., and can still maintain stable performance in a variety of environments such as high altitude, high temperature, and high cold.

[0003] As the core part of hydrogen fuel cell vehicles, automotive high-pressure hydrogen storage tanks play a vital role in the vehicle's endurance, safety and stability of vehicle operation. At present, gas storage tanks can be divided into the following four categories: all-metal gas cylinders (Type I), metal liner fiber hoop-wrapped gas cylinders (Type II), metal liner fiber fully wrapped gas cylinders (Type III), and non-metal liner fiber fully wrapped gas cylinders (Type IV). In practical applications, Type I and Type II gas cylinders have a large weight-to-volume ratio and insufficient strength, which makes it difficult to meet the requirements of hydrogen fuel cell vehicles for hydrogen storage density and safety. They are usually only used for fixed storage of hydrogen or mobile storage of conventional gases such as natural gas. Type III and Type IV gas cylinders have the advantages of high performance and high hydrogen storage density per unit mass due to their fully fiber-wrapped structure, and can be used as mobile hydrogen storage carriers in hydrogen fuel cell vehicles.

[0004] At present, taking the commonly used IV type hydrogen storage tank as an example, it is mainly composed of a plastic liner, a metal joint, a carbon fiber winding layer, an outer protective layer and a sealing structure. Among them, the plastic liner mainly plays the role of gas sealing and as a winding core mold, and its material can usually be selected as a high-density polyethylene (HDPE) or polyamide with light weight and high strength. Nowadays, the processes used to prepare hydrogen storage tank lining profiles usually include injection molding, blow molding, and rotational molding. Among them, although the injection molding process can obtain a relatively uniform lining profile (also called "liner"), it is difficult to achieve integrated molding, and the large-size structure molding is difficult, and welding of the head is required; although the blow molding process has a high production efficiency, it has high requirements and restrictions on raw materials. Raw materials with a high melt flow rate must be selected, and the surface of the seal needs to be post-processed, which is time-consuming and labor-intensive, and the cost is high. The equipment requirements for large-size structure molding are also very high.

[0005] Different from the above two molding processes, the rotational molding process is easier to realize the integrated molding of large-sized components. No additional post-processing is required. The integrated molding can be achieved by pre-embedded metal inserts. The molding process is relatively simple and low-cost. Based on the rotational molding process, some existing patents are disclosed as follows:

[0006] CN116006899A discloses a fiber-wound plastic liner hydrogen storage cylinder, wherein the plastic liner comprises an inner layer and an outer layer, and further discloses that the outer layer is first rotationally molded, and then the inner layer is rotationally molded in the outer layer, during which the rotational molding of the inner layer enables a preliminary formation of a polyurethane cross-linked network between the outer layer and the inner layer, thereby improving the connection strength between the inner layer and the outer layer, and the final curing is performed after the winding of the later winding layer is completed, during which the inner layer and the outer layer form a final polyurethane cross-linked network, so that the inner layer and the outer layer are tightly combined, and under the action of the connecting layer, the inner layer, the outer layer, the connecting layer and the winding layer form a whole, thereby avoiding delamination of the hydrogen storage cylinder.

[0007] CN115214061A discloses a rotational molding device and method for the plastic liner of a high-pressure hydrogen storage bottle. The device and method are disclosed in that four rotational molding molds are evenly arranged around the center of the mold mounting seat on the mold mounting seat, each of which is rotatably mounted on the mold mounting seat through a bearing, and a corresponding power mechanism is provided for each of the rotational molding molds, so that the four rotational molding molds can swing left and right, rotate around the center of the mold mounting seat, and rotate on their own, thereby realizing simultaneous molding of four plastic liners, so as to solve the problem that the existing equipment can only mold one liner at a time and has low production efficiency.

[0008] CN113881163A discloses a plastic for a hydrogen storage pressure vessel and a preparation method thereof. The plastic is composed of PVC resin, HDPE resin, ethylene copolymer, and modified potassium tetratitanate whisker, and discloses an inner liner of the hydrogen storage pressure vessel, which is composed of an outer layer, an insulating layer, and an inner layer from the outside to the inside. It is further disclosed that the outer layer is made of nylon 6, the insulating layer is made of the above plastic, and the inner layer is made of PVC resin; during the preparation, nylon 6 is first added to the mold, and rotationally molded at a specific temperature and for a specific rotational molding time to obtain the outer layer, then the above plastic is added to the mold, rotationally molded to obtain the insulating layer, and finally PVC resin is added to the mold, rotationally molded to obtain the inner layer, and then demolding is performed.

