WO2024124718A1

WO2024124718A1 - Production device and production method for polymeric microcellular foamed pipe

Info

Publication number: WO2024124718A1
Application number: PCT/CN2023/081546
Authority: WO
Inventors: 周应国; 刘金凤; 蔡昌松
Original assignee: 江苏科技大学
Priority date: 2022-12-16
Filing date: 2023-03-15
Publication date: 2024-06-20
Also published as: CN115782268A

Abstract

Disclosed in the present invention are a production device and production method for a polymeric microcellular foamed pipe. The production method is implemented on the basis of a mold and a high-pressure closed container capable of driving the mold to rotate, and comprises: forming a thermoplastic polymer or a compound thereof into a pre-foamed pipe; cutting the pre-foamed pipe into a pipe which is not longer than the mold, and placing the pipe in the mold; placing the mold accommodating the pipe in a closed reaction kettle, introducing a supercritical fluid into the closed reaction kettle, and infiltrating the pipe in the supercritical fluid at a corresponding temperature and pressure, wherein the mold is always in a rotating state in the reaction kettle; and quickly releasing the pressure after the temperature in the reaction kettle is reduced for a period of time, and taking out the pipe in the mold to obtain a polymeric microcellular foamed pipe.

Description

Production device and production method of polymer microporous foamed pipe

Technical Field

The invention relates to a production device for a polymer microporous foamed pipe, and also relates to a production method for the polymer microporous foamed pipe.

Background technique

In recent years, tubular products with polymers or their composites as the main raw materials have been widely used in the fields of building water supply and drainage, urban pipe networks, chemical transportation, etc. At the same time, due to the advantages of sound insulation, shock absorption, heat insulation, and saving raw materials, polymer microporous foam products have shown broad application prospects in packaging, construction, electronics, automotive industry, aerospace and navigation industries. Furthermore, open-cell foaming materials are foaming materials with continuous physical and gas phases. The matrix material exists in the form of continuous pore walls. Its unique three-dimensional open-cell structure has excellent absorption and penetration properties. It has a wide range of applications in the fields of sound absorption, conductivity, optics, filtration, adsorption, etc., especially in the fields of biomedical materials (drug controlled release, bone tissue culture, biodialysis), etc. It has huge potential application prospects. However, the polymer microporous foaming pipe obtained by combining the two is relatively rare. On the one hand, the existing foaming pipe is mainly closed-cell, and its foaming ratio is often low, and the advantages of foaming are difficult to reflect; on the other hand, the pore structure of the foaming pipe obtained by the existing method is difficult to accurately control, and the mechanical properties and other performance properties of its products are significantly reduced, which hinders its promotion and application. Among the mainstream processing methods of supercritical fluid microporous foam products such as extrusion, injection, and high-pressure containers (autoclave or molding), the high-pressure container method is easier to obtain uniform pores throughout the product, with high pore density, small size, high degree of uniformity, and more convenient control. However, as an intermittent foaming method, the high-pressure container method is mainly used for foaming experiments of a small amount of material or regular plates. When processing the plate, its upper and lower surfaces can be easily cut off; the molds and equipment used for processing the plate can be easily opened and closed, so that the pressure control is very convenient and free; the plate can easily achieve uniform pressure and temperature control on the entire plane during the infiltration, heating, pressure increase, cooling, and pressure release stages.

Compared with sheet materials, tubular products have more complex shapes, which poses challenges to product shaping, demoulding, and uniform pore control. Especially when the wall of the tubular product is thick, under the existing conditions, it is almost impossible to achieve consistency in process conditions such as temperature, pressure, and temperature and pressure change rate at various parts of the tube wall, and it is also difficult to achieve precise control of the pores. The inner and outer walls of the formed tube are also difficult to be post-cut like sheets. Therefore, it is necessary to directly obtain products with good inner and outer surface quality.

For polymer microporous foam products that obtain pores by changing state parameters such as pressure or temperature, there is often a skin layer without pores on the outer surface of the product. The main reason is that the surface of the product is in direct contact with the outside world, so it is difficult to form a state difference with the outside world, and the state difference is often the main factor inducing the formation and fixation of pores. For polymer microporous foam pipes, the solid outer wall of the inner and outer surfaces will also affect its opening effect. If the inner and outer walls are closed cells, the inner and outer walls often need to be removed first when applying this type of pipe that requires opening function. This brings corresponding troubles to its application.

In the application of open-cell materials, the orientation of the holes also has certain effects. For example, the sound absorption coefficient will be significantly different in the hole orientation direction and other directions. When foaming supercritical fluids, the pressure release direction can be controlled or the orientation of the cells can be regulated. However, for large-sized pipes, it is difficult to make the pressure release direction of each part uniform. Therefore, it is usually difficult to obtain thick-walled pipes with consistent directional cells.

Summary of the invention

Purpose of the invention: The purpose of the present invention is to provide a production device and a production method for polymer microporous foamed pipes. The method realizes precise control of the micropores (pore diameter, pore orientation and pore uniformity) and foaming ratio inside the foamed pipe through a specific mold and a closed high-pressure device that can drive the mold to rotate in combination with a specific process route. The obtained microporous foamed pipe has uniform pores, small and dense pores, good consistency in pore orientation, and an open-pore structure on the inner and outer walls of the pipe. Therefore, the pipe has good mechanical properties while being able to better play the advantages of the existence of micropores inside the product.

Technical solution: The production device of the polymer microporous foamed tube described in the present invention includes a mold; the mold includes a first fixing frame and a second fixing frame arranged relatively to each other and an inner mold core fixed on the first fixing frame; the first fixing frame and the second fixing frame are both provided with cylindrical grooves arranged in an annular shape and corresponding to each other, and also includes an outer mold group, the outer mold group is composed of a plurality of ribs arranged in an annular shape, and the ribs of the outer mold group are arranged one by one corresponding to the cylindrical grooves on the fixing frame; the two ends of the ribs are respectively connected to the first fixing frame and the second fixing frame by limit screws; it also includes a compression spring arranged in the cylindrical groove, one end of the compression spring is connected to the end point of the cylindrical groove away from the center of the fixing frame, and the other end of the compression spring is connected to the limit screw, and the limit screw slides laterally in the cylindrical groove through the compression spring; the cylindrical groove is a through hole structure, and the lateral length of the cylindrical groove is 10 to 100 mm.

