A device and method for producing a polymer microcellular foamed pipe

Abstract

The application discloses a production device and a production method of a polymer microcellular foamed pipe, and the production method is realized based on a mold and a high-pressure closed container capable of driving the mold to rotate. A thermoplastic polymer or a composite thereof is processed through forming to obtain a pre-foamed pipe. The pre-foamed pipe is cut into a pipe with a length not longer than that of the mold, and the pipe is placed in the mold. The mold containing the pipe is placed in a closed reaction kettle, a supercritical fluid is introduced into the closed reaction kettle, and the pipe is immersed in the supercritical fluid under corresponding temperature and pressure. The mold is always in a rotating state in the reaction kettle. The temperature in the reaction kettle is cooled for a period of time, then the pressure is rapidly released, the pipe in the mold is taken out, and a polymer microcellular foamed pipe is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a device for producing a polymer microcellular foamed pipe, and a method for producing the polymer microcellular foamed pipe. BACKGROUND

[0002] In recent years, tubular products mainly made of polymers or their composites have been widely used in the fields of building water supply and drainage, urban pipe network, chemical transportation, etc. At the same time, due to the advantages of sound insulation, shock absorption, heat insulation, and raw material saving, polymer microcellular foamed products show a wide application prospect in the industries of packaging, building, electronics, automobile industry, and aerospace and navigation, etc. Further, open-cell foamed materials are a kind of foamed materials with continuous solid and gas phases, and the matrix material exists in the form of continuous cell walls. The unique three-dimensional open-cell structure has excellent absorption and penetration performance, and has a wide range of applications in sound absorption, electricity conduction, optics, filtration, adsorption, etc. Especially, it has a huge potential application prospect in the field of biological and medical materials (drug controlled release, bone tissue culture, biological dialysis), etc. However, the polymer microcellular foamed pipe obtained by combining the two is relatively rare. On the one hand, the existing foamed pipes are mainly closed-cell, and the foaming ratio is also relatively low, so the advantages of foaming are difficult to be reflected. On the other hand, the cell structure of the foamed pipes obtained by the existing methods is difficult to be accurately controlled, and the mechanical properties and other use properties of the products are significantly decreased, which hinders the popularization and application of the products. Among the several mainstream processing methods of supercritical fluid microcellular foamed products, such as extrusion, injection, and high-pressure container (autoclave pressure or mold pressure), the high-pressure container method is more likely to obtain uniform cells in the entire product, and has high cell density, small cell size, high uniformity, and convenient control. However, as an intermittent foaming method, the high-pressure container method is mainly used for foaming experiments of a small amount of materials or regular plates. When processing plates, the upper and lower surfaces can be easily cut off, the mold and equipment for processing plates can be easily opened and closed, so the pressure control is very convenient, and the pressure and temperature control uniformity of the entire plane can be easily realized during the processes of soaking, heating, pressurizing, cooling, and pressure releasing.

[0003] Compared with plates, the shape of tubular products is more complex, which poses challenges to the product shaping, demolding, and cell uniformity control, especially when the wall of the tubular product is thick. Under the existing conditions, it is almost impossible to realize the consistency of the process conditions such as temperature, pressure, and temperature and pressure change rate of each part of the pipe wall, and it is also difficult to accurately control the cell. The inner and outer walls of the formed pipe are also difficult to be cut off like plates, so it is necessary to directly obtain a product with good inner and outer surface quality.

[0004] For the polymer microcellular foamed product with the change of state parameters such as pressure or temperature to obtain the cells, there is often a skin layer without cells on the outer surface of the product, the main reason is that the surface layer of the product directly contacts with the outside world, so it is difficult to form the state difference with the outside world, and the state difference is often the main factor to induce the formation and fixation of the cells. For the polymer microcellular foamed pipe, the solid outer wall of the inner and outer surfaces will also affect the opening effect, if the inner and outer walls are closed, the inner and outer walls need to be removed first when the pipe with opening function is applied, which also brings corresponding troubles to the application.

[0005] In the application of the open-cell material, the orientation direction of the cells also has certain effect, for example, the sound absorption coefficient will have obvious difference in the orientation direction of the cells and other directions. In the supercritical fluid foaming, the pressure releasing direction can be controlled or the cell orientation can be regulated, but for the large size pipe, it is difficult to homogenize the pressure releasing direction of each part, so it is also difficult to obtain the thick wall pipe with consistent directional cells. SUMMARY

[0006] The purpose of the application is to provide a production device and method of polymer microcellular foamed pipe, the method realizes the accurate control of the internal microcell (pore size, cell orientation and cell uniformity) and foaming ratio of the foamed pipe through the specific mold, the closed high pressure device capable of driving the mold to rotate and the specific process route, the microcellular foamed pipe obtained has uniform cells, small and dense size, good cell orientation consistency, and the inner and outer walls of the pipe have open-cell structure, so that the pipe can better play the advantages of the internal microcell of the product while having good mechanical properties.

[0007] Technical scheme: the production device of the polymer microcellular foamed pipe comprises a mold; the mold comprises a first fixed frame and a second fixed frame arranged oppositely and an inner mold core fixed on the first fixed frame; the first fixed frame and the second fixed frame are both provided with cylindrical grooves arranged in a ring shape and corresponding to each other, further comprising an outer mold group composed of a plurality of rib strips arranged in a ring shape, the rib strips of the outer mold group are arranged one by one corresponding to the cylindrical grooves on the fixed frame; the two ends of the rib strip are connected with the first fixed frame and the second fixed frame through limiting screws; further comprising a compression spring arranged in the cylindrical groove, one end of the compression spring is connected with the end point of the side of the cylindrical groove away from the center of the fixed frame, the other end of the compression spring is connected with the limiting screw, the limiting screw slides transversely in the cylindrical groove through the compression spring; the cylindrical groove is a through hole structure, the transverse length of the cylindrical groove is 10-100mm.

[0008] The height of the inner mold core is not greater than the distance between the first fixed frame and the second fixed frame; the height of the inner mold core is not less than the length of the pre-foamed pipe blank; the outer diameter of the inner mold core is consistent with the inner diameter of the pre-foamed pipe blank.

[0009] The number of ribs is determined based on the inner ring size formed after their combination and the size of the ribs themselves. The inner ring size formed after the ribs are combined is adapted to the shape of the pre-foamed tube blank.

[0010] Preferably, when the shape of the pre-foamed tube blank and the shape of the ribs are both circular, and the diameters of the pre-foamed tube blank and the ribs are R1 and R2 respectively, the number of ribs is determined to not exceed (R1+R2)*3.14 / R2. For ease of processing, this value is generally determined to be an integer multiple of 4. If the two ends of the pre-foamed tube blank have different external dimensions, the smaller of the quantity values ​​determined by the two end dimensions is taken. In addition, due to strength requirements, the diameter of the ribs is 6mm or more.

[0011] It also includes a high-pressure sealed container that drives the mold to rotate. The container has a cavity that is connected to the motor through a coupling. The size of the cavity is the same as that of the mold. The mold for loading the pre-foamed tube blank is placed in the cavity, and the cavity rotates under the drive of the motor.