[0009] CN101472722 A discloses a method for manufacturing a polymer bladder that ensures the internal sealing of a tank relative to a pressurized fluid contained therein, wherein the polymer is a thermosetting polymer, and the method comprises at least one of the following steps: polymerizing at least two parent compounds of the thermosetting polymer in a rotating mold. The disclosure further records that the mixture is polymerized in a rotating mold to obtain the thermosetting polymer, so as to form the bladder by polymerizing the parent and simultaneously rotomolding the thermosetting polymer; and further discloses that the tank is a type IV tank.

[0010] However, the above prior art does not disclose how to overcome the technical problem that bubbles are likely to appear or remain inside the molded body during the rotational molding process. The presence of bubble defects will not only have a serious negative impact on the air tightness, hydrogen cycle performance, and high-pressure stability of the final product (for example, the inner liner of a hydrogen storage tank), but also affect the mechanical strength of the final product, posing a safety hazard, which also greatly limits its service life. Summary of the invention

[0011] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide a method for preparing a polyamide molded body suitable for high-pressure hydrogen tank liners with low energy consumption and convenient large-scale customized production, so as to overcome the technical defects of the traditional rotational molding process that bubbles are easily formed or remain inside the products.

[0012] Another object of the present invention is to provide a polyamide molded body obtained based on the above-mentioned preparation method, which can be used as the inner liner of a high-pressure hydrogen tank. It has good density and dimensional stability, and has the desired hydrogen permeation resistance, high-pressure stability and hydrogen circulation performance, which is convenient for realizing low-carbon continuous production.

[0013] According to one aspect of the present invention, a method for preparing a polymer molded body comprises heating and melting a raw material in a mold, performing rotational molding, and performing at least one step of vacuuming and then pressurizing the mold before cooling the mold.

[0014] Furthermore, a method for preparing a polyamide molded body suitable for a high-pressure hydrogen storage tank lining profile comprises heating and melting the polyamide raw material in a mold, performing rotational molding, and performing at least one step of vacuuming and then pressurizing the mold before cooling the mold.

[0015] According to another aspect of the present invention, the polymer molded article prepared according to the above method, such as a polyamide molded article, can be used as a high-pressure hydrogen tank liner, and has excellent hydrogen permeation resistance, and its hydrogen permeation coefficient is low, for example, its hydrogen permeation coefficient at 55°C is ≤2.5×10 -15 mol·m / m 2·s·Pa, preferably, ≤1.80×10 -15 mol·m / m 2 ·s·Pa, measured according to ISO15105-1:2007 standard.

[0016] Furthermore, the polyamide molded body suitable for high-pressure hydrogen storage tank lining profiles prepared according to the above method has good high-pressure resistance stability and hydrogen circulation stability. A hydrogen circulation test is carried out in accordance with GB / T42610-2023. The change rate of the hydrogen permeability coefficient of the polyamide molded body before and after the hydrogen circulation test is not more than 20%, preferably, not more than 15%.

[0017] The polyamide molded body obtained by the present invention has good internal density, and the density before and after the hydrogen circulation has almost no change, and the appearance quality is high. There are no bubbles inside the obtained molded body, which can effectively avoid the adverse effects of bubbles inside the molded body on the mechanical strength, hydrogen permeability resistance, hydrogen circulation stability and service life of the product. In addition, the preparation method of the present invention has good repeatability, is easy to realize large-scale customized production, can effectively reduce the defective rate of the obtained molded body (i.e., the hydrogen tank liner), reduce raw material loss, save costs, and is conducive to reducing carbon emissions, meeting the needs of green and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 In the figure, (a) is an optical microscope image of a polyamide molded body slice obtained in Comparative Example 2; (b) is an optical microscope image of a polyamide molded body slice obtained in Comparative Example 4; and (c) is an optical microscope image of a polyamide molded body slice obtained in Example 2 of the present invention.

[0019] Figure 2 In the figure, (a) is a SEM image of the cross section of the polyamide molded body prepared in Comparative Example 4; (b) is a SEM image of the cross section of the polyamide molded body prepared in Comparative Example 5, (c) is a SEM image of the cross section of the polyamide molded body prepared in Example 2 of the present invention before the hydrogen circulation test, and (d) is a SEM image of the cross section of the polyamide molded body prepared in Example 2 of the present invention after the hydrogen circulation test. DETAILED DESCRIPTION

[0020] The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, various modifications and improvements can be made to the specific embodiments of the present invention without departing from the concept of the present invention, and these are all within the scope of protection of the claims of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the invention belongs. As used herein, unless otherwise specified, the following terms have the meanings assigned to them below.