Among them, the height of the inner mold core is not greater than the distance between the first fixing frame and the second fixing frame; the height of the inner mold core is not less than the length of the pre-foamed tube blank; the outer diameter of the inner mold core is consistent with the inner diameter of the pre-foamed tube blank.

The number of the ribs is determined according to the size of the inner ring formed after the ribs are combined and the size of the ribs themselves. The size of the inner ring formed after the ribs are combined is adapted to the shape of the pre-foamed tube blank.

Preferably, when the outer shape of the pre-foamed tube and the outer shape of the ribs are both circular, and the diameters of the pre-foamed tube and the ribs are R1 and R2 respectively, the number of ribs is determined as not exceeding (R1+R2)*3.14/R2. For the convenience of processing, this value is generally determined as an integer multiple of 4. If the outer dimensions of the two ends of the pre-foamed tube are different, the smaller of the quantity values determined by the dimensions of the two ends is taken. In addition, due to strength requirements, the diameter of the ribs is 6 mm or above.

It also includes a high-pressure sealed container that drives the mold to rotate. The container is provided with a cavity that is connected to the motor through a coupling. The size of the cavity is consistent with the mold. The mold loaded with the pre-foamed tube blank is placed in the cavity, and the cavity rotates driven by the motor.

The method for producing a polymer microporous foamed pipe based on the above production device comprises the following steps:

(1) selecting at least two thermoplastic polymers and forming a blend by melt blending or solution blending;

(2) subjecting the blend to a molding process to obtain a pre-foamed tube, wherein the wall thickness of the pre-foamed tube is 1 to 20 mm;

(3) cutting the pre-foamed tube to a length equal to the required tube length/(1+blending linear shrinkage δ) to obtain a pre-foamed tube blank;

(4) evenly applying a PVA aqueous solution on 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, wherein the initial thickness of the PVA coating is 30 to 50 μm;

(5) Dry the pre-foamed tube blank until the PVA coating is completely formed, and then apply the PVA aqueous solution on the outer surface of the pre-foamed tube blank again. The thickness of the coating formed is equivalent to the initial thickness of step (4). When the applied PVA aqueous solution is not dried, use a film to wrap n layers on the outer surface of the pre-foamed tube blank; the film coated on 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 pipe; the heat-resistant super-tough film refers to a film whose thermal softening temperature _is at least 20 degrees higher than T, and when T _{is released} , a high tensile speed of 500 mm/min is used. The elongation at break is above 100%; the number of film winding layers n is determined according to the tensile modulus M of the film at high temperature, and can be estimated by the following formula: n is equal to P _release /P _{period release} *P _immersion /M and rounded, that is, it is considered that n is related to the following factors: the tensile strength M of the film at a high tensile speed of 500mm/min at high temperature T _release , the pressure P _immersion of the supercritical fluid, the initial pressure release rate P _release of the high-pressure container at the moment of opening, and the expected pressure reduction rate P _{period release} of the pre-foamed pipe at the initial pressure release after pre-immersion; in the present invention, the P _{period release} of the pre-foamed pipe is 7.5-10MPa;

(6) After the film is adhered, the pre-foamed tube blank is placed on the inner mold core of the mold, and the outer mold group surrounds the outside of the pre-foamed tube blank, and the ribs of the outer mold group are adjusted to a position larger than the outer diameter of the pre-foamed tube blank;

(7) placing the mold containing the pre-foamed tube blank in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pre-foamed tube blank in the supercritical fluid under high-temperature T _immersion and high-pressure P _immersion ; wherein the mold is always in a rotating state in the high-pressure container;

(8) After the soaking time t _soak , the temperature T in the high-pressure container _is lowered to 5 to 20 degrees below the melting point of the polymer. After the temperature reaches equilibrium, the mold stops rotating, the high-pressure container is quickly opened, and the pressure is released to obtain a microporous foamed tube tightly connected to the mold;

(9) The mold with the microporous foamed tube is immersed in water to remove the PVA coating on the inner wall surface. The tube is taken out from the mold, the film layer is removed, and the PVA coating on the outer wall surface is also removed to obtain a polymer microporous foamed tube.

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

The main reason for the above-mentioned 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 due to temperature. Since foaming is carried out near the melting point of high-melting-point polymers, this may cause them to rupture during the foaming process, thereby achieving open-cell foaming.

In step (3), the linear shrinkage δ of the blend is determined by the ratio of its length in a certain direction at high temperature to that at room temperature. The value is determined by: δ = length _Lhigh at high temperature / length Lroom at _room temperature -1, where the high temperature is equal to _Trelease .

Wherein, in step (5), the layer thickness ratio α of the PVA coating before and after drying is 0.4 to 0.6. Within this ratio range, the PVA coating and the foaming material can be more closely bonded, while when the ratio is too low or too high, the bonding between the two is not good.

Wherein, in step (7), the pressure _Pimmersion of the supercritical fluid in the high-pressure container is 10 to 50 MPa, _Timmersion is 0 to 5 degrees below the melting point of the polymer, and the immersion time _timmersion is 5 to 30 minutes; the rotation speed of the mold in the high-pressure container is 300 to 900 r/min.

Wherein, in step (7), the supercritical fluid is supercritical nitrogen or supercritical carbon dioxide or a combination of the two.

Wherein, in step (8), the initial pressure release rate _Prelease of the high-pressure container at the moment of opening is 30 to 70 MPa/second.

The above-mentioned polymer microporous foam tube is used in sound-absorbing materials, and the average sound absorption coefficient of the polymer microporous foam tube exceeds 0.8.

The working process of the present invention is:

When the pre-foamed tube is ready, remove the limiting screw in the cylindrical groove on the second fixing frame, remove the second fixing frame, and put the pre-foamed tube on the inner mold core so that the pre-foamed tube is located between the inner mold core and the outer mold group. The second fixing frame is fixedly connected to the rib again through the limiting screw. The two ends of the pre-foamed tube are respectively in contact with the first fixing frame and the second fixing frame. In this way, the pre-foamed tube is placed in the cavity between the inner mold core and the outer mold group of the mold; adjust the limiting screw to determine the movement distance of each rib in the outer mold group by adjusting the moving distance of the rib in the cylindrical groove. The position of the strip after the compression spring is fully compressed can change the external dimensions of the final foamed pipe; the mold loaded with the pre-foamed tube blank is placed in a high-pressure container, and a cavity connected to the motor through a coupling is provided in the container. The size of the cavity is consistent with the mold. The mold is placed in the cavity, heated in a closed container and immersed in a supercritical fluid at the same time. Due to the rotation, the pre-foamed tube blank can be quickly immersed in the supercritical fluid. At the same time, the temperature distribution of each part of the pre-foamed tube blank is very uniform, so that each part of the pre-foamed tube blank is evenly immersed.