[0012] The method for producing polymer microporous foamed pipes based on the above-mentioned production apparatus includes the following steps:

[0013] (1) Select at least two thermoplastic polymers and form a blend by melt blending or solution blending;

[0014] (2) The blend is subjected to molding processing to obtain pre-foamed pipe with a wall thickness of 1 to 20 mm.

[0015] (3) Cut the pre-foamed pipe to a length equal to the required pipe length / (1 + the shrinkage rate of the blend) to obtain the pre-foamed pipe blank;

[0016] (4) Apply PVA aqueous solution evenly to the inner and outer surfaces of the pre-foamed tube blank to form a PVA coating on the inner and outer surfaces of the pre-foamed tube blank. The initial thickness of the PVA coating is 30-50 μm.

[0017] (5) Dry the pre-foamed tube blank until the PVA coating is fully set, and then apply a PVA aqueous solution to the outer surface of the pre-foamed tube blank again. The resulting coating thickness is equivalent to the initial thickness in step (4). Before the applied PVA aqueous solution dries, wrap n layers of film around the outer surface of the pre-foamed tube blank. The film covering the outer surface of the pre-foamed tube blank provides pressure and plays a limiting role. At the same time, the toughness of the film is used to buffer the foaming process of the tube. The high-temperature resistant and ultra-tough film refers to a film whose thermal softening temperature is higher than T. 浸 At least 20 degrees, and in T 放 At high tensile speeds of 500 mm / min, the elongation at break is above 100%. The number of film winding layers, n, needs to be determined based on the tensile modulus M of the film at high temperatures, and can be estimated using the following formula: n equals P释 / P 期释 *P 浸 / M and rounded down, i.e., n is considered to be related to the following factors: the film at high temperature T 放 Tensile strength M at a high tensile speed of 500 mm / min, and pressure P of the supercritical fluid. 浸 The initial pressure release rate P of the high-pressure vessel at the moment of opening 释 The expected pressure drop rate P of pre-foamed pipes during initial pressure release after pre-impregnation 期释 In this invention, the P of the pre-foamed pipe material 期释 The pressure is 7.5–10 MPa.

[0018] (6) After the film is bonded, the pre-foamed tube blank is placed on the inner core of the mold, and the outer mold assembly is wrapped around the pre-foamed tube blank. The ribs of the outer mold assembly are adjusted to a position larger than the outer diameter of the pre-foamed tube blank.

[0019] (7) Place the mold containing the pre-foamed tube blank in a sealed high-pressure container, and introduce supercritical fluid into the sealed high-pressure container at a high temperature T. 浸 With high voltage P 浸 The pre-foamed tube blank is immersed in a supercritical fluid; the mold is always rotating inside the high-pressure vessel.

[0020] (8) After soaking time t 浸 Then, the temperature T inside the high-pressure vessel is... 放 After the temperature is lowered to 5-20 degrees below the polymer melting point and temperature equilibrium is reached, the mold stops rotating, the high-pressure container is opened quickly, and after depressurization, a microporous foamed tube tightly connected to the mold is obtained.

[0021] (9) Immerse the mold of the microporous foamed pipe in water, and the PVA coating on the inner wall surface is removed. Take the pipe out of the mold, remove the film layer, and the PVA coating on the outer wall surface is also removed to obtain the polymer microporous foamed pipe.

[0022] In step (1), the melting point difference between the polymers in the phase composite is more than 20 degrees. When the melt strength of the low melting point polymer is tested by gravimetric method or force method, the difference in melt strength between the two melting points is more than 50%. The mass ratio of the low melting point polymer is 10-30%, and the mass ratio of the high melting point polymer is 70-90%.

[0023] The main reason for the above material requirements is that the large difference in melt strength between high and low melting points of low-melting-point polymers indicates that the melt strength of low-melting-point polymers varies greatly with temperature. Since foaming is carried out near the melting point of high-melting-point polymers, this can cause them to crack during the foaming process, thereby achieving open-cell foaming.

[0024] In step (3), the linear shrinkage rate δ of the blend is determined by the ratio of its length in a certain direction at high temperature and room temperature: δ = length L at high temperature 高 / Length L at room temperature 室 -1, the high temperature is equal to T 放 .

[0025] In step (5), the thickness ratio α of the PVA coating before and after drying is 0.4 to 0.6. Within this range, the PVA coating and the foaming material can bond more tightly. If the ratio is too low or too high, the bonding between the two will be poor.

[0026] In step (7), the pressure P of the supercritical fluid inside the high-pressure vessel 浸 For 10-50 MPa, T 浸 The temperature is 0–5 degrees Celsius below the polymer's melting point, and the soaking time is t. 浸 The time is 5 to 30 minutes; the rotation speed of the mold inside the high-pressure container is 300 to 900 r / min.

[0027] In step (7), the supercritical fluid is supercritical nitrogen or supercritical carbon dioxide or a combination of both.

[0028] In step (8), the initial pressure release rate P of the high-pressure vessel at the moment of opening is... 释 The pressure is 30–70 MPa / second.

[0029] The above-mentioned polymer microporous foamed pipes are used in sound-absorbing materials, and the average sound absorption coefficient of the polymer microporous foamed pipes exceeds 0.8.

[0030] The working process of this invention is as follows:

[0031] Once the pre-foamed tube blank is prepared, remove the limiting screws in the cylindrical groove of the second fixing bracket, remove the second fixing bracket, and place the pre-foamed tube blank onto the inner mold core, positioning the pre-foamed tube blank between the inner mold core and the outer mold assembly. Reconnect the second fixing bracket to the ribs using the limiting screws, ensuring that both ends of the pre-foamed tube blank are in contact with the first and second fixing brackets respectively. This places the pre-foamed tube blank into the cavity between the inner mold core and the outer mold assembly. Adjust the limiting screws, and by adjusting the movement distance of the ribs in the cylindrical groove, determine the position of each rib in the outer mold assembly. The position of the compression spring after it is fully compressed can change the final dimensions of the foamed pipe. The mold containing the pre-foamed pipe blank is placed in a high-pressure container. The container has a cavity connected to the motor via a coupling. The cavity is the same size as the mold. The mold is placed in the cavity and heated in the sealed container while being immersed in supercritical fluid. Due to the rotation, the pre-foamed pipe blank can be quickly immersed in supercritical fluid. At the same time, the temperature distribution of each part of the pre-foamed pipe blank is very uniform, so that each part of the pre-foamed pipe blank is uniformly immersed.

[0032] When the pressure inside the container is released, the supercritical fluid inside the pre-foamed tube blank transforms into gas, and the material begins to expand and foam. At this time, the pre-foamed tube blank inside the mold expands outward, but its surface is covered with n layers of thin film. In addition, under the action of the spring, the ribs also exert pressure on the tube. However, since the force of the film and the spring is still less than the opening force formed by the gas foaming inside the tube, the cells can still grow, but the foaming speed is well controlled to prevent it from becoming too fast, thus achieving the purpose of controllable foaming. When the tube expands to a certain size, the elongation of the film exceeds its limit, and the film ruptures and fails, but the spring... The pressure increases as the pipe expands, and the compressive force provided by the spring restricts the rapid growth of the bubbles. Thus, the bubbles inside the pipe are still growing under a restricted state, resulting in more uniform foaming in all parts of the pipe. This continues until the ribs on the mold reach their limit positions due to the action of the limit screws. At this point, the pressure inside the high-pressure container is basically released. Since the temperature of the foamed pipe is below the melting temperature of the material, the bubbles inside the pipe can quickly solidify, and the shape of the pipe is fixed. The mold is then removed from the high-pressure container, the second fixing frame is opened, and the obtained foamed pipe is taken out of the mold.