[0022] As used in the present disclosure, the expressions “comprising” and “including” also encompass the expression “consisting of…”, and the symbol “wt %” represents the mass percentage content.

[0023] In this disclosure, terms such as "a", "an" and "the" are not intended to refer to only a single entity, but also include the general class of which a specific example may be used for illustration.

[0024] The terms "a", "an" and "the" are used interchangeably with the term "at least one". The phrases "at least one of" and "comprising at least one of" followed by a list refer to any one item in the list and any combination of two or more items in the list. Unless otherwise indicated, all numerical ranges include their endpoints and non-integer values ​​between the endpoints.

[0025] A method for preparing a polymer molding comprises heating and melting a raw material in a mold, performing rotational molding, and performing at least one step of vacuuming and then pressurizing before cooling the mold.

[0026] Furthermore, a method for preparing a polyamide molded body suitable for a high-pressure hydrogen storage tank lining profile comprises heating and melting the polyamide raw material in a mold, performing rotational molding, and performing at least one step of vacuuming and then pressurizing the mold before cooling the mold.

[0027] As an embodiment, in the above method, the raw materials are added into a mold, and then the mold is heated while being rolled to melt the raw materials.

[0028] It should be understood that for different rotational molding equipment, there are usually the following types of temperature settings in the process conditions: (1) oven temperature, that is, the temperature of heating the entire space containing the mold; (2) peak air temperature (PIAT, Peak Internal Air Temperature) in the mold cavity during rotational molding; (3) mold temperature, etc. In the present invention, the mold temperature is used as the object of temperature selection or setting in the rotational molding process, and the mold temperature can be regarded as the temperature of the polymer melt in contact with the wall surface of the mold cavity.

[0029] As an embodiment, the mold is heated from room temperature to T while rolling. m +10℃~T m +60℃, preferably, T m +20℃~T m+50°C, more preferably, T m +25℃~T m +35℃, where T m is the melting temperature of the raw material.

[0030] Further, the mold is heated from room temperature to T at a heating rate of 5 to 20 °C / min. m +10℃~T m +60℃, or T m +20℃~T m +50℃, or T m +25℃~T m +35℃.

[0031] As an embodiment, the at least one step of first vacuuming and then pressurizing may be performed only once, that is, firstly reducing the pressure in the mold to a gauge pressure of -0.1 MPa to -0.05 MPa by vacuuming, and then filling the mold with inert gas to increase the pressure in the mold to a gauge pressure of 0.15 MPa to 1.2 MPa;

[0032] This operation can also be performed multiple times, that is, first reduce the pressure in the mold to a gauge pressure of -0.1MPa to -0.05MPa by vacuuming, then fill the mold with inert gas to increase the pressure in the mold to a gauge pressure of 0.2MPa to 1.2MPa, and repeat the above operation several times.

[0033] It should be understood that the selection of the above steps of first evacuating vacuum and then pressurizing at least once needs to be selected according to the actual working conditions of rotational molding. The purpose is to stimulate the preformed body gradually formed during the rotational molding process to expel the bubbles formed, accumulated or remaining inside it in time through a single decompression and pressurization operation or multiple decompression and pressurization cycles.

[0034] The present invention has no particular restriction on the number of times of vacuuming and then pressurizing. The operation can be performed once, twice, three times, four times, five times, seven times or more, as long as it is conducive to the effective and timely discharge of bubbles formed, accumulated or remaining inside the preform.

[0035] As another embodiment, the at least one step of evacuating the vacuum first and then pressurizing is performed at T m +10℃~T m +60℃, preferably, T m +20℃~T m +50°C, more preferably, T m +25℃~T mThe process is carried out under a constant temperature condition of +35°C, and the constant temperature time can be controlled to be 20 to 50 minutes, for example, the constant temperature time can be selected to be 20 minutes or 30 minutes.