When the pressure in the container is removed, the supercritical fluid in the pre-foamed tube is converted into gas, and the material begins to expand and foam. At this time, the pre-foamed tube in the mold expands outward on the one hand, but its surface is wrapped with n layers of 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 smaller than the opening force formed by the gas foaming in the tube, the bubbles can still grow, but the foaming speed is greatly controlled and not too fast, so as to achieve 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 degree of pressure increases with the expansion of the tube, and the compression force provided by the spring limits the rapid growth of the bubbles. As a result, the bubbles in the tube continue to grow in a restricted state, achieving more uniform foaming of various parts of the tube, until the ribs on the mold reach their limit positions due to the action of the limit screws. At this time, the pressure in the high-pressure container is basically removed. At this time, since the temperature of the foamed tube is below the melting temperature of the material, the bubbles in the tube can be quickly formed and the shape of the tube can be fixed; the mold is taken out of the high-pressure container, the second fixing frame is opened, and the obtained foamed tube is taken out of the mold.

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

The foamed tube obtained by the method of the present invention is a tubular product, and a large number of interconnected micropores are provided on the tube wall. The inner and outer wall surfaces of the tube also have open-pore structures. The micropores are uniform in size, and the diameters are all within 50 microns. The pore size deviation can be controlled within 5 microns. The micropores are oriented along the wall thickness direction, and the orientation consistency is excellent. The tube foaming ratio is between 3 and 10, the inner diameter of the tube is 10 mm or more, the wall thickness of the tube is between 3 mm and 200 mm, and the cross-sectional shape of the tube is circular, elliptical or other rotational shapes, and the cross-sectional size thereof remains unchanged or changes regularly.

The product of the present invention also has an excellent sound absorption effect. The sound absorption coefficient of the product is measured by the transfer function method. The average sound absorption coefficient measured in the frequency range of 200 to 2000 Hz exceeds 0.8, and it is a Class I sound absorption material.

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

(1) The method of the present invention can achieve precise control of the foam pore structure of the pipe. Through the combined effect of the film coating and the spring (adjusting the pressure), the pore size can be adjusted and the degree of restriction of the pore growth process can be increased, thereby improving the uniformity of the pores. The pore sizes of the pipes with the same wall thickness can be made very small, and the pore sizes of the pipes with different wall thicknesses can also be made very small. The uniformity of the pores is conducive to improving the mechanical properties and sound absorption function of the material.

(2) The orientation direction of the pores can be precisely controlled. Since the gaps between the ribs of the mold are equivalent to the main airway during unloading, the micropores on the film are equivalent to the secondary airway. The uniform distribution of the main and secondary airways can maintain uniform patency at the moment the high-pressure container is opened, and their directions are all along the radial direction of the tube wall. Therefore, the orientation direction of the micropores of the obtained tube is very consistent. The pores with consistent orientation are also conducive to improving the uniformity of the mechanical properties of the material and the sound absorption effect.

(3) The foamed pipe can be easily removed from the mold without damaging the pipe. The PVA coating can make the molded product quickly and damagelessly removed from the inner mold core. At the same time, the PVA coating can also make the inner and outer wall surfaces of the pipe have an open-cell structure, thereby directly obtaining a foamed pipe with open cells on the surface. There is no need to process and open cells on the inner and outer surfaces of the foamed pipe. In addition, the inner and outer surface quality of the pipe is good.

(4) By adjusting the position of the mold limit screw, the moving position of the rib in the cylindrical groove is determined, thereby controlling the shape of the final foamed tube, and then accurately adjusting the foaming ratio of the tube, so as to achieve the production of products with different foaming ratios on a set of molds;

(5) By adjusting the position of the mold limit screw, the moving position of the rib in the cylindrical groove is determined, thereby controlling the shape of the final foamed pipe, realizing the foaming molding of special-shaped pipe products, and realizing the production of products with changing shapes on a set of molds;

(6) The high-speed rotation improves the infiltration efficiency and uniformity of the supercritical fluid inside the material, and achieves consistency in process conditions such as temperature, pressure, and temperature and pressure change rate at various parts of a certain thick-walled pipe, thereby improving The production efficiency of foamed pipes is such that the wetting time for 10mm thick pre-foamed pipes can be as short as 5 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of a method for preparing a polymer microporous foamed pipe according to the present invention;

FIG2 is a schematic structural diagram of a mold;

FIG3 is a schematic diagram of the structure of the mold after foaming when the pressure is removed and the ribs are opened;

FIG4 is a schematic diagram of the structure of the mold placed in a high-pressure container;

FIG5 is a schematic diagram of the appearance of a pre-foamed tube blank having a fixed rotation cross section;

FIG6 is a schematic diagram of the appearance of a pre-foamed tube blank having a regularly changing inclined rotational cross section;

FIG7 is a low-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 1;

FIG8 is a high-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 1;

FIG9 is a scanning electron microscope image of the cell morphology of the foamed tubular product prepared in Comparative Example 1;

FIG10 is a low-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 2;

FIG11 is a high-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 2;

FIG12 is a scanning electron microscope image of the cell morphology of the foamed tubular product prepared in Comparative Example 2;

FIG13 is a scanning electron microscope image of the cell morphology of the foamed tubular product prepared in Comparative Example 3;

FIG14 is a low-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 3;

FIG15 is a high-magnification scanning electron microscope image of the cell morphology of the foamed tubular product obtained in Example 3;

Figure 16 is a scanning electron microscope image of the pore morphology of the foamed tubular product prepared in Comparative Example 4.

Detailed ways

As shown in FIG4 , the high-pressure container of the present invention is composed of an upper cover plate 12 and a lower box body 15. After the cover plate 12 and the box body 15 are sealed, no gas leakage occurs within the range of 0 to 70 MPa and 0 to 260 degrees. The cover plate 12 is provided with an injection port 17. The supercritical fluid is injected into the container through the injection port 17 and the pressure in the container is controlled. A columnar reaction chamber 18 is provided in the box body 15. The columnar reaction chamber 18 is placed in a groove of the box body 15. A temperature control device 16 is also provided on the side wall of the box body 15. The pre-foamed tube 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 is separated from the lower box body 15, the high-pressure container opens quickly, and its response time is within 0.05 seconds.