[0033] In addition, the inner diameter of the pipe corresponds to the size of the inner mold core of the mold, and its inner diameter is only 0.04 to 0.1 mm larger than that of the inner mold core of the mold, that is, the difference is twice the thickness of the PVA layer; the outer diameter of the pipe corresponds to the position of each rib of the outer mold assembly, and its outer diameter is smaller than the inner diameter of the cavity formed by each rib of the mold, which is equal to twice the thickness of the two PVA coating layers plus n film layers (by diameter).

[0034] The foamed pipe obtained by the method of this invention is a tubular product with a large number of interconnected micropores on its wall. The inner and outer surfaces of the pipe also have open-pore structures. The micropores are uniform in size, with diameters all within 50 micrometers and the deviation in pore size can be controlled within 5 micrometers. The micropores are oriented along the wall thickness direction with excellent orientation consistency. The foaming ratio of the pipe is between 3 and 10, the inner diameter of the pipe is 10 mm or more, the wall thickness of the pipe is between 3 mm and 200 mm, and the cross-sectional shape of the pipe is circular, elliptical, or other rotational shapes, with its cross-sectional dimensions remaining constant or changing regularly.

[0035] The product of this invention also has excellent sound absorption effect. The sound absorption coefficient of the product was measured using the transfer function method. The average sound absorption coefficient measured in the frequency range of 200 to 2000 Hz all exceeded 0.8, which is a Class I sound absorption material.

[0036] Beneficial effects: Compared with the prior art, the present invention has the following significant effects:

[0037] (1) The method of the present invention can achieve precise control of the bubble structure of the pipe. Through the combined action of the film coating and the spring (adjusting the pressure), the bubble size can be controlled and the degree of restriction of the bubble growth process can be increased, thereby improving the uniformity of the bubble. The bubble size of the pipe with the same wall thickness can be very small, and the bubble size of the pipe with different wall thicknesses can also be very small. The uniformity of the bubble is conducive to improving the various mechanical properties and sound absorption function of the material.

[0038] (2) The orientation of the bubble cells can be precisely controlled. Since the gaps between the ribs of the mold are equivalent to the main air channel when the pressure is released, and the micropores on the film are equivalent to the secondary air channel, the uniform distribution of the main and secondary air channels can maintain uniform unobstructed flow when the high pressure vessel is opened. Moreover, their directions are all along the radial direction of the pipe wall, so the micropore orientation of the obtained pipe is very consistent. The consistent orientation of the bubble cells is also conducive to improving the uniformity of the mechanical properties of the material and the sound absorption effect.

[0039] (3) The foamed pipe can be easily removed from the mold without damaging the pipe. The PVA coating enables the molded product to be quickly and undamagedly removed from the inner mold core. At the same time, the PVA coating also enables the inner and outer wall surfaces of the pipe to have open structure, thereby realizing the direct acquisition of foamed pipe with surface opening, without the need to process the opening on the inner and outer surfaces of the foamed pipe. Moreover, the inner and outer surface quality of the pipe is good.

[0040] (4) By adjusting the position of the mold limiting screw, the movement position of the rib in the cylindrical groove is determined, thereby controlling the shape of the final foamed pipe and accurately controlling the foaming ratio of the pipe, so as to produce products with different foaming ratios on a set of molds.

[0041] (5) By adjusting the position of the mold limiting screw, the movement position of the rib in the cylindrical groove is determined, thereby controlling the shape of the final foamed pipe, realizing the foaming and molding of irregularly shaped pipe products, and realizing the production of products with different shapes on a set of molds.

[0042] (6) By rotating at high speed, the wetting efficiency and uniformity of supercritical fluid inside the material are improved, and the consistency of process conditions such as temperature, pressure and temperature and pressure change rate in various parts of the pipe with a certain thickness is achieved, thereby improving the production efficiency of foamed pipe. For 10mm thick pre-foamed pipe, the wetting time can be as short as 5 minutes. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of the method for preparing polymer microporous foamed pipes according to the present invention;

[0044] Figure 2 This is a schematic diagram of the mold structure;

[0045] Figure 3This is a schematic diagram of the structure when the ribs open up after the pressure is released from the mold after foaming;

[0046] Figure 4 A schematic diagram of a mold placed inside a high-pressure container;

[0047] Figure 5 A schematic diagram of the external shape of a pre-foamed tube blank with a fixed cross-section of rotation;

[0048] Figure 6 A schematic diagram of the external shape of a pre-foamed tube blank with a regularly varying inclined gyratory cross section;

[0049] Figure 7 This is a low-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 1;

[0050] Figure 8 This is a high-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 1;

[0051] Figure 9 Scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Comparative Example 1;

[0052] Figure 10 This is a low-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 2;

[0053] Figure 11 This is a high-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 2;

[0054] Figure 12 Scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Comparative Example 2;

[0055] Figure 13 Scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Comparative Example 3;

[0056] Figure 14 This is a low-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 3.

[0057] Figure 15 This is a high-magnification scanning electron microscope image of the cell morphology of the foamed pipe product prepared in Example 3;

[0058] Figure 16 The image shows a scanning electron microscope (SEM) image of the cell morphology of the foamed pipe product prepared in Comparative Example 4. Detailed Implementation

[0059] like Figure 4As shown, the high-pressure container of the present invention consists of an upper cover plate 12 and a lower housing 15. After the cover plate 12 and the housing 15 are sealed, no gas leakage occurs within the range of 0-70 MPa and 0-260 degrees. The cover plate 12 has an injection port 17, through which supercritical fluid is injected into the container and the pressure inside the container is controlled. A cylindrical reaction chamber 18 is provided inside the housing 15 and is placed in a groove in the housing 15. A temperature control device 16 is also provided on the side wall of the housing 15. The pre-foamed pipe 14 is placed in the mold 8 and the mold 8 is placed in the reaction chamber 18. The reaction chamber 18 is connected to an external motor through a coupling 11. The rotation of the motor drives the reaction chamber 18 to rotate, thereby driving the mold 8 to rotate. When the upper cover plate 12 and the lower housing 15 are separated, the high-pressure container opens quickly, with a response time of less than 0.05 seconds.

[0060] Example 1

[0061] A method for producing polypropylene / linear low-density polyethylene microporous foamed pipes using supercritical fluids:

[0062] Regarding raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S, with a melting point of 165 degrees Celsius. The linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050, with a melting point of 120 degrees Celsius. Through gravimetric analysis, the melt strength of this material at 120 degrees Celsius and 165 degrees Celsius were found to be 1.16 g and 0.52 g, respectively. This was achieved using a [unspecified equipment / process]. Figure 4 The container shown is a high-pressure (70MPA) and high-temperature (250°C) resistant sealable container. After the container is sealed, there is no gas leakage within the range of 0-70MPA and 0-260°C. The container is equipped with a cavity that is connected to the motor via a coupling. The mold for loading the pre-foamed tube blank is placed in the cavity, and the cavity rotates under the drive of the motor.