[0036] As a further embodiment, when performing the step of first vacuuming and then pressurizing at least once, a suitable rotational speed of the rotating shaft can be selected according to the actual working conditions. For example, for a rotational molding mold with one rotating shaft (such as a laboratory-level uniaxial rotational molding mold), a rotational speed of 50 to 600 r / min, for example, 85 r / min, can be selected, and for a rotational molding mold with two mutually perpendicular rotating shafts (such as a factory-level biaxial rotational molding mold), the rotational speed of the orbiting rotating shaft can be selected to be 1 to 20 r / min, and the rotational speed of the self-rotating rotating shaft can be selected to be 2 to 20 r / min. The present invention has no particular restriction on the selection of the rotational speed of the rotating shaft, which is based on the fact that the raw material melt can be rolled over the inner cavity surface of the mold more evenly.

[0037] As another embodiment, during the cooling of the mold, the pressure in the mold is slowly reduced to normal pressure, and the mold is naturally cooled to room temperature, and then demolded to obtain the polymer molded body.

[0038] As an embodiment, the water content of the raw material is ≤0.2wt%, preferably ≤0.1wt%, more preferably ≤0.05wt%.

[0039] The water content of the raw material can be controlled, for example, by drying the raw material at 70 to 100° C. and a gauge pressure of −0.01 MPa to −0.05 MPa for 4 to 8 hours.

[0040] As another embodiment, the raw material is preferably a granular raw material, and its particle size distribution is: the mass content of particles with a particle size of less than 100 μm is 0-25%, the mass content of particles with a particle size of 100 μm≤≤600 μm is 50-100%, and the mass content of particles with a particle size of more than 600 μm is 0-25%, wherein the particle size distribution is measured according to ASTM D1921 standard.

[0041] Preferably, the particle size distribution of the granular raw material is: the mass content of particles with a particle size of less than 100 μm is 0-15%, the mass content of particles with a particle size of 100 μm≤≤600 μm is 70-100%, and the mass content of particles with a particle size of more than 600 μm is 0-15%, wherein the particle size distribution is measured according to ASTM D1921 standard.

[0042] As another preferred embodiment, the raw material is a granular raw material, and its powder fluidity is ≤30s / 100g, measured according to GB / T 40934-2021 standard.

[0043] Preferably, the powder fluidity of the granular raw material is ≤26s / 100g, measured according to GB / T40934-2021 standard.

[0044] Further preferably, the powder flowability of the granular raw material is ≤22s / 100g, measured according to GB / T40934-2021 standard. For example, the powder flowability of the granular raw material is 10s / 100g, 12s / 100g, 13s / 100g, 14s / 100g, 15s / 100g, 16s / 100g, 18s / 100g, or 20s / 100g, measured according to GB / T 40934-2021 standard.

[0045] As a further preferred embodiment, the granular raw material contains 91-100 wt % of base resin, 0-2 wt % of antioxidant, and 0-7 wt % of other auxiliary agents except the antioxidant.

[0046] Regarding the selection of the base resin, either a single polyamide (such as PA1012) or a blend of several different polyamides (such as a blend of PA1012 and PA610, or a blend of PA1012, PA610 and PA12) can be selected as the base resin.

[0047] Further, the base resin comprises at least one aliphatic long-chain polyamide, and at least one monomer used to prepare the aliphatic long-chain polyamide is an aliphatic monomer having 10 or more carbon atoms. For example, the monomers used to prepare the aliphatic long-chain polyamide are decanediamine having 10 carbon atoms and an aliphatic dibasic acid having 12 carbon atoms, that is, the base resin is PA1012 or polyamide 1012.

[0048] As an embodiment, the aliphatic monomer has 10 to 40 carbon atoms, preferably, 10 to 20 carbon atoms.

[0049] As another embodiment, the polyamide is selected from at least one of the following groups: a polyamide comprising a repeating unit of formula I, a polyamide having a repeating unit of formula II, and any combination thereof;

[0050] Wherein, Formula I is R 1 is an alkyl group having 9 or more carbon atoms, preferably an alkyl group having 9 to 40 carbon atoms;

[0051] Formula II is R 2 and R 3are alkyl groups having 4 or more carbon atoms, preferably alkyl groups having 4 to 40 carbon atoms, and should satisfy at least one of the following conditions:

[0052] 1) R 2 is an alkyl group having 10 or more carbon atoms;

[0053] 2) R 3 It is an alkyl group having 8 or more carbon atoms.

[0054] Further preferably, the polyamide includes at least one of the following groups: PA10, PA11, PA12, PA410, PA510, PA512, PA513, PA515, PA610, PA612, PA613, PA614, PA618, PA810, PA812, PA1010, PA1012, PA1014, PA1018, PA1210, PA1212, PA1214, PA1313, PA1410, PA1412, PA1414, PA1418 or a combination thereof.