Example 1

A method for producing polypropylene/linear low-density polyethylene microporous foamed pipes using supercritical fluid:

In terms of raw materials, the polypropylene (PP) used is the common domestic T30S on the market, and its melting point is 165 degrees. The linear low-density polyethylene (LLDPE) used is the common domestic 7050 on the market, and its melting point is 120 degrees. Through the weight measurement method, it can be known that the melt strength of the material measured at 120 degrees and 165 degrees is 1.16 and 0.52g respectively. A high-pressure (70MPA) and high-temperature (250 degrees) resistant sealable container as shown in Figure 4 is used. After the container is sealed, the temperature is between 0 and 70MPA and There is no gas leakage within the range of 0 to 260 degrees. A cavity connected to the motor through a coupling is arranged in the container. A mold loaded with the pre-foamed tube blank is placed in the cavity, and the cavity rotates driven by the motor.

The PVA used is the common domestic 1788 on the market. At room temperature, it is dissolved in distilled water twice its mass to prepare a PVA aqueous solution. The heat-resistant super-tough film with micropores (R260 porous isolation Teflon FEP film) used can withstand high temperatures up to 260°. It is commercially available with a thickness of 20 microns, a pore size of 10 microns, and a pore spacing of 8 mm. The film is measured at 150 degrees with a tensile speed of 500 mm/min to obtain an elongation at break of 182% and a tensile strength of 21.3 MPa.

The above method is implemented based on the following mold, the mold is shown in Figure 2, the mold 8 includes a first fixing frame 31 and a second fixing frame 32 arranged opposite to each other and an inner mold core 4 fixed on the first fixing frame 31; the first fixing frame 31 and the second fixing frame 32 are both provided with cylindrical grooves 5 arranged in a ring and corresponding to each other, the mold 8 also includes an outer mold group 1, the outer mold group 1 is composed of a plurality of ribs 6 arranged in a ring, and the ribs 6 of the outer mold group 1 are arranged one by one with the cylindrical grooves 5 on the fixing frame 3; the two ends of the rib 6 are respectively connected to the first fixing frame 31 and the second fixing frame 32 by limit screws 7; the mold 8 also includes a compression spring 2 arranged 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 fixing frame 3, and the other end of the compression spring 2 is connected to the limit screw 7, and the limit screw 7 slides laterally in the cylindrical groove 5 through the compression spring 2.

The rib shape is a straight round rod with a diameter of 6 mm. The number of ribs is determined to be no greater than (20+6)*3.14/6. For ease of processing, 12 ribs are selected.

The above method specifically comprises the following steps:

(1) Pure PP material and LLDPE material were mixed in a weight percentage of 7:3, and then melt-blended by extrusion to obtain a PP/LLDPE blend. The linear shrinkage rate δ of the blend between 150 degrees and 25 degrees was determined to be 1.5% by experiment;

(2) The PP/LLDPE blend is processed by extrusion molding into a pre-foamed tube with an inner diameter of 9.96 mm and an outer diameter of 20 mm, the appearance of which is shown in FIG5 . The stretching ratio of the material during the extrusion process is 3;

(3) cutting the pre-foamed tube to a length of 295.6 mm to obtain a pre-foamed tube blank;

(4) evenly coating the inner and outer surfaces of the pre-foamed tube with a layer of PVA aqueous solution, with a coating thickness of 50 μm;

(5) The pre-foamed tube blank is placed in a blast drying oven and dried until the PVA is completely formed and its thickness is about 20 μm. The PVA aqueous solution is coated on the outer surface of the pre-foamed tube blank again, and the amount used is close to the first time. When it is not dried, a heat-resistant super-tough film with micropores is used to wrap the outer surface with 3 layers;

Among them, the number of layers is estimated based on the tensile strength M of the film at a high tensile speed of 500mm/min at high temperature T _release , which is 21.3MPa, that is, n is equal to P _release /P _{period release} *P _immersion /M and rounded, the pressure of the supercritical fluid P _immersion is 15MPa, the initial pressure release rate P _release of the high-pressure container at the moment of opening is 30MPa, and the expected pressure reduction rate P _period release of the pre-foamed tube blank at the initial pressure release after pre-immersion is 7.5MPa;

(6) The treated pre-foamed tube blank is placed on the inner mold core of the mold, and the outer mold group surrounds the outside of the tube, and its ribs are adjusted to a position where the inner diameter (the inner diameter of the cavity enclosed by the outer mold group) is 40.1 mm;

(7) placing the mold containing the pre-foamed tube in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pre-foamed tube in supercritical _CO2 at 165 degrees and 15 MPA for 5 minutes, wherein the mold rotates at a speed of 900 r/min in the high-pressure container;

(8) The temperature inside the high-pressure container is lowered to 145 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, and the high-pressure container is quickly opened. After the pressure is released, a microporous foamed tube tightly connected to the mold is obtained;

(9) The microporous foamed tube is immersed in water, the PVA layer on the inner and outer wall surfaces is removed, the film layer is removed, and the tube is taken out from the mold to obtain a tube with open holes on the surface and excellent surface quality; the outer diameter of the tube is 40 mm, and the foaming ratio of the tube is 5 times.

The ring compression strength test of the tubular product obtained in Example 1 was carried out, and its ring compression strength was 1623KN/100mm. At the same time, the morphology of the bubbles in the product was observed, and the results are shown in Figures 7 and 8. It was found that the uniformity of such bubbles was very good, and in the wall thickness direction (the up and down direction of Figure 7), the average size deviation of the bubbles at different wall thicknesses was also within 5 microns. Such bubbles all had orientation along the wall thickness direction and were open-cell structures. After testing, the open cell rate of such bubbles reached 95.5%.

The sound absorption coefficient was measured using the transfer function method. The average sound absorption coefficient of the tube wall was found to be 0.901 in the frequency range of 200 to 2000 Hz. The obtained product has excellent sound absorption effect.