[0063] The PVA used was ordinary commercially available domestic 1788, which was dissolved in twice its weight of distilled water at room temperature to prepare a PVA aqueous solution. The high-temperature resistant ultra-tough membrane (R260 porous Teflon FEP membrane) used can withstand temperatures up to 260°C. It is commercially available, with a thickness of 20 micrometers, a pore size of 10 micrometers, and a pore spacing of 8 millimeters. At 150°C, the film was measured to have an elongation at break of 182% and a tensile strength of 21.3 MPa at a tensile speed of 500 mm / min.

[0064] The above method is implemented based on the following mold, such as... Figure 2As shown, the mold 8 includes a first fixed frame 31 and a second fixed frame 32 arranged opposite to each other, and an inner mold core 4 fixed on the first fixed frame 31; both the first fixed frame 31 and the second fixed frame 32 are provided with cylindrical grooves 5 arranged in a ring and corresponding to each other. The mold 8 also includes an outer mold assembly 1, which is composed of multiple ribs 6 arranged in a ring. The ribs 6 of the outer mold assembly 1 are arranged one-to-one with the cylindrical grooves 5 on the fixed frame 3; the two ends of the ribs 6 are respectively connected to the first fixed frame 31 and the second fixed frame 32 through limiting screws 7; the mold 8 also includes a compression spring 2 disposed in the cylindrical groove 5. One end of the compression spring 2 is connected to the end point of the cylindrical groove 5 away from the center of the fixed frame 3, and the other end of the compression spring 2 is connected to the limiting screw 7. The limiting screw 7 slides laterally in the cylindrical groove 5 through the compression spring 2.

[0065] The ribs are straight round bars with a diameter of 6 mm. The number of ribs is determined to be no more than (20+6)*3.14 / 6. For ease of processing, 12 ribs are selected.

[0066] The above method specifically includes the following steps:

[0067] (1) Pure PP material and LLDPE material were mixed at a weight ratio of 7:3, and then PP / LLDPE blend was obtained by extrusion melt blending. The linear shrinkage rate δ of the blend between 150 degrees and 25 degrees was determined to be 1.5% through experiments.

[0068] (2) The PP / LLDPE blend is extruded into a pre-foamed pipe with an inner diameter of 9.96 mm and an outer diameter of 20 mm. Its shape is as follows: Figure 5 As shown, the stretch ratio of the material during extrusion is 3;

[0069] (3) Cut a pre-foamed pipe with a length of 295.6 mm to obtain a pre-foamed pipe blank;

[0070] (4) Coat the inner and outer surfaces of the pre-foamed tube blank with a layer of PVA aqueous solution with a coating thickness of 50 micrometers.

[0071] (5) Place the pre-foamed tube blank in a forced-air drying oven to dry until the PVA is completely set. Measure its thickness as about 20 micrometers. Apply PVA aqueous solution to the outer surface of the pre-foamed tube blank again. The amount used is close to that used the first time. Before drying, wrap the outer surface with a heat-resistant ultra-tough membrane with micropores in 3 layers.

[0072] The number of layers is based on the film's temperature T. 放 The tensile strength M was estimated to be 21.3 MPa at a high tensile speed of 500 mm / min, meaning n equals P. 释 / P 期释 *P 浸 / M and rounded down, the pressure P of the supercritical fluid in the total pressure. 浸 The initial pressure release rate P of the high-pressure vessel at the moment of opening is 15 MPa. 释 The expected pressure drop rate P of the pre-foamed tube blank during initial pressure release after pre-impregnation is 30 MPa. 期释 It is 7.5 MPa;

[0073] (6) Place the pre-foamed tube blank into the inner core of the mold, and surround the outer mold assembly around the tube. Adjust the ribs to a position where the inner diameter (inner diameter of the cavity enclosed by the outer mold assembly) is 40.1 mm.

[0074] (7) Place the mold containing the pre-foamed tube blank in a closed high-pressure container, introduce supercritical fluid into the closed high-pressure container, and immerse the pre-foamed tube blank in supercritical CO2 for 5 minutes at 165 degrees and 15 MPa, wherein the mold rotates at a speed of 900 r / min in the high-pressure container.

[0075] (8) Reduce the temperature inside the high-pressure container to 145 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, the high-pressure container is opened quickly, and after depressurization, a microporous foamed pipe tightly connected to the mold is obtained.

[0076] (9) Immerse the microporous foamed pipe in water, remove the PVA layer and film layer from its inner and outer wall surfaces, and take the pipe out of the mold to obtain a pipe with open surface and excellent surface quality; the outer diameter of the pipe is 40mm and the foaming ratio of the pipe is 5 times.

[0077] The tubular component prepared in Example 1 was subjected to a ring crush strength test, and its ring crush strength was 1623 KN / 100 mm. Simultaneously, the morphology of the bubbles within the component was observed, and the results are as follows. Figures 7-8 As shown, it was found that the uniformity of this type of bubble is very good, and moreover, in the wall thickness direction ( Figure 7 The average size deviation of the bubbles at different wall thicknesses is within 5 micrometers (in the vertical direction). These bubbles all have an orientation along the wall thickness direction and are all open-cell structures. The open-cell rate of these bubbles reaches 95.5% after testing.

[0078] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall was found to be 0.901 in the frequency range of 200 to 2000 Hz, indicating that the resulting product has excellent sound absorption performance.

[0079] Comparative Example 1

[0080] To illustrate the effects of the present invention, Comparative Example 1 is provided. The preparation process of its raw materials is similar to that of Example 1. Regarding the raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S with a melting point of 165 degrees Celsius, and the linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050 with a melting point of 120 degrees Celsius. Both raw materials are exactly the same as in Example 1. A high-pressure (70 MPa) and high-temperature (250 degrees Celsius) sealable container with an inner diameter of 50 mm is used. After sealing, no gas leakage occurs within the range of 0–70 MPa and 0–260 degrees Celsius. The container has a cavity connected to a motor via a coupling, and its structure is basically the same as that of Example 1. The only difference is that Comparative Example 1 did not use the mold used in Example 1, nor did it use a film and mold to control the foam cells as in Example 1. The production method of its polymer microporous foamed pipe follows existing conventional methods, specifically including the following steps:

[0081] (1) After mixing pure PP material and LLDPE material at a weight ratio of 7:3, the PP / LLDPE blend is obtained by extrusion melt blending. The PP / LLDPE blend is then extruded into a pre-foamed pipe with an inner diameter of 10 mm and an outer diameter of 20 mm. The stretch ratio of the material during the extrusion process is 3, and the pipe is cut into pipes with a length of 300 mm.

[0082] (2) Place the pipe directly into a sealed high-pressure container, introduce supercritical CO2 into the sealed high-pressure container, and immerse it at 175 degrees and 15 MPa for 30 minutes; (the experiment was unsuccessful after immersion at 165 degrees for 5 minutes in Example 1).

[0083] (3) Cool the temperature inside the high pressure vessel to 145 degrees, and after 10 minutes, quickly depressurize and remove the pipe inside the high pressure vessel. The foaming size of each part of the pipe is not uniform, and the inner and outer dimensions are not uniform. The foaming ratio of the pipe is about 8 times.