[0055] There is no particular limitation on the choice of antioxidant, and commercially available aromatic amine antioxidants, hindered phenol antioxidants, etc. may be selected.

[0056] Specifically, the aromatic amine antioxidant can be selected from at least one of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N-phenyl-N'-(p-toluenesulfonyl)-p-phenylenediamine, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, or octylated diphenylamine. The hindered phenol antioxidant can be selected from at least one of 2,6-di-tert-butyl-4-methylphenol, tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl]pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate n-octadecanol, or 2,2'-methylenebis(4,6-di-tert-butylphenol).

[0057] Regarding the selection of other additives, suitable additives may be added according to actual needs, such as plasticizers, lubricants, nucleating agents, heat stabilizers, colorants, etc. The present invention has no particular restrictions on the selection of other additives, and commercially available conventional additives may be selected.

[0058] The present invention is described in detail below with reference to specific embodiments.

[0059] In the following specific examples 1-3 and comparative examples 1-6, the raw materials used are shown in Table 1 below.

[0060] Table 1 Raw material related information

[0061]

[0062]

[0063] Pretreatment of raw materials:

[0064] Taking polyamide (PA1012) raw material as an example, a commercially available low-temperature grinder with liquid nitrogen cooling function (a 28-40 mesh screen is installed at its discharge port, which corresponds to a pore size of 600-350 μm according to the Chinese industrial standard) is used to grind the PA1012 raw material. The grinding can be repeated several times according to actual conditions to obtain a PA1012 powder having a particle size distribution as shown in Table 2-1 below, wherein the particle size distribution is measured according to ASTM D1921 standard.

[0065] The PA1012 pellets having the particle size distribution shown in Table 2-1 are dried for 5 hours at, for example, 85° C. and a gauge pressure of −0.04 MPa to obtain PA1012 powder having a moisture content shown in Table 2-2.

[0066] Table 2-1 Particle size distribution of raw materials in Examples 1-3 and Comparative Examples 1-6

[0067]

[0068] Table 2-2 Moisture content of raw materials in Examples 1-3 and Comparative Examples 1-6

[0069] project Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Moisture content 0.2wt% 0.2wt% 0.2wt% 0.1wt% 0.05wt% 0.05wt% 0.05wt% 0.4wt% 0.4wt%

[0070] Preparation of polymer moldings

[0071] Next, the PA1012 pellets obtained by pretreatment in the above Examples 1-3 and Comparative Examples 1-6 were used for rotational molding through a laboratory-grade uniaxial cylindrical rotational molding mold to obtain a polymer molded body (i.e., a hydrogen tank liner product).

[0072] It should be noted here that the above-mentioned laboratory-grade uniaxial cylindrical rotational molding mold includes a mold body, which has a cylindrical hollow mold cavity inside; a mold roller, one end of which is inserted into the cylindrical hollow mold cavity of the mold body, and the other end is connected to the motor transmission. In the working state, the motor can drive the mold body to rotate around the mold roller.

[0073] The mold body is provided with an air inlet and an exhaust port respectively connected to the cylindrical hollow mold cavity, wherein the air inlet is connected to an external nitrogen storage tank through an external air pump, and the exhaust port is connected to an external gas collecting bottle through a vacuum pump. In the working state, the operation of vacuuming and pressurizing the cylindrical hollow mold cavity can be realized by adjusting the alternating opening or closing of the exhaust port and the air inlet.

[0074] The mold body may also be provided with a heating element (for example, an electric heating sleeve is provided outside the mold body) for heating the cylindrical hollow mold cavity inside the mold body. The structure and installation of the heating element of the mold body can be conventionally selected according to actual needs and will not be described in detail here.