Comparative Example 1

In order to illustrate the effect of the present invention, Comparative Example 1 is listed, and the preparation process of its raw materials is similar to that of Example 1. In terms of raw materials, the polypropylene (PP) used is ordinary commercial domestic T30S, and its melting point is 165 degrees. The linear low-density polyethylene (LLDPE) used is ordinary commercial domestic 7050, and its melting point is 120 degrees. The two raw materials are exactly the same as those in Example 1. A high-pressure (70MPA) and high-temperature (250 degrees) resistant sealed container is used, with an inner diameter of 50 mm. After the container is sealed, there is no gas leakage within the range of 0-70MPA and 0-260 degrees. The container is provided with a cavity connected to the motor through a coupling transmission, and its structure is basically the same as that of Example 1. The only difference is that Comparative Example 1 does not use the mold used in Example 1, nor does it use a film and a mold to regulate the bubbles according to Example 1; the production method of its polymer microporous foamed pipe refers to the existing conventional method, and specifically includes the following steps:

(1) Pure PP material and LLDPE material were mixed in a weight percentage of 7:3, and a PP/LLDPE blend was obtained by extrusion melt blending. The PP/LLDPE blend was extruded to form a pre-foamed tube with an inner diameter of 10 mm and an outer diameter of 20 mm. The stretching ratio of the material during the extrusion process was 3, and the tube was cut into tubes with a length of 300 mm;

(2) The pipe was directly placed in a sealed high-pressure container, supercritical CO ₂ was introduced into the sealed high-pressure container, and the pipe was immersed at 175 degrees and 15 MPA for 30 minutes; (corresponding to Example 1, after immersion at 165 degrees for 5 minutes, the experiment did not success)

(3) The temperature inside the high-pressure container was cooled to 145 degrees. After 10 minutes, the pressure was quickly released and the pipe in the high-pressure container was taken out. The foaming dimensions of each part of the pipe were not uniform, and the internal and external dimensions were not uniform. The foaming ratio of the pipe was about 8 times.

The ring compression strength test was conducted on the tubular product obtained in Comparative Example 1, and the best result of the ring compression strength was only 1137 KN/100 mm. At the same time, the pore morphology in the product was observed, and the results are shown in FIG9 .

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

By comparing Example 1 with Comparative Example 1, it can be seen that since the pipe fitting in Comparative Example 1 is not foamed under controllable conditions, its pores are very uneven, the pore density and pore size of each part vary greatly, and although the pores have a certain open-cell structure, the open-cell rate is only 53%, the consistency of the pore orientation is very poor, the shape of the pipe fitting is very poor, the inner and outer wall surfaces are both solid structures, and the size of each part varies greatly. In addition, from the comparison of the sound absorption coefficient, it can be seen that the sound absorption effect of the comparative example is much different from that of Example 1, and the sound absorption effect of Example 1 is better.

Example 2

In terms of raw materials, the polypropylene (PP) used is the common domestic T30S on the market, and its melting point is 165 degrees. The linear low-density polyethylene (LLDPE) used is the common domestic 7050 on the market, and its melting point is 120 degrees. A high-pressure (70MPA) and high-temperature (250 degrees) sealed container is used. After the container is sealed, there is no gas leakage in the range of 0-70MPA and 0-260 degrees. A cavity is provided in the container 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 driven by the motor.

The above method is implemented based on the following mold. The mold is shown in Figure 2. The mold 8 includes a first fixing frame 31 and a second fixing frame 32 arranged opposite to each other and an inner mold core 4 fixed on the first fixing frame 31; the first fixing frame 31 and the second fixing frame 32 are both provided with cylindrical grooves 5 arranged in an annular shape and corresponding to each other. The mold 8 also includes an outer mold group 1, which is composed of a plurality of ribs 6 arranged in an annular shape. The ribs 6 of the outer mold group 1 are arranged one by one corresponding to the cylindrical grooves 5 on the fixing frame 3; the two ends of the rib 6 are respectively connected to the first fixing frame 31 and the second fixing frame 32 by limit screws 7; the mold 8 also includes a compression spring 2 arranged 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 fixing frame 3, and the other end of the compression spring 2 is connected to the limit screw 7, and the limit screw 7 is compressed by the compression spring 2 in Slide laterally in the cylindrical groove 5.

The rib shape is a straight round rod with a diameter of 10 mm. The number of ribs determined at both ends of the pre-foamed tube is no more than (90+10)*3.14/10 and (100+10)*3.14/10, and finally 28 ribs are selected.

The above method specifically comprises the following steps:

(2) The PP/LLDPE blend was compacted at a pressure of 10 MPA and a temperature of 200 degrees to form a pre-foamed tube 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, the shape of which is shown in FIG6 ;

(3) evenly coating the inner and outer surfaces of the pre-foamed tube with a layer of PVA aqueous solution, with a coating thickness of 50 μm;

(4) placing the pre-foamed tube blank in a blast drying oven and drying until the PVA is completely formed and its thickness is about 30 μm, and coating the outer surface of the pre-foamed tube blank with a PVA aqueous solution again, with the amount being close to that of the first time. When the pre-foamed tube blank is not dried, the outer surface is wrapped with a microporous heat-resistant super-tough film with 5 layers;

The number of layers is estimated based on the tensile strength M of the film at a high tensile speed of 500 mm/min at high temperature T _release , which is 21.3 MPa, that is, n is equal to P _release / P _{period release} * P _immersion / M and rounded, the pressure of the supercritical fluid P _immersion is 20 MPa, the initial pressure release rate P _release of the high-pressure container at the moment of opening is 40 MPa, and the expected pressure reduction rate P _period release of the pre-foamed tube blank at the initial pressure release after pre-immersion is 8 MPa;

(5) The treated pre-foamed tube is placed on the inner mold core of the mold, and the outer mold assembly surrounds the tube, and the ribs at both ends are adjusted to the positions of inner diameters of 160.16 mm and 170.16 mm respectively;

(6) placing the mold containing the pre-foamed tube in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pre-foamed tube in supercritical _N2 at 160 degrees and 20 MPA for 10 minutes, wherein the mold rotates at a speed of 300 r/min in the high-pressure container;

(7) The temperature inside the high-pressure container is lowered to 155 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, and the high-pressure container is quickly opened. After the pressure is released, a microporous foamed tube tightly connected to the mold is obtained;

(8) The microporous foamed tube is immersed in water, the PVA layer on the inner and outer wall surfaces is peeled off, the film layer is removed, and the tube is taken out from the mold to obtain a tube with open holes on the surface and excellent surface quality; the outer radii at both ends of the tube are 160 mm and 170 mm respectively, and the foaming ratio of the tube is about 6.36 times.