[0084] The tubular part prepared in Comparative Example 1 was subjected to ring crush strength testing, and the optimal ring crush strength result was only 1137 KN / 100 mm. Simultaneously, the morphology of the bubbles within the part was observed, and the results are as follows: Figure 9 As shown.

[0085] The sound absorption coefficient was measured using the transfer function method, and the average sound absorption coefficient of the pipe wall was found to be 0.553 in the frequency range of 200–2000 Hz.

[0086] A comparison between Example 1 and Comparative Example 1 reveals that, because the pipe fitting in Comparative Example 1 was not foamed under controlled conditions, its pores were highly uneven, with significant differences in pore density and size across different areas. Although the pores possessed some open-cell structure, the open-cell rate was only 53%, resulting in poor consistency in pore orientation. Consequently, the pipe fitting exhibited a poor shape, with both the inner and outer walls being solid structures, and significant dimensional differences across different areas. Furthermore, a comparison of the sound absorption coefficients shows that the sound absorption effect of this comparative example is considerably worse than that of Example 1, which demonstrates superior sound absorption.

[0087] Example 2

[0088] A method for producing polypropylene / linear low-density polyethylene microporous foamed pipes using supercritical fluids:

[0089] In terms of raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S with a melting point of 165 degrees Celsius, and the linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050 with a melting point of 120 degrees Celsius. A high-pressure (70MPA) and high-temperature (250 degrees Celsius) sealable container is used. After the container is sealed, there will be no gas leakage in the range of 0-70MPA and 0-260 degrees Celsius. The container is equipped with a cavity that is connected to the motor through a coupling. The mold for loading the pre-foamed tube blank is placed in the cavity, and the cavity rotates under the drive of the motor.

[0090] The PVA used was ordinary commercially available domestic 1788, which was dissolved in twice its weight of distilled water at room temperature to prepare a PVA aqueous solution. The high-temperature resistant ultra-tough membrane (R260 porous Teflon FEP membrane) used can withstand temperatures up to 260°C. It is commercially available, with a thickness of 20 micrometers, a pore size of 10 micrometers, and a pore spacing of 8 millimeters. At 150°C, the film was measured to have an elongation at break of 182% and a tensile strength of 21.3 MPa at a tensile speed of 500 mm / min.

[0091] The above method is implemented based on the following mold, such as... Figure 2 As shown, the mold 8 includes a first fixed frame 31 and a second fixed frame 32 arranged opposite to each other, and an inner mold core 4 fixed on the first fixed frame 31; both the first fixed frame 31 and the second fixed frame 32 are provided with cylindrical grooves 5 arranged in a ring and corresponding to each other. The mold 8 also includes an outer mold assembly 1, which is composed of multiple ribs 6 arranged in a ring. The ribs 6 of the outer mold assembly 1 are arranged one-to-one with the cylindrical grooves 5 on the fixed frame 3; the two ends of the ribs 6 are respectively connected to the first fixed frame 31 and the second fixed frame 32 through limiting screws 7; the mold 8 also includes a compression spring 2 disposed in the cylindrical groove 5. One end of the compression spring 2 is connected to the end point of the cylindrical groove 5 away from the center of the fixed frame 3, and the other end of the compression spring 2 is connected to the limiting screw 7. The limiting screw 7 slides laterally in the cylindrical groove 5 through the compression spring 2.

[0092] The ribs are straight round bars with a diameter of 10 mm. The number of ribs determined at both ends of the pre-foamed tube blank is no greater than (90+10)*3.14 / 10 and (100+10)*3.14 / 10, and finally 28 ribs are selected.

[0093] The above method specifically includes the following steps:

[0094] (1) Pure PP material and LLDPE material were mixed at a weight ratio of 7:3, and then PP / LLDPE blend was obtained by extrusion melt blending. The linear shrinkage rate δ of the blend between 150 degrees and 25 degrees was determined to be 1.5% through experiments.

[0095] (2) The PP / LLDPE blend is compacted at 10 MPa pressure and 200 degrees Celsius to process a pre-foamed tube blank with a length of 98.5 mm, an inner radius of 69.94 mm and an outer radius of 90 mm at one end, and an inner radius of 79.94 mm and an outer radius of 100 mm at the other end. Its shape is as follows. Figure 6 As shown;

[0096] (3) Coat the inner and outer surfaces of the pre-foamed tube blank with a layer of PVA aqueous solution with a coating thickness of 50 micrometers;

[0097] (4) Place the pre-foamed tube blank in a forced-air drying oven to dry until the PVA is completely set. Measure its thickness as about 30 micrometers. Apply PVA aqueous solution to the outer surface of the pre-foamed tube blank again. The amount used is close to that used the first time. Before drying, wrap the outer surface with 5 layers of heat-resistant ultra-tough membrane with micropores.

[0098] The number of layers is based on the film's temperature T. 放 The tensile strength M was estimated to be 21.3 MPa at a high tensile speed of 500 mm / min, meaning n equals P. 释 / P 期释 *P 浸 / M and rounded down, the pressure P of the supercritical fluid in the total pressure. 浸 The initial pressure release rate P of the high-pressure vessel at the moment of opening is 20 MPa. 释 The expected pressure drop rate P of the pre-foamed tube blank during the initial pressure release after pre-impregnation is 40 MPa. 期释 It is 8MPa;

[0099] (5) Place the pre-foamed tube blank into the inner core of the mold, and wrap the outer mold around the tube. Adjust the ribs at both ends to positions with inner diameters of 160.16 mm and 170.16 mm, respectively.

[0100] (6) Place the mold containing the pre-foamed tube blank in a closed high-pressure container, introduce supercritical fluid into the closed high-pressure container, and immerse the pre-foamed tube blank in supercritical N2 for 10 minutes at 160 degrees and 20 MPa, while the mold rotates at a speed of 300 r / min in the high-pressure container.

[0101] (7) Reduce the temperature inside the high-pressure container to 155 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, the high-pressure container is opened quickly, and after depressurization, a microporous foamed pipe tightly connected to the mold is obtained.

[0102] (8) Immerse the microporous foamed pipe in water, remove the PVA layer and film layer from its inner and outer wall surfaces, and take the pipe out of the mold to obtain a pipe with open surface and excellent surface quality; the outer radii of the two ends of the pipe are 160mm and 170mm respectively, and the foaming ratio of the pipe is about 6.36 times.

[0103] The disc-shaped part prepared in Example 2 was subjected to longitudinal compressive strength testing, and it could withstand a pressure as high as 2942 KN / 100 mm. Simultaneously, the morphology of the bubbles within the part was observed, and the results are as follows... Figures 10-11 As shown, it was found that the uniformity of this type of bubble is very good, and moreover, in the wall thickness direction ( Figure 10 The average size deviation of the bubbles at different wall thicknesses is within 5 micrometers (up and down directions). These bubbles all have an orientation along the wall thickness direction and are all open-cell structures. The open-cell rate of these bubbles reaches 93.7% after testing.

[0104] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall obtained in this embodiment was 0.884 in the frequency range of 200 to 2000 Hz.