[0075] The preparation process of the polymer molding is described in detail as follows:

[0076] Embodiment 1:

[0077] The PA1012 powder obtained after pretreatment is added to the cavity of the uniaxial cylindrical rotational molding mold, the motor is turned on, and the motor speed is adjusted to 85r / min, driving the mold body to rotate around the mold roller, and the mold body is heated at the same time, so that the temperature of the cylindrical hollow mold cavity inside the mold body is increased at a rate of 13℃ / min, and the mold temperature is increased to 220℃ for rotational molding. During this process, the PA1012 powder is heated and melted into a molten liquid phase. Under the action of rotation, it gradually rolls on the inner wall of the cylindrical hollow mold cavity and forms a blank that conforms to the shape of the cylindrical hollow mold cavity. When the mold temperature reaches At 220°C, maintain a constant temperature, and open the vacuum pump and the exhaust port on the mold body, evacuate to reduce the pressure in the cylindrical hollow mold cavity to a gauge pressure of -0.1 MPa, and keep warm for 10 minutes. Then close the exhaust port and the vacuum pump, and open the air inlet and the air pump to fill nitrogen into the cylindrical hollow mold cavity to increase the pressure in the cylindrical hollow mold cavity to a gauge pressure of 1.15 MPa. Keep warm for 10 minutes, then stop heating the mold body, and slowly release the pressure to balance the pressure in the cylindrical hollow mold cavity. At the same time, cool the mold naturally to reduce the mold temperature to room temperature. After demolding, the polyamide molded body (i.e., polyamide liner) can be obtained.

[0078] Embodiment 2:

[0079] The preparation process of the molded body in this embodiment is basically the same as that in Example 1, except that, in this embodiment, the temperature of the cylindrical hollow mold cavity inside the mold body is heated at a rate of 18°C / min, and when the mold temperature reaches 220°C, the constant temperature is maintained. After completing the first vacuuming and nitrogen filling steps, the second vacuuming and nitrogen filling steps under the same conditions are performed, and then the heating of the mold body is stopped, and the pressure is slowly released to balance the pressure in the cylindrical hollow mold cavity. At the same time, the mold is naturally cooled so that the mold temperature is reduced to room temperature. After demolding, the polyamide molded body (i.e., polyamide liner) can be obtained.

[0080] Embodiment 3:

[0081] The preparation process of the molded body in this embodiment is basically the same as that in Example 1, except that, in this embodiment, the temperature of the cylindrical hollow mold cavity inside the mold body is heated at a rate of 6°C / min, and when the mold temperature reaches 220°C, the temperature is maintained constant, and after the first vacuuming and nitrogen filling steps are completed, the second vacuuming and nitrogen filling steps under the same conditions are performed, followed by the third vacuuming and nitrogen filling steps, wherein the operating conditions of the third vacuuming and nitrogen filling are: the vacuum pump and the exhaust port on the mold body are turned on, and the vacuuming and nitrogen filling are performed. The mold body is heated to -0.05 MPa and the pressure in the cylindrical hollow mold cavity is reduced to 0.2 MPa. ...

[0082] Comparative Example 1-2:

[0083] The preparation process of the molded body of Comparative Example 1-2 is exactly the same as that of Example 1.

[0084] Comparative Example 3:

[0085] The preparation process of the molded body in this comparative example is basically the same as that in Example 3, the difference is that in this comparative example, the mold temperature is raised to 220°C and maintained at a constant temperature, the vacuum pump and the exhaust port on the mold body are turned on, and a vacuum is drawn to reduce the pressure in the cylindrical hollow mold cavity to a gauge pressure of -0.1 MPa, and the temperature is kept for 50 minutes, and then the heating of the mold body is stopped, and the cylindrical hollow mold cavity is connected to the external atmosphere, and the pressurization is slowly applied to balance the pressure in the cylindrical hollow mold cavity. At the same time, the mold is naturally cooled so that the mold temperature is reduced to room temperature, and then demolded to obtain a polyamide molded body (i.e., a polyamide liner).

[0086] Comparative Example 4:

[0087] The preparation process of the molded body of this comparative example is basically the same as that of Example 3, except that, in this comparative example, the mold temperature is raised to 220°C and directly kept warm for 50 minutes, and then the heating of the mold body is stopped, and the mold is naturally cooled so that the mold temperature drops to room temperature. After demolding, the polyamide molded body (i.e., the polyamide liner) can be obtained.

[0088] Comparative Example 5:

[0089] The preparation process of the molded body in this comparative example is exactly the same as that in Example 3.

[0090] Comparative Example 6:

[0091] The preparation process of the molded body in this comparative example is exactly the same as that of comparative example 3.

[0092] Table 3 below shows the test / characterization results of the polyamide molded bodies (i.e., polyamide liners) obtained in Examples 1-3 and Comparative Examples 1-6 above.