The disc-shaped product obtained in Example 2 was tested for longitudinal compressive strength, and the pressure it withstood was as high as 2942KN/100mm. At the same time, the morphology of the cells in the product was observed, and the results are shown in Figures 10 and 11. It was found that the uniformity of such cells was very good, and the average size deviation of the cells at different wall thicknesses in the wall thickness direction (the up and down direction of Figure 10) was also within 5 microns. Such cells all had an orientation along the wall thickness direction and were all open-cell structures. After testing, the opening rate of this type of bubbles reached 93.7%.

The sound absorption coefficient was measured by the transfer function method, and the average sound absorption coefficient of the tube wall obtained in this embodiment was measured to be 0.884 within a frequency range of 200 to 2000 Hz.

Comparative Example 2

In order to illustrate the effect of the present invention, Comparative Example 2 is listed. The preparation process of its raw materials is similar to that of Example 2. In terms of raw materials, the polypropylene (PP) used is ordinary commercial domestic T30S, whose melting point is 165 degrees, and the linear low-density polyethylene (LLDPE) used is ordinary commercial domestic 7050, whose melting point is 120 degrees. A high-pressure (70MPA) and high-temperature (250 degrees) resistant sealed container is used, with an inner diameter of 170 mm. After the container is sealed, there is no gas leakage within the range of 0-70MPA and 0-260 degrees. A cavity connected to the motor through a coupling transmission is provided in the container, and its structure is basically the same as that of Example 2. The only difference is that Comparative Example 2 does not use the mold used in Example 2, nor does it use a film and a mold to regulate the bubbles according to Example 2; the production method of its polymer microporous foamed pipe refers to the existing conventional method, and specifically includes the following steps:

(1) Pure PP material and LLDPE material were mixed in a weight percentage of 7:3, and similar to Example 2, compacted at a pressure of 10 MPA and a temperature of 200 degrees to form a pre-foamed tube blank with a length of 98.5 mm, an inner radius of 69.97 mm and an outer radius of 90 mm at one end, and an inner radius of 79.97 mm and an outer radius of 100 mm at the other end;

(2) The pre-foamed tube was directly placed in a sealed high-pressure container, supercritical _N2 was introduced into the sealed high-pressure container, and the tube was immersed at 180 degrees and 20 MPA for 40 minutes; (corresponding to Example 2, after immersion at 160 degrees for 10 minutes, the experiment was unsuccessful)

(3) The temperature inside the high-pressure container was cooled to 155 degrees. After 10 minutes, the high-pressure container was opened and the pressure was quickly released. The pipe in the high-pressure container was taken out. The foaming dimensions of each part of the pipe were not uniform, and the internal and external dimensions were not uniform. The foaming ratio of the pipe was about 7.7 times.

The longitudinal compressive strength test of the tubular product prepared in Comparative Example 2 was conducted, and the optimal result of the longitudinal compressive strength was only 2267 KN/100 mm. At the same time, the morphology of the cells in the product was observed, and the results are shown in Figure 12. In Figure 12, the left and right directions are the wall thickness directions, and it can be seen that the orientation of the cells is basically along this direction, but the cell sizes at different wall thicknesses vary greatly.

By comparing Example 2 with Comparative Example 2, it can be seen that since the pipe fittings in Comparative Example 2 are not foamed under controllable conditions, the pores are very uneven, the pore density and pore size of each part vary greatly, and although the pores also have a certain open-cell structure, the open-cell rate is only 62.8%. The appearance of the obtained pipe fittings is very poor, the size of each part varies greatly, and the inner and outer wall surfaces are both solid structures.

The sound absorption coefficient was measured by the transfer function method, and the average sound absorption coefficient of the tube wall obtained in this embodiment was measured to be 0.475 within a frequency range of 200 to 2000 Hz.

Comparative Example 3

In order to illustrate the effect of the present invention, Comparative Example 3 is listed, and the preparation process of its raw materials is similar to that of Example 2. In terms of raw materials, the polypropylene (PP) used is ordinary commercially available domestic T30S, and its melting point is 165 degrees. The linear low-density polyethylene (LLDPE) used is ordinary commercially available domestic 7050, and its melting point is 120 degrees. A high-pressure (70MPA) and high-temperature (250 degrees) resistant sealed container is used, and the inner diameter is 170 mm. After the container is sealed, there is no gas leakage within the range of 0-70MPA and 0-260 degrees. The container is provided with a cavity connected to the motor through a coupling transmission, 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 a mold to regulate the bubbles according to Example 2; specifically includes the following steps:

(2) The PP/LLDPE blend was compacted at a pressure of 10 MPa and a temperature of 200 degrees to form a pre-foamed tube 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, the shape of which is shown in FIG. 6 ;

(3) The pre-foamed tube is placed on the inner mold core of the mold, and the outer mold group surrounds the outside of the tube, and the ribs at both ends are adjusted to the positions of inner diameters of 160 mm and 170 mm respectively;

(4) placing the mold containing the pipe in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pipe in supercritical _N2 at 160 degrees and 20 MPA for 10 minutes, wherein the mold rotates at a speed of 300 r/min in the high-pressure container;

(5) The temperature in the high-pressure container is lowered to 155 degrees. After reaching temperature equilibrium, the mold stops rotating, the high-pressure container is quickly opened, and the microporous foamed tube tightly connected to the mold is obtained after instant pressure relief;

(6) Due to the different sizes at both ends, although the microporous foamed tube is tightly fitted on the inner core of the mold, after some effort, once the tube shows signs of movement, it can be removed from the inner core of the mold, thus obtaining a tube with outer radii of 160 mm and 170 mm at both ends, respectively. The foaming ratio of the tube is about 6.37 times.

The longitudinal compressive strength test of the tubular product prepared in Comparative Example 3 was performed, and the optimal result of the longitudinal compressive strength was 2451 KN/100 mm. At the same time, the morphology of the cells in the product was observed, and the results are shown in Figure 13. In Figure 13, the left and right directions are the wall thickness directions, and it can be seen that the orientation consistency of the cells is poor, but the cell sizes at different wall thicknesses are significantly different, and even the cell sizes at the same wall thickness are also quite different.

The sound absorption coefficient was measured by the transfer function method, and the average sound absorption coefficient of the tube wall obtained in the comparative example was measured to be 0.522 within a frequency range of 200 to 2000 Hz.