[0105] Comparative Example 2

[0106] To illustrate the effects of the present invention, Comparative Example 2 is provided. The preparation process of its raw materials is similar to that of Example 2. Regarding the raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S with a melting point of 165 degrees Celsius, and the linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050 with a melting point of 120 degrees Celsius. A high-pressure (70 MPa) and high-temperature (250 degrees Celsius) sealable container with an inner diameter of 170 mm is used. After sealing, no gas leakage occurs within the range of 0–70 MPa and 0–260 degrees Celsius. The container has a cavity connected to a motor via a coupling, and its structure is basically the same as that of Example 2. The only difference is that Comparative Example 2 did not use the mold used in Example 2, nor did it use a film and mold to control the foam cells as in Example 2. The production method of its polymer microporous foamed pipe follows existing conventional methods, specifically including the following steps:

[0107] (1) After mixing pure PP material and LLDPE material at a weight ratio of 7:3, similar to Example 2, the mixture was compacted at a pressure of 10MPA and a temperature of 200 degrees Celsius and processed into a pre-foamed tube blank with a length of 98.5mm, an inner radius of 69.97mm and an outer radius of 90mm at one end, and an inner radius of 79.97mm and an outer radius of 100mm at the other end.

[0108] (2) The pre-foamed tube blank was placed directly into a sealed high-pressure container, and supercritical N2 was introduced into the sealed high-pressure container. It was then immersed at 180 degrees and 20 MPa for 40 minutes. (The experiment was unsuccessful after immersion at 160 degrees for 10 minutes, which corresponds to Example 2.)

[0109] (3) Cool the temperature inside the high pressure container to 155 degrees. After 10 minutes, open the high pressure container and quickly depressurize. Take out the pipe inside the high pressure container. The foaming size of each part of the pipe is not uniform and the inner and outer dimensions are not uniform. The foaming ratio of the pipe is about 7.7 times.

[0110] The longitudinal compressive strength of the tubular part prepared in Comparative Example 2 was tested, and the optimal result was only 2267 KN / 100 mm. Simultaneously, the morphology of the bubbles within the part was observed, and the results are as follows: Figure 12 As shown. In Figure 12 In the middle, the left and right directions represent the wall thickness direction. It can be seen that the orientation of the bubbles is basically along this direction, but the bubble size varies greatly at different wall thicknesses.

[0111] By comparing Example 2 with Comparative Example 2, it can be seen that since the pipe fitting in Comparative Example 2 was not foamed under controlled conditions, its pores were very uneven, and the pore density and pore size of each part varied greatly. Although the pores also had a certain open structure, the open rate was only 62.8%. The shape of the obtained pipe fitting was very poor, and the size difference of each part was also very large. The inner and outer wall surfaces were all solid structures.

[0112] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall obtained in this embodiment was 0.475 in the frequency range of 200 to 2000 Hz.

[0113] Comparative Example 3

[0114] To illustrate the effects of the present invention, Comparative Example 3 is provided. The preparation process of its raw materials is similar to that of Example 2. Regarding the raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S with a melting point of 165 degrees Celsius, and the linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050 with a melting point of 120 degrees Celsius. A high-pressure (70 MPa) and high-temperature (250 degrees Celsius) sealable container with an inner diameter of 170 mm is used. After sealing, no gas leakage occurs within the range of 0–70 MPa and 0–260 degrees Celsius. The container has a cavity connected to a motor via a coupling, and its structure is basically the same as that of Example 2. The only difference is that Comparative Example 3 uses the mold used in Example 2, but does not use a film and mold to control the bubble structure as in Example 2. Specifically, it includes the following steps:

[0115] (1) Pure PP material and LLDPE material were mixed at a weight ratio of 7:3, and then PP / LLDPE blend was obtained by extrusion melt blending. The linear shrinkage rate δ of the blend between 150 degrees and 25 degrees was determined to be 1.5% through experiments.

[0116] (2) The PP / LLDPE blend is compacted at 10 MPa pressure and 200 degrees Celsius to process a pre-foamed tube blank with a length of 98.5 mm, an inner radius of 70 mm and an outer radius of 90 mm at one end, and an inner radius of 80 mm and an outer radius of 100 mm at the other end. Its shape is as follows: Figure 6 As shown;

[0117] (3) Place the pre-foamed tube blank on the inner core of the mold, and wrap the outer mold around the tube. Adjust the ribs at both ends to positions with inner diameters of 160mm and 170mm respectively.

[0118] (4) Place the mold containing the pipe in a closed high-pressure container, introduce supercritical fluid into the closed high-pressure container, and immerse the pipe in supercritical N2 for 10 minutes at 160 degrees and 20 MPa, while the mold rotates at 300 r / min in the high-pressure container.

[0119] (5) Reduce the temperature inside the high-pressure container to 155 degrees. After the temperature balance is reached, the mold stops rotating, the high-pressure container opens quickly, and after instantaneous depressurization, a microporous foamed pipe tightly connected to the mold is obtained.

[0120] (6) Due to the different dimensions at both ends, although the microporous foamed tube is tightly fitted onto the inner core of the mold, with effort, once the tube shows signs of movement, it can be removed from the inner core of the mold, thus obtaining the tube with outer radii of 160mm and 170mm at both ends, and the foaming ratio of the tube is about 6.37 times.

[0121] The longitudinal compressive strength of the tubular part prepared in Comparative Example 3 was tested, and the optimal result was 2451 KN / 100 mm. Simultaneously, the morphology of the bubbles within the part was observed, and the results are as follows: Figure 13 As shown. In Figure 13 In the middle, the left and right directions represent the wall thickness direction. It can be seen that the orientation consistency of the bubbles is poor, but the bubble size varies significantly at different wall thicknesses, and even at the same wall thickness, the bubble size varies considerably.

[0122] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall obtained in the comparative example was 0.522 in the frequency range of 200 to 2000 Hz.

[0123] A comparison between Example 2 and Comparative Example 3 shows that although the pipe fitting in Comparative Example 3 was foamed under certain controllable conditions, the degree of control was not precise. As a result, the cell structure was very uneven, and the cell density and size varied greatly in different parts. Although the cells also had a certain open structure and the open rate was as high as 83.1%, the shape of the obtained pipe fitting was not perfect. Both the inner and outer wall surfaces had a fairly thick solid layer, and the size difference in different parts was also very large, making it unsuitable for direct use.

[0124] Meanwhile, the sound absorption effect shows that, compared with Example 2, the sound absorption effects of Comparative Example 2 and Comparative Example 3 are much worse than those of Example 2, and the sound absorption effect of Example 2 is very good.

[0125] Example 3

[0126] A method for producing thermoplastic polyurethane microporous foamed pipes using supercritical fluids:

[0127] In terms of raw materials, two types of thermoplastic polyurethane (TPU) with different degrees of softness and hardness were used, namely the commercially available 60D and 75A, with melting points of 170 degrees and 150 degrees respectively. According to the force measurement method, the melt strength of 75A material at 170 degrees and 150 degrees is 17.1mN and 9.3mN respectively. A high-pressure (70MPA) and high-temperature (250 degrees) sealable container was used. After the container was sealed, no gas leakage occurred in the range of 0-70MPA and 0-260 degrees. The container has a cavity connected to the motor through a coupling. The mold for loading the pre-foamed tube blank is placed in the cavity, and the cavity rotates under the drive of the motor.