[0093] Table 3 Test / characterization results

[0094]

[0095] It can be seen from the characterization results of Comparative Examples 1 and 2 and Example 1 in Table 3 that when the mass content of raw material particles with a particle size of less than 100 μm is too large, for example, 40 wt%, bubbles exist in the cross section of the polyamide molded body obtained by the rotational molding process, and these bubbles are difficult to eliminate, and the presence of bubbles will have an adverse effect on the performance and service life of the polyamide molded body. However, if the mass content of raw material particles with a particle size of more than 600 μm is excessively increased to reduce the mass content of raw material particles with a particle size of less than 100 μm as much as possible, such as Comparative Example 2, although it helps to eliminate the bubbles in the final polyamide molded body, due to the excessively high mass content of raw material particles with a particle size of more than 600 μm, it is inevitable that some raw material particles will not be fully melted, so that there are unmelted particles in the obtained polyamide molded body, which is manifested as the presence of unmelted particle morphology in the cross section of the obtained polyamide molded body, and the unmelted particles often cause undesirable stress concentration in the obtained molded body, which will have an adverse effect on the mechanical strength and stability of the molded body, and there are safety hazards.

[0096] In addition, by comparing and analyzing the characterization results of Example 3, Comparative Examples 3 and 4 in Table 3, it can be found that if only vacuum is drawn during the rotational molding process (such as Comparative Example 3), or no decompression or pressurization steps are taken (such as Comparative Example 4), it is difficult to eliminate the bubbles inside the molded body. The density of the polyamide molded body obtained in Comparative Example 4 is poor, and the density is only 1.035 g / cm 3 By comparing and analyzing the characterization results of Example 3, Comparative Examples 5 and 6 in Table 3, it can be found that if the moisture content of the raw material particles is high, for example, the moisture content is 0.4wt%, even if multiple vacuuming and nitrogen filling cycles are adopted (such as Comparative Example 5), it is still difficult to completely eliminate the bubbles, and a small amount of bubbles still exist inside the obtained polyamide molded body. In Comparative Example 6, since only vacuuming is performed during the rotational molding process without providing inert gas for protection, it is difficult to prevent or inhibit the thermal aging phenomenon of the resin during long-term heating. There are still obvious bubbles inside the final molded body, and the compactness, inner surface smoothness and yellowing resistance of the profile are relatively poor, with a density of only 1.040g / cm 3 .

[0097] The polyamide molded bodies (i.e., polyamide liner) obtained in Examples 1-3 were tested for hydrogen permeability according to ISO15105-1:2007 standard, and a hydrogen circulation test was performed according to GB / T 42610-2023 to test the hydrogen permeability and density of the molded bodies after the hydrogen circulation test. The specific test results are shown in Table 4 below.

[0098] Table 4 Test results

[0099]

[0100] Based on the test results in Table 4 above, the polyamide molded body prepared by the method of the present invention has excellent hydrogen permeation resistance, and its hydrogen permeability coefficient is low. For example, its hydrogen permeability coefficient at 55°C is ≤1.80×10 -15 mol·m / m 2 ·s·Pa, and has good high-pressure stability and hydrogen cycle stability. A hydrogen cycle test is carried out in accordance with GB / T 42610-2023. The rate of change of the hydrogen permeability coefficient of the polyamide molded body before and after the hydrogen cycle test is no more than 20%. In addition, the obtained polyamide molded body has good internal density, and the density has hardly changed before and after the hydrogen cycle, and the appearance quality is high. There are no bubbles inside the obtained molded body, which can effectively avoid the adverse effects of bubbles inside the molded body on the mechanical strength, hydrogen permeability resistance, hydrogen cycle stability and service life of the product. In addition, the preparation method of the present invention has good repeatability, is easy to realize large-scale customized production, can effectively reduce the defective rate of the obtained molded body (i.e., the hydrogen tank liner), reduce raw material loss, save costs, and is conducive to reducing carbon emissions, meeting the needs of green and sustainable development.

[0101] The structures, materials, components, compositions and methods described herein are intended to be representative examples of the present invention, and it should be understood that the scope of the present invention is not limited by the scope of the examples. Those skilled in the art will recognize that the present invention can be practiced by changes to the disclosed structures, materials, compositions and methods, and these changes are considered to be within the scope of the present invention. Therefore, the present invention is intended to cover these modifications and changes within the scope of the appended claims and their equivalents.

Claims

1. A method for preparing a polymer molded body, characterized in that: The method comprises heating and melting the raw material in a mold, performing rotational molding, and performing at least one step of vacuuming and then pressurizing before cooling the mold.