By comparing Example 2 with Comparative Example 3, it can be seen that although the pipe fitting in Comparative Example 3 is foamed under certain controllable conditions, the control degree is not precise, so the pores are very uneven, the pore density and pore size of each part vary greatly, and although the pores have a certain open-cell structure and the open-cell rate is as high as 83.1%, the appearance of the obtained pipe fitting is The shape is not perfect either, there is a fairly thick solid layer on the inner and outer wall surfaces, and the size differences between various parts are also very large, so it cannot be put into use directly.

At the same time, from the sound absorption effect, it can be seen that by comparing with Example 2, the sound absorption effects of Comparative Examples 2 and Comparative Example 3 are much worse than that of Example 2, and the sound absorption effect of Example 2 is very good.

Example 3

A method for producing thermoplastic polyurethane microporous foamed pipes using supercritical fluid:

In terms of raw materials, two thermoplastic polyurethanes (TPU) with different degrees of hardness are used, which are the commonly available commercial 60D and 75A, and their melting points are 170 degrees and 150 degrees respectively. The force measurement method shows that the melt strength of 75A material measured at 170 degrees and 150 degrees is 17.1mN and 9.3mN respectively. A high-pressure (70MPA) and high-temperature (250 degrees) sealed container is used. After the container is sealed, there is no gas leakage in the range of 0-70MPA and 0-260 degrees. A cavity is provided in the container, which 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 driven by the motor.

The rib shape is a straight round rod with a diameter of 10 mm. The number of ribs is determined to be no greater than (60+10)*3.14/10. For ease of processing, 20 ribs are selected.

The above method specifically comprises the following steps:

(1) After two TPU materials are mixed in a weight percentage of 7:3, a TPU blend is obtained by solvent blending, and the linear shrinkage rate δ of the blend between 150 degrees and 25 degrees is determined to be 1.0% by experiment;

(2) The TPU blend is processed by extrusion molding into a pre-foamed tube with an inner diameter of 49.96 mm and an outer diameter of 60 mm, the appearance of which is shown in FIG5 ;

(3) cutting the pre-foamed tube to a length of 495.0 mm to obtain a pre-foamed tube blank;

(5) The pre-foamed tube blank is placed in a blast drying oven and dried until the PVA is completely formed and its thickness is about 20 μm. The PVA aqueous solution is coated on the outer surface of the pre-foamed tube blank again, and the amount used is close to the first time. When it is not dried, the outer surface is wrapped with 5 layers of a heat-resistant and ultra-tough film with micropores;

Among them, the number of layers is estimated based on the tensile strength M of the film at a high tensile speed of 500mm/min at high temperature T _release , which is 21.3MPa, that is, n is equal to P _release /P _{period release} *P _immersion /M and rounded, the pressure of the supercritical fluid P _immersion is 25MPa, the initial pressure release rate P _release of the high-pressure container at the moment of opening is 50MPa, and the expected pressure reduction rate P _period release of the pre-foamed tube blank at the initial pressure release after pre-immersion is 10MPa;

(6) The treated pre-foamed tube is placed on the inner mold core of the mold, and the outer mold assembly surrounds the tube, and its ribs are adjusted to a position where the inner diameter is 120.14 mm;

(7) placing the mold containing the pre-foamed tube in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pre-foamed tube in supercritical _CO2 at 165 degrees and 25 MPA for 10 minutes, wherein the mold rotates at a speed of 600 r/min in the high-pressure container;

(8) The temperature inside the high-pressure container is lowered to 150 degrees. After 20 to 60 minutes, the internal temperature reaches equilibrium, the mold stops rotating, and the high-pressure container is quickly opened. After the pressure is released, a microporous foamed tube tightly connected to the mold is obtained;

(9) The microporous foamed tube is immersed in water, the PVA layer on the inner and outer wall surfaces is peeled off, the film layer is removed, and the tube is taken out from the mold to obtain a tube with open holes on the surface and excellent surface quality; the outer diameter of the tube is 120 mm, and the foaming ratio of the tube is 10.82 times.

The tubular product obtained in Example 3 was tested for ring compression strength, and it was not damaged by the test. At the same time, the morphology of the cells in the product was observed, and the results are shown in Figures 14 and 15. It was found that the uniformity of such cells was very good, and they were all open-cell structures. After testing, the open-cell rate of such cells reached 97.9%, and in the wall thickness direction (up and down direction of Figure 14), the average size deviation of the cells at different wall thicknesses was also within 5 microns, and such cells all had orientation along the wall thickness direction.

The sound absorption coefficient was measured by the transfer function method, and the average sound absorption coefficient of the tube wall obtained in this embodiment was measured to be 0.921 within a frequency range of 200 to 2000 Hz.

Comparative Example 4

In order to illustrate the effect of the present invention, Comparative Example 4 is listed. The preparation process of its raw materials is similar to that of Example 3. In terms of raw materials, two thermoplastic polyurethanes (TPU) with different hardness and softness are used, which are ordinary commercially available 60D and 75A, and their melting points are 170 degrees and 150 degrees respectively. A high-pressure (70MPA) and high-temperature (250 degrees) resistant sealed container with an inner diameter of 50 mm is used. After the container is sealed, there is no gas leakage within the range of 0-70MPA and 0-260 degrees. The container is provided with a cavity connected to the motor through a coupling transmission. Its structure is basically the same as that of Example 3. The only difference is that Comparative Example 4 does not use the mold used in Example 3, nor does it use the same method as in Example 3. The film and the mold regulate the pores; the production method of the polymer microporous foamed tube refers to the existing conventional method, and specifically includes the following steps:

(1) After mixing two TPU materials in a weight percentage of 7:3, a TPU blend is obtained by solvent blending, and the TPU blend is extruded to form a pre-foamed tube with an inner diameter of 50 mm and an outer diameter of 60 mm. The stretching ratio of the material during the extrusion process is 3, and the tube is cut into tubes with a length of 500 mm;

(2) Place the pipe directly in a sealed high-pressure container, pass supercritical _CO2 into the sealed high-pressure container, and soak it at 180 degrees and 25 MPA for 30 minutes; (corresponding to the experiment of Example 3 where the experiment failed after soaking at 165 degrees for 10 minutes)

(3) The temperature inside the high-pressure container was cooled to 150 degrees. After 10 minutes, the pressure was quickly released and the pipe in the high-pressure container was taken out. The foaming dimensions of each part of the pipe were not uniform, and the internal and external dimensions were not uniform. The foaming ratio of the pipe was about 13.2 times.