[0128] The PVA used was ordinary commercially available domestic 1788, which was dissolved in twice its weight of distilled water at room temperature to prepare a PVA aqueous solution. The high-temperature resistant ultra-tough membrane (R260 porous Teflon FEP membrane) used can withstand temperatures up to 260°C. It is commercially available, with a thickness of 20 micrometers, a pore size of 10 micrometers, and a pore spacing of 8 millimeters. At 150°C, the film was measured to have an elongation at break of 182% and a tensile strength of 21.3 MPa at a tensile speed of 500 mm / min.

[0129] The above method is implemented based on the following mold, such as... Figure 2 As shown, the mold 8 includes a first fixed frame 31 and a second fixed frame 32 arranged opposite to each other, and an inner mold core 4 fixed on the first fixed frame 31; both the first fixed frame 31 and the second fixed frame 32 are provided with cylindrical grooves 5 arranged in a ring and corresponding to each other. The mold 8 also includes an outer mold assembly 1, which is composed of multiple ribs 6 arranged in a ring. The ribs 6 of the outer mold assembly 1 are arranged one-to-one with the cylindrical grooves 5 on the fixed frame 3; the two ends of the ribs 6 are respectively connected to the first fixed frame 31 and the second fixed frame 32 through limiting screws 7; the mold 8 also includes a compression spring 2 disposed in the cylindrical groove 5. One end of the compression spring 2 is connected to the end point of the cylindrical groove 5 away from the center of the fixed frame 3, and the other end of the compression spring 2 is connected to the limiting screw 7. The limiting screw 7 slides laterally in the cylindrical groove 5 through the compression spring 2.

[0130] The ribs are straight round bars with a diameter of 10 mm. The number of ribs is determined to be no more than (60+10)*3.14 / 10. For ease of processing, 20 ribs are selected.

[0131] The above method specifically includes the following steps:

[0132] (1) Two TPU materials were mixed at a weight ratio of 7:3 and then solvent blended to obtain a TPU blend. The linear shrinkage rate δ of the blend between 150 degrees and 25 degrees was determined to be 1.0% through experiments.

[0133] (2) The TPU blend is extruded into a pre-foamed pipe with an inner diameter of 49.96 mm and an outer diameter of 60 mm, and its shape is as follows. Figure 5 As shown;

[0134] (3) Cut a pre-foamed pipe with a length of 495.0 mm to obtain a pre-foamed pipe blank;

[0135] (4) Coat the inner and outer surfaces of the pre-foamed tube blank with a layer of PVA aqueous solution with a coating thickness of 50 micrometers.

[0136] (5) Place the pre-foamed tube blank in a forced-air drying oven to dry until the PVA is completely set. Measure its thickness as about 20 micrometers. Apply PVA aqueous solution to the outer surface of the pre-foamed tube blank again. The amount used is close to that used the first time. Before drying, wrap the outer surface with 5 layers of heat-resistant ultra-tough membrane with micropores.

[0137] The number of layers is based on the film's temperature T. 放 The tensile strength M was estimated to be 21.3 MPa at a high tensile speed of 500 mm / min, meaning n equals P. 释 / P 期释 *P 浸 / M and rounded down, the pressure P of the supercritical fluid in the total pressure. 浸 The initial pressure release rate P of the high-pressure vessel at the moment of opening is 25 MPa. 释 The expected pressure drop rate P of the pre-foamed tube blank during initial pressure release after pre-impregnation is 50 MPa. 期释 It is 10 MPa;

[0138] (6) Place the pre-foamed tube blank into the inner core of the mold, and surround the outer mold assembly around the tube. Adjust the ribs to the position with an inner diameter of 120.14 mm.

[0139] (7) Place the mold containing the pre-foamed tube blank in a closed high-pressure container, and introduce supercritical fluid into the closed high-pressure container. At 165 degrees and 25 MPa, the pre-foamed tube blank is immersed in supercritical CO2 for 10 minutes, during which the mold rotates at a speed of 600 r / min in the high-pressure container.

[0140] (8) Reduce the temperature inside the high-pressure container to 150 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, the high-pressure container is opened quickly, and after depressurization, a microporous foamed pipe tightly connected to the mold is obtained.

[0141] (9) Immerse the microporous foamed pipe in water, remove the PVA layer and film layer from its inner and outer wall surfaces, and take the pipe out of the mold to obtain a pipe with open surface and excellent surface quality; the outer diameter of the pipe is 120mm and the foaming ratio of the pipe is 10.82 times.

[0142] The tubular component prepared in Example 3 was subjected to a ring crush strength test, and it did not break under the test pressure. Simultaneously, the morphology of the bubbles within the component was observed, and the results are as follows: Figures 14-15 As shown, the uniformity of this type of bubble structure is very good, all being open-cell structures. Testing revealed that the open-cell rate of this type of bubble reaches 97.9%, and furthermore, in the wall thickness direction ( Figure 14 (Up and down direction), the average size deviation of the bubbles at different wall thicknesses is also within 5 micrometers, and these bubbles all have an orientation along the wall thickness direction.

[0143] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall obtained in this embodiment was 0.921 in the frequency range of 200 to 2000 Hz.

[0144] Comparative Example 4

[0145] To illustrate the effects of the present invention, Comparative Example 4 is provided. The preparation process of its raw materials is similar to that of Example 3. Regarding the raw materials, two types of thermoplastic polyurethane (TPU) with different hardness were used: commercially available 60D and 75A, with melting points of 170°C and 150°C, respectively. A high-pressure (70MPa) and high-temperature (250°C) sealable container with an inner diameter of 50 mm was used. After sealing, no gas leakage occurred within the range of 0–70MPa and 0–260°C. The container has a cavity connected to a motor via a coupling, and its structure is basically the same as that of Example 3. The only difference is that Comparative Example 4 did not use the mold used in Example 3, nor did it use a film and mold to control the cell structure as in Example 3. The production method of its polymer microporous foamed tube follows existing conventional methods, specifically including the following steps:

[0146] (1) Mix the two TPU materials at a weight ratio of 7:3 and then obtain a TPU blend by solvent blending. The TPU blend is then extruded into a pre-foamed tube with an inner diameter of 50 mm and an outer diameter of 60 mm. The stretch ratio of the material during the extrusion process is 3, and the tube is cut into tubes with a length of 500 mm.

[0147] (2) Place the pipe directly into a sealed high-pressure container, introduce supercritical CO2 into the sealed high-pressure container, and immerse it at 180 degrees and 25 MPa for 30 minutes; (the experiment was unsuccessful after immersion at 165 degrees for 10 minutes in Example 3).

[0148] (3) Cool the temperature inside the high pressure container to 150 degrees, and after 10 minutes, quickly depressurize and take out the pipe inside the high pressure container. The foaming size of each part of the pipe is not uniform and the inner and outer dimensions are not uniform. The foaming ratio of the pipe is about 13.2 times.