2. The method according to claim 1, characterized in that Melting the raw material in the mold includes heating the mold from room temperature to T while rolling. m +10℃~T m +60℃, preferably, T m +20℃~T m +50°C, more preferably, T m +25℃~T m +35℃, where T m is the melting temperature of the raw material.

3. The method according to claim 2, characterized in that The heating rate of the mold is 5-20° C. / min.

4. The method according to any one of claims 1 to 3, characterized in that: Before cooling the mold, a step of first evacuating and then pressurizing is performed, including first reducing the pressure in the mold to a gauge pressure of -0.1MPa to -0.05MPa by evacuating, and then filling the mold with inert gas to increase the pressure in the mold to a gauge pressure of 0.15MPa to 1.2MPa; or, Before cooling the mold, the steps of vacuuming and then pressurizing are performed N times, wherein N is an integer ≥ 2, including first reducing the pressure in the mold to a gauge pressure of -0.1MPa to -0.05MPa by vacuuming, then filling the mold with inert gas to increase the pressure in the mold to a gauge pressure of 0.15MPa to 1.2MPa, and then repeating the operation N-1 times.

5. The method according to claim 1, characterized in that The at least one step of first evacuating the vacuum and then pressurizing is performed at T m +10℃~T m +60℃, preferably, T m +20℃~T m +50°C, more preferably, T m +25℃~T m It is carried out under a constant temperature condition of +35°C, and the constant temperature time is 20 to 50 minutes.

6. The method according to claim 1, characterized in that The raw material has the following particle size distribution: the mass content of particles with a particle size of less than 100 μm is 0-25%, the mass content of particles with a particle size of 100 μm≤≤600 μm is 50-100%, and the mass content of particles with a particle size of more than 600 μm is 0-25%, wherein the particle size distribution is measured according to ASTM D1921 standard.

7. The method according to claim 1, characterized in that The powder fluidity of the raw material is ≤30s / 100g, preferably ≤26s / 100g, and more preferably ≤22s / 100g, measured according to GB / T 40934-2021 standard.

8. The method according to claim 1, characterized in that The water content of the raw material is ≤0.2wt%, preferably ≤0.1wt%, more preferably ≤0.05wt%.

9. The method according to claim 1, characterized in that: The raw material comprises polyamide.

10. The method according to claim 9, characterized in that The polyamide includes at least one aliphatic long-chain polyamide, and at least one monomer used to prepare the aliphatic long-chain polyamide is an aliphatic monomer having 10 or more carbon atoms.

11. The method according to claim 10, characterized in that The aliphatic monomer has 10 to 40 carbon atoms, preferably, 10 to 20 carbon atoms.

12. The method according to any one of claims 9 to 11, characterized in that The polyamide is selected from at least one of the following groups: a polyamide comprising a repeating unit of formula I, a polyamide comprising a repeating unit of formula II, and any combination thereof; Wherein, Formula I is R 1 is an alkyl group having 9 or more carbon atoms, preferably an alkyl group having 9 to 40 carbon atoms; Formula II is R 2 and R 3 are alkyl groups having 4 or more carbon atoms, preferably alkyl groups having 4 to 40 carbon atoms, and should satisfy at least one of the following conditions: 1) R 2 is an alkyl group having 10 or more carbon atoms; 2) R 3 It is an alkyl group having 8 or more carbon atoms.

13. The method according to claim 12, characterized in that The polyamide includes at least one of the following groups: PA10, PA11, PA12, PA410, PA510, PA512, PA513, PA515, PA610, PA612, PA613, PA614, PA618, PA810, PA812, PA1010, PA1012, PA1014, PA1018, PA1210, PA1212, PA1214, PA1313, PA1410, PA1412, PA1414, PA1418 or combinations thereof.

14. A polymeric shaped article produced by the process of claim 1.

15. The polymer molded article according to claim 14 is used as a hydrogen tank liner.

16. The use according to claim 15, wherein the hydrogen permeability coefficient of the hydrogen tank liner at 55°C is ≤2.5×10 - 15 mol·m / m 2 ·s·Pa, preferably, ≤1.8×10 -15 mol·m / m 2 ·s·Pa, measured according to ISO15105-1:2007 standard.

17. The use according to claim 15, wherein a hydrogen circulation test is performed according to GB / T 42610-2023, and the change rate of the hydrogen permeability coefficient of the hydrogen tank liner before and after the hydrogen circulation test is not greater than 20%, preferably, not greater than 15%.

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