The morphology of the cells in the tubular product prepared in Comparative Example 4 was observed, and the results are shown in Figure 16. By comparing Example 3 with Comparative Example 4, it can be seen that since the tubular product in Comparative Example 4 was not foamed under controlled conditions, its cells were very uneven, the cell density and cell size of each part varied greatly, and although the cells also had a certain open cell structure, the open cell rate was only 72.9%, the consistency of the cell orientation was very poor, the shape of the tubular product was very poor, the inner and outer wall surfaces were both solid structures, and the sizes of each part varied greatly.

The sound absorption coefficient was measured by the transfer function method. The average sound absorption coefficient of the tube wall obtained in Comparative Example 4 was measured to be 0.499 in the frequency range of 200 to 2000 Hz. By comparing 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

A production device for a polymer microporous foamed tube, characterized in that: it comprises a mold (8); the mold (8) comprises a first fixing frame (31) and a second fixing frame (32) arranged opposite to each other and an inner mold core (4) fixed to the first fixing frame (31); the first fixing frame (31) and the second fixing frame (32) are both provided with cylindrical grooves (5) arranged in an annular manner and corresponding to each other, and also comprises an outer mold group (1), the outer mold group (1) is composed of a plurality of ribs (6) arranged in an annular manner, and the ribs of the outer mold group (1) are (6) is arranged in one-to-one correspondence with the cylindrical groove (5) on the fixing frame (3); the two ends of the rib (6) are respectively connected to the first fixing frame (31) and the second fixing frame (32) through the limit screw (7); and it also includes a compression spring (2) arranged 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 fixing frame (3), and the other end of the compression spring (2) is connected to the limit screw (7), and the limit screw (7) slides horizontally in the cylindrical groove (5) through the compression spring (2).
The production device of polymer microporous foamed tube according to claim 1 is characterized in that: the height of the inner mold core (4) is not greater than the distance between the first fixing frame (31) and the second fixing frame (32); the height of the inner mold core (4) is not less than the length of the pre-foamed tube blank; the outer diameter of the inner mold core (4) is consistent with the inner diameter of the pre-foamed tube blank.
The production device of polymer microporous foamed tube according to claim 1 is characterized in that it also includes a high-pressure closed container that drives the mold to rotate, a cavity is provided in the container and is connected to the motor through a coupling, the size of the cavity is consistent with the mold, the mold loaded with the pre-foamed tube blank is placed in the cavity, and the cavity rotates driven by the motor.
The method for producing a polymer microporous foamed pipe based on the production device according to claim 3 is characterized in that it comprises the following steps:

(1) selecting at least two thermoplastic polymers and forming a blend by melt blending or solution blending;

(2) subjecting the blend to a molding process to obtain a pre-foamed tube, wherein the wall thickness of the pre-foamed tube is 1 to 20 mm;

(3) cutting the pre-foamed tube to a length equal to the required tube length/(1+blending linear shrinkage δ) to obtain a pre-foamed tube blank;

(4) evenly applying a PVA aqueous solution on 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, wherein the initial thickness of the PVA coating is 30 to 50 μm;

(5) drying the pre-foamed tube blank until the PVA coating is completely formed, and applying the PVA aqueous solution on the outer surface of the pre-foamed tube blank again, the thickness of the coating formed is equivalent to the initial thickness of step (4), and when the applied PVA aqueous solution is not dried, using a film to cover the outer surface of the pre-foamed tube blank with n layers;

(6) After the film is adhered, the pre-foamed tube blank is placed on the inner mold core of the mold, and the outer mold group surrounds the outside of the pre-foamed tube blank, and the ribs of the outer mold group are adjusted to a position larger than the outer diameter of the pre-foamed tube blank;

(7) placing the mold containing the pre-foamed tube blank in a sealed high-pressure container, introducing a supercritical fluid into the sealed high-pressure container, and immersing the pre-foamed tube blank in the supercritical fluid under high-temperature T immersion and high-pressure P immersion ; wherein the mold is always in a rotating state in the high-pressure container;

(8) After the soaking time t soak , the temperature T in the high-pressure container is lowered to 5 to 20 degrees below the melting point of the polymer. After the temperature reaches equilibrium, the mold stops rotating, the high-pressure container is quickly opened, and the pressure is released to obtain a microporous foamed tube tightly connected to the mold;

(9) The mold with the microporous foamed tube is immersed in water to remove the PVA coating on the inner wall surface. The tube is taken out from the mold, the film layer is removed, and the PVA coating on the outer wall surface is also removed to obtain a polymer microporous foamed tube.
The method for producing a polymer microporous foamed tube according to claim 4 is characterized in that: in step (1), the melting point difference of the composite polymers is more than 20 degrees, and when the melt strength of the low-melting-point polymer is tested by gravimetric or dynamometric method, the difference in melt strength between the two melting points is more than 50%, the mass proportion of the low-melting-point polymer is 10-30%, and the mass proportion of the high-melting-point polymer is 70-90%.
The method for producing a polymer microporous foamed tube according to claim 4 is characterized in that: 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 actual temperature: δ = length Lhigh at high temperature / length Lroom at room temperature -1, wherein the high temperature is equal to Trelease .
The method for producing a polymer microporous foamed tube according to claim 4 is characterized in that: in step (5), the layer thickness ratio α of the PVA coating before and after drying is 0.4 to 0.6.
The method for producing a polymer microporous foamed tube according to claim 4 is characterized in that: in step (7), the supercritical fluid in the high-pressure container is supercritical nitrogen or supercritical carbon dioxide or a composite of the two, the pressure Pimmersion of the supercritical fluid is 10 to 50 MPa, Timmersion is 0 to 5 degrees below the melting point of the polymer, and the immersion time timmersion is 5 to 30 minutes; the rotation speed of the mold in the high-pressure container is 300 to 900 r/min.
The method for producing a polymer microporous foamed tube according to claim 4 is characterized in that: in step (8), the initial pressure release rate P release of the high-pressure container at the moment of opening is 30 to 70 MPa/second.
The use of the polymer microporous foamed tube obtained by the method of claim 4 in sound-absorbing materials is characterized in that the average sound absorption coefficient of the polymer microporous foamed tube exceeds 0.8.