[0149] The morphology of the bubbles inside the tubular part prepared in Comparative Example 4 was observed, and the results are as follows: Figure 16 As shown. By comparing Example 3 and Comparative Example 4, it can be seen that because the pipe fitting in Comparative Example 4 was not foamed under controlled conditions, its cell structure was very uneven, with large differences in cell density and size in different parts. Although the cells also had a certain open structure, the open rate was only 72.9%, the consistency of cell orientation was very poor, the shape of the pipe fitting was very poor, the inner and outer wall surfaces were both solid structures, and the size difference in different parts was very large.

[0150] The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the pipe wall in Comparative Example 4 was 0.499 in the frequency range of 200 to 2000 Hz. By comparison with Example 3, it can be seen that the sound absorption effect of Comparative Example 4 is much worse than that of Example 3, and the sound absorption effect of Example 3 is excellent.

Claims

1. An apparatus for producing a polymeric microcellular foamed pipe, characterized by: The utility model provides a kind of mould for preparing microcellular foamed pipe, including mould (8);The mould (8) includes oppositely arranged first fixed frame (31) and second fixed frame (32) and inner mould core (4) fixed on first fixed frame (31);The first fixed frame (31) and second fixed frame (32) are equipped with the cylindrical groove (5) corresponding with each other in annular arrangement, and still include outer mould group (1), the outer mould group (1) is made of multiple rib (6) in annular arrangement, the quantity of rib (6) is determined according to the inner circle size formed after combination and rib (6) own size, the inner circle size formed after combination of rib (6) is adapted to the appearance of pre-foamed pipe blank;The rib (6) of outer mould group (1) is set up with cylindrical groove (5) on fixed frame (3) one by one;Rib (6) both ends are connected with first fixed frame (31) and second fixed frame (32) respectively through limiting screw (7);Still include compression spring (2) arranged in cylindrical groove (5), one end of compression spring (2) is connected with the endpoint of cylindrical groove (5) away from the center side of fixed frame (3), the other end of compression spring (2) is connected with limiting screw (7), the limiting screw (7) is slid laterally in cylindrical groove (5) through compression spring (2).

2. The apparatus for producing a polymeric microcellularly foamed pipe according to claim 1, characterized by: The height of the inner mold core (4) is not greater than the distance between the first fixed frame (31) and the second fixed frame (32);The height of the inner mold core (4) is not less than the length of the pre-foamed pipe blank;The outer diameter of the inner mold core (4) is consistent with the inner diameter of the pre-foamed pipe blank.

3. The apparatus for producing a polymeric microcellularly foamed pipe according to claim 1, characterized by: It also includes a high-pressure sealed container that rotates the mold, the container has a cavity connected to the motor through a shaft coupling, the size of the cavity is consistent with the mold, the mold loaded with the pre-foamed pipe blank is placed in the cavity, and the cavity rotates under the motor.

4. The method of producing a polymeric microcellular foamed pipe according to claim 3, characterized in that, It includes the following steps: (1) Select at least two thermoplastic polymers to form a blend by melt blending or solution blending. The melting point difference of the polymers is more than 20 degrees. When testing the melt strength of the low melting point polymer by weight method or force method, the difference of the melt strength at the two melting points is more than 50%. The mass fraction of the low melting point polymer is 10-30%, and the mass fraction of the high melting point polymer is 70-90%; (2) Apply forming processing to the blend to obtain a pre-foamed pipe, and the wall thickness of the pre-foamed pipe is 1-20 mm; (3) cutting the prefoamed tubing to a length equal to the desired tubing length / (1 + blend line shrinkage (4) Uniformly apply PVA aqueous solution to the inner and outer surfaces of the pre-foamed pipe blank to form a PVA coating on the inner and outer surfaces of the pre-foamed pipe blank, and the initial thickness of the PVA coating is 30-50 μm; ), to obtain a prefoamed tube blank; (6) After the film is adhered, the pre-foamed pipe blank is sleeved on the inner mold core, and the outer mold group surrounds the pre-foamed pipe blank. Adjust the rib of the outer mold group to a position greater than the outer diameter of the pre-foamed pipe blank; (5) Dry the pre-foamed tube blank until the PVA coating is fully formed, and then apply a PVA aqueous solution to the outer surface of the pre-foamed tube blank again. The thickness of the coating is equivalent to the initial thickness in step (4). Before the PVA aqueous solution is dried, use a film to cover and wrap the outer surface of the pre-foamed tube blank. n Layer; the thermal softening temperature of the thin film is higher than T. 浸 At least 20 degrees, and in T 放 At high tensile speeds of 500 mm / min, the elongation at break is above 100%. The number of film winding layers, n, needs to be determined based on the tensile modulus M of the film at high temperatures, and can be estimated using the following formula: n equals P 释 / P 期释 *P 浸 / M and rounded down, i.e., n is considered to be related to the following factors: the film at high temperature T 放 Tensile strength M at a high tensile speed of 500 mm / min, and pressure P of the supercritical fluid. 浸 The initial pressure release rate P of the high-pressure vessel at the moment of opening 释 The expected pressure drop rate P of pre-foamed pipes during initial pressure release after pre-impregnation 期释 ; (9) The mold with the microcellular foamed pipe is immersed in water, the PVA coating on the inner wall surface is removed, the pipe is taken out of the mold, the film layer is removed, the PVA coating on the outer wall surface is also removed, and a polymer microcellular foamed pipe is obtained. (7) placing the mold containing the prefoamed parison in a closed high-pressure vessel, introducing a supercritical fluid into the closed high-pressure vessel, and foaming the prefoamed parison at a high temperature T 浸 with high pressure P 浸 wherein the mold is always in a rotating state in the high-pressure vessel; (8) soaking time t 浸 After that, the temperature in the high-pressure vessel is T 放 The temperature is reduced to 5-20 degrees below the melting point of the polymer, and after temperature equilibrium is reached, the mold stops rotating, the high-pressure vessel is quickly opened, and after pressure relief, the microporous foamed pipe closely connected with the mold is obtained; The average sound absorption coefficient of the polymer microcellular foamed pipe is more than 0.

8.

5. The method of producing a polymeric microcellular foamed pipe according to claim 4, characterized in that: In step (3), the linear shrinkage of the blend ​ determined by the ratio of the length in one direction at high temperature to the length at room temperature: ​ = length at high temperature L 高 / length at room temperature L 室 - 1, said high temperature being equal to T 放 .

6. The method of producing a polymeric microcellular foamed pipe according to claim 4, characterized in that: The ratio of the layer thickness of the PVA coating before and after drying in step (5) is 0.4 to 0.

6. α 0.4 to 0.

6.

7. The method of producing a polymeric microcellular foamed pipe according to claim 4, characterized in that: In step (7), the supercritical fluid in the high-pressure container is supercritical nitrogen or supercritical carbon dioxide or a combination of both, and the pressure of the supercritical fluid is 10-50 MPa. P 浸 The temperature of the high-pressure container is 10-50 MPA. T 浸 The temperature of the high-pressure container is 10-50 MPA. t 浸 The temperature of the high-pressure container is 10-50 MPA.

8. The method of producing a polymeric microcellular foamed pipe according to claim 4, characterized in that: In step (8), the initial pressure release speed of the high-pressure container at the opening moment is 30 to 70 MPa / sec. P 释 is 30 to 70 MPa / sec.

9. Use of the polymeric microcellular foamed tubing produced by the process of claim 4 in sound absorbing materials, characterized in that: ​

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